JOURNAL OF CHROMATOGRAPHY LIBRARY - volume 46
ion chromatography principles and applications
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JOURNAL OF CHROMATOGRAPHY LIBRARY- volume 46
ion chromatography principles and applications
Paul R. Haddad and Peter E. Jackson Department of Analytical Chemistry, University of New South Wales, P.O. Box 7, Kensington, N.S. W. 2033, Australia
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ELSEVIER SCIENCE B.V. Sara Burgcrliartstraat25 P.O.Box 2 I I, loOn AE Arnstcrdam, Thc Ncthcrlands
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Clt8loqing-in-Publication Data
Hadda.3, Paul P. I m chroma:,yraphy : p r i n c i p l c o and applications I Paul R. Haddad and Filter E. J a c k s o n . p. crn. -- IJc-urnal o f chromarography l i b r a r y ; v . 4 6 ) 111 .lucfes t.ibliuqx+~.hic.dl r e t e r e n c e r . I r i c l u 3 c u iridex. Tfl?}! 0-444-8873?-6 1 . Ion nxchangc chr.mnatcqraphy. I. J a c k s o n , P c t c r E. 11. Title. 111. S e r i e s . 91873. :4531133 133'2 90- 3 60 0 1
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First cditioti I990 Second imprcssion 1994
Third imprcssion 2003 ISBN:
0444-8x2324
@. The p a p - uscd in this publication mccts thc rcquircmcnts of ANSlMlSO 239.48-1992 (Pcrmancncc of P a p ) . Printed in TIic Netherlands.
To Simone, Lianne, Christopher and, most of all, to Kerry
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vii
Preface Ion chromatography (IC) was first introduced in 1975 and since that time, the technique has grown in usage at a phenomenal rate. The reasons for this are clear; IC offers the only simple, reliable and inexpensive means for the simultaneous separation and determination of inorganic (and organic) ions in complex mixtures. The growth of IC has been accompanied by a blumng of the original definition of the technique, so that it now embraces a very wide range of separation and detection methods, many of which bear little resemblance to the initial concept of ion-exchange separation coupled with conductivity detection. We have chosen to define IC to encompass those modem column liquid chromatographic methods which can be used for the determination of inorganic anions and cations, water-soluble organic acids and bases, and ionic organometallic compounds. Using this definition, the separation methods which are applicable to IC include ion-exchange chromatography, ion-interaction chromatography, ion-exclusion chromatography, and some further, miscellaneous techniques. Appropriate detection methods include conductivity, amperometry, coulometry, polarography, potentiometry, spectrophotometry, atomic spectroscopy, refractive index measurements, luminescence techniques and post-column reactions. This text is structured into five logical parts, each of which groups chapters on related topics. Accordingly, Part I (Chapters 2-5) discusses ion-exchange separation methods, whilst Part I1 (Chapters 6-8) treats the remainder of the separation methods listed above. Part 111 (Chapters 9-13) is devoted solely to detection methods, and Part IV (Chapters 14,15) concerns some practical aspects of IC. Part V (Chapters 16-22) comprises a detailed, structured listing of experimental conditions for the numerous applications of IC. The applications section is a unique feature of this book and we hope it will become a valuable reference source for practitioners of the technique. Throughout the book, we have attempted to integrate suppressed and non-suppressed IC methods in the discussion of each aspect: that is, we have emphasized the similarities between these two approaches, rather than their differences. In writing this book, we have endeavoured to provide a m l y comprehensive text which treats the principles and applications of IC and is suitable as a reference work for both researchers and those involved with the use of IC in practical situations. Every effort has been made to ensure that the literature coverage is as complete as possible for the period 1975 to the early part of 1989, but we have also included some references which are more recent than this. Throughout the text, each topic is discussed both from a descriptive standpoint, in order to illustrate the underlying principles, and also from a theoretical standpoint, in which a full mathematical treatment is provided. Theoretical aspects, such as retention models and detector response equations, are presented either as separate chapters or as clearly identified Sections. In this way, the theory can be examined in depth or bypassed, according to the interests of the reader. The text has been amplified by liberal usage of chromatograms and Tables showing practical examples of each of the principles of IC, as they are discussed. We hope that this
viii
approach assists in the understanding of each point. Schematic overviews are also used extensively so that the organization of each topic is clear. Abbreviations and acronyms have been kept to a minimum and those that have been used are collected for ease of reference in Appendix R, together with all of the symbols employed in the book. Special attention has been given to the compilation of a comprehensive, detailed and crossreferenced Index. Writing a book of this size is an arduous task which cannot be accomplished by the authors alone. We are greatly indebted to our many friends and colleagues who provided assistance along the way and we would like to thank them sincerely for their time and effort. Martin Dudman used his impeccable drafting skills to produce all of the chromatograms and Helen Shumsky performed all of the photographic work required for preparation of the Figurcs. The staff of the Physical Sciences Library of the University of New South Wales, and of the Technical Library at Millipore Waters, cheerfully procured hundreds of journal articles. Only through their capable efforts have we been able to achieve a comprehensive coverage of the literature. Numerous colleagues, both within Australia and overseas, provided valuable and enlightened comments on the manuscript, or helped with proof reading. In this regard, thanks are due especially to Jim Fritz and Petr Jandik, and to the following students in the IC research group at the University of New South Wales; Roy Foley, Chris Cowie, John Brayan, Andrew Sosirnenko and Peter Fagan. We gratefully acknowledge those publishers and authors who have granted permission for us to reproduce Figures from their publications. Finally, this book would never have been completed without the support, encouragement and love of the members of the fladdad family; Simone made the coffee, Lianne filed the reprints, Christopher shared his bedroom with a computer and Kerry's patience and acceptance kept everything and everyone together over two years with a part-time husband and father. Paul R. Haddnd, Peter E. Jackson Kensington, I990
Technical nofe: Text and artwork (with the exception of chromatograms) for this book were produced on an Apple Macintosh@ IIcx microcomputer, using Microsoft@ Word 4.0 (Microsoft Corporation), McDraw (Apple@ Computer Inc.), Cricket Graph (Cricket Software) and MathWriteP (Cooke Publications) software packages, and was printed in camera-ready form on an Apple Laserwrite@.
ix
Short Contents Chapter I PART I
Introduction
1
ION-EXCHANGE SEPARATION METHODS
An Introduction to Ion-Exchange Methods Ion-Exchange Stationary Phases for Ion Chromatography Eluents for Ion-Exchange Separations Retention Models for Ion-Exchange
Chapter 2 Chapter 3 Chapter 4 Chapter 5 PART 11
15 29 79 133
ION-INTERACTION, ION-EXCLUSION AND MISCELLANEOUS SEPARATION METHODS
Chapter 6 Chapter 7 Chapter 8
Ion-Interaction Chromatography Ion-Exclusion Chromatography Miscellaneous Separation Methods
165 195 223
PART III DETECTION METHODS
Chapter 9 Chapter 10 Chapter I1 Chapter 12 Chapter 13 PART IV
Chapter 14 Chapter 15
Conductivity Detection Electrochemical Detection (Amperometry, Voltammetry and Coulometry) Potentiometric Detection Spectroscopic Detection Methods Detection by Post-Column Reaction
245 29 1 323 343 387
PRACTICAL ASPECTS
Sample Handling in Ion Chromatography Methods Development
409 463
PART V APPLICATIONS OF ION CHROMATOGRAPHY
Overview of the Applications Section Chapter 16- Environmental Applications Chapter I7 Industrial Applications , Chapter 18 Analysis of Foods and Plants Chapter 19 Clinical and Pharmaceutical Applications Chapter 20 Analysis of Metals and Metallurgical Solutions Chapter 21 Analysis of Tkated Waters Chapter 22 Miscellaneous Applications
487 489 543 593 633 667 695 717
Appendix A Statistical Information on Ion Chromatography Publications Appendix B Abbreviations and Symbols
735 745
Index
751
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xi
Full Contents Chapter 1
Introduction 1.1 BACKGROUND TO ION CHROMATOGRAPHY
Hardware and software components The chromatographic separation process Thechromatogram Mechanisms of interaction 1.2 WHAT IS ION CHROMATOGRAPHY? 1.2.1 Historical aspects 1.1.1 1.1.2 1.1.3 1.1.4
1.2.2 Definition 1.3 ORGANIZATION OF THIS BOOK 1.4 SOME FUNDAMENTAL CHROMATOGRAPHIC CONCEPTS 1.4.1 Chromatographic efficiency 1.4.2 Factors affecting band broadening Eddy diffusion, 10. Longitudinal diffusion, 10. Resistance to mass transfer, 10. Extra-column band broadening, 11. 1.5 REFERENCES
PART I
1 1 2 2 4 5 6 6 6 7 8 8 10
12
ION-EXCHANGE SEPARATION METHODS
Chapter 2 An Introduction to Ion-Exchange Methods 2.1 INTRODUCTION TO ION-EXCHANGE
15 15 15 17
h c i p l e s of ion-exchange Configuration of an ion-exchange chromatographic system Open-column(chsical)ion-exchange,17. Modern ionexchange chromatography,18. Eluent characterirtics, 19. 2.1.3 Types of ion-exchange materials 2.1.4 Characteristics of ion-exchangers Ion-exchange capacity, 21. Swelling characterirtics,22. Ion-exchange selectivity,22. 2.2 CLASSIFICATION OF ION CHROMATOGRAPHIC METHODS EMPLOYING ION-EXCHANGE SEPARATION 2.2.1 Non-suppressed ion chromatography 2.2.2 Suppressed ion chromatography 2.2.3 Similarities between non-suppressed and suppressed methods 2.3 REFERENCES
24 24 25 26 27
Chapter 3 Zon-Exchange Stationary Phases for Zon Chromatography
29
3.1 INTRODUCTION 3.2 SILICA-BASED ION-EXCHANGE MATERIALS 3.2.1 Types of silica-based ion-exchangers
29 29 29
2.1.1 2.1.2
20 21
'
Contents
xii
3.3
3.4
3.5
3.6
3.7
3.2.2 Functionalized silica ionexchangers 3.2.3 Polymer-coated silica ionexchangers 3.2.4 Advantages and limitationsof silica-basedTC packings Chromatographic mciency, 33. pH limitariom, 35. Retention of metal ions on silica anion-exchangers,36. Sample size, 37. RESIN-BASED ION-EXCHANGERS 3.3.1 Polymerization reactions 3.3.2 Surface-functi0naliz.dcation-exchange resins Synthesis, 40. Characteristics,42. 3.3.3 Surface-funcaonalizedanion-exchangeresins Synthesis, 45. Characteristics,47. Effect of functional group, 48. Nature of the polymeric substrate,52. 3.3.4 Advantages and disadvantagesof resin-based ion-exchangers pH tolerance,53. Chromatographic efficiency,53. Pressure limitations,55. Operating conditions,55. AGGLOMERATED ION-EXCHANGE RESINS 3.4.1 Description 3.4.2 Synthesis Electrostatic binding, 57. Hydrophobic binding, 59. Mechanical binding, 60. 3.4.3 Characteristics of agglomerated ion-cxchangers Chromatographicefficiency, 60. Stability, 63. Selectivity, 63. HYDROUS OXIDE ION-EXCHANGERS 3.5.1 Introduction 3.5.2 Silica 3.5.3 Alumina Ion-exchange characteristics,67. Effect of pH, 69. Selectivity,69. SIMULTANEOUS SEPARATION OF ANIONS AND CATIONS 3.6.1 Tandem anion- and cation- exchange columns 3.6.2 Mixed-bed ion-exchangers 3.6.3 Bi-functional ionexchange materials REFERENCES
Chapfer 4
Eluents for Ion-Exchange Separations
4.1 INTRODUCTJON 4.2 ELUENT CHARACI'ERISTICS 4.2.1 Compatibility with the detection mode 4.2.2 Nature and concentration of the competing ion 4.2.3 Effect of eluent pH 4.2.4 Complexation characteristics 4.2.5 Use of organic solvents in ion-exchange separdtions 4.3 ELUENTS FOR NON-SUPPRESSED ION CHROMATOGRAPHY 4.3.1 Eluents for anion separation in non-suppressed IC Aromatic carhxylic acids and their salts, 84. Aliphatic carboxylic acids, 88. Aromatic and aliphatic sulfonic acids, 88. Potarsiwn hydroxide, 90. Polyol-borate complexes, 91. ErhyIenediaminetetraacetic acid, 94. Inorganic eluents, 95. 4.3.2 Eluents for cation separation in non-suppressed 1C
30 31 33
37 38
40 45
53
56 56 57
60 66 66 67 67 70 71 72 73 74 79
19 79 79 80 81 83 83 84 84
98
Contents
4.4
4.5
4.6
4.7
xiii
Inorganic acidr, 98. Organic bases, 98. lnorganic eluents, 99. Complexing eluents, 101. ELUENTS FOR SUPPRESSED ION CHROMATOGRAPHY 4.4.1 Eluent requirements for use with suppressors 4.4.2 Eluents for anion separations in suppressed IC 4.4.3 Eluents for cation separations in suppressed IC GRADIENT ELUTION IN ION-EXCHANGE SEPARATIONS 4.5.1 Principles of gradient elution 4.5.2 Gradient elution using detection methods other than conductivity 4.5.3 Gradient elution with conductivity detection High capacity suppressors, 115. Isoconductivegradients, 119. Baseline balancing methodr, 121. EXTRANEOUS (SYSTEM)PEAKS IN ION-EXCHANGE IC 4.6.1 Introduction 4.6.2 Extraneous peaks in non-suppressed IC The injection peak, 124. The system peak, 124. 4.6.3 Extraneous peaks in suppressed IC REFERENCES
106 106 107 109 114 114 115 115
123 123 123 126 128
Chapter 5 Retention Models f o r Ion-Exchange
133
5.1 INTRODUCTlON 5.2 RETENTION MODELS FOR ANION-EXCHANGE 5.2.1 Single eluent competing anion Effects of KAE, Q and w/Vm,137. Effect of charges on solute and competing anions, 138. Effect of [EL], 139. 5.2.2 Multiple eluent competing anions Dominant equilibrium approach, 140. Competing anion "effective charge" approach, 140. Dual eluent species approach, 142. 5.2.3 Gradient elution in anion-exchange IC 5.3 RETENTION MODELS FOR CATION-EXCHANGE 5.3.1 Single eluent competing cation 5.3.2 Complexing eluents Separation by cation-exchange, 156. Separation by anionexchange, 160. 5.4 REFERENCES
133 133 133
PART II
Chapter 6
140
149 152 152 156
161
ION-INTERACTION, ION-EXCLUSION AND MISCELLANEOUS SEPARATION METHODS Ion-Interaction Chromatography
6.1 INTRODUCIlON 6.2 MECHANISM 6.2.1 Trends in solute retention in ion-interaction chromatography 6.2.2 The ion-pair model 6.2.3 The dynamic ion-exchangemodel 6.2.4 The ion-interaction model
165 165 166 166 166 168 168
Contents
xiv
6.2.5 Evaluation of mechanistic models in retention of inorganic ions 6.3 STATIONARY PHASES AND ELUENTS 6.3.1 Stationary phases 6.3.2 Type of ion-interaction reagent Rquirements of the IIR, 173. " D y m ' ccoating" ion-interaclhn chromatography, I73. "Permanentcwn'ng" ion-interaction chromorography,I75. 6.3.3 Role of the countdon of the IIR 6.3.4 S u m of eluent and stationary phasc effects 6.3.5 Guidelines for eluent selection in ion-inmactiOn chromatography Anion separations, 181. Catwn separations, 181. 6.4 RETENTION MODELS FOR DYNAMIC COATING ION-INTERACTION
CHROMATOGRAPHY 6.4.1 Model for anion retention Effect of [A-j m and p-j,,,,183. Effect of the concentration of IIR in the eluent, 184. 6.4.2 Model for cation retention
169 171 171 173
177 179 181 182 182
6.5 APPLICATIONS 6.6 REFERENCES
186 188 190
Chapter 7
195
Zon-Exclusion Chromatography
7.1 INTRODUCllON 7.1.I Basic principles 7.2 STATIONARY PHASES 7.3 ELUENTS 7.3.1 Waterelwnts 7.3.2 Acideluents 7.3.3 Complexing eluents 7.4 FACTORS INFLUENCING RETENTION IN ION-EXCLUSION CHROMA TOG^ 7.4.1 Degree of ionization of the solute Dependence of solute retention on pK,, 203. Dependence of solute retention on eluent pH, 205. 7.4.2 Molecular size of the solute 7.4.3 Hydrophobic interactions between the solute and stationary phase Use of organic modfiers in the eluent, 207. 7.4.4 Ion-exchange capacity of the stationary phase 7.4.5 Ionic form of the ion-exchange resin 7.4.6 Temperature
7.4.7 summary 7.5 RETENTION MODEL FOR ION-EXCLUSION CHROhlATOGRAPHY 7.6 APPLICATIONS OF ION-EXCLUSION CHROMATo<jRAPHY 7.6.1 Carboxylic acids 7.6.2 Weak inorganic acids and bases 7.6.3 Water 7.7 REFERENCES
195 195 197 199 199 199 202 202 202
205 206
209 210 211 21 1 212 215 215 216 218 220
Contents
xv
Chapter 8 Miscellaneous Separation Methods
223
8.1 INTRODUCI'ION 8.2 REVERSED-PHASE LIQUID CHROMATOGRAPHY 8.2.1 Coordination cornpounds Dithiocarbmate complexes, 225. Formation of the chelate,225. 8.2.2 Organometallicmpounds 8.2.3 Carboxylic acids (Ion-suppression) 8.3 CHELATING STATIONARY PHASES 8.3.1 Chemically-boundligands 8.3.2 Crown ether stationary phases Synrhesis of stationaryphases. 233. Chromatographicproperties, 235. Applications,236. Gradient elruion on macrocyclic stationary phares, 237. 8.4 MICELLE EXCLUSION CHROMATOGRAPHY 8.4.1 Introduction 8.4.2 Micelle exclusion chmatography of anions 8.4.3 Micelle exclusion chromatographyof cations 8.5 REFERENCES
223 224 224
PART III
DETECTION METHODS
Chapter 9
Conductivity Detection
9.1 INTRODUCTION 9.2 PRINCIPLES OF CONDUCl'IVITY DETJZCI'ION 9.2.1 Nature of electrical conductivity of electrolyte solutions 9.2.2 Factors influencing limitingequivalent ionic conductance 9.2.3 Theory of conductivity response 9.3 MODES OF CONDUCI'MTYDETECTION 9.3.1 Direct and indirectconductivity detection Simultaneour direct and indirect conductiviry detection, 254. 9.3.2 Magnitude of conductance change on sample elution 9.4 ELECTRONIC CIRCUITRY AND CELL DESIGN FOR CONDUCTIVITY DETECTION 9.4.1 Introduction 9.4.2 AC conductance bridge 9.4.3 Bipolar-pulse circuitry 9.4.4 Four-electrode conductance measurement 9.4.5 Differentialconductivity detection 9.5 SUPPRESSORS IN IC 9.5.1 Function of the suppressor 9.5.2 Packedcolurhn suppressors 9.5.3 Hollow-fibre membrane suppressors Operating principle,264. Regeneranu,266. Packed-fibre suppressors, 266. 9.5.4 Micromembrane suppressor Design of the micromembrane suppressor,268. aperating principles, 269. Advantagesof the micromembrane suppressor,269.
228 230 232 232 233
237 237 238 240 240
245 245 245 245 249 249 252 252
254 255 255 256 258 258 260 261 261 262 264
267
Contents
xvi 9.5.5 Post-suppressors Design of post-suppressors,270. Advantages of post-suppression,271. 9.5.6 Other post-column signal enhancing devices Electrochemical suppressor, 271. Signal enhancement devices for ion-exclusionchromatogrqhy, 273. 9.5.7 Response equation for suppressed conductivity detection 9.5.8 Suppression based on precipitation or chelation reactions 9.6 PERFORMANCE CHARACTERISTICS OF CONDUCI'MTY DETECTORS 9.6.1 Non-linearity of calibration plots in suppressed IC Effect of hydrogen ions in the sample band, 277. Practical considerationof the hydrogen ion effect, 279. Effect of suppression mciency on linearity of calibration,280. 9.6.2 Temperature effects in conductivity detection 9.6.3 Conductivity detection without the use of standards 9.6.4 Utilization of the injection peak in conductivity detection 9.7 APPLICATIONS OF CONDUCTIVITY DETECTION IN IC 9.7.1 Anions 9.7.2 Cations 9.7.3 Weakly ionized species 9.8 REFERENCES
Chapter 10
Electrochemical Detection (Amperometry, Voltammetry and Coulometry)
10.1 INTRODUCIlON 10.1.1 Definitions Voltammetry andpolarography,291. Amperometry and coulometry, 291. 10.1.2 Interrelationships between voltammetry, amperometry, and coulometry Potential window, 292. Addition of an electroactivesolute, 293. Hydrodynamic voltammograms,294. Analysis of mixtures of electroactive species, 294. 10.I .3 Basic instrumentation for electrochemical detection in IC 10.1.4 Usage patterns for electrochemical detection in IC 10.2 MODES OF OPERATION OF ELECIROCHEMJCAL DJTECTORS 10.2.1 Direct and indirect detection Direcr elec~mhemicaidetection, 297. lndirect electrochemical detection,298. 10.2.2 Amperomemc detection with pulsed potential Problems with conventional DC amperometry,301. Pulsed amperomerric detection (PAD),302. Reverse-pulsemethods, 303. 10.3 ELECTRODES FOR AMPEROMETRIC DETECTION 10.3.1 Reference and auxiliary electrodes 10.3.2 Working electrode materials Mercury, 306. Carbon,306. Silver, platinum and gold, 307. Criteriafor selection of the working electrode material,308. 10.4 FLOW-CELL DESIGN AND RESPONSE EQUATIONS 10.4.1 Thin-layer cells 10.4.2 Row-through, highefficiency cells
270 27 1
275 276 277 277
28 1 282 283 285 285 285 285 288
29 1 29 1 29 1
292
294 295 297 297
30 1
304 304 305
309 310 311
Contents
xvii
10.4.3 Wall-jet cells 10.4.4 Polarographic cells 10.4.5 Multi-functional cells 10.4.6 Dual-electrode ampemmeuic cells 10.5 APPLICATIONS OF ELECTROCHEMICALDETECTION 10.6 REFERENCES
312 313 313 314 319 319
Chapter 11
Polentiornetrie Detection
11.1 INTRODUCTION 11.2 PRINCIPLES OF POTENTIOMETRIC DETECTION 11.2.1 General response equation 11.2.2 Instrumental considerations 11.3 INDICATOR ELECTRODES AND RESPONSE PROFILES 11.3.1 Ion-selective indicator electrodes pH electrodes, 326. Solid-state ion-selectiveelectrodes, 327. Liquid membrane electrodes, 327. 1 1.3.2 Coated-wire indicator electrodes Coating materials, 328. Calibration and response characteristics,.329. 1 1.3.3 Metallic copper indicator electrode Modes of operation of a metallic copper indicator electrode,331. 1 1.4 FLOW-CELLS FOR POTENTIOMETRIC DE"ION 1 1.4.1 Flow-cellsfor cylindrical ISEs 11.4.2 Other flow-cells 1 1.5 APPLICATIONS OF POTENTIOMETRIC DETECTION IN IC 11.5.1 Halides and pseudohalides 1 1.5.2 Weak acid anions 11.5.3 Cations 11S . 4 Applications of the metallic copper indicator electrode Direct detection,337. Indirect detection,338. 11.6 REFERENCES
323 323 324 324 324 325 325
328 329 333 333 334 336 336 337 337 337 34 1
Spectroscopic Detection Methods
343
12.1 INTRODUCTION 12.1.1 Types of spectroscopic detection in IC 12.1.2 Direct and indirect spectroscopic detection 12.2 UV-VISIBLESPECTROPHOTOMETRICDETECTION IN IC METHODS USING ION-EXCHANGE SEPARATIONS 12.2.1 Detection response equations for ion-exchange 12.2.2 Direct spectrophotomeaic detection in ion-exchange IC Direct detection of anions, 347. Direct detection of cations, 348. Replacement IC with spectrophotometric detection,350. 12.2.3 Indirect spectrophotometric detection in ionexchange IC Sensitivity of indirect spectrophotometric detection, 351. Indirect spectrophotometric detection of anions, 354. Indirect spectrophotometric detection of cations, 356. Simultaneour indirect detection of anions and cations,358. Indirect spectrophotometric detection without standards,360.
343 343 343
Chapter 12
344 344 347
35 1
xviii
Contents
12.3 SPECIROPHOTOMETRICDETECTION IN IC METHODS USING ION-INTERACTIONSEPARATIONS 12.3.1 Direct and indirect detection in ion-interactionchron%ttography Spectrophoromenic detection in permmently coated ioninteraction chromntogrophy, 361. Specwophoromenic detection in dynamically coated ion-interactionchromatography, 361. 12.3.2 W visualization detection in ion-interaction chromatography Mechanism of W visualization,363, Applications of W visualizanon in IC, 366. 12.4 SPEClXOPHOTOMETRICDETECTION IN IC METHODS USING ION-EXCLUSION SEPARATIONS 12.5 REFRACTIVEINDEX DEECTION 12.5.1 Direct refractive index detection 12.5.2 indirect refractive index detection 12.6 PHOTOLUMINESCENCE DETECTION IN IC 12.6.1 Direct fluorescenccdetection 12.6.2 Indirect fluorescence detection 12.6.3 Indirect phosphorescence detection 12.7 ATOMIC SPECTROSCOPICDETECTION IN 1C 12.7.1 Atomic absorption specaoscopy Discrete sampling, 376. Flow-rate matching, 376. Indirect detection using AAS, 377. 12.7.2 Atomic emission spectroscopy Plarma excitation,379. Replacement IC with spectroscopicdetection 379. 12.8 REFERENCES
360 360
363
369 369 369 370 37 1 37 1 372 374 376 376
378 380
Detection by Post-Column Reaction
387
13.1 INTRODUCTION 13.1.1 T p s of PCR systems Solution PCR. 387. Packed-bed PCR, 388. 13.2 HARDWARE FOR POST-COLUMNREACTTON 13.2.1 Pumps for PCR Effect ofpump pulsations, 389. Materialsfor pump construction, 3 PO. 13.2.2 Mixing chambers Tee-piece mixers, 391. Membrane reactor, 393. Comparison of dizerent mixing chambers,394. 13.2.3 Reactors 13.3 PCR DETECTION OF INORGANIC ANIONS 13.3.1 Phosphorus oxo-anions 13.3.2 Fe(CiO4)j as a postcolumn reagent 13.3.3 Other PCR methods for anions 13.4 PCR DETECTION OF INORGANIC CATIONS 13.4.1 Choice of the PCR reagent 13.4.2 PCR detection of transition mtals using PAR 13.4.3 PCR detection of lanthanides using Arsenazo dyes 13.4.4 PCR detection of other metal ions 13.5 PCR DETECTION OF ORGANIC SPECIES 13.6 REFERENCES
387 387
Chapter I 3
389 389 391
394 394 394 395 398 398 398 400 402 403 403 404
Contents
PART IV
xix
PRACTICAL ASPECTS
Chapter 14 Sample Handling in Ion Chromatography
409
14.1 INTRODUCTION 14.2 SAMPLE COLLECTION PROCEDURES 14.2.1 General 14.2.2 Sampling of gases, aerosols and particulates for IC analysis Filter media, 410. Impingers, 411. Solid aakorbents, 413. Diffusion denuders, 415. 14.3 EXTRACTION OF IONIC SPECIES FROM SAMPLES 14.3.1 Introduction 14.3.2 Simple extraction methods 14.3.3 Aciddigestion 14.3.4Alkali fusion 14.3.5 Combustion methods Ashing, 419. Schoenigerjlask combustion,419. Parr oxygen bomb combustion,420. Furnace combustion,421. Composition of absorbing solution, 421. 14.4 SAMPLE CLEANUP METHODS 14.4.1 Introduction 14.4.2 Sample filtration 14.4.3 Chemical modification of the sample using ioncxchange resins 14.4.4 Chemical modification of the sample using membranes Passive dialysis,425, Donnan dialysis,426. Electrochemical dialysis, 431. 14.4.5 Chemical modification of the sample with disposable cartridge columns Modes of operation, 432. Practical aspects,433. 14.4.6 Chemical modification of the sample by pre-columnreaction 14.5 CONTAMINATION EFFECI'S 14.5.1 Introduction 14.5.2 Contamination from physical handling of the sample 14.5.3 Contamination from filtration devices and cartridge columns 14.5.4 Contamination fmm chromatographic hardware components 14.5.5 Contamination of the column Contamination by organic species,440. Contamination by metal ions, 440. 14.6 SAMPLE HANTILING FOR ULTRA-TRACE ANALYSIS 14.6.1 Introduction 14.6.2 Large injection volumes 14.6.3 Trace enrichment with preconcenmtion columns Hardware considerations, 444. Choice of eluent, 446. Sample loading &em, 449. Concentrator column characteristics, 449. Preconcenrration of samples of low ionic strength, 451. Preconcentration of samples of high ionic strength, 452. Conclusions,453. 14.6.4 Dialytic trace enrichment methods 14.7 MATRIX ELIMINATION METHODS 14.7.1 Introduction 14.7.2 Oncolumn maaix elimination Matrix elimination with concentrator columns, 454.
409 409 409
410
417 417 417 418 418 419
423 423 423 424 425 432 435 435 435 435 436 437 440 441 441 442 443
453 454 454 454
Contents
xx
14.7.3 Post-column matrix elimination 14.8 REFERENCES
456 457
Chapter 15
463
Methods Development
15.1 INTRODUCTION 15.2 SELECTION OF APPROPRIAE CHROMATOGRAPHIC PARAMETERS 15.2.1 The separation method Anion separations, 465. Cation separations, 465. 15.2.2 Thedetectionmode 15.2.3 The nature of the eluent 15.3 OPTlMlZATION OF THE ELUENT COMPOSITION 15.3.1 Empirical selection of eluent composition 15.3.2 Principlesof computer optimization procedures Defining the optimizationproblem, 469. The search area, 469. Oprimization strategies. 469. Optimizationcriterion, 471. Response sutface, 471. 1 5.3.3 Application of computer optimization to IC Factorial design and Simplex methods, 472. Interpretive met&, 474. Summary, 475. 15.4 MULTI-DIMENSIONAL(COUPLED) IC METHODS 15.4.1 Introduction 15.4.2 Column switching methods 15.4.3 Coupled ion-exclusion / ion-exchange IC 15.5 AUTOMATION IN IC 1 5.6 REFERENCES
PART V
463 465 465 467 467 468 468 468
47 1
476 476 476 477 48 1 482
APPLICATIONS OF ION CHROMATOGRAPHY
Overview of the Applications Section
487
En vironm e n ta 1 Applications
489
16.1 OVERVLEW Table 16.1 Acid rain and rainwaters Table 16.2 Seawater and brines Table 16.3 River, stream, pond and lakewaters Table 16.4 Other natural waters Table 16.5 Air, aerosols and airborne particulates Table 16.6 Soils and soil extracts Table 16.7 Geological materials 16.2 REFERENCES
489 490 495 500 506 513 523 528 534
Chapter I 7
543
Chapter I 6
Industrial Applications
17.1 OVERVIEW Table 17.1 industrial wastewaters and effluents Table 17.2 Other industrial waters Table 17.3 Organic compounds Table 17.4 Pulp and paper liquors
543 544 550 559
566
xxi
Contents
Table 17.5 Acids and bases Table 17.6 Detergents and polymers Table 17.7 Fuels, oils and engine products 17.2 REFERENCES
570 576 582 585
Chapter 18 Analysis of Foods and Plants
593
18.1 OVERVIEW Table 18.1 Foods Table 18.2 Beverages Table 18.3 Plants and plant products 18.2 REFERENCES
593 594 605 617 627
Chapter 19
Clinical and Pharmaceutical Applications
633
19.1 OVERVIEW Table 19.1 Blood, serum and plasma Table 19.2 Urine Table 19.3 Other clinical and biological samples Table 19.4 Pharmaceuticals 19.2 REFERENCES
633 634 641 646 651 662
Chapter 20 Analysis of Metals and Metallurgical Solutions
667
20.1 OVERVIEW Table 20.1 Metal plating solutions Table 20.2 Metallurgical processing solutions 20.2 REFERENCES
667 668 683 69 1
Chapter 21
Analysis of Treated Waters
695
21.1 OVERVIEW Table 21.1 Drinking water Table 21.2 High purity waters 2 1.2 REFERENCES
695 696 706 713
Chapter 22
717
Miscellaneous Applications
22.1 OVERVIEW Table 22.1 Chemicals, chemical products and reaction mixtures Table 22.2 Photographic solutions and explosives Table 22.3 Miscellaneous applications 22.2 REFERENCES
Appendix A Statistical Information on Ion Chromatography Public ation s Appendix B Abbreviations and Symbols Index Journal of Chromatography Library (other volumes in the series)
717 718 725 728 732
735 745 75 1 773
This Page Intentionally Left Blank
1
Chapter 1 Introduction 1.1
BACKGROUND TO ION CHROMATOGRAPHY
Ion chromatography (abbreviated throughout this text as IC) is an analytical technique for the separation and determination of ionic solutes. A more detailed definition is presented later in Section 1.3. IC falls into the general classification of liquid-solid chromatographic methods, in which a liquid (called the eluent) is passed through a solid stationary phase and then to a flow-through detector. The stationary phase is usually in the form of small-diameter (e.g. 5 pm), uniform particles which are packed into a cylindrical column. This column is constructed from a rigid material (such as stainless steel or plastic) and is generally 5-30 cm long, with an internal diameter in the range 4-9 mm. The stationary phase particles are packed uniformly into the column and are retained by means of porous frits located at each end of the column. A high-pressure pump is required to force the eluent through the column at typical flowrates of 1-2 ml/min. The sample to be separated is introduced into the flowing eluent stream by means of an injection device inserted into the flow-path prior to the column. The detector usually contains a low volume (e.g. 4 pl) cell through which the eluent flows. The components of an ion chromatograph are shown schematically in Fig. 1.1. The ion chromatograph is operated in the elution mode. That is, a discrete amount of the sample is applied to the top of the column (via the injector), whilst the eluent is passed continuously through the column. The sample components progress through the column at different rates and therefore enter the detector at different times. The detector senses the sample components and produces the chromatogram. This process is illustrated schematically in Fig. 1.2.
Eluent delivery
Sample injection
Fig. 1.1 Components of an ion chromatograph.
Separation
Detection
2
Chapter 1
Eluent
Sample A+B
A
B
Time Fig. 1.2 Schematic illustration of the separation of two components (A and B) by IC.
1.1.1 Hardware and software components
Any chromatographic system of the type shown in Fig. 1.1 can be divided into hardware and software components. The hardware comprises the instrumentation (pump, injector, detector and data station), whereas the software consists of the variable components of the system (principally the nature of the stationary phase, the composition of the eluent and the flow-rate). This book concentrates on the software of IC. Hardware components will not be discussed, since these components are derived from (and in many cases are identical to) instrumentation developed for High Performance Liquid Chromatography (HPLC). The construction and operation of HPLC equipment has been treated thoroughly elsewhere 1e.g. 11. We need only note that a typical IC instrument uses a loop injector, a dual reciprocating piston pump (often with pulse dampeners to reduce pressure pulsations) and a chart recorder or computing integrator. The nature of the detector used is variable, but conductivity detectors are employed most frequently. We can further note that the hardware components in contact with the eluent can be constructed from either a polymeric material (e.g. PTFE) or stainless steel. The former material may be preferable when trace metal determinations are to be performed, since there is some possibility of contamination of the sample and eluent by metal ions produced from corrosion of stainless steel. 1.1.2
The chromatographic separation process
When a sample is introduced into an IC system, an equilibrium is established for each sample component between the eluent and stationary phases. Thus, for a component A we can write:
3
Introduction
Fig. 1.3 Schematic illustration of the distribution of solute molecules (represented by the black
dots) between the stationary and mobile phases when the distribution coefficient DA is (a) low and (b) high.
Am % A, where the subscript m refers to the mobile (eluent) phase and r refers to the stationary phase. The distribution of component A between the two phases is given by the distribution coefficient, DA,where:
The value of DA is dependent on the size of the population of molecules of component A in the stationary and eluent phases. This is represented schematically in Fig. 1.3, which shows the distribution of component A between the stationary and eluent phases for a small (Fig. 1.3(a)) and a large (Fig. 1.3(b)) value of DA. Since the equilibrium shown in eqn. (1.1) is dynamic, there is a continual, rapid interchange of molecules of component A between the two phases. The fraction of time, fm, that an average molecule of A spends in the mobile phase is given by:
fm =
amount of A in mobile phase total amount of A
(1.3)
That is, (1.4)
(1.5)
where Vm is the volume of the mobile phase and w is the weight of stationary phase (this
Chapter I
4
latter parameter is more convenient, but perhaps less logical, to use than the volume of the stationary phase). If we now define a new variable called the cupucityfuctor, k', as:
k' = DA($)
(1.6)
then eqn. (1.5) can be rewritten as:
f, =
1 1 +k'
(1.7)
Now the rate of travel of component A through the chromatographic system can be obtained by multiplying fm by the average linear velocity of the mobile phase, u, to give:
Rate of travel of A = u
(1L)
(1.8)
The rate of travel will therefore be determined by the average velocity of the mobile phase, the volume of mobile phase, the weight of stationary phase and the distribution coefficient for the particular component. If the chromatographic parameters remain constant, the only factor which changes from one sample component to the next is the distribution ratio. Provided that each component has a unique value of the distribution ratio, then each component will have a different (and characteristic) rate of travel through the stationary phase. That is, each component will emerge from the column at a characteristic retention time.
1.1.3 The chromatogram A representative chromatogram for two sample components is shown in Fig. 1.4. This chromatogram shows three peaks; one for each sample component (A and B) and a so-called "solvent" or "injection" peak. The first of these peaks contains the solvent in which the sample is dissolved, together with those components of the sample which show no interaction with the stationary phase. The sample solvent and unretained components take some time to pass through the column and interconnecting tubing, even though they do not interact with the stationary phase. This time is designated as the void time, to. Similarly, the time at which each retained solute appears is known as the retention time, tR, for that component. The values of to and tR will depend on the flow-rate of the mobile phase and the physical dimensions of the column and connecting tubing. It is therefore often convenient to express the retention of a component in terms of its capacity factor, which is expressed as: (1.9)
5
Introduction
Solvent
lime
-
Fig 1.4 A typical ion chromatogram resulting when a mixture of two sample components (1 and 2) is injected. 1.1.4
Mechanisms of interaction
Up to this stage, we have not specified the manner in which the sample components interact with the stationary and mobile phases. The actual mechanism by which this interaction occurs is one simple means for classifying chromatographic methods into broad groups. For example, the sample components may be retained on the stationary phase through the interaction of permanent dipoles on the component with permanent dipoles on the stationary phase. This results in an adsorption mechanism and gives rise to the general class of adsorption chromatographic methods in which polar stationary phases are employed. Similarly, partition chromatographic methods may be classified as those which involve the distribution of sample components between two immiscible fluid phases, one of which is immobilized to form the stationary phase. Subdivision of these general classes can then be made.according to the physical states of the stationary and mobile phases. For example, gas-liquid chromatography uses a gaseous mobile phase and a liquid stationary phase; liquid-solid chromatography (which embraces IC) uses a liquid mobile phase and a,solid stationary phase. It is unfortunate that IC does not lend itself readily to such a simple definition, because a wide range of different interaction mechanisms is employed. In the following Section, we will provide a working definition of IC which will be used to define the scope of this book.
6
1.2
Chapter 1
WHAT IS ION CHROMATOGRAPHY?
1.2.1 Historical aspects The foundations for modem IC were laid down by Small, Stevens and Bauman in 1975, when they described a novel ion-exchange chromatographic method for the separation and conductimetric detection of anionic and cationic species [2]. Their method employed a low-capacity ion-exchange stationary phase for the separation step, together with a second column and conductivity detector which comprised the detection system for continuous monitoring of the eluted ions. The second column was called a "stripper" column (which was later called a "suppressor") and this column served to reduce the background conductance of the eluent in order to enhance the detectability of the eluted ions. The term "Ion Chromatography" was introduced only when this technology was licensed to the Dionex Corporation for commercial development. For this reason. IC was originally interpreted to mean the specific use of the same combination of separation and detection modes as reported in the original publication. The growth of IC was very rapid because it provided, for the first time, a reliable and accurate method for the simultaneous determination of many simple inorganic anions and cations. In the early stages of its development, IC was seen essentially as a tool for inorganic analysis, but this perception changed with the realization that many organic solutes could also be analyzed using the same approach. This, in turn, led to the use of different stationary phases and detectors, so the original definition of IC became somewhat inaccurate. Later developments in 1979 by Gjerde, Fritz and Schmuckler [3-51 showed that the stripper column was not essential to successful conductivity detection, provided the correct types of stationary phase and eluent were used. At about the same time, the separation of inorganic ions on traditional c18 reversed-phase columns was demonstrated [e.g. 61. Although not specifically suggested by the authors of these papers, the new methods became commonly referred to as IC. 1.2.2 Definition
We are therefore left with the situation where the technique of 1C is very loosely defined, both in terms of the manner in which the solutes are separated and the types of solutes applicable to the technique. For this reason, it is pertinent to begin this book by delineating the range of techniques and applications which are to be included in our working definition of IC. We will consider IC to encompass those column liquid chromatographic techniques which can be used for the determination of Inorganic anions, such as Cl-, B r , Sod2-,efc. Inorganic cations, including alkali metal, alkaline earth, transition metal and rare earth ions, but not including neutral metal chelates. (iii) Low molecular weight (water soluble) carboxylic acids, such as formic acid, acetic acid, etc., and organic sulfonic acids, including detergents. (iv) Low molecular weight (water soluble) organic bases. (v) Ionic organometallic compounds, such as tributyltin, etc-.
(i) (ii)
Intrdction
7
It can be noted that amino acids and carbohydrates are not included, despite the fact that these species are sometimes considered to be part of IC, especially when ionexchange separations are used [7]. The justification for excluding these compounds is that, at best, they fall at the periphery of IC and as the reader is now aware, this text has already reached a considerable size. The column liquid chromatographic techniques applicable to the separation of the species listed in (i)-(v) above will be used to define the IC separation modes. These are: (i) Ion-exchange chromatography. (ii) Ion-interaction (or "ion-pair") chromatography using reversed-phase columns. (iii) Ion-exclusion chromatography. (iv) Miscellaneous separation methods, such as reversed-phase liquid chromatography, the use of chelating stationary phases, etc. Each of these techniques can be coupled with one or more of the following detection methods: (i) (ii) (iii) (iv) (v)
Conductivity detection. Electrochemical (amperometric or coulometric) detection. Potentiometric detection. Spectroscopicdetection. Post-column reaction detection.
Naturally, many of these separation and detection procedures are used routinely for the determination of species other than those listed earlier. Thus, the core of our definition of IC is the types of solutes to be considered, rather than the more conventional chromatographic approach of classification according to the interaction mechanism or the physical states of the stationary and mobile phases.
1.3
ORGANIZATION OF THIS BOOK
The separation and detection methods used in IC are manifold and in most cases, each separation method can be used with a number of different detection methods. We have elected to begin by discussing each of the separation methods used in IC, and to follow this with discussion of the detection methods. Accordingly, Part I (Chapters 2-5) of this book is devoted solely to ion-exchange separations, with separate chapters discussing stationary phases, eluents and retention models. Other separation methods, such as ion-interaction chromatography, ion-exclusion chromatography and reversedphase chromatography are covered in the chapters comprising Part I1 (Chapters 6-8). All of the detection methods listed above are then treated sequentially in Part 111 (Chapters 9-13). Part IV (Chapters 14 and 15) is concerned with some practical considerations in IC, including sample handling and methods development procedures. Finally, an extensive listing of applications is presented in Part V (Chapters 16-22).
Chapter 1
8
1.4
SOME FUNDAMENTAL CHROMATOGRAPHIC CONCEPTS
In this section we will provide a brief overview of some of the more important definitions applicable to modem liquid chromatography. The interested reader seeking further background information on chromatographic concepts is referred to the many excellent texts available on this topic (e.g. [8]). 1.4.1
Chromatographic efficiency
As sample components traverse a chromatographic column, the width of the band travelling through the stationary phase increases. This process is known as band broadening and is evident in Fig. 1.2, where the band due to each component in the mixture is more compact near the head of the column than it is when it reaches the detector. The degree to which two components are separated on a chromatographic system is governed, amongst other factors, by the amount of band broadening which has occurred. The best chromatographic systems are those in which band broadening is kept to a minimum. The "Plate Theory" of chromatography relates band broadening to solute migration [9, 101. This theory uses the concept of theoretical plates, in which the column is considered to consist of a series of thin sections, or "plates", each of which permits a solute to equilibrate between the mobile and stationary phases. The movement of a solute along the column is viewed as a stepwise transfer from one plate to the next. An efficient chromatographic system is one in which there is a large number of theoretical plates, or looked at another way, one in which each theoretical plate occupies only a very short portion of the overall column length. We therefore introduce the term N for the number of theoretical plates and HEW for the height equivalent to a theoretical plate (usually expressed in mm). These terms are related as follows:
HETP =
L N
(1.10)
where L is the length of the column (in mm). The value of N can be calculated from a chromatographic peak by considering the peak to be a population of solute molecules, each with a discrete retention time. This population can be characterized by the mean retention time of the molecules comprising the population (which is the retention time at the peak maximum) and the standard deviation, 0 , of the population. The latter parameter will define the width of the peak. N is given by:
[z) 2
N =
(1.11)
From eqn. ( l . l l ) , it can be seen that a high value of N (and hence an efficient chromatographic system) occurs when the standard deviation of the peak remains small while the retention time is large. The value of 0 can be estimated in a number of ways if
Introducrion
9
Fig. 1.5 Methods for estimating the standard deviation, (T. of a peak in which the retention times of the component molecules follow a Normal distribution.
the population of solute molecules is considered to be a Normal (Gaussian) distribution. Fig. 1.5 shows that the width of the peak at half height (wso) is equal to 2.3450. the width of the peak between tangents drawn to each side of the peak (WT)is equal to 40, and the width of the peak at 4.4% of peak height (w4.4) is equal to 50. Thus, 0 for a Gaussian peak is given by: (1.12)
So that N can be calculated by the following relationships:
(1.13)
For a number of reasons, values of N are meaningful only if they are calculated for peaks with moderately large values of capacity factor (e.g. k' > 5). We can express the separation of two peaks in terms of the resolution, Rs,which can be calculated from the retention time and standard deviation of each peak: (1.14)
10
Chapter 1
Using eqn. (1.12) we can rewrite eqn. (1.14) in terms of the width of each peak between tangents: (1.15)
We should note that all of the above relationships are valid only for Gaussian peaks, but for convenience, they are usually applied also to non-symmetrical peaks. 1.4.2 Factors affecting band broadening
We have already seen that the standard deviation, 0, of a chromatographic peak can be used to estimate the degree of band broadening which has occurred for that particular solute. It is more common to express the width of a Gaussian distribution in terns of the variance, 02. In this Section, wc will examine briefly the physical processes which contribute to the obscrvcd variance. These processes must be considered in the correct design of any chromatographic system so that variance (and hence peak width) can be minimized and efficiency therefore maximized. Eddy diffusion The solute molecules traversing a packed chromatographic column can follow a multitude of paths through the column. Each of these paths is of a different length, so that different molecules of the same component will take slightly varying times to travel through the column. This band broadening process is independent of the flow-rate (average linear velocity) of the mobile phase. The eddy diffusion effect can be minimized if the column is packed uniformly with particles of constant size. Longitudinal diffusion Molecules constituting a band of sample component in a chromatographic system will tend to diffuse out of the sample band during passage through the column. This diffusion occurs both in the direction of flow of the mobile phase, and in the opposite direction. Since diffusion is a time-dependent process, the longitudinal diffusion effect increases at low mobile phase flow-rates. Resistance to mass transfer In an ideal chromatographic system, the interchange of solute molecules between the mobile and stationary phases (i.e. the muss transfer process) would be instantaneous. This does not occur in practice. Additionally, different molecules of the same sample component may spend different amounts of time in the stationary and mobile phases. This leads to a band broadening effect which increases as the mobile phase flow-rate increases. Band broadening due to mass transfer can be. minimized through the use of packing materials which are either of small diameter (and therefore have short diffusion paths) or which have an active layer of stationary phase confined to the outer surface of the particle.
11
introduction
-E0.2 -
k E
W
I
0.1-
I
I
I
0.5 1.a Eluent flow-rate (mllmin)
1
1.5
Fig. 2.6 Plot of HETP versus mobile phase flow-rate for typical modern IC columns. The particle size for the packing material in A is 7 pm and in B is 10 pm.
Extra-column band broadening The sample band will undergo further broadening as a result of diffusion and mixing processes occurring outside the chromatographic column. These effects will be present in the injector, the detector flow-cell, the tubing used to interconnect the chromatographic components, etc. These areas are known as "dead volume" since they do not contribute to the separation process. In all types of chromatographic systems, dead volume should be minimized. The total measured variance for a solute peak can be considered to be the sum of the variances arising from each of the above sources. That is, (1.16)
where the subscripts ed, Id, mt and ec indicate eddy diffusion, longitudinal diffusion, mass transfer and extra-column variances, respectively. When a well-constructed ion chromatograph is used with a column containing uniformly packed, small diameter particles, the most significant of the terms in eqn. (1.16) is the variance arising from mass transfer effects. It is informative to assess the performance of a column in terms of a plot of HETP (which is directly proportional to the measured variance) versus the mobile phase flow-rate. Examples of such plots (often called van Deemter plots) for typical modem IC columns are given in Fig. 1.6, for two different particle sizes of packing material. There is an increase in HETP as the flow-
Chapter I
12
rate increases because of mass transfer effects, but it can be seen that the rate of increase of HETP with flow-rate is lower for the particles of smaller diameter. This permits the use of relatively high flow-rates without undue loss of chromatographic efficiency and shows why there is a trend towards smaller diameter packing materials.
1.5
9 10
REFERENCES Bristow P.A., LC in Practice, HETP,1976. Small H.. Stevens T.S. and Bauman W.C., Anal. Chem., 47 (1975) 1801. Gjerde D.T., Fritz J.S. and Schmuckler G., J. Chromarogr., 186 (1979) 509. Gjerde D.T., Schmuckler G. and Fritz J.S., J. Chromarogr., 187 (1980) 35. Fritz J.S., Gjerde D.T. and Schmuckler G., US Purenf,4,272,246 (1981). Molnar I., Knauer H. and Wilk D., J . Chromafogr.,201 (1980) 225. Weiss J., Handbook of Ion Chromatography,Dionex Corporation, Sunnyvale, CA, 1986. Snyder L.R. and Kirkland J.J., Introduction to Modern Liquid Chromatography, 2nd Ed., Wiley, New York, 1979. Martin A.J.P. and Synge R.L.M., Biochem:J., 35 (1941) 1358. van Deemter J.J., Zuideweg F.J. and Kiinkenberg A., Cbem. Eng. Sci., 5 (1956) 271.
Ion-Exchange Separation Methods
14
Principles Ion-exchangers
Classical 5 Modern Capacity Characteristics f Swelling Selectivity
INTRODUCTION (Chap 2)
Ion chromatSuppressed _I Non-suppressed ography
II
- Surfacefunctionalized
Resin-based ion-exchangers Agglomerated ion-exchangers
STATIONARY PHASES (Chap 3)
r Electrostatically bound
t
Hydrophobically bound Mechanically bound
Hydrous oxide ion-exchangers Carboxylic acids Sulfonic acids
KOH
Anions IONEXCHANGE
-
Polyol-borate EDTA I- Inorganic eluents Non-suppressed I r Nitric acid Organic bases Inorganic elueirts Complexing eluents I
, .
ELUENTS (Chap 4)
--
Anions
I
Suppressed
Gradient elution
F t
G & n a t e buffers Borate Phenate Amino acids Nitric acid High capacity suppressors lsoconductive gradients Baseline balancing
-E
Single eluent competing anion
-
RETENTION MODELS (Chap 5 )
Schematic overview of Part 1.
Cation-exchange
I
competing anions Single eluent competing cation Complexing eluenls
15
Chapter 2 An Introduction to Ion-Exchange Methods 2.1 INTRODUCTION TO ION-EXCHANGE This section introduces the fundamental terminology and principles of ion-exchange chromatography and is intended to provide an overview of the technique. The structures, classifications and important characteristics of ion-exchangers are described. From the basis given in this introduction, detailed treatment of specific ion-exchangers and eluent types used in IC will be provided in subsequent chapters of Part I.
2.1.1
Principles of ion-exchange
An ion-exchanger in aqueous solution consists of anions, cations and water, where either the cations or the anions are chemically bound to an insoluble matrix. The chemically bound ions are referred to as the fixed ions and the ions of opposite charge are referred to as the counter-ions. The insoluble matrix may be inorganic or may be a polymeric organic resin, and especially in older types of ion-exchangers, is generally porous in nature. These pores contain water from the aqueous solution, together with a sufficient concentration of counter-ions to render the whole exchanger electrically neutral. Counter-ions may move through the matrix either by diffusion or under the influence of an electric field and in the ion-exchange process itself, are replaced by ions of the same charge from the external solution. The ion-exchanger is classified as a cation-exchange material when the fixed ion carries a negative charge, and as an anionexchange material when the fixed ion carries a positive charge. The ion-exchange process can be illustrated by considering an anion-exchange material, for which the counter-ion is E-. The exchanger can therefore be represented as M+E-, where M+ denotes the insoluble matrix material containing the fixed (positive) ion. When a solution containing a different anion, A-, is brought into contact with the ion-exchanger, an equilibrium is established between the two mobile ions E- and A- as follows:
M+E- + A-
+ M+A- + E-
(2.1)
Since the electroneutrality of the solution must be maintained during the ionexchange process, the exchange is stoichidmetric, such that a single monovalent anion Adisplaces a single monovalent counter-anion E-.Eqn. (1) can be generalized for y moles of AX- exchanging with x moles (i.e. the stoichiometric amount) of EY- to give:
Chapter2
16
where the subscript m denotes the mobile (i.e. solution) phase and r denotes the stationary (or resin) phase. It should be noted that eqn. (2.2) is an equilibrium and under conditions where the exchanged ions remain in contact with the ion-exchange matrix, complete exchange will not be attained. Furthermore, the solution phase contains a co-ion of the same charge as the fixed ion, but this co-ion plays no part in the ion-exchange process and is therefore not shown. The equilibrium constant for the reaction shown in eqn. (2.2) is called the selectivity coefficient, and is given by:
where the parentheses indicate the activity of the designated species. Since the ion activity in the resin phase cannot be determined, KA,E is not a thermodynamically defined equilibrium constant but a coefficient which is defined according to practical requirements. Under conditions where the activity coefficients approximate unity, eqn. (2.3) can be simplified to:
where the brackets indicate molar or molal concentrations, or equivalent fraction units. For convenience, concentrations are often expressed in the units molesA for the solution phase, and millimoles/g for the matrix phase. The selectivity coefficient derives its name from the information it provides on the likelihood of exchange between two particular ions. In the above example, if K=l, then the ion-exchange matrix shows no selectivity for anion AX-over Ev-;that is, the ratios of the concentrations of these ions in the matrix and solution phases are equal. If K is greater than unity, the matrix (or resin) phase will contain a higher concentration of ion AX- than the solution phase, and will select AX- preferentially over Ey-. The reverse situation applies for values of K less than one. Clearly, a competition for the ionexchange sites exists between the two ions AX-and Ey-.It is convenient to designate EYas the competing anion and to describe AX-as the solute anion. For cation-exchange equilibria, a similar series of equations can be derived. Thus, for an ion-exchange reaction between the ion Ax+ and ion EY+, the equilibrium can be written:
YA,
X+
+ XE, Y+
+ YA:++
Y+ XE,
(2.5)
Introduction to Ion-Exchange
17
and after assuming that the activity coefficients are close to unity, the selectivity coefficient is given by: (2.6)
A more detailed discussion of retention in ion-exchange chromatography, as applied to modern ion chromatographic ion-exchangers, is presented in Chapter 5. Another parameter commonly used to express the position of an ion-exchange equilibrium is the distribution coefficient, DA, which is defined as the ratio of the concentrations of the ionic species in the exchanger phase and in the solution phase. Using the equilibrium shown in eqn. (2.2) as an example, the weight distribution coefficient for the solute ion AX- is given by:
Note that different symbols (e.g. KD)may be used for the distribution coefficient. The concentration units used in eqn. (2.7) are the same as those for eqn. (2.4). Distribution coefficients are concentration dependent, but under conditions where the exchanged ion exists in trace amounts in the presence of a higher concentration of competing ion, the distribution coefficient becomes constant. 2.1.2 Configuration of an ion-exchange chromatographic system Open-column (classical) ion-exchange chromatography Historically, ion-exchange separations have been performed in the open-column mode, wherein the ion-exchange matrix is loosely packed as small particles into a glass column of 1-2 cm diameter. The mobile phase, or eluent as it is usually called in ionexchange chromatography, contains the competing ion and is passed continuously into the column and percolates through it under gravity. When a separation is to be performed, the flow of eluent is stopped and a small amount of the sample mixture is applied to the top of the column and allowed to pass into the bed of ion-exchange material. Eluent flow is then resumed and fractions of eluent are collected at regular intervals from the column outlet, to be later analyzed for the solute components. The results of these analyses are then combined to provide an elution profile showing the volume of eluent required,to elute each sample component from the column. Fig. 2.1 shows a schematic representation of the apparatus used and a typical set of results obtained. This analysis procedure is described as the elution mode of chromatography, and whilst different alternatives are possible, this mode is the most commonly used in open column ion-exchange chromatography. Open column ion-exchange is not ideal for trace analysis for a number of reasons. First, the process is very slow because of the low eluent flow-rates employed, and attempts to increase the flow-rate (e.g. by raising the height of the eluent container
18
n
Chapter2
B
Fraction Number
Fig. 2.1 Apparatus for classical open column ion-exchange chromatographyand the type of result typically obtained. A and B are two components eluted from the column.
above the head of the column) invariably result in poorer separation efficiency. This effect is primarily a result of the poor mass-transfer characteristics of the relatively large particles used for the column packing. Second, the chromatographic efficiency attained is rather poor and some important separations cannot be achieved using this method. Third, it is inconvenient to collect and separately analyze fractions of eluent to determine the elution volumes of the sample components.
Modern ion-exchange chromatography Modem IC using ion-exchange separations circumvents these difficulties through the use of high efficiency ion-exchange materials combined with continuous flowthrough detection. Separations are performed in the column mode, where the ionexchanger exists as particles of uniform size packed into a column housing constructed of rigid material. The size of this column is dependent on a number of factors, including the chromatographic efficiency of the ion-exchange material and its mechanical stability. Typical columns are 15 cm in length, with an internal diameter of 3-5 mm. The particles of ion-exchange material are generally very much smaller than those used for classical open column ion-exchange chromatography. The further instrumental components of a chromatographic system used for ion-exchange follow the general outline presented in Fig. 1.1. The eluent must be pumped through the column since the small particle size of the stationary phase precludes appreciable flow under gravity. The sample mixture is introduced into the eluent via the injection port and is
Introduction to Ion-Exchange
19
separation takes place. Finally, the separated ions are detected with a flow-through detection device.
Eluent characteristics The eluent used in ion-exchange chromatography generally consists of an aqueous solution of a suitable salt or mixture of salts, with a small percentage of an organic solvent being sometimes added. The salt mixture may itself be a buffer, or a separate buffer can be added to the eluent if required. The prime component of the eluent is the Competing ion, which has the function of eluting sample components through the column within a reasonable time. The three foremost properties of the eluent affecting the elution characteristics of solute ions are: (i) The eluent pH. (ii) The nature of the competing ion. (iii) The concentration of the competing ion. The eluent pH can have profound effects on the form in which the functional group on the ion-exchange matrix exists, and also on the forms of both the eluent and solute ions. The selectivity coefficient existing between the competing ion and a particular solute ion will determine the degree to which that competing ion can displace the solute ion from the stationary phase. Since different competing ions will have different selectivity coefficients, it follows that the nature of the competing ion will be a prime factor in determining whether solute ions will be eluted readily. Finally, the concentration of the Competing ion can be seen to exert a major effect by influencing the position of the equilibrium point for ion-exchange equilibria, such as those depicted in eqns. (2.2) and (2.5). The higher the concentration of competing ion in the eluent, the more effectively the eluent displaces solute ions from the stationary phase and thus the more rapidly is the solute eluted from the column. In addition to the above three factors, elution of the solute is influenced by the eluent flow-rate and the temperature. Faster flow-rates lead to lower elution volumes because the solute ions have less opportunity to interact with the fixed ions. Temperature has a less predictable effect, which is somewhat dependent on the type of ion-exchange material used. An elevated temperature increases the rate of diffusion within the ion-exchange matrix, generally leading to increased interaction with the fixed ions and therefore larger elution volumes. Chromatographic efficiency is usually improved at higher temperatures. Prior to sample injection, the column must be equilibrated with eluent so that all the exchange sites on the stationary phase contain the same counter-ion. A point of terminology arises here, when one considers that equilibration of a column with a solution of competing ion (i.e. the eluent) results in the counter-ions associated with the fixed ions being completely replaced with competing ions. When the column is in this condition, the competing ions become the new counter-ions at the ion-exchange sites and the column is said to be in the forin of that particular ion. For example, an anionexchange column which is fully equilibrated with il NaOH eluent is in the hydroxide form. Reproducible elution volumes are obtained only when the column is converted to the same form prior to the injection of each sample and this becomes especially
Chapter2
20
ION-EXCHANGERS
I SILICA-BASEDMATERIALS polymer-coated silica+ functionalised silica*
I
I 1 ORGANIC MATERIALS INORGANICMATERIALS synthetic polymeric resins* aluminosilicates celluloses insoluble salts
dextrans
heteropolyacids clays hydrous oxides'
Fig. 2.2 Classification of ion-exchangers.
important when the eluent is changed. The time required for a column to equilibrate to a new eluent depends on the selectivity coefficient for the competing ion in that eluent over the previous competing ion, and also on the concentration of the competing ion in the new eluent. 2.1.3 Types of ion-exchange materials Ion-exchangers are characterized both by the nature of the ionic species comprising the fixed ion and by the nature of the insoluble ion-exchange matrix itself. The matrix types used for ion-exchange chromatography can be subdivided broadly into inorganic materials and organic (polymeric) materials, as illustrated in Fig. 2.2. The four materials shown in bold face type. and marked with an asterisk are those that are used for IC, and these will be discussed in detail in Chapter 3. However, it is pertinent to include here a brief general description of some of the more important properties common to all ionexchange materials, so that the special characteristicsof the four materials used for IC can be better appreciated when these materials are discussed more fully. With the exception of the hydrous oxide materials, the fixed ion in the above ionexchangers forms part of afuncrional group which is bound covalently to the surface of the material. The fixed ion in hydrous oxide exchangers is introduced by protonation or deprotonation reactions. Table 2.1 shows the types of functional groups commonly encountered in synthetic ion-exchangers. The chemistry involved in the introduction of these functional groups onto silica and synthetic polymers is discussed in Chapter 3. Cation-exchange resins are classified into srrong acid and weak acid types. The former retain the negative charge on the fixed ion over a wide pH range, whereas the latter type are ionized (and hence act as cation-exchangers) only over a much narrower pH range. Sulfonic acid exchangers are strong acid types, whilst the remaining cationexchange functional groups in Table 2.1 are weak. The weak acid types require a sufficiently high pH for use, and this is exemplified by the use of a NaOH eluent with a carboxylic acid cation-exchanger.
Resin-COOH + NaOH % Resin-COO-Na'
+ 30
(2.8)
Introduction to Ion-Exchange
21
TABLE 2.1 FUNCTIONALGROUPS FOUND ON SOME TYPICAL SYNTHETICION-EXCHANGE MATERIALS
Cation-exchangers Type
Functional group
Sulfonic acid carboxylic acid
Phosphonic acid Phosphinic acid Phenolic Arsonic acid Selenonic acid
-SO3- H+ -COO-H+ -PO3H- H+ -P02H- H+ -0H+ -As03R H+ -SeO3- H+
Anionexchangers
Type Quaternaryamine Quaternary amine Tertiary amine Secondary amine Primaryamine
Functional group -N(CH3)3+ OH-N(CH3)2(EtOH)+ OH-NH(CH3)2+ OH-NH2(CH3)+ OH-NH3+ OH-
Similarly, the anion-exchangers are classified as strong base and weak base exchangers. Quaternary amine functional groups form strong base exchangers, whilst less substituted amines form weak base exchangers. A weak base material will function only when the pH is sufficiently low to protonate the nitrogen atom in the functional group. This is illustrated below for a primary amine functionality in the presence of HCl eluent.
Resin-NH2 + HC1 % Resin-NHiCl-
(2.9)
Whilst a diverse range of ion-exchange functionalities exists, most IC separations with silica and organic ion-exchangers are performed on strong acid cation-exchangers of the sulfonic acid type, and on strong base anion-exchangers of the quaternary ammonium type. These strong cation-exchangers and strong anion-exchangersare often labelled SCX and SAX,respectively. 2.1.4
Characteristics of ion-exchangers
Ion-exchange capacity
The ion-exchange capacity of an ion-exchanger is determined by the number of functional groups per unit weight of the resin. It may be measured in a variety of units, the most common of which are milliequivalents (of charge) per gram of dry resin, or milliequivalents per millilitre of wet resin. In the latter case, it is usual to state the type of counter-ion present on the resin since this affects the degree of swelling of the resin and hence its volume. The ion-exchange capacity is often measured by saturating a known weight of resin with a particular ion, followed by washing the resin and then quantitative displacement of this ion. The number of moles of the displaced ion can then be determined. It should be noted that the capacity measured in this way is often somewhat higher than that applicable when the resin is packed as the stationary phase in
22
Chapter 2
a chromatographic column. The ion-exchange capacity of a resin plays a large role in determining the concentration of competing ion used in an eluent to be employed with that resin. Higher capacity resins generally require the use of more concentrated eluents, and as will become evident in Chapter 4, the eluent concentration is of paramount importance in IC. Classical ion-exchangeresins of the types described above have capacities which typically fall into the range 3-5mequivlg.
Swelling characteristics Organic resin exchangers consist of cross-linked polymer chains containing ionic functionalities. When such a material comes into contact with water, the outermost functional groups are solvated and the randomly arranged polymer chains unfold to accomodate the larger solvated ions. A very concentrated internal solution of fixed ions and counter-ions therefore exists and the mobile counter-ions tend to diffuse out of the exchanger into the external aqueous solution. The fixed ions cannot diffuse, and as a result, external water molecules are forced into the resin in an attempt to reduce the internal ionic concentration in the resin. The cross-linking of the resin provides mechanical stability which prevents dissolution of the resin, but swelling persists as a result of the equilibrium pressure due to the differences in concentration between the external and internal ionic solutions. The swelling pressure may be as high as 300 atmospheres for a polymeric resin of high ion-exchange capacity [l]. It is clear from the above description that the degree of swelling of the resin is dependent on the composition of the solution with which it is equilibrated. Thus, changes of eluent are accompanied by changes in the level of swelling and this effect has important ramifications on the types of resins suitable for use as stationary phases in chromatographic columns of fixed volume. Resins of low cross-linking (c 2%) exist as soft gels in aqueous solution and exhibit large volume changes when the eluent is altered; for this reason, they are unsuitable as stationary phases for high performance applications where the eluent is delivered under pressure. Macroporous resins (which are discussed in detail in Section 3.3) are more rigid due to their high cross-linking and their resistance to swelling effects renders them more suitable as chromatographic stationary phases for column packing purposes. Ion-exchange selectivity Selectivity coefficients (eqn. (2.3)) provide a means for determining the relative affinities of an ion-exchanger for different ions. It might be considered that a welldefined affinity series for anions and cations could be obtained by simple experiment, but in reality, the relative affinities show considerable variation with the type of ionexchanger and the conditions under which it is used. In some cases, simple ion-exchange may not be the sole retention mechanism operating; for example, partitioning of solute ions between the eluent and the pores of the stationary phase may occur, or the solute ion could be adsorbed onto the surface of the ion-exchange matrix. In view of these factors, it is possible to provide only approximate guidelines for the relative affinities of ionexchangers for different ions.
Introduction to Ion-Exchange
23
Selectivity coefficients for the uptake of cations by a strong acid cation-exchange resin are generally in the following order [2]:
Pu4+ >> La3+> Ce3+> Pr3+> Eu3+ > Y3+> Sc3+> A13+ >> Ba2+> Pb2+> Sr2+> Caz+> NiZ+> Cd2+> Cu2+ > Co2+> Zn2+> Mg2+> U022+ >> Tl+ > Ag+ > Cs+ > Rb+ > K+> N&+ > Na+ > H+ > Li+ It follows from this series that a cation-exchange eluent of 0.1 M KC1 will be stronger than that containing 0.1 M NaCl, provided other factors are equal. Selectivity coefficients for unions on strong base anion-exchangersfollow the general order:
> W0d2- > M 0 0 4 ~> - C104~- > C ~ 0 4>~ citrate > salicylate > C104- > SCN- > I- > S~o3~S042- > SO-j2- > HP042- > NO3- > Br- > NOz- > CN- > C1- > HCO3- > H2P04- > CH3COO- > 103- > HCOO- > BrO3- > ClO3- > F > OHSome general rules can be offered to assist in the prediction of the affinity order. These are based on a number of properties of the solute and the ion-exchanger and include: (i) (ii) (iii) (iv) (v) (vi) (vii)
The charge on the solute ion. The solvated size of the solute ion. The degree of cross-linking of the ion-exchange resin. The polarizability of the solute ion. The ion-exchange capacity of the ion-exchanger. The functional group on the ion-exchanger. The degree to which the solute ion interacts with the ion-exchange matrix.
An increase in the charge on the solute ion increases its affinity for an ionexchanger through increased coulombic interactions. This trend is known as electroselectivity and becomes more pronounced as the external solution in contact with the ion-exchanger becomes more dilute. Electroselectivity may be explained in terms of the Donnan potential, which is the potential difference arising because of the imbalance in the ionic concentra;ions in the resin bead and in the external solution [3]. An exchange involving the replacement of two bound monovalent ions with a single divalent ion causes this imbalance to be diminished, and is thus a favourable process. Electroselectivity is reflected in the following series of selectivity coefficients: Pu4+ >> La3+ >> Ba2+ >> T1+. For cations, the trend is very strong, such that the selectivity differences between these four ions are large. The size of the solvated solute ion also exerts a significant effect, with ions of smaller solvated size showing greater binding affinity than larger ions. Thus the selectivity sequence Cs+ > Rb+ > K+ > Na+ > H+ > Li+ is exactly the reverse of the sequence of ionic radii for the hydrated' ions, and follows the well-known lyotropic series with the most strongly hydrated ion, Li+, being held most weakly. This behaviour is related directly to swelling of the resin, since a smaller ion is more easily
Chapter2
24
accommodated in the resin pores. Thus, the higher the degree of cross-linking, the greater the preference of the resin for smaller solute ions. The combination of factors (i) and (ii) above suggests that binding affinity should increase with increasing polarizing power; that is, for ions with a high charge and small hydrated radius. Ion-exchange selectivity coefficients increase with the degree of polarizability of the solute ion. Thus, sulfonic acid fixed ions show greater affinity for the more polarizable Ag+ and Tl+ than for the alkali metal ions. Similarly, I- is more strongly retained on an anion-exchanger than Br- or Cl-.However, polarization does not explain why C l o g has a higher anion-exchange affinity than I-. The strong retention of anions such as Clod-, which are large, have low charge and a~ weak bases, can be attributed to the interaction of these ions with the water structure at the resin surface. Large, polarizable ions with a diffuse charge do not easily form a well-orientated layer of water molecules at their surface, and so tend to disrupt the surrounding water structure. This leads to an increase in free energy, which is the driving force for these ions to bind (that is, to form an ion-pair) with the fixed ion of an ion-exchanger, thereby diminishing both the disruption to the water structure and the free energy. This binding process is called water-structure induced ion-pairing 14). The trends evident from the remaining factors ((v) - vii)) listed above are not as clear-cut. The ion-exchange capacity of the ion-exchanger can affect the selectivity coefficients for some anions and cations, but for most ions, the selectivity coefficient remains essentailly constant as the ionexchange capacity is decreased. Similarly, the nature of the functional group exerts little effect for most ions, but significantly affects the selectivity coefficients for other ions. Large, polarizable anions such as BF4', I-, ClO4- and C l o g show changes in selectivity as the alkyl- substituents in trialkylammonium strong-base anion-exchangers are varied. This may be related to the waterstructure induced ion-pairing mechanism discussed above, with the larger functional groups (i.e. those with the largest alkyl- substituents) causing greatest disruption to the water structure, causing them to bind large, polarizable ions more strongly than smaller functional groups (5.61. Interactions between the solute ion and the ion-exchange matrix are difficult to predict, and are of course specific to individual ions. Factors (v)-(vii) above will be discussed later in Part 1 as a component of the detailed treatment of those ion-exchangers developed specifically for IC. 2.2
CLASSIFICATION OF ION CHROMATOGRAPHIC METHODS EMPLOYING ION-EXCHANGE SEPARATION
Ion-exchange methods have always formed the basis of IC, and due to a combination of historical development and commercial marketing influences, these methods have been divided somewhat arbitrarily into two main groups. 2.2.1 Non-suppressed ion chromatography
The first of these groups comprises all of the methods in which an ion-exchange column is used to separate a mixture of ions, with the separated solutes being passed directly to the detector. The hardware configuration employed is shown schematically
Introduction to Ion-Exchange
25
I
I Recorder or integrator Fig. 2.3 Block diagram showing the instrumental components used in non-suppressed IC.
in Fig. 2.3, from which it can be seen that this configuration parallels the traditional HPLC approach in which the chromatographic column is coupled directly to the detector. Some of the names proposed for this technique are [7-111: (i) "non-suppressedion chromatography", (ii) "single-columnion chromatography". (iii) "electronically-suppressedion chromatography". The first two names indicate that only a single chromatographic column is employed and that the eluent is not chemically modified prior to entering the detector, whereas the last name pertains to the fact that the background conductance of the eluent can be nulled electronically by certain types of conductivity detectors, "Non-suppressed IC" is the most frequently used term and will be employed throughout this text.
2.2.2
Suppressed ion chromatography
The second group of ion-exchange methods consists of those in which an additional device, called the suppressor, is inserted between the ion-exchange separator column and the detector, as shown in Fig. 2.4. The function of the suppressor is to modify both the eluent and the solute in order to improve the detectability of the solutes with a
7 Regenerant
I
Recorder integrator OrI
Fig. 2.4 Block diagram showing the instrumental components used for suppressed IC.
Chapter2
26
conductivity detector. The suppressor requires a regenerant (or scavenger) solution to enable it to operate for extended periods. Methods using the configuration shown in Fig. 2.4 are referred to as [7-131: (i) (ii) (iii) (iv)
"suppressed ion chromatography", "chemically-suppressedion chromatography", "eluent-suppressed ion chromatography", "dual-column ion chromatography".
The last of these names is misleading because modem suppressors are not columns, but rather flow-through membrane devices. The term "suppressed IC" is preferable and will be used in this text.
2.2.3
Similarities between non-suppressed and suppressed methods
The contention that the division of ion-exchange procedures into non-suppressed and suppressed methods is arbitrary merits further discussion. The first point to be made is that the detection mode employed in IC is the chief factor which determines the type of eluent and column used. Conductivity detection gives excellent sensitivity when the conductance of the eluted solute ion is measured in an eluent of low background conductance. This suggests that dilute eluents should be preferred, and in order for such eluents to act as effective competing ions (and so elute solute ions within a reasonable time), the ion-exchange capacity of the column should be low when conductivity detection is used. This principle applies equally well to both the non-suppressed and suppressed IC methods, although in the latter case, somewhat higher column capacities (and hence less dilute eluents) can be used because the suppressor serves to decrease the eluent conductance. With the exception of the suppressor itself, the only real distinctions which can be made between suppressed and non-suppressed methods are the small difference in column capacities and the use of a specialised group of eluents. These distinctions become pertinent only when conductivity detection is employed. This situation is quite common, but as Part I11 of this book will show, there are many alternative detection methods applicable to IC which do not require the use of a suppressor. The second point is that the suppressor is a device designed to improve detection (and will hence be discussed in detail in Part 111) and therefore exerts no influence on the ion-exchange separation, except for the fact that the eluent components must be compatible with the suppressor. The ion-exchange columns used with the nonsuppressed and suppressed approaches have very similar separation characteristics and this permits them to be used satisfactorily with either technique, provided that attention is paid to the ion-exchange capacities and pH limitations of each column. Indeed, the literature of IC abounds with examples of this practice. The above discussion suggests that little difference exists between non-suppressed and suppressed IC from a separation standpoint, and the stationary phases used for both approaches will be therefore be discussed together in Chapter 3. However, some aspects of suppressed and non-suppressed IC differ when eluents are considered, and the distinction between these approaches will be made in the discussion of eluents in Chapter
Introduction to Ion-Exchange
27
4. It is one of the prime aims of this book that non-suppressed and suppressed IC will be treated together wherever possible, so that the reader is directed towards the common elements of these approaches, rather than towards their differences.
2.3 1 2 3 4 5 6 7 8 9 10 12 13
REFERENCES Samuelson 0.. Ion Exchangers in Analytical Chemistry, Wiley, New York, 1953. Peters D.G.,Hayes J.M. and Heiftje G.M., Chemical Separations and Measurements, Saunders, Philadelphia, 1974, p. 583. Paterson R., An Introduction to Ion Exchange, Heyden, London, 1970, p. 30. Diamond R.M., J. Phys. Chem., 67 (1963) 25 13. Barron R.E. and Fritz J.S., J . Chromatogr., 316 (1984) 201. Barron R.E. and Fritz J.S.,J . Chromatogr., 284 (1984) 13. Fritz J.S., Gjerde D.T. and Pohlandt C., Ion Chromatography, Huthig, Heidelberg, 1982. Fritz J.S. and Gjerde D.T.,Ion Chromatography, 2nd edn., Huthig, Heidelberg, 1987. Smith F.C. and Chang R.C., The Practice of Ion Chromatography, Wiley, New York, 1983. Tarter J.G. (Ed.), Ion Chromatography, Marcel Dekker, New York. 1987. Weiss J.. Handbook of Ion Chromatography, Dionex Corporation, Sunnyvale, CA, 1986. Smith R.E., Ion ChromarographyApplications, CRC Press. Boca Raton, FI, 1988.
This Page Intentionally Left Blank
29
Chapter 3 Ion-Exchange Stationary Phases for Ion Chromatography 3.1
INTRODUCTION
The main factor which differentiates the ion-exchange materials used in IC from the conventional ion-exchangers discussed in Section 2.1.3 is their ion-exchange capacity. Ion-exchange separations in IC are generally performed on ion-exchangers with low ionexchange capacity, typically in the range 10-100 pequiv/g. As discussed earlier, this characteristic can be attributed chiefly to the fact that IC was developed originally for use with conductivity detection, which introduces a preference for eluents of low background conductance. The diversity of detection methods currently available (see Part 111) now makes it possible to use columns of much higher ion-exchange capacity, but because conductivity detection is still the most commonly employed detection mode, the majority of separations continue to be performed on low capacity materials. It is convenient to discuss the different types of ion-exchangers used in IC according to the groupings which were shown in Fig. 2.2.
3.2
SILICA-BASED ION-EXCHANGE MATERIALS
3.2.1 Types of silica-based ion-exchangers Silica-based materials constitute one of the most important classes of ionexchangers used in chromatography. Two distinct groups of materials can be recognized. The first comprises polymer-coated materials, in which a silica particle is first coated with a layer of polymer, such as polystyrene, silicone or fluorocarbon, and this layer is then derivatized to introduce functional groups of the types listed in Table 2.1. The main advantage of such a particle is that diffusion within the thin layer of polymer is very much faster than that occurring with totally polymeric particles. This leads to favourable mass-transfer characteristics and hence improved chromatographic efficiency for polymer-coated particles. The second group of silica-based ionexchangers comprisesfunctionalized silica materials, where a functional group (which acts as the fixed ion) is chemically bonded directly to a silica particle. The silica particles used for both polymer-coated and functionalized silica ionexchangers can be either pellicular or microparticulate. Pellicular materials have a solid, inner core and ion-exchangers formed from these particles have the functional
Chapter3
30
groups confined to the outer surface of the particle, or to a thin outer surface layer. Superficially-porous particles are one example of pellicular materials and these consist of solid, spherical glass beads of relatively large diameter (e.g. 30 pm), with a thin (approximately 1 pm) layer of porous silica on the surface. Zipax (Du Pont) is the chief example of such a pellicular, superficially porous material. Microparticulate materials are small diameter (e.g. 5 pm), fully porous particles, which can be irregular or spherical in shape. Ion-exchangers formed from microparticulate particles have functional groups distributed throughout the internal pore structure. Pellicular and microparticulate materials provide similar chromatographic efficiencies, but the pellicular materials are restricted to the separation of small amounts of sample because of their low active surface area. On the other hand, pellicular materials are more easily packed into columns than are microparticulate materials. The chromatographic properties of spherical and irregular microparticulate particles are similar.
3.2.2 Functionalized silica ion-exchangers ion-exchangers produced by chemically bonding the ion-exchange functional groups to a silica backbone were initially the main type of column packings commercially available for non-suppressed IC. Typically, quaternary ammonium functionalities or sulfonic acid groups are bound to microparticulate silica to produce strong base anion-exchangers or strong acid cation-exchangers, respectively. Functionalized silica IC packings have found most application in anion separations. Weak-base exchangers with a primary amine functional group can also be employed provided the eluent is sufficiently acidic to generate adequate anion-exchange capacity in order to give suitable retention of sample anions. Functionalized silica ion-exchangers can be produced by a variety of synthetic methods. Well-established and reliable procedures exist for the chemical bonding process and these reactions form the basis for the preparation of stationary phases for reversed-phase HPLC. The most commonly used method involves reaction of the silanol groups on silica with organochlorosilanes or organoalkoxysilanes. as shown in Fig. 3.1. This produces a siloxane-type (Si-0-Si-C) bonded phase, where the bonded layer can be monomolecular or polymeric in nature. The field of HPLC has provided a vast amount of experience in the preparation and handling of silica-based stationary phases. Many different types of functionalized silica ion-exchangers were in use in 1979, when non-suppressed IC was first introduced [l].
I -SOH
I I
-%OH
I
I + SOCI, - b - - S i - C I
H2NC%CH2NH2
I
+ CISiR3 or ROSiR3
b
I
-Si-NH-CH2CH2NH2 I I
-Si-O-SiR3 I
Fig. 3.1 Reaction schemes for the preparation of functionalized silica ion-exchangers.
Ion-ExchangeStationary Phases
31
These materials were of the moderate to high capacity type and, as such, were unsuitable for use with conductivity detection because of the high eluent concentrations required. For this reason, specially designed low-capacity exchangers were produced, with ionexchange capacities of about 100 pequiv/g. Table 3.1 lists the characteristics of some functionalized silica IC packing materials, together with those of the polymer-coated silica IC materials discussed in the next Section. When employed with dilute eluents, these columns give excellent separations of common anions, together with adequate sensitivity using conductivity detection. Fig. 3.2(a) shows a typical separation obtained with a low-capacity silica-based anion exchanger (TSKgel IC-Anion-SW), whilst a separation of inorganic cations on a lowcapacity functionalized silica cation-exchanger (Vydac 400 IC) is illustrated in Fig. 3.2(b). The traditional types of strong or weak silica-based ion-exchangers can also be employed for IC, especially when a detection method other than conductivity is used. Chromatograms obtained on high capacity functionalized silica SAX and SCX exchangers are shown in Fig. 3.3, whilst Fig. 3.4 illustrates the use of a weak-base amino column.
3.2.3
Polymer-coated silica ion-exchangers
Pellicular ion-exchangers formed by coating an impervious silica core with a polymeric ion-exchange material have found widespread application in non-suppressed IC. These packing, marketed under the name of Zipax, are of low ion-exchange capacity, have rapid radial mass transfer characteristics [26] and their relatively large particle size (ca. 35 pm) provides for ease of packing. Fig. 3.5 shows representative separations of anions and cations on polymer-coated silica ion-exchangers. The characteristics of some polymer-coated IC materials are included in Table 3.1. Polymer-coated silica cation-exchangers for IC can be synthesized by depositing varying film thicknesses of a pre-polymer onto 5 pm porous silica, with subsequent immobilization of the polymer by in-situ cross-linking reactions using radical starters or y-radiation [46, 471. Poly(butadiene-maleic acid) (PBDMA, see below) is the preferred polymer and the film thickness can be varied to regulate the ion-exchange capacity of the final product. Ionization of the carboxylate functionalities in the polymer is significant above pH 3, so weak acid eluents can be used to separate inorganic cations. Fig. 3.6 illustrates the simultaneous separation of monovalent and divalent cations on PBDMAcoated silica.
COOH . .
COOH Poly(butadiene-maleicacid) (PBDMA).
.E
-
+
32
El
0
mi=
;-
Q-n
In-
- E,
i -
-!e -$!
;=
.-C
- E .-
-a--
-* -0
I,
I D
.-c E
-
-2 -L"
-0'
c
.-E
-a'
-m
-0
Chapter 3
33
Ion-ExchangeStationary Phases
TABLE 3.1 SOME COMMERCIALLY AVAILABLE SILICA-BASEDIC COLUMN PACKINGS Column
Silica type
Vydac 302.IC Vydac 300.IC Wescan ANon/S TSKgel IC Anion SW Nucleosil SB PartisillO SAX Zorbax NH2 zipax SAX Vydac 400.IC vydac sc Wescan CatiodS TSK gel IC Cation SW Nucleosil 10 SA PartisillO SCX Zipax SCX Nucleosil-5-100-PBDMAa
Functionalized Functionalized Functionalised Functionalized Functionalized Functionalized Functionalized Polymer-coated Functionalized Functionalized Functionalised Functionalized Functionalized Functionalized Polymer-coated Polymer-coated
Class
Particle size (PI
Anion Anion
8 5.5 10
Anion
Anion Anion Anion Anion Anion Cation Cation Cation Cation Cation Cation Cation Cation
5-8
5
Capacity (Wg) 100 250 400 lo00
10 10 25-37 4.5 30-44 10
500
5
450 lo00
10 10 15-37
12
Refsb
2-5
6-8 9-12 13-16 17-20
21-23 24 25,26 6
100
500
5
5
27-29 30-33 34-36 37 38-41 42-45 46,47
a PBDMA = polyfiutadiene-maleic acid). b This listing is not comprehensive, but provides some examples of the use of each column.
Nafion, a cation-exchange material manufactured by Du Pont, may be coated onto an octadecylsilyl reversed-phase column by simple hydrophobic interaction [49]. The resultant material can then be used to pack ion-exchange columns of unusual selectivity. This approach has been demonstrated for the separation of aromatic base cations and may prove to be applicable also to the separation of inorganic cations. 3.2.4
Advantages and limitations of silica-based IC packings
Chromatographic efficiency The prime advantage of 1C columns packed with silica-based materials is the favourable chromatographic efficiency they produce when correctly packed into chromatographic columns. As an illustration of this efficiency, the peak for nitrate ion in a typical separation gave 16,652 theoretical plates per metre using the 5 0 method of calculation [50]. Silica can be obtained as small diameter particles with a very narrow size distribution, and being a non-swelling, rigid material, can be packed at high pressure to produce a uniform and stable ,chromatographic bed which is not subject to stringent pressure or flow-rate limitations during usage. For this reason, columns packed with silica-based ion-exchangers may be relatively long (e.g. 30 cm) and tolerate backpressures as high as 4,000 psi. Moreover, organic modifiers can be used freely with
34
Chapter3
I
0
I
1
1
I
I
2
3
6
I
1
5 6 7 Time ( m i n )
I
I
8
I
9
I
1
0
Fig. 3.4 IC on an amino column. Zorbax NH2 (250 x 4.6 m m ID)column using 0.03 M H3P04 at pH 3.2 as eluent. Solute concentrations 25-100 ppm. Spectrophotometricdetection at 205 nm was used. Reprinted from [24] with permission. Time (min) 0
1
I
I
I
1
0
2
4
6
0
Time Imin) (01
I
10
I
20
1
lb)
Fig. 3.5 IC on polymer-coated silica ion-exchangers. (a) Zipax-SAX (200 x 4.5 m m ID)
column, using 2 mM sodium adipate as eluent. Solute concentrations: 2-20 ppm. Conductivity detection was used. Reprinted from [26] with permission. (b) Zipax-SCX (250 x 4.6 mm ID) column using 2.5 mM copper sulfate as eluent. The peaks are. in the negative direction because indirect spectrophotometric detection was employed (see Ch. 12). Reprinted from [45]with permission.
Ion-ExchangeStationary Phases
35
Na*
I
0
I
4
I
0
I
12
I
16
I
20
I
21
1
27
Time (rnin]
Fig 3.6 Separation of monovalent and divalent cations on a poly(butadiene-maleic acid)-coated silica cation-exchange (125 x 4.5 mm ID) column. The eluent was 10 mM tartaric acid, and conductivity detection was employed. Reprinted from [46] with permission.
functionalized silica materials (but not with polymer-coated silica exchangers) to manipulate ion-exchange selectivities or to reduce column fouling by organic sample components. The cost of silica-based IC columns is generally significantly less than for alternative packings. A further advantage of silica-based materials is that the retention mechanism operating is frequently more simple than with other materials because of the low probability of secondary interactions between solute ions and the silica substrate [45]. This means that rctention times are often shorter on silica columns than on other packings having similar ion-exchange capacities. p H limitations A number of serious drawbacks exists with the use of silica-based IC materials. The first of these is the restricted pH range over which the columns can be operated. At pH values below 2.0, the covalent bond linking the ion-exchange functionality to the silica substrate may become unstable and prolonged usage at low pH can result in a progressive loss of ion-exchange capacity as the functional groups are cleaved. Eluents or samples of alkaline pH must also be avoided because of dissolution of the silica matrix itself. The upper limit of pH which can be tolerated by silica-based IC columns varies with the type of column, however severely curtailed column lifetime is often observed when 'eluents of pH greater than 7 are used. This pH limitation is more severe than
36
Chapter3
Zn
0
5
Time (min)
10
Fig. 3.7 Elution of cations from an anion-exchange column. A Vydac 302.IC (250 x 4.1 m m ID) column was used with 2mM potassium phthalate at pH 5.0 as eluent. Detection: conductivity. Solute concentrations: 4 mM for the metal ions. Reprinted fnnn [54]with permission.
that commonly applied to reversed-phase HPLC packing materials, but this can be rationalized by the more exposed nature of the silica surface in the very lightly functionalized IC packings. When this form of column degradation has occurred, column regeneration is not possible [51]. Wide variation in ion-exchange capacities of new silica-based IC columns (from 0.19 to 0.66 mequiv/column for Vydac 302.IC columns) has been reported [52], leading to variation in retention times between columns used under the same eluent conditions. The same authors have devised a simple procedure for compensating for these capacity variations.
Retention of metal ions on silica aninn-exchangers Metal ions are retained on silica-based anion-exchange IC columns and may cause interference with anions by eluting in the same time frame. This phenomenon has been observed for Cu2+,Pb2+and Zn2+ on a Vydac column operated with phthalate eluents in the pH range 4-5 [53]. Under the same conditions, Na+, K+,Ca2+, Mgz+, Ni2+, Mn2+ and Cd2+were unretained, whilst Fe3+,A13+ and Hg2+ were not eluted from the column. Silica itself can act as both an anion- or cation-exchanger, as discussed in Section 3.5. Although silica-based IC columns are often "end-capped" (i.e. reacted with trialkylsilane reagents) to reduce the number of silanol (SOH) sites present at the stationary phase surface, it is to be expected that some cation-exchange capacity would exist when neutral or alkaline eluents are employed. However, studies have shown [54] that metal ion
Ion-ExchangeStationary Phases
37
retention is not dependent on the concentration of free silanol groups at the silica surface and it has been proposed that the metal ions showing moderate retention on the silica column are retained by adsorption of their anionic complexes formed with eluent species. Fig. 3.7 shows the elution of metal ions and nitrate in the same chromatogram.
Sample size The final limitation of silica-based IC columns is their susceptibility to overloading. This results in severe distortion of the chromatographic peaks and is a direct result of the combination of low ion-exchange capacity and use of a dilute eluent. When the concentration of solute ions in the sample increases beyond a critical point, the solute ions are no longer confined to a discrete, well-shaped band on the Stationary phase. Some ions move along the column at a relatively faster rate than the main band of solute ions, producing a "fronted" peak at the detector. This limitation is common to any ionexchanger of low capacity and is therefore not specific to silica-based materials.
3.3 RESIN-BASED ION-EXCHANGERS Low-capacity ion-exchange resins were the stationary phases with which nonsuppressed IC was initially introduced to the scientific community by Gjerde, Fritz and Schmuckler in 1979 [l, 551. These materials are produced by chemical derivatization of synthetic organic polymers. Fig. 3.8 shows the manner in which ion-exchange resins may be classified.
I IC ION-EXCHANGE RESINS1
+
Macro porous
Microporous
SURFACE-FUNCTIONALIZED MATERIALS I
I
1
Surface sulfonated
Surface aminated
AGGLOMERATED MATERIALS
binding
binding
U Polystyrenedivinylbenzene
Polymethacryiate
Fig. 3.8 Classification of resin-based ion-exchangers for IC.
Mechanical binding
38
Chapter3
Fig. 3.9 Reaction of styrene (1) with divinylbenzene (2) to produce styrene-divinylbenzene copolymers (3).
Organic materials, in the form of synthetic polymeric resins, are the most widely used types of ion-exchangers. They are manufactured by first synthesizing a polymer with suitable physical and chemical properties, and this polymer is then further reacted to introduce the functional group which acts as the fixed ion in the ion-exchange process. The polymer used as the backbone of the ion-exchange resin must be mechanically stable and pxsess the required degree of insolubility for use in aqueous systems, even after the derivatization process which invariably incorporates polar functionalities onto the resin. Whilst a number of polymers satisfy these criteria, most ion-exchange resins are made from copolymers produced from styrene and divinylbenzene, with a small number consisting of copolymers of divinylbenzene and acrylic or methacrylic acid. 3.3.1
Polymerization reactions
In polystyrene-divinylbenzene(PS-DVB) copolymers, the styrene is cross-linked with itself and with divinylbenzene into a polymeric network, according to the reaction scheme shown in Fig. 3.9. The reaction of methacrylic acid with divinylbenzene to produce cross-linked polymethacrylate resin is shown in Fig. 3.10. Of the two types of copolymer depicted in Figs. 3.9 and 3.10, the PS-DVB is by far the most commonly used. It can be seen from Fig. 3.9 that reaction of styrene with itself produces linear chains, whilst the difunctional divinylbenzene causes these chains to become cross-linked. This cross-linking imparts mechanical stability to the polymer and increases the average molecular weight. The degree of cross-linking is determined by the percentage of divinylbenzene in the reaction mixture. The reaction is carried out by suspending the reactants as droplets in an aqueous phase. Ethylbenzene is usually present in the divinylbenzene and the reaction proceeds via a free-radical chain mechanism. Radical-producing initiators such as benzoyl peroxide are commonly used, together with a polymerization inhibitor (such as sodium dichromate) and a protective colloid (such as inorganic clays, alumina or carboxymethylcellulose) [56]. When the reaction mixture is stirred at an appropriate rate, oil droplets are formed, which on heating polymerize to
Ion-ExchangeStationary Phases
CH=CH,
39
-6-
CH,-
I
I
COOH
CH3 CH=CH,
-C-
I
COOH
CH,-CH-CH,-
I I COOH C-
Fig. 3.10 Reaction of rnethacrylic acid (1) with divinylbenzene (2) to produce methacrylatedivinylbenzene copolymer (3).
form the polymer beads. The characteristics of the polymeric resin bead are regulated by the reaction conditions. Particle size is determined to a large degree by the oil-water ratio in the reaction, the rate of agitation, the geometry of the reaction vessel, and the nature of the protective colloid. The resin beads are essentially solid. Resins prepared in this way are described as microporous to indicate that they have low porosity. Microporous resins are relatively rigid (depending on the degree to which they are cross-linked) and have low surface area due to the lack of a significant internal pore structure. The surface area of the resin can be increased enormously if internal pores are introduced into the resin, particularly if these pores are of sufficient size for penetration by solvents. This may bc achieved by conducting the polymerization reaction in a solvent system in which the solvent will dissolve the monomer but tends to precipitate the polymerized material. Alcohols and hydrocarbons are examples of solvents suitable for this purpose with PS-DVB polymerization. When this solvent is removed after polymerization, a proliferous material containing an open, porous structure is produced. Such polymers are called macroporous, or macroreticular (this latter name was originally applied to some of the resins produced by Rohm Rr Haas) to describe their open network structure. Porous resins can also be produced if the cross-links in the polymer are introduced after polymerization by a chemical reaction in the preformed resin bead. Performance of this reaction in the presence of a solvent which will dissolve the monomer and non-cross-linked polymer, leaves a solid resin which is permeated with channels of uniform size. Toluene and xylene are suitable solvents for PS-DVB copolymers. Resins manufactured in this way have been called isoporous. All types of porous resins require a sufficient degree of cross-linking to ensure that the structure does not collapse. Macroporous resins have well-regulated pore sizes and materials can be produced with pore diameters up to lWA. The surface areas of macroporous resins are often in excess of 500 m2/g. Fig. 3.11 shows a schematic representation of a microporous and a macroporous resin bead.
40
Chapter3
Schematic cross-sectionai structure of (a) microporous and (b) macroporous (macroreticular) resin beads.
Fig. 3.1 I
The procedures by which these polymers are converted into functional ionexchangers, and the chromatographic characteristics of the resultant materials, are discussed in the following Sections.
3.3.2
Surface-functionalized
cation-exchaneeresins
Synthesis Conversion of polymeric resins into cation-exchange materials can be achieved by chemically treating the surface of the resin to introduce the functional groups which form the fixed ions of the ion-exchanger. Some of the main classes of functional groups which can be introduced onto polymeric resins were listed in Table 2.1, with H+being shown as the counter-ion in each case. The sulfonic acid functional group produces a strong type of exchanger, whilst the rest are classified as weak. Sulfonic acid groups can be introduced onto PS-DVB copolymers by reaction with sulfuric acid, sulfur trioxide, fuming sulfuric acid or chlorosulfonic acid, as shown in Fig. 3.12. A potential problem with these reactions is to ensure intimate contact between the sulfonating agent and the hydrophobic polymer surface. However, this problem is generally not severe since as the surface of the beads become sulfonated, the bead swells in the aqueous reagent solution, thereby increasing contact with the sulfonating reagent. The end result of this process is that sulfonation occurs in a relatively uniform manner throughout the bead. Sulfuric acid is the most commonly employed sulfonation reagent and is used at elevated temperatures, sometimes with a catalyst. If the reaction is allowed to go to completion, monosulfonation of the aromatic rings occurs, with the functional groups being located in the orrho, mera or puru positions relative to the bond between the ring and the hydrocarbon chain. The benzene rings from both the styrene and the divinylbenzene become sulfonated. Resins with low cross-linking do not become fully functionalized, even under severe reaction conditions, because they do not swell sufficiently to ensure adequate contact with the sulfonating reagent. In these cases, the use of organic swelling agents, such as chlorinated hydrocarbons, results in improved physical properties of the finished product and increased reaction rates. The pre-formed
Ion-ExchangeStationary Phases
41
Fig. 3.12 Reaction schemes for the introduction of sulfonic acid functional groups onto styrenedivinylbenzenecopolymers.
polymer bead is swollen by direct contact with the solvent in aqueous suspension, after which the solvent-swollen bead is sulfonated. The solvent leaves the bead during or prior to sulfonation, or may react with the sulfonating agent and in so doing, become a better swelling agent for the sulfonated polymer. Sulfuric acid may itself serve as the slurtying agent during sulfonation, but must be present in excess concentration in order to remove the water produced in the reaction. Organic solvents are generally used as the reaction medium when chlorosulfonic acid or sulfur trioxide are used as the sulfonating agents. Sulfur trioxide may also be employed in the gaseous phase, but this process is only applicable to macroporous resins which do not require the use of a swelling agent. The ion-exchange capacity of sulfonated resins can be regulated by controlling the sulfuric acid concentration and also the reaction temperature and time. Correct design of the reaction apparatus permits the resin-sulfuric acid reaction mixture to be immediately separated on a vacuum-assisted filter system once the prescribed reaction time is completed 1571. The reaction can then be quenched by placing the resin in a large volume of cold water, or by washing the resin with water, ethanol and acetone [58]. Table 3.2 lists the ion-exchange capacities reported for various reaction conditions. Further details of the synthesis of cation-exchangers are available elsewhere [57,59-611. The utility of the above sulfonation procedures is not restricted to PS-DVBresins. For example, phenyl-modified Kel-F (polychlorotrifluoroethylenereacted with phenyllithium) has been sulfonated [62] to give a cation-exchange capacity of 20 pequiv/g.
Chapter3
42 TABLE 3.2
TYPICAL REACTION COhQITIONS FOR THE SYNTHESIS OF SLJLFONATED CATIONEXCHANGE RESINS
Ion-exchange capacity (pequiv/g)
Reaction time
Reaction temperature
(h)
(OC)
XAD-2
9.7
54
6.5% PS-DVB 8% PS-DVB 8% PS-DVB 8% PS-DVB 12%PS-DVB
47
10 1.5 90 90 35 103 103
90
XAD-2 4% PS-DVB
Base resin
88
70
70 25 25
90
-10
80 80 90
80 60 80
[H2S04] (%)
Ref
70 90 96 96
59 59 60
100 100 100
96
60 57 57 57
60
Characteristics The low-capacity cation-exchangers produced by partial sulfonation of PS-DVB have characteristics which differ markedly from classical ion-exchange resins, where the sulfonation reaction is permitted to go to completion. The classical materials attain capacities of about 5 mcquiv/g by the introduction of sulfonic acid groups throughout the macroporous structure of the resin. This results in poor chromatographic mass-transfer characteristics because of the requirement for solute ions to traverse long diffusion paths, thereby leading to the elution of relatively broad bands of solute. Mass-transfer is improved markedly if the sulfonic acid groups are confined to the outer surface of the resin bead, producing a material which is essentially pellicular in nature. This can be achieved by limiting the degree of sulfonation, which at the same time decreases the ionexchange capacity. Such materials are often described as surface-sulfonated cationexchange resins. Several studies have examined the manner in which the sulfonate functional groups are distributed on the resin bead [57, 60.631. Stevens and Small [63] performed an experimental optimization of the depth of the sulfonation layer. Working on the assumption that the bead is composed of a 100% sulfonated layer ( i . e . every benzene ring has one sulfonic acid group) residing on a non-sulfonated core, they found that the optimal thickness of the sulfonated layer was 200 A for a 50 prn bead. Hajos and Inczedy 1571 used secondary electron image scanning electron microscopy to demonstrate that sulfur (from sulfonic acid groups) was present only on the surface of the bead. In a similar experiment, Sevenich and Fritz [60] obtained transmission electron micrographs of thin sections of functionalized resin which had been saturated with uranyl ions in order to provide high electron capture at the functional group sites. This study showed that the sulfonatcd zone consisted of a band of complete sulfonation extending some 200 A into the bead. The density of sulfonate groups in this layer was similar to that existing throughout the entire bead of a typical high capacity, fully sulfonated cation-exchange
Ion-ExchangeStationary Phares
43
Fig. 3.Z3 Schematic representation of the cross-section of a surface-sulfonated cation-exchange resin. The negative charges represent sulfonic acid groups which are located on the surface of the resin bead. Note that the interior of the bead is not sulfonated as occurs in high capacity, fully functionalized materials. resin. These results confirm that the resins are indeed surface-sulfonated and are pellicular in nature. Fig. 3.13 gives a schematic representation of a surface-sulfonated cation-exchange resin. There is a significant side-effect resulting from this partial sulfonation of PS-DVB. The relatively sparse distribution of the functional groups on the resin surface means TABLE3.3 SOME COMMERCIALLY AVAILABLE SURFACE SULFONATED RESIN-BASED CATlONEXCHANGERS USED FOR IC
Polymer
Column
Particle size
Capacity (Pew
Refsa
5 10 12 35 100 560
66-68 69-7 1 72-75 76 77 78 79 80 81-85
(Pm)
Dionex HPlC CS- 1 Dionex HPIC CS-2 Waters 1C Pak C Hamilton PRP-X200 Interaction ION-200 Interaction ION-210 Wescan Cation/R Wescan SACb Aminex A5 Aminex A9 Mitsubishi MCI CPK-08 a This listing is not
PS-DVB PS-DVB PS-DVB PS-DV,B Polyvinyl aromatic PS-DVB PS-DVB PS-DVB PS-DVB PS-DVB PS-DVB
20 15 10 I0 10
5 10 10 13 11 20
40 5000 5000 1700
41, 85
96
comprehensive, but provides some examples of the use of each column. anion- and cation-exchange capabilities.
b This column has both
44
Chapter3
( Li-Cs
Li+
1
la+
l g 2' K'
1[
0.3pS
IHZ
Rb*
L-
0
L
8
12 16 20 Time (min)
L
b
I
I
0
L
I
I
8 12 l i m e lmin)
1
16
Ib)
Fig. 3.14 Typical chromatograms obtained with surface sulfonated resins. (a) Dionex HPICCSI column using 5 mM HCI as eluent and conductivity detection. Reprinted from [64]with permission. (b) Column packed with surface-sulfonated 35-55 pm resin, with 2.5 mM mphenylenediaminedihydrochloride and 2.5 mM HN@ as eluent. Conductivity detection was used. Reprinted from [65] with permission. that a significant portion of the surface remains as unfunctionalized resin, which can contribute to solute retention by simple adsorption effects. This behavior has been shown to be particularly important in the retention of organic cations [59], where solutes such as (m-ninobenzy1)trimethyl-ammoniumions are retained by a combination of ionexchange and surface adsorption processes. Under some circumstances, surface adsorption may also play an important role in the retention of inorganic cations, especially when they are chromatographed as complexes with an organic ligand. Low-capacity surface-sulfonated cation-exchange relrins have proved to be very successful in routine applications. Fig. 3.14 shows typical separations of monovalent or divalent cations obtained with these materials. Some commercially available IC resins of this type are listed in Table 3.3; all the materials shown exhibit similar chromatographic selectivities because the functional group is the same in each case.
Ion-ExchangeSmtionary Phases
45
Fig. 3.25 Two step reaction scheme for the production of anion-exchangers from styrenedivinylbenzenecopolymers.
3.3.3 Surface-functionalized anion-exchange resins Synthesis
Reaction of PS-DVB copolymer to produce a strong-base anion-exchange resin generally proceeds via chloromethylation, which can be accomplished readily using chloromethylmethylether in the presence of a suitable catalyst. This reagent also serves as a swelling agent which promotes intimate contact between the resin and reagents, leading to more uniform and rapid reaction. The reaction may be carried out at moderate temperature (58 OC) with a mild catalyst such as zinc chloride, or at lower temperatures with more active catalysts. This procedure results in high yields, but has the disadvantages of the extreme toxicity of chloromethylmethylether, and difficulty in controlling the degree of chloromethylation. After chloromethylation, a second reaction with an amine produces the required anion-exchange material. The complete reaction scheme is shown in Fig. 3.15. The ion-exchange capacity is regulated both by the time permitted for the chloromethylation reaction to continue and by the reaction temperature. Table 3.4 shows some capacities obtained by reacting 3 g portions of various resins with 10 ml of chloromethylmethylether, 10 ml of methylene chloride, 3 ml of nitromethane and 3 g of zinc chloride at room temperature for varying amounts of time. These results show clearly the dependence of the reaction on the type of base polymer employed. Whilst Fig. 3.15 shows the method for the introduction of quaternary ammonium functionalities onto a PS-DVB polymer, the same reactions are applicable to other types of polymer with an aromatic moiety. The type of amine used in the second step of the above synthesis determines the nature of the functional group formed on the resin. Some typically used amination reagents and the functional groups formed on the resin are listed in Table 3.5. Alternative chloromethylation procedures have been reported in which the use of highly carcinogenic chloromethylmethyletheris avoided. Barron and Fritz [88] used paraformaldehyde and aqueous hydrochloric acid in the absence of a catalyst. This approach simplifies control of the reaction and eliminates secondary cross-linking reactions found in the presence of Lewis acid catalysts. Furthermore, reaction in
46
Chapter 3
TABLE 3.4 ANION-EXCHANGE CAPACITIES OF POLYMERS CHLOROMETHYLATEDFOR VARYING AMOUNTS OF TIME. DATA TAKEN FROM REFS [ 11 AND [87] Resin
Surface area (m2/g)
XAD- 1
Pore diameter
(Angstroms)
Chloromethylation time (min)
205
100
XAD-2
300
90
XAD-4
784
50
Capacity (wquiv/g)
7
<14 20 210 15 90
40 350 920 220 480 590 130 260 630
120 5 10
90
TABLE 3.5 ANION-EXCHANGE FUNCTIONAL GROUPS PRODUCED FROM TYPICAL AMINE REACTANTS Amine
Rl
R2
R3
Functional group
Ammonia Methylamine Dimethylamine Trimethy lamine Dimethylethanolamine
H CH3
H H
H H
c113
c113
II
CH3 CH3
CH3 CH3
CH3 C2H40H
Resin-CHz-N+(H)3 Resin-CH2-N+(H)zCH3 Resin-CH2-N+(H)(CH3)2 Resin-CHz-N+(CH3)3
Resin-CHz-N'(C2bOH)(CH3)2
aqueous solution prevents swelling of the polymer, which serves to confine the introduction of the functional groups to the easily accessible surfaces of the resin. l'he mechanism of this reaction is thought to proceed via an HOCH2+ reactive intermediate which is substituted onto the aromatic nucleus, after which the -OH group is replaced by -CI,with the equilibrium lying far to the right in this replacement step [89]. Chloromethylation of polymeric aromatic hydrocarbons using dimethoxymethane, sulfuryl chloride and chlorosulfonic acid has been reported 1901 and has been applied successfully lo the synthesis of a phenyl-modified Kel-F anion-cxchangcr (621. Table 3.6 lists some of the commercially available polymer-based anion-exchangers used for IC. Several of these exchangers employ a methacrylate polymer as the base material. The reaction scheme used to functionalize these polymers differs from that used for PS-DVB polymers. Little dctail is available, however the reaction of hydroxyethyl copolymers with aqueous solutions of arnines has been reported [113]. The
47
Ion-ExchangeStationary Phases
TABLE 3.6 SOME COMMERCIALLY AVAILABLE SURFACE AMINATED RESIN-BASED ANIONEXCHANGERS FOR IC Column
Polymer
Waters IC Pak A Waters IC Pak Anion HR Waters IC Pak Anion HC TSKgel IC anion PW Bio-Gel TSK 1C anion PW Mitsubishi MCI SCA-01 Hamilton PRP Xl00 Wescan Anion/R Wescan SAC” Aminex A-27 Aminex A-28 Interaction ION-100 a This listing is not
Methacrylate Methacrylate Methacrylate Methacrylate Methacrylate Poly acrylate PS-DVB PS-DVB PS-DVB PS-DVB PS-DVB Polyvinyl aromatic
Particle size
Capacity
10
30 30 30 30 30
7 10 10 10 20 10
10 10 13 9 10
Refsa
(Cldg)
10
170 200 3200 3200 100
9 1-94 95-97 98-100 101-103 104 86 105-107 108 80 109, 110 111 50,77, 112
comprehensive, but provides some examples of the use of each column. anion- and cation-exchangecapabilities.
b This column has both
ion-exchange capacity of the resin was controlled by regulating the mine concentration and the reaction time. In addition to the materials discussed above, several other polymeric anionexchangers have been studied as potential stationary phases for JC. Low-capacity polyvinylchloride resins (5-460 pequiv/g) have been successfully synthesized [ 1 141, but were soluble in the aqueous eluents used in IC. Polyacrylonitrile cross-linked with divinylbenzene has been surface-functionalized to give anion-exchange capacities in the range 7-53 pequiv/g [I 141 and preliminary studies showed that this material gave good separation of common anions using very dilute eluents. However, no detailed investigation of the chromatographic characteristics of this resin has been reported.
Characteristics Surface-aminated anion-exchange resins are similar to their surface-sulfonated counterparts in that they are essentially pellicular in nature, with the exchange groups being confined to the surface of the resin bead. This again leads to the desirable characteristics of rapid mass-transfer and low ion-exchange capacity. These factors, coupled with the resistance to swelling of such materials, renders them ideal for the preparation of high efficiency IC columns. Fig. 3.16 shows a schematic representation of a surface-aminated anion-exchanger. For some years after their introduction, resin-based anion-exchangers gave somewhat poorer efficiencies than silica-based materials of the same capacity, and this was probably due to the use of relatively large diameter particles and difficulties in
4%
Chqpter3
Fig. 3.16 Schematic representation of the cross-section of a surface-aminated anion-exchanger.
The positive charges represent quaternary ammonium functionalities which are located on the surface of the resin bead. Note that the interior of the bead is not aminated as occurs in high capacity, fully functionalized materials. column packing. Modem packings, such as those shown in Table 3.6, are capable of excellent separations. Fig. 3.17 shows representative chromatograms obtained on derivatized PS-DVBand polymethacrylate ion-exchange resins. It should be noted in passing that it is not essential for the functional groups to reside on the exterior of the resin bead, provided that the thickness of the functionalized zone is minimal. Thus, centrally-grafted ion-exchangers are possible in which a small, central part of the resin bead is functionalized, and this is surrounded by a thicker layer of neutral resin. The utility of such resins for IC has been investigated [ 1151 and it has been suggested that chromatographic efficiency should be maintained in these materials because the diffusion of ions through the unfunctionalized zone of the resin bead occurs at the same rate as that in the bulk mobile phase. The chromatograms obtained with a 20-25 pm, irregular shaped resin of 50 pequiv/g capacity showed long retention times and broad peaks, indicating that centrally-grafted ion-exchange resins require further optimization for high efficiency IC. The problem of metal ion retention causing interference in anion determinations was noted earlier for silica-based anion-exchangers. The same behavior has been reported for resin-based anion exchangers [54] synthesized from styrenedivinylbenzene or methacrylate polymers. The absence of any cation-exchange sites on these polymers suggests strongly that retention of metal ions occurs through adsorption of complexes formed with the eluent, which in the case under discussion was phthalate.
Effect of functional group A considerable range of substituents can be incorporated into the quaternary ammonium functionality of a strong-base anion-exchanger,either as the linkage between the quaternary nitrogen atom itself and the resin, or as one of the alkyl groups bound to the nitrogen atom. Fritz and other workers have made extensive studies of the effects on ion-exchange selectivity caused by the nature of the substituents on the functional group
Ion-ExchangeStationary Phases
49
I"'
r 0
I
5
I
I
10
15
1
I
1 7 0
I
I
2
Time Imin)
L Time (min)
la)
lb)
I
6
Fig. 3.Z7 Separation of anions on (a) polymethacrylate-based and (b) PS-DVB-based surfaceaminated anion exchangers. Conductivity detection was used in each case. (a) Waters IC-Pak Anion HR column was used with standard borate/gluconate at pH 8.5 as eluent and (b) Hamilton PRP-X1M) (150 x 4.1 mm ID) column using 4 mMp-hydroxybenzoic acid at pH 8.6as eluent. Chromatogramscourtesy of Waters and Hamilton.
[116-1201, and the results of these studies are summarized below. The relative retention times of some monovalent anions on a series of benzyltrialkylammonium resins with different functional groups (but similar ion-exchange capacities), using the same eluent (benzoate) are shown in Fig. 3.1 8(a). The functional groups used are trimethylammonium (TMA), triethylammonium (TEA), tripropylammonium (TPA), tributylammonium (TBA), trihexylammonium (THA) and uioctylammonium (TOA), which show a steady progression in size. The data were derived by dividing the retention time for each solute by that of chloride obtained on the same column. Weak acid anions such as acetate (and formate, lactate, glycolate and nicotinate, which are not displayed in Fig. 3.18(a)) show virtually no changes in selectivity as the functional group is varied. The same is true for fluoride, dihydrogen phosphate, azide and methanesulfonate, which for purposes of clarity, are also not displayed. Increases in relative retention (and hence an increase in the selectivity coefficient) are noted for nitrite, bromate, nitrate, chlorate, and particularly for the larger, more polarizable ions iodide and tetrafluoroborate. Confirmatory results have been reported for a different series of anion-exchangers [ 1191. (ii) Similar experiments for divalent anions using a phthalate eluent showed the opposite trend [ 117, 1191, where relative retention (and hence selectivity
(i)
CI-
TMA
TEA
T ~ A TEA
Functional group la)
TAA
0
0
0 T ~ A
TMA
TAA
Functional group (bl
Fig. 3.18 Dependence of relative retentions of (a) monovalent and (b) divalent anions on functional group structure. Surface aminated PS-DVB resins were used as column packings, with (a) benzoate and (b) 0.4 mM potassium hydrogen phthaiate at pH 5.0 as eluents. Data taken from [118and 1161.
P (r,
51
Ion-Exchange Stationary Phases
coefficients) decreased as the size of the functional group was increased. This is illustrated in Fig. 3.18 (b), which for comparison, also shows data for some monovalent anions. (iii) The above selectivity behavior is much more evident on columns of higher ion-exchange capacities (e.g. 90 pequiv/g) than on columns of lower capacity. (iv) The length of the alkyl chain connecting the quaternary ammonium functional group to the benzene ring of the base polymer can be varied. A study using resins in which this alkyl chain ("spacer-arm") length was varied from one to six carbon atoms showed virtually no changes in relative retentions of monovalent and divalent anions, except for large polarizable ions [121]. These ions (e.g. nitrate and iodide) showed decreased relative retention on resins with longer spacer-arms, as shown in Table 3.7. To summarize, polarizable monovalent anions will be retained longer in relation to chloride using resins with larger (more hydrophobic) functional groups, whereas divalent anions exhibit behavior which is roughly opposite. The effect of functional group size on the monovalent anions can be rationalized in terms of the water-structure induced ion-pairing mechanism discussed in Section 2.1.4. Polarizable, poorly hydrated anions such as bromide, iodide and nitrate do not readily form a well-orientated water layer at their surface and this causes a disruption of the surrounding water structure. This provides impetus for the formation of an ion-pair between the anion and the cationic functional group on the resin, since the resultant ion-pair can form a tighter water structure than the separate anion and cation. Increased ion-pair formation leads to TABLE 3.7 EFFECT OF "SPACER-ARM' LENGTH ON ADJUSTED RETENTION TIME RATIOS OF MONO- AND DNALENT ANIONS. DATA FROM [ 1211 Anion
~R'/~R',cI
C1 Resin Chloride Methylsulfonate Ethylsulfonate Nitrite Bromide Nitrate Propylsulfonate Chlorate Sulfate Thiosulfate Iodide t ~for ' C1- (min) aA
C2 Resin
C3 Resin
C4 Resin
C6 Resin
1.oo
1.oo
1.00 1.40 1.47 2.13 3.07 3.40 4.47 8.27 16.67 12.20 1.43
1.oo 1.07 1S O 1S O 2.00 2.46 3.29 3.86 8.53 18.43 8.86 1.33
1.oo
1.09 1.55 1.78 2.53 3.62 3.79 7.13 7.36 16.21 17.59 1.66
1.oo 1.06 1.35 1.32 1.88 2.65 3.06 4.12 8.50 18.29 11.24 1.62
1.14 1.57 1.36 1.79 2.43 3.36 3.71 8.50 15.36 8.57 1.33
0.2 mM sodium phthalate eluent (pH 6.0) was used at a flow-rate of 1.0 ml/min.
52
Chapter 3
increased retention. The same applies when one considers the size of the cationic functional group forming the fixed ion on the resin. An increase in size leads to greater disruption of.the water layer and hence increased ion-pair formation with solute ions, and therefore greater retention. This effect can be expected to be most pronounced for polarizable solute anions, as shown in Fig. 3.18(a). The same mechanism can be used to explain the influence of the alkyl chain "spacer-arm'' on selectivity. As the length of the spacer-arm increases, the cationic functional group becomes less water-structure breaking because it is well-removed from the bulky aromatic rings comprising the base polymer. Resins with long spacer-arms will therefore show weaker relative retention of large polarizable anions than will resins with short spacer-arms. The behavior of well hydrated, divalent ions, such as sulfate, can be explained by considering the electroselectivity effect, wherein ions of higher charge are attracted more strongly to the fixed ion and are therefore retained more strongly (see Section 2.1.4). Larger functional groups have a more diffuse charge, leading to reduced electroselectivity and hence shorter retention times. The conclusion which can be reached is that the water-structure induced ionpairing effect is dominant for monovalent anions, whereas the electroselectivity effect dominates for divalent anions. It must be remembered that these effects are, at best, only qualitative and can provide no more than a very general guide to the prediction of anion-exchange selectivities. Moreover, the nature of the functional group used in commercial IC anion-exchange columns is often proprietary information which is not disclosed. In addition to the water-structure and electroselectivity effects discussed above, the nature of the functional group may influence retention in yet another manner [120]. The surface functionalization of the resin means that the external, ionic functional groups reside in close proximity to the internal, non-polar matrix which is comprised, on a microscopic level, of an entangled mesh of polymer chains having some degree of mobility. Formation of an ion-pair between the functional group of the resin and a solute ion would be favoured because such an ion-pair would be more hydrophobic than the functional group alone. Interaction between the ion-pair and the non-polar matrix would be increased as the charge on the solute ion becomes more diffuse (e.g. for large, polarizable ions) and the ion-pair becomes more hydrophobic. Nature of the polymeric substrate The low degree of functionalization required for IC use implies that a significant proportion of the surface area of the resin exists as neutral polymer. It has been calculated for PRP-X100 anion-exchange resin (produced by amination of a PS-DVB resin of 415 m2/g surface area and 0.79 cm3/g pore volume) that the degree of functionalization is about 0.15 [105]. This means that approximately one in every seven of the surface aromatic rings of the polymer is functionalized. It can therefore be expected that some of the reversed-phase character of the original polymer will be retained. This has been confirmed for PRP-X100 [lo51 and also for other PS-DVB anion- and cation-exchangers. This reversed-phase character leads to the existence of surface adsorption effects which contribute to the retention of some species. Adsorption of organic ions with some
Ion-ExchungeStationary Phases
53
lipophilic character is observed [59] and this factor also causes some differences in ionexchange selectivities between resin- and silica-based ion-exchangers. These differences are quite small because ion-exchange is the dominant retention mechanism on both types of material, however selectivity changes can be exploited when required. A further ramification of the reversed-phase characteristics of PS-DVB resins is that lipophilic (presumably organic) sample components may be very strongly bound to the resin, resulting in column fouling. This effect is particularly prevalent when aqueous eluents are used because water has the lowest reversed-phase eluotropic strength of any solvent. In comparison, polymethacrylate is a hydrophilic resin and so is less prone to fouling by lipophilic sample components. Additionally, surface adsorption makes a less significant contribution to solute retention than is the case for PS-DVB exchangers. The differences in selectivity between silica, PS-DVB, polyvinyl aromatic, and methacrylate anion-exchangers can be seen from Fig. 3.19, which shows chromatograms for these ion-exchangers using the same type of eluent. The eluent strength has been adjusted to give approximately the same retention time for sulfate. The ions separated in Fig. 3.19 all show little or no selectivity changes with variation of the functional group on the exchanger, so the differences in selectivity can be attributed largely to the nature of the polymer. It is interesting to note that relative retention times differ markedly between columns and the elution order of sulfate and iodide on the polyvinyl aromatic polymer differs from that observed on the other materials. 3.3.4
Advantages and disadvantages of resin-based ion-exchangers
p H tolerance When compared with silica-based materials, the prime advantage of resin-based ion-exchangers is their tolerance towards eluents and samples with extreme pH values. Most of the resins listed in Tables 3.3 and 3.5 may be used with eluents of pH 0-14. This has a number of important effects. For cations, acidic eluents such as 10 mM nitric acid can be used, and for anions, alkaline eluents such as 1 mM potassium hydroxide can be employed. The range of ion-exchange separations is therefore extended to include ions such as silicate and cyanide which are not ionized significantly (and are hence unretained) in the eluent pH range accessible to silica-based columns. Moreover, the ability to vary eluent pH over a wide range makes it possible to exploit selectivity effects which arise for solutes which are subject to protolytic equilibria, and this factor will be further explored in the discussion of eluent pH in Section 4.2.3.
Chromatographic efficiency The earliest developed IC resin-based exchangers gave somewhat disappointing chromatographic efficiencies [55, 571. However, modern, small diameter ion-exchange resins give efficiencies which are equivalent or superior to those obtained on silica exchangers of similar characteristics. For example, it is not uncommon for columns packed with surface-functionalized resins to provide in excess of 25,000 theoretical plates per metre. This point is illustrated in Table 3.8, which shows some experimental values of the number of theoretical plates for a range of columns.
54
Chapter3 INJECTION
1 INJECTION
;I-
NOj
Br-
r
0
1
1
I
I
5
10
15
20
Tlme
I
0
I
5
10
15
Time ( m i n ) (bl
{min)
(a 1
INJECTION
I
0
5
10
Time ( m i n ) IC
I
15
I
I
20
0
I
1
5
10
15
Time Iminl (d)
Fig. 3.19 Selectivity differences between (a) silica, (b) polyvinyl aromatic, (c) PS-DVB and (d) methacrylate anion-exchange substrates. The following columns and conditions were used: (a) Vydac 302.IC 4.6 column with 3 mM phthalate at pH 5.3 as eluent, (b) Interaction ION-100 column with 1 mM phthalate at pH 4.1 as eluent, (c) Hamilton PRP-X100 column with 1 mM phthalate at pH 5.3 as eluent and (d) Waters IC Pak A column using 1 mM phthalate at pH 7.0 as eluent. Reprinted from [50] with permission.
55
Ion-ExchangeStationary Phases
TABLE 3.8 CHROMATOGRAPHIC EFFICIENCIES OF SOME ANION-EXCHANGE COLUMNS. DATA TAKEN FROM [SO] Column
Vydac 302.IC Interaction ION- 100 HamiltonPRP-X100 TSK IC Anion PW Waters IC Pak A
Packinga
Silica PVA PS-DVB PMA PMA
Dimensions (mm)
250~4.6 50 x 3.2
150~4.1 50 x 4.6 50x4.6
Eluent (phthalate) mM
PH
3 1 1
5.3 4.1 5.5 5.3 7.0
1
1
Flowrate (mvmin) 2.0 1.0 2.0 1.2 1.2
Theoretical plates per column
4163 605 2356 959 1306
Pa metre
16652 12100 15706
19180 26120
a PVA =polyvinyl aromatic, PS-DVB =polystyrene divinylbenzene, PMA = plymethacrylate.
Examination of the schematic cross-sectional diagrams of surface-functionalized resins shown in Figs. 3.13 and 3.16 could lead one to speculate as to why the solute ions do not diffuse into the interior, unfunctionalized zones of the resin bead. This diffusion would result in broadening of solute bands and loss of chromatographic efficiency. The explanation which can be advanced is that the interior of the resin is very hydrophobic and so there is negligible diffusion by highly ionic solute species [63, 651.
Pressure limitations One significant drawback of the use of polymeric resins as ion-exchangers is that they are often subject to pressure limitations. Polymethacrylate in particular is a relatively soft material and this characteristic restricts the column length and the eluent flow-rates which can be used. Columns of 50 mm length are common and since the column length influences the number of theoretical plates per column, these short columns may not be suitable for the separation of some complex mixtures unless high efficiency packing materials are employed. On the other hand, macroporous crosslinked PS-DVB polymers, such as those listed in Tables 3.3 and 3.5, have high mechanical rigidity and stability and can therefore be used in long columns and at higher eluent flow-rates (see Table 3.8). Operating conditions A restriction on the.pcrmissible percentage of organic modifier in the mobile phase generally applies to resin-based columns, with the actual limits imposed being dependent on the type of resin and the degree of cross-linking. This restriction can often limit the approaches taken to regenerate columns fouled with organic materials. Low-capacity resin-based exchangers are prone to overloading with increased sample size in exactly the same manner as discussed previously for their silica-based counterparts.
Chapter3
56
3.4 3.4.1
AGGLOMERATED ION-EXCHANGE RESINS
Description
Agglomerated ion-exchange resins contain an internal core particle, to which is attached a monolayer of small-diameter particles which carry the functional groups comprising the fixed ions of the ion-exchanger. Provided the outer layer of functionalized particles is very thin, the agglomerated resin exhibits excellent chromatographic performance due to the very short diffusion paths available to solute ions during the ion-exchange process. Schematic illustrations of agglomerated anion and cation-exchangersare given in Fig. 3.20. The central core (or support) particle is generally PS-DVB of moderate crosslinking, with a particle size in the range 10-30 pm. It has been shown experimentally that 2-5% cross-linking gives optimal physical stability to the core particle. The outer microparticles consist of finely ground resin or monodisperse latex (with diameters in the approximate range 20-100 nm) which has been functionalized to contain an appropriate ion-exchange functional group. It is this functional group which determines the ion-exchange properties of the composite particle, so that aminated latexes produce agglomerated anion-exchangers (Fig. 3.20(a)), whilst sulfonated latexes produce agglomerated cation-exchangers (Fig. 3.2qb)). The polymers used for latex formation include divinylbenzene-vinylbenzylchloride [ 1221, polystyrene [1201 and acrylate [ 1201. 3
Aminated latex particles
Sulfonated latex particles
&
(a)
(b)
Fig 3.20 Schematic representation of agglomerated (a) anion- and (b) cation-exchangers.
Ion-Exchange Smtionary Phases
57
so; Electrostatic attraction
i.
0; * * * * * * N R3
&R3 NR3
Aminated latex
so; Fig. 3.22 Formation of an agglomerated anion-exchange resin using electrostatic binding. Note that the core and the latex particles are not drawn to scale.
3.4.2
Synthesis
The key step in synthesis of an agglomerated resin is the manner in which the latex particles are bound to the central support particle. As indicated in Fig. 3.8, this binding can be achieved through electrostatic interactions, hydrophobic interactions, or by mechanical means.
Electrostatic binding Of the three approaches, electrostatic binding is by far the most commonly used. The central support particle is functionalized with ionic groups of opposite charge to that of the functionalized latex. Thus, an anionic, surface-sulfonated core particle will attract and bind cationic aminated latex particles, and the resultant agglomerated anionexchange particle is illustrated schematically in Fig. 3.21. An agglomerated cationexchanger can be produced using a sulfonated (anionic) core particle, which is coated firstly with an aminated (cationic) latex and secondly with a sulfonated (anionic) latex. It is also possible to form an agglommeratej cation-exchange resin by reacting sulfonated latex particles directly with an aminated PS-DVB core particle, but this procedure is not favoured because amination of PS-DVB is a rather difficult procedure. The tendency for particles of ion-exchange resins of opposite charge to clump together in aqueous solution is well known. The agglomerated resin can be made by first packing a column with the functionalized core particles and then pumping a suspension of functionalized latex through the column until the latex suspension saturates the column 161, 1221. Alternatively, the agglomerate can be formed by simple mixing of the two components to form a precipitated agglomerate, which is then used to pack the chromatographic column in the conventional m .nner [123]. The former approach has been shown to produce more efficient columns, Cnd provided column plugging with the latex suspension can be avoided, is considered to be the best method for preparing
58
Chapter 3
TABLE 3.9
SOME COMMERCIALLY AVAILABLE AGGLOMMERATE ION-EXCHANGE COLUMNS. ALL COLUMNS ARE MANUFACTURED BY DIONEX. DATA COURTESY DIONEX CORPORATION Column
Class
Core size
Latex size (nm)
Latex crosslinking
Functional group
(a) HPIC-AS 1 HPIC-AS2 HPIC-AS3 IONPAC-AS4 IONPAC-AS4A IONPAC-ASS IONPAC-AS 5A IONPAC-AS6 IONPAC-AS7 IONPAC-AS9
Anion Anion Anion Anion Anion Anion Anion Anion Anion Anion
IONPAC FAST ANION OMNIPAC PAX- 100 OMMPAC PAX-500 IONPAC-CS3 IONPAC-CSSd
Anion Anion Anion Cation Cation
IONPAC FAST CATION I IONPAC FAST CATION 11
Cation Cation
a
25 25 25 15 15 15 5 10 10 15
200 200 300 100 200 100 60 350 350 125
15
70 100
5 .o 5.0 2.0 3.5 0.5 1.o 4.0 5.0 5.0 2P
4oa
8c 10 13
100 225 100
4.0 4.0 5.0 2.0
13 13
225 250
5.0 2.5
8b
Acrylate type crosslinking.
b Very highly crosslinked (> 50%) PS-DVB solvent-compatible microporous substrate. C Very highly crosslinked (> 50%) PS-DVB solvent-compatible macroporous substrate with
approximately 300 m2/g surface area. Column is capable of multiple retention mechanisms, such as ion-exchange, adsorption and ion-interaction. d Mixed anion- and cation-exchange. agglomerate packings [ I 221. Regardless of the coating procedure used, dense, uniform agglomeration of the microparticles can be achieved only when the agglomeration step is performed in the presence of a polyvalent salt solution. This serves to suppress the electrostatic repulsion forces which increase as the latex layer is established [ 1231. Some commercially available agglomerated ion-exchangers formed by electrostatic attraction are listed in Table 3.9.
lon-ExchangeStationary Phases
59
Hydrophobic interaction
+ R3 NR3
Aminated latex Fig. 3.22 Formation of an agglomerated anion-exchanger using hydrophobic binding of the latex. The component particles are not drawn to scale.
Hydrophobic binding Recent studies by Warth et al. 11201 have shown chat agglomerated anionexchangers can be synthesized without the presence of a functional group on the core particle. Core particles of neutral PS-DVB resin were mixed with aminated latex particles in aqueous sodium chloride solution, and stable monolayers of latex were formed on the surface of the core particle, despite the lack of electrostatic attraction. The authors have suggested that latex adsorption would occur readily on any neutral resin which is sufficiently hydrophobic. Fig. 3.22 shows a schematic representation of a hydrophobically-bound agglomerated anion-exchanger. The mechanism of adsorption of the anionic latex can be explained by the SternGuoy-Chapman model of the electrical double layer [124], which has been shown to be applicable to the adsorption of organic ions on neutral or functionalized resins 159, 1251. Initial adsorption of the latex occurs by hydrophobic interaction and the adsorbed latex establishes a primary charged layer, with small inorganic counter-ions (such as chloride from the surrounding aqueous solution) occupying a diffuse secondary layer. Addition of an electrolyte to the coating solution increases the number of counterions in the bulk solution. The surface potential remains constant, so more organic ions must adsorb onto the resin surface in order to maintain this potential, thereby creating a more dense latex coating. The ion-exchange capacity of the agglomerated exchanger can be varied by altering the type of latex particle, the concentration of the electrolyte (sodium chloride) in the coating solution, or the concentration of latex in the coating solution. More concentrated electrolyte or latex solutions produce higher capacity materials, whilst the ion-exchange capacity is related invetsely to the degree of functionalization of the latex. The less functionalized latexes can adsorb more readily onto the core particle via dispersion forces, leading ultimately to a higher capacity of the final agglomerated material. At the time of writing, hydrophobically-bound agglomerate ion-exchangers are not available commercially.
Chapter3 NR,
Binding material
Aminated latex
Fig. 3.23 Schematic representation of a mechanically-bound agglomerate anion-exchanger. The component particles are not drawn to scale.
Mechanical binding The third approach suggested for synthesis of agglomerated ion-exchangers is to bind the latex to the core particle using mechanical means. Hanaoka et al. [126] have formed an anion-exchange latex by grinding strong-base anion-exchange resin (AG 1X8), mixing a methanolic suspension of this latex with 10 pm underivatized PS-DVB core particles, and then evaporating the methanol. Just prior to complete evaporation, small amounts of chlorornethylstyrene, divinylbenzene and a polymerization catalyst were added, and the polymerization allowed to proceed for an hour at 80 O C . in a final step, the agglomerated beads were aminated with mmethylamine. The resultant material is depicted schematically in Fig. 3.23. The binding material used for the synthesis of mechanically-bound agglomerates can also be a water-insoluble glue. Cellulose nitrate type PSV and poly(viny1 butyrate) type BF-2 have proven to be suitable for this purpose [127]. In this case, 25-40 pm ethoxymethacrylate-ethylenedimethacrylatecopolymer core particles were mixed with water-soluble anion-exchange particles and glue solution in ethanol. Evaporation of the solvent in a rotary evaporator produced an agglomerated resin which was chemically and physically stable. 3.4.3
Characteristics of agglomerated ion-exchangers
Chromatographic efficiency The outstanding characteristic of agglomerate ion-exchangers is their chromatographic performance. Very efficient separations are possible owing to the existence of short diffusion paths, leading to excellent mass-transfer characteristics. The prime factor which determines the diffusion path length (and hence the chromatographic
6
I 12
F-
NO2;
I I
0
i I -
2 4 6 Time (mini 10)
rr
0
I
15 Time (min) (b)
so&
uoz11
I
30
I
0
2
1
I
I
4 6 6 Time b i n )
1
1
1
0
(C)
Fig. 334 Separations obtained on (a) electrostatically-bound, (b) hydrophobically-bound and (c) mechanically-bound agglomerateanion-exchangers. (a) Dionex HPIC-AS4A column, using 1.8 mM Na2C03 and 1.7 mM NaHCe as eluent with conductivity detection. Reprinted from I1281 with permission. (b) Home-packed column prepared frompolyacrylate latex agglomerated onto a polystyrene core resin. The eluent was 70 mM nicotininc acid at pH 3.5, and conductivity detection was used. 1-methyl acrylate, 2-lactate, 3-fomate, 4-fluoride, 5-iodate. ddihydrogen phosphate, 7-monochlomacetate, 8-ethylsulfonate,')-sulfamate, 10-n-pmpylsulfonate, 11-bromate, 12-chloride (25-100 ppm). Reprinted from [1201 with permission. (c) Home-packed column prepared by polymerization binding of PS-DVB latex onto a PS-DVB core particle. The eluent was 4 mM Na2Co.j and 4 mM NaHCO3. Reprinted from [ 1261 with permission.
Chapter3
62
F-
I
I
0
4
1
1
I
1
I
1
I
8 12 16 20 24 28 32 (a1
F-
CI-
NO3T
I
I
I
I
I
1
I
I
I
I
I
1
0 4 8 12 16 2 0 24 28 32 36 LO LL (b) F’
Fig. 3.25 Comparison of the ion-exchange selectivities of some agglomerate anion-exchangersof differing characteristics. (a) HPIC-AS1 column, (b) HPIC-AS2 column, (c) HPIC-AS3 column, (d) HPIC-AS4 column. The eluent in each case was 2.8 mM NaHCO3 and 2.3 mM Na2C03. Conductivity detection was used. Reprinted from [130]with pemiission.
Ion-ExchangeStationary Phases
63
efficiency of the resultant material) is the size of the latex particle, but in the case of electrostatically-bound agglomerates, the surface charge on the core particle also serves to prevent the penetration of solute ions (which of course have the same charge as the functional group on the core particle) into the interior of the resin bead. Fig. 3.24 shows typical separations obtained on agglomerate anion-exchangers synthesized by electrostatic, hydrophobic and mechanical binding of the latex.
Stability Agglomerate exchangers show excellent chemical stability over the entire fl range. The bond between the latex and the core in electrostatically-bound materials retains its integrity even in the presence of very caustic eluents. Mechanical stability is also good, allowing high flow-rates to be used. Backpressures in packed columns are only moderate because of the relatively large diameter of the particles used, together with their pellicular nature. However, these resins are susceptible to some organic solvents which may cause mechanical failure of the agglomerated resin beads. Selectivity The selectivity of agglomerated resins is influenced chiefly by the nature of the functional group on the latex and to a lesser extent by the chemical natures of the core and latex particles and also by the degree of cross-linking [129]. Because the latex is prepared separately to the core particle, it is a practical proposition to produce a range of columns of differing selectivities, such as those listed in Table 3.9. The following general guidelines on the selectivity of agglomerate anion-exchangers have been reported [130]. (i) Selectivity for the AS1, AS3 and AS4 materials in Table 3.9 is similar. (ii) The selectivity of the AS2 material in Table 3.9 is different due to the use of a hydrophilic functional group on the latex. The retention order of nitrate and sulfate on this column is opposite to that of other columns, with sulfate being eluted first. It is interesting to compare this behavior with that for sulfate on the surface aminated anion-exchangers discussed earlier in this chapter. There, sulfate was eluted more rapidly on exchangers with large functional groups, whilst ions such as nitrate showed longer retention under the same conditions. (iii) The ion-exchange capacity of the packings decreases with the particle size of the resin bead, but chromatographic efficiency increases. The use of very small diameter core particles is not practical because the capacity of the resins would be too low for use with routine samples. These effects can be seen in Fig. 3.25, which compares chromatograms obtained on AS1, AS2, AS3 and AS4 columns. A recent, detailed study on the selectivity characteristics of agglomerate anionexchangers [129] provides more valuable insight into the factors which govern the performance of these materials. Agglomerated resins were prepared by coating 5 pm surface-sulfonated core particles with anion-exchange latexes of 59-68 nm diameter,
100
90
80
70
60
-8
i;
c
50
% " .-
8
s" 1o 30
d
20
2 1 B B 1
10
CI-
F-
Ion-ExchangeStationary Phases
0 1
Time (min) L 6 8
2 1
1
1
1 1
65
0
I
-
0
lime lminl 2 L 6
J
NH;
K+
NOf
la)
Fig. 3.27 Anion- and cation-exchange characteristics of an anion agglomerate column (Dionex HPIC-CAS1). Eluents: (a) 0.50 mM phthalic acid and 0.61 mM sodium tetraborate, (b) 0.50 mM CuClz. Indirect spectrophotomemc detection (see Chapter 12) at (a) 254 nm and (b) 215 nm was used in each case. Reprinted from [131] with permission.
containing methyldiethanolammonium (MDEA), dimethylethanolammonium (DMEA), trimethylammonium (TMA) or miethylammonium (TEA) functional groups. These functional groups can be arranged in order of decreasing hydrophilicity to give MDEA>DMEA>TMA>TEA. Fig. 3.26 shows retention data for common anions on these columns, using carbonate and hydroxide eluents. The hydrophilic functional groups (MDEA and DMEA) generally show weaker retention of anions than the more hydrophobic functional groups (TMA and TEA). This can be rationalized in terms of increased hydroxide selectivity for the hydrated, hydrophilic functional groups, leading to greater eluting power for hydroxide, and hence shorter retention. Thus the sample anions are barely retained on the MDEA column with hydroxide as eluent (Fig. 3.26(b)), and only weakly retained on the same column with the carbonate eluent (Fig. 3.26(a)). The effects of functional group size can be seen by comparing capacity factors obtained on the TMA and TEA columns. In the same manner as discussed earlier for surface aminated resins, monovalent anions show increased retention with increasing functional group size, whereas polyvalent ions tend to show decreased retention. As a final comment on agglomerate ion-exchangers, the possibility of these materials exhibiting simultaneous anion- and cation-exchange characteristics should be
Chapter3
66
pointed out. This behavior can be anticipated for electrostatically-bound materials in which the coverage of latex over the functionalized core particle is incomplete. As an example, an anion-exchange agglomerate might exhibit some cation-exchange capacity due to exposure of some of the sulfonic acid groups on the core particle (see Fig. 3.21). This is illustrated in Fig. 3.27 for a Dionex HPIC-CAS1 column. 3.5 3.5.1
HYDROUS OXIDE ION-EXCHANGERS Introduction
As shown in Fig. 2.2, hydrous oxide ion-exchangers form part of the general classification of inorganic ion-exchangers. lnorganic materials were the earliest form of ion-exchangers and include the zeolites, which have become a most important group of cation-exchangers. Some minerals can act as ion-exchangers because the skeleton or matrix material carries an excess charge which is compensated by mobile counter-ions. This excess charge arises for a variety of reasons; for example, in aluminosilicates such as the zeolites, surface charge is known to be a consequence of the fact that some of the Si4+ ions in the silicate lattice are replaced by A13+. The reduced positive charge is replaced by alkali or alkaline earth ions which are present with free mobility as counterions in the matrix. Hydrous metal oxides, formed by precipitating the metal hydroxide from aqueous solution, followed by filtration and drying at moderate temperature, can also show ionexchange properties. Typical examplcs of this class of ion-exchangers are alumina (A1203.nH20), silica (SiO2.nH20) and zirconia (ZrOz.nH20). A hydrous oxide prepared in this manner will have some of the original metal-hydroxide (M-OH) bonds remaining intact. Eqns. (3.1) and (3.2) show this metal-hydroxide group acting as both an acid and a base, and indicate the possibilities of cation- and anion-exchange behavior, respectively.
IM-O-€1 % EM-O- + H+ =M-O-II EM+ + OH-
+,
[cation-exchanger] [anion-exchanger]
(3.1) (3.2)
The ion-exchange properties of hydrous metal oxides, as with many inorganic materials, show strong pH dependence. The pH values at which the above reactions occur are dependent on the type of hydrous oxide under consideration, but the general ion-exchange behavior of these materials is depicted in Fig. 3.28, which shows the number of moles of anions or cations adsorbed per kilogram of oxide, at various pH values. In this examplc, cation-exchange behavior is first apparent at pH 3 and becomes more pronounced (i.e. more cations can be reversibly bound to the material) at higher pH valucs. In contrast, anion-exchange behavior is first apparent at pH 7 and becomes more pronounced at lower pH values. It can be noticed from Fig. 3.28 that the intersection of the two curves marks the point where there are equal numbers of positive and negative charges on the matrix. The pH at which this situation exists is called the isoeiectric point.
Ion-ExchangeStationary Phases
0
2
4
67
6
8
10
12
PH
Fig. 3.28 Typical pH dependence of the ion-exchange behaviour of hydrous oxide ionexchangers. The open triangles show the cation-exchange characteristics, whilst the closed triangles
show anion-exchange characteristics. 3.5.2
Silica
Silanol (=SOH) groups are present on the surface of moderately activated silica, and these groups can ionize as shown in Eqns. (3.1) and (3.2). The isoelectric point for silica is at pH 2 [132], so at pH < 2, silica acquires a positive charge (and hence acts as an anion-exchanger), whilst at pH > 2, a negative surface charge is acquired and cationexchange characteristics are evident. Since the isoelectric point occurs at such a low pH, silica is most useful as a cation-exchange material. Smith and Pietrzyk [133] have utilized silica as a stationary phase for IC of cations. Capacity factors for alkali metal ions show a progressive increase when the pH is varied from 4.0 to 7.0, in accordance with the expected increase in ion-exchange capacity as the silanol groups become more ionized. The retention order for alkali metals, alkaline earths and lanthanides is the same as that observed with conventional ion-exchangers, indicating that silica exhibits no special selectivity effects. Fig. 3.29 shows the separation of alkaline earth metal ions on silica, using a complexing eluent.
3.5.3
Alumina
Zon-exchange characteristics It has been known 'for many years that alumina can retain inorganic anions and cations. Three views have been advanced to explain this behavior 11341. The first considers that interactions between analyte ions and alumina are due to hydrolytic and precipitation processes. The second centres on adsorption of the analyte ion and a counter-ion, followed by travel of this neutral species over the alumina surface. The third utilizes an ion-exchange concept wherein the analyte ion is retained through the formation of an electrical double layer at the alumina surface, with the alumina
68
Chapter3
-
0
3
mL
6
9
Fig. 3.29 Ion chromatography of alkaline earth metal ions on a silica stationary phase. The eluent was 1:4 methano1:water containing 3 mh4 sodium citrate at pH 7.41. Conductivity detection was used. Reprinted from [ 1331 with permission.
acquiring an initial charge through dissociation reactions of =AIOH groups in the same manner as shown in Eqns. (3.1) and (3.2). Of these three possible mechanisms, ionexchange is considered to be dominant in an aqueous environment. The amphoteric character of alumina and its conversion into an anion- and cationexchanger via hydration and subsequent treatment with acid or base (or buffers of appropriate pH) has been attributed to the reactions shown in Fig. 3.30 [135]. Anionexchange occurs between solute anions and hydroxyl ions at the alumina surface, whereas cation-exchange occurs between solute cations and hydrogen ions produced by dissociation of the alumina hydroxyl groups. The isoelectric point for alumina depends both on the manner in which the alumina has been mated and on the nature of the buffer used, and can vary between pH 3.5 (for citrate buffer) and 9.2 (for carbonate buffer). Alumina can therefore exhibit marked anion- and cation-exchange characteristics in acidic and alkaline media, respectively. The changeover from one mode of exchange to the other is gradual and occurs in the vicinity of the isoelectric pH. Favourable rates of ion-exchange occur and it has been
Ion-Exchange Stationary Phases
69
acidic alumina / - A I - - -ci
O\
?-A<
+
/ - A l - - -OH-
Alumina
+
30
-
/
O \ -A1 / \@-
%O
\U--H+
/
HCI t l N a O H
- H+
/ -Al--
-OH-
O\ / -A1
L NaOH
basic alumina Fig. 330 Ion-exchange properties of alumina.
suggested that under appropriate conditions of pH, alumina is a monofunctional cationexchanger and a plyfunctional anion-exchanger [ 1361.
Effect of p H Schmidt and Pietrzyk [134] have shown that pH has a rather complex effect on anion retention because retention is influenced simultaneously by the following factors: Use of buffers to control the pH (and hence the ion-exchange behavior) provides competing anions which will influence retention due to both mass action effects and the magnitude of the affinity of the competing ion for the alumina exchange site. (ii) The retention of analytes derived from weak acids will be favoured by conditions under which they are fully ionized. (iii) The type of buffer influences the isoelectric pH. (i)
The general trend observed for common anions is that capacity factors decrease as the eluent pH is increased from 4.0 to 7.0. Over the same pH range, the opposite trend exists for cations 11371.
Selectivity A separation of anions on alumina using acetate buffer at pH 4.05 is illustrated in Fig. 3.31. It is immediately apparent that the anion-exchange selectivity of alumina differs from that of conventional strong-base exchangers with quaternary ammonium
Chapter3
70
I-
r
0
I
I
I
1
1
5
10
15
20
25
mL
Fig. 3.31 Ion chromatography of anions on an alumina stationary phase. A Spherisorb A5Y column was used with an eluent of 100 mM NaCl and 1 rnM acetate buffer at pH 4.05. Conductivity detection was usrd. Reprinted from [I341 with permission. functional groups. The latter selectivity order was listed earlier in Section 2.1.4, whilst that for alumina is 1134, 1371:
F- > s04*-> C r ~ 0 7>~HCOO> benzoate > C102- > BrO3- > Cl- > NO2- > NO3- > Br- > ClO3- > SCN- > I- > ClO4- > CH3COOThe order of retention of halide ions on alumina is opposite to that for conventional exchangers, so that ions which are well retained on these exchangers, such as perchlorate, thiocyanate and chlorate, are only weakly held on alumina. The halide elution order on alumina is consistent with the Al-halide formation constants, and this suggests that anion interaction occurs at an A1 atom, as shown in Fig. 3.30. The value of logp6 for .41F63- is 19.84 [138], which explains why fluoride cannot be eluted from an alumina column, even with a strong eluent. Phosphate (not listed in the above selectivity order) shows similar behaviour. The elution order for cations on alumina is the same as that observed for conventional sulfonated cation-exchangers [ 1371. 3.6
SIMULTANEOUS SEPARATION OF ANIONS AND CATIONS
The preceding detailed discussion of ion-exchange stationary phases for IC has focused exclusively on the independent use of anion- and cation-exchangers for separate determination of anions and cations, respectively. The possibility for simultaneous
Ion-Exchange Stationary Phases
71
determination of these species also exists and the following approaches can be envisaged: (i)
Use of specialized hardware to permit the coupling of two ion chromatographs, or the formation of a dual-channel system in which the anions and cations are determined via separate channels. (ii) A single-channel system in which an anion-exchange column. is operated in tandem wilh a cation-exchange column. (iii) The use of a single ion-exchange column which exhibits both anion- and cation-exchange capacity, such as a mixed-bed ion-exchanger or a bifunctional exchange material (e.g. alumina). (iv) Chemical derivatization procedures in which, for example, cations are converted to anions and chromatographed on an anion-exchanger, together with the common anions. Since this Chapter is concerned with stationary phases, only approaches (ii) and (iii) will be discussed here, The interested reader is referred to Chapters 4 and 15 for further discussion of approaches (i) and (iv).
3.6.1 Tandem anion- and cation-exchange columns The use of columns in tandem is potentially the most straightforward approach to the simultaneous determination of anions and cations. Provided that the ion-exchange capacities of the two columns can be manipulated to give appropriate retention times for anions and cations using the same eluent, and a suitable detection mode can be found, then simultaneous analysis should be possible. Tarter and co-workers [2,139-1431and others [43]have utilized tandem columns with some success. An inorganic salt such as
I 0
I
2
I
I
L 6 Time (min)
I
8
I
10
Fig. 3.32 Simultaneous separation of anions and cations using tandem ion-exchange columns and two conductivity detectors. Wescan 269-004 and Vydac 302.IC 4.6 columns in tandem, using 4 mM lithium phthalate as eluent. Reprinted from [2] with permission.
72
Chapter3
CI'
1 0
I
10 mL
I
20
Fig. 333 Simultaneous separation of anions and cations on a mixed-bed ion-exchange column. The column was packed with equal amounts of Hamilton PRP-X100 anion-exchanger and suifonated Hamilton PRP-1 cationexchanger. The eluent was 5.00 mM acetic acid and 4.97 mh4 lithium hydroxide at pH 6.65. Conductivity detection was used. Reprinted from (1441 with permission.
lithium phthalate can be used as eluent, with the salt cation acting as the competing ion on the cation-exchange column, and the salt anion performing the same function on the anion-exchange column. Fig. 3.32 shows the simultaneous separation of anions and cations using this method. 3.6.2
Mixed-bed ion-exchangers
Mixed-bed ion-exchangers are used widely for the removal of electrolytes in water treatment procedures. A mixed-bed exchanger may be formed simply by mixing anionand cation-exchange resins in appropriate proportion and then packing a column in the usual way. When this is done, both exchangers function as if they were individually packed into columns. In other words, the anion chromatogram is similar to that obtained by packing a column with the same amount of anion-exchanger diluted with an inert material, and likewise for the cation chromatogram. Piemyk and Brown [ 1441 have prepared mixed-bed columns using Hamilton PRPXlOO as the anion-exchanger and sulfonated PRP-I as the cation-exchanger. Lithium
Ion-ExchangeStariOmry Phases
73
S
-
0
10 Time (min)
Fig. 3.34 Simultaneous separation of anions and cations on a bi-functional (alumina) ionexchanger. The column was packed with Spherisorb alumina A3Y and the eluent was 0.5 m M potassium biphthalate at pH 5.2. UV detection at 230 nm was used. S is a system peak. Reprinted from [1371 with permission.
acetate at neutral pH was found to be a functional eluent, since lithium is a sufficiently weak competing cation to enable separation of other alkali metal ions, and acetate can be used for the separation of anions. Fig. 3.33 shows a simultaneous separation of anions and cations on a mixed-bed ion-exchange column. The same authors [I451have also demonstrated that a mixed-bed ion-exchange column can be made by mixing alumina and silica. At an eluent pH of about 5, silica acts as a cation-exchanger and alumina acts as an anion-exchanger, so simultaneous separation of both anions and cations is possible.
3.6.3
Bi-functional ion-exchange materials
The ion-exchange behavior of hydrous oxides illustrated in Fig. 3.28 suggests that there is a pH region in which these materials are bi-functional; that is, they exhibit both anion- and cation-exchange characteristics at the same time. It should therefore be possible for these materials to be used for the simultaneous separation of anions and cations. Such a separation is illustrated in Fig. 3.34 for an alumina column operated at
Chapter 3
74
pH 5.2, using potassium phthalate as eluent [ 1371. Bi-functional agglomerate ion-exchangers were discussed in Section 3.4.3 and their chromatographic characteristics were illustrated in Fig. 3.27. These materials should also be suitable for simultaneous anion and cation separation, however no studies on this approach have yet been reported.
3.7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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81 82 83 84 85
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79
Chapter 4 Eluents for Ion-Exchange Separations 4.1
INTRODUCTfON
In any liquid chromatographic technique, the eluent composition provides the greatest flexibility for manipulating the retention of solutes in order to achieve a desired separation. The range of eluents used for ion-exchange separations in IC is enormous, but many eluents can be classified into groups of similar characteristics. The approach taken in this Chapter will be to first provide an overview of the general eluent characteristics which exert the greatest effects in ion-exchange IC, and to follow this with a discussion of the different classes of eluents used for both suppressed and nonsuppressed IC.
4.2
ELUENT CHARACTERISTICS
In an ion-exchange separation, the role of the eluent is to compete with solute ions for the fixed ions on the stationary phase and to separate the mixture of solute ions into well-defined bands. Some of the more important eluent characteristics are listed below: Compatibility with the detection mode. Nature of the competing ion. Concentration of the competing ion. Eluent pH. Buffering capacity. Complexing ability. Organic modifier content.
4.2.1 Compatibility with the detection mode '
The detection mode to be used is the major factor which determines the types of eluents which are suitable for a desired separation. Detection in IC is discussed in Part 111 and the specific requirements that each detection mode imposes on the eluent will be enumerated later. At this stage, it is sufficient to point out that the background detector signal generated by the eluent must be commensurate with that required for sensitive detection, and this clearly limits the types of eluent species which are applicable to each detector.
80
Chapter4
4.2.2 Nature and concentration of the competing ion
The factors which influence ion-exchange retention will be discussed quantitatively in Chapter 5, where for convenience, all mathematical treatments of retention models and mechanisms are presented together. In qualitative terms, however, the eluent characteristics which influence solute retention are: (i)
The value of the selectivity coefficient, KA,E, for the ion-exchange reaction occurring between the solute ion A and an eluent competing ion E. Retention increases as the value of KAE increases.
(ii) The concentration of the competing ion in the eluent, with retention decreasing as this concentration increases. The selectivity coefficient describes the extent to which the solute ion is able to displace the competing ion from the stationary phase. Since solute retention becomes greater as KAE increases, a suitable eluent is one which provides a value of K A Ewhich leads to an appropriate degree of retention for the solute ion. Several factors are known to influence the selectivity coefficients of eluents for a particular solute ion. These factors are, of course, the same as those which govern the ion-exchange selectivity of solute ions themselves, and include the size, charge, degree of hydration and polarizability of the eluent ion (see Section 2.1.4). Electroselectivity exerts the greatest effect, with eluents of greater charge having the stronger affinity for
s0,Z-
c 10-
.-
0 c
C 0, c
NO3ErCI-
0,
E
0 0.1
0:2 Eluent concentration (mM)
Fig. 4.1 Variation of retention time of anions with eluent concentration. A TSKgel IC anion PW column was used with l,Zdihydmxybenzene-3,5-disulfonicacid (Tiron) as eluent. Reprinted from [I] with permission.
Eluents for [on-ExchangeSeparations
+
B
81
+
+H
BH+
Kb 1
+ H.
2+
BH,
---.
Kb2
decreasing pH Fig. 4.2 Dissociation of a weak polyprotic acid (HnA), and protonation of a weak base (B).
the fixed ions of the stationary phase, and hence being stronger eluents. It is therefore most convenient to choose the type of eluent by initially selecting the appropriate eluent charge and to then exploit additional selectivity effects (due to the size, polarizability etc. of the eluent ion) within a group of eluent ions having the desired charge. The eluent concentration can then be manipulated to produce the required separation. As Chapter 5 will show, the rate at which retention can be varied by changing eluent concentration depends on the charges carried by both the solute and the eluent ions. For a particular solute, retention changes more slowly with eluent concentration for a doubly charged eluent ion than for a singly charged eluent ion. This occurs despite the fact that the former (having a higher charge) is the stronger eluent and will elute solutes in a shorter time than the latter. Fig. 4.1 shows a typical plot of retention time of anions versus eluent concentration for an eluent with a charge of -2 [I].
4.2.3 Effect of eluent pH The eluent pH is a vital parameter in determining the characteristics of the eluent, and influences the charges on both the eluent and solute ions. These effects are particularly important in anion separations, where they play a large part in governing solute retention. Polyprotic weak acids or their salts are used commonly as eluents for IC of anions, and weak bases are finding increasing usage as eluents for cation IC. Fig. 4.2 shows the stepwise dissociation of a polyprotic acid, HnA,and the stepwise protonation of a weak base, B. The charge on,the acid anion increases with pH, so the eluting power of weak acid eluents therefore increases with pH until the acid is completely dissociated. The opposite trend occurs for weak base eluents, with decreasing pH resulting in a higher degree of protonation and hence stronger eluting power. In a similar manner, solute ions derived from weak acids or weak bases will show pH effects, since their charge will also be governed by the eluent pH. In this case, increased solute charge results in increased retention because the electroselectivity effect for the solute ion is enhanced with higher charge. Examples of solutes showing these pH
82
Chapter 4
I-
szof-
so'?-
Br -
-02
.
-
I L.3
---".a-
l
l
I
t
47
I
l
l
1
50
I
1
53
1
1
I
I
5.1
I
I
e1-
I
60
Eluent pH
Fig, 4.3 Effect of eluent pH on retention behaviour of anions. A Vydac 302 IC4.6 column was used with 5.0 mM phthalate as eluent, at the indicated pH values. Reprinted from 121 with
permission. effects include carboxylate anions, F-, C032-, P043-, Si032-, CN- and amines. When these ions are present in mixtures with other solute ions showing no plI effects, the control of eluent pH is an important variable to be manipulated in the search for a suitable eluent composition. A further influence of eluent p1-I is on the formation of system peaks. These are peaks i n a chromatogram which are not attributable to the elution of a solute ion, but are due to a disturbance of the complex equilibria existing between the eluent and stationary phase. The exact origin of a particular system peak is dependent on the type of eluent used, and system peaks will be discussed separately in Section 4.6. However, a common aspect of these system peaks is that the eluent pH largely determines whether such peaks are observed. All of the above-mentioned pH effects are illustrated in Fig. 4.3, which shows the retention behaviour of some anions on a functionalized silica anion-exchanger using eluents comprising 5.0 mM phthalate at various pll values [2]. The capacity factors for singly charged anions which do not participate in protolytic equilibria over the indicated pli range (e.g. CI-, Br-, I-) show a decrease as the eluent pH is raised and the negative
Eluents for Ion-Exchange Separations
83
charge on the phthalate eluent is increased. The capacity factor for sulfate is affected more than for singly charged anions. Ions such as HzP04-and ( 2 ~ 0 4 show ~ - dissociation effects over the pH range studied and their retention behaviour is therefore unpredictable. In the case of HzPO4, dissociation leads to such an increase in negative charge that retention increases with increased pH, despite the presence of eluent species with higher anion-exchange affinity at the higher pH values. The system peak also shows marked pH dependence. The above effects on retention behaviour by eluent pH show that some buffering capacity is desirable for IC eluents. This enables the eluent to maintain a stable pH and to provide reproducible retention times, even when acidic or basic samples are injected.
4.2.4
Complexation characteristics
The ability of eluent species to form complexes with solute (usually metal) ions or sample components is often highly desirable and so the complexation characteristics of the eluent may sometimes be of importance. The most common application of complexing eluents is in the separation of multivalent cations, which have such high affinities for sulfonated cation-exchangers that they are difficult to. elute with eluents which depend on a simple ion-exchange displacement action. In such cases, an anionic organic complexant is added to the eluent, so that the resultant metal-eluent complexes have reduced charge and are therefore eluted more easily from the column. Once again, the detailed mechanism of this approach is discussed in Chapter 5. However, it will be sufficient to note here that the degree of complexation of solute ions is determined chiefly by the type and concentration of the complexing agent in the eluent, and by the eluent pH. 4.2.5 Use of organic solvents in ion-exchange separations Water-miscible organic solvents, such as methanol, ethanol, butanol, glycerol, acetonitrile and acetone are sometimes used as additives to the eluent for ion-exchange separations. These solvents can exert a variety of effects; for example, acceleration of the formation of complexes between solute ions and eluent species, alteration of the ionexchange selectivities for ions which exhibit hydrophobic interaction with the stationary phase, and reduction of column contamination from hydrophobic sample components by preventing the binding of these components on the column. The first of these effects is typified by the enhanced formation of metal-chloride complexes in water-acetone mixtures [3,4], enabling anion-exchange separation of these complexes to be achieved in dilute HCI. The second of the above functions of organic solvents is illustrated in Fig. 4.4,which shows the variation in retention of some anions in phthalate eluents containing acetonitrile. Separation of these species on the column used is possible only in the presence of acetonitrile. Similar effects have been observed in IC of strongly retained ions, such as SCN-, ClO4-and phthalic acid isomers, using carbonate eluents containing acetonitrile [6] or aliphatic alcohols [7].
Chapter4
84
Chloride Phosphote
Lactate
Acetate
0
10
20
30
40
50
*I. ACN
Fig. 4.4 Effect of added acetonitrile on the retention of some anions on an ion-exchange column. A Hamilton PRP-X100 column was used, with 0.3 mh4 phthalate at pH 6.0 as eluent. Reprinted from [S] with permission.
4.3
ELUENTS FOR NON-SUPPRESSED ION CHROMATOGRAPHY
This section covers all eluents which do not require the use of a suppressor column. Non-suppressed IC methods are characterized by the wide range of eluents used and Fig. 4.5 shows a listing of the eluent types employed for the separation of anions and cations. Each of these eluent types is discussed in the following sections.
4.3.1 Eluents for anion separations in non-suppressed IC Aromatic carboxylic acids and their salts Salts of aromatic carboxylic acids, such as those shown in Fig. 4.6, are the most widely employed eluent species for the separation of anions by non-suppressed IC. They have low limiting equivalent ionic conductances (see Chapter 9) and when used in dilute solution, provide eluents with low background conductance. The aromatic moiety is an excellent UV chromophore, so aromatic acid salts are also ideal as eluents when indirect spectrophotometric detection (see Chapter 12) is utilized. Indirect refractive index detection also gives optimal sensitivities when aromatic acid salts are used as eluents. Whilst the subsequent discussion will be focused on benzene carboxylic acids, it should be noted that other aromatic carboxylic acids, particularly hydroxy- substituted species such as p-hydroxybenzoic acid, 2.4-dihydroxybenzoic acid and salicylic acid, are also
Eluentsfor Ion-ExchangeSeparations
r
NONSUPPRESSED IC
1
AN1oNS
85
t
Aromatic carboxylic acids and salts Aliphatic carboxylic acids and salts Sulfonic acids and salts Potassium hydroxide Polyol-borate complexes EDTA Inorganic eluents Inorganic acids Organic bases Complexing eluents Inorganic eluents
Fig. 4.5 Eluent types used for non-suppressed IC.
widely used [8-131. All of the acids listed in Fig 4.6 are relatively weak and so can exhibit buffering action over an appropriate pH range. In addition, all but benzoic acid are polyprotic and their stepwise dissociations occur over the range of pH values accessible to most IC columns. This means that the effective charge on the eluent competing anion can be varied simply by altering the pH. A tetraprotic acid, h A , will dissociate in four steps, with each of the deprotonated forms (i.e. H3A-, H2A2-, HA3-and A43 being capable of acting as competing anions in an anion-exchange separation. The fraction of the total species present as uncharged &A
acooH
P K a l 4.20
benzoic acid
pKal 3.10 p Q 2 3.90 pKa3 4.70
trimesic acid
PKa12.95
PKa2 5.41
o-phthalic acid
p & l 1.80 pKa22.80 PKa3 4.50 P&4 5.80
pyromellitic acid
Fig. 4.6 Aromatic carboxylic acids used as eluent components in non-suppressed IC.
Chapter4
86
can be defined by ao,which is calculated according to eqns. (4.1) and (4.1 a). Similarly, a1, a2, a3,and CQ are the fractions present with charges -1, -2, -3, and -4, respectively, and they may be calculated using eqns. (4.2)-(4.5).
a. =
a2 =
a4=
EH4AI CH4Al + [H3A-l + [H2A2-l + [HA3-] + [A4-]
[H2A2-l [H4A] + [H3A-l
+ [H2A2-l + [HA3-] + [A4-]
[A4-] [H4Al + [H3A-l + [H2A2-l + [HA3-] + [A4-]
where Kal, Ka2, Ka3 and K d are the stepwise deprotonation constants for H4A. The Q values calculated above can then be used to calculate the effective charge (y) on the eluent, as shown in eqn. (4.6).
Eluentsfor Ion-ExchangeSeparations
87
DH
Fig. 4.7 Variation with pH of the effective charge (-y) on the competing ion when benzene
carboxylic acids are used as eluent species. The above equations can be simplified for weak acids having fewer ionizable protons. The variation of effective charge with eluent pH for the benzene carboxylic acids shown in Fig. 4.6 is illustrated in Fig. 4.7. It can be seen that eluents of any desired effective charge between 0 and -4 can be obtained, so that a wide choice in eluent strengths is possible. In practice, most anions can be eluted effectively by a competing ion with a -2 charge, so phthalate salts find most application [5, 12, 14-17] in nonsuppressed IC. Moreover, the ortho- isomer gives optimal results [181. Benzoate is useful for the resolution of weakly retained anions, such as acetate, formate and F-, whilst highly ionized trimesate and pyromellitate are very strong eluting species and are suitable for strongly retained anions such as Mood2- and C104~[ 19-24], as well as more common anions 1251, Eluents formed from aromatic carboxylate salts are prepared very simply by dissolving the required amount in water and adjusting the pH with a base. Lithium hydroxide is the preferred base because Li+ is less conducting than Na+ or K+, so the background conductance of the eluent is minimized. It will be noticed that all of the acids in Fig. 4.7 are essentially fully ionized in neutral solution. It is often desirable to use alkaline eluents to increase the retention of anions derived from weak acids [23]. In such cases, it is not recommended that the pH be raised simply by addition of further base, since the resulting eluent has no buffering capacity. Instead the pH can be raised using borate buffer. It is interesting to note that aromatic acids can function as anion-exchange eluents even at pH values where the acid exists predominantly in the undissociated, molecular form [26]. This can be explained by considering benzoic acid (HBz) as the eluent. The equilibria existing in the ion-exchange column are shown in Fig. 4.8. A small amount of
88
Chapter 4
HBz JP Resin S' + H+ + B i % Resin- B i + H+ + S'
-
Fig. 4.8 Ion-exchange equilibria for a solute ion, S-, when bcnzoic acid (HBz) is used as eluent.
the benzoic acid is dissociated and the resultant benzoate participates in ion-exchange with the solute S-. This causes further dissociation of the benzoic acid and this process continues for as many solute ions as are present. The major disadvantages of aromatic acid salts are that the eluent pH must be strictly controlled if reproducible retention times are to be obtained, and they have a tendency to be adsorbed strongly onto PS-DVBresins [26]. This behaviour occurs most noticeably with the molecular, fully protonated form of the aromatic acid and is a major contributor to the formation of system peaks. For this reason, it is often advisable to use an eluent pH at which all of the eluent species are present as ions. Nicotinic acid has been suggested as an eluent for non-suppressed IC because it is highly water soluble and shows only weak adsorption onto the column [12]. Typical retention times obtained with aromatic carboxylate eluents are shown in Fig. 4.9, which compares a range of eluents on a surface-aminated methacrylate ionexchanger. A liphatic carboxylic acids
Eluents prepared from salts of aliphatic carboxylic acids have been employed widely in non-suppressed IC. Citric [13, 311. tartaric [30, 32, 331, succinic 113, 34-36], malic [30], fumaric (131, acetic [37] and formic [38] acids have all been used as eluent species. These species are only weakly adsorbed onto PS-DVB resins [131, but are characterized by high background conductances, low to moderate UV absorption and, with the exception of citrate, low ion-exchange selectivity coefficients. The latter property means that they are, in general, rather weak eluents [30, 331 and have therefore found most application in the separation of mixtures of weakly retained anions. A separation of this type is illustrated in Fig. 4.10. Citrate is a stronger competing ion, especially when used in the fully ionized form [391. Retention data for a tartrate eluent are given in Fig. 4.9.
Aromatic and aliphatic sulfonic acids Sulfonic acids are usually fully ionized in aqueous solution over the eluent pH range employed in non-suppressed IC. Eluent pH is therefore not a critical factor in determining retention times. Aromatic sulfonic acids have most of the advantages of their carboxylate counterparts, showing low limiting equivalent ionic conductances, strong U V absorption and large ion-exchange selectivity coefficients. They are therefore suitable for conductivity and indirect spectrophotometric detection and are strong eluents. However, they have a drawback in that they do not exhibit any buffering capacity and if this property is required, then a buffer must be added separately to the
Weaker
Stronger
b Sodium Potassium Ammonium p-hydroxybenzoate trimesate phthalate citrate 1.8mM OJmM 1mM OJmM pH 8.6 . pH-63 pH 6.5 pH 8.7
-
HPO:
- so:-
CN-
Tartrateborate 1mM pR 4.0
Phosphate Gluconate- p-toluene- Potassium borate sulfonate hydroxide buffer JmM 13mM 35mM 1mM pH 6.0 pH 11 pH 6.5 pH 8.6
Potassium benzoate 1 mM pH 6.0
Sodium tartrate 2 mM pH 3 3
. m;-
- so:Oxal
Fig. 4.9 Comparative retention data for anions using a variety of eluents on a methacrylate anion-exchange column (Waters IC Pak A or TSKgel IC PW, 50 x 4.6 mm, ID, 30 pequiv/g). Ac=acetate, Cit=citrate, Form=formate. Oxal=oxalate. Data taken from [27-301and courtesy of Waters Chromatography Division and A.D. Sosimenko.
m \o
90
Chapter4
c
I
I
0
5
I
10 Time (min)
I
1
15
20
Fig. 4.10 Separation of weakly retained anions using a tartaric acid eluent. A TSKgel IC-anionSW column was used with 1 m M tartaric acid at pH 3.2 as eluent. Reprinted from 1331 with
permission. eluent. Aliphatic sulfonic acids have higher conductances (but the limiting equivalent ionic conductance decreases with the length of the aliphatic chain), have weak UV absorption and moderate ion-exchange selectivities, and are hence suitablc mainly for direct UV detection. Table 4.1 lists some of the aromatic and aliphatic sulfonic acids which have been used for non-suppressed IC, and also indicates the detection modes employed in each case. Toluenesulfonic acid has been recommended as an eluent for sample preconcentration procedures using concentrator columns (see Chapter 14) [29]. Representative retention times for some sulfonic acid eluents are included in Fig. 4.9.
Potassium hydroxide Potassium hydroxide eluents were first proposed by Okada and Kuwamoto [53]. The hydroxide ion is the weakest ion-exchange competing anion and has a very high limiting equivalent ionic conductance (in fact, the second highest after hydrogen ions). Thus hydroxide can be used as an eluent for weakly retained anions, such as F-, ClO3-, BrO3-, CI-, N02-, Br- and NO3-, using indirect conductivity as the detection mode [53]. However, the chief value of hydroxide eluents is their high pH, which enables anions of weak acids to be ionized and therefore retained. These eluents have been used successfully for the separation of substituted benzoic acids, phenols, silicate, CN-, S2- and H2AsO3- [28,53-55]. Retention data for a hydroxide eluent are included in Fig. 4.9.
Eluentsfor Ion-Exchange Separations
91
TABLE 4.1 AROMATIC AND ALIPHATIC SULFONIC ACIDS USED FOR THE SEPARATION OF ANIONS IN NON-SUPPRESSED IC Eluent Species
Detection mode*
References
Aromatic sulfonic acids p-Toluenesulfonic Sulfobenzoic
C, ISpec ISpec
29,40 41
5-Sulfoisophthalic sulfonic acid 2-Naphthylamine-1-sulfonicacid 4-Amino-1-naphthalenesulfonicacid 6,7-Dihydroxynaphthalenesulfonicacid 1,2-Dihydroxybenzene-3,5-disulfonic(Tiron)
ISpec C, ISpec IF IF C, ISpec
42 9 43 43
Aliphatic sulfonic acids Methanesulfonicacid Chloromethane sulfonic acid Heptanesulfonic acid Octanesulfonicacid
spec Spec C, Spec C
44-41 48,49 50 51,52
1
* C = conductivity, Spec = spectrophotometry, ISpec = indirect spectrophotometry,IF = indirect fluorimetry. Polyol-borate complexes
It is well known that both boric acid and borate form neutral or anionic complexes with polyhydroxy compounds. The chromatographic utility of the borate complexes of a wide range of polyhydroxy compounds has been studied by a number of authors [30,56601. These polyhydroxy compounds have included neutral species such as mannitol, glucose, fructose, xylose, glycerol, sorbitol, sucrose, and maltose, and acidic compounds such as gluconic acid, tartaric acid, glucuronic acid, galacturonic acid and mannonic acid. Equilibria existing between the above species are summarized in Fig. 4.11, where boric acid is designated as BO, borate as B-, neutral polyhydroxy compounds as L, and acidic polyhydroxy compounds as L-. Because of their many diol functions, polyhydroxy compounds can form a wide variety of complexes, and Fig. 4.1 1 therefore shows only some of the possibilities. Boric acid (PKa 9.24) is in equilibrium with borate, according to Fig. 4.11(a). Boric acid reacts with neutral and acidic polyhydroxy compounds to form diol ester complexes of the type [BOL] or a-hydroxycarboxylic acid esters of the type [B-LJ (where the subscript a denotes an a-hydroxycarboxylic acid ester). These reactions are shown in Figs. 4.11(b) and 4.11(c). Borate also forms diol and a-hydroxycarboxylic acid esters of the types [B-Ll-, [B-LzI-, [(B-)2L12-. [B-L-12-,[B(L-)2I3-or [BLJ, as shown in Figs. 4.1 l(d) - 4.1 l(i).
92
Chapter 4
OH HO-B;
+
OH
OH-=
HO,o,OH B HO' 'OH
B"
B'
[i
OH
OH
HO-B< OH OH
B"
OH ,O,OH
~~
R B0
[B- La] -
OH 2[{
R B'
+ H,O
R
L-
+
B-OH
[BOLI
0 8 +
(b)
R
L
HO-B; OH
+2qo
e
+
R
HOO HO ,O,OH 'OH
(a)
-
H HO
R
R L
4%0
~~~+
[B- L, I
-
(C)
EIuents for Ion-Exchange Separations
93
Fig. 4.22 Complexes formed between boric acid (BO), borate (B-), neutral polyhydroxy compounds (L) and polyhydroxycarboxylic acids (L-). The subscript a indicates an ahydroxycarboxylicacid ester.
94
Chapter4
In alkaline solution, and under conditions where neither reactant is present in large excess, the neutral polyhydroxy compounds tend to form mono-borate complexes of the type [B-LI-. These have only a single negative charge and act as very weak ion-exchange competing ions [57, 591. On the other hand, acidic polyhydroxy compounds can form complexes of higher charge and hence are very useful as strong eluent components. Gluconic acid, tartaric acid and mannonic acid form complexes which appear to have optimal chromatographic properties, and of these, gluconic acid is the most widely used. A typical eluent is formed from 1.48 mM sodium gluconate and borate buffer (5.82 mM boric acid and 1.30 mM borate, with a pH of approximately 8.6), often with a small percentage of acetonitrile (to facilitate phase transfer) and glycerol added. This eluent provides an excellent separation of common anions (see Fig. 3.17(a)) and having only moderate background conductance, is well suited for use with conductivity detection. The nature of the species acting as the ion-exchange competing anion in gluconateborate eluents has been studied by a number of authors [56, 58, 59, 611. Schmuckler et al. (561 used titration and 13C NMR experiments to conclude that an anionic complex of some kind was formed. Erkelens et al. [58] suggested that the competing ion was a triply charged borate-gluconate diester of the type [B-(L-)2j3-, and used this as a basis for explaining that observed basclinc disturbances from calcium were due to elution of a negatively charged complex of this diester with Ca2+. In a comprehensive study, Girard el al. [59] found that anion retention times obtained with gluconate-borate eluents decreased as the eluent pH was raised from 8.0 to 9.5, indicating increased esterification. They suggested that diesters would not be formed in conventional borate-gluconate eluents because gluconate was not present in molar excess. The conclusions reached were that the main complex formed by gluconate at pII 8.5 was a diol ester of the type [B-L-I2-, and that smaller concentrations of a [(B-)2LI2- complex and the ahydroxycarboxylic acid ester, [B-LaJ-,were also formed. These conclusions were supported by previous studies on the structure of borate complexes 162-651. It is possible that the nature of the dominant complex may be different when the mole-ratio of borate to gluconate in the eluent is altered [60].Finally, Walter and Cox [61] used I 'B-NMR to study the composition of borate-gluconate-glyceroleluents and they also found that the [B-L-I2-and [B-Lal- complexes of borate with gluconate were present, but only in very small amounts. However, larger quantities of the [B-LJ-type complexes of borate with glycerol were present. The latter complexes act as weak anion-exchange competing ions, and the elution of solutes is accomplished primarily by the gluconateborate complexes. Tartrate forms boric acid complexes of the type [B-LaJ-at plI values less than 5 1271. Tartrate-borate eluents are therefore possible and these have been shown to have moderate elution strengths. The elution characteristics of gluconate-borate and tartrateborate eluents are shown in Fig. 4.9. Ethylenediaminetetrnaceiic acid (EDTA) EDTA can be used as an eluent for IC of anions in two ways. Firstly, the carboxylatc groups on EDTA can be ionized to give a charge of up to -4, so EDTA can function as a very powerful competing anion. EDTA eluents of this type are especially suitable for the elution of very strongly retained polyvalent anions such as
Eluents for Ion-ExchangeSeparations
95
polyphosphates [66, 671. Small additions of EDTA to conventional eluents have been found to assist in the analysis of some difficult samples, such as toothpaste [68] and oil shale retort water [69]. The second approach involves the use of anionic metal-EDTA complexes as eluents. Copper(I1) [70-721 and cobalt(II1) form suitable EDTA complexes which are substitution inert. As such, they will not readily undergo ligand exchange during the chromatographic process, which means that the interactions between these complexes and inorganic anions are due solely to outer-sphere ion interactions. Both of the above complexes are relatively weak eluents, with retention times being more than double those for a phthalate eluent of the same concentration [70]. No selectivity effects are observed and all solute anions are eluted in the same order as for phthalate. In view of the above, it might seem that EDTA offers only limited advantages as an eluent. However, the major application of EDTA is in the elution of metal ions when these are present as anionic EDTA complexes. At a pH of 5.5, the tetraprotic H4EDTA exists as a mixture of [HEDTAI3- and [H2EDTAI2-. Eqns. (4.7)-(4.10) show typical reactions of divalent and trivalent metal ions with these forms of EDTA.
+ [H,EDTA]” f M2+ + [HEDTAI3- % M3’ + [H2EDTAf-$ M3+ + [HEDTAI3- $ M2’
+ 2H’ [MEDTAI2- + H’ [MEDTAI- + 2H’ [MEDTAI- + H+ [MEDTAf-
(4.7)
(4.8)
(4.9) (4.10)
As mentioned briefly in Section 3.6, the formation of anionic metal chelates opens up the possibility for simultaneous determination of these metal chelates and common inorganic anions on an anion-exchange column. Manipulation of the pH of an EDTA eluent enables the charge on the competing anion to be varied, together with the charge on the metal-EDTA complexes. Injection of free metal ions into an EDTA mobile phase of appropriate pH leads to the in-situ formation of EDTA complexes, provided the conditional formation constants for these complexes are sufficiently high. This approach has been successful for Ca2+, Mg2+, Ni2+, Zn2+, Cu2+, Mn2+, Fe3+and Cr3+ [73-771. Detection can be achieved using conductivity or spectrophotometry, but the final chromatogram contains both positive and negative peaks. It is more convenient to use an eluent comprising free EDTA to facilitate the formation of complexes of injected metals, together with the UV absorbing [CuEDTAI2-complex to act both as the competing anion and to permit indirect spectrophotometric detection. This mixed eluent provides similar separation characteristics for anions as does divalent phthalate [70]. A separation of anions and metal-EDTA complexes is shown in Fig. 4.12.
Inorganic eluents Inorganic anions themselves can be used as the competing anion in an ion-exchange eluent, but the high limiting equivalent ionic conductances of these species almost invariably precludes the use of conductivity detection. For example, P043-, so42-,C1-
96
A
Chapter4
4
I
10 Time (mml
1
15
-1
20
Fig. 4.12 Simultaneous separation of anions and metal-EDTA complexes. The column was a Mitsubishi MCI SCA-01 anion-exchanger with 0.5 mM Na2[Cu(EDTA)] and 0.05 mM Na2H2EDTA as eluent. Detection was by indirect spectrophotometry at 290 nm. Reprinted from [70]with permission.
and Clod- can be used alone, or as mixed eluents. Phosphate at appropriate pH provides suitable buffering action, but it is often necessary to add a separate buffer to eluents comprising other inorganic anions. Dilute solutions of strong mineral acids can also find use as eluents for anionexchange separations in non-suppressed IC. Many metal ions form anionic chlorocomplexes in hydrochloric acid solution and these may be separated on a low-capacity anion-exchanger using HCl eluents [78]. Nitric acid is a versatile eluent which is most often used for the separation of polyvalent anions of weak acids, such as plyphosphates [79], polyphosphonates [79, 801, EDTA (79, 81, 821 and other aminoplycarboxylic acid cornplexing agents [81]. The low pH of dilute nitric acid solutions serves to suppress the ionization of these solutes, which reduces their otherwise strong affinities for anionexchangers, whilst the nitrate ion in the eluent acts as the competing anion. Once again, conductivity is not an appropriate detection mode and post-column reactions or refractive index detection must be used. The separation of some polyvalent solutes with a nitric acid eluent is shown in Fig. 4.13. Extensive tabulations of retention data for a wide range of solutes using nitric acid eluents can be found elsewhere 1891. Table 4.2 lists some typical inorganic eluents. together with the detection mode used in each case. Retention times obtained with a phosphate eluent are included in Fig. 4.9.
Eluentsfor Ion-ExchangeSeparations
0
2
Time (minl
97
I
Fig. 4.13 Separation of polyvalent anions with a nitric acid eluent. A Dionex HPIC-AS7 column was used with 50 mM nimc acid as eluent. Detection was by post-column reaction with Fe(1II) perchlorate. Reprinted from [79] with permission.
TABLE4.2 INORGANIC ELUENTS FOR ANION SEPARATIONS IN IC Eluent 0.1 M NaCl + 5 mM phosphate buffer 2 mM phosphate (pH 7.0) 5.0 mM NaC104 10.0 mM Na2S04 30 mM sulfate + 10 mM Tris buffer 50 mM NaH2P04 + 3 mM NaCl 12 mM HNO3 30-70 mM HN@ 24 mM HNO3 a
Solutes determined
Detectionmod8
Ref
Iodide organic acids Halides, pseudohalides Halides, pseudohalides organic acids Nitrate and nitrite Polyphosphonates Polyvalent anions Phosphorus 0x0-acids
RI = refractive index, PCR = post-column reaction.
Ampemmetry Potentiometry Potentiometry Potentiometry W absorption W absorption
83 84 85 85 86
RI
87 80
PCR PCR
79 88
98
Chapter 4
4.3.2 Eluents for cation separations in non-suppressed IC
Inorganic acids Dilute solutions of inorganic acids, such as nitric acid, are the most popular eluents for the separation of alkali metal cations and amines by non-suppressed 1C [78, 90, 911. The hydrogen ion is an effective competing cation for these solutes and the very high conductance of these eluents permits sensitive detection to be achieved using indirect conductivity. The eluent strength is therefore determined solely by the eluent pH. Table 4.3 lists capacity factors obtained for amines and inorganic cations using a nitric acid eluent with both silica- and resin-based cation-exchange columns. Differences in selectivity between the two types of stationary phases can be noted, particularly for ethanolamines, which are eluted as a group on the surface-sulfonated resin, but are wellresolved on the functionalized silica stationary phase. Similar separations to those shown in Table 4.3 are possible when solutions of perchloric or hydrochloric acids are used as eluents, but these species can cause corrosion problems with chromatographic hardware components, or may require the use of post-column, colour-forming reactions as the detection mode [92]. Organic bases In a manner entirely analogous to the use of carboxylic acids and their salts for the separation of inorganic anions, organic bases may be employed for the separation of inorganic cations. Organic bases become increasingly protonated with decreasing pN, according to the reactions shown in Fig. 4.2, and hence act as useful cation-exchange eluents at low pH. Bases which are singly protonated are effective eluents for
TABLE 4.3 CAPACITY FACTORS FOR AMINES AND ALKALI METAL CATIONS ON CATIONEXCHANGERS USING 3.0 m M NITRIC ACD AS ELUENT. DATA FROM [91] Solute Lithium Sodium Ammonium Potassium Ethanolamine Diethanolamine Triethanolamine Methylamine DimethyIamine Morpholine Rubidium Cesium
Resin-based Wescan 269024 4.63 7 .oo 11.5 15.0 11.5 11.5 11.5
9.60 11.9 15.2 16.3 17.7
Silica-based Wescan 269041 2.32 3.05 4.29 5.47 5.34 8.95 13.34 6.87 11.73 16.7 6.32 8.33
Eluents for Ion-ExchangeSeparations
99
monovalent cations, whilst diprotonated bases are generally more suited to the elution of divalent solute cations. Monofunctional aromatic bases, such as pyridine, benzylamine and dimethylpyridine have been shown to provide good separation of monovalent cations [93-971. These eluents are weakly conducting and have moderate UV absorptivities, and therefore offer sensitive detection using direct conductivity or indirect spectrophotometry as the detection modes. The range of aromatic bases suitable for this type of separation is somewhat restricted since it is'necessary for the base to be protonated in the neutral to alkaline pH range [93]. Acidic eluents cannot be employed because the hydrogen ion present acts as a competing ion (in addition to the protonated base cation) and this leads to a major reduction in detection sensitivity. This aspect is discussed further in Section 9.3.1. Eluents can be prepared by dissolving the required amount of the free base in water and then adjusting the pH to the desired value with acid. Retention data obtained with some aromatic base eluents are included in Fig. 4.14, whilst Table 4.4 provides a more comprehensive listing of the aromatic base eluents which have been reported for non-suppressed IC. Monofunctional aromatic bases can also be used for the elution of divalent cations, but only when the eluent concentration is high. For example, 10 mM phenethylamine can elute Mg2+ and Ca2+from a Waters IC Pak C column in less than 10 minutes [96]. Such high eluent concentrations may create problems with the detection mode and it is therefore preferable to use a diprotonated base as the eluent cation, since this acts as a much stronger competing ion. Diamines are particularly suitable for this purpose, with ethylenediamine (en) being widely employed as an eluent for alkaline earth cations. The enH22+ cation is formed at pH values less than 6 and since this cation is strongly conducting, indirect conductivity detection is the preferred mode of detection. Retention data for an ethylenediamine eluent are included in Fig. 4.14 and Table 4.4 also includes some difunctional organic bases.
Inorganic eluents Dilute aqueous solutions of copper(I1) sulfate were proposed initially by Small and Miller [24] as suitable eluents for both monovalent and divalent cations and have since been used by a number of authors [102-1041. The aquated Cu(I1) cation is a strong competing cation, which shows sufficient UV absorbance to permit indirect spectrophotometricdetection to be employed. An example of the separation which can be achieved with copper sulfate eluents was shown in Fig. 3.5(b). The detection sensitivity and linearity of response for copper sulfate eluents have been shown to be improved if other inorganic cations, such as cobalt(II1). nickel(II), zinc(I1) or cobalt(II), are added to the eluent [105, 1061. Aqueous solutions of cerium(II1) sulfate are also suitable as eluents for mono- and divalent cations. The use of Ce(1II) as the competing cation permits both indirect specuophotometric detection at 254 nm and indirect fluorimetric detection [102, 107, 1081. Ce(II1) exhibits very strong affinity for sulfonic acid cation-exchange sites and has over 10 times the eluting power of an equimolar solution of Cu(I1). This permits very dilute eluents to be used, as illustrated in Fig. 4.15(a), which shows the simultaneous separation of alkali metals and alkaline earth cations.
Weaker
Stronger 2-phenyleth lamine dmM pH 5.7
0
5
.-a h
.-i2
- Sr
2+
E v
2-methylethylene- ethylene- 4-methyldiamine diamine, benzylamine yridine citrate 0.1 mM 8.5 mM 0.5 mM 3.5/10 mM pH 6.92 DH 6.0 pH 5.46 PH 2.80
- Ml' - Ca 2+
lo
I
Li+
Mi+
-C2+ - s?+
e
QI
d
15
20
- Na+ - Li+ - K + - KNH;+ 'bR' - cs' - cs+ Rb'
Y
. . I
10
- Na+ - NH;
. . I
.-d
nitric benz lamine acid 0 . d mM 2.0 mM pH 7.14 pH 2.7
2+
Ba
- Ba
2+
Mn2
+
rcb*
=5
-- Li+ Na+
- NH;
h
c
Y
#lo
K+
Rb'
- cs+
2 .-i *
.-*[: : . . I
d B15
-20
Fig. 4.14 Comparative retention data for cations using a variety of eluents. A PS-DVB cation-exchange column (Waters IC Pak C, 50 x 4.6 mm ID. 12 pequiv/g) was used for all eluents. except for the ethylenediamine-citrate eluent, for which a silica-based TSKgel IC cation SW column (50 x 4.6 mm ID, 450 pquiv/g) was employed. Data taken from 193,981 and courtesy of Waters ChromatographyDivision .
1Q
101
Eluentsfor Ion-ExchangeSeparations
TABLE4.4 ORGANIC BASES AS ELUENT COMPONENTS FOR CATION SEPARATIONS IN NONSUPPRESSED IC Eluent 2.74 mM anilinium nitrate, pH 4.65 1 mM knzmetrhethylammoniumchloride 0.5 mM picolinic acid, pH 3.22 0.5 mM benzylamine, pH 7.15 0.5 mM 2-methylpyridine, pH 5.46 0.2 mM 2,6dimethylpyridine, pH 6.35 0.1 mM 4-methylbenzylamine,pH 6.92 10 mM phenylethylamine,pH 5.49 5 mM pyridinium chloride, pH 4.5 5 mM bipyridyl dihydrochloride 0.5 mM ethylenediamine. pH 4.5 5.48 mM l&phenylenediamine, pH 2.68 8.23 mM p-phenethylamine, pH 2.94 a
Solutes
Detection
determined
m o d e
Alkalimetals Alkali metals, amines Alkalimetals
IRI ISpec ISpec c , ISpeC c , ISpec C, ISpec c , ISpeC C, ISpec ISpec ISPec C c , ISpec C
Alkali metals
Alkalimetals Auralimetals Alkalimetals Alkaline earths Alkali metals Alkalineearths Alkaline earths Aluminium Aluminium
Ref 99 97 93 93 94 94 94 94 95 95 100 94 101
IRI = indirect refractive index, ISpec = indirect spectrophotometry,C = conductivity.
Cationic complexes formed between Cu(I1) or Co(II1) and various chelating agents have also found use as competing cations in eluents for non-suppressed IC. Chelating agents have included ethylenediamine (en), triethylentetramine (trien) and acetylacetone (acac), with the relevant complex cations being [Cu(en)2I2+1701, [Cu(trien)12+[72] and [Co(en)2(acac)12+ [log]. These complex cations do not react with sample species, require no pH adjustment and also allow very sensitive indirect spectrophotometric detection. Elution strengths of the above two copper complexes are up to 10 times those of equimolar Cu(I1) solutions, which can be attributed to the increased size of these complexes relative to the Cu(I1) cation [70]. A separation attained with [Cu(en)2]SO4 as eluent is shown in Fig. 4.15(b).
Complexing eluents All of the eluents for cation separations which have been discussed thus far operate solely on a cation-exchange basis, wherein elution of solute cations results from effective competition for the cation-exchange sites by the eluent cation. This mode of operation is suitable for the separation of cations which show moderate affinity for the sulfonic acid functional groups, e.g. alkali metals and alkaline earth metal ions. As the ion-exchange affinity of the solute cation increases, either the charge on the eluent cation or the eluent concentration must be increased proportionally to enable the solute to be eluted in a reasonable time. The requirement that the eluent be compatible with the detection mode ultimately limits the use of concentrated eluents or highly charged eluent cations. More subtle alternatives are created by the use of a complexing agent as the eluent, or by the addition of a complexing agent to an eluent which already contains a competing
102
Chapter4 l i m e Imin)
0
L
8
12
16
0.002 AU
No'
n
L
K*
la I
I
f
0.
5
I
10 Time (rnin]
I
15
(bl
Fig. 4.25 Separation of cations using inorganic eluents. (a) An Interaction ION-210 transition metal column was used with 0.1 mhl Ce(II1) as eluent. Reprinted from [ 1021 with permission. (b) A Mitsubishi MCI CPK-08 suifonated PS-DVB column was used, with 10 m M [Cu(en)21S04 as eluent. Note that the peaks in (b) are in the direction of decreasing absorbance. Reprinted from
1701 with permission. cation. This serves the dual purpose of reducing the effective charge on the solute cation (and hence its affinity for the cation-exchange sites) and also introduces a further dimension of selectivity between solutes which does not exist when ion-exchange is the only retention mechanism in operation. The above approaches are illustrated schematically in Fig. 4.16, which shows the equilibria existing between a divalent metal solute ion @+,a complexing agent (HzL), and an ethylenediamine (en) eluent, at the surface of a cation-exchange or an anion-exchange resin. In Fig. 4.16(a), the eluent contains only the ligand species. Retention of the solute ion on a cation-exchange resin is moderated by the complexation effect of the deprotonated ligand, which can be said to exert a pulling effect on the solute. The eluent pH determines the degree to which the ligand is deprotonated, which in turn governs the retention of the solute. Retention is also regulated by the type and concentration of the ligand. A further possibility is for the ligand to form an anionic complex with the metal ion, as shown in Fig. 4.16(b). This anionic complex can be retained on an anionexchange resin and can be eluted by a competing anion added to the eluent, or even by the excess anionic ligand which is already present as an eluent component. Fig. 4. I6(c) shows the case where the eluent contains both a ligand and a competing cation (enHz2+). The retention of the solute ion, M2+, is influenced by the competitive effect for the sulfonic acid groups exerted by enH~*+,and also by the complexation of M2+ by the deprotonated ligand L2-. Once again, complexation reduces the effective
-
Eluents for Ion-ExchangeSeparations "Pulling" effect of ligand
H2L
+
ML JF L2-+ 2d
+
M2
+
0
103 M2 +
+
2H2L f 2 L2-+4H+ JF r MLZ 12+ * * +
(b)
(a)
"Pushing" effect of eluent cation
"Pulling" effect of ligand
Fig. 4.26 Schematic illustration of the equilibria existing between a solute cation (M2+), ethylenediamine (en) and an added ligand (H2L) at the surface of a cation- or anion-exchanger. In (a) and (b), the eluent contains only the ligand, whilst in (c). the eluent contains both ligand and
ethylenediamine. concentration of M2+ and the solute is therefore less successful in competing for the cation-exchange sites. This shows that elution of the solute results from a combination of the pushing, or displacement, effect of the competing cation in the eluent and the complexation, or pulling, effect of the complexing agent. The eluent pH influences both the protonation of ethylenediamine and the deprotonation of the added ligand, which in turn controls the degree of complex formation and hence the retention of the solute. The type and concentration of the added ligand again play a major role in determining solute retention. For solute ions of similar ion-exchange selectivities, the retention order closely follows the reverse sequence of the conditional formation constants for the solute-ligand complexes. The eluent ligand for the first of the separation approaches represented in Fig. 4.16(a) is most often tartaric acid, citric acid, oxalic acid or 2-hydroxyisobutyric acid (HIBA) [ 110-1141. The eluent is prepared by adjusting the pH of a solution of the ligand acid (e.g. tartaric acid) with lithium hydroxide [ l l l ] . The resulting eluent therefore contains Li+ as the cationic component, and since lithium is a very weak competing
Mn2' 1
Pb2'
I
rO.002 AU
r
I
I
I
I
1
0
10
20 Time (rnin) (a)
30
40
45
1
0
1
2
1
*
E
qi
1
-Fez' A
I 1
1
1
1
1
1
4 6 8 10 12 14 16 18 Time (min) (b)
r
0
I
I
I
8 12 Time (rnin)
4
1
16
(C)
Fig. 4.27 Separation of metal ions when complexing agents are used as eluent components. (a) A Nucleosil SA-10 column was used with 0.5 M tartrate at pH 2.76 as eluent. Detection by post-column reaction. Reprinted from [115] with permission. (b) A Dionex HPIC-CSS column was used with an eluent containing 3 mM pyridine-2,6dicarboxylic acid, 4.3 mM LiOH, 2 mM Na2S04 and 25 mM NaCl. Detection by post-column reaction. Chmatogram courtesy of Dionex. (c) A TSK IC-Cation SW column was used with 3.5 mM citric acid-10.0 mM ethylenediamine at pH 2.8 as eluent. Detection by conductivity. Reprinted fmm [98] with permission.
$ Q
Eluenrs for Ion-ExchangeSeparations
105
cation, cation-exchange can be considered to make little or no contribution to the overall retention mechanism. It is also possible to use ligand mixtures in the eluent in order to achieve a desired separation. Fig. 4.17(a) shows a separation of transition metal and alkaline earth cations using a tartaric acid eluent, illustrating the excellent separation power of this approach, The absence of an effective competing cation in the eluent means that purely comptexing eluents can be employed only for solutes which undergo strong complexation reactions with the particular ligand(s) in use. It can be noted that detection of eluted metal complexes is generally achieved with a colour-forming postcolumn reaction of some type, however detection can be simplified through the use of a ligand which itself forms coloured complexes. This technique has proved successful using o-cresolphthalein complexone [ 116, 1171, chlorophosphonazo I11 [118] and arsenazo 111 1119, 1201 as eluent components. The second separation approach, shown in Fig 4.16(b), is typically achieved with pyridine-2,6-dicarboxylicacid (H2PDCA) as the complexing agent [121, 1221. This species reacts with many metal ions to form anionic complexes, as shown in eqns. (4.1 1) -(4.13) [149].
M3+ + 2PDCA2- % [M(PDCA)2]where M3+ = Fe3+,Ga3+,Cr3+,etc. M2+ + 2PDCA2- % [M(PDCA)2fwhere M2+ = Cu2+,Ni2+,Zn2+,etc. M3+ + 3PDCA2- % [M(PDCA),I3where M3+ = La3+,Ce3+,Pr3+,etc.
(4.11)
(4.12)
(4.13)
The stationary phase used for the separation of these anionic complexes is an anionexchange latex agglomerate material (Dionex HPIC-CSS), in which the aminated latex does not completely cover the sulfonic acid functionalities on the core particle (see Fig. 3.20). This material therefore exhibits both anion- and cation-exchange properties, so that both the anionic complex and the unreacted metal ion are retained to some extent. However, anion-exchange is the dominant retention mechanism. Fig. 4.17(b) shows a typical separation of metals as their anionic PDCA complexes. The third separation approach, in which the eluent contains both a ligand and an effective competing cation (Fig. 4.16(c)), offers much more versatility since there are more options to select from when attempting to manipulate retention. The eluent ligands are usually tartaric acid' or citric acid, and once again, mixtures of ligands can be employed when required. Several authors [112, 115, 123-1261 have determined the relative merits of these different ligands and have noted some selectivity differences between ligands, which appear as changes in elution order. Fig. 4.17(c) shows the separation of some alkali metal and transition metal cations using an ethylenediaminecitrate eluent. The presence of a competing cation in the eluent enables the noncomplexing alkali metal cations to be separated. Representative retention data for complexing eluents are included in Fig. 4.14.
Chapter4
106
4.4
4.4.1
ELUENTS FOR SUPPRESSED ION CHROMATOGRAPHY Eluent requirements for use with suppressors
The brief introduction presented in Section 2.2 showed that the suppressor is a device inserted between the chromatographic column and a conductivity detector. The function of the suppressor is to reduce the background conductance of the eluent, and where possible, to simultaneously enhance the detectability of the solute ions. The detailed design and operation of suppressor devices will be discussed fully in Section 9.5, but some of the chemical reactions by which suppressors operate are included here so that the reader can appreciate the special restrictions on eluent selection which are imposed when suppressors are used. Suppressors operate through one of the following mechanisms: (i) Exchange of eluent cations for hydrogen ions. The most common mode of suppressor operation is one in which the eluent cations are replaced by hydrogen ions. This results in protonation of those eluent components which are conjugates of weak acids. This mode of suppression is used for anion-exchange eluents and the pertinent reaction is illustrated in eqn. (4.14) for an eluent made up of the sodium salt of the weak acid, HE. Suppressor-H+
+ Na+ + E-
% Suppressor-Na'
+ HE
(4.14)
The background conductance of the eluent is therefore reduced because the relatively strongly conducting ions Na+ and E' are replaced by the weakly conducting species HE. A solute ion, S-, which is the conjugate base of a strong acid (e.g. CI-, NO3-, Sod2-, e r c . ) undergoes the following reaction in the suppressor: Suppressor-H+
+ Na+ + S- %
Suppressor-Na'
+ H+ + S-
(4.15)
Here, the conductance signal of the solute is increased as a result of the replacement of Na+ by highly conducting H+. The net effect of the suppressor therefore is to reduce the eluent conductance and to enhance the conductance of the solute band. ( i i ) Exchange of eluent anions for hydroxide ion. The opposite mechanism to that described above involves the replacement of eluent anions with hydroxide ions from the suppressor. The hydroxide introduced into the eluent may then be used to neutralize acidic eluents, or to precipitate metal ions from the eluent. The first case is exemplified in eqn. (4.16). which shows the suppressor reaction undergone by a cation-exchange eluent formed from a strong acid, HA. The suppression of an eluent formed from a metal nitrate, M(NO3)2 is shown in eqn. (4.17).
Eluents for lon-Exchange Separations
107
+ H' A- + Suppressor-A- + H20 2 Suppressor-OH- + M2++ 2NOj % 2 Suppressor-NO; + M(OH)2(s) Suppressor-OH-
(4.16) (4.17)
Cationic solute ions pass through the suppressor without reaction, except for those solutes which precipitate readily as insoluble hydroxides.
(iii) Complete removal of eluent components. In some cases, it is possible for both the eluent anion and cation to be removed, usually with the aid of a precipitation reaction. For example, a cation-exchange eluent formed from AgN03 can be suppressed by exchange of the eluent NO3- ions for C1- using a suppressor in the C1- form (eqn. (4.18). Alternatively, an anion-exchange eluent formed from NaI can be suppressed by exchange of the eluent Na+ ions by Ag+i using a suppressor in the Ag+ form (eqn. (4.19):
+ Ag' + NO; f Suppressor-NO; + AgCl(S) . Suppressor-Ag' + Na+ + I- f Suppressor-Na' + AgI (9 Suppressor-C1-
(4.18) (4.19)
(iv) Coniplexation reactions. The conductance of an eluent can be suppressed though the use of a suitable complexation reaction which converts the eluent components into non-conducting or weakly conducting components. One example of this approach is the use of dipotassium ethylenediamine-N,N'-diacetate (KzEDDA) as an anion-exchange eluent, which is passed through a suppressor in the Cu2+ form and is converted into the neutral complex Cu-EDDA 1127). The following reaction occurs: Suppressor-Cu"
+ 2K+ + EDDA2-
f Suppressor-(K+)2 + Cu-EDDA (4.20)
(v) Other chemical reactions. Any chemical reaction which causes the eluent components to be converted into less-conducting species can be used as the basis of a suppressor. An example is the use of a thermal decarboxylation reaction. Each of the above suppression mechanisms operates effectively only when the eluent used is compatible with the chemical reaction upon which the suppressor is based. Therefore, each suppression mode imposes restrictions on the types of eluents which may be used, and indeed, the types of solute ions which can be detected using that particular suppression mode. Some of these restrictions are listed in Table 4.5,together with the suppressor mechanisms to which they apply.
4.4.2 Eluents for anion separations in suppressed IC Table 4.5 shows that special requirements exist for both the anionic and cationic components of eluents which are to be used for anion separations in which a suppressor device is employed. The eluent cation must be able to displace H+from the suppressor,
108
Chapter 4
TABLE4.5 ELUENT AND SOLUTE REQUIREMENTS FOR USE WlTH SUPPRESSORS
Type of separation
Anion Anion
Anion Cation Cation Cation cation
Cation
Anion Anion Anion
Anion a
Suppressor form S-H+ S-H+ S-H+ S-OHSOHS-OH-
s-xs-x-
S-M+ S-M+ s-cu2+
s-cu*+
Requirement
Suppression mechanisma
Eluent cation must displace H+ from the suppressor Eluent anion must be easily protonated to a less conducting form Analyte anion must remain deprotonated and conductive Eluent anion must displace OH- from the suppressor Eluent cation must react with OH- to give a less conducting form Analyte cation must not form a precipitate with OHEluent cation must form a precipitate with XAnalyte cation must not form a precipitate with XEluent anion must form a precipitate with M+ Analyte anion must not form a precipitate with M+ Eluent anion must form a neutral complex with Cu2+ Analyte anion must not form a complex with C U ~ +
See text for details of these suppression mechanisms.
and the eluent anion must be readily protonated to give a weakly conducting acid. A further requirement, which is common to all forms of anion-exchange, is that the eluent anion must have a sufficiently strong affinity for the anion-exchange material to enable the solute anions to be eluted within a reasonable time. The eluent concentration is also limited to that which will not exceed the capacity of the suppressor device. Eluent anions which satisfy the above requirements include OH-, B 4 0 ~ ~HCO3-, -, C032-, phenate, and some amino acid anions, whilst Na+ is a suitable eluent cation. Sodium salts of these anions therefore constitute the range of eluents used in suppressed IC. On an equimolar basis, OH- is the weakest eluting anion (although its strength on a relative basis is increased when it is used with stationary phases containing one or more hydroxyethyl groups) and consequently is usually used at higher concentration than the other eluent anions. High capacity suppressors are therefore required with hydroxide eluents. Modem suppressors are capable of neutralizing relatively high concentrations of OH- (e.g. 100 mM), such as those used for the gradient elution separations discussed later in Section 4.6. Bicarbonate ion is a weak eluting species and despite being readily protonated to form carbonic acid, does not find widespread use as an eluent because of the high concentrations needed to elute anions with high anion-exchange selectivity coefficients. On the other hand, carbonate is a powerful eluting anion which is also readily suppressed to form carbonic acid. When bicarbonate and carbonate are used together, the resulting eluent is buffered and has an elution strength which can be varied easily by alteration of the ratio between the two anions, or their total concentrations. For these reasons, NaHCOyNa2C03 mixtures at pH values in the approximate range 8-11 are the most widely used eluents for suppressed IC.
Eluentsfor Ion-ExchangeSeparations
109
Fig. 4.18 shows typical retention behaviour for several eluents of this type. The concentration of HCO3-is held constant at 2.8 mM in Fig. 4.18(a), whilst the concentration of C032- is increased. Under these conditions, the capacity factors show a steady decrease, showing that the concentration of C032- is a useful parameter in manipulating retention. In contrast, Fig. 4.18(b) shows the very much smaller decreases in retention which result when the concentration of HCO3- is increased whilst maintaining the concentration of C032- constant at 2.22 mM. Several examples of chromatograms obtained with carbonate buffer eluents may be seen in Fig, 3.25. It might appear at first glance that use of a very limited number of eluent types would severely restrict the separation capability of suppressed IC. In practice this is not so because the wide range of stationary phases available commercially permits most desired separations to be achieved. The agglomerate anion-exchangers used in suppressed IC (see Table 3.9) offer a variety of functional groups and ion-exchange capacities, and these factors combine to give different separation selectivities. These characteristics become evident when one considers the separation of large, polarizable anions such as I-, SCN-, M004~-,etc. From previous discussions of these anions, we know them to be well retained on anion-exchangers having a large, hydrophobic functional group, and this behaviour is evident on the Dionex HPIC-AS1 to HPIC-AS4 columns, which require relatively concentrated carbonate buffers to elute these ions. The peak shape obtained is poor, due to a combination of the long retention and adsorption effects at the stationary phase surface. Well-shaped peaks for these solutes are obtained only when a stationary phase with a hydrophilic functional group is used (such as the HPIC-ASS column), and p-cyanophenol is added to the eluent to increase its elution strength and to minimize the adsorption effects discussed above. Table 4.6 shows some typical eluent components used for anion separations in suppressed IC, together with the products formed after passage of these eluents through a suppressor. Amino acid eluents, such as tyrosine, and complexing eluents, such as KzEDDA, are among the most recently introduced of the species shown in Table 4.6. The former offer the considerable advantages of powerful elution characteristics, strong adsorption onto PS-DVB resins (which therefore prevents the adsorption of hydrophobic solute anions), and ease of suppression [6, 136, 1451. A chromatogram obtained with a tyrosine eluent is shown in Fig. 4.19. Complexing eluents offer many interesting possibilities and Fig. 4.20 shows a chromatogram obtained with this type of eluent.
4.4.3 Eluents for cation separations in suppressed IC The requirements for the anionic and cationic components of eluents intended for use in cation-exchange separations in suppressed IC are listed in Table 4.5. The most widely used eluents for monovalent cations are HC1 and HNO3. since the H+ ion is an effective competing cation for these species and both C1- and NO3- readily displace hydroxide ion from the suppressor. Moreover, H+ in the eluent is easily suppressed by neutralization with the OH- released from the suppressor. A typical separation achieved with dilute HCl as eluent was shown previously in Fig. 3.14(a). HCl eluents cannot be used for divalent cations (such as alkaline earths) because the eluent concentration required to elute these solutes exceeds the capacity of the suppressor and can also initiate corrosion in stainless steel chromatographic hardware components.
c c
0
C
1
I
I
I
1
0.5
1 .o
1.5
2 .o
2.5
0.5
1.o
1.5
2 .Q
2.5
Fig. 4.18 Effect of variation of (a) [C032-]and (b) [HC03-] on the retention of anions. In (a), the WCO3-1 was maintained at 2.8 mM, whilst in (b), the [C03*-]was maintained at 2.22 mM. A Dionex HPIC-AS4 column was used. Data taken from [ 1281.
3Q
111
Eluentsfor Ion-ExchangeSeparations TABLE4.6 ELUENTS USED FOR SUPPRESSED IC Eluent
Competing ion in eluent
Anion eluents Na~B407 NaOH Na2C03 NaHCO3 NaHCOfla~C03 N~[(w~)o-I~ Na[ CN(GjH4)O-] N-cOOHd Na[N-S03-IC NaI K2EDDAf
Suppressor forma
Products of suppressorreaction
Ref
S-H+ S-H+ S-H+ S-H+ S-H+ S-H+ S-H+ S-H+ S-H+ S-Ag+
S-Na’ + H3B03 S-Na+ + H2O S-Na+ + H2CO3 S-Na+ + H2CO3 S-Na+ + H2CO3 S-Na+ + (C6Hs)OH S-Na+ + CN(CgH4)OH
129 130 131 132 133 134 135 136 137 138 127
s-cu2+ SOHS-OHS-OHS-OHs-c1s-So4” ~ 0 4 2 -
s-103S-NH2 a the suppressor is represented by
s-+mooS-Na+ + +N-SO3S-Na+ + AgI(s) S-K+ + CU-EDDA
S-Cl- + H20 S-NO3- + H2O S-NO3- + Zn(OH)2(,) + H20 S-Cl- + m-PDA + H20 S-NO3- + AgCl(,) S-NO3- + BaS04(s) S-NO3- + PbS04(,) S-NO3- + Pb(103)2(s) S-NH~-CU(NO~)~
139 140 141
142 134 143 143 144 134
S.
sodium phenate. sodiump-cyanophenate. N-COOH is an amino acid such as tyrosine. C +N-S@is a zwitterionic buffer such as 2-(N-morpholino)ethanesulfonicacid. dipotassium ethylenediamine-N,N-diacetate. g m-phenylenediamine dihydrochloride. Many metal ions precipitate as hydroxides when passed through a suppressor in the OHform, so these metal ions cannot be separated on suppressed systems of this type. Divalent cations are best eluted with stronger competing cations such as phenylenediammonium, Ag+, Pb2+, Zn2+, Ba2+or Cu2+. The meta isomer of phenylenediamine has proved more suitable than the para isomer because of the tendency of the latter to oxidize in the presence of light,’ forming coloured species which are adsorbed onto the cation-exchange resin [142]. A separation of alkaline earth cations using rnphenylenediamine as eluent was shown previously in Fig. 3.14(b).
112
Chapter 4 F-
sotI
I
I
I
I
1
I
I
1
0
2
L
6
8
10
12
I4
lime ( m i d
Fig. 4.19. Separation of anions using a tyrosine eluent and suppressed conductivity detection. A Dionex HPIC-AS4A column was used with 1 mM tyrosine as eluent. Reprinted from [129] with permission.
SOL*-
I
I
I
I
I
0
10
20 Time (mid
30
LO
Fig. 4.20 Chromatogram obtained for anions using eluent suppression with a complexation reaction. A TOSOH IC anion PW column was used with a TOSOH SCX column in the Cu2+ form as the suppressor. The eluent was 2 mh4 dipotassium ethylenediamine-N,N-diacetateat pH 10.08. Conductivity detection was used. Reprinted from [ 1271 with permission.
Eluents for Ion-Exchange Separations
113
Eluents formed using metal ions as the competing cations can be suppressed in a number of ways. Firstly, precipitation reactions can be employed when there is no possibility that the solute cations will also precipitate. For example, eluents containing Ag+ can be suppressed by precipitating AgCl using a suppressor in the C1- form [134], and both Pb2+ and Ba2+ eluents can be suppressed by precipitation of the respective sulfates with a suppressor in the Sod2- form [143]. Similarly, Zn2+eluents can be suppressed by precipitation of Zn(OH)2 using a suppressor in the OH- form. An alternative form of suppression involves the use of complexation reactions to remove a conductive species from the eluent. This can be illustrated for Cu2+eluents suppressed by complexation with an amine ligand bound to the suppressor [134]. Table 4.6 includes relevant suppressor reactions for cation-exchange eluents, and Fig. 4.21 shows some comparative retention data for a range of cation-exchange eluents used on the same column.
Stronger m-phenylene dismine 2.0 mM, HCI 2.0 mM
nitric acid 4 mM, zinc nitrate 2.5 mM
Weaker
lead nitrate 1.0 mM pH 4.0
barium nitrate 2.0 mM pH 4.0
hydrochloric acid 5 mM
nitric acid 2.5 m M pH 2.6
- Li+
- Rb+ - c$ Rb’
Fig. 4.221 Comparative retention data for cations using a variety of suppressed eluents. A Dionex HPIC-CS 1 column was used in all cases. MA=methylamine, EA=ethylamine, DMA=dimethylamine,TMA=trimethylamine, PA=propylamine. Data from [141, 143, 1461 and courtesy of Dionex.
Chapter 4
114
4.5
GRADIENT ELUTION IN ION-EXCHANGE SEPARATIONS
4.5.1
Principles of gradient elution
The preceding discussion on the various eluents employed for IC has shown that most desired separations can be achieved with the correct combination of eluent and stationary phase. All of the eluents discussed thus far have been intended for use in isocratic separations, that is, where the eluent composition is constant throughout the course of the analysis. Whilst adequate resolution of sample components can generally be achieved with this approach, the distribution of peaks throughout the chromatogram may not be optimal. For example, resolution of a group of early-eluted solutes may be possible only at the expense of very long retention (and hence long analysis times) for some later-eluted solutes. Under these conditions, it is desirable to implement a gradient elution method in which the eluent composition is varied during the chromatographic run to produce a better distribution of peaks over the chromatogram. Examination of the factors influencing solute retention in ion-exchange (see Sections 2.1.2 and 4.2) suggest that an effective eluent gradient can be produced using one (or more) of the following methods: The concentration of competing ion in the eluent can be increased over the course of the separation. (ii) The eluent pH can be varied, provided that this produces an increase in the Concentration of the competing ion in the eluent. (iii) The type of competing ion itself can be changed in order to introduce a more powerful competing ion into the eluent. (i)
Alternatives (i) and (ii) above produce what is known as a concentrationgradient, in which the concentration of the competing ion increases during the separation. Alternative (iii) produces a compositional gradient. The former method is the most commonly used in IC because it is easier to re-establish starting conditions at the conclusion of the gradient when only one type of competing ion is involved. Moreover, it is generally simpler to generate the concentration gradient by directly increasing the concentration of the competing ion, rather than through the use of pH changes. One reason for this is that pH gradients can lead to the adsorption of neutral eluent components on the column and these may desorb rapidly at a particular pH value [ 1351. Both concentration and composition gradients can be generated in a continuous mode (where the eluent components undergo continuous change) or a stepwise mode (where the eluent components are altered in a stepwise manner). The principal problem which arises when gradient elution is applied to ionexchange methods is the prevention of baseline changes resulting from the altered eluent composition. For detection modes in which the eluent provides a negligible detection signal only, this problem becomes trivial. This is the case for most colour-forming, post-column reaction and electrochemical detection methods. However, there are many detection methods in which the eluent contributes an appreciable background detection signal ( e . 8 . conductivity, indirect spectrophotometry) and in these cases, it may be
Eluents for Ion-ExchangeSeparations
115
difficult to implement gradient elution techniques without interference from large baseline disturbances [ 1471. The theory of gradient elution is treated fully in Chapter 5 and the discussion here will be concerned only with the eluent types which are best suited to gradient elution separations using ion-exchange. 4.5.2
Gradient elution using detection methods other than conductivity
Post-column reaction detection (see Chapter 13) involves the reaction of eluted solutes with suitable reagents in order to form easily detectable species. The majority of post-column reactions are designed to give coloured products which show good detection response in the UV-Vis spectral region. The eluent components are usually quite transparent at the detection wavelength, so it is a straightforward exercise to generate a concentration or compositional gradient in the eluent. A prime example of this approach is the separation of lanthanides by cationexchange using a concentration gradient of a complexing agent such as ct-hydroxyisobutyric acid (HIBA) [148-1501or 2-methyllactic acid [151]. Separation is achievqd by the complexation (or pulling) mechanism depicted in Fig. 4.16(a) and a representative chromatogram is shown in Fig 4.22(a). Lanthanides can also be separated by anionexchange using a concentration gradient of oxalic acid, diglycolic acid, and pyridine dicarboxylic acid (PDCA), all of which form anionic complexes with lanthanides [149, 1521. Fig. 4.22(b) shows a simultaneous separation of transition metals and lanthanides achieved by this method. Some other gradient elution separations using post-column reaction detection are listed in Table 4.7. Some electrochemical detection methods are insensitive to changes in the ionic strength of the eluent and so are compatible with gradient elution. Examples are included in Table 4.7. Indirect spectrophotometric detection may also be applied to gradient elution in which the pH of a phthalate eluent is vaned [147]. At the initial pH (4.6), phthalate exists predominantly in the singly ionized form, but is converted to the doubly ionized form at the final pH (6.3). The strength of the eluent therefore increases over the gradient by virtue of the increasing concentration of a more powerful competing anion. Monitoring of the absorbance of the eluent at an isosbestic point (262 nm) gives a fairly stable baseline. 4.5.3
Gradient elution with conductivity detection
High capacity suppressors The most direct approach to gradient elution with conductivity detection is to utilize a suppressor which has sufficient capacity to reduce the conductance of the increasing concentration of competing ion in the eluent to the same background level. The suppressor best capable of achieving this is the micromembrane suppressor, which has a very high suppression capacity. The design and operation of this device are discussed in Section 9.5.4. The anion micromembrane suppressor exchanges eluent cations for hydrogen ions, whilst the cation micromembrane suppressor exchanges eluent anions for hydroxide ion. Gradients should therefore be possible for any eluent which is suppressed by these reactions.
Sm
I C 1
Ho
Dy3*
Fe3'
\
I
I
I
0
6
12
I
18 Time (min)
la)
1
I
24
30
I
I
I
I
1
0
10
20
30
LO
Time (min)
Ibl
Fig. 4.22 Gradient elution in (a) cation- and (b) anion-exchange separations using post-column reaction detection. (a) A Nucleosil lOSA column was used with an eluent formed by a linear gradient from 10-40 mM 2-methyllactic acid (pH 4.6) over a 30 min period. Reprinted from [151] with permission. (b) A Dionex HPIC-CSS column was used with a complex eluent formed by step-gradient mixtures of 6 mM PDCA, 100 mM oxalic acid and 100 mM diglycolic acid. Reprinted from [I521 with pemission.
5
4
Eluena for Ion-ExchangeSeparations
117
TABLE 4.7 GRADIENT ELUTION IN ION-EXCHANGE SEPARATIONS
Solutes
Anion separations Halides Inorganic anions Phosphates Organic, inorganic anions Inorganic anions Inorganic anions Sulfur anions Organt, inorganic anions Inorganic anions Inorganic anions Cation separations Lanthanides Lanthanidesc Lanthanides Transition metals Transition metals Alkalineearths Na+, K+, M P ,Ca2+ Lanthanides and transition metalsC a
EluenP
Parameter varied in gradient
Detection mocieb
Ref
POT
NaClO4 NaC104, HClO4 EDTA-NaCl NaOH NaOH NaHCO3, Na2Ca NaHCO3, Na2CO3 NH4(PCP) CS+/Li+(Glu-bor) KHphthalate
C ISPec
85 153 154 135 155 155 156 135 157 147
MLA OX-DGA HIBA Na2(tartrate) NaOactate) KCI CuSO4. CoSO4 PDCA, Ox, DGA
PCR PCR PCR PCR PCR spec ISPec PCR
151 149 148 151 151 117 105 152
ESD PCR
sc
SC, POT SC, POT
sc sc
PCP =p-cyanophenate, Glu-bor = gluconate-borate complex, MLA = methyllactic acid, Ox = oxalate, DGA = diglycolic acid, HIBA = a-hydroxyisobutyric acid, PDCA = pyridine dicarboxylic acid. POT = potentiomtry, ESD = electrosorptive detection, PCR = postcolumn reaction, SC = suppressed conductivity, C = conductivity without a suppressor, ISpec = indirect spectrophotometiy. Spec = spectrophotometry. Anion-exchange was the separation mode used.
Table 4.6 showed that most anion-exchange eluents require a suppressor in the H+ form and so are potential candidates for gradient elution. The major factor which must be recognized here is that when a concentration gradient is used, the increasing concentration of competing ion in the eluent will lead to a corresponding increasing concentration of the suppressor product. The ultimate baseline stability of the suppressed eluent will therefore depend on the extent of any hydrolysis reactions involving the suppressor product. This, in turn, limits the choice of eluents to salts of weak acids of PKa > 7 which will not undergo any significant hydrolysis and therefore will not lead to significant changes in bdseline conductance as their concentration in the
118
Chapter4
11
19
L
r
0
I
5
I
10
I
15
1
20
I
25
1
30
Time (min)
Fig. 4.23 Gradient elution using conductivity detection and a high capacity suppressor. A Dionex HPIC-ASSA column was used. The eluents used were eluent A, 0.75 mM NaOH and eluent B, 100 mM NaOH. The gradient program is shown below. Peak identities: 1= fluoride, 2 = ahydroxybutyrate, 3 = acetate, 4 = glycolate, 5 = butyrate, 6 = gluconate, 7 = a-hydroxyvalerate, 8 = formate, 9 = valerate, 10 = pyruvate, 1 1 = monochloroacetate, 12 = bromate, 13 = chloride, 14 = galacturonate, 15 = nimte, 16 = glucuronate, 17 = dichloroacetate, 18 = trifluoroacetate, 19 = phosphite, 20 = selenite, 21 = bromide, 22 = nitrate, 23 = sulfate, 24 = oxalate, 25 = selenate, 26 = a-ketoglutarate, 27 = fumarate, 28 = phthalate, 29 = oxaloacetate, 30 = phosphate, 31 = arsenate, 32 = chromate, 33 = citrate, 34 = isocitrate, 35 = cis-aconitate, 36 = trans-aconitate. Reprinted from [135] with permission. 0 5 15 30 Gradient program Time(min) %A 100 100 70 14 %B 0 0 30 86
suppressed eluent builds up. Using this criterion, suitable eluents for gradient elution include NaOH, sodium tetraborate, salts of phenates (such as p-cyanophenate) and anions forming zwitterions in the suppressor. It is noteworthy that the HC03-/C032- buffers, which have proved so versatile for isocratic elution in suppressed IC, have limited suitability for gradient elution because the suppressor product (H2CO3) has pK,1 = 6.35 and so is too strong an acid. However, it has been shown [I551 that a porous polypropylene tubular membrane (called a "post-suppressor"), incorporated between the suppressor and the detector, results in removal of dissolved C 0 2 and hence permits gradient elution with carbonate buffers. In addition, gradients which involve only small
Eluents for Ion-ExchangeSeparations
119
increases in the concentration of a carbonate buffer have been used [ 1581. Sodium hydroxide is a more useful eluent for gradient elution because the suppressor product is water, regardless of the original concentration of NaOH in the eluent. The anion micromembrane suppressor can fully suppress 100 mM NaOH at a flow-rate of 1.0 ml/min [129], so concentration gradients up to this level are possible. Fig 4.23 shows the separation of 36 anions using a 0.75-100 mM NaOH gradient. The major problem with NaOH as an eluent for gradient elution is contamination by C032produced from the absorption of carbon dioxide from the atmosphere. This can cause a drift in the conductance of the suppressed eluent. NaOH gradients are therefore successful only when suitable precautions are taken in eluent preparation and storage. Indeed, eluent purity is an inherent problem in gradient elution because even trace levels of impurities build up at the head of the column in the early portion of the gradient and are eluted only when the eluent concentration increases.
Isoconductive gradients An alternative approach to gradient elution with conductivity detection is the use of two eluents which have different elution strengths, but the same background conductance. Such eluents may be described as isoconductive an'd the use of these eluents has been reported for anion-exchange separations in non-suppressed IC [ 157, 1591. The background conductance of an anion-exchange eluent formed from a competing anion E- and a cation M+ is calculated by taking into account the limiting equivalent ionic conductances and concentrations of both E- and M+ (see Section 9.2). It follows that two eluents formed from the same concentration of E-, but with different cations, will have different conductances. Viewed another way, it should then be possible for two eluents comprising different concenlrations of E and different cations, to have the same conductance, i.e. to be isoconductive. The weaker eluent used at the start of the gradient has a low concentration of E- in the presence of a highly conducting cation, such as MI+. On the other hand, the stronger eluent used later in the gradient has a higher concentration of E- in the presence of a less-conducting cation such as M2+. Fig. 4.24 gives a schematic representation of an isoconductive gradient, and Fig. 4.25 shows a gradient separation of anions using this method. The limitation of isoconductive gradients is that only a relatively small range in the concentration of competing anion is accessible, In other words, the difference in eluting strengths between the starting and finishing eluents in the gradient is quite small. This can be illustrated by considering two isoconductive eluents, the first (weaker eluent) containing c1 mM of the salt MIE, and the second (stronger eluent) containing c2 mM of , as in the salt M2E. The attainable gradient strength is given by the ratio C ~ C I calculated eqn. (4.21) [ 1571. (4.21)
Chapter 4
Eluent A
Eluent B
MlE c1 mM
M2E c2mM
A
B
Eluent
.
Fig. 4.24 Schematic representation of the composition of an isoconductive gradient for anionexchange separations. The two isoconductive eluents are formed from MIE (cl mM) and M2E (c2 mM), where the eluent competing anion is E-, MI+is a strongly conducting cation, and M2+ is a weakly conducting cation. Modified from [ 1591.
1
0
~
~
~
'
5
"
"
'
Time ( m i d
l
10
'
'
'
'
1s
l
Fig. 4.25 Anion-exchange separation using an isoconductive gradient. A Waters IC Pak Anion HR column was used. The column was equilibrated with eluent A (8.25 mM boric acid, 1.11 mM gluconic acid, 3.08 mM cesium hydroxide, 0.48 mM glycerin and 12% acetonimlef and a step gradient to eluent B (12.65 mM boric acid, 1.70 mM gluconic acid, 4.72 mM lithium hydroxide, 0.75 mM glycerin and 12% acetonitrile) was initiated at the moment of injection. Note that with the pump used, there was a considerable lag time before the gradient reached the column. Reprinted from [ 1571 with permission.
Eluentsfor Ion-ExchangeSeparations
121
where X represents the limiting equivalent ionic conductance. The gradient strength is therefore dependent chiefly on the difference in X values between the cations MI+and M2+, and also on the X value for the eluent anion. Values of X for Rb+, K+,Li+ and tetrabutylammonium (TBA+) are 78, 73,37 and 20, respectively. Typical combinations of cations for isoconductive gradients would therefore be Rb+/TBA+ or K+/Li+. The gradient strengths attainable with these cation combinations are shown in Fig. 4.26 for a range of different eluent anions. It can be seen that isoconductive gradients formed from Rb+ and TBA+ salts of the gluconate-borate complex anion offer the highest gradient strength for any of the eluent anions shown.
Baseline balancing methods Gradients with conductivity detection are possible if careful steps are taken to balance the changing conductance of the eluent in some way. Two methods by which this may be achieved have been suggested. In the first method, a step gradient is used between two carbonate buffer eluents which give identical concentrations of H2CO3 in the suppressor, and hence identical background conductances [156]. The simplest case is to use equimolar concentrations of NaHC03 and Na2C03 as the two eluents and the gradient is achieved as a result of the greater eluting strength of the C032- eluent. This approach can be extended to the use of NaHC03/Na2C03 buffers as the two eluents, provided that the total molarities of the two eluents are the same. The second method of baseline balancing is to counteract the increasing conductance encountered during the gradient with another species added to the weaker
‘n 3
RblTBA
Limiting equivalent ionic conductance I X ) of eluent anion Fig. 4.26 Isoconductive gradient strengths (given by cz/cl - see text) attainable for Rb+/TBA+ and K+/Li+ cation combinations with different eluent anions. Reprinted from [159] with
permission.
122
r 0
Chapter 4
lil
17
I
5
I
10 Time (min)
I
I
15
20
Fig. 4.27 Gradient elution by suppressed 1C with baseline balancing using borate-mannitol. A Dionex HPIC-AS6 column was used with a gradient of ammoniump-cyanophenate. Mannitol is added to the eluent and borate forms pan of the regenerant in the suppressor. The following eluents were used. Eluent A, 35 mM pcyanophenol, 50 mM ammonium hydroxide, 2% acetonitrile; eluent B, 50 mM mannitol, 2% acetonitrile; eluent C, 2% acetonitrile. The gradient program is shown below. Peak identities: 1 = 2 = acetate, 3 = formate, 4 = pyruvate, 5 = monochloroacetate, 6 = BrOg-, 7 = Cl-, 8 = NOz', 9 = HP042-, 10 = HA SO^^-, 11 = glutarate, 12 = succinate, 13 = maleate, 14 = S042-, 15 = NOg-, 16 = oxalate, 17 = fumarate, 18 = trichloroacetate, 19 = oxaloacctate, 20 = pyrophosphate, 21 = citratc, 22 = iswitrate. Reprinted from [I351 with permission. Gradient program: Time(&) 0 3 3.1 7 13 15 53 100 %A 30 53 7 15 40 30 25 0 %B 45 40 17 22 0 30 %C 48 45 F-9
eluent. One successful approach to this in suppressed IC is to add mannitol to the weaker eluent, whilst at the same time adding boric acid to the regenerant [135]. Mannitol is a neutral polyalcohol and has little effect on either separation or detection, but can react with neutral boric acid permeating from the suppressor regenerant into the eluent to form a conductive anionic species. If the mannitol concentration entering the suppressor is decreased in inverse proportion to the increase in eluent concentration in the gradient, a steady baseline can be achieved. Fig. 4.27 shows a separation achieved with such a gradient. Baseline balancing can also be accomplished with a computer which automatically subtracts the baseline signal for a blank gradient from the conductance signal produced during the gradient separation of a sample.
Eluentsfor Ion-ExchangeSeparations
123
INJECTION PEAK
I
0
I
I
G
I
I
8
I
Time Imin)
I
12
I
1
16
Fig. 4.28 Illustration of the injection and system peaks observed in non-suppressed IC.
4.6 EXTRANEOUS (SYSTEM) PEAKS IN ION-EXCHANGE IC 4.6.1
Introduction
When a solute is injected into an IC system, additional peaks sometimes appear in the chromatogram. These peaks, which are often detectable only with certain types of detectors, are referred to by names such as system peaks, pseudo peaks, ghost peaks, vacuncy peaks or inducedpeuks. Most analysts treat these peaks as a nuisance because of the possibility of interference with solute peaks.
4.6.2 Extraneous peaks in non-suppressed IC System peaks are most commonly observed in anion-exchange non-suppressed IC, where the phenomenon can be seen by looking at a chromatogram resulting from the injection of a solute Na+S- into an eluent formed from a weak acid, HE. Fig. 4.28 shows that a peak directly attributable to the solute (in this case, nitrite) is observed, together with two additional peaks. The first of these is eluted at the column void volume and will be referred to as the injection peak (sometimes also called the solvent peak). The second additional peak is eluted later in the chromatogram and will be referred to as the system peak. It should be emphasized that the injection peak occurs in almost every chromatogram, whilst the system peak is present only when the eluent and sample meet certain conditions, and only with some detection methods, Both the injection and system peaks can be positive or negative in direction. The origins of these peaks have been studied by numerous authors [31. 58, 1601671 and some of the conclusions reached are summarized below. For simplicity, we will consider only the situation where a conductivity detector is used with an anionexchange IC system.
chapter 4
124
The injection peak We assume that the sample consists of an aqueous solution of Na+S-and the column is equilibrated with an eluent HE, containing the competing anion, E-. When the sample reaches the head of the column, the solute anions become adsorbed onto the stationary phase by displacing E- ions. The sample band therefore contains Na+ ions and E-, together with some HE. This band moves through the column and since it has a different composition to that of the bulk eluent, gives rise to a detector signal. The resultant injection peak has the following characteristics [166,167]: The retention time is constant regardless of the eluent pH or the concentration of the injected solute. (ii) The conductance of the injection peak increases in proportion to the concentration of the injected solute. (iii) The conductance of the injection peak relative to that of the eluent shows little variation with changes in eluent composition. (iv) The conductance of the injection peak may be greater or less than that of the eluent, depending on the sample concentration and the eluent composition. The direction of the injection peak can therefore be positive or negative.
(i)
The injection peak can be attributed to the solute cations which are excluded from the anion-exchange resin, together with displaced eluent anions. Hershcovitz et al. 11671 have used characteristic (ii) above to show that when a mixture of solute anions is injected, the area of the injection peak is related stoichiometrically to the combined areas of the solute peaks. They have demonstrated that it is possible to predict accurately the area of a nominated solute peak if the areas of the injection peak and the other solute peaks are known. Further studies [ 1681 have indicated that the injection peak can be used for a range of analytical purposes, which are discussed in Section 9.6.4.
The system peak The following characteristics have been noted for the system peak in nonsuppressed IC [ 160, 1661. The retention time of the system peak is dependent on the eluent composition and on the type of stationary phase used in the column. (ii) The height of the system peak varies with the eluent pH and is also dependent on the difference in pH between the eluent and sample. (iii) The height of the system peak depends on both the volume and concentration of the injected sample.
(i)
These characteristics indicate clearly that the system peak is the result of some kind of disturbance of column equilibria caused by injection of the sample. The fact that the size of the system peak is greater for some solutes than others has led to the erroneous conclusion by some early workers that the system peak was due to the elution of a specific anion. This confusion is particularly evident when HCO3- is the solute and an eluent of pH=5 is used. Under these conditions, HCO3- forms H2CO3 and is therefore
Eluentsfor Ion-ExchangeSeparations
Hydrophobic surface
125
Ionexchange site
Fig. 4.29 Schematic illustration of eluent equilibria at the surface of an anion-exchange stationary
phase. unretained, appearing in the chromatogram as part of the injection peak. The latereluted system peak may therefore be mistaken easily for the HCO3- peak. There are several schools of thought regarding the origin of the system peak, but the essential aspects of most of these can be incorporated into the following model. The sample injection causes a disruption of the equilibria existing between eluent species in the flowing solution and eluent species adsorbed onto the stationary phase. This is followed by a relaxation process which results in a decrease in the velocity of the solute (which initially enters the column at the velocity of the mobile phase) towards the equilibrium velocity dictated by the distribution coefficient for that particular solute. At the same time, the velocities are also decreased for mobile phase components whose concentrations are different to those present in the bulk eluent. We note that both an excess or deficiency of an eluent component (relative to the concentration of that component present in the bulk eluent) will move through the column at the same speed, which is determined by the distribution coefficient for that particular species. The final result is a chromatogram which contains a peak for the solute, as well as peaks for some or all of the eluent components. This effect will be observed for any chromatographic system in which the eluent contains more than one component [163, 1641 and we can expect peaks to appear at the characteristic retention times for each eluent component. The column equilibria are represented schematically in Fig. 4.29. All samples, including water, will cause some disturbance of these equilibria. For example, sample injection may cause a change in the concentration of an anionic competing ion in the eluent. This change may be an increase or a decrease in concentration of the competing anion, relative to that in the bulk eluent. However, a decrease is the more probable outcome. The changed concentration of competing ion will appear at the characteristic ion-exchange retention time for the competing anion [165]. This mechanism is readily illustrated using a phthalate eluent which also contains some C1-. Injection of any solute will produce a peak for that solute, as well as a peak at the retention time of C1- [165, 1691. The same model can apply if we consider an eluent which contains some of the neutral eluent acid (i.e. HE in the example under consideration). Adsorption of HE onto
126
Chapter4
the unfunctionalized parts of the ion-exchange material can be expected to occur (see Fig. 4.29). It should be remembered here that PS-DVB resins show strong reversedphase properties and there is ample evidence for adsorption of neutral or ionic eluent components onto the resin [170-1721. There is an equilibrium concentration of HE both on the resin and in the eluent. These concentrations are altered by sample injection and once again, there follows a relaxation process which produces a change in eluent composition at the detector. The retention time of this change (and hence the system peak) is determined by the retention time of the neutral eluent species, HE [26, 1601. Eluents formed from aromatic carboxylic acid salts are particularly prone to system peaks, but these are generally eluted late in the chromatogram where interference with solute peaks is minimal. System peaks can be eliminated with these eluents by adjusting the pH so that the eluent acid is completely ionized (e.g. phthalate eluents above pH 6.5). Under these conditions, the eluent therefore contains a single competing anion. Apart from the above general mechanism, some system peaks can be attributed to specific chemical interactions existing in certain eluents. For example, gluconate-borate eluents give a negative system peak when Ca2+ is present in the injected sample. This peak has been assigned to an anionic complex of calcium with a borate-gluconate diester present in the eluent [%I. The complex is retained by an anion-exchange mechanism and being less conducting than the eluent itself, gives a negative baseline change. Removal of Ca2+ from the sample with an ion-exchange pre-column was shown to eliminate this system peak. 4.6.3 Extraneous peaks in suppressed IC Extraneous peaks also appear in the chromatograms produced in suppressed IC. These occur despitc the fact that the eluent composition is normalized to some extent after passage through the suppressor. Fig. 4.30 shows typical peaks appearing in the early part of a chromatogram using suppressed IC with a carbonate-bicarbonate eluent [ 1731. It can be seen that injection of a HC03-/C032- sample of higher concentration than the eluent produces two positive peaks (Fig. 4.30(a)), whereas samples of lower concentration than the eluent produce two negative peaks (Fig. 4.30(c) and (d)). Samples with the same concentration as the eluent show no peaks (Fig. 4.30(b)). It is the second and larger of the two extraneous peaks which can cause problems in suppressed IC, chiefly by distorting the peaks due to early eluted solutes such as F- and C1-. This peak is most often negative in direction since most samples in IC contain relatively low levels of HCO3- and C032-. For this reason, it is often referred to as the water dip. The water dip is produced by the same mechanism as that encountered in non-suppressed IC for the formation of the injection peak. That is, injection of the sample onto the column results in adsorption of the solute anions of the sample and dcsorption of the competing anions, HCO3- and C032-, from the stationary phase. The injected volume therefore consists of HCO3- and C032-, along with the cations from the sample. This band passes through the separator column to the suppressor, where the usual suppressor reactions occur. l h a t is, the sample cations are exchanged for H+ and H2CO3 is formed. The concentration of H2CO3 produced in this manner is directly proportional to the concentration of adsorbable solute anions in the sample, and the water dip can therefore also be termed the ionic concentration peak [ 1731. The second,
Eluents for Ion-Exchange Separations
0-
127
Retention volume fmlJ
Fig. 4.30 Extraneous peaks produced from injection of Na~C03-NaHC03mixtures into a suppressed IC system with a packed-bed suppressor. The eluent is 3 mM NaHC03 + 2.4 mM Na2C03. The total injected concentrations were (a) 10.8 mM, (b) 5.4 mM, (c) 2.7 mM, (d) distilled water. Reprinted from [I731 with permission.
smaller peak in Fig. 4.30 has been attributed tentatively to the temperature change resulting from the heat of neutralization produced as the sample encounters the first part of the suppressor, which is rich in hydrogen ions [173]. A further complication arises when a packed-bed suppressor column is used. The retention time of the band comprising the sample solvent, the sample cations and the displaced HCO3- and C032- in the suppressor column will depend slightly on the degree of depletion of the suppressor. The reason for this is that the band will be unretained (because of Donnan exclusion) on the parts of the suppressor which have been depleted of H+ ions, but as soon as the active zone in the suppressor is reached and the suppression reaction occurs, the H2CO3 produced can be adsorbed by the resin. This occurs because H2CO3 is a neutral species and there is no Donnan exclusion effect to prevent its retardation. Keeping in mind that it is this H2CO3 which leads to the water dip, then it can be appreciated that the actual elution time of the water dip will change (and hence interference effects will vary) with the degree of suppressor depletion. This effect does not occur with fibre or micromembrane suppressors which are continuously regenerated, since their degree of depletion is constant for a specified eluent and flowrate.
Chapter4
128
4.7 1 2 3 4 5 6
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Dionex Technical Note 24. Sevenich G.J. and Fritz J.S., Anal. Chem., 55 (1983) 12. Haddad P.R., Alexander P.W. and Trojanowicz M., J . Chromatogr., 294 (1984) 397. Haddad P.R., Alexander P.W. and Trojanowicz M.. J . Chromatogr.. 324 (1985) 319. Yan D. and Schwedt G.,Fres. Z . Anal. Chem., 320 (1985) 121. Sato H. and Miyanaga A., Anal. Chem., 61 (1989) 122. Weiss J., Handbook of ion Chromatography, Dionex Corporation, Sunnyvale, CA, 1986. Stillian J., LC, 3 (1985) 802. Bouyoucos S.A., J. Chromatogr., 242 (1982) 170. Nonomura M., Anal. Chem., 59 (1987) 2073. Watanabe T., Nagaoka M. and Yamazaki S., Ryusan to Kogyo, 38 (1985) 162. Stevens T.S., Davis J.C. and Small H., Anal. Chem., 53 (1981) 1488. Small H., Stevens T.S. and Bauman W.C., Anal. Chem., 47 (1975) 1801. Rocklin R.D., Pohl C.A. and Schibler J.A., J . Chromatogr., 411 (1987) 107. Zolotov Y.A., Shpigun O.A., Pazukhina Y.E. and Voloshik I.N.,Int. J. Environ. Anal. Chem., 31 (1987) 99. Ivey J.P., J. Chromatogr., 287 (1984) 128. Pohl C.A. and Johnson E.L., J. Chromatogr. Sci., 18 (1980) 442. Slingsby R.W. and Riviello J.M., LC, 1 (1983) 354. Mulik J.D., Estes E. and Sawicki E., in Sawicki E., Mulik J.D. and Wittgenstein E., (Eds.) Ion Chromatographic Analysis of Environmental Pollutants, Vol. I, Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 41. Wimberley J.W., Anal. Chem., 53 (1981) 2137. Dionex Application Note 17. Nordmeyer F.R., Hansen L.D., Eatough D.J., Rollins D.K. and Lamb J.D., Anal. Chem., 52 (1980) 852. Lamb J.D., Hansen L.D., Patch G.G.and Nordmeyer F.R., Anal. Chem., 53 (1981) 749. Franklin G.O., Am. Lab., 17 (1985) 65. Kifune I. and Oikawa K., Niigara Rihgaku, 5 (1979) 9. Jenke D.R., Mitchell P.K. and Pagenkopf G.K., Anal. Chim. Acta, 155 (1983) 279. Elchuk S. and Cassidy R.M., Anal. Chem., 51 (1979) 1434. Heberling S.S., Riviello J.M. Shifen M. and Ip A.W., Res. & Dev., September (1987) 74. Mazzucotelli M., Dadone A., Frache R. and Baffi F., Chromatographia, 15 (1982) 697. Wang W., Chen Y.and Wu M., Analyst (London), 109 (1984) 281. Dionex Technical Note 23. Ramstad T. and Weaver M.J., Anal. Chim. Acta, 204 (1988) 95. Yamaguchi H., Nakamura T., Hirai Y. and Ohashi S., J. Chromatogr., 172 (1979) 131. Shintani H. and Dasgupta P.K., Anal. Chem., 59 (1987) 802. Sunden T., Lindgren M., Cedergren A. and Siemer D.D., Anal. Chem., 55 (1983) 2. Jones W.R., Jandik P. and Heckenberg A.L., Anal. Chem., 60 (1988) 1977. Tarter J.G, Anal. Chem., 56. (1984) 1264. Jones W.R. and Jandik P., Res. & Dev., September (1988) 92. Jackson P.E. and Haddad P.R., J . Chromatogr., 346 (1985) 125. Brandt G., Vogler P. and Kettrup A. , ires. Z. Anal. Chem., 325(1986) 252. Brandt G., Matuschek G. and Kettrup A.. Fres. Z. Anal. Chem., 321 (1985) 653. Levin S. and Grushka E., Anal. Chem., 58 (1986) 1602.
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164 Levin S. and Grushka E., And. Chem., 59 (1987) 1157. 165 Papp E., J . Chromutogr., 402 (1987) 211. 166 Okada T. and Kuwamoto T., Anal. Chem., 56 (1984) 2073. 167 Hershcovitz H., Yarnitzky C. and Schmuckler G., J . Chromurogr., 244 (1982) 217. 168 Strassburg R., Fritz J.S.,Berkowitz J. and Schmuckler G., J . Chrornatogr.. 482 (1989) 343. 169 Hertz J. and Baltensperger U.. LC,2 (1984) 600. 170 Afrashtehfar S. and Cantwell F.F.. Anal. Chem., 54 (1982) 2422. 171 Cantwell F.F. and Puon S., Anal. Chem., 51 (1979) 623. 172 Hux R.A. and Cantwell F.F., Anal. Chem., 56 (1984) 1258. 173 Doury-Berthod M.. Stammose D. and Poitrenaud C., Reucr. Polymers, 2 (1984) 37.
133
Chapter 5 Retention Models for Ion-Exchange 5.1
INTRODUCTION
The equilibria which govern ion-exchange separations are well understood, and detailed retention models providing a quantitative description of the factors which govern solute retention can therefore be developed for the various types of ion-exchange methods discussed in the previous two Chapters. For the purpose of clarity, these models are discussed together in this Chapter, along with experimental data used to validate each model.
5.2 RETENTION MODELS FOR ANION-EXCHANGE 5.2.1 Single eluent competing anion
The most straightforward situation in anion-exchange IC is where the eluent contains a single type of competing anion. Derivation of a retention model proceeds as follows [1-6]: The ion-exchange equilibrium for binding of a solute anion, AX-. to a stationary phase which has been conditioned with an eluent containing a competing anion, Ey-, is given by: (5.1)
where the subscripts m and r refer to the mobile and stationary phases, respectively. The selectivity coefficient for the system is given by:
where the parentheses represent the activity of the particular species. When activity coefficients are included, eqn. (5.2) becomes:
(5.3)
134
Chapter 5
As the ensuing discussion will show, i t is generally not necessary to consider activity effects in IC because of the very dilute eluents and low sample concentrations which are routinely used. Moreover, the inclusion of activity factors would require knowledge of the activities of species in the resin phase, and these cannot be determined. For these reasons, and also in the interests of simplicity of presentation, no further reference to activity coefficients will be made in the subsequent derivations. However, the reader should be aware of the implied assumption that activity coefficients are very close to unity in all the cases to be considered. Notwithstanding these comments, there will be a number of occasions on which it will be necessary to reconsider activity effects. The weight distribution coefficient for solute A is designated as DA and is given by:
In general, the weight distribution coefficient is related to the capacity factor (kA') for solute AX-by the expression:
where w is the weight of the stationary phase and V m is the volume of mobile phase. From eqns. (5.4) and (5.5) we obtain:
Substituting into eqn. (5.3),and neglecting the activity coefficients, gives:
If we assume that the eluent ion, Ey-, occupies y ion-exchange sites on the stationary phase (we will re-evaluate this assumption at a later stage), then the ion-exchange capacity of the column, Q, is given by:
Eqn. (5.7) now becomes:
Retention Models for Ion-Exchange
135
Rearranging gives:
(5.10) Taking logarithms provides the relationship: (5.1 1)
Eqn. (5.11) is of fundamental importance in IC, since it provides a quantitative relationship between capacity factor and some measurable column and eluent parameters. If an experiment is conducted in which the concentration of competing anion in the eluent is varied and the column and solute anion are the same, then KA,E, Q, w and Vm can be considered to be constant. Eqn. (5.1 1) therefore reduces to: (5.12)
where C1 is a constant, Eqn. (5.12) predicts that when the results of the above experiment are presented as a plot of log k' versus log [EmY-1, a straight line should result with a negative slope equal to x/y. We can now consider the ion-exchange equilibrium existing between a second solute ion, Bz-and the same eluent competing anion, Ey-. This equilibrium can be written: ZYzx B m + zEr % x B r
+ zE,Y-
(5.13)
where the subscripts r and m have the same meanings as previously used. The selectivity coefficient for solute BZ-is K B ~which , is given by:
We can also write the ion-exchange equilibrium existing between the two solutes AX-and B", as follows: (5.15)
and the selectivity coefficient between the two solute anions is given by:
Chapter5
136
(5.16)
Eqn. (5.6) can be rewritten for solute B2- and rearranged to give: (5.17)
The chromatographic separation factor for solutes AX- and B2- is given by which is calculated according to:
aA3.
(5.18)
Eqn. (5.18) can be manipulated and rewritten as:
(5.19)
Substitution of eqns. (5.16) and (5.17) into eqn. (5.19) gives:
(5.20)
In a similar manner we can obtain: x-2
(5.21)
Eqn. (5.20) can be rewritten in a logarithmic form to give: (5.22)
When the two solutes have the same charge, i.e. x = z, eqn. (5.22) reduces to:
Retention Models for ion-Exchange
137
Eqns. (5.11). (5.12). (5.22) and (5.23) are of great significance to IC and allow the following predictions to be made for the situation in which only a single type of competing anion is present in the eluent: When a solute anion, AX-. is eluted with a competing anion, Ey-, eqn. (5.11) shows that the capacity factor for AX- is determined by the selectivity coefficient, KA,E, the ion-exchange capacity of the column, Q, the ratio of stationary to mobile phases, WNm, and the concentration of competing anions in the eluent, [EYm]. Increases in KA,E,Q or wNm lead to increased capacity factors. whilst increasing [EY'm] leads to decreased capacity factors. Increased eluent charge leads to decreased capacity factors, whilst increased solute charge leads to increased capacity factors. Under conditions where the same solute anion, AX-.is chromatographed on the same column with varying cbncentrations of competing anion (Ey-) in the eluent, then eqn. (5.12) predicts that a plot of log kA' versus log [Epm] will be a straight line with a slope equal to -x/y. From eqn. (5.231, it can be concluded that the separation factor, (XA,B, for two anions of the same charge depends only on the selectivity coefficient KA,B and on the charge of the solute anions. Providing that the selectivity coefficient remains constant, the separation factor does not depend on the concentration, charge or type of competing anion in the eluent. When two solutes have different charges, the separation factor depends on the capacity factor of one of the solute anions (note that the capacity factors of the solute anions are not independent). The capacity factor can be altered by changing the parameters listed in (i) and (ii) above. We can now examine the validity of these predictions.
Effects of KA,E,Q and wN, By definition, an increase in KA,E indicates enhanced binding of the solute anion to the ion-exchange stationary phase, which must result in increased capacity factors. Similarly, the phase ratio, W N m , has an obvious effect on capacity factor, with higher phase ratios giving longer retention. This explains why pellicular or surfacefunctionalized anion-exchangers provide smaller values of k' than porous, fully functionalized materials. The effect of resin capacity, Q,is of particular importance to IC. If it is assumed that the selectivity coefficient does not change significantly with Q (and this has been shown to be a valid assumption [7]) and the phase ratio is assumed constant, then the following proportionality holds: (5.24)
138
Chapter 5
41
3
3
Y 2
4
Slope -2 Slope -1
1
Slope -1 Slope - 0 . 5
Fig. 5.1 Plots of log k’ versus log [EYarn] for different combinations of singly and doubly charged solute and competing anions.
That is, constant capacity factors can be obtained when Q is decreased only by proportionally decreasing the concentration of competing anions in the eluent. Experimental evidence supports this relationship [7]. It is for this reason that the dilute eluents required in 1C are applicable only to columns of low ion-exchange capacity.
Effect of charges on solute and competing anions As the charge on the solute anion increases, electroselectivity effects suggest that the solute will be more strongly held on an anion-exchanger (i.e. KA,E increases). This effect can be seen from Fig. 4.1, where sulfate had a longer retention time than the monovalent solute anions. By analogy, increasing the charge on the eluent competing anion will cause a reduction in Ir‘ because KA,Edecreases. These effects are evident from eqn. (5.10), which can be simplified by assuming that the column capacity and phase ratio are constant, to give the proportionality:
k,’ a
KA, -
(5.25)
lE~Jx’y
Isocapacitivc elucnts (i.e. those giving identical capacity factors) can be produced by simultaneously increasing the charge and decreasing the concentration of the eluent competing anion, or vice-versa.
Retention Moakls for ton-Exchange
139
log [OH-]
Fig. 5.2 Plots of log kA‘ versus log [EY-m] for NaOH eluents of varying concentration. A
Dionex HPIC-ASSA column was used. Reprinted from [S] with permission.
Effect of [EJ’-m] Eqn. (5.12) shows that the manner in which k‘ is affected by the concentration of competing anions in the eluent is dependent on the charges on both the solute and competing anions. Prediction (iii) above is that a plot of log k’ versus log [EY-m] should be a straight line with a slope of -x/y. The magnitude of the intercept of such a plot is determined by KA,E,Q and wN,. Fig. 5.1 shows schematic plots for singly and doubly charged solute anions, eluted with singly or doubly charged eluent anions. It can be seen that changing the concentration of a competing anion has a greater effect on the retention of a doubly charged solute in comparison to a singly charged solute, and that singly charged competing anions cause the largest changes in retention. The behaviour illustrated in Fig. 5.1 has been verified in numerous practical studies [e.g. 1, 2, 3, 5, 6 , 8, 91. A typical plot of log k’ versus log [Em] is shown in Fig. 5.2. The slopes of the plots are generally quite close to those predicted from eqn. (5.12), and the observed differences between theory and practice can be attributed to the assumptions made in the derivation. This is especially true of activity effects, which are most evident for the triply charged citrate ion. Under the conditions used in Fig. 5.2, activity coefficients vary between 0.755 - 0.900 for monovalent anions, between 0.355 - 0.660 for divalent anions, and between 0.1 15 0.405 for trivalent anions [5]. It is therefore not surprising that citrate shows a large deviation from the slope of -3 predicted by eqn. (5.12). 4
Chapter 5
140
5.2.2 Multiple eluent competing anions Many anion separations in IC use an eluent which contains more than one type of competing anion. Sometimes two quite separate components are added to the eluent, but it is more common that the multiple eluent species are different dissociated forms of the same weak acid. For example, carbonate buffers contain both HCO3-and C0s2- as competing anions, whilst phthalate eluents at suitable pH values can contain both the singly and doubly charged anions produced by dissociation of phthalic acid. For simplicity, we will consider initially only the case where the eluent contains two competing anions, which will be designated HP-and P2-. The solute will again be represented by AX-, so the relevant ion-exchange equilibria are:
A,
X-
+ XHP; %
2p;b'+ 2-
P,
xP:-
+ 2HP;
4-+ x H P i X-
% 2A, 2-
% P,
+ xP,2-
+ 2HPm
(5.26)
(5.27)
(5.28)
There are three approaches to developing a retention model for the above situation, namely the dominant equilibrium approach, the competing ion "effective charge" approach, and the dual eluent species approach. These are discussed separately below.
Dominant equilibrium approach This method assumes that the equilibrium shown in eqn. (5.28) lies well to the right because the P2- competing anion would be bound most strongly to the ion-exchange resin on the basis of electroselectivity The outcome of this assumption is that the doubly charged form of the competing anion is responsible solely for the elution of the solute, even when some H P is present. The charge on the competing anion is therefore -2. This approach has been found to yield satisfactory results with succinate eluents, where slopes of log k versus log [P2-] were -0.55 for monovalent anions and-1.15 for divalent anions using eluents which contained only 18% of the doubly charged succinate anion [31. Competing anion "effective charge '' approach When the two eluent competing anions are in rapid protolytic equilibrium (such as HP-and P2-), we can define the "effective charge" (-y) of a mixture of these species using the following relationship [2. 6, 81:
y = a1
+
2a2
(5.29)
where a1 and a2 are the fractions of total eluent species present as HP- and P2-, respectively. Eqn. (5.29) is a simplified version of eqn. (4.6).
Retention Modelsfor lon-Exchange
141
1.o
0.8
0.6
OA log k '
czop I-
0.2
5201-
0
5012HZPOi
Br-
-0.2
-0.L -27
a-26
-2.5
-2L -2.3 log [eluent]
-2.2
-2.1
-2.0
Fig. 5.3 Plots of log kA' versus log CEfor 2.0 - 10.0 mM phthalate eluents at pH 5.3. At this pH, the eluent contains 47.6% H P and 52.2% P2-. Reprinted from 121 with permission.
Eqn. (5.12) can be rewritten to include the effective charge on the competing anion, to give: (5.30)
where C2 is a constant and CEis the total eluent concentration, which is equal to:
CE = [HP-]
+ [P2-]
(5.31)
It is assumed in this approach that both competing anions have similar selectivities for the solute anion. Fig. 5.3 shows some experimental data [2] for plots of log k versus log CE for phthalate eluents containing both singly and doubly charged forms of phthalate, and Table 5.1 gives the slopes of these plots. Shown also are the theoretical slopes calculated using the dominant equilibrium approach (i.e. assuming that only P2- contributes to elution) and the competing anion "effective charge" approach. Using eqn. (5.29), we can calculate that the "effective charge" in this case is -1.52. It can be seen that linear plots were observed, as predicted from eqn. (5.30), but the observed slopes do not agree for all solutes with those predicted by either of the above approaches. The dominant
142
Chapter5
TABLE 5.1 OBSERVED AM) PREDICTED SLOPES OF LOG k VERSUS LOG CE PLOTS USING 2.010.0 mM PHTHALATE ELUENTS AT pH 5.3 Slope
Ion
Observed
-0.63 -0.63 -0.67 -0.60 -1.13 -1.10 -0.98
Dominant equilibrium
Effective charge
method y=2
method y = 1.52
-0.5 -0.5 -0.5 -0.5 -1.0 -1.0 -1.0
-0.66 -0.66 -0.66 -0.66 - 1.33 -1.33 -1.33
equilibrium approach gives best agreement for divalent solutes, whilst the effective charge approach gives best agreement for monovalent solute anions. It can be concluded that, for phthalate eluents at least, the IP-competing anion contributes to the elution of monovalent solutes on an approximately equal basis with P2-, whereas divalent solutes are eluted almost entirely by P2-.
Dual eluent species approach It is evident that neither of the above approaches gives reliable results for all solutes and this can be attributed to the fact that the different selectivity coefficients for the solute with both compcting anions are not considered. The dual eluent species approach, suggested by Hoover [ 101 2nd Jenke and Pagenkopf [ 11-13], is a more rigorous method which takes into consideration all of the relevant equilibria listed in eqns. (5.26) - (5.28). From eqn. (5.28) we can write: (5.32)
which can be rearranged to give: (5.33)
143
Retention Modelsfor Ion-Exchange
If we continue to assume that the eluent contains only two competing anions, HPand P2-, then the column capacity, Q, is given by:
Q = [HPJ
+ 2[P:-]
(5.34)
Combination of eqns. (5.33) and (5.34) yields:
(5.35)
which is a quadratic equation in [HP;]. Solution of this equation by the quadratic formula gives:
(5.36)
From eqn. (5.26), we can write:
(5.37)
which, from eqn. (5.4), can be rewritten:
(5.38)
Combination of eqns. (5.5), (5.38) and (5.36) gives: X
(5.39)
which can be simplified to give:
Chapter 5
144
Use of eqn. (5.40) requires knowledge of the concentrations of both Hp-and P2-. It is more common in IC to describe the eluent in terms of the total concentration of eluent acid (which we have designated above as CE)and the eluent pH. Eqn. (5.40) can be made more practically applicable if we consider the protolytic dissociation reaction of HP-,that is: 2-
+
HPi%PP,+H
(5.41)
From eqn. (5.41) we can write: (5.42)
which can be rearranged to give: (5.43)
If we assume that the eluent acid, H2P, is present only as HP- and P2-, then eqn. (5.31) holds, which combined with eqn. (5.43) gives: (5.44)
Substituting eqns. (5.43)and (5.44) into eqn. (5.40) gives:
(5.45)
Under circumstances where the eluent contains some undissociated H2P, eqn. (5.31) must be rewritten as:
Retention Modelsfor Ion-Exchange
[HPJ
+ IPkI = (1 - a
~ ~ CE p )
145
(5.46)
and eqn. (5.45)then becomes:
(5.47)
It can be noted in passing that eqn. (5.47)does not include the term K A , (i.e. ~ the selectivity coefficient for exchange between the solute AX-and the competing anion P2-). The reason for this is that K A , is ~ not independent of KA,HP and K p ~ pand so its inclusion is not necessary. The selectivity factor a A , B for the two solutes AX-and BZ-istherefore given by:
(5.48)
Jenke and Pagenkopf have successfully used eqn. (5.47)to predict the retention behaviour of a wide range of solutes using phthalate eluents with surface functionalized silica, surface functionalized resin or agglomerated ion-exchangers [l1, 12, 141. Retention data for each solute anion are obtained for a variety of different eluent concentrations (CE) and pH values, and these data are substituted into eqn. (5.47)to give a series of simultaneous equations with KA,HPand K p , ~ pas the only unknowns (correct values of Vm,w and Q are not necessary to the solution and arbitrary values are used). This process gives values of KA,HPand KP,HPfor each solute anion and Table 5.2 lists some typical results. Monovalent anions give very similar results for KPJP, and so do divalent solute anions, but the values determined for each group differ. This is a result of eqn. (5.47) taking a different form for divalent anions (i.e. when x = 2) to that used for monovalent anions (i.e. when x = I). The values of KA,HPfor monovalent anions follow the same sequence as the retention times for these solutes, with a larger value of KA,HP corresponding to longer retention. The same applies to the divalent solutes, but again it is not possible to directly compare selectivity coefficients for monovalent and divalent anions because of the different form of eqn. (5.47) used for their calculation. The minimized errors for the calculation of KA,HP values are shown in Table 5.2,from which it can be seen that this error varies from 2.57% for C1- to 6.13% for Sod2-.
3.0I I
= Br0 = CI-
"0 Calculated retention time iminl
2
4 6 8 10 12 1L 16 Calculated retention time (mint
18
20
Ibl
Fig. 5.4 Comparison of observed and predicted (eqn. 5.48) retention times for (a) monovalent and (b) divalent solute anions using 2 mM phthalate eluents with pH values in the range 4.0-5.5. Under these conditions, the eluent contains both singly and doubly charged phthalate ions. Reproduced from [13] with permission.
bl
Retention Models for Ion-Exchange
147
TABLE 5.2 SELECTIVITY COEFFICIENTS AND MODEL FIT PARAMETERS FOR THE MULTIPLE ELUENT COMPETING ION MODEL, APPLIED TO PHTHALATE ELUENTS USED ON A HAMILTON PRP-X100 COLUMN. REPRINTED FROM [ 131 WITH PERMISSION
Solute
Selectivity coefficients KPJIP
so42~2032-
N0-jB r-
c1-
3.14 2.95 1.70 1.63 1.70
10-3 10-3 10-3 10-3
10-3
KA,IIP
3.59 5.89 4.61 3.90 2.65 x
10-5
10-5 10-3 103
lW3
%RSD in KA,HP
Retention time error (%RSD)
6.13 5.78 2.86 3.12 2.57
2.65 3.22 3.22 1S O 1.61
Model fit parameters: slope = 0.980, intercept = 0.07, correlation coefficient = 0.9973.
The values of KA,HPand K p , ~ pdetermined above can now be used to calculate predicted retention times for solute anions under a variety of eluent and column conditions. For this calculation, V m , w and Q must be known. Fig. 5.4 shows the agreement obtained between predicted and observed retention times and illustrates that excellent correlation is observed (see model fit parameters in Table 5.2). The average error in the determination of retention times for individual solutes is also listed in Table 5.2, which shows that a maximum error of 3.22% was observed. These results are not surprising since the predictions are made on the basis of selectivity coefficients determined using experimental conditions which are very similar to those used to test the model. Nevertheless, the multiple eluent competing ion model gives the most reliable description of retention behaviour when the eluent contains two competing anions. The multiple eluent competing ion model has also been used for eluents which contain three competing anions [lo, 13, 151. A typical example would be the use of an alkaline carbonate buffer in suppressed IC, where OH-, HCO3- and C032- all act as competing anions in the eluent. Under these circumstances, the derivation of a retention model proceeds along the same lines as for eluents containing only two competing anions. The capacity factors for monovalent and divalent solute anions, designated as kl' and k i , respectively, are given by the following equations:
(5.49)
148
Retention Models for Ion-Exchange
149
(5.50)
where HP- and P2- represent HCO3- and C032-, respectively, whilst A- and A2- are monovalent and divalent solute anions. Again, the selectivity coefficients in eqns. (5.49) and (5.50) are determined by substituting experimental retention data for known eluent compositions and solving the resultant simultaneous equations. Table 5.3 lists values of the selectivity coefficients obtained for three solute anions on a Dionex HPIC-AS1 column. It is evident that the C032- component of the eluent dominates the elution of solutes (as indicated by the high selectivity coefficient for this species) and the selectivity coefficients for the solutes parallel their elution order. Fig. 5.5 shows the excellent agreement obtained between measured retention times and those predicted by eqns. (5.49) and (5.50) for a three component eluent system.
5.2.3 Gradient elution in anion-exchange IC The retention models developed above can be extended to gradient elution separations in which the concentration of the competing anion in the eluent is varied over the course of the separation. For simplicity, the discussion of gradient elution will be limited to the case where the eluent contains a single competing anion, Ey-. The following derivation is based on that reported by Rocklin et al. [5]. Assuming a linear gradient, beginning at zero concentration of the competing anion and increasing with time, the instantaneous concentration of the competing anion at the column inlet at any given time is:
TABLE5.3
SELECTIVITY COEFFICIENTS FOR SOLUTES INAN OH-~HCO~-/CO~~ELUENT SYSTEM, CALCULATEDFROMEQNS.(5.49)AND(5.50).DATAFROM[15] Selectivitycoefficients
Solute ion
c1NQso42a
KP,HP
KOH,HP
KA,HP
5.0 5.0 5.0
0.01 0.01
3.02 16.8
0.01
18.5
P = ~ 0 3 2 - ,HP = HCO~-.A = solute anion.
Chapter5
150
[EL-] = RV
(5.51)
where V is the volume of eluent pumped since the gradient was initiated and R is the slope of the gradient ramp (e.g. in mM/ml). If a solute, AX-, was injected onto the column and the composition of the eluent was kept constant until that solute eluted (i.e. the solute was eluted isocratically), the capacity factor, k A ' , would be given by a combination of eqns. (5.10) and (5.51):
Under gradient elution conditions, kA' must be integrated from injection to elution. This can be achieved by considering k A ' as dV/dx, where a fractional volume of eluent, dV, passes over the band maximum for the solute and moves the band a distance of dx down the column. It should be noted here that x is expressed as the column void volume, rather than as a length. This gives:
(5.53) If we consider w, Vm, KA,E and Q to remain constant during the separation, then eqn. (5.53) reduces to: (5.54)
where C3 is a constant. Eqn. (5.54) can be rearranged and integrated as follows:
It is convenient to describe retention in terms of (VR - V,)/Vm (where VR is the retention volume of the solute) instead of kA' (note that in isocratic elution, the two are equal). Solving eqn. (5.55) and rearranging gives:
(5.56)
We can collect the constant terms on the right hand side to give a single constant,
C,, which can be referred to as the gradient constant.
Retention Modelsfor Ion-Exchange
151
t
Citrate
-0.77
-
Fumarate 0.65
-0.47
- 0.67
\r Chloride 0.21
0.2
I
0.L
I
1
0.8
0.6
I
1.0
- 0.50
I 1.2
log R
Fig. 5.6 Plot of log (VR - Vm)/Vm) versus log R for gradient elution using NaOH eluents. A Dionex HPIC-ASSA column was used. Reprinted from [5] with permission.
(5.57)
Expressing eqn. (5.57) in logarithmic form gives:
Eqn. (5.58) is very similw in form to eqn. (5.12), which was developed for isocratic elution when a single competing anion was present in the eluent. From eqn. (5.58), we can predict that a plot of log ((VR - Vm)/V,) versus log R should be a straight line with a slope determined by the charges on the solute and competing anions. When the competing anion has a single charge, the slopes are predicted to be -0.5, -0.66 and -0.75 for mono-, di- and trivalent solute anions, respectively. Eqn. (5.58) has been evaluated experimentally using NaOH gradients with varying gradient ramps [5]. Fig. 5.6 shows the required plots and Table 5.4 presents pertinent data taken from these plots. Excellent linearity was obtained and the slopes showed good agreement with the predicted values. Moreover, it was even possible to predict the values of C, for most solutes on the basis of C3 values determined from isocratic elution of the solutes (see Fig. 5.2), together with values for the remaining constant terms in eqn. (5.56).
Chapter5
152
T A B E 5.4 PARAMETERS FROM THE GRADIENT PLOTS SHOWN IN FIG. 5.6.DATA FROM [5]
Solute anion
PallMEter ~
Measured slope Predicted slope (eqn. (5.58)) c, (measured) C, (calculated)
Chloride
Nitrate
Sulfate
Fumarate
Citrate
-0.50 -0.50 7.4 7.0
-0.47
-0.67 -0.67 20 19
-0.65 -0.67 26
-0.77 -0.75 42
24
65
-0.50 15 14
It can be concluded from the above results that the retention model in eqn. (5.58) gives a satisfactory description of the behaviour of solutes under gradient elution conditions in which the gradient is generated by linearly increasing the concentration of the competing anion in an eluent which contains no other competing anion.
5.3 5.3.1
RETENTION MODELS FOR CATION-EXCHANGE Single eluent competing cation
We begin by considering the simplest case in cation-exchange IC, in which the eluent contains a single type of competing cation. The ion-exchange equilibrium for to a stationary phase which has been conditioned with an binding of a solute cation, Mx+, eluent containing a competing cation, Ey+, is given by: (5.59)
where the subscripts m and r refer to the mobile and resin phases, respectively. If activity coefficients are assumed to be equal to unity, the selectivity coefficient, KMJ, can be written:
If we now follow the same derivation used in Section 5.2.1 for the development of retention equations for anions, we can produce the following important equations for the retention of cations with a single type of eluent competing cation:
Retention Models for Ion-Exchange
153
Eqn. (5.10) gives us:
(5.61)
Eqn. (5.1 1) gives: (5.62)
Eqn. (5.12) gives: (5.63)
Eqns. (5.20) and (5.21) give:
for two solutes Mix+ and M2z+. And finally, from eqn. (5.22) we can write: (5.65)
Since eqns. (5.61) - (5.65) take the same form as the corresponding anion-exchange equations derived earlier, we can make the same generalizations regarding retention behaviour which were made for anions in Section 5.2.1. That is, solutes are eluted earlier with eluent competing cations of higher charge, whilst retention increases with increasing charge on the solute cation. These trends have been confirmed in practice [16]. The major test of the above derivation is the validity of eqn. (5.63), which predicts a linear relationship between log kM' and log [EY+,,,].We can begin by examining this relationship for monovalent cations eluted with a nitric acid eluent [17]. Fig. 5.7 shows that linear plots are observed with this system and the slopes are in good agreement with the theoretical slope of -1.0 for univalent solute and competing cations. Sevenich and Fritz [16] have tested eqn. (5.63) for divalent and trivalent cations retained on a lowcapacity (0.06 mequiv/g) cation-exchanger using perchloric acid eluents. Linear plots were observed only when activity effects were considered; that is, when log kM' was plotted against log (HClO4). where the parentheses indicate activity. Fig. 5.8 illustrates such a plot for several trivalent rare earth cations and Table 5.5 summarizes some of the slopes obtained for divalent and trivalent cations.
154
Chapter 5
''7
0
Li+
0 = Na*
Slopes -1.13 -1.07
-1.06 -1.07 I
-3.0
-2.9
i
1
-2.8 -2.7 log [H+l
I
I
-2.6
-2.5
Fig. 5.7 Plots of log k M qversus log [H+I for nimc acid eluents used on a Waters IC Pak C surface-sulfonated cation-exchange column. The slope of each plot is given in the Figure. Reprinted from 171 with permission.
TABLE 5.5
SLOPES OF PLOTS OF LOG kM' VERSUS LOG (HC104) USING PERCHLORIC ACID ELUENTS. DATA FROM 116,181
Cation
Slope
Mg2+ Ca2+ Sr2+
- 1.66 -1.87 -1.91 - 1.97 - 1.89 - 1.98 -1.87 - 1.96 - 1.92
B82+
Mn2+ Zn2+ Ni2+ Ua2+ CU2+
Cation
Slope
Fe2+
- 1.79 -1.86 -2.08 -2.00 - 1.92 -2.88 -2.67 -2.99
Co2+ Cd2+
Pb2+ Hg2+ A13+ Bi3+ Fe3+
Cation
Slope
Cation
Slope
h3+
-2.78 -3.01 -2.95 -2.99 -2.95 -2.95 -3.01 -3.01
Tb3+ Gd3+ Eu3+ sm3+ Nd3+
-3.02 -2.99 -3.01 -2.97 -2.97 -2.95 -3.01 -3.04
LU3+ Yb3+ Tm3+ Y3+
Er3+ HO~+
Dy3+
~r3+
Ce3+ ~a3+
Retention Models for Ion-Exchange
155
1.82 log k'
1.32
~03+
Nd3' Eu3+ Tb3+
0.82
HO~+
0.321, -0.55
, -045
,
,
,
,
Lu 3+
-0.35
-0.25
-0.15
-0.05
log (HCIOh activity)
Fig. 5.8 Plots of log kM'versus log (HClO4) for perchloric acid eluents used on a low-capacity surface-sulfonated cation-exchanger. Reprinted from [ 161 with permission.
Agreement between the slopes obtained experimentally and those predicted from eqn. (5.63) is generally good, although there are some exceptions. Lederer 1191 has reviewed a large volume of literature relating to the effective charge on a metal ion (or metal complex ion) when this charge is measured using ion-exchange methods. The conclusions of this study are: Activity effects are of importance, especially for polyvalent cations and when the eluent strength is high. Complete correction for activity effects requires knowledge not only of the activity coefficient of the competing cation in the eluent phase, but also of the activity coefficients for metal ion in the eluent phase and the metal ion and the competing cation in the resin phase. Most of these coefficients are not available. Neglecting activity effects will tend to produce slopes which are smaller than those predicted from eqn. (5.63). (ii) For some cations, the effective charge is reduced due to steric effects which prevent the cation interacting with a stoichiometric number of functional groups on the resin surface. For example, a trivalent cation may not be able to approach closely three functional groups. This effect will tend to be most significant for large, polyvalent cations and for stationary phases of low ionexchange capacity which therefore have a diffuse spread of functional groups.
(i)
156
Chapter5
Reduction in the effective charge on the solute cation by this effect will result in slopes which are smaller than those predicted from eqn. (5.63). (iii) Under conditions of relatively high eluent strength, ion-pair formation may occur between the solute cation and the sulfonic acid groups on the resin surface. The outcome of this is that the interaction between the solute and the resin will be much stronger than that expected from purely electrostatic attraction. The effective charge on the solute is therefore increased and the slope becomes greater than that predicted from eqn. (5.63). Examination of the probable magnitudes of these effects in IC, where dilute eluents are used with low capacity ion-exchange resins, suggests that effects (i) and (ii) can be expected to occur to a significant degree, especially for solute cations with a charge greater than 2. Effect (iii) is likely to be the least significant because the chromatographic conditions employed are not favourable for ion-pair formation. There is some evidence from the data of Table 5.5 to support the occurrence of effect (3). The deviation of the experimentally observed slopes for divalent alkaline earth cations from those predicted by eqn. (5.63) follows the order Mg2+ > Ca2+> Sr2+ > Ba2+,which is the same order for the diameters of the hydrated ions (181. It is clear from the above discussion that, under conditions where the eluent contains a single type of competing cation (which is the normal situation for cationexchange), eqn. (5.63) is followed closely when monovalent cations are used as solutes. Deviations may occur for solutes of higher charge, with these species requiring the use of activity corrections if meaningful estimates of effective charge are to be made. 5.3.2
Complexing eluents
Separation by cation-exchange In Section 4.3.2, we noted that eluents containing a complexing ligand are frequently used for the separation of cations. Fig. 4.16 showed schematically a number of ways in which such a complexing eluent could be employed. We will now extend the above cation-exchangeretention model to include a complexing eluent component. When a solute cation, W+,is eluted by a competing cation, Ey+. and the eluent also contains H2L. where L2- is a ligand capable of reacting with h P ,we have the situation depicted in Fig. 4.16(c). Under these conditions, the equilibrium shown in eqn. (5.59) applies, but we must also consider the further equilibria shown in eqns. (5.66)-(5.69):
H2L f HL;, +
(5.66)
(5.67)
%++ L,2- ej x-2
ML,
x-2
ML,
+ L,2- %
x-4
ML2
(5.68)
(5.69)
Retention Models for Ion-Exchange
157
We can now define a M as the fraction of the total concentration of metal ion in the eluent which is present in the free form, i.e. as W+:
(5.70)
where CM is the total concentration of metal ion in the mobile phase, regardless of the form in which it is present. CMis given by:
Assuming that Mx+is the only form of the metal which is bound to the cationexchange resin ( i x . the complexes formed with L2- are either neutral or anionic), then the distribution coefficient for solute Mx+ can be defined as:
(5.72)
Substituting eqns. (5.70) and (5.71) into eqn. (5.60) gives:
(5.73)
Rewriting eqn. (5.5) for the cation case and employing eqn. (5.8), we obtain:
(5.74)
which can be presented in logarithmic form as:
If we now consider only the case of a divalent metal cation (x = 2) and we assign equilibrium constants of Pal,Ka2, (i.e. acid dissociation constants) to eqns. (5.66)and (5.67), and K1 and K2 (stepwise formation constants) to eqns. (5.68) and (5.69), then aM is given by: a M
1
=
1
+ K l a L C L + K1K2aLC[
(5.76)
Chapter5
158
2.0-
1.5-
tog tk ~a3*
1.0~ e 3 +
~r 3+
0.5
-
Nd3+ Dy3+ Er 3' Tm3. Lu 3+
-2.1
-3.0
-2.5
-2.L -2.3
log [en ~ ~ 2 * ]
Fig. 5.9 Plots of log t
~ versus ' log [enH22+]for ethylenediamine-tartrate eluents, in which the total tartrate concentration is maintained at 2.0 niM and the pH is consrant at 4.5. A low capacity surface-sulfonated cation-exchanger was used. Reprinted from [20] with permission.
where CL is the total concentration of ligand species in the eluent and aL is the fraction of CL which exists as L2-. aL is given by:
Eqn. (5.75) applies to any cation-exchange separation mechanism which uses a complexing eluent. It is therefore applicable to both of the methods depicted in Fig. 4.16(a) and 4.16(c). The only difference between these two methods is that complexation of Mx+exerts an overwhelming effect in Fig. 4.16(a) (where Na+ or Li+ act as very weak competing cations), whilst separation in Fig. 4.16(c) results from a combination of complcxation and cation-exchange because an effective competing cation (enHz2+)is prescnt. Some rctcntion data for cations using ethylcnediamine-tartrate eluents are available for experimental vcrification of cqn. (5.75) [20]. Fig. 5.9 shows plots of the logarithm of the adjusted retention time, t', versus the logarithm of the ethylenediamine Concentration, obtained under conditions where the tartrate concentration in the eluent
Retention Models for Ion-Exchange
159
1.5r
1.0
Log tk
0.5
-
-1.80
-1.50
-1.20 ''9 aMILl
-0.90
Fig. 5.10 Plots of log tM' versus log a M for ethylenediamine-tartrate eluents, in which the ethylenediamine concentration is maintained at 2.0 mM and the pH is constant at 4.5. The column used was identical to that in Fig. 5.9. Reprinted from [20] with permission.
and the pH (and hence CXM) are constant. The adjusted retention time is equal to t,k', where to is the retention time for a non-retained solute. Thus substitution oft' for k' in eqn. (5.75) does not alter the equation except for an additional log(b) term on the right hand side. Under the conditions used, all terms in eqn. (5.75) are constant, except for log[EY+,], so we expect a straight line plot of slope -x/y. The solutes used have a charge of +3, whilst the competing cation in the eluent has a charge of +2, which gives a theoretical slope of 1.5. Fig. 5.9 shows that the predicted linear plots were obtained, with slopes that are all close to -1.0. The discrepancy between theory and experiment may have been due to the fact that no activity corrections were applied in this study. Divalent solute cations showed much better agreement with theory, giving slopes averaging -0.9 1201. If the pH and the concentration of ethylenediamine are now kept constant while the concentration of tartrate is varied, aM will change. It is therefore possible to further versus ) log t'. Since all terms except CLM are test eqn. (5.75) by plotting ~ O ~ ( C X M constant, we expect a linear plot of slope equal to 1.0. The results are presented in Fig. 5.10, which shows that linear plots were obtained, with slopes averaging 1.2. This is in reasonable agreement with the theoretical slope.
Chapter5
160
Separation by anion-exchange Some ligands will form anionic complexes with the solute cations, leading to the possibility of separation by anion-exchange. This process was illustrated in Fig. 4.16(b) and a representative chromatogram was shown in Fig. 4.17(b). A retention model for this situation can be developed using the same approach as that employed for cationexchange with a complexing species present in the eluent. To simplify the derivation, we will assume that the solute ion is divalent. Eqns. (5.66) and (5.67) apply to this case and we can rewrite eqns. (5.68) and (5.69) for a divalent cation to give: 2-
ML,
+ L;
(5.78)
f ML;-
(5.79)
The anion-exchange equilibrium for the solute, MLz2-, and a competing anion, Ey-,
is
YMLi-
m
+
Y-
2-
2E, 6 yML2
r
Y-
+ 2E,
(5.80)
which enables us to write the relevant selectivity coefficient:
Defining a M L Z as the fraction of total metal species in the eluent (CM)existing as MLz2-, we have:
(5.82)
where CMis as defined by eqn. (5.71). We can calculate am2 according to:
where K1 and K2 are the stepwise formation constants for eqns. (5.78) and (5.79), ~ as previously defined (eqn. (5.77)). Since ML22- is the respectively, and CL and c 1 are only form of M which is retained on the column, the distribution coefficient for M is given by:
Retention Models for Ion-Exchange
161
(5.84)
Substituting eqns. (5.82) and (5.84) into eqn. (5.81) gives:
If we rewrite eqn. (5.85) in terms of the capacity factor and make the usual substitution for column capacity, Q,we obtain:
(5.86)
which in logarithmic form becomes:
Turning now to the case where the solute cation is trivalent and forms an anionic bis complex with L2- of the type M L i , eqn. (5.87) can be rewritten:
When the total ligand concentration, CL,and the pH are constant, we expect the same linear relationship between log kM' and log [EY-,,,which ] was found earlier to be valid for anion-exchange (Section 5.2.1)). Under conditions where the concentration of competing anion in the eluent is constant, we also expect a linear relationship between log kM' and log aML2. 5.4 1 2 3
REFERENCES Gjerde D.T., Schmuckler G. and Fritz J.S., J. Chromatogr., 187 (1980) 35. Haddad P.R. and Cowie C.E., J. Chromatogr.,303 (1984) 321. Van 0 s M.J., Slanina J., De Ligny C.L., Hammers W.E. and Agterdenbos J., Anal. Chim. Acza, 144 (1982) 73. Vlacil F. and Vins I., J. Chromatogr., 391 (1987) 133. Rocklin R.D., Pohl C.A. and Schibler J.A., J. Chromatogr.,41 1 (1987) 107. Diop A., Jardy A., Caude M. and Rosset R., Analusis, 14 (1986) 67. Gjerde D.T. and Fritz J.S., J . Chromatogr., 176 (1979) 199. Jardy A., Caude M., Diop A., Curvale C. and Rosset R., J. Chromutogr.,439 (1988) 137.
162 9 10 11 12 13 14 15 16 17 18 19 20
Chapter 5
Diop A., Jardy A., Caude M. and Rosset R., Analusis, 15 (1987) 168. Hoover T.B., Sep. Sci. Technol., 17 (1982) 295. Jenke D.R. and Pagenkopf G.K., Anal. Chem., 56 (1984) 85. Jenke D.R. and Pagenkopf G.K., Anal. Chem., 56 (1984) 88. Jenke D.R. and Pagenkopf G.K., in Jonsson J.A., (Ed.), Chromatographic Theory and Basic Principles, Marcel Dekker, New York, NY, 1987, p. 313. Jenke D.R., Anal. Chem., 56 (1984) 2674. Jenke D.R. and Pagenkopf G.K., J . Chromutogr.,269 (1983) 202. Sevenich G.J. and Fritz J.S.,J. Chromutogr., 371 (1986) 361. Foley R.C.L. and Haddad P.R., J . Chromurogr.,366 (1986) 13. Gjerde D.T., J . Chromutogr.,439 (1988) 49. Lederer M., J . Chromorogr.,452 (1988) 265. Sevenich G.J. and Fritz J.S., Anal. Chem., 55 (1983) 12.
Part II Ion-Interaction, Ion-Exclusion and Miscellaneous Separation Methods
164
Stationary phases
. ION-INTERACTION
Eluents
CHROMATOGRAPHY (Chap 6)
L
-E
Dynamic coating
-€
Permanent coating Anions
Retention model
Cations
,Stationary phases
FURTHER SEPARATION METHODS
ION-EXCLUSION -CHROMATOGRAPHY (Chap 7)
IiDVB
+
Eluents
Microporous
Macroporous
L
Acids Complexing eluents
Retention model Reversed-
Coordination compounds Organometallics
MISCELLANEOUS - SEPARATION METHODS (Chap 8)
Schematic overview of Part II.
t
Carboxylic acids Chemically phases
Micelle exclusion
Crown ethers Anions { Cations
165
Chapter 6 Ion-Interaction Chromatography 6.1
INTRODUCTION
Hydrophilic ionic solutes, such as the inorganic anions and cations of interest in IC, show little or no retention on lipophilic stationary phases when typical reversed-phase eluents are used. However, retention and subsequent separation of such ionic solutes on these stationary phases can be achieved by the addition to the eluent of a lipophilic reagent ion having the opposite charge sign to that of the solute ion. This added reagent ion, and the chromatographic process itself, have been described by a variety of names, some of which are listed in Table 6.1. Most of these names impIy some sort of mechanism for the process and may therefore be misleading. Throughout this book, the terms ion-interaction chromatography and ion-interaction reagent (IIR) will be used, since these are quite general terms. In this Chapter, we will examine some of the mechanisms which have been proposed for ion-interaction chromatography and we will then consider the types of stationary phases and eluents which are used with this technique. Specific applications of ion-interaction chromatography to the separation of inorganic anions and cations will then be discussed.
TABLE6.1 ALTERNATIVE NAMES USED TO DESCRIBE ION-INTERACTION CHROMATOGRAPHY AND THE REAGENT ION ADDED TO THE ELUENT [11 Chromatographic process
Reagent ion
Reference
Ion-pair chromatography Paired-ion chromatography Surfactant chromatography Dynamic ion-exchangechromatography Ion-interactionchromatography Hetaeric chromatography Mobile phase ion chromatography (MPIC)
Pairing ion PIC reagent Surfactantion Ion-pairing reagent Ion-interaction reagent Hetaeron Pairing reagent
2 3 4 5
6 7
7
Chapter 6
166
6.2
MECHANISM
6.2.1
Trends in solute retention in ion-interaction chromatography
A convenient way to highlight the trends in solute retention is to compare the retention of a solute on a chromatographic system comprising a lipophilic stationary phase and an eluent consisting of an IIR dissolved in a mixture of water and one or more organic solvents with the retention of the same solute under the same chromatographic conditions, except using an eluent which does not contain the IIR. When this comparison is made, the following trends are observed: The retention of neutral solutes is not altered significantly when the IIR is added to the eluent. (ii) The retention of solutes having the same charge as the IIR is decreased when the IIR is added to the eluent. (iii) The retention of solutes having the opposite charge to the IIR is increased when the IIR is added to the eluent.
(i)
In addition, the following effects on retention are observed when the composition of the eluent is altered: (iv) The retention of solutes having the opposite charge to the IIR is increased when the concentration of IIR in the eluent is increased. (v) The retention of solutes having the opposite charge to the 11R is increased when the lipophilicity of the IIR is increased. (vi) Retention of all solutes decreases when the percentage of modifier in the eluent is increased, and vice versa. Any mechanism suggested for ion-interaction chromatography must necessarily explain these trends in retention behaviour. A large volume of literature has been devoted to the study of such mechanisms and a detailed discussion of this literature is beyond the scope of this book. Moreover, the most of these studies have been devoted to mechanisms for the retention of orgunic ionic species, such as carboxylic acids and organic bases. A summary of the most commonly suggested mechanisms [l] will be presented below and this will be followed by an evaluation of these mechanisms in terms of their applicability to the retention of inorganic ions. 6.2.2
The ion-pair model
In this model [7- 1 I], an ion-pair is envisaged to form between the solute ion and the IIR. This occurs in the aqueous-organic eluent and the resultant neutral ion-pair can then be adsorbed onto the lipophilic stationary phase in the same manner that any neutral molecule with lipophilic character is retained in reversed-phase chromatography. Retention therefore results solely as a consequence of reactions taking place in the eluent. The degree of retention of the ion-pair is dependent on its lipophilicity, which in turn depends on the lipophilicity of the IIR itself. Neutral solute molecules are unaffected by
Ion-InteractionChromatography
167
Bulk eluent
Fig. 6.2 Schematic illustration of (a) the ion-pair, (b) the dynamic ion-exchange and (c) the ioninteraction models for the retention of anionic solutes in the presence of a lipophilic cationic IIR. The solute and the IIR are labelled on the diagram. The large, hatched box represents the lipophilic stationary phase, the black circle with the negative charge represents the counter-anion of the IIR, whilst the white circle with the positive charge represents the counter-cationof the solute. Adapted from [ 11.
the presence of the IIR in the eluent and interact with the stationary phase in the conventional reversed-phase manner. An increase in the percentage of organic solvent in the eluent decreases the interaction of the ion-pairs with the stationary phase and therefore reduces their retention. The ion-pair model is illustrated schematically in Fig.
168
Chaprer6
6.l(a), using a positively charged IIR and a negatively charged solute as an example. 6.2.3 The dynamic ion-exchange model The dynamic ion-exchange model [12-151 proposes that a dynamic equilibrium is established between IIR in the eluent and IIR adsorbed onto the stationary phase, as follows:
where the subscripts E and S refer to the eluent and stationary phases and the superscript on the IIR indicates that it may carry either a positive or negative charge. The adsorbed 1IR imparts a charge to the stationary phase, causing it to behave as an ion-exchanger. The total concentration of IIR adsorbed onto the stationary phase is dependent on the percentage of organic solvent in the eluent, with higher percentages of solvent giving lower concentrations of IIR on the stationary phase. In addition, the more lipophilic the IIR, or the higher is its concentration, then the greater is its adsorption onto the stationary phase. Thus, for a given eluent composition, the concentration of adsorbed IIR (and hence the "ion-exchange'' capacity of the stationary phase) remains constant. However, constant interchange of IIR occurs between the eluent and stationary phase, so the stationary phase can be considered to be a dynamic ion-exchanger. Introduction of a solute with opposite charge to the IIR results in retention by a conventional ion-exchange mechanism. The competing ion in this ion-exchange process may be the counter-ion of the IIR, or another ionic species deliberately added to the eluent. Since the retention times will be dependent on the ion-exchange capacity of the column, they are also dependent on the lipophilicity of the IIR and the percentage of organic solvent in the eluent. Solutes having the same charge as the IIR are repelled from the charged stationary phase surface and show decreased retention times in comparison to those observed in the absence of IIR, whilst retention times for neutral solutes are unaffected by the IIR. Fig. 6.l(b) gives a schematic representation of the dynamic ion-exchange model, again using a positively charged IIR and a negatively charged solute as an example. 6.2.4 The ion-interaction model
The ion-interaction model [ I . 6, 16-19] can be viewed as intermediate between the two previous models in that it incorporates both the electrostatic effects which are the basis of the ion-pair model and the adsorptive effects which form the basis of the dynamic ion-exchange model. The lipophilic IIR ions are considered to form a dynamic equilibrium between the eluent and stationary phases, as depicted in eqn. (6.1). This results in the formation of an electrical double-layer at the stationary phase surface. The adsorbed IIR ions are expected to be spaced evenly over the stationary phase due to repulsion effects, which leaves much of the stationary phase surface unaltered by the IIR. The adsorbed IIR ions constitute a primary layer of charge, to which is attracted a diffuse, secondary layer of oppositely charged ions. This secondary layer of
Ion-InteractionChromutogrqhy
169
charge consists chiefly of the counter-ions of the IIR. The amount of charge in both the primary and secondary charged layers is dependent on the amount of adsorbed IIR, which in turn depends on the lipophilicity of the IIR, the IIR concentration, and the percentage of organic solvent in the eluent. The double-layer is shown schematically in the top frame of Fig. 6.l(c). Transfer of solutes through the double-layer to the stationary phase surface is a function of electrostatic effects and of the solvophobic effects responsible for retention in reversed-phase chromatography. Neutral solutes can pass unimpeded through the double layer, so their retention is relatively unaffected by the presence of IIR in the eluent. A solute having opposite charge to the IIR can compete for a position in the secondary charged layer, from which it will tend to move into the primary layer as a result of electrostatic attraction and, if applicable, reversed-phase solvophobic effects. The presence of such a solute in the primary layer causes a decrease in the total charge of this layer, so to maintain charge balance, a further IIR ion must enter the primary layer. This means that the adsorption of a solute ion having opposite charge to the IIR will be accompanied by the adsorption of an IIR ion. The overall result is that solute retention involves a pair of ions (that is, the solute and IIR ions), but not necessarily an ion-pair. This process leads to increased retention of the solute compared to the situation in which the IIR is absent from the eluent. The lower frame of Fig. 6.l(c) depicts this process for a positively charged IIR and a negatively charged solute. Solutes having the same charge as the IIR will show decreased retention due to electrostatic repulsion from the primary charged layer. 6.2.5 Evaluation of mechanistic models in retention of inorganic ions
Many studies have examined the applicability of the above models to the retention of organic species [e.g. 20-231, but we will consider here only the case of inorganic ions. Such species are very hydrophilic and, in most cases, are unlikely to form ion-pairs in aqueous-organic solutions. Moreover, conductance measurements would be expected to reveal the formation of ion-pairs and such measurements have failed to provide supporting evidence for significant ion-pair formation [6,241. Furthermore, the ionpair model would require that the neutral ion-pairs formed by different solute ions should have varying degrees of lipophilicity in order for them to be separated. These differences can be expected to be very slight for a series of inorganic ions (e.g. C1-, Br-, N a - , NOS-and S04*-),yet the ensuing discussion in this chapter will show that these species are separated readily by ion-interaction chromatography. Despite these shortcomings, there is a persistent trend in the literature to discuss the retention of inorganic ions in this form of chromatography in terms of interactions occurring between the solute and IIR in the eluentphse. The dynamic ion-exchange model generally provides an accurate prediction of the retention order of solutes, since this usually follows the established ion-exchange selectivity order discussed earlier in Chapter 2. In addition, the role of the counter-ion of the IIR is also predicted correctly if this counter-ion is considered to act as an ionexchange competing ion. Nevertheless, there are some shortcomings to the dynamic ionexchange model. Once such shortcoming can be seen by comparing the elution behaviour of solutes in an ion-interaction system in which a particular competing ion is
170
Chapter6
Ion-Interaction Chromatography
17 1
used to that of a conventional fixed-site ion-exchange system in which the same competing ion is employed. In the latter system, there will be a stoichiometric exchange of solute and competing ions at the ion-exchange site, so that the elution of a solute ion will always be accompanied by a decrease in the concentration of competing ion. This behaviour is not always observed in ion-interaction chromatography, where increases in the concentration of the IJR and its counter-ion often occur [25]. A more detailed discussion of this aspect and its utility for detection purposes will be found in Section 12.3.2. A study of the retention of inorganic anions in ion-interaction chromatography showed results which were in general agreement with the dynamic ion-exchange retention model, but some significant deviations from the predicted dependences indicated that the actual mechanism was more complex [26]. The ion-interaction model, and the formation of an electrical double-layer at the stationary phase surface, gives the most consistent agreement with experimental measurement. Consideration of the double-layer in terms of the Stern-Gouy-Chapman theory enables the effect on solute retention of the ionic strength of the eluent to be predicted accurately for lipophilic organic solute ions [ 161. This approach also permits the effect on solute retention of the concentration of IIR to be predicted. Similarly, electrostatic surface potential calculations, coupled with a Langmuir isotherm for adsorption of the IIR, predicts solute retention behaviour which is in good agreement with experimental results [17, 181. Moreover, studies concerned specifically with the retention of inorganic anions [27] and cations [28] in ion-interaction chromatographic systems have concluded that the ion-interaction model is the most appropriate.
6.3
STATIONARY PHASES AND ELUENTS
6.3.1 Stationary phases Ion-interaction chromatography has been performed successfully on a wide range of stationary phases, including neutral polystyrene divinylbenzene (PS-DVB) polymers 1e.g. 29, 301 and bonded silica materials with c18 [e.g. 311, c8 [32], phenyl [33] and cyano [34] groups as the chemically bound functionality. Each of these stationary phases gives satisfactory retention of ionic solutes, provided the eluent composition is such that an appropriate amount of the IIR is adsorbed. The choice between stationary phases is usually based on such considerations as chromatographic efficiency [35], pH stability [36] and particle size 1371, rather than on differences in chromatographic selectivity. However, it has been noted 1381 that the elution order for solutes can vary when the nature of the stationary phase used to support the IIR is altered. This point is illustrated in Fig. 6.2, which shows chromatograms for inorganic anions, obtained on three different stationary phases. It can be noted that the elution position of sulfate differs markedly between the c18 and PS-DVB stationary phases. Also apparent is the improved chromatographic efficiencies of the silica-based stationary phases compared to that of the PS-DVB material. Further factors to be considered sin the selection of a stationary phase for ioninteraction chromatography are specific interactions existing between the stationary phase and either the IIR or the solutes, and the role of residual silanol groups on silica-
172
Chapter 6
TABLE 6.2 TYPICAL REAGENTS USED AS IIRs IN DYNAMIC COATING ION-INTERACTION CHROMATOGRAPHY OF ANIONS AND CATIONS IIR
Detection mode$
References
Tetramethylammonium Tetrapmpylammonium Tetrabutylammonium Tetrapentylammonium Hexylammonium
spec C, Indirect Spec, Amp C, Spec,Amp spec c,spec, Indirect spec c,spec, Indirect spec spec, ICP C, Spec,Amp spec Spec. Amp Indirect spec Indirect spec Indirect spec Indirect spec Indirect spec Indirect Fluor
38,42 36,43,44 45-47 17, 24, 29 48 49-5 1 41,52-54 26, 31, 53, 55 56 57 58.59 59, 60 59, 60 61 62-64 65
spec RI, ICP spec Spec, PCR. RI PCR Indirect spec Spec,Indirect Amp
66
octylammonium
Hexadecyltrimethy l u m cetyl~thyl~nium Tricaprylylmethylammonium Dodecyltriethylammonium Benzyltributylammonium Naphthylmethy lmbutylammonium Naphthylmethy l t r i p r o p y l a m m o n i u m Methylpyridinium Iron(II)-l,I@phenanthroline Ruthenium(II)-l,lO-phenanthroline on -ations Butanesulfonate Pentanesulfonate Hexanesulfonate Octanesulfonate Dodecylsulfate
Naphthalenesulfonate Diethyldithidamate a
6, 67 66 28, 68,69 70 71 72,73
Spec = spectmphotometry, Amp = axnperomeay, C = conductivity, Fluor = fluorescence, ICP = inductively coupled plasma atomic emission, PCR = post-column reaction, RI = refractive index.
based stationary phases. Some IIRs (e.g. cetylpyridinium ions) and solutes (e.g. iodide) show particularly strong adsorption to PS-DVB stationary phases and this has been attributed to the occurrence of K-x interactions with the aromatic moiety of the polymer [35]. Residual silanol groups on silica-based packings have been shown to act as weak cation-exchange sites and this behaviour exerts an influence on the ion-interaction separation of both anions and cations on these stationary phases [29]. Scrutiny of the literature reveals that the majority of ion-interaction separations are performed on conventional Cis silica-based reversed-phase materials or on neutral PSDVB polymers (such as Hamilton PRP-I, Rohm & Haas XAD-2 and Dionex MPIC columns).
173
Ion-Interaction Chromatography
TABLE6.3 EFFECT OF THE ALKYL CHAIN LENGTH OF THE IIR ON RETENTION TIMES OF ANIONS [37] Solute
Retention ti&
Chloride Bromide Fluoride Iodide Nitrate
(min)
Hexylamine salicylate
Octylamine salicylate
DeCyl& Salicylae
n.r.b n.r. n.r. n.r. n.r.
2.0 f 0.3 2.0 f 0.3 2.3 f 0.3 2.5 f 0.3 2.5 f 0.3
7.0 f 0.3 7.3 f 0.4 8.0 f 0.4
6.5 f 0.3
8.3 f 0.4
A Lichrosphere RP-18column (5 p n particle size) was used. The eluent concentration was 5 mM and the flow-rate was 2.0 mumin. b n.r. = not retained.
a
6.3.2 Type of ion-interaction reagent
Requirements of the IIR The most important component of the eluent in ion-interaction chromatography is the IIR itself. The prime requirements of the IIR are as follows: (i) (ii) (iii) (iv)
An appropriate charge, which is unaffected by eluent pH. Suitable lipophilicity to permit adsorption onto non-polar stationary phases. Compatibility with other eluent components. Compatibility with the desired detection system.
"Dynamic coating" ion-interaction chromatography Anion separations are normally performed using strong base cations, such as tetraalkylammonium ions, as the IIR whilst cation separations are usually performed using strong acid anions, such as aliphatic sulfonate ions. Table 6.2 lists some IIRs which are used for ion-interaction separations. In each case, the IIR is present at a constant, specified concentration in the eluent in order to maintain a desired concentration of IIR on the stationary phase. That is, the coating of IIR is in dynamic equilibrium, as shown in eqn. (6.1). and the column can be said to be "dynamically coated" with IIR. Table 6.2 shows that the IIRs used for dynamic coating ion-interaction chromatography vary from moderately lipophilic (e.g. tetrabutylammonium ions) to very lipophilic (e.g. hexadecyltrimethylammonium ions). The lipophilicity of the IIR governs the degree of adsorption of the IIR onto the stationary phase, which in turn governs the effective ion-exchange capacity of the column and hence the retention times of solute ions. This point is illustrated in Table 6.3, which lists retention times for
r
f
i
0.032AU
L co
0.01 AU
i
n Pr NI
M
1
I
I
0
2
I
I
4 6 Time (minl (a1
I
I
1
I
I
I
I
1
8
10
11
0
4
8 Time (minl (bl
12
16
Fig. 6.3 Separation of cations by dynamically coated ion-interaction chromatography. (a) A C1g column was used with 10 mM octanesulfonate and 45 mM tartrate at pH 3.4 as eluent. Reprinted from [5] with permission. (b) A 5pm Supelco C1g column was used with an eluent formed from a linear gradient of 0.05-0.40 mM a-hydroxyisobutyric acid at pH 4.2, containing 30 mM octanesulfonate and 7.5% methanol. Reprinted from [68] with permission. Post-column reaction detection was used in each case.
B o\
Ion-Interaction Chromatography
175
anions obtained using IIRs with differing alkyl chain lengths (and therefore differing lipophilicity). Some of the detection modes available for use with the various IIRs are also listed in Table 6.2 and a discussion of detection for this mode of chromatography will be presented in Part I11 of this book. It is interesting to note that inorganic complexes, such as the 1,lo-phenanthroline complexes of iron(II1) and ruthenium(I1) can be employed as IIRs. Pietrzyk and co-workers [62, 64, 65, 741 have shown that these complexes are adsorbed readily onto PS-DVB stationary phases and their absorbance or fluorescence can be used for indirect detection of anions. Some typical chromatograms obtained for the separation of anions by dynamic coating ion-interaction chromatography were presented in Fig. 6.2, and typical separations of cations are shown in Fig. 6.3. These chromatograms illustrate the excellent chromatographic efficiency which can achieved using ion-interaction as the separation mode. Many of the species listed in Table 6.2 are surfactants which will form micelles if the IIR concentration exceeds the critical micelle concentration for that particular species. These micelles can be adsorbed onto the stationary phase in the same manner as other IIRs. However, it has been shown that the retention times of anionic solutes in micellar eluents decreases as the concentration of the micellar IIR is increased [53]. This behaviour is opposite to that normally observed and has been attributed to interaction of the solute anions with micelles in the eluent, which reduces the electrostatic interaction of these solutes with adsorbed micelles and thereby reduces their retention. The elution order observed for anions in this system is similar to that for conventional anionexchangers, as illustrated in Fig. 6.4.
"Permanent coating" ion-interaction chromatography A quite distinct alternative to the dynamic coating method can also be used. In this approach, a very lipophilic IIR is used to initially equilibrate the stationary phase and is then removed from the eluent in the actual separation step [5, 35, 401. The equilibration process establishes a very strongly bound coating of IIR on the stationary phase and this coating persists for long periods of subsequent usage. For this reason, the method is known as "permanent coating" ion-interaction chromatography. Since the stationary phase has now been converted into an ion-exchanger by virtue of the adsorbed IIR, the eluents used in the separation step are identical to those employed with conventional fixed-site ion-exchange materials (see Chapter 4). Permanent coating ion-interaction chromatography has a number of attractive features when compared with conventional ion-exchange chromatography. These include:
The ion-exchange capacity of the column can be varied over a wide range by altering the composition of the equilibrating solution. Parameters which may be varied are the lipophilicity and concentration of the IIR and the percentage of organic solvent in the equilibrating solution. (ii) The adsorbed layer of IIR can be removed or renewed as desired. Removal of the adsorbed coating can be accomplished by washing the column with an organic solvent, such as methanol or acetonitrile. (iii) The same column can be converted into an anion-exchanger or a cationexchanger through the use of an appropriate IIR.
(i)
176
r~
0
Chapter6
2
I
6
I
I
10 14 Time (min)
1
18
1
22
Fig. 6.4 Separation of anions by dynamic coating ion-interaction chromatography using a micellar eluent. A Spherisorb c18 column was used with 0.01 M cetyltrimethylammonium chloride (buffered at pH 6.8) and acetonitrile (35%) as eluent. Detection was by UV absorption at 205 nm. Reprinted from [53] with permission.
(iv) The high chromatographic efficiency of reversed-phase packing materials is retained when these packings are converted into permanently coated ionexchangers. Table 6.4 lists some of the IIRs used for permanent coating ion-interaction separations of anions and cations. It will be noted that cetyltrimethylammonium is listed as an IIR in Table 6.4 for the permanent coating method and also appears in Table 6.2 for the dynamic coating method. However, when used for permanent coating, cetyltrimethylammonium is not present in the eluent during the separation step. Permanent coating of the column is usually achieved by passing a solution (approximately M)of the IIR in dilute (5%) methanol or acetonitrile through the column for about 20 min. The purpose of the organic solvent is to wet the surface of the lipophilic stationary phase in order to improve binding of the IIR. This coating procedure typically results in the immobilization of about 50 mg of IIR onto a 25 cm column [401, giving an ion-exchange capacity similar to that for fixed-site ionexchangers used in IC. These coated columns have been found to be stable for at least one week [5].
Ion-Interaction Chromatography
177
TABLE 6.4 REAGENTS USED AS IIRs IN PERMANENT COATING ION-INTERACTION CHROMATOGRAPHYOF INORGANIC ANIONS IIR
structure
References
CH3(m2)15(m3)3N+ ~3(cH2)15N+c5HS ~3t~3(cH2)1113N+ [CHdCH2)714N+ CH3[CH3(m2)713N+
75-79 37,40. 80-84 5, 85 5, 82 5 86.87
Anions Cetyltrimethylammonium Cetylpyridinium Tridodecylmethy l a i m Tetraoctylammonium Trioctylmethylammonium Methyl Green
Cations Eicosanesulfate
As mentioned earlier, the eluents used in permanently coated ion-interaction chromatography are the same as those employed in IC using ion-exchange columns. Thus, aromatic carboxylate ions, such as phthalate [77, 881, hydroxybenzoate [86], salicylate [81] and aimesate [80] are commonly used for anion separations, and tartrate has been used for cations [5]. Fig. 6.5 shows typical chromatograms for the separation of inorganic anions and cations using the permanent coating ion-interaction method. 6.3.3 Role of the counter-ion of the IIR The counter-ion of the IIR fills a very important role in dynamic coating ioninteraction chromatography of anionic solutes. This counter-ion usually acts as an ionexchange competing anion and is responsible for the elution (and in many cases also the detection) of the solute anions. Typical counter-ions are hydroxide [38], fluoride [29], chloride [53], perchlorate [49], bromide [24, 441, phthalate [23, 891, citrate [26] and salicylate [90]. The nature of the counter-ion determines the type of separation which is achieved and the following strengths of counter-ions in reducing the retention of anionic solutes has been reported for a PRP-1 column using a quaternary ammonium salt as the IIR [24,91]:
The counter-ion of the IIR also influences the detection modes which are applicable to a particular separation. This occurs in exactly the same manner as applies in ionexchange chromatography with fixed-site exchangers. Thus, counter ions such as citrate, phthalate and hydroxide are suitable for conductivity detection; hydroxide, fluoride and chloride are suitable for direct spectrophotometric detection; and phthalate is suitable for
CI-
cu
I
02-
k: I
I
I
0
L
8
I
I
12 16 Time (min) (a I
I
I
20
2L
r
0
I
I
50
I
I
I
I
150 100 Time Is) (b)
I
I
200
I
1
250
Fig. 6.5 Separation of (a) inorganic anions and (b) inorganic cations using permanent coating ion-interaction chromatography. (a) A Hamilton PRP1 column coated with cetyltrimethylammonium bromide was used with 24% methanol - 1 mM potassium hydrogen phthalate - 20 mM Tris buffer (pH 9.3) as eluent. Detection was by indirect spectrophotometry at 282 nm. Reprinted from [84] with permission. (b) A C18 column coated with C20H41S04Na was used with 75 mM tartrate at pH 3.4 as eluent. Detection was by spectrophotometry at 530 nm after post-column reaction. Reprinted from [5 ] with permission.
179
Ion-InteractionChromatography Tetrabutylammonium salicylate (0.4 mM) C18
20
Octylamine (5 .mM) salicylate (5 mM) C18
Cetrimide (1 mM) citrate (4 mM) C18
Cetrimide (0.1 C ) phosphate (0.1 M)
CN
Tetrapentylammonium fluoride (1 mM) PRP-1
I s20;-
Fig. 6.6 Typical retention times for anions in dynamic coating ion-interaction chromatography using c18. CN and PRP-1stationary phases. Data taken from [31,34,37,90,91].
indirect spectrophotometric detection. Fig. 6.6 shows some typical retention times for anionic solutes in dynamic coating ion-interaction chromatography. It is not essential that the counter-ion of the IIR serves as the ion-exchange competing anion. An alternative approach is to use a separate eluent component, such as phosphate [92], citrate [26, 661, oxalate 1661 or phthalate [27], for this purpose. This method is sometimes used to assist in the elution of strongly retained ions. The nature of the counter-ion of the IIR is of less importance in ion-interaction chromatography of cations. The reason for this is that the elution of solute cations is usually accomplished with the aid of a complexing ligand, such as a-hydroxyisobutyric acid 1681, which is added to the eluent. 6.3.4 Summary of eluent and stationary phase effects
The discussion thus far has indicated a number of parameters which affect the adsorption of the IIR onto the stationary phase in ion-interaction chromatography. These parameters are summarized below, together with some other factors which influence the retention of solutes:
180
Chapter 6
Fig. 6.7 Dependence of the capacity factor of inorganic anions on the concentration of IIR in the eluent. A Partisil ODs-3 column was used with an eluent containing 1.5 mM phthalate and the indicated concentrationsof tetrabutylanumniurniodide. Reprinted from [27] with permission.
(i) (ii) (iii) (iv) (v) (vi) (vii)
The nature of the stationary phase. The lipophilicity of the IIR. The concentration of the IIR in the eluent. The ionic strength of the eluent. The nature of the competing ion in the eluent. The concentration of the competing ion in the eluent. The eluent pH.
The first four of these factors will determine the surface concentration of the IIR on the stationary phase, and hence the surface charge density and the effective ionexchange capacity. The higher the surface concentration of IIR, the greater is the retention of solutes having a charge sign opposite to that of the IIR. Thus, retention times will increase as the lipophilicity of the IIR is increased and as the percentage of modifier in the eluent is decreased. We can also note that solute retention generally increases with the concentration of IIR in the eluent, but there is a threshold concentration above which solute retention decreases with further increases in the concentration of IIR. This retention pattern is illustrated in Fig. 6.7 and the reasons underlying this behaviour will be explored fully in Section 6.4.1 below. At this stage, it will be sufficient to note that the stationary phase surface becomes saturated with IIR and any further addition of IIR to the eluent results in decreased retention because of the increased concentration of the IIR counter-ion. The nature and concentration of the eluent competing ion (whether this is the counter-ion of the IIR or an ion which is added separately) will determine the retention times and elution order for solute ions. Increases in the concentration of the eluent
Ion-InteractionChromatography
181
competing ion will result in decreased solute retention, in the same manner as observed for ion-exchange separations. Finally, the eluent pH will influence the charges on the competing ion and the solutes, provided that these species are weak acids or bases. An example of this effect is the influence of pH in an ion-interaction chromatographic system using tetrabutylammonium as the IIR and phthalate as the competing anion. Increases in eluent pH over the range 4.0-6.0 cause a decrease in solute retention as a result of increased ionization of phthalate, leading to the formation of a strong, divalent competing anion. 6.3.5
Guidelines for eluent selection in ion-interaction chromatography
It is apparent that selection of the correct eluent composition in ion-interaction chromatography requires consideration of all of the factors discussed in the preceding section. This is especially true of the dynamic coating approach, in which small changes in eluent composition can often result in large variations in retention times. Guidelines for eluent selection in this mode of chromatography are available [8], and are summarized below.
Anion separations The most commonly used IIRs are tetraalkylammonium salts. The more lipophilic IIRs (i.e. those with longer alkyl substituents) are best suited to the separation of NOa-, Br and NO3-, whilst the less lipophilic IIRs are hydrophilic anions, such as F,0, best suited to the separation of hydrophobic anions, such as aromatic sulfonates or sulfates. The counter-anion of the IIR must be selected on the basis of the desired ionexchange competing effects and the detection mode which is to be employed. For example, counter-anions such as phthalate, salicylate or Br- will result in shorter solute retention times than F- and OH, but the use of OH- as the counter-anion is necessary if suppressed conductivity detection is to be employed. The degree of retention which is achieved can then be manipulated by varying the type and amount of organic modifier added to the eluent. Further changes in solute retention times can be accomplished by addition to the eluent of an additional competing anion (e.g. S042-, C032-or Ct), sometimes referred to as an "inorganic modifier", or by varying the eluent pH when the solutes are weak acid anions. Cation separations The major factors to be considered in the separation of cations by ion-interaction chromatography are the type of IIR used, the nature of the eluent ligand, and the eluent pH. Aliphatic sulfonic acids are the most commonly used IIRs and the lipophilicity of the IIR (as determined.by the length of the alkyl chain) exerts a strong effect on solute retention. Elution of solute cations is achieved predominantly by complexation with the eluent ligand, so the conditional formation constants for the solutes are of prime importance. These conditional formation constants are determined by the nature and concentration of the ligand and by the eluent pH. Ligands such as citrate, tartrate, oxalate and a-hydroxyisobutyric acid are suitable, with each of these species showing increased complexation as the eluent pH is raised. This effect occurs only until
Chapter6
182
ionization of the ligand is complete, beyond which point further increases in pH do not significantly alter retention times. 6.4
6.4.1
RETENTION MODELS FOR DYNAMIC COATING IONINTERACTION CHROMATOGRAPHY
Model for anion retention
The following retention model for ion-interaction chromatography under dynamic coating conditions was proposed originally by Iskandarani and Pietrzyk [24] and later modified by Xianren and Baeyens [27]. The model is based on adsorption of the IIR onto the stationary phase. We will consider the situation where a lipophilic stationary phase is equilibrated with an eluent consisting of an IIR (which will be assumed to be a quaternary ammonium salt, designated as Q'C-) and a competing anion, A-:
where A, is the number of free adsorption sites on the stationary phase and the subscripts m and r refer to the mobile (eluent) and stationary phases, respectively. The equilibrium constant for eqn. (6.3) will be denoted by K1 and is given by:
The ion-exchange equilibrium between the competing anion (A') in the eluent and the counter-ion, C-, is given by: (6.5)
and the equilibrium constant, K2,for this equation can be written:
If a solute anion, X-, is now introduced into the chromatographic system, we can write an ion-exchange equilibrium as follows:
and the equilibrium constant, K3, for this equation can be written:
ton-Interaction Chromatography
183 (6.8)
The sorption capacity, KO,for the stationary phase is a measure of the total number of sites that can be occupied in the retention process. We can write a mass balance equation which accounts for all occupied and free sites, as follows:
Now the capacity factor, kx’,for solute X- can be written as: (6.10)
where q is the phase ratio. Combining eqns. (6.3)-(6.9) with elimination of Ar, (QA), and (QB), and substitution of the solution for (QX), into eqn. (6.10) gives:
which can be rearranged to give:
Eqn. (6.12) predicts that the reciprocal of the capacity factor is linearly related to [C-],, [A-lm and [X-lm, and inversely related to [Q+]m.
Effect of [AA‘],,, and [X-1, Fig. 6.8 provides a plot of the reciprocal of capacity factor versus the concentration of competing anion (i.e. [A-lm) in the eluent. In this example, the competing anion was phthalate and each of the parameters [Q+]m, [C-], and [X-], was held constant. The predicted linear relationship between the reciprocal of capacity factor and [A-]m is observed. Fig. 6.9 shows a plot of the reciprocal of capacity factor versus the amount of sample injected (i.e. [X-],), with the parameters [Q+Im,[C-], and [A-]m being held constant. Again, the predicted linear relationship is observed. It is important to note that the amounts of injected sample shown in Fig. 6.9 are relatively high and when smaller amounts of sample are injected, the reciprocal of capacity factor does not alter appreciably when the sample size is varied [24].
184
Chupter 6
30
1
0.0
: 1
I
I
2
I
I
3
I
1
I
[KHP] lmM1 Fig. 6.8 Dependence of the capacity factor of inorganic anions on the concentration of the competing anion bhthalate) added to the eluent. A Partisil ODs-3 column was used with an eluent containing 1 mM tetrabutylammonium iodide and the indicated concentrations of potassium hydrogenphthalate. Reprinted from [27] with permission.
Effect of the concentration of IIR in the eluent Eqn. (6.12)'also allows us to examine the effect of increasing the concentration of IIR in the eluent [27]. Increasing the concentration of the IIR (i.e. Q+C-)will increase simultaneously both [Q+Im and [C-],. Two opposing effects are predicted from eqn. (6.12). The f i s t is an increase in analyte retention due to increased adsorption of IIR onto the stationary phase, so we expect the reciprocal of the solute capacity factor to be linearly related to the reciprocal of [Q+]m. The second is a decrease in analyte retention where the reciprocal of the capacity factor is expected to be linearly related to [C-1,. The observed changes in retention which accompany an increase in the eluent concentration of the IIR were illustrated in Fig. 6.7. We can now use eqn. (6.12) to rationalize this behaviour, but first this equation can be rewritten by using eqn. (6.4) to obtain the following expression for [C-],: (6.13)
which can be substituted into eqn. (6.12) to give:
Ion-Interaction Chromatography
185
0.180.16
-
Amount injected (mg)
Fig. 6.9 Dependence of the capacity factor of inorganic anions on the concentration of the analyte. A PRP-1 column was used with 1 mM tetrapentylammoniumfluoride in 1:3 acetoniaile-wateras eluent. Reprinted from [91] with permission. When [A-]m and [X-1, are constant, eqn. (6.14) can be simplified to: (6.15)
where [Q+]m can be considered to be the amount of IIR not adsorbed at equilibrium, (QC), is the amount of IIR adsorbed at equilibrium and A, is the number of free sites at equilibrium. We will now consider the effects of increasing the eluent concentration of the IIR. At low IIR concentrations, [Q+]m is low, Ar is high and (QC), is small compared to A,. From eqn. (6.15), this gives:
1 a-
, or kx a
I
kx
[Q'lm
(6.16)
[Q'Im
This relationship is evident in the early part of Fig. 6.7. When half of the available adsorption sites on the stationary phase are occupied, then A, and (QC), are equal, so that: (6.17)
This means that the slope of the plot of kx' versus the concentration of IIR is half that observed at lower eluent concentrations of IIR. We can see that this slope will decrease progressively as more IIR is adsorbed. This process continues until a
186
Chapter 6
maximum in the plot is attained, as in Fig. 6.7. At this point, A, is very small in comparison to (QC),, such that: (6.18)
Considering the relative magnitudes of A, and (QC),, the slope of the plot of capacity factor versus the concentration of IIR will be very small, or even zero. Further increases in the concentration of IIR will not result in further adsorption of Q+ onto the stationary phase since all of the available adsorption sites have been exhausted. However, [C-1, will continue to rise, so that the solute capacity factor will fall in accordance with eqn. (6.12).
6.4.2 Model for cation retention In order to develop a retention model for cations in dynamic coating ioninteraction chromatography, we recognize that the eluent composition used in this case usually differs from that employed for a typical anion separation. Eluents for anion separations contain a cationic IIR and its counter-anion, together with an added competing anion. On the other hand, eluents for cation separations contain an anionic IIR and its counter-cation, together with an added ligand which assists in solute elution by complexation effects. This difference between anion and cation eluents also exists in ion-exchange separations (see Chapter 4) and arises because of the strong ion-exchange affinities of many cations. We can therefore consider the situation where a lipophilic stationary phase is equilibrated with an eluent comprising an IIR (which will be assumed to be an aliphatic sulfonic acid salt, designated as P-C+)and a ligand, L-. Using the same approach adopted above for anions. we can write:
A,
+ P, + C,+
% (PC),
(6.19)
where A, is again the number of free adsorption sites on the stationary phase and the subscripts r and m denote the stationary and eluent phases, respectively. The equilibrium constant for eqn. (6.19) will be denoted by Kq and is given by: (6.20)
When a solute cation, X+, is introduced, the following ion-exchange equilibrium exists:
(PC), +
x;
% (PX), +
c,+
and the equilibrium constant (Ks)for this equation can be written:
(6.21)
Ion-Interaction Chromatography
187
(6.22)
The solute cation will also participate in complexation reactions with the eluent ligand, L-,so that the solute X will exist as both the free ion (i.e. X+) and as a complex. If we define ax as the fraction of the total concentration of solute cation existing as the free ion, X+, then we have:
ax =
R'Im -
(6.23)
[X'IT
where [X+]T is the total concentration of solute X in the eluent, regardless of whether it is present in the free or complexed forms. We again write a mass balance equation in terms of the sorption capacity, KO, of the stationary phase:
KO = A,
+ (PC), + (PX),
(6.24)
The capacity factor kx' of solute X+ can be written in terms of the phase ratio, q,
as: (6.25)
Combining eqns. (6.19) - (6.25) gives: (6.26)
Eqn. (6.26) represents rhe simplest case in which the solute cation and the countercation of the IIR are both singly charged. The form of this equation will therefore alter when the solute cation has a multiple charge. Nevertheless, from eqn. (6.26) we can predict that the capacity factor for a solute cation will be directly proportional to ax and [P-lm, and inversely proportional to [C'], and [X+]m. Few published data are available to investigate the validity of these relationships for inorganic cations, despite the fact that this separation mode is commonly employed for transition metal and lanthanide ions. However, a study of the retention behaviour of transition metal cations on a reversedphase column using octanesulfonate as the IIR and oxalate as the eluent ligand has been reported [93]. This work shows that there is a linear relationship between log kx' and log ax when all other variables are held constant (in accordance with eqn. (6.26)), and that a plot of log kx' versus log [Pa], (illustrated in Fig. 6.10), again with all other variables held constant, has the same general shape as that observed for anions. That is, an initial proportionality exists between log kx' and log [P-lm, but the curve reaches a
188
Chapter6
-0.2 O.O\
I
-0.4 -2h
I
-2.5
I
-2.6
I
-2.7 log
rw
I
-2.8
1
-29
1
-3.0
Fig. 6.10. Dependence of the capacity factor of inorganic cations on the concentration of IIR in the eluent. A Waters pBondapak Clg column was used with an eluent containing 2.5 m M oxalic acid at pH 3.4 and the indicated concentrations of octanesulfonate. Reprinted from [93] with
permission. maximum due to saturation of the available adsorption sites with P- and the increased concentration of the counter-cation, C+. in the eluent. These results are in general agreement with eqn. (6.26). 6.5
APPLICATIONS
Ion-interaction chromatography has found extensive application in the separation of inorganic anions and cations. The technique offers some advantages over the use of fixed-site ion-exchangers in that there is a wide range of eluent variables which can be used to manipulate the retention of solutes. For this reason, ion-interaction chromatography is often applied to the resolution of difficult mixtures of solutes. Numerous examples of such applications can be found in Part V of this book, however some representative applications are listed in Table 6.5 in order to illustrate the scope of the technique. As a general observation, it can be said that ion-interaction chromatography finds its strongest usage in the separation of transition metal and lanthanide cations, for which it is undoubtedly the method of choice. These species may be separated as simple, hydrated metal ions, or as anionic complexes, using a suitable ligand. The first of these approaches has been developed extensively by Cassidy and co-workers and was illustrated in Fig. 6.3(b), which shows an excellent separation of lanthanides. The
ton-Interaction Chromarography
189
second approach is illustrated in Fig. 6.11, which shows the separation of anionic metal cyan0 complexes. Both of these methods have been applied to a wide variety of complex sample matrices.
TABLE6.5 APPLICATIONS OF ION-INTERACTION SEPARATIONSIN IC Solute(s)
Sample
Stationary phasea
IIRb
Det'n Ref methodc
9 8
TBA sulfate TBAphosphate
DSpec ICP
94 95
ISpec DSpec ISpec C ISpec DSpec Amp DSpec
75
Anions Alkylbenzene sulfonates A s O ~ ~organo-, arsenic compounds Carboxylic acids CI-, NO^-, ~043-, ~ 0 4 2 EDTA, ~2042-, citrate F-, C104~-, BF4-, F,cI-, NO^, ~ 0 4 2 IIIO~-.BIO.~-, NO~-,N%-, I-, SCN, Fe(CN)64N&; Br-, NO3N@-,NO3P043-, Cl-, Bf, NOg',
Detergents Shale oil
c18
Lysimeter solns Plants, soils Reactor water Plating baths Tapwater salt Serum various
CIMA chlorided TBA hydroxide PRP- 1 8chlorided MPIC-NS1 TBA hydroxide TBA phthalate C18 Ouylamine c18 HDTMA chloride ClS PS-DVB CTMA citrate
Foods PRP- 1 Meat,vegetables Ci8 C18 Fruit juices
TPAbromide TBAphosphate TBAsalicylate
DSpec DSpec C
98
Pharmaceuticals Urine Batteries
Amp
47 92
c8
TBA sulfate TBA sulfate OctylamineTSA
DSpec
SCN-
ISpec
51
Cis MPIC-NS1 MPIC-NS1 C18
Octanesulfonate Hexanesulfonate TBA hydroxide TBAhydroxide
PCR C C DSpec
68
c18
Hexanesulfonate
PCR
103
I-,so~~s&-. Iso42-
CIS cl8
CIS c18
96 80 30
97 50 54 55
99 87
Cations
Rare earths Ethanolamines Au(I), Au(III) cyanides CN- complexes of transition metals Transition metals a
Leach liquor Ambient air Plating baths Gold process solutions Brass, urine
MPIC-NS1, PRP-1 and PS-DVB are all styrene-divinylbenzenestationary phases. TBA = tetrabutylammonium, CIMA = cetyltrimethylammonium,CP = cetylpyridinium, HDTMA = hexadecyltrimethylamnium, TPA = tetrapentylammonium, TSA = toluenesulfonate. DSpec = direct spectrophotometry, ISpec =indirect spectrophotometry, C = conductivity, Amp = ampemmeay, PCR = post-column reaction, ICP = inductively coupled plasma. Permanent coating ion-interaction chromatography.
100 101 102
190
Chapter 6
Pd(ll1
k PliIII
0I
10 I
20
Time imin
30
LO
I
Fig. 6.11 Ion-interaction separation of metal-cyano complexes. A Waters Nova Pak C18 column was used with 23:77 acetonitrile-water containing 5 mM Waters Low UV PIC A as eluent. Detection was by direct spectrophotometry at 214 nm. Reprinted from [38] with permission.
6.6 1 2 3 4 5 6
7 8 9 10 11 12 13
14
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Ion-InteractionChromatography 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57
191
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192 58 59 60 61 62 63
Chapter6
Hammers W.E., Aussems C.N.M. and Janssen M., J. Chromatogr., 360 (1986) 1. Barber W.E. and Cam P.W., J . Chromatogr.. 301 (1984) 25. Barber W.E. and Can P.W., J. Chromarogr., 316 (1984) 211. Arvidsson E., Crommen J., Schill G. and Westerlund D., Chromatographia,24 (1987) 460. Rigas P.G. and Pietnyk D.J.. Anal. Chem., 59 (1987) 1388. Rigas P.G. and P i e q k D.J., Poster presented at "11thInternational Symposium on Column Liquid Chromatography",Amsterdam, 1987. 64 Rigas P.G. and Pietnyk D.J., Anal. Chem., 60 (1988) 454. 65 Rigas P.G. and Pietnyk D.J., Anal. Chem., 60 (1988) 1650. 66 Kirk A.D. and Hewavitharana A.K., Anal. Chem., 60 (1988) 797. 67 Krull I.S., Bushee D., Savage R.N., Schleicher R.G. and Smith S.B., Jr., Anal. Left., 15 (1982) 267. 68 Barkley D.J., Blanchette M., Cassidy R.M. and Elchuk S., Anal. Chem.,58 (1986) 2222. 69 Bushee D., Krull I.S., Savage R.N. and Smith S.B., Jr., J. Liq.Chromatogr.. 5 (1982) 463. 70 Lavine B.K., McMillan S., Ward A.J.I. and Donoghue O., in Jandik P. and Cassidy R.M.(Eds.) Advances in Ion Chromarography,Vol. 1, Century International, Inc., Franklin, MA, 1989, p. 195. 71 Hackzell L., Rydberg T. and Schill G., J. Chromatogr.,282 (1983) 179. 72 Smith R.M., Anal. Proc., 21 (1984) 73. 73 Smith R.M. and Yankey L.E., Analyst (London), 107 (1982) 744. 74 Rigas P.G. and Pietnyk D.J., Anal. Chem., 58 (1986) 2226. 75 Barkley D.J., Dahms T.E. and Villeneuve K.N., J. Chromarogr.,395 (1987) 631. 76 Frohlich D.H., J. HRC & CC, 10 (1987) 12. 77 Mullins F.G.P., Analyst (London), 112 (1987) 665. 78 Takeuchi T. and Yeung E.S.,J . Chromatogr.,370 (1986) 83. 79 Takeuchi T., Suzuki E. and Ishii D., J. Chromatogr.,447 (1988) 221. 80 Cassidy R.M. and Elchuk S . , Anal. Chem.,57 (1985) 615. 81 Heffer W.D., Takeuchi T. and Yeung E.S., Chromntographia,24 (1987) 123. 82 DuVal D.L. and Fritz J.S., J. Chromatogr., 295 (1984) 89. 83 Papp E., J . Chromarogr.,402 (1987) 211. 84 Papp E. and Fehervari A., J. Chromatogr.,447 (1988) 315. 85 Al-Omair A.S. and Lyle S.J., Talantu,34 (1987) 361. 86 Golombek R. and Schwedt G., J. Chromatogr.,452 (1988) 283. 87 Schmuckler G., Rossner B. and Schwedt G., J . Chromatogr., 302 (1984) 15. 88 Fuchtner F. and Schmidt W., Z. Chem., 28 (1988) 149. 89 Pilkington A.E. and Waring R.H., Med. Sci. Res., 16 (1988) 35. 90 Bidlingmeyer B.A., Santasania C.T. and Warren F.V., Jr.. Anal. Chem., 59 (1987) 1843. 91 Iskandarani Z and Pietnyk D.J., Anal. Chem..54 (1982) 2427. 92 Kalbasi M. and Tabatabai M.A., Commun Soil Sci. Plant Anal., 16 (1985) 787. 93 Haddad P.R. and Foley R.C., J. Chromarogr., 500 (1990) 301. 94 Bear G.R., J. Chromatogr., 371 (1986) 387. 95 LaFreniere K.E., Fassel V.A., and Eckels D.E., Anal. Chem., 59 (1987) 879. 96 Bossle P.C., Reutter D.J. and Sarver E.W., J . Chromurogr.,407 (1987) 399. 97 Perrone P.A. and Grant J.R., Res. Do..September (1984) 96. 98 Iskandarani Z. and Pietnyk DJ., Anal. Chem.,54 (1982) 2601.
Ion-InteractionChromatography 99 100 101 102 103
Wootton M., Kok S.H.and Buckle K.A., J . Sci. Food Agric.. 36 (1985) 297. Bouyoucos S.A. and Melcher R.G..Am. I d . Hyg.Assoc. J., 47 (1986) 185. Dionex ApplicationNote 4OR. Grigorova B., Wright S.A. and Josephson M., J. Chromutogr.,410 (1987) 419. Schmidt G.J. and Scott R.P.W.,Analyst (London), 109 (1984) 997.
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195
Chapter 7 Ion-Exclusion Chromatography 7.1
INTRODUCTION
Ion-exclusion chromatography, first introduc d by Wheaton and Bauman in 1953 [l], involves the use of strong anion- or cation-exchange resins for the separation of ionic solutes from weakly ionized or neutral solutes. In this mode of chromatography, the charge sign on the ion-exchange resin used is the same as that of the weakly ionized solutes. That is, solutes with a partial negative charge (such as carboxylic acids) are separated on a cation-exchange resin having anionic sulfonate functional.groups, whereas solutes with a partial positive charge (such as weak bases) are separated on an anionexchange resin having cationic quaternary ammonium functional groups. This is the opposite situation to that occumng in ion-exchange chromatography. As with other IC separation techniques, ion-exclusion chromatography has been described by a variety of names, some of which are listed in Table 7.1. Each of these names implies a mechanism for the separation process and as we will see in the ensuing discussion, the actual mechanism of the process is not clearly defined, but is certainly quite complex. We shall therefore continue to use the term "ion-exclusion chromatography" to describe the technique, whilst recognizing that this title is probably somewhat inaccurate.
7.1.1 Basic principles Ion-exclusion chromatography finds application in the separation of a wide range of small, neutral or partially ionized molecules. Applying the definition of IC used in this text, we will limit discussion of the technique to include its application to certain TABLE 7.1 ALTERNATIVENAMES FOR ION-EXCLUSION CHROMATOGRAPHY Name
Reference
Ion-exclusion chromatography Ion-chromatography exclusion (ICE) Ion-exclusion partition chromatography Donnan exclusion chromatography Ion-moderatedpartition chromatography
1 2 3 4 5
1%
Chapter 7
Fig. 7.2 Schematic representation of ion-exclusionchromatography for (a) acidic solutes, such as acetic acid and HCI, and (b) basic solutes, such as N H 3 and NaOH.
solute types only; namely, carboxylic acids, inorganic weak acid anions, weak organic bases, and water. It may appear that this restricted group of solutes could diminish the importance of ion-exclusion chromatography in comparison to ion-exchange and ioninteraction chromatography, but it will be demonstrated later in this chapter that ionexclusion chromatography is of major importance in IC. The principles of ion-exclusion chromatography can be illustrated in a schematic manner by considering the chromatographic system to be comprised of three distinct phases. The first of these is the flowing eluent, which passes between the beads of ionexchange resin (i.e. through the interstitial volume). The second zone is the polymeric network of the resin material itself, together with its bound ionic functionalities, whilst the third zone is liquid occluded inside the pores of the resin bead. The polymeric resin can be considered as a semi-permeable, ion-exchange membrane which separates the flowing eluent from the stationary occluded liquid inside the resin [ I , 31. The manner in which solutes are separated in ion-exclusion chromatography is illustrated in Fig. 7.1. We fiist consider the behaviour of two solutes, hydrochloric acid and acetic acid, on a cation-exchange resin using water as the eluent. From Fig. 7.l(a), we see that Cl- cannot penetrate into the occluded liquid phase because it is repelled by the anionic functional groups on the resin, in accordance with the Donnan exclusion effect. The C1-ions therefore remain in the flowing eluent phase and are not retained by the column. On the other hand, the acetic acid is only weakly ionized and exists predominantly as neutral acetic acid molecules, with only a small percentage present as acetate anion. The ionized and neutral acetic acid molecules are in dynamic equilibrium with each other, so that the effective negative charge on the acetic acid is therefore determined by the proportions existing in each form. In a water eluent, this effective charge is quite small and because of this, acetic acid can penetrate the negatively charged resin zone and move into the occluded liquid phase. This results in some degree of retention of acetic acid, so that it is eluted somewhat later than hydrochloric acid. As an historical note, this particular separation was that originally reported in the first publication on ion-exclusion chromatography [ 11. In a similar manner, an anion-exchange resin can be used to separate a weak base (ammonia) from a strong base (NaOH), again using water as eluent. This is illustrated in Fig. 7.l(b), which shows that Na+ is repelled by the cationic functional groups on the
Ion-ExclusionChromatography
197
resin phase and is unretained. On the other hand, ammonia, by virtue of its low degree of ionization and hence its low overall charge, can penetrate into the occluded liquid phase and is therefore retained. Fig. 7.1 suggests that retention of solutes in ion-exclusion chromatography is influenced solely by the charge on the solute. That is, all fully ionized solutes can be expected to be unretained and so be eluted together at the void volume of the column, and the retention of partially ionized solutes can be expected to increase as the degree of ionization decreases. These predictions are not fully supported in practice and it can be shown that other factors also play a role in solute retention. These factors will be discussed in Section 7.4, but at this stage we will make the assumption that solute charge is the dominant parameter in determining retention. 7.2
STATIONARY PHASES
Ion-exclusion chromatography was first performed on large particle size, high capacity, fully functionalized polystyrene-divinylbenzenepolymers. Modem stationary phases are essentially the same materials, but differ in some important respects. Some of the stationary phase parameters which can exert an influence on solute retention are: (i) (ii) (iii) (iv)
Particle size. Ion-exchangecapacity. Resin structure. Degree of resin cross-linking.
As with other chromatographic techniques, the separation efficiency is strongly influenced by the particle size of the column packing material. Modem ion-exclusion chromatography is generally performed on 5 or 10 pn particles, however some of the resins used are relatively soft and the use of small diameter particles means that eluent flow-rates must be kept low to avoid compression of the resin bed. The ion-exchange capacity of a typical ion-exclusion packing material is generally greater than that of packings used for ion-exchange separations in IC. These high capacity materials are preferred so that the number of functional groups on the resin is sufficient to exert an appropriate Donnan exclusion effect. The resin structure is also important, with microporous or gel-type resins being most commonly used (for a description of this type of resin, see Section 3.3). However, there has been a recent trend towards macroporous materials of greater rigidity [ 6 ] . Early studies [3] showed that the degree of cross-linking of the resin exerts a considerable effect on solute retention. Highly cross-linked materials (e.g. those with 812% divinylbenzene) show stronger Donnan exclusion effects than resins of lower crosslinking. This means that both strongly and weakly ionized species show more penetration into thk occluded liquid phase on softer resins of low cross-linking (e.g. those with 2% divinylbenzene). Most commercial ion-exclusion resins have approximately 8% cross-linking, with materials of lower cross-linking being used for the separation of those solutes likely to show higher degrees of ionization under the experimental conditions used (e.g. acids in the pKa range 2-4). Ion-exclusion columns
Chapter 7
198
TABLE 7.2 CHARACTERISTICS OF SOME TYPICAL ION-EXCLUSION COLUMNS Column
Aminex A-5
Aminex HPX-87H Brownlee Polypore H anion-exclusion Dionex HPICE-AS1 Dionex HPICE-AS2 Dionex HPICE-AS3 Dionex HPICE-ASS Dowex 50W-X2 Dowex 50W-X4 Dowex 50W-X12 Hamilton PRP-X300 Hitachi 2613 cation-exchanger Hitachi 2632 anion-exchanger Interaction ORH-801 Interaction ION-310 Sarasep WA 1 SP-Sephadex C-25 TSK-gel SCX Waters Fast Fruit Juice Waters Ion-exclusion Wescan 269-006 exclusion Wescan 269-038 exclusion Wescan 269-051 Yokagawa Elecmc YEW SCS 5-252
linking
Particle size
(a>
(vm)
Cross-
8 8
13
-b
5-8 10 10 25 25 7 38-75 75- 180 38-63 7 18 18 8 8 10 50-100
20 15 15 8 8 9 30
7 7 10 10 10 6
.b
8 8 4 6 2 4 12 -b
8 8 8 8 8
5
Ion-exchange capacity (mequiv/g)
Refa
1.7 1.7
7 8,9 10, 11 12-14 15 16 17 18, 19 20-22 3 6, 23 24-27 28 30-33 34 35 36, 37 38-41 42 43-45 46 47,48 49 50,51
-b
3-5 3-5 3-5 1.5
1.1 0.6 2.1 0.17 4.5 -b -b -b
3.0 4.5 4.2 5.0 5.0 1.4 1.4 1.8 4.5
a These references include some publications in which the indicated columns have been utilized.
Data unavailable. are usually large in comparison to conventional IC columns because a considerable volume of resin material is necessary to provide sufficient occluded liquid phase to permit the separation of solutes of similar size and charge. A typical column would be 30 cm in length, with an internal diameter of 7 mm or more. The characteristics of some representative ion-exclusion packing materials are listed in Table 7.2. Cation-exchange resins are generally used in the H+ form, whilst anion-exchangers are used in the OH- form.
lon-Exchion Chromatography
7.3
199
ELUENTS
7.3.1 Water eluents The eluents used in ion-exclusion chromatography are often very simple in composition. Most of the early work was performed using deionized water as eluent [2, 18, 22,521 and the degree of ionization of the solutes (and hence their retention times) is therefore determined by their pKa or pKb values. The limitations of water as an eluent are that stronger acids or bases show too great a degree of ionization to be retained and the peak shape obtained for solutes which are retained is often poor. This is illustrated in Fig. 7.2(a) for carboxylic acid solutes. In view of the problems observed with peak shape, water is rarely used as an eluent in modem ion-exclusion chromatography, except for the separation of very weakly ionized compounds. An example of such a separation is given in Fig. 7.2(b).
7.3.2
Acid eluents
Following from the original suggestion by Turkelson and Richards [22], it is now common for dilute solutions of strong mineral acids to be employed for the elution of anionic solutes, or dilute solutions of strong bases to be employed for the elution of cationic solutes. In this way, ion-exclusion chromatography can be extended to the separation of relatively strong acids and bases by limiting their degree of ionization. The most commonly used eluents are formed from strong acids, such as sulfuric acid [e.g. 5,7, 10.54, 551, hydrochloric acid [e.g. 13,56-591 and aliphatic sulfonic acids [8,43,45, 60,611. When sulfuric acid is used as the eluent, detection of eluted solutes is generally accomplished by monitoring UV absorbance at low wavelength (200-220 nm). Fig. 7.2(c) shows a typical chromatogram obtained with this eluent. On the other hand, hydrochloric acid is most often used with conductivity detection, after the eluent is passed through a suitable suppressor (see Section 9.5). Aliphatic (and aromatic) sulfonic acids can also be employed for conductivity detection, but because of the relatively low background conductance of these eluents, suppression is not necessary. Weak acids may also be utilized as eluents in ion-exclusion chromatography. Examples include phosphoric acid [62-641, tridecafluoroheptanoic acid (perfluorobutyric acid) 1651, carbonic acid [66, 671, n-butyric acid [19] and benzoic acid [53]. It is interesting to note that eluents of the same pH, when used on the same stationary phase, produce virtually identical chromatograms, regardless of the nature of the acid used. The choice between different eluent acids is therefore governed primarily by the detection method which is to be used. We can also note in passing that organic modifiers, such as methanol, acetonitrile or acetone, are sometimes added to the eluents used in ion-exclusion chromatography. The function of these modifiers is related to the participation of solute adsorption effects in the retention process. This factor is discussed more fully in Section 7.4.3. Some typical capacity factors for carboxylic acids, obtained with various eluents and column types, are illustrated in Fig. 7.3. General trends for the retention of carboxylic acids in ion-exclusion chromatography have been reported [3] and are summarized below:
CO32-
P
loxalic
I Formic
,Lactic Propionic Ektyric
Ja
,Fumoric
Valcric
I
0
1
l
10
l
l
l
l
20 30 Time lminl la)
l
l
60
I
1
50
-
0 6 8 12 16 20 Time fminl fb)
I
I
I
0
2
4
I
I
6 8 Time fmin) Icl
I
I
10
12
11
_i!
U
1-
0
6
8121620
T i m (mid Id1
Fig. 72 Ion-exclusion chromatograms with various eluents. (a) A 5 pm TSK cation-exchange resin was used with water as eluent. Reprinted from [53] with permission. (b) A Dionex HPICE-AS1column was used with water as eluent. Reprinted from [12] with permission. (c) An Interaction ORH-801 column was used with 0.01 N H2SO4 as eluent. Chromatogram courtesy of Interaction (d) A Dionex HPICE-AS1 column was used with 50 mM mannitol as eluent. Reprinted from [12] with permission.
P u
Interaction ORH-801 10 mN H2SO4 35 o c oxalic aconitic maleic oxaloacetic a=ketoglutaric citric isocitric pyruvic tartaric. ascorbic malic lactic succjnic formic acetic
-
1
L
0
c
0
m
2-i
4
Loxalic
aconitic oxaloacetic rnaleic a detoalutaric citric isocitric pyruvic tartaric ascorbic rnalic succinic lactic
-
formic acetic Dropionic
kpropionic
Q
4
Interaction ORH-801 10 mN H2SO4 65 OC
kfumaric
'
I
Bio-Rad HPX-87H 4 rnN H2SO4 5OoC
-
oxalic maleic oxaloacetic B.-ke tog Iuta r ic
F Cp:I:U' "v c \tartaric
Benson OA850 1 mN H s O 4 25 OC a-ketoglutaric malgic -L isocitric
i
\;tl$p
-succinic /formic 'lactic -acetic adipic
-
Dionex HPICE-AS5 Perfluorobutyric acid IDH 2.8)
E
pyruvic
-
-0
oxalic
-1
tartaric orrnic
acetic
L
rnalonic ascorbic lactic rnaleic
propionic -adipic
malic
I
Fig. 7.3 Typical capacity factors for organic acids using ion-exclusion chromatography. Data courtesy of Dionex, Benson, Interaction and Bio-Rad.
I4
Chapter 7
202
(i)
Members of a homologous series, such as the aliphatic carboxylic acids, are eluted in order of increasing molecular weight, decreasing acid strength (i.e. increasing pKa) and decreasing water solubility. Thus. the elution order of low molecular weight carboxylic acids is formic c acetic c propionic. (ii) Dibasic acids are generally eluted earlier than monobasic acids of the same carbon number. For example, oxalic acid is eluted earlier than acetic acid, and malonic acid earlier than propionic acid. (iii) Carboxylic acids with branched structures are eluted earlier than the corresponding straight chain isomer. For example, iso-butyric acid is eluted earlier than n-butyric acid. (iv) A double bond serves to increase the retention of an acid. For example, acrylic acid is eluted after propionic acid.
7.3.3
Complexing eluents
The retention and detection properties of some solutes can be enhanced if a complexing agent is added to the eluent. An example of this approach is the use of a mannitol eluent for the determination of boric acid [12], in which the mannitol serves to complex the boric acid to form a species which is more easily detectable by conductivity measurements than is boric acid alone. Fig. 7.2(d) shows a typical chromatogram obtained with this approach. A further application of complexing eluents is the use of a tetraborate eluent in the determination of formaldehyde [68, 691.
7.4 7.4.1
FACTORS INFLUENCING RETENTION IN ION-EXCLUSION CHROMATOGRAPHY Degree of ionization of the solute
The degree to which the solute is ionized is the most significant factor which determines solute retention. As the solute becomes more ionized, the Donnan exclusion effect increases in magnitude and this leads to decreased retention. When only the Donnan exclusion effect is considered. solute retention (expressed as the retention volume, VR)is given by:
where Vo is the interstitial volume of eluent (i.e. the volume of eluent flowing between the particles of stationary phase), Vi is the internal volume of eluent (i.e. the volume of occluded liquid inside the pores of the stationary phase) and DA is the distribution coefficient for the solute between the interstitial eluent and the occluded liquid. The value of DA is dependent on the degree of ionization of the solute. Fully ionized solutes have DA = 0, due to the total exclusion of such solutes in accordance with the Donnan effect. The retention volume of fully ionized solutes is therefore given by:
Ion-Exclusion Chromatography
203
and we expect all solutes of this type to be eluted at the same retention volume. On the other hand, neutral solutes have DA = 1, since these solutes can distribute freely between the interstitial eluent and the occluded liquid, without influence from the Donnan effect. The retention volume for neutral solutes is therefore given by:
and again we expect all neutral solutes to be eluted at the same retention volume. Solutes which are ionized partially will be eluted at retention volumes intermediate between the two extremes given by eqns. (7.2) and (7.3), with the observed retention volume for a particular solute being dependent on the acid or base dissociation constant of that solute. The above equations are identical in nature to those which are used to describe retention in size-exclusion (gel permeation) chromatography, in which retention volumes fall between the two extremes determined by total exclusion of solutes, and total penetration of solutes.
Dependence of solute retention on pK, The effect of solute charge on retention in ion-exclusion chromatography has been examined for acidic solutes on a strong cation-exchanger (8% cross-linked) in the H+ form, using water as the eluent [27]. Under these conditions, the degree of ionization of the solute is determined solely by the acid dissociation constant (pKa) of the solute. A plot of retention volume versus pKa1 for a range of solutes is given in Fig. 7.4. The retention behaviour depicted in Fig 7.4 is in close accordance with the predictions made above in eqns. (7.1) - (7.3). Strong acids, such as HNO3, H2SO4, HCl, etc., are completely excluded from the stationary phase and are eluted at the same retention volume (12.8 ml). This volume corresponds to the volume of interstitial eluent present in the chromatographic column (Vo). Solutes which exist as neutral species in the water eluent, such as methanol, HCN and H2CO3, are eluted together at a retention volume of 28.5 ml (Vo + Vi). Solutes which are ionized partially in water, such as H3B03, HCOOH and CH3COOH, are eluted at retention volumes between 12.8 and 28.5 ml. There is a strong correlation between pKa1 and VR. Substitution of the measured values of VR,Vo and Vi into eqn. (7.1) permits the calculation of values of DA for each solute. These values are listed in Table 7.3. Inspection of the data in Table 7.3 shows that some values of DA exceed the theoretical maximum of 1.0. This behaviour is evident for propionic acid and H2S and it can be seen that these solutes show anomalous retention volumes in Fig. 7.4. The reasons underlying this will be discussed further below. A similar study of solute retention volumes has been undertaken using a highly cross-linked (30%)cation-exchange column, with acidic eluents [50]. The results of this study are presented in Fig. 7.5, which shows some of the same characteristics as Fig. 7.4, in that a fully ionized solute (H2SO4) defines the lower limit of retention volume, with neutral solutes (methanol and H2CO3) defining the theoretical upper limit of retention volume. A straight line is drawn through the points for oxalic acid, HF and H2CO3, as was done for Fig. 7.4, and it can be seen that many of the solutes tested do not conform to the retention behaviour evident from Fig. 7.4. That is, there is poor correlation
204
Ckpter 7
p Methanol
151-
E-
-vo-
0
5c
"25
I
m (Y
0
Y
n
-5
104
I
.*#.I
-10
Retention volume (mll
Fig. 7.4 Relationshipbetween retention volumes and first dissociationconstants (pKal) for acids on a stationary phase with 8% cross-linking, using water as the eluent. Reprinted from 1271 with permission. TABLE 7.3 DISTRIBUTION COEFFICIENTS FOR ACIDS, CALCULATED FROM THE RETENTION DATA SHOWN IN FIG. 7.4 [27] Acid
DA
0 0 0 0 0 0 0.01 0.06 0.08 0.09 0.11
Acid
DA
0.36
0.43 0.65 0.81 1.10 1.00 1.00 1
.oo
0.98 1.02 1.40
Ion-Excluswn Chromatography
-Vo
10
-
__z(t___
I I
205
Vi
Methanol
I I
Monocarboxylic acid
I
5-
-
Dicarboxylic acid
0
Y
a.
0-
I
I
I I I
''W O L
I I I
I
I
I
I
Fig. 7.5 Relationship between retention volume and first dissociation constant (PKal) for carboxylic acids on a stationary phase with 30% cross-linking,using 1 mM H a 0 4 as eluent. Reprinted from [50] with permission.
between pKa1 and retention volume. This behaviour indicates that retention of many solutes is influenced by parameters other than the degree of ionization of the solute.
Dependence of solute retention on eluent pH When changes in the eluent pH produce a change in the degree of ionization of the solute, we can expect this to cause a change in the retention time of that solute. This behaviour is illustrated in Fig. 7.6,for both mono- and dicarboxylic acids on a highly cross-linked cation-exchanger. Each of the solutes shown has at least one fully ionized carboxylate group at pH 6 and is therefore eluted at a retention volume of Vo (i.e. k' = 0) at this pH. For lower pH values, the expected decrease in retention volume (and hence k') with increasing pH is evident. 7.4.2 Molecular size of the solute
The results presented in the preceding Section show that for some solutes, DA (and hence the retention volume) is somewhat less than that predicted by consideration of charge alone. This behaviour is evident in Fig. 7.5 for the C3' and C4' dicarboxylic acids. It has been suggested by a number of authors [4,36,70-741that size-exclusion effects may contribute to the retention process in ion-exclusion chromatography by restricting the
Chapter 7
206
4r
PH (a) Fig. 7.6 Effect of eluent pH on the capacity factors of (a) monocarboxylic acids and (b) dicarboxylic acids. A 30% cross-linked stationary phase was used with 1 m M Na2HP04 (pH adjusted with oxatic acid) as eluent. Reprinted from [50] with permission.
access of larger solute molecules to the occluded liquid in the pores of the stationary phase. Size-exclusion effects should result in the following retention characteristics: Retention volumes for large, partially ionized solutes should be smaller than expected on the basis of solute charge. (ii) Large, neutral molecules can be expected to show DA values which are less than the theoretical value of 1 .O. (iii) Large, neutral solutes which are eluted at retention volumes less than (Vo + Vj) should be eluted in order of decreasing molecular size. (i)
The retention volumes of the C3' and C4' dicarboxylic acids in Fig. 7.5 are in accordance with (i) above and the retention characteristics described in (ii) and (iii) have been confirmed for neutral lactones [70] and oligosaccharides [ 5 ] . From these results, we can conclude that size-exclusion effects make some contribution to the retention of large solutes.
7.4.3 Hydrophobic interactions between the solute and stationary phase The retention behaviour of the C6'- Cg' dicarboxylic acids and the C3 - C5 monocarboxylic acids in Fig. 7.5 cannot be explained on the basis of solute size and charge. All of these solutes show retention volumes which are larger than those
Ion-Exclusion Chromatography
207
predicted on the basis of solute charge and they are eluted in order of increcising molecular weight (which is the opposite of that expected from size exclusion effects). It is clear that the retention of these solutes is influenced by a third factor, in addition to solute charge and size-exclusion effects. The anomalous retention behaviour described above can be attributed to hydrophobic adsorption of the solutes onto the neutral, unfunctionalized regions of the polymeric stationary phase [50, 53, 751. We have noted previously in the discussion of resin-based ion-exchange columns that many organic molecules and ions show strong reversed-phase interactions with styrene-divinylbenzene packing materials. A plot of the logarithm of capacity factor versus the number of carbon atoms is close to linear for many solute types eluted by ion-exclusion chromatography [5]. This behaviour is similar to that observed in reversed-phase HPLC and gives strong support to the proposal that reversed-phase, hydrophobic interactions play a part in the ion-exclusion retention process. Hydrophobic adsorption effects can be expected to increase in magnitude as the alkyl chain length of the solute is increased, leading to larger retention volumes. This behaviour is evident from Fig. 7.5. We can also note that the size-exclusion effect discussed above will be in competition to the hydrophobic adsorption effect. That is, an increase in alkyl chain length of the solute will cause a decrease in retention under the size-exclusion effect and an increase in retention under the hydrophobic adsorption effect (provided the solute charge is constant). This competition can be used to explain the shape of the retention plot for dicarboxylic acids in Fig. 7.5, where size-exclusion is dominant for the C3' and C i acids, whereas hydrophobic adsorption dominates for the Cg' - C{ acids.
Use of organic modifiers in the eluent The existence of hydrophobic adsorption effects creates the possibility for manipulation of solute retention by adding typical reversed-phase organic modifiers, such as methanol or acetonitrile, to the eluent. A decrease in the retention volume for some solutes can be anticipated and this behaviour has been demonstrated by Tanaka and Fritz [53] using benzoic acid as the eluent. Fig. 7.7(a) shows the effect of the addition of methanol to the eluent and it can be seen that small solute molecules, such as CH3COOH and HCOOH, show little or nn change in retention with increasing methanol, whereas larger solutes, such as valeric acid, show decreased retention. It is evident that the chromatographic resolution of a mixture of all the solutes in Fig. 7.7(a) will decrease with increasing modifier content. A further, opposing effect can result from the addition of an organic modifier to the eluent. When the added modifier has a low dielectric constant (e.g. dioxane), the decreased dielectric constant of the eluent causes an increase in the pKa of the solutes [24]. That is, the solutes become weaker acids and their ionization is therefore suppressed, leading to increased retention. This effect is illustrated in Fig. 7.7(b) for some condensed phosphates, which can be separated only when the organic modifier content in the eluent is high. It can be seen that chromatographic resolution of these solutes increases as dioxane is added. This same effect has been reported for the retention of NH4+ on a strong anion-exchange column [28].
LO
-
PZOf
9 0105~,0,3Methanol concn. % ( v l v ) (a1
Dioxane concn. % (vlv)
(b)
Fig. 7.7 Effect of organic modifiers on solute retention in ion-exclusion chromatography. (a) A 5 pm TSK cation-exchange resin (H+ form) was used with an eluent comprising 0.5 mM benzoic acid and the indicated concentrationsof methanol. Reprinted from [53]with permission. (b) An 18 pm Hitachi 2613 cation-exchangeresin (H+form) was used with an eluent comprising water and the indicated concentrationsof dioxane. Reprinted fmm [24] with permission.
n
88 w
Ion-Exclusion Chromatography
209
Many ion-exclusion columns have definite limits to the amount of organic modifier which can be added to the eluent without causing column damage. It is therefore essential that column specifications be consulted before organic modifiers are used to alter solute retention. In conclusion. we note that the ability to manipulate retention in ion-exclusion chromatography using organic modifiers opens up the possibility of gradient elution. This has been achieved using a sulfonated macroporous resin with a methanol gradient [76], and is illustrated in Fig. 7.8.
7.4.4 Ion-exchange capacity of the stationary phase The effect of the ion-exchange capacity of sulfonated resins on the retention of carboxylic acids has been studied by Lee and Lord 1761. They have synthesized a range of sulfonated macroporous PS-DVB resins in which the degree of functionalization ranges from 0-91% and the retention behaviour of carboxylic acids on these resins is shown in Fig. 7.9. It can be seen that there is an increase in retention for most solutes when the ionexchange capacity is increased from 0 (i.e. for the unfunctionalized resin) to 0.20 mequiv/g (i.e. for a partially functionalized resin). This trend is surprising since an increase in the negative charge density due to sulfonate groups would be expected to
Formic
Propionic
I
0
I
I
4
8
Time ( m i d
1
12
Fig. 7.8 Gradient elution in ion-exclusion chromatography. A Hamilton PRP-X300 column was used with an eluent consisting of a linear gradient (over 5 min) of 6-641methanol in 1 mN H2SO4. Detection was by UV absorbance at 210 nrn Reprinted from [76] with permission.
Chapter 7
210
3
k' 2 1
0 0.0 0.2
0.4 0.6 0.8 1.0 1.2 Exchange capacity (mequiv/g)
Fig. 7.9 Effect of stationary phase ion-exchange capacity on retention of carboxylic acids in ionexclusion chromatography. The eluent was 1 m N H2SO4. S = succinic acid, A = acetic acid, L = lactic acid, C = citric acid, M = malic acid, T = tartaric acid. Reprinted from [76] with permission.
cause a decrease in the retention of the partially ionized solute acids. A suggested explanation is that hydrogen bonding between the neutral solute molecules (which are present in far grcatcr numbers than the ionized solute molecules) and the sulfonic acid groups on the resin may contribute towards solute retention [76]. The presence of some sulfonate groups on the resin could then lead to the observed increase in retention. However, further increases in ion-exchange capacity (beyond 0.20 mequiv/g) show predictable behaviour in that solute retention decreases as the surface charge on the resin increases. It can be concludcd from these results that there is an optimal ion-exchange capacity for each resin type, so that the use of fully functionalized materials is thereforc not always advantageous. 7.4.5
Ionic form of the ion-exchange resin
In the discussion thus far, all of the parameters affecting retention have been related to ion-exclusion chromatography performed either on cation-exchange resins in the Ii+ form, or on anion-exchange resins in the OH- form. We now turn to the effects which arise when the ionic form of the resin is varied. It has been demonstrated [50J that the retention of carboxylic acids on cation-exchangers decreases in the following sequence of ionic forms:
Ion-ExclusionChromatography
211
This sequence is the reverse of that found for the hydrated radii of these cations, except for NH4+, which has the same radius as K+. It has been suggested that the presence of a bound cation of large radius serves to decrease the available hydrophobic surface area of the resin and to alter the values of both Vo and Vi for the column, all of which can result in reduced solute retention [50]. Some ion-exclusion separations are possible only if the column is in a particular form. This is especially true of the separation of monosaccharides on a calcium-form cation-exchanger, for which ligand-exchange involving interaction between calcium ion and the non-bonding orbitals of the sugar oxygen is thought to occur [5].
7.4.6
Temperature
Temperature can affect retention in ion-exclusion chromatography either by alteration of the chromatographic efficiency in the same manner as observed in most forms of chromatography, or by influencing the degree of ionization of the solute. The first of these effects is evidenced by somewhat reduced retention volumes, improved peak shapes and better separations at elevated temperature due to faster mass-transfer characteristics. In addition, the lower solvent viscosity at higher temperatures permits the use of faster flow-rates on gel-type stationary phases which are subject to pressure limitations. The effects of temperature on solute ionization often vary from solute to solute, as can be seen in the first two columns of Fig. 7.3, which differ only in the temperature used. Some solutes show changes in form at elevated temperature and may therefore be eluted at different retention volumes at different temperatures. An example of this behaviour is the increased retention of partially ionized aldonic acids at higher temperature. due to their conversion into neutral lactones [70]. Increased temperature can also cause a change in the dielectric constant of the eluent, especially when an organic modifier is present. This, in turn, will affect the PKa of the solute and hence its retention. An example of the effects of temperature on retention is illustrated in Fig. 7.10, for phosphate, phosphite and hypophosphite ions eluted with an aqueous acetone eluent [26].
7.4.7
Summary
From the discussion thus far in Section 7.4, we can appreciate that numerous factors play a part in the retention process in ion-exclusion chromatography. These factors are listed below in approximate order of importance. The relative influences of these factors have been determined by examining retention data for carboxylic acids, and may therefore differ for other solutes. The degree of ionization of the solute (which is determined by the pKa of the solute, the eluent pH and the organic modifier content of the eluent). (ii) Hydrophobic (reversed-phase) interactions between the solute and the stationary phase (which are dktermined by the nature of the solute and the organic modifier content of the eluent).
(i)
212
Chapter 7
"0.5 Or
i tu H PO32-
o*o10
0
10 20 30 40 50 60 70 80 Column temp. ('C)
Fig. 7.10 Effect of temperature on the retention of inorganic phosphates using ion-exclusion chromatography. A Hitachi 2613 stationary phase was used with 4050 (v/v) acetone-water as eluent. Reprinted from [26] with permission.
(iii) (iv) (v) (vi) (vii)
The molecular size of the solute. The degree of cross-linking of the stationary phase. The temperature at which the separation is performed. The ion-exchange capacity of the stationary phase. Hydrogen-bonding (normal-phase) interactions between the solute and the stationary phase. (viii) The ionic form of the stationary phase.
7.5
RETENTION MODEL FOR ION-EXCLUSION CHROMATOGRAPHY
The fact that many parameters influence retention in ion-exclusion chromatography makes it difficult, if not impossible, to develop a retention model unless certain simplifying assumptions are made. The most important of these assumptions is that the retention process is dominated by a Donnan exclusion equilibrium mechanism. That is, none of the additional retention processes discussed in Section 7.4 above plays any significant role in solute retention. Using this assumption, Glod and Kemula [77] have reported the following derivation of a retention model. We consider a weak acid, HA, which dissociates according to:
Zon-Exclusion Chromatography
HA % H+ + A-
213 (7.4)
Both HA and A- may exist in both the mobile phase and the stationary (resin) phases (designated by the subscripts m and r, respectively). In a thermodynamic Donnan equilibrium, the chemical potentials of the acid on both sides of the membrane are equal, and if activity effects are neglected, the equilibriumcondition assumes the form:
The dissociation constant of the acid, HA, in both phases is given by: (7.6) The electroneutrality conditions in both phases can be written: (7.7) (7.8) where the Concentration of dissociated functional groups in the stationary phase is given by [S03-lr. Now the concentration, c. of the sample at the peak maximum can be written in terms of the total concentration of all forms of the acid, to give:
The distributioncoefficient, DA.is given by: (7.10) From eqns. (7.6), (7.7) and (7.9) we can write: (7.1 1)
The value of [A-Im can be obtained from eqns. (7.6)-(7.9). if we make the following assumption: c cc
[SO;],
This enables us to write the following expression for DA:
(7.12)
Chapter 7
214
1.0
-
- 2.8 -
0
-
-
- 2.L -
0.6DA 0.L
- 2.0
0.8
-
-
"R
- 1.6 -
c
- 1.2
0.2-
-
-
- 0.8
0l
l
l
l
l
t
l
l
l
l
l
l
l
l
l
Fig. 7.11 Plot of the distribution coefficient, DA,as function of log (C/Ka). The solid line is calculated from eqn. (7.14), whilst the points represent experimental values obtained for 33 solutes. LiChrosorb KAT was used as the stationary phase, with water as eluent. Reprinted from [77]with
permission.
DA
=
2c
+ K, - JKZ + 8K,c 2~ - 2Ka
(7.13)
which can be rewritten as:
(7.14)
2-
G
-2
Ka
Eqn. (7.14) shows that DA (and hence VR) depends only on one experimental parameter, the ratio C/Ka. A plot of the theoretical relationship between DA and log (C/Ka) is shown in Fig. 7.11, together with experimental points obtained for 33 solutes (mineral acids, carboxylic acids and nitrophenols). Good agreement is obtained between theory and experiment. The above retention model has been recently extended to remove the requirement to calculate the sample concentration at the peak maximum (c), and to consider the case where a buffer is added to the eluent [78]. An iterative, numerical procedure is required in order to calculate DA for different solute and eluent conditions. Since this is a lengthy and complex process, the extended model will not be considered here.
Ion-Exclusion Chromatography
215
n5
1
I
I
0
5
I
1
15 ‘firnc (min)
I
I
20
25
Fig. 7.12 Analysis of human urine using ion-exclusion chromatography. An Interaction ORH801 column was used with an eluent comprising 10 mN H2SO4 containing 10% methanol. Detection was by spectrophotometryat 254 nm. Solute identities: 1 = oxalic acid, 2 = oxaloacetic acid, 3 = a-ketoisovaleric acid, 4 = ascorbic acid and a-keto-P-methyl-n-valeric acid, 5 = pphenylpyruvic acid, 6 = uric acid, 7 = a-ketobutyric acid, 8 = homoprotocatechuic acid, 9 = unknown, 10 = unknown, 11 = hydroxypheylacetic acid, 12 = p-hydroxyphenyllactic acid, 13 = homovanillic acid. Reprinted from 1321 with permission.
7.6
APPLICATIONS OF ION-EXCLUSION CHROMATOGRAPHY
Ion-exclusion chromatography has many applications in IC, but for the purposes of illustration, we will consider here only three of the more important applications. These are the determination of carboxylic acids, weakly ionized inorganic compounds, and water. Further applications may be found in the Tables comprising Part V of this book. 7.6.1
Carboxylic acids
The separation of carboxylic acids is the most common application of ion-exclusion chromatography. This mode of chromatography is undoubtedly the method of choice for these solutes. When coupled with direct spectrophotometric detection at low wavelength, ion-exclusion chromatography yields excellent separations and relatively
216
Chqpter 7
TABLE 7.4 SOME APPLICATIONS OF THE DETERMINATION OF CARBOXYLIC ACIDS BY IONEXCLUSION CHROMATOGRAPHY Sample Acid rain Antarcticice Blood coffee Fhit juice Milk
Warrnaceuticals Plasma Plating baths Ringers solution Solder fluxes Sugar cane juice Urine Urine Wine Wine a
COlUmn
Dionex HPICE-AS2 Aminex HPX-87H Dionex HPICE-AS1 Dionex HPICE-AS1 Bio-Rad AG5OW-X2 Aminex HPX-87H Dionex HPICE-AS1 Dionex HPICE-AS1 Wescan 269-006 Dionex HPICE-AS1 Waters Ion-Exclusion Aminex HPX-87H Interaction ORH-801 Aminex HPX-87H Intaaction ORH-801 Dionex HPICE-AS1
EluenP 2.0 mM HCl 5.0 mM MSA 10 mM HCl 10 mM HCl 0.75 mv1n-BA 10 mM H2SO4 25 mM 0.5 mMH2CO3 3.2mMHN03 5.4 mM H2CO-J 1.O mM OSA 5 mM H2SO4 10 mM H2SO4 25 mM H2SO4 10 mM H2SO4 2.0 mM OSA
Detection
Detection Ref
methdb
limit
C
0.03 ppm 15 8 79 lppm 56 0.5 ppm 83 1 ppm 5 1 ng 84 2ppm 67 0.5 ppm 89 0.1 ppm 16 50ppb 90 5PPm 9 0.3 ppm 32 0.5 ppm 54 0.5 ppm 30 1PPm 60
Spec (200nm) 6-9 ppb
C C C Spec (210 nm)
RI C C C C
RI Spec (254 nm) Spec (200nm)
Spec (210 nm) C
MSA = methane sulfonic acid, n-BA = n-butyric acid, OSA = octane sulfoNc acid. C = conductivity. RI = refractive index, Spec = spectrophotometry.
clean chromatograms for a wide variety of very complex sample matrices. These samples include biological materials, such as urine [54, 791, tissue [13], blood 1801, plasma [67, 80,811, serum [82] and bile [82]; foods and beverages, such as wine [31,60, 76, 831, coffee [56], milk [5] and cane juice 191; and pharmaceuticals, such as Ringers solution [16, 661, tablets [67] and intravenous solutions [84, 851. Fig. 7.12 shows a chromatogram for a urine sample, obtained without sample pretreatment, and illustrates the relatively clean chromatograms which can be achieved for the above complex samples. Industrial and environmental applications of carboxylic acid determinations are also common and include samples such as acid rain [ 151, diesel exhaust [86], plating baths [87-891 and sewage [Sl]. Table 7.4 lists some of the chromatographic conditions employed in these separations.
7.6.2 Weak inorganic acids and bases Ion-exclusion chromatography has found increasing usage for the determination of weakly ionized inorganic species. It is especially attractive as an adjunct to ion-exchange chromatography since the selectivities obtained by these two techniques are quite different (see Sections 2.1.4 and 7.4). Solutes such as fluoride [43, 911, carbonate [39],
Ion-ErcluswnChromarography
217
A s (V)
32-
[O.Ol AU
-
Anions
L rill
0
1
2
Time (min)
3
0
6
12 18
Time (min) (b)
Fig. 7.13 Determination of inorganic species by ion-exclusion chromatography. (a) A Brownlee Polypore high-speed anionexclusion column was used with 6 mM H2SO4 as eluent. Detection was by amperometry using a Pt electrode at +0.4V versus AdAgCl. The sample was peppers in vinegar. Reprinted from [l 11 with permission. (b) An Aminex HPX-87H column was used with 10 mM H3PO4 as eluent. Detection was by spectrophotomeay at 200 nm. Reprinted from [62]
with permission. cyanide [58], borate [42]. sulfite [47], phosphates [24], nitrite 1921, arsenite 1621. arsenate [62] and ammonium [92] have been determined using this approach. Interference from strongly ionized species is minimal because these solutes are unretained and appear at the column void volume. Ion-exclusion chromatography can therefore readily separate weakly ionized solutes in samples containing high concentrations of ionic species, e.g. seawater and wastewater. Table 7.5 lists some of the applications of this technique in inorganic analysis. Fig 7.13 shows typical chromatograms obtained in two important applications, namely the determination of sulfite (Fig. 7.13(a)) and inorganic arsenic ions (Fig. 7.13(b)). The fact that all strongly ionized solutes are eluted at the void volume in ionexclusion chromatography opens up the possibility of a two-dimensional chromatographic system in which these solutes are collected and then separated on an ion-exchange system. This type of chromatographic system will be discussed in Section 15.4.
218
Chapter 7
TABLE7.5 SOME EXAMPLES OF THE DETERMINATION OF INORGANIC SPECIES BY IONEXCLUSION CHROMATOGRAPHY
Solute(s)a
Sample
column
Eluentb
Demc Ref
Plating baths Mineral water Seawater Fluxes Mouthwash Wastewater Biological fluids Water Water Disinfectant Effluents
Dionex HPICE-AS 1 Aminex HPX-87H Aminex HPX-87H Waters ion-exclusion Wescan 269-006 Cation-exchange resin Dionex HPICE-AS 1 TSK-gel SCX Waters Fruit Juice Waters Fruit juice Dionex HPICE-AS 1 TSK-gel SCX
1 mMH2SO4 lOmMH3P04 5mMH3po4 1.0 mM OSA 3mMH2SO4 40% M e o w 2 0 Water 1 mM benzoic acid 1.25 mM H2SO4 1 mMH2SO4 50mMmannitol 0.1 M fructose
Amp 87 Amp 62 spec 63 C 43 93 C Coul 91 82 C C 39 42 RI 94 RI 12 C C 41
Water Foods Process water Process water Process water Process water
Bio-Rad AG50W-X8 Wescan ion-exclusion Hitachi 2632 Anion-exchange resin Cation-exchange resin Hitachi 3613
C 58 Amp 47 C 28 Coul 92 Spec 92 Spec 95
Hitachi 2613
1 mM HCl 5mMH2SO4 Water 10%MeOH/H20 10%MeOH/H20 0.1 mMH2SO45% MeOH Dioxane-water
Coul
24
Wescan 269-05 1 Dionex HPICE-AS I
5mMH2SO4 5.4mMH2C03
Amp
49 16
C
a DMSO = dimethylsulfoxide.
OSA = mane sulfonic acid. Amp = amperornetry, Spec = spectrophotomeay,C = conductivity, Caul= coulomeay, RI = refractive index
7.6.3
Water
One of the more significant recent developments in ion-exclusion chromatography is the application of the technique to the determination of water. This determination is a very important and frequently encountered analytical problem. Water, being a small, neutral molecule, can be expected to show retention on an ion-exclusion column, provided a suitable non-aqueous eluent is employed. Stevens et al. [20] showed that water can be separated from other sample components by ion-exclusion chromatography on a short column packed with Aminex 50W-X4resin (H+) form, using an eluent comprising methanol and a small amount of HCI, H2SO4 or p-toluenesulfonic acid. Detection was achieved by conductivity measurements, with the water showing decreased conductance relative to that of the eluent. Fig. 7.14(a) shows the chromatogram
219
Ion-ExclusionChromatography
(0)
lime lminl 0 2 1 8
Fig. 7.14 Determination of water using ion-exclusion chromatography. (a) A short (9 x 21 mm) column packed with Aminex 50W-X4 (H+form) resin was used, with a methanolic eluent containing 1.2 mM HCI. Conductivity detection was used. Reprinted from [20] with permission. (b) A 150 x 2.1 mm I.D. column packed with Aminex Q-150s resin in the H+ form was used with 1.0 mM cinnamaldehyde in methanol as eluent. Detection was by spectrophotometry at 300 nm. The sample was 0.184% H20 in dichloroethane. Reprinted from [97] with permission.
obtained. The main drawback with this method was variability in the detector response as the concentration of water in the sample was altered. Fritz and co-workers [96, 971 have reported an alternative ion-exclusion method in which the water is separated using a cation-exchange column in either the Li+ or H+ form, with cinnamaldehyde in methanol as the eluent. Detection is accomplished by spectrophotometric monitoring of the equilibrium existing between cinnamaldehyde and cinnamaldehyde dimethylacetal:
2CH30H + cinnamaldehyde % H 2 0
+ cinnamaldehyde dimethylacetal
(7.15)
This reaction does not occur to any appreciable extent until an acid catalyst is present. The catalyst may be the hydrogen-form cation-exchange resin in the column, or
Chaprer 7
220
an acid can be added to the eluent. After catalysis, the above equilibrium lies well to the right. When water is injected, there is a small shift in the equilibrium towards the formation of cinnamaldehyde. This change can be detected spectrophotometrically at 300 nm. Excellent sensitivity is achieved by this method and the analysis can be completed in less than 2 min. Fig. 7.14(b) shows a typical chromatogram obtained using this approach. Both of the methods depicted in Fig. 7.14 have been applied to a wide range of sample types, with good results. 7.7 1 2 3 4 5
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
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45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
22 1
Woo D.J. and Benson J.R., Am. Lab., January (1984) 50. Interaction Separations#1, March (1989). Gjerde D.T. and Mehra H., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromatography,Vol. 1, Century International, Inc., Franklin, MA, 1989, p. 139. Waki H. and Tokunaga Y..J. Liq. Chromutogr.,5 (1982) 105. Tokunaga Y., Waki H. and Ohashi S., J. Liq. Chromatogr.,5 (1982) 1855. Tanaka K. and Fritz J.S., J. Chromatogr.,409 (1987) 271. Tanaka K. and Fritz J.S., Anal. Chem., 59 (1987) 708. Okada T., Anal. Chem.,60 (1988) 1336. Okada T. and Kuwamoto T., Fres. Z . Anal. Chem., 325 (1986) 683. Jones W.R., Heckenberg A.L. and Jandik P., J. Chromutogr., 366 (1986) 225. Dunn M.H., LC.GC, 7 (1989) 138. Heckenberg A.L., Jones W.R., Wildman WJ., Krol J.A. and Alden P., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromatography,Vol. 1, Century International, Inc., Franklin, MA, 1989, p. 333. Jones W.R., Jandik P. and Swartz M.T., J. Chromatogr.,473 (1989) 171. Jupille T., Burge D. and Togami D., Chromutographia, 16 (1982) 312. Kim H.-J. and Kim Y.-K.,J. FoodSci., 51 (1986) 1360. Kim H.-J. and Kim Y.-K., in Jandik P. and Cassidy R.M. (Eds.). Advances in Ion Chromatography,Vol. 1, Century International, Inc.. Franklin, MA, 1989, p. 391. Nguyen J.H., Kim H.-J. and Gjerde D.T., Am. Lab., May (1988) 122. Kihara K., Rokushika S. and Hatano H., J. Chromutogr., 410 (1987) 103. Murayama T., Kubota T., Hanaoka Y., Rokushika S., Kihara K. and Hatano H., J . Chromatogr.,435 (1988) 417. Manning D.L.and Maskarinec M.P., J. Liq. Chromatogr..6 (1983) 705. Tanaka K. and Fritz J.S., J. Chromutogr., 361 (1986) 151. Buchanan D.N. and Thoene J.G.,Anal. Biochem., 124 (1982) 108. Haginaka J., Wakai J., Yasuda H. and Nomura T., J. Chromatogr., 447 (1988) 373. Dionex Application Note 19. Muller H., Nielinger W. and Horbach A., Angew. Makromol. Chem.,108 (1982) 1. Pohlandt C., NIM Report No. 2107 (1981). Rossiter W.J., Jr., Godette M., Brown P.W. and Galuk K.G., Sol. Energy Mat., 11 (1985) 455.
Dionex Application Note 21. Waters IC Lab. Report No. 241A. Butler E.C.V., J. Chromatogr..450 (1988) 353. Ivey J.P. and Haddad P.R., J. Chromatogr.,391 (1987) 309. 64 Hanai T. and Hubert J.,J. Chromutogr., 316 (1984) 261. 65 Dionex Technical Note 17. 66 Itoh H. and Shinbori Y., Bull. Chem. SOC.Jap., 58 (1985) 3244. 67 Itoh H., Shinbori Y.and Tamura N., Bull. Chem.SOC.Jap., 59 (1986) 997. 68 Kim W.S., Geraci C.L. and Kupel R.E., Am. Ind. Hyg. Assoc. J., 41 (1980) 334. 69 Kim W.S., Geraci C.L., Jr. and Kupel R.E., in Sawicki E. and Mulik J.D.(Eds.), Ion ChromatographicAnulysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 171. 70 Hicks K.B., Lim P.C. and Haas M.J., J. Chromatogr., 319 (1985) 159. 71 Wheaton R.M. and Bauman W.C., Ann. N.Y. Acid. Sci., 45 (1953) 228 60 61 62 63
222 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97
Chapter 7 Asher D.R. and Sirnpson D.W.. J. Phys. Chem.. 60 (1956) 518. Reichenberg D.,Chem. Ind (London), (1956) 958. Reichenberg D. and Wall W.F.. J. Chem. SOC..(1956) 3364. Waki H., Tsuruta K. and Tokunaga Y . , J. Liq. Chromarogr.. 8 (1985) 2105. Lcc D.P. and Lord A.D., LC.GC. 5 (1987) 261. Glod B.K. and Kernula W.. J. Chromurogr.. 366 (1986) 39. Glod B.K., Piasecki A. and Slafiej I., J. Chromurogr., 457 (1988) 43. Rich W.E.. Jr. and Johnson E.L., Eur. Par. Appl., EP. 38720 (1981). Rich W.E., Johnson E.. Lois L.,Stafford B.E., Kabra P.M. and Marton L.J., in Kabra P.M. and Marton L.J. (Eds.), Liquid Chromurographyin Clinical Analysis, Hurnana: Clifton, NJ, 1981, p. 393. Rich W., Johnson E., Lois L., Kabn P., Stafford B. and Marton L.. Clin. Chem, 26 (1980) 1492. Krcling J.R. and DeZwaan J., Anal. Chem., 58 (1986) 3028. Monk P.R. and Hand P.G., Food Technol. Ausr., 36 (1984) 18. Iwinski G. and Jenke D.R., J. Chromutogr., 392 (1987) 397. Waters IC Lab. Report No. 292. Bodek 1. and Menzies K.T.. Chemical. Hour& in the Workplace, ACS Symp. Ser. 149 (1981) 599. Dionex Application Update 110. Haak K.K.. Plat Su$ Finish. 70 (1983) 34. Wescan Application #136a. Waters IC Lab. Report No. 299. Tanaka K., Bunseki Kagaku, 32 (1983) 439. Tanaka K., Bunseki Kagaku, 31 (1982) T106. Wescan Application #90. Waters IC Lab. Report No. 257. Tanaka K. and Ishihara Y . ,Mizu Shod Gijrrrsu. 23 (1982) 855. Fortier N.E. and Fritz J.S., J. Chromarogr.. 462 (1989) 323. Chen J. and Fritz J.S., J. Chromutogr., 482 (1989) 279.
223
Chapter 8 Miscellaneous Separation Methods 8.1
INTRODUCTION
In addition to the mainstream separation methods discussed thus far, we will also consider a number of alternative approaches which can be used for the separation of inorganic ions and carboxylic acids. In the strict sense, none of these methods can be defined accurately as IC, yet the fact that they can be employed for the same solutes as those normally encountered in IC suggests that a brief discussion is merited. The purpose of this discussion will be to indicate the operating principles of each approach and to provide some representative chromatograms in order to facilitate comparison with the ion-exchange, ion-interaction and ion-exclusion methods discussed in Chapters 2-7. Fig. 8.1 provides an overview of the separation methods which will be considered.
Coordination compounds
Reversed-
- phase
HPLC
i -r
Organometallics Carboxylic acids (Ion-suppression)
Miscellaneous separation methods
-
Chelating stationary phases
Chemically bound ligands
L Crown ether stationary phases Anions
chromatography
Cations
Fig. 8.2 Overview of miscellaneous separation methods.
Chapter 8
224
8.2
REVERSED-PHASE LIQUID CHROMATOGRAPHY
Ionic or partially ionized solutes are generally retained only weakly on conventional c18 HPLC stationary phases. We have already seen in Chapter 6 that retention of these solutes can be increased through the use of an ion-interaction reagent added to the eluent. In this Section, we now turn to the use of non-polar stationary phases for the separation of coordination compounds, organometallics and carboxylic acids.
Coordination compounds
8.2.1
A convenient and frequently used method for the determination of metal ions is to first complex the metal ions with a suitable ligand, and to then separate the resultant coordination compounds by conventional reversed-phase or normal-phase HPLC. The complexes formed are often uncharged and this permits separation to be achieved on Cis or silica stationary phases. Several comprehensive reviews on HPLC of coordination compounds are available 11-61, from which it can be seen that there are a number of desirable properties of both the ligand and the chelate. These include [3-51:
(i) (ii)
(iii)
(iv)
(v)
The ligand should form neutral complexes with a large number of metals, using relatively simple preparation methods. The complexes formed should be coordination saturated, since this gives the greatest probability of separation of complexes formed from different metals. Moreover, the ligand should not be too large, so that specific properties of the central metal atom are retained in the coordination complex. The donor atoms in the ligand should have low total electronegativity to minimize adsorption effects on silica-based reversed-phases. Preferred donor atoms are N-. 0- and S-. Separation selectivity increases when ligand substituents do not have large induction or steric effects, and also when electronegative atoms exist in close proximity to the chelate ring. The complexes should have high stability, good detectability and high solubility in non-polar organic solvents.
Many ligands have found application in HPLC separations of metal chelates. These ligands include dithiocarbamates (71, 8-hydroxyquinoline [8, 91, P-diketones [lo]. 4-(2pyridylaz0)-naphthol [ 11],4-(2-pyridylazo)-resinol [ 121, dialkyldithiophosphates[ 13, 141, xanthates [ 151, 2.3-diaminonaphthalene [16], pyrazolones [17] and hydrazones [18. 191. No single ligand is suitable for all metal ions and typically only a few metals are determined in a single chromatographic separation. In most cases, water-insoluble chelates are formed and these must be extracted into a suitable organic solvent, prior to the chromatographic separation step. This sometimes involves extraction with solvents which cannot be injected directly into a reversed-phase HPLC system, so that evaporation and redissolution become necessary. Alternatively, complexes can be formed in-situ by injecting metal ions into a mobile phase which contains the ligand and
Miscellaneous Separation Methods
225
an appropriate buffer [20] or through the use of solid-phase reaction on a suitable precolumn 1141. The stability of the metal complexes is also of great importance because these complexes are generally injected at very low concentrations and are therefore prone to dissociation as they traverse the chromatographic system. This is particularly true of complexes which may undergo ligand-exchange reactions at the surfaces of metallic chromatographic components, such as the injector, interconnecting tubing and the inlet and outlet frits in the column. Kinetic stability is of more importance than thermodynamic stability, since kinetically inert complexes are more likely to pass intact through the chromatographic system. The large volume of literature on HPLC of metal chelates precludes a comprehensive discussion of this topic. Table 8.1 provides a selected listing of some applications of HPLC of metal chelates. To illustrate the utility of this technique, we will focus attention only on the use of dithiocarbamate ligands, since these reflect most of the trends which exist for other ligands.
Dithiocarbamate complexes Alkyldithiocarbamate ligands form complexes with a very wide range of metal ions and therefore offer the potential for separation of a larger number of metal ions than any other ligand. Diethyldithiocarbamate (DEDTC) complexes have been studied extensively and Fig. 8.2 shows a typical separation of metal-DEDTC complexes achieved on a reversed-phase column with a ternary eluent comprising water, methanol and acetonitrile [7]. Two important characteristics are evident from this chromatogram. First, there is a peak due to the ligand oxidation product, bis(diethy1thio-carbamy1)disulfide (usually referred to as disulfiram), which results either from excess ligand in the extracting solution, or from ligand produced by dissociation of labile complexes. Second, the peak shape for Pb(I1) is very poor, due to the low kinetic stability of this complex and the resultant likelihood of dissociation or ligand-exchange reactions. This behaviour occurs with other unstable complexes, such as those of Cd(II), Fe(II1) and Zn(II), and is especially evident when columns with stainless-steel frits are used. The porous nature and high surface areas of these frits provide ideal sites for ligand-exchange reactions to occur between the injected metal complexes and metal ions produced from the oxidation of stainless steel components, especially nickel. These reactions can be minimized either by using columns without porous metallic frits, such as radial compression columns [7], by deactivating the frits with an organosilane [25],or by addition of EDTA to the mobile phase 171. Formation of the chelate It should be stressed that it is the metal chelates which are separated in the above example, rather than the metal ions themselves. Therefore, these chelates must be formed before the sample reaches the analytical column. Chelate formation is usually achieved by buffering the sample and then extracting with a solution of the ligand in a suitable organic solvent. This process can be automated using the apparatus shown in Fig. 8.3, wherein the sample is added to a solution stream of ligand (diethyldithiocarbamate) in acetonitrile [26]. The mixture is then passed, in turn, to a heated
TABLE 8.1 TYPICAL DETERMINATIONS OF METAL CHELATES BY REVERSED-PHASEHPLC Solute(s)
Liganda
Stationary phase
Al(III), In(1LI) As(III), Sb(III), Bi(II1) Cd(II), PWII), Ni(II), Co(III), Hg(I1). Cr(III), Se(IV), Cu(II), Te(W Cd(II), Co(II), Pb(II), Ni(II), Wrr)
PMBP DEDTP DEDTC
BHEDC
BHEDC Oxine HFAA Oxine DEDTC sew) Ti(IV), FeOII), U(VI), V(V)
DAN DAPMP, DAPMT
Detection modec
Detection limitd
Ref
Shim-Pack CLC-ODs ACN-MeOH 10 mM DEDTP in ACN Hypersil ODS Waters C18 Rad-Pak 40:35:25 MeOH-ACNwater
S (290 nm) S (280 nm) S (254 nm)
21-121 ng 2 ng 0.5
17 14 7
O.lmM HEDC in 40:a MeOH-water with 0.1 m~ Zn2+ SUPelCO cl8 25 mM TEA acetate Cg Reversed-phase 1 mM oxine in borate buffer (pH 9) 100% cHZC12 Silica c18 reversed-phase 10 mM oxine, ACN an^ acetate buffer (pH 6) 0.05% DEDTC in waterHypersil ODs MeOH-cHC13 60:40MeOH-water pBondapak C18 Polymer Labs PLRP-S 10%-40% ACN-water gradients
S (300 nm)
7-53 ppb
21
S (255 nm) S (254 nm)
5 PPb
22 23
DCP S (400 nm)
n.s. 100 PI--
24 8
S (350 nm)
0.5 ppm
20
S (254 nm), Fluor S (340 nm)
10 ppb n.s.
16
pBondapak cl8
Mobile phaseb
n.s.
19
PMBP = l-phenyl-3-methyl-4-benzoyl-5-pyrazolone, DEDTP = diethyldithiophosphate, DEDTC = diethyldithiocarbamate, BHEDC = bis(2hydroxyethy1)dithiocarbamate. Oxine = 8-hydroxyquinoline, HFAA = hexafluoroacetylacetone, DAN = 2,3 diaminonaphthalene, DAPMP = 2,6diacetylpyridine bis (N-methylenepyridiniohydrazone),DAPMT = 2,kliacetylpyridine bis(N-methylene-N,N,N,-trimethylammoniohydnuone). MeOH = methanol, ACN = acetonitrile, TEA = tetraethylarmnonium. S = spectrophotometry, Fluor = fluorhetry, DCP = direct current plasma atomic emission spectrometry. n.s = not stated. a
5
00
Miscellaneous Separation Methods
227
I
0.005 Ahsorhancc
Fig. 8.2 Separation of a mixture of diethyldithiocarbamate complexes by reversed-phase HPLC. The mobile phase comprised 40:35:25 methanol-acetonitrile-waterand a Waters c18 Rad-Pak was used as the column. The flow-rate was 2.0 rnl/rnin and the detection wavelength was 254 nm. Peak identities: A-disulfiram, B-Cd(II), C-Pb(II), D-Ni(II), E-Co(III), F-Cr(III), G-Se(IV), HCu(II), I-Hg(II), J-Te(1V). Reprinted from [7] with permission.
reaction coil, a bubble capture device and to the sampling loop of an auto-injector. Excess ligand in the solution is removed by an anion-exchange guard column placed before the c18 analytical column. An alternative method for the formation of the dithiocarbamate complexes is to inject the metal ions into an eluent which contains the ligand. On-column complex formation provides a potentially quick and easy method for multi-element identification and determination. When DEDTC is added to the mobile phase, Cd(II), Pb(II), Co(II), Hg(I1) and Cu(I1) can be separated [20, 271. The chief problem encountered with oncolumn complexation is the high background detector signal produced by the presence of the ligand in the mobile phase. This requires that a selective wavelength be used in the case of spectrophotometric detection, or alternatively, amperometric detection must be used [28]. A further problem is the poor solubility of many dithiocarbamate complexes in typical mobile phases for reversed-phase HPLC, but this may be overcome either by the addition of a small amount of chloroform to the mobile phase [20], or through the use of a ligand which forms water-soluble complexes [21]. An example of the latter approach is the use of bis(2-hydroxyethy1)dithiocarbamate (BHEDTC), in which the
Ckpter 8
228
DEDTC in acetonitrile prewure Sample
Fig. 8.3 Schematic diagram of apparatus for automated pre-column formation of diethyldithiocarbamate (DEDTC)complexes, prior to separation by reversed-phase HPLC. Reprinted from [26] with permission.
hydroxy groups on the ligand cause metal complexes to be water-soluble at low concentrations [22]. Fig. 8.4 compares chromatograms obtained using pre-column (Fig. 8 4 a ) ) and on-column (Fig. 8 4 b ) ) complex formation with BHEDTC. 8.2.2 Organometallic compounds
One of the factors which limits the applicability of HPLC analysis of metal chelates is the necessity to form the chelate itself. This limitation does not exist for many of the organometallic species which are amenable to chromatographic analysis, since these species often occur in a wide range of samples. The more important organometallic species which can be analyzed by HPLC include alkyllead, alkylmercury, alkylarsenic and alkyltin compounds. Of these, the organoarsenic species are the most widely studied. Monomethylarsonate, dimethylarsinate and phenylarsonate (as well as the inorganic ions arsenate and arsenite) are formed by the action of many common yeasts, fungi and bacteria on arsenic present in soils. The high toxicities of these compounds necessitate their accurate determination, especially in water samples. Separation can be accomplished by reved-phase chromatography [29], as well as by anion-exchange [30, 311 or ion-interaction 132, 331 methods. Organomercury compounds, such as methylmercury and ethylmercury, have also been separated by reversed-phase HPLC [34]. In most of the above examples, atomic spectroscopic detection methods have been employed Table 8.2 lists some further applications of the determination of organometallic species by reversed-phase HPLC, and Fig 8.5 shows chromatograms obtained for organomercury and organotin compounds.
% c;.
TABLE 8.2 TYPICALDETERMINATIONS OF ORGANOMETMC SPECIES BY REVERSED-PHASE HPLC Solute(s)
Sample
Alkyl Hg compounds Alkyl Pb compounds Ethyl Sn compounds Fe, Mo carbonyl complexes Methylmucury, ethylmacury Methyl Sn compounds Organo As compounds Organo Hg compounds
n.s. PeIml
Tetraphenyl Pb Transition metal cluster complexes
Stationary phase
Eluent
Detection modes
Detection limit
ICP ICP
Reactionmixtures
HyperSd c18 H m f i c18 Spherisorb S5W ODs ZarbaXCg
ICP
n.s. 35 llppb 35 50-100pg 36 1 PPb 35
Tuna
Waters pic0 Tag
1:2 EtOH-0.05 M NaBr 75% EtOH-water 7030 acetone-pentane 7030 EtOH-water or J3OH-water gradients 6omManrmoniumacetate, 0.005% 2-mer~aptOethan01 6040 acctone-pentane 100% MeOH 4050 MeOH-water + 0.06 M ~ O A + C 0.01% 2-mexaptOethanol 90:lO MeOH-water 7525 MeOH-water
ICP-MS
1 PPb
34
Hydride AAS GFAAS
2-2opg 5 ng 2 PPb
37 38 39
480pg n.s.
40 41
Water
n.s. n.s. Fish
n.s. n.s.
FtI
DP Amp ZeemanAAS
spec
I B = inductively coupled plasma atomic emission spe!cmehy, Hydxide AAS = hydxide generation atomic absorption spectrometry, GFAAS = graphite furnace atomic absorption specaometry,RI = refractive index, MS = mass spectrometry,DP Amp = differential pulse. ampemmefry, Spec = specfrophotomefry. n.s. = not stated.
a
Ref
is
E
8e
I
230
Chapter8
CO2'
0
L
8
l i m e (minl (a)
12
-
0
5 10 lime (minl (bl
15
Fig. 8.4 Comparison of chromatograms obtained using (a) pre-column and (b) on-column formation of bis(2-hydroxyethy1)dithiocarbamate (BHEDTC) complexes. (a) The pre-formed BHEDTC complexes were injected onto a Supelcosil c18 column using an eluent comprising 4060 methanol-water containing 25 mM triethylammonium acetate. Detection was by spectrophotometry at 255 nm. Reprinted from [22]with permission. (b) Metal ions were injected onto a Waters WBondapak cl8 column using an eluent comprising 4050 methanol-water containing 0.1 mM Detection was by spectrophotometry at 300 nm. Reprinted from [21] BHEDTC and 0.1 mM a*+. with permission.
8.2.3
Carboxylic acids (Ion-suppression)
A further strategy which can be employed in the determination of ionizable solutes by reversed-phase HPLC is to suppress the ionization of these solutes by adding a buffer of appropriate pH to the eluent. Retention of the solutes on non-polar stationary phases is therefore increased and separation can then be accomplished. Acidic buffers are used for the separation of weak acids, whilst alkaline buffers are used for the separation of weak bases. This method, often described as "ion-suppression",is generally considered to be applicable only to those weak acids and bases for which the ionization can be suppressed using buffers having pH values in the range 3 - 8 [42]. The reason for this is that C1g stationary phases are unstable outside this pH range. Although this is undoubtedly a major limitation, many weak acids may separated on C18 columns, as demonstrated by Skelly [43]. Restrictions in eluent pH do not apply to the use of non-
23 1
Miscellaneous Separation Methods
MeSn( EtSnCI: Me2SnCI; Me3SnCI MebSr
#Hg+
I I
1
1
1
1
.L 1
1
1
1
0 2 4 6 8 10 12 14 16 Time (min) (a)
1 1 1 T
-
0 1 2 3 Time (min)
0 1 2 3 1 5 Time (min)
(bl
(C 1
Fig. 8.5 Separation of (a) organomercury, (b) methyltin and (c) ethyltin compounds by reversedphase HPLC. (a) A Spherisorb ODS column was used with an eluent comprising 40% methanolwater, 0.06 M NH4OAc (pH 5.5) and 0.01% 2-mercaptoethanol. Detection was by differential pulse amperometry. MeHg+ = methylmercury, EtHg+ = ethylmercury, @Hg+= phenylmercury. Reprinted from [39] with permission. (b) A Spherisorb ODs column was used with 60:40 acetonepentane as the eluent and hydride generation atomic absorption spectrometricdetection. Reprinted from [37] with permission. (c) Conditions as for (b) except that a 70:30 acetone-pentane eluent was used. Reprinted from [37] with permission.
polar polymeric stationary phases, so these materials can therefore be employed for the separation of a wider range of solutes using the ion-suppression technique than is possible with c18 stationary phases. The utility of ion-suppression on polymeric stationary phases can be appreciated by considering the separation of the homologous series of aliphatic carboxylic acids. Neither ion-exchange nor ion-exclusion chromatography yields a complete separation of these species. However, ion-suppression coupled with gradient elution and suppressed conductivity detection enables the separation of butyric through to stearic acid, as illustrated in Fig. 8.6. The gradient used involved an increase in the percentage of organic modifier in the eluent and a decrease in eluent pH. Carboxylic acids more hydrophilic than butyric acid were eluted as a single peak at the column void volume.
232
Chupter8
ityric
Lauric
Capric
I I
0
I
5
I
10
I
15
I
I
20 25 lime (min)
I
30
I
35
1
LO
I
45
Fig. 8.6 Gradient elution ion-suppression chromatogram of carboxylic acids, obtained on a polymeric reversed-phasecolumn. A Dionex MPIC-NS1 column was used with a gradient of 100% eluent A ( t 4 ) to 100% eluent B (t=20 min), with maintenance of eluent B after this time. Eluent A is 24% acetonitrile and 6%methanol in 0.03 mM HC1. Eluent B is 60% acetonitrile and 24% methanol in 0.05 mM HCl. Detection was by suppressed conductivity. The baseline conductance for a blank w e n t has been subtracted in the chromatogram shown. Reprinted from I441 with permission.
8.3
CHELATING STATIONARY PHASES
8.3.1 Chemically-bound ligands Metal ions may be separated on a stationary phase in which a suitable ligand is immobilized onto the stationary phase. Numerous chelating stationary phases have been synthesized using stryene-divinylbenzenepolymers or silica as the support material. In each case, the ligand is chemically bound to the support using an appropriate reaction, such as silylation reactions with silica. Some examples of the ligands which can be bound in this way include iminodiacetate (Chelex 100, Dow Chemical Company), propylene-diaminetetraacetate 1451. P-diketones (e.g. trifluoroacetoacetate [461), 8hydroxyquinoline [47], isothiuronium (481, hydroxamic acids [49], dithiocarbamates (501, phenylhydrazones [51] and dithizone [52]. Solute retention can be manipulated by varying the eluent pH or through the addition of a competing ligand to the eluent. The key factor in the success of the above materials as chromatographic stationary phases is the rate at which the metal-ligand complex is formed and dissociated. Slow rates will lead to poor peak shape in the chromatogram. An evaluation of the literature suggests that most ligands give unacceptably slow rates of reaction, so that chromatograms are typically characterized by very broad peaks. A recent study has compared 9 different chelating stationary phases and has shown that some useful separations can be achieved on dithizone silica gels, as illustrated in Fig. 8.7. It is interesting to note that the same metal ions shown in Fig. 8.7 can be well separated using either ion-exchange or ion-interaction chromatography (e.g. see Figs. 4.17 and 6.3).
Miscellaneous Separation Methotlr
233
Pb2
1 1 1 1 1
0
10 20 Time (mid
Separation of metal ions on a stationary phase formed by binding dithizone functionalities to silica gel. The eluent was 15 mM tartrate at pH 4.0. Detection was by specaophotometry after post-column reaction with 4-(2-pyridylazo)-resinol. Reprinted from [52] with permission.
Fig. 8.7
8.3.2 Crown ether stationary phases
Considerable effort has been expended over recent years on the development of stationary phases in which a crown ether is chemically bound to a suitable support, such as silica or an appropriate polymer. Crown ethers (or cyclic polyethers) are cyclic compounds which possess an inner cavity, generally consisting of oxygen atoms linked by ethylene bridges. Fig. 8.8 shows two examples of these compounds. Crown ethers are non-systematically named according to the total number of atoms in the ring, the number of oxygen atoms and any substituents on the ring. Thus the fiist crown ether in Fig. 8.8 is called 18-crown-6 (total of 18 atoms in the ring, with 6 oxygen atoms), whilst the second is called benzo-18-crown-6 (to indicate the benzene ring substituent). Cryptands are related compounds having two interconnected rings which produce a three dimensional cavity. The final compound in Fig. 8.8 is one such cryptand.
Synthesis of stationary phases Crown ether stationary phases may be synthesized in three ways. The simplest approach is to impregnate a silica particle with a solution of a suitable crown ether in formic acid, followed by cross-linking with formaldehyde [53], and is illustrated schematically for dibenzo-18-crown-6 in Fig. 8.9(a). The resultant material is
234
Chapter 8
18-crown-6
Benzo- 18-crow n-6
O
d
Cryptand-n-decyl-2.2.2 Fig. 8.8 Structures of some cyclic polyethers
Fig. 8.9 Structures of some crown ether stationary phases. (a) The crown ether is coated onto silica and then polymerized. (b) Typical bonding arrangement of a crown ether onto silica. (c) Typical bonding arrangement of a crown ether onto a resin. Reprinted from [53, 581 with permission.
Miscellaneouy Separation Methods
235
stable mechanically and is resistant to hydrolysis. Alternatively, the crown ether can be chemically bound to silica by silyl ether linkages using conventional silylation reactions. An example of the resultant stationary phase structure is shown in Fig. 8.9(b) for benzo18-crown-6. Finally, similar bonding reactions can be performed using resins as the support and a typical stationary phase structure is depicted in Fig. 8.9(c), again using benzo- 18-crown-6 as the ligand. Chromatographic properties The chromatographic utility of crown ether stationary phases rests in their ability to complex cations of a specified size. As the size of the cavity in the crown ether is altered, so too does the selectivity of the stationary phase. For example, Li+, Na+ and K+ are bound preferentially to 12-crown-4, 15-crown-5 and 18-crown-6 stationary phases, respectively, by virtue of the increasing cavity size. However, it is not essential for the solute cation to reside within the cavity since layered structures in which the solute is located between two cavities can also be formed [54]. The bound metal ion imparts a positive charge to the crown ether and this is balanced by a suitable counter anion. The binding of metal ions on crown ether stationary phases is .dependent on the following factors: (i) The size of the cation. (ii) The nature of the associated anion. (iii) The organic modifier content of the eluent. The influence of cation size has been discussed above. The most common elution trend for alkali metal ions on benzo-18-crown-6 stationary phases (which show preference for K+) is for K+ to be eluted last, with the remainder being eluted in order of size. That is, retention usually follows the sequence:
The nature of the associated anion can sometimes exert an influence on retention which dominates all other effects. "Soft" (polarizable) anions such I- and SCN- are more strongly associated with the bound cation than are "hard" anions, such as S04*-and C1-. It has been demonstrated that, when a mixture of anions and cations is injected, the most strongly retained species will be the preferred cation associated with the softest anion [55]. For example, injection of a mixture of Li+, K+,C1-, Br- onto a dibenzo-18-crown6 stationary phase gives four peaks corresponding to LiCI, KCI, LiBr and KBr [56]. The first eluted peak (LiCI) contains the least preferred cation (Li+) and the hardest anion (Cl-), whilst the last eluted peak (KBr) contains the preferred cation (K+) and the softest anion (Br-). Water alone can be used as an eluent in this form of chromatography, but the separations which are obtained are often relatively poor. The reason for this is that water complexes the solute cations and competes effectively with the crown ether. Addition of an organic modifier, such as methanol, to the eluent lowers its polarity and
236
Chapter8
5Br
KBI
Liar
KBr
1
0
I
5
1
I
1
10 15 20 Time (min) (a 1
I
25
-
0 10 20 30 LO Time (min) (b)
Fig. 8.10 Separation of (a) cations and (b) anions on crown ether stationary phases. (a) A paly(benzo-l5-crown-5)-modifiedsilica was used as stationary phase with water as eluent. Detection was by conductivity. Reprinted from [64]with permission. (b) A benzo-18-crown-6 modified silica stationary phase was used with water as eluent. Conductivity detection was used. Reprinted from [65] with permission.
decreases complexation with the solutes. This, in turn, results in increased solute retention and therefore improved separation. However, detection is more simple with a water eluent than with aqueous-organic mixtures, so the former eluent is preferable.
Applications Crown ether stationary phases can be used in two ways. First, a series of alkali metal salts with a common anion can be separated. These salts will be eluted with the cations following the sequence determined by the preference of the particular crown ether used 153, 57-62]. An example of such a separation on silica coated with poly(benzo-t5-crown-5) is shown in Fig. 8.lqa). We note that the cations must be present as their Br- salts for the separation to be reproducible. An alternative application is the separation of anions, using the cation bound to the crown ether as a site for selective retention of anions. The salts will be eluted in the sequence of reducing hardness of the anions [53,56, 57, 59, 60,62, 631. A typical separation by this method is given in Fig. g.lO(b). We again note that the separation is dependent on each anion being present as the K+ salt. If other cations are present, the elution order could vary.
MiscellaneousSeparation Methods
237
The separations shown in Fig. 8.10 are of limited practical applicability because of the need to specify a particular counter-anion or counter-cation for the solute ions. It has been suggested that a sample could be converted to the correct form by passage through a suitable ion-exchange column prior to analysis [54], but no results using this approach have been reported. A more attractive alternative is to use a sufficiently high concentration of the desired counter-cation or anion in the eluent so that the sample counter-ions do not influence solute retention. This approach has been reported for anion determinations using a stationary phase comprising the macrocycle cryptand ndecyl 2.2.2, which has the structure shown in Fig. 8.8, coated onto reversed-phase supports with alkali metal hydroxides as eluents [66, 671. The cryptand is hydrophobically bound to the support in the same manner as used in "permanentcoating" ion-interaction chromatography (see Section 6.3.2). Excellent chromatographic efficiencies were obtained and solute retention was not dependent on the cations present in the sample.
Gradient elution on macrocyclic stationary phases The above-mentioned studies with the cryptand n-decyl 2.2.2 have opened a new possibility for gradient elution of anions. The cation bound to the macrocycle acts as an anion-exchange site for solute anions. The number of bound cations, and hence the anion-exchange capacity of the column, is dependent on the identity of the alkali metal hydroxide used as eluent. The highest anion-exchange capacity is produced with KOH eluents (because of the preferential binding of K+ to the macrocycle), whereas the smallest capacity results when LiOH is used as the eluent. Thus, a gradient in which the eluent is changed from, for example, 30 mM NaOH to 30 mM LiOH will therefore result in a progressive decrease in column ion-exchange capacity. The change in baseline conductivity in such a system will be minimal, especially if a suppressor is employed. Fig. 8.1 1 shows a chromatogram obtained using this method, which has been called "gradient capacity IC" [67]. This method has considerable promise, especially in view of the ease with which the stationary phase can be prepared. 8.4 8.4.1
MICELLE EXCLUSION CHROMATOGRAPHY
Introduction
Many surfactant molecules form micelles in concentrated solution. Micellar chromatography [68, 691 utilizes micellar eluents as a means of improvement of the chromatographic selectivity. We have seen earlier (Section 6.3.2, Fig. 6.4) that micellar eluents can be employed,in ion-interaction chromatography of inorganic anions. The chromatograms obtained show good chromatographic efficiency, but the elution order of solutes (and hence the selectivity of the method) is the same as that for conventional ionexchange chromatography. This can be explained by the fact that in this particular case, the surfactant was strongly adsorbed onto the reversed-phase column which was used, so that ion-exchange was the dominant retention mechanism. On this basis, use of a different type of stationary phase, such as a size-exclusion material, could lead to changes in chromatographic selectivity. Okada [70,711 has investigated this approach
238
Chapter 8
F-
p-
Acct, SC N-
I r
0
I
10
1
20 Time (min)
30 1
LO I
Fig. 8.11 Gradient elution on a macrocyclic stationary phase using variation of the ion-exchange
capacity of the column. A Dionex MPIC-NS1 column was used after conditioning with cryptand-ndecyl-2.2.2. The eluent was a linear gradient (over 20 min) from 30 mM NaOH to 30 mM LiOH. Detection was by suppressed conductivity. Chromatogram courtesy of John D. Lamb. for the separation of inorganic anions and cations. The eluent consists of an aqueousorganic mixture containing a micellar solution of a surfactant of appropriate charge. The micelles in the eluent are excluded from part of the stationary phase, whilst the solute ions partition between the micelle and the bulk solvent in the eluent, and also between the stationary phase and the eluent, This method has been entitled "micelle exclusion chromatography" on the basis of this separation mechanism. 8.4.2
Micelle exclusion chromatography of anions
When anionic solutes are to be separated, the surfactant in the eluent should be positively charged. Hexadecyltrimethylammonium chloride (HTAC) and dodecyltrimethylammonium chloride (DTAC) are therefore suitable surfactants [71]. Use of a size-exclusion stationary phase means that the aggregated surfactant forming the micelle
Miscellaneous Separation Methodr
239 Mnll
L I I'
0
30
Time (rnin) (01
I
LO
r
0
I
10
I
20 lime (rnin)
I
30
1
LO
(bl
Fig. 8.12 Determination of (a) inorganic anions and (b) inorganic cations by micelle exclusion chromatography. (a) An Asahipak GC910H (poly(viny1 alcohol)) size-exclusion column was used with 0.01 M hexadecyltrimethylammonium chloride as eluent. Detection was by spectrophotometry at 210 nm. Reprinted from [70]with permission. (b) The same column as for (a) was used, with a 10 min gradient from 100%eluent A (commencing at t = 10 min) to 100%eluent B. Eluent A was 25 mM sodium dodecyl sulfate (SDS) and 80 m M a-hydroxyisobutyric acid at pH 4.0. Eluent B was 25 mM SDS and 60 mM tartaric acid at pH 4.0.Detection was by spectrophotometry after post-column reaction with 4-(2-pyridylazo)-resorcinol.Reprinted from [71] with permission.
can penetrate only partially into the pores of the stationary phase, whereas the monomeric surfactant can penetrate fully by virtue of its smaller size. The small solute anions can also penetrate into the pores and are therefore retained in this region of the stationary phase by ion-interaction chromatography. Solute anions will also partition between the bulk eluent and the surfactant micelles, and between the bulk eluent and the liquid inside the pores of the column. Retention is therefore based on three distinct processes. Fig. 8.1 2(a) shows a chromatogram obtained using HTAC as the surfactant. The elution order in Fig. 8.12(a) is different from that exhibited by conventional ionexchange or ion-interaction systems, particularly for I- and Br-. The retention order and
Chaprer 8
240
retention times observed in this system are dependent on a number of parameters, including: (i) (ii) (iii) (iv) (v)
The concentration of surfactant The nature of the surfactant used The nature of the surfactant counter-anion The Concentration of added salt The concentration of organic solvent in the eluent
All of these parameters also affect retention in ion-interaction chromatography, which supports the hypothesis that this process plays a significant role in the mechanism of micelle exclusion chromatography. However, the observed chromatographic selectivity shows that there are additional conmbutions to solute retention which are attributable to the partitioning processes described above.
8.4.3 Micelle exclusion chromatography of cations Micelle exclusion chromatography of cations requires an anionic surfactant, such as sodium dodecylsulfate (SDS),and a size-exclusion stationary phase [71]. Again, the surfactant micelles are partially excluded from the pores of the stationary phase, whereas monomeric surfactant and solute cations can penetrate fully. Retention occurs by the same mechanisms outlined above for anions and the retention times are dependent on the same parameters as listed earlier. As with ion-exchange and ion-interaction methods, further control over solute retention can be accomplished through the addition of a complexing agent, such as citrate, to the eluent. Moreover, gradient elution can be achieved by changing the nature of the complexing agent whilst keeping other eluent parameters constant. Fig. 8.12(b) shows a chromatogram obtained using this approach.
8.5
REFERENCES
1 2
Nickless G., J . Chromurogr.. 313 (1985) 129. Krull I.S., in Bemhard M.,BMkman F.E. and S d e r P.J. (Eds.), The fmponance of Chemical "Speciation" in Environmenral Processes, Springer-VerlagBerlin, Heidelberg,
3 4 5 6
Timerbaev A.R., Petrukhin O.M.and Zolotov Yu.A., Fres. 2. Anal. Chem., 327 (1987) 87. Steinbrech B., J. Liq. Chromurogr., 10 (1987) 1. OLaughlin J.W.. J . Liq. Chromurogr.,7 (1984) 127. Machnald J.C., in MacDonald J.C. (Ed.) Inorganic Chromatographic Analysis, WileyInterscience, 1985, p. 285. Hutchins S.R., Haddad P.R. and Dilli S., J. Chromufogr.,252 (1982) 185. Mooney J.P., Meaney M., Smyth M.R., Leonard R.G. and Wallace G.G., Analyst
1986, p. 579.
7 8
(London), 112 (1987) 1555.
9 10 11
12
Heisz O., GfT Fuchz. Lob., 29 (1985) 113. Gierira R.C. and Can P.W., J. Chromurogr.Sci., 20 (1982) 461. Schwedt G. and Rudde R.,Chromographia, 15 (1982) 527. Roston D.A., Anal. Chem., 56 (1984) 241.
Miscellaneous Separation Methodr
13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
51 52 53
241
Cardwell T.J. and Caridi D.. J. Chromatogr., 193 (1980) 53. Irth H., Brouwer E.. De Jong G.J., Brinkman U.A.T. and Frei R.W., J. Chromatogr.,439 (1988) 63. Eggers H. and Russel H.A.. Chromatographia, 17 (1983) 486. Wheeler G.L. and Lott P.F., Microchem. J., 19 (1974) 390. Tong A., Akarna Y. and Tanaka S., J. Chromatogr.478 (1989) 408. Casoli A., Mangia A. and Predieri G., Anal. Chem., 57 (1985) 561.. Main M.V. and Fritz J.S., Anal. Chem., 61 (1989) 1272. Smith R.M., Butt A.M. and Thakur A.. Analyst (London), 110 (1985) 35. Ge H. and Wallace G.G.. Anal. Chem., 60 (1988) 830. King J.N. and Fritz J.S.. Anal. Chem., 59 (1987) 703. Hoffman B.W. and Schwedt G., J. HRC & CC, 5 (1982) 439. Mazzo D.J..Elliott W.G., Uden P.C. and Barnes R.M., Appl. Spectrosc., 38 (1984) 585. Shih Y-T. and Carr P.W., Talanta, 28 (1981) 41 1. Bond A.M., Garrard W.N.C.. Heritage I.G., Majewski T.P.. Wallace G.G., McBumey M.J.P., Crosher E.T. and McLachlan L.S., Anal. Chem., 60 (1988) 1357. Smith R.M. and Yankey L.E., Analyst (London), 107 (1982) 744. Bond A.M., Knight R.W., Reust J.B.. Tucker D.J. and Wallace G.G., Anal. Chim Acta, 182 (1986) 47. Irgolic K.J., Stockton R.A.. Chakraborti D. and Beyer W., Spectrochim Acta, 38B (1983) 437. Fish R.H., Brinkman F.E. and Jewett K.L., Environ. Sci. Technol., 16 (1982) 174. Haswell S.J.. ONiell P. and Bancroft K.C.C.. Talanta, 32 (1985) 69. Lawrence K.L., Rice G.W. and Fassel V.A., Anal. Chem.. 56 (1984) 289. LaFreniere K.E., FasseI V.A., and Eckels D.E., Anal. Chem., 59 (1987) 879. Bushee D.S.. Analyst (London), 113 (1988) 1167. Cast C.H., Kraak J.C., Poppe H. and Maessen F.J.M.. J. Chromatogr.. 185 (1979) 549. Burns D.T., Glockling F. and Harriott M., J. Chromatogr.. 200 (1980) 305. Burns D.T.. Clockling F. and Haniott M..Analyst (London), 106 (1981) 921. Brinkman, F.E., Blair W.R., Jewett K.L. and Iverson W.P.. J. Chromatogr. Sci., 15 (1977) 493. MacCrehan W.A. and Durst R.A., Anal. Chem.. 50 (1978) 2108. Vickrey T.M.. Howell H.E. and Paradise M.T., Anal. Chem., 51 (1979) 1880. Enos C.T., Geoffroy G.L. and Risby T.H., J. Chromatogr. Sci.. 15 (1977) 83. Bidlingmeyer B.A.. J. Chromatogr. Sci., 18 (1980) 525. Skelly N.E., J. Chromatogr.,250 (1982) 134. Slingsby R.W., J. Chromatogr.. 371 (1986) 373. Moyers E.M. and Fritz J.S., AnaL Chem., 49 (1977) 418. DenBleyker K.T., Arbogast J.K. and Sweet T.R., Chromatographia,8 (1983) 449. Jezorek J.R and Freiser J.R., Anal. Chem., 5 1 (1979) 366. Koster G. and Schmuckler G., Anal. Chim.Acta, 38 (1967) 179. Phillips R.J. and Fritz J.S.. Anal. Chim Acta. 121 (1980) 225. Raja R.. Am. Lab., 14 (1982) 35. Simonzadeh N. and Schilt A.A., Talunta, 35 (1988) 187. Faltynski K.H. and Jezorek J.R.. Chromatographia,22 (1986) 5. Blasius E. and Janzen K.P., Israel J. Chem. 26 (1985) 25.
242 54
55
56 57 58 59 60 61 62 63
64 65 66 67 68 69 70 71
Chapter 8 Dasgupta P.K., in Tarter J.G. (Ed.), Ion Chromurogruphy, Marcel Dekker, Inc.. New York, NY, 1987, p. 191. Blasius E., Janzen K-P., Klein W., Nguyen V.B., Nguyen-Tien T., Pfeiffer R., Scholten G.,Simon H., Stockemer H. and Touissant A.. J . Chromutogr.. 201 (1980) 147. Igawa M., Saito K., Tsukamoto J. and Tanaka M., A d . Chem., 53 (1981) 1942. Lauth M. and Gramain P.,J. Liq. Chromutogr., 8 (1985) 2403. Iwachido T., Naito H., Samukawa F., Ishimaru K. and Toei K., Bull. Chem. SOC.Jap., 59 (1986) 1475. Igawa M., Ito I. and Tanaka M., Bumeki Kuguku, 29 (1980) 580. Nakajima M., Kimura K. and Shono T., Bull. Chem. SOC.Jup., 56 (1983) 3052. Nakajima M., Kimura K., Hayata E. and Shono T., J. Liq. Chromatogr., 7 (1984) 21 15. Blasius E., Janzen K-P.. Simon H. and Zender J., Fres. 2.A d . Chem., 320 (1985) 435. Igawa M., Saito K., Tanaka M. and Yamabe T., Bumeki Kuguku, 32 (1983) E137. Nakajima M., Kimura K. and Shono T., Anal. Chem., 55 (1983) 463. Lauth M. and Gramain P.,J. Chromutogr., 395 (1987) 153. Lamb J.D. and Drake P.A., J. Chromatogr.,482 (1989) 367. Lamb J.D., Drake P.A. and Wooley K.E., 2nd Int. lon Chromutogr. Forum, Boston, September (1989). Armstrong D.W. and Nome F., Anal. Chem., 53 (1981) 1662. Armstrong D.W. and Fendler J.H., Biochim. Biophys. Acta, 478 (1977) 74. Okada T., Anal. Chem., 60 (1988) 1511. Okada T., Anal. Chem., 60 (1988) 21 16.
Part III Detection Methods
244
Principles
AC bridge Bipolar pulse 4-electrode cell Differential detection Packed column Hollow-fibre Packed-fibre Micromembrane Electrochemical Post-suppressors
and :ONDUCTIVITY $Cellscircuitry Chap 9 ) Suppressors
Principles
E-
Modes
Amperometry Coulometry Polarography Direct F n p t
Electrodes
$ :a Reference i;
Types
2LECTROCHEMICAL Chap 10)
z-. z-, z-
Cells
DETECTION METHODS
Thin-layer
Fl?l;:tpugh
-
Principles
Ion-selective electrodes Coated-wire Metallic copper Direct Indirect
Indicator electrodes POTENTIOMETRY (Chap 11)
Modes Cells
Spectrophotometry
UV visualization
?:z$.t
Refractive index SPECTROSCOPY (Chap 12)
.POST-COLUMN REACTION (Chap 13)
Atomic spectroscopy -C
fluorescence Indirect fluorescence Indirect phosphorescence Atomic absorption Atomic emission
Types
Solution PCR Packed-bed PCR
Photoluminescence
Hardware
'M"iz:ichambers
Anions
Phosphorus oxoanions Ferric perchlorate
Cations
L Organics Schematic overview of Pan 111.
+Direct
- = -
~ ~ , n a z o
245
Chapter 9 Co n d u c tiv ity D e tec tion 9.1
INTRODUCTION
The first report on the use of conductivity as a method for the detection of ions in the eluate from a chromatographic column can be credited to James et al. in 1951 [l]. The technique was used sporadically over the next 25 years or so, being seen as too insensitive for all but preparative scale chromatography. Conductivity detection gained popularity only after the introduction of specialized IC columns and post-column signal enhancement methods, the former of which have been described in Chapter 3 and the latter of which will be discussed later in this Chapter. Conductivity detection has two major advantages for inorganic ion analysis. The first of these advantages is that all ions are electrically conducting, so that conductivity detection should be universal in response, and the second is that conductivity detectors are relatively simple to construct and operate. Conductivity detection is very widely employed in IC and applications are therefore abundant. A survey of the literature (Appendix A) shows that this form of detection is employed in approximately 55% of publications dealing with IC and is utilized with ion-exchange, ion-interaction and ionexclusion separation methods. Conductivity detection will be discussed here in terms of the principles of its operation, the modes of detection employed, cell designs, postcolumn signal enhancement (suppression), performance characteristics of conductivity detectors, and applications.
9.2 9.2.1
PRINCIPLES OF CONDUCTIVITY DETECTION Nature of electrical conductivity of electrolyte solutions
A solution of an electrolyte will conduct an electrical current if two electrodes are inserted into the solution and a potential is applied across the electrodes. The more current conducted by the solution, the higher is its electrical conductivity. Ohm's Law applies, so that:
V = IR
(9.1)
where V is the applied potential (volts), I is the current (amps) and R is the resistance (ohms), The reesislance of the solution will be determined by several factors, including the concentration and type of ionic species in the solution, and the temperature. The
Chapter 9
246
conductance of the solution, G, (having the units of Siemens, which are represented by the symbol S) is given by the reciprocal of resistance. Note that the older units for conductance are reciprocal ohms (mhos).
G = -1
R
(9.2)
The resistiviry (p). in units of ohms.cm, is given by:
p=- A R
L
(9.3)
where A is the cross-sectional area (cm2) of the electrodes inserted into the solution, and L (cm) is the distance between them, The inverse of resistivity is the conductivity, k, which has units of S.cm-', and is also often referred to as the specific conductance.
The specific conductance of an electrolyte will vary with concentration, so it is necessary to introduce a further term to facilitate the comparison of electrolytes. This term is the equivalent conductance (A) and has the units S.cm2equiv-'. A is given by:
where C is the concentration of the electrolyte, expressed as equivalents per lo00 em3 of solution. We can now combine the geometrical characteristics of the cell (i.e. A and L) into a single term, called the cell constant, K, which has units of cm-'. K is given by:
K = -L
A
(9.6)
This enables us to rewrite eqn. (9.4) as:
k=GK
(9.7)
so that the conductance can now be defined as:
G=- AC 1000 K If G is expressed in pS, eqn. (9.8) becomes:
(9.8)
Conductivity Detection
G =
247
1OOOAC -- A C K 10-~K
(9.9)
The conductance of a solution can be seen to be proportional to the equivalent conductance of the electrolyte and its concentration. In addition, the lower the cell constant, the higher the conductance. Looking at the factors which influence K (eqn. (9.6)), we see that conductance is increased for cells with large surface area electrodes which are close together. The equivalent conductance is subject to activity effects (particularly ion-ion interactions) and therefore shows variation with increasing concentration of the electrolyte solution. lon-pairs may form as a result of ion-ion interactions, leading to a decrease in the effective conductance of the solution. The relationship between G and C therefore becomes non-linear at high ionic strength. If the value of equivalent conductance for an infinitely dilute solution of the electrolyte is given by ho, then the decrease in equivalent conductance observed at higher concentrations is given by the Debye-Huckel-Onsager equation: 1
A = 120 - (A + BAJ (C)?
(9.10)
where A is a constant dependent on the dielectric constant, temperature and viscosity of the solvent, and B accounts for the relaxation effect resulting from asymmetrical charge distribution arising from movement of the solvated ions under the influence of the applied potential. This latter effect serves to retard the movement of ions and causes a decrease in the effective conductance. Eqn. (9.10) applies only when the electrolyte concentration is significantly higher than that commonly encountered in IC. Thus, conductances in IC can be calculated within acceptable error using A0 (limiting equivalent Conductance) values by substitution in eqn. (9.9), which is more correctly written as: (9.11)
It must be appreciated that the conductance of the solution results from bofh the anions and cations of the electrolyte. We must therefore calculate conductance using values for the limiting equivalent ionic conductances (h) of the individual anions and cations in solution. Eqn. (9.1 1) can now be rewritten as:
G =
(h, + hJ
c
(9.12)
K where A+ and Ic are the limiting equivalent ionic conductances of the cationic and anionic components of the electrolyte, respectively. Typical limiting equivalent ionic conductances for common solute and eluent species used in IC are listed in Table 9.1. It
Chapter 9
248 TABLE9.1
LIMITING EQUIVALENT IONIC CONDUCTANCES OF SOME IONS IN AQUEOUS SOLUTION AT 25 OC [2]
OH Fe(CN)64Fe(CN)63m42-
CN' so42-
BrI-
a' Cz042'
m2NQm430 4 -
SCN-
clo3ciaate3-
HCOO F HWcH3cooPhthalate? c2HscooBenzoate'
198 111 101 85 82 80 78 77 76 74 72 71 69 67 66 65 56 55 54 45
41 38 36 32
H30+
Rb+ cs+
K+ NH4+ Pb2+ Fe3+ Ba2'
A ? ca2+
Sr*+ CH3NH3'
350 78 77 74 73 71 68
64 61 60 59 58
cu2+ cd2+
55
Fe2+ Mg2+
54
co2+
7h2+
Na+ Phenylethylammonium+ Li+ N(c2H5>4+ Benzyhmmonium+ Methylpyridinium+
54 53 53 53 50 40
39 33 32 30
can be noted that H30+ is a very strongly conducting cation, showing a 5 value about 5 times higher than other cations. Similarly, OH- is the most strongly conducting anion, having a A value which is 2-3 times greater than most other anions. As an example of the practical application of eqn. (9.12), we can calculate the conductance of an eluent comprising 5 mM LiOH, measured in a cell with a cell constant of 10 cm-l. From Table 9.1 we note that the limiting equivalent ionic conductances of Li+ and OH- are 39 and 198 S.cm2 equiv-', respectively. Substitution into eqn. (9.12) gives: (9.13)
ConductiviryDetection
249
9.2.2 Factors influencing limiting equivalent ionic conductance
The limiting equivalent ionic conductance of an ion is given by eqn. (9.14) [3]: (9.14)
where e is the electronic charge, F is the Faraday constant, Z j is the number of charges on the ion, q is the viscosity, and r is the ionic radius. An increase in the number of charges on an ion does not necessarily lead to an increase in Xi, since an inverse proportionality exists between and the ionic radius, r. Thus, large ions with multiple charges can exhibit the same Li value as smaller, singly charged ions. This has important ramifications for IC in that eluent ions of multiple charge are powerful competing ions, but may have inappropriately high background conductances unless the ionic radius is large. When the combined attributes of high eluotropic strength and low background conductance are required, large ions with multiple charge, such as phthalate, citrate and trimesate, are therefore suitable. 9.2.3
Theory of conductivity response
The operating principles of conductivity detection in IC can best be illustrated by reference to ion-exchange as the separation mode, and by considering the conductance of a typical eluent prior to and during the elution of a solute ion. For simplicity, we will consider only anion-exchange at the present time, but the detector response equations which will be developed are equally applicable to cation exchange, provided the obvious amendments are made. The response equations developed here below follow the method of Fritz et al. [4-61. We first calculate the background conductance of the eluent; i.e. the conductance which results when onZy the eluent is flowing through a fully equilibrated ion-exchange column and thence to the cell of a conductivity detector. It is assumed that the eluent contains a single species which may be only partially dissociated into the ions E+and E-. Eqn. (9.12) can be modified slightly to give: (9.15)
where CE is the total concentration of the eluent and IE is the fraction of eluent species which is present in the ionic form, i.e. as E-.We note in passing that the cell constant can be readily determined in practice by measuring the conductance of a solution containing species with known limiting equivalent ionic conductances ( e . g . KCl, for which 5 = 74 and A- = 76 S.cm2.equiv-l at 25OC). The values of conductance calculated from eqn. (9.15) are, of course, only approximate because values of limiting ionic equivalent conductance are used and the cell constant determined by the above-mentioned method is of limited accuracy. We must now examine the concentration changes which occur when a solute anion is eluted from the column through which the above eluent flows. In the anion-exchange
Chapter 9
250
C
.-0
C
Eluent
E! C 3 C
C
Solute 1 Eluent flow
-
0
0
(a 1 C
.-0
Eluent
C
E
C
C
Eluent f Low
-
s C 0
0
(b)
Fig. 9.1 Schematic representation of ion concentrations on the column and in the eluent in ion-
exchange chromatography. (a) shows concentrations immediately after injection, whilst (b) shows concentrations during peak elution. Reprinted From [7] with permission. system under consideration, we can write the following simple equilibrium:
Si
+ E;
f S;
+ Em
(9.16)
where the subscripts m and r refer to the mobile and resin phases, respectively, and S- is the solute ion. When the solute is injected at the head of the equilibrated column, S - ions are bound to the column and E- ions are released. The concentration of E- in the sample volume therefore depends on the concentration of S - in the sample. A band of E- of concentration greater or less (depending on the sample concentration) than that of the bulk eluent is produced and, to a first approximation, moves through the column to produce the characteristic solvent peak observed in IC. This solvent peak can therefore be positive or negative (Fig. 9.1(a)). Eluent ions, which continue to be pumped through the column, compete with S- for the ion-exchange sites, causing the sample ions to move down the column at a speed determined by their selectivity coefficients. The total ion concentration in the column and eluent remains constant throughout this elution process, as illustrated schematically in Fig. 9.l(b). The eluted S - ions therefore displace an equivalent number of E- ions from the eluent. If the concentration of solute passing through the detector is given by Cs and the degree of ionization of the solute is Is. then the eluent concentration in the detector cell during sample elution is given by: (9.17)
Conductivity Detection
25 1
The conductance measured in the cell at .this time originates from the eluent and solute anions, together with the eluent cations which are required to maintain electroneutrality. The solute cations need not be considered since these are unretained on the anion-exchange column used in this example. The conductance during solute elution is therefore given by: (9.18) The change in conductance (AG) which accompanies the elution of the solute can be obtained by subtracting the background conductance (eqn. (9.15)) from the conductance during solute elution (eqn. (9.18)) to give: (9.19) The solute concentration during elution will follow an approximately Gaussian profile and the detector response will therefore change in a similar manner. Eqn. (9.19) is applicable to all forms of ion-exchange TC and shows that the detector response depends on solute concentration, the limiting equivalent ionic conductances of the eluent and solute anions, and the degree of ionization of solute. The last of these parameters is governed by the eluent pH (since the eluent is generally well buffered) and eqn. (9.19) suggests that weak acid anions such as acetate, fluoride, formate, phosphate, oxalate, etc., should show appreciable decreases in sensitivity as the eluent pH is lowered; this behaviour has been observed in practice [ 5 ] . However, many of the solutes determined by IC are fully ionized in aqueous solution, so eqn. (9.19) generally takes the form:
AG =
(As- - AE-)cs
(9.20)
10-~K This equation shows that if a conductivity detector is used to monitor the effluent from an ion-exchange column, the signal observed for an eluted solute is proportional to the solute concentration and to the difference in limiting equivalent ionic conductances between the eluent and solute ions. A similar relationship (eqn. (9.21)) can be derived for the conductimetric detection of cations after ion-exchange separation [8]. (9.21) where S+ and E+ are the solute and eluent cations, respectively. Eqns. (9.20) and (9.21) are fundamental to the understanding of the function of conductivity detection and can be used as a basis for discussing the various modes of conductivity detection employed in IC. as outlined in the next Section.
Chapter 9
252
-
x
GC 0
CI
u
3 '0
c
0
0 c
C
0,
Solute
d
0
.-> 3
(A,)
CT P,
0)
.-cC
z
Eluent 2
3
(AEZ)
Schematic representation of indirect (negative peak) and direct (positive peak) conductivity detection using an eluent competing ion with high (eluent 1) or low (eluent 2) limiting equivalent ionic conductance. Fig. 9.2
9.3
MODES OF CONDUCTIVITY DETECTION
9.3.1 Direct and indirect conductivity detection From eqns. (9.20) and (9.21), it is clear that sensitive detection can result as long as there is a considerable difference in the limiting equivalent ionic conductances of the solute and eluent ions. This difference can be positive or negative, depending on whether the eluent ion is strongly or weakly conducting. It should be remembered here that the response equations developed are applicable to any ion-exchange system in that they describe the conductance changes occurring at the column outlet. When no further chemical change is imposed prior to passage of the eluent-solute mixture to the conductivity detector, then eqns. (9.20) and (9.21) give an accurate description of the conductivity detector signal. This situation exists for non-suppressed IC,but not for suppressed IC. It will therefore be necessary to extend the above response equations to cover the case of suppressed IC and this extension is provided in Section 9.5. If the limiting equivalent ionic conductance of the eluent ion is low, then an increase in conductance occurs when the solute enters the detection cell. In general, we can define this detection mode as direct, where the solute has a higher value of the measured property than does the eluent ion. Alternatively, an eluent ion with a high limiting equivalent ionic conductance can be employed and a decrease in conductance would occur when the solute enters the detection cell. Once again, we can generally define this type of detection as indirect, where the solute has a lower value of the measured property than does the eluent ion. These detection modes are illustrated schematically in Fig. 9.2, which shows that positive peaks occur with direct detection and negative peaks result with indirect detection.
253
ConductivityDetection
K4
r 0
,
5
1
10 l i m e (min)
I
1
15
20
1
0
1
1
4
1
1
1
I
0 12 Time (min)
I
r'6
1
Fig. 9.3 Direct conductivity detection of (a) anions and (b) cations. (a) A TSK-GELEX-620 anion-exchange column was used with 1.3 mM Na2Bq07 - 5.8 mM H3B03 - 1.4 mM potassium gluconate (pH 8.5) in water-acetonitrile (88:12). Reprinted from [12] with permission. (b) A Waters IC Pak C column was used with 0.15 mM benzylamine (pH 7.14) as eluent. Reprinted from [1I] with permission. Direct conductivity detection is used for most IC methods involving the separation of anions. Eluents for non-suppressed IC, formed from salts such as potassium hydrogen phthalate [9] or sodium benzoate [lo] contain competing anions with moderately low limiting equivalent ionic conductances (see Table 9.1). Similarly, direct conductivity detection of cations is possible with eluents formed from organic bases [8, 111. Chromatograms showing direct conductivity detection of anions and cations are given in Fig. 9.3. Indirect conductivity detection can be applied to anions using hydroxide eluents [ 131, and to cations using mineral acid eluents [ 111. Examples of these separations are given in Fig. 9.4. Each of the eluents used in these examples provides excellent detector response because of the very high limiting equivalent ionic conductances of the hydroxide and hydrogen ions, which act as the competing ions.
254
Chapter 9
(b) Timelmin)
0
L
8
12
16 I
I
Fig. 9.4 Indirect conductivity detection of (a) anions and (b) cations. (a) A TSK-GEL 620 SA column was used with 2 mM KOH as eluent. Reprinted from [ 131 with permission. (b) A Waters IC Pak C column was used with 2 mM HNO3 as eluent. Reprinted from [l 11 with permission.
Simultaneous direct and indirect conductivity detection
The possibility also exists for two eluent ions to contribute simultaneously to the detector response. This may occur when the eluent contains two competing ions, provided that the concentrations and selectivity coefficients of the two ions are not such that only one dominates analyte elution. When both eluent ions participate in solute elution and both have similar valucs of limiting equivalent ionic conductance, there is little change in detection sensitivity compared to the use of each eluent alone. However, when one eluent ion produces direct conductivity dctection and the other produces indirect detection, then the overall detector response will be much lower than for the individual eluents. This behaviour has been reported [81 for cation elution with aromatic base eluents operated at acidic pH. Solute elution is accomplished jointly by the aromatic base cation (low h+, direct detection) and H3O+ (high A+, indirect detection). The net outcome is that solutes give negative or positive peaks (or even no peak at all), depending on the relative influences of the two eluent ions. Similar behaviour can be expected for anion separations using aromatic acid elucnts at high pH. 9.3.2
Magnitude of conductance change on sample elution
An estimate can be made of the conductance change occurring on elution of a typical solute in IC. If we assume that a 10 ppm CI- solution is injected and that a fivefold dilution of the sample occurs during passage of the solute through the
255
Conductivity Detection
chromatographic column, then the concentration of C1- in the detection cell is 2 ppm (5.63 x M). Assuming a cell constant of 10 cm-' for the conductivity detector, then the conductance change on sample elution, together with the background conductance of the eluent can be calculated. These parameters are shown in Table 9.2, for typical anionexchange eluents. It is seen readily that the conductance changes which occur are very small indeed and this places stringent requirements on the conductivity detectors which are applicable to IC. TABLE 9.2
CONDUCTANCE CHANGE ON ELUTION OF 10PPM CHLORIDE WITH VARIOUS ELUENTS
Eluent
Background conductance (PS)
Conductance change (AG)
1 mM KBza, pH 7 1 mM K2Pb, pH 7 1 mM KOH
10.6 18.4 27.2
0.25
Direct Direct
1.7 rnM NaHC03, 1.8 mM Nap203
48.1
0.13 -0.69 O.OlC, 0.09d
Detection mode
(ClS 1
Indirect Direct
a Bz = benzoate anion.
P = phthalate di-anion. Calculated assuming that CI' is eluted only by COs2-. Calculated assuming that C1' is eluted equally by HCO3- and C032-.
9.4 9.4.1
ELECTRONIC CIRCUITRY AND CELL DESIGN FOR CONDUCTIVITY DETECTION Introduction
The measurement of conductivity in liquids is performed by the application of an electric potential between two electrodes. Under the influence of this field, anions move towards the anode, whilst cations move towards the cathode. The current which results is dependent on the applied potential and also on the nature and concentration of ionic species present in the solution. The limiting equivalent ionic conductances listed in Table 9.1 show that different ionic species have different ionic mobilities in solution. I: is usual for the potential to be applied in a pulsed or sinusoidal manner, i.e. as an alternating current. The amplitude of this potential must be such that thermal effects or chemical reactions at the electrode surfaces (generally Faradaic oxidation or reduction) do not occur to any significant extent. At the same time, the amplitude should be as high as possible, since the detection signal i s directly related to the applied potential. The suitable range of frequencies for the applied potential is from approximately 50 Hz to 10,000 Hz [3]. As the frequency of the applied potential increases, ions gradually become unable to transfer all the energy imposed on them by the field into translational
Chapter 9
256
Fig. 9.5 AC conductance bridge (a) and equivalent circuit of the conductance cell in full (b) and simplified (c) forms. R, is the solution resistance, GJis the double layer capacitance at the electrode surface, ZFis the Faradaic impedance, Rc is the contact and lead resistance, Cc is the contact and lead capacitance, Ci is the inter-electrode capacitance, C, is the combined parallel capacitance, and C, is the combined series capacitance. Reprinted from [161 with permission.
motion. Other phenomena such as distortion of the counterionic atmosphere or the formation of dipoles also become predominant [14].
9.4.2 AC conductance bridge The simplest alternating current conductance circuit is based on the Wheatstone bridge design. Fig. 9.5(a) shows the circuit used. There are several problems involved in the balancing of such a bridge circuit and these arise from phenomena occumng within the cell itself. The more important of these phenomena are [15]:
A double-layer of ions can arise due to the attraction of a thin layer of ions to the electrode surface, which in turn causes a more diffuse layer of ions of opposite charge to collect in the adjacent solution. That is, local ordering of ions at the electrode surfaces occurs. This double-layer acts as a capacitor (at each electrode) capable of storing charge and its structure is greatly influenced by interactions of the solvent with the solute ions, and by the nature of the electrode surface. Faradaic (or electrolytic) processes may occur at the electrodes. These processes act to partially short-circuit the double-layer and behave as impedances. Concentration polarization may occur if Faradaic removal of ions at the electrodes occurs at a faster rate than they can be supplied by diffusion from the bulk electrolyte.
ConductivityDetection
out
257
In
Fig. 9.6 Simple two-electrode, flow-through conductance cell using annular electrodes. El and E2 are the measuring electrodes, which are separated by FTFE isolators (designated by Ins in the Figure). The modulated voltage is applied to electrode El. The internal cell volume is approximately 3 p1. Reprinted from [17] with permission. (iii) The sample liquid in the conductance cell itself imposes a resistance to the motion of ions because they must overcome frictional forces. (iv) Whilst imposition of an alternating field can largely eliminate the Faradaic effects discussed in (ii) above, this can itself introduce further complications. The electrical components themselves show frequency dependence which must be considered. The above factors can be incorporated into an equivalent circuit for the conductance cell, such as that shown in Fig. 9.5(b). This circuit includes the resistance of the solution (Rx),the double layer capacitance at each electrode ( c d ) , the Faradaic impedance at each electrode (ZF), the resistance and capacitance of the contacts and leads in the circuit (& and Cc), and the inter-electrode capacitance (Cj). It is convenient to simplify the equivalent circuit by combining the series capacitances and the parallel capacitances, as shown in Fig. 9.5(c). This type of conductance cell has found very widespread use and is employed in many conductivity detectors used for IC. A simple, low-volume, two-electrode, flowthrough cell design for this type of detector can be made using annular stainless steel electrodes. Fig. 9.6 shows a typical cell of this type. Conductivity cells with internal volumes of less than 0.5 pl have been reported for use with microcolumn IC [lS, 191 and a combined conductivity-amperometry cell of 15 nl internal volume has also been described [20].
258
Chopter 9
BPD
I I'
II
Cell A H S u D p r e s s o H Cell
B
b
Waste
Fig. 9.7 Experimental arrangement for a comparison of the sensitivities of bipolar-pulse (BPD) and conventional AC conductance bridge (ACCB) conductivity detectors. Cell A was taken from a Wescan 219-900 detector, cell B is from a Dionex model 10 [23].
9.4.3
Bipolar-pulse circuitry
The drawbacks of the conventional conductance bridge include slow response to rapidly changing conductances, inapplicability to solutions of high conductance, and the existence of the series and parallel capacitances. One approach to overcoming these drawbacks is the bipolar-pulse technique, in which two consecutive voltage pulses of equal amplitude and pulse width, but of opposite polarity, are applied to the cell. The current is measured precisely at the end of the second pulse [21, 221. The advantage of this approach is that parallel and series capacitances of the equivalent circuit of the conductance cell no longer influence the cell current. Thus, measurement of this current cnables calculation of the electrolytic conductance, free of Faradaic and other distortions. The first application of bipolar-pulse conductivity measurement in IC was reported by Keller [23], who used a home-made bipolar-pulse detector prior to the suppressor in a suppressed IC system and a commercial AC conductance bridge-type of detector after the suppressor. The arrangement of chromatographic components in this experiment is shown in Fig. 9.7. The sensitivity of the bipolar-pulse detector in the non-suppressed mode exceeded that of the conventional detector monitoring the suppressed eluent. Bipolar-pulse conductivity detectors for IC are available commercially from a number of manufacturers. 9.4.4
Four-electrode conductance measurement
The simplest practical arrangement for measurement of the resistance of the sample solution (and hence its conductance) is through the use of two electrodes, as discussed above. However, i t has also been noted that this measurement is complicated by the presence of contact resistances and other extraneous phenomena. An alternative experimental arrangement is the four-contact mode, where leads and contacts supplying the current are separated from those probing the voltage drop across the sample solution. This arrangement is illustrated in Fig. 9.8. Since only an infinitesimal current (12) now flows through the probing circuit, the potential drop corresponding to the contact resistances R,I and Rc2 can, for all practical purposes, be neglected. This gives a more accurate measurement of the unknown (solution) resistance, Xu. Pig. 9.9 shows a simplified experimental set-up for fourcontact measurement of resistance and conductance in static solutions (24).
ConductivityDetection
259
I
Voltmeter
Source of current
Fig. 9.8 Circuitry for four-contact measurement of resistance (and hence conductance). Ru is the unknown resistance, &l and &2 are contact resistances. Note that I p - 1 2 .
The same approach can be applied to flowing solutions using a series of annular electrodes. Fig. 9.10 shows a four-electrode, flow-through conductivity cell of low internal volume (4 pl) [25]. A variable AC generator (ACG) controlled by a differential amplifier (DA1) supplies a sinusoidal current to the outer two electrodes of the cell (El, E4). The two inner electrodes (E2, E3) are connected to the input terminals of DA1, which forces the current generator to maintain a constant potential drop between E2 and E3. The current flow through E2 and E3 is negligible, so Faradaic impedances, contact resistances, etc., are largely eliminated. As DA1 forces the ACG to vary the current flow in response to changes in conductance between E2 and E3, the potential across the range resistor (RR) will also vary. These changes are converted by the differential amplifier (DA2) to an appropriate analog signal, which is measured by the voltmeter V1.
Fig. 9.9 Apparatus for four-contact measurement of resistance and conductance. Reprinted from [24] with permission.
260
Chapter 9 ACG
out
CH
CH
Fig. 9.20 Four-electrode conductimetric cell. See text for an explanation of the symbols.
Reprinted from [25] with permission. In this manner, the conductivity of the liquid flowing through the cell is measured. The cell holder (CH)is connected to ground and also through a resistor (R)to the output of DA2. The cell holder thus serves as a guard electrode against capacitance effects to ground [26].
9.4.5
Differential conductivity detection
A dual-cell configuration, in which the column effluent passes through a sample cell and eluent is passed through a reference cell (Fig. 9.11(a)), has been suggested for differential conductivity detection [27, 281. Subtraction of the signal arising in the reference cell from that in the sample cell should permit cancellation of the background conductance of the eluent itself and should also provide a means to compensate for temperature fluctuations. When applied to eluents with conductance of 30 pS or less, this approach permits full-scale recording of a conductance difference between the eluent and column effluent of 0.1 pS, with low baseline drift. This, in turn, permits the detection of common anions at ppb levels. Differential conductivity detection has also
Column effluent
te
Refercnc eluent fl
Column eMuent
Waste Reference cell (a)
Reference cell (b)
Fig. 9.22 (a) Two-cell configuration for differential conductivity detection. (b) Cell configuration for first derivative conductivity detection. Reprinted from [30]with pennission.
ConductivityDetection
261
I
--
0
2
L
lime (min) (aI
6
0
2
4
lime (mint
6
(bl
Fig. 9.12 Use of first derivative conductivity detection for identification of co-eluted peaks. Chromatogram (a) shows the direct conductivity signal for two co-eluted solutes, whilst chromatogram (b) shows the first derivative signal for the same injection. Reprinted from [30]with
permission. been applied to the simultaneous detection of anions and cations when eluents of relatively high conductance are used [29]. If a dual-cell conductivity detector is modified so that the column effluent passes through the sample cell, a delay loop, and finally returns to the reference cell, a first derivative conductivity signal results [30, 311. Fig. 9.11(b) shows the flow-path used. The first derivative signal can be used to identify coelution of peaks (Fig. 9.12) or to improve the apparent separation of poorly resolved peaks. 9.5
SUPPRESSORS IN IC
9.5.1 Function of the suppressor Table 9.2 shows that direct conductivity detection of anions in HC03-/C032-eluents is quite insensitive because of the limiting equivalent ionic conductances of these ions. However, this situation can be improved greatly by exchanging hydrogen ions for the cations in the eluent, prior to the measurement of conductance. The HCO3- and C032ions are thereby converted into weakly conducting HzCO3, and the background
262
Chapter 9
conductance of the eluent is said to be suppressed. The most simple means of accomplishing eluent suppression is to pass the eluent through a cation-exchange column in the hydrogen form. As an example of the reactions which take place in such a suppressor column, consider the case of CI-ions as solute and an eluent composed of NaHC03. The eluent reaction in the suppressor is given by eqn. (9.22), whilst the reaction of the solute is given by eqn. (9.23). Resin-H++ Na'HCO; Resin-H+
% Resin-Na+
+ Na+ + C1'
+ 3C0,
% Resin-Na+
+ H+ + C1-
(9.22) (9.23)
The combined result of these processes is that the eluent conductance is decreased greatly, whilst the conductance of the sample is increased by virtue of the replacement of sodium ions (A+= 50 S.cm*.equiv-') with hydrogen ions (k+= 350 S.cm2.equiv-'). The detectability of the solute is therefore enhanced. A similar procedure can be applied to cation-exchange, where the suppressor is now an anion-exchange column in the OH- form and operates by the addition of OH- ions to the eluent. As an example, consider the suppressor reactions of Na+ ions eluted with a HCI eluent, as shown in eqns. (9.24) and (9.25).
+ Resin-C1' + H 2 0
Resin-OH-
+ H+ + CI-
Resin-OH-
+ Na+ + C1- %
Resin-Cl-
+ Na' + OH
(9.24) (9.25)
The eluent is converted into water, whilst the conductance of the sample band is increased due to replacement of CI- ion (h. = 76 S.cm2.equiv-') by OH- ions (h. = 198 S.cm2.equiv-1). It is important to note that suppression reactions are not limited to acid-base reactions, such as those shown in the above examples. Indeed, any post-column reaction which results in a reduction of the background conductance of the eluent can be classified as a suppression reaction. We have seen earlier in Table 4.6 some other suitable suppressor reactions. However, the ensuing discussion of suppressor design and performance will be restricted to those which employ acid-base reactions, since these are the most widely used.
9.5.2
Packed-column suppressors
The original suppressor device [32] was an ion-exchange column in the H+ or OHform, which operated according to the mechanism discussed above. To enable the suppressor to be used for as long a time as possible, high capacity ion-exchange materials were used. The suppressor was regenerated periodically by passing an appropriate solution (such as 0.25 N H2SO4 for the H+ form suppressor) through the column to displace the accumulated eluent cations. Packed-column suppressors suffer from a
263
ConductivityDetection HNOl
I
'a
so;
+
v
HNO,
Fig. 9.13 Ion-exclusion processes occumng in the resin bead of a hydrogen form packed-column suppressor. It can be noted that H N e , produced in the suppressor by protonation of the solute N02-, is retained on the suppressor resin by ion-exclusion. This process will occur for any solute which is the conjugate base of a weak acid. Ionized solutes (e.g. NO33 are not retained.
number of disadvantages which include: (i)
The limited total ion-exchange capacity of the packing material in the suppressor means that periodical regeneration is necessary. (ii) Significant broadening of the solute band occurs in the suppressor, resulting in loss of chromatographic efficiency. (iii) Solute ions which are protonated easily may show variable retention in the suppressor column due to ion-exclusion effects. This process is illustrated in Fig. 9.13 for nitrite. The nitrite will not become protonated until it reaches an active zone of the suppressor (i.e. where unexchanged H+ ions exist), so penetration of HNO2 into the resin will not commence until this time. Clearly, the length of active suppressor (which is a variable quantity) will determine the elution time for this species. (iv) Some ions undergo chemical reaction in the suppressor. For example, nitrite has been shown to undergo oxidation reactions in the suppressor [33]. The "water dip" resulting from elution of the sample solvent (usually water) (v) often hampers trace analysis of those solute ions which are eluted early in the chromatogram.
Chapter9
264 Silicone rubber
Centre tube
Eluent + inlet
+ Eluent
outlet
+
fibres
Regenerant outlet
4
Regenerant inlet
Fig. 9.14 Schematic drawing of a hollow-fibre suppressor. Reprinted from [34] with permission.
Despite these disadvantages, packed column suppressors provided the foundation on which suppressed IC was built. These suppressors were in use from 1975-1981,at which time the first of the membrane-based suppressors was introduced.
9.5.3
Hollow-fibre membrane suppressors
Hollow fibres constructed from polymeric ion-exchange material provided an alternative means for eluent suppression. These fibres may be prepared by introducing a liquid monomer into the walls of a porous fibre, after which the monomer is polymerized to give a cross-linked ion-exchange polymer. The eluent is passed through the interior of the fibre, whilst a suitable regenerant (or scavenger) solution passes over the exterior of the fibre, usually in a countercurrent direction.
Operating principle The first hollow-fibre suppressor was reported by Stevens et al. [34] and consisted of a collection of sulfonated cation-exchange fibres, with which sulfuric acid was used as the regenerant. The physical design of this suppressor is shown in Fig. 9.14 and its mode of operation with a HC03-/C032- eluent is illustrated schematically in Fig. 9.15(a). The operation of a cation suppressor, with which HCI is used as eluent and barium hydroxide as regenerant, is shown in Fig. 9.15(b). In the suppression of anion-exchange eluents (Fig 9.15(a)), there is a transfer of sodium ions out of the eluent stream, with concomitant transfer of hydrogen ions into the eluent stream. Cation-exchange eluents (Fig. 9.15(b)) are suppressed by transfer of CI- out of the eluent and OH- into the eluent. The overall results of these processes are identical to those achieved by the column suppressor, but the hollow-fibre design has the chief advantages of greatly reduced bandbroadening and continuous regeneration [35,36]. It has also been noted that suppression efficiency is increased at elevated temperatures because of improved diffusion of ions both in solution and through the membrane [35,371. The operation of the hollow-fibre suppressor with a typical eluent (e.g. tetrabutylammonium hydroxide, TBA+OH-)used for ion-interaction separation of anions is illustrated in Fig. 9.15(c), in which sulfuric acid is employed as the regenerant. It can be seen that the suppression process converts the eluent species to water. Similarly, suppression of a typical eluent (HCI) for ion-exclusion chromatography of carboxylic acids is illusaated in Fig. 9.15(d), in which TBA+OH-is used as the regenerant. In this case, the eluent species are converted in the suppressor to the weakly conducting TBA+CI-salt.
ELUENT
ELUENT
Ha
TBA+OH-
TBA)zSO,
'4
I ~
+
TBA+OIT ~
Anion-exchange hollow-fibre
TBA+CI- TBA+OA' Catton-exchange
llpa hollow-fibre
Fig. 9.15 Schematic operation of a hollow-fibre suppressor for eluents used with (a) anion-exchange (b) cation-exchange, (c) ion-interaction and (d) ion-exclusion separation modes.
h,
E
Chapter 9
266
Fig. 9.16 Zig-zag packing of beads inside a packed-fibre membrane. Reprinted from [40] with
permission.
Regen era n ts The regenerant used with hollow-fibre suppressors must be selected with care. The regenerant must supply the ion required for effective eluent suppression (e.g. H+ or OH-), but must not contaminate the eluent with any other ion. The chief potential contaminant is the regenerant ion having the same charge sign as that of the solute. This ion is theoretically prevented from entering the eluent stream as a result of Donnan exclusion by the ion-exchange functionality on the hollow-fibre. However, this repulsive effect may not totally prevent penetration of the forbidden ion, especially when the regenerant concentration is high. It has been demonstrated that large ions have a smaller penetration rate through the membrane [35,361. Thus, dodecylbenzenesulfonic acid is a useful regenerant for an anion-exchange suppressor [38] because of the low penetration rate by dodecylbenzenesulfonate ions through the anionic fibre. Packed-fibre suppressors The hollow-fibre must have a very narrow bore to permit a sufficient rate of transfer of ions. A bore diameter of less than 400 pm is desirable, but tubing of this type is not readily available. For this reason, some type of inert packing is usually employed inside the tube. This may be a nylon filament (such as fishing line) [3Y] or polystyrene beads [40,41]. in the first case, insertion of a nylon filament permits coiling the hollow-fibre into a helix so as to increase suppression efficiency. In the second case, the beads used have a slightly larger diameter than the bore radius of the hollow-fibre,
n
Packed-f ib re
n
Regenerant outlet
Eluent outlet
Eluent inlet
Regenerant inlet Rod (28 x 100 rnm)
Cylinder (34 ID x 100 rnrn)
Fig. 9.17 Design of a packed-fibresuppressor. Reprinted from [41] with permission.
Conductivity Detection
267
p so&
I
0
1
1
2
1
1
1
1
L 6 Time (min)
1
1
8
1
1
1
10
(01
1
0
1
1
2
1
1
1
1
i 6 lime (min)
1
1
8
1
1
1
10
fb)
Fig 9.18 Chromatograms obtained with (a) a hollow-fibre and (b) a packed-fibre suppressor. Note the improved resolution and sharper peaks for early eluted solutes. Reprinted from [41] with
permission.
so that the beads become arranged in a zig-zag pattern as shown in Fig. 9.16. This configuration reduces the dead volume inside the suppressor and provides turbulent flow, which improves the transfer of ions across the membrane. The packed-fibre is then wound around a central support, as shown in Fig. 9.17. The improvement in chromatographic efficiency resulting from the use of an inert packing inside the hollowfibre is evident from Fig. 9.18. The packed-bead fibre suppressor has been the subject of many innovative suggestions designed to increase its suppression efficiency. These have included replacing the inert beads with ion-exchange resin beads, packing beads around the exterior of the fibre to provide mechanical support, altering the shape of the packing beads and application of an ultrasonic field to the system. The effects of such approaches have been discussed in some detail by Dasgupta [42], who in the same article also provides an excellent treatment of practical aspects of the preparation of fibre suppressors, such as packing procedures and methods for joining fibres to conventional PTFE tubing. 9.5.4
Micromembrane suppressor
Hollow-fibre suppressors had provided a solution to the problem of frequent regeneration which existed for packed suppressors, but introduced a new limitation relating to the ion-exchange capacity of the fibre. The small internal diameters of the fibres employed in these suppressors meant that the surface area of the fibre available
268
Chqpter 9
Eluent Regenerant
t I
out
in
Regenerant Eluent
+I
out
I
in
\ \
I
1
Regeneran t
Regenera n t out
in
Ion-exchange membrane Ion-exchange screen Gasket material
n
Fig. 9.19 Design of a micromembrane suppressor. Adapted from [43].
for exchange between eluent and regenerant ions was low, and this, in turn, led to low ionexchange capacity. The eluent concentrations suitable for use with such a suppressor were therefore restricted. In addition, the hollow-fibres were intolerant towards some organic solvents and ion-interaction reagents. These factors provided stimulus for the development of an improved suppressor which was capable of continuous regeneration, possessed high ion-exchange capacity, and showed minimal band-broadening effects.
Design of the micromembrane suppressor The micromembrane suppressor is able to meet the above requirements by replacing the ion-exchange tubing used in the hollow-fibre suppressor design with flat sheets of membrane [43].The surface area available for exchange between eluent and regenerant ions is thereby increased greatly in comparison to the hollow-fibre suppressor, and so is the ion-exchange capacity. The design of a micromembrane suppressor is shown in Fig. 9.19. The eluent passes through a central chamber which has ion-exchange membrane sheets as the upper and lower surfaces. Regenerant flows in a countercurrent direction over the outer surfaces of both of these membranes. Mesh screens constructed from a polymeric ion-exchange material are inserted into the eluent cavity and also into the cavities which house the flowing regenerant solution. The entire device is constructed in
Conductivity Detection
269
a sandwich layer configuration with gaskets being used to define the desired flow-paths. The volume of the eluent chamber is very small (40pl [43]), so band-broadening is minimal.
Operating principles The micromembrane suppressor operates on the same principles as the hollow-fibre suppressor, as illustrated in Fig. 9.15. That is, regenerant ions (H+ or OH-) are transferred into the eluent across the membrane, whilst eluent counter-ions pass simultaneously into the regenerant. However, unlike the hollow-fibre suppressor, which relies on diffusion to transport the appropriate ions to the membrane surface, the micromembrane suppressor utilizes high-capacity ion-exchange screens to perform this task. These screens promote ion transport in two ways. First, the three-dimensional over-and-under square weave pattern of the screens causes a disruption to laminar eluent flow and directs eluent flow to the membrane surface. Second, the ion-exchange sites on the screen enable site-to-site transport of the desired ions to the membrane. The latter mechanism of ion transport plays an increasingly important role as the eluent passes from the suppressor inlet towards the outlet. During this passage, the suppressor reaction advances towards completion and there are relatively fewer eluent ions remaining to react. The transport of these residual eluent ions to the membrane surface is greatly facilitated by the ion-exchange screens. It is useful at this stage to describe suppressor performance in terms of dynamic capacity. That is, the number of microequivalents of eluent which can be suppressed per unit time. Clearly, there must be a limit to the eluent concentration which can be suppressed by a membrane of a specified surface area. It has been shown that the dynamic capacity of the micromembrane suppressor increases with increasing ionexchange capacity of the screen material [43].Dynamic capacity also increases with the concentration of the regenerant solution, but practical limits exist above which there is some penetration of the forbidden regenerant ion through the membrane into the eluent. It is often convenient to use a regenerant concentration considerably less than that at which penetration of the forbidden ion occurs, but to increase the flow of the regenerant in order to increase dynamic capacity. When 12.5 mM sulfuric acid is used as regenerant at a flow-rate of 10 ml/min, the dynamic capacity of the micromembrane suppressor exceeds 100 pequiv/min [a]. This means that an eluent of 100 mM (i.e. 100 pequiv/ml) NaOH, flowing at 1 ml/min, can be suppressed effectively. We can note that in this example, the flux of H+ions in the regenerant is 250 pequiv/min, which exceeds the flux of OH- ions in the eluent by a factor of 2.5. This factor is close to the minimum required for effective operation of the micromembrane suppressor. Advantages of the micromembrane suppressor The micromembrane suppressor combines the advantages of other suppression devices and at the same time, eliminates their drawbacks. These advantages can be summarized as: (i)
Small internal volume, leading to minimal band-broadening effects and hence low detection limits.
Chapter 9
270
(ii) Continuous regeneration. (iii) High dynamic suppression capacity which can be varied readily by changing the nature, concentration and flow-rate of the regenerant. (iv) Suitable for gradient elution with appropriate eluents. (v) Resistant to many organic solvents and ion-interaction reagents. (vi) A wider choice of eluent types is possible because of the high dynamic suppression capacities which can be achieved.
9.5.5
Post-suppressors
Post-suppressors are devices inserted between the suppressor and the detector for the purpose of further lowering of the background conductance of the eluent in suppressed anion-exchange IC systems. When a carbonate buffer is used as eluent, the fully suppressed eluent contains HzCO3, which is dissociated partially in aqueous solution (to form H+ and HCO3-) and so contributes to the background conductance. Moreover, the HCO3- present in the suppressed eluent also causes a reduction in the conductance of a sample peak by reaction with the H+ ions which accompany the elution of the anion of a strong acid. This effect is discussed in more detail in Section 9.6.1. A further disadvantage of the formation of H2CO3 in the suppressed eluent is that this species diffuses through the suppressor membrane at a rate which is dependent on pressure, and this may lead to the formation of pump pulsations in the detector baseline [42]. It is therefore desirable if H2CO3 can be removed from the suppressed eluent.
Design of post-suppressors A convenient way to remove H2CO3 is to pass the suppressed eluent through a length of tubing which is permeable to carbon dioxide [45]. Quantitative removal of dissolved C02 from the suppressed eluent will result in the background conductance of the eluent approaching that of pure water. Post-suppressors constructed of porous PTFE tubing have been shown to remove 90% of dissolved COz. This removal was attained only with the aid of some mechanical means of improving mass transport to the membrane wall, such as inserting a knotted nylon fishing line or a twisted stainless steel wire into the PTFE tubing. An air current around the outside of the post-suppressor tubing is used to cany the C02 away after diffusion through the tubing. Leaking of the eluent through the tubing does not occur at moderate pressure because of the hydrophobic nature of the tubing material. The design of this post-suppressor is illustrated in Fig. 9.20. Improved post-suppression can be achieved through the use of silicone rubber tubing (which is highly permeable to C02. but is non-porous) and by passing a heated solution of KOH over the outside of the tubing in order to remove the C02 as it diffuses from the eluent 1461. Shintani and Dasgupta 1471 have developed a specialized postsuppressor membrane tubing consisting of porous polypropylene coated with silicone rubber, with a nylon monofilament inserted into the interior of the tubing. Transport of C 0 2 to the silicone rubber layer is very rapid because of the porous nature of the underlying polypropylene membrane. This post-suppressor tubing was shown to be superior to the use of silicone rubber tubing or uncoated porous polypropylene tubing.
Conductiviry Detection
From
+
suppressor
27 1
To detector
4
L--=+;r Ascarite Fig. 9.20 Schematic design of a post-suppressor. Reprinted from [45] with permission.
Advantages of post-suppression The advantages which may be attained through the use of post-suppressors include: Decreased baseline noise resulting from pump pulsations. Decreased baseline conductance. Virtual elimination of the water and carbonate dips from the final chromatogram. Enhanced detectability of eluted anions since there is no loss of conductance signal due to reaction of H+ ions in the analyte band with H2CO3 in the suppressed eluent. Gradient elution using carbonate buffers as eluents is possible with postsuppressors of suitable efficiency. 9.5.6
Other post-column signal enhancing devices
Electrochemical suppressor A type of micromembrane suppressor in which transfer of ions across the membrane is enhanced with an electric field has been suggested as a more efficient design in comparison to those suppressors in which ion transport is accomplished by diffusion alone [48]. This suppressor is illustrated in Fig. 9.21(a). The eluent flow compartment consists of a chamber packed with cation-exchange resin, with cationexchange membranes forming the chamber walls. Two chambers containing 0.1 M sulfuric acid are located on the outer surfaces of these membranes and platinum-plated titanium electrodes are housed in each of these chambers. Application of a suitable voltage (about 4 V) to give a cell current of 50 mA creates an electric field, under the influence of which H+ from the regenerant moves rapidly into the eluent compartment
Chqter 9
272 ELUENT: NazCOf, NaHC(?I Anodc
SAMPLE: Na* +
cT
:atbode
Cation-excbange bollow-fibre Cation-exchange
0 resin
t
Steel tubing (4 Cation-exebange membrane Cation-excbange membrane Pt wire (+)
Regenerant flow-paths Eluent flow-path
(b) Fig. 9.21 Schematic designs of electrochemical suppressors. Adapted from [48,49].
and Na+ from the eluent migrates towards the cathode. Using this process, the complete suppression of 5 mM Na2C03 eluent at a flow-rate of 2 ml/min can be accomplished. It should be noted that this suppression efficiency is achieved with a static regenerant solution, resulting in simplified operation and reduced consumption of regenerant. A flow-through type of electrochemical membrane suppressor has also been reported [49]. In one of several possible configurations, this device uses a concentric arrangement of the following components, in sequence: a platinum wire, a cationexchange membrane fibre (400 pn ID, 50 pm wall thickness), a second cation-exchange membrane fibre (625 p ID. 125 pm wall thickness), and a length of stainless steel tubing (Fig. 9.21(b)). The eluent flows through the annular cavity between the two membranes, whilst regenerant flows in a countercurrent direction through the two remaining annular cavities (i.e. between the Pt wire and the inner membrane, and between the outer membrane and the steel tubing). A dc potential of 3-8 V is applied between the PI wire and the steel tubing, with the Pt wire being positively polarized. The above study provides an interesting comparison between chemical suppression and electrochemical suppression. When an acid (e.g. dodecylbenzenesulfonic acid) is
ConductivityDetection
273
used as the regenerant with a NaOH eluent, suppression efficiency is roughly the same (about 95%), regardless of whether a potential is applied across the electrodes. The reason for this is that in the absence of potential, both membranes contribute towards the removal of Na+ from the eluent. However, when a potential is applied, Na+ is removed from the eluent onfy through the outer (or cathodic) membrane, albeit at a faster rate than without the potential. Nevertheless, a significant finding of this work is that electrochemical suppression can function effectively even when water is used as the regenerant. The same operating principles apply, but there is now no longer any requirement for specialized regenerant solutions.
Signal enhancement devices for ion-exclusion chromatography Organic species (such as carboxylic acids) eluted from an ion-exclusion column by an acidic eluent are difficult to detect using conductivity measurements. The reason for this is that these solutes are retained on the column only in their neutral or weakly ionized forms, which show little conductance. It therefore becomes necessary to modify the eluted solutes if conductivity detection is to be employed. Cation-exchange membrane suppressors have been applied successfully when sulfuric or octanesulfonic acids are used as eluents [50-531. A suitable alkaline regenerant (such as tetrabutylammmonium hydroxide or dilute NaOH) leads to a reduction in the conductance of the acidic eluent and at the same time, ionization of the solute acids occurs. This mechanism is depicted in Fig. 9.22(a). An interesting effect occurs if the concentration of the NaOH regenerant is increased (e.g. from 10 mM to 500 mM). Under these conditions, the peak direction changes from positive (increasing conductance) for the 10 mM regenerant to negative (decreasing conductance) for the 500 mM regenerant [52]. The reason for this is that the more concentrated regenerant overcomes the Donnan exclusion effect of the cation-exchange membrane, so OH- ions move into the eluent, giving a high background conductance. This process is shown in Fig. 9.22(b). The eluted carboxylic acids react quantitatively with OH-, causing a decrease in conductance and hence indirect conductivity detection. This detection mode is more sensitive than direct conductivity because of the high limiting equivalent ionic conductance of OH- (see eqn. (9.20)). Finally, it can be noted that signal enhancement in ion-exclusion chromatography of organic acids can be achieved using a regenerant comprising a solution of a neutral salt (e.g. KzSO.4). The exchange of H+ ions from the eluent and the solute acids with K+ from the regenerant, as shown in Fig. 9.22(c), leads to a reduction in the eluent conductance and an enhancement of the solute conductance 1531. Post-column enhancement of the conductivity signal has also been applied to the detection of HzCO3 after ion-exclusion separation [54]. The effluent from the ionexclusion column is first passed through a cation-exchange column in the K+ form, and then through an anion-exchange column in the O H form. The first of these columns converts HzCO3 into KHC03, whilst the second converts KHCO3 into KOH, which is the species ultimately detected.
From column
From column
H2SQ
10 mM NaOH
Na2S04 RCOO'Na' To detector
From column
H2 SQ
H2S04
10 mM NaOH
500 mM
NaOH
Na2S04 500 mM RCOO"a+ NaOH NaOH To detector
K2SO4
K ~ S O ~ K2SO4 RCOOK+ To detector
(b)
Fig.9.22 Signal-enhancing devices for conductivity detection of carboxylic acids after ion-exclusion separation. A cation-exchange fibre is used in each case, with (a) 10 m M NaOH, (b) 500 mM NaOH or (c) K2SO4 as the regenerant solution.
B
Y)
275
ConductivityDetection
9.5.7
Response equation for suppressed conductivity detection
Development of a response equation for conductivity detection in suppressed IC systems can be approached by considering the factors which contribute to the detector signal during elution of a sample band [55]. Because of the diversity of suppression reactions, we will confine the present discussion to the case of a suppressed anionexchange IC system in which the eluent consists of an ionic salt, NaA, present at concentration CE, whilst the regenerant consists of a solution of a suitable acid. A fully ionized sample anion, S-, is eluted from the column at a concentration of Cs. This solute is accompanied by an equivalent concentration of H+ as a result of the suppression reaction. For suppression to be effective, the eluent anion, A-, must be the conjugate of a weak acid, HA. Passage of the eluent through the suppressor results in the formation of HA, which ionizes according to:
HA % H+ + A-
(9.26)
For which we can write: (9.27)
When the eluent is converted fully to HA in the suppressor, the conductance of the suppressed eluent and the suppressed sample results from H+, A- and S-ions. However, when the suppression reaction is not quantitative (i.e. not all of the Na+ ions from the eluent are removed), we can expect the suppressed eluent to contain some residual Na+ ions which will also contribute to the conductance. Finally, we must consider any OHwhich may be present in the suppressed eluent, so that:
Kw = [H+l[OHl
(9.28)
and we can write the following charge balance and mass balance equations:
[H+l + "a+] = [A-I + [OH-] [HA] + [A-I = CE - Cs
+ [S-I
(9.29) (9.30)
Eqns. (9.27)-(9.30) can be combined to give an expression for [H+], as follows:
Solution of this equation permits the value of [H+]to be calculated for given values of the parameters KHA, Kw, CE, Cs and "a+]. This value can then be used to calculate
276
Chapter 9
the remaining parameters using eqns. (9.32)-(9.34). That is: (9.32)
(9.33)
(9.34)
The conductance measured during sample elution is given by:
In the ideal case, the suppression reaction will be quantitative (i.e. "a+] = 0) and the product of the suppressor reaction (HA) will not dissociate to any appreciable extent (i.e. [A-1 = 0). Under these conditions, the detector signal arises entirely from S-and an equivalent amount of H+. That is: (9.36)
Similar derivations can be used to formulate detector response equations for suppressed conductivity detection in cation-exchange, ion-interaction and ion-exclusion separation modes. 9.5.8
Suppression based on precipitation or chelation reactions
Thus far, we have considered only those suppressors in which an acid-base reaction forms the basis of the suppression mechanism. It is important to note that other types of chemical reactions can also be employed as a means of reducing the conductance of the eluent. This topic has already been discussed in Section 4.4, but it is pertinent to reiterate briefly the major reactions used, as part of the present discussion of suppressors. One simple example is the use of precipitation reactions to physically remove an eluent component. This approach has been used for the suppression of NaI eluents using a suppressor in the Ag+ form (resulting in the formation of a precipitate of AgI) [56] and for the suppression of Ba(N03)2 eluents using a suppressor in the S042- form (resulting in the formation of a precipitate of BaS04) [57]. Other examples of suppressors using precipitation reactions were presented in Table 4.6. A further interesting possibility is the use of complexation reactions to achieve suppression of the eluent conductance. When an eluent containing a complexing agent
ConductivityDetection
277
(such as dipotassium ethylenediamine-NN-diacetate, K2EDDA) passes into a suppressor containing a cation-exchange resin in the Cu2+form, the K+ from the eluent binds to the suppressor, releasing Cu2+ ions which then complex with the eluent anion (EDDA2-), forming the neutral complex, Cu-EDDA. This effectively lowers the eluent conductance [58]. An example of a chromatogram obtained using this approach was presented in Fig. 4.20.
9.6
PERFORMANCE CHARACTERISTICS OF CONDUCTIVITY DETECTORS
9.6.1 Non-linearity of calibration plots in suppressed IC Effect of hydrogen ions in the sample band From eqn. (9.36), we see that the conductance change accompanying the elution of a solute ion from a suppressor is proportional to the solute concentration in the detector cell (Cs).Linear plots of the conductance signal versus Cs can therefore be expected from an ideal system, provided that care is taken not to overload the low-capacity ionexchange columns used. That is, provided the calibration plot is prepared over a concentration range in which the adsorption isotherm for the solute is linear. However, we must consider an additional complication which arises when a suppressor is used. In the case used for the derivation of a response equation in Section 9.5.7 above, we have noted that the sample passes through the detector as a dissociated, strong acid (ix.H+ and S-). The hydrogen ions in the sample band will exert an influence on the dissociation equilibrium for HA (eqn. (9.26)) by forcing this reaction to the left. That is, the conductance of the baseline during sample elution will be lower than the background level existing when eluent alone passes through the suppressor. This effect is summarized graphically in Fig. 9.23. The background conductance of the eluent (in the absence of sample) is given by GIII. GI shows the Gaussian change of conductance due only to the solute anion and its accompanying hydrogen ions. The decrease in background conductance caused by the influence of sample on the eluent equilibrium is given by GII. This latter effect gives a non-Gaussian profile. The overall conductance change during sample elution (AG) is given by: (9.37)
Detailed mathematical expressions for each of the above terms have been derived by Doury-Berthod et al. [59] and these permit the conductance changes depicted in Fig. 9.23 to be calculated. The contribution GI describes the rise and fall of the conductance signal during the lifetime of the peak, whilst GI[ shows the change in eluent background conductance during development of the same peak. As the concentration of the sample (and associated hydrogen ions) reaches a maximum, GII is depressed to its minimum value. This minimum value will depend on the sample concentration, since this determines the [H+] in the sample band. The final peak shape, given by eqn. (9.27), is non-Gaussian. The end result of this effect is that the slope of the peak height calibration curve varies with the concentration of injected sample. As the sample concentration
Chapter 9
27 8
AG
GI
t
G I I (non goussion)
G I , ( n o n goussion)
Volume Fig. 9.23 Three contributions to the shape of the eluted peak in suppressed IC with conductimemc detection. See text for an explanation of the origins of GI, Gl1 and G ~ I Reprinted . from [591 with permission.
Conduetonce ( o r b i t r o r y units)
Fig. 9.24 Non-linear peak height calibration plots in suppressed IC resulting from the influence of hydrogen ions in the sample band on the eluent conductance. The curve has two limiting slopes, one at low sample concentration (hli,) and one at high sample concentration (h'lim). Reprinted from [591 with permission.
279
Conductivity Detection
decreases, the slope approaches a limiting value (hlim), whilst at higher concentrations of solute, the slope approaches a different limiting value (h’lim). The final calibration curve is similar to that depicted in Fig. 9.24. Similar studies on the non-linearity of calibration curves in suppressed IC have been conducted by other workers [55, 60-631. In one of these studies 1601,an equation is presented which permits correction for the influence of sample elution on the background conductance. Using this correction equation, linear calibration plots were obtained using peak areas for solute concentrations in the range 0-40ppm.
Practical consideration of the hydrogen ion effect The degree to which the above effect exerts an influence on the linearity of calibration curves in practical situations depends on a number of factors [631. First, the higher the PKa of the eluent acid, the less pronounced will be the effect of hydrogen ions in the sample band on background conductance. The reason for this is that the equilibrium shown in eqn. (9.26) already lies well to the left for very weak acids. This behaviour is illustrated in Fig. 9.25, which shows that the linearity of calibration plots improves as the PKa of the eluent acid increases. Thus, hydroxide eluents can be expected to give calibration plots which are very close to linear since the eluent acid produced in the suppressor i s H20. Similarly, the strong acid eluents (HCl, HNO3) used for cation separations should give linear calibrations. Second, lower eluent concentrations should minimize the sample acid effect, resulting in a more linear calibration curve. Finally, the effect of hydrogen ions in the sample band will be dependent on the type of suppressor used. Micromembrane
Sample Concn. 1 0 5 M
Fig. 9.25 Peak height calibration plots in suppressed IC for eluent acids of differing strengths. The PKa of the eluent acid is (1) 12, (2) 10,(3) 8 and (4) 6. The peak heights were calculated by assuming that the solute ion was C1-. Reprinted from [55] with permission.
Chuprer 9
280
'5
1
l2
1
12
E,
E
' ? 9
9
f
i
,u
F
P
6
I
r
X
-.L
c
0
k
3
0
0 Sample Concn.
loJ M
(4
6
12
18
24
30
Sample Concn. lo-' M
(b)
Fig. 9.26 The effect of residual "a+] in the suppressed eluent on peak height calibration plots for suppressed IC. The p b of the eluent acid is 10 for (a) and 6.36 for (b). The residual "a+] in each Figure is (1) 0, (2) 50 pM, (3) 100 pM and (4) 150 pM. Reprinted from [55] with
permission. suppressors give a lower background conductance than packed suppressors due to diffusion of carbon dioxide through the membrane, so the effect of hydrogen ions in the sample band is decreased. Similarly, penetration of the HzSO4regenerant in the micromembrane suppressor into the eluent will further decrease the effect of hydrogen ions in the sample band. A study of linearity in suppressed IC has demonstrated that calibration curves for anions and cations show excellent linearity from the detection limit, measured in partsper-billion, to above 0.196, when dilute eluents are used in conjunction with a micromembrane suppressor [63]. This concentration range covers almost five orders of magnitude.
Effect of suppression efficiency on linearity of calibration A further factor which may cause non-linearity of calibration curves in suppressed IC is the efficiency of the suppressor. If we again consider a chromatographic system in which the eluent is an aqueous solution of NaA (where A is an anion such as HCOj) and the injected solute is C1-, then the efficiency of suppression can be judged by the concentration of sodium ions present in the suppressed eluent. A perfectly efficient suppressor will give a residual "a+] of zero (seeeqns. (9.35) and (9.36)). The effect of the residual "a+] on the shape of calibration plots has been studied by Tian et al. (551. Calibration curves calculated for eluent acids of pK, 10 and 6.36 are shown in Figs. 9.26(a) and 9.26(b), respectively. for various values of residual "a+]. From Fig. 9.26(a), it can be seen that the calibration plot is linear provided that the
Conductiviry Detection
281
sample concentration, [S], exceeds the residual “a+]. When [S]< residual “a+], the peak height is severely depressed, due chiefly to replacement of H+in the sample band by the weakly conducting Na+ ion. This reduction in [H+]causes the equilibrium depicted in eqn. (9.26) to move to the right, which partially compensates the decreased sample conductance due to reduced [H+]in the sample band. The magnitude of this latter effect will be greater for eluents acids which are more ionized (i.e. lower p k ) , as illustrated in Fig. 9.26(b). This shows that an eluent acid with pK, of 6.36 (i.e. carbonic acid) is less influenced by residual “a+] than is a weaker eluent acid. Thus, the linearity of calibration plots prepared using carbonate eluents show decreased dependence on suppression efficiency in comparison to those prepared in hydroxide eluents. However, in both cases, the sensitivity, linearity and reproducibility of conductivity detection of low concentration samples are seriously affected by the residual “a+], especially at low sample concentrations. 9.6.2 Temperature effects in conductivity detection Temperature fluctuations have been shown to affect both the sensitivity and reproducibility of conductivity detection in IC [64-671. Improvements in detection limits of up to 20-fold have been achieved by insulating the separation column and other exposed components of the IC [65]. The precision of analytical results was also improved considerably. The four most common equations describing the temperature dependence of electrolytic conductance measurements have been evaluated [67]. These relationships are given below: (9.38)
(9.39)
(9.40) (9.41)
where G25 and GT are the conductances at 25OC and P C , respectively, TT is the viscosity of water at temperature P C , and K1-K4 are constants. Literature values for conductances of KCl were used to assess the validity of each of the above equations. Fig. 9.27 shows the difference between the measured and calculated values of the parameter (G~~/GT at)several temperatures, for each of the equations. The best agreement between calculated and measured conductances was obtained for eqn. (9.38). It can be seen from Fig. 9.27 that the popular rule-of-thumb calculation (as described by eqn. (9.39)) [68], which estimates a 2% conductance change for each degree of temperature change, holds well only in a very narrow temperature range of 10-25OC. Outside this range, this calculation may be in error by as much as 25%.
Chapter 9
282
'"I
O' 0.05
.
\
'
'0
\ 0
\
.-0 4
\
\
-0.15
\
0 CK -0.20
\ \
-0.25
0
1
1
1
1
10
20
30
40
Temperature,
b
I
50
OC
Fig. 9.27 Difference between calculated and literature values of conductance ratios for KCI at various temperatures. The calculated values were determined by eqns. (9.28) [o],(9.29) [a], (9.30) [o] and (9.31) [A]. Reprinted from [67] with permission.
9.6.3 Conductivity detection without the use of standards Non-suppressed IC can be applied quantitatively to samples in which the identities of the sample component ions are unknown [69]. The conductivity detector response is measured using first an eluent competing ion of low limiting equivalent ionic conductance and then an eluent competing ion of high limiting equivalent ionic conductance. Two equations of the same form as eqn. (9.20) result and these can be solved simultaneously for the two unknowns Cx (the solute concentration) and h, (the limiting equivalent ionic conductance of the solute ion). In this way, the identity and concentration of each solute ion can be determined. The equations derived for this method are:
c, =
x, =
(F") +
s,
(9.42)
(9.43)
where C represents molar concentrations, S represents peak areas, and h is limiting
Conductivity Detection
283
Sample concentration (mM1
Fig.9.28 Dependence of the conductance of the injection peak on the concentration of an injected monovalent anion. Calculated and experimental (0)values are compared. The eluent is 2 mM benzoic acid at pH 4.37. Reprinted from 1701 with permission.
equivalent ionic conductance. The subscripts have the following meanings: 1 refers to the first eluent; 2 refers to the second eluent; a denotes the peak area of the anion of eluent 1 when eluted by eluent 2; b denotes the peak area of the anion of eluent 2 when eluted by eluent 1. Provided the values of Sa, Sb, S1, S2, C1, C2, hl and h2 are known (or have been determined from previous experiments), it becomes possible to solve the above equations for Cx and Ax. For similar determinations without the use of standards in suppressed IC, the authors recommend the use of a third column, which in the case of anion separations could be an anion-exchanger in the chloride form. All anions eluting from the suppressor after their separation on the separator column would thus be exchanged for C1- in the third column. The number of equivalents of Cl- indicated by a detector calibrated with a standard solution of CI- would thus correspond to an equal number of equivalents of the analyzed anion. 9.6.4
Utilization of the injection peak in conductivity detection
Chromatograms obtained with conductivity detection show an injection peak corresponding to elution of the sample co-ions, displaced eluent ions, and the sample solvent. This peak is analogous to the void volume peak encountered in other liquid chromatographic methods, and is sometimes called the solvent peak or the water dip. In a non-suppressed IC system, the injection peak may be positive or negative and its conductance is related quantitatively to the total ionic content of the injected sample.
284
Chapter 9
KC I
NaCl M
6.0 x lomL M
r-121737
4=9L25&
6.05 Y
A=5&6&0
A-53861
I
CaClz 3.0 x
M
\=91053
A-5333:
I
Time Pig. 9.29 Injection peaks and sarnpie peaks for three different chloride salts. The area of each peak is indicated in the Figure. The eluent was 1.5 mM phthalate at pH 4.3. Reprinted from [71] with permission.
Fig. 9.28 illustrates this relationship, which may be used to assist in the quantification of a sample mixture. For example, a solute mixture comprising a well-retained ion (such as S042-) and several ions of short retention time (such as Cl-, NOy, Br) can be quantitated by measuring the peak areas of the injection peak, together with those of all solutes except the well-retained ion. Since the injection peak contains the sample cations and the eluent ions displaced by initial adsorption of all solute ions injected onto the column, the area of the well-retained ion can be deduced 1701. If samples contain eluent ions at the same concentration and pH as those present in the eluent itself, the injection peak in a non-suppressed anion-exchange IC system can be used to obtain quantitative data on the cation concentration of the injected salts [71]. Under the above experimental conditions, the area of the injection peak is linearly proportional to the cation concentration in the sample. Moreover, the ratio of the areas of the solute anion peak and the injection peak is specific for a given combination of solute anion and cation. This is illustrated in Fig. 9.29, which shows chromatograms for solutions of three chloride salts, each of which has the same [Cl-I. The C1- peaks are therefore of almost equal area, but the areas of the injection peaks differ as the cation is varied. This characteristic ratio can therefore be used to identify the components of an injected sample, because the solute anion is readily identifiable by its retention time, and the area ratio determines the identity of the solute cation. Binary salt mixtures, or mixtures of salts with acids and bases, have been analyzed using this approach [71].
ConductivityDetection
9.7
285
APPLICATIONS OF CONDUCTIVITY DETECTION IN IC
Conductivity detection has always been the mainstay of IC and a brief perusal of the numerous applications listed in Part V of this book will reveal the frequency with which this detection mode is employed. Moreover, most of the chromatograms included thus far in this text have provided ample illustration of the utility of conductivity detection. It is therefore difficult to offer a comprehensive summary of the areas in which conductivity detection is employed. Instead, the current status of conductivity detection will be described by reference to its application to a few selected classes of ions.
9.7.1
Anions
The analysis of anions of strong inorganic acids has been, and continues to be, the most common application of IC. Detection limits for direct injections of these species vary from anion to anion, and with the nature of the conductimetric method used. Generally, it can be said that detection limits between 50 and 100 ppb can be achieved in both suppressed and non-suppressed conductivity methods without the need for sample preconcentration. With suitable preconcentration methods (see Section 14.6). detection limits in the lower half of the parts-per-trillion range result. The real limits in this case are imposed more by sample handling considerations than by the sensitivity of the conductivity detection used. One of the strengths of conductivity detection, arising from its character as a bulk property technique, is its utility for speciation after separation. That is, the identification of different forms of the same element. Fig. 9.30 shows the speciation of anions of sulfur, chlorine and phosphorus using conductivity detection.
9.7.2 Cations Conductivity detection of alkali metal cations and ammonium is extremely sensitive with both suppressed and non-suppressed conductivity methods. Detection limits for direct injection are often a factor of 5-10 times lower than those for anions, so preconcentration is rarely necessary for these solutes. Low molecular weight bases can also be detected readily. Divalent cations are amenable to conductivity detection, although not with the sensitivity attainable with post-column colour reactions (see Chapter 13). However, conductivity detection represents a simple and often preferable approach, as is illustrated in Fig. 9.31.
9.7.3 Weakly ionized species Detection of partially ionized inorganic and organic species has always presented a challenge for conductivity detection. In the suppressed mode, the ionization of weak acids is suppressed, whilst in the non-suppressed mode, the sensitivity of detection is impaired for any ion which is not fully dissociated. The use of high pH eluents (such as hydroxide), coupled with indirect conductivity detection, gives optimal results for these species in non-suppressed IC. On the other hand, the sensitivity of conductivity detection of weak acids can be improved with signal enhancing devices such as those shown earlier in Fig. 9.22. This method is illustrated in Fig. 9.32 for borate as the solute.
CIOi
203-
SCN-
CI'
I
I
0
10
I
I
20 30 Time (min) (a1
I
1
40
50
Y
0
I
f
1
I
5
10
15
0
mL
(b)
I
I
5 10 Time (min)
1
15
(C)
Fig. 9.30 Speciation of (a) sulfur, (b) chlorine and (c) phosphorus using conductivity detection. (a) Lichrosphere c18 column with an eluent containing 1 mM tetrabutylammonium hydroxide, 7.5 mM H3B03 and 50% acetonitrile. Solute concentrations 1 ppm. Detection by suppressed conductivity. Reprinted from [72] with permission. (b) Spherisorb A5Y column with 0.5 mM H3P04 as eluent. Detection by non-suppressed conductivity. Reproduced from [73] with permission. (c) Waters IC Pak Anion SW column with 2 mM tartaric acid as eluent. Solute concentrations 20 ppm. Reprinted from [3] with permission.
B i7 E:
v,
287
Conductivity Detection
15 (min.)
I
Fig. 9.31 Conductimetric detection of divalent metals. Waters IC Pak C column with 3.5 mM ethylenediamine and 10 mM cimc acid as eluent. Solute concentrations: 5 ppm. Reprinted fiom [31 with permission.
Carbonate
I 0 Borate J
0
2
4
8 1 0 1 2 1 4 Minutes
6
Fig. 9.32 Detection of borate using a membrane suppressor. Dionex HPIC-AS1 column with 1 mM octanesulfonic acid as eluent. The regenerant used in the micromembrane suppressor was 10 mM m0H. The borate concentration was 10 ppm. Reprinted from [74] with permission.
Chapter 9
288
9.8 1 2 3 4 5 6 7 8 9 10 11 12 13 14
15 16 17 18 19 20 21 22 23 24
25 26 21 28 29 30 31 32 33 34 35 36 37 38
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ConductivityDetection 39
40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57
289
Dasgupta P.K.. Anal. Chem.. 56 (1984) 103. Stevens T.S., Res. Dev., September (1983) 96. Stevens T.S.. Jewett G.L. and Bredeweg R.A., Anal. Chem.. 54 (1982) 1206. Dasgupta P.K.. in Tarter J.G., (Ed.) Ion Chromatography. Marcel Dekker, New York, 1987, p. 191. Stillian J., LC,3 (1985) 802. Rocklin R.D., Pohl C.A. and Schibler J.A.. J. Chromatogr., 411 (1987) 107. Sunden T., Cedergren A. and Siemer D.D., Anal. Chem., 56 (1984) 1085. Siemer D.D. and Johnson V.J., Anal. Chem., 56 (1984) 1033. Shintani H. and Dasgupta P.K., Anal. Chem, 59 (1987) 802. Tian ZW., Hu R.Z. Lin H.S. and Hu J.T., J. Chromatogr., 439 (1988) 159. Strong D.L. and Dasgupta P.K., Anal. Chem., 61 (1989) 939. Rocklin R.D.. Slingsby R.W. and Pohl C.A., J. Liq. Chromatogr.. 9 (1986) 757. Slingsby R.W., J. Chromutogr., 371 (1986) 373. Haginaka J., Wakai J., Yasuda H. and Nomura T., J. Chromatogr., 447 (1988) 373. Murayama T., Kubota T., Hanaoka Y., Rokushika S., Kihara K. and Hatano H., J. Chromatogr.. 435 (1988) 417. Tanaka K. and Fritz J.S.. Anal. Chem.. 59 (1987) 708. Tian Z.W., Hu R.Z.,Lin H.S. and Hu W.L., J. Chromatogr., 439 (1988) 151. Pohl C.A. and Johnson E.L., J. Chromatogr. Sci., 18 (1980) 442. Nordmeyer F.R., Hansen L.D., Eatough D.J.. Rollins D.K. and Lamb J.D.. Anal. Chem, 52 (1980) 852.
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72 73 74
Weidenauer M., Hoffmann P. and Lieser K.H., Fres. Z Anal. Chem., 331 (1988) 372. Schmitt G.L.,PhD Thesis, University of Iowa, Iowa City (1985). Weiss J., Handbook of Ion Chromatography, Dionex Corporation, Sunnyvale, CA, 1986, p. 102.
(1985) 2257. 169.
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29 1
Chapter 10 Electrochemical Detection (Amperometry, Voltammetry and C o u lo me try) 10.1 INTRODUCTION
10.1.1
Definitions
The term "electrochemical detection" is applied loosely to describe a range of detection techniques involving the application of an electric potential (via suitable electrodes) to a sample solution, followed by measurement of the resultant current. Conductivity detection, which was discussed in full in Chapter 9, quite properly falls into this category, but is usually treated as a distinct detection method. In a similar manner, potentiometric detection, which is discussed in Chapter 11, can also be validly regarded as an electrochemical technique, but has some distinguishing features which render it more suitable for separate consideration. For the purposes of the discussion in this Chapter, we will interpret electrochemical detection to embrace the techniques of voltammetry, amperometry and coulometry. The common characteristic of these techniques is that a chemical reaction (e.g. a Faradaic oxidation or reduction) occurs during the measurement. It will be remembered that steps to avoid such reactions were taken in conductivity detection, and the same is true of potentiometry.
Voltammetry and polarography Voltammetry is a well-established technique which involves the application of a changing potential (measured with respect to a reference electrode) to a working electrode, followed by measurement of the current resulting from the reaction of analyzed species at the working electrode. Within the general field of voltammetry, we can identify polarographic techniques as those which measure current-voltage relationships using mercury as the working electrode. The key factor in voltammetry (and polarography) is that the applied potential is varied over the course of the measurement. Amperometry and coulometry The term amperometry describes the technique in which a fixed potential (again measured with respect to a reference electrode) is applied to a working electrode and the current resulting from oxidation or reduction reactions occurring at the working
292
Chapter 10
electrode is measured. In the case of chromatographic detection. the working electrode is located in a suitable flow-cell, through which the eluent stream passes. The analyte to be detected undergoes a Faradaic reaction if the applied potential has appropriate polarity and magnitude. However, the surface area of the working electrode in amperometry is generally quite small (0.5 cm2 or less), so the Faradaic reaction of the analyte is incomplete, causing only a fraction of the total analyte to react. In fact, less than 10% of the analyte is reacted in a typical amperometric flow-cell at flow-rates around 1 ml/min. The use of working electrodes of larger surface area can lead to quantitative reaction of the analyte at the electrode, and when this occurs, the technique used is described as high-efficiency amperometry, or coulometry. Thus, amperometry and coulomeny can be distinguished by the extent to which the analyte undergoes a Faradaic reaction at the working electrode. 10.1.2
Interrelationships between voltammetry, amperometry, and eoulometry
Potential window Consider the situation where a working electrode is inserted into a solution containing an electrolyte (e.g. KCl), but with no electrochemically-active(i.e. oxidizable or reducible) solute present. The potential of the working electrode is now varied with time from a negative value (E2) through to a positive value (El). This potential-time profile is shown in Fig. lO.l(a). The experimental configuration will require that a reference electrode be in electrolytic contact (but not necessarily inserted into) the sample solution. Current flow will be measured between the working electrode and an inert, auxiliary electrode, which is also inserted into the sample solution. Three electrodes are therefore present; the working electrode to which the potential is applied, the auxiliary electrode which measures the current flowing, and the reference electrode. The current which flows in the above experiment varies with the applied potential and follows the general shape depicted in Fig. lO.l(b), which is called a voltammogram. The current is negligible over most of the potential range because no electroactive solute is present, and appreciable current flow is observed only at the extremes of the potential range. At the most positive potential (El), the observed current is due to oxidation of the electrolyte in the solution, or of the working electrode itself, and is therefore represented as an oxidative current. At the most negative potential (E2). the observed current is due to reduction of the electrolyte or of the working electrode, and is therefore represented as a reductive current. Clearly, the actual potentials at which these oxidative and reductive currents occur will be dependent on the nature of the working electrode and the type of electrolyte used. Thus, for a given combination of electrode material and supporting electrolyte, there exists a range of potentials over which current flow is minimal when no electroactive solute is present. This range of potentials is known as the potential window for that system. The potential window in Fig. lO.l(b) is indicated by Ew. Most IC applications of electrochemical detection are performed at positive (oxidative) potentials because the reduction of oxygen occurs at small, negative potentials and this severely limits the reductive potentials which can be used in solutions which have not been
Elecbochemical Derection
1
293
Ired
Fig. 20.2 Voltammograms obtained by applying the potential profile illustrated in (a) to a solution of supportingelectrolyte alone (b) and to the same electrolyte containing an oxidizable species (c) or
a reducible species (d). deoxygenated.
Addition of an electroaetive solute When an electroactive solute (i.e. one capable of Faradaic oxidation or reduction at the working electrode) is added to the electrolyte solution, and the potential is again varied from E2 to El, a different potential-current relationship results. Fig. lO.l(c) shows the potential-current relationship when the added solute is oxidizable. An S shaped step (i.e. a wave) appears in the voltammogram. The height of the wave (given by the anodic current, Ia) is proportional to the concentration of the oxidizable solute (Co), whilst the position of the middle point of the wave on the potential axis (called the half-wave potential, El@) is characteristic of the oxidizable solute. Fig. lO.l(d) shows the voltammogram which results for a reducible solute and it can be seen that a cathodic, reduction current IC results, which is proportional to the concentration of the reducible species (CR).Again, the half-wave potential is characteristic of the reducible solute involved.
Chapter 10
294
Fig. 10.1 shows that voltammetry can be used to identify a solute and to determine its concentration. Provided only one electroactive species is present, the same result could be achieved by monitoring the current flow at a fixed potential, that is, by amperometry. The potential used should be one at which the analyte gives maximal current flow, but the residual current due to the electrolyte, working electrode. etc., is minimal. Thus, E3 would be a suitable potential for amperometric measurement of the oxidizable solute in Fig. lO.l(c), and E4 would be suitable for the reducible solute in Fig. lO.l(d).
Hydrodynamic voltammograms Successful amperomemc or coulometric detection can result only if the applied potential is chosen correctly. Extensive compilations of half-wave potentials for many solutes, measured with various working electrodes and under differing experimental conditions, are available in the literature (e.g. [ 11). These compilations are valuable, but sometimes do not contain information which is specific to the actual experimental conditions being employed. In these circumstances, voltammograms such as those shown in Fig. 10.1 must be obtained. This is a relatively simple matter when voltammetric instrumentation is available which permits the potential to be varied continuously whilst the current is monitored. However, amperometric instruments are designed to operate at a fixed applied potential, so true voltammograms cannot be generated. In these cases, a voltammogram can be obtained by measuring the current output for a fixed concentration of analyte, using a series of discrete potentials covering the desired range. When the amperometric instrumentation used for this procedure consists of a flow-through cell, the voltammogram .is obtained under flowing conditions and is referred to as a hydrodynamic voltummogram [2]. Hydrodynamic voltammograms find extensive use in chromatographic applications of amperometry and coulometry and are especially useful for the comparison of the performance of different electrochemical detectors. Analysis of mixtures of electroactive species Mixtures of electroactive species can be analyzed by simple voltammetry, provided that.the half-wave potentials and relative concentrations of the components of the mixture are such that the separate waves for each component can be discerned. Amperometry is not suitable for such mixtures because the measured current will often be due to more than one solute. However, when amperometry is coupled with chromatographic separation, a powerful combination results. The sample components are separated in the chromatographic system and pass sequentially over the working electrode, where they are detected amperometrically. Moreover, this form of chromatographic detection is specific for electroactive solutes and in IC therefore serves as a valuable adjunct to universal detectors, such as conductivity detectors. 10.1.3
Basic instrumentation for electrochemical detection in IC
An electrochemical detector can be formed from a potential supply, appropriate circuitry for the measurement of current, and a suitable sample cell. In the case of IC,
Electrochemical Detection
Reference electrode
Auxiliary electrode
295
Buffer
= I
Voltage
Current-
Eluent stream
Fig. 10.2 Basic configuration of an electrochemical detector
a flow-through type of sample cell is used and details of such cells are provided later in Section 10.4. As discussed above, the cell should accommodate three electrodes. Fig. 10.2 shows a schematic representation of the basic configuration of an electrochemical detector for flowing sample streams. The recorded analog signal is commonly generated by conversion of amplified oxidative or reductive currents generated in the cell to voltages, using the current-voltage converter shown in Fig. 10.2. More detailed descriptions of the electronic circuitry for voltammetric and amperometric measurements can be found elsewhere [2-71. It should be noted that considerable versatility of detection can be achieved by varying the manner in which the potential is applied to the working electrode. It is not necessary that a simple DC voltage be used for this purpose. Indeed, it is often very advantageous to use potential pulses, or sequences of pulses, and to measure the resultant current at specific times. Pulsed detection will be discussed further in Section 10.2.2. Table 10.1 provides a summary of the more important characteristics of voltammetric, amperometric and coulometric detection.
10.1.4 Usage patterns for electrochemical detection in IC Voltanimetry (including polarography [8-lo]), amperometry and coulometry have all found application as detection methods for IC. Other electrochemical methods, such as electrocatalytic detection [1 11, double-layer capacitance electrosorptive detection [ 12, 131 and indirect electrosorptive detection [ 141 have also been successfully used. However, it is fair to say that amperometry and coulometry are the most widely applicable methods, and of these, amperometry predominates. It is interesting to speculate on why this usage pattern exists. The difficulty in constructing a low-volume cell containing the dropping mercury electrode, coupled with the limited range of oxidative potentials available with a mercury electrode, combine to restrict the application of polarographic detection in IC. Voltammetry at solid electrodes does not offer significant advantages over amperometry using the same
s:
TABLE 10.1 BASIC PRINCIPLES OF VOLTAMMETRIC, AMPEROMETRIC A N D COULOMETRIC DETECTION
Q,
Method
Controlled quantity
Measured quantity
Cell design
Electronic unit
Remarks
Ampemmetry
Potential is held constant
Current
Three e l e c d e s
Potentiostat
Less than 10% conversion of the analyte at the electrode. Electrode materials: carbon, silver, gold, mercury. Wellestablished technique. Large choice of commercialinstrumentation.
Coulornetry
Potential is held constant
Current, charge
Working electrodes larger than used for
Potentiostat
A p p x . 10% conversion of rhe analye. WelleStabllished technique. Few commercial instruments available
Voltammetric instnunentation providing modulated potentials and various current sampling modes
This technique can be used by combining ampemmetric flow-cells with voltammetric instrumentation.
See voltammetry. MicrOproCeSSOr instrumentation is necessary
Reproducibility of ampemmetric detection on some solid electrodes is improved with this technique.
~pemmetry
Voltammetry
Potential is changed as a function of time
Current is evaluated either continuously or by sampling
Pulsedampemmetry
Potential is applied as pulses to clean the electrodebetween measurements
Current is evaluated between two cleaning pulses
electrodes
Three electrcdes
3
Electrochemical Detection
297
TABLE 10.2 SOME ELECI’ROACITVESOLUTES SUITABLE FOR DIRECT AMPEROMETRIC DETECTION IN IC ArseNte
Mde
Bromate Bromide Carbohydrates Chlorate Chloride chlorite
Chromate
Cyanide Hexathionate Hypochlorite
Iodate Iodide Nitrate Nitrite Oxalate Pentathionate
Sulfide sullite Sufite adducts
Teaathionate Thiocyanate Thiosulfate Transition metals
Transition metal complexes
electrode types, and requires more sophisticated instrumentation. Amperometry and coulometry therefore remain as the electrochemical methods of choice. The relative merits of these two techniques has been the subject of some debate [15171. At first sight, it might appear that coulometry would offer better sensitivity than amperometry because of the greater extent of reaction of the electroactive species which occurs in coulometric detection. However, as the electrode surface area is increased in order to improve the efficiency of the Faradaic reaction, the background current due to breakdown of the solvent electrolyte also increases. Little, if any, gain in sensitivity therefore results. Coulometric cells are often awkward in design and difficult to dismantle and maintain. In addition, these cells are sometimes expensive and can be used with only a limited range of working electrode materials. Considered together, these factors provide some cogent reasons why amperometry is used more frequently than coulometry. In view of the above discussion, the ensuing treatment of electrochemicaldetection techniques in this Chapter will focus on amperometry, with passing reference to coulometry and polarography.
10.2 MODES OF OPERATION OF ELECTROCHEMICAL DETECTORS 10.2.1 Direct and indirect detection
Direct electrochemical detection The majority of amperometric and coulometric applications in IC involve the direct detection of electroactive solutes. That is, the recorded current arises from a Faradaic reaction involving the particular solute ion under consideration. Table 10.2 gives a partial listing of the inorganic and organic ions which show Faradaic reactions in the potential windows accessible to modem electrode materials. This listing includes only a small fraction of the ions detectable using conductivity measurements, so direct electrochemical detection can be considered to be quite selective, as well as offering extreme sensitivity. This selectivity is illustrated in Fig. 10.3, which shows peaks for S2-
298
Chapler 10 1
Slan d a i d
Saniple 1
.-. u
2
E
C -
I
18 niin
18 min
Fig. 10.3 Direct amperometric detection of (1) sulfide and (2) thiosulfate in standard solutions and in Kraft White liquor. Solute concentrations in the standard solution were 1 pprn and the sample was diluted 1:1O,OOO. A Waters M460 amperometric detector was used with a silver electrode. The eluent was 5 mM Na2HP04 at pH 6.5. Chromatograms courtesy of Waters.
and Sz0j2- obtained in a Kraft White liquor produced in pulp and paper processing. None of the electroinactive anions (such as C1- and OH-) present in the sample appear in the final chromatogram. Direct electrochemical detection will be discussed at some length in the remainder of this Chapter.
indirect electrochemical detection In recent years, some indirect electrochemical detection methods have also been developed to enable the detection of solutes which are not electroactive. Indirect detection methods can be defined as those in which the measured current is not due to a Faradaic reaction involving the solute ion. One approach to indirect detection is to use an eluent competing ion which is itself electroactive and to monitor the changes i n concentration of this species as solute ions are eluted [18]. Salicylate or 2,Sdihydroxybenzoate have been suggested as suitable eluent ions for anion-exchange IC and Fig. 10.4 shows indirect amperometric detection of CI- and NO3- after their separation on an anion-exchange column, It is noteworthy that the electroactive eluent anion need be present at very low concentrations only and may therefore be used in conjunction with a second eluent anion which has the prime function of separating the desired
Electrochemical Deitction
299
-
0 1 2 3 Time Imin)
Fig. 10.4 Chromatogram obtained with indirect amperometric detection. A Biotronik BT I1 AN anion-exchange column was used with 0.1 mM salicylic acid-0.9 mh4 sodium salicylate as eluent. Amperometric detection using a carbon-paste electrode at +950 mV was used. Sample concentrations were 5 ppm for Cr and 10 ppm for NOg. Reprinted from [18] with permission.
solutes. The eluent ions responsible for separation and detection of the solute anions can therefore be different, giving more flexibility in eluent choice than when a single eluent anion serves both functions. The latter situation, of course, exists in all other forms of indirect detection. Indirect amperometric detection has been applied to suppressed IC by utilizing the pH change which accompanies the elution of strong acid anions or metal ions. In the simplest case, the hydrogen ions eluting together with strong acid anions after their passage through the suppressor, have been found to give a change in the baseline current of an amperometric detector [19, 201. This permits detection of electroinactive species, as illustrated in Fig. 10.5(a), which also shows the pH change occurring during elution of the same sample peaks. This pH change may be used in yet another way by virtue of its effect on the protolytic equilibrium of a suitable electroactive species. For example, p-benzoquinone undergoes a reversible reduction to p-hydroquinone, as shown below:
p-benzoquinone + 2H++ 2e- 5 p-hydroquinone
(10.1)
n NO3
.i
[
100 nA
_-
[10
nA
SOL*-
I,
iL
f
L I
,
0
2
i
,
6
1
1
1
1
e 1 0 1 2 l i
Time (min) (a)
r
0
. I
5
JQ* N"L+
L Rb* Cs+
I
I
1
I
I
1
10
15
20
0
30
60
Time (min) (b)
Time (min) (C 1
Fig. 10.5 Indirect electrochemical detection in suppressed IC using the pH change which accompanies sample elution. (a) A Dionex HPIC-AS3 column was used with a Dionex AFS fibre suppressor. The eluent was 3 mM NaHCO3 and 2.4 mM Na2C03 and the sample concentrations were 4 ppm for F-and C1-, and 20 ppm for the remaining ions. The amperometric detector was operated at 0.3 V versw AglAgCl. Reprinted from [191with permission. (b) A Dionex column was used. The effluent from the suppressor was mixed with 10 mMp-benzoquinone, 1 mM hydroquinone and 0.1 M KCl. Coulomemc detection using a carbon cloth working electrode at 0.45 V versus Ag/AgCl was employed. Solute concentrations were 5 ppm and 1 ml of sample was injected. Reprinted from [21] with permission. (c) A Dionex cation column was used with 3 mM HNo3 as eluent, and with a cation fibre suppressor. Hydrcquinone was added to the suppressor effluent. Coulometric detection at 0.45 V versus AglAgI was used. Solute concentrations: 20 ppm of each ion. Reprinted from [26] with permission.
z
301
Elecrochem'cal Detection
This reaction is pH dependent and will therefore be influenced by H+or OH- ions eluted in the sample band. Indirect amperometric or coulometric detection has been accomplished in suppressed IC using this approach for anions (by detecting the co-eluted H+ ions) [21-241 and for cations (by detecting the co-eluted OH-ions) [21,25,26]. Both ion-exchange and ion-exclusion separation methods have been used. Fig. 10.5(b) shows the detection of anions using indirect coulometry, whilst Fig. 10.5(c) shows this approach applied to the detection of cations. Indirect electrochemical detection of metal ions after ion chromatographic separation can also be achieved by adding an electroactive ligand (or an electroactive metal complex) to the column effluent. Complexation or ligand exchange reactions occurring with the eluted metal ions lead to a reduction in the detector signal due to the added component. This method has been used with dithiocarbamate ligands [27, 281, dithiocarbamate complexes [29] or diethylenetriaminepentaacetic acid (DTPA) 1211 as the post-column reagent. In the latter case, the ligand is added as a labile complex of Cu(II), which reacts with eluted metal ions to give the following electrode reaction: [Cu-DTPAI3-
+ M2+ + 2e-
% [M-DTPAI3- + Cuo
(10.2)
where I$+ represents an eluted metal ion. Fig. 10.6 shows a chromatogram obtained with this approach.
10.2.2 Amperometric detection with pulsed potential
Problems with conventional VC amperometry The discussion thus far has concentrated on single potential (dc) amperometry. In this mode, the selected potential is applied continuously between the working electrode and the reference electrode. The auxiliary electrode (also called the counter electrode) prevents a deleterious current flow through the reference electrode. The sample is in direct contact with the working electrode. A serious problem encountered with this mode of amperometric detection is a gradual loss of detection sensitivity. To understand the nature of this problem, it must be appreciated that the amperometric detector utilizes a heterogeneous electrochemical reaction which occurs at the interface between the working electrode and the sample solution. In some cases, reaction products can accumulate and adhere to the electrode surface, thereby blocking the surface and hindering further reaction. In other cases, the electrode surface itself can show deterioration. The outcome of either of these processes is a decline in the efficiency of the Faradaic reaction occumng at the working electrode. This leads to a decrease in the current produced and is manifested in a flowing system as a decrease in the peak height recorded for the particular solute under study. In addition, baseline noise and drift may also increase as the electrode becomes coated (or "poisoned"). The sensitivity must therefore be monitored carefully by frequent injections of a standard and, when the detector response becomes unacceptable, the cell must be reconditioned by replacing or polishing the working electrode.
Chapter I0
302
I
0
I
15 Time (min)
$0
Fig. 10.6 Indirect coulometric detection of metal ions using post-column ligand exchange reactions. An Aminex A-4 column was used with 0.18 M sodium tartrate, 0.04 M tartaric acid and 0.04 M sodium chloride as eluent. The post-column reagent was 10 mM Cu-diethylene-
triaminepentaacetate, 1.0 M NhOH, 0.1 M NH4NO3. The coulometric detector was operated at 0.75 V. Solute concentrations 0.5 ppm. Reprinted from [21] with permission.
Pulsed amperometric detection (PAD) One elegant method for overcoming the problem of adsorption of reaction products on certain electrode surfaces is to use potential pulses instead of a continuously applied dc potential [30-321. In the pulsed mode, the detector measures current only during a short sampling interval, so there is less likelihood of electrode fouling. In addition, the potential can be stepped to values more negative or positive than the measuring potential as a means of cleaning the electrode surface or activating it to improve detection response. Fig. 10.7 shows a typical pulsed potential waveform which might be applied to a working electrode. The measuring potential (El) is applied and the current is determined over a suitable time period. Some reaction products become deposited on the electrode during this process, but if the potential El is applied for only a short time, then these deposits can be expected to occur in only very small amounts. After measurement, the potential is raised for a short time (E2) and then lowered (E3) for a further short interval. Note that E2 and E3 are more positive and more negative, respectively, than El. These steps permit the desorption from the working electrode of reaction products which are oxidizable or reducible. At the conclusion of this cycle, the measuring potential can then be applied to a clean electrode surface.
Elecnochemical Detection
E
303
Cleaning
Cleaning
E2 Measuring
El
El Activation E3
E3
)t Fig. 10.7 Typical triple-pulse potential waveform used for pulsed amperometric detection.
A further advantage of pulsed amperometric detection is that activation of the working electrode may occur due to the cycling of potentials. For example, at the potential E3, activation may result from reduction of surface sites on the electrode or possibly adsorption of the analyte [30, 331. An important example of this effect is the catalytic oxidative detection of carbohydrates at a platinum or gold electrode, as illustrated in Fig. 10.8 [34]. Using this approach, Johnson and co-workers have reported the detection of several classes of compounds which were thought previously to be undetectable by amperometry [30, 351. A summary of the applications of pulsed amperometric detection in IC is available [36].
Reverse-pulse methods We have noted previously that electrochemical detection is generally performed at positive potentials, since the presence of dissolved oxygen limits the accessible range of reductive potentials. This means that direct detection of metal ions is not possible unless oxygen is removed. Oxygen can be eliminated using a variety of procedures (e.g. [37]), and further steps must also be taken to prevent redissolution of oxygen. For example, the entire chromatograph can be blanketed with nitrogen. Reverse-pulse amperometry provides a means to detect metal ions through their reduction reactions at a dropping mercury electrode, without interference from dissolved oxygen 1381. This is achieved by use of a potential waveform in which a large, negative initial potential (Ei) is applied during the majority of the lifetime of the mercury drop. Transport-limited reduction of the analyte ions occurs and the analyte is deposited onto the elecuode surface, forming an amalgam. The potential is then stepped to a positive, final value (Ef), near the anodic limit for mercury. An oxidative current results as the deposited analyte is oxidized from the electrode. Dissolved oxygen does not react. Hence, cathodically active (reducible) analytes are detected by way of an anodic reaction. Fig. 10.9 shows the detection of some transition metal ions using this method.
Chapter 10
304
6 8
10
1
3
'1516
1 I
I
I
I
I
0
5
10
15
20
I
25.
I
I
30
35
I LO
Time (min)
Fig. 10.8 Pulsed amperometric detection of carbohydrates following separation by gradient elution. A Dionex HPIC-AS6A column was used with a gradient of 0-50 mM NaOH. NaOH (0.3 M) was added as a post-column reagent. Peak identities (and concentrationsin ppm): 1 - inositol (15), 2 - sorbitol (40),3 - fucose (25), 4 - deoxyribose, (25) 5 - deoxyglucose (20), 6 - arabinose (25), 7 - rhamnose (25), 8 - galactose, 9 - glucose, 10 - xylose, 11 - mannose, 12 - fructose, 13 melibiose, 14 - isomaltose. 15 - gentiobiose, 16 - cellobiose, 17 - turanose, 18 - maltose. Reprinted from [34] with permission.
10.3 ELECTRODES FOR AMPEROMETRIC DETECTION 10.3.1
Reference and auxiliary electrodes
Early cell designs included only two electrodes. that is, the working and reference electrodes. We have already noted that this configuration is undesirable because the reference electrode must c a m a current and hence its potential does not remain constant. The auxiliary electrode is therefore included to carry the cell current, so that the reference electrode is maintained under conditions of zero current flow. The most widely utilized reference electrodes are the Ag/AgCl electrode and the saturated calomel electrode (SCE). A palladium-hydrogen electrode and quasi-reference electrodes based on platinum and other metals have also been employed. Potentials of
ElectrochemicalDetection
305
-
0
5 10 Time (min)
15
Fig. 10.9 Detection of reducible metal ions by reverse-pulse ampemmetry, without removal of dissolved oxygen. A column packed with Dunum DC-4A cation-exchange resin was used with 0.10 M sodium hydrogentartrate and 60 mM Mg2+at pH 4.0 as eluent. The potential values used were Ej = -1.30 V,Ey = -1-0.20V. Reprinted from [38] with permission.
reference electrodes are available in the literature [39] and should be considered when an attempt is made to reproduce a detection method developed originally with a different reference electrode. Auxiliary electrodes should be constructed of inert material and should ideally be situated as close as possible to the working electrode. This minimizes potential drop due to the resistance of the sample solution. Typical auxiliary electrode materials are platinum and glassy carbon. In some detector cells, the stainless steel capillary tubing used to connect the chromatographic column to the cell may serve as the auxiliary electrode. This function may also be filled by the cell body itself, provided that it is constructed of a suitably conducting, inert material.
10.3.2
Working electrode materials
Many different materials have been used for the constmction of working electrodes for amperometric detection. Several comprehensive reviews on electrochemistry include discussion on this subject [5-7,40,41]. In this Section, the significant characteristics of the more important electrode materials will be listed.
306
Chapter 10
Mercury For reduction reactions, the electrode material of choice has been, and remains, mercury. The primary reasons for this choice are the high overpotential for reduction of the hydrogen ion, the formation of amalgams with many metals, and the ease of replacement of mercury-drop electrodes. The high hydrogen overpotential on mercury means that mercury electrodes can be used in acid solution without interference by the reduction of hydrogen ions. Mercury electrodes have the widest negative potential range of any electrode material. On the other hand, mercury is quite easily oxidized (at about 0.4 V versus SCE) and this prevents its use for the study of most oxidative processes. This limitation can be overcome when analytes forming complexes or precipitates with mercury ions are involved. Representative reactions of this type are shown below, where the analyte is represented as Ln- [7]: Hg
+ 2Ln-
2Hg
2(1-n)+ % HgL, + 2e-
+ 2Ln-
% Hg,L,
2( 1-n)+
+ 2e-
(10.3)
(10.4)
Since these electrode processes involve oxidation of mercury in the presence of complex-forming species, they occur at potentials less positive than for oxidation of the mercury itself. Removal of oxygen is unlikely to be necessary and only a moderate positive potential is required. This can be contrasted to the case where the oxidation of the same species is conducted on other electrode materials. Here, more positive potentials would be required and the likelihood of interference is therefore increased. Examples of the inorganic anions which react with mercury include S2-and CN-, which form a precipitate and a complex, respectively, as shown below:
Hg
+ S2- f
Hg
+ xCN- %
HgSl
+ 2e-
[Hg(CN),]
(10.5)
(2-x)+
+ 2e-
(10.6)
Both of these ions have been detected by amperometry with a mercury electrode [421.
Mercury electrodes can be formed from mercury drops (either flowing or static) or from thin films of mercury coated onto a suitable substrate. Mercury adheres well to silver and platinum, but since it slowly dissolves these materials, the thickness of the mercury film decreases with time. Carbon Carbon can be used as an electrode material in a number of forms, including carbon paste, carbon impregnated into a suitable binder, glassy carbon, pyrolytic graphite, carbon fibres, etc. Carbon paste electrodes are manufactured from particles of carbon suspended in an oil (such as Nujol) or a wax which is immiscible with the
307
ElectrochemicalDetection
solution phase. These electrodes are relatively simple to manufacture and replace, and give high detection sensitivity due to the very low residual currents produced. Disadvantages of carbon paste electrodes include some variability in electrode performance which results even when successive electrodes are prepared from the same constituent materials, and the long equilibration times required for sensitive operation [40]. Composite electrodes, in which the carbon is impregnated into a suitable binder such as polyvinylchloride, neoprene rubber or Kel-F, give more consistent performance but are more difficult to prepare. Glassy carbon is a very popular electrode material because it can be formed into a variety of shapes and can be easily polished. Glassy carbon is a gas impermeable material formed by the heating of phenol-formaldehyde resins in an inert atmosphere. Electrodes of this type give higher residual currents than carbon-paste electrodes, but can be used over a 2 V working potential range which covers both positive and negative potentials. In addition, carbon is resistant to the formation of oxides at the electrode surface, so the electrode maintains integrity over prolonged periods of usage. Glassy carbon is sometimes also used for the construction of auxiliary electrodes as well as working electrodes.
Silver, platinum and gold Working electrodes may also be constructed of pure metals, which are usually inert materials so that the available potential window is not unduly restricted. It can be noted in passing that some reactive metals, such as copper [43],nickel [44]and copperized cadmium [45], have also found limited application as working electrodes in amperometry. Platinum and gold have wide potential windows which extend above +1.0 V in the oxidative region. Silver has a much smaller potential window, but is a valuable electrode material because of the reactions it can undergo with solutes during the detection process. It has been shown that amperometric detection of inorganic anions can be improved through the use of electrode materials that mediate or participate directly in the electrode reaction. This participation may be in the form of complexation or precipitation reactions, along the same lines discussed earlier for mercury electrodes. Silver has special importance in this regard and is a suitable electrode material for the amperometric determination of halides, CN-, S2-, S03*-, SCN- and S ~ 0 3 ~ As - . an example, we will consider the detection of CN-at a silver electrode. Cyanide can be oxidized to cyanate at a glassy carbon electrode, but only at a moderately high positive potential. The possibility of interference by other oxidizable anions therefore exists. With a silver electrode, the silver itself is oxidized in the presence of CN-to form a silver cyan0 complex, as shown in the following reaction [46]:
Ag
+ 2CN-
% Ag(CN)i
+ e-
(10.7)
This oxidation occurs readily at 0.0 V versus AgIAgCl, at which potential interferences are considerably less than encountered with a glassy carbon electrode operated at the higher potential necessary with this electrode material [7]. The ability of silver, gold and platinum electrodes to form complexes with halide ions restricts the
308
Chapter 10
potential range accessible to these electrodes in eluents which contain halides. Metal electrodes constructed from inert materials, such as gold and platinum, can show pronounced changes in performance with use. This behaviour arises from the adsorption of electrode products or of components from the sample itself. An example of this effect is the response of a platinum electrode used for the amperometric (oxidative) detection of I- [47]. A new electrode gave very low response to I-, whereas a used electrode which had just been polished gave very high sensitivity, but the signal produced was unstable and the baseline drifted severely. Reproducible electrode performance was obtained only when the platinum was conditioned by immersing it in a saturated solution of KI for 30 minutes, in order to form a uniform layer of chemisohed 1- on the electrode surface. It was necessary to repeat this procedure after 5 working days. Similar adsorption effects have been noted for S2- on silver working electrodes [48] and in the detection of CrOq2- with an iodized platinum working electrode [49].
Criteria for selection of the working electrode material The preceding discussion has revealed a wide range of materials which are available for the construction of working electrodes in amperometric detection. Some guidelines for selection of the correct material for a given application are therefore required. The following aspects should be considered when making this selection 1411: The potential window for the working electrode in the chromatographic eluent to be used. (ii) The involvement of the electrode itself in the electrochemicalreaction. (iii) The kinetics of the electron-transfer reaction. (i)
The potential window will vary with the pH of the eluent. Fig. 10.10 shows the approximate potential windows accessible to five common electrode materials when used in acidic and basic solution. As the applied potential approaches the potential limit, background current increases. This increase is much more rapid for metal electrodes than for carbon. Glassy carbon and platinum have the highest accessible positive potentials and are therefore preferred for oxidations. Mercury, glassy carbon and silver are preferred for reductions. Involvement of the electrode material itself in the electrochemical reaction can often allow a particular material to find use in a potential range in which other electrode materials are normally considered to be preferable. This behaviour has been illustrated above for the oxidative reaction of CN- with a silver electrode. Rocklin [41] has suggested that a formation constant of loio for reaction of the analyte ion with the electrode material indicates a high probability that sensitive detection will be achieved for that ion. Electrode reactions with fast kinetics require a working electrode potential slightly (about 100 mV) more positive (for an oxidation reaction) than the standard reduction potential (EO)for that reaction. At this potential, all of the oxidizable species reaching the electrode surface will react and further increases in potential will not lead to larger currents (and hence larger peaks). However, electrode reactions with slow kinetics do
ElectrochemicalDerecrion -1.5
- 2 .O
309 -1.0
I
I
I
I I
I I
1.0
I
I
I
I
I
I
Gold
I
I
I I
I
I
I
I I
I
I
I I
I
I
I
I
I
I
II t)
I
Silver
I
I
I I
I
I I
I I I I
I
-1.0
I
I
I I
II
I
Mercury
-1.5
I
I
Platinum
I
1 I
!
I
I '
I
I -2.0
0.5
I
I
I
I
0
I
Glassy carbon
I
I
-0.5
I
-0.5
I
I
!
!
I
0 0.5 VOLTS (wrt Ag/ApCl)
I
! I
1.0
1.5
Fig. 10.10 Approximate potential windows accessible with various electrode materials in acidic solution (white boxes) and in alkaline solution (shaded boxes). Data from [6,41].
not follow this rule and require substantially more positive potentials to achieve quantitative reaction of the analyte at the electrode surface. The reaction kinetics therefore play a prominent role in determining the optimal applied potential and this, in turn, affects the choice of the working electrode material. The eluent used for the particular IC separation under consideration also exerts a considerable influence on the selection of the working electrode. For example, when basic eluents are used for the ion-exchange separation of anions of weak acids, different electrode materials may be required in comparison to the detection of the same solutes under acidic conditions, such as after elution from an ion-exclusion column. 10.4 FLOW-CELL DESIGN AND RESPONSE EQUATIONS
Electrochemical cells for use with flowing streams may be classified as flow-by, in which the eluent flows parallel to the surface of the working electrode;flow-through, in which the eluent follows a tortuous path between surfaces of the working electrode; and flow-at, in which the eluent i,mpinges perpendicularly onto the surface of the working electrode.
Chapter I0
310 Outlet (to reference electrode)
t
eiectrpde
n
WoriLlng electrode
Fig. 10.11 Thin-layer amperometric flow-cell in (a) schematic form and (b) in commercial form. a - cell inlet, b - holder for working electrode, c - contact for working electrode, d - gasket, e FTFE holder for reference electrode, f - flow-through diaphragm, g - outlet. Courtesy of Waters. 10.4.1
Thin-layer cells
The most common type of amperometric cell is the flow-by, which is illustrated schematically in Fig. 10.1l(a). A thin spacer (in the form of a gasket) held between two rigid blocks defines the thickness, width and length of the flow-channel, and thereby the cell volume. In early versions of this cell, the working electrode was housed in one of the blocks comprising the cell, whilst the auxiliary and reference electrodes were mounted downstream in another compartment. Newer designs have the auxiliary electrode positioned close to the working electrode, and in some cases, even the reference electrode is positioned in the same cell compartment. A commercial cell design of this type is shown in Fig. 10.1l(b). These changes result in greatly improved
Electrocktnikal Detecrion
311
cell performance because the electrical resistance of the cell is lower and potential control is improved. In addition, the cell is simple to dismantle and the working electrode can be polished easily. The cell current for a thin-layer amperometric cell is given by [35]:
(10.8)
where i is the cell current in amperes, n is the number of electrons in the electrode halfcell reaction, F is the Faraday constant, A is the electrode area in cm2, D is the diffusion coefficient in cm2s-', h is the flow-channel thickness and d is the flow-channel width in cm, Uv is the volume flow-rate in cm3s-l, and C is the analyte concentration in mol ~ m - ~ . Eqn. (10.8) predicts that there is a linear relationship between cell current and analyte concentration, under conditions of constant flow-rate. It is also predicted that the cell current will increase with flow-rate, but this has been shown to be invalid for real cells [17]. Thin-layer cells attain detection limits in the sub-nanogram range, have wide linear dynamic ranges (three to five orders of magnitude) and exhibit good measuring reproducibility. Cell volumes of less than 1 pl can be achieved by decreasing the thickness of the spacer, but the baseline noise increases rapidly with decreasing cell thickness. The quality of polishing of the faces of the two cell blocks is also important, since the better the polishing, the thinner the spacer can be without the baseline noise becoming too great. 10.4.2
Flow-through, high-efficiency cells
The electrochemical efficiency of a cell can be increased by using electrodes of large surface area. This can be achieved in a thin-layer cell configuration by using a long, planar working electrode, but the design can be made more compact through the use of a flow-through electrode made from a packed bed of porous particles or from a porous plug of electrode material (such a.; reticulated vitreous carbon). Reaction of the analyte in this type of cell approaches 100%; that is, the cell operates in the coulometric mode. The response of such high-efficiency cells is given by [17]:
i = nFCUv
(10.9)
where the terms have the same meanings as for eqn. (10.8). If the current is integrated during the passage of the analyte through the cell, we obtain:
Q = nFM
(10.10)
where Q is the integrated current (i.c. the coulombs of electricity from the analyte) and M is the moles of analyte injected. Eqns. (10.9) and (10.10) show that the cell current for a high efficiency flow-through cell is larger and much more dependent on flow-rate than is the thin-layer cell, but the integrated current, Q, is independent of flow-rate.
312
Chaprer 10
Inlet Inlet
(a)
Working elect rode (b)
Fig. 20.12 Wall-jet cells in (a) constrained and (b) unconstrained formats.
Whilst the relative merits of amperometry and coulometry (and hence those of high-efficiency flow-through cells and thin-layer cells) may be debated, certain attributes of the high-efficiency cell are clear. These cells are well-suited for screening and sample clean-up applications where electroactive interferences in the sample or eluent can be reacted before the analyte band reaches the detector. On the other hand, these cells are not well-suited to applications in which the potential is swept or pulsed because the large surface area has an associated large double-layer capacitance effect. 10.4.3
Wall-jet cells
The wall-jet cell (shown schematically in Fig. 10.12(a)) is the most common example of the flow-at type of electrochemical cell. The sample flow is directed perpendicularly onto the surface of the working electrode and may exit from the cell through a narrow flow-tube (as shown in Fig. 10.12(a)), or may pass into a larger volume compartment surrounding the working electrode (Fig. 10.12(b)). The theoretical response equation for this type of cell is given by [50]: (10.11)
where v is the kinematic viscosity, R is the radius of the working electrode in cm, and a is the inside diameter of the jet in cm. The other terms in eqn. (10.1 1) are as previously defined. The theoretical flow-rate dependency of the wall-jet cell differs from that for the thin-layer cell, but in practical studies, cells such as that shown in Fig. 10.12(a) exhibit the same flow-rate dependency as a thin-layer cell. These are called constrained wall-jet cells, since the design causes the reflected flow to move parallel to the working electrode surface, so the cell is effectively a thin-layer type with radial flow patterns and therefore responds according to eqn. (10.10). A true wall-jet cell, which responds in accordance with eqn. (lO.ll), has a jet diameter, a, which is smaller than the radius of the working electrode, R. A sufficient
ElectrochemicalDetection
313
gap between the jet and the working electrode is also required, so that the tip of the jet does not interfere with the reflected flow from the electrode surface. Such cells are called unconstrained wall-jet cells, or large-volume wall-jet cells, and are depicted schematically in Fig. 10.12(b). Some important characteristics of wall-jet cells deserve mention. The effective cell volume is much smaller than the volume of the electrode compartment, since the effective volume actually consists only of the thin layer of liquid at the electrode surface. After detection, the sample band disperses rapidly in the relatively large electrode compartment, so wall-jet detectors can be used in tandem with other detectors only when placed last in line. (ii) Wall-jet cells show a greater flow-rate dependence than thin-layer types and are therefore more susceptible to flow-pulsations in the pumping system. (iii) Wall-jet cells are suitable for miniaturization without loss of concentration detection limits because the ratio of electrode radius to jet diameter is more important than electrode radius alone. (iv) The relatively small size of the working electrode results in small doublelayer capacitance effects and therefore a shorter time constant for the cell. Thus, this cell is suitable for those applications in which the electrode potential is changed rapidly, such as pulsed-amperometric detection. (i)
10.4.4
Polarographic cells
Polarographic cells require that a dropping mercury electrode (DME)or a hanging mercury drop electrode (HMDE)is used as the working electrode. The most difficult problem encountered with the DME is the attainment of a small cell volume without impairing the function of the DME. Two typical cell constructions are shown in Figs. 10.13(a) and 10.13(b), in which the DME is arranged vertically and horizontally, respectively. Cell volumes as low as 1 pl can be achieved, but current oscillations occur as a result of the physical disturbance of the solution as the drop falls. These current oscillations may be suppressed using an RC filter, but this increases the time constant of the cell and renders it unsuitable for rapid potential changes. Alternatively, a very short drop time may be employed, and this is best achieved with a horizontal capillary (Fig. 10.13(b)). A wall-jet type polarographic cell can also be used in which the eluent jet is directed vertically onto a macroscopic DME placed in a vessel containing a base electrolyte (Fig. 10.13(c)). The effective volume of such a cell is around 1 pl. The construction of detectors with a HMDE is more simple than with a DME,but the advantage of periodical renewal of the electrode surface is lost in these cells. 10.4.5
Multi-functional cells
More than one mode of electrocheqical detection can be combined into the same cell as long as the correct electrodes for each detection mode are supplied. For example, amperometry (at a glassy carbon working electrode) and polarography (at a DME)can be performed simultaneously using a bi-electrode cell [53]. The flowing sample solution
Chapter 10
314
1
Fig. 10.13 Polarographic detector flow-cells. (a) Thin-layer type with vertical DME. 1 - DME, 2 - inlet, 3 - reference electrode, 4 - auxiliary electrode. (b) Thin-layer type with horizontal DME. 1 - inlet, 2 - DME. 3 - mercury pool auxiliary electrode, 4 - tube to mercury reservoir. (c) Wall-jet type. 1 - DME, 2 - jet, 3 - base electrolyte, 4 - reference electrode, 5 - auxiliary electrode. Reprinted from [Sl, 521 with permission.
contacts both electrodes and the combination of electrode materials which is employed permits reductive and oxidative chromatograms to be recorded simultaneously on the electrode material most suited to each. It is also possible for conductivity and amperometric detection in IC to be used in the same detector cell [53]. The electrode arrangement (Fig. 10.14(a)) utilized in this case consists of a platinum working electrode inserted concentrically into a stainless steel capillary tube, with suitable insulation between the platinum and steel. Eluent flow is directed onto the working electrode in a wall-jet configuration and the cell volume is only 15 nl. Chromatograms with simultaneous conductivity and amperomeuic detection were obtained on a microcolumn for common anions, using an ion-interaction separation with phthalate as eluent (Fig. 10.14(b)). It is noteworthy that the amperometric and conductivity signals from the cell are quite independent. 10.4.6
Dual-electrode amperometric cells
Thin-layer cells, such as those shown in Fig. 10.11, can be modified by inclusion of a second working electrode. This electrode can be arranged in parallel or in series with the first working electrode. These configurations are illustrated in Fig. 10.15, together with typical operating modes of the dual-electrode cell. It is should be noted that the dual, parallel arrangement can also be produced in the cell shown in Fig. 10.11(a) by mounting a second working electrode in the position of the auxiliary electrode. In the dual, series electrode configuration, the first electrode (set at a positive potential) can be used to oxidize solutes, whilst the second electrode (set at a negative potential) can be used for reduction. Solutes which undergo reversible or quasireversible reactions will be oxidized at the first electrode, and then reduced at the second electrode, if the potentials are correctly chosen. On the other hand, solutes which are irreversibly oxidized will not be detected at the second electrode (Fig. 10.15(a)).
Electrochemical Detection
3 15
c I-
i,: NOf
4\
c
1 nA
/l
Hydroquinone
1 mm
(a)
I
0
I
I
10 20 Time (min)
I
30
(b)
Fig. 10.14 Simultaneous conductivity and amperomemc detection in IC using the same flowcell. (a) Design of the flow-cell. 1 - platinum working electrode, 2 - stainless steel capillary tube, 3 - insulation, 4 - stainless steel body of the cell. Arrows indicate the flow-path of the sample. (b) Chromatograms obtained with conductivity (upper trace) and amperomemc (lower trace) detection. A clfjmicrobore column was used with 0.75 mM teaabutylammonium phosphate and 0.25 mM phthalate at pH 6.3 as eluent. Solute concentrations: (21-, NOz-, Br- and NO3- all 1 mM; hydroquinone 0.1 mM. A polarizing voltage of +1.1 V was used. Reprinted from [54] with permission.
Interferences can therefore be eliminated. This approach has been utilized for the - , I- alone is reduced at the second electrode detection of I- in the presence of S Z O ~ ~since without interference from S 2 0 ~[55]. ~In the dual, parallel electrode cell configuration, different potentials (El and E2) are applied to each working electrode and the resulting currents are ratioed or subtracted (Fig. 10.15(b)). The two solutes (A and B) depicted in the Figure have different half-wave potentials. Solute B will give the same current at both electrodes, whereas solute A will give a higher current at El than at E2. The ratio of these currents can be used for identification of the solutes and as a measure of peak homogeneity, whilst the difference between the currents can be used to eliminate interferences. This
2 ch
TABLE 10.3 SOME TYPICAL APPLICATIONS OF ELECrrZOCHEMICAL DETECTION IN IC Solutes
Aldehydes Aldehydes (as adducts with S032') As(II1) As(IW, AsW) Bf Bi c2042-
CNCN-, HS-, I', BrCu2+, Ni2+ F ,ci-, PO^, NO^HS-, CNHS-, CN-
r, s2032-
II' IInorganic anions Inorganic anions
Sample
M
Standards Wines
PAD
Mineral water Standards Waters Plasma Urine Dust, particulates Standards Urine Standards Standards Drinking water Pharmaceuticals Iodized salt, KF Sedimentary rocks Seawater Standards Standards
Amp
d
Amp
Cod Amp Amp Amp Amp Amp Amp
Indirect Amp Amp
Pol Amp, DPE Amp Amp Amp Amp
Indirect cod
Working elecrmcleb Au GC
Reference electrodec
Potential
Sensitivity
Ref
Pulsed 0.75
1-3 pprn 5 PPm
57 58
1.oo 0.16 0.10 0.03 1.25 0.02 0-0.3 0.8 0-0.45 0.06 0.00 1.05, 1.15 0.8 0.17 1.o 1.1 v 0.16
0.012 pM n.s 10 PPb 10 PPb 100 PPb 1 PPb 2-30 ppb < 80 ppb c 0.5 pprn 20 PPb 1-2.5 ppm 10-50 ppb 10 PPb 10 PPb 5 PPb 0.05-19 ng c 0.1 ppm
59
W)
60 61 62 63 64 46 65 19 48 42 55
47 66 67 68 21
TABLE 10.3 (Continued)
Lactose Maltose NHs+ No3N@-,NOy Organic acids Po43-
Polythionates, ~ 2 0 3 ~ ~032s2e2S2s2-, s,2-, so32-, s2032-
s2-.s2032S2-, Br, CN-
Transition metals Transition metals Transition metals UWI)
Au
Pulsed pulsed
Potato chips Corn syrup Sewage Natural waters Smked meat, fish Urine Wastewaters Standards Foods Urine, plasma Turbid waters Coal desulfinizaaon samples Kmft White liquor Sour waters
PAD PAD Indirect cod Amp Amp, DPE
Amp Amp
n.s.
Standards
Indirect coul F s Pol IndirectAmp Pol
0.75 -1.30,0.20
Standards Seawater Urine, waters
Au C-cloth
cu-cd
Indirect cod DP Pol
GC GC n.s. HMDE
Amp
Pt
Amp, DPE
GC Ag DME
Amp
Amp
Indirect Pol
0.45 -1.15
1.10, 1.00 1.10 0.45 0-1.6 0.4 0.7,0.9 0.00 0.08
1.0
0.65 -0.65
n.s. 50 PPb 3.3 ng 6.2 pp b 50 n.s. 27 PPb n.s. 0.1 ppm 10pmol 1.9 ppb n.s.
32 32
n.s. n.s. < 0.5 ppm 13-64ppb 0.2-1.0 ppm 80 ng
73 74 21 38
25 45 69
70 23 8
71 56
72 10
29 9
Amp = ampemmetry, Coul = coulometry, Pol = polarography, PAD = pulsed ampemmetry, DPE = dual, parallel electrodes. RP = reverse-pulse, DP = differential pulse. GC = glassy carbon, DME = dropping mercury electrode, HMDE = hanging mercury drop elemode, WAG = wax-impregnated graphite, I-Pt = iodized Pt, C = carton, Cu-Cd = coppenzed cadmium. Fe(1I)FeQII) = fem/femcyanide, SCE = saturated calomel electrode. n c. = not specified. a
I
I
A
B
A'
A -EAl " A "E2
8
-+ El
,E2
8
No reaction
(a)
(bl
Fig. 10.15 Configurations for dual-electrode amperomemc detection in IC. (a) Dual, series electrodes. Irreversibly reacted solute B is excluded from interfering with the detection of reversibly reacted solute A at the second working electrode. (b) Dual, parallel electrodes, which may be operated separately and independently to yield difference and ratio chromatograms for solutes A and B. Reprinted from [7] with permission.
3
$ r, 0
Electrochemical Detection
319
approach can again be illustrated using I- and S Z O ~as~ solutes, ’ with El = +1.05 V and V [55]. The current ratios were found to be reproducible and were characteristic of each solute. A further application of dual, parallel electrode detection ~ -urine, without interference from uric acid in amperometry is the detection of S ~ 0 3 in or other electroactive components of urine [56]. E2 = +1.15
10.5 APPLICATIONS OF ELECTROCHEMICAL DETECTION Electrochemical detection has been applied in IC in situations where extreme sensitivity or special selectivity is required. Most commonly, the electrochemical detector has been operated in tandem with a universal, non-selective (e.g. conductivity) detector so that a more general sample analysis can be obtained than is possible with the electrochemical detector alone. Table 10.3 gives a representative listing of some typical applications of electrochemical detection in 1C and includes the approximate detection limits which can be attained. The chromatograms given throughout this Chapter provide further illustration of other applications.
10.6 REFERENCES 1 2 3 4 5 6 7
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Meites L., Zuman P. and co-workers,CRC Handbook Series in Inorganic Electrochemistry, Vols. I-V, CRC Press Inc., Boca Raton, FL, 1980-1985. Kissinger P.T. and Heineman W.R., (Eds.),Laboratory Techniques in Electroanalytical Chemisrry, Marcel Dekker Inc.. New York, 1984. Sawyer D.T. and Roberts J.L., Experimental Electrochemistryfor Chemisrs, John Wiley, New York. 1974. Rveki R., Talanta, 27 (1980) 147. Stulik K. and Pacakova V., J . Electroanal. Chem., 129 (1981) 1. Palmisano F. and Zambonin P.G., Ann. Chimia, 74 (1984) 633. Johnson D.C., Weber S.G., Bond A.M., Wightman R.M., Shoup R.E. .and Krull I.S., Anal. Chim. Acta, 180 (1986) 187. Takano B.. McKibben M.A. and Barnes H.L., Anal. Chem.. 56 (1984) 1594. Cassidy R.M. and Elchuk S., Inter. J. Environ. Anal. Chem., 10 (1981) 287. Uddin Z., Markuszewski R. and Johnson D.C., Anal. Chim. Acta, 200 (1988) 115. Heuser J.R. and Girard J.E., Anal. Chem., 57 (1985) 2847. Ramstad T. and Weaver M.J., Anal. Chim. Acta, 204 (1988) 95. Ramstad T. and Weaver M.J., J. Chromatogr., 456 (1988) 307. Ramstad T., Anal. Leu., 21 (1988) 331. Kissinger P.T., Anal. Chem., 49 (1977) 487A. Weber S.G. and Purcjue W.C., Anal. Chim. Acta, 100 (1978) 531. Roe D.K., Anal. Lerr., 16 (1983) 613. Horvai G., Fekete J.. Niegreisz Z., Toth K. and Pungor E., J . Chromatogr., 385 (1987) 25. Tarter J.G., J. Liq. Chromatogr., 7 (1984) 1559. Jones V.K. and Tarter J.G., J. Chromurogr., 312 (1984) 465. Girard J.E., Anal. Chem., 51 (1979) 836. Tanaka K. and Ishizuka T., J. Chromatogr., 190 (1980) 77.
320 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
40 41 42 43 44 45 46 47 48 49 50 51 52
53 54 55 56 57 58 59
60 61 62 63
chapter 10 Tanaka K. and Ishizuka T., Water Res., 16 (1982) 719. Tanaka K., Bunseki Kaguku, 32 (1983) 439. Tanaka K., Ishizuka T. and Sunahara H., J. Chromatogr., 177 (1979) 21. Tanaka K., Ishihara Y.and Nakajima K . , Bunreki Kagnku, 32 (1983) 626. Hojabri H., Lavin A.G.. Wallace G.G. and Riviello J.M.. Anal. Proc., 23 (1986) 26. Barisci J.N., Wallace G.G. and Riviello J.M., Chromarogruphia, 25 (1988) 162. Hojabri H.. Lavin A.G., Wallace G.G. and Riviello J.M., Anal. Chem., 59 (1987) 54. Hughes S. and Johnson D.C., Anal. Chim. Acta, 149 (1983) 1. Anderson J.E.. Bond A.M., Heritage I.D., Jones R.D. and Wallace G.G., Anal. Chem., 54 (1982) 1702. Edwards P. and Haak K.K., Amer. Lob., April (1983) 78. Berger T.A., U.S.Patent 4,496,454. January 29 (1985). Dionex Technical Note 20. Weber S.G., J. Elecrrounul. Chem., 145 (1983) 1. Dionex Technical Note 11R. Bratin K. and Kissinger P.T., J. Liq. Chromutogr.,4 (1982) 321. Hsi T. and Johnson D.C., Anal. Chim. Acta, 175 (1985) 23. Sejeant E.P., Potentiometry and Potentiomenic Tinutiom, John Wiley & Sons, New York, 1984. White P.C., Analyst (London), 109 (1984) 677. Rocklin R.D., LC, 2 (1984) 588. Bond A.M., Heritage I.D., Wallace G.G. and McCormick M.J., Anal. Chem., 54 (1982) 582. Kok W.Th., Brinkman U.A.Th. and Frei R.W., J . Chromatogr., 256 (1983) 17. Buchberger W., Winsauer K. and Breitwieser Ch., Fres. Z. Anal. Chem., 31 1 (1982) 517. Sherwood G.A. and Johnson D.C., Anal. Chim. Acta. 129 (1981) 101. Rocklin R.D. and Johnson E.L.. Anal. Chem., 55 (1983) 4. Han K., Koch W.F. and Pratt K.W., Anal. Chem., 59 (1987) 731. Han K. and Koch W.F., A w l . Chem., 59 (1987) 1016. Lamhelle J.H. and Johnson D.C., Anal. Chem., 50 (1978) 240. Gunasingham H. and Fleet B., Anal. Chem., 55 (1983) 1409. Stulik K. and Pacakova V., CRC Crit. Rev. Anal. Chem., 14 (1982) 297. Stulik K. and Pacakova V., Die Nahrwtg, 5 (1985) 501. Kunter W. and Kemula W., Chromurographia, 17 (1983) 322. Slais K., J . Chromutogr., 436 (1988) 413. Lookabaugh M., Krull I.S. and LaCourse W.R., J. Chromurogr.,387 (1987) 301. Kawanishi T., Togawa T., Ishigami A., Tanabe S.and Imanari T., Bunseki Kagaku, 33 (1984) E295. Rocklin R.D., in Turnski V. (Ed.), Formaldehyde: Analytical Chemistry and Toxicology, American Chemical Society Advances in Chemistry Series, 1985, p. 210. Lawrence J.F. and Charbonneau C.F., J . Chromatogr., 403 (1987) 379. Butler E.C.V., J. Chromatogr., 450 (1988) 353. Hu Z. and Tang Y., Analyst (London), 113 (1988) 179. Pyen G.S. and Erdmann D.E., Anal. Chim. Acta, 149 (1983) 355. Waters Ion Brief No. 88106. Mayer W.J., McCarthy J.P. and Greenberg M.S., J. Chromtogr. Sci., 17 (1979) 656.
Electrochemical Detection 64 65 66 67 68 69 70 71 72 73 74
32 1
Koch W.F., J . Res. Nur. Bur. Srd., 88 (1983) 157. Bond A.M., Knight R.W., Reust J.B., Tucker D.J. and Wallace G.G., Anal. Chim. Actu, 182 (1986) 47. Yang X.-H. and Zhang H., J . Chromutogr.,436 (1988) 107. Itoh K. and Sunahara H., Bunseki Kuguku, 37 (1988) 292. Mingjia W., Pacakova V., Stulik K. and Sacchetto G.A., J. Chromurogr., 439 (1988) 363. Lookabaugh M. and h l l IS., J . Chromurogr.,452 (1988) 295. Woo D.J.and Benson J.R., LC, 1 (1983) 238. Kim H.-J. and Kim Y.-K., J . Food Sci., 51 (1986) 1360. Goodwin L.R., Francom D.,Urso A. and Dieken F.P., Anal. Chem,. 60 (1988) 216. Cox D.. Jandik P. and Jones W., Pulp Pap. Conado, 88 (1987) "3 18. Nadkami R.A. and Brewer J.M., Am. Lob., 19 (1987) 50.
This Page Intentionally Left Blank
323
Chapter 11 Potentiometric Detection 11.1 INTRODUCTION
Potentiometry is the process in which potential changes at an indicator electrode are measured with respect to a reference electrode, under conditions of constant current (usually zero) flow. The potential of the indicator electrode varies with the concentration of a particular ion (or ions) in the solution contacting the electrode and thereby provides a means for determining ion concentrations. Potentiometric detection in IC is attractive because it has the following characteristics: Simplicity of the cell design, the measurement technique used, and the signal handling necessary. Measurements can be made without interference from dissolved oxygen. When certain types of indicator electrodes are used, the electrode potential is not greatly influenced by the eluent flow-rate. Potentiometric detection functions best when the eluent has a moderate and constant ionic strength, so it is particularly well-suited to IC applications. The indicator electrode does not participate in electrolysis reactions which could result in surface contamination of the electrode. The ohmic resistance existing between the indicator and reference electrodes is not critical. The latter factor permits the reference electrode to be placed remotely from the indicator electrode, provided that electrical contact between the two is maintained via the flowing solution. Potentiometry has been applied widely to the determination of ionic species (particularly inorganic anions) in aqueous solution, generally through the use of ionselective electrodes (ISEs), and for a number of years represented the most attractive approach to this type of analysis. This period saw intensive development of ISEs, which resulted in improvements to their detection sensitivity and also to their selectivity. Whilst high selectivity is essential for the analysis of solutions containing interfering species, and also for potentiometric detection in flow-injection analysis applications, the resulting response to only a limited number of solutes can often represent a disadvantage when potentiometric detection is coupled with a chromatographic separation technique. In such cases, it is desirable that the detector show more general response so that it can be applied to the detection of a wider range of solutes.
Chapter I I
324
Despite the advantages listed above, the usage of potentiometric detection in IC has been somewhat limited. This can be attributed to the moderate sensitivity of the technique and to the problem of high detection selectivity discussed above. Further drawbacks existing with some indicator electrodes in flowing solutions are slow response and poor baseline stability. This instability arises because the electrode potential is poorly defined under conditions where the concentration of the active solute ion is zero; that is, when the eluent alone is in contact with the indicator electrode. It is therefore sometimes necessary to stabilize the baseline electrode potential by addition to the mobile phase of a low, constant concentration of the active solute ion.
11.2 PRINCIPLES OF POTENTIOMETRIC DETECTION 11.2.1 General response equation The response of an indicator electrode is given by the Nernst equation:
E = Const +
(
'e3:FT)
log x
(11.1)
where E is the potential of the indicator electrode in volts, R, T and F have their usual meanings and X is the activity of the solute ion sensed by the electrode. The symbol n refers to the equivalents of electrons per mole of reaction (when a redox couple is involved), or the equivalents of charge per mole of analyte for a membrane electrode. When an inert indicator electrode is used to monitor a redox reaction, the same equation applies except that X becomes the ratio of chemical activities of the oxidized to reduced forms of the redox couple. The potential change (AE) accompanying a change in the activity of the solute ion from XI to Xp is given by: (11.2)
Eqn. (1 1.2) implies that a logarithmic electrode response profile results as the activity of the solute ion is increased. This is sometimes seen as a disadvantage of potentiometric detection, but as will be shown in the next Section, linear response can also occur in the low concentration ranges typically encountered in chromatographic methods of analysis.
11.2.2 Instrumental considerations The instrumentation required for potentiometry consists of a measurement cell comprising the indicator (variable potential) and reference (constant potential) electrodes, together with suitable electronics for accurate determination of the potential of the cell. Fig. 1 1. I shows a schematic representation of this arrangement. The prime requirement is that the current flow through the indicator electrode is kept close to zero,
Fi$
Porenriometric Detection
325
Power supply
1-'
R e f e r e nce electrode
Indicator electrode
Fig. 11.1 Potentiometry using a high impedance voltmeter for potential measurement. Reprinted from [ 13 with permission.
since any current flow will alter the electrode potential. For this reason, high impedance voltmeters are used so that the current flow is very small (typically amp) and the measured voltage is within the experimental error of the true potential of the system.
11.3 INDICATOR ELECTRODES AND RESPONSE PROFILES 11.3.1
Ion-selective indicator electrodes
Both solid-state and membrane type ion-selective electrodes have been employed as indicator electrodes in IC. The solid-state type has the advantage of rapid response in swiftly flowing streams in which the width of the diffusion layer at the electrode surface is minimal, but the selectivity is often too high for chromatographic applications. For this reason, potentiometric detection with solid-state electrodes finds most use when it is used in conjunction with a more general detection method, such as conductivity. On the other hand, membrane electrodes are less selective and are therefore more suited to chromatographic detection, but give slower response and may show marked dependence on eluent flow-rate. The response time of a membrane electrode has been shown to be improved by coating the membrane surface with a Nafion ion-exchange membrane, but this process adversely affected the sensitivity and linearity of response 121. Calibration plots of electrode potential versus analyte concentration show either a linear or logarithmic relationship, depending on the concentration range studied. Under conditions where a background concentration of analyte is added to the eluent stream in order to stabilize the baseline potential, the detector response is usually Nernstian and follows eqn. (1 1.2). In this case, X1 would be equal to the background concentration of analyte in the eluent. However, when theltotal analyte concentration at the electrode surface is very low, a linear relationship dependence on electrode potential may be observed [3-61. That is, the detector is operating in the sub-Nernstian region.
Chapter I I
326
p H electrodes
Glass electrcdes for the measurement of pH can be applied directly to the detection of organic acids 171 but are also useful for the indirect detection of common anions. We have already noted (Section 9.5) that most solute anions in suppressed IC are eluted as fully dissociated strong acids. This phenomenon was utilized in conductivity detection as a means of enhancing the detection signal for such ions. It is also apparent that a decrease in the pH of the eluent will occur as a result of the hydrogen ions introduced into the sample band by the suppressor. This pH change can be utilized for indirect detection of anions using potentiometric detection with a pH indicator electrode [8-10]. A chromatogram of common anions obtained using pH detection was shown in Fig, 10.5(a). The magnitude of the pH change is dependent on the eluent used. A typical carbonate-based eluent comprising 2.4 mM Na2C03 and 3 mM NaHC03 gives 5.4 mM H2CO3 when fully suppressed, resulting in a background eluent pH of 4.28. An analyte band composed of 1.5 ppm (42 pM) CI- gives 42 pM HCI after suppression, which results in a pH of 4.11 at the elution peak [9]: This gives a pH change of 0.17 pH units. On the other hand, a KOH eluent which is converted to water i n the suppressor, gives a pH change of 2.62 pH units for 1.5 ppm of C1-. Some representative limits of detection using pH measurements are 2.8 ppb for CI- and 128 ppb for NO3-, and it has been demonstrated that this form of detection generally gives detection limits which are superior to conductivity detection when a polymer pH electrode is used [lo]. The response equation for pH detection can be derived as follows [9]. If the background pH of the eluent is x, where the acidity is contributed solely by penetration of a strong acid regenerant through the suppressor, the background [H+] is M. An analyte band containing y M of a monovalent anion at the peak apex will have [H+]equal to + y) M, giving a pH of -[log(lOx + y)]. The pH change during sample elution is given by the difference between the background pH and the pH of the analyte band.
Eqn. ( 1 1.3) can be rearranged to give:
loz = 1 + 10Xy
(11.4)
Fig. 11.2 shows some calibration plots for pH detection of common anions, obtained using KOH or Na2C03 eluents. A plot of 10” versus y for the chloride data in Fig. 11.2 is linear and has an intercept of 1.023, which is in agreement with eqn. (1 1.4). We can also note that pH detection in suppressed IC is applicable to the detection of cations which are eluted with an acidic eluent and passed through a suppressor in the OHform. In this case, the suppressor contributes OH- to both the eluent and the sample, so that an increase in pH accompanies the elution of solute cations. The principles of this form of detection are identical to those described above for anions and once again, the detection limits obtained with a polymer pH electrode are generally superior to those for conductivity detection [lo].
PotentiometricDetection
321
x. .1
0.3 7 5
-
h
u)
.-
L
C
0.300 -
Anion concentration,p.M
Fig. 12.2 Calibration plots for anions in suppressed IC using pH detection. The solid lines are for a 30 mM KOH eluent, whilst the broken lines are for a 5 mM Na2C03 eluent. (1) C1-, (2) so42-,(3) NOj. Reprinted from [9] with permission.
Solid-state ion-selective electrodes Solid-state, or crystalline. ISEs use a conducting solid material as the ion-selective barrier between an internal filling solution and the external, sample solution. The most common examples of solid-state electrodes are the fluoride electrode (which uses a LaF3 crystal as the ion-selective barrier) and halide electrodes based on mixtures of AgzS and silver halides. Solid-state ISEs have been employed in IC for the detection of F- [11- 141, Bf 113, 151, I- 13, 151, C1- [15] and SCN- 1151. A solid-state copper ISE has been used for the detection of non-UV absorbing amino acids after post-column addition of 0.1 mM Cu(I1) in acetate buffer 1161. Here, reaction with the eluted amino acids caused a reduction in the concentration of Cu(I1) reaching the electrode, leading to a change in potential and hence indirect detection. At low values of amino acid concentration and for high values of the stability constant for the copper-amino acid reaction, it can be shown that the theoretical potential change of the electrode is linearly proportional to the total amino acid concentration. This relationship was found to be valid in practice, provided formation of the 1:2 copperamino acid complex was negligible. Liquid membrane electrodes ISEs of the liquid membrane type have a membrane separating the internal filling solution from the external analyte solution. The membrane consists of an organic liquid (immiscible with water) held on a porous plastic support. The organic liquid is often an
328
Chapter 11
ion-exchange material. As discussed earlier, these electrodes are generally less selective than the solid-state type and can therefore be used for the chromatographicdetection of a wider range of analyte ions. Commercially available liquid membrane ISEs have been used for the detection of N02- and NO3- [17] and CN- [2] after separation by IC. Home-made electrodes containing valinomycin. benzo- 15-crown-5, nonactin or tetranactin as neutral carrier ligands in a PVC membrane have been used for the detection of alkali metal cations and NH4+1181. 11.3.2.
Coated-wire indicator electrodes
Some very useful potentiomemc detectors have been developed using coated-wires as indicator electrodes. A simple example is a silver-silver chloride electrode prepared by treating a length of silver wire with hydrochloric acid. However, any insoluble silver salt can be used as the coating material. The potential of such an indicator electrode is given by [4,191:
where Ks is the solubility product of the salt, AgX, used to coat the electrode and a,- is the activity of the analyte ion, X-. When the electrode is immersed in a flowing stream, a certain amount of the AgX salt dissolves from the surface, giving rise to a steady state concentration of Ag+ and hence a stable background potential. A new potential is established if X - is added to the flowing stream (e.g. by elution from the chromatographic column), since the concentration of free silver ions will change. The difference between the new electrode potential and the baseline value is governed by the added concentration of X-. By analogy, low concentrations of other anions which form insoluble silver salts should also produce potential changes proportional to the concentrations in which they are added. Thus, a potentiometric detector of this type should be capable of detecting anions such as halides, SCN-and S2032-.
Coating materials A range of coating materials, including AgCI, AgBr, AgI, Ag3P04, Ag2S and AgSCN, have been examined for the preparation of coated silver wire electrodes [20]. When an eluent of sodium perchlorate was used, the AgCl and AgSCN coated electrodes gave optimum response and reproducibility. The coatings were produced by electrical oxidation of a silver wire in an aqueous solution of the selected anion for a period of 3-7 min. Electron microscopy of the coating showed a wide variation in particle size for the precipitated layer and with the exception of silver sulfide, coatings of smaller particle sizes were observed to have faster response kinetics in flowing solution. It was also found that newly prepared electrodes required conditioning by repeated immersion (and rinsing with water) in a solution containing 1 mM concentrations of each of the ions to be detected. When this conditioning process had been performed, the electrode surface was a composite of many silver salts covering the underlying layer of silver chloride precipitate.
Potentiometric Detection
329
Calibration and response characteristics The response of coated-wire indicator electrodes will again be dependent on the concentration of analyte injected and will also be influenced by the nature of the eluent used. A silver-silver chloride electrode used with an acetate eluent has been found to give a linear relationship between electrode potential and analyte concentration for chloride in the sub-ppm range [4]. Hershcovitz et al. [ 191 observed Nemstian response with a silver-silver salicylate electrode for several anions in the 0.1-1 mM concentration range, after separation with a salicylate eluent. On the other hand, Lockridge et al. [20] found the response of a silver-silver chloride electrode in a perchlorate eluent to be neither linear nor logarithmic. However, curvature of the logarithmic plot was sufficiently slight that the calibration was still useful for analytical purposes. Calibration plots obtained with coated-wire electrodes are shown in Fig. 11.3. Potentiometric detectors based on coated-wire electrodes show peak shape characteristics which are dependent on the re-equilibration kinetics of the precipitate film existing at the electrode surface. The response profiles observed for these electrodes are also influenced by consumption of a small, but significant, proportion of the analyte as a necessary part of the detection process. This effect may be an explanation for the fact that response with these electrodes can vary from linear to logarithmic, with unexplained effects occumng most often at low concentration levels. Mass-transfer processes and surface kinetics therefore assume an important role for indicator electrodes which are based on insoluble silver salts, particularly when largearea electrodes are used in conjunction with microbore columns, and these factors merit further investigation.
11.3.3.
Metallic copper indicator electrode
Metallic copper in the form of a wire or tube has been employed as an indicator electrode for IC and flow-injection methods [21-321. When a metallic copper electrode is placed in a flowing stream of an oxygenated, buffered eluent, copper ions (both cuprous and cupric) are formed at the electrode surface. Considering only the cupric ions and assuming that the eluent buffer contains a species B which complexes copper (11), the potential of the electrode may be described by the equation [231: (11.6)
where CCu11 is the total cupric ion concentration at the electrode surface and q u ~ ~ ( ~ , is the side-reaction coefficient for the binding of cupric ions by component B and hydroxyl ion. If a copper complexing ligand, L, now passes the electrode as an eluted peak, the new electrode potential is given by: (11.7)
where
330
L.
70
e
0
e
5
Chapter I I
Potentiometric Detection
331
and the a values describe the side reaction coefficients for Cu(1I) with the indicated components. Under conditions where the complexation of cupric ions by the added ligand is much stronger than by the buffer component and hydroxyl ions, and a 1:l complex is assumed between Cu(I1) and L, then for constant pH and constant composition of the eluent it can be shown that the difference between El and 5 (i.e. the peak height, H, in volts) is given by:
E2 - El = H = Const,
+RT log 2F
(-)PlCL D~L(H)
(11.9)
where is the stability constant for the Cu(1I)L complex, CL is the total concentration of ligand L, D is the dispersion factor and CXL(H) is the side-reaction coefficient for ligand protonation. A similar equation may be derived for complexation of the ligand with cuprous ions. Thus, if a single, stable compound (either a soluble complex or a precipitate) is formed by the solute ligand L with cuprous or cupric ions, a logarithmic relationship with Nernstian slope can be expected between the peak height H and CL (or N, the total number of moles of solute injected). When several complexes are formed in comparable amounts, then a more complicated relationship can be predicted. Similarly, the above Nernstian relationship will not be followed for very small concentrations of injected ligand, and it can be shown that under these conditions the peak height is given by [301:
Regardless of the response relationship applicable, the electrode potential is dependent on the concentration of copper ions which is, in turn, governed by a number of factors which are either constant over the period of the analysis or show variation. Factors of the former type include the oxygen content of the eluent and the flow-rate, whilst the chief variable factor is the changing concentration of the solute species.
Modes of operation of a metallic copper indicator electrode A metallic copper indicator electrode can operate in a variety of detection modes and these are summarized below: If the eluted solute forms a more stable complex with copper ions than does the eluent ion, a local decrease in copper ion concentration will occur at the electrode surface, leading to a decrease in the electrode potential. (ii) If the eluted solute forms a less stable complex with copper ions than does the eluent ion, a local increase in the copper ion concentration will occur at the
(i)
Chapter I1
332 N , nmol 6;
1
-
--
2
0.2
0.4
Succinate
10
Y
m
m
0
1
EI
5
0.5
10
Fig. Z2.4 Calibration plots obtained with a metallic copper indicator electrode operated in (a) direct and (b) indirect detection modes. Reprinted from [33] with permission.
electrode surface, leading to an increase in the electrode potential. This process assumes that an ion-exchange separation is being employed, so that solute ions replace an equivalent number of eluent ions in the mobile phase at the time of elution. (iii) If the eluted solutes are strong oxidants and are able to oxidize the surface of the metallic copper electrode, a local increase in copper ion concentration will occur and the electrode potential will increase. Reducing solutes can also be detected by the reduction of cupric ions to cuprous and this will also result in an increase of the electrode potential due to the higher standard electrode potential of the Cu+/Cuocouple (4.520 V) compared to the Cu2+/Cu0couple (4.337 V). A potentiometric detector employing a metallic copper indicator electrode can therefore function i n a direct mode, wherein only copper complexing ions are detected, or in an indirect mode in which only the eluent needs to show copper complexation properties. Fig. 11.4 shows typical calibration plots for direct and indirect detection. A further consideration is that the direction of the measured peak can be used as a further means of identification of the eluted solute. This type of detector is the most widely applicable potentiometric detector in IC and is influenced by analyte consumption or surface kinetic effects to a lesser degree than other indicator electrodes, such as those based on insoluble silver salts.
Potentiometnk Detection
333
+
Eluent in
n
Eluent in Eluent out (a 1 OUT t"FLAlRFIT" 1
f
IN ...
+J
Eluent out (b)
-
LKrn$!!
Fig. ZZ.5 Typical flow-cell designs for cylindrical ISEs. (a) flow-cap; (b) and (c) electrode housing types. Reprinted from [3, 11, 171 with permission.
11.4 FLOW-CELLS FOR POTENTIOMETRIC DETECTION To enable successful potentiometric detection to be achieved, it is necessary that the indicator electrode (and often the reference electrode as well) be incorporated into a suitable flow-cell. For the maintenance of chromatographic efficiency, it is essential to minimize dispersion of the solute by placing the flow-cell close to the column outlet, by reducing flow turbulence in the cell, and by ensuring that the internal volume of the cell is as low as possible.
11.4.1
Flow-cells for cylindrical ISEs
When cylindrical ISEs are used as indicator electrodes, it is possible to obtain reliable potentiometric readiGgs merely by allowing the column effluent to flow under gravity over the sensing membrane of an inclined electrode [9]. However, it is generally more convenient to use a flow-cell of some kind. The simplest flow-cell configuration is a flow-cap designed to fit over the end of the electrode. A typical flow-cap is illustrated in Fig. 11.5(a) and in the design shown, a small cavity of 5 pl volume, drilled into the
Chapter I 1
334
Eluent
Teflon spacer Fig. 11.6 Typical flow-cell designs for wire indicator electrodes. (a) copper wire indicator electrode (l), silver-silver chloride reference electrode (2), agar gel (3); (b) cell for silver-silver chloride coated wire indicator electrode. Reprinted from [20,2l]with permission.
inside bottom of the cap, serves as the detection chamber [ 171. Most efficient operation of the electrode was achieved when the inlet stream was directed vertically onto the electrode surface and the entrapment of air bubbles was prevented when the outlet tube was orientated at 45O. When flow-caps are used, the distance between the indicator and reference electrodes is generally large and electrical contact between the electrodes can be enhanced by inserting platinum wire into the connecting tubing 1161. Cylindrical indicator electrodes can also be housed in a variety of alternative flow-cells and two suitable designs are shown in Figs. 1 1 S(b) and (c). Both cells are of very low volume (6-10 pi), provide for high linear flow velocities over the electrode surface to promote rapid electrode response [3], and permit the indicator and reference electrodes to be placed in close proximity to each other. 11.4.2
Other flow-cells
Wire indicator electrodes are more easily accommodated into a flow-cell than cylindrical electrodes by virtue of their smaller size, and the design of the flow-cell does
PotentiometricDetection
335
Iodide feed solution out
Eluent inlet
+
4
Iodide feed
solution in
Fig. 11.7 Concentric-flow diffusion cell for post-column addition of an electroactive species to the mobile phase. (1) external feed solution; (2) collars from heat-shrinkable plastic; (3) 1.6 mm OD polyethylene tubing transporting the eluent; (4) hollow-fibre dialysis tubing. Reprinted from [3] with permission. not appear to exert a major influence on electrode performance. Fig. 11.6 shows two flow-cells which are representative of published designs. The simple design in Fig. 11.6(a) has low volume (4 pl) and permits easy removal and cleaning of the metallic copper wire indicator electrode [21], whilst the flow-cell shown in Fig. 11.6(b) [20] is more suited to indicator electrodes which do not require frequent treatment. A membrane cell has been reported for potentiometric detection in IC [34]. This cell consists of an ion-exchange membrane which separates two chambers, each of which contains a reference electrode. The column effluent passes through one chamber, whilst eluent is pumped through the second chamber. When a solute ion is eluted into one chamber of the cell, and provided that the concentration of the solute is very small compared to that of the eluent, then the potential of the cell changes linearly with solute concentration. As discussed previously, it is often advantageous if a low background level of an electroactive solute is added to the eluent in order to give a stable baseline electrode potential. Whilst this can be achieved by adding the solute ion to the eluent, such an approach has a number of disadvantages. Samples with levels of the solute less than that present in the eluent will produce negative detector signals, whilst those with concentrations similar to this level cannot be detected at all. An alternative method is to add the desired ion to the eluent after the separation column. A concentric flow diffusion cell has been described 131 for this purpose, wherein addition of I- is required. This cell contains a length of hollow-fibre dialysis tubing, through which the column effluent is passed, whilst eluent containing 0.1 mM I- is circulated around the exterior of the tubing with the aid of a peristaltic pump (Fig. 11.7). Provided pressure fluctuations from the eluent pump are eliminated with a suitable pulse dampener, the rate of diffusion of I- into the column effluent is constant.
Chapter I I
I'
0
2
4
6
Time (min)
Fig. 11.8 Gradient elution with ptentiometric detection using a silver-silver chloride coated wire indicator eleclrode. Eluent: 3.5-10.0 mM sodium perchlorate at 1.6 ml/min; injection volume, 20 pl; analyte concentrations, 1.0 mM. Reprinted from [u)]with permission.
11.5 APPLICATIONS OF POTENTIOMETRIC DETECTION IN IC 11.5.1
Halides and pseudohalides
One of the more commonly encountered applications of potentiometric detection in IC involves the use of a solid state electrode for the detection of F-. This species is eluted early in a chromatogram under eluent conditions suitable for the separation of common anions, such as halides, N O i . NO3-, Pod3- and S042-. In many cases, it is difficult to distinguish the F peak from the solvent front eluted at the column void volume and this provides strong justification for coupling potentiometric detection for Fwith a general purpose detection mode, such as conductivity [ l l , 131. Use of an iodide ISE for the analysis of I- in seawater has also been reported [3]. Silver wire electrodes coated with insoluble silver salts have been applied to the detection of halide and pseudohalide (SCN-and S2O3*-) ions. A silver salicylate coating
Potentiomem*cDetection
337
coupled with the use of a salicylate eluent for the ion-exchange separation has been suggested to provide a stable baseline potential [ 191, whereas other authors [4,201 have found that a silver chloride coating is suitable when the eluent used does not form an insoluble silver salt. Under the latter conditions, the baseline potential of the electrode is not dependent on eluent concentration and this leads to the possibility of gradient elution with potentiometric detection. Fig. 11.8 shows a chromatogram obtained using a silversilver chloride indicator electrode with a linear concentration gradient of sodium perchlorate in the eluent. 11.5.2
Weak acid anions
Problems are often encountered with the conductivity detection of anions of weak acids because these species are weakly retained by anion-exchangeunless the eluent pH is high, and they become partially or fully protonated after passage through a suppressor. For these reasons, potentiometric detection is attractive and the use of a silver sulfide membrane electrode has been reported for the detection of CN- and S2- [2]. No interference from Br', I- and SCN- was observed, provided that chromatographic conditions were chosen so that these ions did not co-elute with the analyte ions. A glass membrane electrode has been employed for the detection of carboxylic acids after ionexchange separation [7] and a liquid-membrane electrode of low selectivity has been successfully used for the determination of NO2- and NO3-, as well as phthalate isomers [171. 11.5.3
Cations
A homemade PVC matrix membrane electrode has been reported for the detection of monovalent cations [18]. The polymer coating contained small quantities of active ligands, such as valinomycin. A calcium liquid-membrane ISE has been applied to the determination of calcium using measurements of conductance rather than potential [35]. An instrument using the bipolar pulse method was employed for conductance measurements and whilst the sensitivity of the electrode under these conditions was similar to that obtained when the electrode was operated in the potentiometric mode, the electrode response time was dramatically shorter for the conductance mode. The times required for the electrode to reach 90% of total response were 10 ms and 4-5 s for the conductance and potentiometric modes, respectively. It is therefore likely that conductance measurements using ISEs could find wider application to IC analysis. 11.5.4
Applications of the metallic copper indicator electrode
Direct detection A metallic copper indicator electrode housed in the flow-cell shown in Fig. 11.6(a) has been widely applied in IC,. Direct detection of copper complexing solutes eluted with weakly complexing eluent ions has been reported for carboxylic acids, halides and amino acids using eluents such as tartrate, phosphate and phthalate, in both ion-exchange and ion-exclusion separation systems [33]. Fig. 1 1.9 shows chromatograms for direct potentiometric detection after ion-exchange separation. Similarly, direct detection of
338
Chaprer 11
EC"
I
CI
1
1
-
1
I
I
Time, min Fig. 11.9 Chromatogram of species exhibiting direct response with a metallic copper indicator electrode. Column: Vydac 302 IC 4.6. Eluent: (a) 1 mM sodium tartrate at pH 3.2, (b) 1 mM potassium orthophosphate at pH 7.0. Injected amounts: (a) 0.5-50 nmol. (b) 5 nmol of each species. Reprinted from [33] with permission.
oxidizing anions (IO3-, BrO3- and ClO3-) and reducing species (ascorbic acid, hydrazine and hydroxylamine) has been achieved [32, 331. Fig. 11.10 illustrates the direct potentiometric detection of oxidizing solutes. The high degree of selectivity offered by direct detection has proven to be advantageous in the determination of oxalate in urine, where differentiation of oxalate from closely eluting excess sulfate is required. Use of the potentiometric detector enabled sample preparation to be confined to simple dilution and no interference from sulfate was observed [31].
Indirect detection Indirect detection with a metallic copper indicator electrode can be applied to inorganic anions and some weakly complexing ciirboxylic acids, as well as alkaline earth and transition metal ions. provided that the eluent used for the ion-exchange separation shows appreciable copper complexation ability. Thus NOz-, NO3- and Sod2- are detectable in a phthalate eluent [29], and alkaline earth and transition metal ions are detectable in an eluent comprising ethylenediamine and a complexing agent such as tartrate, citrate or oxalate 1301. Fig. 11 .I 1 shows chromatograms obtained with indirect potentiometric detection. Post-column addition of Cu(11) has been employed for the indirect potentiometric detection of reducing carbohydrates, using a metallic copper electrode and an ion-exchange column 1251. The ubiquitous complexation characteristics
PotentiometricDetection
339
I
EC"
I
4 I
I
0
5
Time, min Fig. 22.20 Chromatogram of oxidizing anions detected at a metallic copper indicator electrode. Column: Vydac 302 IC 4.6. Eluent: 20 mM sodium tartrate at pH 3.2. Injected amounts: 1-100 nmol. Reprinted from 1331with permission.
ECU
1
NO;
I
I
I
I
I
L
0
5
10
0
5
10
Timc,min
Fig. 11.11 Chromatogranis of inorganic and organic anions exhibiting indirect potentiometric response with a metallic copper electrode. Column: Vydac 302 IC 4.6. Eluent: 2 m M potassium phthalate at pH 4.6 (a) or 4.0 (b). Injected amounts: (a) 60-120 nmol, (b) 250 nmol of each species. Reprinted from [33] with permission.
Chapter I1
340
of copper enable a wide range of eluents to be used with the indirect detection mode, which suggests that this form of detection could be applied to almost any ion which can be separated by IC. Table 1 1.1 summarizes some of the published applications of potentiometric detection in IC. TABLE 11.1 APPLICATIONS OF POTENTIOMETRIC DETECTION IN IC Species separated
Indicator electrode
Separation mode
Detection limitsa
Ref.
Alkaline eanh ions Amino acids Amino acids, diamines Ascorbic acid, N2H.4, NH2OH BrCarboxylic acids Carboxylic acids Carboxylic acids CN-, S2-
Metallic copper Metallicqpr Copper - ISE Metallic copper
Ioncxchange RWd-PhaSe Reversed-phase Ionexchange
1 PPm 75-300 ng 10-100 ng 2-10 nmol
27 36 16 32
Hg~Br2- ISE Metallic copper Metalliccopper H+ - glass AgzS - ISE Fluoride - ISE Ag - AgCl AgzS - ISE Ag - Ag salicylate Ag - A@ Iodide - ISE Lead phosphate glasses H+- glass H+ - polymer Metallic copper
Ionexchange Ionexchange Ion-exclusion Ionexc hange Ion-exchange Ionexchange Ionexc hange Ioncxchange Ionexchange Ionexchange Ion-exchange Ionexchange
20 PPb 20-50 nmol 0.2-5.3 C(g 1 pquiv 10 PPb 10-20 ppb 0.5 ppm 10 pM 0.2 ppm
0.05 mM 0.015 pM 50 PPb
13 28 31 7 2 11-14 4 15 19 20.37 3 38
Ion-exchange Ionexchange Ionexchange
0.08-2.0 pM 1.1-6.5 pM 0.02- 10 nmol
9 10 29
PVC membrane H+ - polymer Non-selective membrane cell Nitrate - ISE Metallic copper Metalliccopper Metallic *per
Ionexchange Ionexchange Ion-exchange, ion-interaction Ionexchange Ioncxchange Ionexchange Ion-exchange
1 w 4.7-7.8 pM 10 nmol
18 10 34
0.1-0.3 nmol 1 PPm 1-5 nmol 1-10 nmol
17 26,31 25 24.30
F Halides Halides, SCNHalides, SCNHalides, SCN', Sfl3'IIInorganic anions Inorganic anions Inorganic anions, IO3', B e - , ClO3Monovalent cations Monovalent cations Na+, Li+, F,P043-, CH3COO', Sod2N@-,NO3oxalate
Reducing carbohydrates Transition metal ions a
Detectionlimits are expressedik the same units as used in the original publication.
PotentiometricDetection
341
11.6 REFERENCES 1
2 3 4 5 6 7 8 9 10 11
Kennedy J.H.. Analytical Chenhtry Principles,Harcourt Brace Jovanovich, San Diego, 1984, p. 582. Wang W., Chen Y. and Wu M.X, Analyst (London), 109 (1984) 281. Butler E.C.V. and Gershey R. M., Anal. Chim.Acta, 164 (1984) 153. Franks M.C. and Pullen D.L., Analyst (London), 99 (1974) 503. Roehse W., Roewer G.,Boran R. and Hellmig R.. Z. Chem., 22 (1982) 226. Trojanowicz M. and Matuszewski W., Anal. Chim.Acta, 151 (1983) 77. Egashira S., J. Chromatogr., 202 (1980) 37. Tarter J.G., J. Liq. Chromatogr.,7 (1984) 1559. Shintani H. and Dasgupta P.K., Anal. Chem., 59 (1987) 802. Meyerhoff M.E. and Trojanowicz M., Anal. Chem., 61 (1989) 787. Keuken M.P., Slanina J., Jongejan P.A.C. and Bakker F.P., J. Chromarogr.,439 (1988) 13.
12
13
Speitel L.C., Spurgeon J.C. and Filipczak R.A.. in Sawicki E. and Mulik J.D. (Eds.), Zon ChromatographicAnalysis of Environmental Pollutants,Vol. II, Ann Arbor Sci. Publishers, Ann Arbor, MI, 1979, p. 75. Slanina J., Bakker F.P., Jongejan P.A.C., Van Laxnoen L. and Mols J.J., Anal. Chim. Acta, 130 (1981) 1.
14 15 16 17 18 19 20
Talasek R.T., J . Chromatogr.,465 (1989) 1. Muller H. and Scholz R., Ion-SelectiveElectrodes,ACS Anal. Chem. Symp. Series, Vol. 22, 1984, p. 4. Loscombe C.R.. Cox G.B. and Dalziel J.A.W., J. Chromatogr., 166 (1978) 403. Schultz F.A. and Mathis D.E., Anal. Chem., 46 (1974) 2253. Suzuki K.,Aruga H. and Shirai T.. Anal. Chem., 55 (1983) 2011. Hershcovitz, H., Yarnitzky C. and SchmucklerG.,J. Chromatogr.,252 (1982) 113. Lockridge J.E., Fortier N.E., Schmuckler G. and Fritz J.S., Anal. Chim.Acta. 192 (1987) 41.
27 28 29 30 31
Alexander P.W., Trojanowicz M. and Haddad P.R., Anal. Lett., 17 (1984) 309. Alexander P.W., Haddad P.R. and Tmjanowicz M., Anal. Chim. Acta, 177 (1985) 151. Alexander P.W., Haddad P.R. and Trojanowicz M., Anal. Chem., 56 (1984) 2417. Alexander P.W.,Haddad P.R. and Tmjanowicz M., Anal. Chim.Acta, 177 (1985) 183. Cowie C.E., Haddad P.R. and Alexander P.W., Chromatographia,21 (1986) 417. Croft M.Y. and Haddad P.R., Australian Association of Clinical Biochemists Monograph Series, 1986, p. 138. Haddad P.R., Alexander P.W. and Trojanowicz M.. J. Chromatogr.,294 (1984) 397. Haddad P.R., AIexander P.W. and Trojanowicz M., J. Chromatogr.,315 (1984) 261. Haddad P.R.. Alexander P.W.and Trojanowicz M., J. Chromatogr.,321 (1985) 363. Haddad P.R., Alexander P.W. and Trojanowicz M., J . Chromatogr.,324 (1985) 319. Haddad P.R., Alexander P.W., Croft M.Y. and Hilton D.F., Chromatographia,24 (1987)
32 33 34
Haddad P.R., Alexander P.W. and Trojanowicz M., J. Liq. Chromatogr.,9 (1986) 777. Alexander P.W., Haddad P.R. and Trojanowicz M.. Chromatographia,20 (1985) 179. Deelder R.S.. Linssen H.A.J., Koen J.G. and Beeren A.J.B., J. Chromatogr., 203 (1981)
35
Powley C.R., Geiger R.F., Jr. and Nieman T.A., Anal. Chem.,52 (1980) 705.
21 22 23 24 25 26
487.
153.
342 36 37
38
Chapter 11
Alexander P.W., Haddad P.R.,Low G.K.-C. and Maitra C., J . Chromutogr.. 209 (1981) 29. Suzuki K., Aruga H., Ishiwada H., Oshirna T., Inoue H. and Shirai T., Bunseki Kaguku, 32 (1983) 585. Nornura T., Hikichi Y. and Nakagawa G., Bull. Chem. Soc. Jup., 61 (1988) 2993.
343
Chapter 12 Spectroscopic Detection Methods 12.1 INTRODUCTION 12.1.1 Types of spectroscopic detection in IC Spectroscopic methods of detection are very commonly employed in IC and are second only to conductivity detection in their frequency of usage. These spectroscopic methods are listed schematically in Fig. 12.1, from which it can be seen that they can be divided broadly into the categories of molecular spectroscopic techniques and atomic spectroscopic techniques. Molecular spectroscopy includes UV-Visible spectrophotometry, refractive index measurements and photoluminescence techniques (fluorescence and phosphorescence). Atomic spectroscopy includes atomic emission spectroscopy (using various excitation sources) and atomic absorption spectroscopy.
12.1.2
Direct and indirect spectroscopic detection
It will become apparent throughout the discussion in this Chapter that many of the spectroscopic detection methods can operate in a direct or indirect mode. The definitions of these terms are the same as those used to describe the electrochemical detcction modes discussed in previous chapters. That is, direct spectroscopic detection results when the solute ion has a greater value of the measured detection parameter than does the eluent ion. Indirect detection results when the reverse is true.
SPECTROSCOPIC DETECTION IN IC I
Molecular spectroscopic methods Spect rop h otomet ry Refractive index Photoluminescertce
I
Atomic spectroscopic methods
t
Atomic absorption Atomic emission
Fig. 12.1 Schematic representation of spectroscopic detection modes in IC.
Chapter 12
344
12.2 UV-VISIBLE SPECTROPHOTOMETRIC DETECTION IN IC METHODS USING ION-EXCHANGE SEPARATIONS 12.2.1
Detection response equations for ion-exchange
We will begin by illustrating the operating principles of UV-Vis spectrophotometric detection using anion-exchange chromatography as a typical example. Equations will be developed for the absorbance of an eluent prior to and during the elution of a solute ion and from these, a detection response equation will be derived. The general approach used for this derivation has been described previously [l-31. Consider an anion-exchange system in which the eluent consists of the species HE, which is dissociated partially into H+and E-.If the degree of dissociation of the eluent is IE and the total eluent concentration is CE,then:
(12.2)
The background absorbance of an eluent flowing through a fully equilibrated column will arise from both HE and E . In this example, the eluent cation (H+) does not absorb and we will assume this to be true in all cases. The background absorbance can be calculated from Beer’s Law to be:
where EE-is the molar absorptivity of the eluent anion, &HE is the molar absorptivity of the undissociated eluent, and m is the path-length of the detector cell. The elution of a solute S, which is dissociated to a degree Is to form S-,will result in the displacement of an equimolar amount of E-from the eluent (see Fig. 9.1 for a schematic representation of this process). This solute will be eluted as a Gaussian peak, with a concentration of Cs- at the peak maximum. The concentration of E-at the peak maximum is therefore given by:
The absorbance measured at the peak maximum is then given by:
where ES- and ENS are the molar absorptivities of the dissociated and undissociated forms of the solute, respectively. The change in absorbance (AA) accompanying the elution of the solute can now be obtained by subtracting the background absorbance (eqn. (12.3)) from the absorbance during sample elution (eqn. (12.5)) to give:
Spectroscopic DetectionMethods
345
Solute
(ES)
Eluent 2 ( E E 2 ) Fig. I22 Schematic representation of direct and indirect spectrophotomeaicdetection in IC.
Under conditions where the solute is fully dissociated (i.e. Is = 1). which is the usual case for ion-exchange separation, eqn. (12.6) can be simplified to give:
AA =
(ES-
- EE-)CS~
(12.7)
We see that the absorbance change measured by the detector on elution of a sample is proportional to the solute concentration, the cell path-length and to the difference in molar absorptivities between the solute and eluent anions. Eqn. (12.7) applies to the case where both the eluent and solute anions have a single charge. This equation may be rewritten for the general case in which the solute is represented by Sx- and the eluent by Ey-. We therefore obtain [4]:
Y
(12.8)
Eqn. (12.7) shows that direct detection will result when the molar absorptivity of the solute anion exceeds that of the eluent anion, leading to a positive value for AA. Conversely, indirect detection results when the molar absorptivity of the solute anion is less than that of the eluent anion, leading to a negative value for AA. These detection modes are illustrated schematically in Fig. 12.2. Eqn. (12.8) can be rewrigen for the cation case (i.e. for a solute Sx+ and an eluent EY+), as follows: (12.9)
346
Chapter 12
TABLE 12.1
SOLUTES AND TYPICAL OPERATING CONDITIONS FOR DIRECT SPECTROPHOTOMETRIC DETEXTION IN 1C AFTER ION-EXCHANGESEPARATION Solute(s)
Eluent
Wavelength (nm)
Detection limit
Ref
HCl K2m4 N aC1 CH3S03H NaC104 Na2COflaHCO3 TridSO4’-
200
1.5 ppm 0.6 ng 50 PPb 50 PPb 50 PPb 160 PPb 50 ng 300 ng 30 PPb 3 PPb 0.2 ppm 4 PPm <1 PPb 2 PPm 0.4 ppm 20 ng 50 PPb 80PPb 5-70 ng 0.3 ppm 0.5 ppb 0.2-1 ppb 0.01 mM 5 PPb 60 PPb 3000 ng 1 PPm 0.6-40 ppm 2 PPb 0.4 ppm 0.5 ppm 15 PPm 3000 ng lo00 ng
7 8 9 10 11 7 12 12 13 14 7 7
CH3S03H NaC104 Na2COflaHCO3 Na2COflaHCO.j HNO3, NaOH EDTA
HCl CH3S03H NaC104 Na2COflaHC03 EDTA
Na2C03/NaHC03 NaCl NaC104 H2m4-/ClLiOH Na2m4 CHjS03H Na2CO3, NaOH CIO4-, H2P04‘
195
214 205 210 195 205 205 190 190 195
195 365 350,220 225 190 210 195 210 195
K2km4
210 200-209 214 214 210 190 215 205 195
Na2CO3 Na2C03, NaHCO3 Na2C03, NaHCO3 CH3S03H NaC104
195 195 195 190 190
15 16 17
13 11 7 18, 19 7
20 14 21 22 23 13 24 25 26 7 7 7
13 14
Specnoscopic Detecrion Methods
347
r 6 1 2
I--
0
0.001 AU
h
I
1
I
I
1
6 Time (min)
12
0
6 lime (min)
12
(a)
(bl
Fig 12.3 Effect of wavelength on detection sensitivity in direct spectrophotometric detection of anions after ion-exchange separation. The detection wavelengths were (a) 190 nm and (b) 210 nm. A Vydac 302 IC column was used with 10 mM phosphate (pH3.7) as eluent. Solute identities: (1) acetone, 0.01%, (2) propionate, lo4 M, (3) butyrate, lo4 M, (4) lactate, 10" M, (5) selenite, 1 mg/l as Se, (6) arsenate, 1 mg/l as As, (7) formate, lo4 M, (8) succinate, M, (9) chloride, 5 mgJ, (10) nitrite, 10 pg/l as N, (11) bromide, 10 pg/l, (12) nitrate, 10 pg/l as N. Reprinted from [28] with permission. 12.2.2
Direct spectrophotometric detection in ion-exchange IC
Direct monitoring of UV absorbance is perhaps the most straightforward method for the detection of solutes in IC. A considerable number of ions show appreciable absorptivities in the range 175-220 nm [5-71; these include many inorganic anions and cations, metal complexes, and some organic acid anions. Table 12.1 lists some of the ionic solutes which are amenable to this form of detection and shows suitable eluents, detection wavelengths and approximate detection limits for these solutes.
Direct detection of anions It can be seen from Table 12.1 that many inorganic anions absorb UV radiation at detection wavelengths above 200 nm. Others, such as C1-, F-, so42-, P043-, ClO4- and CN-, do not show appreciable absorption, except at lower wavelengths. Some degree of detection selectivity therefore exists and this permits common interferences, such as high levels of C1- or S042-, to be minimized or even eliminated. Alternatively, choice of a low wavelength, such as 190 nm, permits direct UV spectrophotometry to be used as a more general detection mode [13, 271. The effect of detection wavelength can be seen from the chromatograms in Fig. 12.3. At 190 nm (Fig. 12.3(a)), all twelve solutes in
348
Chapier 12
pl5A.U. A
iI
B
0.05 A.U.
-
0
5
10
15
1
IJ
1
I
I
I
0
5
10
15
Time lrnin)
Time Iminl
(a1
(b)
2r
1
1 1 1 1 0 5 10 15 Time Imin) (C)
Fig. 12.4 Separation of nitrite (A) and nitrate (B) in standards (a), bacon sample (b) and spiked bacon sample (c). The sample for (c) was spiked with 0.5 ug of nitrite and nitrate in a 25 ul injection. Column: Vydac 302 IC 4.6. Eluent: 11.0 m M chloromethanesulfonicacid at pH 5.0. Detection at 210 nm. For chromatogram (a), 10 ul of a 50 ppm solution of ninite and nitrate was injected. Reprinted from 1311 with permission.
the mixture can be detected, whereas at 210 nm (Fig. 12.3(b)), Se032- and C1- are no longer detected and sensitivity for the other solutes is reduced [28]. An obvious restriction on the eluent composition in direct spectrophotometric detection is that all components must be transparent, or at least only weakly absorbing, at the detection wavelength employed. For this reason, eluents such as phosphate buffer, NaCI, Na2S04. carbonate/bicarbonate buffer, citrate and alkylsulfonates have been used. Direct spectrophotometric detection is commonly employed for the determination of NO2- and NO3- [20, 21, 29-33]. for which it is particularly suited in view of the relatively high molar absorptivities of these ions (e.g. goo0 1 mol-* cm-' at 210 nm for NO3-). Fig. 12.4 shows a chromatogram obtained for the determination of NO2- and NO3- in cured meats, using chloromethanesulfonic acid as eluent [31]. It can be seen that no interference from the large amounts of chloride present in the sample is observed. Direct detection of cations
Simple inorganic cations are usually not amenable to direct spectrophotometric detection because their molar absorptivities are generally quite small. However, some cations can be detected readily in the UV range after they have been complexed with a suitable ligand. The chromatography of metal chelates has been covered in Chapter 8, where we have noted that ligands such as dithiocarbamates are very widely used and that
SpectroscopicDetection Methods
349
CN’
NO2
Fe
0
Time (min)
~
I
0
I
I
S0 10 Time (min)
1
15
Fig,12.5 Direct spectrophotometric detection of metal complexes after ion-exchange separation. (a) Detection of metal-chloro complexes at 215 nm. Column: Dionex HPIC-ASS separator. Eluent: 0.30 M NaC104 and 0.05 M HCI. Reprinted from [34] with permission. (b) Detection of anions and metal-EDTA Complexes at 210 nm. Column: TSK IC Anion-SW. Eluent: 1 mM EDTA at pH 6.0. Reprinted from [ I @ with permission.
the metal complexes can be formed prior to separation or within the column itself. Ligands such as C1- [34] or EDTA [16, 181 form ionic complexes which can be separated by ion-exchange and detected by direct spectrophotometry. Fig. 12.5(a) shows the detection of metal chloro- complexes, whist Fig. 12.5(b) depicts the simultaneous detection of UV absorbing anions and anionic metal-EDTA complexes. In the latter case, the metal complexes show strong absorbance at 210 nm, whilst the eluent is only weakly absorbing at this wavelength, leading to sensitive detection. A similar method has been reported using 1,2-diaminocyclohexanetetraacetic acid (DCTA) as the complexing agent [ 191. An alternative approach for the detection of inorganic cations is to include a colour-forming reagent in the eluent. For example, alkaline earth cations can be separated by cation-exchange using sulfosalicylic acid as eluent, with chlorophosfonazo I11 added as the colour-forming reagent [35]. The cations are eluted as coloured complexes which absorb at 679 nm. This same method has also been applied to the detection of alkaline earth and transition metal cations using Arsenazo 111 [36, 371, Xylenol Orange [38] and o-cresolphthalein complexone [39-411 as colour-forming reagents.
Chapter 12
350
-
3
p-
50 mAU
CI-
10: NOj. Br-
U
t1
1
0
2
I
1
6 6 8 Time (min)
la)
l
1
l
1
0
0
1
2
1
1
4 6 8 Time (minl (b)
I
1
1
0
Fig. 12.6 Replacement ion chromatography of anions using direct spectrophotometric detection. A Dionex AS4A column was used in both cases, with 25 mM KOH as eluent. (a) Replacement solution, 0.5 mM Ce3+. Detection wavelength 256 nm. (b) Replacement solution: 10 mM anthranilic acid. Detection wavelength 210 nm. Reprinted from [44]with permission.
Replacement IC with spectrophotometric detection Solute ions which absorb poorly in the UV region can be detected by means of post-column reactions in which they are exchanged quantitatively for ions which are easily detected. This process has been called "replacement IC" [42] and is usually accomplished by an ion-exchange mechanism, where the solute ions exchange with the desired "replacement" ions. The characteristics of this approach include [43]: Ion replacement permits the most desirable detection method to be used, rather than that stipulated by the particular solute ions in the sample. Detectors which are more sensitive and less susceptible to temperature changes than the conductivity detector can therefore be employed. (ii) The replacement ion should be one which h a s a low affinity for the charged sites on the replacement column, compared to that of the solute ion.
(i)
Spectroscopic Detection Methods
351
(iii) A monovalent replacement ion is most desirable in order to maximize the detector signal. (iv) The replacement column should operate continuously, efficiently and reproducibly, and introduce minimal dead volume. Hollow-fibres are therefore ideal for this purpose. (v) The integrated detector response of all solutes should be the same because each solute is converted stoichiometrically into a single detected form. Consequently, replacement IC is a universal detection method and a single calibration curve should apply to all solutes having the same charge. (vi) The major disadvantage is the additional solute dispersion introduced by the replacement column. Replacement IC can be applied to the detection of anions using a conventional suppressed IC system, followed by a continuously regenerating anion-exchange fibre, which serves as the replacement column [a]. For example, the eluted sample anions can be replaced with anthranilate, which is then detected by direct UV absorption at 210 nm. Alternatively, the H+ions introduced into the sample band by the suppressor (see Section 9.5) may be exchanged for Ce3+, which is then detected spectrophotometrically at 256 nm. Detection limits attainable by these methods can be better than for conductivity detection, but membrane deterioration is a problem. Fig. 12.6 shows the direct spectrophotometric detection of anions using replacement IC. Inorganic cations may also be detected by UV absorption using replacement IC [43], in a similar manner to that described above for the detection of anions. After separation by suppressed IC using nitric acid as eluent, the O H ions introduced into the sample band by the suppressor are exchanged for 103- [431, NO3- [43], I- 1451, or p naphthalenesulfonate [45] in the replacement column. These ions are then detected sensitively at an appropriate absorption wavelength. Detection limits for monovalent cations are in the range 1-15 ng when 103- is used as the replacement ion. Fig. 12.7 shows the UV detection of cations using replacement IC.
12.2.3
Indirect spectrophotometric detection in ion-exchange IC
Eqns. (12.8) and (12.9) show that indirect spectrophotometric detection results when the eluent ion has a higher molar absorptivity than the solute ion (when both are univalent). Indirect spectrophotometric detection, also called "indirect photometric chromatography" [3] and "vacancy detection", is a very widely used detection method in IC. Decreased absorbance accompanies the elution of solutes, but the polarity of the detector output is usually reversed in order to give positive peaks on the recorder. Provided that Beer's law is followed, then linear calibration plots will result, thereby permitting sample quantitation.
Sensitivity of indirect spectrophotometric detection The sensitivity attainable with this method will depend on a number of factors. In the first place, it is clear from eqns. (12.8) and (12.9) that for solute ions with low molar absorptivities, the absorbance change accompanying solute elution is maximized
352
Chnprer 12 I*
0.002 AU
Li'
[
0.001 AU
K*
Na*
I
0
1
I
5
10
Time (minl (a1
I 15
-
0
10
Time (min) (b)
Fig 12.7 Replacement ion chromatography of cations using direct spectrophotometric detection. (a) A Dionex CS2 separator, CSC-2 suppressor and fibre replacement column were used, with 7.0 mM HNO3 as eluent. The detector wavelength was 215 nm and the replacement ion was IO3-. Solute concentrations were 1 mM Li+, K+ and 0.5 mM Na+, Reprinted from [43] with permission. (b) A TSK gel IC-cation column was used with 2 mM HN@ as eluent. The detector wavelength was 225 nm and the replacement ion was fbnaphthalenesulfonate. Solute concentrations: 1 mM of each ion. Reprinted from [45] with permission.
m+.
when the molar absorptivity of the eluent ion is greatest. This can be achieved by selection of the wavelength of maximum absorption for the eluent ion. However, this may create problems in that the resultant high background absorbance of the eluent might mean that the detector is incapable of being zeroed, or that baseline noise is increased. Using anion-exchange as an example, and assuming full ionization of the eluent and solute anions, we can express the absorbance changeon sample elution, AA, as a fraction of the baseline absorbance by writing [3]:
(12.10)
Spectroscopic Detection Metho&
353
There will be noise in the baseline absorbance signal, appearing as random fluctuations, which will be represented by the term N. We can now use eqn. (12.10) to give:
(12.1 1)
Considering the case where the solute anion does not absorb at the detection wavelength (i.e. ESX- = 0), and neglecting signs (which are not significant in this case), we obtain:
-@-aSi al Noise
CS NCE
(12.1 2)
and from eqn. (12.8) we can write: (12.13)
These expressions permit the following conclusions to be reached regarding the sensitivity of indirect spectrophotometricdetection: (i)
The absorbance change is increased as the molar absorptivity of the eluent anion increases. (ii) The absorbance change is decreased as the ratio of the charge on the solute anion to that of the eluent anion (i.e. x/y) decreases. This ratio has been called the displacement ratio, R, [46]. This suggests that eluent ions of multiple charge are not desirable. (iii) The signal-to-noise ratio for indirect spectrophotometric detection improves as the concentration of eluent decreases. These conclusions can be embodied in a single equation [46], which defines the minimum detectable concentration (Clim) of the solute as:
CE C,im = -
RD
(12.14)
where CE is the concentration of the absorbing component in the eluent, R is the displacement ratio defined above, and D is the dynamic reserve (defined as the ratio between the background signal and its noise level). The best sensitivity (i.e. lowest Clim) is achieved with a low value of CE and high values of R and D. We note that the molar absorptivity of the eluent, EE, is incorporated into the dynamic reserve term, with a high molar absorptivity giving rise to a high D value.
354
Chapter 12
These requirements must be viewed in juxtaposition with the penalties which arise from the long retention times and increased band dispersion resulting when the eluent is too dilute or has an inappropriately low charge. Therefore, the ability of the eluent anion to effectively displace the solute anion (i.e. the selectivity coefficient of the eluent anion) from the column must also be considered. Furthermore, photometric error is reduced if the detector is operated in the approximate absorbance range 0.2-0.8, so it is desirable that the background absorbance be maintained within this range. The above considerations show that the results obtained with indirect spectrophotometric detection will be strongly dependent on the type of eluent anion used, and also on the performance characteristics of the particular detector employed. Similar conclusions apply to the indirect spectrophotometric detection of cations. Indirect spectrophotometric defection of anions
Indirect spectrophotometric detection of anions was first introduced in 1978, using NaNO3 as eluent [471. Its rapid development since that time can be related directly to a rapid increase in the use of eluents containing aromatic acid anions as competing ions in anion-exchange methods employing conductivity detection. As discussed in Chapter 9, the rationale for this was that these species have low limiting equivalent ionic conductances and so enable sensitive detection to be achieved in the non-suppressed mode of 1C. These ions also have high molar absorptivities in the UV region and so indirect spectrophotometric detection became possible with the same eluents already in common usage for conductivity detection. In many cases, conductivity and spectrophotometric detectors were used in tandem. Eluents such as phthalate, nitrate, sulfobenzoate and benzenetricarboxylate are commonly used for the separation of anions. The properties of different benzenecarboxylic acids have been compared by several authors [48-501. Typical chromatograms obtained with phthalate or pyromellitate as the eluent are shown in Fig. 12.8. Table 12.2 lists some examples of indirect spectrophotometric detection of anions and shows cluents, detection wavelengths and representative detection limits for the technique. The eluent pH is an important variable in indirwt spectrophotometric detection. As well as influencing the charge on the eluent anion, the pH may also affect the molar absorptivity of the eluent. In addition, use of an incorrect eluent pH may lead to a decrease in detection sensitivity. For example, the use of alkaline pH values may be disadvantageous when aromatic acid salts are used as eluents for anion-exchange separations because the OH- ions in the eluent can act as ion-exchange competing anions and may therefore contribute to the elution of the solute anions. Elution of solutes by OH- does not lead to any measurable indirect absorbance change at the detector. Thus, the detector signal observed for an aromatic acid eluent will generally be lower at alkaline pH than at acidic pH, provided that the form of the eluent anion does not alter between these pH values. In view of this, detection sensitivity for phthalate eluents will begin to decrease at pH values greater than about 7.0, where phthalate is fully ionized. However, it should also be remembered that fully ionized eluent species are less prone to the formation of system peaks (see Section 4.6.2) than those that are ionized partially [7S]. Higher eluent pH values are therefore preferable from this viewpoint. The final
SpecnoscopicDetection Methods
355
eluent pH which is selected will clearly be a compromise between maximizing the detection sensitivity and the elimination of system peaks. TABLE 12.2 SOLUTES, ELUENTS AND TYPICAL OPERATING CONDITIONS FOR INDIRECT SPECTROPHOTOMETRIC DETECTION OF ANIONS AND CATIONS AFTER ION-EXCHANGE SEPARATION Solute(s)
Anions Common anions Common anions CH3C0Om,H C W , P043-, C1C104-, Cl', SCN-, sod2-, F', C1-, B i , so42-,S2032-,1Cl', Br-, NOy. so42C I - , N O ~ , N O ~S042-, C1-, Br-, NOi, sod2C1-, NOi, Br-, NO3CI-, NO^, ~ 0 4 2 C1-, Br-, NOj, sod2H ~ P O ~ - , C NO^, I, ~042P2074-,P30105Si032-, F-, Cl-, Br-, P043-, S0425042-
Cations Alkyl quaternary ammonium ions Monovalent cations, amines Li', Na+, N a + . K', Rb+, Cs+ Li+, Na', N a + . K+, Rb+, Cs+ Li+, Na', N a + , K+, Rb', Cs+ Li+, Na', N&+, K+, Rb+, Cs+ Na', K' Na', N a + , K+ Na', K+, Rb+, Cs+, Ca2+. Mg2+ Na+, K+, Rb+, Cs', Ca2', Mg2+ Na+, K+, Mg2+, Ca2' Ca2', Mg2+ Ca2', Mg2' Ba2' Mg2+, Ca2+,,'?S Mg2+, Ca2', S?+, Ba2' Mg2+, Ca2', ,'?S Ea2'
EluenP
h
Detection limit
Ref
(nm)
NaN03 Phthalate Benzoate Trimesate Pyromellitate Ciaate Salicylate p-Toluenesulfonate 2-Naphthylaminesulfonate [Cu(EDTA)IZ Tiron Sulfobenzoate Trimesate 2,443hydroxybenzoate 5-Sulfoisophthalate
247 300 254 317 285 290 254 280 300 290 290 270 285 312 240
1-10 ppm 0.1-0.3 pg 0.1 ppm 0.5 ppm 0.05 ppm 0.2 ppm 1-2 ng 50 PPb 2-10 ppb 1.6-11 ng 50 PPb 300 pmol 1 PPm 0.2 ppm 50 pmol
47 53
Benzyltriethylamine Benzyltrimethylamine 4Methylbenzylamine 2,6-Dimethylpyridine 2-Methylpyridine 2-Phen yleth y lamine Pyridinium C1-
270 275 262 269 262 257 260 252 220 254 218 254 290 257 262 255
0.6-0.8 pg 0.2-1 ppm 0.2-10 ppb 0.4-11 ppb 0.4-11 ppb 0.7-14 ppb 0.2 ppm 10 PPm 30-300 ppb 4 PPb 7-34 ng 10 PPb 1.7-2.3 ng 1-58 ppb 1-58ppb 0.2-10 ng
64 65,66 67 67 67 67 68 3 69 70,71 72 73 58 67 67 74
cuso4 cuso4 Ce2(SO4)3 CoSO4 [~o(en)2(acac)l2+ [Cu(EDTA)122-Phenylethylamine
4-Meth ylbknzylamine [~u(trien)l2+
a en = ethylenediamine, acac = acetylacetone, trien = triethylenetetramine.
54
48 52 55 56 57 57 58 59 60 61 62 63
356
Chapter 12 (bl
(a1
Time (min)
0
L
L
Y
8
12
16
0
L
Time lmin) 8
12
16
J
1
0.002AU
c I-
Fig. 12.8 Typical chromatograms for the detection of anions using indirect spectrophotometry. (a) A Vydac 302 4.6 IC column was used with 5 mM potassium hydrogen phthalate at pH 4.0 as eluent. Detection was at 285 nm. Reprinted from 2511 with permission. (b) A Hamilton PRP X100 column was used with 0.5 mM pyromellitate at pH 4.0 as eluent. Detection was at 300 nm. Reprinted from [52] with permission.
Indirect spectrophotometric detection of cations Aromatic bases represent the primary class of eluents which are applicable to indirect spectrophotometric detection of cations. It might appear at first sight that these bases would serve as ideal eluents for indirect detection, since they are the cationic counterparts of the aromatic acid eluents which have proven so successful in anionexchange chromatography. When aromatic base eluents are used at acidic pH, for example picolinic acid at pH 3.5 [2]. it is found that only very small changes in absorbance are observed when a solute cation is eluted. The reason for this is that elution of solute cations is being accomplished jointly by the protonated aromatic base cations and also by hydrogen ions present in the eluent. These hydrogen ions are a very effective eluent for monovalent cations, as evidenced by the routine use of nimc acid as an eluent for these species when conductivity detection is used. The detector signal therefore decreases when hydrogen ions participate in solute elution for the same reason as explained above for the anion case. In view of this, only those aromatic bases which are protonated appreciably at approximately neutral pH values can find application to
Spectroscopic Detection Methodr
357
(a)
0
(b)
Time Imin) 4 8 1
2
0
I
Tlmc (min)
8
12
16
NHLI-
K*
[
1 xlO-LAU
la*
Fig. 12.9 Indirect spectrophotometric detection of cations using aromatic bases as eluents. A Waters IC Pak C column was used in each case. (a) Eluent: 0.1 mh4 4-methylbenzylamine at pH M of each ion. (b) Eluent: 10 mM 6.92. Sample: 15 pl of a solution containing 2 x phenylethylamine at pH 5.49. Sample: 60 pl of a solution containing los5M of each ion. Reprinted from [67] with permission.
sensitive indirect spectrophotometric detection. These include species such as 2.6dimethylpyridine isomers (PKa 6.72), 2-methylpyridine (PKa 5.92), 2-phenylethylamine (PKa 9.84) and 1,4-phenylenediamine @Kal 6.16). The use of indirect spectrophotometric detection for monovalent and divalent cations using aromatic bases as eluents is illustrated in Fig. 12.9. Inorganic species form the second broad class of suitable eluents for indirect detection of cations. Species such as Cu(II), Co(II), Ni(II), Ce(II1) and ionic metal complexes, such as bis(ethy1enediamine copper(II)), all have suitable absorbance in the UV region to enable them to be used. Examples of indirect spectrophotometric detection of cations with inorganic eluents are included in Table 12.2, and typical chromatograms obtained using this approach were given previously in Fig. 4.15.
Chapter 12
358
Simultaneous indirect detection of anions and cations
Indirect spectrophotometric detection has been applied successfully to the simultaneous, independent determination of anions and cations using a single detector [3, 761. The requirements of this method are that both the eluent anion and cation must be effective competing ions so that separation of solute ions is attained, and both must have a sufficient molar absorptivity at a suitable detection wavelength to permit indirect detection to be performed. A dual-column system, comprising an anion-exchange column and a cation-exchange column connected in series, may be used with eluents such as copper nitrate or copper o-sulfobenzoate. A desirable feature of this technique is for the eluent anion and cation to have absorption maxima at different wavelengths and for each species to be transparent at the absorption wavelength of the other. This is not possible with the copper o-sulfobenzoate eluent, so it is necessary to monitor the absorbance of the eluent at two wavelengths and to apply ratio and scaling techniques to obtain independent chromatograms of solute anions and cations. A dual-channel, variable-wavelength detector with ratio capability is therefore required. The principle of the method can be described briefly as follows. If the two wavelengths monitored by the detector are A1 and Ah.2, then the ratio of the peak heights or areas obtained at these wavelengths is determined by the ratio of the molar absorptivities of the eluent species at the same two wavelengths. Since different components of the eluent are responsible for elution of solute cations and anions (i.e. copper ions and o-sulfobenzoate, respectively), then this ratio will be different for cations and anions. If the ratio for cations is given by Rc and that for anions is given by RA, and the detector is operated so that its output signal (S) is the difference in the absorbance readings at the two wavelengths, that is:
S =
A2
- A1
(12.15)
then application of the ratio factors RC and R A can enable deconvolution of the anion and cation chromatograms. That is, the cation chromatogram is obtained by plotting Ac versus time, whilst the anion chromatogram is obtained by plotting A A versus time, where Ac and AA are given by:
(12.17)
This procedure is illustrated in Fig. 12.10, for which the two detection wavelengths were 240 nm and 270 nm, giving values of 0.44 and 0.74 for the ratio factors Rc and RA, respectively. It is worthy of note that the approach described above is applicable only to those absorbance detectors which enable simultaneous monitoring at two detection wavelengths, together with the facilities for applying a scaling factor to the absorbance signal at one wavelength and subtracting from this the absorbance signal measured at the second wavelength. A high level of instrumental sophistication is clearly necessary.
359
SpectroscopicDetection Methods
I-
I’
0.04 AU
B
A K+
s02-
10 V (mll
5
1:
15
0
so&
0
V (mll
V (mll
Fig. 12.10. Joint and independent separations of anions and cations. Columns: Zipax SAX and SCX columns in tandem. Eluent: 0.5 mM copper o-sulfobenzoate at pH 4.3. Detection: U V absorbance at 240 rim (A) and 270 nm (B). Chromatograms (C) and (D) were obtained by applying the scaling factors 0.44 and 0.74 to eqns. (12.17) and (12.16), respectively, to obtain deconvoluted chromatograms for anions (C) and cations (D). Note that the peaks are in the direction of decreasing absorbance, except for (C), where the peaks have opposite polarity (i.e. increasing absorbance). Reprinted from [76] with permission.
360
chapter 12
Indirect spectrophotometric detection without standards The similarity in form of eqns. (12.8) and (9.20) suggests that the method of quantitating unknown solutions without the use of standards (which was discussed in detail for conductivity detection in Section 9.6.3)should also be applicable to indirect spectrophotometricdetection. This suggestion has been shown to be valid when applied to the determination of anions [77]. Peak areas are obtained for a solute anion (x) using two eluents, 1 and 2. This process is then repeated for two known solute anions, A and B. The concentration (C,) of the unknown solute anion is given by:
(12.18)
where C is the concentration of eluents 1 and 2, and S is the peak area. The superscripts refer to the eluent used and the subscripts refer to the particular anion. The molar absorptivity of solute x ( E ~ )can also be determined using:
(1 2.19)
It will be noticed that the previous two equations permit quantitation and identification of an unknown solute without any knowledge of parameters for the eluent anions.
12.3 SPECTROPHOTOMETRIC DETECTION IN IC METHODS USING ION-INTERACTION SEPARATIONS 12.3.1 Direct and indirect detection in ion-interaction chromatography Spectrophotometricdetection can be applied to ion-interaction chromatography in a number of ways. In Chapter 6, we noted that ion-interaction chromatography involves the modification of a hydrophobic stationary phase with an ion-interaction reagent (IIR). The IIR is used either to pre-treat the stationary phase (and is absent from the eluent utilized in subsequent separations), or forms a part of the eluent. The first of these alternatives, called "permanent coating", converts the stationary phase into an ionexchange surface, whilst the second is termed "dynamic coating".
SpectroscopicDetection Methods
361
TABLE 12.3 SOLUTES AND CHROMATOGRAPHICCONDITIONS FOR INDIRECT SPECI'ROPHOTOMETRIC DETECTION IN IC USING PERMANENTLY COATED ION-INTERACTION COLUMNS ma
Eluent
Solute(s)
h (nm)
Detectip limit
Ref
CPBr CPBr CPBr CI'MABr CIMABr Methyl green CMABr CIMABr
Phthalate Benzoate Tiimesate Nitrophthalate Phthalate Hydroxybenzoate Phthalate Salicylate Salicylate Sulfosalicylate
C ~ 0 4 ~DCTA -, C ~ 0 4 ~FeEDTA -, EDTA, cimte Inorganic anions Inorganic anions Inorganic anions Inorganic anions Inorganic anions Organic acids Organic acids
280 265 280 270 254 311 300 254 293 295
1-6 ppm 2-20 ppm 2-20 ppm 0.2 ppm 0.2-0.5 ppm 0.02-1.5 pprn 0.5 pprn
78 78 78 79 80
CTMAQ
CPBr a
10 ng 10 PPb 0.8-3 ppm
81 82 46 83 78
Ion-interactionreagents: CPBr = cetylpyridinium bromide, CTMABr = cetylmmethylammonium bromide, C"MACl=cetyltrimethylammoniumchloride.
Spectrophotometric detection in permanently coated ion-interaction chromatography The detector response equations for the permanent coating approach are identical to eqns. (12.8) and (12.9) and the eluents used for direct and indirect spectrophotometric detection are the same as those listed in Tables 12.1 and 12.2 for fixed-site ion-exchange separations. The usual procedure followed with this approach is to treat a c18 column with a solution of the hydrophobic IIR, followed by washing with water, and then use of an appropriate ion-exchange eluent. Table 12.3 shows some examples of the conditions required for indirect spectrophotomehic detection (which is employed more frequently than the direct mode) in ion-interaction chromatography. Spectrophotometric detection in dynamically coated ion-interaction chromatography Ion-interaction chromatography using the dynamic coating method offers more possibilities for spectrophotornetricdetection than does the permanent coating approach. We will again begin by considering the separation of anions. The IIR, which is a cationic species with its associated counter anion, will be represented as IIR+A-. Three possibilities exist for spectrophotometricdetection. (i)
Both IIR+ and A- are non-absorbing at the detection wavelength. It therefore becomes possible to detect directly those solute anions which absorb at the detection wavelength. That is, eqn. (12.7) applies and A- fills the same role as E-in the anion-exchange case. An example of direct detection of inorganic
(bl
I Of 0 L
SC N-
5
10
I
I
Time (minl
15
20
25
I
I
1
,BrOf
i I
0
8
I
I
16
Time (min) (a1
Fig. 12.11 Direct (a) and indirect (b) detection in ion-interaction chromatographyusing dynamically coated columns. (a) A Lichrosorb RP-2 column was used with 0.5%w/v tricaprylylmethylammonium chloride in 5 0 5 0 acetonim1e:wateras eluent. Detection wavelength: 205 nm. Reprinted from [84] with permission. (b) A Waters Resolve C18 Radial Pak cartridge was used with 0.4 mh4 tetrabutylammonium salicylate as eluent. Detection wavelength: 288 nm. Reprinted from [85] with permission.
5 c,
N
Spectroscopic Detection Methods
363
anions in dynamic coating ion-interaction chromatography is given in Fig. 12.1 l(a), in which tricaprylylmethylammonium chloride is used as the IIR. Table 12.4 lists typical chromatographic conditions which may be employed for this detection mode. (ii) IIR+ is non-absorbing and A- absorbs at the detection wavelength. Eqn. (12.7) is still applicable and A- again fills the same role as E-, but now the molar absorptivity of A- is significant. Solutes which do not absorb are therefore detectable indirectly in exactly the same manner as was used for fixed-site ion-exchangers [85, 102, 108, 1121. Fig. 12.1 l(b) shows an example of this approach, wherein tetrabutylammonium is used as IIR+ and salicylate as the absorbing counter ion, A- [85]. Further examples and typical chromatographic conditions are given in Table 12.4. (iii) IIR+ is absorbing and A- is non-absorbing at the detection wavelength [1131171. This method will be referred to as "UV visualization" in order to distinguish it from (ii) above. The mechanism of indirect spectrophotomeuic detection by UV visualization is complex and is discussed in detail below. Each of the above possibilities can theoretically apply also to the detection of cations. However, method (i) is most often employed with metal ions, which are detected directly as their anionic complexes with ligands such as cyanide, using tetrabutylammonium phosphate (or hydroxide) as the IIR [92, 94, 118-1201. 12.3.2
UV visualization detection in ion-interaction chromatography
As indicated above, detection by UV visualization involves the use of an IIR which has the opposite charge sign to the solute ion and also shows absorption at the detection wavelength. This method has been applied only to the detection of anions, so cationic IIRs are used. The chromophoric IIR will contribute to the background absorbance, since the detector is set at the absorption wavelength of the IIR. Injection of solute anions onto a column equilibrated with an absorbing IIR will cause a perturbation of the distribution equilibria of the IIR between the eluent and the stationary phase. Movement of the solute band through the column alters the concentration of IIR within the band, relative to that in the bulk eluent. When the analyte band reaches the detector, the absorbance therefore changes because of the altered concentration of IIR. Peaks corresponding to the elution of solute anions are therefore called "induced peaks" [ 1211.
Mechanism of UV visualization A great deal of study has been devoted to elucidation of the manner in which the spectrophotomeuic detector responds in UV visualization detection [113-115, 121-1231. There are two types of peaks produced when a solute of charge opposite to the IlR is injected: an induced peak, which is eluted at a retention time characteristic of the particular solute, and a system peak, which is eluted at a retention time characteristic of the IlR. These peaks have the following characteristics:
364
Chqxer 12
TABLE 12.4 SOLUTES AND CHROMATOGRAPHIC CONDITIONS FOR DIRECT AND INDIRECT SPECTROPHOTOMETRIC DETECTION IN IC USING DYNAMICALLY COATED IONINTERACTION COLUMNS Solute(s)
1
Detection limit
Ref
(MI)
215
2-90 ng
86
220 205 200
1-10 ng 5-30 ppb 0.1 pprn
87 88 89
205 215 210 254 214 214 214 235 212 205 214 215 210 210
50 PPb 0.1 ppm 50 PPb 1 PPm 1-3 ng 0.4 ppb 0.1 ppm 50 PPb 10-100ppb 2 ng 0.1 ppm 0.1 ppm 50ppb 50ppb
90 91 92 93 94 95 96 97 98 84 99 91 4 100
0.5ppm 0.5pprn 50ppb 0.2 ppm 660ppb
101 102 103-109 110, 11I 85
Direct detection + -
OA+ H2po4TBA' OHTBA' OH' TBA' O H TBA+ H2P04' TBA' H2P04' TBA' H2P04TBA' HzP04TBA' HSO4TcMA+c1TMA+H2P04TOMA' OHTPA+ BrTPA+ F I n direct detection
CTMA'TSAOA+ SaITBA' PhthTBA+ PhthTBA+ Sal-
a
CIUA = cetyltrimethylammwiurn, HDTMA = hexadecyl ei m et hyt i um , OA = octylammonium, TBA = tetrabutylammonium,TCMA = mcaprylylmethylanium, TOMA = hioctylmethylammonium,TPA = tehapentylammonium,TSA = toluenesulfonate. Sal = salicylate, Phth = phthalate.
365
SpectroscopicDetection Methods
Induced peaks which are eluted earlier than the system peak are negative in direction (decreased absorbance relative to that of the bulk eluent) and exhibit poor sensitivity. (ii) Induced peaks which are eluted later than the system peak are positive in direction (increased absorbance relative to that of the bulk eluent) and exhibit good sensitivity. (iii) Induced peaks eluted close to the system peak show the greatest sensitivity. (i)
When the injected solute ion has the same charge as the IIR, then (i) and (ii) are no longer true and the following characteristics are observed: (iv) Induced peaks which are eluted earlier than the system peak are positive in direction (increased absorbance relative to that of the bulk eluent) and exhibit poor sensitivity. (v) Induced peaks which are eluted later than the system peak are negative in direction (decreased absorbance relative to that of the bulk eluent) and exhibit good sensitivity. In the interests of simplicity, we will consider only characteristics (i) - (iii) above; that is, when the solute ion and the IIR have opposite charges. Furthermore, the discussion will be confined to the situation where the solute is anionic and the IIR is cationic. An explanation for the observed detection behaviour can be found by considering the localized changes in concentration of eluent components as the solute band passes through the column. The treatment given below for UV visualization of anions is a condensed version of that published by Stranahan and Deming [121] and the interested reader seeking a more detailed discussion is referred to this publication. Fig. 12.12(a) shows the UV absorbing eluent component IIR+ in equilibrium with the stationary phase. The solute anion, represented by the black zone, is about to enter the column. In Fig. 12.12(b) the solute band has reached the column and has the effect of causing some additional IIR+ to be adsorbed onto the stationary phase [124]. The concentration of IIR+ in the eluent is therefore reduced, whilst that on the stationary
m Solute
rm IIR'
in eluent
EZ IIR+ o n stationary phase
Fig. 22.22 Schematic representation of the changes in concentration of IIR in the eluent and stationary phases, caused by passage of a solute ion through the column. The upper box in each frame represents the eluent. whilst the lower box represents the stationary phase. See text for
discussion. Adapted from [ 1211.
366
Chapter 12
phase is increased. As the solute band passes further along the stationary phase, the amount of excess IIR+ which was adsorbed is then released (Fig. 12.12(c)). The final outcome of these changes, which will be visualized by the detector, will depend on the relative rates of migration through the column of the solute ion and IIR+. Fig. 12.13 shows the three possibilities which may occur: that is, when the solute is elutedfaster than IIR+ (Fig. 12.13(a)), when the solute is eluted at the same time as IIR+ (Fig. 12.13 (b)) and when the solute is eluted more slowly than IIR+ (Fig. 12.13(c)). In the first frame of Fig. 12.13(a), the appearance of the solute causes increased IIR+ on the stationary phase and a depletion of this component in the eluent. As the solute moves into the column, the adsorbed IN+is released and causes a localized increase of IIR+ in the eluent (frame 2 of Fig. 12.13(a)). This process continues as the solute band moves further along the column (frame 3 of Fig. 12.13(a)), but the IIR+ which is released from the stationary phase enters a deficiency band of IIR+ in the eluent, so no net change occurs. The result of these effects is the appearance of a deficiency of IIR+ (negative peak) at the retention time of the solute, and an excess of IIR+ at its own retention time (i.e. a positive system peak occurs). The resultant chromatogram is shown at the bottom of Fig. 12.13(a). In the middle sequence (Fig. 12.13(b)), the same processes occur, but the deficiency and excess bands of IIR+ move down the column at similar speeds. The IIR+ which is adsorbed on the column as a result of the passage of the solute continues to be taken from the same deficiency zone in the eluent, and is added to the same excess zone in the eluent, so the changes in concentration which finally appear at the detector are much greater than in Fig. 12.13(a). The solute therefore appears as a deficiency of IIR+ (negative peak) whilst the excess IIR+ gives a positive system peak. The changes occurring in the third sequence (Fig. 12.13(c)) are similar to those of Fig. 12.13(a), except that the initial deficiency of IIR+ in the eluent, caused by the presence of the solute, now moves at a faster rate than does the solute ion. In this case, the excess of IIR+ which is released behind the solute zone is continually swept above the more slowly moving solute zone where it is again adsorbed onto the stationary phase. The result of this is that the system peak comprises a deficiency of IIR+ (and is therefore negative), whilst the sample zone has an excess of IIR+ (and is therefore positive). The explanations described above have received general support from other workers, but this support has not been unanimous. For example, Rigas and Pietrzyk [122] have suggested that the direction of the analyte peak is not determined by the location of the system peak in the chromatogram. but depends on the ion-exchangc selectivities and concentrations of the solute anion and the eluent anion. Nevertheless, the Stranahan and Deming model provides a reasonable basis for understanding the mechanism of a very complex detection process. Applications of UV visualization in IC
In order to maximize detection sensitivity in UV visualization, it is desirable that the system peak due to elution of the IIR occur early in the chromatogram. Detection of inorganic anions and organic base cations has been reported. A representative chromatogram for the former case is presented i n Fig. 12.14. Table 12.5 lists
367
Spectroscopic Detection Methods
chromatographic details for some published applications. It should be noted that the retention times and detection properties achieved with these methods are quite variable, and will depend on the actual chromatographic conditions used.
1
2
3
4
soiute
Fig. 12.13 Schematic representation of the changes in concentration of IIR in the eluent and stationary phases when solutes of different elution characteristics move through the column. The representations used for the solute, eluent IIR and stationary phase IIR are the same as for Fig. 12.11. See text fordiscussion. Adapted from 11211.
368
Chapter 12
Fig. 12.14 Detection of anions by ion-interaction chromatography using UV visualization detection. A Supelco LC-18DB column was used with 4 mM naphthylmethyltributyylammonium, 10 mM acetate buffer (pH 4.75) and 0.25 mh4 hexanesulfonate as eluent. Solute concentrations: 1 mM of each ion. Detection wavelength: 3 16 nm. Reprinted from [ 1131 with permission. TABLE 12.5 SOLUTES AND CHROMATOGRAPHIC CONDITIONS FOR UV VISUALIZATION DETECTION IN IC USING DYNAMICALLY (XIATED ION-INTERACTION COLUMNS Solute(s)
BTBA' C H 3 W Fe(~hen)3~+ ClO4Fe(phen)32+ClO4R~(phen)3~+ ClodNMTl3A+ CH3COONMTPA' CH3COOP E P CH3COONSA- H+ a
Inorganic anions F-, Cl-, B i , N e ' , N@-. ClOi, I-, BF4Carboxylic acids F-, CP, Br-, N@-, HP042-, HzAsOd-. NOi, ClO3', s04*-, Cro4'-, I-, BF4Inorganic anions el-,N@-, Br-, N@Carboxylic acids Alkylamines, alkylsulfates
x
Ref
(nm)
Detection limit
254 510 510 448
25 nmol 0.5 ng 10 ng 0.4 ng
116 117, 122 125 126
316 316 254 254
0.5 nmol 1 nmol 0.1 nmol 0.5 ppm
113, 115 114 127 128, 129
BTBA = benzyltributylammonium, NMTBA = naphthylmethyltributylammonium, NMTPA = naphthylmethyltripropylammonium, PEP = 1-phenethyl-2-picolinium, NSA = naphthalenesulfonate, phen = 1.10-phenanthroline.
SpectroscopicDetection M e t W
369
12.4 SPECTROPHOTOMETRIC DETECTION IN IC METHODS USING ION-EXCLUSION SEPARATIONS Derivation of a spectrophotometric detection equation for ion-exclusion chromatography requires a somewhat different approach than we have used earlier, because a direct substitution of solute ions for eluent ions no longer occurs in the elution process. Moreover, the degree of ionization of the solutes is often quite small. We will consider the case where the eluent is a solution of a fully dissociated, strong acid, HE. The eluent therefore contains only Hi and E-ions and the background absorbance is given by: ABackground
= EE-CE
(12.20)
where CE is the eluent concentration and EE- is the molar absorptivity of the eluent ion. Assuming that the solute is eluted as an equilibrium mixture of undissociated (HS) and dissociated (S-) forms, then the absorbance at the peak maximum is given by:
where Cs is the total concentration of the solute, Is is the degree of dissociation of the solute, and ES- and EHS are the molar absorptivities of the two forms of the solute. The absorbance change occurring during sample elution is:
The detector signal therefore depends on the degree of ionization of the solute and the molar absorptivities of the ionized and neutral forms of the solute. Chromatograms showing direct spectrophotometric detection of carboxylic acids after ion-exclusion separation have been presented earlier in Chapter 7 (e.g. Fig. 7.2(c)).
12.5 REFRACTIVE INDEX DETECTION 12.5.1
Direct refractive index detection
Most of the solutes normally encountered in IC are not detectable directly by refractive index (RI)measurements. The general exceptions to this are carboxylic acids, large species such as polyphosphonates and sulfonium ions, and some inorganic ions. This mode of detection is characterized by poor to moderate sensitivity and is usually adopted only when other detection methods have been shown to be unsuitable. However, RI detection does have a major advantage in ion-exclusion chromatography of carboxylic acids in that the detection signal does not depend greatly on the degree of ionization of the solutes. Therefore, weakly ionized or neutral solutes can be detected at roughly the same sensitivity as their fully ionized counterparts. Fig. 12.15 illustrates the application of direct RI detection to polyphosphonates and to boric acid. Table 12.6 lists some further examples of this form of detection.
370
Chapter 12
“3003
1
6.2 x10-7
RI
Units
2
11 ir
1
0
5
1
1
10 15 Time (min) (a)
1
20
0
5
0
Time (min)
(bl
Fig. 12.15 Direct refractive index detection of (a) polyphosphonates of the Dequest series, and (b) boric acid. (a) A Waters IC PAK A column was used with 15 m M HNO3 as eluent. Peak identities: (1) 2010, (2) 2054, (3) 2006, (4) 2041, (5) 2060 Dequest phosphonates. Reprinted from [I381 with permission. (b) A Waters Fast Fruit Juice column was used with 10 mN H2SO4 as eluent. The sample was 2000 ppm boron as boric acid. Reprintedfrom [ 1301with permission.
12.5.2
Indirect refractive index detection
Many of the eluents used with indirect spectrophotometric detection are suitable also for indirect RI detection. For example, eluents containing aromatic carboxylic acids have an appreciable background RI, which can be monitored to detect indirectly those anions which do not themselves show significant RI. RI measurements are conventionally made in a differential mode by comparison of the column effluent with pure eluent contained in a reference cell. The background RI of the eluent is therefore not restricted to any maximum level, unlike indirect spectrophotometric detection where photometric error limits the background absorbance of the eluent. This means that indirect RI detection can be used with relatively concentrated eluents and hence with ionexchange columns of much higher ion-exchange capacity than those employed with other detection modes. Detection sensitivity is governed largely by the performance of the detector used, which imposes a practical limitation in that most RI detectors available commercially are designed to operate with large solute concentrations and are generally not optimized for high-sensitivity applications. Despite this. indirect Rl detection has been shown to have detection limits which are comparable to those obtained using indirect spectrophotomctric detection or direct conductivity detection, when phthalate eluents are employed I531.
Spectroscopic Detection Methodr
37 1
TABLE 12.6 SOLUTES AND CHROMATOGRAPHIC CONDITIONS FOR DIRECT AND INDIRECT REFRACTIVE INDEX DETECTION IN IC Solute(s)
EluenP
Direct detection H3B03 Carboxylic acids Cr(III), Cr(V1) H2AsOi. H2As04' HPo42-
Polyphosphonates
Sulfonium salts
a
Separation mode
Detection Ref
H2S04 H2S04 Pentanesulfonate TBA+ OHTBA' HCDCY HNO3 NaC104, CH3CN
Ion-exclusion Ion-exclusion Ion-interaction Ion-interaction Ion-interaction Ion-exchange lon-interaction
20 ppm 5 ppm 15 ppm 4 ppm 5 ppm 2- 15 ppm 1 ppm
Salicylate Hydroxybenzoate
Ion-exchange Ion-exchange
. 1-3 ppm 0.2 pprn
90, 140 141
Phthalate
Ion-exchange
1-3 ppm
Cetrimide, citrate Phthalate Anilinium TBA+ HCOO'
Ion-interaction Ion-exchange Ion-exchange Ion-exchange
10 ng 1 ppm 1-4 pprn 1 ppm
43, 140, 142-144 87 145 53 140
limit
130, 13 1 132- 134 135 136 137 138 139
TBA = tetrabutylammonium.
Indirect RI detection has been used chiefly for the detection of anions, but the possibility of its application to cations has been confirmed [53]. Fig. 12.16 shows representative chromatograms for this detection mode and further examples are included in Table 12.6.
12.6 PHOTOLUMINESCENCE DETECTION IN IC
12.6.1
Direct fluorescence detection
Fluorescence detection is well known to offer excellent sensitivity and therefore represents an attractive method for detection in IC. Direct fluorescence detection in IC is very limited in scope due to the fact that almost all of the solutes under consideration do not exhibit fluorescenoe. However, two examples of this approach are the fluorometric detection of the ruthenium complex of 1.10-phenanthroline ([Ru(phen)3I2+) 11471, and of metal ions using 8-hydroxyquinoline-5-sulfonic acid as an eluent component [ 1481. Ion-interaction chromatography was used in the former case, whilst ion-exchange was used in the latter. Replacement ion chromatography of anions after
312
Chopler 12 (a) Time (min)
OL
L
8
12
16
7
Lx
RI
Fig. 12.16 Indirect refractive index detection of (a) inorganic anions and (b) inorganic cations. (a) A Vydac 302 IC 4.6 column was used with 6 m M phthalate at pH 4.0 as eluent. Solute concentrations 2.5-7.5 ppm. Reprinted from [146] with permission. (b) A Wescan cation column was used with 2.74 m M anilinium ion at pH 4.65 as eluent. Solute concentrations: 20 ppm. Reprinted from [53]with permission.
separation using suppressed IC has been applied to fluorescence detection by exchanging the eluted solute anions with anthranilate ions, or by exchanging the co-eluted H+ ions with Ce(II1) [44]. A membrane reactor was used in each case and the detection limits attained were in the picomole range (e.g. 26 pmol for C1-). Cation-exchange of coeluted H+ ions with Ce(II1) was found to be the more sensitive detection mode, and was also applicable for use with gradient elution.
12.6.2
Indirect fluorescence detection
Indirect fluorescence detection can be applied to IC in a number of ways. In ionexchange separations, simple exchange of a fluorescent eluent ion for the eluted solute ion provides indirect detection in the same manner as was used for indirect spectrophotometric detection. Eluents such as salicylate [56, 1491 and Ce(II1) [150] have been shown to give a suitable level of background fluorescence and to exhibit appropriate elution characteristics. Ion-interaction chromatography with permanently coated columns can be used with the same eluents [46]. Fig. 12.17 shows chromatograms obtained for inorganic anions using indirect fluorescence detection and Table 12.7 lists further examples of this technique.
Spectroscopic Detection Methods
373
(a1
Time (min) 0
10
20
n
-
30
SOL2
:IK*
N HL+
ystem
)eak
Fig. 12.17 Indirect fluorescence detection of (a) inorganic anions and (b) inorganic cations after ion-exchange separation. (a) A Vydac 302 IC column was used with 1.7 mM salicylate as eluent. Solute concentrations: 0.5-1 ppm. Reprinted from [56] with permission. (b) An Interaction ION210 Transition Metals column was used with 0.01 mM Ce(II1) as eluent. Solute concentrations: 0.16-1.2 ppm. Reprinted from [150] with permission.
Indirect fluorescence detection potentially offers great sensitivity. Eqn. (12.14), which is quite general and applies to any indirect detection method in which a detectable eluent component is replaced by an eluted solute, shows that sensitivity is maximized under conditions where a low eluent concentration is accompanied by a high dynamic reserve. This is just the case for fluorescence, where R maintains a level of 5000 even when CEfalls below M [ 1491. The solute peaks in indirect fluorescence detection appear as decreases in the background fluorescence, unless the eluent concentration is such that self-quenching of the fluorescence of the eluent ion occurs. In this case, a decrease in concentration of the eluent ion will lead to an increased fluorescence (due to decreased self-quenching) and thereby give positive peaks. An example of this approach has been reported in which 6,7-dihydroxy-2-naphthalenesulfonicacid is used as the fluorescent eluent [ 1541. The chief problem encountered with indirect fluorescence detection is the elimination of baseline noise and it has been found necessary to use a modulated double-beam laserexcited fluorometric detector in order to overcome the inherent flicker noise of the laser source [ 1491.
Chapter 12
374
TABLE 12.7 SOLUTES AND CHROMATOGRAPHIC CONDITIONS FOR INDIRECT PHOTOLUMINESCENCE DETECTION IN 1C Solute(s)
h(nm) ex em
Detection limit
Ref
mode
Salicylate Saliiylate Salicylate Salicylate Cerium(III)
Ion-interaction lon-exchange Ion-interaction Ion-exchange Ion-exchange
325 325 280 325 247
2 Pg 6.7 ng 0.2pmol 1-2 ng 3-160ppb
46, 151 149 152 56 150
Ceriurn(m)
Ion-exchange
247 350
0.2-100ppb 153
DHNSA
Ion-exchange Ion-interaction Ion-interaction
254 420 404 480 225 553
7.5 nmol 10 ng 28 Pg
154 126 155
Ion-exchange
400 515 400 515 415 520
20 pmol 2 ng 0.3pM
156 157 158
Eluent'
R~(phen)3~+ W13b
Biacetylb Biacetylb Biacetylb a
Separation
Ion-interaction
Ion-interaction
420 420 390 404 350
DHNSA = 6,7-dihydroxy-2-naphthalenesulfonicacid, phen = 1,lO-phenanthroline. Indirect phosphorescence detection.
The UV visualization detection method for ion-interaction chromatography, which was discussed earlier in Section 12.3.2, has been adapted for indirect fluorescence detection. The principles leading to the creation of a fluorescence detection signal are identical to those which applied earlier for spectrophotometric detection, except that the IIR must now possess a fluorophore. Cationic ruthenium complexes with 1,lOphenanthroline or 2,2'-bipyridine (i.e. R~(phen)3~+ and R~(bipy)3~+) have been found to be suitable for this purpose [126]. In this case, the peaks are observed as positive fluorescence changes. Fig. 12.18 shows a chromatogram obtained using this method.
12.6.3
Indirect phosphorescence detection
An alternative photoluminescence method for the detection of anions involves the use of phosphorescence quenching reactions. Solute anions may quench the phosphorescence of a suitable luminophore by energy transfer or electron transfer reactions. For example, the phosphorescence of biacetyl can be reduced from an initial intensity, 10, to a lower value, I, by reaction of excited (triplet) molecules with NO2- or s ~ O 3 [156]. ~The phosphorescence intensities before and after quenching are related by the Stern-Volmer expression [159]: (12.23)
Spectroscopic Detection Methou3
375
F-
1
a-
I
I
0
10
I
I
20 30 Volume (ml)
I
t
40
50
Fig. 22.18 Indirect fluorescence detection of inorganic anions by ion-interaction chromatography using a fluorescent IIR. A Hamilton PRP-1column was used with 0.1 mM Ru(phen)g(ClO& and 0.1 mM citrate buffer (pH 7.1) as eluent. Reprinted from [126] with permission.
where kA is the rate constant (1 mole-' sec-I) for the bimolecular reaction between the anion (A) and biacetyl, TO is the triplet state lifetime (sec) in the absence of A and [A] is the molar concentration of A. The success of the phosphorescence quenching method is therefore dependent on a long lifetime of the excited luminophore and a large rate constant. Biacetyl as a luminophore allows very sensitive detection of NO2- and SO3*(after oxidation of the latter to S ~ 0 3 ~ -giving ), detection limits as low as 20 pmol. However, oxygen must be removed from the eluent and this entails special procedures. Europium(ll1) and terbium(II1) are alternative luminophores which do not require the removal of oxygen [155]. These species emit long-lived phosphorescence and are suitable for the indirect detection of a range of anions, as listed in Table 12.7. Further examples of indirect phosphorescence detection are also included in this Table.
376
Chapter I2
12.7 ATOMIC SPECTROSCOPIC DETECTION I N IC 12.7.1
Atomic absorption spectroscopy
Atomic absorption spectroscopy (AAS) can, in theory, be employed as an elementselective detector for IC. The chief problem which emerges when an AAS instrument is coupled directly to the column effluent line of an IC is the different flow-rates existing with each technique. The sample uptake rate for a typical AAS nebulizer is 5 ml/min, whereas the typical operating flow-rate for an IC instrument is 1-2 ml/min. There are two possible approaches to overcome this problem; use of discrete sample fractions or flow-rate matching methods.
Discrete sampling In this approach, discrete fractions of sample from the ion chromatograph are collected and then introduced sequentially into the AAS. When a flame AAS is used, 50100 pl aliquots of sample can be collected in conical funnels mounted vertically in front of the spectrometer [160]. Alternatively, the column can be connected directly to the nebulizer with a tube containing a side-arm which permits the nebulizer to draw air between aliquots of the sample. Graphite furnace AAS is particularly suited to discrete sampling methods since this is the manner in which the instrument conventionally operates. The final "chromatogram" consists of a series of discrete signals, which if acquired at regular time intervals (such as with an auto-injector), gives a fair approximation of a normal chromatogram, as shown in Fig. 12.19(a) [161]. Discrete sampling AAS has been applied to the speciation of arsenic [161], selenium 1162, 1631and tin E1601. Flow-rate matching If the nebulizer uptake rate does not match the sample delivery rate, baseline noise and drift become unacceptable. Thus, direct coupling of A A S and IC requires some means to match the flow-rates of the two techniques. The most simple method is to measure accurately the nebulizer uptake rate and to use this as the IC flow-rate. For example, Cr04*- can be determined by IC-AAS using a flow-rate of 4.7 ml/min [164]. In most cases, this method will not be applicable because the IC flow-rate necessary will be inappropriately high. As an alternative, it has been shown that addition of distilled water in a post-column reactor can be used to increase the output flow-rate of the IC to that required by the AAS [165]. In this work, it was found that baseline noise remained unacceptably high when the IC and AAS were connected directly, but this could be reduced through the use of a dripaspirator in which the eluent and water were added into a small volume container, to which was connected the nebulizer feed line. Flow-rate matching is not necessary if a hydride generation system is used with the AAS. In this application, a reducing agent and acid are added to the column effluent by means of a post-column reagent delivery system and argon is then introduced into the stream. Volatile hydrides are removed from the sample and are carried to the AAS for measurement. This approach is most successful in the determination of arsenic species [166, 1671 and Fig. 12.19(b) shows a typical chromatogram.
SpectroscopicDetection Methods
377 MA
HASOL
MMA cO.01 A U
~ ~ 0 ~ 3 -
1
fl APA
" I
I
0
10
I
I
20 30 Time ( m i d (a)
1
1
40
50
I
0
I
2
1
I
4 6 8 Time (minl
I
I
1
0
(bl
Fig. 12.19 Atomic absorption detection in IC. using (a) discrete sampling and (b) hydride generation. (a) An Altex SCX column was used with 37.5 mM ammonium acetate buffer as eluent. Detection by graphite-furnace A A S with discrete sample introduction. Reprinted from [la11 with permission. (b) A Dionex anion column was used with 2.4 mM NaHCa and 1.9 mM Na2C03 as eluent. Detection by arsine generation AAS after post-column addition of NaBH4, HCI and K2S20g. Solute identities: MMA = monomethylarsinate, DMA = dimethylaninate, APA = paminophenylarsinate. Reprinted from [166] with permission.
Indirect detection using AAS All of the methods described above refer to direct detection of analytes, wherein a hollow-cathode lamp is used for the selective detection of one element only. This approach affords high selectivity and is therefore valuable for the determination of analytes in complex sample matrices. AAS can also be operated in an indirect mode. For example, a lithium based eluent can be used for the separation of monovalent cations by ion-exchange, with the eluted cations being detected indirectly by AAS using a lithium hollow-cathode lamp [165]. In a similar manner, divalent cations may be detected indirectly by AAS with a CuSOs eluent and a copper hollow-cathode lamp. It is even possible to use indirect AAS detection for anions by employing [Cu@DTA)]*- as the eluent and again using a copper lamp [165]. All of these indirect AAS detection methods are characterized by noisy baselines and moderate sensitivity. Some examples of AAS detection in IC are given in Table 12.8.
378
Chapter 12
TABLE 12.8 SOLUTES AND CHROMATOGRAPHIC CONDITIONS FOR ATOMIC SPECTROSCOPIC DETECTION IN IC
Detection methcda
Solute(s)
Eluentb
Separation modec
Dem limit
AAS
As compounds
NaH2m4
Ion-exchange
5ppb
AAS AAS AAS AAS AAS
F-, C1' Na+, K+ Mn2+, Mg2+, Co2+,Ni2+ SeQ2-, SeO42Sn(II), Sn(lV), mbutyltin Alkaiineearthmetals F'. Cl-, N%', N a - , BrLanthanides Li+, Na+, N&+, K+ P043-, P2O7'-, P3O1o5Alkali metals, transition
[cUEDTAl2LiN@ CuSO4 Na2C03 NaH2P04 HNO3 Na2C03, NaHC03 Cimc acid HNO3 TEA'OHPentanesulfonate
Ion-exchange Ion-exchange Ion-exchange Ion-exchange Ion-exchange Ion-exchange RIC Ion-exchange RIC Ion-interaction Ion-interaction
161, 166, 167 50ppm 165 1 ppm 165 50ppm 165 0.2 ng 162 200ng 160 0.5 ppm 168 1 ppm 42, 169 0.5 ppm 168 1 pprn 42, 169 0.1 Fg 170 1 ppm 136
A~03~-,As04~-, Pentanesulfonate dimethylarsinate Br-, A s O ~ ~ -HTMA+ , ICPAES A ~ 0 3 ~SeO3*-, Po43ICPAES As compounds TBA+HzP04ICPAES As compounds (m)2C03 ICPAES Cr(III), Cr(V1) Pentanesulfonate ICPAES Cr(III), Cr(V1) Phthalate DCPAES As(III), As(V) Na2C03, NaHC03 DCPAES Cr(III), Cr(V1) Citrate, oxalate Na2C03, NaHC03 DCPAES Se(IV), Se(V1)
Ion-interaction
1 pprn
Ion-interaction
0.1 pprn 171
Ion-interaction Ion-exchange Ion-interaction Ion-exchange Ion-exchange Ion-exchange Ion-exchange
40ppm 0.2 pprn 10ppb long 3ppb 1 ppb lppm
FES FES €33.3
FES FES ICPAES
Ref
llletalS
ICPAES
a
136
172 173-176 135 177 178 179 178
GAS = atomic absorption spectrometry, FTS = flame emission spectroscopy, ICPAES = inductively coupled plasma atomic emission spectrometry, DCPAES = direct current plasma atomic emission spectrometry. HTMA = hexadecylmmethylammonium,TBA = teaabutylammonium, TEA = methylammonium. RIC = replacement IC after ion-exchange separation.
12.7.2
Atomic emission spectroscopy
Atomic emission techniques have proved relatively successful for selective detection in IC. The excitation source can be a simple flame (i.e. flame photometry) or a high temperature plasma. The former approach is typified by the detection of alkaline earth and lanthanide elements after separation on a pellicular ion-exchange column with citrate as eluent [ 1681, and by the selective detection of phosphorus- and sulphur-containing solutes using the emission of the molecular species HPO and S2 [170, 1801. Fig. 12.2qa)
Spectroscopic Detection Methods
-
0
2 4 6 Time (min) (a)
8
379
I
0
I
I
1
2
I
3
I
I
4 5 Time (min) (b)
I
6
I
7
I
8
I
9
Fig. 12.20 Atomic emission detection in IC, using (a) flame and (b) ICP as the excitation source. (a) A Hamilton PRP-1 column was used with 10 mM tetraethylammonium hydroxide and 20 mM formic acid as eluent. A dual-flame photometric detector was used at 'the HFQ emission wavelength. Reprinted from [ 1701 with permission. (b) A Hamilton PRP-X100 column was used in conjunction with a Vydac c18 column. The eluent was 3 mM N b H 2 P 0 4 at pH 6.0. An ICP was used as the excitation source. 1 = dimethylarsinic acid, 2 = monomethylarsinic acid, 3 = arsenobetaine, 4 = As(III), 5 = As(V). Reprinted from [175] with permission. shows a chromatogram obtained using flame photometric detection and further examples of this approach are included in Table 12.8.
Plasma excitation High temperature emission sources such as direct current, microwave-induced or inductively coupled plasma (ICP) systems have been applied to IC by direct connection of the IC effluent line to the ICP nebulizer. The uptake rate of these nebulizers is about 2 ml/min, which is compatible with normal IC flow-rates. The detection limits achievable under these conditions generally fall short of those attained when the ICP spectrometer is used as a stand-alone instrument. This stems directly from the inherent inability of the pneumatic nebulizer used in such ICP systems to equilibrate to the rapidly changing concentration of analyte which is eluted from the IC in a very small volume (e.g. 100 ul), since such nebulizers typically have large internal volumes. Direct current plasma atomic emission spectrometers (DCP) have more suitable spray chambers for sample introduction and these devices give greatly improved sensitivity in comparison to ICP systems, when interfaced to an ion chromatograph [181]. Alternatively, a direct injection nebulizer can be used [172]. Fig. 12.20(b) shows a chromatogram obtained with ICP detection and Table 12.8 provides further examples. Replacement IC wiih atomic spectroscopic detection Replacement IC (see Section 12.2.2) can be performed with atomic spectroscopic detection [42, 169, 1821. Stoichiometric replacement of the counter-cation associated
380
Chupter 12
CI-
Li'
Na'
I
F-
I
I
1
I
I
I
I
I
0
1
2
3
4
5
6
7
Time lminl
la)
l
l
I
I
I
8
0
2
4
6
0.1p A
1
1
8 1 0
I
1
12
14
Time (min) lbl
Ik
Fig. 12.21 Replacement IC using atomic emission detection. (a) A Dionex anion separator
column was used with 2.4 mM Na2C03 and 3.0 mM NaHCO3 as eluent. (b) A Dionex cation separator column was used with 5 mhf HNO3 as eluent. Li+ was used as the replacement ion in each case. A microwave-induced nitrogen discharge at atmospheric pressure was used as the excitation some. Reprinted from [ 1821 with permission. with an eluted anion by a cation which shows good flame photometric response (e.g. Li+) permits indirect detection of these anions. The replacement column or membrane fibre is situated after the separation column and the eluent from the replacement column is directed into a flame photometer. The resulting signal observed for lithium emission at 670 nm provides an indirect, but quantitative, measure of the concentration of the eluted solute anion. Similarly, the concentrations of eluted cations can be determined after their replacement in the eluent with Li+. The detection limits attainable when an atmospheric pressure microwave-induced nitrogen discharge is used as the excitation source are in the 30-50 ng range for anions and cations. Fig. 12.21 shows chromatograms for the detection of anions and cations by RIC.
12.8 REFERENCES 1
2 3
4 5 6 7 8 9 10
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SpectroscopicDetection Metho& 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 1 12 1 13 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138
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SpectroscopicDetection Methods 177 178 179 180 181 182
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387
Chapter 13 Detection by Post-Column Reaction 13.1 INTRODUCTION Detection using post-column reaction (PCR) involves the chemical reaction of solutes as they are eluted from the column, prior to their passage to the detector. The chief aims of this approach are to enhance the specificity and sensitivity of the detection method so that detection can be achieved at low concentrations of analyte or in the presence of high concentrations of interferences. PCR detection has had considerable impact in IC and is widely used with conductivity, spectroscopic and electrochemical detectors. In particular, the use of a suppressor with conductivity detection (as discussed in Section 9.5) can be considered as one form of PCR, whilst enhancement and replacement columns with conductivity or spectroscopic detection (discussed in Sections 9.5.6, 12.2.2 and 12.7.2) can also be considered as PCR methods. Since these have been treated earlier, we will therefore confine the discussion in this Chapter to PCR approaches for all detection methods excluding conductivity. In addition, PCR reactions involving the addition of acid or base to the chromatographic eluent will not be discussed further.
13.1.1 Types of PCR systems PCR is performed by the introduction of suitable reagents into the column effluent. These reagents may be added as a solution which is mixed directly with the column effluent, or through the use of a solid-phase (or packed-bed) reactor of some kind, where the PCR occurs at a solid surface. The first of these possibilities can be defined as solution PCR and the second as packed-bed PCR. It can be noted that solution PCR is the most widely employed method in IC. Fig. 13.1 shows schematic representations of both of the above PCR methods and indicates that a reaction coil is sometimes necessary to provide sufficient time for the reaction to proceed.
Solution PCR The desirable features of reagents for solution PCR can be summarized as [I]: The reagent musf'give a suitable chemical reaction with the analytes to ,provide suitable detection. Typically, the reagent (or its reaction product with the analyte) contains a strong chromophore or fluorophore. (ii) The reagent should be stable in order to minimize baseline drift and noise in the detector.
(i)
388
Chapter 13
~
t;;t;
4
,
-
Column
Mixing
Delay
Packed-bed reactor
Delay coil-
4
Detector
Fig. 13.1 Schematic representation of (a) solution PCR and (b) packed-bed PCR systems.
The reagent must be miscible with the eluent and should not form precipitates in the presence of the eluent. Solubility of the reaction products with the analyte is of lesser importance because of the very low concentrations of analyte typically used. The reaction time between the analyte and the added reagents should be very short so that the use of reaction coils can be avoided. This, in turn, minimizes the band-broadening effects resulting from the PCR procedure. The reagent should have similar detection properties to that of the eluent, so that variations in the degree of mixing of the reagent and the eluent do not cause elevated baseline noise. The reagent must not cause corrosion or other reactions with either the postcolumn reactor itself. or the detector.
Packed-bed PCR In packed-bed PCR, the derivatization reagent is immobilized onto a solid support which can be organic or inorganic in nature. The reagent can be physically adsorbed or attached to the support by ionic or covalent bonds. A heterogeneous reaction occurs between the analyte and the immobilized reagent. Packed-bed PCR offers a number of significant advantages when compared to solution PCR. Additional instrumentation, such as a pump, reaction coil and mixing chamber, are not required and the band broadening introduced is generally less than that for solution PCR. Moreover, there is no derivatizing reagent present in the eluent which could lead to an increase in the level of baseline noise. Finally, reactions which are possible in solution only at low concentration because of low solubility of the reagent may be carried out at higher concentrations using a solid support.
Detection by Post-ColumnReaction
389
The requirements of a packed-bed PCR system can be summarized as [2]: (i) The immobilized reagent should be stable in the eluent used. (ii) The solid support should be mechanically stable at the operating pressures used. (iii) The packed-bed reactor should not contribute excessively to broadening of the analyte band. (iv) The packed-bed reactor should be capable of extended use before the immobilized reagent is exhausted. (v) Reaction products should not be retained irreversibly on the packed-bed reactor, nor should gases or precipitates be produced from reactions with the analyte or eluent. Packed-bed suppressor columns (Section 9.5.2), replacement columns (Section 12.7.2) and signal enhancement columns (Section 9.5.6) are all examples of packed-bed PCR in IC.
13.2 HARDWARE FOR POST-COLUMN REACTION 13.2.1 Pumps for PCR
Effect of pump pulsations When solution PCR is to be used, some form of pump is required to deliver a constant flow of reagent to the mixing chamber. The baseline noise measured at the detector is given by [3]: 1
BaselineNoise = [(DN)2 + (CN)2 + (IvfN)2 + (FN)2]z
(13.1)
where DN is detector noise, CN is cell noise, MN is mixing noise and FN is noise from flow pulsations. The detector noise arises from the electronics of the detector itself, whilst the cell noise occurs when the background eluent flowing through the detector (in the absence of analyte) produces a finite detector signal. Cell noise usually results from thermal effects and is dependent on the magnitude of the detector signal produced by the background eluent. Mixing noise is the result of imperfect mixing of the eluent and the PCR reagent. The final contribution to baseline noise is flow noise resulting from pulsations in either the eluent pump or the PCR pump. Any variations in the rate at which the PCR reagent and eluent are mixed will cause baseline noise in the detector, especially when the reagent itself gives some detector signal under the conditions used to monitor the reaction product formed between the analyte and the added reagent. As an example, we can consider a PCR system in which the added reagent forms a coloured complex (with the analyte ion) which shows maximal absorbance at 500 nm. We will assume that the added reagent absorbs weakly at this wavelength, such that the absorbance of the mixed eluent-reagent solution passing through the detector (in the absence of analyte ions) is 0.01 absorbance units (AU) higher than the eluent itself. A
390
Chapter 13
c
C
/
1x
AU
0I
1
1
0
1
2
Time (min)
Fig. 13.2 Detector noise caused by pump pulsations in a PCR system in which the eluent is delivered by a dual piston, reciprocating pump and the PCR reagent by gas pressure. Curve A: reagent and eluent flow-rate 0.1 ml/min, back-pressure 100 psi. Curve B: reagent and eluent flowrate 0.5 ml/min, back-pressure 700 psi. Curve C: reagent and eluent flow-rate 0.1 mumin, backpressure 3000 psi. Curve D:reagent and eluent flow-rate 0.5 mumin, back-pressure 3000 psi. Reprinted fmm [3] with permission.
variation of 1% in the delivery flow-rate of the PCR pump will cause a change in the detector baseline of O.OOO1 AU. Whilst this value may appear to be small, it is about 10100 times higher'than that encountered in HPLC using UV absorbance detectors [l]. Flow noise resulting from pump pulsations has been shown to account for more than 90% of the observed baseline noise in a PCR system [31. The observed noise is dependent on the flow-rate and back-pressure at which the pump is operated, as illustrated in Fig. 13.2. For this reason, syringe pumps are often preferred for delivery of the PCR reagent. Alternatively, a simple overpressure pneumatic delivery system may be used. In such devices, a regulated gas pressure is maintained over the surface of the reagent, which is housed in a suitable vessel. This gas pressure drives the reagent solution to the mixing chamber without the pressure pulsations which would result from a reciprocating piston pump. Pneumatic PCR pumps are available commercially from a number of manufacturers and Fig. 13.3 shows a schematic representation of one such device. If a reciprocating piston pump is to be used, it is essential that adequate pulse dampening be provided so that baseline noise is acceptable. It must be stressed that these limitations imposed on the pressure pulsations of the PCR pump are less severe when the difference in detector signals for the eluent and PCR reagent is very small.
Materials for pump construction The subsequent discussion in this Chapter will show that PCR in IC is used predominantly for the detection of metal ions. It is therefore imperative to minimize contamination of the eluent or PCR reagent by metal ions released from the PCR pump.
39 1
Detection by Post-Column Reaction
From gas cylinder
Pressure regulator
+
+To detector I
n
+ Eluent
(from pump)
PCR reagent forced upwards by gas pressure Fig. 13.3 Schematic diagram of a commercial pneumatic device for pulseless delivery of the PCR reagent. Courtesy of Waters Chromatography Division.
Given the extreme conditions of pressure and friction encountered in high pressure pumps, a reliable contamination-free pump may be difficult to construct, even when non-metallic materials are employed. The pneumatic reagent delivery systems discussed above and illustrated in Fig. 13.3 are constructed completely from inert materials, such as PTFE, and are not subject to frictional wear. These factors represent further advantages for this type of pump. An alternative pumping procedure, which may be followed in cases where pneumatic pumps are unavailable, is to isolate the pumping system from the PCR reagent. This can be achieved with a series of switching valves which enables a fixed volume of PCR reagent (e.g. 15 ml) to be displaced from a loop by 2-propanol delivered from a conventional pump [41. 2-Propanol is used to minimize metal solubility from the pump and to maintain separation from the PCR reagent solution by density difference. Such an arrangement suffers from the fact that only a limited volume of PCR reagent can be delivered before the loop must be refilled, however the construction materials used in the pump are no longer significant, since none of these materials comes into direct contact with the PCR reagent. Moreover, use of inert materials for the switching valves, loops and interconnecting tubing can eliminate any contact of the PCR reagent with metallic components. The same type of system can be used to deliver eluent in cases where contamination by metal ions is of extreme importance.
13.2.2 Mixing chambers The function of the mixing chamber is to accomplish intimate mixing of the eluent and the PCR reagent in the smallest volume possible. That is, mixing efficiency should be maximized whilst band-brodening of the analyte should be minimized.
Tee-piece mixers The simplest type of mixing chamber is a three-way junction which accommodates inlet tubes for the eluent and PCR reagent and an outlet tube to pass the mixed reagents to a reaction coil or directly to the detector. The angles at which the inlet and outlet
Chapter 13
392
PCR reagent
PCR reagent I
I
To Eluate
detector
*
+
To detector
Eluate
+
+
To Eluat
--*
detector +
Fig. 13.4 Typical tee-piecesused as mixing chambers for PCR applications. All tubing is 1/16 inch OD and .007inch ID. Reprinted from [3.5’,61 with permission.
tubes are arranged in such a junction can vary somewhat, but a 90° tee-piece is conventionally used. Examples of such tee-pieces are shown in Fig. 13.4. The device shown in Fig. 13.4(a) can be constructed by cutting two lengths of stainless steel tubing at 4 5 O and butting the ends together. An outlet tube is then pressed against the joined inlet tubes [ 5 ] . The mixed eluent and PCR reagent flow out and around the small spaces in the tubing joint and pass into the outlet tube. The bandbroadening of this mixing chamber is minimal. Fig. 13.4(b) shows a tee-piece constructed from a length of conventional 1/16 inch OD stainless steel HPLC tubing (0.007 inch ID) joined at its centre with a perpendicularly arranged length of the same tubing [6]. The tubing was joined by machining the components of the joint at 60°. The band-broadening of this mixing chamber was determined to be the same as that for an equivalent length of straight tubing. The final tee-piece design, depicted in Fig. 13.4(c), uses square-cut tubing and incorporates a 120-mesh stainless steel screen situated between the eluent inlet and detector outlet tubes [3]. The PCR reagent solution flows around the exterior of the eluent inlet tube, before passing into the screen and thence to the detector. Each of the tee-pieces shown in Fig. 13.4 provides very efficient mixing; for example, the screen-tee reactor illustrated in Fig. 1 3 . q ~ has ) been shown to give a mixing homogeneity better than 99.9% of theoretical perfect mixing [3]. It is noteworthy that although the angle of impingement between the eluent and PCR reagent is 900 for each of the tee-pieces shown in Fig. 13.4, it is also possible for 1800 impingement to be used. That is, the two inlet solutions flow in opposite directions into the tee-piece and emerge from the perpendicular outlet tube. A detailed treatment of the flow and mixing characteristics of various tubes and mixing devices can be found elsewhere [7].
Detection by Post-Column Reaction
I
Post-column reagent under gas pressure
I
E+S+R
Semi-permeable hollowfibre membrane
(a)
393
Post-column reagent under gas pressure
,
E+S+R
Monofilament nylon fishing line
(b)
Fig. Z3.5 Schematic illustration of (a) membrane reactor and (b) annular membrane reactor used for PCR applications. E is the eluent, S is the analyte and R is the post-column reagent.
Membrane reactor The PCR reagent solution can be introduced into the eluent by means of a semipermeable membrane in the form of a hollow-fibre. The eluent stream passes through the centre of the fibre, whilst the PCR reagent flows around the exterior of the fibre. The reagent diffuses through the fibre wall under external pressure and mixes with the eluent. Longitudinal mixing, which causes broadening of the analyte bands, is reduced by coiling the fibre, which also enhances radial mixing. This type of device, illustrated schematically in Fig. 13.5(a), operates on similar principles to the hollow-fibre membrane suppressor discussed in Section 9.5.3, and was originally proposed as a device for PCR of organic analytes [8]. However, membrane reactors are now used commonly for PCR of inorganic analytes and a commercial device of this type is available from the Dionex Corporation. The type of membrane material used in the construction of the hollow-fibre should be chosen to permit maximum penetration of the PCR reagent, with minimal loss of the analyte species. Since the peaks eluting from an IC contain relatively dilute concentrations of the analyte, it is possible to use a membrane which has little permeation selectivity of the PCR reagent over the analyte and to maintain a high concentration of the PCR reagent at the exterior wall of the fibre. In this way, permeation of only a small percentage of the PCR reagent will result in a relatively high concentration in the eluent, whilst loss of the analyte by diffusion out of the fibre is insignificant. The dead volume of a membrane reactor is normally high (up to 100 pl) in comparison to that of a typical tee-piece because the reactor must be of sufficient length for diffusion of the PCR reagent to occur. This can result in significant broadening of the analyte band. On the other hand, the elastic nature of the membrane may be of some benefit in reducing pressure pulsations from the eluent pump.
Chapter I3
394
The problem of large dead volume can be overcome through the use of an annular membrane reactor in which a monofilament nylon fishing line is inserted into a microporous hollow-fibre (Fig. 13.5(b)) [3]. The composite tubing can be heated in water and coiled into a helical configuration. A 5 cm membrane reactor formed in this way has an internal volume of 1.5 pl, with an effective hydraulic radius of 97 pm. The PCR reagent is delivered to the reactor by pneumatic pressure using a pump similar to that illustrated in Fig. 13.3. Mixing efficiency of the eluent and PCR reagent with the annular membrane reactor was found to be very close to theoretical perfect mixing.
Comparison of differen: mixing chambers Under conditions where the chemistry of the PCR system involves very rapid reaction, all of the mixing chambers described above give satisfactory (and equivalent) mixing efficiency. In a recent study comparing annular membrane and screen-tee reactors, Cassidy et al. [3] found that both reactors gave identical mixing efficiency and the band-broadening characteristics of the two reactors (as reflected in the chromatographic efficiencies calculated for eluted analyte peaks) were very similar for flow-rates in the range 0.5-2.0 ml/min. The only significant difference noted between the two reactor types was that the membrane reactor was prone to leaks at elevated flowrates. 13.2.3
Reactors
After the PCR reagent and the analyte are mixed, it may be necessary for them to be passed to a suitable reactor to provide appropriate conditions for reaction to occur. For example, the kinetics of the reaction might be slow, so that a sufficient delay time is necessary before detection can take place; alternatively, it may be necessary to heat the mixture to stimulate reaction. Reactors can take various forms, ranging from a simple coil designed to provide time for the reaction to occur, to more complex devices such as stitched capillaries or knitted open tubes. The characteristics of the latter types have been described in detail elsewhere [7]. Fortunately, the chemical reactions utilized in PCR detection of inorganic species generally have very rapid kinetics, so reactors are usually unnecessary. In the worst cases, a simple delay coil may be required.
13.3 PCR DETECTION OF INORGANIC ANIONS 13.3.1 Phosphorus 0x0-anions The determination of P043- by reaction with acidic ammonium molybdate to form phosphomolybdic acid and subsequent reduction of this acid to form the coloured molybdenum blue complex, has been an established analytical method for many years. Condensed polyphosphates can also be determined by this approach if they are first degraded to Pod3-. On the other hand, lower phosphates must be oxidized to Pod3- prior to analysis. The chemistry of these reactions can be made more suitable for PCR in chromatography by conducting the hydrolysis at elevated temperature and pressure and by using a mixture of Mo(V) and Mo(V1) to react directly with P043- in a single step [9, lo]. Fig. 13.6 shows a chromatogram of P043- and polyphosphates obtained using this
Detection by Post-Column Reaction
395
I
I
I
I
I
I
l'8
2.4
30
36
$2
48
Time (min)
Fig. 13.6 Chromatogram obtained for a mixture of orthophosphate (Pl), diphosphate (P2), mphosphate (P3) and tetraphosphate (P4). A TSK-GELEX-220SA anion-exchange column was used with 0.21 M KCl at pH 10 as eluent. The detection wavelength was 830 nm. Solute concentrations: 40 nmol (as P). Reprinted from [lo] with permission.
method. Lower 0x0 anions of phosphorus, such as phosphinate and phosphonate, can be oxidized to P043- with NaHS03, which can then be converted to the molybdenum blue complex using the Mo(V)-Mo(V1)reagent [ 111. Indirect detection of polyphosphates (and other complexing species, such as aminopolycarboxylic acids) by PCR has been reported using a coloured methylthymol blue complex of magnesium or calcium as the PCR reagent [12]. Complexation reactions occurring between the analyte and calcium or magnesium result in the formation of colourless complexes and hence a decrease in the absorbance of the mixed eluent and PCR reagent solution. This absorbance change can be used as an indirect measure of the concentration of the analyte ligand.
13.3.2 Fe(C104)3 as a post-column reagent One of the most versatile reagents for PCR of anions is Fe(C104)3. Under acidic conditions, many anions form coloured complexes with Fe(II1) which exhibit maximal absorbance in the wavelength range 300-350nm [13, 141. As an example, sulfate reacts with Fe(II1) as follows [ 151: (13.2)
396
Chapter 13
TABLE 13.1 COMPLEX FORMTION OF INORGANIC ANIONS WITH Fe(III) IN HC104 SOLUTION Anion
Emax
(nm) m42-
SCNFe(CN)b4Fe(CN)b3s04’-
c1~207~-
I‘ P30i05S2s2032NQm43-
305, 344 3 10 305 305 306 335 310 306,350 310 -300 308 372.360 310
Detection
DeDection limit (nm0l)a
0.4 1.3
1.6 1.9 2.8 4.8 5.2
5.6 6.4 7.1 8.1 10.8 11.8
limit (nmol)a 308 -300 -300 -300 -300 -300 -300 -300 -300 -300
12.7
24.8 28.8 73.7 141.3 144.3 206.4 93 1.7 392.2 285.7
b b b
Reactions were carried out in 0.8 M HClO4 containing 0.05 M Fe(C104)3. No chromatographic column was used. Data taken from [ 161. a A detection wavelength of 340 nm was used. No reaction was observed. Imanari el a/. [I61 have examined a wide range of anions for the formation of detectable complexes with Fe(II1) and of the anions tested, only NO3-, F- and ClO3showed no colour formation. Table 13.1 lists the wavelengths of maximum absorption of the complexes formed, together with the detection limits obtainable in a flow-injection mode (i.e. without the chromatographic column). Some 14 anions showed sufficient absorbance at 340 nm to enable sensitive detection. Anion-exchange separation of a limited number of anions, coupled with PCR using 0.8 M He104 and 0.05 M Fe(C104)3, yielded the chromatogram shown in Fig. 13.7(a). The sensitivity of the above method is only moderate in comparison to other detection methods for the same anions, and since the PCR mode responds to many ions, this approach offers no advantages over alternative detection methods. However, further studies have shown that the same PCR chemistry is applicable to polyphosphates and aminopolycarboxylic acids [17]. A comprehensive listing of the solutes of this type which show positive colour development with Fe(II1) can be found in this reference. Such species are difficult to detect by other means and so the PCR approach becomes the method of choice for these solutes [18, 191. Separation can be achieved using gradient elution with a nitric acid eluent. Fig. 13.7(b) shows a typical chromatogram, obtained after PCR with Fe(C104)3 and detection at 340 nm. This separation has particular importance for the analysis of detergents. A similar separation using a different column was shown in Fig. 4.13.
397
Detection by Post-Column Reaction
I-
p-
SCN-
r 0
I
I
0 lime lmin)
4
I
I
12
16
la) Dequest 2046 , Oequest 2060
\
Dequcst 2010
I
0
I
5
1
10
I
I
20 lime (mint
'5
I
I
25
30
I
35
Fig. 13.7 Detection of anions using acidic Fe(ClO4)j as the post-column reagent. (a) A TSK-Gel EX-520column was used with 0.05 M sodium acetate and 0.05 M sodium nitrate at pH 5.48 as eluent. Reprinted from [16] with permission. (b) A Waters IC Pak A column was used with a step gradient of nitric acid as eluent. Detection in each case was at 340 nm. Courtesy of Waters ChromatographyDivision.
Chapter 13
398
The reaction of Fe(C104)3 with sulfate has been used for the development of a sulfur-selective PCR detection method which has been applied to the determination of individual sulfur species containing any combination of Sz, %h2-, S203;?-,S(h2-, s3062-, S4O6;?-and S ~ 0 6 [~151. - The ions are separated by ion-exchange chromatography and the column effluent is reacted with bromine to convert the eluted species to S04;?',which is then detected by PCR with acidic Fe(C104)3. The chromatographic efficiency of this system is poor due to the requirement for two separate post-column reactions.
13.3.3 Other PCR methods for anions Fluorescence detection of NO;?-,s ~ O 3and ~ - I- can be achieved after PCR of these ions with cerium (IV), to produce the fluorescent species cerium(II1) [20]. Nitrate can also be detected in this manner if it is first reduced to NO;?-on a copperized reductor. In the PCR, NO;?-,S;?03;?-and I- are oxidized to NO3-, s;?0g2and I;?, respectively, whilst cerium(1V) is reduced to cerium(II1). Detection limits in the low ppb range were obtained. Other PCR methods have been reported for the detection of specific anions. These methods are listed i n Table 13.2, which also includes further details of the PCR methods discussed above. 13.4 PCR DETECTION OF INORGANIC CATIONS 13.4.1
Choice of the PCR reagent
PCR detection of inorganic cations, such as alkaline earths, transition metals and lanthanides, has been developed to the point where it can be considered to be the optimal detection mode for most of these species. In the majority of cases, the eluted metal ions are reacted with a colour-forming reagent and spectrophotometric detection is used. However, other detection methods, such as fluorescence and amperometry are also applicable. An important point which must be considered in the development of PCR detection methods for cations is that these species may be eluted from ion-exchange and ioninteraction columns as complexes with the eluent ligands. It will be remembered from Section 4.3.2 that cations with a multiple charge show such strong affinity for sulfonated cation-exchange resins that they can be eluted only when a complexing ligaud (such as oxalate, tarvate, citrate, etc.) is added to the eluent. Thus, the PCR reagent must be
PAR
Arsenazo Ill
Fig. 13.8 Structuresof common colour-forming reagents used in PCR of metal ions.
399
Detection by Post-Column Reaction
TABLE 13.2 SOME EXAMPLES OF POST-COLUMN REACTIONS FOR THE DETECTION OF ANIONS IN IC Solutes
Post-column reagenta
Aminopolycarboxylic acids, Ca-methylthymol blue polyphosphates Aminopolycarboxylic acids, Fe(N0313 polyphosphates, etc. CN-, SCN-
Inorganic anions NOy,NO3N02-,N03-,S2032-,I' Phosphorus 0x0 acids Phosphonic acids Polyphosphates, phosphonates s2-,~032-, ~203*-, ~042-, s3062-, S40(j2-, ss0(j2~032~042a
Na2MoO4 Ba-chloroanilate
Reaction product(s)
Detection modeb
Ref
Colourless complexes Fe(II1) complexes
Spec (605 nm)
12
Spec (330 nm)
21
Polymethine dye
Fluor (607 nm)
22
Fe(II1) complexes
Spec (340 nm)
18,
Heteropoly blue
Spec (830 nm)
19 10
Heteropoly blue Catalytic reaction
Spec.(830 nm) Spec (600nm)
Fe(II1) complexes Nitrate Ce(II1) Al(III) complexes Fe(II1) complexes P-vanadomolybdate Fe(II1) complexes
Spec (340 nm) Amper (+1.0 V) Fluor (350 nm) Fluor (480 nm) Spec (300 nm) Spec (410 nm)
9 23, 24 16 25 20 26 17 27
Spec (335 nm)
15
Molybdosilicate Bas04
Spec (410 nm) Spec (530 nm)
28 29
DMAPM = 4,4'-bis(dimethylamino)diphenylmethane. Spec = spectrophotometry,Fluor = fluorescence, Amper = amperometry.
capable of displacing the eluent ligand from the metal ion. This necessarily limits the number of colour-forming species which are applicable to PCR detection of metal ions. A further consideration in the choice of the PCR reagent is whether detection selectivity is desirable or not. Broad-spectrum reagents, which form detectable complexes with a wide range of metal ions, are useful for general detection, whereas more specific reagents can be applied to selective detection. The most commonly employed broad-spectrum PCR reagents are 4-(2-pyridylazo)resorcinol [PAR] and 2,7-bis(2-arsonophenylazo)-l,8-dihydroxynaphthalene-3,6-disulfonic acid [Arsenazo (III)]. The structures of these compounds are shown in Fig. 13.8. Table 13.3 indicates some of the cations which show positive colour reactions with these species. In general use, PAR i s the preferred reagent for the PCR detection of transition metal ions, whilst Arsenazo I11 is preferred for lanthanide ions.
400
Chapter 13
TABLE 13.3
COLOUR-FORMING REACTIONS OF PAR AND ARSENAZO I11 WITH SOME METAL IONS. DATA FROM [W] AND PUBLISHED APPLICATIONS Metal ion
PCR reagent
Arsenaimm Aluminium(m) Bismuth(II) Cadmium@) Calcium@) Chnxnium(Ii1) Cobalt(II) Copper(n, Hafnium(IV) Iron(II) Iron(II1) Lanthanides a
.a
.. . a
.
I
Metalion
PAR
. . .. .. .. a
PCR reagent Arsenazom
Lead@) Magnesium(U) Manganese0 MeKury(lI> Nickel@) Thorium(IV)
Uranium(VI) Vanadium(IV) zinc(II> zirconiumov)
.
0
PAR
.
.
a
.. .. . 0
. .. 8
8
Indicates a positive colour reaction.
13.4.2 PCR detection of transition metals using PAR
A s indicated from Table 13.3, PAR forms complexes with a wide range of metal ions. The colour-forming reaction is rapid and so can be carried out by direct mixing of the PCR reagent and eluent in a simple mixing tee-piece, without the requirement for a delay coil. The PCR reagent consists of dilute PAR solution in an appropriate alkaline buffer (for example, 0.2 mM PAR in 2 M ammonia and 1 M ammonium acetate), and a detection wavelength in the range 500-540 nm is generally used. Some typical detection limits which can be attained under these conditions are listed in Table 13.4, which shows that sensitive detection is possible for lanthanides and transition metals, but not for calcium and magnesium 1311. The detection limits for PCR with PAR are dependent on the reaction conditions, especially the concentration of PAR used, since this affects the baseline noise. The lowest possible concentration of PAR should be employed, consistent with the concentration of metal ions in the sample. Cassidy and Elchuk [31-331 have demonstrated that trace enrichment procedures (see Section 14.6) enable the detection limits shown in Table 13.4 to be reduced substantially. The use of PAR for PCR detection of transition metals has proven successful after separation of these species by either ion-exchange or ion-interaction chromatography. A chromatogram illustrating ion-exchange separation and PCR detection was given earlier in Fig. 4.17(b), whilst Fig. 13.9 illustrates an ion-interaction separation with PCR detection using PAR. Both of these separations are quite rugged and can be applied to complicated samples without the requirement for extensive cleanup procedures. This can be illustrated by the determination of selected transition metal ions in nuclear materials [34), process liquors [35], urine [36], serum [37,381, whole blood [38J,soils
Detection by Post-Column Reaction
r 0
l
I
I
I
I
I
401
I
I
I
I
I
I
I
10
5
I
1
15
Time (min) Fig. 23.9 PCR detection of transition metals with PAR, after separation by ion-interaction chromatography. A Waters pBondapak c18 column was used with 50 mM tartaric acid and 2 mM
sodium octanesulfonate at pH 3.4 as eluent. The detection wavelength was 546 nm. Solute concentrations: Co (5 ppm); Ni, Cd (2 ppm); remainder (1 ppm). Chromatogram courtesy of Waters Chromatography Division. TABLE 13.4 DETECTION LIMITS ATTAINABLE FOR SOME METAL IONS USING POST-COLUMN REACI'ION DETECTION WITH PAR DATA FROM [31] Metal ion
Bismuth(II1) Cadmium(II) Calcium(Il) Cobalt(ll) COPPem Iron(II)
Detection limiP (ng)
Metal ion
5 25 2500 0.5 1 25
Lanthanides(1Il) Magnesium0 Mmgane=(II) Nickel(ll) M(II) =c(Jn
Detection limP
(4.9 1-5 8300 5 1 5 3
The PCR reagent was 0.2 mM PAR and the detection wavelength was 540 nm. a Measured at a signal-to-noise ratio of 2. [39], etching solutions [40], wastewaters [41] and electroplating solutions [42]. In many of these applications, acid digestion of the sample is required, but the resulting acidity of the sample digest does not interfere in the final chromatographic analysis. The detection sensitivity of PCR with PAR can be enhanced if an equimolar solution of PAR and Zn(I1)-EDTA complex is used as the PCR reagent [43-481. When a
402
Chapter 13 Tb
cu
BLANK GRADIENT I
0
I
1
I
2
I
3
I
L
I
5 Time (min)
I
I
7
6
I
8
I
9
Fig. 13.10 Gradient separation of the lanthanides with PCR detection using Arsenazo 111. A Supelco LC18 column was used. The eluent was formed using a linear gradient at pH 4.6 from 0.05 M HlBA to 0.40 M HIBA over 10 min at 2.0 ml/min, with a constant concentration of 10 mM 1-octanesulfonate in the eluent. The detection wavelength was 635 nm. Reprinted from [54] with permission.
metal ion is eluted, the following reaction occurs:
M(I1)
+
Zn[EDTA]
+
PAR % M(II)[EDTA]
+
Zn[PAR]
(13.3)
Detection is therefore based on the absorbance of the Zn[PAR] complex at 490 nm. This procedure is especially suitable for the detection of alkaline earth metal ions, which do not form strongly absorbing complexes with PAR.
13.4.3 PCR detection of lanthanides using Arsenazo dyes Extensive studies by Cassidy and co-workcrs [49-541have shown that Arsenazo I and Arsenazo I11 are ideal PCR reagents for the detection of lanthanide elements. Reaction of Arsenazo dyes with these ions is very rapid at room temperature and detection sensitivity is relatively uniform for the entire lanthanide series. A typical detection limit attained by this method is 80 ppb [49]. PCR detection is applicable after either ion-exchange or ion-interaction separation. The latter method often gives superior chromatographic resolution and octanesulfonic acid is commonly used as the ion-interaction reagent. Moreover, gradient elution can be applied in this detection mode. A chromatogram obtained using a concentration gradient of a complexing ligand in the eluent, with ion-exchange separation, was shown in Fig.4.22(a), whilst that for ion-interaction separation is given in Fig. 13.10. In the first example, 2-methyllactic acid was used as the ligand and Arsenazo I as the PCR reagent, whereas in the second example, a-hydroxyisobutyric acid (HIBA) is used as the ligand and Arsenazo IT1 as the PCR reagent. With a slight modification of the eluent composition used in Fig. 13.10,
Detection by Post-Column Reaction
403
TABLE 13.5 ANALYSIS OF STANDARD SOLUTIONS OF LANTHANIDES BY ION-INTERACTION CHROMATOGRAPHY WITH POST-COLUMN REACTION DETECTION USING ARSENAZO n1 [SO] Element L a Pr Sm
Gd
DY Ho Tm
Lu
Injected (ng)
Found (ng)
Deviation
60.4 22.3 34.4 46.9 57.7 12.1 6.16 5.71
61.0 22.5 34.7 46.9 58.6 12.1 6.24 5.69
1.o 0.9 0.9 0.0 1.5 0.0 1.3 0.3
Element
Injected (ng)
Found (ng)
Deviation
ce
146.0 108.9 13.9 8.64 195.8 37.7 39.2
146.8 109.1 14.1 8.72 193.1 37.7 39.9
0.5
(%I Nd Eu
Tb Y Er Yb
0.1 1.4 1.0 1.0 0.0 1.8
yttrium, thorium and uranium can be separated in the same chromatographic run, together with the elements shown in the chromatogram [49]. PCR detection of lanthanides using Arsenazo I11 has proven to be an outstanding method for the analysis of complex samples, such as uranium dioxide fuels [52, 541 and rocks [SO]. Table 13.5 shows the excellent agreement between the true and observed concentrations of lanthanides in standard solutions, as determined by IC. 13.4.4 PCR detection of other metal ions A wide range of other PCR reagents has been reported for the selective detection of particular metal ions using a variety of detection modes. These methods are normally developed for a specific analysis and therefore do not have the general applicability of PCR procedures which use PAR or Arsenazo dyes. Table 13.6 lists some of the pertinent details of these methods. It can be noted from Table 13.6 that several of the methods listed involve indirect detection. For example, monitoring at the absorption wavelength of dithizone or Eriochrome Black T permits the indirect detection of metal ions which form complexes with these species [68]. Similarly, use of an electroactive dithiocarbamate ligand as a PCR reagent permits indirect amperometric detection of metal ions which form electroinactive complexes with the ligand 166,671.
13.5 PCR DETECTION OF ORGANIC SPECIES Some less commonly used applications of PCR detection involve organic species as the analytes. Organic acids eluted from an ion-exclusion column with nitric acid as eluent may be detected by PCR with an acid-base indicator (4-nitrophenol) after passage through a hydrogen form suppressor [701. The pH changes which accompany the sample
Chapter I3
404 TABLE 13.6
SOME EXAMPLES OF FOST-COLUMN REACTION DEIECTION OF CATIONS IN IC Solutes
Postcolumn reagenta
Detection modeb
Detection limits
Ref
Al3+ Alh
Oxine-5-sulfonate Tiron Arsenam I Neo-thorin Luminol DPC PAR BPDSA Oxine
Fluor (512 nm) Spec (310 nm) spec (590 m) Spec (570 nm) Fluor Spec (520 nm) Spec (520 nm) Spec (530 nm) Fluor (530 nm)
1
Pa
55
2-6ng 50ppb 0.5 ng/l 1. 100ppb 1.5pM 10ppb 1-84ng
59 4, 60 61 62 63 64,65
Amper (+0.65V)c Spec (590 nm)c Spec (610 Fluor (534 nm)
0.2ppm 2-long 2-10 ng 16ngSn
66,67 68 68 69
Ca2+,Mg2+ Ca2+,Mg2+
co2+
wm,Cr(VI)
Fe2+,Fe3+ Fe2+,Fe3+ Zr(IV), Ga3+,Sc3+,Y3+, h 3 + , AQ+,h 3 + , ~2+, Cd2+,Ca2+,Mg2+ Transition metals SPDC Transition metals Dithime Transition metals Eriochrome Black T Tributyl tin Morin a
56.57 58
DPC = diphenylcarbohydnzide, BPDSA = bathophenanthroline disulfonic acid, SPDC = sodium pyrrolidinedithiocarbamate. Spec = spectrophotometry,Fluor = fluorescence, A m p = ampenmetry. Indirect detection method.
bands as they leave the suppressor are visualized by changes in the absorbance of the acid-base indicator at 400 nm. This detection system is applicable to gradient elution. PCR has also been used for the detection of formaldehyde after separation by ionexclusion chromatography [7 11. Reaction of the eluted formaldehyde with acetylacetone gives a detection limit of 10 ppb using absorbance at 420 nm. Post-column addition of Cu(1I) has been employed for the detection of amino acids [72] and reducing carbohydrates [73]. In each of these examples, the change in concentration of free copper ions caused by reaction with the eluted analyte species is detected by potentiometry, either with a copper ion-selective electrode or a metallic copper indicator electrode.
13.6 REFERENCES 1 2
3
Schlabach T.D. and Weinberger R., in Krull I.S. (Ed.), Reaction Detection in Liquid Chromatography,Chromatographic Science Series, Vol. 34, Marcel Dekker, New York, 1986, Ch. 2. Colgan S.T.and Krull I.S., in Krull I.S. (Ed.), Reaction Detection in Liquid Chromatography,Chromatographic Science Series, Vol. 34, Marcel Dekker. New York, 1986, Ch. 5. Cassidy R.M., Elchuk S. and Dasgupta P.K., Anal. Chem., 59 (1987) 85.
Detection by Post-Column Reuction
405
Boyle E.A., Handy B. and Van Geen A., Anal. Chem., 59 (1987) 1499. Elchuk S. and Cassidy R.M., Anal. Chem., 51 (1979) 1434. Schmidt G.J.and Scott R.P.W., Anulyst (London), 109 (1984) 997. Lillig B. and Engelhardt, H., in Krull LS. (Ed.), Reaction Detection in Liquid Chromutogruphy, Chromatographic Science Series, Vol. 34, Marcel Dekker, New York. 1986, Ch. 1. Davis J.C. and Peterson D.P.. Anal. Chem., 57 (1985) 768. 8 9 Hirai Y., Yoza N. and Ohashi S.. J . Chromutogr.,206 (1981) 501. 10 Yoza N., It0 K.. Hirai Y. and Ohashi S., J. Chromutogr., 196 (1980) 47 1. 11 Hirayama N. and Kuwamoto T., J. Chromutogr.,447 (1988) 323. 12 Yoza N., Miyaji T., Hiria Y. and Ohashi S., J. Chromutogr.,283 (1984) 89. 13 Nakae A.. Furuya K., Mikata T. and Yamanaka M., Nippon Kaguku Kaishi, (1977) 1655. 14 Nakae A., Furuya K., Mikata T. and Yamanaka M., Nippon Kaguku Kaishi, (1976) 1426. 15 Goguel R., Anal. Chem., 41 (1969) 1034. 16 Imanari T., Tanabe S., Toida T. and Kawanishi T., J. Chromutogr.,2% (1982) 55. 17 Tschabunin G., Fischer P. and Schwedt G., Fres. Z. Anal. Chem., 333 (1989) 117. 18 Dionex Application Note 44R. 19 Waters IC Lab. Report No. 309. 20 Lee S.H. and Field L.R., Anal. Chem., 56 (1984) 2647. 21 Weiss J. and Hagele G., Fres. 2.Anal. Chem., 328 (1987) 46. 22 Toida T., Togawa T., Tanabe S. and Imanari T., J. Chromutogr., 308 (1984) 133. 23 Buchberger W., J. Chromutogr.,439 (1988) 129. 24 Buchberger W. and Winsauer K., Mikrochim. Acta, 1985 III (1986) 347. 25 Lookabaugh M. and Krull I.S., J. Chromutogr.,452 (1988) 295. 26 Meek S.E. and Pietrzyk D.J., Anal. Chem., 60 (1988) 1397. 27 Vaeth E., Sladek P. and Kenar K., Fres. Z. Anal. Chem., 329 (1987) 584. 28 Dionex Application Update 113. 29 Brunt K., Anal. Chem., 57 (1985) 1338. 30 Fritz J.S. and Story J.N.. Anal. Chem., 46 (1974) 825. 31 Cassidy R.M. and Elchuk S., J. Chromutogr.Sci., 18 (1980) 217. 32 Cassidy R.M. and Elchuk S., J. Chromutogr.Sci., 19 (1981) 503. 33 Cassidy R.M., Elchuk S. and McHugh J.O., Anal. Chem., 54 (1982) 727. 34 Cassidy R.M. and Elchuk S., J. Liq. Chromatogr.,4 (1981) 379. 35 Byerley J.J., Scharer J.M. and Atkinson G.F., Analyst (London). 112 (1987) 41. 36 Blaszkewicz M., Baumhoer G., Neidhart B., Ohlendorf R. and Linscheid M., J. Chromatogr.,439 (1988) 109. 37 Takayanagi M. and Yashm T., J. Chromutogr..374 (1986) 378. 38 Ong C.N., Ong H.Y. and Chua L.H., Anal. Biochem., 173 (1988) 64. 39 Waters IC Lab. Report No. 272. 40 Waters IC Lab. Report No. 273. 41 Waters IC Lab. Report No. 276. 42 Wescan Application #283. 43 Arguello M.D. and Fritz J.S., Anal. Chem., 49 (1977) 1595. 44 Yan D. and Schwedt G., Fres. Z. Anal. Chem., 320 (1985) 325. 45 Yan D. and Schwedt G., Anal. Chim. Acta, 178 (1985) 347. 46 Yan D., Stumpp E. and Schwedt G.. Fres. Z. Anal. Chem., 322 (1985) 474. 4 5 6 7
406 47 48 49
50 51 52 53 54 55 56 57 58 59
60 61 62 63
64 65
66 67 68 69 70 71 72 73
Chapter I3 Yan D., Zhang J. and Schwedt G., Fres. 2.Anal. Chem., 331 (1988) 601. Schwedt G., GIT Fachz. L.ub., 7 (1985) 697. Barkley D.J., Blanchette M.. Cassidy R.M. and Elchuk S.. Anal. Chem., 58 (1986) 2222. Cassidy R.M., Chem. Geol., 67 (1988) 185. Cassidy R.M. and Fraser M., Chromurographia,18 (1984) 369. Cassidy R.M., Elchuk S., Elliot N.L., Green L.W.. Knight C.H., Recoskie B.M., Anal. Chem., 58 (1986) 1181. Cassidy R.M., Miller F.C., Knight C.H., Roddick J.C. and Sullivan R.W., Anal. Chem., 58 (1986) 1389. Knight C.H., Cassidy R.M., Recoskie B.M. and Green L.W., Anal. Chem., 56 (1984) 474. Jones P., Ebdon L. and Williams T., Analyst (London), 113 (1988) 641. Bertsch P.M. and Anderson M.A., Anal. Chem., 61 (1989) 535. Dionex Application Note 42. Smith D.L. and Fritz J.S., Anal. Chim. Acta, 204 (1988) 87. Nagashima H., Bunseki Kagaku, 35 (1985) 7. Jones P., Williams T. and Ebdon L., Anal. Chim. Acta, 217 (1989) 157. Dionex Application Note 26. Moses C.O., Herlihy A.T., Herman J.S. and Mills A.L., Talanra, 35 (1988) 15. Saitoh H. and Oikawa K., J. Chromutogr., 329 (1985) 247. Karcher B.D. and Krull I S . , J. Chromutogr. Sci., 25 (1987) 472. Karcher B.D., Krull IS., Schleicher R.G.and Smith S.B., Jr., Chromatographia, 24 (1987) 705. Hojabri H., Lavin A.G., Wallace G.G. and Riviello J.M., Anal. Proc., 23 (1986) 26. Hojabri H., Lavin A.G., Wallace G.G. and Riviello J.M., Anal. Chem., 59 (1987) 54. Hobbs P.J., Jones P. and Ebdon L., Anal. Proc., 20 (1983) 613. Ebdon L. and Alonso J.I.G., Analyst (London), 112 (1987) 1551. Okada T. and Dasgupta P.K., Anal. Chem., 61 (1989) 548. McClure J.E., Anal. Lett.. 21 (1988) 253. Loscombe C.R., Cox G.B. and Dalziel J.A.W., J . Chromutogr., 166 (1978) 403. Cowie C.E., Haddad P.R. and Alexander P.W., Chromutographia,21 (1986) 417.
Part IV Practical Aspects
408
r
1
Extraction Acid di estion Alkali &ion L Combustion Filtration Ion-exchange resins Dialytic methods Cartridge columns
Extraction
Cleanup
SAMPLE HANDLING (Chap 14)
-€
Contamination
-+
Physical handling Filtration devices Cartridge columns Hardware components
Ultra-trace analysis PRACTICAL ASPECTS
Filters Impin ers Adsorgents Denuders
Sample collection
I
Large injection volumes Concentrator columns Dialytic methods
On-column L Matrix elimination <post-column
E-,
Selection of chromatographic parameters
-
METHODS DEVELOPMENT (Chap 15)
Optimization Multi-dimensional methods Automation
Schematic overview of Part IV.
Separation mode
E;;4;i;pyde
Empirical methods Computer methods
Chapter 14 Sample Handling in Ion Chromatography 14.1 INTRODUCTION In the context of sample handling in IC, a prime consideration is the diversity of separation and detection methods described in earlier Chapters. A judicious selection of the separation and detection modes, and also the eluent used, can often mean that sample preparation is minimal. For example, ion-exchange provides good separation of charged species, with uncharged or partially charged species being eluted as a group at the column void volume. In contrast, the reverse applies to ion-exclusion chromatography where fully ionized species are usually totally excluded and are eluted at the void volume, whereas partially charged and uncharged solutes are retained. In other words, the two techniques are best suited to different sample matrices. The same can be said for the detection mode used, since many solutes can be detected selectively and this greatly reduces the requirement for sample preparation. For example, nitrate and nitrite can be determined in cured meats using a simple aqueous extraction, coupled with ion-exchange separation and direct UV absorption detection at low wavelength. Under these conditions other ions in the sample, particularly the very high levels of chloride present, are not detected (see Fig. 12.4). It is thus pertinent to begin this discussion of sample handling in IC by emphasizing that the correct choice of separation and detection modes is imperative if laborious sample preparation procedures are to be avoided. The chromatographer must therefore be fully conversant with the alternatives available. The sample handling methods discussed in this Chapter should be viewed as a secondary means of ensuring the success of an ion chromatographic analysis. 14.2 SAMPLE COLLECTION PROCEDURES 14.2.1 General The main concerns when collecting a sample for any analytical method are that the sample taken is representative of the material to be analyzed and that no contamination occurs during the sampling process. Statistically-based procedures for acquisition of a representative sample have been treated extensively in numerous texts and further discussion is beyond the scope of this Chapter. Contamination is a very important issue and is discussed separately in Section 14.5. Sampling of solids and liquids for subsequent ion chromatographic analysis is subject to the same requirements which apply to any analytical method and will therefore receive no further discussion.
410
Chapter 14 37mm Fitter cassette
Support ‘Adapter
Fig. 141 Filter unit for the collection of gas, aerosol and particulate samples.
14.2.2
Sampling of gases, aerosols and particulates for IC analysis
IC has made a strong impact on the analysis of gases, aerosols and particulates in the fields of environmental chemistry and occupational hygiene. Indeed, some of the standard methods of analysis published by the US National Institute for Occupational Safety and Health (NIOSH) employ IC determinations. The reason for this is that many pollutant gases can be converted readily into anions which are amenable to accurate and sensitive determination by IC. The methods used in the sampling of gases, aerosols and particulates for subsequent IC analysis are outlined below. Filter media Gases, aerosols and particulates can be collected on a suitable filter medium, such as a polytetrafluorethylene membrane or a glass fibre filter. It is common practice to impregnate the filter medium with an absorbing solution of some kind, such as an alkaline solution for the collection of acidic gases, or an acidic solution for the collection of basic gases. A known volume of air is drawn through the filter medium, often using a dichotomous sampler which permits the aerosol to be fractionated into aerodynamic size ranges. Fig. 14.1 shows a typical filter unit employed for this type of sampling. Alternatively, a passive sampling method may be used in which the sample reaches the filter medium by diffusion. This approach is often employed for “badge“ samplers used in personal monitoring. The absorbed gases and aerosols are then extracted from the filter medium with an appropriate solution, such as hot deionized water, hydrogen peroxide (to oxidize the dissolved gases to an anion of known composition), or even the ion chromatographic eluent itself. The major problem encountered in this approach is contamination of the sample by ionic species which are leached from the filter medium. Actual levels of leachable ions are reported in the discussion of sample contamination presented in Section 14.5.
Sample Handling in IC
41 1
TABLE 14.1 TYPICAL EXAMPLES OF THE COLLECTION OF GAS, AEROSOL AND PARTICULATE SAMPLES USING FILTER MEDIA Sample
Filter medium
Extactant
Aerosols Aerosols Aerosols Paint aerosols Particulates
Quartz fibre Membrane PTFE membrane PVC membranes Paper
0.05 mM HClO4 0.05 mM HC104, ooc 1 mM phthalate 2% NaOH, 3% Na2C03 Hot distilled H20
Particulates Acidic gases
PTFE membrane Paper coated with 1 M KOH Paper coated with Na2CO3 Membrane coated with 10%H3P04
Sulfur dioxide Ammonia
Species actually quantified by IC
Ref
NH4+
8
Deionized H20 Deionized H f l
Distilled H20
Table 14.1 lists some filter media which have been employed for the determination of airborne pollutants by IC, together with the extractant solution used in each case. Numerous further examples of specific applications of IC to environmental analysis are included in Chapter 16. It should be noted that air sampling using impregnated filter media usually provides the total amount of the particular pollutant which is present in the air; i.e. the sum of the gaseous, aerosol and particulate components. Individual components can be determined by preceding the impregnated filter with a membrane suitable for removal of the particulates only, or through the use of denuders to remove gaseous components. The latter alternative is discussed below.
Impingers Impingers (or bubblers) consist of a suitable vessel containing an absorbing solution, through which is drawn a measured quantity of air. The absorbing solution is selected to provide quantitative retention of the sample components of interest. Fig. 14.2 shows a typical impinger apparatus and illustrates the requirement for a second container placed downstream from the impinger itself, which serves to collect any aerosol particles of the impinger absorbing solution. Quantitation of the sample includes analysis of both the trapping solution and washings from the glass wool in the second vessel. Although impingers have'been used widely for sample collection, they suffer from a number of disadvantages. The absorbing reagent can be spilled or the impinger broken easily and because the absorbing solutions are often strongly acidic or alkaline, impingers may be unsuitable for personal monitoring. In addition, the bubble size must be kept very small and bubbles must remain in contact with the absorbing solution long
412
Chapter 14
Air in
Bubbler
Trap
Fig. 24.2 Irnpinger unit. Reprinted from [9] with permission.
TABLE 14.2
SOME TYPICAL ABSORBING SOLUTIONS USED IN IMPINGERS FOR COLLECTION OF GAS AND AEROSOL SAMPLES PRIOR TO IC ANALYSIS Sample
Absorbing solution(s)
0.6% H202 + 0.06 rnM HCI 80% PAa, 3% H202 0.25 M KMnO4 + 1.25 M NaOH 0.1 N H2S04,3% H202 0.1 N NaOH, 3% H202 0.2 N NaOH 5 mM KOH 3 rnM N a H C Q + 2.5 mM Na2C03 80%IPAa, H202 Deionized H20 12 mM Na2S03, pH 8.7 10 mM Ki in phosphate buffer a
isopropyl alcohol.
species actually quantified by XC
Ref
9 10 11 10 10 12 13
14 15
16 17
18
Sample Handling in IC
413
enough to trap the sample gases. This places severe constraints upon the air sampling rates which can be used. Table 14.2 lists some absorbing solutions used in impingers for the collection of gas samples, prior to IC determination.
Solid adsorbents Gas samples can be conveniently collected using solid sorbents packed into suitable sampling tubes. A known volume of gas is drawn through the tube and the desired sample components are strongly adsorbed. The adsorber tube generally comprises a main adsorbent and an auxiliary, or back-up, adsorbent designed to detect breakthrough of the sample gas from the main adsorbent. Fig. 14.3 shows the construction of a typical adsorber tube for gas sampling. The material used to fill the adsorber tube may be a simple adsorbent, such as activated charcoal, alumina or silica, or may be a solid which has been impregnated (or coated) with a suitable solution which effectively traps the desired sample gases from the air. Details of the physical and chemical composition of sorbent materials may be found elsewhere [19]. Examples of the use of simple adsorbents include the collection of sulfur dioxide [20], alkanolamines [21] and acidic gases [22] on charcoal, alumina and silica, respectively. A typical example of the use of impregnated or coated materials is the adsorption of formaldehyde onto charcoal impregnated with an oxidizing solution (of proprietary composition) [23]. Formaldehyde reacts with the oxidizing solution to produce formate ion, which can be desorbed using dilute hydrogen peroxide solution prior to ion chromatographic analysis. Table 14.3 lists some of the adsorber tube materials used for gas sampling prior to IC analysis. An important aspect of gas analysis is the procedure used to provide calibration standards. Some standards are available commercially, or alternatively a sample generator can be employed. Fig. 14.4 shows one type of sample generator in which standard solutions are injected into a flowing stream of air for subsequent evaporation and deposition onto an adsorber tube. Solid sorbent tubes can also be used for the collection of components from liquid samples, especially water. Activated carbon shows strong adsorption of organic matter from aqueous solution and this adsorbent has proven to be successful for the collection of organohalides from water [37-391. The loaded carbon can then be pyrolized and the resultant gases collected and analyzed for ions representative of substituents on the original organic species.
*
Air in
+ t 100'mg
t
50 mg
Impregnated charcoal Fig. Z4.3 Solid sorbent tube for sampling of gases in air.
Air out
Chapter 14
414
TABLE 14.3 COMPOSITION AND APPLICATION OF SOME ADSORBER TUBES USED FOR GAS COLLE(JI?ON AND SUBSEQUENT IC DETERMINATION Sample
Material in adsorber tube
Species actually quantified by IC
Ref
Ammonia Ammonia Chloroacetyl chloride Ethanolamines Formaldehyde Formic acid
Carbon impregnated with H2S04
NH4' NHq+, amines Chloroacetate,Cl'
24 25 26
Silica impregnated with H2SO4 Silica Alumina Charcoal impregnated with oxidant Chromosorb 103 Silica Silica
21 23 21 22 28
S02, NO;?
Anion-exchange resin in OH- form Silica Charcoal impregnated with NaOH Palmes tube containing TEA Paper impregnated with TEA Sep-Pak impregnated with TEA Activated charcoal Sep-Pak impregnated with TEA-KOH
29 30 31 32 33 34 20 35
SO2, NO;?
Molecular sieve impregnated with TEA
36
HF HCI, H3P04, HBr m o 3 , H2so4 HzS, SO2 Inorganic acids Iodine NOz NO2 NO2
so2
a
MEA = monoethanolamine,
, purpJ
11
DEA = diethanolamine, TEA = triethanolamine.
GLASS WOO^
PLUG
I M
GLASSBEADS WATER BATH
NEEDLE VALVE
Fig. 24.4 Sample generator for calibration of sorbent tubes. Reprinted from [23] with permission.
Sample Handling in IC
I )
Air in
415
I )
To chotornous sampler
Fig. 14.5 Cross-sectional view of an N H 3 gas diffusion denuder. Reprinted from [2] with
permission. Diffusion denuders A diffusion denuder (or diffusion scrubber) is a device for selective removal of a gas from a gas-aerosol or gas-particulate mixture. The denuder operates on the principle that gaseous components of an inlet stream will diffuse in a direction at right angles to the direction of flow, whereas aerosols and particulates will be carried in the direction of flow. Provision of a suitable absorbing medium (e.g. a liquid film coated on a thin tube orientated in the direction of flow) will therefore allow the gaseous components to be removed from the flowing stream of sample. It has been shown that the collection efficiency is dependent on the diffusion coefficient of the gaseous component, the sampling flow-rate and the length of the device [40]. However, collection efficiency is independent of the diameter of the tube, so it is common to increase the sampling rate by operating a number of small diameter denuder tubes in parallel [21. An illustration of this configuration is given in Fig. 14.5, which depicts a multitube denuder for the absorption of ammonia. Here the tubes are coated with phosphorous acid and the inlet stream is therefore stripped of ammonia, whilst the aerosol components pass through the denuder to a dichotomous sampler. Other configurations for liquid-film type denuders are possible; e.g. an annular arrangement in which the film of absorbing liquid is coated onto the cavity walls between two concentric glass tubes, and the sample is drawn through the same zone. It can also be noted that diffusion denuders with differing absorbing solutions can be operated in series for the collection of a range of sample gases. For example, Fig. 14.6 shows a five-stage denuder containing NaF, H3P04, KOH, NaF and H3P04 as the absorbing solutions [41]. Nitric and hydrochloric acids are absorbed by the first NaF denuder, whilst the second and third denuders trap ammonia and organic acids, respectively. Particulate sulfuric acid is evaporated in the heating stage and is collected on the fourth denuder, along with HNO3 and HCI liberated from-the thermal decomposition of NH4NO3 and NbCI. The final denuder is to colIect any ammonia produced in the heating stage. The remaining particulates pass through the sampler and are collected on a suitable filter medium. This example provides a good illustration of the versatility of air sampling with denuders.
Chapter 14
416
+m 1 5 inlet NaF
a
5
H3PO4
KOH
C
b
NaF
H3*4
w outlet
Fig. 14.6 A five-stage denuder assembly for collection of HNO3, HCI. NH3 and H2SO4,
showing tubing connector (a), PTFE tubing (b) and tubing heater (c). The coating on each stage of the assembly (which is operated in the vertical configuration) is indicated in the diagram. See text for an explanation of the operation of this device. Reprinted from [41] with permission.
Denuders can also operate by the diffusion of gaseous components through an appropriate membrane. Lindgren and Dasgupta I421 have reported an elegant porous membrane diffusion denuder in which soluble effluent gases are collected into H2@, which is then automatically injected onto an ion chromatograph. Continuous monitoring is therefore achieved. The device is shown in Fig. 14.7. The absorbing solution passes slowly through the membrane tube whilst the gaseous sample is pumped in a countercurrent direction around the outside of the membrane. The absorber solution passes to the injection loop of the IC instrument. where it is injected on a 6 minute cycle. In summary, denuders are generally employed in the following ways: (i j (ii)
To collect gaseous components for analysis, without interference from aerosols and particulates. A denuder used in conjunction with a filter which does not absorb aerosols will remove all components from the sample stream except aerosols, which may then be collected on an impregnated filter medium. In this way. all components of an air sample can be determined simultaneously.
Table 14.4 shows some of the types of denuders which have been used for sampling prior to IC analysis.
F I
L
IG
I
Fig. 14.7 Diffusion denuder for collection of 5%. A, B: 30- and 20- gauge PTFE tubes; C male nut; D: female connector; E:nylon ferrule; F disc segment; G: polypropylene tee; H: 5- gauge PTFE tube; I: glass jacket tube; J: PVC segment; K: Nichrome wire crimp; L: Celgard microporous membrane tube. Reprinted fmm [42] with permission.
Sample H a n d h g in IC
417
TABLE 14.4 SOME DIFFUSION DENUDERS USED FOR SAMPLE COLLECTION PRIOR TO IC
ANALYSIS Sample
Denuder type and function
H2SO4 aerosol
H3P04 coated tubes to remove NH3. NaOH coated tubes to remove S0.2 NaOH coated tubes to absorb HNO3 NaZCQ coated tubes to absorb HNO3 Five-stage denuder with NaF, H3P04. KOH, NaF. H3P04 coated tubes Porous membrane, 0.5 M H2SO4 as the scrubbing solution to absorb NH3 Guaiacol coated denuder to absorb N@ Porous membrane. 1 mM H202 as
Gaseous HN@ Gaseous HNO3 Organic and inorganic acids NH3 NO2
soz
Species actually quantified by IC
Ref
the scrubbing solution to absorb S@
14.3 EXTRACTION OF IONIC SPECIES FROM SAMPLES 14.3.1
Introduction
Many samples collected for IC analysis require very little sample treatment. This applies particularly to water samples which contain only moderate levels of ionic species and are devoid of interfering organic material. However, other samples, especially solid materials, are not so amenable to analysis and in this Section, we will look at procedures which can be adopted for extracting ionic species from such samples. 14.3.2
Simple extraction methods
The removal of ionic species from solid samples prior to IC analysis can often be achieved simply by aqueous extraction of the homogenized sample. This process relies on the high solubility of ionic species in water. Generally, a weighed amount of the dry sample is mixed with a known volume of water, extractant solution or eluent, and is then homogenized in a blender or an ultrasonic cell disrupter for a specified time. The digest is then filtered, subjected to further cleanup where required and injected onto the ion chromatograph. The choice of extracting solution is very dependent on both the sample matrix and the nature of the solute ions to be extracted, however water is the preferred extractant whenever possible because alternative extractants often introduce extraneous peaks into the chromatogram. Use of eluent as the extractant is successful only when small injection volumes are to be used in the final analysis since the presence of eluent ions in the sample precludes band compression at the head of the column, with subsequent loss of chromatographic efficiency through solute dispersion.
Chapter 14
418
Some samples require extraction with organic solvents before they are suitable for analysis. For example, commercial bromine solutions produced from seawater contain high levels of chloride ion and the analysis of the chloride can be performed after dissolution of the sample in potassium bromide solution, followed by extraction with carbon tetrachloride [491. Free bromine is extracted and the remaining aqueous solution can be analyzed directly by IC using conductivity detection. Methanol extraction of tetramethylammonium ion from shellfish has been reported [50], but the methanol must be evaporated and the sample redissolved in HCl before injection. 14.3.3
Acid digestion
When samples (particularly solids) are not amenable to simple aqueous extraction, it becomes necessary to digest the sample to obtain a quantitative measure of the ionic
components. Traditionally, sample digestion prior to analysis of inorganic species has been performed using concentrated acids, used either alone or in mixtures. This approach can often be inappropriate for IC because of the large excess of the acid anion(s) introduced and the resulting low pH of the sample digest. The excess anion may cause overloading of anion-exchange columns or the appearance of a major, interfering peak in the final chromatogram, whilst the low pH of the digest can cause disruption of the multiple equilibria existing between the eluent species and the column, leading to severe baseline perturbations. For these reasons, acid digestion has not been used widely in the preparation of samples for anion determinations. The exceptions to this generalization are when a selective detection method is used, or when special steps are taken to separate the solute ion(s) from the sample digest. An example of the first case is the amperometric detection of oxalate in urine samples which have been treated -with HC1 [51]. The second case is exemplified by the dissolution of geological samples in phosphoric acid prior to the determination of fluorine (as fluoride) by IC [52]. The fluorosilicic acid produced in the digest is volatilized and collected on a simple condenser apparatus inserted into the digestion tube. The condensed fluorosilicic acid is removed with sodium hydroxide and is converted to fluoride ion, which is then determined by IC. Acid digestion is better suited to the treatment of samples which are to be analyzed for cations. The only significant problem arises in the determination of monovalent cations, for which the high concentration of hydrogen ions in the sample digest causes interference by altering retention times of solute ions. In such cases, it becomes necessary to dilute the sample or to lower the concentration of hydrogen ions by chemical methods (see Section 14.4). These problems are not apparent when acid digestion is used for samples to be analyzed for transition metals or rare earth species. Post-column reaction detection is commonly used for these solutes and this detection mode is not sensitive to the acidity of the sample. 14.3.4
Alkali fusion
An attractive alternative to acid digestion of samples is the use of fusion techniques. In this process, the sample is mixed with a suitable flux material and is heated until the flux becomes molten. The mixture is then allowed to cool and the fusion cake dissolved
Sample Handling in IC
419
in a suitable solvent and then analyzed.
Typical flux materials include sodium hydroxide, sodium carbonate and lithium tetraborate. Once again, the main problem with this method is the compatibility of the final digest solution with the IC eluent, but in this case some of the fluxing materials are identical to eluent components. For example, NaOH and Na2C03 - NaHC03 are common eluents in IC. Thus, fluoride [53] and chloride [54] have been determined successfully in geological materials after fusion with sodium carbonate and injection onto an IC using a carbonate-bicarbonate eluent, and boron and fluoride have been determined in glasses after fusion with sodium hydroxide [55]. Fusion methods are generally quite time-consuming because of the necessity to redissolve the fusion cake and in some cases the high pH of the digest presents a problem. Further disadvantages are the limited applicability of the method, possible interference from the high level of sodium or lithium present, and the loss of nitrate from the sample during fusion, which may occur as a result of the formation of volatile oxides of nitrogen. 14.3.5
Combustion methods
Two distinct types of sample combustion processes are applicable to IC. The first involves sample combustion in air (i.e. ashing), followed by analysis of the residue. The second involves total combustion of the sample in oxygen, conversion of some (nonmetallic) elements into volatile gaseous compounds, collection of these gases in a suitable absorber and finally, analysis of the absorber solution using IC. This approach is suited to the determination of halides (to form such products as HF, HCI, HBr and HI) and sulfur and phosphorus (which form SO2 and P205, respectively). Several experimental configurations are possible in the oxygen combustion method, including the Schoeniger flask, Pan oxygen bomb and furnace methods. These are discussed below.
Ashing The organic content of samples can be removed conveniently by holding the sample at high temperature (e.g. 500 "C) until combustion is complete, leaving an inorganic residue which is usually redissolved in acid, This process is known as dry ashing and can be applied only to samples in which the solutes of interest are non-volatile. In the context of IC, this limits the application of dry ashing to the determination of metals. Schoeniger flask combustion The simplest apparatus for combustion of organic samples is a Schoeniger flask, as shown in Fig. 14.8. A Pyrex glass or quartz vessel containing absorber solution and a small amount of sample (about 0.lg) in a paper cup is filled with oxygen and inverted. The sample is then ignited manually or electrically and the gases produced are trapped in the absorber solution, which provides a gas-tight seal at the mouth of the flask. After an appropriate amount of time has elapsed, the, absorber solution is removed and analyzed. The advantages of this method are that it is inexpensive, rapid and simple, whereas the major disadvantage is that the oxygen pressure is limited to atmospheric pressure. This, in turn, limits the size of the sample which can be analyzed and ultimately renders the method fairly insensitive.
420
Chapter 14
Platinum Sample Carrier Absorption Liquid
c
Fig. 14.8 Schoeniger combustion flask apparatus.
Parr oxygen bomb combustion Larger samples (up to lg) can be accommodated in a bomb combustion apparatus, such as that shown schematically in Fig. 14.9. Here high pressures of oxygen (e.g. 40 a m ) are used to facilitate complete combustion of the sample. Because of the high pressure generated within the bomb, obvious safety considerations apply and analysis is relatively lengthy due to the time taken to achieve complete absorption of combustion products in the absorber solution. Absorption may be monitored with a pressure gauge.
Oxygen
charging valve
Pressure relief valve
Sample' cup
Fig. 14.9 High pressure oxygen (Pam) combustion bomb.
421
Sample Handling in IC
Combustion tube
Induction coil
b C r u c i ble W S a m p l e plus Cu-Fe accelerator
solut Ion
L-0 2
inlet
Fig. 14.10 Furnace combustion apparatus. Reprinted from [56] with permission.
Furnace combustion Some samples, particularly those of a geological origin, may be combusted using furnace techniques. In this method, the sample is mixed with a suitable combustion accelerator (such as a mixture of iron and copper, or iron, tin and vanadium pentoxide) and heated in a ceramic crucible in an induction furnace, whilst oxygen is passed over the sample. Alternatively, a stream of water vapour is used instead of oxygen and when this is done, the technique is referred to as pyrohydrolysis. The combustion products are collected in a suitable absorbing solution, Furnace combustion is very rapid due to the high temperature used and large numbers of samples can be handled with ease. In addition, results are very precise and calibration does not require the use of a large number of geochemical standard materials. Fig. 14.10 shows a furnace combustion apparatus. Composition of absorbing solution The experimental conditions employed for the combustion determine the nature of the final products and in some cases, multiple products are formed for the same element. When this occurs, the composition of the absorber solution should be carefully chosen to convert all forms of an element to a single species suitable for IC determination. During combustion, elements such as fluorine and chlorine are converted quantitatively to I-IF and HCl, respectively, and so can be absorbed with water or dilute sodium hydroxide. Hydrogen halides are also produced from bromine and iodine, but
Chapter 14
422 TABLE 14.5
TYPICAL ABSORBING SOLUTIONS USED FOR COLLECTION OF GASEOUS PRODUCTS FROM SAMPLE COMBUSTION PROCEDURES Elements
Absorbing solution
Ref
F, C1, S F, C1, S F, CI C1, Br, P, S CI, Br, S c1, s c1, s
H2O 3 mM NaHCO3,2.4 mM Na2C03.0.025% H f i 6 mM Na2CO3 10 ml H20 + 3 drops 30% H202 6% H202 in 0.18 M NaOH 3 mM NaHCO3,2.4 mM Na2CO3 3 mM NaHCO3,2.4 mM Na2C03,3% H202 0.6% H202 2 mM Na2C03 1 N KOH, 1 % hydrazine sulfate 2 mM Na2C@ + 5 drops hydrazine sulfate 50 ml H20 + 50 p1 hydrazine + 3 mlO.1 M KOH 15 ml H20 + 5 drops 30% H202 2 mM Na2C03 + 5 drops 30% H202 10 ml0.7% HNO3 + KMnO4
57-59 60,61 62 63
c1, s c1 Br, I Br I S S Se
64 56, 65, 66 67 68 69 67 69 70 71 69 72
TABLE 14.6 EXAMPLES OF COMBUSTION METHODS FOR SAMPLE TREATMENT PRIOR TO IC ANALYSIS Sample
Combustion method
Species determined
Ref
Organic reagents
Schoeniger flask
F,Cl,Br,I,S,P,N
Plant materials Lignite Coal, oil shale Geological samples Geological samples Tantalum powder Polymers Fuel oils Fuels Biological samples Foods Drugs
Dry ashing
Na, K, Mg, Ca F S F, CI, S F, CI, S F, CI F, CI, Br, P, S S S CI, Br, S I Se
59,63,64, 68,73,74 75
Parr oxygen bomb Pam oxygen bomb Pyrohydrolysis (induction furnace) Pyrohydrolysis (combustion furnace) Pyrolysis Combustion furnace Schoeniger flask Pan oxygen bomb Schoeniger flask Schoeniger flask Schoeniger flask
58 76 56,65
60 62 77 71,78 66 69 70 72
Sample Handling in IC
423
other more oxidized products such as HBrO, and H I 0 3 are also formed. For these species, a reducing agent (such as hydrazine sulfate) should be added to the absorber solution so that only bromide and iodide are present in the final solution. For sulfur and phosphorus, it is desirable that they be quantitated as sulfate and phosphate, respectively, and therefore the absorber solution should contain an oxidant, such as dilute hydrogen peroxide. Table 14.5 lists some of the absorbing solutions which have been reported for use with 1C analysis, whilst Table 14.6 gives some examples of IC analysis of samples treated using combustion techniques.
14.4 SAMPLE CLEANUP METHODS 14.4.1
Introduction
After the sample has been dissolved, it is often necessary that some modification of the sample digest be performed before an injection can be made onto the ion chromatograph. This modification may involve a simple filtration step, or it may be more extensive and involve selective removal of the analyte from the sample or removal of interfering matrix components. Alternatively, it may be necessary to change the chemical form of the analyte to improve its separation or detection in the final analysis. These sample cleanup procedures often take the majority of the total analysis time and may contribute significantly to the final cost of the analysis, both in terms of labour and the consumption of materials. In addition, manipulation of the sample can often introduce a major source of imprecision which can greatly outweigh any variables in the chromatographic process itself. The degree of success achieved in the sample cleanup step often determines the ultimate success of the analysis. Sample cleanup can be performed off-line, prior to the chromatographic analysis, or can be incorporated as an on-line process linked with the chromatographic hardware. The goals of cleanup are to achieve: (i)
Reduction of the overall loading of sample on the column in order to prevent peak distortion and loss of chromatographic efficiency. (ii) Removal of matrix interferences. (iii) Concentration or dilution of the analyte. (iv) Preparation of the sample in the solution most appropriate to the analysis. With the exception of sample preconcentration, which will be treated in Section 14.6.3, the achievement of these goals is discussed below.
14.4.2
Sample filtration
As with all other liquid Chromatographic methods, IC requires that the sample be free from particulate matter to prevent fouling of capillary tubing, column end frits and other hardware components. Many samples, such as water samples, are obtained in a fairly clean form, which might appear to require no further treatment prior to injection. Despite appearances, all samples must be filtered through a membrane filter of porosity 0.45 pm or less. Failure to perform this simple step will invariably decrease the column
424
Chapter 14
lifetime. Fortunately, sample filtration is very straightforward if disposable filter units are employed. Careful attention must be paid to sample contamination from these units, particularly by nitrate ion released from the filter membrane. Ultrafiltration devices, wherein the sample is forced under pressure through a membrane, can also be applied to difficult samples; e.g. the removal of free iodide, calcium and magnesium from protein material in biological samples such as serum, milk and egg white [79,80]. 14.4.3 Chemical modification of the sample using ion-exchange resins Perhaps the most common chemical modification of the sample performed in IC is adjustment of the pH of strongly acidic or alkaline samples. Injection of such samples without pH adjustment may produce an unacceptable chromatogram because of baseline disturbances. In particular, system peaks are often caused by large discrepancies in pH between the sample and eluent. This is especially true when aromatic carboxylate salts are used as eluents with indirect spectrophotometric detection. It is usually not possible to adjust the,sample pH by simple addition of acid or base because of contamination of the sample by the acid anion or base cation, since these species may be of interest in the sample. In such cases, it is often possible to use an ionexchange resin in the batch mode to perform the pH adjustment. For example, high capacity cation-exchange resin in the hydrogen form can be added to an alkaline sample in order to lower the pH. The usual procedure is to stir a known weight of resin (e.g. 1 g) with a known volume of sample (e.g. 5 mi) and to monitor the pH of the solution, noting the time required for the sample to reach the desired pH (which is usually that of the eluent to be used). When this reaction time is determined, the process is repeated with a second sample aliquot, but with the pH electrode removed. This prevents contamination of the sample by chloride from the electrode filling solution. The procedure can be adapted to suit different sample types, or the form of the resin used can be varied to achieve alternative chemical modification of the sample. For example, a cation-exchange resin in the silver form will result in the precipitation of chloride from the sample, or a cation-exchanger in the barium form can be used to lower the sulfate concentration in a sample. The above approach is simple and relatively effective, but suffers from a number of drawbacks. First, the sample volume required is large and the reaction time must be adjusted whenever the composition of the sample changes. Second, the resin used must be cleaned thoroughly to prevent contamination of the sample by ions leached from the resin material. Third, the sample volume may change due to uptake or release of solvent from the resin. Finally, some loss of sample components may occur due to adsorption on the resin. Cleanup with ion-exchange resins in the column mode is also common in IC. Here the resin is packed into a suitable container (which may be as simple as a Pasteur pipet), and the sample passed through. The principles discussed above for cleanup using the batch method apply equally well to the column mode. Some applications of the use of resins for sample cleanup are given in Table 4.7. This Table also illustrates the common requirement in IC for removal of chloride from samples.
Sample Handling in IC
425
TABLE 14.7 APPLICATIONS OF SAMPLE CLEANUP USING ION-EXCHANGERESINS Species determined
Resin type
Bread Brine Brine
BeAnions
Water Water NaOH Na2C03 fusion
Aldehydes Anions Anions
Dowex 5OWX8-10 Dionex ICE suppressor Cation-exchanger Dowex 1x8 Bio-Rad X-4,X-8.X-16 Rexyn 101 16-50 mesh Bio-Rad AGSOW-X12
Sample
so42-
AniOlU
Resin form Ag+ Ag+ H+ Acetate
Purposeof cleanup
Ref
c1-~moVal c1- removal c1-nmoval c1-removal
81 82 83 84
Ag+
c1-nmoval
85
H+
pH reduction pH reduction
86
H+
87
melt Water HC1
Urine
F,SiQ2Cations Br
Dowex SOW8 Anionexchanger Cationexchanger
H+
Cation removal 88
OH-
pH increase Removal of
m2-
89
90
interferences
14.4.4 Chemical modification of the sample using membranes Dialytic techniques, in which selected sample components are transferred across a membrane, may be subdivided into passive dialysis and active (or Donnan) dialysis procedures. Passive dialysis involves diffusion of particles of a specified molecular weight range through a neutral membrane. On the other hand, active or Donnan dialysis is the transfer of ions of a specified charge sign through an ion-exchange membrane. Both approaches have been applied to the cleanup of samples for IC. Passive dialysis Passive dialysis is a slow process which requires appreciable volumes of sample (e.g. 5 ml) and normally results in severe sample dilution. These factors have mitigated against its widespread use. Nordmeyer and Hansen [91] have described an automated device for the rapid dialysis of very small samples (e.g. 40 PI) which enables direct injection of the dialysate onto an ion chromatograph. This device is shown schematically in Fig. 14.1 1, from which it can be seen that the sample is introduced into the annular cavity formed between a hollow dialysis fibre and an external, concentrically mounted, small diameter PTFE tube. The eluent is contained inside the fibre and flow is stopped whilst, solute components from the sample dialyse into the interior of the hollow-fibre. Because of the small volumes involved, dialysis time is very short (typically less than 1 min), and the sample is then injected directly. When applied to the removal of free calcium from human serum, linear calibration curves were obtained and peak heights showed a relative standard deviation of less than 5% over a two-week period.
426
Chapter 14 Sample in
1
I
-
TO e column
Eluent
ll
C
Sample out
Hollow dialysis fibre
Fig. 14.11 Schematic representation of a passive dialysis-injecti n device. Adapi d with permission from [91]. Donnan dialysis
Active or Donnan dialysis involves the transfer of ions through membranes which cany an ion-exchange functionality (92-941. The process can be illustrated by reference to a dialysis system comprising 0.1 M NaCl (solution 1) separated from 0.001 M KCI (solution 2) by a cation-exchange membrane. This experimental arrangement is shown in Fig. 14.12. Cations can diffuse rapidly through the membrane, according to the following equilibrium:
Na+
+ K L + NaL + K+
(14.1)
where the subscript M refers to the membrane phase. The equilibrium constant for this exchange is given by: (14.2)
where the parentheses denote the activity of the species. Since the equilibrium must exist at both surfaces of the membrane, then: (14.3)
where the subscripts 1 and 2 refer to the two solutions on either side of the membrane. There can be no concentration gradients for the same ion across the membrane,
427
Sample Handling in IC
Solution 2
Solution 1 0.1 M NaCl
I
0.05 M NaCl
0.0005 M KCI
I
0.05 M NaCl 0.0005 M KCI
I
$;;xiurn
Fig. 14.12 Schematic representation of Donnan dialysis. The black line represents a cationexchange membrane which separates solutions 1 and 2.
therefore:
and
Eqn. (14.3) can be simplified to give:
(14.6)
Assuming that the activity coefficient is unity, we can write (14.7)
where the brackets represent molar concentrations. In the system under consideration, there is a strong tendency for the sodium ions to diffuse from the high concentration zone (solution 1) to the low concentration zone (solution 2). As this process occurs, corresponding transfer of potassium ions from solution 2 to solution 1 proceeds in order to preserve electroneutrality. Thus, diffusion of 1% of the sodium into solution 2 is accompanied by transfer of 99% of the potassium
428
Chaptzr 14
Receiver solution
El
Sample solution Ion-exchange membrane
Fig. 14.13 Simple apparatus for Donnan dialysis. Stimng bars are shown in each solution.
into solution 1. If the volume of solution 1 is less than that of solution 2, then the concentration of potassium in solution 1 is greater than that originally present in solution 2. In this way, sample preconcentration can be accomplished. Eventually the system will attain chemical equilibrium, but this state is achieved only slowly because transfer of chloride across the membrane is hindered. In the short term therefore, sample modification occurs. A simple form of apparatus for Donnan dialysis is shown in Fig. 14.13.
In terms of IC sample cleanup, Donnan dialysis can be used to achieve both matrix normalization and sample preconcentration. That is, moderate amounts of potential interferents, such as suspended solids, neutral solutes and ions of opposite charge sign to that of the analyte, neither influence the rate of Donnan dialysis nor are transported to a significant degree into the receiver [94-961. At this stage, we will focus on the matrix normalization capabilities of Donnan dialysis, for which two distinct possibilities exist. First, Donnan dialysis can be used to selectively add an ion to a sample, or second, to remove a selected species from a sample. ( i ) Selective addilion of an ion to the sample The first of the above two alternative applications of Donnan dialysis in IC is the most commonly used. It will be noted from Fig. 4.12 that an ion from the receiver solution enters the sample solution during the dialysis. Thus, use of an acid as the receiver will result in transfer of hydrogen ions into the sample, which can be useful if the sample is highly caustic. This treatment is, in effect, the same process by which chemical suppression of the eluent is achieved in suppressed IC. Sample treatment using this method can be illustrated by the dialysis of sodium hydroxide solution using sulfuric acid as the receiver solution. Here, hydrogen ions from the sulfuric acid solution exchange with sodium ions from the sodium hydroxide through a cation-exchange membrane. The pH of the sample is therefore lowered, whilst the anion content is theoretically unaltered, allowing subsequent determination of these anions by IC.
Sample Handling in IC
hollow Samplefibre inside
429
f i
Fig.14.14 A commercially available flow-through dialysis apparatus ("Milli-trap" from Millipore Corporation). Courtesy of Millipore.
This method suffers from a practical limitation which seriously detracts from its routine use. This limitation is that the cation-exchange membrane is not entirely impervious to sulfate ions from the receiver solution, which means that the sample ultimately becomes contaminated with sulfate during dialysis. This problem can be minimized by increasing the permselectivity of the membrane (i.e. its ability to permit the transfer of ions of only one charge sign), or by using an acid whose anion shows little tendency to penetrate the membrane. Aliphatic sulfonic acids have been shown to be suitable for this purpose. A commercial sample cleanup device based on Donnan dialysis with an acidic receiver solution has been released by Millipore [97]. This device is illustrated schematically in Fig. 14.14. A similar approach in which chloride can be removed from samples using AgNO3 as the receiver solution and a cation-exchange membrane is also possible. An attractive alternative to the use of an acid as the receiver solution has been reported by Cox and Tanaka [98], who used a slurry of ion-exchange resin in the hydrogen form in place of the receiver solution. Since the counter-anion is therefore the resin bead itself, transfer across the membrane is eliminated for physical reasons. This process has been called "dual ion-exchange". It should be noted that the ion-exchange membrane may also be used in the form of a tube inserted into the resin slurry [99]. (ii) Selective removal of an ion from the sample The second type of application of Donnan dialysis to sample cleanup in IC involves the extraction of the analyte ion(s) into a suitable receiver. This process accomplishes sample normalization, since the analyte ions are ultimately collected in a solution of known composition. A potential problem exists with this method in that determination
Chapter 14
430 TABLE 14.8
APPLICATIONS OF SAMPLE CLEANUP FOR IC USING MEMBRANE TECHNIQUES Sample
Processa
Membrane
Receiver
Ref
NaOH NaOH NaOH Na2C03 NaCl
DIE ME DIE DIE DIE
Dowex 50WX4 (H+)
Sugarb,
DD
Dowex 50WX4 (H') Dowex 50WX4 (H+) Dowex 50WX4 (H+) Na2C03-NaHC03 Dowex 50WX4 (H+) Na2C03-NaHC03 Dowex 50WX4 (H+) Dowex 50WX4 (H+) Na2C03-NaHC03 Dowex 50WX4 (H+) Dowex 50WX4 (H') Dowex 1x4 (Cl-) Na2C03-NaHC03
99 102 98 99 99 95
H20
syrupb River water Coalc Coalc
Analytes
CI-, NO^-. ~ 0 4 2 Cations Anions
DIE DIE
m
Nafiion 81 1 cation Nafiion 901 cation Nafion 117 cation Nafion 81 1 cation Nafion 8 11 cation RAI R- 1035 anion Nafon 117 cation RAI R-1035 anion Nafion 117 cation Nation 117 cation RAI R-1035 anion Nafion 117 cation Nafion 117 cation RAI R- 1035 anion Home-made anion
Ca*+
PD
Cuprophane CllM
Anions
DIE DD DIE DIE DD
DIE Leave& Polyelecaulyte Serum
95 95 95 95 98 103 91
a DIE =dual ion-exchange, DD = Donnan dialysis, PD = passive dialysis, ME = membrane
electrolysis. Sample treated by carbonate fusion. Sample treated by oxygen bomb combustion using Eschka mixture (1:2 NqCOyMgO) as absorbing solution.
of the analyte(s) by IC may be precluded as a result of interference from the high concentration of ions in the receiver electrolyte. One possible solution to this problem is to use a carbonate or bicarbonate salt solution as the receiver and to further treat this solution by the dual ion-exchange procedure discussed above. The carbonate and bicarbonate in the receiver are converted in the dual ion-exchange step to carbonic acid, following which the sample can be injected directly or the dissolved carbon dioxide can be removed prior to sample injection. The combination of Donnan dialysis and dual ionexchange is a powerful method for the treatment of complex samples.
In both of the above methods of sample treatment, the membrane can be in sheet or tubular form [loo]. I t has been demonstrated that transfer of solutes across the membrane surface is improved if the sample is recirculated around the outside of the membrane tubing during dialysis [ l o l l . Table 14.8 shows some applications of Donnan dialysis sample cleanup in IC.
Sample Handling in IC
Cathode
431 Anode
Dilute NaOH
Anode:
Sample 19N NaOH)
Catex membrane 4OH-% Q+ H f l +4e-
Cathode: 4H20 + 4e-
+ 2H, + 40H-
Fig. 14.15 Apparatus for electrodialysis of highly caustic samples. Reprinted from [lo21 with
permission.
Electrochemical dialysis Further refinement to dialysis methods can be achieved by coupling electric fields with membrane processes. For example, the transfer of ions through a membrane can be stimulated by application of an electric field across the membrane; this process is known as electrodialysis. The apparatus shown in Fig. 14.13 can be modified easily to include platinum gauze electrodes on either side of the membrane. This approach has been applied to the electrodialysis of metal ions using a cation-exchange membrane, NaN03 as the receiver and a 5 V/cm (peak-to-peak) sine wave potential at 1 MHz frequency [104]. The rate of transfer through the membrane was increased by up to 2.7 times as a result of application of the potential. Electrodialysis has been reported as a sample treatment method for differential pulse polarography but has not yet been applied to IC. A two-part electrolysis cell (Fig. 14.15), in which the anode and cathode compartments are separated by a cation-exchange membrane, has been suggested for the treatment of highly caustic samples prior to IC analysis [102]. The sample is placed in the anode compartment, whilst a larger volume of dilute NaOH is used to fill the cathode compartment. During electrolysis, OH- reacts at the anode to produce 02 and H 2 0 , whereas water reacts at the cathode to produce HZand OH-. The concentration of O H in the anode compartment therefore decreases, whilst that in the cathode compartment increases. Transfer of OH- through the membrane cannot occur, so sodium ions move from the anode compartment into the cathode compartment. The net result of this process is that the concentration of NaOH in the sample is lowered progressively. Use of an electrolysis current of 0:15 A for 3 hr lowered the NdOH concentration in the sample from 19 M to 0.3 M. The latter concentration was suitable for direct injection into a suppressed IC system.
Chapter 14
432
14.4.5 Chemical modification of the sample with disposable cartridge
columris One of the most versatile and convenient means available for sample cleanup is the use of commercially available disposable cartridge columns. These devices offer rapid sample treatment and can usually be employed in tandem with disposable filters so that filtration and sample cleanup can be performed in a single operation. Some of the common stationary phases available commercially as cartridge column packings are: Silica. c18.
Alumina (acidic, basic, neutral). Anion-exchange resins. Cation-exchange resins (H+ or metal form). Polymers (e.g. stryrene divinylbenzene or polyvinylpyrrolidine). Activated carbon. Chelating resins. Amino-bonded silica.
Modes of operation Cartridge columns can be employed in one of two ways. The first method is the selective removal of the solute ions from the sample matrix and in this approach, the solvent used to elute the sample through the cartridge should provide chromatographic conditions giving very strong retention of the solute ions. That is, the capacity factors for these solutes should be as large as possible. The alternative operational mode for cartridge columns is to selectively retain matrix components under conditions where the solute ions are unretained. That is, their capacity factors approach zero. It is generally inadvisable to use a cartridge column to attempt chromatographic separation of solutes which have capacity factors intermediate between the above-mentioned extremes. The reasons for this are that experimental factors are often variable (e.g. column efficiency, flow-rate, and packing reproducibility) and in most cases the passage of solutes along the column cannot be monitored visually. Thus, even if a chromatographic separation is optimized for a particular stationary phase, it is probable that the separation would be irreproducible in practical situations. Keeping in mind that we wish the solute to be either well-retained or not retained at all, then several possibilities emerge from the stationary phases listed above. Stationary phases which show some ion-exchange ability (such as silica, alumina, anion- and cationexchangers, and amino phases), and stationary phases which show chelation ability, should be suitable for the selective retention of ionic solutes from a matrix composed largely of neutral, organic species. Alternatively, hydrophobic stationary phases (such as octadecylsilane and the polymeric phases) should be useful for the removal of neutral organic components, while showing little retention of ionic solutes. A further potential application of cartridge columns is their use for adjusting the pH of a sample in the same manner as that described earlier for ion-exchange resins used in the batch mode. Most of these possibilities have been realized in practice and Table 14.9 lists some examples of successful applications.
Sample Handling in IC
433
TABLE 14.9
EXAMPLES OF SAMPLE CLEANUP USING CARTRIDGE COLUMNS Matrix
Solute ions
Stationary phase
Ref
Plant extract Urine Urine Soil extract Cheese Kraft liquor Plasma Serum Plant extract Surfactants High chloride NaOH River water Jxachate Air samples Digests Natural waters Serum Surfactants Aromatics
NO;?-,NO3-,S042"hiosulphate oxalate
c18 c18
105, 106 107 108
so,2Na+, N&+. K+ sZ-,~2032-
NOz-,NOgICl-, NOj, Alkylbenzenesulfonates Anions Anions HCO3-, C1-, NOi, S042As(IW, AsW) Anions Metal 0x0-anions Anions
sod2 Anions Anions
CIS CIS c18 c18 cl8
Cl8 Silica Silica Cation-exchange (Ag+) Cation-exchange (H') Cation-exchange(H+) Cation-exchange Charcoal
Anion-exchange Amino Polymer Polymer Polymer
106 109 110 111 112 113 114 29
86 115 116 117 118 119 120 121 121
Practical aspects Several practical aspects should receive attention when using cartridge columns, namely column pretreatment, flow-rate, method of sample application, and sample pH. First, the columns almost invariably require pretreatment in order to remove very fine particles of the packing material, to elute any contaminants, or to condition the stationary phase in order to improve the efficiency of sample binding. Significant levels of inorganic contaminants are commonly encountered in cartridge columns (see Section 14.5). generally as a result of residual reagents from the manufacturing process. Hydrophobic stationary phases usually require pretreatment with an organic solvent, such as methanol, in order to wet the stationary phase surface so that effective binding of hydrophobic solutes is achieved from aqueous sample solutions. The flow-rate of sample or flushing solution through the cartridge column should be kept as low as practicable so that mass transfer effects are minimized. Most column cartridges are designed for use with disposable syringes and the low packing density of the stationary phase permits very high flow-rates (e.g. 50 ml/min) to be easily achieved. Experience with analytical chromatographic columns suggests that such a high flow-rate is unlikely to produce the degree of selective separation required, so it is advisable to use flow-rates less than 10 ml/min.
Chapter 14
434
TABLE 14.10 EXAMPLES OF PRE-COLUMN DERNATIZATION REACTIONS IN IC Analyte
Additive
Effect
Ref
Anions
Methanol
123
Ascorbic acid
Boric acid
Boron
Chromompic acid Hydrofluoric acid
[CtQ2-] is reduced by reaction with methanol, producing formate Prevents oxidation of ascorbic acid (borate convened to H3B03 in suppressor) HgBOj-chromonopicacid complex formed Boron converted to BF4- and quantitated in this form 4-Bromoacetanilide formed is used as a meaSure of RrComplexes some metal ions CN- + 2H20 5 NH3 + HCOO-, with HCWY used as an indirect measure of CNCN- + OC1’ f OCN- + Cl-, with cyanate used as an indirect measure of CN12 + HCN % H+ + I- + ICN, with iodide used as an indirect measure of CN‘ H2@ + S032- % H20 + sod2-, with S04*used as an indirect measure of H2@ Reacts with H2S to form methylene blue, which is used to quantitate S2Fluoride converted to BF4‘ to eliminate interference of F on silica analysis S 0 3 2 - converted to hydroxymethane sulfonate N&+ produced is used to quantitate urea
Roron
Bf
Cations HCN
2-iodosobenzoic acid + acetanilide MTA Water
CN-
Hypm hlorite
CN-
Iodine
H202
Sulfite
S2-
N,N dimethylphen ylenediamine Boric acid
~ 0 3 ~ -
Formaldehyde
Urea
Urease
124 125 126 127 128 12 129, 130 131 132 133 134 135 136
The third important practical consideration is the manner in which the sample is applied to and eluted from the cartridge column. It is possible to apply a known volume of the sample to the head of the column and to elute the sample band through the column with a suitable eluent. However, this method is inadvisable in practice because of the difficulty in applying an accurate volume of sample using the syringes compatible with the cartridge column, and is recommended only when the sample volume is small or the concentration of the sample is high enough to quickly saturate the cartridge. It is generally more appropriate to pass sample continuously through the column, discarding the first two or three column volumes and to then collect sufficient effluent for analysis. Finally, the sample pH has an important bearing on the selection of a suitable stationary phase. Apart from the obvious consideration that some stationary phases are intolerant of acidic or alkaline solutions, the sample pH is often a very useful indicator of the ionic strength. In cases where the ionic strength is unacceptably high, it may be necessary to use a second cartridge column, or an alternative cleanup procedure, to
Sample Handling in IC
435
remove some of the ionic components from the sample. In conclusion, it should also be noted that cartridge columns packed with hydrophobic stationary phases can also be used to retain ionic solutes (rather than neutral, organic solutes) if they are first conditioned with an ion-interaction reagent. The success of this approach is dependent on retention of the ion-interaction reagent on the stationary phase during sample elution, thus it is desirable that relatively hydrophobic ion-interaction reagents be used and the sample volume be limited. Tetramethylammonium hydroxide and pentanesulphonic acid have been employed as ioninteraction reagents for the removal of anionic and cationic surfactants, respectively, using a cartridge column packed with a polymeric divinylbenzene stationary phase [121].
14.4.6 Chemical modification of the sample by pre-column reaction For some samples, cleanup can be best achieved using an appropriate chemical reaction to eliminate a matrix component. Alternatively, it may be necessary to derivatize a solute in order to enhance its detectability or to convert it into a form suitable for separation. Much has been written on the principles of chemical derivatization of organic solutes [e.g. 1221, and the same principles apply here to inorganic solutes. Table 14.10 lists some reactions which have been employed as sample treatment methods for IC, or as mobile phase reactions designed to modify the nature of the solute in an IC determination. 14.5 CONTAMINATION EFFECTS 14.5.1 Introduction One of the most important considerations in sample handling is the possibility of contamination arising from various sources, such as the manipulative procedures used, the volumetric ware employed, filtration or cleanup devices, or the chromatographic hardware itself. Such contamination may alter the true concentration of solutes of interest, either directly by contributing detectable levels of the analytes to the final solution, or by promoting chemical reactions which cause levels of analytes to alter. In addition, the sample itself may be a source of contamination of the chromatographic system, causing column poisoning or memory effects resulting from adsorption of sample constituents on chromatographic components. In this Section, the chief sources of contamination are discussed.
14.5.2 Contamination from physical handling of the sample The prime sources of sample contamination from physical operations, such as weighing and volumetric manipulations, are contact of the sample or apparatus with the skin, or leaching of contaminants from volumetric ware. Contact with the skin introduces detectable levels of sodium and chloride to the sample [137] and in cases where trace determination of these solutes is desired, high background levels will invariably occur unless protective gloves are worn.
436
Chapter 14
Volumetric ware should be made from polyethylene or some other inert material and should be washed in non-ionic detergent (sulfate-free) and rinsed thoroughly before use [138]. Even when these precautions are taken, it is still possible that contamination of the sample may occur, especially with low molecular weight carboxylic acids [139]. Standard solutions used for calibration of the IC should be stored in inert containers. There is ample evidence to show that even brief exposure of aqueous solutions to conventional laboratory glassware results in significant contamination, particularly by sodium and silicate. Two further sources of sample contamination have been noted. First, aqueous samples have been observed to become readily contaminated with bicarbonate, ammonium and nitrite ions produced by absorption of carbon dioxide, ammonia or nitrogen dioxide from the atmosphere [ 1401. Second, reagents used as sample additives may contribute detectable levels of contaminant ions to the solution. This has been observed for citrate added to samples in trace enrichment procedures [141], and for sodium carbonate used in fusion techniques [87]. 14.5.3
Contamination from filtration devices and cartridge columns
As mentioned in the earlier discussion on the use of disposable filtration devices and cartridge columns for the clarification and chemical cleanup of samples for IC, contamination from these devices must be considered. In most cases, these devices have been manufactured for the general HPLC market, where sample contamination by inorganic ions would be a minor problem unless the particular contaminants involved were capable of participating in chemical reactions with the sample components. For this reason, it is not uncommon for inorganic reagents to be employed during the manufacturing process. Some disposable membrane filters, and both Clg and alumina cartridge columns, have been evaluated for contamination effects [I421 and some of the results obtained are summarized in Tables 14.11 and 14.12. Table 14.1 1 shows that disposable filtration devices release appreciable quantities of nitrate, and lesser amounts of chloride and sulfate, into the initial fraction of solution passed through them. However, the leachable ions are very labile and are essentially removed completely if the filter is pre-washed with 20 ml of water. Care should therefore be taken that such filters are washed adequately before they are used on samples to be subsequently analyzed by IC. Detectable levels of chloride, nitrate, sulfate and lead are leached from cartridge columns by water (Table 14.12), and a reduced, but still detectable, level of these ions persists after the column has been washed with 20 ml of water. The levels of ions leached from the cartridge are sufficiently low that they would present a problem only for ultra-trace analyses using sample preconcentration methods. In such cases, it would be necessary to run a blank solution. Alumina columns produce much more severe contamination, undoubtedly due to residues of the reagents used to modify its surface properties during manufacture. The above resuits are specific to one brand of product, but similar levels can be expected in alternative products, unless appropriate means were employed by the manufacturer to remove inorganic contaminants. This has been confirmed in a recent study of leachable nitrate from twelve different commercial membrane filters [143], for
Sample Handling in IC
437
TABLE 14.11 CONTAMINATIONFROM FILTRATIONDEVICES. DATA TAKEN FROM [142]
Ion
Concn @pb)in successive 20 ml fractions Millipore HA filters
Fraction 1
Fraction 2
c0.2 84.6 698.8 17.8
<0.2 13.6 e0.4 2.2
MilliponHvhlters
Fraction 1 23.4 73.2 409.5 111.9
Fraction 2 <0.2 13.2 c0.4 8.7
TABLE 14.12 CONTAMINATIONFROM C18 CARTRIDGE COLUMNS. DATA TAKEN FROM [142]
Ion
Concn (ppb) in successive 20 ml fractions Fraction 1
F-
<0.2
Na-
101.2 69.9 99.4 76.3
c1-
so42Pb2+
Fraction 2 <0.2 29.4 36.4 39;O 21.4
Notes 1. No contamination observed for Cd2+,Cu2+,Mn2+,Ni2+ and Zn2+. 2. Other stationary phases (particularlyalumina) contain significantquantities of leachable material
which comparable levels of nitrate (1-4 ppb after washing with 25 ml of water) were observed from all but one of the filters. The latter was a cellulose ester type and approximately 18 ppb of nitrate was leached, even after washing with 25 ml of water. 14.5.4 Contamination from chromatographic hardware components
Over recent years there has been considerable discussion relating to the Suitability of conventional HPLC hardware components for use in IC applications. The major instrumental components of an IC, namely the pump, injector, data management system, and sometimes also the detector, are often identical to those used in a typical HPLC system. In view of this, it has been common for HPLC hardware to be used in IC systems and this raises the question of the suitability of stainless steel components for use with the aqueous eluents and sample types employed in IC. Types 304 and 316 stainless steels are typically used in the construction of solventwetted HPLC components. Studies with reversed-phase eluents [144] have shown that
Chapter 14
438
TABLE 14.13
TYPICAL COMPOSITION OF TYPES 304 AND 316 STAINLESS STEEL
Percentage
Element
Carbon Manganese Phosphms Sulfur
Silicon Chromium Nickel Molybdenum
Type 304
Type 316
0.08 (max) 2.00 0.045 0.030 1 .oo 18.00-20.00 8.00- 12.00
0.08 ( m a ) 2.00 0.045 0.030 1 16.00-20.00 10.00-14.00 2.00- 3.00
.oo
components with small diameter openings, such as capillary tubing, are susceptible to corrosion resulting from mechanical erosion of the protective surface oxide layer, due to high fluid velocity. There is also evidence that sample components, such as proteins and metal chelates, can undergo complexation or ligand exchange reactions at stainless steel surfaces [145,1461. Aqueous buffers used for the analysis of anions and cations in IC provide a suitable environment for corrosion and in some cases, also exhibit strong complexation properties. It is therefore possible that contamination effects could arise from the use of these eluents on stainless steel hardware components. Several possibilities exist where contamination of the eluent by metal ions leached from metallic components in the chromatographic system could present serious problems. The first of these is the direct elevation of detector baseline levels in cation analyses using post-column reaction detection [ 1471. Secondly, interference effects resulting from complexation reactions with solutes can be expected to occur in some anion-exchange separations. For example, iron(II1) forms a strong complex with many common inorganic anions and this complex would have different chromatographic and detection characteristics to those exhibited by the free anions. A further effect resulting from eluent contamination occurs in the ion-exchange separation of monovalent cations. Here, the presence of multiply charged cations in the eluent would lead to rapid column deterioration caused by irreversible binding of these ions onto the exchange sites of the low capacity cation-exchange columns used. In such methods, it is common practice to include an ion-exchange guard column between the pump and injector in order to remove any multivalent cations from the eluent. However, this approach would be ineffective against ions produced as corrosion products within the injector or the column itself. Table 14.13 shows the compositions of types 304 and 316 stainless steel. These materials are corrosion resistant by virtue of a protective coating of chromium-rich This coating can develop gradually during oxides which forms on the surface [la]. usage, or can be formed rapidly by exposing the surface to relatively strong nitric acid solutions. If the latter method is used, the surface is said to be 'pussivuted".
Sample Handling in IC
439
Consideration of the composition of the steel suggests that the species most likely to be produced by corrosion reactions are iron, chromium, manganese, molybdenum and nickel. These metal ions could be leached from the metallic surface through either direct oxidation or by complexation reactions with eluent components. The latter mechanism can be expected to be most prevalent with eluents containing strong complexing agents, such as citrate, tartrate, phthalate and ethylenediamine. Side-reaction coefficients for complexation of the above metal ions with the eluents typically used for IC suggest that significant complexation of iron, chromium and, to a lesser extent, nickel can be anticipated [ 1481. In a study of these effects [148], corrosion products were allowed to accumulate to detectable levels by recirculating aqueous eluents through a HPLC system, and the eluents were then analyzed by inductively coupled plasma atomic emission spectrometry. The experiment was performed on the chromatographic hardware alone, and also with an empty stainless steel column included in the flow-path. The results of this study are summarized in Table 14.14, which shows clearly that the levels of contaminant metal ions (especially iron) found in the eluent were extremely low when the eluent passed only through the chromatographic hardware (pump and injector), but increased markedly when the column was incorporated into the flow-path. It is interesting to speculate on the source of the corrosion products observed with the stainless steel column. The most probable source is the column frits, which have a very high surface area in comparison to the rest of the column and the external chromatographic system. These frits inevitably also contain stress points at which the rate of corrosion would be accelerated. Calculations show that if the eluent wets the entire surface of the column frits, then these frits account for approximately 96% of the total metal surface in contact with the eluent and should therefore be the prime source of eluent contamination. TABLE 14.14 CONTAMINATION OF ELUENTS BY STAINLESS STEEL CHROMATOGRAPHIC COMPONENTS. DATA TAKEN FROM [148]
Metal concentration (ppb) per eluent cycle
Eluent?
HNO3 HNO3 EDA-TA EDA-TA EDA-CA EDA-CA KHP a
Fe
Cr
Mn
MO
Ni
31 1.8 <1.0 9.5 1.9 20.0 3.8 <1.2
<1.0 4.4 c1.5 4.3 4.4 c2.d 3.2
33.6 <0.3 c0.3 0.4 <0.3 c0.6 4.3
<0.8
4.5 c1.6 4.5 4.7 c3.2 4.7
11.7 c1.5 4.6 c1.5 4.7 c3.2 c1.7
Column
Yes no Yes no Yes no Yes
Key to eluent identities. HNO3: 10 mM nitric acid. EDA-TA: 0.5 mM ethylenediamine and 1.3 mM tiutaric acid. EDA-CA: 3.5 mM ethylenediamine and 10 mM citric acid. KHP: 1 mM potassium hydrogen phthalate.
Chapter 14
440
It can be concluded that oxidizing or complexing eluents used for cation-exchange separations may become contaminated with detectable levels of iron, chromium and nickel from stainless steel column frits. Accordingly, cation-exchange columns designed for use with these eluents should be fitted with non-metallic frits. or alternatively, metallic frits should be deactivated by passivation or silanization reactions. Eluents typically used for IC of anions do not show any contamination from the metallic components of the chromatographic system and this result indicates that metallic frits are suitable for use in anion-exchange columns. Chromatographic hardware components, such as pumps and injectors, do not appear to contribute significant levels of metal ions, unless the particular analysis under consideration is concerned with ultra-trace determination. It should be noted that the contamination levels shown in Table 14.14 were obtained on an unpassivated HF'LC system and that lower levels were observed when the metallic surfaces were passivated by treatment with nitric acid. 14.5.5
Contamination of the column
In the preceding section it was pointed out that metal ions introduced into the eluent from the chromatographic hardware could cause poisoning of cation-exchange columns through irreversible binding of exchange sites. This example serves to illustrate the possibility of column contamination and in the following discussion, such contamination from the sample will be considered.
Contamination by organic species Perhaps the most commonly encountered example of column poisoning by the sample is the binding on the column of organic sample components. This problem can be easily circumvented by pretreatment of the sample with a cartridge column, use of an ion-exchange guard column, or by periodical flushing of the analytical column with a water-methanol mobile phase (when the column packing is sufficiently resistant to the use of organic solvents). Contamination by metal ions A more insidious problem is the effect of metal ions on both anion and cation separations. In the former case, metal ions such as calcium and magnesium may form complexes with mobile phase components (e.g. gluconate), leading to system peaks or an unstable baseline in the final chromatogram [ 1491. Silica-based anion-exchangers can also show retention of metal ions, with iron(III), aluminium(II1) and mercury(I1) being strongly retained, whilst copper(II), lead(I1) and zinc(I1) may elute at retention times similar to those observed for anions on the same column [150]. It has been shown [151] that the latter group of metal ions forms complexes with phthalate eluents which are retained to varying degrees on silica and polymeric anion-exchangers. It is therefore evident that polyvalent metal ions should be removed from samples on which anion determinations are to be performed, and this may be achieved conveniently by passage of the sample through a cation-exchange cartridge column. Fig. 14.16 shows the effect of treating a drinking water sample in this manner and it is clear that the removal of
Sample Handling in IC
441
Fig. Z4.Z6 Effect of calcium and magnesium on the baseline produced in the determination of anions in drinking water. Chromatogram (a) is for a sample contaminated with calcium and magnesium and chromatogram (b) is the same sample after Ereatment by passage through a cationexchange cartridge column. Column: Waters IC PAK A. Eluent: 1.3 mM Na2B4O7- 5.8 mM H3BO3 - 1.4 mM K-gluconate in water-acetonitrile (88: 12). Chromatogram courtesy of Waters.
calcium and magnesium resulted in an improved baseline. Polyvalent cations can also exert a detrimental effect on the determination of monovalent cations by cation-exchange. The relatively weak eluents used for the monovalent cations are unable to elute polyvalent cations, with the result that these species remain bound strongly to the column. The outcome of this is that chromatographic performance of the column for monovalent cations is degraded in terms of decreased retention, loss of efficiency, poor resolution and reduced peak heights [ 1521. The latter three characteristics are directly attributable to the fact that the solute ions do not compress into a compact band at the head of the column when ion-exchange sites are occupied by polyvalent metal ions. For these reasons, it is therefore advisable that a cation-exchange guard colrimn be inserted into the flow-path prior to the analytical column. 14.6 SAMPLE HANDLING FOR ULTRA-TRACE ANALYSIS
14.6.1
Introduction
The sensitivity of an IC method is strongly dependent on the type of detector used, with amperometric and direct spectrophotometric detection being among the most sensitive, and refractive index being relatively insensitive. Most of the universal detection modes, such as conductivity and indirect spectrophotometry. have comparable practical detection limits of about 100 ppb for a 100 pl injection. This means that for reliable quantitation to be achieved, routine analysis by direct sample injection can be most conveniently used for solute concentrations of about 1 ppm or higher. Below this concentration level, either larger injection volumes must be employed or a sample
442
Chapter 14
> 100 ppm
I
LARGE INJECTION VOLUME ZONE (sample 100 pi 5 ml)
-
I
I00 ppb
PRECONCENTRATION ZONE
c 1 ppb
Fig. 14.Z7 Approximate working concentration ranges in IC.
preconcentration method is necessary. Fig. 14.17 shows a schematic representation of the approximate sample concentration ranges applicable to the above-mentioned approaches, each of which is discussed below. 14.6.2
Large injection volumes
The zone compression (or "re-launch") effect occurring on ion-exchange columns makes it possible to inject very large volumes of sample onto an analytical column, without significant loss of chromatographic efficiency. Several authors have utilized this approach and typical operating conditions are summarized in Table 14.15. An upper practical limit of about 2 ml exists for the sample injection volume, otherwise the large solvent peak in the final chromatogram may mask early eluted solutes. However, the maximum volume which can be injected may be greater if certain detection modes are used and if the ion-exchange capacity of the column is high. Thus, very large injection volumes (10-50 ml) are possible in the determination of nitrite using direct spectrophotometric detection and a column having a capacity of 3 mequiv/g [153]. Indirect specuophotometric detection has been shown to be superior to conductivity detection when large injection volumes are employed because the former method shows a more rapid return to baseline after passage of the large injection peak [ 156, 1591. Fig. 14.18 shows a chromatogram obtained using indirect spectrophotometric detection and a 1 mi sample injection volume. Andrew 11631 has noted that large injection volumes are not applicable to ion-interaction IC because of destabilization of the column equilibria by the sample volume. To increase the volume of sample above the practical limit mentioned above, it is essential that the size of the solvent peak be decreased so that interference with early eluted solutes does not occur. One method to achieve this is to flush the interstitial sample from the column by pumping a measured volume of eluent through the column
Sample Handling in IC
443
in the reverse direction to that used for sample elution [156]. The solute ions remain bound to the column during this operation, but the injection peak is reduced because the sample solvent has been displaced from the column. This method permits the use of sample volumes up to 5 ml, but requires the use of two switching valves and therefore seems to offer little advantage over the use of similar hardware with preconcentration columns, as discussed below. 14.6.3
Trace enrichment with preconcentration columns
The most widely used approach to trace enrichment in IC involves the use of a separate pre-column designed to trap trace levels of solutes from a large volume of sample. The pre-column method is popular because it is simple and convenient to apply, is amenable to automation, offers high enrichment factors, and is less prone to sample contamination effects than other methods 1141, 164-1671. In precolumn trace enrichment, an accurately known volume of sample is pumped at a precise flow-rate through a small ion-exchange pre-column (or a reversed-phase pre-column coated with a suitable ion-interaction reagent), called the concentrator column. Solute ions contained in the sample are trapped selectively on the concentrator column and are then eluted onto an ion-exchange analytical column for separation and quantitation. This procedure can be effective as an analytical method only if the processes of binding of solute ions on the concentrator column, and their subsequent transfer to the analytical column, are quantitative.
TABLE 14.15 EXAMPLES OF THE USE OF LARGE INJECTION VOLUMES IN IC Sample
Water Ice Ice Water Water Water Water Water Water Methanol Water a
Solutes
N02' Cations, anions CH3SO3Anions Anions CI-, NO^-, ~ 0 4 2 Anions Anions
Cations C1NH4'
Injection volume (mu
Detection modea
10-50 5.5 5.5 5 5 2 1-3 1 1 0.8 0.75
DSpec
Detection limits (PPb)
sc sc
NSC ISpec NSC
sc
rspx NSC
sc sc
0.1 0.5 (for N&+) 0.1 4.5 (for CI-) 0.45 (for Cl-)
40 (for C13 2.0 (for Cl-) 5.4 (for C1-) 0.4 (for Ni2+) 10
0.1
Ref
153 154 155 156 156 157 158 159 160 161 162
DSpec = direct spectrophotometry, SC = suppressed conductivity, NSC = non-suppressed conductivity, ISpec = indirect spectrophotometry.
444
Chapter 14 H
L L-b F
I
-0
8
L Time
12
16
Iminl
Fig. 14.18 Use of large injection volumes for anion analysis. Column: Vydac 302 IC 4.6. Eluent: 2.5 mM potassium hydrogen phthalate at pH 4.0. Injection volume: 1 ml. Detection: UV absorption at 285 nm. Solute concentrations: 50-200 ppb. Peak identities: A - solvent peak, B dihydrogen phosphate, C - chloride, D - nitrite, E - bromide, F - nitrate, G - iodide, H - system peak. Reprinted from [ 1591 with permission.
Hardware considerations ( i ) Single-valve preconcentration system The simplest form of sample preconcentration system utilizes a single, six-port, high pressure, switching valve, which can be actuated either manually or automatically 11681. Fig. 14.19 shows the plumbing arrangement and operation of this system. In the first step, the concentrator and analytical columns are equilibrated with eluent. The valve is then rotated a d the concentrator column is removed from the flow-path whilst eluent continues to be pumped through the analytical column. A measured volume of sample is passed through the concentrator column using either a pump or a large-volume syringe, with the effluent being directed to waste. At this stage, the solute ions from the sample are assumed to be retained on the concentrator column. In the subsequent step, rotation of the valve permits eluent to be pumped in the reverse direction (i.e. the flow direction opposite to that used for sample loading) through the concentrator column. This operation is known as "backflushing" and is designed to transfer the solute ions to the analyticai column in the smallest possible volume of eluent. In the final step, the valve is again rotated and eluent then carries the solute ions through the analytical column for separation and detection, in the usual way.
Sample Handling in IC
Equilibrate
Load Sample
Backflush
Analysis
Fig. 14.19 Sample preconcentration using two pumps, a single high-pressure switching valve and a concentrator column. EP - eluent pump, SP - sample pump, C - analytical column, D detector. The concentrator column is indicated by the hatched area and flow-paths are shown by the solid lines. Note that the sample pump is turned off for the final analysis stage.
This system has the advantages of simplicity and ease of operation. The backflush volume is generally selected to be high enough to guarantee that all the ions are transferred. It should be noted here that the volume of eluent used to backflush the solute ions to the analytical column will necessarily have a lower concentration of eluent ions than that present in the bulk eluent. This is because some eluent ions are required to re-equilibrate the concentrator column, which has been depleted of eluent ions during the passage of sample. The result of this is that severe baseline disturbances often occur in the final chromatogram when the detection method employed is sensitive to the background level of eluent ions in the mobile phase. Conductivity detection falls into this category and when this is used, the initial baseline disturbance in the chromatogram may mask early eluted solutes. (ii) Two-valve preconcentration system A more flexible preconcentration system is produced by the combination of a single, programmable pump with two high-pressure switching valves and a low-pressure solvent selection valve [ 169, 1701. Here, the same pump can be used to deliver eluent and to load the sample onto the concentrator column. Fig. 14.20 shows the interconnections used for these valves and Fig. 14.21 illustrates some of the flow-paths achievable with this system. Using a suitable configuration of the valves, the pump tubing and interconnecting lines can be flushed with sample solution or eluent, with both the concentrator and analytical columns removed from the flow-path. In Fig. 14.21(a), a measured volume of sample is loaded onto the concentrator column at a precise flow-
446
Chaprer 14
I
WASTE
I
TO DETECTOR
Fig. 14.20 Apparatus for sample preconcentration using a single pump, a low-pressure solvent selection valve (A), two high-pressure switching valves (B and C ) and a concentrator column (D). E is the analytical column. Reprinted from [I703with permission.
rate, after which a small, accurately known volume of eluent is pumped through the concentrator column in the same flow direction as that used for sample loading (Fig. 14.21(b)). This is termed a "wash" step and serves to partially re-equilibrate the concentator column with eluent ions, without loss of the bound solute ions. Fig. 14.21(c) shows the sample stripping step, in which the solute ions are backflushed from the concentrator column onto the analytical column using an accurately known volume of eluent. In the final step of the analysis, the concentator column is removed from the flow-path and the eluent is pumped directly to the analytical column. Clearly, this multi-valve system is more complex than the single-valve approach and requires the use of a sophisticated pump. It does, however, offer the advantages of unlimited and precise control over the volumes of eluent used for the washing and stripping steps, and these may be readily manipulated to adapt to the requirements of a particular sample. In addition, incorporation of the washing step produces a more stable baseline i n the final chromatogram than that obtained with a single-valve preconcentration system which omits this step. Choice of eluent The most important factor to be considered in the selection of an appropriate eluent for a preconcentration method is that eluents which are perfectly suitable for direct injection IC may be quite inappropriate for use with preconcentration techniques. In the latter case, the eluent must perform three distinct functions: (i)
It must permit solute ions to bind onto the concentrator column during the
sample loading step.
Sample Handling in IC
447
p I
WASTE
1
TO DETECTOR
Fig. 14.21 Important flow-paths in the preconcentration of a sample using the apparatus shown in Fig. 14.20. (a) sample loading, (b) concentrator column washing, (c) sample stripping. Reprinted from 1170] with permission.
Chaprer 14
448
(ii)
It must transfer quantitatively these solute ions from the concentrator column to the analytical column during the stripping step. (iii) It must provide adequate resolution of the sample components on the analytical column. These multiple requirements will limit the number of eluents which are suitable for preconcentration methods. The following desirable eluent characteristics may be enumerated for the preconcentration of anions using conductivity detection: Selectivity It is preferable for the solute ions to be eluted within a range of capacity factors of 4-30.The lower limit is chosen to minimize interference of early eluted solutes from the relatively large solvent peak which often results in preconcentration chromatograms, whilst the upper limit ensures that excessive retention does not preclude reliable quantitation. (ii) Sensitivity Since the purpose of sample preconcentration is to improve the sensitivity of an ion chromatographic method, the eluent should be chosen to maximize the detectability of the solute ions. For this reason, an eluent anion with low limiting equivalent ionic conductance is preferred. In addition, it is desirable that the eluent anion be singly charged in order to provide the greatest detector response to the elution of univalent solute anions. (iii) Eluent pH Apart from the above considerations, the pH of the eluent exerts two additional important effects on the final chromatogram. In the first place, the presence of neutral, protonated forms of the eluent can result in the appearance of system peaks due to elution of these neutral components under a reversed-phase mechanism. Secondly, bicarbonate ion is present in the majority of samples due to absorption of carbon dioxide from the atmosphere and if quantitation of this species is not requued, the resultant large peak can represent a major interference to early eluted solutes. Both of these problems can usually be circumvented through the use of a fully ionized eluent, operated at pH = 6. Under these conditions, bicarbonate becomes fully protonated and is eluted from the column with the solvent front. fi)
A wide range of carboxylic and sulfonic acids has been evaluated for use as eluents i n preconcentration methods for anions [171]. Aromatic monosulfonic acids, such as p-toluenesulfonic acid and 2-naphthylamine-1-sulfonic acid, have proven to be the most suitable for use with conductivity detection, whilst aliphatic sulfonic acids with methyl-, heptyl- or octyl- side chains are applicable when direct spectrophotometric detection is employed. In addition, the longer chain aliphatic sulfonic acids can also be used with conductivity detection, provided that their surfactant properties are not intrusive.
Sample Handling in IC
449
Sample loading effects It is clear that sample preconcentration is not an open-ended technique and that practical limitations must exist on the amount of sample which can be loaded and recovered quantitatively. It is desirable that large sample volumes can be accommodated and that the sample be loaded at a high flow-rate in order to minimize the time required for the analysis. Studies with fixed-site anion-exchangeconcentrator columns [165] have shown that the maximum permissible flow-rates and sample volumes are dependent on the nature of the eluent used to condition the concentrator column prior to sample loading. As the ion-exchange affinity of the eluent increases, then binding of weakly retained solutes onto the concentrator column reduces markedly with larger sample volumes. However if the eluent conforms to the requirements listed above, sample volumes as high as 100 ml may be loaded at a flow-rate of 8 ml/min, with quantitative binding of solute ions being maintained. It has been suggested that solute binding is improved if the concentrator column is conditioned using a weak eluent competing ion (e.g. hydroxide), with a stronger eluent (e.g. HC03’/C032-) then being employed for removal of the bound ions from the concentrator column [172]. Concentrator column characteristics It might appear at first sight that the ion-exchange capacity of the concentrator column should be as high as possible in order to provide ample ion-exchange sites for the binding of solute ions. Certainly, this situation will encourage quantitative solute binding, but as the ion-exchange capacity of the concentrator column increases, it becomes more difficult to transfer the bound ions onto the analytical column using a small volume of eluent. Attempts to use a high eluent strength for sample stripping and a lower strength for sample elution have not proven successful [ 1701, so the same eluent should be used for both purposes. In this case, the optimal total ion-exchange capacity of the concentrator column is approximately 40% of that of the analytical column [173]. Increasing the ion-exchange capacity of the concentrator column beyond this value leads to the requirement for larger strip volumes, causing interference with early eluted solutes and band broadening effects. The nature of the resin used to support the bonded ion-exchange functionalities can also exert a considerable effect on preconcentration. Studies have shown [173] that concentrator columns packed with aminated methacrylate and aminated styrenedivinylbenzene resins of similar ion-exchange capacity give markedly different performance in breakthrough experiments using a mixture of chloride, nitrate and sulfate. Both chloride and nitrate showed very poor retention on the styrenedivinylbenzene resin in comparison to that obtained using the methacrylate resin, Finally, it is pertinent to comment on the possibility of replacing the fixed-site ionexchanger in the concentrator column with a neutral, reversed-phase material which has been coated with an ion-interaction reagent (IIR). In the case of anion preconcentration, this IIR could be a very hydrophobic species such as cetylpyridinium ion or cetyltrimethylammonium ion. Provided that the IIR remains permanently bound to the stationary phase surface during sample loading, then an ion-exchange column can be produced [174]. The main attractions of this approach are that the nature of the
450
Chapter 14 03-
CI -
v02F-
F'
r
0
,
lb
l i m e (min)
$0
L
,
,
6
1
,
lim e (min.1
,
12
1
16
Fig. 14.22 Preconcentration of anions. (a) Standard mixture. Eluent 1.0 mM gluconate-borate. Column: Waters IC Pak A. Sample volume: 65 ml. Solute concentrations: 1.3 ppb fluoride, 3 ppb chloride, 4 ppb nitrite, 4 ppb bromide, 4 ppb nitrate, 6 ppb phosphate and 6 ppb sulfate. Chromatogram courtesy of Waters. (b) Preconcentration of anions in water purified by reverseacid at pH 6.0. Column: Waters IC Pak A. osmosis. Eluent: 0.4 mM 2-naphthylamine-1-sulfonic Sample volume: 6 ml, Solute concentrations: 5 ppb fluoride, 20 ppb chloride and 3 ppb nitrate. Reprinted from [ 1841 with permission.
functional group may be varied by re-coating the stationary phase with an alternative IIR, and the ion-exchange capacity of the concentrator column can be manipulated easily by altering the conditions under which the concentrator column is coated. It has been shown [175] that concentrator columns prepared in this way do not show the degree of binding of solute ions expected from consideration of their ion-exchange capacities alone. A comparison of a fixed-site concentrator column with one prepared by the permanent coating method showed that equivalent retention of solute ions was obtained only when the total ion-exchange capacity of the latter column was a factor of fifteen times higher than that of the former column. Less hydrophobic IIRs, such as tetrabutylammonium (TBA) ions, may also be used to condition a C 18 concentrator column for sample preconcentration. The obvious problem to be anticipated in this case is that the IIR will not adhere strongly enough to the (218 column during sample loading, resulting in incomplete binding of the solute. In practice, this problem does not occur, provided that the sample volume is kept relatively low. Thus, Au(CN)2- has been successfully preconcentrated from a 2 ml sample volume using TBA as the IIR [ 1761.
45 1
Sample Handling in IC
O.OE
:n
I n [plus Ca)
:0 01 V
c
e
n L
5:
0.04
n
a
0
I
8
I
I
I
12 16 20 2!L Time (min)
I
28
Fig. 14.23 Reconcentration of cations in river water. Eluent: tartrate gradient (0.35-0.50 M). Sample volume: 40 ml. Solute concentrations: 5 ppb copper, 47 ppb zinc, 0.9 ppb lead, 7.2 ppb nickel, 1.8 ppb cobalt, 38 ppb manganese, 430 ppb magnesium. Reprinted from [185] with
permission.
Preconcentration of samples of low ionic strength Most of the samples used for preconcentration methods consist of very dilute aqueous solutions. Examples include pristine waters [139, 1401, purified water [ 177, 1781, steam [179, 1801 and boiler feed water for power station generators [181-1831. In each case, the sample contains parts-per-billion levels of ionic species and is relatively free from organic impurities. Despite the low levels of ions present, accurate analysis may be essential in order to assess baseline levels for environmental studies, or to prevent damage to expensive equipment, such as steam turbines. The determination of anions in these samples can be illustrated by the preconcentration of a standard mixture using a fixed-site ion-exchange concentrator column and gluconate-borate eluent (Fig. 14,22(a)). The extreme sensitivity of this method is apparent. A chromatogram obtained for the preconcentration of a purified water sample using an aromatic sulfonic acid eluent is shown in Fig. 14.22(b). The determination of trace levels of metal ions in river water using a prcconcenuation technique is illustrated in Fig. 14.23. The analysis of samples of the above type is relatively straightforward and provided that the correct eluent is chosen, the condition of the concentrator column is periodically monitored, and the performance of the system is assessed routinely using recovery experiments, then a high level of confidence can be assigned to the results.
Chapter 14
452
1
0
I
L
8
1
I
12 16 Time (min.1
I
20
24
z'e
Fig. 14.24 Preconcentration of an aqueous extract of coastal vegetation leaf litter. The concentrator column was packed with aminated styrene-divinylbenzeneresin. Eluent: 1.0 m M
tetraborate, 4.2 mM boric acid and 1.0 mM gluconic acid. Wash volume: 200 p1. Strip volume: 650 pl. Solute concentrations: 50 ppb phosphate, 150 ppb sulfate and 200 ppb oxalate. The analytical column was a Waters IC Pak A. Reprinted from [ 1841 with permission.
Preconcentration of samples of high ionic strength It is a challenging prospect to attempt preconcentration analysis of trace components in samples which contain high levels of other ionic species. In such cases, it is likely that binding of the trace components to the concentrator column will be adversely affected by mass-action influences of the bulk constituents. Indeed, successful preconcentration can be anticipated only after sample cleanup or when the ions of interest have a much higher affinity for the ion-exchange resin than do the matrix components. An example of the latter case is the determination of phosphate, sulfate and oxalate in a leaf litter extract taken from coastal vegetation [184]. Preliminary analysis of the extract showed high levels of chloride and nitrate. Two strategies were therefore employed to successfully analyze this sample. First, a high eluent pH was selected in order to convert the phosphate to HF'04*- and so increase its affinity for the ionexchange resin in the concentrator column. Second, a styrene-divinylbenzene ionexchange material was used in the concentrator column because this resin has been shown to have relatively poor affinity for chloride and nitrate. The final chromatogram obtained using gluconate-borate buffer at pH 8.5 as eluent, with a concentrator column packed with aminated polystyrene-divinylbenzneresin, is shown in Fig. 14.24.
Sample Handling in IC
453
In many cases it is beneficial to couple selective detection with sample preconcentration to achieve the desired sensitivity. An example of this approach is the determination of anions using direct spectrophotometric detection in the wavelength range 200-220 nm. Only a relatively small number of anions show absorbance under these conditions and if a suitable UV-transparent eluent is chosen, then selective analysis is possible.
Conclusions Sample preconcentration is a complex procedure and should not be considered to be a simple extension of direct injection IC. Care must be applied to the selection of both the eluent and the concentrator column to ensure quantitative retention on the concentrator column of the solute ions of interest, and their subsequent quantitative transfer onto the analytical column. The ability to optimize the wash and strip volumes of eluent for individual samples provides a high level of flexibility in attaining these goals. The technique can be applied to very dilute aqueous samples of low ionic strength and to more complex samples containing high levels of interfering ionic species. 14.6.4
Dialytic trace enrichment methods
Trace enrichment using concentrator columns suffers from the disadvantage of matrix dependence. It is therefore of interest to note that preconcentration can also be performed by Donnan dialysis. Moreover, this approach results in the sample ions being transferred to a solution of known composition, regardless of the nature of the sample matrix itself. That is, matrix normalization occurs. The principles of Donnan dialysis, wherein solute ions are transferred from the sample to a receiving electrolyte solution via an ion-exchange membrane, have been discussed in Section 14.4.4. When applied to preconcentration, all that needs to be done is to ensure that the volume of the receiver solution is considerably less than that of the sample. Transfer of the solute ions is never complete, so the enrichment factors achieved are somewhat less than the volume ratio existing between the sample and receiver solutions. The volume of the receiver solution should therefore be kept as low as possible and typical apparatus [186, 1871 comprises a flat membrane inserted into the stirred sample (as shown schematically in Fig. 14.13), or a tubular membrane around which the sample solution flows [loll. The sample preconcentration itself is relatively straightforward to accomplish, but some important additional steps must be taken before the receiver solution can be injected onto an IC. The reason for this is the high ionic strength of the receiver, which is essential for effective Donnan dialysis to occur. In the case of cations, the optimal receiver solution consists of 0.1 M A12(S0& adjusted to pH 0.5 with sulfuric acid [186]. When injected into an ehent comprising 0.01 M tartrate buffer at pH 5 , the buffer capacity of the eluent greatly reduces the hydrogen ion concentration in the sample and the aluminium(II1) forms a strong, anionic complex with tartrate and so is effectively eliminated from interacting with the cation-exchange column. Anions may be dialyzed into a receiver solution comprised of 0.04 M Na2C03 and 0.16 M NaHC03 [187] and after dialysis, the receiver solution can be subjected to dual ion-exchange treatment (see
Chapter 14
454
Section 14.4.4) with a cation-exchange resin in the hydrogen form. This process converts the receiver components to dissolved carbon dioxide, which is removed by application of a vacuum. The final solution therefore consists of the solute anions in water. The enrichment factors achieved in the above examples were approximately 80 for cations after 1 hour of dialysis, and approximately 15 for anions after 30 min of dialysis. Donnan dialysis therefore offers useful preconcentration but may have some limitations in application because of constraints on the nature of the receiver solution and the eluent to be used for the final IC analysis.
14.7 MATRIX ELIMINATION METHODS 14.7.1
Introduction
To conclude this Chapter, the technique of matrix elimination will be discussed briefly. Matrix elimination will be defined as any instrumental method whereby matrix components are removed from the sample. It is therefore quite distinct from the removal of matrix components using such sample treatment procedures as passing the sample through a cartridge column. Matrix elimination can be applied on-column, usually with the aid of switching valves, or post-column, and has the chief advantage that it can be easily automated. These approaches are described below. 14.7.2
On-column matrix elimination
One simple way of eliminating the detector signal produced by interfering matrix Components is to divert the column effluent to waste during elution of these matrix components. This approach has been described for the determination of ppm levels of sulfate in the presence of 0.05% chloride [l88]. Here, the sample was injected onto an analytical column and a six-port valve was used to direct the column effluent either to waste or to a second analytical column. The eluent fraction corresponding to chloride was vented to waste, whilst that corresponding to sulfate was passed to the second column and thence to the detector. A similar approach has been shown to be successful for the determination of alkaline earth cations in pharmaceutical preparations, in which alkali metal cations are present in excess [1891.
Matrix elimination with concentrator columns Matrix elimination can be combined with sample preconcentration using a concentrator column, provided the matrix components do not interfere with the concentration process. The method is therefore especially suited to samples in which the analytes show very strong retention on the concentrator column. An example of such an application is the determination of aurocyanide in tailings solutions produced from a cyanidation process for the extraction of gold from its ores. These tailings solutions contain very low levels of aurocyanide (10-20 ppb) in the presence of much higher levels of other metal cyano complexes, and require sample preconcentration for reliable analysis. Preconcentration of the tailings solution on a C 18 concentrator column conditioned with tetrabutylammonium ion as the ion-interaction reagent yields
Sample Handling in IC
455
0
pz
Au
1 I
0
I
2
I
L
I
I
I
I
h I
l
6 8 10 12 1L 16 Time [min)
1
1
1
1
1
0
2
L
6
8
1
1
1012
Time (mtn)
(b) Fig. 14.25 Matrix elimination in the analysis of gold(1) cyanide in mine process liquors. Chromatogram (a) shows the interference of 5 ppm of hexacyanocobalt (111) on the preconcentration determination of 2 ml of 50 ppb gold(1) cyanide. Chromatogram (b) shows a process liquor containing 25 ppb gold and large excesses of other metal cyan0 complexes, preconcentrated using the two valve system shown in Fig. 14.20. Separator column: Waters Nova Pak c18. Concentrator column: Waters c18 Guard Pak. Analytical eluent: 3070 (v/v) acetonitrile-watercontaining 5 mM Waters Low UV PIC A. Wash volume: 800 p1 of 2080 (v/v) acetonitrile-water containing 5 mM Waters Low UV PIC A. Strip volume: 1600 pl of the analytical eluent. Detection: direct spectrophotometryat 214 nm. Reprinted from [I901 with permission.
quantitative binding of gold for sample volumes less than 2 ml, but other metal cyanides are also retained to some extent and produce severe interference in the final chromatogram (Fig. 14.25(a)). Matrix elimination on the concentrator column can be achieved using similar apparatus to that shown in Fig. 14.20, but adapted to permit the use of two eluents. By careful control of the strengths and volumes of the eluents used to wash the concentrator column and to transfer the adsorbed aurocyanide to the analytical column, it is possible to largely eliminate the interferences without loss of aurocyanide (Fig. 14.25(b)). This process can be applied readily to a variety of other sample types. An alternative approach to matrix elimination using concentrator columns is to add a component to the sample which acts as a strong eluent for interfering matrix components, but is a weak eluent for analyte ions. An example of this i s the
456
Chapter 14
determination of trace amounts of calcium and magnesium in brines. Acidification of the sample before loading onto a cation-exchangeconcentrator column causes the sodium ions to pass through the concentrator column to waste, whilst the alkaline earth cations are retained [191]. The latter can then be transferred to the analytical column with a suitable eluent. 14.7.3
Post-column matrix elimination
In some cases, it is possible to eliminate a matrix peak after it has eluted from the analytical column. For example, Brown et al. [ 1921 have observed that the interference of dopamine on the determination of anions in a pharmaceutical product using a phthalate eluent with indirect spectrophotometric detection could be eliminated by passing the column effluent through a hollow-fibre suppressor device. Under the conditions used, the dopamine became protonated and diffused through the cationexchange membrane comprising the hollow fibre suppressor, so that no interfering peak was monitored by the UV detector. Re-injection techniques, wherein a designated portion of the column effluent containing the analyte ions is collected and returned to the analytical column for further separation, represent yet another approach to post-column matrix elimination. An example of this method is the determination of low ppb levels of selenate, selenite and arsenate in drinking water, where nitrate may be present at concentrations of up to 10 ppm [193]. The band of eluent corresponding to the elution of the desired analyte ion is passed to an in-line concentrator column, before being re-injected onto the analytical column. This approach is applicable only to suppressed IC because the presence of eluent ions in the effluent from a non-suppressed system would preclude the preconcentration step. A statistical evaluation of the manner in which the analyte peak is collected before preconcentration and re-injection has been reported [ 1941. When the interfering matrix component is UV absorbing and the indirect spectrophotometric detection mode is employed, it may be possible to eliminate the matrix peak by a judicious choice of detection wavelength. This can be illustrated by reference to eqn. (12.7), which shows the factors which influence the detector signal in spectrophotometric detection. If a detection wavelength is selected such that:
where ES and EE are the molar absorptivities of the solute and eluent ions, respectively, then no peak should be observed for that particular solute. For example, the peak for nitrate ion in samples prepared by nitric acid digestion can be eliminated using a benzenesulfonate eluent and a detection wavelength of 239 nm [195]. Fig. 14.26 shows the chromatograms obtained for a mixture of anions at 239 nm and 225 nm. Note that the detection sensitivities for chloride and nitrite change with wavelength and that the peak direction for nitrite reverses at 239 nm because of a change in sign for eqn. (12.7) at this wavelength.
Sample Handling in IC
457
B
A
0.004 A
1
Time
-
Fig. 14.26 Elimination of the peak of an absorbing anion (nitrate). Column: TSK-GELIC Anion PW. Eluent: 1 mM benzenesulfonate. Detection: UV absorption at 225 nm (a) and 239 nm (b). Peak identities: (1) chloride, (2) nitrite, (3) nitrate. The arrow in (b) shows the elution position of nitrate. Reprinted from [1951 with permission.
14.8 REFERENCES 1 2
3 4 5 6 7 8 9 10 11 12 13
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Kennedy W.T., Hubbard W.B. and Tarter J.G., Anal. Lett., 16 (1983) 1133. Wilson S.A. and Gent C.A., Anal. Lett., 15 (1982) 851. Wilson S.A. and Gent C.A., Anal. Chim. Acta, 148 (1983) 299. McCrory-Joy C., Anal. Chim. Acta, 181 (1986) 277. Evans K.L. and Moore C.B., Anal. Chem., 52 (1980) 1908. Busman L.M., Dick R.P. and Tabatabai M.A., Soil Sci. SOC.Am. J., 47 (1983) 1167. Chakraborti D., Hillmann D.C.J., Zingaro R.A. and Irgolic K.J., Fres. Z . Anal. Chem., 319 (1984) 556. Colaruotolo J.F., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion Chromatographic Analysis of EnvironmentalPollutants, Vol. I, Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 149. Hall G.E.M., MacLaurin A.I. and Vaive J., J. Geochem. Exp., 26 (1986) 177. Pohlandt C. and Cameron A., Mintek Report No. M153 (1984). Ishibashi W., Kikuchi R. and Yamamoto K., Bunseki Kagaku, 30 (1981) 604. Colaruotolo J.F. and Eddy R.S., Anal. Chem., 49 (1977) 884. Quinn A.M., Siu K.W.M., Gardner G.J. and Berman S.S., J . Chromatogr., 370 (1986) 203. Evans K.L., Tarter J.G. and Moore C.B., Anal. Chem., 53 (1981) 925. Mizisin C.S., Kuivinen D.E. and Otterson D.A., in Mulik J.D. and Sawicki E. (Eds.), Ion Chromatographic Analysis of EnvironmentalPollutants, Vol. 11, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 129. Smith F., Jr., McMurtrie A. and Galbraith H., Microchem. J., 22 (1977) 45. Kreling J.R., Block F., Louthan G.T. and DeZwaan J., Microchem. J., 34 (1986) 158. Saitoh H. and Oikawa K., Bunseki Kagaku, 31 (1982) E375. Hurst W.J., Snyder K.P. and Martin R.A., Jr., J. Liq. Chromatogr., 6 (1983) 2067. McCormick M.J., Anal. Chim. Acta, 121 (1980) 233. Murayama M., Suzuki M. and Takitani S., J. Chromatogr., 463 (1989) 147. Kan M., Ohnishi K. and Shintani M., Yakugaku Zasshi, 104 (1984) 763. Smith R.E. and Davis W.R., Topical Report BDX-613-3053(1984). Basta N.T. and Tabatabai M.A., Soil Sci. SOC.Am. J., 49 (1985) 76. Nadkami R.A. and Pond D.M., Anal. Chim. Acta, 146 (1983) 261. Dionex Application Note 13. Viswanadham P.,Smick D.R., Pisney J.J. and Dilworth W.F., Anal. Chem., 54 (1982) 2431. Hurst W.J., Evans S.L., White W.W. and Miller K.L., LC.GC, 6 (1988) 5. Matsushita S., And. Chim. Acta, 172 (1985) 249. Oikawa K., Saito H., Sakazume S. and Fujii M., Bunseki Kagaku, 31 (1982) E251. Kehr P.F., Leone B.A., Harrington D.E. and Bramstedt W.R., LC.GC, 4 (1986) 1118. Buytenhuys F.A., J . Chromatogr., 218 (1981) 57. DuVal D.L., Rogers M. and Fritz J.S., Anal. Chem., 57 (1985) 1583. Bagchi R. and Haddad P.R., Proc. 9th. Amt. Symp. Anal. Chem., 1987, p. 147. Hill R.A., J. HRC & CC, q(1983) 275. Green L.W. and Woods J.R., Anal. Chem., 53 (1981) 2187. Golombek R. and Schwedt G., J. Chromatogr., 367 (1986) 69. Waters IC Lab. Report No. 258. Moore H., Riusech D.J. and Duer W.C., J. Vet. Res., 2 (1987) 297. Nordmeyer F.R. and Hansen L.D., Anal. Chem., 54 (1982) 2605.
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Cox J.A. and Twardowski Z., Anal. Chim. Acra, 119 (1980)39. Jones W.R. and Jandik P., J. Chromatogr. Sci., 27 (1989)449. Cox J.A. and Tanaka N., Anal. Chem., 57 (1985)385. Cox J.A. and Tanaka N., Anal. Chem., 57 (1985)383. Cox J.A. and Twardowski Z.. Anal. Chem., 52 (1980)1503. Cox J.A. and Litwinski G.R., Anal. Chem., 55 (1983)1640. Pettersen J.M., Johnsen H.G. and Lund W.. Talanta, 35 (1988)245. Cox J.A. and Dabek-Zlotorzynska E., Anal. Chem., 59 (1987)534. Cox J.A. and Twardowski 2..A d . Lett., 13 (1980)1283. Jackson P.E., Haddad P.R. and Dilli S . , J . Chromutogr.,295 (1984)471. Ferguson N.M., Lindberg S.E.and Vargo J.D., Int. J . Environ. Anal. Chem., 1 1 (1982)61. Kalbasi M. and Tabatabai M.A., Commun. 5oil Sci. Plant Anal., 16 (1985)787. Haddad P.R. and Croft M.Y., Chromurographia,21 (1986)648. Cox D., Harrison G., Jandik P. and Jones W., Food Technol., July (1985)41. Cox D., Jandik P. and Jones W., Pulp Pap. Canada, 88 (1987)T318. Osterloh J. and Goldfield D., J. Lig. Chromutogr.,7 (1984)753. Buchberger W. and Winsauer K., Mikrochim.Acta, 1985 111 (1986)347. Wellbum A.R., New Phyrol., 100 (1985)329. Bear G.R., J. Chromurogr.,371 (1986)387. Hironaka T., Oshima, M. and Motomizu S.. Bunseki Kaguku, 36 (1987)503. Tan L.K. and Dutrizac J.E., J. Chromutogr.. 405 (1987)247. Kamiura T., Mori Y. and Tanaka M., Anal. Chim.Acra, 154 (1983)319. Zolotov Y .A., Malofeeva G I . , Petrukhin O.M.and Timberbaev A.R., Pure & Appl. Chem.,
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59 (1987)497. Marko-Varga G., Csiky I. and Jonsson J.A., Anal. Chem., 56 (1984)2066. Reiter C., Muller S. and Muller T., J. Chromurogr.,413 (1987)251. Slingsby R., Dionex Corporation Technical Report, July 1987. Frei R.W. and Lawrence J.F. (Eds.), Chemical Derivatization in Analytical Chemistry,Vol. 1, Plenum, New York, 1981. Waters Ion Brief No. 881 10. Robertson W.G. and Scum D.S.,Clin. Chim. Acra, 140 (1984)97. Jun Z., Oshima M. and Motomizu S., Analyst (London), 113 (1988)1631. Hill C.J. and Lash R.P., Anal. Chem.,52 (1980)24. Verma K.K., Sanghi S.K., Jain A. and Gupta D., J. Chromatogr., 457 (1988)345. Sevenich G.J. and Fritz J.S., Anal. Chem., 55 (1983)12. Silinger P., Plat. Sutf. Fin., 72 (1985)82. Nonomura M., Anal. Chem., 59 (1987)2073. DuVal D.L., Fritz J.S. andGjerde D.T., Anal. Chem., 54 (1982)830. Jenke D.R., J. Chromutogr.Sci., 24 (1986)352. Haddad P.R. and Heckenberg A.L., J. Chromurogr.,447 (1988)415. Okada T.and Kuwamoto T., Anal. Chem., 57 (1985)258.
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Beveridge A., Pickering W.F. and Slavek J.. Talantu,35 (1988) 307. Uchiyama S., Tohfuku Y.,Suzuki S. and Muto G., Anal. ChimActa, 174 (1985) 313. Hertz J. and Baltensperger U.,LC,2 (1984) 600. Fulmer M.A., Penkrot J. and Nadalin R.J., in Mulik J.D. and Sawicki E. (Eds.), Zon ChromatographicAdysalysis of Environmental Pollutants. Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 381. Saigne C., Kirchner S. and Legrand M., Anal. Chim Acta. 203 (1987) 11. Legrand M., De Angelis M. and Delmas R.J.. Anal. Chim Acta. 156 (1984) 181. Cassidy R.M. and Elchuk S., J. Chromatogr. Sci., 19 (1981) 503. Bagchi R. and Haddad P.R., J. Chromatogr.,351 (1986) 541. Grunau J.A. and Swiader J.M., in Jandik P. and Cassidy R.M. (Eds.) Advances in Ion Chromarogruphy,Vol. 1, Century International, Inc., Franklin, MA, 1989, p. 361. Mowrey R.A., Jr., J. Chromatogr. Sci., 23 (1985) 22. Trumbore C.N., Trembley R.D., Penrose J.T., Mercer M. and Kelleher F.M., J. Chromatogr.,280 (1983) 43. Hutchins S.R., Haddad P.R. and Dilli S., J. Chromutogr.. 252 (1982) 185. Dasgupta P.K., Soroka K. and Vithanage R.S.. J. Liq. Chromatogr., 10 (1987) 3287. Haddad P.R. and Foley R.C.L., J. Chromatogr.. 407 (1987) 133. Erkelens C., Billiet H.A.H., De Galan L. and De Leer E.W.B., J. Chromarogr..404 (1987) 67.
150 151 152 153 154 155 156 157 158 159 160 161
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Jenke D.R. and Pagenkopf G.K.,Anal. Chem., 55 (1983) 1168. Siriraks A., Girard J.E. and Buell P.E., Anal. Chem, 59 (1987) 2665. Jenke D.R., J. Chromatogr.,370 (1986) 419. Okada T., Bunseki Kagaku, 36 (1987) 702. Ivey J.P. and Davies D.M..Anal. Chim. Acta, 194 (1987) 281. Davies D.M. and Ivey J.P., Anal. Chim. Acta, 194 (1987) 275. Okada T. and Kuwamoto T., J. Chromatogr.,350 (1985) 317. Buchholz A.E.. Verplough C.I. and Smith J.L., J. Chromatogr..20 (1982) 499. Oikawa K. and Saito H., Chemasphere, 11(1982) 933. Heckenberg A.L. and Haddad P.R., J. Chromutogr.,299 (1984) 301. Kourilova D., Thao N.T.P. and Krejci M., Int. J. Environ. Anal. Chem. 31 (1987) 183. Dionex Application Note 32. Conklin G.C., Smith J.L. and Gross G.W., J. Chromatogr. Sci., 26 (1988) 80. Andrew B.E.. LC.GC, 4 (1986) 1026. Andrew B.E., Paper presented at 7th Aust. Con5 Anal. Chem, Adelaide. August (1983). Haddad P.R. and Jackson P.E., J. Chromatogr.,367 (1986) 301. Dionex Technical Note 8R. Cassidy R.M. and Elchuk S., J. Chromatogr. Sci., 18 (1980) 217. Wetzel R.A., Anderson C.L., Schleicher H. and Crook G.D., Anal. Chem, 51 (1979) 1532. Haddad P.R. and Heckenberg A.L.. J. Chromutogr..318 (1985) 279. Heckenberg A.L. and Haddad P.R.. J. Chromatogr.. 330 (1985) 95. Jackson P.E. and Haddad P.R., J. Chromutogr.,355 (1986) 87. Takehara H., Bunseki Kagaku, 36 (1987) 457. Jackson P.E. and Haddad P.R., J. Chromatogr.,389 (1987) 65. Cassidy R.M. and Elchuk S.. J. Chromatogr., 262 (1983) 311. Haddad P.R. and Jackson P.E., J. Chromatogr., 407 (1987) 121.
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176 Haddad P.R. and Rochester N.E., Anal. Chem., 60 (1988) 536. 177 Krull IS., in M. Bernhard, F.E. Brinkrnan and P.J. Sadler (Eds.) The ImDortance of Chemical ”Speciation”in EnvironmentalProcesses, Springer-Verlag Berlin, Heidelderg, 1986, p 579. 178 Dionex Application Note 34. 179 Borman S., Anal. Chem.. 52 (1980) 1409A. 180 Pensenstadler D.F. and Fulrner M.A., Anal. Chem., 53 (1981) 859A. 181 Brandt F. and Trost R., Vorr.-VGB-Konf. T h e m Krafhoerk”, (1983) 24. 182 Dionex Application Update 101. 183 Law J.J., Power Eng., 85 (1981) 94. 184 Jackson P.E. and Haddad P.R., J . Chromatogr.,439 (1988) 37. 185 Cassidy R.M., Elchuk S. and McHugh J.O., Anal. Chem., 54 (1982) 727. 186 DiNunzio J.E. and Jubara M., Anal. Chem., 55 (1983) 1013. 187 Cox J.A. and Tanaka N., Anal. Chem., 57 (1985) 2370. 188 Naish P.J., Analyst (London), 109 (1984) 809. 189 Jenke D.R., Anal. Chem., 59 (1987) 624. 190 Haddad P.R. and Rochester N.E.,J. Chromatogr., 439 (1988) 23. 191 Dionex Application Update 106. 192 Brown D., Payton R. and Jenke D., Anal. Chem., 57 (1985) 2264. 193 Hoover T.B. and Yager G.D., Anal. Chem., 56 (1984) 221. 194 Hoover T.B. and Yager G.D., J . Chromatogr. Sci., 22 (1984) 435. 195 Okada T. and Kuwamoto T., J. Chromatogr., 325 (1985) 327.
463
Chapter 15 M e th ods D e ve lopm e n t 15.1 INTRODUCTION The preceding Chapters of this book have revealed that there is a wide variety of separation and detection methods available for IC. The development of a suitable procedure for a desired analysis can therefore present the chromatographer with a somewhat confusing array of choices. However, consideration of a number of fundamental questions can assist in reducing the range of choices to a manageable level. These questions include: (i) (ii) (iii) (iv) (v) (vi)
Which ions are to be separated? What is the sample composition? What are the concentration levels of the ions of interest in the sample? What columns are available? What detectors are available? Is there a suitable (or related) method in the literature?
The first two of these questions are the most important in that they define the analytical problem. Question (i) enables us to narrow the range of choices for the separation method, since many analyte species will be amenable to separation using specified techniques. Moreover, the choice of separation method is often influenced by more pragmatic considerations, such as the types of columns available at the time the analysis is required (question (iv)). The sample composition allows us to anticipate the likely inte.rferences and to estimate the degree of sample preparation which will be required. This information leads to the choice between selective and universal detection, which when coupled with the answers to questions (iii) and (v), gives sufficient grounds for the selection of the most suitable detection method. In this Chapter, we will consider the two major steps involved in methods development for 1C. The first of these steps is the selection of appropriate chromatographic parameters (i.e. the separation mode, the detection mode and the type of eluent), whilst the second step is the optimization of the eluent composition. The diversity of IC methods precludes a detailed discussion of this topic, so methods development procedures will be treated in outline only. The interested reader seeking further detail is referred to the discussion of separation and detection presented in earlier Chapters.
SEPARATION MODE
CLASS OF ANALYTE
I
I Inorganic ions F; CI; SO$; etc.
I
Organic ions carboxyiates, sullonates c C 4
k
DETECTION MODE
m -
-
Direct Spec, Conductivity
Selectlre
Uaiverrai 1
Hydrophilic ions Inorganic ions
Ion-exclusion,
I-
1
*-
1
Amverometrv -
I
0ANIONS
Indirect Spec
Amperometry,
I-
va
-,
Organic and inorganic ions
I',ClOi * suironates > ~4
Conductfvity, Indirect Spec
Ion-exchange, Ion-interaction Selecth
Dlrect Spec, Amperometry
Fig. 25.2 Scheme for the development of a method for the determination of anions by IC. Direct Spec = direct spectrophotometry, Indirect Spec = indirect specnophotometry,Atomic spec = atomic spectroscopy.
P$ z
Methodr Development
465
15.2 SELECTION OF APPROPRIATE CHROMATOGRAPHIC PARAMETERS 15.2.1 The separation method Anion separations Fig. 15.1 shows a schematic representation of the most commonly employed separation methods for different classes of anionic analytes. This scheme was proposed originally by Wetzel el al. [I J and has been both adapted and updated in the version shown. It must be emphasized at the outset that a schematic such as Fig. 15.1 can show only the more commonly used options and in many specific examples, ions will be separable using approaches not included in the scheme. However, the general trends shown are offered as an introductory guide to suitable separation methods. We can see that anions may be subdivided broadly into hydrophilic and hydrophobic ions. Within each class, we can further distinguish between those analytes which are the conjugate bases of strong acids and therefore exist as anions over the majority of the pH scale, and those analytes which are the conjugate bases of weak acids and may therefore exist as neutral, undissociated species over a significant pH range. The distinction between these two classes will be made by refemng to the former group as those with pKa < 7, and the latter group as those with PKa > 7. The value of PKa chosen to delineate these groups is somewhat arbitrary and it may be difficult to decide where some analytes (e.g. Pod3-) should be placed. The intention therefore is to give a very general classification. Fig. 15.1 suggests that strong acid anions, whether they be hydrophilic or hydrophobic in nature, are best separated using their size and charge as the primary considerations. This leads to ion-exchange or ion-interaction as the most favourable separation methods. On the other hand, weak acid anions are more suited to ionexclusion or ion-suppression methods, wherein they are chromatographed in their neutral, protonated forms. Cation separations Fig. 15.2 shows a schematic representation of the most commonly employed separation methods for cations. Once again, this scheme is an updated version of that published by Wetzel et al. [l]. In the case of cations, the distinction between the degree of ionization of different solutes is of minor importance since virtually all of the cations falling under the general umbrella of IC are fully ionized, with the exception of ammonia and some other weak bases. Similarly, the division of analytes into hydrophilic and hydrophobic species is of less significance for cations than was the case for anions, since most underivatized cations fall into the former class. In view of this, separation methods for cations are dominated by ion-exchange and ion-interaction techniques. We can note, however, that both of these approaches give best results for polyvalent cations when employed with a complexing agent in the eluent, which serves to decrease the very strong interaction of many analyte cations with the stationary phase.
- Alkali mstal ions, N H J
,
Ion-exchange
Universal
- Alkaline earth
Iiydrophilic ions
-
-
Transition metal ions
,
Conductivity, Indirect Spec
,
Atomic Spec,
Ion-interaction Selective
i
Ion-exchange, lon-interaction
Rare earth ions
0
Conductivity, Indirect Spec
~,,
Universal
PCR
CATIONS
I
I Amines < C3
Ion-exchange, Ion-interaction
Univ
Conductivity
Conductivity Hydrophobic ions
Amines
=- C3
Fig. 25.2 Scheme for the development of a method for the determination of cations by IC. PCR = Post-column reaction, Direct Spec = direct spectrophotometry,Indirect Spec = indirect spectrophotornetry, Atomic spec = atomic spectroscopy.
P5 z
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467
The detection mode
The major factors to be considered in the selection of a suitable detection mode for a particular analysis are the detection limits required and the interferences likely to be found in the sample. Detection limits and working concentration ranges applicable to most detection methods are well documented (see Chapters 9-13) and often permit a rapid selection of the most appropriate technique to be made. For example, the determination of parts-per-billion levels of S032-in foods can be accomplished only with the aid of amperometric detection. On the other hand, parts-per-million levels of the same ion can be determined satisfactorily using conductivity detection. The interferences present in the sample influence whether a selective or universal detection mode is to be employed. Samples with relatively low levels of interfering species can be analyzed using a universal detection mode, such as conductivity or indirect spectrophotometry, whilst selective detection is often necessary when interference levels are high. For example, the determination of NO3- in river water can be approached using conductivity detection, whilst determination of the same ion in saline waters requires the use of a selective detection method, such as direct spectrophotometry. Nonselective detectors yield more analytical information than do selective detectors, but place greater demands on the separation step. Figs. 15.1 and 15.2 include the most commonly applied detection method(s) for each group of analyte ions. Conductivity measurements are preferred for the nonselective detection of strongly ionized acids and bases. Amperometry, direct spectrophotometry, atomic spectroscopy or post-column reactions are often used when selective detection is required. 15.2.3
The nature of the eluent
When the separation and detection modes have been chosen, the final choice which must be made is the type of eluent to be used. This choice is often simplified by the nature of the detection method, since many detection methods require the use of specific classes of eluents. For example, direct spectrophotometric detection can be utilized only when the eluent is transparent (or at least only weakly absorbing) at the detection wavelength. However, when universal detection is to be used, the chromatographer can be faced with wide range of potential eluent species. This point can be well illustrated by reference to conductivity detection, for which more than 50 different eluent species have been employed. In these cases, the best approach is to locate a published IC method in which the ions of interest, or similar ions, have been separated. It is specifically for this purpose that the very extensive applications Tables are provided in Part V of this book. These applications are arranged according to sample type so that relevant methods can be located rapidly.
Chapter 15
468
15.3 OPTIMJZATION OF THE ELUENT COMPOSITION The final step in the process of methods development is to select the specific eluent composition which provides the desired separation. At this stage, we must decide: The concentration of the eluent species. The eluent pH. Is there need for any additional eluent components (e.g. organic modifiers)? Is gradient elution necessary?
(i) (ii) (iii) (iv)
These decisions may be reached either by a trial-and-error process or through the use of a systematic approach, often using a computer. These two alternatives are discussed below. 15.3.1
Empirical selection of eluent composition
The empirical, or trial-and-error, method for selecting the optimal eluent composition is the most widely used approach. Here, an initial eluent composition is selected from the literature and this eluent is then applied to the desired analysis, often using standard mixtures to evaluate the separation. If the resultant separation is unsatisfactory, the eluent composition is varied, after consideration of known eluent characteristics. These characteristics have been discussed in detail in Chapters 2-8. This process is repeated until the desired separation is achieved. If all attempts meet with failure, it is customary to exploit secondary eluent effects, such as the addition of organic modifiers, in an effort to alter the chromatographic selectivity. The empirical approach is often very time-consuming and its success depends greatly on the level of experience (or good fortune) of the operator. IC columns are usually slow to equilibrate to a new eluent composition, which leads to considerable wastage of time, even when each new eluent examined is an improvement on its predecessor. Further problems often arise when the newly developed separation is actually applied to the sample, leading to the necessity for a further series of optimization experiments.
15.3.2
Principles of computer optimization procedures
An attractive alternative to the trial-and-error method is the use of a systematic, computer-based procedure for the selection of eluent composition. Such procedures have been used widely in other liquid chromatographic techniques, especially reversedphase liquid chromatography (RPLC)[2], and generally follow the sequence of steps outlined below: (i) (ii) (iii) (iv)
Definition of the optimization problem. Selection of an optimization search area. Acquisition of retention data using an appropriate strategy. Evaluation of potential separations in the search area using a suitable criterion.
Methods Development
469
(v) Construction of a response surface. (vi) Selection of the optimal eluent composition.
Defining the optimization problem The key equation in optimization describes the factors which influence chromatographic resolution. For two solutes, this resolution can be defined as: (15.1)
where Rs is the resolution, a is the separation factor (given by the ratio of capacity factors for the two solutes between which resolution is being calculated), k' is the average capacity factor for the two solutes under consideration, and N is the number of theoretical plates for the column on which the separation is performed. Eqn. (15.1) shows that Rs is influenced by three, somewhat independent, factors. The first is N, the second is k and the third is a. The plate count, N, exerts the smallest influence on Rs,since it can be seen that N must increase by a factor of 4 to achieve a twofold improvement in Rs. The retention (capacity factor) term in eqn. (15.1) can be optimized independently of the other terms simply by ensuring that the capacity factors for the two solutes to be separated are neither too high nor too low. Capacity factors larger than 1 are desirable to eliminate interference with solvent peaks, and for capacity factors greater than 10,the retention term in eqn. (15.1) exerts almost no effect on the resolution. For these reasons, retention can be considered to be optimized if capacity factors fall within the range 1 c k c 10. The third factor in eqn. (15.1) is the most important, since its'magnitude is determined by the value of a, which in turn is a measure of the ability of the chromatographic system to select between the two solutes. For this reason, the optimization problem can be considered to be one of maximizing chromatographic selectivity. In RPLC, selectivity can be varied most conveniently simply by altering the mobile phase composition.
The search area The range of eluent compositions which can be considered in the optimization of selectivity is potentially infinite. It is possible to restrict the number of mobile phases in RPLC optimizations by defining a search area of those mobile phases which satisfy the retention condition (i.e. all solutes to be separated are eluted within the range lek'e10). In this way, the number of potentially useful mobile phase compositions is reduced to a manageable level. Optimization s trategies The next step in the optimization process is to obtain information on the retention behaviour for the solutes in question, over the eluent compositions to be considered. This retention information will ultimately be used to assess the separations which can be achieved, leading to selection of the optimal eluent composition. Several distinct strategies can be applied to the task of acquiring knowledge of retention behaviour:
Chap& 15
4
L
*
i
a"
B
Parameter 2
Fig. 15.3 Operation of the Simplex algorithm. Initial experiments were undertaken with the parameters defined by points A, B and C. Point B gave the poorest result and on this basis, point D was selected as the next experiment to be performed.
(i) Factorial design methods The parameters to be optimized are used to define a search area over which an evenly spaced grid is drawn. Each intersection of grid lines defines a combination of parameters which represents a particular set of chromatographic conditions. Retention times are then measured at each of these points for each solute in the mixture to be separated. An equation is then fitted to the data for each solute, so as to describe the retention behaviour of that solute over the entire search area. In this manner, retention times at any eluent composition within the search area can be calculated. Clearly, this strategy requires a large number of chromatographic experiments. ( i i ) Scouting techniques In this approach, an initial experiment(s) is run using any desired mobile phase composition. A suitable algorithm is then applied to define subsequent experiments until the optimal mobile phase is reached. The best-known example of such an algorithm is the Simplex method [3], in which the results from three initial experiments are compared and a new experiment is selected by moving away from the mobile phase giving the worst result. The operation of this algorithm is depicted in its simplest form in Fig. 15.3, which shows three initial experiments A, B and C, for which experiment B yielded the worst separation. Experiment D is therefore selected as that most likely to yield an improved separation. This process continues until the same mobile phase continues to be selected. The chief disadvantage of this approach is that many experiments may be required before an optimum is attained.
Methods Development
47 1
(iii) Interpretive strategies Here, a limited number of experiments is conducted and the retention data obtained are fitted to an appropriate model which describes the relationship between retention time and mobile phase composition. This model then allows retention times to be predicted for any mobile phase in the search area. The reliability of these predicted retention times is dependent on the suitability of the retention model used. Optimization criterion Once retention data have been acquired for the search area, the quality of all chromatograms produced by the eluents comprising the search area must then be assessed. This is generally achieved using an optimization criterion which assigns a numerical rating to each of these potential chromatograms. The simplest criteria, termed elemental criteria [2], describe the degree of separation of two peaks only, and include parameters such as the separation factor a,the resolution R,, peak-to-valley ratios, and area overlap. These elemental criteria for each peak pair in a chromatogram may then be combined to give a composite criterion, which describes the quality of the chromatogram as a whole. For example, when Rs is used as the elemental criterion (as is commonly the case), then a suitable composite criterion might be the product of the Rs values for all adjacent peak pairs, as given by r in the following equation: n-
1
(15.2) i= I
Response surface The optimal mobile phase composition can be selected by locating the point in the search area which yields the highest value of the composite criterion. It is also common to display some form of response surface depicting the manner in which the composite criterion varies over the search area. 15.3.3 Application of computer Optimization to IC The optimization procedures developed for RPLC can often be applied with only minor modification to IC separations. The chromatographic selectivity in IC can be altered by varying both the nature of the stationary phase and the nature of the eluent, and it is therefore feasible for these parameters to be included in the optimization process. However, all optimization methods reported to date have used a specified stationary phase and eluent type, and have optimized only the composition of the eluent. This approach limits the scope of optimization procedures and it is hoped that a broadly based expert system capable ofaimultaneous optimization of the nature of the stationary phase, the eluent type and the eluent composition will be developed in the future.
47 2
Chapm15
I
I
1
1
0
5
10
15
‘/mi n
Fig. 15.4 Chromatogram obtained using the experimental conditions determined by Simplex optimization. Two Dionex anion pre-columns (4 X 50 mm) were used in series with a step gradient from eluent A (4.8 mM NaHCq / 4.7 mh4 Na2C03) to eluent B (7.2 mM NaHCO3 / 9.1 m M Na2Ca). Reprinted from [4] with permission.
Factorial design and Simplex methods Factorial design optimization strategies, wherein a specific stationary phase and range of eluent parameters are selected as the most likely to provide a desired separation, appear to be applicable IC. However, these methods have some major drawbacks; first, it is necessary that numerous experiments be undertaken and this can require a great deal of time because of the requirement to fully equilibrate the stationary phase with each new eluent composition. Second, the success of the optimization depends entirely on the suitability of the range of eluent parameters chosen. Simplex methods should also be applicable to IC since these require no knowledge of chromatographic behaviour and can be used for the simultaneous optimization of several parameters. Simplex optimization of eluent composition in IC has been reported for the separation of S032-, Sod2- and S2032- [4], and for minimizing the effect of ammonia on trace anion determinations in suppressed IC [ 5 ] . In the first case, a step gradient method was employed and the Simplex algorithm was used to optimize four variables; namely, the concentrations of NaHC03 and Na2C03 in both eluents employed for the gradient. The function to be minimized in the Simplex procedure was the sum of three terms. as follows: (i) (ii)
The retention time for ~2032-. An estimate of the separation between S 0 3 2 - and S042-, taken as the distance from the baseline to the valley between the peaks for these two ions. (iii) An estimate of the separation between the S04*- peak and the baseline shift caused by the eluent change in the step gradient.
Methods Development
473
clc1-
I
I
1
I
I
I
0
4
8
0
4
8 Time (min) Ib)
Time (min) (a)
1
12
Fig. Z5.5 Comparison of chromatograms obtained (a) under standard eluent conditions and (b) with a Simplex-optimized eluent. A Dionex HPIC AS4A column was used and the optimized eluent was 2.55 mM NaHCO.j/ 0.60 mM Nap203 @H9.62). Reprinted from [5] with permission.
Fig. 15.4 shows the chromatogram produced by the optimal eluent compositions selected using this procedure. The second example of Simplex optimization used a two-factor optimization to select the most suitable concentrations of NaOH and NaHC03 in the eluent. In this case, the critical factors in the separation were the resolution between the C1- peak and the water dip (eluted at a retention time of 1.3 min), and the length of the chromatogram (given by the retention time of S042-). The function calculated for each eluent composition was: (15.3)
The value of R increases as the separation of C1- from the water dip increases, and also as the retention time of Sod2- decreases. The first of these parameters has the greatest influence on R, since the second term in eqn. (15.3) is raised to the power of 0.25. The result of this optimization is shown in Fig. 15.5, in which chromatograms obtained with a standard eluent and a Simplex optimized eluent are compared. These examples indicate that Simplex optimization is of great practical value in IC and illustrate that the optimization criterion can be tailored to suit the requirements of the particular separation under study. However, it should again be noted that the Simplex method will usually require a large number of time-consuming experiments.
414
Chapter 15
N
6 ul
e
rr t
Fig. 15.6 Chromatograms obtained after optimization using an interpretive strategy. (a) The concentration of phthalate in the eluent was optimized at constant pH (5.3). (b) The eluent pH was optimized at constant concentration of phthalate in the eluent (5.0 mM). A Vydac 302 IC column was used. The eluent compositions were (a) 4.7 mM potassium hydrogen phthalate at pH 5.3, (b) 5.0 mM potassium hydrogen phthalate at pH 5.3. Reprinted from [6] with permission. interpretive methods Interpretive optimization strategies are potentially of great value in IC because they can limit the amount of experimentation required to select the optimal eluent. These strategies rely on a suitable retention model, which can be used to predict solute retention times for specified eluent conditions. In Chapters 5-7, we have discussed a range of such models applicable to the various separation methods used in IC. Whilst optimization using an interpretive method is possible with any of these models, only two examples have been reported 16, 71. Furthermore, these examples consider only anionexchange separations. In the first example (61, the optimization is conducted by first defining the search area of eluent compositions to be considered, after which retention data are obtained at eluent compositions forming the boundaries of the search area. A linear relationship is then assumed between log k and log [El, where E is the competing anion present in the
Methodr Development
415
eluent. This relationship has been discussed in detail in Section 5.2.1 and is summarized in eqn. (5.12). The retention model is then used to interpolate retention data for intermediate eluent compositions and the optimization criterion is calculated for all possible eluent compositions. The optimal eluent is then selected as that showing the highest criterion value. It must be remembered here that even when the strategy and retention model used are fully appropriate, the optimization is limited by the search area over which it applies. The above process has been used to optimize separately the pH and eluent concentration of phthalate eluents for the separation of anions on Vydac silica-based anion-exchange columns [6]. In each case, a range of eluent concentrations or pH values ( i . ~the . search area) was selected and retention data were obtained at the extreme values. That is, two experiments were conducted for each optimization. Fig. 15.6 shows the chromatograms obtained when the eluent concentration was optimized over the range 210 mM using a fixed pH of 5.3 (Fig. 15.6(a)), and when the eluent pH was optimized over the range 4.3-6.0 using a fixed phthalate concentration of 5 mM (Fig. 15.6(b)). It can be seen that both approaches led to the selection of very similar eluent compositions. Fig. 15.6 also shows that the optimization was successful, despite the fact that the pH range considered embraced both singly and doubly charged species in the eluent. In the second example [7] of interpretive optimization in IC, the same retention model has been applied to the optimization of phthalate eluents containing two eluting species, by using the model to construct window diagrams to portray elution behaviour. Window diagrams show the variation of an optimization criterion over the range of eluent compositions considered. For example, the separation factor, a,for all peak pairs in a solute mixture can be plotted against eluent concentration to yield a result such as that shown in Fig. 15.7, which depicts a typical IC window diagram for three solutes, A, B and C. The horizontal broken line represents the minimum acceptable criterion level (in this case, a = 1S), below which separation is considered to be inadequate. The solid lines represent the separation factors for each pair of peaks in the mixture. It can be seen that the separation between peaks C and B is the critical factor in achieving a desired separation. Separation of this pair of peaks (and all other peak pairs in the mixture) is above the threshold of a = 1.5 in the shaded area, but the optimal eluent is selected to be 4.6 mM, since this eluent would provide the fastest separation commensurate with the desired minimum acceptable separation.
Summary Computer optimization techniques have been applied to IC only on a limited basis. Factorial design strategies and scouting methods such as Simplex optimization can be applied to IC, but the number of experiments involved may represent a disadvantage because of the time required for IC columns to equilibrate to each new eluent. Interpretive strategies based on suitable retention models represent an attractive approach, but to date have been used successfully only for the optimization of a single eluent parameter at a time. More advanced optimization methods, such as an expert system capable of selecting the stationary phase, eluent parameters and detection parameters, are feasible provided a reliable rctention model is used.
476
Chapter 15 5
L
L
0
z3
1
0
1
2
3
4
5
6
[Eluent], m M Fig. 15.7 Typical window diagram for IC. Adapted from [7].
15.4 MULTI-DIMENSIONAL (COUPLED) IC METHODS 15.4.1
Introduction
In this Chapter, and indeed throughout the majority of this book, we have assumed that a desired IC method can be developed using the correct combination of a single separation method and a single detection method. In some cases, this assumption is not true and it may be necessary to utilize a combination of separation methods. This approach can be called multi-dimensional, or coupled, IC. For the purposes of the discussion in this Chapter, we will define multi-dimensional IC to include columnswitching techniques, together with those methods which combine two columns and use either a common eluent or a different eluent for each column. We will exclude methods in which two or more columns of the same type are simply joined together [e.g. 8.91, and also methods for the simultaneous separation of anions and cations using tandem anion-exchange and cation-exchange columns, since these have been discussed earlier in Section 3.6.1. 15.4.2
Column switching methods
The selectivity of an IC separation can be enhanced by switching the column at an appropriate time during the separation. This is usually performed with a rotary valve, as shown in Fig. 15.8. The sample is injected with the valve in the position shown in Fig. 15.8(a), so that the sample is passed through column A to the detector. Rotation of the valve (Fig. 15.8(b)) directs some of the effluent from column A to the second column (B), where further separation occurs before the sample components pass to the detector. The eluent used must be compatible with both columns.
Methods Development
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1
3
Column A
?Iumn
To detector (a)
Column
Column
B
B
t
To detector (b)
Fig. 15.8 Instrumental configuration for column switching techniques. The circle represents a high-pressure 6-port rotary valve.
Column switching has been employed for the separation of P043-and BF4-, using two anion-exchange columns of different selectivity [ 101, whilst F- has been separated from sample interferences using a complex switching sequence between three anionexchange columns [l 1]. Further examples of this approach include the separation of C1from large excesses of S042- [12] (illustrated in Fig. 15.9), and the separation of inorganic and organic arsenic compounds by switching between an anion-exchange and a reversed-phase column [13, 141. A chromatogram obtained using the latter method has been presented previously in Fig. 12.20(b). The column switching technique can be modified for use with a single column and two or more valves. This configuration permits some of the eluted sample ions to be re-injected onto the analytical column for further separation [ 151. 15.4.3
Coupled ion-exclusion / ion-exchange IC
One of the most popular methods for performing multi-dimensional IC is to couple ion-exclusion and ion-exchange separation modes. The selectivities of these two methods are virtually opposite, in that weakly ionized solutes (such as carboxylic acids, F-, CNetc.) are retained much less strongly than fully ionized solutes (such as Cl-, B r and S 0 4 2 - ) on an anion-exchanger, whereas the reverse is true for ion-exclusion chromatography. Therefore, a mixture of strongly and weakly ionized solutes can be separated in two ways. First, the mixture can be injected onto an anion-exchange column and the early part of the chromatogram (containing the weakly ionized solutes) can be collected and then separated on an ion-exclusion column. Alternatively, the mixture can be injected o g o an ion-exclusion column and the early part of the chromatogram (containing the fully ionized solutes) can be collected and injected onto an anion-exchange system. These steps can be performed using the same eluent for each separation mode (Fig. 15.10(a)), or by using separate eluents and a valve to transfer the required solutes to the second system (Fig. 15.10(b)).
Chapter 15
478
sop
i 7
0
10 Time lminj (a1
5
15
I
I
0
5
I
10 l i m e (min)
I
15
fbl
Fig. 15.9 Chromatograms obtained for the determination of trace chloride in sulfuric acid (a) without column switching and (b) with column switching. Two Dionex HPIC columns are connected in series and the first column is switched out of line after the front part of the sulfate peak (which also contains the chloride) has passed onto the second column. Reprinted from [12] with permission.
V Ion-exclusion
column
D,
DZ Ion-exclusion column
Fig. 15.10 Schemes for multi-dimensional IC. (a) A single eluent is used with two columns. (b) Two eluents (El and E2) are used with two columns and two detectors (D1 and D2). I is the injector and V is a rotary valve.
Methods Development
I
I
0
5
tb
479
1'5
Time (min)
2b
i5
Fig. 15.11 Chromatogram obtained by multi-dimensional IC using the scheme depicted in Fig. 15.10(a). The ion-exclusion column was packed with BioRad AG 50W-X4cation-exchange resin (€ form) I+ and the anion-exchangecolumn was a Dionex anion separator. The eluent was 4.5 mM NaHCO3 - 3.6 mM Na2C03. Reprinted from [16] with permission.
In Fig. 15.10(a), a single eluent (NaHCO3 - Na2C03) is used. The strongly ionized solutes are separated on the anion-exchange column and after elution, pass through the suppressor and thence immediately through the ion-exclusion column (where they are not retained due to their charge) to the conductivity detector (D). At the same time, the weakly ionized solutes pass rapidly through the anion-exchange column and suppressor to the ion-exclusion column, where separation occurs. The anion-exchange eluent is converted in the suppressor to H2CO3, which acts as the acidic eluent necessary for the ion-exclusion step. Fig. 15.11 shows the simultaneous separation of strongly and weakly ionized solutes using this approach [16]. Fig. 15.10(b) shows a more commonly used configuration. Here, the sample is injected onto the ion-exclusion column and is passed through this column using eluent El. On emergence from this column, a selected portion of the sample is collected in a valve (V) and passed through the anion-exchange column, using eluent E2. Two detectors, D1 and D2, are used to monitor the effluent from the two columns. There are many variations which can be introduced into the scheme shown in Fig. 15.10(b); for example, the first detector (D1) can be placed prior to the switching valve, and a concentrator column can be included between the switching valve and the anionexchange column when trace enrichment is required. In setting up this type of coupled IC system, care must be taken that the two eluents used are compatible, since a small amount of El is transferred to the ion-exchange system along with the strongly ionized solutes. Table 15.1 lists some typical experimental conditions and applications of coupled IC, whilst Fig. 15.12 shows representative chromatograms recorded at each of the detectors.
P
TABLE 15.1
E?
TYPICAL EXPERIMENTAL CONDITIONS AND APPLICATIONS OF COUPLED IC USING ION-EXCLUSION AND ION-EXCHANGEAS THE SEPARATION MODES Solute(s)
Sample
Ion-exclusion column
Ion-exchange column
Ela
E2b
Df
D$
Ref
Carboxylic acids, inorganic anions Carboxylic acids, inorganic anions CI-,c103-, SO$-, CO32-
Water
Waters IC Pak A
17
C
C
18
NaOH
Dionex IE-B- 1
Dionex HPIC-AS 1
H20
C
C
19
F-, Fomate, acetate, C1-, B r , NO3-, I-, SO$-
Solder fluxes
Waters lonexclusion Dionex HPICE
Waters IC-Pak A
C
C
20
Yokogawa AX-I
1.O mM octanesulfonic acid^ 1 mMHC1
C
C
21
Waters Fast Fruit Juice Dionex HPICE Dionex HPICE
Waters IC Pak A
1.25 rnN H2SO4
RIf
C
22
Dionex HPIC-AS 1 Dionex HPIC-AS 1
0.01 M HCl 0.01 M HCl
C C
C C
23,24
Sod?-, acetate, formate
Cooling water Plasma Biological materials Brine
3.0mM sodium octanesulfonate 3rnMNaHCO3, 2.4 rnM Na2CO-j 3mMNaHCO3, 2.4 mM Na2CO3 4.0mM sodium octanesulfonate 4rnMNaHCOj4 mM Nap203 3 mM sodium octanesulfonate 0.66mMNaHCO3 0.66mMNaHCO3
C
Dionex HPIC-AS 1
1.O mM octanesulfonic acid 0.01 M HCl
Ce
Coffee
Waters Fast Fruit Juice Dionex HPICE
Dionex IE-B-1
Dionex €€PIC-AS 1
H20
C
C
19
Vanillylmandelic acid
Urine
Dionex HPICE
Dionex HPIC-AS 1
0.01 M HCl, 14% ACNg
C
C
23
Air
Lactate, pyruvate Organic acids
a
3mMNaHCO3, 2.4 mM Na2CO3 6 mM Na2C@
25
Eluent for ion-exclusioncolumn. b Eluent for ion-exchange column. C Detector for ion-exclusion system. d Detector for ion-exchange system. C = conductivity. RI = refractive index. g ACN = acetonimle.
5
z
Methodr Development
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48 1
[
0.19 ps
0.13 pS
lycolate Formate
L
I
1
I
1
t
0
5
10
15
r
20
0
Time imin) (a)
I
5
I
10 Time (min)
1
I
15
20
(b)
Fig. Z5.12 Chromatograms obtained by multi-dimensional IC using the scheme depicted in Fig. 15.10(b). Chromatogram (a) is from the ion-exclusion system (Waters Fast Fruit Juice column with 1 mM octanesulfonic acid as eluent, using conductivity detection). Chromatogram (b) is from the anion-exchange system (Waters IC Pak A column with 3.0 mM sodium octanesulfonate as eluent, using conductivity detection). Solute concentrations were in the range 0.5-20 ppm. Reprinted from [171 with permission.
15.5 AUTOMATION IN IC Many applications in IC involve repetitive analyses which may be amenable to automation. When compared with manual analyses, automated methods have the following advantages: (i) (ii) (iii) (iv)
Improved precision. Improved quality control. Greater accuracy through the elimination of tedious and repetitive tasks. Cost benefits due to increased throughput, reduced staff requirements and extended hours of operation.
Of these advantages, cost benefits are often viewed as the major attraction of automation and it has been dehonstrated [26]that these cost benefits are substantial when an IC is automated. The degree of automation may vary according to the demands of the analysis. Total automation, as is required for on-line analyzers, involves the entire analytical process and includes sample collection, sample treatment, instrument calibration, analysis and report preparation. On the other hand, partial automation
482
Chapter 15
usually involves only the calibration, analysis and reporting steps. Many examples of automation in IC have been reported, but these will not be discussed in detail since most are complex and are applicable to a single application only. On-line, fully automated IC has been used successfully in the power generation industry for the determination of anions and cations in water [27-321. Partial automation has been applied to the routine analysis of water 1331, precipitation 18, 34-36], plating solutions [37] and vehicle emissions [38], and an inexpensive remote IC instrument has been described for the analysis of radioactive samples 1391.
15.6 REFERENCES 1
2 3 4 5 6
7 8 9 10 11
I2 13 14
15 16 17
18 19 20 21 22 23 24
Wetzel R.A., Pohl C.A., Riviello J.M. and MacDonald J.C.. Chem. Anal. (N.Y.), 78 (1985) 355. Schoenmakers P.J., Optimization of Chromatographic Selectivity, Journal of Chromatography Library Vol. 35, Elsevier, Amsterdam, 1986. Berridge J.C., Analyst (London), 107 (1984) 291. Sunden T., Lindgren M., CederFen A. and Siemer D.D., Anal. Chem., 55 (1983) 2. Balconi M.L. and Sigon F., Anal. Chim. Acta, 191 (1986) 299. Haddad P.R. and Cowie C.E., J. Chromarogr., 303 (1984) 321. Jenke D.R., Anal. Chem., 56 (1984) 2674. Slanina J., Lingerak W.A., Ordelman J.E., Borst P. and Bakker F.P., in Sawicki E. and Mulik J.D., (Eds.), Ion Chromatographic Analysis of Environmenral Pollutants, VoI. 11, AM Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 305. Wang C.-Y., Bunday S.D. and Tarter J.G., Anal. Chem., 55 (1983) 1617. Lai S.-T., Nishina M.M. and Sangermano L., J. HRC & CC, 7 (1984) 336. Conrad V.B. and Brownlee W.D., Anal. Chem., 60 (1988) 365. McNair H.M. and Polite L.N., Am. Lab., October (1988) 116. Low G.K.-C., Batley G.E. and Buchanan S.J., J. Chrornatogr., 386 (1986) 423. Low G.K.-C., Batley G.E. and Buchanan S.J., Anal. Chim. Acta, 197 (1987) 327. Hoover T.B. and Yager G.D., Anal. Chem., 56 (1984) 221. Pimminger M., Puxbaum H., Kossina 1. and Weber M., Fres. Z. Anal. Chem., 320 (1985) 445. Jones W.R., Jandik P. and Swartz M.T., J . Chromatogr., 473 (1989) 171. Dionex Application Note 19. Rich W., Smith F., Jr., McNeil L. and Sidebottom T., in Sawicki E. and Mulik J.D., (Eds.), ion Chromatographic Analysis of Environmental Pollutants, Vol. 11, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 17. Dunn M.H., LC.GC, 7 (1989) 138. Tanaka S., Yamanaka K., Yamagata K., Komazaki Y. and Hashimoto Y., Bunseki Kagaku, 36 (1987) 159. Jones W.R., Heckenberg A.L. and Jandik P., J. Chromatogr., 366 (1986) 225. Rich W., Johnson E., Lois L., Kabra P., Stafford B. and Marton L., Clin. Chem., 26 (1980) 1492. Haak K.K., Rich W.E. and Johnson E., in Kabra P.M. and Marton L.J., (Eds.), Clinical Liquid Chromatography, Vol. 11, CRC Press, Roca Raton, 1984, p. 155.
Method Development 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
483
Rich W.E., Johnson E., Lois L., Stafford B.E., Kabra P.M. and Marton L.J., in Kabra P.M. and Marton L.J., (Eds.), Liquid Chromatography in Clinical Analysis, Humana Press, Clifton, NJ, 1981, p. 393. Jackson C.J. and Ferrett J., Anal. Proc., 21 (1984) 420. Blair C., Mullenix J., Barker J. and Angers L., Proc. In?. Water Conf., Eng. Soc. West Pa., (1985) p. 305. Balconi M.L., Pascali R. and Sigon F., Anal. Chim. Acta, 179 (1986) 419. Miller T., ISA Trans., 18 (1979) 59. Potts M.E. and Stillian J.R., J. Chromatogr. Sci., 26 (1988) 315. Simpson J.L., Robles M.N. and Passell T.O., ASTM Spec. Tech. Publ., 742 (1981) 116. Robles M.N., Simpson J.L., Brobst G., Alvi A. and Passel1 T.O., Water Chem. Nucl. React. Syst., 3 (1983) 339. Hoffmann E., Marko-Varga G., Csiky I. and Jonsoon J.A., Inter. J. Environ. Anal. Chem., 25 (1986) 161. Hedley A.G. and Fishman M.J., Tech. Report USGSIWRDIWRIl82-028,(1982). Slanina J., Bakker F.P., Jongejan P.A.C., Van Lamoen L. and Mols J.J., Anal. Chim. Acta, 130 (1981) 1. Slanina J., Keuken M.P. and Jongejan P.A.C., J. Chromutogr., 482 (1989) 297. Smith R.E. and Smith C.H., LC, 3 (1985) 578. Tejada S.B., Zweidinger R.B., Sigsby J.E., Jr. and Bradow R.L.. in Sawicki E., Mulik J.D. and Wittgenstein E.,( a s . ) , Ion ChromatographicAnalysis of Environmental Pollutants, Vol. I, Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 111. Lautensleger A.W., Tech. Report PNL-SA-I1760 (1983).
This Page Intentionally Left Blank
Part v Applications of Ion Chromatography
486
ENVIRONMENTAL (Chap 16)
INDUSTRIAL (Chap 17)
Acid rain, rain water Seawater, brines River, stream, pond and lake water Other natural Waters Air, aerosols, airborne particulates Soils, soil extracts Geological materials Waste waters, effluents Other industrial waters Or anic compounds P u t and paper liquors Acids and bases Detergents and polymers Fuels, oils, engine products
FOODS AND PLANTS (Chap 18)
Plants and plant products
CLINICAL AND
Blood, serum, plasma
(Chap 19)
Other clinical and biological
APPLICATIONS
METALS AND METALLURGICAL<Metal plating solutions Metallurgical processing solutions SOLUTIONS (Chap 20) TREATED WATERS (Chap 21)
MISCELLANEOUS (Chap 22)
Schematic overview of Part V.
c Drinking water High purity waters Chemical, chemical products, reaction mixtures Photographic solutions Explosives Miscellaneous
487
Overview of the Applications Section INTKODUCTION Perhaps the single greatest reason for the remarkable growth of JC over the past decade has been its ability to provide rapid and simple solutions to a wide variety of analytical problems. Much of the large volume of literature published on IC is devoted to practical applications of the technique. These applications embrace a diversity of solutes and an extremely broad range of samples, and vary from simple analyses involving little or no sample preparation to very complex procedures requiring extensive sample treatment. A detailed summary of the trends evident from published papers on IC is given in Appendix A.
ORGANIZATION OF THE APPLICATIONS SECTION Coverage Unlike most application reviews, which tend to be either bibliographical or take the form of a series of intcrconnected discussions on various applications, the applications section of this text consists of seven Chapters comprising Tables (with brief introductory comments) listing experimental conditions for published applications of IC. The Tables were derived from a data base containing over 1800 articles on IC, including monographs, published papers, symposium and conference papers, technical reports and application notes from the major instrument manufacturers. The coverage of the literature is comprehensive up to the start of 1989. Arrangement of data The data presented in these Tables are arranged according to specific separations or samples, so a particular publication containing more than one application will be referenced more than once. Separations appearing in fundamental reviews on IC have not been included when these separations have been published elsewhere. The aim of the applications Section is to enable readers to replicate a particular method without the necessity to examine the original publication. To achieve this aim, we have included all relevant experimental conditions, such as the identities of the solutes determined, the sample type, sample preparation procedures, the column (and its dimensions), the eluent composition (and the flow-rate used), and the detection method(s) employed. On some occasions, a particular set of experimental conditions has been used widely for the analysis of a certain sample type. In such cases, we have grouped these related references into a single entry in a Table, with the reference listed first being that from which the actual experimental conditions listed in the Table were taken.
Overview of the Applications Section
488
Retention times Where possible, the retention time for each solute is shown in parentheses, after the solute name. However, it should be noted these retention times are generally only approximate, except when exact values are cited in the original publication. In such cases, the retention times are quoted to one or two decimal places in the Tables. The absence of retention time values in the Tables generally indicates that no chromatogram appeared in the original article or that no time scale was provided for the chromatogram. Abbreviations Where the solutes separated are weak acids, the word "acid" has usually been omitted to conserve space. Thus, oxalic acid appears simply as "oxalic". The use of abbreviations in the Tables has been kept to a minimum, with standard abbreviations only being used. A complete listing of the abbreviations used throughout this text is included in Appendix B. Organization Part V is divided into seven Chapters, each of which deals with a broad application area of IC. These application areas are listed below: (i) (ii) (iii) (iv) (v) (vi) (vii)
Environmental applications (Chapter 16). Industrial applications (Chapter 17). Food and plant analysis (Chapter 18). Clinical and pharmaceutical applications (Chapter 19). Metals and metallurgical applications (Chapter 20). Analysis of treated waters (Chapter 21). Miscellaneous applications (Chapter 22).
Within each Chapter, applications relating to specific sample types are grouped into separate Tables. Where possible, the emphasis has been to provide relatively compact Tables in order to simplify the search for an application of interest. When there is a large number of literature references devoted to a single sample type, a Table has been dedicated to the analysis of that sample. In other cases, related sample types have been combined into a single Table, with the nature of the sample being identified in each entry. The sequence of entries in the Tables follows the heirarchy shown below. Within each classification below, determinations of large groups of solutes are presented first, followed by smaller groups of solutes and lastly, determinations of individual solutes. (i) (ii) (iii) (iv) (v)
Anions and weak acids. Monovalent cations. Divalent cations. Transition metals and other metals. Simultaneous determinations of anions and cations.
489
Chapter 16 Environmental Applications 16.1 OVERVIEW Environmental applications of IC are presented according to the scheme shown in Fig. 16.1:
Acid rain, rain waters (Table 16.1) Seawater, brines (Table 16.2) River, stream, pond and lake waters (Table 16.3) APPLICATIONS OF IC
4
Other natural waters (Table 16.4) Air, aerosols, particulates (Table 16.5) Soils, soil extracts (Table 16.6) Geological materials (Table 16.7)
Fig. 16.1 Environmental applications of IC.
'TABLE 16.1
ANALYSIS OF ACID RAIN AND RAIN WATERS USING IC Solutes (min)
Sample Prep.
Column
Eluent
Fluoride (1.8), chloride (2.5). nitrate (5.3), sulfate (6.3)
-
Acetate ( 3 3 , formate (4.8), methane sulfonate (6.9), hydroxymethane sulfonate (8.1), chloride (13.0) Fluoride (1.9), chloride (2.7). nitrite (4.0). sulfite (7.6). niuate (9.1). sulfate (12.7)
Addition of formaldehyde, 5.5 ml injection Filtration, 2 ml injection
Dionex fast-run anion separator 250 x 4.0 mm ID Dionex AS-3
Acetate (2.63). formate (2.97), chloride (3.23), nitrate (15.00), sulfate (24.55)
Filtration
Conductivity 3.0 mM bicarbonate, 2.4 mM carbonate 3.0 mumin Conductivity 1 mM bicarbonate, 0.2% (vh.) formaldehyde 2.0 mumin Conductivity 2.0 mM carbonate, 5.0 mM hydroxide 156 mVhr Conductivity 2.0 mM bicarbonate, 1.67 mM carbonate 0.5 mumin 1.4 mM succinic acid, pH 7.0 Conductivity, ampemmetry 3.0 mumin Conductivity, direct 2.0 mM carbonate, spectrophot. at 220 1.O mM bicarbonate nm, potentiometry 3.0 mumin
Dionex anion separator 500 x 3.0 mm ID Dionex AS-3 250 x 4.0 mm ID Zipax SAX 250 x 4.6 mm ID
Chloride (2.25). nitrite (3.22), nitrate (6.07), sulfate (8.32) Fluoride, chloride, bromide, nitrate, sulfate
Preconcentration on Dionex anion separator Zipax SAX precolumn 250 x 3.0 mm ID
Fluoride, chloride, bromide, nitrate, phosphate, sulfate
Preconcentration (5 mu
Fluoride (4), chloride (6), nitrate (7), sulfate (22)
-
Detection
Ref 1-19
20 21 22 23 24
WE) Dionex anion separator (x2) 500 x 3.0 mm ID 250 x 3.0 mm ID Vydac 302 IC 250 x 4.6 mm ID
2.0 mM bicarbonate, pH 9.6 and 10.0 4.6 d m i n
Conductivity
25
2 mM N,N-bis(2-hydroxyethyl-2-aminoethane) sulfonic acid, 1.5 mM hydroxide 2.0 mumin
Conductivity
26
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
h
3 .-
TABLE 16.1 (CONTINUED) ANALYSIS OF ACID RAIN ANT) RAIN WATERS USING IC Solutes (min)
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride (1.6), chloride (2.2), nitrate ( 4 3 , sulfate (6.1)
Addition of eluent
27,28
-
3.0 mM bicarbonate, 2.4 mM carbonate 180 mVhr 4.0 mM phthalate, pH 4.5 2.0 mvmin 1.7 mh4 bicarbonate, 1.8 mM carbonate 1.2 mljmin
Conductivity
Chloride (3.8), nitrate ( L O ) , sulfate (12.3), bicarbonate (18.2) Chloride (1.9), nitrate (3.0), sulfate (4.9)
Dionex anion separator 250 x 3.0 mm ID Vydac 302 IC 250 x 4.6 mm ID Dionex AS-4A 200 x 4.5 mm ID
$ 2
Chloride (5.88), nitrate (8.03), sulfate (21.87) Chloride (4.7), bromide (6.0), nitrate (6.8)
Cleanup on pre-column loaded with manganese dioxide and activated carbon Millex filter, large injection volume
-
Wescan 269-001 2.0 mh4 phthalate, pH 4.5 250 x 4.6 mm LD Wescan anion 2.0 mM methanesulfonic acid, 250 x 4.6 mm ID pH 5.0 2.0 mvmin Zipax SAX 0.5 mM phthalate, pH 6.5 50x2.1 mm ID 1.0mljn-h 2.0 mM phthalate, Synchropak AX300 0.1 mM citrate, pH 7.0 3.0 mljmin
Chloride (2.9), nitrate (8.6), sulfate (17)
-
Chloride (2.2), nitrate (4.6), sulfate (1 1)
Filtration
Methanesulfonate (6.5), chloride (7.8)
Cat-ex in Ag form to Dionex fast-run remove chloride, anion separator large injection volume
0.9 mM bicarbonate
Conductivity
29
Conductivity, potentiomtry (ISE)
30
Conductivity
31-33
5
ti3 =.
2
Direct spectrophot. at 34 214 nm,conductivity Indirect spectrophot. 35-37 at 240 nm Indirect spectrophot. 38 at 265 nm Conductivity
39
P
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
22
& h)
TABLE 16.1 (CONTINUED) ANALYSIS OF ACID RAIN AND RAIN WATERS USING IC
Solutes (min)
Sample Prep.
Formic (1.8). acetic (2.2)
Formic (21). acetic (23) Nitrite, nitrate Nitrate (4.67) Fluoride Sodium (3.8). ammonium (4.6), potassium (5.2)
Filtration
Column
Eluent
Detection
Ref
CIRreversed phase
5 mM octylamine,
Conductivity after passing through silver-loaded suppressor Conductivity
40
Ampemmetryat glassy carbon, 4.9v Conductivity, indirect specmphot. at 280 nm Conductivity
42
10 mM hydrochloric acid, MeOH gradient 1.2 ml/min Dionex AS-2 ion 2.0 mM hydrochloric acid exclusion 0.66 d m i n 200 x 9.0 mm ID TSK gel QAE- 50 mM sodium chloride 0.5 d m i n 2sw 150 x 4.0 mm ID 4.0 mM phthalic acid, adjusted Vydac 302 1C 250 x 4.6 mm ID to pH 5.0 with borate 2.0 d m i n Dionex anion 0.3 mM bicarbonate separator (x2) 500,250 mm 5.0 mM hydrochloric acid Dionex cation separator 180 250 x 6.0 mm ID
Sodium (1.9), ammonium (3.3), potassium (4.6)
Interaction ION210
Sodium, potassium
Dionex cation 4.0 mM nitric acid separator 250 x 6.0 mm ID
3.5 j N cerium (HI) nitrate 1.O ml/min
41
43 44
45-47, 2, 6, 9, 10, 15, 17 Indirect fluorescence 48 Conductivity
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for R@erences. Abbreviations are listed in Appendix B (p. 745).
12
b
TABLE 16.1 ( C 0 ” U E D ) ANALYSIS OF ACID RAIN AND RAIN WATERS USING IC Solutes (min)
Sample Prep.
Magnesium (4.6), calcium (6.4)
Magnesium (4.3, calcium (7.5) Zinc (8.03), cadmium (9.43), manganese (10.53)
Fluoride (3.0), chloride (4.3, nitrate (8.4), sulfate (1 1:9), sodium (3.3, ammonium (4.0), potassium (4.8), magnesium (10.7), calcium (12.4)
Preconcentration
-
Sodium (3), potassium (ll),chloride (3). bromide (6),nitrate (7), sulfate (10)
-
Magnesium (4), calcium (9), chloride (6), nitrate (25).sulfate (31)
-
Column
Eluent
Dionex cation 2.5 mM hydrochloric acid, separator 2.5 mM m-phenylenexliamine 250 x 3.0 mm ID dihydrochloride 115 mvhr Dionex CS- 1 28 pM cerium (111) nitrate 1.0 Wmin Dionex CS-5 3 mM pyridine dicarboxylic 250 x 4 mm ID acid and 4.3 mM lithium hydroxide, then 2 mM sodium sulfate, then 25 mM sodium chloride 1.0 Wmin Dionex A S 4 and 1.8 mM carbonate, 2.2 mM cs-3 carbonate and 12 to 48 mM 250 x 4.0 mm ID HC1,0.25 to 4.0 mM diamino 250 x 4.0 mm ID propionic acid hydrochloride, 0.25 to 4.0 mM histidine gradient 1.1 d m i n Dionex AS-3 and 1.6 mM lithium carbonate, 2.4 m M lithium acetate, CS- 1 in series 15Ox4,OmmID pH 10.4 200 x 4.0 mm ID 1.5 d m i n Vydac 302 IC 3.3 mM copper phthalate and Dionex CS-1 1.5 Wmin in series 250 x 4.6 mm ID 200 x 4.0 mm ID
Detection
Ref
Conductivity
45, 17
s.a
$ Indirect fluorescence 48 Direct spectrophot. at 49 520 nm after postcolumn reaction with PAR Conductivity
50
Conductivity, amperometry
51
Conductivity, amperometry
51
Seep. 487 for notes on the organization of this Table. Seep. 534 for RtIferences. Abbreviations are listed in Appendix B (p. 745).
1 8
P
TABLE 16.1 (CONTINUED) ANALYSIS OF ACID RAIN AND RAIN WATERS USING IC
3
Solutes (min)
Sample Prep.
Column
Eluent
Detection
Chloride (2.9). sodium (2.9). ammonium (6.7), potassium (8.3), nitrate (8.3), sulfate (22.6)
.
Zipax SAX and SCX in series 500 x 2.1 mm ID 500 x 2.1 mm ID TSK-gel ICAnion-SW 50 x 4.6 mm ID
0.25 mM copper o-sulfobenzoate 1.O mumin
Indirect spectrophot. 52 (dual channel detector) at 240 and 270 nm Conductivity,direct 53, 54 spectrophot. at 210 nm
Chloride (3.0). nitrate (3.6). calcium (5.8). Filtration magnesium (6.8). sulfate (9.0)
1.O mM EDTA, pH 6.0 I .O mumin
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
Ref
TABLE 16.2 ANALYSIS OF SEAWATER AND BRINES USING IC Y
Solutes (min)
Sample Prep.
Column
Dionex anion separator Dilution, on-line ppt Dionex A S 4 250 x 4.0 mm ID of chloride by Ag cat-ex column Dionex B-1 ion Formate (8), acetate (1 1). carbonate (18), Dilution exclusion and chloride (23), sulfate (29) anion separator 500 x 6.0 mm ID 500 x 3.0 mm ID Dionex AS-2 Chloride (3.3), sulfate (7.Q bromide (9.7), Dilution, filtration nitrate (1 1.2)
Fluoride (6), chloride (1l), bromide (28), nitrate (32), sulfate (46) Chloride (2.0), nitrite (2.5), phosphate (3.3, nitrate (6.0), sulfate (9.8)
Chloride (5.15), nitrite (5.71), nitrate (8.59), sulfate (14.94) Chloride (3), nitrite (6.5), bromide (7), nitrate (8) Acetate (3.2), chloride (4.7), bromide (1 1.8)
Dilution
Eluent 3.0 mM bicarbonate, 2.5 mM carbonate 3.0 mM bicarbonate, 1.5 mM carbonate 1.0 mumin Deionized water and 3.0 mM bicarbonate, 2.4 mM carbonate 46 mVhr and 138 ml/hr
4.5 mM carbonate, 2.0 mM hydroxide, 0.8 mM p-cyanophenol (2% ACN) 1.5 d m i n 1.3 mM tetraborate, 5.8 mM Waters IC Pak Ag form cat-ex membrane for boric acid, 1.4 mM gluconate A/HC chloride removal 150 x 4.6 mm ID (12% ACN) 2.0 d m i n Waters IC Pak A 1.3 mM tetraborate, 5.8 mM Dilution 50 x 4.6 mm ID boric acid, 1.4 mM gluconate (12% ACN) 1.O d m i n Dionex anion 3.0 mM bicarbonate, Extraction into 2.4 mM carbonate chloroform, peroxide separator 215 x 3.0 mm ID 2.0 d m i n reduction
Detection
Ref
Conductivity Conductivity
14, 55-57 58
Conductivity
59
Conductivity
60
Conductivity
61
Conductivity
62
Conductivity
63
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
4
k P
3.g
p.
TABLE 16.2 (CONTINUED) ANALYSIS OF SEAWATER AND BRINES USING IC Solutes (min)
Sample Prep.
Column
Chloride (3,bromide (12)
DilUtiW
Chloride (7.2). bromide (8.8)
Dilution
0.01 M phosphate, pH 3.6 2.0 mumin 0.01 M perchloric acid 0.5 mi/min 0.1 M potassium nitrate, 25%(v/v) phosphate buffer, pH 7.6 1 .O mVmin Dionex AS-3 3.0 mM bicarbonate, 2.4 mM carbonate 2.0 d m i n 1 mM phthalate, Home-packed SAR-40-0.6 1.0 mM boric acid, pH 9.0 250 x 4.0 mm ID 2.5 mumin 6.0 mM carbonate Dionex anion 2.3 ml/min separator 50 x 3.0 mm ID Partisil ODs-3 10 mM octylamine, adjusted to pH 6.2 with phosphoric acid 2.0 d m i n 4.5 mM carbonate, 2.0 mM Dionex AS-5 hydroxide, 0.8 mM p-cyanophenol (2%ACN) 1.5 ml/min
Chloride (3.4)’ bromide (4.0)
Chloride (4), sulfate (13) Chloride (3), sulfate (16)
In-line an-ex precolumn to remove sulfate from eluent Dilution
Chloride (2.2). perchlorate (7.8)
Dilution
Bromide ( 4 3 , iodide (1 1.0)
Dilution
Iodide (5.3), thiosulfate (12.0)
Dilution, filtration
Vydac 302 IC 250 x 4.6 mm ID Interaction ION. 110 Nucleosil SB 10 anion 250 x 4.0 mm ID
Eluent
2 Detection
Ref
Direct specuophot at 64 175 nm Direct spectrophot.at 65 210 nm 66 Potentiometry with silver sulfide electrode Conductivity
67
Indirect spectrophot. 68 at 254 nm Conductivity
69
Direct spectrophot.at 70 205 nm
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
60
TABLE 16.2 (CONTINUED) ANALYSIS OF SEAWATER AND BRINES USING IC Solutes (min)
Sample Prep.
Column
Nitrite (4.80),nitrate (6.25)
Dilution
2.5 mM succinic acid, Vydac 302 IC 250 x 4.6 mm ID 10 mM sulfate, adjusted to pH 5.8 with tetraborate
Bromide (as 4-bromoacetanilide) (7.7)
PFe-column derivatization. dilution, filtration c18 Sep-Pak, preconcentration (2-10 ml)
Zorbax C1g Water (65%MeOH) 250 x 4.6 mm ID 1.0 d m i n
Dilution
Brownlee AXMP weak base anion-exchanger 100 x 4.6 mm ID TSK Gel IC anion SW 50 x 4.6 mm m TSK gel ICAnion-PW 50 x 4.6 mrn ID Dionex AS4
Sulfate (13.5)
Dilution
Dionex anion separator Dionex CS-5
Perchlorate (18)
Dilution
Iodide (6)
Iodide (20)
Ascorbic acid reduction, column switchisg
Iodide (4.0) Iodide (18) Fluoride
Eluent
Detection
Ref
Fluorescence after 71 post-column reaction with Ce(IV). conductivity Direct spectrophot at 72 240 nm
0.1 M sodium nitrate, 0.01 M phosphate buffer, pH 6.7 1.5 d m i n 0.5 mM citmte. pH 4.96 1.0 d m i n
Potentiometry at iodide ISE
73
Potentiometry at glass electrode
74
0.1 M sodium chloride, phosphate buffer, pH 6.7 1.2 d m i n 8.0 mM carbonate 2.0 d m i n 2.5 mM disodium tetraborate
Amperometryat glassy carbon electrode, +l.OV Conductivity
75
Conductivity
57
0.5 mM carbonate, 5.0 mM hydroxide 1.5 d m i n
Conductivity
76
Conductivity
77
Dionex DC-X8 5.0 mM sodium iodide 150 x 4.0 mm ID 2.3 d m i n
Seep, 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
56
P
v, 4
P
TABLE 16.2 (CONTINUED) ANALYSIS OF SEAWATER AND BRINES USING IC Solutes (min)
Sample Prep.
Column
Carbonate (12.5)
Dilution, filtration
Acetic (3.6) Dimethylsulfoxide (13.1) Sodium (2), potassium (6)
Dilution
Magnesium (0.8). calcium (2.2)
Dilution
Magnesium (3.7). calcium (5.8)
Dilution, filtration
Magnesium (3. I), calcium (5.2)
Filtration, dilution
Magnesium (5.2), calcium (8.7)
'0
Eluent
Detection
Ref
Dionex AS- 1 ion Deionized water exclusion 1.O ml/min
Conductivity
60
Partisil ODs-3 100 x 9.4 mm ID Bio-Rad HPX87H 300 x 7.8 mm ID Wescan 269004 cation 100 x 3.0 mm ID Wescan 269004 cation 100 x 3.0 mm ID Dionex CS-3
0.01 M sulfuric acid 2.0 d m i n 5 mM phosphoric acid 1.2 mVmin
Direct spectrophot. at 78 214 nm Direct spectrophot. at 79 195 nm
3 mM nitric acid 1.5 mumin
Indirect conductivity
1 mM ethylenediamine, pH 6.1 1.5 mVmin 48 mM hydrochloric acid, 8 mM diaminopropionic acid dihydnxhloride 1.O d m i n Waters IC Pak C 10 mM 2-phenethylamine, 50 x 4.6 mm ID pH 5.7 1.O d m i n TSK gel Chelate 0.05 M phosphate buffer, 5-PW 0.2 M chloride, 75 x 47.5 mm ID 0.1 mM o-cresol-phthaleine, pH 5.3 0.7 d m i n
80
Indirect Conductivity 8 1 Conductivity
60
Direct conductivity, indirect spectrophot.
82
Direct spectrophot. at 83 575 nm after in situ formation of 0-cresolphthaleine complexes
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
4
01
TABLE 16.2 (CONTINUED) ANALYSIS OF SEAWATER AND BRINES USING IC ~
~-
Solutes (min)
Sample Prep.
Column
Cobalt (8)
AF'DC-ChlOrOfO~ extraction, preconcentration Preconcentratiom (100 ml) on 4 cm ODs pre-column
Dionex CS-2
Tributyltin (12)
Chloride (3.4). nitrate (5.0),calcium (7.4), Dilution, fitration magnesium (8.7). sulfate (14.2)
Eluent
0.02 M hydrochloric acid 0.5 to 2.0 W m i n flow gradient Partisil 10 SCX 0.15 M acetate buffer 250 x 4.6 mm ID (80%MeOH) 1.O d m i n TSK-gel ICAnion-SW 50 x 4.6 mm ID
1.0 mM EDTA, pH 6.0 1.0 d m i n
Dewdon
Ref
Chemiluminescence 84 after post-column reaction with luminol Fluorescence (408, 85 534 nm) after postcolumn reaction with morin, Triton X- 100 Conductivity, direct 53,54 spectrophot. at 210 nm
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 16.3
VI
8
ANALYSIS OF RIVER, STREAM, POND AND LAKE WATERS USING IC Solutes (min)
Sample Prep.
Chloride (2.9). nitrate (7.0), sulfate (9.0)
Filtration
Column
Dionex anion separator 500x3.0mmID Fluoride (2.1), chloride (4.4), nitrite (5.8), Pemxodisulfate and Dionex anion phosphate (10.8),.nitrate (17.2), sulfate hydroxide digestion, separator Chelex 100clean-up 250 x 4.0 mm ID (29) Silicate (6.3), fluoride (7.0). chloride Catex pre-column TSK gel IC(10.01,nitrate (15.4). sulfate (30) Anion-PW clean-up 50 x 4.6 mm ID Chloride (3.8), nitrate (5.0), sulfate (12.3), vydac 302 IC bicarbonate (18.2) 250 x 4.6 mm ID Bicarbonate (2), chloride (3), nitrate (6), Cat-ex Camidge to TSK gel IC anion sulfate (10) remove interfering PW Ca and Mg ions 50 x 4.6 mm ID Sulfate (1,7), chloride (1.9), nitrate (2.2), Fiitration HOme-pWked carbonate (2.5) polyamide crown resin coated on silica gel 250 x 4.0 mm ID Chloride (2.1), cyanate (2.9), chlorate Spiking, oxidation Dionex AS-QA with sodium (5.8). sulfate (9.2) hypochlorite Chloride (2.3), cyanate (3.0), nitrate (4.3), Spiking, heating Dionex A W A sulfate (7.8) with c h l d e - T
Eluent
Detection
Ref
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity
16, 86-90
5.0 mh4 bicarbonate, 1.5 mM carbonate
Conductivity
91
2.5 d m i n 0.8 mM potassium hydroxide Indirect conductivity 92 1.2 d m i n 4.0 mM phthalate, pH 4.5
2.0 mvmin 0.4 mM trimellitate, pH 7.6 1.0 mvmin
Water
Conductivity
29
Indirect spectrophot. 93 at 267 nm Conductivity
94
2.2 mM carbonate 1.5 Wmin
Conductivity
95
2.2 mM carbonate 1.5 Wmin
Conductivity
96
0.018 mvmin
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 16.3 (CONTINLTED) ANALYSIS OF RIVER, STREAM, POND AND LAKE WATERS USING IC Solutes (min)
Sample Prep.
Column
Eluent
Detection
Ref
10 mM phenate 1.0 mvmin
Conductivity
97
4.0 mM bicarbonate, 4.0 mM carbonate, pH 10.2 2.15 Nmin 2.0 mM phthalate, pH 4.0
Conductivity
98
Conductivity
89
Preconcentration (15
Home-packed agglomerated Dowex 2 resin 300 x 2.8 mm ID Home-packed YEW Ax-1 47 x 0.19 m m ID vydac 302 IC 250 x 4.6 mm ID vydac 302 IC 250 x 4.6 mm ID Waters IC Pak A 50 x 4.6 mm ID
0.5 mM o-phthalate, pH 5.2 2.0 mumin 5 mM heptanesulfonic acid, pH 7.0 1.0 mvmin 1 mM phthalate, pH 4.1
Indirect specmphot 99 at254nm Conductivity. direct 100 specmphot. at 210 nm Indirect specmphot 101 at 264 nm IndirectRI 102
~~
Chloride (2.7), carbonate (4.4), sulfate (7.0) Chloride ( 5 . 3 , nitrate (9.3, sulfate (12) Chloride (3,nitrate (9), sulfate (17) Chloride (4.0), nitrate (7.0), sulfate (13.9) Chloride (4.3), nitrate (8.3), sulfate (17.5)
Partisill0 SAX
Chloride (5.6), nitrate (7.7), sulfate (11.6) Chloride (12), nitrate (14), sulfate (17)
catex clean-up
Chloride (5.5). nimte ( 5 . 3 , nitrate (6.4) Chloride (3). cyanide (4). carbonate (6) Chloride (4.8). nitrate (8.7)
Dilution
Nucleosil 10 SB 0.07 M phydroxybenzoate, 250 x 4.6 mm ID DH5.0 b.5 Wmin Partisill0 SAX 1 mMphthalate, pH 3.95 150 x 2.0 mm ID 0.6 Wmin Waters IC Pak A 5 mM potassium hydroxide 50 x 4.6 mm ID 1.2 mvmin 0.5 mM phthalate, pH 5.4 vydac 302IC 250 x 4.6 mm ID 2.0 mVmin
Inckct specmphot. 103 at 265 nm AmPe-=Y at Ag 104 electrode, indirect conductivity Streamingcurrent 105 detector
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are Ikted in Appendix B (p. 745).
cn
'TABLE 16.3 (CONTINUED) ANALYSIS OF RIVER, STREAM, POND AND LAKE WATERS USING 1C
Solutes (min)
Sample Prep.
Chloride (5.0). nitrate (8.1)
Clg Sep-Pak
Nitrite (7.8). nitrate (8.0) Nitrate (10). nitrite (16) Nitrate (2.5). nitrite (4.2) Nitrite ( X O ) , nitrate (4.7)
Spherisorb ODS2 coated with CTMABr 250 x 5.0 mm ID CIRSep-Pak, cat-ex SA Dowex 2 in line before injector 150 x 3.0 mm ID Dilution, filtration Hitachi 3613 cation exchanger 550 x 9.0 mm ID Dilution, filmtion Hitachi 3613 cationexc hanger 100 x 9.0 mm ID Filtration Waters Rad-Pak VBondapak cl8
Glyphosphate (4), chloride (1 1)
Spiking
Tungstate (9.0). molybdate (12.0)
Filtration, preconcentration on Chelex 100
Selenite (12.5). selenate (21.2)
Column
Eluent
5 mM phthalate, pH 4.19
8 Detection
Ref
Indirect spectrophot. 106 300 nm
2.0 mVrnin
at
0.05 M sulfate 2.0 mumin 0.1 mM sulfuric acid 1.O mumin
Direct spectrophot. at 107 210 nm Direct spectrophot. at 108 210 nm
0.1 mM sulfuric acid (5% MeOH) 1.O mumin 5.0 mM tetramethylammonium phosphate 3.0 mVmin 40 mM succinic acid, pH 2.9 1.7 mVmin 6.0 mM carbonate 90ml/hr
Direct spectrophot. at 108 210 nm
Hamilton PRPXloo 100 x 4.1 mm ID Dionex anion separator 250 x 3.0 mm ID 8.0 mM carbonate Dionex anion 0.46 mYmin separator 150 x 3.0 mm ID
Direct spectrophot. at 109 214 nm Conductivity
110
Conductivity
111
Conductivity, GFAAS
112
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 16.3 (CONTINUED) ANALYSIS OF RIVER, STREAM, POND AND LAKE WATERS USING IC Solutes (min)
Sample Prep.
Column
Nitrate (4.67)
Filtration
Orthophosphate (7.56)
Filtration
Selenate (27)
Re-injection
Selenate (8.4)
Preconcentration
Arsenate (25) Boric acid (3.5)
Lithium (3.0), sodium (5.0), potassium (11.3)
Detection
Ref
Vydac 302 IC 4.0 mM phthalic acid, 250 x 4.6 m m ID adjusted to pH 5.0 with borate 2.0 d m i n Dionex AS-3 0.252 @l sodium bicarbonate, 0.2544 g/l sodium carbonate
Conductivity, indirect specmphot. at 280 nm
43
Conductivity
113
Dionex AS-3
Conductivity
114
Conductivity
115
Conductivity
114
Conductivity
114
3.0 mM bicarbonate, 2.4 mM carbonate, pH 9.72 1.51 mVmin 3.0 mM carbonate 230 ml/hr
Dionex anion brine 500 x 3.0 mm ID Re-injection Dionex AS-3 3.0 mM bicarbonate, 2.0 mM carbonate, pH 9.24 1.5 1 mVmin Re-injection Dionex AS-3 2.5 mM bicarbonate, 1.5 mM carbonate, pH 9.56 1.5 1 d m i n Re-column addition TSK gel IC 0.2 M perchlorate, anion-PW of chromotropic 1 mM acetate buffer, pH 5.6 acid, EDTA, octyl50 x 4.6 mm ID 1.O mVmin mimethyl ammonium chloride Dionex CS-2 8.0 mM hydrochloric acid 250 x 4.0 mm ID 1.6 mVmin
(100
Selenite (20)
Eluent
Direct spectrophot. at 116 350 nm
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
117, 45
i2
TABLE 16.3 (CONTINUED) ANALYSIS OF RIVER,STREAM, POND AND LAKE WATERS USING IC Solutes (min)
Sample Prep.
Column
Sodium (3.0). magnesium ( 6.0),calcium (8.5)
Diiution
Magnesium (4.6). calcium (6.4)
Magnesium ( 5.4), calcium (7.1)
Magnesium (1.8). calcium (2.6)
Calcium (6.0) Copper (2. l), cobalt (2.7), zinc (3.2), lead (9.4), iron (14.3). manganese (21.9) Copper (2.7). zinc (6.7), lead (7.7). iron (16.3), manganese (23.4), calcium (28)
Dilution
Detection
Ref
1.0 mM barium nitrate, Dionex cation separator pH 4.0 250 x 6.0 mm ID 2.3 mVmin
Conductivity after sulfate-suppression of barium (ppt)
118
2.5 mM hydrochloric acid, Dimx cation s e p ~ ~ 2.5 mM m-phenylenediamine 250 x 3.0 mm ID dihydmchloride 115 mvhr Dionex cation 1.0 mM lead nitrate, separator pH 4.0 250 x 6.0 mm ID 2.3 d m i n
Conductivity
45
Home-packed 0.12 M perchloric acid cationexchanger 1.0 mVmh 250 x 2.0 mm ID
Direct spectrophot. at 120 590 nm after postcolumn reaction with Arsenam-l Direct spectrophot. at 121 679 nm
Hitachi custom cationcxchanger 150 x 2.6 mm ID Preconcentration (up Aminex A5 100 x 4.0 mm ID to 200 mL) on Aminex A5
Eluent
0.7 M sulfosalicylic acid, 0.05 mM chlorophosfonam 1.5 ml/min 0.08 M to 0.2 M citrate gradient, pH 4.6 1.0 d m i n
0.35 M to 0.5 M tartrate Preconcentration (up Aminex A5 100 x 4.0 mm ID gradient. pH 3.5 to 2.0 lims) on Aminex A5 1.0 d m i n
Conductivityaftm 119 iodate-suppression of lead (ppt)
Direct spectrophot. at 122 540 nm after postcolumn reaction with PAR Direct spectrophot. at 123 540 nm after postcolumn reaction with PAR
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
trl
TABLE 16.3 (CONTINUED) ANALYSIS OF RIVER, STREAM, POND AND LAKE WATERS USING IC Solutes (min)
Sample Prep.
Column
Eluent
z
Detection
Ref m
Y
Iron (In) (4.6), iron (XI) (12.5)
Cobalt (8) Fluoride (3.0), chloride (4.3, phosphate (5.4). nitrate (8.4), sulfate (11.9), sodium (3.5). ammonium (4.0). potassium (4.8). magnesium (10.7), calcium (12.4)
Filtration, acidification
Reconcentration
-
6 mM 2,6-pyridinedicarboxylic acid, 100 mM acetate buffer, pH 4.5 1.O ml/min Dionex CS-2 1.0 mMoxalic acid, 7.5 mM citric acid, pH 4.1 2.5 ml/min Dionex A S 4 and 1.8 mM carbonate. 2.2 mM cs-3 carbonate and 12 to 48 mM 250 x 4.0 mm ID HCl. 0.25 to 4.0 mM 250 x 4.0 mm ID diaminopropionic acid hydrochloride, 0.25 to 4.0 mM histidine gradient 1.1 ml/min
Dionex CS-5
Direct spectrophot. at 124 520 IIIII after postcolumn reaction with PAR Chedumkesamce 84 after post-column reaction with luminol conductivity 50
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
E
a. b
TABLE 16.4 ANALYSIS OF OTI-IER NATURAL WATERS USING IC Sample
Sample Prep.
Fluoride ( l S ) , chloride (2.6). nitrate (7.4), sulfate (10.5)
Natural water
Filtration
~
~
~
Solutes (min)
Column
Dionex anion separator 500 x 3.0 mm ID Bisulfide (5.3), chloride (6.0), Natural water Dionex AS-3 cyanide (7.2) 250 x 4.0 mm ID Nitrate, sulfate, phosphate Natural water Dionex anion separator Chloride (2.7), methylphosNatural water Dilution Dionex anion phonic acid (6.5) separator 500 x 3.0 mm ID Isopropyl methylphosphonic Dionex anion Natural water acid (1.6). chloride (6.0) separator 500 x 3.0 mm ID Nucleosil amino Home-packed Natural water Nitrate (4), sulfate (12) containing humic column clean-up anion-exchanger acids 50 x 5.0 mm ID Water with Bonded amino Dionex anion Nitrate (2.2), sulfate (8.7) humic substances pre-column separator 50 x 5.0 mm ID clean-up, preconcentration on Mono Q Chromium (VI), chromium(II1) Natural water Dionex CS-2 oncolumn preconcentration 250 x 4 mm ID
~
Eluent
Detection
3.0 mM bicarbonate, 2.4 mM Conductivity carbonate
1.0 mM carbonate, 10 mM sodium dihydrogen borate 1.8 m M carbonate, 1.9 mM hydroxide 10 mM hydroxide
__
~~~~
Ref 125-134,
90
Conductivity, ampemmetry Conductivity
126, 136
Conductivity
137
5.0 mM tetraborate 184mvhr
Conductivity
137
0.5 mM phthalate, pH 5.5 2.0 mumin
Conductivity
138
0.35 mM phthalate, pH 4.8 2.0 mVmin
Conductivity
139
135
322 mvhr
Water with multiple injections 3 elecucde of 1.0 M hydrochloric acid plasma atomic 2.0 mVmin emission spectroscopy
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
140
9
TABLE 16.4 (CONTINUED) ANALYSIS OF OTHER NATURAL WATERS USING IC Solutes (min)
Sample
Sample Prep.
Bromide (6.0)
U.S. Geological Survey standard reference natural water Magnesium (6.5), calcium (12) Natural water Fluoride (1.86), chloride (2.44), nitrate (4.89), sulfate (6.66) System peak (0.15), chloride (0.3), nitrate (0.55), sulfate (1.7) Chloride (5.39), nitrite (6.97), bromide (8.80), nitrate (10.56) Fluoride (3.7), bicarbonate (5.2), chloride (8.5), nitrate (20) Carbonate (1.65), chloride (2.19), sulfate (8.67)
Formate (5.70), acetate (8.83), propionate (11.04)
Surface, ground waters
Filtration
Ground water
Filtration with filter paper then Millex filters
Ground water
Column
Eluent
Dionex anion separator 250 x 4.0 mm ID
3.0 mh4 bicarbonate, 2.0 mM Conductivity, 141 carbonate ampemmetry 2.3 mumin at Ag electrode
Dionex cation separator Dionex fast-run anion separator 250 x 4.0 mm ID Wescan Ion Guard anion cartridge 40 x 6.0 m m ID Waters IC Pak A 50 x 4.6 mm ID
3.5 mM hydrochloric acid, 3.5 mM lysine 3.0 mM bicarbonate, 2.4 mM carbonate 2.0 ml/min 15 mM phthalic acid, pH 2.5 5 ml/min
Ground water
Filmtion
Ground water
Dilution in eluent Waters IC Pak A 50 x 4.6 mm ID
Surface water
Waters ion exclusion 300 x 7.8 mm ID
Waters IC Pak A 50 x 4.6 mm ID
2.6 mM lithium benzoate, pH 6.7 1.2 ml/min 10 mM sodium acetate 1.2 mumin
Detection
Ref
Conductivity
126
Conductivity
19, 86, 88, 141, 142 143, 144
Indirect spectrophot. at 300 nm Conductivity 145 Conductivity
146
0.54 g/l boric acid, 0.14 ml/l Conductivity gluconic acid, 0.16 @ lithium l hydroxide, 2ml glycerine (12.5% ACN) 1.2 ml/min 0.1 mM sulfuric acid (10% Conductivity ACN) 1.2 ml/min
147
See p. 487 for notes on the organizarion of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
148
5. s3
VI
TABLE 16.4 (CONTINUED) ANALYSIS OF OTHER NATURAL WATERS USING IC Solutes (min)
Sample
Chloride, nitrate, sulfate
Sample Prep.
63 0
Column
Eluent
Detection
Ground water
Waters IC Pak anion 50 x 4.6 mm ID
0.54 gil boric acid, 0.14 ml/l Conductivity gluconic acid, 0.16 g/l lithium hydroxide, 2ml glycerine (12.5%ACN)
Bromide (l.l), iodide (6.0)
Ground water
Nitrate (4.10)
Ground water
Dionex anion separator Dilution in eluent Waters IC Pak A 50 x 4.6 m m ID
Nitrate (as o-nitrophenol) (6.2)
Surface, ground waters
Chromate (4.4)
Surface water
Zinc (2.8), iron (11) (9.2)
Ground water
Uranium (7)
Ground water
5.0 mM carbonate, 1.0 mM Ampenmeny pcyanophenol(2.5% MeOH) Direct 2.5 mM octanesulfonate 1.2 mumin spectrophot. at 214 nm Amperomeay, RP-18 50 mM phosphate buffer, Pre-column -0.47V derivatization pH 5.4 (55% MeOH) 1.5 Mmin with phenol Dilution SpherisorbODs 0.2mM tembutylammonium Quenched 120 x 4.6 m m ID chloride, 5.0 mM biacetyl, phosphorescence 2.0 mM phosphate buffer, pH 7.1 (5% ACN) 1 .O ml/min ReversedDurmm DC-4A 0.25 M tartrate, pH 4.0 pulse cation-exchanger 0.62 ml/rnin 50 x 4.0 m m ID pol~graPhY Direct Preconcentration Brownlee bonded- 0.12 to 0.2 M a-hydroxyspectrophot. at on Brownlee phase cationisobutyric acid, pH 4.5 650 nm after bonded cation exchanger gradient post column pre-column 250 x 4.0 mm ID 2.5 M m i n reaction with Arsenazo
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
Ref 149
150 147 151 152
153 154
f5
Irl
TABLE 16.4 (CONTINUED)ANALYSIS OF OTHER NATURAL WATERS USING IC Solutes (min)
Sample
SarnpleRep.
Column
2 Eluent
Detection
Ref
sli
m
Fluoride (2.0). chloride (3.2). bromide ( K O ) , sulfate (14)
Well water (geothermal)
2
Dilution
Dionex anion separator
2.0 mM bicarbonate, 1.6 mM Conductivity carbonate
500x3.0mmID
115mVhr 3.0 mM bicarbonate, 2.4 mM carbonate, pH 9.72 1.5 1 Wmin 3.0 mM bicarbonate, 2.0 mM carbonate, pH 9.24 1.51 ml/min 2.5 mM bicarbonate, 1.5 mM carbonate, pH 9.56 1.51 Wmin 3.0 mM nitric acid 184 mVhr
155
B
?$ =: * Q
Selenate (27)
Well water
Re-injection
Dionex AS-3
Selenite (20)
Well water
Re-injection
Dionex AS-3
Arsenate (25)
Well water
Re-injection
Dionex AS-3
Lithium (4.6). sodium (6.0). ammonium (9.3). potassium (11.2), rubidium (15) Lithium (4.0), sodium (5.4), ammonium (7.9), potassium
Well water (geothermal)
Dilution
Well water
Dilution
Dionex cation separator 250 x 6.0 mm ID TSK gel IC cation 2.0 mM nitric acid 50 x 0.35 mm ID 2.8 plfmin
(8.8)
Conductivity
114
Conductivity
114
Conductivity
114
Conductivity
155
Indirect 156 spectrophot. at 225 nm after postsuppressor anion
Sodium (3.8). ammonium (4.6). potassium (5.2)
Well, run-off waters
Dionex cation separator 250 x 6.0 mm ID
5.0.mM hydrochloric acid 180 rnlJhr
replacement Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
45
3
z
2
TABLE 16.4 (CONTINUED) ANALYSIS OF OTHER NATURAL WATERS USING 1C Solutes (min)
Sample
Sample Prep.
Magnesium (4.6), calcium (6.4) Well, run-off waters
0
Column
Eluent
Detection
Ref
Dionex cation separator 250 x 3.0 mm ID
2.5 mM hydrochloric acid, 2.5 JIMm-phenylenediamine dihydrochloride 115 m l k 2.5 mM phthalate, 0.4 mM ciuate, pH 6.8 3.0 mVmin
Conductivity
45
Indirect 38 speceophot. at 265 nm
Fluoride (1.83). chloride (2.5), Bore water nitrate (4.99, sulfate (13.41)
Filmtion
Synchropak AX300
Fluoride (2.7). chloride (3.3, nitrate (8.5), sulfate (12)
Interstitial, core and glacial slab waters Interstitial water
Hydraulic press
SAV-300 centre grafted ionite 700X4mmLD Vydac 302 IC 250 x 4.6 mm ID
2.4 mM bicarbonate, 0.7 mM Conductivity carbonate 2.0 mllmin 4.0 mM phthalate, pH 4.5 Conductivity 2.0 ml/min
Interstitial sediment water
An-ex precolumn, filtration, complexation of iron with cyanide Ag form cat-ex to remove chloride Formaldehyde addition, whirlpak storage, 5.5 ml injection
Dionex AS- 1 250 x 3.0 mm ID
3.6 mM bicarbonate, 2.4 mM Conductivity carbonate 150 mvhr
158
Dionex anion separator 250 mm Dionex AS-3
3.0 mM bicarbonate, 2.4 mM Conductivity carbonate
159
1 mM bicarbonate, 0.2% (v/v) formaldehyde 2.0 mumin
20
Chloride (3.8), nitrate (5.0), sulfate (12.3), bicarbonate (1 8.2) Chloride (4.4). phosphate (6.0). nitrate (12.0), sulfate (17.9)
Chloride (5.9), nitrate (14.3), sulfate (21.5)
Sediment core pore water
Acetate (3.3, formate (4.8), Antarctic ice methanesulfonate(6.9), hydroxymethanesulfonate(8. l), chloride (13.0)
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
157 29
h
TABLE 16.4 (CONTINUED) ANALYSIS OF OTHER NATURAL WATERS USING IC Solutes (min)
Sample
Acetate (8.7). fluoride (8.7), formate (10.4). methanesulfonate (12.5), chloride (16.8) Acetic (9.8), formic (10.5), propionic (12.9), butyric (14.7), system peak (17.0)
Antarctic ice
Chloride (4), nitrate (1 l), sulfate (14)
Antarctic ice, snow
Antarctic ice
Chloride (3), sulfate (9), nitrate Antarctic ice, (16) snow Nitrate, sulfate
Antarctic ice
Sodium (lo), ammonium (12), Antarctic ice, potassium ( 14) snow Sodium, ammonium
Antarctic ice
Chloride (2.5), nitrate (6.0), sulfate (9.6)
Snow
Sample Prep. Large injection volume, melting in laminar flow cabinet Preconcentration (7 mi) on Waters anion concentrator Air-free melting of ice cores, preconcenmtion Air-free melting of ice cores, preconcentration Large injection volume, melting in laminar flow cabinet Air-free melting of ice cores, preconcentration Large injection volume, melting in laminar flow cabinet Filtration
Column
2-. Eluent
Detection
Dionex AS-3
0.7 mM bicarbonate 2.0 ml/min
Conductivity
Bio-Rad HPX87H organic acid 300 x 7.8 mm ID
5.0 mM methanesulfonic acid, pH 2.7 0.8 ml/min
Direa
Dionex anion separator 250 x 4.0 mm ID Dionex AS-2 125 x 4.0 mm ID
2.5 mM bicarbonate, 2.0 mM Conductivity carbonate 280 m l b 3.0 mM carbonate, 2.0 mM Conductivity hydroxide 250 mvhr 2.0 mM carbonate Conductivity 2.0 d m i n
Dionex AS-3
Ref 160-162
spectrophot. at 200 nm 164, 162, 165 164 160, 161
Dionex cation separator 250 x 6.0 mm ID Wescan cationexchanger
5.0 mM hydrochloric acid 280 mvhr
Conductivity
164, 162
4.0 mM nimc acid 2.0 mumin
Conductivity
160, 161
Dionex anion separator 500 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM Conductivity carbonate 2.0 Wmin
166, 165, 167
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
$
-3
L?1 h)
TABLE 16.4 (CONTINUED) ANALYSIS OF OTHER NATURAL WATERS USING 1C Solutes (min)
Sample
Sample Prep.
Chloride (2.1), nitrate (2.5), sulfate (5.9)
Snow
Chloride, nitrate
Snow
Filtration
Sulfate
Snow
Filtration
Chloride (3.4), nitrate (5.0), calcium (7.4), magnesium (8.7),sulfate (14.2)
Snow
Dilution, filtration
Column
Eluent
Deuxtion
Ref
Home-packed resin-based anionexchanger 500 x 2.0 mm ID Vydac 302 1C 250 x 4.6 mm ID Vydac 302 IC 250 x 4.6 mm ID TSK-gel ICAnion-SW 50 x 4.6 mm ID
0.4 mM phthalic acid, pH 5.6 Conductivity 0.93 ml/min
168
1 mM phthalate, pH 4.0 3.0 mVmin 1 mM phthalate, pH 5.2 3.0 mVmin 1.0 mM EDTA, pH 6.0 1.O mVmin
Conductivity
166
Conductivity
166
Conductivity, 53 direct specaophot. at 210 nm
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p, 74.5).
P6
‘r
0%
TABLE 16.5 ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC x
Solutes (min) Fluoride (4), chloride (3, nitrate (12), sulfate (19)
Sample
Chloride (3.3), nitrite (5.0), nitrate (8.4), sulfate (14)
Propionic (1.3), acetic (1.6), lactic (5.0), formic (7.5) Formate (9.3), acetate (11.2), propionate (12.5)
Column
Ambient air (high Carbonate buffer Dionex anion altitude) extraction of separator filtem 500 x 3.0 mm ID
Chloride (2.2), nitrogen oxides Ambient air as nitrite (2.6), nitrate (4.3), sulfur dioxide as sulfite (6.3), sulfate (6.8) Acetate (2.63), formate (2.97), chloride (3.23), nitrite (6.67), nitrate (15.00), sulfate (24.55)
Sample Prep.
Detection
Ref
3.0 mM bicarbonate, 2.4 mM Conductivity CarboMte 1.3 ml/min
169-181
2.0 mM carbonate, 0.75 mM Conductivity bicarbonate 1.7 ml/min
182, 183
2.0 mM b i c h n a t e , 1.67 mM carbonate 0.5 Wmin
Conductivity
22
Waters IC PaK A
0.75 mM phthalate, pH 6.5
Conductivity
184
TSK-gel IC anion
sw
Conductivity
185
50 x 4.6 mm ID
1.0 mM phthalic acid (5% ACN) 0.6 ml/min
Dionex AS-2 ion exclusion 250 x 4.0 mm ID
1.0 mM aidecafluoroheptanoic acid (1% isopropanol) 1.8 Wmin
Conductivity
22
Sorption on c18 Dionex A S 4 Sep-Pak coated with triethanolamine and hydroxide Filtration Dionex AG-3 250 x 4.0 mm ID
Exaacts from hydroxide impregnated air filters Nitration plate Coating (passive monitor) xemoval, aqueous dissolution, filtration Ambient air Alkaline sorption, evaporation concentration Aqueous extracts Filtration from air filters
Eluent
50 x 4.6 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
2 f?.
@ B 6'
@ t:
2
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC Solutes (min)
Sample
Sample Prep.
Column
Inorganic acids as nitrate (1 1). sulfate (19)
Atmospheric air
Home-packed anion-exchanger 500 x 3.0 mm ID
3.0 mM carbonate 1.7 d m i n
Conductivity
Hydrochloric acid (as chloride) (3.8), nimc acid (as nitrate) (9.1)
Ambient air
Extraction of sodium carbonate coated denuder and filter Aqueous extraction of membrane filters
Vydac 302 IC 250 x 4.6 mm ID
1.7 rnM salicylate, pH 4.8 1.68 ml/min
NitTogen oxides (as nitme), sulfur dioxide (as sulfate)
Ambient air
Extrdction of filters
4.0 mM phthalate, pH 4.5
Monochloroacetyl chloride as monochloroacetate (4.8), chloride (8.7)
Air collected on silica gel
1.5 mM bicarbonate 3.0 d m i n
Conductivity
189, 190
Methanesulfonate (6.5), chloride (7.8)
Air filter extracts
Dionex fast-run anion
0.9 mM bicarbonate
Conductivity
39
Formaldehyde (as formate), acetaldehyde (as acetate)
Ambient air
Bicarbonate extraction, sonication, filtration Cat-ex in Ag form to remove chloride, large injection volume Peroxide sorption, dilution
Wescan standard anion 260 x 4.6 mm ID Dionex anion separator 500 x 3.0 mm ID
187 Indirect spectrophot. at 254, indirect fluorescence at 326,370 nrn Conductivity 188
1.5 mM bicarbonate 103 mVhr
Conductivity
191
Formic acid, acetic acid
Ambient air
Dionex anion separator (x2) 250 x 3.0 mm ID 500 x 3.0 mm ID Wescan ion exclusion
0.25 mM sulfuric acid
Conductivity
192
Aqueous extraction of denuder tubes
Eluent
P
Detection
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
Ref 186
83
4 o\
b
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AND AIRBORME PARTICULAT?ZSUSING IC Solutes (min)
Sample
Formaldehyde (as formate) (5.2)
Air collected on impregnated charcoal
Sample Prep.
Column
Eluent
2-. Detection
Ref
2 rb
Hydroxymethanesulfonic acid, sulfur dioxide (as sulfate) Sulfate (10)
Sulfate (15)
Aqueous peroxide extraction, sonication, filtration Ambient air Sorption, formaldehyde addition Coating Sulfation plate (passive monitor) removal, carbonate buffer dissolution, pH adjustment, filmion Sulfation plate Coating (passive monitor) removal, carbonate buffer dissolution, pH adjustment,
Dionex anion separator 500 x 3.0 mm ID
5.0 mM tetraborate 2.3 Wmin
Dionex anion separator 250 x 3.0 mm ID Waters IC PAK A 50 x 4.6 mm ID
1.O mM potassium hydrogen Conductivity phthalate 2.3 ml/min
194
0.54 g/l boric acid, 0.14 ml/l gluconic acid, 0.16 gll lithium hydroxide, 2nd glycerine (12.5% ACN)
Conductivity
184
Waters IC PAK A 50 x 4.6 mm ID
0.75 mM phthalate, pH 6.5
Conductivity
184
Dionex anion separator 500 x 3.0 mm ID Dionex cation separator 250 x 9.0 mm ID
3.0 mM bicarbonate, 2.0 mM Conductivity carbonate 2.3 Wmin 1.5 mM hydrochloric acid Conductivity 3.5 ml/min
195
Conductivity
193
Ambient air
Ammonia (9.7), monomethylamine (12.0), dimethylamine (15.6), mmethylamine (18.2)
Ambient air
Aqueous desorption of filters Desorption with acidified aqueous methanol
E b
8z
filtration Ammonium sulfamate (3.3)
t
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
196
8.i:
za
TABLE 16.5 (CONTINLIED) ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC Solutes (min)
Sample
Ammonia ( 11.4), methylamine Ambient air (12.9), dimethylamine (15.1), mmethylamine (17.3) Ambient air Monoethanolamine (1 lS), diethanolamine (14.7), methanolamine (17.8) Sodium (6.5), ammonia (10.0), Ambient air potassium (12.2) Ammonia
Ambient air
Fluoride (5.7), chloride (7.2), phosphate (1 1.4). nitrate (14.8). sulfate (19.6)
Airborne particulates
Fluoride (2.0). foxmate (2.5). Airborne aerosol acetate (3.3), chloride (4.8). nitrite (5.7). nitrate (16), sulfate (27) Chloride (4.7), nitrite (6.8), bromide (7.4), nitrate (lo.@, sulfate (17.9)
Atmospheric aerosols
Sample Prep.
Column
Aqueous extraction of glass fiber fdters Desorption with water, frlmtion
Dionex cation separator 250 x 6.0 mrn ID Dionex NS- 1 separator
Aqueous extraction of air filters Aqueous extraction of denuder tubes Carbonate extraction of air filters Extraction of filters
Aqueous extraction (sonication) of filters
Eluent
Detection
Ref
2.5 mM nitric acid ll0mvhr
Conductivity
197, 198
5.0 mM hexanesulfonic acid 1.O ml/min
Conductivity
199
Dionex cationseparator 250 x 4.0 rnm ID Wescan cation exchanger
6.0 mM nitric acid 276 mVhr
Conductivity
200
2.0 mM nimc acid
Indirect conductivity
192
Dionex anion separator
3.0 rnM bicarbonate, 2.4 mM Conductivity carbonate
Dionex anion separator and B i e Rad AG 50W-X4 in series 250 x 4.0 mm ID 100 x 9.0 mm ID Vydac 302 IC 250 x 4.6 mm ID
1.5 mM bicarbonate, 1.2 mM Conductivity carbonate 150 mvhr
1.0 mM phthalate, pH 5.5 2.0 d m i n
Conductivity
See p . 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
201219. 1. 128. 138, 192 220
221
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC Solutes (min)
Sample
Sample Prep.
Column
Chloride (2.4). nitrite (2.6), nitrate (3.6). sulfite (7.9), sulfate (9.8). oxalate'(l3j Chloride (2.3). bromide (2.9), nitrate (3.3), sulfate (5.7)
Fog droplets
Filtration, dilution
Dionex AS-4A
Atmospheric aerosol
Aqueous Vydac 302 IC extraction of 250 x 4.6 mm ID glass-fibre filters Aqueous Vydac 302 IC 250 x 4.6 mm ID extraction of membrane filters
Chloride (3.8). nitrate (9.1). sulfate (15.5); system peak'' (20.0)
Aerosols
Chloride (2.2), nitrate (4.0), sulfuric acid (as sulfate) (6.0), benzoate (7.5)
Atmospheric aerosol
Bromate (6.9), nitrite (10.0), bromide (12.8), nitrate (14.9)
Suspended Aqueous parriculatematter extraction of air filters Suspended Aqueous Permaphase AAX parriculatematter extraction of air film Suspended Aqueous ZipaxSAx particulate matter e x d o n of air 500 x 2.1 mm ID filters
Nitrite (4.0), nitrate (4.9), iodide (12.3), thiocyanate (29.7) Bromate (1.3). nitrite (2.0), bromide (3.7), nitrate (4.9)
Benzaldehyde extraction of filters, backextraction, reinjection IC
Dionex AS-2 ion exclusion and YEW anion separator 200 x 9.0 mm ID 250 x 4.6 mm ID Permaphase AAX
Eluent
Detection
0.5 mM bicarbonate, 1.3 mM Conductivity carbonate 2.0 d m i n 3.0 mM phthalate, pH 5.0 Indirect 2.0 d m i n spectrophot. at 280 nm 1.7 mM salicylate,pH 4.8 Indirect 1.68 ml/min spectrophot. at 254, indirect fluorescence at 326,370 nm 1.O mM hydmchloric acid Conductivity and 4.0 mM bicarbonate, 4.0 mM carbonate 2.7 d m i n 4.5 ppm copper sulfate 4.5 ppm copper sulfate
300 mgfl magnesium sulfate 1.5 d m i n
Ref 222, 223 224 187
225
Direct 226 spectrophot. at 210 nm Direct 226 specmophot. at 210 nm Direct 227 spectrophot. at 200 nm
Seep. 487 for notes on the ofganizationof this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
-
v1
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC
30
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Chloride (2.7). bromide (4.0), nitrate (5.3)
Atmospheric aerosol
Aqueous
Vydac 302 IC 250 x 4.6 mm ID
20 mM methanesulfonicacid, pH 4.5 2.0 d m i n 2.0 mM perchlorate, pH 5.4 2.0 d m i n
224 Direct specmphot. at 190 rim 224 Direct specmphot. at 190 nm Conductivity 188
Chloride (5.7), bromide (6.1), nitrate (6.7)
Atmospheric aerosol
Chloride, nitrite, nitrate, sulfate Particulates, fogwater Chloride, nitrate, sulfuric acid (as sulfate)
Atmospheric aerosol
Fog droplets Fluoride (5.4), acetate (6.I), formate (7.6) Hydrogen cyanide (as formate) Ambient aerosol (7.0)
Formaldehyde as formate
Ambient aerosol
Formic acid (7.1)
Ambient aerosol
extraction of
glass-fibre filters Aqueous extraction of glass-fibre filters Extraction of filters
Vydac 302 IC 250 x 4.6 mm ID
Wescan standard anion 260 x 4.6 mm ID Extraction of air YEW anion filters separator 250 x 4.6 mm ID Filmtion, Dionex AS-4A dilution Hydroxide Dionex anion sorption, separator hydrolysis, 500 x 3.0 mm ID dilution, cat-ex clean-up Peroxide elution Dionex anion of impregnated separator charcoal sorbent 500 x 3.0 mm ID tube Aqueous Dionex anion extraction of separator Chromosorb 500 x 3.0 mm ID collection tube
4.0 mM phthalate, pH 4.5
Ref
4.0 mM bicarbonate, 4.0 mM Conductivity carbonate 2.0 d m i n I .5mM tetraborate Conductivity 1.0 ml/min 5.0 mM sodium borate Conductivity 138 mVhr
228
5.0 mM sodium tetraborate 138 ml/hr
Conductivity
230, 23 1
2.5 mM sodium tetraborate
Conductivity
232
222, 223 229
115ml.h
Seep, 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
P5
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC Solutes (min)
Sample
Sample Prep.
Column
Methanesulfonic acid
Atmospheric aerosol
Dionex anion separator
0.17 mM carbonate, 0.22 mM bicarbonate
Conductivity
233
Sulfur dioxide (as sulfate)
Atmospheric aerosol Airborne particulates collected on Teflon filters Airborne particulates Atmospheric particulates
YEW anion separator 250 x 4.6 mm ID Dionex anion separator 250 x 3.0 mm ID
4.0 mM bicarbonate, 2.0 mM Conductivity carbonate 2.0 ml/min 3.5 mM carbonate, 2.6 mM Conductivity hydroxide 69 mvhr
234
Sulfate
Carbonate buffer extracts of glass filters and impingers Extraction of air filters, peroxide oxidation Extraction
YEW Anion SAX-1 Dionex anion separator 250 x 3.0 mm ID
4.0 mM bicarbonate, 4.0 mM carbonate 3.3 mM bicarbonate, 2.6 mM carbonate 1.5 ml/min
Direct 237 spectrophot. at 224 nm
Dionex anion separator
0.8 mM borate buffer
Conductivity
233
vydac 400
2 mM nimc acid
238
Dionex cation separator 200 x 4.0 mm ID
3.0 mM hydrochloric acid 1.92 ml/min
Indirect conductivity Conductivity
Phosphate (4.5) Benzoic acid (1.3)
Pyruvic acid
Lithium (4), sodium (6), ammonium (8), potassium (10) Sodium (4.8), ammonium (6.7), potassium (7.3)
Extraction of filters, centrifugation, evaporation, dissolution in eluent Atmospheric Aqueous aerosol extracts of glass filters and impingers Filter dust residue Dilution in eluent, filtration Ambient aerosol Aqueous extraction of filters
Eluent
Detection
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendir B (p. 745).
Ref
235
236
2 18, 202, 203
VI N
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AMD AIRBORNE PARTICULATE3 USING IC Solutes (min)
Sample
Sample Prep.
Column
Sodium (3.7), ammonium (5.9). potassium (7.1) Sodium (5.8), ammonium (8.3). potassium (9.6)
Fog droplets
LCA KO1 cation separator Dionex cation separator
Sodium, ammonium
Particulates, fogwater
Filtration, dilution Aqueous extraction of air filters Extraction of filters
Ammonia
Atmospheric aerosol
Aqueous extraction of air filters Filtration, dilution
Dionex CS- 1 200 x 4.0 mm ID LCA KO1 cation separator
Air particulates
Magnesium (4.7), calcium (7.1) Fog droplets
Inorganic acids as chloride (3.2), bromide (9,nitrate (6), sulfate (12) Inorganic acids as bromide, nitrate, sulfate, phosphate Chloride (1.8), sulfite (4.8), sulfate (5.4)
Desorption of filters or tubes with eluent, filtration, dilution Industrial Silica gel vapours, sorbent, particulates desorption in eluent Packed tower air Sodium sulfite sorption, dilution Wmkroom vapours and aerosol
Eluent
0
Detection
Ref
4.5 mM nitric acid 1 .O d m i n 5.0 mM nitric acid 4mVmin
Indirect conductivity Conductivity
222, 223 205
Wescan high speed Nitric acid, pH 2.5 cation
Indirect conductivity
188
5.0 mM hydrochloric acid 2.0 mVmin
Conductivity
234, 239
Conductivity
222, 223
Wescan anion 250 x 4.6 mm ID
1.0 mM histidine, 1.0 mM diaminopropionicacid, 12 mM hydruchloric acid 1 .O d m i n 4.0 m M phthalate, pH 4.5 1.0 mVmin
Conductivity
240
Dionex anion separator 50Ox3mID
3.0 mM bicarbonate, 2.4 mM Conductivity carbonate 138rnVhr
241, 242
Dionex AS-4A
0.75 mM bicarbonate, 2.2 mM carbonate 2.0 mVmin
243
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
b
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC Solutes (min)
Sample
Sample Prep.
Column Dionex AS-3 25Ox4mmID
Eluent
3
Detection
Ref
d
3 3 (D
Workplace air Chlorine dioxide (as chlorite) (10). chlorine (as chloride) (20)
Chloride (2.8), azide (4.8). nitrate (6.5). sulfate (9.3)
effluent
Formic (15.4), acetic (23.31, carbonic (28.8)
Diesel exhaust, mine air
Sorption in iodide and phosphate buffer, column switching Aqueous dissolution, filtration Carbonate sorption
Acetic (7.0),formic (9.6)
Diesel exhaust, mine air
Carbonate sorption
Inorganic acids as chloride, sulfate
Ambient aerosol Sorption from cement kilns
Fluorine (as fluoride)
Paniculates from Hydrochloric brickworks and acid dissolution, aluminium dilution in eluent smelting plant Ambient aerosol Filters extracted from Al smelting with hot 2% Plant NaOH, dilution Paint aerosol Extraction of filters, cenaifugation, filtration
Fluoride Chromate (6.5)
Air bag inflator
3
0.75 mht bicarbonate 138mVhr
Conductivity
244
B
Bp g
Dionex anion separator 500x3.0mmID Dionex ion exclusion 250 x 9.0 mm ID Dionex anion separator 500 x 3.0 mm ID Dionex anion separator 500 x 3.0 mm ID Dionex AS-4
Dionex standad anion separator 500 x 4.0 mm ID Dionex AS-5
2.4 mMcarbonate, 2.0 mM hydroxide 184& 0.1 mM hydrochloric acid 0.7 Wmin
Conductivity
245, 246
Conductivity
247
5.0 mM sodium tetraborate 2.3 W m i n
Conductivity
247
6.0 mM carbonate
Conductivity
248
7.5 mM tetraborate
Conductivity
249
0.3 mM bicarbonate
Conductivity
44
7.0 mM carbonate, 0.5 mM hydroxide
Conductivity
250
103mVhr
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
p’
v,
TABLE 16.5 (CONTINUED) ANALYSIS OF AIR, AEROSOLS AND AIRBORNE PARTICULATES USING IC
Solutes (min)
Sample
Sample Prep.
Ammonium
Industrial hygiene Sorption on Dionex cation aerosols activated carbon separator coated with 500 x 3.0 mm ID sulfuric acid, dilution
Column
Eluent
5.0 mM hydrochloric acid 138 rnm
t4 t 4
Detection Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
Ref
25 1
h
.a’
TABLE 16.6
3
ANALYSIS OF SOILS AND SOIL EXTRACTS USING IC Solutes (min)
Sample Prep.
Chloride (3.6), nitrate (9.3, sulfate (16.0)
Chloride (2.6). nitrite ( 3 3 , bromide (4.6), nitrate (6.1). sulfate (7.8) Nitrite (5. I), selenite (5.8), phosphate (7.2), system peak (9.0), chloride (12. l), nitrate (19.8) Chloride (2.4), nitrite (3.8), nitrate (5.8), sulfate (12.6), selenate (14.4), system peak (21) Chloride (3.6), nitrate (6.2), selenite (8.3), sulfate (1 1.8), selenate (13.5) Fluoride (3,chloride (6), phosphate (1 l), nitrate (14), sulfate (22) Chloride (5.4), nitrate (KO), phosphate (13.3), sulfate (18.4)
Column
Detection
Ref
Extraction, filtration Dionex anion 3.0 mM bicarbonate, 2.4 mM separator carbonate 500 x 3.0 mm ID 138 mVhr
Conductivity
Aqueous extraction, Waters ICPAK A filtration 50 x 4.6 mm ID Aqueous extraction, Vydac 302 IC 250 x 4.6 mm ID filtration, clean-up on Ag pre-column
1.0 mM phthalate, pH 6.5 1.2 ml/min
Conductivity
252258, 16, 128 259
1.5 mM phthalic acid, adjusted to pH 2.7 with formic acid 3.0 ml/min Vydac 302 IC 4.0 mM phthalate, pH 4.6 Aqueous extraction, 250 x 4.6mm ID 2.0 d m i n filtration
Conductivity
260, 261
Conductivity
262
Conductivity
263
Conductivity
264
Aqueous extraction, Wescan 269-069 anion filmtion 250 x 4.1 mm ID Home-packed anion-exchanger 500 x 3.0 mm ID Home-packed Centrifugation, ODs Clg Sep-Pak, 250 x 4.6 mm ID dilution
Eluent
4.0 mMp-hydroxybenzoic acid, pH 8.0 2.0 ml/xnin 9.0 mM bicarbonate, 3.0 mM carbonate 1.38 d m i n 0.5 mM tetrabutylammonium hydroxide, adjusted to pH 7.1 with phthalate (5% MeOH) 1.5 d m i n
z
3,
b
Fs’
g. 2
Indirect spectrophot. 265 at 257 nm
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
ul h)
W
TABLE 16.6 (CONTINUED) ANALYSIS OF SOILS A N D SOIL EXTRACTS USING IC
v, h,
P
Column
Solutes (min)
Sample Prep.
System peak (0.15),chloride (0.3), nitrate (0.55). sulfate (1.7)
Filtration with paper Wescan Ionthen Millex filters Guard anion cartridge 40 x 6.0 mm ID Filtration Synchropak Ax300
Fuoride (1.7). chloride (2.2), nitrate (4.6). sulfate (1 1) Chloride (5.8), nitrite (7.6), bromide (10.3), nitrate (11.1) Chloride (4), nitrate (6), sulfate (10). tungstate (12) Chloride (1.8), nitrate (2.3), sulfate (5) Nimte (I 1.8), chloride/nitrate (14.3). various tracers ions Inositol phosphate (27), phosphate (31), inositol tetraphosphate (49), inositol hexaphosphate (58)
Aqueous extraction, Waters IC-PAK filtration A 50 x 4.6 mm ID Aqueous extraction, Wescan 269-069 centrifugation, anion filtration. silica 250 x 4.1 mm ID Column clean-up Extraction. Wescan 269013 sonication, filtration anion/HS 100 x 4.6 mm ID Extraction, filtration Partisil SAX 250 x 4.6 mm ID
Eluent
Detection
15 mM phthalic acid, pH 2.5 5d m i n
Indirect spectrophot. 143 at 300 nm
2.0 mM phthalate, 0.1 mM citrate, pH 6.8 3.0 Mmin
Indirect spectrophot. 38 at 257 nm
2.5 mM benzoic acid, pH 6.72 1.2 d m i n 5.0 mMp-hydmxybenzoic acid, pH 8.5 2.0 d m i n
Conductivity
259
Conductivity
266
20 mM phthalic acid 2.4 ml/min
Conductivity
267
5.0 mM phosphate buffer, pH 4.0 (10% ACN) 2.0 ml/min Alkaline hmination Bio-Rad Aminex 0.5 mM tetrasodium EDTA, extraction A27 0.1 to 0.5 M sodium chloride 250 x 4.0 mm JD gradient, pH 10.0 0.4 d m i n
Ref
Direct spectrophot. at 268 205 nm Direct spectrophot. at 269 885 nm after persulfate oxidation of 0.4 ml fractions
Seep. 487 for notes on the organizationof this Table. Seep. 534 for Rderences. Abbreviations are listed in Appendix B (p. 745).
h 3,
TABLE 16.6 (CONTINUED) ANALYSIS OF SOILS AND SOIL EXTRACTS USING IC Solutes (min)
Sample Prep.
Column
Eluent
Detection
Ref
Alkyl methylphosphonic acids - EMPA (7), PMPA (11)
Sonication, centrifugation, centriflow membrane cone separation Aqueous salt extraction, filtration
Dionex MPICNSI separator
2.0 mM tetrabutylammonium hydroxide, 1.O mM sodium carbonate (5% ACN) 1.O d m i n 3.0 mM bicarbonate, 1.8 mM carbonate 3.0 d m i n 0.7 gil cimc acid, 0.05 gil cemmide, pH 5.5 (30% MeoH) 1.0 d m i n 5 mM potassium hydroxide 1.2 d m i n Water saturated with tetraheptyl ammonium nitrate, pH 7.6 (25% MeOH) to MeOH gradient 1.0 d m i n 5.0 mM tetrabutylammonium phosphate, pH 7.3 (5% MeOH) 0.5 d m i n 0.0375 M acetate, 0.0375 M aceticacid 0.15 Wmin
Conductivity
270
Conductivity
27 1
Nitrate (5.5). sulfate (10.0) Nitrite (4.6), nitrate (6.4)
Cyanide (4), thiosulfate (16) Arsenite (6). dimethylarsinic acid (lo), methylarsonic acid (23), arsenate (37)
Dionex anion separator 250 x 3.0 mm ID Aqueous extraction, S A X 4 centrifugation 125 x 5.0 mm ID Aqueous extraction, Waters IC Pak A dilution 50 x 4.6 mm ID Extraction Lichrosorb Rp-18 250 x 4.6 mm ID
Arsenate (1l), arsenite (19)
Extraction
Waters Wondapak c18 300x4.0mmID
Arsenate (22). arsenite (35)
Extraction
Altex SCX 250x3.2mmID
0’ 3
k
B3
Direct spectrophot. at 272 220 nm, ampemmetry at +l.OV ArnpemmetryatAg 104 electrode Graphite furnace 273 atomic absorption specaoscopy Graphite furnace atomic absorption SPecaosCoPY
273
Graphite furnace atomic absorption spectroscopy
273
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
ul VI h)
v,
TABLE 16.6 (CONTINUED) ANALYSIS OF SOILS AND SOIL EXTRACTS USING IC Solutes (min)
Sample Prep.
Column
Tungsten (8.6), molybdenum (9.7)
Acid digestion, extraction, ashing, addition of Tiron
Cosmosil CIS 1.5 mM Tiron, 30 mM Direct spectrophot. at 274 150 x 4.6 mm ID teuabutylammonium bromide, 315 nm 1.5 mM acetate buffer, pH 3.8 (57% MeOH) 0.7 ml/min
Nitrate (4.67)
Extraction. filtration Vydac 302 IC 4.0 mM phthalic acid, 250 x 4.6 mm ID adjusted to pH 5.0 with borate 2.0 ml/min Dionex AS-4 1.8 mM bicarbonate, 1.2 mM Fusion at 800 OC carbonate with sodium 2.0 mVmin peroxide, dilution, filuation Phosphate Vydac 3001 2.0 mM phthalic acid, extraction, adjusted to pH 5.5 with centrifugation, tetraborate filtration 1.5 ml/min Sieving, extraction, Vydac 401 TP 10 mM nimc acid, pH 2.1 filtration 250 x 4.6 mm ID 1.O mllmin
Conductivity, 43, indirect spectrophot. 275 at 280 nm Conductivity 27 6
Aqueous extraction, Zipax SCX filtration 50 x 2.1 mm ID Extraction Dionex cation separator 250 x 6.0 mm ID Filtration, extraction, Dionex cation dilution separator 250 x 6.0 mm ID
3.0 mM hydrochloric acid 1.5 f l m i n
Indirect conductivity 279
5.0 mM hydrochloric acid 180 mVhr
Conductivity
45
1 .O mM barium nitrate, pH 4.0 2.3 ml/min
Conductivity after sulfate-suppression of barium (ppt)
1 18
Sulfate (6.1)
Sulfate
Lithium (1.5). sodium (2.2), ammonium (3.0), potassium (3.9) Sodium (2.5), lithium (3.5). ammonium (5.0) Sodium (3.8), potassium (5.2)
Magnesium (6.0), calcium (8.5)
Eluent
N
cn
Detection
Conductivity
Ref
277
Indirect conductivity 278
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
9
280
h
TABLE 16.6 (CONTINUED) ANALYSIS OF SOILS AND SOIL EXTRACTS USING IC Solutes (min)
Sample Prep.
Column
Magnesium (1.8), calcium (2.8)
Sieving, extraction, filtration
5.0 mM ethylenediammonium Conductivity Vydac 401 TP 250 x 4.6 mm ID dinitrate, pH 6.1 1.O d m i n
27 8
Magnesium (3.6), calcium (5.8)
Aqueous extraction
281
Iron (111) (3.32), lead (5.15), zinc (7.73, nickel (8.38), cobalt (11.28), cadmium (15.15), iron (XI) (15.35), manganese (19.08) Aluminium (3.23), magnesium (14.87)
Dilution, filtration, c18 Sep-Pak
Dionex CS-2 2.0 mM citric acid, 25Ox4.OmmID 2mMEDTA 1.5 d m i n Waters 2.0 mM octanesulfonate,50 @ondapak c l 8 mM tartaric acid, pH 3.4 150 x 3.9 mm ID 0.8 ml/min
Chloride (3.4), nitrate (KO), calcium (7.4), magnesium (8.7), sulfate (14.2)
Aqueous extraction, TSK-gel ICAnion-SW dilution, filtration 50 x 4.6 mm ID
Nitric acid digest. fination, dilution
Eluent
3 e
LiChrosphere 2.27 mM n-cctanesulfonic RP-18 acid, 8.18 mM tartaric acid, 125 x 4.0 mm ID 52.9 mM a-hydroxyisobutyric acid, pH 4.1 (10.7% Meom 0.8 d m i n
1.0 mM EDTA, pH 6.0 1.0 d m i n
Detection
Conductivity
Ref
Direct spectrophot. at 282 520 nm after postcolumn reaction with PAR Fluorescence of 283 oxine derivative after post-column membrane phase extraction with 8hydroxyquinolinein MIBK Conductivity,direct 53 spectrophot. at 210 nm
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
3.
s
v,
TABLE 16.7
N
W
ANALYSIS OF GEOLOGICAL MATERIALS USING IC
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride (2.6). sodium (4.0), chloride (5.7)
Geological samples
Dionex AS-3 250 x 3.0 mrn ID
3.0 mM bicarbonate, 2.4 mM carbonate 138 ml/hr
Conductivity
284
Fluoride, chloride, sulfate
Geological
Fusion, dilution, filtration. cat-ex clean-up Pyrolysis with vanadate, sorption in eluent Fusion, dilution, filtration
Dionex AS-3 250 x 6.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 175 mvhr
Conductivity
285
3.0 mM bicarbonate, 2.4 mM carbonate 138 mvhr 3.0 mM carbonate, 1.5 mM hydroxide 138 mvhr 1.5 mM bicarbonate 2.15 Wmin
Conductivity
286
Conductivity
284
Conductivity
287
3.0 mM bicarbonate, 2.4 mM carbonate 156 mvhr
Conductivity
288
5.0 mM tetraborate
Conductivity
288
XMterialS
Fluoride (3.6), carbonate (4.9)
Geological samples
Chloride (9)
Geological samples
Dionex fast anion separator 250 x 3.0 mm ID Fusion, dilution, Dionex AS-2 fitration 250 x 3.0 mm ID
Fluoride
Geological materials
Dionex AS-3 250 x 3.0 mm ID
Fluoride (2.3). chloride (3.7), phosphate (4.3, sulfate (6.9) Fluoride (3.7), acetate (5.0). propionate (5.0),fonnate (7.3)
Hydropyrolytic extraction with humidified air Rocks, oil shales Phosphoric acid volatilization, hydroxide sorption Rocks,oil shales Phosphoric acid volatilization, hydroxide sorption
Dionex fast-run anion 250 mm
Dionex fast-run anion 250 mm
156 mvhr
See p . 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviatiom are listed in Appendix B (p. 745).
EQ
h
TABLE 16.7 (CONTINUED) ANALYSIS OF GEOLOGICAL MATERIALS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride, chloride, sulfate
Rocks
3.0 mM bicarbonate, 2.4 mM carbonate 1383.0 mM carbonate, 1.5 mM hydroxide 138 mVhr 3.0 mM bicarbonate, 2.4 mM carbonate 2755.0 mM phthalic acid 1.0 d m i n
289, 290
Oil shales
Dionex anion separator 500x3.0mmID Dionex AS-2 (x2) 250 x 3.0 mm ID
Conductivity
Chloride (8), sulfate (23)
Combustion, sorption in eluent Sintering, dilution, filtration
Conductivity
29 1
Thiosulfate (4)
Oil shale leachatis
Phosphate (1 1)
Standard rocks
Magnesium (3.6), calcium (5.8) Rocks Lutetium (2.8), ytterbium (3.1). Rocks thulium (3.4), erbium (3.7), holium (4. l), ytmum (4.2). dysprosium (4.3), terbium (4.9). gadolinium (5.7), europium (6.1), samarium (6.8), neodymium (8.5), praseodymium (9.1), cerium (9.9), lanthanum (11.3)
Dionex anion separator 75x3.0mmID Hyhfluoric Wescan 269-001 acid liberation of anion volatile 250 x 4.6 mm ID phosphorus, sorption in eluent Aqueous Dionex CS-2 extraction of 250 x 4.0 mm ID powdered rock NitricNuclwil C18 hydrofluoric 125 x 4.6 mm ID acid digest, oxalic acid dissolution, ionexchange precolumn cleanup
5 3
2.0 mM citric acid, 2 mM EDTA, pH 4.0 1.5 Wmin 10 mM octanesulfonate, 0.05 to 0.5 M hydroxyisobutyric acid gradient, pH 3.8 1.5 Wmin
s2
B
$
3=.
8 Conductivity
292
Conductivity
293, 294
Conductivity
281
Direct specaophot. at 658 nm after post-column reaction with Arsenau, ID
295
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
tn
s:
VI
TABLE 16.7 (CONTINUED) ANALYSIS OF GEOLOGICAL MATERIALS USING IC
w
0
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride (2.6). chloride (3.1). nimte (3.6), nitrate (5.9), sulfate (7.7), thiosulfate (1 1)
coal
Dionex anion separator 250 x 4.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 2.3 mlfmin
Conductivity
296298
Chloride (8), sulfate (23)
Coal
Conductivity
3, 299
Fluoride
coal
3.0 mM carbonate, 1.5 mM hydroxide 138 mvhr 2.9 mM bicarbonate, 2.3 mM carbonate 2.0 d m i n 1.5 mM bicarbonate 2.15 ml/min
29 I
coal
Dionex anion separator 500 x 3.0 mm ID Dionex AS-4
Conductivity
Sulfate
Conductivity
287
Iron (111) (7). gallium (8), copper (13). indium (17), lead (22). zinc (27). iron (11) (31)
Ores
Pan; oxygen bomb, hydroxide sorption Sintering, dilution, filtration Carbonate fusion, dilution, Donnan dialysis Hy&op@yzation with molybdite , sorption in eluent Digestion, filtration, dilution
Partisil 10 SCX precolumn and Nucleosil 10-SA 50 x 3.0 mm ID 200 x 4.6 mm ID
0.1 M tartrate, 0.12%
300
Fluoride (4.8), chloride (5.2), bicarbonate (8). phosphate (17)
Phosphite ores
3.0 mM bicarbonate 3.5 mlfmin
Fluoride (2.7), chloride (3.2), sulfate (14)
Hydrothermal quartz
Dionex anion separator 250 x 4.0 mm ID SAV-300 centre grafted ionite
Direct spectrophot. at 495 nm after post-column reaction with PAR-Zn-EDTA Conductivity Conductivity
157
Milling, carbonate fusion, dilution Aqueous exuaction, heating
Dionex AS-3 250 x 3.0 mm ID
700X4mmID
sodium chloride, pH 2.25 0.7 mllmin
2.4 mM bicarbonate, 0.7 mM carbonate 2.0 mllmin
Seep. 487 for notes on the organizarion of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B {p, 745).
301
TABLE 16.7 (CONTINUED) ANALYSIS OF GEOLOGICAL MATERIALS USING IC Solutes (min)
Sample
Chloride (4), phosphate (8), sulfate (16) Chloride (4.9), sulfate (17.9)
Scheelite Geothite
Fluoride (0.9)
Texas lignite
Sodium (12.8), ammonium (16.8), potassium (18.4)
Buddingtonite
Dysprosium (3.3, gadoliniun (4.7), europium (5.1), samarium (5.8), neodymium (7.7), praseodymium (8.3), cerium (8.9), lanthanum (10.2)
Zircon, basalt
Ytterbiuddysprosium (lo), terbium (14), gadolinium (18), europium (20), samarium (24). neodymium (29), praseodymium (31). cerium (35). lanthanum (40)
Monazitesand
Sample Prep.
Column
Eluent
Detection
Ref
XAD- 1
0.1 mM citrate, pH 6.0 1.5 nd/min 1.O mM bicarbonate, 0.5 mM carbonate 92 mVhr
Conductivity
302
Conductivity
303
3.0 mM bicarbonate, 1.2 mM carbonate 2.3 mllmin 8.0 mM nimc acid 1.2 mllmin
Conductivity
304
Conductivity
305
Direct spectrophot. at 658 nm after post-column reaction with Arsenazo III Direct spectrophot. after postcolumn reaction with Arsenazo
306
1oOOx3mmID
Hydrochloric acid dissolution, cat-ex removal of iron, dilution Milling, Parr bomb, dilution, fimtion Hydrofluoric, hydrochloric acid microwave dissolution, dilution Hydrofluoric, nitric acid dissolution, ionexchange pretreatment, Millex filmtion
Home-packed pellicular anionexchanger 300 x 3.0 mm ID Dionex anion separator 250 x 3.0 mm ID Dionex CS-1 250 x 6.0 mm ID
Supelcosil LC-18 100 x 4.6 mm ID
10 mM ocranesulfonate, 0.1 to 0.4 M hydroxyisobutyric acid gradient, pH 3.8 2.0 d m i n
-
LiChrosorb KAT 250 x 4.6 mm ID
0.08 to 0.32 M hydroxyisobutyric acid gradient 1.O d m i n
III
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 74s).
307
#
TABLE 16.7 (CONTINUED) ANALYSIS OF GEOLOGICAL MATERIALS USING IC Solutes (min) Iodide (14)
h)
Sample
Sample Prep.
Column
Eluent
Detection
Sedimentary
Aqueous extraction of finely powdered rock, filtration Aqueous extraction of finely powdered rock,filtration Aqueous extraction of finely powdered rock,filtration Hydrochloric acid extraction, peroxide oxidation, preconcentration Filtration
Dionex AS-3 250 x 6.0 mm ID
8 mM carbonate
Amperometryat 308 Ag elecaode, tQ.17V
Dionex AS-3 250 x 6.0 mm ID
20 mM nitrate
Ampemmetryat 308 Ag electrode, 4.17V
Dionex AS-3 250 x 6.0 mm ID
20 mM nitrate, 0.025 mM hydroxide
Amperometryat 308 Ag electrode, 4.17V
Dionex anion separator 500 x 3.0 mm ID
3.0 mM bicarbonate, 1.4 mM carbonate 137 mvhr
Conductivity
309
Vydac 302 IC 250 x 4.6 mm ID
1.0 mM o-phthalic acid, pH 5.0 2.0 d m i n 4.0 mM bicarbonate, 4.0 mM carbonate 3.0 mM bicarbonate, 1.2 mM carbonate
Conductivity
310
Conductivity
236
Conductivity
311
rocks Iodide (6.5)
Sedimentary rocks
Iodide (8.1)
Sedimentary rocks
Chloride (4.0). phosphate (9.2), Core sediment anenate (14.0), sulfate (22.3)
Chloride (5.5). bromide (6.2). nitrate (1023, sulfate (20.0)
River sediment, floc
Phosphate (4.5)
Estuarine
Chloride (2.1)
w
sediment Organohalogens Hexane extraction, in sediment vapour phase reduction over Pt, sorption in eluent
YEW Anion SAX- 1 Dionex anion separator 250 x 3.0 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
Ref
QP
h
TABLE 16.7 (CONTINUED) ANALYSIS OF GEOLOGICAL MATElUALS USING IC Solutes (min)
Sample
Sample Prep.
Column
Sulfate (29.8)
Mud cores
Centrifugation, filtration
Nucleosil SB 150 x 4.6 mm ID
Sulfate (10.8)
Mud cores
Centrifugation, Ntration
Nucleosil SB 150 x 4.6 mm ID
Sulfate (9)
Mud cores
Centrifugation, filtration
Nucleosil SB 75 x 4.6 mm ID
Fluoride (2.5),chloride (3.6), sulfate (12.6)
Volcanic ashes
Aqueous extraction, ultrasonication
Dionex anion separator lo00 x 3 mm ID
2 Eluent 2.0 mM sulfobenzoate, pH 4.7 1.5 d m i n 1.6 mM sulfobenzoate, 0.2 mM trimesic acid, pH 5.5 1.0 d m i n 0.4 mM 5-~~lf0isophthalic acid, pH 4.5 0.8 d m i n
2.0 mM carbonate, 5.0 mM hydroxide 156 mVhr
Detection
Indirect specmphot. at 274 nm Indirect spectrophot. at 285 nm
Ref 312 312
1’
2 ibs.
%R 5:
Indirect 313 spectrophot. at 240 nm, on-line scintillation counter 314 Conductivity
See p . 487 for notes on the organization of this Table. Seep. 534 for References. Abbreviations are listed in Appendix B (p. 745).
VI W
W
Chapiw 16
534
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15 16 17
18 19 20 21 22 23 24 25
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140 141 142 143 144 145 146 147 148 149
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Chapter 16 156 157 158 159 160 161 162 163
164 165 166 167 168 169 170 171
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Kifunc 1. and Oikawa K., Niigata Rikagaku. 5 (1979) 9. Kifune I. and Oikawa K., Bunseki Kagaku, 28 (1979) 587. Bouyoucos S.A. and Melcher R.G., Am. Ind. Hyg. Assoc. J.. 47 (1986) 185. Mulik J.D., Estes E. and Sawicki E., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1978. p. 41. Mueller P.K., Mendoza B.V., Collins J.C. and Wilgus E.S., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromtographic Analysis of Environmental Pollutants, Vol. II. Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 87. Anlauf K.G., Barrie L.A., Wiebe H.A. and Fellin P., Can. Res., 13 (1980) 49. Anlauf K.G.. Wiebe H.A. and Fellin P., J. Air Pollut. Cont. Assoc.. 36 (1986) 715. Appel B.R. and Wehrmeister W.J.. in Sawicki E. and Mulik J.D. (Eds.). Ion Chromatographic Analysis of Environmental Pollutants, Vol. 11, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 223. Butlcr F.E., Jungcrs R.H., Porter L.F., Riley A.E. and Toth F.J., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion Chromatographic Analysis of Envilanmental Pollutants, Vol. I, Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 65. Forrest J., Spandau D.J., Tanner R.L. and Newman L., Atmos. Environ., 16 (1982) 1485. Frazier C.D., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 21 1. Fuchs G.R., Lisson E., Schwarz B. and Bachman K.,Fres. Z Anal. Chem., 320 (1985) 498. Fung K.K.. Hcislcr S.L.,Price A., Nuesca B.V. and Mueller P.K., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 203. Galvin P.J., Samson P.J., Coffey P.E. and Romano D., Environ. Sci. Technol., 12 (1978) 580. Hara H., Nagara K.,Honda K. and Goto A., Osen Gakkaishi, 15 (1980) 380. Lathouse J. and Coutant R.W., in Sawicki E., Mulik J.D. and Wittgcnsicin E. (Eds.), Ion Chromatographic Analysis of Eidronntental Polhittrim, Vol. I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 53. Lewis C.W. and Macias E.S., Atmos. Environ., 14 (1980) 185. Mason D.W. and Miller H.C., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion Chromatographic Analysis of Environmental Pollcrttrnts, Vol. I, Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 193. Mulik J.D. and Sawicki E., Environ. Sci. Technol.. 13 (1979) 804. Mulik I., Puckett R., Sawicki E. and Williams D., NBS Spec. Publ., 464 (1977) 603. Mulik J., Puckett R., Williams D. and Sawicki E., Anal. Lett., 9 (1976) 653. Murano K., Mizuochi M., Uno I., Fukuyama T. and Wakamatsu S., Bunseki Kagakrc, 32 (1983) 620. Stevens R.K., Dzubay T.G.,Russwurm G. and Rickcl D., Atmos. Environ., 12 (1978) 55. Pimminger M., Puxbaum H.. Kossina I. and Wcbcr M., Fres. Z Anal. Chem.. 320 (1985) 445. Willison M.J. and Clarke A.G.,Anal. Chem., 56 (1984) 1037. Baltensperger U. and Kern S., J. Chroniatogr., 439 (1988) 121. Baltensperger U. and Kern S., PSI-Ber., 8 (1988) 88. Ferrer N. and Percz J.J., Inter. J. Environ. Anal. Chem., 27 (1986) 273. Tanaka S., Yamanaka K.. Yamagata K., Komazaki Y. and Hashimoto Y., Bimseki Kagaku. 36 (I 987) 159.
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Environmental Applications
541
262 Karlson U. and Frankenberger W.T., Jr., J. Chromatogr., 368 (1986) 153. 263 Mehra H.C. and Frankenberger W.T., Jr., Chromatographia, 25 (1988) 585. 264 Shpigun O.A., Obrezkov N.O., Voloshchik LN. and Zolotov Y.A.. Zh.Anal. Khim, 40 (1985) 1925. . 265 Bradfield E.G. and Cooke D.T., Analyst (London), 110 (1985) 1409. 266 Mehra H.C. and Frankenberger W.T.. Jr., Anal. C h i n Acta, 217 (1989) 383. 267 Wescan Application #232. 268 Bowman R.S., J. Chromatogr., 285 (1984) 467. 269 Minear R.A., Segars J.E., Elwood J.W. and Mulholland P.J., Analyst (London), 113 (1988) 645. 270 Bossle P.C., Reutter D.J. and Sarver E.W., J. Chromatogr., 407 (1987) 399. 271 Tabatabai M.A. and Dick W.A., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. Il, Ann Arbor Sci. Publ.. Ann Arbor, MI, 1979, p. 361. 272 Wheals B.B., J. Chromatogr., 262 (1983) 61. 273 Brinckman F.E., Jewett K.L., Iverson W.P., Irgolic K.J., Ehrhardt K.C. and Stockton R.A.,J. Chromatogr., 191 (1980) 31. 274 Yamada H. and Hattori T., J. Chromatogr., 41 1 (1987) 401. 275 Nieto K.F. and Frankenberger W.T., Jr., Soil Sci. SOC.A m J.. 49 (1985) 587. 276 Stallings E.A.. Candelaria L.M. and Gladney E.S., Anal. Chem, 60 (1988) 1246. 277 Fox R.L., Hue N.V. and Para A.J., Commun. Soil Sci. Plant Anal., 18 (1987) 343. 278 Nieto K.F. and Frankenberger W.T.. Jr., Soil Sci. SOC.Am. J., 49 (1985) 592. 279 Ahmad M. and Khan A., The Nucleus, 18 (1981) 29. 280 Basta N.T. and Tabatabai M.A., Soil Sci. SOC.Am. J., 49 (1985) 84. 281 Yan D. and Schwedt G., Fres. Z Anal. Chenr, 320 (1985) 121. 282 Waters IC Lab. Report No. 272. 283 Karcher B.D., Krull I.S., Schleicher R.G. and Smith S.B.. Jr.. Chromarographia, 24 (1987) 705. 284 Wilson S.A. and Gent C.A., Anal. Chim Acta. 148 (1983) 299. 285 Hall G.E.M., MacLaurin A.I. and Vaive J., J. Geochem. Exp., 26 (1986) 177. 286 Wilson S.A. and Gent C.A., Anal. Lett., 15 (1982) 851. 287 Conrad V.B. and Brownlee W.D., Anal. Chem.. 60 (1988) 365. 288 Kennedy W.T., Hubbard W.B. and Tarter J.G., Anal. Lett., 16 (1983) 1133. 289 Evans K.L., Tarter J.G. and Moore C.B., Anal. Chem., 53 (1981) 925. 290 Evans K.L. and Moore C.B., Anal. Chem, 52 (1980) 1908. 291 Gent C.A. and Wilson S.A., Anal. Lett., 18 (1985) 729. 292 Trujillo F.J., Miller M.M., Skogerboe R.K., Taylor H.E. and Grant C.L., Anal. Chem., 53 (1981) 1944. 293 Maketon S. and Tarter J.G.. Anal. Lett., 18 (1985) 181. 294 Cox J.A. and Saari R.. Analyst (London), 112 (1987) 321. 295 Cassidy R.M.. Chem. Geol., 67 (1988) 185. 296 Nadkami R.A. and Pond D.M., Anal. Chim. Acta, 146 (1983) 261. 297 Nadkarni R.A., Proc. Coal Test Cant, 3rd, 1983, p. 135. 298 BUKOWS E.P., Brueggeman E.E. and Hoke S.H., J. Chromatogr., 294 (1984) 494. 299 Lathouse J. and Heffelfinger R.E., in Sawicki E. and Mulik J.D. (Eds.). Ion ChromatographicAnalysis of Environmental Polllitants. Vol. II, Ann Arbor Sci. Publ.. Ann Arbor, MI, 1979, p. 59.
542
Chapter 16
300 301 302 303 304
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305 306 307 308 309 310 31 1 312 313 314
543
Chapter 17 I n d u st ria 1 A p p lie at ion s 17.1 OVERVIEW Industrial applications of IC are presented according to the scheme shown in Fig. 17.1.
Wastewaters, effluents (Table 17.1) Other industrial waters (Table 17.2) Organic compounds (Table 17.3) INDUSTRIAL APPLICATIONS OF IC
Pulp and paper (Table 17.4) Acids and bases (Table 17.5) Detergents and polymers (Table 17.6) Fuels, oils, engine products (Table 17.7)
Fig. 17.1 Industrial applications of IC.
E
TABLE 17.1 ANALYSIS OF INDUSTRIAL WASTEWATERS AND EFFLUENTS USING 1C Solutes (min)
Sample Prep.
Fluoride (4.67),chloride (6.91), nitrate (16.26), sulfate (19.39) Fluoride ( 3 . 3 acetate (4.3, formate (7.1), chloride (10.1). carbonate (15.0). nitrate (16.8), sulfate (17.4), phosphate (24.0) Fluoride (1.83), chloride (2.5), nimte (3.2), Filtration phosphate (7.1), sulfate (1 I ) Chloride (4.7), nimte (5.8). phosphate (8.4), nitrate (12.8). sulfate (18.9) Fluoride (2.1), chloride (4.4), phosphate (10.8), nitrate (17.2), sulfate (29) Chloride (2.44), nitrate (4.79, phosphate (6.91), sulfate (10.14)
Eluent
Detection
Ref
Dionex anion separator Dionex AS-5A
3.0 mM bicarbonate, 2.4 mM carbonate 0.75 to 100 mM sodium hydroxide gradient 1.O d m i n 2.0 mM phthalate, 1.0 mM citrate, pH 7.0 3.0 mumin
Conductivity
1-10
Conductivity
9
Indirect spectrophot. at 257 nm
11
Conductivity
12, 13
Conductivity
14
Conductivity
15, 16
Conductivity
17
Conductivity
18
Synchropak Ax300
Ag cat-ex column to Dionex anion separator remove chloride 500x3.0mmID Dionex anion Peroxodisulfate, hydroxide digestion, separator Chelex 100 clean-up 250 x 4.0 mm ID Waters IC Pak A Dilution 50 x 4.6 mm ID
Fluoride (2.6), acrylamide (3.0), chloride (4.9), sulfate (25.0) Fluoride (3), chloride (3.3, nitrate (4.7), sulfate (15)
Column
Dilution
3.0 mM bicarbonate, 2.4 mM carbonate 115mlhr
5.0 mM bicarbonate, 1.5 mM carbonate 2.5 d m i n 0.54 g/l boric acid, 0.14 mv1 gluconic acid, 0.16 gfl lithium hydroxide, 2nd glycerine (12.5% ACN) 1.2 d m i n Dionex anion 3.0 mM bicarbonate, separator 2.4 mM carbonate 250 x 3.0 mm ID 125 mlhr Wescan 269029 2 mM phthalate anion/R 1.6 d m i n 250 x 4.1 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
4
u
3
TABLE 17.1 ICONTINUED) ANALYSIS OF INDUSTRIAL WASTEWATERS AND EFFLUENTS USING IC
8 M
Solutes (min)
Sample Prep.
Fluoride (2.8), chloride (3.4), nitrate (8.9), sulfate ( 11.7)
Dilution, filtration
Column
Detection
Ref
3.0 m M bicarbonate, 2.4 mM carbonate
Conductivity
19-24
Water 1.0 d m i n
Conductivity
25
1.42 mM gluconate. 5.82 mM boric acid, 0.25% glycerine, pH 8.5 1.0 d m i n Dionex A WA 2.2 mM carbonate 1.5 d m i n Dionex anion 3.0 mM bicarbonate, separator 2.4 mM carbonate 500x3.0mmID 184mVhr Partisil ODs-3 10 mM octylamine, 10 mM phosphate buffer, pH 6.2 2.0 d m i n Wescan anion/R 1.0 mM boric acid, 250 mm 0.3 mM phthalate, pH 11.9 (10%ACN) 1.7 d m i n Anion separator 1.2 Mbicarbonate, (x2) in series 1.2 mM carbonate 300 x 2.8 mm ID 1.0 d m i n
Conductivity
26
Conductivity
27
Conductivity
28
Dionex anion separator 150 x 4.0 mm ID Acetic (4), propionic (7), butyric (8), valeric Acidification, ðyl Zorbax ODs (13), hexanoic (30) ether extraction, 250 x 4.6 mm ID evaporation Fluoride, chloride, nitrate, phosphate, Waters IC Pak A sulfate 50 x 4.6 mm ID Chloride (2.5), cyanate (3.2), chlorate (5.3), sulfate (9.8) Chloride (2.0). sulfite (4.8), sulfate (7.5) Glycolic acid (2.5), nitrite (3.3, nitrate (4.8)
Hypochlorite oxidation, dilution Stabilization of sulfite with foxmaldehyde Dilution
Sulfide (5.6), chloride (6.0), cyanide (6.4)
-
Diethylphosphate(5.0),diethylphosphorothioate (1 1.8), chloride (14.0)
Dilution
Eluent
p
8
Direct specimphot. at 29 214 nm Conductivity
30
Conductivity, direct spectrophot. at 210 nm
31
Seep. 487 for notes on the organization of this Table. Seep. 585 for Rejerences. Abbreviations are listed in Appendix B (p. 745).
wl
P u l
w
TABLE 17.1 (CONTIPUZIED) ANALYSIS OF INDUSTRIAL WASTEWATERS AND EFFLUENTS USING IC Solutes (min)
Sample Prep.
Column
Hexanoic (lo), heptanoic (13).octanoic
Acidification, djethyl Zorbax ODS ether extraction, 250 x 4.6 mm ID evaporation Sulfide (2.4, sulfate (103, thiosulfate (22) Dilution Bio-Gel TSK ICanion-PW 50 x 4.6 mm ID
(25)
Sulfite (3.88). sulfate (4.85). thiosulfate (14.7 1)
-
Dionex AS-3
Sulfate (4.4), thiosulfate (15.2). thiccyanate ( 18.0)
-
Dionex anion brine 500 x 3.0 mm ID Wescan 269029 anion/R 250 x 4.1 mm ID Dionex AS-5
Thiocyanate (8.5), sulfate (1 1.5)
Thiocyanate (6), thiosulfate (12)
Dilution, filtration
Sulfite (7.71, sulfate (9.8)
Phosphate (13), carbonate (22)
Filtration
Eluent
P
a
Detection
Ref
Water (50%MeOH) 1.0 mumin
Conductivity
25
1.2 mM gluconate, 1.3 mM borate, 40 mM boric acid, 54.2 mM glycerol, 0.02 mM EDTA, pH 7.6 (12%ACN) 1.O mVmin 3.0 mM bicarbonate, 2.4 mM carbonate 253 ml/hr
Amperometry at Ag elecucde, conductivity
32
Conductivity
10
Conductivity
33
9.0 mM bicarbonate, 7.2 mM carbonate 151 mlhr 10 mM perchlorate 2.7 mVmin
4.5 mM bicarbonate, 3.6 mM carbonate, 3.36 mM p cyanophenol (2%ACN) 2.2 mumin Dionex anion 3.0 mM bicarbonate, brine 2.4 mM carbonate 500 x 3.0 mm ID 151 mVhr Hitachi 2613 Water (60%acetone) cationexchanger 1.0 mumin
Direct spectrophot at 34 210 nm Conductivity
7
Conductivity
33
Flow-coulometry 35 after reaction with pbenzoquinone
Seep. 487 for notes on rhe organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
2
B
? .-.
u
TABLE 17.1 (CONTINUED) ANALYSIS OF INDUSTRIAL WASTEWATERS AND EFFLUENTS USING IC Solutes (min)
Sample Prep.
Bisulfide (4.0),cyanide (10.0)
Column
Eluent
Dionex AS-2 14.7 mM ethylenediamine, 150 x 3.0 mm ID 10 mM borate, 1 .O mM carbonate, pH 11.0 TSK-GEL IEX- 0.05 M sodium nitrate, 0.05 520 QAE M acetate buffer, pH 5.48 150 x 4.0 mm ID 0.8 d m i n
Chloride (5.3), sulfate (7.1)
Fluoride (7.4),chloride (14.1)
Dilution
Carbonate (12.60)
Filtration
Fluoride (2.5)
Dilution in eluent
Fluoride (9.8)
Dilution
Cyanide Sodium (8), ammonium (lo), potassium (12)
Dilution
Sodium (2), ammonium (3), potassium (5)
Dilution
Interaction ION100 100 x 3.2 mm ID Waters fast fruit juice (x2) 150 x 7.8 mm ID Interaction ION100 100 x 3.2 mm ID Brownlee Polypore H 250 x 7.0 mm ID Waters IC Pak A 50 x 4.6 mm ID Dionex cation separator 250 x 6.0 mm ID Wescan 269024 cationJHS 50 x 3.0 mm ID
2.0 mM hydroxide 0.5 d m i n
Detection
Ref
Direct spectrophot. at 37 340 nm after postcolumn reaction with Fe(III) perchlorate Indirect Conductivity 38
0.1 mh4 sulfuric acid 1.0 d m i n
Conductivity
16
0.5 1.5 rnI/min mM phthalate, pH 5.11
Conductivity
38
2.0 sulfuric acid, pH 2.8 0.6 d m i n
Conductivity
38
5 mM hydroxide 1.OmUmin 5.0 mM nitric acid
Indirect conductivity, 26 -mew 20, 12 Conductivity
92 mvhr 3 mM nitric acid 1.5 ml/min
Indirect conductivity
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
39
f >
fi'
VI P
TABLE 17.1 (CONTINUED) ANALYSIS OF INDUSTRIAL WASTEWATERS AND EFFLUENTS USING IC -
~~
~
__
~
~
Solutes (min)
Sample Prep.
Column
Eluent 5.0 mM octanesulfonic acid,
Ammeline (9.19, melamine (10.03)
adjusted to pH 3.0 with acetic acid (28% MeOH) 1.5 d m i n 0.25 mM rn-phenyleneDionex 30831 Guanidinium (5.1) cation separator diamine dihydrochloride, 0.25 mM hydrochloric acid 2.5 d m i n Dionex cation 1.3 mM o-phenylenediamine Sodium (1.9). magnesium (3.3, calcium hydrochloride separator (5.5) 250 x 6.0 mm ID 138 ml/hr 2.0 mM octanesulfonate, Iron (111) (2.681, copper (4.18). lead (5.38), Nitric acid digestion, Waters c18 50 mM tartaric acid, pH 3.4 pondapak zinc (9.35). nickel (10.35), cobalt (14.72), dilution 300 x 3.9 mm ID 1.O d m i n cadmium (19.43, iron (11) (20.32), manganese (26.62) 2mMsodium Nitric acid and Waters c18 Iron (III) (2.4), copper (4.3), lead (5.4), octanesulfonate, 50 mM peroxide digest, pondapak zinc (9.8), nickel (10.5), cobalt (15.4), 300 x 3.9 mm ID tartaric acid, pH 3.4 resuspension in cadmium (17.0), manganese (28) 1.0 d m i n 0.5% nitric acid 0.35 M to 0.5 M tartrate o n Arninex A5 Preconcentration Copper (2.1), zinc (8.2), lead (10.4), nickel 100 x 4.0 mm ID gradient, pH 3.5 Aminex A5 (12.11, cobalt (15.4) 1.0 ml/min Iron (III) (0.99), copper (4.27), nickel (7.22), zinc (11.33)
Dilution in eluent
TSK silica cation 1.07 gA citric acid, 7.5 gA 50 x 4.6 mm ID tartaric acid, 120 pUl ethylenediamine 1.O d m i n
Detection
Ref
Direct spectrophot. at 40 235 nm conductivity
40
Conductivity
28.41
Direct speccrophot at 520 nm after postcolumn reaction with PAR Direct spectrophot. at 520 nm after postcolumn reaction with PAR Direct spectrophot. at 530 nm afta postcolumn reaction with PAR Direct spectrophot. at 546 ~nafter postcolumn reaction with PAR
42,43
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
44
45
46
85 v
Ir
TABLE 17.1 (CONTINUED)ANALYSIS OF INDUSTRIALWASTEWATERS AND EFFLUENTS USING IC Solutes (min)
Sample Prep.
Column
Tungstate (9.9). molybdate (15.0), arsenate Preconcentration (21.0), chromate (24.9)
Chmium (In) (0.9). chromium (VI) (4.0)
chromium @I) Chromium 0, Chromium (VI)(3.5)
Chromate (6.0)
Dionex anion brine 500x3.0mmID Addition of cyanide TSKgel ICto prevent chromium Anion-PW 100 x 4.0 mm ID hydroxide ppt
oncolumn preconcenmtion, filtration Neutralization, dilution in eluent
Dionex CS-2 250 x 4 mm ID
Preconcentration (10 ml at 4.0
Dionex AS-2
Wmin)
Dionix CS-5
Eluent 3.0 mM carbonate, 5.0 mM hydroxide 230ml/hr 0.5 mM phthalate, pH 6.5 1.2 d m i n
& E Detection Conductivity
Inductively coupled plasma atomic emission spectrometry Water with multiple injections 3 e l d p l a s m a of 1.O M hydrochloric acid atomic emission 2.0 d m i n spectromeay 10 mM p y r i d i n e d i x y l i c Direct spectrophot. at acid, 148 mM durn 520 ~I after I I postcolumn reaction with hydroxide methanolic diphenyl1.0 Wmin carbohydrazide 20 mM nitric acid, Direct specaophot. at 30 mM hydroxide 365 nm 1.5 mVmin
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
Ref 47 48
5
B
&
z 2
49
50
51
VI P
W
v,
TABLE 17.2
iz: v
ANALYSIS OF OTHER INDUSTRIAL WATERS USING IC ~~
~
Solutes (min)
~~
~
~
Sample
Sample Prep.
Column
Fluoride (2.1), chloride (3.5). Industrial waters phosphate (7.0), bromide (9.0), nitrate (1 l.O), sulfate (15.5) Chloride (4.3), nitrite (5.0), Indusmal nitrate (12.0). sulfate (18) process waters, water-formed deposits Fluoride (3.66), chloride Industrial run-off (8.64). ninate (19.77) waters
Samples diluted in bicarbonate buffer Dilution, filtration
Dionex anion separator 250 x 4.0 mm ID Dionex anion separator 500 x 3.0 mm ID
Filtration
Waters IC Pak A 50 x 4.6 mm ID
Magnesium (3.9),calcium (5.0) Industrial waters
-
Toyo Soda TSKgel SP-NPR 35 x 4.6 mm ID
Chloride (4.59, sulfate (21.14) Indusmal brine
Dilution, filtration
Waters IC Pak Anion HC 150 x 4.6 mm ID
Lithium (3.16), sodium (4.1I), potassium (6.74)
Indusmal brine
Dilution, filtration
Waters IC Pak C 50 x 4.6 mm ID
Magnesium (2.73), calcium (3.68)
Indusmal brine
Dilution, filtration
Waters IC Pak C 50 x 4.6 mm ID
Eluent
Detection
Ref
3.0 mM bicarbonate, 2.4 mM carbonate 161 ml/hr 3.0 mM bicarbonate, 2.4 mM carbonate 138 mVhr
Conductivity
52
Conductivity
53
10 mM acetate, pH 7.6 (10%ACN) 1.2 mumin 0.05 M phosphate buffer, 0.075 M potassium chloride, 1.0 mM Arsenazo 111, pH 6.0 0.7 mumin
Conductivity
54
1.42 mM gluconate, 5.82 mM boric acid, 0.25% glycerine, pH 8.5 (12% ACN) 1.2 ml/min 2.0 mM nitric acid, 0.05 mM disodium EDTA 1.5 ml/min 0.5 mM ethylenediamine, nimc acid, pH 6.0 1.2 ml/min
Direct 55 spectrophot. at 600 nm after in situ formation of Arsenazo complexes Conductivity 56, 57
Indirect conductivity
56
Indirect conductivity
56
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B ( p . 745).
TABLE 17.2 (CONTINUED). ANALYSIS OF OTHER INDUSTRIAL WATERS USING IC Solutes (min)
Sample
Magnesium (6.8), calcium (10.4)
Chlor-alkali brine Dilution, Dionex CS-2 preconcentration on Dionex MFC-1 Processreclaim Wescan 269001 water anion 250 x 4.6 mm ID Processbath Wescan 269001 anion 250 x 4.6 mm ID Process water Vydac anion 250 x 4.6 mm ID
Chloride (2.5), nitrate (4), system peak (7), sulfate (12) Phosphate (lo), chloride (13), chlorate (16), sulfate (17) Chloride (4.4), nimte (5.0), nitrate (10)
Sample Prep.
Chloride (2.9), chlorate (4), sulfate (7)
Processliquor
-
Sulfite (2.5), sulfate (2.8), thiosulfate (8.6)
Process stream solution
-
Phosphate
Processing water Dilution, aqueous extraction
Magnesium (7), calcium (9)
Process water
-
Column
Wescan 269001 anion 250 x 4.6 mm ID Dionex AG-3 (x2) in series 50 x 4.0 mm ID Waters Resolve 150 x 4.6 mm ID Dionex cation separator 250 x 6.0 mm ID
Eluent
Detection
Ref
25 mM hydrochloric acid, 2.0 mM hystidine 1.0 d m i n
Conductivity
58
4.5 mM phthalate, 0.5 mM phthalic acid 3.7 d m i n 5 mMphthalic acid 2.5 d m i n
Conductivity
59
Conductivity
60
1mM phthalate 2.0 d m i n
8.7 mM phthalate, 1.3 mM phthalic acid 2.5 mumin 6.0 mM carbonate 4.6 d m i n 10 mM tetrabutylammonium phosphate, 20 mM formic acid (20% MeOH) 1.O d m i n 2.5 mM nitric acid, 2.5 mM phenylenediamine dihydrochloride 1.15 Wmin
-9 a
$
3
2.
2
Indirect 61 spectrophot. at 280 nm Conductivity 62 Conductivity
63
Direct RI
64
Coulometry, 65 +0.45V, after reaction with hydroquinone v,
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
v, c
VI
TABLE 17.2 (CONTINUED). ANALYSIS OF OTHER INDUSTRIAL WATERS USING IC Sample
Zinc (4.0), samarium (10.0). gadolinium (13.4), terbium (15.7). dysprosium (17.5)
Process stream (lanthanide manufacturing)
Dionex CS-5 cation 2.0 mM pyromellitic acid, separator
50 mM oxalic acid, adjusted to pH 3.5 with lithium hydroxide 1.o d m i n
Succinate (16), formate (17). acetate (201, propionate (211, butyrate (32) Oxalate (2.4),EDTA (6.3), citrate (8.1)
Synfuels plant stream water
Dionex AS-2 ion exclusion
10 mM hydrochloric acid 2.0 d m i n
Reactor decontamination water
sUplc4d c18 coated with cetylpy-ridinium chloride 75 x 4.0 mm ID Dionex anion separator 500 x 3.0 mm ID Dionex anion separator 500 x 3.0 mm ID
1.5 mM phthalic acid, Indirea 68 1.8 mM rris(hydmxymethy1) specmphot. at 254 nm aminomethane (7% ACN) 2.0 d m i n
UraniUm processing solution Fuel reprocessing solutions
Tetrafluomborate (10.8)
Nuclear fuel dissolvent solutions
Column
Eluent
N
Solutes (min)
Dibutylphosphate (2.3, monobutylphosphate (4.7), phophate (14.1) Dibutylphosphoric acid (3.3, monobutylphosphoricacid (5.8)
Sample Prep.
VI
3.0 mM bicarbonate, 2.4 mM carbonate 138 mvhr 1.5 mM carbonate, 0.5 mM hydroxide 138 mvhr
Barium ppt of oxalate and carbonate, C18 Sep-Pak Reconcentration Dionex brine anion 3.0 mM bicarbonate, separator 4.0 mM carbonate on Amberlite XE-243, 500 x 3.0 mm ID 138 mvhr acidification, hydroxide elution
Detection
Ref
Direct 66 specmphot. at 520 nm after post-column reaction with PAR Conductivity 67
Conductivity
69
Conductivity
70
Conductivity
71,72
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 17.2 (CONTINUED). ANALYSIS OF OTHER INDUSTRIALWATERS USING IC Solutes (min)
Sample
Sample Prep.
Column
Dibutylphosphate (6.4)
Nuclear fuel reprocessing
Hydroxide extraction, centrifugation Preconcentration on Amberlite XE-243, acidification, hydroxide elution Reconcentration on Dionex TCC- 1
Dionex anion separator 500 x 3.0 mm ID Dionex anion separator 150 x 3.0 mm ID
Dionex CS-3
2.3 diaminopmpionicacid Conductivity monohydrochloride,histidine monohydrochloride 8 mM phthalate. conductivity 2 mMphthalic acid 2.5 ml/min 5.0 mM phthalate. pH 3.8 Conductivity 4.0 ml/min
streams
Terrafluomborate(13)
Nuclear fuel dissolvent solutions
Calcium (8.6), strontium (12.6) Nuclear reprocessing solutions Chloride (2), system peak (4). Refinery accumulated sulfate U),thiosulfate (9) water Chloride (0.9), sulfite (l.l), Refinery sulfate (4.7), thiosulfate (7.0) accumulated Water Sulfide (2.2) Refinery waters
Wescan 269001 anion 250 x 4.6 mm ID Wescan anion/HS
-
Dionex AS-3
Eluent
Detection
Ref
3.0 mM hydroxide 92 ml/hr
conductivity
73-75, 69
3.0 mM bicarbonate, 2.4 mM carbonate 138 ml/hr
conductivity
71,72
1.0mM carbonate, 10 mM sodium dihydrogen borate, 15 mM ethylenediamine 2.0 ml/min 3.0 mM tetraborate 2.0 ml/min
Phenol (4.40)
Refinerywaters
-
Dionex AS-3
Ammonia (5.15). monoethylamine (6.41), diethylamine (8.45), methylamine (10.74)
Refinery waters
-
Dionex MPIC NS-1 5.0 mM hexanesulfonicacid Separator 1.0 ml/min
76 77 30
Ampmmetry 67 at Ag electrode,
0.oov 67 at Pt electrode, +1.ov Conductivity 67 Amperomeay
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
v1
TABLE 17.2 (CONTINUED). ANALYSIS OF OTHER INDUSTRIAL WATERS USING 1C Solutes (min)
Sample
Sample Prep.
Column
Monoethanolamine (20), diethanolamine (29), methyldiethanolamine (36) Chloride (2), nitrate (2.7), sulfate (7), hydroxylamine disulfonate (lo), dithionate (19) Chloride (3.0). sulfide (5.8). sulfate (12), sulfite (12)
Refmerywater
-
Dionex MPIC NS-1 5.0 mM octanesulfonic acid separator 1.O mumin
Flue gas desulfurization liquors Scrubber liquor
Dilution
Eluent
vl
Detection
Ref
Conductivity
41
Wescan 269013 anion/HS 100 x 4.6 mm ID Dionex anion separator 500 x 3.0 mm ID
4 mM phthalate, pH 3.8 2.7 d m i n
Conductivity
78
1.5 mM bicarbonate, 1.5 mM carbonate 2.2 mumin
Conductivity
79
Fluoride, chloride, nitrate, arsenate. sulfate
Flue gas, extract Adsorption, liquor from Cu, dilution Al, Fe refineries
Dionex anion separator 500 x 3.0 mm ID
0.25 @ bicarbonate, I 0.25 @ carbonate I 1.5 d m i n
Conductivity
80
Chloride (4), adipate (14), sulfite (19), sulfate (31)
Scrubber liquors Filtration
Dionex anion separator 500x3.0mmID Dionex anion separator 500 x 3.0 mm ID
1.5 mM bicarbonate, 1.2 mM carbonate
Conductivity
81
138mMr 3.0 mM bicarbonate, 2.4 mM carbonate 2.3 mumin
Conductivity
82
Dionex anion separator 500x3.0mmID Dionex anion separator 500 x 3.0 mm ID
9.0 mM bicarbonate, 7.2 mM carbonate 184mvhr 3.0 mM bicarbonate, 2.4 mM carbonate 138 mvhr
Conductivity
83
Conductivity
84
Chloride (1.8), adipate (3.8), sulfate (4.9)
Flue gas from desulfurization systems
Chloride (2.5), sulfate (4.4), thiosulfate (17)
Scrubber liquors, processing waters Flue gas Dilution scrubber solution
Chloride (3.8), sulfite (1 l.O), sulfate (17.3)
Filtration, peroxide oxidation
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
PB
c,
u
TABLE 17.2 (CONTINUED). ANALYSIS OF OT
R INDUSTRIALWATERS USING IC
Solutes (min)
Sample
ample Prep.
Chloride (1.3), sulfite (4.3, sulfate (7.0)
Lime, limestone- :&ration, sulfite based sulfur stabilized with dioxide scrubber formaldehyde solutions Flue gas Dilution scrubbing liquor
Chloride (2.7), nitrate (7.4), sulfate (15.0) Sulfate (9.0), oxalate (13.1)
Scrubber liquor, pitch
Nitrate (8.6), sulfate (11.0)
Stack gas trap solution
Sulfite (23), sulfate (45)
Scrubberliquor from flue gas coal desulfurization Flue gas Dilution scrubbing liquor Flue gas Dilution desulfurization liquor Flue gas Dilution scrubber solution
Imidodisulfate (7.3, hydroxyimidodisulfate (16.5) Bicarbonate (6) Sodium (13), ammonium (20), potassium (26) Sodium (2), potassium (7)
Flue gas desulfurization liquors
Column
Detection
Ref
Dionex anion separator 500 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity
85, 83
Dionex AS-4
5 mM bicarbonate, 5 mM carbonate 2.0 d m i n
Conductivity
86
2.4 mM bicarbonate, 3.0 mM carbonate
Conductivity
87
5.0 mMp-hydroxybenzoic acid, pH 8.6 2.0 d m i n 1.5 mM bicarbonate, 1.2 mM carbonate 1.5 d m i n
Conductivity
30
Conductivity
88
12 mM carbonate 1.5 d m i n Deionized water 1.Od m i n
Conductivity
86
Conductivity
89
5.0 mbl nitric acid 184 mvhr
Conductivity
84
3 mM nitric acid 1.5 ml/min
Indirect conductivity
90
Combustion, Dionex AS-3 sorption in alkaline peroxide Wescan anion R 250 mm
Dilution
Eluent
Dionex anion separator 500 x 3.0 mm ID Dionex AG-4 500 x 3.0 mm ID Wescan 269038 exclusion 250 x 7.1 mm ID Dionex cation separator 250 x 6.0 mm ID Wescan 269024 cation/HS 50 x 3.0 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
VI
TABLE 17.2 (CONTINUED). ANALYSIS OF OTHER INDUSTRIAL, WATERS USING IC
x "I
Solutes (min)
Sample
Sample Rep.
Lime, limestone- Filtration based sulfur dioxide scrubber solutions Dilution Magnesium (6.6).calcium (9.9) Flue gas scrubber solution
Sodium (1.6),magnesium (3.4), calcium (5.2)
Fluoride (2.6).chloride (3.2), phosphate (4.4), nitrate ( 5 . 3 , sulfate (7.0)
Water-insoluble wastewater precipitate
Fluoride (5), chloride (6). Sewage phosphate (1 l), nitrate (14), sulfate (22) Chloride (4). nitrate (6), sulfate Sewage sludge (lo), tungstate (12)
Fluoride, chloride, phosphate, sulfate
Sewage sludge
Chloride (7.0),bromide (9.0), nitrate (1 1.5)
Sewage water
Sodium carbonate fusion, SCX in hydrogen form
Column
Detection
Ref
Dionex cation separator 500 x 6.0 mm ID
2.0 mM p-phenylenediamine dihydrochloride
Conductivity
85
Dionex alkaline earth separator 250 x 6.0 mm ID Dionex M30170 anion separator 500 x 3.0 mm ID
1.O mM p-phenylenediamine dihydrochloride 138 mvhr 2.1 mM bicarbonate, 1.7 mM carbonate 2.0 mumin
Conductivity
84
Conductivity
91
9.0 mM bicarbonate, 3.0 mM carbonate 1.38 Wmin 5.0 mM p-hydmxybenzoic acid, pH 8.5 2.0 d m i n
Conductivity
92
Conductivity
93
3.0 mM bicarbonate, 2.4 mM carbonate 4dmh 0.01 M phosphate, pH 3.8 2.0 d m i n
Conductivity
94
Home-packed anion-exchanger 500 x 3.0 mm ID Ashing, aqueous Wescan 269-069 extraction, anion centrifugation, 2 5 0 ~ 4 . 1mmID filtration, barium ppt of sulfate, silica column clean-up, concentration Dionex anion Oxygen bomb separator Dilution
Eluent
Vydac 302 IC 250 x 4.6 mm ID
Direct 95 specmphot. at 190 nm
See p. 487 for notes on the organizarion of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
2
TABLE 17.2 (CONTINUED). ANALYSIS OF OTHER INDUSTRIAL WATERS USING IC Solutes (min)
Sample
Sample Prep.
Chloride (1.9), bromide (4.0), sulfate (6.9)
Pollutant water
Column
Nimte (7.71, nitrate (9.5)
Sewage sludge
Nitrite (3.3, nitrate (4.8)
Silage extract
Adsorption onto Dionex A S 4 carbon, combustion, all
Acetic (7.6), carbonate (10.6)
Sewage water
-
Ammonia (17.2)
Activated sludge Filtration process water
Biological Chloride (4.2),nimte (4.7), phosphate (7.0),nitrate (12.6), nitrificationsulfate (23) denitrification process water Nitrate (3), nitrite (3, Nimficationammonium (1 6) deniaification process water
Dilution
Eluent 2.8 mM bicarbonate, 2.0 XIlhf' C a r b O M k 2.0 ml/min
Detection
Ref
Conductivity
96,97
k
'", B' a.
2
0.03 M sulfate, 0.01 M Tris buffer, pH 7.0
Direct 98 spectmphot. at 210 nm 10 mM octylamine, adjusted Direct 29 to pH 6.2 with phosphoric spectmphot. at acid 205 nm 2.0 ml/min YEW SCX-252 2 mM sulfuric acid Conductivity 99 250 x 6.0 mm ID 1.5 mVmin with peak enhancement Hitachi 2632 anion- Deionized water Coulometry. 100 1.0mVmin exchanger conductivity 535 x 9.0 mm ID Dionex anion 3.0 mM bicarbonate, conductivity, 101 2.4 mM carbonate separator direct 500 x 3.0 mm ID 115 d h r spectrophot. at 220 nm Cation- and anion- Water (10% MeOH) Coulometry, 102 exchangers in series 1.O d m i n direct 110 x 9.0 mm ID spectrophot. at 550 x 9.0 mm ID 210 nm
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
ul ul
4
w
TABLE 17.2 (CONTINUED). ANALYSIS OF OTHER INDUSTRIAL WATERS USING IC Solutes (min)
Sample
Sample Prep.
Column
Nitrate (2.5), nitrite (4.2)
Biological nimficationdenitrification process water Nitrite-inhibited cooling system water Biological denimfication water
Dilution, filtration
Hitachi 3613 cation-exchanger 100 x 9.0 mm ID
0.1 mM sulfuric acid (5% MeOH) 1.0 mumin
Direct 103 specmphot. at 210 nm
-
SS-SAR 3.2 mm ID
5.0 mM phenol, pH 10.0 2.0 mVmin
Conductivity
Dionex cation separator 250 x 6.0 mm ID
3.0 mM hydrochloric acid 1.15 ml/min
Wescan 269001 anion 250 x 4.6 mm ID Dionex anion separator 750 x 2.8 mm ID
4.5 mM phrhalate, 0.5 mM phthalic acid 3.7 mumin 3.0 mM bicarbonate, 2.4 mM carbonate 161 mVhr
Conductivity, 65 coulomehy , +0.45V,after reaction with hydrquinone Conductivity 105
Nimte, nitrate
Ammonium (1 8)
Phosphate (2), chloride (2.5), system peak (7). sulfate (12)
Acid plant blowdown water
Chloride (3.5). phosphate (8.7), Water from bromide (13.6), sulfate (22) secondary oil recovery
Eluent
VI 30
Detection
Conductivity
Seep. 487 for notes on the organizanon of this Table. Seep. 585 for References. Abbreviations are listed in Appendir B ( p . 745).
Ref
104
106
TABLE 17.3 ANALYSIS OF ORGANIC COMPOUNDS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride (3.3, bromate (4.0), chloride (4.3, bromide (8.0)
organic compounds
Dionex anion separator 550 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 98 mVhr
Conductivity
107-113
Fluoride (2.5),chloride (3.3), nitrite (3.7), nitrate (6.3), sulfate (9.0) Chloride (1.6),nitrite (2.2), nitrate (3.6). sulfate (10.3)
organic compounds
Schoeniger flask combustion, sorption in hydroxide Oxygen flask combustion
YEW anion separator
4.0 mh4 bicarbonate, 4.0 mM carbonate 2.0 mVmin 2 mM phthalic acid, pH 5 (10%acetone)
Conductivity
114
Conductivity
115
Chloride (3), nitrite (3.3, nitrate (41, sulfate (10)
organic compounds
2 mM phthalate, pH 4.5 1.7 d m i n
Conductivity
116
Chloride ( 3 . 3 , bromide (7.6), sulfate (17)
organic compounds
2.0 mh4 carbonate 2.6 d m i n
Conductivity
117
Chloride (1.9),nitrate (7.0), sulfate (10.8) Chloride (4.3, bromide (7.3, iodide (26)
organic compounds organic compounds @chlorobenzoic acid)
0.01 M carbonate 2.0 d m i n 1.O mM potassium biphthalate
Conductivity
118
Conductivity
119
organic compounds
Schoeniger flask Hamilton PRP-X combustion, 100 sorption in alkalimeperoxide Combustion Wescan 269029 anionJR 250 x 4.1 mm ID Combustion, Dionex anion separator sorption in 750 x 3.0 mm ID oxidizing carbonate solution Combustion MCI GEL CAO4S flask 50 x 3.0 mm ID Oxygen Permaphase AAX combustion 300 x 5.0 mm ID flask, sorption in peroxide and biphthalate
1 .OmVmin
Seep. 487for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 17.3 (CONTINUED). ANALYSIS OF ORGANIC COMPOUNDS USING IC
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride (2.7). nitrite (5.0), nitrate (9.9)
Organic compounds (benzoic acid)
Pan oxygen
Dionex anion separator 500 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 110 ml/hr
Conductivity
120, 121
Dionex anion separator 500 x 3.0 mm ID
3.0 m M bicarbonate, 2.4 mM carbonate 230 ml/hr
Conductivity
122
Dionex A S 4 ~
2.9 mM bicarbonate, 2.3 mM carbonate 2.0 mumin 2 mM phthalic acid, pH 3.5-5.5 1 .OWmin
Conductivity
123
SAX 1 250 x 4.6 mm ID
4 mM carbonate, 4 mM
Conductivity
125
Dionex anion separator 500 x 3.0mm ID
1.5 mM bicarbonate 138 ml/hr
Conductivity
122
Conductivity
126
bomb, sorption in bicarbonate and carbonate Chloride (4.2), carbonate (5.2). Organic Schoeniger flask sulfate (14.4) compounds combustion, sorption in eluent, peroxide Chloride, phosphate, sulfate Organic polymer Combustion, (polyacrylic acid) dilution, D O M dialysis Chloride, bromide, sulfate Organic Schoeniger flask compounds decomposition, sorption in alkaline peroxide Fluoride, chloride, bromide Organic Combustion compounds tube with sorption into eluent Schoeniger flask Chloride ( 1 0 3 , carbonate (15) Organic compounds combustion, sorption in eluent and pemxide Chloride, chlorate organic Chnate compounds impregnation, ashing
Vydac 302 IC 250 x 4.6 mm ID
YEW anion
Conductivity, 124 indirect spectrophot.
bicarbonate, pH 10.26 2.0 mumin
4.0 mh4 bicarbonate, 4.0 mM carbonate separator 250 x 4.6 mm Tz) 2.2 wm n i
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
85 L.
u
TABLE 17.3 (CONTINUED). ANALYSIS OF ORGANIC COMPOUNDS USING IC Solutes (min)
Sample
2 9
Sample Prep.
Column
Eluent
Detection
Ref
2. ”.
Sodium (8.5). potassium (12)
Organic compounds
Oxygen flask combustion
Chloride, sulfate
Organic liquids
Chloride, bromide
Liquid bromine
Chloride (2.0), nitrite (2.7), phosphate (3.1), bromide (3.6), nitrate (4.8), sulfate (8) Chloride (2.11, bromide (4.3), iodide (17)
Organic compounds in water Organohalogens in water and sediment
Combustion, sorption in permanganate and bicarbonate buffer Dissolution in potassium bromide, extraction with carbon tetrachloride Adsorption on activated carbon, pyrohydrolysis Hexane extraction, vapour phase reduction over I‘t, eluent sorption
Fluoride, chloride, bromide
Organohalogens in water
Purging, combustion, sorption in hydrazine and eluent
Dionex cation separator (x2) 15Ox6mmID 250 x 6mm ID Dionex AS-4A
5 mM nimc acid 120 mvhr
Conductivity
127
0.126 g/l sodium bicarbonate, Conductivity 0.21 g/l sodium carbonate
128
Dionex anion separator 450 x 3.0 mm ID
2.0 mM bicarbonate, 2.0 mM carbonate 1.5 d m i n
129
Gynkochrom
0.7 mM phthalic acid, pH 7.0 Indirect 130, 131 1.2d m i n specmphot. at 254 nm 3.0 mM bicarbonate, Conductivity 132 1.2 mM carbonate
Ax-5 60 x 4.6 mm ID Dionex anion separator 250 x 3.0 mm ID
Dionex anion separator 500X3mmID
3.0 mM bicarbonate, 2.4 mM carbonate 128 mvhr
Conductivity
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
133
B3
VI
TABLE 17.3 (CONTINUED). ANALYSIS OF ORGANIC COMPOUNDS USING IC Solutes (min)
Sample
Sample Prep.
Column
Chloride (2.0), bromide (4.8)
Organic compounds in water Trihalomethanes in drinking waters Organophosphate breakdown products Organophosphate breakdown products Polycarboxy phosphorous compounds Organicsulfate hydrolysis products Organic sulfate hydrolysis products Encapsulation plastic
Volatilization
Dionex AS-4 250 x 3.0 mm ID
Bromide ( 12) Fluoride (2), chloride (2.7), methylphosphonate(9.8), system peak (19) Methylphosphonate (5.81, fluoride (7.5) Onhophosphoric acid (9), phosphorous acid (13), hypophosphorous acid (18) Methyl sulfate ( 5 3 , ethyl sulfate (5.7), sulfate (26) Monosec-butyl sulfate (5.7), sulfate (1 8) Chloride (2.5), bromide (5.8), nitrate (6.4), sulfate (8.1) Chloride (8.0)
Encapsulation plastic
m N
Detection
Ref
Conductivity
134
Conductivity
135
Conductivity
136
Conductivity
137
Conductivity
138
20 mM phthalic acid 2.7 mVmin
Conductivity
139
20 mM phthalic acid 2.7 d m i n
Conductivity
140
3.0 mM bicarbonate, 2.4 mM carbonate 3.0 d m i n
Conductivity
141
2.0 mM bicarbonate 3.0 d m i n
Conductivity
141
Eluent
2.9 mM bicarbonate, 2.3 mM carbonate 9omlnu Oxidation of Dionex trace anion 3.0 mM bicarbonate, mhalomethanes, 2.4 mM carbonate preconcentration 2.3 mumin Wescan 269029 4 mMp-hydroxybenzoate, anion/R pH 8.5 250 x 4.1 mm ID 1.6 mumin Wescan 269006 2 mM nitric acid exclusion 1.0 d m i n 300 x 7.8 mm ID 0.02 M succinic acid Vydac 302 IC 250 x 4.5 mm ID 4.0 mumin Wescan 269001 anion 250 x 4.6 mm ID Wescan 269001 anion 250 x 4.6 mm ID Grinding, reflux Dionex fast-run anion separator exaaction 250 x 4.0 mm ID -
Grinding, reflux Dionex fast-run extraction anion separator 250 x 4.0 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
c
v
s
TABLE 17.3 (CONTINUED). ANALYSIS OF ORGANIC COMPOUNDS USING IC
E
~~~~~
Solutes (min)
Sample
Sample Prep.
Sodium (6.8),ammonium (9.9),potassium (11.8)
Encapsulation plastic
Citrate (7.0),malate (8.4), succinate (10.8),formate (1lS),acetate (13.0) Formate (3.7).chloride (4.1), system peak (7),sulfate (10)
Natural rubber latex serum
Oxalic (7.3),lactic (14.2), formic (15.0),acetic (17.5) Lactate (3.3)
Degraded glycol
Column
Eluent
Detection
Ref
Grinding, reflux Dionex cation extraction separator 200 x 4.0mm ID Propanol Dionex AS-1 ion removal of exclusion proteins Combustion Wescan 269001 anion 250 x 4.6 mm ID Dilution Dionex ion exclusion Dilution Dionex anion separator Extraction, Dionex anion filtration separator 500 x 3.0 mm ID
5.0 mM hydrochloric acid 3.0 d m i n
Conductivity
141
1.0 mM hydrochloric acid 0.8 d m i n
Conductivity
142
5 mM phthalic acid, pH 3.1 1.7 d m i n
Conductivity
143
1.0 mM hydrochloric acid 0.85 mlfmin 0.85 mM bicarbonate 2.0 d m i n 1.O mM bicarbonate, 1 .O mM carbonate 1.0 d m i n
Conductivity
144, 145
Conductivity
144
Wescan 269001 anion 250 x 4.6 mm ID Carbonate buffer Dionex anion extraction separator 500 x 3.0 mm ID Aqueous Waters IC Pak A extraction, c18 50 x 4.6 mm ID Sep-Pak
5 mM phthalic acid 1.5 d m i n
2
2..-. b
Rubber
solutions
Degraded glycol
solutions Chloropyrifos Dimethylphosphate (4.2), dimethylphosphorothioate(5.4), (pesticide) monomethylphosphate(1 1.9), bromide (16.1),phosphate
8
Conductivity, 31 direct spectmphot. at 210 nm
(22.6) Endothall (2.2).system peak (3) Endothall (herbicide) Fluoride, chloride, nitrate, sulfate
Halocarbon hydrolysates
Fluoride (3.52),chloride (7.65) Freon
Conductivity
146
3.0 mM bicarbonate, 2.4 mM Conductivity carbonate, pH 10.3
147
ll0mvhr 2.6 mM lithium benzoate, pH 6.71 1.2 mumin
148
Conductivity
VI
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
01
w
TABLE 17.3 (CONTINUED). ANALYSIS OF ORGANIC COMPOUNDS USING IC
i!
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Acetic (21.31, propionic (24.8)
Poly-e-capre
Hydrolysis
Dionex ion exclusion 120 x 9.0 mm ID Dionex AS4 250 x 4.0 mm ID Dionex A S 4 250 x 4.0 mm ID Dionex fast-run anion separator 250 x 4.0 mm ID
0.1 mM hydrochloric acid 46 mvhr
Conductivity
149
0.5 mM bicarbonate, pH 7.8 2.0 d m i n 4.0 mM bicarbonate, pH 8.1 2.0 ml/min 2.0 mM bicarbonate (2095 MeOH) 2.3 d m i n
Conductivity
150
Conductivity
150
Conductivity
151
1.42 mM gluconate, 5.82 mM Conductivity boric acid, 0.25% glycerine, pH 8.5 (12% ACN) 1.2 d m i n 5.0 mM nimc acid Conductivity 138 mvhr
152
lactam
Fluoride (4.6), acetate (5.4) Trifluoroacetate (7) Chloride (10.5)
Chloride (3), sulfate (6)
Synthetic peptides Synthetic peptides High purity methanol
Aqueous extraction Aqueous extraction Large injection
Hexamethyl-
Waters IC Pak A 50 x 4.6 mm I D
diSilaZane
Dimethylfortnamide (3,sodium (8), ammonium (13), monomethylamine (16), dimethylamine (19), himethylamine (24) Sodium (2.4), ammonium (2.81, potassium (3.5) Sodium (4.3 1)
Dimethylformamide
Propanol and other organic solvents Hexamethyldisilazane
Dilution
Aqueous chloroform extraction
Dionex cation separator 250 x 6.0 mm ID
153
Wescan 269-004
7.2 mM nimc acid 2.0 d m i n
Indirect conductivity
154
Waters IC Pak C 50 x 4.6 mm ID
120 pl/l nimc acid 1.2 d m i n
Indirect conductivity
155
See p . 487 for notes on the organizarionof this Table. Seep. 585 for References. Abbreviationsare listed in Appendix 3 (p. 745).
TABLE 17.3 (CONTINUED). ANALYSIS OF ORGANIC COMPOUNDS USING IC ~
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Water
3-mercaP@ propioi~c acid
Methanolic solution
Aminex 0 1 5 0 s (lithium form) 100 x 8 mm ID
0.79% cinnamaldehyde, 60% acetonitrile, 40% methanol 1.O ml/min
Water (4)
Isopropanol, toluene
-
Aminex 0 1 5 0 s (lithium form) 50 x 4.6 mm ID
0.79% cinnamaldehyde, 60% acetonitrile, 40% methanol 0.8 ml/min
Direct 156 spectrophot. at 310 nm after post-column hydrogen form reactor Direct 156, 157 spectrophot. at 310 nm after post-column hydrogen formreactor
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
Ref
TABLE 17.4 ANALYSIS OF PULP AND PAPER LIQUORS USING IC Solutes (min)
Sample
Krdft black liquor Sulfide (2.0),sulfite (6.0), sulfate (7.2), oxalate (9.5), thiosulfate (26) Carbonate (1.6). chloride (2.0). Kraft black liquor phosphate (6.6). sulfate @.I), thiosulfate (1 8)
Acetate (0.8).chloride ( 1 . 3 , bicarbonate (3.0), sulfate (7.4), thiosulfate (12.8) Hypochlorite (2.0). chlorite (2.5),chloride (4.0),chlorate (KO), sulfate (10.7) Bicarbonate (3). chlorite (6), chloride (8). chlorate (20), carbonate (23) Hypochlorite (2.0),chloride (4.4),chlorate (1 1.O)
Sample Prep.
Column
Eluent
Detection
Dilution
Dionex anion separator 500 x 3.0 mm ID Waters IC Pak A 50 x 4.6 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 138 mVhr 1.42 mM gluconate, 5.82 mM boric acid, 0.25%glycerine, pH 8.5 (12%ACN) 1.2 d m i n 4.0 mM phthalate, pH 3.7 2.0 mumin
Conductivity, 69. 158amperometry 161
Dilution, addition of antioxidants
Kraft black liquor Dilution Bleach plant filtrate
Dilution, filtration
Bleaching solution
Dilution
Bleach
Dilution in eluent
Chloride ( 5 . 3 , nitrate (8.5), Paper industry sulfate (10.3, thiosulfate (15.5) process waters
Wescan anion HS
Ref
Conductivity
162
Conductivity
163
Bicarbonate, carbonate buffer
Conductivity, 158, amperometry 160, 161
0.5 mM hydroxide 1.2 mumin
Indirect conductivity
Dionex anion separator
2.0 mM carbonate
Conductivity, 164 amperomtry
Vydac 302 IC 250 x 4.6 mm ID
5 mM phthalate, pH 4.75
Conductivity, 165 indiltct spectrophot. at 280 nm
Dionex anion separator 250 x 4.0 mm ID Waters IC Pak A 50 x 4.6 mm ID
1.0 ml/min
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
162
2=-
TABLE 17.4 (CONTINUED). ANALYSIS OF PULP AND PAPER LIQUORS USING IC ~~~
Solutes (min)
Sample
Sample Prep.
Column
Eluent
~
Detection
Ref
9
2. L1
b
Sulfite (4.2), sulfate (4.8), Kraft black liquor Dilution oxalate (5.4), thiosulfate (16.8)
Chloride, sulfite, sulfate, thiosulfate
Chloride (5.3), sulfate (14), oxalate (18) Lactic (17), formic (18), acetic (20) Sulfide (2.7), sulfite (3.3, sulfate (7.8)
Kraft black liquor Dilution, filtration, stabilization of sulfite with formaldehyde Black pulping Dilution, liquor filmtion
Dionex AS-3
Dionex anion separator (x2) 500 x 3.0 mm ID Dionex ion Kraft black liquor Dilution exclusion 200 x 9.0 mm ID Kraft green liquor Dilution, Millex Waters IC Pak A filter, addition 50 x 4.6 mm ID of antioxidants
Chloride, sulfate, oxalate
Kraft black liquor Dilution
Sulfide (3), thiosulfate (15)
Kraft white liquor Dilution, c18 Sep-Pak, addition of antioxidants Kraft white, Dilution, cat-ex in hydrogen green liquors form
Sulfate (7.3, thiosulfate (12)
Dionex AS-5
Dionex anion separator Waters IC Pak A 50 x 4.6 mm ID Wescan 269013 anion/HS 100 x 4.6 m m ID
1.0 mM carbonate, 5.0 mM hydroxide, 0.8 mM p-cyanophenol 2.0 d m i n
Conductivity
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity, 167 amperometry
6.0 mM carbonate 138 mvhr
Conductivity
168
10 mM hydrochloric acid
Conductivity
5.0 mM phosphoric acid, adjusted to pH 6.5 with lithium hydroxide 1.2 d m i n Bicarbonate
Conductivity
159, 158, 160,161 162
Conductivity
169
Amperomeny at Ag
162
5.0 mM &sodium hydrogen phosphate 1.2 d m i n
4 mMphthalate, 1 mM phthalic acid 2.5 Wmin
166
%
3
a.
.?.
electrode Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 585 f o r References. Abbreviations are listed in Appendix B (p. 745).
170
TABLE 17.4 ( C 0 " U E i D ) . ANALYSIS OF PULP AND PAPER LIQUORS USING IC Solutes (min)
Sample
Sample Prep.
Bicarbonate (2.8). sulfide (4.1) Kraft white, green liquors Chloride (1.76). sulfate (6.20)
Chloride (0.75), sulfate (1.96)
Sulfite (6.7), sulfate (9.2) Glycolate (7), chloride (10) Sulfide (1.4) Sulfide
Sulfide
Kraft green liquor Dilution with 0.1% hydrochloric acid, filtration Kraft green liquor Dilution with 0.1% hydrochloric acid, filtration Spent sulfite Dilution liquor Carboxymethyl MeOH, water cellulose extraction Kraft white liquor Dilution Kraft black liquor Dilution, chelating resin pre-column Kraft black liquor Dilution
Column
Eluent
Detection
Ref
Wescan 269038 exclusion 250 x 7.1 mm ID Dionex anion separator 250 x 4.0 mm ID
Deionized water 1.5 d m i n
Conductivity
171, 172
2.8 mM bicarbonate, 2.2 mM carbonate 2.0 mVmin
Conductivity
173, 174
Dionex anion guard 50 x 4.0 mm ID
2.8 mM bicarbonate, 2.2 mM carbonate 2.0 ml/min
Conductivity
173
Dionex anion separator 250 x 4.0 mm ID Partisill0 SAX 250 x 4.6 mm ID Dionex anion separator 250 x 4.0 mm ID Dionex AS-5
2.0 mM carbonate,0.75 ml/l ethy lenediamine (5% isopropanol) 0.035 M salicylate, pH 5.0 1.0 d m i n 4.0 mM carbonate
Conductivity
159, 161
Indirect RI
175
Dionex AS-3
0.25 mM carbonate, 5.0 mM hydroxide, 1.5 mM ethylenediamine 2.0 d m i n
Amperometry 159, 161 Amperometry
166
at Ag electrode,
0.ov
1.0 mM carbonate, 10 mM Direct hydroxide, 10 mM boric acid, spectrophot. 15mM ethylenediamine at 215nm
174, 167
2dmin
Seep. 487 for notes on the organization of this Table. Seep. 585 for Rejerences. Abbreviations are listed in Appendix B (p. 745).
4
u
TABLE 17.4 ( C 0 ” U E D ) . ANALYSIS OF PULP AND PAPER LIQUORS USING IC Solutes (min)
Sample
Sample Prep.
Sulfate
Kraft green liquor Dilution
Sulfate
Paper wrapping
Column
Eluent
Detection
Ref
Dionex AS-3
3.0 mM bicarbonate, 2.4 mM carbonate 2.8 Wmin
Conductivity
174
2 mM phthalate, pH 7.0 2.0 Wmin
Conductivity, 176 indirect spectrophot. at 280 nm Conductivity 158,
Aqueous Vydac anion 250 x 4.6 mm ID extraction, preconcentration with post-flush Carbonate (13) Kraft smelt Dilution Dionex ion exclusion 200 x 9.0 mm ID CarbOMte Kraft black liquor Dilution Dionex AS-3 ion exclusion Dilution Wescan 269024 Sodium (2.4), potassium (6.2) Paper pulping liquor catiodHS 50 x 3.0 mm ID Sodium (7.0), potassium (12.5) Kraft white liquor Dilution Dionex cation separator Sodium ( 5 ) Kraft black liquor Dilution Waters IC Pak C 50 x 4.6 mm ID
10 mM hydrochloric acid
160, 161
Water
Conductivity
167
5 mM nitric acid 1.5 Wmin
Indinxt conductivity
177
Hydrochloric acid
Conductivity
158,160
2.0 mM nitric acid
Indirect conductivity
162
1.0 Wmin
Seep. 487 for notes on the organizationof this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 17.5 ANALYSIS OF ACIDS AND BASES USING IC Solutes (min)
Sample
Sample Prep.
Column
Chloride (2.91), ninate (4.53). iodide (9.39), sulfate ( I 1.95), fluoride (7.24), formate (8.94)
Boric acid solutions
Boric acid (1.7), fluoride (2.2). acetate (2.6). formate (3.7). chloride (7.8) Fluoride (1.7), chloride (2.2). phosphate ( 3 . 9 , sulfate ( 5 . Q chromate (14)
Boric acid
Preconcentration Waters fast fruit (32 juice (x2) and 1C Pak A 150 x 7.8 mm ID 50 x 4.6 mm ID Preconcentration Dionex AS-4A 250 x 4.0 mm ID (5
Chromic acid
Dilution
Dionex anion guard 50 x 4.0 mm ID
Chloride (2.97), nitrate (4.68), Glycolic acid sulfate (1 1.82), glycolate (8.27)
Dilution
Chloride (4.4), nitrite (5.9), nitrate (9.3, sulfate (20.4)
Dilution
Waters fast fruit juice (x2) and IC Pak A 150 x 7.8 mm ID 50 x 4.6 mm ID Waters IC Pak Anion HC 150 x 4.6 mm ID
Perchloric acid solution
Chloride (4.4), phosphate (6.8), Phosphoric acid nitrate (12.0), sulfate (16.0)
Dilution
Dionex fast-run anion separator (x2) in series 250 x 4.0 mm ID
Eluent
Detection
Ref
1.0 mM octanesulfonic acid and 4.0 mM octanesulfonate 1.O mumin
Conductivity
178
5.0 mM tetraborate 2.0 mumin
Conductivity
179
3.0 mM bicarbonate, 2.4 mM Conductivity carbonate switched to 5.4 mM carbonate at 7.5 min 3.0 mumin 1.O mM octanesulfonic acid Conductivity and 4.0 mM octanesulfonate 1.O d m i n
180
1.42 mM gluconate, 5.82 mM boric acid, 0.25% glycerine, pH 8.5 (12%
Conductivity
182
Conductivity
183
ACN) 2.0 mumin 3.0 mM bicarbonate, 2.4 mM carbonate 3.0 d m i n
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
181
TABLE 17.5 (CONTINUED). ANALYSIS OF ACIDS AND BASES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Acetate, nimte, nitrate, sulfate, oxalate
Acetic acid
Dilution
184
Mixed acid
Dilution
Conductivity
185
Borate (3.8), chloride (3, sulfate (22) Chloride (1.8), sulfate (3.3), chromate (12)
Boric acid
Preconcentration Wescan anion 250 x 4.6 mm ID Dilution Dionex anion guard 50 x 4.0 mm ID Dilution Dionex fast-run anion separator (x2) in series 250 x 4.0 mm ID Dilution Dionex AS-2 150 x 3.0 mm ID
2.4 mM bicarbonate, 3.0 mM carbonate 160 mljhr 0.54 gJl boric acid, 0.14 ml/l gluconic acid, 0.16 gJl lithium hydroxide, 2 ml glycerine (12.5% ACN) 1.2 ml/min 3.9 mM phthalate, pH 4.1 2.3 mumin 5.4 mM carbonate 3.0 mumin
Conductivity
Nitrate (4.22), sulfate (7.42), perchlorate (28.52)
Dionex anion separator 500 x 3.0 mm ID Waters IC Pak A 50 x 4.6 mm ID
Conductivity
186
Conductivity
180
3.0 mM bicarbonate, 2.4 mM carbonate 3.0 d m i n
Conductivity
183
3.0 mM carbonate, 2.0 mM hydroxide 2.3 mVmin 5.0 mM hydroxide 138 ml/hr
Conductivity
186
Conductivity
187
1.0 mM bicarbonate, 2.0 mM carbonate 1.5 N m i n
Conductivity
188
Chromic acid
Phosphate (6.8), bromide (9.3), Sulfuric acid sulfate (12) Borate (1.3), chloride (3.8), sulfate (13)
Boric acid
Fluoride, acetate, chloride
Battery acid
Chloride (2.6), nitrite (3.25)
Inorganic acids
Neutralization with barium hydroxide Dilution, reinjection of fraction from 1.5 ml loop
Dionex anion separator 500 x 3.0 mm ID Dionex AS-4 250 x 4 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 17.5 (CONTINUED). ANALYSIS OF ACIDS AND BASES USING IC
u?
4
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Phosphate (7.6), sulfate (13)
Hydrofluoric acid
Dilution
3.0 mM bicarbonate, 2.4 mM carbonate 3.0 mVmin
Conductivity
183
Fluoride (1.7). chloride ( 18.2)
Hydrofluoric acid
Dilution
1.O mM bicarbonate 3.0 mVmin
Conductivity
183
Acetate (2.7), chloride (1 1.8)
Acetic acid
Dilution
1.O mM bicarbonate 3.0 mVmin
Conductivity
183, 184
Chloride (1.8), sulfate (6.7)
Sulfuric acid
2.0 mM bicarbonate 2.0 d m i n
Conductivity
189
Bromide (5.5). nitrate (6.4)
Sulfuric acid
Dionex fast-run anion separator (x2) in series 250 x 4.0 mm ID Dionex fast-run anion separator (x2) in series 250 x 4.0 mm ID Dionex fast-run anion separator (x2) in series 250 x 4.0 mm ID Dionex AS-4 250 x 4.0 mm ID Zorbax Amino 250 x 4.6 mm ID
0.03 M phosphate, pH 3.2 2.0 mumin
Waters IC Pak A 50 x 4.6 mm ID
Direct 190 spectrophot.at 214 nm Conductivity 181
DH 6.3
Sulfate (8.52)
Glycolic acid
Dilution Dilution
1.0 mM lithium phthalate, 1.2 d m i n
Sulfate (8.91)
Hydrochloric acid
Dilution in eluent
Waters IC Pak A 50 x 4.6 mm ID
0.54 g/l boric acid, 0.14 ml/l Conductivity gluconic acid, 0.16 g/l lithium hydroxide, 2 ml glycerine (12.5% ACN) 1.2 d m i n
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
191
Eluent
Detection
Ref
c
Dilution, reDionex AS-4 injection of 250 x 4 mm ID fraction from Dionex TAC-1 concentrator column An-ex resin in Waters IC Pak C hydroxide form 50 x 4.6 mm ID
1.0 mM bicarbonate, 2.0 mM carbonate 1.5 Wmin
Conductivity
188
$
2.0 mM nitric acid 1.2 d m i n
Indirect conductivity
192
Dilution
10 mM nitric acid 2.4 d m i n
Indirect conductivity
193
0.25 mM cerium (III)
Indirect 192 spectrophot. at 254 nm Direct 194 spectrophot. at 520 nm after post-column reaction with PAR Conductivity 195
TABLE 17.5 (CONTINUED). ANALYSIS OF ACIDS AND BASES USING IC Solutes (min)
Sample
Sample Prep.
Sulfate (8.8)
Inorganic acids
Lithium (2.64), sodium (3.48), Hydrochloric ammonium (5.00), potassium acid (6.14) Lithium (6.07), ammonium Hydrochloric (9.19) acid Magnesium (4,15),calcium (8.68)
Hydrochloric
acid
Column
Waters Protein Pak SP-5PW 75 x 7.5 mm ID Preconcentration Interaction ION (1 ml) 210
1.0 mlhnin
Copper (4.66), zinc (10.59), Hydrofluoric nickel (11.68), iron (II) (22.34) acid
Dilution
Waters c18 pBondapak 300 x 3.9 mm ID
2.0 mM octanesulfonate, 50 mM tartaric acid, pH 3.4 1.O d m i n
Caustic soda
Dilution
Dionex AS-6
20 mMp-cyanophenol, 40 mM hydroxide 1.0 d m i n
Chloride (6.0). nimte (7.0), sulfate (7.9), phosphate (8.6), oxalate (10.2), chlorate (15.7), nitrate (16.8)
P
8
.=?.
E
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviationsare listed in Appendix B (p. 745).
VI 4 P
TABLE 17.5 (CONTINUED). ANALYSIS OF ACIDS A N D BASES USING IC Solutes (min)
Sample
Sample Rep.
Column
Eluent
Detection
Ref
Carbonate (6.0), chloride (10.8), chlorate (14.0), sulfate (16.5)
4% sodium hydroxide
Dilution
Deionized water and 3.0 mM bicarbonate, 2.4 mM carbonate 92 ml/hr and 138 mUhr
Conductivity
196, 69
Fluoride (1.7). chloride (2.2), hypochlorite (2.2). chlorate (5.1), sulfate (9.7)
50% caustic solution
Dilution
Dionex B-1 ion exclusion and anion separator 500 x 6.0 mm ID 500 x 3.0 mm ID Dionex anion separator 500 x 2.8 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 207 mVhr
Conductivity
106
Chloride (4.0). bromide (5.2), nitrate (6.1),sulfate (13.4)
50% sodium
Vydac 302 IC 250 x 4.6 mm ID
1.0 mM phthalate, adjusted to Conductivity pH 5.5 with tetraborate
197
Chloride (3.0), nitrate (6.0). sulfate (7.3, chromate (45)
50% sodium hydroxide
Dionex AS-4
3.0 m i bicarbonate, 2.4 mM carbonate
Conductivity
198
Fluoride (1.45). chloride (2.59), sulfate (10.10)
Sodium hydroxide
SCX in hydrogen form, Millex filter, c18 Sep-Pak Electrolysis with cation-selective membrane Cat-ex in hydrogen form
Waters IC Pak A 50 x 4.6 mm ID
192
Chloride (2.3), sulfate (13.5)
50% caustic
0.54 g/l boric acid, 0.14 ml/l Conductivity gluconic acid, 0.16 g/l lithium hydroxide, 2 ml glycerine (12.5%ACN) 1.2 ml/min 20 mM phthalic acid Conductivity 3.5 d m i n
0.1 M hydroxide, 0.5 M acetate, 0.5% ethylenediamine 1.O ml/min
200
hydroxide sohtion
solution Sulfide (3.7), cyanide (5.5)
Alkaline solutions
Dilution, cat-ex in hydrogen form
Wescan 269001 anion 250 x 4.6 mm ID Dionex AS-7
Amperometry at Ag electrode, 0.ov
199
3
‘0,
?
Seep. 487 for notes on the organization of this Table. Seep 585 for References. Abbreviations are listed in Appendix B ( p . 745).
TABLE 17.5 (CONTINUED). ANALYSIS OF ACIDS AND BASES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Chloride (3.2)
Sodium hydroxide, sulfuric acid Sodium hydroxide, sulfuric acid Sodium hydroxide
Dilution
Dionex 030828 anion separator 500 x 3.0 mm ID Dionex 030828 anion separator 500 x 3.0 mm ID Waters IC Pak Anion HR 75 x 4.6 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 3.0 nVmin 10mM borate 3.0 mvmin
Conductivity
201
Conductivity
201
Conductivity
193
Conductivity
183
Chloride (7.1) Sulfate (10.13)
Sodium (1 1.9), potassium (12.8)
Potassium hydroxide
Dilution Dilution
Dilution
Dionex cation separator (x2) 250 x 4.0 mm ID
1.42 mM gluconate, 5.82 mM boric acid, 0.25%
glycerine, pH 8.5 (12% ACN) 1.0 mumin 5.0 mM hydrochloric acid 3.0 mVmin
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 17.6
ANALYSIS OF DETERGENTS AND POLYMERS USING IC Solutes (min)
Sample
Sample Prep.
Phosphate (1.28), EDTA (1.92). dipolyphosphate (1 1.08), sulfate (12.08), tripolyphosphate (16.45)
Detergent
Tripolyphosphite (12), sulfate ( 1 3) tripolyphosphate (14), dipolyphosphate (16). orthophosphate (30) Octyl sodium sulfate (4.9). decyl sodium sulfate (8.2), dodecyl sodium sulfate (1 1.2), tetradecyl sodium sulfate (13.8)
Detergent
Octyl sodium sulfate (3.0), decyl sodium sulfate (5.2). dodecyl sodium sulfate (9.2), tetradecyl sodium sulfate (16.3) Octyl sodium sulfate (3.1), decyl sodium sulfate (5.2), dodecyl sodium sulfate (10.8)
Column
Eluent
Detection
Ref
Dilution, pH Waters IC Pak A adjustment, Cis 50 x 4.6 mm ID Sep-Pak, filtration
Nitric acid gradient 1.2 mVmin
202, 203
Dilution
Hitachi 2613 cation-exchanger 540 x 9.0 mm ID
80% dioxane to water gradient 1.0 d m i n
Direct spectrophot. at 340 nm after post-column reaction with Fe(II1) perchlorate Coulomeny, conductivity
Synthetic detergent solution
IBM Cis 250 x 4.6 m m ID
Indirect spectrophot. at 242 nm
205
Synthetic detergent solution
IBM (28 250 x 4.6 mm ID
Indirect spectrophot. at 252 nm
205
Synthetic detergent solution
IBM C18 250 x 4.6 mm ID
0.01 M sodium nitrate, 0.01 M phosphate (30% MeOH) to 0.01 M sodium nitrate, 0.01 M phosphate (90%MeOH) to water ternary gradient 1 .O mVmin 0.01 M sodium iodide, 0.01 M phosphate (72%MeOH) 1 .O mumin 0.01 M sodium nitrate, 0.01 M phosphate (42%ACN) 1.0 d m i n
Indirect spectrophot. at 242 nm
205
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
204
4
u
TABLE 17.6 (CONTINUED). ANALYSIS OF DETERGENTS AND POLYMERS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Orthophosphate (3.6). pyrophosphate (4.2), sulfate (5.2), mpolyphosphate (10.8)
Laundry detergent
Dilution, filtration
Dionex AS-7
0.07 M nitric acid
Direct spectrophot. at 330 nm after post-column reaction with Fe(W pexchlorate
206
Monophosphate (6.90), diphosphate (7.85), mphosphate (13.90)
Washing powder Aqueous dissolution, filmtion
Direct specnophot. at 410 nm after post-column reaction with molybdovanadate reagent Direct spectrophot. at 330 nm after post-column reaction with Fe(III) nitrate Dual tlame photometry with phosphorusselective detector Inductively coupled argon plasma emission spectrometer
207
Washing product Dilution Orthophosphate (4.7), diphosphate ( 5 . 3 , sulfate (7.8), mphosphate (15)
Orthophosphate (2.0), pyrophosphate (3.31, mpolyphosphate (5.2) Sulfate (1.7), dodecyl sulfate (8.8), tetradecyl sulfate (17.3)
Detergents and raw materials
0.5 d m i n
Dionex AS-7
0.17 M potassium chloride, 3.2 mMEDTA,pH 5.1
Dionex AS-7
0.07 M nitric acid 0.5 mVmin
Aqueous Hamilton PRP- 1 dilution, c18 150 x 4.1 mm ID Sep-Pak, dilution in buffer Wastewater with Spiking Hamilton PRP-1 detergents 2 5 0 ~ 4 . 1mmID
0.01 M ternethylammonium hydroxide, 0.02 M formic
acid (25% MeOH)
2.0 d m i n 10 mM ammonium acetate (80% MeOH) 0.8 mvmin
Seep. 487 for notes on the organization of this Table, Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
208
209
210
2.-.
Ln
TABLE 17.6 (CONTINUED). ANALYSIS OF DETERGENTS AND POLYMERS USING IC Solutes (min)
Sample
Sample Prep.
Dodecylsulfate (4), tetradecylsulfate (9). hexadecylsulfate (22)
Shampoo
Orthophosphate, pyrophosphate, sulfate, mpol yphosphate
Cleaning agents
Dionex MPIC guard column clean-up
Alkylbenzene sulfonates - C1 (2.0), C4 (6.0),C8 ( 1 5 3 , C9 (18), C10 (20), C12 ( 2 2 ) , C16 (33) Fluoride (3), synthetic surfactants - C8 (7),C12 (12). C20 (16). chloride (21) Cimte, pyrophosphate, EDTA, sulfate
Commercial surfactants
Silica gel cleanUP
Dishwashing liquid
Dionex MPIC guard column clean-up
Synthetic surfactant SD hT-3 (3), chloride (S), nitrate (9)
Laundry effluent water
-
Laundry effluent water
-4 '34
Column
Eluent
Detection
Ref
Wescan 269046 R PIS 250 x 4.6 mm ID Dionex AS-7
0.01 g/l ammonium acetate (50% MeOH) 2.0 mumin 70 mM nitric acid 0.5 mumin
Conductivity
21 1
212
Zorbax C18 250 x 4.6 mm ID
0.1 M tetnbutylamrnonium sulfate, pH 5.0 (ACN gradient) 2.0 mumin 0.1 mM bicarbonate 138 mllhr
Direct spectrophot. at 330 nm after post-column reaction with Fe(1II) perchlorate Direct spectrophot. at 225 nm Conductivity
214
Direct spectrophot. at 330 nm after postcolumn reaction with Fe(II1) perchlorate Conductivity
212
Dionex anion exchanger 500 x 3.0 mm ID Dionex AS-7
Dionex anionexchanger 500 x 3.0 mm ID
70 mM nitric acid 0.5 mumin
5.0 mM succinic acid 138 mlhr
Seep. 487 for notes on the organization of this Table. Seep. 585 f o r References. Abbreviations are listed in Appendix B (p. 745).
213
214
Column
Eluent
Detection
Ref
ziz8.
Dionex anionexchanger 500 x 3.0 mm ID R-Sil AN anionseparator
0.1 mM bicarbonate, 0.1 mM carbonate
Conductivity
214
tiz
TABLE 17.6 (CONTINUED). ANALYSIS OF DETERGENTS AND POLYMERS USING IC Solutes (min)
Sample
Sodium dodecyl sulfate (6), chloride (11)
Laundry effluent water
Pymphosphate (8). mpolyphosphate (16)
Granular detergents
Dodecyl sulfate (3), tetradecyl sulfate (10)
Detergent (sodium lauryl sulfate)
Sulfate (9.79), dodecylsulfate (16.32)
Detergent
Dodecylsulfate (6), tetradecylsulfate (10)
Dishwashing detergent
Phosphate (12), silicate (14)
Laundry detergent
Isethionate (7.6)
Commercially available alkyl esters
Sample Prep.
Aqueous dissolution, h4illex filtration Dilution
Dilution
Wescan RP/S
Vydac 302 IC 250 x 4.6 mm ID
h
ii
ct
Indirect
215
spectrophot.at 285 nm Conductivity
216
Conductivity
217
0.008 g/l ammonium acetate (60%MeOH) 2.0 mumin
Conductivity
218
0.2 mM hydrochloric acid
Direct spectrophot. at 410 nm after post-column reaction with molybdate Conductivity
219
0.02 gh ammonium acetate (50%MeOH) 1.5 d m i n
TSK IC anion SW 5.0 mM phthalate, pH 6.5 and Waters pBondapak c18 in series 50 x 4.6 mm ID 100 x 8.0 mm ID Wescan 269046 RP/S 250 x 4.6 mm ID Dionex AS-1 ion exclusion
Aqueous dissolution, filtration
138 ml/hr 4.0 mM rrimesate, pH 7.5 1.0 d m i n
(35% ACN) 1.2 mumin
5 mM phthalic acid (15% MeOH) 3.0 ml/min
*
Seep. 487for notes on the organization of this Table. Seep. 585 for References. Abbreviationsare listed in Appendix B (p. 745).
220
2
WI
TABLE 17.6 (CONTINUED). ANALYSIS OF DETERGENTS AND POLYMERS USING IC Eluent
Detection
Ref
0.01 M sulfuric acid 1.O ml/min
Direct spectrophot. at 235 nm Conductivity
22 1
Direct spectrophot. at 330 nm after post-column reaction with Fe(III) perchlorate Conductivity
222
Conductivity
223
Conductivity
224
Conductivity
225
Solutes (min)
Sample
Sample Prep.
Acetate (6.6)
Alkylphenol ethoxylate Sequestering agent solution
Anion-exchange Polypore H anion pretreatment exclusion 250 x 7.0 mm ID Dilution in Dionex A S 4 mobile phase 250 x 4.0 mm ID
Sequestering agent solution
Dilution in mobile phase
Dionex AS-7 250 x 4.0 mm ID
50 mM nimc acid 0.6 d m i n
Fluoride, chloride, nitrate, phosphate, sulfate
Polyurethanes
Hydrolysis
Dionex anion separator
Formate, acetate, oxalate, carbonate, d o n a t e Chloride, nitrate, phosphate, sulfate
Polyurethanes
Hydrolysis
Poly(sodium-4styrene sulfonate), polyacrylic acid Dionex CG-2 cation-exchange resin
Dilution, Donnan dialysis enrichment
Dionex ion exclusion Dionex AS-4
3.0 mM bicarbonate, 2.4 mM carbonate 2.9 d m i n 0.1 mM hydrochloric acid 0.7 ml/min 1.0 mh4 carbonate, 4.0 mM bicarbonate 2.0 d m i n
surfactants
Acetate/formate (1.2),chloride (1.7). n-methylaminodi(methylenephosphonicacid) (1.7), h ydroxymethy lenephosphonate (4.2). phosphate (4.7, phosphite (5.2) Hydmxyrnethy lenephosphonate (4.6),n-methylaminodi(methylenephosphonicacid) (4.9). aminommethylenephosphonic acid (9.8)
Sulfate
Column
Schoeniger flask Dionex A S 4 combustion, sorption into peroxide
0 m
7.0 mM bicarbonate, 0.7 mM carbonate 2.7 mVmin
1.5 mM sodium bicarbonate, 1.2 mM carbonate 1.5
See p . 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
222
223
PT
TABLE 17.6 (CONTINUED). ANALYSIS OF DETERGENTS AND POLYMERS USING IC Solutes (min)
Sample Prep.
Colunn
Eluent
Detection
Ref
Sodium, ammonium, potassium Polyurethanes
Hydrolysis
Dionex cation separator
Hydrochloric acid
Conductivity
223
Sodium (3,ammonium (8)
-
3 mM nitric acid 1.5 ml/min
Indirect
226
COndUCtiVity
SOdiUm
Copper (11) (6.2), iron (XU) (8.3)
Sample
Resin extract Water-soluble Polymers Anaerobic adhesive formulations
Wescan 269024 cation/Hs 50 x 3.0 mm ID Aqueous Dionex CS-1 sonication 200 x 4.0 mm ID Dichlmmethane Supelchem LC- 18extraction, DB centrifuge. c18 250 x 4.6 mm ID Sep-Pak
5 mM hydrochloric acid 2.0 ml/min 5 mM oxine. 0.05 M potassium nitrate, 0.05 M acetate buffer, pH 6.0 (50% ACN)
Conductivity
227
Direct spectrophot. at
228
m n m
Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
$
3=. p
TABLE 17.7 ANALYSIS OF FUELS, OILS AND ENGINE PRODUCTS USING IC Solutes (min)
Sample
Glycolate (1.7), phosphate (2), formate (2.3), chloride (2.7), nitrite (3.5). bromide (4.2), chlorate (4.7). nitrate (5.4), benzoate (6.3), sulfate (13) Arsenite (5.2). monomethyl arsonite (6.3), dimethyl arsonate (6.8), arsenate (13.7), benzene arsonate (19.0) Fluoride (1.84), chloride (3.04). bromide (4.14), nitrate (4.83), sulfate (12.48)
Anti-freeze
Fluoride (2.7), chloride (4.0). nitrite (5.0), nitrate (9.9), sulfate (14.0)
Column
Eluent
Detection
Ref
Wescan 269001 anion 250 x 4.6 mm ID
4 mM phthalate, pH 3.9 3.4 mumin
Conductivity
229
5 mM tetrabutylammonium phosphate (10% MeOH) 0.75 mumin
ICP-AES with 15% of column effluent to nebulizer Indirect conductivity
230
Shale oil (acidic fraction)
Silica gel Partisil ODs-3 column clean-up 250 x 4.2 mm ID
Fuels, oils
Pam bomb, dilution, Cis Sep-Pak, filmtion Parr oxygen bomb with sorption into bicarbonate and carbonate Dilution
Fuels
Glycolate, chloride, phosphate, Engine coolants nitrite, nitrate
Chloride (2.3), bromide (5.6), nitrate (6.9), sulfate (8.0)
Sample Prep.
Oil (shale) processing products
Parr oxygen bomb
Waters IC Pak A 50 x 4.6 mm ID
3.0 mM hydroxide 1.2 mVmin
Dionex anion separator 500 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 100 mlhr
Conductivity
121, 120
Dionex anion separator 500 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 138 mlhr
Conductivity
232
Dionex A S 4
3.0 mM bicarbonate, 2.4 mM carbonate 1.O mumin
Conductivity
67
23 1
PB Seep. 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 17.7 (CONTINUED). ANALYSIS OF M L S ,OILS AND ENGINE PRODUCI'S USING IC Ref
2. +
1.42 mM gluconate, 5.82 mh4 Conductivity boric acid, 0.25%glycerine, pH 8.5 (12%ACN) 1.O d m i n 3.0 mM bicarbonate, Conductivity 1.8 mM carbonate 2.5 d m i n
233
%
61
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Fluoride (2.38), chloride (3.88), sulfate (15.29)
Hydraulic fluid
Eluent extraction, centrifugation
Waters IC Pak Anion HR 75 x 4.6 mm ID
Detection
b
Chloride (4), bromide (lo), sulfate (19)
Waste oil
Reflux, cat-ex resin clean-up, extraction
Chloride, nitrate, sulfate
Lubricants
Schoeniger flask Vydac anion combustion 250 x 4.6 mm ID
1 mM phthalate 2.0 ml/min
Chloride (6.0), bromide (23.5)
Waste oil
Reflux, cat-ex resin clean-up, extraction Oxygen bomb, filtration, dilution, precolumn cut
3.0 mM bicarbonate 2.5 d m i n
Fluoride (3.65), chloride (6.33) Fuels
Dionex anion separator 500 x 3.0 mm ID
Dionex anion separator 500 x 3.0 mm ID Waters IC Pak A 50 x 4.6 mm ID
3.
$ 234
Conductivity, indirect spectrophot. at 254 nm Conductivity
234
2.6 mM lithium benzoate, pH 6.71 1.2 d m i n
Conductivity
235
Nitrate (1I), sulfate (17)
Fuels
Pan bomb Dionex anion combustion, separator aqueous rinsing, 500 x 3.0 mm ID filtration
2.4 mM carbonate, 2.0 mM hydroxide 138 ml/hr
Conductivity
236
Sulfate (21)
Fuel oils
Schoeniger flask Dionex fast anion combustion, separator sorption into 250 x 3.0 mm ID peroxide
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity
237, 238
See p . 487 for notes on the organization of this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
3
VI
00
w
Ln
TABLE 17.7 (CONTINUED). ANALYSIS OF FUELS, OILS A N D ENGINE PRODUCTS USING IC
03
P
Solutes (min)
Sample
Sample Rep.
Column
Eluent
Detectiofl
Ref
Sulfate (17)
Fuels
Dionex anion separator 500 x 3.0 mm ID
2.0 mM carbonate 2.6 mVmin
Conductivity
117
Sulfate
Fuel oil, diesel
Combustion, sorption into oxidizing carbonate solution Oxygen bomb
Dionex anion separator
Conductivity
94
Alkylbenzene sulfonates
Pemleum
Silica gel clean-
Zorbax cl8 250 x 4.6 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 4 mlhnin 0.1 M tetrabutylammonium sulfate, pH 5.0 (ACN gradient) 2.0 d m i n 0.01 M nitric acid 138 mVhr
Din33 spectrophot. at 225 nm
213
Conductivity
232
Direct
239
UP
Sodium, monoethanolamine, Engine coolants diethanolamine, methanolamine Lanthanum (3.6)
Dilution
Artificial uranium Dilution in dioxide fuels eluent
Dionex cation separator 250 x 6.0 mm ID SupelcosilLC-18 150 x 4.6 mm ID
20 mM octanesulfonate, 0.18 M hydroxyisobutyric acid, pH 4.6 1.0 mVmin
spectrophot. at 653 nm after postcolumn reaction with Arsenazo III
Seep. 487 for notes on the organizarionof this Table. Seep. 585 for References. Abbreviations are listed in Appendix B (p. 745).
Industrial Applications
17.2 REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12
Deister H. and Runge E.-A., Arch. Eisenhuttenwes.,54 (1983) 405. Resch G.and Grunschlager E., Vortr.-VGB-Konf,"Chem.Kraftwerk", 1981, p. 34. Resch G.and Grunschlager E., VGB Krajherkstech., 62 (1982) 127. Resch G.and Grunschlager E., Vom Wusser, 62 (1984) 207. MacDonald J.C., Am. Lab., January (1979) 45. Merz W. and Panzel H., Vom Wasser, 63 (1984) 239. Potts M.E. and Potas T.A., J. Chromatogr.Sci.,23 (1985) 411. Rich W.E., Inst. Technol., 24 (1977) 47. Rocklin R.D., Pohl C.A. and Schibler J.A., J . Chromatogr.,411 (1987) 107. Coerdt W. and Mainka E., Fres. Z . Anal. Chem., 320 (1985) 503. Dornazetis G.,Chromutogruphiu, 18 (1984) 383. Mizobuchi M.. Ohmae H., Tanaka T.,Urnoto F., Ichirnura K., Ueda E. and Itano T., Zenkoku Kogaiken Kushi, 7 (1982) 67. 13 Mizobuchi M., Ueda E. and Itano T., Yosui to Haisui, 23 (1981) 1437. 14 Takami K., Ohkawa K., Kuge Y. and Nakarnoto M., Bunseki Kagaku, 31 (1982) 362. 15 Waters IC Lab. Report No. 233. 16 Waters IC Lab. Report No. 247. 17 Taguchi Y., Koyanagi S., Ohizumi M., Mashima M.and Sakai N., Niigata Daigaku Kogakubu Kenkyu Hokoku, 32 (1983) 49. 18 Wescan Application #206a. 19 Lipski A.J. and Vaim C.J., Can. Res., 13 (1980) 45. 20 Dionex Application Note 11. 21 Felder R.M.. Kelly R.M., Ferrell J.K. and Rousseau R.W., Environ. Sci. Technol., 14 (1980) 658. 22 Fitchett A.W., Proc.-AWWA Water Quul. Technol. Conf.,1982, p. 149. 23 Long T.S. and Reinsvold A.L., Int. Conf. Sens. Environ. Pollut., 1978, p. 624. 24 Shan Y., Huunjing Baohu (Beijing), 1 (1986) 23. 25 Manning D.L. and Maskarinec M.P.,J. Liq. Chromutogr.,6 (1983) 705. 26 Tusset V. and Hancart J., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromurography,Vol.I, Century International, Inc., Franklin, MA, 1989, p. 421. 27 Nonornura M., Met. Fin., 85 (1987) 15. 28 Holcombe L.J. and Meserole F.B., Water Qual. Bull., 6 (1981) 37. 29 Skelly N.E., Anal. Chem., 54 (1982) 712. 30 Behrend P., Kipplinger A. and Behnert J., LaborPraxis,9 (1985) 324. 31 Bouyoucos S.A. and Armentrout D.N., J. Chromutogr., 189 (1980) 61. 32 Poulson R.E. and Borg H.M., J. Chromutogr. Sci., 25 (1987) 409. 33 McFadden K.M. and Garland T.R., Tech. Report PNL-SA-7592, 1980. 34 Wescan Application #161. 35 Tanaka K. and Ishizuka T., Water Res., 16 (1982) 719. 36 Mu S., Han K., Luo Y. and Hou X., Fenxi Huarue, 13 (1985) 457. 37 Irnanari T., Tanabe S., Toida T. and Kawanishi T., J. Chromatogr.,250 (1982) 55. 38 Hannah R.E., J . Chromatogr. Sci., 24 (1986) 336. 39 Wescan Application #206b. 40 Burrows E.P., Brueggeman E.E. and Hoke S.H., J. Chromatogr., 294 (1984) 494.
585
586 41 42 43 44 45 46 47 48 49 50 51 52
53 54 55 56 57
sa 59 60
61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
80 81
Chapter 17 Dionex Application Note 39. Waters IC Lab. Report No. 288. Waters IC Lab. Report No. 276. Waters Ion Brief No. 88101. Cassidy R.M., Elchuk S. and McHugh J.O., Anal. Chem., 54 (1982) 727. Waters IC Lab. Repon No, 250. Zolotov Y.A., Shpigun O.A. and Bubchikova LA., Fres. 2.Anal. Chem., 316 (1983) 8. Nakata F., Hara S.,Matsuo H., Kumamaru T. and Matsushita S., Anal. Sci., 1 (1985) 157. Urasa I.T.and Nam S.H., J . Chrornatogr. Sci., 27 (1989) 30. Dionex Technical Note 24. Dionex Application Note 51. Mosko J.A., Anal. Chem., 56 (1984) 629. Rawa J.A. and Henn E.L., Proc. Int. Water Conf., Eng. SOC. West P A , 40rh, 1979, p. 213. Waters IC Lab. Report No. 254. Toei J.-I., Chromutographia, 23 (1987) 583. Waters IC Lab. Report No. 295. Waters IC Lab. Report No. 304. Dionex Application Update 106. Wescan Application #131a. Wescan Application #306. Andrew B.E., Paper presented at inr. Conf. Corr. fnhib., Dallas, May, 1983. Wescan Application #107. Dionex Application Note 7R. Cox D., Harrison G., Jandik P. and Jones W., Food Techno/.,July (1985) 41. Tanaka K., Ishihara Y. and Nakajima K., Bunseki Kagaku, 32 (1983) 626. Dionex Application Update 105. Nadkarni R.A. and Brewer J.M., Am. Lab., 19 (1987) 50. Cassidy R.M. and Elchuk S., Anal. Chem., 57 (1985) 615. Cuff D., CHEMSA, 7 (1981) I t . Keller J.M. and Rickard R.R., Tech. Reporr ORNLITM-7569, 1981. Hill C.J. and Lash R.P., Anal. Chem., 52 (1980) 24. Hill C.J. and Lash R.P., Can. Res., 13 (1980) 53. Lash R.P. and Hill C.J., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environniental Pollutants, Vol. I!, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 67. Lash R.P. and Hill C.J., J . Liq. Chromatogr., 2 (1979) 417. Dionex Application Note 16. Lamb J.D., Drake P.A., Nordmeycr F.A. and Lash R.P., in Jandik P. and Cassidy R.M. (Eds.). Advances in Ion Chromatography, Vol. I , Century International, Inc., Franklin, MA, 1989, p. 177. Wescan Application #129. Wescan Application #239a. Mansfield G.H., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. / I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 271. Steiber R. and Merril R., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Polluranrs, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 99. Meserole F.B., Lewis D.L. and Kurzawa F.T., EPA Reporr EPA-600/7-7Y-I5/,1980.
Industrial Applications 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109
110 111 112 113 114
587
Dempsey J.H., Cruse P. and Yates K., in Sawicki E. and Mulik J.D. (Eds.), Ion ChromatographicAnalysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 89. Holcombe L.J., Jones B.F., Ellsworth E.E. and Meserole F.B., in Sawicki E. and Mulik J.D. (Eds.), Ion ChromatographicAnalysis of Environmental Pollutants, Vol.II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 401. Dionex Application Note 11. Holcombe L.J. and Terry J.C., Proc. Annu. Meet. Air Pollut. Control Assoc., 71st, 1979, 78-71.6. Littlejohn D. and Chang S.-G., Anal. Chem., 58 (1986) 158. The K. and Roussel R., Light Met. (Warrendale,PA), 1984, 115. Steiber R. and Statnick R.M., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion ChromatographicAnalysis of Environmental Pollutants, Vol.I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 141. Wescan Application #239b. Wescan Application #239c. Green L.W. and Woods J.R., Anal. Chem., 53 (1981) 2187. Shpigun O.A., Obrezkov N.O., Voloshchik I.N. and Zolotov Y.A., Zh. Anal. Khim., 40 (1985) 1925. Mehra H.C. and Frankenberger W.T., Jr.. Anal. Chim. A m , 217 (1989) 383. Butler F.E., Toth F.J., Driscoll D.J., Hein J.N. and Jungers R.H., in Sawicki E. and Mulik J.D. (Eds.), Ion ChromatographicAnalysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 185. Gerritse R.G. and Adeney J.A., .I. Chromatogr.,347 (1985) 419. Schnitzler M., GIT-Suppl.,4 (1985) 32. Morimoto K. and Esaka S., Kyoto-Fu Eisei Kogai Kenkyusho Nenpo, 24 (1979) 128. Gerritse R.G., J. Chromatogr., 171 (1979) 527. Murayama T., Kubota T., Hanoaka Y., Rokushika S., Kihara K. and Hatano H., J. Chromatogr.,435 (1988) 417. Tanaka K., Ishizuka T. and Sunahara H., .I Chromatogr., . 177 (1979) 227. Tanaka K. and Ishihara Y., Mizu Shori Gijutsu, 23 (1982) 767. Tanaka K., Bunseki Kagaku, 31 (1982) T106. Tanaka K. and Ishihara Y., Mizu Shori Gijutsu, 23 (1982) 855. Andrew B.E., Proc. Corros. 88 Conf., 1988, paper no. 89. Wescan Application #131b. Rich W.E., Tillotson J.A. and Chang C.C., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion ChromatographicAnalysis of Environmental Pollutants, Vol. I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 185. Yonemori S. and Noshiro M., Asahi Garmu Kenkyu Hokoku, 31 (1981) 17. Pohlandt C. and Cameron A., MINTEK Report No. M153, 1984. Colaruotolo J.F., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion ChromatographicAnalysis of Environmental Pollutants, Vol.I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 149. Colaruotolo J.F. and Eddy R.S., Anal. Chem.,49 (1977) 884. Kreling J.R., Block F., Louthan G.T. and DeZwaan J., Microchem. .I34 .,(1986) 158. Westwell A., Anal. Proc., 21 (1984) 320. Smith R.E. and Davis W.R., Topical Report BDX-613-3053, 1984. Amano C. and Shimada M., Kanzei Chuo Bunsekishoho, 25 (1985) 109.
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Chapter 17
115 116 117 118 119 120 121
Schaefer J., Burmicz J. and Palladino D., Am. Lab.,February (1989) 70. Wescan Application #193. Saitoh H. and Oikawa K., Eunseki Kuguku, 31 (1982) E375. Kan M., Ohnishi K. and Shintani M., Yukuguku Zasshi, 104 (1984) 763. Xiang L., Luo 2.and Hu Z., Vouji H m u e , 4 (1985) 314. Mizisin C.S., Kuivinen D.E. and Otterson D.A., Tech. Report NASA-TM-78971,1978. Mizisin C.S., Kuivinen D.E. and Otterson D.A., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromaographic Analysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI. 1979, p. 129. Smith F., Jr., McMurtrie A. and Galbraith H., Microchem.J., 22 (1977) 45. Cox J.A., Dabek-Zlotorzynska E., Saari R. and Tanaka N., Analyst (London), 113 (1988) 1401. Quinn A.M., Siu K.W.M., Gardner G.J. and Berman S.S., J. Chromutogr., 370 (1986) 203. Honma H., Suzuki K., Yoshida M. and Yanashima H., Eunseki Kuguku, 36 (1987) T9. Nishikawa T. and Hozumi K.,Microchem. J., 35 (1987) 201. Nagashima H., Kuboyama K. and Ono K., Sunkyo Kenkyuurho Nempo, 35 (1983) 59. Assenmacher H. and Frigge J., Fres. Z . Anal. Chem., 332 (1988) 41. Reigler P.F., Smith N.J. and Turkelson V.T., Anal. Chem., 54 (1982) 84. Brandt G. and Kettrup A., Fres. Z. Anal. Chem., 327 (1987) 213. Brandt G. and Kettrup A., Inter. J. Environ.Anal. Chem., 31 (1987) 129. Okamoto T. and Shirane Y., Hiroshima-kenKunkyo Senta Kenkyu Hokoku, 5 (1983) 39. Zuercher F., Comm. Eur. Commun.Rep. EUR 7623, 1982. Mani Y. and Arikawa A., Ebaru Infiruka Jiho, 90 (1984) 8. Morrow C.M. and Minear R.A., Water Res.. 21 (1987) 41. Wescan Application #178. Wescan Application #115. Ryder D.S., J. Chromutogr., 354 (1986) 438. Wescan Application #269a. Wescan Application #269b. Dionex Application Note 33. Crafts R.C., Polymer Testing, 5 (1985) 193. Wescan Application #165. Rossiter W.J., Jr., Brown P.W. and Godette M., Sol. Energy Mat., 9 (1983) 267. Rossiter W.J., Jr., Godette M., Brown P.W. and Galuk K.G., Sol. Energy Mar., 11 (1985) 455. Wescan Application #210. Otterson D.A., Tech. Report NASA TM 79020, 1978. Waters IC Lab. Report No. 298, Muller H., Nielinger W. and Horbach A., Angew. Makromol. Chem., 108 (1982) 1. Nakazawa H., Nagase M. and Onuma T., Eunseki Kuguku, 36 (1987) 396. Dionex Application Note 32. Waters ILC Series Application Brief No. 6003. Dionex Application Note 6. Johnson K. and Tarter J.G., LC.GC, 7 (1989) 266. Waters IC Lab. Report No. 285.
122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140
141 142 143 144 145 146 147 148 149 150 151 152 153 154 155
Industrial Applications
589
156 Fortier N.E. and Fritz J.S.. J . Chromatogr.,462 (1989) 323. 157 Fritz J.S., in Jandik P.and Cassidy R.M. (Eds.), Advances in Ion Chromatography,Vol. I , Century International, Inc., Franklin, MA, 1989, p. 1. 158 Franklin G.. Pulp & Pap., 56 (1982) 91. 159 Franklin G.O., Proc. Pulping Conf., 1981, p. 255. 160 Franklin G.O. and Fitchett A.W., Pulp Pap. Can., 83 (1982) 40. 161 Franklin G.O., Tappi, 65 (1982) 107. 162 Cox D., Jandik P.and Jones W., Pulp Pap. Cun., 88 (1987) T318. 163 Behnert I. and Behrend P.,LaborPrais, 8 (1984) 1204. 164 Dionex Application Note 29R. 165 Richardson D.E. and Jewel1 I.J., Appita, 38 (1985) 113. 166 Dionex Application Note 30R. 167 Easty D.B., Borchardt M.L.and Webb A.A., Pap. Puu, 67 (1985) 501. 168 Dionex Application Note 5. 169 Stauber B. and Weismann H., Escher Wyss News, 53 (1980) 119. 170 Wescan Application #198a. 171 Wescan Application #198b. 172 Jupille T., Znt. Lab., November (1985) 82. 173 Parigi J.S., Am. Lab., September (1984) 124. 174 Easty D.B. and Johnson J.E., Tappi, March (1987) 109. 175 Buytenhuys F.A., J . Chromatogr.,218 (1981) 57. 176 Andrew B.E., Paper presented at 7th Aust. Anal. Conf..Adelaide, August, 1983. 177 Wescan Application #198c. 178 Waters IC Lab. Report No. 278. 179 Franklin G O . , Am. tab.. 17 (1985) 65. 180 Smith R.E. and Davis W.R., Plat. Surf. Finish, 71 (1984) 60. 181 Waters IC Lab. Report No. 287. 182 Waters IC Lab. Report No. 310. 183 Dionex Application Note 35. in Sawicki E. and Mulik J.D. (Eds.), Ion 184 Pinschmidt R.K. and Katrinak T.P., ChromatographicAnalysis of Environmental Pollutants, Vol.II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 31. 185 Waters IC Lab. Report No. 268. 186 Streckert H.H. and Epstein B.D., Anal. Chem., 56 (1984) 21. 187 Posner R.D. and Schoffman A., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 51. 188 Murayama M., Suzuki M. and Takitani S., J . Chromatogr..466 (1989) 355. 189 Watanabe T.,Nagaoka M. and Yamazaki S., Ryusan to Kogyo, 38 (1985) 162. 190 Cortes H.J., J. Chromarogr.,234 (1982) 517. 191 Waters IC Lab. Report No. 237. 192 Waters IC Lab. Report No. 258. 193 Waters IC Lab. Report No. 317. 194 Waters IC Lab. Report No. 306. 195 Dionex Application Update 104.
590
Chapter 17
196 Rich W., Smith F., Jr., McNeil L. and Sidebottom T., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. 11, Ann Arbor Sci. Pub]., Ann Arbor, MI, 1979, p. 17. 197 Hill R.A., J . HRC & CC, 6 (1983) 275. 198 Pettersen J.M., Johnsen H.G. and Lund W., Talanta, 35 (1988) 245. 199 Wescan Application #271. 200 Dionex Application Update 107. 201 Smith R.E., Anal. Chem., 55 (1983) 1427. 202 Waters IC Lab. Report No. 309. 203 Waters IC Lab. Report No. 307. 204 Tanaka K. and Ishizuka T., J . Chromatogr., 190 (1980) 77. 205 Boiani J.A., Anal. Chem., 59 (1987) 2583. 206 Fitchett A.W. and Woodruff A., LC, 1 (1983) 48. 207 Vaeth E., SIadek P. and Kenar K., Fres. Z. Anal. Chem., 329 (1987) 584. 208 Weiss J. and Iiagele G., Fres. Z. Anal. Chem., 328 (1987) 46. 209 Chester T.L., Smith C.A. and Culshaw S . , J . Chromarogr., 287 (1984) 447. 210 Irgolic K.J. and Hobill J.E., Spectrochim. Acta, 42B (1987) 269. 21 1 Wescan Application #139. 212 Dionex Application Note 44R. 213 Bear G.R., J . Chromatogr., 371 (1986) 387. 214 Ivanov A.A., Shpigun O.A., Kurnoskin A.V. and Zolotov Y.A., Zh. Anal. Khim., 40 (1985) 1699. 215 MacMillan W.D., J. HRC & CC, 7 (1984) 102. 216 Behnert J., Behrend P. and Kipplinger A., LuborPruxis, 9 (1985) 38. 217 Waters IC Lab. Report No. 320. 2 18 Wescan Application #3 18. 219 Dionex Application Update 113. 220 Ianniello R.M., J . Liq. Chromatogr., 11 (1988) 2305. 221 Ianniello R.M., Anal. Lett., 21 (1988) 87. 222 Pacholec F., Rossi D.T., Ray L.D. and Vazopolos S., LC, 3 (1985) 1068. 223 Von Unterrichter-Worthman J. and Quella F., Kunstoffe, 74 (1984) 682. 224 Cox J.A. and Dabek-Zlotorzynska E., Anal. Chem., 59 (1987) 534. 225 Galindo I.C. and Tarter J.G., J. Chromafogr.,445 (1988) 21 1. 226 Wescan Application #289. 227 Maurer J.J. and Klemann L.P., J . Liq. Chromatogr., 10 (1987) 83. 228 Mooney J.P., Meaney M.,Smyth M.R., Leonard R.G. and Wallace G.G., Analyst (London), 112 (1987) 1555. 229 Wescan Application #307. 230 LaFreniere K.E., Fassei V.A., and Eckels D.E., Anal. Chem., 59 (1987) 879. 23 1 Waters IC Lab. Report No. 274. 232 Dionex Application Note 4. 233 Waters IC Lab. Report No. 316. 233 Koch W.F., J. Res. Nut. Bur. Std., 84 (1979) 241. 235 Waters IC Lab. Report No. 230. 236 Dionex Application Note 15. 237 McComiick M.J., Anal. Chirn.Acta, 121 (1980) 233.
Industrial Applications 238 Viswanadham P., Smick D.R., Pisney J.J. and Dilworth W.F., Anal. Chem., 54 (1982) 2431. 239 Cassidy R.M. and Fraser M., Chromatographia, 18 (1984) 369.
591
This Page Intentionally Left Blank
593
Chapter 18 Analysis of Foods and Plants 18.1 OVERVIEW Applications of IC in the analysis of foods and plants are presented according to the scheme shown in Fig. 18.1.
Foods (Table 18.1) ANALYSIS OF FOODS AND PLANTS USING IC
Beverages (Table 18.2) Plants, plant materials (Table 18.3)
Fig. 28.2 Applications of IC in the analysis of foods and plants
TABLE 18.1 ANALYSIS OF FOODS USING IC ~~~~
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Chloride, nitrate, bicarbonate, sulfate
Foods
Dilution, filtration
Nucleosil- 10 Anion
25 mM salicylate, pH 4.0 0.8 mVrnin
Indirect RI
1
N-acetylgalactosamine, galactose, n-acetylneuramino acid
Foodstuffs
Carrez reagent
Dionex DA-X8-I 1 0.5 M borate buffer, 75 x 6.0 rnrn ID 0.3 M sodium acetate, pH 8.0 40 mVhr
2
Lactose, galactose, glucose
Foodstuffs
Carrez reagent
Dionex DA-X8-11 0.8 M borate buffer, 75 x 6.0 mm ID pH 8.0
Direct spectrophot. at 570 nrn after post-column reaction with orcinol Direct specuophot. at 570 nm after post-column reaction with orcinol Conductivity
40 mVhr
2
3, 4
Dionex AS-5
3.0 mM bicarbonate, 2.4 mM carbonate 1.Omumin
Foods
Flash distillation, formaldehyde and hydroxide sorption Dilution
Nuc~eosil-Clg
10 mM octylamine, phosphoric acid, pH 4.0 1.0 d m i n
Direct spectrophot. at 210 nm
1
Foods
Dilution
Zorbax Amino
10 gh phosphate, pH 3.0
Direct specuophot. at 205 nm
1
Sulfite (3.2), sulfate (3.6)
Foods
Nitrate (19.0)
Nitrate (5.2)
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
b
TABLE 18.1 (CONTINUED). ANALYSIS OF FOODS USING IC
2 ~
Solutes (min)
~
~~
\
Eluent
Detection
Aqueous or Wescan anion acidic extraction, exclusion 300 x 7.8 mm ID filtration
5 mM sulfuric acid 0.5 ml/min
Conductivity, amperometry at Pt electrode, 4.4v
5
Aqueous or Brownlee acidic extraction, Polypore H ion filtration exclusion 100 x 4.6 mm ID
6 mM sulfuric acid 0.5 d m i n
Amperometry
6
Sample
Sample Prep.
Freeze dried foods
Column
Ref
Sulfite (2.3)
Freeze dried and other foods
Aluminium (3.8), iron (XI) (7.2) Foods
Lactate/pyruvate, chloride, Meat and meat fructose, nitrate, sulfate, products phosphate Chloride (3.2). phosphate (6.3), Ham nimte (9.2) Chloride (3.2), nitrite (3.6), nitrate (4.2)
Cooked ham
Homogenization and extraction. filtration Homogenization and dilution in eluent, filtration Homogenization and extraction, centrifugation, Millex filtration
Dionex CS-2 250 x 4.0 mm ID
20 mM sulfosalicylate, 3.0 mM ethylenediamine, pH 5.0 1.5 Wmin
Dionex AS-1
3.0 mM carbonate, 2.0 mM hydroxide
Dionex AS-3
2.1 mM bicarbonate, 1.68 mM carbonate 3.0 ml/min 0.04 M sodium perchlorate 2.0 d m i n
Ionosphere tm A 250 x 4.6 mm ID
2’
B
~
Sulfite (13)
M
at Pt elecmde, +0.4V, direct specmphot. at 210 nm Direct spectrophot. at 630 nm after post-column reaction with chrome Amrol S Conductivity
& Q
% 2 3E:
s5. 7
8
8
Conductivity
9, 10
Direct spectrophot. at 190 nm
11
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
h
0 0
u, W VI
k2
TABLE 18.1 (CONTINUED).ANALYSIS OF FOODS USING IC
Solutes (min)
Sample
Nimte (6.7), system peak (7.8). Corned beef nitrate (10.4)
Chloride (4.9). nitrate (7.7), system peak (18)
Corned beef
Nitrite (7.1). nitrate (9.9)
Corned beef, salami, bacon
Nimte (6.5), nitrate (8.4)
Corned beef
Nitrite (2.5), nitrate (4.0)
Meat products
Sample Prep.
Column
Eluent
Detection
Ref
Homogenization and extraction, cenmfugation, fttration, c18 Sep-Pak Homogenization and extraction, centrifugation, filtration, c18 Sep-Pak Homogenization and extraction, centrifugation, filtration. c18 Sep-Pak Homogenization and extraction, cenmfugation, filtration, cl8 Sep-Pak Mincing, dilution, heating, Carrez solution addition, cenmfugation, filtration
Waters CN RadPak 100 x 5.0 mm ID
1.O% cemmide, 0.1 M potassium dihydrogen phosphate (35% MeOH) 1.0 d m i n
Direct spectrophot. at 214 nm
12
Vydac 302 IC 250 x 4.6 mm ID
2.5 mM phthalate, pH 4.2 2.0 d m i n
Indirect spectrophot. at 265 nm
12
Vydac 302 IC 250 x 4.6 mm ID
11.O mM chlommethane sulfonic acid, pH 5.0 2.0 mvmin
Direct spectrophot. at 214 nm
12
Waters Amino Rad-Pak 100 x 5.0 mm ID
16.0 mM Dotassium dihydrogin phosphate, pH 3.0
Direct spectrophot. at 214 nm
12
Direct spectrophot. at 214 nm
13
1.0 nvmin
Waters Radial Pak 5.0 mM low UV PIC A 3.0 d m i n c18
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 18.1 (CONTINUED). ANALYSIS OF FOODS USING IC Y
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Nitrite (4.4). nitrate (11.2)
Meat products
Biotronik anion separator
5.0 mM methanesulfonyl
Direct spectrophot. at 210 nm
14
Nitrite (12.5), nitrate (18)
Mats
Homogenization and extraction, Carrez reagent, filtration Extraction, dilUtion
2 m M dodecylmethyl ammonium phosphate (lM MeOH) 0.8 wmin
qmperomeay. dmxt
15
Direct
Dionex anion separator 500 x 3.0 mm ID
1.0 mM tetrapentyl ammonium bromide (33%ACN) 1.0 wmin 3.0 mM bicarbonate, 2.4 mM carbonate 138 ml/hr
Conductivity
17
QAEA25Gel 22x l0mmID
0.09 M sodium nitrate 76 ml/hr
Direct spectrophot. at 215 nm Quenched phosphores-
18
G E;.
x
~~~~~
Nitrite (10.6), nitrate (12.8)
Bacon, baby food
Chloride, nitrite, sulfate
Nitrite, nitrate Nitrite (4.9)
Nitrite (10)
Bacon extract
Homogenization Hamilton PRP-1 and dilution, 150 x 4.1 mm ID filtration Comminution
with water, Ag ppt of chloride, filtration Aqueous Ham extraction, filtration Processed meats Homogenization and extraction
Ham
Econosil 250 x 4.6 mm ID
chloride, pH 6.2 1.0 wmin
Micropak SAX 10 10 mM phosphate buffer, 300 x 4.6 mm ID 1.4 mM biacetyl, pH 3.35 (55% ACN) 2.0 wmn i Aqueous Brownlee 20mM sulfuric acid homogenization, Polypore H 0.8 mumin 100 x 4.6 mm ID filtration
spectrophot. at 220 nm, photolytic amperometry spectrophot.
16
19
cence Ampmetryat 20 Pt electrode. 4.8V
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendrjr B (p. 745).
v,
TABLE 18.1 (CONTINUED). ANALYSIS OF FOODS USING IC Solutes (min)
Sample
Nitrate (10)
Meat preserver
2
Sample Prep.
Column
Eluent
Detection
Aqueous
Dowex 1-XS 100 x 2.0 mm ID
5.0 mM perchloric acid 1.O d m i n
Amperometryat 21 copperized Cd electrode,
Waters IC Pak A 50 x 4.6 mm ID
5 mM phosphate buffer I .2 mumin
Amperometryat 22 Ag electrode
3.0 mM bicarbonate, 1.8 mM carbonate 2.5 mumin
Conductivity
23
2.0 mM carbonate 2.6 mVmin
Conductivity
24
Conductivity
25
Fluorescence at 228,370 nm, direct spectrophot.at 228 nm
26
Ref
~
extraction
-1.15V Sulfite (7)
Beef stew
Fluoride (2.4). chloride (4.2). phosphate (8.6),bromide (10.9). nitrate (12.2), sulfate (21.4) Fluoride (3), chloride (3, nitrate (12), sulfate (14)
Fish powder, rice flour
Fluoride (6), chloride (10)
Krill
Tetra-P (nitrite product) (7.5)
Fish, sausage, ham
Oyster
Aqueous
exmction, liberation of sulfite by nitrogen purging Lyophilization, Dionex anion sonication. separator 500 x 3.0 mm ID filmtion Combustion, sorption in oxidizing carbonate solution Acid diffusion clean-up
Dionex anion separator 750 x 3.0 rnm 1D Dionex fast-run anion
2 mM N,N-bis (2-hydroxy ethyl)-2-aminoethane sulfonic acid, 1.5 mM hydroxide 2.0 mUmin Homogenization TSK GEL LS-410 0.05 M potassium dihydrogen phosphate, pH 4.5 and extraction, ODs filtration,pre150 x 4.0 m m ID (20%ACN) column reaction 1 .O mumin with hydraiazine
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
b
TABLE 18.1 ( C O N T m D ) . ANALYSIS OFFOODS USING IC
3
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Sulfite (5)
shrimp
Dionex AS-3
3.0 mM bicarbonate, 1.5 mM carbonate 1.8 Wmin
Methylmercury (6.0)
Tuna (albacore)
Exuaction (alkaline formaldehydeor water), filtration Acetone wash, centrifugation, toluene exaaction, evaporation Extraction, ether ppt of fats, dilution
Waters Pic0 Tag cl8
0.06 M ammonium acetate, 0.005% 2-mercaptoethanol, pH 6.8 (3%ACN) 1.0 mumin
Amperometry, (pulsed) +0.30V, conductivity Inductively 28 coupled plasmamass specmmetry
Dionex CS-2 250 x 4.0 mm ID
10 mM hydrochloric acid 1.5 d m i n
Conductivity
29
Wescan 269029
5 mM perchlorate 1.7 ml/min
Direct specmphot. at 210 nm Conductivity, direct spectrophot. at 205 nm Conductivity
30 31
Conductivity
35
Y
Sodium ( 5 . 3 , ammonium (8.9), potassium (10.9), tetramine (22) Iodate (3.4), bromate ( 5 . 3 , bromide (6),nitrate (7.5)
ShelKsh Bakery additives
aniOn/R
Ascorbate (2.4), bromate (2.7), Bread improver bromide (3.8), sulfate (8.0) extracts Bromate (28), chloride (32)
Bromate (4.6)
250x4.1mmID Sonication, Bio-Gel TSK IC Millex filtration, anion PW Sep-Pak 50 x 4.6 mm ID
Aqueous extraction, centrifugation, Ag cat-ex cleanUP Bread, fish paste Homogenization centrifugation, filtration, cut of concentrator column fraction
Bread
7.0 mM chloromethane sulfonate, pH 5.5 1.4 ml/min
Dionex anion separator lo00 x 3 mm ID
3.5 mM tetraborate 117invhr
Dionex AS- 1 500 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 115 ml/hr
c U
s 3 E:
8
32-34
cn
Seep. 487 for notes on the organizationof this Table. Seep. 627 for References. Abbreviationsare listed in Appendix B (p. 745).
W W
TABLE 18.1 (CONTINUED). ANALYSIS OF FOODS USING IC Solutes (min)
Sample
Sample Rep.
Column
Eluent
Detection
Ref
Bromate (5.8)
Bread and kamaboko
zipax SAX 500 x 2.1 mm ID
0.25 mM phthalate 0.8 d m i n
Indirect spectrophot. at 230 nm
36
Bromate (7.9)
Bread dough conditioner Bread
Aqueous exmction, acetone ppt of proteins, Ag catex clean-up Dilution, Millex filtration Combustion flask
Waters IC Pak A 50 x 4.6 mm ID Dionex anion separator 750 x 3.0 mm ID Dionex AS-6
1.0 mM benzoic acid, pH 6.0 Conductivity 1.2 d m i n 2.0 mh4 carbonate Conductivity 156 mVhr
37, 38
150 mM hydroxide 1.0 mvmin
39
Bromide (7.7)
Sucrose (7.3), raffinose (11.9), Soy flour stachyose (13)
Aqueous extraction, filmtion Dilution
Waters IC Pak A 50 x 4.6 mm ID
Phosphate (5.4)
Flow
Phytic acid (7)
Flour, bran, bread, infant formula
Homogenization Dionex AS-3 extraction, centrifugation, Millex filtration
cobalt (7)
Rice flour
Dry-ashing, hybhloric acid digestion, dilution
Dionex CS-2 250 x 4.6 mm ID
Amperometty (pulsed) at Au
electrode 1.3 mM tetraborate, 5.8 mM Conductivity boric acid, 1.4 mM gluconate (12% ACN) 1.2 mvmin Direct 0.11 M nitric acid spectrophot. at 1.0 rnl/min 290 nm after post-column reaction with Feu10 perchlorate Chemilumin0.12 M lactic acid, adjusted ewllce after to pH 3.8 with hydroxide post-column addition of lUminol
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
32
37
40
41
E5
TABLE 18.1 (CONTINUED).ANALYSIS OF FOODS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection ~
Chloride (3.5). phosphate (6.7). Infant formula (milk based) nitrate (9.3) Sulfite (4.5). sulfate (7.5) Parental formulations Sulfite (2)
Infant formula, yeast
Sodium (5.0), potassium (10.0) Infant formula (soy based) Infant formula Choline (17.7) (soy based) Magnesium (2.3). calcium (4.0) Infant formula (milkbased) Chloride (4.OO), phosphate Color additives (7.75). bromide (10.60), nitrate (12.60), sulfate (19.05) Color additives Acetate (5.05), iodate (6.05), formate (7.40), chloride (31.25) Acetate (3.95). forrnate (4.80), iodate (4.90), chloride (9.95)
Color additives
certifiablecolor Chloride (3.28). phosphate (5.851, bromide (7.79), sulfate additives (dyes) (12.74)
Nitric acid digest, dilution Aqueous formaldehyde dilution Aqueous extraction
Ref
$ 2. 0
\
~~
Dionex AS-2
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity
42
Dionex AS4
3.5 mM carbonate 1.0 Wmin
Conductivity
43
‘+I
i%
E-u
ij.
Wescan anion exclusion lOOx 4.6 mm ID Dilution in nitric Dionex CS-1 acid Dilution in Dionex MPIC-CS 1 eluent Aqueous Dionex CS-1 dilution Dilution, Dionex anion cleanup on an-ex separator pre-column 500 x 3.0 XIUII ID Dilution, Dionex anion cleanup on an-ex separator PR-ColUmn 500 x 3.0 mm ID Dilution. Dionex anion cleanup on an-ex separator p-column 500 x 3.0 mm ID Dionex anion Dissolution in separator eluent 500x3.0mmID
5.0 mMnimc acid
Ampennnetryat 20 R elecaode, M.6V Conductivity 42,44
2.0 mM hexanesulfonic acid
Conductivity
42
Nitric acid, p-phenylene diamine dihydruchloride 3.0 mM bicarbonate, 1.8 mM carbonate 138 ml/hX 1.5 mM tetraborate 115 ml/hr
Conductivity
42
Conductivity
45.46
conductivity
45
1.5 mM bicarbonate 115*
Conductivity
45
3.0 mM bicarbonate, 2.4 mM carbonate 138&
Conductivity
47
20 mM sulfuric acid 0.6 mVmin
Seep. 487for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
$
8. 5
&
8
TABLE 18.1 (CONTINUED). ANALYSlS OF FOODS USING 1C Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Iodide (12)
Color additives
9.6 mM carbonate, 2.0 mM hydroxide 138 ml/hr 0.16 M hydroxide 1.O mVmin
45
Potato chips, seasoning
Dionex anion precolumn 150 x 3.0 mm ID Dionex AS-6
Conductivity
Glucose (4.0). fructose (4.7), lactose (6.4), sucrose (8.0)
Dilution, anionexchange precolumn clean-up Dilution, filtration
48,49
Glucose (1.8), maltose (2.2), Corn syrup maltotriose (2.7), maltotetraose (3.7), maltopentaose (5.3, maltohexaose (8.7) Saccharides - DPl to DP22 Corn starch (hydrolyzed)
Dilution
Hamilton PRPXloo 150 x 4.1 mm ID
75 mM hydroxide 2.0 d m i n
Ampemmetry (pulsed) at Au electrode Direct RI
Dilution, filtration
Dionex AS-6
Amperomtry (pulsed) at Au electrode
51.48
Chloride (7), bromide (8.5), iodide ( 18)
Table salt
Dilution
Iodide (2.0)
Iodized salt
Dilution in eluent
Nucleosil SB 10 anion 250 x 4.0 mm ID Dionex AS-2
0.15 M hydroxide to 0.15 M hydroxide + 0.5 M acetate went I .O mumin 50 mM potassium ninate 1.O d m i n
Iodide (7)
Iodized table salt Dilution
Dionex AS-1
Iodide (7.58)
Iodized salt
Partid 10 ODs-3 250 x 4.6 mm ID
Aqueous dissolution
Potentiomtry with silver sulfide electrode 40 mM sodium nitrate, Amperomtry at iodized Pt 4 mM nimc acid 2.6 d m i n electrode. 4.8V Amperometry at 0.01 M sodium nitrate Ag electrode, 4.3v 1.66 mill mylamine, adjusted Direct to pH 6.44 with phosphoric spectrophot.at acid (7.5% ACN) 226 nm 2.0 Wmin
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviarions are listed in Appendix B (p. 745).
50
52 53
54,42
55
b .
TABLE 18.1 (CONTINUED). ANALYSIS OF FOODS USING IC
3 ~~~
Sample
Sample Prep.
Column
Eluent
Detstion
Ref
Iodide (4.2)
Table salt
1% solution
56
Sauerkraut juice
Dilution
Conductivity
57
Acetic (24), lactic (25), citric (28) Maleic (4.4), citric (4.8), lactic (7.3), acetic (8.0), propionic (8.5), butyric (10.4) Citric (3.2), lactic (3.6), acetic (5.0). succinic (7.0)
Sauerkraut juice
Filtration
Yogurt, sour
cream
Centrifugation, filtration
5 mM sodium perchlorate 2.7 mumin 4.0 mM phthalic acid, pH 4.5 2.0 ml/min 1.0 M sodium formate 62 mVhr 10 mM sulfuric acid 0.8 mlfmin
Amperomeiry
Chloride (1.3), nitrate (2.1), sulfate (3.3), bicarbonate (4.8)
Wescan aniodRHS Wescan standard anion 250 x 4.6 mm ID Aminex A25
59-61
Yoghurt
Dilution
Solutes (min)
xt’ B
~
9oomm
Bromide (6.4), nitrate (7.9)
Cheese, whey, flour,rice
Nitrite (7.1), nitrate (9.9)
Cheese
Nitrate (4.0), iodide (7.1)
Butter
Homogenization with water and C m z solution, centrifugation, filtration Homogenization and extraction, centrifugation, filtration, c18 Sep-Pak Alkali ashing, neutralization
Interaction ORH801 organic acid 300 x 6.5 mm ID Hamiiton PRP-
x300
Sulfuric acid, pH 3.0 1.1 Wmin
150 x 4.1 mm ID Waters amino pBondapak 300 x 3.9 mm ID
10 g/l potassium dihydrogen phosphate, pH 3.0 1.O mlfmin
Direa spectrophot. at 210 nm Direct spectrophot. at 210 Nn Direct spectrophot. at 210 nm
Vydac 302 IC 250 x 4.6 mm ID
11.0 mM chloromethanesulfonic acid, pH 5.0 2.0 mumin
Direct spectrophot. at 214 nm
12
Wescan anion 250 x 4.6 mm ID
10.0 mM methanesulfonic acid, pH 5.0 2.0 mVmin
Direct spectrophot. at 214 nm
64
%
0 0
s Q 3
SL
3 09
5
62 63
m
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviationsare listed in Appendix B (p. 745).
w 0
P
TABLE 18.1 (CONTINUED). ANALYSIS OF FOODS USING IC Solutes (min)
Sample
Sample Prep.
Column
Iodide (27)
Chocolate
Grind and sieve, Waters CISRCM combustion 100 x 8.0 mm ID flask, dilution
Eluent
Detection
Ref
Direa
65
Homogenization centrifugation, Sep-Pak, Millex filtration Aqueous exaaction
Waters IC Pak C 50 x 4.6 mm ID
2.5 mM hexadecyltrimethylammonium chloride, 50 mM phosphate, pH 6.8, (25%ACN) 2.5 mumin 2.0 mM nitric acid 1.2 d m i n
LiChrosorb KAT 15Ox4mmID
Water 1Opllsec
Phosphoric acid distillation, aqueous peroxide sorption, dilution in eluent Magnesium (4.0), calcium (6.7) Oatmeal (instant) Homogenization and dilution in hydrochloric acid, filtration Calcium (6.0). magnesium Egg white Ultrafiitration, (6.9), sulfate (9.7) addition of EDTA
Dionex anion separator 250 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 3.8 d m i n
Dionex CS- 1
2.5 mM m-phenylenediamine Conductivity dihydrochloride,2.5 mM hydrochloric acid 2.0 d m i n 1.0 mM EDTA, pH 6.5 Conductivity 1.0 d m i n
Sodium (3.6), ammonium (5.1), potassium (6.4)
Blue cheese
Benzoic (2.2)
Mustard
Sulfate (16)
Malt
TSK-gel ICAnion-SW 50 x 4.6 mm ID
specnophot. at 226 nm I n h t conductivity
17, 66
Streaming current and potential Conductivity
67
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
68
9
69
TABLE 18.2
ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Citric (11.O), tartaric (11.4), malic (12.0), lactic (14.2), succinic (15.9), acetic (19.7), bicarbonate (21.4), ethanol (25.5) Acetate (1.2), levulinate (2.3), chloride (3.0), phosphate (4.8), succinate (12.4), malate (13.3). sulfate (22.6) Phosphate (7.2), citrate (7.8), malate (8.6), succinate (1 O.O), lactate (12.2), pyruvate (12.2), carbonate (16) Straight-chain oligosaccharides of maltose-DP.2 (2.11, DP3 (2.8), DP4 (4.7); DP5 (6.0), DP6 (7.4), DP7 (9) Sorbitol(3.0), arabinose (5.0), fructose (6.9), ribose (7.51, isomaltose (9.9), maltose (25) Fluoride (1.4), chloride (2.0), nitrite (2.3), phosphate (2.8), sulfate (6.0) Oxalic 13.2). citric 15.0). acetic (8.51, p;opionic (9.7),fumaric (10.5)
Beer, sake
Dilution
TSK SCX 50 x 7.5 mm ID
1.0 mM sulfuric acid 1.0 d m i n
Conductivity
70
Beer, white wine, sake
Dilution
Oyobunko ASA4000 250 x 4.6 mm ID
0.5 mM &sodium phthalate
2.0 d m i n
Indirect 71 spectrophot. at 240 nm
Beer
Dilution
Dionex AS-1 ion exclusion 250 x 9.0 mm ID
5.0 mM hydrochloric acid 0.8 d m i n
Conductivity
Beer, maltose
Dilution
Dionex AS-6 250 x 4.0 mm ID
0.15 M sodium hydroxide, 0.15 M sodium acetate 1.O d m i n
Amperometry 72.74 at Au electrode
Beer, wort
Dilution
Dionex AS-6 250 x 4.0 mm ID
0.15 M sodium hydroxide 1.0 d m i n
Amperometry 12.74 (pulsed) at Au
Beer
Dilution
Dionex AS4 250 x 4.0 mm ID
Beer
Dilution
Interaction ORH801 organic acid 300 x 6.5 mm ID
2.8 mM bicarbonate, 2.2 mM carbonate 2.0 d m i n 10 mM sulfuric acid 0.8 d m i n
72-74
el-
Cond~ctivity 72-75 Direct 59,61 spectrophot. at 210 nm
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
i?
TABLE 18.2 (CONnNUED). ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Maltose (4.1). glucose (5.2). fructose (5.8), ethanol (10)
Beer
Dilution
10 mM sulfuric acid 0.8 mumin
Direct RI
59,61
Chloride (2.5), bromide (4), sulfate (6), oxalate (7.5)
Beer
2gfl disodium EDTA 2.7 mVmin
Conductivity
76
Nimte (10.6), bromide (1 1.3), nitrate (12.8)
Beer
Dilution, filuation
Interaction ORH801 organic acid 300 x 6.5 mm ID Wescan 269001 anion 250 x 4.6 mm ID Hamilton PRP-1 150 x 4.1 mm ID
Direct spectrophot.
16
Glycerol (8.6), ethanol (15)
Beer
Dilution
Amperornetry (pulsed)
72.74
Nimte (10)
Beer
20 mM sulfuric acid 0.8 ml/rnin
Iodide (7)
Beer
Dilution
Dionex AS- 1 ion exclusion 250 x 9.0 mm ID Brownlee Polypore H 100 x 4.6 mm ID Dionex AS-1
1.OmM tetrapentyl ammonium fluoride (33% ACN) 1.Ornllmin 0.1 M perchloric acid 1.O d m i n
Sodium (5.9), ammonium Beer (9.0), potassium (12.5) Sodium (2), ammonium (3.3, Beer potassium (4) Magnesium (3.8), calcium (6.0) Beer
Dilution
Dionex CS- 1 200 x 4.0 mm ID Waters IC Pak C 50 x 4.6 rnm ID Dionex CS- 1 200 x 4.0mm ID
5.0 mM hydrochloric acid 2.5 d m i n 2.0 mM nimc acid 1.2 ml/min 2.5 mM hydrochloric acid, 2.5 mM m-phenylenediarnine 2.5 d m i n
Amperometry 20 at PI electrode, +0.8V Amperometry 54.42 at Ag electrode, +0.3V Conductivity 72,74
Dilution
0.01 M sodium nitrate
7
Indirect conductivity Conductivity
.
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 74.5).
77 72,44
b
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Sample Prep.
3
Column
Eluent
Detection
Ref
g E;. ’h
Chloride (2.5), phosphate (9), sulfate (12), oxalate (12.5) Lactic (4.4), acetic (6.5), azide (9.1) Acetic (10.4) Sodium (4), ammonium (7), potassium (9)
Fermentation broth Fermentation broth Fermentation broth
Magnesium (2.9), calcium (5.5) Fermentation broth Zinc, magnesium, calcium
Wescan 269029 anion/R 250 x 4.1 mm ID Hamilton PRP-
Fermentation broth
wort
Tartaric (2.2), malic (2.6), Wine ascorbic (3.1), lactic (3.6), acetic (4.0), citric (5.0), succinic (5.4), fumaric (5.9), aconitic (8.3), glutaric (9.7) Cimc (6.0), tartaric (6.4), malic Red, white wine (7.3), succinic/lactic (8.8). fumaric (10.9), acetic (11.4), carbonate (13.7)
X300 250x4.1mmID Dionex AS-1 ion exclusion 250 x 9.0 mm ID Wescan 269024 Dilution catiodHS 50 x 3.0 mm ID Dilution Wescan 269024 cation/HS 50 x 3.0 mm ID Dilution, cis Waters IC Pak C Sep-Pak, Millex 50 x 4.6 mm ID filtration Waters Rad cl8
4 mMp-hydroxybenoate, pH 8.5 2.0 ml/min 40 mM sulfuric acid 1.5 ml/min 1.0 mM perfluoroheptanoic acid 1.O ml/min 3.2 mM nimc acid 0.7 mVmin
Dionex AS- 1 ion exclusion
78
2
8-
Q 3
Direct 50 spectmphot. at 210 nm Conductivity 79
a b
s 3
E;
E,
3”’
09
is Indirect conductivity
80
1 mM ethylenediamine, pH 6.1 1.9 ml/min Ethylenediamine, cimc acid 1.2 mumin
Indirect conductivity
81
Conductivity
37
Phosphate buffer 1.5 mumin
Direct 82, 37 spectmphot. at 214 nm
2.0 mh4 octanesulfonic acid (2% 2-propanol)
Conductivity
100 x 8.0 mm ID c18 Re-Sep, dilution, filaation
Conductivity
83.84
0.8 Wmin
h
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
s
8 Do
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Sample Prep.
Column
Acetate (2.42). lactate (3.00), phosphate (3.66), chloride (4.48), nitrate (6.46), tartrate (13.81) Propionic (1.9). acetic (2.4). levulinic (2.8), lactic (4.8). formic (8.1), succinic (8.7), chloride (11) Cimc (4.8), tartaric (5.4), malic (6.0), succinic (6.9), lactic (7.3), acetic (8.0), propionic (8.5) Tartaric (0.9), malic (2.2), cimc (2.7),lactic (3.3), ethanol (3.61, fumaric (7) Tartaric (OS),malic (0.9), cimc (lS), lactic (2.0), acetic (2.8), succinic (4.5) Sulfite (7.5). malate (10.3), sulfate (1 1S), tartrate (13.3)
White wine
Ultrasonication, c18 Sep-Pak
Rice wine
Dilution
Succinic (12.7), malic (13.6), sulfate (17.8), tartaric (20.0)
Detection
Ref
4 mM phthalate, pH 4.0 Vydac 302 1C 250 X 4.6 mm l D 2.0 mumin
IndirectRI
85
TSK-gel IC anion
Conductivity
86
sw
50 x 4.6 mm ID White, red wine
-
Wine (chardonnay) Red, white wine
-
Wines
Dilution in hydroxide and formaldehyde, c18 Sep-Pak, filtration Dilution
Wine
Eluent
1.O mM phthalic acid, pH 4.0 1.O ml/min
Interaction ORH- 10 mM sulfuric acid 801 organic acid 0.8 ml/min 300 x 6.5 mm ID
Direct 59, 60 spectrophot. at 210 nm
Hamilton PRPx300 250 x 4.1 mm ID Hamilton PRP-1 (sulfonated) 150 x 4.1 mm ID Dionex AS-3
50 Dinct spectrophot. at 210 nm Direct 87 spectrophot. at 210 nm Conductivity 88
Dionex AS-6 250x4.0mmID
1 mM sulfuric acid 2.0 N m i n 1 mM sulfuric acid 2.0 d m i n 2.8 mM bicarbonate, 2.2 mM carbonate, pH 9.6 2.0 ml/min 20 mM carbonate, 2.0 mM hydroxide 1.5 d m i n
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviationr are listed in Appendix B (p. 745).
79
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Lactic (6.9), tartaric (8.0), malic White wine (10.0), acetic (13.2)
Sample Prep.
Column
Eluent
Detection
Ref
Dilution, filtration
Dionex AS-1 ion exclusion 250 x 9.0 mm ID
2.0 mM sulfuric acid 0.8 Wmin
89,84
15 mM phthalic acid, pH 2.5 2.0 Wmin 0.4 M sorbitol, 50 mM boric acid 1.O Wmin 0.05 mM boric acid, pH 4.92 0.8 Wmin
Conductivity with various suppressor &vices Conductivity
90,91
Conductivity
92
System peak (6.0), chloride (7.9, nitrate (10.4). sulfate (17.0) Sucrose (91, glucose (lo), ethanol (20)
White wine
Wescan anion
Rice wine
Glucose (19.3), fructose (21.3). glycerol (25)
Wine
TSK-gel SCX (x2) 300 x 7.6 mm ID TSK-gel SCX 300x 7.8 mm ID
Sulfite adducts - formaldehyde (6.9)
Wine
Sulfite (3.05)
Red wine
Filtration
Wescan 269-051
Sulfite (2.0)
Wine
Dilution
DMAEAX10 100 x 4.6 mm ID
Sodium (3.4), calcium (4.0), potassium ( 4 4 , magnesium (8.0)
White wine
Dilution
Nucleosil-5- 100PBDMA 125 x 4.5 mm ID
Dilution, an-ex cartridge to remove organic acids
Vydac 302 IC 250 x 4.6 mm ID
Conductivity, direct spectrophot. at 200 nm 10 mM potassium dihydrogen Ampemmetry at glassy phosphate, pH 5.0 1.5 Wmin carbon electrode, +0.75V 5 mM sulfuric acid Ampemmetry, 0.85 Wmin 4. 6 V Quenched 20 mM phosphate buffer, 25 mM sulfate, 5.0 mM phosphorescence biacetyl, pH 7.0 (ACN solvent) 1.0 Wmin 3.75 mM pyridineConductivity 2,6-dicarboxylic acid 1.O Wmin
Seep. 487 for notes on the organizationof this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
93
94
95 19
96
2
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Sodium (3.2). potassium (4.3). White wine magnesium (6.7),calcium (7.2)
Dilution
10 mM tartaric acid 1 .O mVmin
Conductivity
96
Sodium (5.4). ammonium (7.9). potassium (8.8)
Dilution
Nucleosil-5-100PBDMA 125 x 4.5 mm ID TSK gel IC-cation 50 x 0.35 mm ID
2.0 mM nimc acid 2.8 pl/min
Indirect 97 spectrophot. at 225 nm after postsuppressor
Red wine
anion Sodium (7.7), potassium (17.5) Red wine Copper (2.4). zinc (5.2), iron (11) (9.3). manganese (13.7). magnesium (17.7), calcium (20.7)
Wine, fruit juices -
Acetic (2.18), succinic (5.22), Vinegar malic (7.20), tartaric (10.07), system peak (15.52) Phosphate (3.8), chloride (4.3). Apple, orange system peak (4.4), nitrate (5.8), juice sulfate (9.3)
Dionex cation separator 250 x 4.0 mm ID Nucleosil 10-SA 250 x 4.0 mm ID
Hydrochloric acid 1.O mh4 oxalic acid, 2.5 mM ethylenediamine, pH 3.5 2.0 mVmin
Dilution
LiChrosorb RP-18 5.0 mM octylamine salicylate 2.0 mumin
Dilution
LiChrosorb RP-18 0.5 mM tetrabutylammonium 250 x 4.6 mm ID hydroxide, salicylic acid, pH 3.4 1.0 d m i n
replacement Conductivity
84
Direct 98 spectrophot. at 490 nm after postcolumn reaction with PAR-ZnMTA Conductivity 99 Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
100
4
03
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC ~~~
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Ketoglutaric (lo), cimc (15), fumaric (22). succinic (24)
Orange, grapefruit juice
Dilution, filmtion
Aminex 50W-X4 cation-exchanger 3oOx13mmID Interaction ORH801 organic acid 300 x 6.5 mm ID Dionex AS-6
1 mM hydrochloric acid 1.0 d m i n
Cimc (4.8),tartaric (5.4),rnalic Fruit juice (5.6), succinic (6.9)
Filtration
Sorbitol (3.9), glucose (6.5), fructose (7.0). sucrose (1 1.3) Citric (28), malic (30),tartaric (33) Chloride ( 3 . 3 , nitrate (7.9). sulfate (13)
Apple juice
Dilution
Fruit juice
Filtration
Cocktail vegetable juice
Tartaric (OS),maIic (0.9), cimc Orangejuice (1.5) Ascorbic acid (3.1), dehydroascorbic acid (5.2)
Unidentified organic acids
Aminex A25 m m m
Dilution, c l 8 Waters IC Pak A SepPak, Millex 50 x 4.6 mm ID Ntration Hamilton PRP-1 (sulfonated) 150 x 4.1 mm ID
Waters p-BondaOrange juice and Re-column derivatization of pak CN dehydroascorbic acid with phenylenediamine, dilution, filtration Filtration Home-packed Fruit juices YEW Ax-1 600 x 0.2 mm ID
drink
10 mM sulfuric acid
0.8rnl/min 0.15 M hydroxide 1.0 d m i n 1.0 M sodium formate 62 ml/hr 1.0 mM phthalate 1.2 &min 1 mM sulfuric acid
2.0 d m i n 2% acetic acid (5% MeOH) 1.Omumin
Direct spectrophot. at 210 nrn Direct spectrophot. at 210 nm Amperometxy (pulsed) Direct RI Conductivity
101 59,61
9
58 37, 102
Conductivity, 87 direct spectrophot. at 210 nm Direct 103 spectrophot. at 254 then 348
nm
4.0 mM bicarbonate, 4.0 mM carbonate, pH 10.2 3.4 pumin
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
104
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Sodium (3,ammonium (8)
Fruit juice
Dilution
10mM hydrochloric acid 160 mvhr
Conductivity
105
Magnesium (10). calcium (12)
Orangejuice concentrate
-
Home-packed sulfonated PSDVB resin 250 x 9.0 mm ID Partisil 10 SCX
8.0 mM o d i c acid, 2.0 mM ethylenediamine, pH 4.2 1.Od m i n
Direct 106 spectmphot. at 490 nm after post-column reaction with PAR-&-
Copper (3), zinc (7). iron (9). manganese (13), magnesium (161, calcium (19)
Fruit juice
ETYTA
Nucleosil 10-SA 250 x 4.6 mm ID
1.0 mM oxalic acid, 2.5 mM ethylenediamine, pH 3.5 1 .O d m i n
Dionex anion separator 250x3.0mmID Dionex AS-1 ion exclusion 250 x 9.0 mm ID
3.0 mh4 bicarbonate, 2.4 mM carbonate 184mvhr 0.5 mM octanesutfonic acid (1.5%2-propanol)
TSK-gel SCX 300 x 7.8 mm ID
0.1 mM boric acid, pH 4.92 0.8 d m i n
Direct 106 spectmphot. at 490 nm after post-column reaction with PAR-ZnEDTA
Lactate (1.9). chloriddwruvate Milk (2.3), phosphate (5.3),* sulfate (8.0) Citric (6.1), pyruvic (7.4), Milk lactic (10.5) Lactose (18), glucose (19.3)
Milk
Centrifugation, dilution Dilution
Centrifuge, filter, dilution, an-ex camidge to remove organic acids
1.O d m i n
Conductivity
107,44
Conductivity, 79 dim3
spectrophot. at 215 nm Conductivity, 94
direct spectmphot. at 200 nm
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC Solutes (min)
Sample
Sample Prep.
Column
Iodide (9.5)
Milk, milk powder
MeOH ppt of Vydac 302 IC proteins, dilution 250 x 4.6 mm ID
Eluent
Detection
4.5 methanesulfonic acid, 0.2 @4,4'-bis (dimethyl
Direct 108 specmophot. at 600 nm after post-column reaction with chloramine-T Amperomtry 54.42 at Ag electrode, M.3V Direct 65 specmophot. at 226 nm
amino) diphenylmethane. pH 4.0 (14% MeOH) 1.0 Wmin Iodide (7)
Whole milk
Iodide (27)
Non-fat dry milk Combustion flask,dilution
Fluoride (2.0)
Milk product
Nitrate (6.0)
Milk
Cimte (15)
Milk
Dilution
Centriifugation, dilution, protein coagulation, filtration camz ppt of protein, filtration Centrifugation, dilution
Dionex AS-1
0.01 M sodium nitrate
Waters C1g RCM 100 x 8.0 mm ID
2.5 mM hexadeqlnimethyl
Dionex anion sepator 500 x 3.0 mm ID Home-pXked methamylate anion- exchanger 15ox 3.3 mm ID Dionex brine anion separator 250 x 3.0 mm ID
ammonium chloride, 50 mM phosphate, pH 6.8 (25% ACN) 2.5 Wmin 5.0 mM t e t r a h t e 138 mVhr
40 m M perchlorate, 5 mM phosphoric acid 0.5 Wmin 10 mM carbonate 184 mvhr
Conductivity
Ref
107
Direct 109, specmophot.at 110 205 nm
conductivity
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
107
E
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC
P
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Sodium (0.9). ammonium (1.4). potassium (1.8), magnesium (5.0), calcium (14.5) Sodium (12). ammonium (16), potassium (20)
Whole milk
Dilution
Interaction ION210
0.05 mM cerium (111) 1.O mumin
Indirect 111 specmphot. at 254 nm
Mdk
Centrifugation, dilution
5.0 mM hydrochloric acid 138 mvhr
Conductivity
108
Calcium (6.0). magnesium (6.9). sulfate (9.7)
Milk
1.O mM EDTA, pH 6.5 1.O mVmin
Conductivity
69
Borate (2.3), fluoride (2.6). chloride (4,1), nitrate (8.0), sulfate (9.0), system peak (14)
Mineral water
Ultrafitration, addition of J2Dr.A Degassing, catex pretreatment
Mineral water
6 mM 4-hydroxybenzoic acid, 50 mgh methyl green, hydroxide, pH 9.0 1.O mVmin 10 mM potassium hydrogen phthalate, pH 7.0 1.5 mVmin
Indirect 112 spectrophot. at 311 nm
Bicarbonate (3.0),chloride (3.9), phosphate (4.7). nitrate (629, sulfate (7.5)
Dionex cation separator 250 x 6.0 mm ID TSK-gel ICAnion-SW 50 x 4.6 mm ID Hamilton PRP-1 (coated with methyl green) 125 x 4.6 mm ID Nucleosil 10 Anion 250 x 4.0 mm ID
Chloride (3.8), nitrate (5.0). sulfate (12.3), bicarbonate (18.2) Chloride, nitrate, bicarbonate, sulfate
Mineral water
Wescan 269-001 250 x 4.6 mm ID
Mineral water
Nucleosil- 10
Fluoride, chloride, bromide
Sonication, oxalate ppt of CdCiUm
Anion Mineral spring water
Dionex anion separator 500x 3.0 mm ID
4.0 mM phthalate, pH 4.5 2.0 mumin 25 mM salicylate, pH 4.0 0.8 d m i n
3.0 mM bicarbonate, 2.4 mM carbonate 115mVhr
Ref
Indirect RI
113
Conductivity
114, 57, 115
IndirectRI
1
Conductivity
116
B
P
9
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
-Pb
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC
3
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Arsenic (V) (9), arsenic (HI) (14)
Mineral water
Sulfur dioxide treatment, spiking
Aminex HPX87H 300x 7.8 mmID
0.01 M orthophosphoric acid 0.6 mVmin
Amperometry 117 at Pt electrode, (+1 .OOV). direct spectrophot. at 200 nm Conductivity 118
Bicarbonate (6.2), chloride (7.1), phosphate (8.6) Citrate (2.75),phosphate (3.65), sulfate (15.04)
Cola drink Diet soft drink
Cimc (4.3, phosphoric (3, chloride (9)
Diet cola
Phosphate (3.2), saccharin (3.8), citrate (7.1)
Diet cola
Chloride (8). cyclamate (14)
Soft drink
C18 Sep-Pak
Dilution
Home-packed XAD- 1 500 x 2.0 mm ID Waters IC Pak A 50 x 4.6 mm ID
Wescan 269001 anion 250 x 4.6 mm ID Dionex AS-5
Wescan 269001 anion 250 x 4.6 mm ID
0.1 mM benzoate, pH 6.25 2.0 d m i n
Ref
i;.
-4
0 0
3 Q
% b
F 3 E:
E
s.
00
Nimc acid gradient 1.2 d m i n
4 mM phthalic acid, 8 mM benzoic acid 2.7 d m i n 0.8 mM p-cyanophenol, 7.7 mM carbonate, 33 mM hydroxide 1 .O d m i n 5 mM phthalic acid 1.6 d m i n
Direct 119 spectmphot. at 340 nm after post-column reaction with perchlorate Conductivity
120
Conductivity
121
Conductivity
122
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
5
2 m
TABLE 18.2 (CONTINUED). ANALYSIS OF BEVERAGES USING IC -
Detbon
Ref
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Phosphate (2.22)
Soft drink
Dilution in eluent, filtration
Waters IC Pak A 50 x 4.6 mm ID
1.62 g/l boric acid, 0.42 mv1 Conductivity gluconic acid, 0.48 g/l lithium hydroxide, 2 ml glycerine (12.5% ACN)
123
Citrate (3)
Cola beverage
Waters IC Pak A 50 x 4.6 mm ID
Phthalate 1.2 d m i n
Conductivity
124
Calcium (7.4), magnesium (8.7), sulfate (14.2)
Isotonic drink
Degassing, dilution, filtration Dilution
TSK-gel ICAnion-SW 50 x 4.6 mm ID
1.O mM EDTA, pH 6.0 1.O Wmin
Conductivity, 125 direct specmphot. at 210 nm conductivity 126
1.4 Wmin
Acetate (5.0). glycolate (6.3). Coffee quinate (7.4). formate (8.7), chloride (12.3), tartrate (17.8). oxalate (18.4), fumarate (21.9), phosphate (23.7). citrate (26.9) Phosphate (15), quinic (17). Coffee malonichnalic (19). lactic (22), formic (24), acetic (26), propionic (30) Nitrate, sulfate, oxalate Coffee
~~~
Aqueous dilution Dionex AS-5A
Aqueous extraction, filtration
Dionex ICE ion exclusion 250 x 9.0 mm ID
Aqueous extraction, filtration, cut from ICE fraction
Dionex anion separator 500 x 3.0 mm ID
Ternary gradient of 0.75 mh4 hydroxide to 200 mM hydroxide to 200 mM boric acid
2.0 Wmin 10 mM hydrochloric acid 0.86 mVmin
3.0 mM bicarbonate, 2.4 mM carbonate 2.3 d m i n
Conductivity
127,44
Conductivity
127
~
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 18.3 ANALYSIS OF PLANTS AND PLANT PRODUCTS USING IC ~
~~
Solutes (min)
Sample
Fluoride (5.6), chloride (7.3), phosphate (1 1.O), nitrate (14.0), malic acid (17.9), sulfate (19.3) Glycolate (1.9). chloride (3.1). phosphate (5.2). nitrate (6.1), malate (8.8), sulfate (9.7) Glycolate (1.03), chloride (1.68), phosphate (2.88), nitrate (3.91). malate (5.25), sulfate (6.32) Phosphate (3.7). phosphite (4.3, chloride (6.4)
Plant materials
Chloride (2.0), nitrate (4.7). sulfate (7.3)
Plant materials
Sample Prep. Aqueous exmaion
Column
~~
~
Eluent
Detection
Ref
3.0 mM bicarbonate, 1.8 mM carbonate 118 mvhr 2.8 mM bicarbonate, 2.2 mM carbonate 2.0 d m i n 2.8 mM bicarbonate, 2.2 mM carbonate 2.0 mllmin
Conductivity
128
Hamilton PRPXl00 100 x 4.1 mm ID
Dionex anion sepmtor 50 x 4.0 mm ID
Dionex AS-3 250 x 3.0 mm ID
Q
‘+1
8
&
3
b a
b
Conductivity
129132
F t:
Conductivity
129
3
100mM succinic acid, pH 2.75 4.0 d m i n
Conductivity
133
3.0 mM bicarbonate, 1.8 mh4 carbonate 150 mlfhr
Conductivity
134137
1.42 mM gluconate, 5.82 mM Conductivity boric acid, 0.25% glycerine, pH 8.5 (12% ACN) 2.0 d m i n Chloride (1.59), nitrate (3.84) Plant nutrient Dionex AS4A 0.8 mM bicarbonate, Conductivity medium 2.2 mM carbonate 2.0 d m i n Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
138
Plant leaves Plant leaves
Plant material
Chloride (4.36), sulfate (18.39) Plant food powder
Aqueous Dionex AS-3 extraction, boiling, dilution Aqueous Dionex AS4 extraction, boiling, dilution F&c acid and isopropanol extraction, chlorofm clarification, catex and an-ex clean-up Combustion flask, sorption in hydrogen peaiJxide Dilution
Waters IC Pak Anion HC 150 x 4.6 mm ID
E.
A
129
z!
4
52 00
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCJTS USING 1C Solutes (min)
Sample
Sample Prep.
Sulfare (7.17)
Plant tissue
Nitrate (2)
Plants
Molybdate (1 3.4)
Plant nutrient (hydroponic) solution
Schoeniger flask Vydac 302 IC combustion, 250 x 4.6 mm ID sorption in hydrogen peroxide, dilution Wescan 269013 Extraction anionMS 100 x 4.6 mm ID Reconcentration Waters IC Pak A with pre-column 50 x 4.6 mm ID
Lithium (2.54), sodium (3.39). Plant food ammonium (5.04), potassium powder (6.20) Sodium (4.4). potassium (6.9) Plant materials
Magnesium (4.6), calcium (6.4) Plant materials
Copper (4.59), zinc (10.1I), iron (11) (22.20)
Plant food powder
Column
matrix elimination Dilution Ashing, hydrochloric acid digestion, cennifugation Ashing, hydrochloric acid digestion, cenmfugation Nitric acid digestion, dilution
Waters IC Pak C 50 x 4.6 mm ID Dionex cation separator 250 x 6.0 mm ID Dionex cation separator 250 x 3.0 mm ID Waters Clg VBondapak 300 x 3.9 mm ID
Eluent
Detection
Ref
4.0 mM phthalic acid, adjusted Conductivity to pH 5.0 with borate 2.0 mVmin
139
7 mM phthalate 7d m i n
Conductivity
140
5 mM phosphate, pH 9.5 1.0 mumin
Direct spectrophot. at 245 nm
141
2.0 mM nitric acid, 0.05 mM disodium EDTA 1.2 mVmin 5.0 mM hydrochloric acid 180 ml/hr
Indirect conductivity
138
Conductivity
142
2.5 mM hydrochloric acid, 2.5 m M m-phenylenediamine dihydmhloride 115 mVhr 2.0 mM octanesulfonate, 50 mM tartaric acid, pH 3.4 1.0d m h
Conductivity
142
Direct
138
spectrophot. at 520 nm after post-column readon with
PAR
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCTS USING IC
3
Solutes (min)
Sample
Sample Prep.
P t’
Tungsten (8.6),molybdenum (9.7)
Plants
Acid digestion, Cosmosil CIS 150 x 4.6 mm ID extraction, ashing, addition of Tiron
Fluoride (2.0). chloride (2.6), nitrite (3.1), bromide (4.0), niuate (5.7), sulfate (15.1)
Vegetable juice
Phosphate (3.9), chloride (5.8), nitrate (1 l.O), bicarbonate (15.8), sulfate (29.9) Chloride (4.3, nitrite (5.1), Vegetables nitrate (12.6) (salted) Chloride (2.4), nitrate (5.9), sulfate (13.6)
Vegetables
Nitrite (7.1), nitrate (9.9)
Vegetables
Nitrite (2.5),nitrate (4.0)
Vegetables
Dilution, centrifugation, Millex filtration, Sep-Pak Homogenization and fitration, dilution Extraction
Maceration, aqueous extraction, c18 Sep-Pak Homogenization and extraction, centrifugation, filtration, C18 Sep-Pak Homogenization and dilution, heating, filtration
Column
Hamilton PRP x-100 150 x 4.1 mm ID Wescan 269-001 anion 250 x 4.6 mm ID YEW SAX-1 250 x 4.6 mm ID
Eluent
a
Detection
Ref
1.5 mM Tiron, 30 mM Dired tetrabutylammonium bromide, specuophot. at 1.5 mM acetate buffer, pH 3.8 315 nm (57% MeOH) 0.7 d m i n 0.4 mM phthalate, pH 7.0 Indirect 2.0 d m i n spectrophot. at 254 nm
143
4.4 mM phthalate, pH 3.9 2.0 mumin
Conductivity
145, 146
15 mM tetraborate, 1 mM carbonate 2.0 mumin
Conductivity,
147
direa
a
144
E
E’
Zipax SAX 50x2.1mmID
0.5 mM disodium phthalate
Vydac 302 IC 250 x 4.6 mm ID
11 .O mM chloromethanesulfonic acid, pH 5.0 2.0 mumin
Direct spectrophot. at 214 nm
12
Dhect spectrophot. at 214 nm
13
See p . 487 for notes on the organization of this Table. See p . 62 7 for References. Abbreviarions are listed in Appendix B (p. 745).
E:
rn
spectrophot. at 210 nm Indirect spectrophot. at 240 nm
Waters Radial Pak 5.0 mM low UV PIC A cis 3.0 mVmin
& b s 3
148, 140
$2 0
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCTS USING IC __
-
~-~
~
~
~
~
Solutes (min)
Sample
Sample Prep.
Chloride (1.4), nitrate (2.8)
Vegetables
Chloride (1.7), nitrate (3.3)
Vegetables
Bromide (6.4), nitrate (7.9)
Vegetables
Terra-P (nimte product) (7)
Vegetables
Sodium (2.3), ammonium (3.7), potassium (4.7). magnesium (12.2), calcium (17.9) Chloride (1). benzoate (3), nitratelsulfate (5). ascorbate (7). trihydroxybenzoate(1 l), phosphate (17) Chloride (2.7), phosphate (2.7), bromide (4.7), nitrate (5.8)
Vegetables
Homogenization Home-packed BAKC-1 and filmtion 150 x 2.0 mm lD Homogenization Home-packed BAKC- 1 and filtration 60 x 4.0 mm ID Homogenization Waters amino and extraction, pBondapak addition of 300 x 3.9 mm ID c m z solution, centrifugation, filtration Homogenization TSK GEL LS-410 and extraction, ODs 150 x 4.0 mm ID filmtion, precolumn reaction with hydralazine Maceration, zipax SCX 250 x 4.6 mm ID aqueous extraction, C18 Sep-Pak Maceration, Dionex anion aqueous separator extraction 25Ox3mmID
Mushrooms, cucumbers Carrot exmct
Column
Hamilton PRPXloo 150 x 4.1 mm ID
Eluent
Detection
Ref
1.5 mM gluconic acid, 1.5 mM boric acid, pH 8.6
Conductivity
150
1.O mM phthalate. pH 5.2 0.8 ml/min
Conductivity
150
10 gA potassium dihydmgen phosphate, pH 3.0 1.0 mVmh
Direct spectrophot. at 210 nm
63
0.05 M potassium dihydrogen phosphate, pH 4.5 (20% ACN) 1.O mYmin
Fluorescence at 228, 370 nm, direct spectrophot. at 228 nm Indirect spectrophot. at 220 nm
26
1.5 mM carbonate, 1.1 mM hydroxide 238 mvhr
Conductivity
151
0.5 mM pymmellitate buffer, pH 3.0 1.0 ml/min
Indirect spectrophot. at 295 nm
152
.o
1 mVmin
2.5 mM copper sulfate
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B ( p . 745).
148
b
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCIS USING IC Solutes (min)
Sample
Chloride (3.2). phosphate (6.3), Carrots nitrate (9.2) Nitrite (10) Sulfite (3.05)
Lettuce
Dried potatoes, peppers
Sodium (6.8). ammonium (9.8). potassium (12.2)
Corn
Manganese (3.7), iron (4.7). zinc (6.0)
Tomato leaves
Zinc (3.7), iron (11) (12.8)
string beans
Sample Prep.
Column
Homogenization Dionex AS-3 and dilution in eluent, filtration Aqueous Brownlee homogenization, Polypore H filtration 100 x 4.6mmID Homogenization Wescan 269-051 with buffer, ion exclusion filtration Homogenization Dionex CS-1 and dilution in eluent, filtration Dry ashing, acid Chromasorb 5 pn dissolution silica coated with 2-pyridinecarboxy aldehyde phenylhydrazone 250 x 4.6 mrn ID Homogenization Dionex CS-2 and dilution
Eluent
Detection
Ref
s
2.1 mM bicarbonate, 1.68 mM carbonate 3.0 ml/min 20 mM sulfuric acid 0.8 Mmin
Conductivity
9, 10
-i
i;.
a
i% c)
Ampennnetryat 20 Pt electrode, 4.8V
5 mM sulfuric acid 0.85 ml/min
Amperomeny 4.6V
95
5.0 mM hydrochloric acid 2.0 mvmin
Conductivity
9
0.041 M perchlorate buffer, 0.1%hydroxylamine hydrochloride, pH 4.5 0.47 d m i n
Direct specmphot. at 550 nm after post-column reaction with PAR Direct specmphot. at 520 nm after post-column kction with PAR
153
3 FL
b
Ei 3
i:
5. L3
?i
10 mM oxalic acid, 7.5 mM ciaic acid, pH 4.3 1.0 Mmin
Seep. 487for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
9
m
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCTS USING IC Solutes (min)
Sample
Sample Prep.
Copper ( 10)
Tomato leaves
Dry ashing, acid Chromasorb 5 p n 0.041 M oxalate buffer, 0.1% Dilect
Sulfite (7.0)
Raisins
Oxalate (7)
Rhubarb
Oxalic (15.9).cimc (19.08). maleic (19.52),ketoglucaric (20.051, phosphoric (20.261, t d c (20.41), pyruvic (22.33), malic (22.90), malonic (23.67). succinic (28.23), lactic (30.35), formic (33.09), acetic (35.99, isobutyric (48.30) Chloride (2.1), phosphate (2.6). nitrate (4.5). sulfate (5.3), oxalate (7.2) Chloride, phosphate, nitrate, sulfate
Sugar cane juice
Aconitic, lactic, acetic, citric
Column
dissolution
silica coated with 2-pyridinecuboxyaldehyde phenylhydrazone 250 x 4.6 mm ID Homogenization Hamilton PFWX 100 and headspace sampling 150 x 4.1 mm ID
Dilution, filtration
Dionex AS-4
Cane sugar
Aqueous Dionex AS-4 dilution, DoMan dialysis Dilution, Dionex ion filtration exclusion
Detection
Ref
153 hydroxylamine hydrochloride, spectrophot. at 550 nm after pH 4.5 post-column 0.70 mumin reaction with PAR 30 mM methanesulfonic acid, Ampemmetryat 154, glassy carbon 94 pH 11.O (5% ACN) 2.0 mVmin electrode, +0.6V Conductivity 155 2g/l disodium EDTA 2.0 mVmin
Wescan 269001 anion 250 x 4.6 mm ID Filtration, ion- Aminex HPX-87H 5 mM sulfuric acid 0.5 mumin exchange clean- (x2) 300 x 7.8 mm ID UP
Sugar mill products
Sugar mill products
Eluent
!3
2.6 mM bicarbonate, 2.3 mM carbonate 2.0 mvmin 2.9 mM bicarbonate, 2.3 mM carbonate 2.0 mvmin 1.0 mM hydrochloric acid 2.0 mVmin
Direct RI
156
Conductivity
157
Conductivity
158
Conductivity
157
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCTS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Lithium, sodium,ammonium, potassium Magnesium, calcium
sugar mill products sugar mill products
Dilution, filtration Dilution, filtration
Dionex CS-1
5.0 mM hydrochloric acid Conductivity 2.0 mvmin 2.5 mM hydrochloric acid, 2.5 Conductivity
Chloride, sulfate, phosphate, nitrate
Maple trees
Acetate, malate, oxalate, formate Maple trees Acetate, d a t e , oxalate, formate Maple trees Phosphate (2.7), chloride (3, bromide (7), nitrate (8.5)
Cocoa
Iodide (27)
Cocoa beans
Aqueous extraction (reflux) Aqueous extraction (reflu) Aqueous extraction (reflux)
Grinding, sieving, combustion flask, dilution
Dionex CS- 1
Detection
Ref 157
157
mM m-phenylenediamine
dihydmchloride 2.0 ml/min 3.0 mM bicarbonate, 2.4 mM carbonate 1.9 mVmin
Conductivity
159
Dionex ion exclusion
0.05 M hydrochloric acid 0.38 d m i n
Conductivity
159
TSK Gel ICAnion-SW 5 0 x 4.6 mm ID Wescan 269013 anion/HS 100 x 4.6 mm ID Waters cl8 RCM 100 x 8.0 mm ID
1.0 mM phthalate 0.77 d m i n
Conductivity
159, 160
5 mM phthalic acid 2.0 mvmin
A m p m e t r y a t 161 Ag electrode
2.5 mM hexadecylmmethyl ammonium chloride, 50 mM phosphate, pH 6.8 (25%ACN) 2.5 ml/min
Direct spectrophot. at 226 nm
Dionex anion separator
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
65
o\
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCB USING IC Solutes (min)
Sample
Sample Prep.
Inositol phosphates - IP4 (17), 1(1,2,3,4,6)P5 (20). 1(1,2,3,4,5)P5 (211, 1(1,2,4,5,6)P5 (221, 1(1,3,4,5,6)P5 (23), IP6 (28)
Soyabean seeds
Dionex AS-3 Pulverization, acid extraction, filtration, concentration on AG 1-X8, lyophilization
Chloride (5.4), nitrate (8.0), phosphate (13.3), sulfate (18.4), malate (19.6)
Oilseed rape, wheat shoots
Chloride (3.9, nitrate (5.4), sulfate (10.5) Phosphate (31), inositol tetraphosphate (49). inositol hexaphosphate (58)
Chloride (4), bromide (6) Chloride (4.3). nitrate (9.4), phosphate (13.7), sulfate (18.6), oxalate (24)
Grinding, aqueous extraction, filtration Canola (plant) oil Pan: bomb, dilution, SepPak, Millex filtration Wheat bran Desiccation, mchloroacetic acid extraction, filmtion
Column
H0tW-packed ODs 250 x 4.6 mm ID Waters IC-Pak A
Bio-Rad Aminex
A27 250 x 4.0 mm ID
Wescan 269013 anion/HS 100 x 4.6 mm ID Leaf litter extract Preconcentration Waters IC Pak A with pre-column 50 x 4.6 mm ID matrix elimination Almonds
Extraction
Eluent
Y
DetMion
180 mgh pyrocatechol to 0.155 Direct spectrophot. at M nimc acid gradient 1.O d m i n 290 nm after post-column d o n with Fe(II1) perchlorate 0.5 mM tetrabutylammonium indirect hydroxide adjusted to pH 7.1 spectrophot. at 255 nm with phthalate (5% MeOH) 1.5 mVmin 1.48 mM gluconate, 5.82 mM Conductivity boric acid, 1.30 mM borate, 12% ACN, 0.25% glycerol 1.2 d m i n 0.5 mM teaasodium EDTA, Direct 0.1 to 0.5 M sodium chloride spccaophot. at 885 nm after gradient, pH 10.0 0.4 d m i n persulfate oxidation of 0.4 ml fractions 5 mM phthalic acid Ampmetryat 2.0 Wmin Ag elecnode 1.0 mM tetraborate, 4.2 mM boric acid, 1.O mM gluconic acid, pH 8.5 1.0 ml/min
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
Ref 162
163
164
165
166 141
$
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCTS USING IC Eluent
Detection
Ref
B 2’
Wescan 269001 anion 250 x 4.6 mm ID Barley plastids Homogenization Dionex A S 4 centrifugation, filtration, dilution, c18 Sep-Pak Bacterial growth, Trifluoroacetic Dionex AS-6 fermentation acid hydrolysis, 275 x 7.5 mm OD products dilution Legumes Nucleosil 10 SA 250 x 4.0 mm ID
8 mM benzoic acid, 4 mM phthalic acid 2.5 mVmin Bicarbonate, carbonate
Conductivity
167
0
Sulfate (2.7). pyrophosphate (4.4)
Fertilizer
1.5 gll &sodium EDTA,
Orthophosphate (4)
Fertilizer
Sodium (12), ammonia (urea) (18), potassium (23)
Fertilizer
Solutes (min)
Sample
Citric ( 5 . 3 , chloride (lo), nitrate (15)
Tobacco
Chloride (2.6), nimte (3.3), phosphate (4.4), sulfite (6.4), nitrate (7.8), sulfate (10.5) Glucose, mannose, rhamnose, succinate, glutamate, ethanol Nickel (8), cobalt (9)
Sample Prep.
Column
Extraction
6
& b
s Conductivity
168, 169
Q.
2 3t: E
s’
00
0.15 M hydroxide
Ampemmetry
0.1 M tartaric acid, pH 2.7 2.5 ml/min
(pulsed) at Au electrode Direct spectrophot. at 320 nm after post-column reaction with
1.Oml/min
170
3
171
dithiocarbamate
Dilution, immobilized urease reactor
Wescan 269001 anion 250 x 4.6 mm ID Wescan 269001 anion 250 x 4.6 mm ID Dionex cation separator
pH 5.0 2.6 mumin 5 mM phthalic acid 2.7 ml/min 5 mM nitric acid
Conductivity
172
Conductivity
173
Conductivity
174
m
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
N VI
2!
TABLE 18.3 (CONTINUED). ANALYSIS OF PLANTS AND PLANT PRODUCTS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Ammonium (urea)
Fertilizers
Urease hydrolysis, acidification, dilution
Dionex CS- I
5 mM hydrochloricacid 2.3 d m i n
Conductivity
I75
Seep. 487 for notes on the organization of this Table. Seep. 627 for References. Abbreviations are listed in Appendix B (p. 745).
Analysis of Foodr and Plants using IC
627
18.2 REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Luckas B., Fres. 2.Anal. Chem., 320 (1985) 519. Reimerdes E.H. and Rothkitt K.-D., GIT Fachz. Lab., 28 (1984) 97. Sullivan D.M. and Smith R.L., Food Technol., 39 (1985) 45. Anderson C., Warner C.R., Daniels D.H. and Padgctt K.L., J. Assoc. Off. Anal. Chem.,69 (1986) 14. Kim H.-J. and Kim Y.-K., J. Food Sci., 51 (1986) 1360. Kim H.-J., Park G.Y. and Kim Y.-K., Food Technol., 41 (1987) 85. Yan D. and Schwedt G.,Fres. Z . Anal. Chem., 320 (1985) 252. M h a A., Wagner H., Kloetzer E. and Fausel E., Lebensmitrelchem. Gerichrl. Chem., 38 (1984) 18. Edwards P., Food Technol., 37 (1983) 53. Tateo F., Faleschini M.L. and Fossati M., Ind. Conserve, 57 (1982) 30. Eek L. and Ferrer N., J . Chromatogr., 322 (1985) 491. Jackson P.E., Haddad P.R. and Dilli S., J . Chromurogr., 295 (1984) 471. Wootton M., Kok S.H. and Buckle K.A., J. Sci. Food Agric., 36 (1985) 297. Schreiner G.,Kiesel K.H., Gehlen K.H. and Fischer A., Arch. Lebensmittelhyg., 39 (1988) 49. Lookabaugh M. and Krull I.S., J. Chromatogr., 452 (1988) 295. Iskandarani Z. and Pietrzyk D.J., Anal. Chem., 54 (1982) 2601. Posner R.D. and Schoffman A., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. 11, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 51. Laurent A. and Bourdon R., Annal. Pharm. Franc., 36 (1978) 453. Gooijer C., Markies P.R., Donkerbroek J.J., Velthorst N.H. and Frei R.W., J. Chromarogr., 289 (1984) 347. Kim H.-J. and Kim Y.-K., in Jandik P. and Cassidy R.M. (Us.), Advances in Ion Chromatography, Vol. I , Century International, Inc., Franklin, MA, 1989, p. 391. Shenvood G.A. and Johnson D.C., Anal. Chim. Acra, 129 (1981) 101. Jandik P.,Cox D. and Wong D., Int. Lab., June (1986) 66. Koch W.F., J. Res. Nat. Bur. Srd., 84 (1979) 241. Saitoh H. and Oikawa K., Bunseki Kagaku, 31 (1982) E375. h e y J.P., J. Chromatogr., 287 (1984) 128. Noda H., Minemoto M., Asahara T., Noda A. and Iguchi S., J. Chromatogr., 235 (1982) 187. Coopcr P.L., Marshall M.R., Gregory J.F., IT1 and Otwell W.S., J. Food Sci., 51 (1986) 924. Bushee D.S., Analyst (London), 113 (1988) 1167. Saitoh H., Oikawa K., Takano T. and Kamimura K., J. Chromarogr., 281 (1983) 397. Wescan Application #164. Haddad P.R. and Jackson P.E.. Food Technol. Aust., 37 (1985) 305. Oikawa K., Saito H., Sakazume S. and Fuji M., Chemosphere, 11 (1982) 953. Oikawa K., Saito H., Sakazume S. and Fujii M., Bunseki Kagaku, 31 (1982) E251. Osbome B.G., Anal. Proc., 23 (1986) 359. Watanabe I., Tanaka R. and Kashimoto T., Shokuhin Eiseigaku Zasshi, 23 (1982) 135.
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40 41 42 43 44 45 46 47 48 49 50 51
52 53 54 55
56 57
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64 65 66 67 68 69 70 71 72 73 74 75 76
Chapter I8
Yamamoto A., Matsunaga A., Sekiguchi H., Hayakawa K. and Miyazaki M., Eisei Kagaku, 31 (1985) 47. Cox D., Harrison G., Jandik P. and Jones W., Food Technol., July (1985) 41. Waters ILC Series Application Brief No. 4005. Dionex Technical Note 20. Phillippy B.Q. and Johnston M.R., J. Food Sci., 50 (1985) 541. Jones P., Williams T. and Ebdon L., Anal. Chim.Actu, 217 (1989) 157. Dionex Application Note 38. Herbranson D.E.. Eliason M.S. and Karnatz N.N., J . Liq. Chromatogr., 10 (1987) 3441. Bauer G.M., Lebensm-Biotechnol., 1 (1985) 18. Fratz D.D., in Sawicki E. and Mulik J.D. (Eds.), Ion ChromatographicAnalysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ.. Ann Arbor, MI, 1979, p. 371. Frau D.D., in Sawicki E., Mulik J.D. and Wingenstein E. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 169. Fratz D.D., J . Assoc. Off. Anal. Chem.,63 (1980) 882. Edwards P. and Haak K.K., Am. Lab.,April (1983) 78. RocMin R.D. and Pohl C.A., J . Liq. Chromatogr.,6 (1983) 1577. Lee D.P., Bunker M.T. and Lord A.D., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromatography,Vol. I , Century International, Inc.. Franklin, MA, 1989, p. 451. Dionex Application Update 108. Muller H. and Scholz R.. Anal. Chem. Symp. Ser., 22. Ion-selective Electrodes, 1984, p. 4. Han K., Koch W.F. and Pratt K.W., Anal. Chem., 59 (1987) 731. Dionex Application Note 37. De Kleijn J.P., Deutsche Leben. Rundrch.,79 (1983) 184. Behnen J., Behrend P. and Kipplinger A., LaborPraxis, 9 (1985) 38. Jupille T., Togami D.W. and Burge D.E., Res. D o . , February (1983) 151. Palmer J.K. and List D.M., J. Agr. Food Chem.,21 (1973) 903. Interaction, organic acid analysis column ORH-801, 1982. Woo D.J. and Benson J.R., LC, 1 (1983) 238. Woo D.J. and Benson J.R., Am. Lob., January (1984) 50. Walser P., J. Chromatogr., 439 (1988) 71. Leuenberger U., Gauch R., Rieder K. and Baumgartner E., J. Chromatogr., 202 (1980) 461. Ivey J.P., J . Chromatogr., 267 (1983) 218. Hurst W.J., Snyder K.P. and Martin R.A., Jr., J. Liq. Chromatogr., 6 (1983) 2067. Waters ILC Series Application Brief No. 4001. Glod B.K. and Kemula W., 1. Chromatogr.. 366 (1986) 39. Dionex Application Note 27. Matsushita S., Anal. Chim. Acta, 172 (1985) 249. Tanaka K. and Fritz J.S., J. Chromatogr., 409 (1987) 271. Yoshida I., Hayakawa K. and Miyazaki M., Eisei Kagaku, 31 (1985) 317. Rocklin R.D., LC,1 (1983) 504. Dionex Application Note 25. Dionex Application Note 46. Jancar J.C., Constant M.D. and Henvig W.C., J. Am. SOC. Brew. Chem., 42 (1984) 90. Wescan Application #150.
Analysis of Foods and Plants using IC
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114
115 116 117 118 119 120 121
629
Waters ILC Series Application Brief No. 4002. Wescan Application #245. Rocklin R.D., Slingsby R.W. and Pohl C.A., J. Liq. Chromatogr., 9 (1986) 757. Wescan Application #138a. Wescan Application #138b. Waters ILC Series Application Brief No. 4007. Dionex Application Note 21. Cuff D.. CHEMSA,7 (1981) 11. Haddad P.R. and Heckenberg A.L., J. Chromarogr.. 252 (1982) 177. Hoshino Y., Saitoh H. and Oikawa K., Bunseki Kagaku, 32 (1983) 273. Lee D.P. and Lord A.D.. LC.GC, 5 (1987) 261. Moore L.F., Bates R.P. and Marshall M.R., Am. J. E d . Vitic., 38 (1987) 28. Haginaka J., Wakai J., Yasuda H. and Nomura T., J. Chromatogr.,447 (1988) 373. Jupille T.H. and Gjerde D.T., J. Chromarogr.Sci., 24 (1986) 427. Jupille T., Inr. Lab.,November (1985) 82. Okada T., Anal. Chem., 60 (1988) 1336. Okada T. and Kuwamoto T., Anal. Chem., 58 (1986) 1375. Lawrence J.F., Chromarographia,24 (1987) 45. Nguyen J.H., Kim H.-J. and Gjerde D.T., Am. Lab.. May (1988) 122. Kondratjonok B. and Schwedt G., Fres. Z . Anal. Chem., 332 (1988) 333. Takeuchi T., Suzuki E.and Ishii D..Chromarographia,25 (1988) 582. Yan D., Stumpp E. and Schwedt G.,Fres. Z. Anal. Chem.,322 (1985) 474. Gennaro M.C., J . Chromatogr.,449 (1988) 103. Schmuckler G., Rossner B. and Schwedt G., J. Chromatogr..302 (1984) 15. Turkelson V.T. and Richards M., Anal. Chem., 50 (1978) 1420. Waters ILC Series Application Brief No. 4003. Haddad P.R. and Lau J., Food Technol. A m . , 36 (1984) 46. Rokushika S., Qiu Z.Y.and Hatano H., J. Chromatogr.,260 (1983) 81. Small H., Stevens T.S. and Bauman W.C., Anal. Chem.,47 (1975) 1801. Schwedt G.,GIT Fachz. Lab., 7 (1985) 697. Dionex Application Note 9. Buchberger W., J. Chromarogr.,439 (1988) 129. Vlacil F., Vins I. and Coupek J., J. Chromatogr.,391 (1987) 119. Vlacil F. and Vins I., Die Nahrung, 29 (1985) 467. Sherman J.H., Danielson N.D. and Hazey J.W., J. Agric. Food Chem., 36 (1988) 966. Golombek R. and Schwedt G., J . Chromatogr.,452 (1988) 283. Schweizer A. and Schwedt G.,Fres. Z . Anal. Chem., 320 (1985) 480. Dogan S. and Haerdi W., Chimia, 35 (1981) 339. Yan D., Rossner B. and Schwedt G.,Anal. Chim Acra, 162 (1984) 451. Nakaoka H., Umoto F,. Kasano M., Ikeda N., Ichimura K., Ueda E. and Itano T.. Bunseki Kagaku. 30 (1981) "97. Butler E.C.V., J. Chromatogr.,450 (1988) 353. Gjerde D.T., Schmuckler G.and Fritz J.S.,J. Chromatogr., 187 (1980) 35. Waters IC Lab. Report No. 300. Wescan Application #185. Dionex Application Note 47.
630
Chopter 18
122 123 124 125 126 127 128 129
Wescan Application #250. Waters IC Lab. Report No. 235. Waters ILC Series Application Brief No. 4004. Matsushita S., J. Chromarogr., 312 (1984) 327. Rocklin R.D., Pohl C.A. and Schibler J.A., J. Chromatogr., 41 1 (1987) 107. Dionex Application Note 19. Kalbasi M. and Tabatabai M.A., Commun. Soil Sci. Plant Anal., 16 (1985) 787. Grunau J.A. and Swiader J.M., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromatography, Vol. I , Century International, Inc., Franklin, MA, 1989. p. 361. Grunau J.A. and Swiader J.M., Commun. Soil Sci. Plant Anal., 17 (1986) 321. Ferguson N.M., Lindberg S.E. and Vargo J.D., Inrer. J . Environ. Anal. Chem., 11 (1982) 61. Lipski A.J. and Vairo C.J., Can. Res., 13 (1980) 45. Smillie R.H., Grant B. and Cribbes R.L., J . Chromarogr., 455 (1988) 253. Busman L.M., Dick R.P. and Tabatabai M.A., Soil Sci. SOC. Am. J . , 47 (1983) 1167. Bartonek G. and Werner H.. GIT Fachz. Lab., 27 (1983) 1075. Stallings E.A., Candelaria L.M. and Gladney E.S., Anal. Chem., 60 (1988) 1246. Peura P. and Koskennierni J., Acta Pilarm. Fenn.. 94 (1985) 67. Waters IC Lab. Report No. 305. Hem J.A., Rutherf0rdG.K. and van Loon G.W., Talanta, 30 (1983) 677. Wescan Application #176. Jackson P.E. and Haddad P.R., J. Chromarogr., 439 (1988) 37. Basta N.T. and Tabatabai M.A., Soil Sci. SOC.Am. 1..49 (1985) 76. Yamada H. and Hattori T., J. Chromarogr., 41 1 (1987) 401. Haddad P.R. and Brownie G.H.. Ed. Chem., February (1988) 12. Hertz J. and Baltensperger U.. Fres. 2.Anal. Chern., 318 (1984) 121. Hertz J. and Bsltensperger U.. LC, 2 (1984) 600. Saitoh H. and Oikawa K., Bunseki Kagaku, 33 (1984) E441. Hayakawa K.. Ebina R., Matsumoto M. and Miyazaki M., Bunseki Kagaku, 33 (1984) 390. Hayakawa K., Hiraki H., Choi B. and Miyazaki G., Hokuriku Koshu Eisei Gakkaishi, 10 (1983) 24. Pentchuk J., Haldna U. and Ilmoja K., J. Chronlarogr., 364 (1986) 189. Zolotov Y.A., Ivanov A.A. and Shpigun O.A., Zh. Anal. Khim.,38 (1983) 1479. Jardy A,, Caude M., Diop A,. Curvale C. and Rosset R.,J. Chromarogr., 439 (1988) 137. Simonzadeh N. and Schilt A.A., Talanta, 35 (1988) 187. Lawrence J.F. and Chadha R.K., J. Chromarogr., 389 (1987) 355. Wescan Application #308. Blake J.D., Clarke M.L. and Richards G.N., J. Chromarogr., 398 (1987) 265. Stewart E.J., Inr. Sugar J., 88 (1986) 126. Cox J.A., Dabek-Zlotorzynska E., Saari R. and Tanaka N.,Analyst (London), 113 (1988) 1401. Shevenell B.J. and Shortle W.C., Phyroparhology, 76 (1986) 132. Maurer W., Hesse W. and Bruins J., Fres. Z. Anal. Chcm., 325 (1986) 73. Wescan Application #73b. Phillippy B.Q. and Bland J.M., Anal. Biochem., 175 (1988) 162. Bradfield E.G. and Cooke D.T., Analyst (London), 110 (1985) 1409.
130 131 132 133 134 135 136 137 138 139 140 141 142 143 144
145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163
Analysis of Foods and Plants using IC
63 1
164 Abraham V. and deMan J.M., J . Am. Oil Chem. Soc., 64 (1987) 384. 165 Minear R.A., Segars J.E., Elwood J.W. and Mulholland P.J., Analyst (London). 113 (1988) 645. 166 Wescan Application #73a. 167 Wescan Application #237. 168 Wellburn A.R., New Phytol., 100 (1985) 329. 1 69 Wolfenden J. and Wellburn A.R., New Phytol., 104 (1986) 97. 170 Bryan B.A., Linhardt R.J. and Daniels L., Appl. Environ. Microbiol., 51 (1986) 1304. 171 Schwedt G. and Schneider P., Fres. Z . Anal. Chern., 325 (1986) 116. 172 Wescan Application #142a. 173 Wescan Application #142b. 174 Uchiyama S., Tohfuku Y., Suzuki S. and Muto G., Anal. Chim Acta, 174 (1985) 313. 175 Menconi D.E., Anal. Chern., 57 (1985) 1790.
This Page Intentionally Left Blank
633
Chapter 19 Clinical and Pharmaceutical Applications 19.1 OVERVIEW Clinical and pharmaceutical appliations of IC are presented according to the scheme shown in Fig. 19.1.
CLINICAL AND PHARMACEUTICAL APPLICATIONS OF IC
r1 1
t
Blood, serum, plasma (Table 19.1) Urine (Table 19.2) Other clinical and biological materials (Table 19.3) Pharmaceuticals (Table 19.4)
Fig. 29.2 Applications of IC in the analysis of clinical and pharmaceutical materials.
8 P
TABLE 19.1 ANALYSIS OF BLOOD, SERUM A N D PLASMA USING IC Solutes (min)
Sample Prep.
Column
Chloride (6.3), phosphate (7.9), bromide (13.1). nitrate (16.8), sulfate (23.4)
Dilution
Chloride (3), sulfate (12), thiosulfate (18)
-
Dionex anion 3 mM bicarbonate, separator 2.4 mM carbonate 250 x 4.0 mm ID 180 ml/hr WeXm 5.0 mM phthalate, pH 3.5 anion/HS 2.5 d m i n
Chloride (4), nitrate (1l), sulfate (16)
Dilution, ACN ppt of protein, centrifugation
3-hydroxybutyrate/acetate(3.1), lactate (4.3), pyruvate (5.0),chloride (7.6), ninate (8.7) Phosphoric (1I), pyruvic (13), lactic (17), hydroxybutyxic (23)
Cleanup on Ag catex
Dilution, ACNppt of protein, centrifugation Lactate (4),pyruvate (7), ketoisovalerate(9) Dilution, ACN ppt of protein, centrifugation
Chloride (3.8), bicarbonate (17.6)
Ultrafluation, dilution
Eluent
Detection
Ref
Conductivity
1, 2
Conductivity
3
4, 5
Dionex ICE ion exclusion and anion separator 250 x 9 mm ID 250 x 3.0 mm ID Partisil 10 SAX 300 x 1.5 mm ID
l O m M hydrochloric acid and 3.0 mM bicarbonate, 2.4 mM carbonate 0.86 ml/min and 2.3 mVmin
Conductivity
1 mM phthalate 0.5 mVmin
Indirect spectrophot. 6 at 2% nm
Dionex ICE ion exclusion 250 x 9mm ID
10 mM hydrochloric acid 0.86 d m i n
Conductivity
4, 5 , 7
Dionex ICE ion exclusion and anion separator 250 x 9 mm ID 250 x 3.0mm ID Wescan 269-001 anion-exchanger 250 x 4.6 mm ID
10mM hydrochloric acid and 0.66 mM bicarbonate 0.86 d m i n
Conductivity
4, 5 , 7
4.0 mM phthalate, pH 4.5 2.0 d m i n
Conductivity
8
See p . 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 19.1 (CONTINUED). ANALYSIS OF BLOOD, SERUM AND PLASMA USING IC Solutes (min)
Sample Prep.
Column
Chloride (10.2), bromide (11.9)
Centrifugation, Nuation
Partisil-10 SAX 30 mM dihydrogen phosphate Direct specimphot. at 9 250 x 4.6 mm ID 0.7 d m i n 195 nm
Chloride (2.8), methyl sulfate (3.5)
Alkylation with an alkyl chloride
Dionex AS-4
Azide (3.2), chloride (4.6) Chloride (3,bromide (7) Nitrite (3.3), nitrate (4.7)
Cyanide (6), thiocyanate (10)
Lactate (2), succinate (16)
Eluent
Detection
1.0 mM tetrabutylammonium Conductivity hydroxide 2.0 mVmin Dilution in eluent Vydac 302 IC 1.0 mM phthalic acid, adjusted Conductivity 250 x 4.6 mm ID to pH 3.5 with pyridine 2.5 mVmin Wescan 269001 5 mMphthalic acid ACN addition, Conductivity filtration, dilution anion 3.7 mlfmin 250 x 4.6 mm ID ACN ppt of protein, Wescan SAX 50 mM phosphate, Direct specimphot at 250 x 4.1 mm ID 3 mM sodium chloride, 214 nm c18 PreCOlUIlXl 4 mM acetic acid, pH 3.95 4.0 d m i n Hemolyzation, TSK Gel LS-222 0.1 M acetate buffer, Fluorescence at 583, ulaafitration, 100 x 3 mm ID 607 nm after dual 0.2 M perchlorate filtration 0.5 d m i n postcolumn reaction with chloramine-T then pyridine and barbituric acid Dilution, ACN ppt Dionex ICE ion 10 mM hydrochloric acid and Conductivity of protein, exclusion and 3.0 mM bicarbonate, centrifugation anion separator 2.4 mM carbonate 250 x 9 mm ID 0.86 d m i n and 2.3 ml/min 250 x 3.0 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
Ref
10 11 12 13
14
4, 5
8 m
TABLE 19.1 (CONTINUED). ANALYSIS OF BLOOD, SERUM AND PLASMA USING IC Solutes (min)
Sample Prep.
Column
Bromide as 4-bmmoacetanilide (7.7)
Pre-column derivatization, dilution, ACN ppt, centrifugation, evaporation Dilution, ultrafiltration
zorbax c1g
Bromide (8.5) Bromide (8.3) Bromide ( 10)
Dilution, ultrafiltration. C18 Sep-Pak Ulnatiltration, dilution
Iodide (1 1)
Ultrafiltration, CIS Sep-Pak
Iodide (13)
Addition of ACN, centrifugation, clean-up by ionexchange
Eluent
Detection
Ref
Water (65% MeOH) 250 x 4.6 mm ID 1.0 mumin
Direct specwphot. at 15 240 nm
Waters IC Pak A (x2) in series 50 x 4.6 mm ID Waters IC Pak A 50 x 4.6 mm ID
Ampemmetry at Ag electrode, +0.03V
1 mM lithium phthalate, pH 6.5 1.2 d m i n 5 mM sodium chloride 1.2 mumin
Vydac 302 IC 3.5 gA methanesulfonic acid, 250 x 4.6 mm ID 0.2 gA4,4'-bis (dimethylamino) diphenylmethane, pH 4.0 (14% EtOH) 1.0 d m i n Vydac 302-IC 4.5 gA methanesulfonic acid, 250 x 4.6 mm ID 0.2 gA 4,4'-bis (dimethylamino) diphenylmethane, pH 4.0 (14% EtOH) 1.O ml/min Spherisorb ODS 1.125 mM hexadecyltrimethyl 300 x 3.9 mm ID ammonium chloride, 12.5 mM phosphate, pH 6.8 (25% ACN) 2.0 d m i n
16
Direct spectrophot. at 16 214 nm Direct specwphot. at 17 600 nm after postcolumn reaction with chloramine-T Direct spectrophot. at 18 600nm after postcolumn reaction with chloramine-T Ampemmetry at Ag electrode, +O.OlV
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
19.20
8
TABLE 19.1 (CONTINUED). ANALYSIS OF BLOOD, SERUM AND PLASMA USING IC Solutes (min)
Sample Prep.
Column
Eluent
Detection
Fluoride
spiking
Wescan anion exclusion
2 nM sulfuric acid 0.8 Wmin
Conductivity
Thiocyanate (10)
Dilution, ACN ppt of proteins, centrifugation, filtration Chlorofonn ppt of proteins, centrifuge C18 Sep-Pak
TSK-gel IC anion-SW 50 x 4.6 mm ID
Thiosulfate (12)
Sulfate
Tetrafluoroborate(1 1) Valproic acid (8.5)
Uric acid (2.8)
Ref
$ 2
u.
Perchloric acid or ACN protein ppt, dilution, PS-DVB pre-column Acidification, heating, dilution
3 i P/
Direct specuophot. at 21 phosphate, 2.0 mM hydrogen 195 nm, conductivity phosphate 1.0 Wmin TSK SAX 0.18 M sodium nitrate Ampemmetry 150 x 4.0 mm ID 1.1 Wmin glassy carbon at dual 22 electrodes. 0.9V and 0.7V 2.8 mM bicarbonate, Conductivity 23 Dionex A S 4 250 x 4.0 mm ID 2.25 mM carbonate 2.0 Wmin
Dionex anion separator 250x3.0mmID Hydroxide and Dionex ICE ion ACN ppt of protein, exclusion centrifugation, 65 x 6.0mm ID dilution Dilution in eluent SAX-1 125 x 5.0 mm ID
4.0 mM dihydrogen
3.0 mM bicarbonate, 2.4 mM carbonate 184mVhr 0.5 mM carbonic acid 0.7 Wmin 0.7 g/l citric acid, 0.05 g/l cetrimide, pH 5.5 (30%MeOH) 1.0 Wmin
Conductivity
24
Conductivity
25
&
8
p
E
Amprometry, +1.OV 26
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
m
Y
s
TABLE 19.1 (CONTINUED). ANALYSIS OF BLOOD, SERUM AND PLASMA USING IC Solutes (min)
Sample Prep.
Sodium (1.61, ammonium (2.2), potaisium Ultrafiltration, dilution (3.2), creatinine (5.7) Sodium (1.6), potassium (4.2
Ulaafilmtion, dilution
Sodium (1.73, potassium (2. 5 )
Ultrafiltration, dilution Dilution
Sodium (1 l), potassium (15) Sodium (2.6), protonated Tris (4. I), magnesium ( 6.0), calcium (8.6)
Dialysis with Tris buffer, ulaafiltration, dilution Sodium (1.8), potassium (2.3), magnesium Ultrafilmtion, (lO.l), calcium (18.5) dilution
Sodium (123). potassium (2.3), magnesium Ulnafrltration, (5.9), calcium (10.5) dilution Sodium (3.0), magnesium ( 6.0), calclium (8.5)
Acidification, centrifugation, filtration, dilution
m
Column
Eluent
Detection
Wescan cation exchanger 250 x 4.6 mm ID Wescan cation exchanger 250 x 4.6 mm ID ASC- 4000 SCX 250 x 4.6 mm ID Dow sulfonated PS-DVB resin 250 x 9.0 mm ID Dionex cation separator (x2) 250 x 6.0 mm ID
Phosphoric acid, pH 2.03 1.0 mumin
Indirect conductivity, 8 direct spectrophot. at 210 nm Indirect conductivity 27-30
6.3 mM nitric acid 1.0 mumin
Ref
1.28 mM copper sulfate 1.O M m i n 10mM hydrochloric acid 160 ml/hr
Indirect spectrophot. 28,29 at 218 nm Conductivity 31
1.O mM barium nitrate 3.45 ml/min
Conductivity after sulfate suppression of barium (ppt)
ASC- 4000 SCX 2.0 mM copper sulfate, 250 x 4.6 mm ID 0.75 mM cobalt sulfate 1.0 ml/min ASC- 4000 SCX 1.28 mh4 copper sulfate to 250 x 4.6 mm ID 1.0 mM copper sulfate, 2.0 mM cobalt sulfate gradient 1.O ml/min Dionex cation 1.0 mM barium nitrate, separator pH 4.0 250 x 6.0 mm ID 2.3 ml/min
32
Indirect spectrophot. 28, 29 at 218 nm Indirect spectrophot. 28. 29 at 218 nm Conductivity after sulfate suppression of barium (ppt)
Seep. 487 for notes on the organizamn of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
33, 34
‘ r
W
TABLE 19.1 (CONTINUED). ANALYSIS OF BLOOD, SERUM AND PLASMA USING IC Solutes (min)
Sample Prep.
Column
Eluent
Detection
Ref
Magnesium ( 5.4), calcium (7.1)
Acidification, centrifugation, filtration, dilution Ultrafiltration, dilution
Dionex cation separator 250 x 6.0 mm ID SCX 1 250 x 4.6 mm ID
1.0 mM lead nitrate, pH 4.0 2.3 d m i n 2.0 mM ethylenediamine, 4.0 mM tartaric acid 1.O mVmin
35
Magnesium (2.4), calcium (3.5)
Ultrafiltration, Toyo-Pack SP catex cartridge
Magnesium (7), calcium (15)
Dilution, filtration
Magnesium (1.8), calcium (3.8)
Ultrafiltration, dilution
Magnesium ( 5 . 9 , calcium (9.2)
Ultrafiltration, dilution Ultrafiltration, dilution
TSK-GEL SP-2 0.1 mM ocresolphthaleine complexone, 0.25 M sw 50 x 4.0 mm ID potassium chloride, 0.02 M acetate buffer, pH 4.0 1.O ml/min Chromex cation 1.O mM phenylenediamine separator dihydrochloride 250 x 9.0 mm ID 115 mvhr Oyobunko cation 0.6 mM ethylenediamine exchanger adjusted to pH 6.1 with phosphoric acid 2.2 ml/min ASC- 4000 SCX 3.2 mM copper sulfate 250 x 4.6 mm ID 1.O ml/min Wescan cation- 0.047 ml/lethylenediamine exchanger hydrate, pH 6.1 250 x 4.6 mm ID 1.1 ml/min Wescan cation- 0.067 ml/l ethylenediamine exchanger hydrate, pH 6.1 250 x 4.6 mm ID 1.1 ml/min
Conductivity after iodate suppression of lead (ppt) Conductivity, direct spectrophot. at 520 nm after post-column reaction with Neothorin Direct spectrophot. at 575 nm after postcolumn addition of 0.4 M ammonia buffer Conductivity
Magnesium (4.9), calcium (6.5)
Magnesium (2.95) Calcium (6.40)
Ultrafiltration, dilution
Conductivity
36
37
38 27
Indirect specnophot. 28.29 at 218 nm Indirect conductivity 28.29 Indirect conductivity
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
28.29
8 W
TABLE 19.1 (CONTINUED). ANALYSIS OF BLOOD, SERUM AND PLASMA USING IC Solutes (min)
Sample Prep.
Calcium (8.5)
Automated dialyzing Dionex cation injection clean-up separator 250 x 6.0 mm ID Dilution with Dionex CS-5 trichloroacetic acid, centrifugation
Copper (2.4), zinc (7.4)
Column
Iron (11) (7.0), iron (HI) (23)
Incubation with Dionex CS-5 trichloroacetic acid, centrifugation
Chromium (VI),chromium (III)
on-column preconcentration
Dionex CS-2 250 x 4 mm ID
Calcium (6.0), magnesium (6.9). sulfate (9.7)
Ultrafiltration, addition of EDTA, dilution
TSK-gel IC Anion-SW 50 x 4.6 mm ID
0
Eluent
Detection
Ref
1.0 mM barium nitrate, pH 4.0 2.3 nVmin 50 mM oxalic acid, 95 mM lithium hydroxide, pH 4.8 1.O mVmin 6.0 mM pyridine-2,6diwboxylic acid, 8.6 mM lithium hydroxide, pH 4.8 0.7 mVmin Water with multiple injections of 1.0 M hydrochloric acid 2.0 d m i n 1.0 mh4 EDTA, pH 6.5 1.O mVmin
Conductivity after sulfate-supression of barium (ppt) Direct specaophot. at 520 nm after postcolumn reaction with PAR Direct spectrophot. at 520 nm after postcolumn reaction with PAR 3 electrode plasma atomic emission specaoxopy Direct/iidimt conductivity
39
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
40
41
42 43
4
v,
2 2.
TABLE 19.2 ANALYSIS OF UEUNE USING IC Solutes (min)
R Sample Prep.
Column
Eluent
Detection ~
Fluoridebactate(1.Q chloride (2.3), bromide (3.4), nitrate (3.9), sulfate (5.1), oxalate (6.8), phosphate (8.6), phthalate (10.6), iodide (12.3) Oxalic (3.4), oxaloacetic (4.1), ketoisovaleric, (5.4), ascorbic, ketomethyl n-valeric (7.0), phenylpyruvic (9.6), uric (1 1.3), ketobutyric, (12.7), homoprotocatechuic (13.8), hydroxyphenyl acetic (22.6), hydroxyphenyl lactic (22.3), homovanillic (24.1) Urinary organic acids (screening)
~
~~~~~
Centrifugation, filtration, cat-ex clean-up, dilution in eluent Filtration
Dionex AS-4 300 x 3.0 mm ID
2.3 mM carbonate, 1.9 mM hydroxide, 0.2 mM phenol 2.0 Wmin
Conductivity
Interaction ORH801 organic acid 300 x 6.5 mm ID
10 mM sulfuric acid (15% MeOH) 0.6 Wmin
Direct specmphot at 254 nm
45.46
Filtration
Aminex HPX-87H and Bio-Rad CIS 300 x 7.8 mm ID 150 mm Interaction ORH801 organic acid 300 x 6.5 mm ID Waters IC Pak A 50 x 4.6 mm ID
2.5 mM sulfuric acid 0.8 Wmin
Directspecmphot at2oonrn
47
10 mM sulfuric acid 0.8 Wmin
Directspecmphot. 48 at 210 nm
Organic acids (screening) Chloride (3), nitrite (4.5). phosphate (6.5), sulfate (8)
Dilution, filtration
Chloride (4), nitrite (6), phosphate (9). sulfate (29)
Dilution, filtration
Chloride (4), phosphate (7), sulfate (lo),
Acidification, dilution, filmtion
oxalate (15)
~~
Ref
Chromex anion separator 500 x 2.8 mm ID Dionex AS-3
44
48
5
1.42 mM gluconate, 5.82 mM Conductivity boric acid, 0.25% glycerine, pH 8.5 (12% ACN)
49
3.5 mM bicarbonate, 1.5 mM carbonate 115 ml/hr 0.242 mM bicarbonate, 0.18 1 mM carbonate 132 mVhr
CondUctivity
38
Conductivity
50,51
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
g
$2
c.
p: N
TABLE 19.2 (CONTINUED). ANALYSIS OF URINE USING IC Solutes (min)
Sample Prep.
Aconitic (8). ketoglutaric (10). cimc (15). isocimc (16), succinic (24)
Aminex 50W-X4 cation-exchanger 300 x 12.7 mm ID Dilution, filtration. Ionosphere SAX 250 x 4.5 mm ID pre-column
Arsenite (2.5), monomethylarsonicacid (4.5). dimethylarsonic acid (7.0), arsenate (8.9) Arsenic (HI)(1.4), dimethylarsine (2.0), monomethyl mine (2.8), arsenic (V) (7.5)
Column
Dilution, filtration
CIS Sep-Pak, di-n-butylamine phosphate to remove chloride interference
Hamilton PRPXl00 250 x 4.1 mm ID
Eluent
Detection
1 mM hydrochloric acid 1.0 mVmin
Direct spectmphot. 52 at 210 m
0.03 M phosphate buffer, pH 6.2 1.7 mumin 10.0 mM ammonium carbonate, 2.5 mM sodium sulfate, pH 8.2 2.0 d m i n
Hydride generation 53 atomic absorption spectrometry ICP-AES 54.55
TSK-GEL IEX-520 0.05 M nitrate, 0.05 M acetate buffer, Qf= 150 4.0 mm ID pH 5.48 0.8 mumin
Phosphate (4.0), chloride (5.3). sulfate (7. l), thiocyanate (14.9)
Chloride (3), sulfate (12), thiosulfate (18)
Dilution
Wescan anion/HS
5.0 mM phthalate, pH 3.5 2.5 ml/min
Chloride (2), phosphate (3,sulfate (8)
Acidification, dilution, fiitration
Sulfate (1I), oxalate (14)
Acidification, dilution,Millex filtration
Dionex anion separator 250 x 4.0 mm ID Waters IC Pak A 50 x 4.6 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 2.3 mumin 0.7 mM phthalate, pH 7.1 1.0 ml/min
Sulfate (16), oxalate (22)
Acidification, dilution, filtration
Dionex AS-4 250 x 4.0 mm ID
2.80 mM carbonate, 2.25 mM bicarbonate 1.6 d m i n
Ref
Direct spectrophot. at 340 nm after post-column reaction with Fe(1II) perchlorate Conductivity
56
Conductivity
5
Potentiorneny at a copper wire electrode, conductivity Conductivity
57,58
Seep. 487for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
3
59-62
a s’
TABLE 19.2 (CONTINUED). ANALYSIS OF URINE USING IC Solutes (min)
Sample Prep.
Column
Uric acid (2.7), oxalate (3.5)
Acidification, centrifugation, filtration
Vydac SCX 250 x 3.2 mm ID
Arsenobetaine (5.0), spurious peak (4.4)
c18 Sep-Pak
Chloride (2.8), methyl sulfate (3.5)
Allcylation with an alkyl chloride
Hamilton PRPXlOO and Vydac 201Tp 250x4.1mmID 2 5 0 ~ 4 . 1mmID Dionex AS4
System peak (9), Octane sulfonate (37)
Dilution
Waters pBondapak Phenyl 100 x 4.6 mm ID
Isopropyl methylphosphonic acid (2.6)
TLC clean-up
Oxalate (13)
Dilution, filtration
Dionex anion separator 500 x 3.0 mm ID Dionex AS-3
Oxalate (20.2)
Acidification, dilution
Eluent
Detection
2.0 mM acetate buffer, 1.O mM tetrabutylammonium tetrathoroborate, pH 2.8 0.6 ml/min 3.0 mM ammonium dihydrogen orthophosphate, pH 6.0
D.C. amperometry 63 at wax impregnated graphite d e c d e , +1.25V. 64,s ICP-AES
1.0 mM tetrabutylammonium hydroxide 2.0 mumin 0.4 mM naphthalene-2sulfonate, 0.05 M phosphoric acid 0.5 mlfmin 5.0 mM teuaborate 138 ml/hr
Conductivity
3.0 mM bicarbonate, 2.4mMcarbonate 2.7 d m i n 6 mM carbonate buffer Dionex fast-run anion separator (x2) 2.3 ml/min in series 250 x 4.0 mm ID
Ref
10
Indirect 65 spectrophot. at 254 nm Conductivity
66
Conductivity
67, 7, 68
Conductivity
69,70
Seep, 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
;i’
i5
E
TABLE 19.2 (CONTINUED). ANALYSIS OF URINE USING IC ~~
~~
Solutes (min)
Sample Prep.
Thiosulfate (12)
Citrate (7.8)
Addition of chloroform, centrifugation, cl8 Sep-Pak Addition of isopmpanol preservative, cl8 Sep-Pak, dilution in mobile phase Dilution, filtration
Citrate (17)
Dilution
Uric acid (2.8)
Dilution in eluent
Sulfate (6.2)
Dilution, filtration
Versapack C18 250 x 4.0 mm ID
Nitrate (12.5)
Filtration
Iodide (11)
Ultrafiltration, c18 Sep-Pak
Partisil 10 SAX 250 mm Vydac 302-IC 250 x 4.6 mm ID
Thiosulfate (7)
Column
TSK SAX
150 x 4.0 mm ID
RSL cl8 250 x 4.6 mm ID
Dionex AG-3 50 x 3.0 mm ID YEW SAX1-251 250 x 4.6 mm ID SAX-1 125 x 5.0 mm ID
Eluent
Detection
0.18 M sodium nitrate 1.1 N m i n
Ref
Ampemmetryat 22 dual glassy carbon electrodes, 0.9V and 0.7V 17.6 mM tetrabutylammonium Ampemmetry at Hg 71 hydrogen sulfate, elecmde. 0.OV 2 mM phosphate, 0.1 mM EDTA, pH 6.0 1.O N m i n 8.0 mM carbonate Conductivity 72 2.2 mVmin 30 mM carbonate Conductivity 73 2.0 ml/min 0.7 gA citric acid, Amperomcay, 26 +l.OV 0.05 g.4 cetrimide, pH 5.5 (30% MeOH) 1.O ml/min 1.O mM tetrabutylammonium Indinct 74 specmphot. at 266 phthalate, pH 6.1 1.5 ml/min nm 22.5 mM phosphate, pH 2.35 Direct specmphot. 75 1.5 d m i n at 214 nm 3 g/l methanesulfonate, 0.2 gl Direct specmphot 18 4,4'-bis (dimethylamino) at 600 nm after diphenylmethane,pH 4.0 post-column (14% MeOH) reaction with chloramine-T 1.0 d m i n
See p . 487 for notes on the organization of this Table. Seep. 662 for Rderences. Abbreviations are listed in Appendix B (p. 745).
s
TABLE 19.2 (CONTINUED).ANALYSIS OF URINE USING IC
a
Solutes (min)
Sample Prep.
Teaafluomborate(11)
Acidification, heating. dilution
Column
Eluent
Detection
Ref
3.0 mM bicarbonate, 2.4 mM carbonate 184ml/hr 10mM hydrochloric acid 0.86 Wmin
Conductivity
24
Ampemmetry at Pt electFode
5
5 mM nimc acid
Conductivity
76
10mM hydrochloric acid 2.0 Nmin
Conductivity
31.77
5 mM hydrochloric acid
conducfivity
38
3
Vanillylmandelic acid (18.5)
Dionex anion separator 250 x 3.0 mm ID Dionex ICE ion exclusion
Acidification, dilution, filtration. 25ox9InmID IC fraction cut Dilution. treatment Dionex cation Sodium (12). ammonia (urea) (18), potassium (23) with immobilized separator urease reactor Dow sulfonated PSDilution Sodium (1l), ammonium (15), potassium DVB resin (17) 250 x 9.0 mm ID Dilution, filtration Qlromex cation Sodium (12), ammonium (16), potassium separator (20) 500 x 6.0 mm ID ION-210 transition Sodium (1.8), ammonium (2.3). potassium Acidification, (3.6) dilution me81 100 x 3.2 mm ID TSK-GEL SP-2 Ultrafiltration, Magnesium (2.4). calcium (3.5) Toyo-Pack SP sw 50 x 4.0 mm ID cat-ex Camidge Zinc (8)
Fiiuation. dilution
cl8 silica 250 x 4.6 mm ID
138mVhr
b.
i 5.
B
$3
0.01 mM cerium (In)sulfate 1.0 mvlnin
Indirect 78 spech-ophot. at 254 nm 0.1 mM o-cresolphthaleine Directspectrophot. 37 complexone, at 575 nm after 0.25 M potassium chloride, postcolumn 0.02 M acetate buffer, pH 4.0 addition of 0.4 M 1.0 ml/min ammonia buffer 10 mM hexanesulfonate, Directspectrophot. 79 45 mM sodium tartrate, after postcolumn pH 3.1 reaction with PAR 1.0 d m i n
~~
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
k ul
p: m
TABLE 19.3 ANALYSIS OF OTHER CLINICAL AND BIOLOGICAL SAMPLES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Chloride (4), nitrite (6). phosphate (9)
Tissue extract
Dilution. filtration
38
Tissue extract
Dilution
3.5 mM bicarbonate, 1.5 mM carbonate 115 d / h r 5 mM hydrochloric acid
Conductivity
Sodium (7.7), ammonium (12.7). potassium (17.5)
Conductivity
80.38
Calcium ( 15)
Tissue extract
Dilution, filtration
38
Muscle tissue (bovine)
Pulverization, acid digestion, dilution
1.0 mM phenylenediamine dihydrcchloride 11s mvhr 5.0 mM nitric acid
Conductivity
Sodium (6.8), ammonium (9.0), potassium (1 1.9)
Chromex anion separator 500x 2.8 mm ID Dionex cation separator 250 x 4.0 mm ID Chromex cation separator 250 x 9.0 mm ID Dionex cation separator 200x 3.0mm ID Dionex AS- 1 ion exclusion
Conductivity
81
1.0 mM hydrochloric acid 0.8 mumin
Conductivity
82
2.4mM bicarbonate,
Conductivity
83
Respiratory tract Methyl acetate, ethyl acetate, and liver tissue propyl acetate, butyl acetate, pentyl acetate, hexyl acetate, octyl acetate, phenyl acetate, butyrolactone Rat brain, liver Lactate (2.6), chloride (3.7), inositol-1-phosphate (5.6), glucose-6-phosphate (6.5), glycerol-3-phosphate (7. l), phosphate (9.8), sulfate (11.91, oxalate (13.5)
Homogenization Dionex AS-SA and extraction, (x2) clean-up on 50 x 4.0 mm ID Dionex CAT-Ag cartridge
150 mVhr
1.9 mM carbonate 1.5 mYmin
P5 See p . 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 19.3 (CONTINUED). ANALYSIS OF OTHER CLINICAL AND BIOLOGICAL SAMPLES USING IC Solutes (min)
Sample
Sample Prep.
Lactate (2.4), inositol-lphosphate (3.3), phosphate (3.6), sulfate (3.8), oxalate (4.5). 6-phosphogluconate (6.9). 3 3 phosphoglycerate (7.2), citrate (7.9, fructose1,6-biphosphate (12), inositol2-phosphate (13). inositol-3phosphate (15) Inositol phosphates I( 1,2,3,4)~4(17). 1(1,3,4,5,6)PS (23). IP6 (28)
Rat brain, liver
Eluent
Detection
Ref
Homogenization Dionex AS4A and extraction, 50 x 4.0 mm ID clean-up on Dionex CAT-Ag carnidge
Gradient of water to 44 mM p-cyanophenol 2.0 d m i n
Conductivity
83
Calfbrains
Homogenization Dionex AS-3 centrifugation, fiiaation, concenmtion on AG 1-X8, lyophilization
Gradient of 180 mg/l pynxatechol to 0.155 M nitric acid 1.O d m i n
Bicarbonate (8.5)
Panmatic extract, bile
Dilution
Dionex AS-1 ion exclusion
Doubly-distilled water 1.5 d m i n
Direct 84 spectrophot. at 290 nm after post-column reaction with Fe(1II) perchlorate 85 Conductivity
Trifluoroacetic acid
Rat bile
Dilution
Chloride (5.1), phosphate (7.3, sulfate (17.2) Lactate (2.6), chloride (3.0)
Saliva, sweat
Ultrafilmtion, dilution Dilution
YEW anion separator Dionex AS- 1 250 x 4.0 mm ID Hamil ton PRPXloo 150 x 4.4 mm ID
4.0 mM bicarbonate, Conductivity 2.0 mM carbonate Carbonate, bicarbonate buffer Conductivity
Sweat
Column
1.5 mMphthalate, pH 5.15 1.O d m i n
86
87
Indirect 88 spectrophot. at 280 nm
Seep. 487for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
2 a
6.
$2
TABLE 19.3 (CONTJNiLTED). ANALYSIS OF OTHER CLINICAL AND BIOLOGICAL SAMPLES USING IC Solutes (min)
Sample
Uric acid (2.8), nitrite (3.2), thiocyanate (6.7)
Saliva
Nitrite (10)
Sample Prep.
Column
Eluent
Dilution in
SAX-1 125 x 5.0 mm ID
0.7 gA citric acid, 0.05 g/l cetrimide, pH 5.5 (30% MeOH) 1.0 mvmin 20 mM sulfuric acid 0.8 ml/min
eluent
Saliva
Magnesium (2.4).calcium (3.5) Saliva
Dilution Ultratiitration, Toyo-Pack SP cat-ex camidge
Calcium (7.4), magnesium (8.8). thiocyanate (11.2). sulfate (14.0)
Saliva
Ascorbic (7.6), uric (12.3), homovanillic (22.3)
Cerebrospinal fluid
Filtration
Oxalate (12)
Kidney stones
Nitrate (12.5)
Faeces extracts
Acidifcation, centrifugation, Ntration Filmtion
Dilution, fination
Brownlee Polypore H 100 x 4.6 mm ID TSK-GEL SP-2
sw
50 x 4.0 mm ID
0.1 mM o-cresolphthaleine complexone, 0.25 M potassium chloride, 0.02 M acetate buffer, pH 4.0 1.0 d m i n
TSK-gel ICAnion-SW 50 x 4.6 mm ID
1.O mM EDTA, pH 6.0 1.0 d m i n
Interaction ORH80 1 organic acid 300 x 6.5 mm ID Dionex fast anion separator
10 mM sulfuric acid (15% MeOH) 0.6 d m i n 3.23 mM bicarbonate, 2.41 mM carbonate
Partisil 10 SAX 250 mm
2.2 d m i n 22.5 mM phosphate, pH 2.35 1.5 d m i n
Detection
Ref
Ampemmetry, 26
+1.OV,direct
spectrophot. at 220 nm Ampemmetry 89 at Pt electmde.
+om Direct
31 spectrophot. at 575 nm after postcolumn addition of 0.4 M ammonia buffer Conductivity, 90
direct spectrophot. at 210 nm Amperomeuy, 45, 46, 91 +om Conductivity
68
Direa
75
spectrophot. at 214 nm
Seep. 487 for notes on the organizationof this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
Ba
TABLE 19.3 (CONTINUED). ANALYSIS OF OTHER CLINICAL AND BIOLOGICAL SAMPLES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Sulfate (7.1), lactate (12.5), formate (13.0), acetate (15.3), carbonate (22.4) Glucose, mannose, rhamnose. succhate, glutamate. ethanol
Sodium sulfate bacteria growth media Bacteria growth, fermentation products
Dilution
Dionex ICE ion exclusion
1.0 mM hydrochloric acid
Conductivity
92
AmperomelIy (pulsed)at Au electrode
93
Chloride (2.0), methylphosphonic acid (3.3)
Nument medium Dilution
10 mM hydroxide 332 ml/hr
Conductivity
66
0.56 mM carbonate, 2.0 mM hydroxide.
Conductivity
94
Iminodiacetic acid (14.7), sulfate (22.2), phosphate (28)
Lactate (1.2), D-2chloropropionic acid (1.4). chloride (1.6). phosphate (3.8) Phosphate (6.9), sulfate (9.6), oxalate (12.2)
Trifluomacetic Dionex AS-6 0.15 M hydroxide acid hydrolysis, 275 x 7.5 mm OD 1.0 ml/rnin dilution
Dionex anion septor 500 x 3.0 mm ID Cell-freeextracts Cell disruption, Dionex AS-3 of biological boiling, mahiceS centrifugation
Treatment with Enzyme assay Dionex A S 4 A D-2-halopmpionate dehalogenase Glycoprotein Drying, aqueous Waters IC F'ak A 50 x 4.6 mm ID hormones dissolution, clean-up on cat-ex Oxalic (4.9). arabinonic (8.2). Oxidation Dilution, Hamilton HCribonic (8.5). glycolic (9.9), products of filtration X8.00 formic (11.5) allraline 500x 9.0 mm ID Dglucose Oxalic (4.8), maleic (6.0). citric Biochemical Dilution, Aminex HF'X-87 (6.4), gluconic (7.3). acetic oxidation filtration 300 x 7.8 mm ID (11.2) products of D-glucose
95 96
3.0 mM sulfuric acid 1.5 ml/&
Direct
97
6.0 mM sulfuric acid 0.8 d m i n
Direct 97 spectrophot. at 210 nm
spectrophot. at 210 nm
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
iz i !5.
B
0.84 mM
4-cyanophenol 1.0 mvmin 0.75 mM bicarbonate, Conductivity 2.2 mMcarbonate 2.0 mvmin 1.5 mM gluconate, 11.1 mM Conductivity borate, 12% ACN, 0.25% glycerol, pH 9.2
ii'
s
TABLE 19.3 (CONTINUED). ANALYSIS OF OTHER CLINICAL AND BIOLOGICAL SAMPLES USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Gluconate (3.2)
Biochemical oxidation products of Dglucose Antigens
Dilution, filtration
Nucleosil 10 Amino 250 x 4.6 mm ID
0.01 M phosphate, pH 2.5 (25% ACN) 2.0 mumin
Direct
97
Hydrochloric acid dissolution, reflux, neutralization, centrifugation, extraction Heparin-derived Hydroxide oligosaccharides pyrolyzation, dilution Heparin Hydrochloric acid hydrolysis, evaporation
TSK Gel IC 620
1.3 mM borate, 1.3 mM gluconic acid, pH 8.5 1.2 mumin
Conductivity
98
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity
99, 100
Conductivity
101, 102
Escherichia coli B pre-incubation buffer Rhizobium japonicum bacteroids
Dilution
YEW anion separator
Conductivity
103
Acid digestion, dilution, filtration
Aminex HPX-87H 0.014 M sulfuric acid organic acid 0.7 ml/min 300 x 7.8 mm ID
Direct
104
Sulfate (13)
Sulfate (8) Sulfate
Hypophosphite, phosphate, pyrophosphate Cmtonic acid (29)
SA 50 x 4.6 mm ID
Dionex AS-3 Waters IC Pak A 50 x 4.6 mm ID
3.0 mumin 6.4 m@ sodium gluconate, 7.2 mg/t boric acid, 10 mg/l sodium tetraborate, 2.5 ml/l glycerine 4.0 mM carbonate, 2.0 mM hydroxide
spectrophot. at 210 nm
spectrophot. at 214 nm
S e e p . 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
2 2.
TABLE 19.4 ANALYSIS OF PHARMACEUTICALS USING IC
B n
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Ciwte (5.4), dextrose (5.6), acetate (9.7), phosphate (5.8), gluconate (5.7), propylene glycol (1 1.3), ethanol (14.4) k'-oxalate (1.56), phthalate (3.071, citrate (5.70)
Pharmaceuticals
Dilution
Dionex AS- 1 ion exclusion 250x 12mmID
25 mM sulfuric acid 1.O ml/min
Direct RI
105
Pharmaceutical solutions
Dilution
Dionex AS- 1
pharmaceutical solutions
Dilution
Dionex AS-1
Direct spectrophot. at 205 nm Direct spectrophot. at 205 nm
106
k'-oxalate (1.70), phthalate (3.57), citrate (5.63) k-oxalate (1.63), phthalate (2.81), ciuate (5.10)
Pharmaceutical solutions
Dilution
Dionex AS-1
Direct spectrophot. at 205 nm
106
Sulfate (4.93, oxalate (6.61)
Pharmaceutical matrices
Dionex AS- 1
Pharmaceutical matrices
Dionex AG-1
Bromide as Cbromacetanilide (7.7)
Pharmaceutical formulations
Indirect spectrophot. at 250 nm Indirect spectrophot. at 250 nm Direct spectrophot. at 240 nm
107
Sulfate (4.3, oxalate (5.7)
10 mM Tris buffer, 30 mM sulfate, pH 6.5 1.0 d m i n 10 mM 3-(N-morpholino)-2hydroxypropanesulfonic acid. 30 mM sulfate, pH 6.5 1.0 d m i n 10 mM N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid, 30 mM sulfate (10% ACN), pH 6.5 1.O mumin 1 mM phthalate, 2 mM borate, pH 9.1 3.0 d m i n 1 mM phthalate, 0.75 mM borate, pH 9.1 2.0 d m i n Water (65% MeOH) 1.O d m i n
Pre-column derivatization, dilution
zQl%aX
250 x 4.6 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbrevianons are listed in Appendix B (p. 745).
106
107 15
2i L
'Cr a-
% h,
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Magnesium (4), calcium (7)
Pharmaceutical electrolytes
Heartcut of samples via switching valves Ultrafiltration, dilution
Wescan 269-024 HS cation (x2)
1 mM ethylenediamine, pH 6 2.0 d m i n
Indirect conductivity
108
SCX 1 250 x 4.6 mm ID
2.0 mM ethylenediamine, 4.0 mM tartaric acid 1.O d m i n
36
Aqueous extraction, Millex filtration, CIS Sep-Pak Aqueous dilution, Millex filtration, CIS Sep-Pak
Waters IC Pak A 50 x 4.6 mm ID
0.6 mM phosphate, 0.4 mM EDTA. pH 5.3 1.2 mVmin
Conductivity, direct spectrophot. at 520 nm after post-column reaction with Neethorin Conductivity
Waters IC Pak A 50 x 4.6 mm ID
Gradient of 10 mM to 25 mM nitric acid 1.2 mumin
110, 111
Aqueous extraction, filtration Cat-ex in hydrogen form
Dionex AS4A
3.0 mM bicarbonate, 2.4 mM carbonate, pH 11.O 1.2 mumin 2 mM succinic acid 3.7 d m i n
Direct spectrophot. at 340 nm after post-column reaction with Fe(II1) perchlorate Conductivity
Magnesium (4.9), calcium (6.5) Electrolyte solution for transfusion
Fluoride (2.0). phosphate (2.6), chloride (5.1). bromide (10.2), monofluorophosphate (18.8). sulfate (27) Phosphate (2,1), monofluorophosphate (4.0), dipolyphosphate (12.3), sulfate (13.0), mpolyphosphate (13.8)
Toothpaste
Toothpaste, raw monofluorophosphate material
Fluoride (2.8), nitrate (7.4). Toothpaste monofluorophosphate (13.6), sulfate (16.2),phosphate (20.5) Formic (1. l), fluoride (1.7), Toothpaste phosphate (4.3, chloride (8), extract monofluoro- phosphate (15), nitrate (18)
Wescan 269031 anion/R-HS 1 0 0 ~ 4 . mmID 1
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
109
112, 113 114
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING IC Solutes (min)
Sample
Sample Rep.
Chloride (2.6). Toothpaste exmct monofluomphosphate (3.3), bicarbonate (4.3, sulfate (11) Fluoride (1 .O), phosphate (1 S ) , Toothpaste monofluorophosphate(2.4) Fluoride (1.2). chloride (1.4), phosphate (3.0). sulfate (3.9)
Toothpaste
System peak (5.0), nitrate (7.3), Dentifrice sluny monofluorophosphate(9.8) Nitrate (7.3). monofluorophosphate(23.4)
Dentiice sluny
Fluoride, phosphate, chloride
Toothpaste
Sonication, centrifugation, dilution Sonication, centrifugation, dilution Dilution, fitration. XAD4 pre-column clean-up
Fluoride
Toothpaste extract
Strontium (5)
Toothpaste
Acetate (2.9), lactate (3.7), chloride (4.8).phosphate (6.6)
Ringers solution, Dilution in eluent electrolyte No. 75
Dilution, filmion
Column
Eluent
Detection
Ref
Wescan anion
4.0 mM phthalate, pH 3.7 2.0 mVmin
Conductivity
3
Interaction ION100 50 x 3.2 mm ID PE c18 silica 83 x 4.6 mm ID
2.0 mM phthalic acid, pH 3.0 Conductivity 1.0 d m i n
115, 116
1.0 mh4 tetrabutvlammonium phthalate, pH 7.3
117
Vydac 302 IC 250x4.6mmID
Conductivity
1 18
mi
0.2 % benzoate, formic acid, pH 5.7 0.9 d m i n 0.05% phthalic acid, sodium borate, pH 5.8 2.0 d m i n 1.0 mM succinic acid 1.0 d m i n
Indirect spectrophot. at 280 nm Conductivity
Conductivity
119
Wescan anion exclusion
3.0 mM sulfuric acid 1.0 d m i n
Conductivity
3
Waters IC PAK guard and cation 50 x 4.6 mm ID Wescan 269-001
Ethylenediamine 1.2 d m i n
Indirect conductivity
120
0.2 mM phthalate, pH 4.11 2.0 mvmin
Indirect
121
SupelcosilLCAmino 250 x 4.6 mm ID
Home-oacked
i?
i! B. B
sb
118
500 x 2.0 mm ID
anion
250 x 4.6 mm ID
spectrophot. at 233 nm
Seep. 487 for notes on the organization of this Table. Seep. 662 for Rderences. Abbreviations are listed in Appendix B (p. 745).
zw
c
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING 1C Solutes (min)
Sample
Sample Prep.
Column
P
Eluent
Hamilton PRP X- 0.3 mM phthalate, pH 6.0 100 (30% ACN) 250 x 4.1 mm ID 1.3 d m i n Chloride (4), phosphate (12). Intravenous Waters IC Pak A 1.42 mM gluconate, 5.82 mM sulfate (1 6) boric acid, 0.25% glycerine, solution 50 x 4.6 m m ID pH 8.5 (12% ACN) 1.2 mVmin Gluconate (3.12), acetate (5.14) Intravenous Extraction, Waters fast h i t 66 rngflphosphoric acid filtration dressings juice 1.0 mumin 150 x 7.8 mm ID Formate (6.1). chloride ( 1 1) Glucose IV TSK-gel IC anion 1.0 mM phthalic acid, pH 4.0 Dilution solution sw 1.Omumin 50 x 4.6 mm ID Chloride (2.8). phosphate (5.7) Ringers solution, Dilution Dionex AS- 1 0.5 mM phthalate, electrolyte No. 0.5 m M borate, pH 9.10 75 and No. 11 2.5 mVmin Chloride (2.9 1) Inawenous Dilution, Waters IC Pak A 1.0 mM lithium phthalate, placebo additive ulnafiltration 50 x 4.6 mm ID pH 6.5 1.2 mVmin Dilution, Millex Dionex AS- 1 Chloride (1.8) Travosol 1.0 mM phthalate, filtration,post0.75 mM borate, pH 9.1 column fiber 3.0 mumin suppressor clean-up Dionex ICE 5.4 mh4 carbonic acid Acetate (11.1) Ringers solution Dilution separator 0.88 W m i n Acetate (8). lactate (9), phosphate (13), chloride (15)
Intravenous solution
Spiking
Detection
Ref
Indirect spectrophot. at 285 nm Conductivity
57. 122
Direct spectrophot. at 210 nm Conductivity
124
Indirect spectrophot. at 250 nm Conductivity
121
123
125
126
Indirect spectrophot. at 280 nm
127
Conductivity
128, 129
Seep. 487for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Intravenous placebo additive Chloride (3.3,phosphate (5.8), Aqueous infusions sulfate (14)
Dilution
2.0 mM nitric acid 1.2 Wmin 1.0mM phthalate, pH 10.0 1.5 ml/min
Dilution
Magnesium (5.0), calcium (9.1) Aqueous infusions
Dilution
Chloride (2.7),phosphate (7.0) Contact lens solution
Dilution
Indirect conductivity Indirect spectrophot. at 260 nm Indirect spectrophot. at 220 nm Indirect spectrophot. at 220 nm Conductivity
126
Sodium (2.6),potassium (4.5) Aqueous infusions
Waters IC Pak C 50 x 4.6 mm ID Oyobunko ASA- 4OOO anion 250 x 4.6 mm ID Oyobunko ASC- 4000cation 250 x 4.6 mm ID Oyobunko ASC- 4000 cation 250 x 4.6 mm ID Waters IC Pak A 50 x 4.6 mm ID
Borate (4.0),chloride (7.7)
Dilution
Wescan anion/R
Conductivity
3
Dilution
Waters fast fruit juice 150 x 7.8 mm ID Waters IC Pak A 50 x 4.6 mm ID Waters Pico Tag
Direct RI
132
Indirect conductivity Inductively coupled plasma-mass
132
Sodium (2.94)
Borate (4.25) EDTA (1.70)
Mercury chloride (S), thimer6sol (preservative with Hg) (17) Fluoride (3,chloride (1 1)
Commercial eyewash Contact lens solution Contact lens solution Contact lens solution Vitamin drops
Dilution
Dilution
c18
Dilution
Wescan 269031 anion/R-HS 100 x 4.1 mm ID
0.1 mM copper sulfate 1.5 Wmin
2.0mM copper sulfate 1.5 Wmin 1.0 mM borate, 1.0mM gluconate 1.2 Wmin 0.1 mM phthalate, pH 11.6 1.7 mVmin 1.0 mM sulfuric acid 1.0 Wmin 10mM Nmc acid 1.2 ml/min 0.06M ammonium acetate, 0.005% 2-mercaptoethanol, 3% ACN, pH 5.3 1.0 Wmin 10mM nicotinic acid 2.7 Wmin
130 130, 131 130, 131 132
133
spectrometry
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
134
$2 o\
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING IC Solutes (min)
Sample
Sample Prep.
Fluoride (1.9)
Vitamin drops
Fluoride (7)
Vitamin powder
Iodide (12)
Vitamin tablet formulation
Dissolution in Wescan 269031 buffer, filtration anion/R-HS 1 0 0 ~ 4 . mmID 1 Wescan 269006 exclusion 300 x 7.8 mm ID Aqueous Waters IC Pak A extraction, 50 x 4.6 mm ID
Iodide
Vitamin tablet exnact Vitamin tablets
Column
Eluent
Detection
Ref
5 mM tetraborate 2.5 mumin
Conductivity
135
3.6 mM sulfuric acid 1.O mVmin
Conductivity
136
Phthalate 1.2 mumin
Conductivity
137
2.0 mM phthalate 1.2 mVmin 0.041 M perchlorate buffer, 0.195 hydroxylamine hydrochloride, pH 4.5 0.47 Wmin
Amperometry at Ag electrude Direct spectrophot. at 550 nm after post-column reaction with PAR Direct spectmphot. at 550 nm after post-column reaction with
138
filmtion
Manganese (3.7), iron (4.7), zinc (6.0)
Vitamin tablets
Chloride (1.8). sodium (3.1), zinc (5.0). sulfate (9), iron (II) (24)
Vitamin extract
Dilution
Waters IC Pak A 50 x 4.6 mm ID Dry ashing, acid Chromasorb 5 pn dissolution silica coated with 2-pyridinecarboxy aldehyde phenylhydrazone 250 x 4.6 mm ID Dry ashing, acid Chromasorb 5 pm dissolution silica coated with 2-pyridinecarboxyaldehyde phenylhydrazone 250 x 4.6 mm ID Dilution in Dionex AS-7 and eluent CG-2 (x2) in series
0.041 M oxalate buffer, 0.1% hydroxylamine hydrochloride, pH 4.5 0.70 mVmin
PAR 5.0 mM oxalic acid, 3.75 mM Conductivity citric acid, lithium hydroxide, pH 4.37 1.0 Wmin
Seep. 487 for notes on the organizationof this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
139
139
140
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING IC Solutes (min)
Sample
Sample Prep.
1-hydroxyethylidene diphosphonic acid (etidronate) (3.6)
Didronel tablets
Homogenization Waters IC PAK A and dissolution 50 x 4.6 mm ID in eluent, filmtion
Valproic acid (8.5)
Depakene tablets Aqueous dissolution, filtration Potassium iodide Grinding, dilution tablets, oral solution
Iodide (1 1.2)
Sulfite (7) Sulfate (2.8)
Medication capsules Antibiotic salts
Sodium (9). potassium (15)
Antibiotic salts
Chloride (4.6), bromide (6.1)
Methamphetamine
Aqueous extraction Drying, dissolution in eluent Drying, dissolution in eluent Aqueous dissolution
Column
Dionex ion exclusion 65 x 6.0 mm ID Alltech Econosphere C18 250 x 4.6 mm ID
Eluent
Detection
7.9 mM nimc acid, pH 2.25 1.0 mI/min
Inductively 141 coupled plasma atomic emission specaometry Conductivity 25
0.5 mM carbonic acid 0.7 mI/min 5.0 mM tetrabutylammonium
Amperometry
hydrogen sulfate, 39.1 mM phosphate buffer, pH 7.0 (15% MeOH) 1.0 ml/min
at dual-series glassy carbon electrodes,
Waters IC Pak A 5 mM phosphate buffer 1.2 ml/min 50 x 4.6 mm ID Dionex anion 3.0 mM bicarbonate, 2.4 mM carbonate separator 150 x 3.0 mm ID 2.25 Wmin Dionex cation 5.0 mM nitric acid 3.0 d m i n separator 250 x 6.0 mm ID YEW S A M 3-125 4.4 mM carbonate, anion-exchanger 1.2 mM bicarbonate 2.0 ml/min
Ref
142
direct spectrophot. at 212 nm Ampemmetry 138 at Ag electmde Conductivity 143 Conductivity
143
conductivity
144
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
rz-. 5
% 00
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING IC Solutes (min)
Sample
Sample Rep.
Column
Eluent
Detection
Ref
Chloride (3.7)
Amphetamine chloride
Dissolution in eluent
SAX-I 125 x 5.0 mrn ID
Direct-indirect specmphot. at 220 nrn
26
Maleate (4.2)
Dexbrornpheniramine maleate
Dissolution in eluent
SAX-1 125 x 5.0 mm ID
Direct-indirect spectrophot. at 220 nrn
26
Hydrogen peroxide as sulfate (7.6)
Cephalothin
Indirect specmphot. at 280 nrn
145
Sulfate (7.9)
Amphetamine sulfate
Pre-column Dionex AS-1 reaction between bisulfite and peroxide Dissolution in SAX-1 eluent 125 x 5.0 mm ID
Direct-indirect spectrophot. at 220 nrn
26
Selenate (6.77)
Drugs (e.g. prednisolone)
0.7 g/l citric acid, 0.05 g/l cetrimide, pH 5.5 (30% MeOH) 1.0 mumin 0.7 gjl citric acid, 0.05 gl cetrimide, pH 5.5 (30% MeOH) 1.0 rnurnin 1 mM phthalate, 0.75 rnM borate (10% MeOH) 3.0 mumin 0.7 g/l citric acid. 0.05 g/l cemmide. pH 5.5 (30% MeOH) 1.O ml/min 4 mM bicarbonate, 4 mM carbonate 1.5 ml/min
Conductivity
146
Naphthyl sulfonate (9.2)
Dexmpropoxyphene napsylate
0.7 citric acid, 0.05 g/l cemmide, pH 5.5 (30% MeOH) 1.0 mvmin
Direct-indirect spectrophot. at 220 nm
26
Oxygen flask combustion, permanganate oxidation, reinjection of fraction from TAC- 1 Column Dissolution in eluent
Dionex AS-4 250 x 4 mm I D
SAX- 1 125 x 5.0 mm ID
See p . 487 for notes on rhe organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
c Y,
9
TABLE 19.4 ( C 0 " U E D ) . ANALYSIS OF PHARMACEUTICALS USING IC
s:
Solutes (min)
Sample
Sample Prep.
Colunm
Eluent
Detection
Ref
Acetic (6)
3-acetoxymethyl cepharosporanic acid injection Paracetam01
Dilution
Amberlite XAD-4 800 x 3.0 rnm ID
1.0 mM bicarbonate 2.0 d m i n
Conductivity
147
Dilution in buffer
Dionex ion exclusion 250 x 5 mm ID Dionex CG-2 (x2) in series 100 X 4.0 mm ID
0.1 mM hydrochloric acid 0.86 mumin
Conductivity
148
8.0 mM hydroxylamine hydrochloride 2.0 d m i n
Dilution
Waters IC Pak C 50 x 4.6 mm ID Dionex AS-I
0.5 mM ethylenediamine, nimc acid, pH 6.2 0.6 d m i n 0.01 M sodium nitrate
Direct spectrophot. at 254 nm, conductivity Indirect conductivity
Acetate N-methyl pyrrolidine (4.2)
Antibiotic
Magnesium (5.8), calcium (9.3) Drug samples
Dilution
Iodide (8.7)
Sterilizing solution
Dilution
Iodide (10.95)
sanitizing solution
Dilution, Amino Waters IC Pak A Sep-Pak 50 x 4.6 mm ID
Fluoride (10)
Mouthwash
Dilution
Citrate, bisulfite
Local anaesthetic solution
Wescan 269006 exclusion 300 x 7.8 rnm ID Wescan anion exclusion
4.0 mM phthalate, pH 6.65 2.0 d m i n
3 mM sulfuric acid 0.7 mVmin Sulfuric acid, pH 2.3 0.5 d m i n
&. &
b
B
2
f.
0
a
149
g. 0
z 150
Ampemmetry 151 at Ag electrode, +0.3V Ammmew 152 at Ag electrohe, +O.lOV Conductivity 153 Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
$ 2
3, 154
TABLE 19.4 (CONTINUED). ANALYSIS OF PHARMACEUTICALS USING IC
Column
Solutes (min)
Sample
Sample Prep.
Lactic (5.8)
Lysimeter leach solution
Chloroform Coated Supelcosil biocide addition, LC-18 dilution in eluent 150 x 4.6 mm ID
Nitrite (1.4)
Germicide solution
Dilution, C18 Sep-Pak
Water (3.8)
..\ntinucrobial solution
Dilution
Sulfate (12.6)
Cosmetic products
Ethylenediaminc (6.8)
Livestock iodine supplement
Dissolution in ethanolic hydroxide, addition of peroxide, dilution Aqueous dissolution
Alipharic cxboxylic acids - C6 (51, C7 (8), C8 (lo), C12 (20)
Cologne
Dilution
Eluent
Detection
Ref
0.5 mM salicyclic acid adjusted to pH 5.5 with "HAM (5% ACN) 1 .O mumin
Indirect specmphot. at 293 nm
155
Direa specmphot. at 214 nm Conductivity
156 157
Conductivity
158
Conductivity
159
Conductivity
160
zorbax ODs
5 mM sulfuric acid (50% MeOH) 1.5 ml/min 12 mM sulfuric acid in Aminex 50WX4 methanol 21x9.0mmID 1.5 mVmin SSC-6-250Banion 3.0 mM carbonate 1.5 mumin separator 250 x 6.0 mm ID 250 x 4.6 m m ID
Dionex cation pre-column 50 x 4.0 mm ID Dionex MPICNS 1 20Ox4mmID
4.0 rnh4 hydrochloric acid, 2.5 mM zinc chloride 1.53 ml/min 0.03 M h y h h l o r i c acid, 24% ACN, 5% MeOH to 0.1 M hydrochloric acid, 60% ACN, 24% MeOH
cent
1.0 d m i n
P5 Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are Iisted in Appendix B (p. 745).
TABLE 19.4 ( C 0 " U E D ) .
3-.
ANALYSIS OF PHARMACEUTICALS USING IC
P
Solutes (min)
Sample
Sample Prep.
Column
Aluminium, zirconium
Anti-perspirant
Acid reflux, evaporation to dryness with perchloric acid
Du Pont PLRP-S 1.0 mM methylfum150 x 4.6 mm ID hydroxamic acid, 0.01 M perchloric acid (25%ACN) 1.0 d m i n Wescan 269004 1 mM ethylenediaminecitrate, cation 2 mM cimc acid, pH 4.5 250 x 2.1 mm ID 1.7 mVmin
Aluminium (5)
Manganese nunitional product
Eluent
Detection
Ref
Direct
161
spectrophot. at 304 nm
g u
i3.
I
2a. Indirect conductivity
162
fi
$R
8.i:
Seep. 487 for notes on the organization of this Table. Seep. 662 for References. Abbreviations are listed in Appendix B (p. 745).
Chapter 19
662
19.2 REFERENCES 1 2 3 4
5
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Gaffney M.H. and Cooke M., Anal. Proc., 22 (1985) 25. Haak K.K., Rich W.E. and Johnson E., in Kabra P.M. and Marton L.J. (Eds.), Clinical Liquid Chronzarography, Vol. 11, CRC, Boca Raton, 1984, p. 155. Shintani H. and Ube S., J. Chromarogr., 344 (1985) 145. Miller M.E. and Cappon C.J., Clin. Chem., 30 (1984) 781. Rychtman A.C., LC.GC, 7 (1989) 508. Mackie H., Speciale S.J., Throop L.J. and Yang T., J. Chromarogr., 242 (1982) 177. Wescan Application #13S. Osterloh J. and Goldfield D., J. Liq. Chromarogr.,7 (1984) 753. Toida T.. Togawa T., Tanabe S. and Imanari T., J. Chromatogr., 308 (1984) 133. Verma K.K., Sanghi S.K., Jain A. and Gupta D., J. Chromatogr., 457 (1988) 345. Waters Ion Brief No. 88106. Buchberger W., J. Chromarogr., 439 (1988) 129. Buchberger W. and Winsauer K., Mikrochirn. A m , 1985,111 (1986) 347. Hurst W.J., Stefovic J.W. and White W.J., J. Liq. Chromarogr., 7 (1984) 2021. Hurst W.J., Evans S.L., White W.W. and Miller K.L., LC.GC, 6 (1988) 5 . Michigami Y., Takahashi T., He F., Yamamoto Y. and Ueda K., Analysr (London), 113
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Kawanishi T., Togawa T., Ishigami A., Tanabe S. and Imanari T., Bunseki Kagaku, 33
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Reiter C., Muller S. and Muller T., J. Chromarogr., 413 (1987) 251. Wilshire J.P. and Brown W.A., Anal. Chem., 54 (1982) 1647. Itoh H., Shinbori Y. and Tarnura N., Bull. Chem. SOC.Jpn., 59 (1986) 997. Wheals B.B., J. Chronrarogr., 262 (1983) 61. Shintani H., Clin. Chern., 32 (1984) 406. Shintmi H., J. Chromarogr., 341 (1985) 53. Shintani H., Tsuji K. and Oba T., Bunseki Kagaku, 34 (1985) 109. Hajos P., Kener A. and Horvath M., Clin.Chem., 33 (1987) 617. Small H., Stevens T.S. and Bauman W.C., Anal. Chem., 47 (1975) 1801. Nordmeyer F.R., Chan G.M. and Ash K.O., Clin. Physiol. Biochem., 2 (1984) 159. Nordmeyer F.R., Hansen L.D., Eatough D.J., Rollins D.K. and Lamb J.D., Anal. Chem.,
34
Rehfeld S.J., Loken H.F., Nordmeyer F.R. and Lamb J.D., Clin. Chem., 26 (1980) 1232. Lamb J.D., Hansen L.D., Patch G.G. and Nordrneyer F.R., Anal. Chem., 53 (1981) 749. Nagashirna H., Bunseki Kagaku, 35 (1985) 7. Toei J.-I., Analyst (London), 113 (1988) 247.
52 (1980) 852.
3s 36 37
Clinical and PharmaceuticalApplications 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77
663
Anderson C., Clin. Chem., 22 (1976) 1424. Nordmeyer F.R. and Hansen L.D., Anal. Chem., 54 (1982) 2605. Ong C.N., Ong H.Y. and Chua LH., Anal. Biochem., 173 (1988) 64. Takayanagi M. and Yashiro T., J. Chromatogr., 374 (1986) 378. Urasa I.T. and Nam S.H., J . Chromatogr. Sci., 27 (1989) 30. Matsushita S., Anal. Chim. Acta, 172 (1985) 249. Moore H., Riusech D.J. and Duer W.C., J. Vet. Res., 2 (1987) 297. Woo D.J. and Benson J.R., Am. Clin. Prod. Rev., January (1984) 20. Woo D.J. and Benson J.R., LC, 1 (1983) 238. Buchanan D.N. and Thoene J.G., Anal. Biochern., 124 (1982) 108. Interaction, organic acid analysis column OW-801, 1982. Waters ILC Series Application Brief No. 7001. Singh R.P. and Nancollas G.H., J . Chromatogr., 433 (1988) 373. Singh R.P., Clin. Chem., 34 (1988) 2390. Turkelson V.T.and Richards M., Anal. Chem.,50 (1978) 1420. Chana B.S. and Smith N.J., Anal. Chim. Acta, 197 (1987) 177. Low G.K.-C., Batley G.E. and Buchanan S.J., Chromatographia, 22 (1086) 292. Low G.K.-C., Batley G.E. and Buchanan S.J., Proc. 9th. Awt. Symp. Anal. Chem., 1987, p. 31. Imanari T.. Tanabe S., Toida T. and Kawanishi T., J . Chromatogr., 250 (1982) 55. Croft M.Y. and Haddad P.R., Australian Association of Clinical Biochemists Monograph Series, 1986, p. 138. Haddad P.R., Alexander P.W., Croft M.Y. and Hilton D.F., Chromatographia, 24 (1987) 487. Orwell R.L., Scurr D.S.. Smith A. and Robertson W.G., Fortschr. Urol. Nephrol., 20 (1982) 263. Classen A. and Hesse A., J. Clin. Chem. Biochem., 25 (1987) 95. Robertson W.G. and Scurr D.S., Clin. Chem. Acta, 140 (1984) 97. Robertson W.G.,Scurr D.S., Smith A. and Orwell R.L., Clin. Chem. Acta, 126 (1982) 91. Mayer W.J., McCarthy J.P. and Greenberg M.S., J. Chromatogr. Sci., 17 (1979) 656. Low G.K.-C., Batley G.E. and Buchanan S.J., Anal. Chim. Acta, 197 (1987) 327. Hackzell L., Rydberg T. and Schill G.,J. Chromatogr., 282 (1983) 179. Schiff L.J., Pleva S.G.and Sarver E.W., in Sawicki E. and Mulik J.D.(Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol.11, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 329. Dionex Application Note 36. Singh R.P. and Nancollas G.H., Anal. Lett., 19 (1986) 1487. Menon M. and Mahle C.J., Clin. Chem., 29 (1983) 369. Mahle C.J. and Menon M.., J. Urol., 127 (1982) 159. Kagedal B., Kallberg M., Martensson J. and S o r b B., J. Chromatogr., 274 (1983) 95. Singh R.P.and Nancollas G.H., Kidney Int., 28 (1985) 985. Ogawa Y., Morozumi M., Tanaka T. and Yamaguchi K., J . Urol., 135 (1986) 178. Pilkington A.E. and Waring R.H.,Med. Sci. Res., 16 (1988) 35. Witter J.P., Gatley S.J. and Balish E., J. Chromatogr., 229 (1982) 450. Uchiyama S., Tohfuku Y., Suzuki S. and Muto G.,Anal. Chim Acta, 174 (1985) 313. Stray H., Kjemi, 4 (1981) 30.
Chapter I9
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87 88 89
90 91 92 93 94 95 96 97 98 99
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(1985) 325. 100 Linhardt R.J., Rice K.G.,Merchant Z.M., Kim Y.S. and Lohse D.L., J . Biol. Chem., 261 (1986) 14448. 101 Bellin M.E., Wentworth B.C. and Ax R.L., Eiol. Reprod., 37 (1987) 293. 102 Bellin M.E., Veldhuis J.D. and Ax R.L., Eiol. Reprod., 37 (1987) 1179. 103 Shimada K. and Shimahara K., Hakko Kogaku Kaishi, 64 (1986) 407. 104 Karr D.B.,Waters J.K. and Emerich D.W., Appl. Environ. Microbiol., 46 (1983) 1339. 105 Iwinski G. and Jenke D.R., J. Chromatogr., 392 (1987) 397. 106 Jenke D.R., J . Chromurogr., 437 (1988) 231. 107 Downey B.P. and Jenke D.R., J. Chromarogr. Sci., 25 (1987) 519. 108 Jenke D.R., Anal. Chem., 59 (1987) 624. 109 Potter J.J., Hilliker A.E. and Breen G.J., J . Chromarogr.,367 (1986) 423. 110 Waters Ion Brief No. 88103. 111 Waters IC Lab. Report No. 271. 112 Talmage J.M. and Biemer T.A., 1.Chromurogr., 410 (1987) 494. 113 Lipski A.J. and Vairo C.J., Can. Res., 13 (1980) 45. 114 Wescan Application #252. 115 Benson J.R., Woo D. and Kitagawa N., LC. 2 (1984) 398. 116 Lee D.P., LC, 2 (1984) 828. 117 Perrone P.A. and Grant J.R., Res. Dev., September (1984) 96.
Clinical and Phumceurical Applications
118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157
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Chen S.S., Lulla H., Sena F.J. and Reynoso V.. J. Chrontatogr. Sci., 23 (1985) 355. Fritz J.S., DuVal D.L. and Barron R.E., Anal. Chem.. 56 (1984) 1177. Waters ILC Series Application Brief No. 1002. Jenke D.R. and Raghavan N.. J. Chromatogr. Sci.. 23 (1985) 75. Haddad P.R. and Croft M.Y., Chromatographiu,21 (1986) 648. Waters ILC Series Application Brief No. 1003. Waters IC Lab. Report No. 292. Hoshino Y., Saitoh H. and Oikawa K.,Bunseki Kagaku, 32 (1983) 273. Waters IC Lab. Report No. 266. Brown D., Payton R. and Jenke D., Anal. Chem, 57 (1985) 2264. Itoh H. and Shinbori Y., Chem Lett., 12 (1982) 2001. Itoh H. and Shinbori Y., Bull. Chem SOC.Jpn., 58 (1985) 3244. Ishikawa M., Yamamoto M., Masui T., Hawakawa K..Miyazaki M., Nakazawa H. and Fuzita M., Bunseki Kagaku. 36 (1986) 309. Hayakawa K.,Hiraki H., Choi B. and Miyazaki G., Hokuriku Koshu Eisei Gakkaishi, 10 (1983) 24. Waters IC Lab. Report No. 257. Bushee D.S., Analyst (London), 113 (1988) 1167. Wescan Application #222a. Wescan Application #222b Wescan Application #222c. Waters ILC Series Application Brief No. 1001. Jandik P., Cox D. and Wong D., Int. Lab., June (1986) 66. Sirnonzadeh N. and Schilt A.A., Talunta. 35 (1988) 187. Jones V.K. and Tarter J.G., Analyst (London),113 (1988) 183. Forbes K.A., Vecchiarelli J.F.. Uden P.C. and Barnes R.M., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromatography,Vol. I , Century International, Inc., Franklin, MA, 1989, p. 487. Lookabaugh M., Krull I.S. and LaCourse W.R., J. Chromurogr.,387 (1987) 301. Whittaker J.W. and Lernke P.R., J. Pharm. Sci., 71 (1982) 334. Suzuki S.-I., Tsuchihashi H., Nakajima K., Matsushita A. and Nagao T., J. Chronmtogr., 437 (1988) 322. Jenke D.R., J. Chromutogr. Sci., 24 (1986) 352. Murayama M., Suzuki M. and Takitani S.. J. Chronmtogr.,463 (1989) 147. Itoh H., Shinbori Y. and Tamura N., Bunseki Kagaku, 32 (1983) 571. Kreilgard B. and Anderson F.M., Arch. Pharm. Chem, Sci. Ed, 12 (1984) 85. Franklin (3.0. Am . Lab., 17 (1985) 65. Waters IC Lab. Report No. 253. Dionex Application Note 37. Waters IC Lab. Report No. 308. Wescan Application #90. Wescan Application #75. Barkley D.J., Dahms T.E.and Villeneuve K.N., J. Chromatogr.,395 (1987) 631. Skelly N.E.,Oornens A.C. and Schuurhuis F.G., J. Chromatogr.,284 (1984) 503. Stevens T.S., Chritz K.M. and Small H.,Anal. Chem, 59 (1987) 1716.
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158 Nakamura K. and Morikawa Y., Bunseki Kagaku. 32 (1983) 224. 159 Buechele R.C. and Reutter D.J., Anal. Chem., 54 (1982) 21 13. 160 Slingsby R.W., J . Chromatogr., 371 (1986) 373. 161 Palmien M.D. and Fritz J.S.,Anal. Chem., 59 (1987) 2226. 162 Wescan Application #316.
Chapter I9
667
Chapter 20 Analysis of Metals and Metallurgical Solutions 20.1 OVERVIEW to
The analysis of metals and metallurgical solutions using IC is presented according the scheme shown in Fig. 20.1.
METALS AND METALLURGICAL APPLICATIONS OF IC
i
Metal plating solutions (Table 20.1)
Metals, metallurgical solutions (Table 20.2)
Fig. 20.1 Applications of IC in the analysis of metals and metallurgical solutions.
TABLE 20.1
ANALYSIS OF METAL PLATING SOLUTIONS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Hypophosphite (3.8), chloride (S.O), phosphite (7.9). sulfate (23) Chlonde (4.31), nitrite (5.77), bromide (7.54),nitrate (9.2) Chlonde (2. l), cyanate (2.9), chlorate (5.8), sulfate (9.2) Phosphate (12). chloride (16), chlorate (18). nitTate (21) Inositol-2-phosphate (1.9), glucose-6-phosphate (2.3), phosphate (4.4) Nitrate (2.3), tetrafluoroborate (5)
Plating solution
hlution
Plating bath solution
Dilution
Plating solutions Hypochlorite oxidation, dilution Plating bath Diluhon solution Plating and cleaning solutions Plating bath -
Sulfate (2.3). chromate (4.4)
Electroplating bath solution
-
Cyanide (3.05)
Plating bath solution
Dilution, pH adjustment
Sodium (4.27), ammonium
Plating bath solution
Dilution
Dionex anion separator 150 x 3.0 mm ID Waters IC Pak Anion HC 150 x 4.6 mm ID Dionex AS-4 Wescan anion 250 x 4.6 mm ID Dionex AS-5 250 x 4.0 mm ID
Wescan 269013 anion/HS 100 x 4.6 mm ID Dionex anion separator 150 x 3.0 mm ID Waters IC Pak A 50 x 4.6 mm ID
Ref
Detection ~~
~
3.0 mM bicarbonate, 2.4 mM carbonate 112 mVhr 1.3 mM tetraborate, 5.8 mM boric acid, 1.4 mM gluconate (128 ACN) 2.0 mumin 2.2 mM carbonate I .5 mumin Phthalic acid, pH 2.7 2.0 mumin 3.0 mM bicarbonate, 2.4 mM carbonate 0.6 mVmin 4.5 mM phthalate, 0.5 mM phthalic acid 3.5 d m i n 6.0 mM carbonate
5.0 mM hydroxide 0.9 mumin
Conducbvity
1
Conductivity
2
Conductivity
3
Conductivity
4
Conductivity
5
Conductivity
6
Conductivity
7
Ampemmemy 8 at Ag electrode,
+0.19V (6.01)
Waters IC Pak C 50 x 4.6 mm ID
2.0 mM nitric acid, 0.05 mM disodium EDTA 1.2 d m i n
Indirect conductivity
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
2
3
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC ~
Solutes (min)
Sample
Sample Prep.
Column
Eluent ~~
Dionex AS-4
Gold (I) cyanide complex (2.3)
Dionex MPIC separator 250 x 4.0 mm ID
Chloride (0.9), nitrate (1.2), Plating solution sulfate (8.5), EDTA complexes lead (1.4),nickel (2.7), zinc (2.9),copper (7.8) Fluoride (1.7), chloride (2.2), Chromic acid phosphate ( 3 . 3 , sulfate (5.8), chromate (14) Chloride (3.05),fluoride (6.08),Chromic plating sulfate (9.07),chromate (16) bath solution
Ref
E
~
Cyano complexes - nickel (4.4), Plating solutions Dilution cobalt (5.4), iron (111) (5.7), gold (I) (5.9), iron (11) (6.9), gold (HI) (14.4) Copper (4.45),zinc (9.44), Plating bath Dilution cobalt (14.52), iron (II) (19.35). solution manganese (24.32)
Plating solutions Dilution, addition of cyanide
Detection
~~
Waters c18 pBondapak 300 x 3.9 mm ID
Dilution, addition of EDTA
Dionex AS-5 250 x 4.0 mm ID
Dilution
Dionex anion guard 50 x 4.0 mm ID
Dilution, filtration
Waters fast fruit juice (x2) and IC Pak A 150 x 7.8 mm ID 50x 4.6 mm ID
2.0 mM tetrabutylammonium hydroxide, 0.2 mM carbonate (40%ACN) 1.5 mumin 2.0 mM octanesulfonate, Direct 2 50 mM tartaric acid, pH 3.4 spectrophot. at 1.0 mVmin 520 MI after post-column &action with PAR 2.0 mM tetrapropyl Conductivity 5,9 ammonium hydroxide, 2.0 mM carbonate (30% ACN) 0.6 mumin 1.5 mM bicarbonate, Conductivity, 5 1.2 mM carbonate direct 2.0 mumin spectrophot. at 250 nm 3.0 mM bicarbonate, 2.4 mM Conductivity 10 carbonate switched to 5.4 mM carbonate at 7.5 min 3.0 mVmh 0.63 mM phthalic acid, Conductivity 11 1.3 mM phthalate, lithium hydroxide, pH 8.0 1.0 nll/min
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 74.5).
B-
=1
P
9 0
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Chloride (2.3), bromide (3.3), fluoride (7.9, sulfate (13.0)
Chromic plating bath solution
Dilution, filmtion
1.0 mM octanesulfonic acid and 4.0 mM ocnnesulfonate 1 .O mumin
Conductivity
12, 13
Chloride (2.0), sulfate (4.9, chromate (13.5)
Chromic acid plating solution
Dilution
Waters fast fruit juice (x2) and 1C Pak A 150 x 7.8 mm ID 50 x 4.6 mm ID Dionex AS-5 250 x 4.0 mm ID
Conductivity
5
Chloride (1.8). sulfate (3.3), chromate (12)
Chromic acid
Dilution
3.0 mM bicarbonate, 2.4 mM carbonate 2.0 ml/min 5.4 mM carbonate 3.0 mumin
Conductivity
10
Conductivity
14, 15
Conductivity
16
Conductivity
17
Conductivity
18, 19
Conductivity
20
Hexafluorosilicate (l.O), sulfate Chromate bath ( 3 3 , chromate (12.0)
Dilution
Dionex anion guard 50 x 4.0 mm ID Dionex CS-5 canon separator
Dilution Chloride (2.82). sulfate (10.47). Chromic acid etchant solutions chromate (19.69)
Waters IC Pak A 50 x 4.6 mm ID
Sulfate (4.5). chromate (8.16)
Chrome plating bath solution
Dilution in eluent
Waters IC Pak A 50 x 4.6 mm ID
Sulfate @.I), chromate (5.5)
Chromium electroplating
Dilution
Dionex anion pre-column (x2) 50 x 4.0 mm ID Wescan 269019 RP/R 100 x 4.6 mm ID
bath Chromate (3), sulfate (5)
Chromic acid plating bath
Dilution
1.0 mM bicarbonate, 5.0 mM carbonate 1.7 mumin 1.0 mM lithium phthalate, pH 7.5 1.2 mumin 2.6 mM tetraborate, 11.6 mM boric acid, 2.8 mM gluconate (12%ACN) 1.2 ml/min 8.0 mM carbonate 5.0 d m i n 2 mM tetrabutylammonium perchlorate (10% ACN)
2.0 d m i n
Seep, 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
%
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC
(D
E kl
Solutes (min)
Sample
Fluoride, sulfate
Qlromium
Sample Prep.
Column
Eluent
Detection
Ref
Dionex anion separator 250x3.0mmID
3.0 mM bicarbonate, 2.4 mM carbonate llOml/hr
Conductivity
21
Dilution in acetic Waters IC Pak A acid, Cis Sep- 50 x 4.6 mm ID
0.54 gA boric acid, 0.14 ml/l Conductivity gluconic acid, 0.16 gA lithium
22
Pak, filtration
hydroxide, 2 ml glycerine (12.5%ACN) 1.2 mVmin 1.3 mM tetraborate, 5.8 mM boric acid, 1.4 mM gluconate (12%ACN) 1.O Wmin 0.54 gA boric acid, 0.14 ml/l gluconic acid, 0.16 g/l lithium hydroxide, 2 ml glycerine (12.5%ACN) 1.0 Wmin 1 mM phthalic acid, pH 11 1 flmin
plating bath Sulfate (8.89)
Chromic plating bath solution
Sulfate (6.4)
Chmme plating bath solution
Dilution, methanol oxidation of Cr (III), filtration
Waters IC Pak A 50 x 4.6 mm ID
Chromate (7.67)
Chmmeplating bath solution
-
Waters IC Pak A 50 x 4.6 mm ID
Fluoroborate (7)
Chromicacid
-
Dionex AS-5
Fluoroborate (3)
Chromicacid
-
Fluoroborate (9)
Chromicacid
-
Hamilton PRPXlOO 150 x 4.1 mm ID Extech Cs
1 mM phthalic acid, pH 6.0 1 Wmin
1mM tetrabutylammonium phthalate, pH 6.0 (10%MeOH) 1mumin
3 g c
4.
B
Bg
Conductivity
13
Direct spectrophot.at 405 nm
23
Indirect spectrophot. at 280-285 nm Indirect spectrophot. at 280-285 nm Indirect spectrophot. at 280-285 nm
24
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
8
g. 1
24 24
9 c
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC Solutes (min)
Sample
Sample Prep.
Copper (4.281, lead (4.78). zinc Chromic acid Dilution, pH (6.58).nickel (7.05).cobalt etchant solutions adjustment ( 8 . 9 3 , cadmium (10.25). iron (11) ( I 1.62). 1llang.lnr.Se ( 11.12)
Column
Eluent
Detection
Ref
Waters c18 pBondapak 150 x 3.9 mm ID
1.0 mM octanesulfonate, 50 mM tartaric acid, pH 3.4
DkCt
16
Dionex CS-5
Hesa-aquo compleses chromium (111) (3.3), iron (111) (j.9) Aluminium (5.53)
Arsenite (14), anenate (19)
9 N
0.75 mVmin
2.0 mM pyridinedicarboxylic acid, 2.0 mM disodium hydrogen phosphate, 10 mM sodium iodide, 50 mM ammonium acetate, 2.8 mM lithium hydroxide, pH 6.7 1.0 mVmin 0.283 mM nimc acid 2.3 mVmin
Chromium Dilution plating and polishing solutions Chromic acid Dilution, pH etchant solutions adjustment
Dionex CG-2
Waters CIS pBondapak 150 x 3.9 mm ID
1.0 mM octanesulfonate, 50 mM tartaric acid, pH 3.4 0.75 mVmin
Gold plating bath Dilution solution
Wescan anion/R
0.6 gA sodium hydroxide, 1.O mM taruate 0.2 d m i n
spectrophot. at 546 nm after post-column reaction with PAR
Direct
14, 15
spectrophot. at 520 nm after post-column reaction with methanolic diphenylcarbohydrazide Direct 25 spectrophot. at 330 and 570 nm, AAS Direct 16 spectrophot. at 570 nm after post-column reaction with pyrocatechol violet Conductivity 26
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
fB
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC
if; u
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
i ;
P
%t Arsenite (7.8)
Dilution
Polyphosphonate- Dequest 2006 (4) Cyanide (3,gold (1) cyanide (lo), gold (111) cyanide (31))
Gold plating baths (noncyanide) Gold-plating bath Gold plating solutions
Cyanide complexes - gold (I! (5.4), gold (111) (1 1.91
Gold cyanide plating baths
Dilution in eluent
Dionex MPICNS1 separator
Gold cyanide complex (4.3)
Gold plating bath
-
Cobalt cyanide complex (14.2)
Gold cyanide plating baths
Aqueous dilution
Wescan 269019 RPm 100 x 4.6 mm ID Dionex MPICNS1 separator
Hypophosphite (2.3), phosphite (3.3, phosphate (1 1.0) Sulfamate (1.8), chloride fZ.O), nitrate (2.8), sulfate (9.7)
Dilution
-
Electroless nickel Dilution bath Nickel sulfamate Dilution, cat-ex bath resin in hydrogen form Sulfamate (2.1), chloride (2.5), Nickel sulfamate Dilution sulfate (8.4) plating bath
Dionex AS-1 ion exclusion
1 mM sulfuric acid (1% ACN) 1.0 mvmin Waters IC PAK A 12 mM nitric acid 50 x 4.6 mm ID 1.5 d m i n Waters PIC A, ACN Waters Rad Pak c18 1.0 d m i n
Dionex AS-3 Wescan 269029 anion/R 250 x 4.1 mm ID Dionex A S 4
2.0 mh4 tetrabutylammonium hydroxide, 0.2 mM carbonate (40%ACN) 1.0 d m h 0.7 mh4 tetrabutylammonium perchlorate (30% ACN) 1.7 ml/min 2.0 mM tetrapmpylammonium hydroxide (10% ACN) 1.0 mvmin 3.0 mM carbonate, adjusted to pH 12 with hydroxide 2 mM phthalate, pH 4.5 1.7 mVmin
3.0 mM bicarbonate, 2.4 mM carbonate
Ampematry
27
(pulsed) at Au electrode DirectRI
28
$ Do
Direct spectrophot. at 214 m Conductivity
29
Conductivity
32
Conductivity
30
Conductivity
33
Conductivity
24
Conductivity
33
See p . 487 for notes on the organization of this Table. Seep, 691 for References. Abbreviations are listed in Appendix B (p. 745).
5
g
s[
30, 31
9 w
TABLE 30.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC
-4 01
p.
Solutes (min)
Sample
Phosphite (5.2). hypophosphite (6.3)
Electroless nickel bath
Chloride (2.7), sulfate (10.6)
Electrolytic nickel bath
Borate (1.2). sulfamate (2.2)
Sample Prep.
Dilution, cat-ex resin in hydrogen form Nickel sulfamate Dilution bath
Borate (8.5). chloride (17)
Electrolytic nickel bath
Cimc (15). succinic (21)
Electroless nickel Dilution plating bath Nickel plating Dilution solution
Citrate (12). lactate (17) Cimc (4), malic ( 5 )
Electroless nickel Dilution in bath eluent
Boric acid (8.6)
Nickeliiin plating bath NickeUin plating bath
Sodium lauryl sulfate (15)
Ethylene thiourea (4.5)
Dilution Dilution
Electroless nickel plating baths
Column
Eluent
Detection
Ref
Wescan 269029 aniom 250 x 4.1 mm ID Wescan 269029 anionm 250 x 4.1 mm ID Wescan 26903 1 anion/R-HS 100 x 4.1 mm ID Wescan 269029 anionm 2 5 0 ~ 4 . 1mmID Dionex AS-2 ion exclusion Home-packed ion exclusion 300 x 9.0 mm ID Wescan 269006 exclusion 300 x 7.8 mm ID Dionex AS-I ion exclusion Dionex MPICNS1 separator
20 mM succinic acid 2.8 mumin
Conductivity
35
2 mM phthalate, pH 4.5 1.7 mumin
Conductivity
36
5 mM hydroxide, 0.1 mM benzoate 1.5 mumin 5 mM hydroxide, 0.1 m i benzoate 1.6 mumin 1.0 mM hydrochloric acid
Conductivity
37
Indirect conductivity
38
Conductivity
33
1.0 mM hydrochloric acid
Conductivity
39
3.2 mM nitric acid 1.2 mumin
Conductivity
40-42
50 mM mannitol 0.75 mumin 10 mM ammonium hydroxide, pH 12 (284 ACN) 1.0 mVmin Water, 1% acetic acid, 5% MeOH 0.8 d m i n
Conductivity
33
Conductivity
33
Direct spectrophot. at 254 nm
43
Dionex MPICNS1 separator
See p . 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviationsare listed in Appendix B (p. 745).
TABLE 20.1 (CONTINUED).ANALYSIS OF METAL PLATING SOLUTIONS USING IC ~~~
Solutes (min)
Sample
Thiocarbanilide (2.7)
E l m l e s s nickel bomhydride plating baths NickeVmn Dilution plating bath
Saccharin (12)
Sample Prep.
Copper (4.43, lead (5.25), zinc NickeVtin plating Dilution bath solution (8.78). nickel (9.33, cobalt (13.78), iron (11) (19.12), manganese (24.72)
Column
Eluent
Detection
Dionex MPICNS1 separator
Water, 0.3% acetic acid, 39% MeOH, 3 1% ACN
Direct 44 spectrophot. at 254 nm Conductivity 33
Dionex MPICNS1 separator Waters cis pBondapak 150 x 3.9 mm ID
Lead (2.13). copper (2.95), cadmium (4.01), cobalt (6.77), nickel (12.53)
Electroless nickel plating bath
Dionex CS-5
Copper (3.7). cadmiudmanganese (4.8), nickel (6.7)
NickeVmn plating bath
Dilution
Dionex AS-4
Nickel (2.9), iron (II) (15.4)
N i ckebn plating bath
Dilution
Dionex CS-2
0.8 ml/min 2.0 mM tetramethyl-
ammonium hydroxide, pH 12 (5% ACN) 1.0 mllmin 2.0 mM octanesulfonate, Direct 50 mh4 tartaric acid, specmophot. at 520 nm after pH 3.4 post-column 1.0 d m i n reaction with PAR Pyridine-2,6-dicarbxylicacid Direct spectrophot. after postcolumn reaction with PAR Direct 25 mM oxalic acid spectrophot. at 520 nm after post-column reaction with PAR 10 mM oxalic acid, Direct specmphot. at 7.5 mM cimc acid, pH 4.3 520 nm afm post-column reaction with PAR
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
Ref
45
46
33
33
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC
9
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Nickel (3.0). cobalt (4.8)
Elecnoless nicke&on plating bath
Dilution
Dionex CS-2
25 mM oxalic acid
Direct
33
spectrophot. at 520 nm after postcolumn
kaaion with PAR Formate (0.9), chloride (1.5), tartrate c].8), sulfate (12)
Elecnoless copper bath
Dilution
Wescan 269029 aniOdR 250 x 4.1 mm ID
2 mM phthalate, pH 4.5 1.5 d m i n
Conductivity
47,41
Tartaric (10.0), formic (13.6). acetic (15.9) Phosphate (4.0), nitrate (6.1)
Electroless copper bath
Dilution
1.0 mM hydrochloric acid
Conductivity
48, 5
copper pyrophosphate plating bath Copper sulfate plating bath
Dilution
Dionex AS-1 ion exclusion Dionex AS-3
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity
48
Dilution
Dionex AS-4
2.8 mM bicarbonate, 2.3 mM carbonate
Conductivity
48
Acid copper sulfate plating solution
Dilution
Dionex AS-4 250 x 4.0 mm ID
4.0 mM bicarbonate switch to 3.0 mM bicarbonate, 2.4 mM
Conductivity
5
neCtm1ytic copperbath
Dilution
Conductivity
49
copper
Dilution
Conductivity
50
Chloride (2.1). sulfate (6.0) Chloride (4.5). sulfate (12)
Chloride (3), sulfate (10) Orthophosphate (10.4)
nitrate
pyrophosphate bath
Wescan 269029 aniOdR 2 5 0 ~ 4 . 1mmID
Wescan 269001 anion 250 x 4.6 mm ID
carbonate 2.0 d m i n 2 mM phthalate, pH 4.5 1.6 ml/min 10 mM phthalic acid 1.5 mVmin
See p . 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC ~
% n
~
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Tartaric (5.9), formic (9.7)
Elecmless copper bath
Dilution
3.0 mM nitric acid 1.0 Wmin
Conductivity
51
EDTA (2.7), copper-EDTA complex (3.4)
Elecmless mpper bath
Dilution
Wescan 269006 exclusion 300x 7.8 mm ID Wescan 269031 anion/R-HS
5 mM sulfuric acid 1.0 Wmin
Indirect conductivity
Dilution
Dionex CS-1
5.0 mM hydrochloric acid
Conductivity
48
Dilution
Dionex AS4
25 mM oxalic acid
Direct
48
1 0 0 ~ 4 . 1mmID
Sodium (4.8), ammonium (7.1), Copper potassium (8.3) pyrophosphate plating bath Copper (2.0), zinc (9.8), nickel Copper plating (1 1.0) bath
Copper bath
Dilution
Wescan cation
Fluoride (2.3), chromate (2.6), Aluminium tetrafluoroborate (3.3), iron (HI) treating baths cyanide (4.6)
Aqueous dilution
Dionex MPICNS 1 separator
Tamate (13.3). formate (18.3), acetate (20.5)
Evaporation, redissolution in eluent
Dionex ion exclusion
Copper (2.5)
Ethanolic ammonium tamate
92 ml/hr
aluminium anodizing electrolyte
Seep. 487for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
n
5
m%
&
spectrophot. at 520 nm after postcolumn reaction with PAR Conductivity 41
10 mM citric acid, pH 4.0 (10'70 MeOH) 2.0 mM tetrabutylammonium Conductivity hydroxide, 0.4 mM carbonate (35% ACN) 1.0 Wmin 1.0 mM hydrochloric acid Conductivity
c;
52
53
x
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC
m
-4
m
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Chloride (6.0). tartrate (20)
Ethanolic ammonium tartrate aluminium anodizing electrolyte Ethanolic ammonium tartrate aluminium anodizing electrolyte Aluminium deoxidizer bath
Evaporation, redissolution in eluent
Dionex anion separator 500 x 3.0 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 138 mVhr
Conductivity
53
Evaporation, redissolution in eluent
Dionex anion separator
1.5 mM bicarbonate 138 ml/hr
Conductivity
53
Dilution
Wescan 269006 exclusion 300 x 7.8 mm ID Dionex cation separator 250 x 6.0 mm ID
1 mM nitric acid 1.2 mumin
Conductivity
54
7.5 mM nimc acid 230 mVhr
Conductivity
53
2 mM phthalate, pH 4.5 1.7 d m i n
Conductivity
55
3.0 mM bicarbonate, 2.4 mM carbonate 3.0 mumin
Conductivity
56
Acetate (4.0). formate (5.1)
Fluoride (5) Ammonia (9.13)
Fluoride (1.8). chloride (2.0), sulfate (9) Fluoride, chloride
Ethanolic ammonium tartrate aluminium anodizing electrolyte T i n lead bath
Halogen tinplating electrolyte solution
Evaporation, redissolution in eluent
Dilution
Filtration,
dilution with aqueous
500 x 3.0 mm ID
Wescan 269029 anion/R 250 x 4.1 mm ID Dionex anion separator 500 x 3.0 mm ID
peroxide
Seep. 487for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
h,
0
s
TABLE 20.1 (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
?!
I-ead (2)
Ti-lead bath
Dilution
57,58
3
Steel etch bath
Dilution
0.5 mM EDTA, 1.0 mM citric acid, pH 4.0 1.6 mVmin 1 mM benzoate 2.7 mumin
Indirect conductivity
Fluoride (1.3), chloride (1.9), nitrate (2.9)
Wescan 269004 cation 250 x 2.1 mm ID Wescan 269031 anion/R-HS 1 0 0 ~ 4 . 1mmID
Conductivity
59
5.
Citrate (a), phosphite (9), hypophosphite (1 1) Fluoride (5)
Cobalt bath
Dilution
Wescan anion
Conductivity
41
i3.
Titanium bath
Dilution
Conductivity
60
Platinum (cyano complex) (13.65)
Platinum plating bath solution
Formation of cyano complexes, dilution
Wescan 269006 exclusion 300 x 7.8 mm ID Waters Nova Pak C18 150 x 3.9 mm ID
5 mM phthalic acid 1.8 mVmin 1 mM nitric acid 1.2 w m i n 5.0 mM PIC A with ACN gradient 1.0 mumin
Direct
61
Wescan 269024 cation/HS 50 x 4.6 mm ID
10 mM citric acid, pH 4.4 2.5 mumin
Indirect conductivity
62
Wescan 269024 cation/HS 50 x 4.6 mm ID
10 mM cimc acid, pH 4.6 2.0 mvmin
Direct
63
Dionex AS-5
4.0 mM carbonate, 1.OmM hydroxide 2.0 mvmin
Sodium ( 1 3 , ammonium (2.7), Galvanizing bath zinc (II) (4.3, iron (11) (9.4)
-
Iron (111) (1.2), zinc (11) (1.8), iron (II) (4.7)
Galvanizing bath Dilution
Acetate (0.9), nitrate (1.Q phosphate (4.3)
Phosphoric acid etchant
Dilution
spectrophot. at 214 nm
spectrophot. at 530 nm after post-column reaction with PAR Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
64
&
g
3. b 8=:
2
TABLE 20.1 (CONTINIJED). ANALYSIS OF m A L PLATING SOLUTIONS USING 1C Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Acetate (3), phosphate (9), nitrate (18)
Phosphate etch bath
Dilution
Wescan 269001 anion 250 x 4.6 mm ID Dionex AS-1 ion exclusion
4 mM phthalic acid 1.6 mVmin
Conductivity
65
1.0 mM octanesulfonic acid (5% 2-propanol) 1.0 mvmin 3 mMethylenediamine, 2 mM tartaric acid, 0.5 mM cimc acid, pH 4 (5% acetone) 3.0 mM bicarbonate, 2.4 mM carbonate 180 mVhr 3 mM nimc acid 1.0 d m i n
Conductivity
64
Conductivity
66
Conductivity
67
Conductivity
68
Nimc (5.0). hydrofluoric (7.4), Mixed acid Dilution acetic (9.7) etchant. buffered oxide etchant Phosphating bath Dilution in Nickel (3.8), zinc (5.7), manganese (12) eluent Fluoride (1.8), nitrate (4.0)
Acid pickling
Dilution
bath
Nucleosil5 SA
Dionex anion separator 250 x 3.0 mm ID Wescan 269038 exclusion 250 x 7.1 mm ID Dionex CS-2
Glycolic (6)
Anodic electrolyte bath
Aluminium (4.4)
Anodizingacid
Aqueous extraction
Borate (6), fluoride (7), silicate (8), formate (lo), chloride (14). system peak (20) Chloride (2.5), cyanate (3.2), chlorate (5.3). sulfate (9.8)
Plating process water
Preconcentration Wescan anion (10 ml)
Plating wastewater
Hypochlorite oxidation, dilution
Dionex AS4A
0.01 M sulfuric acid, 0.2 M ammonium sulfate 1.0 d m i n
5 mM hydroxide, 0.1 mM benzoate 2.0 mvmin 2.2 mM carbonate 1.5 d m i n
69 spectrophot. at 3 10 nm after post-column reaction with Tmn 41 Conductivity Direct
Conductivity
Seep. 487 for notes on the organizationof this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
3
h)
0
TABLE 20.1 (CONTINUED).ANALYSIS OF METAL PLATING SOLUTIONS USING IC
%
m u
Solutes (min)
Sample
SamplePrep.
Column
Chloride (2.3), cyanate (3.0). nitrate (4.3). chloramine-T (8) Fluoride (16), bicarbonate (28)
Plating wastewater Metal industry wastewater
Distillation with Dionex AS4A chloramine-T Cation-exchanger 550x9.0mmID
Eluent
Detection
Ref
2.2 mM carbonate 1.5 Wmin Water (40% MeOH) 1.OWmin
Conductivity
70
Coulomeny 71 after post-colu m n addition of p-benzoquinOne
Bis(2-hydroxyethyl) dithiocarbamate complexes cobalt (5.7). nickel (7.3, copper (10.0) Bis(2-hydroxyethyl) dithiocarbamate complexes mercury (11.7)
Elecaoplating wastewater
Pre-column derivatization with HEDC
Supelcosil C18 250 x 4.6 mm ID
25 mM methylammonium acetate (45% MeOH) 1.0 Wmin
Electroplating wastewater
Supelcosil C8 75 x 4.6 mm ID
Copper, nickel, zinc
Electroplating wastewaters
Pre-column derivatization with HEDC, preconcentxation P. ochrochloron biotrap
25 mM methylammonium acetate, 1.0 mM EDTA (35% MeOH) 1.0 Wmin 3.5 mM ethylenediamine, 10 mM citrate (5% ACN) 1.0 mumin 3.0 mM bicarbonate, 2.4 mM carbonate 1.9 ml/rnin Gradient from 2.5 mM low UV. PIC A to 2.5 mM low W PIC A (70% ACN) 1.2 Wmin 2.0 mM tetxabutylammonium hydroxide, 0.2 mM carbonate (25% ACN)
Interaction ION210 mansition
metal Chloride (5). nickel EDTA Nickel plating Addition of Dionex anion bath waste water EDTA, dilution separator complex (lo), EDTA (12), 500 x 3.0 mm ID nitrate (16). sulfate (25) Brighteners - 2KL (1.79), 22KL Brightener Waters C18 ~Bondapak (2.59), 4KL (6.82), 7KL (8.69) solutions 250 x 3.9 mm ID Disulfide anionic brightener (10.8)
Copper sulfate plating bath
Dilution
Dionex MPICNS1 separator
Dired
72
spectrophot. at 255 nm Dim3 spectrophot. at 275 nm
72
Conductivity
73
Conductivity
74
Direct
75
spectrophot. at 200 and 230
nm Dired
speca-ophot. at 215 nm
Seep. 487 for notes on the organizationof this Table. Seep. 691 for References. Abbreviations are iisted in Appendix B (p. 745).
48
F
a
TABLE 20. I (CONTINUED). ANALYSIS OF METAL PLATING SOLUTIONS USING IC
E2
h)
Solutes (min)
Sample
Sample Rep.
Column
Eluent
Detection
Ref
Brightener (15.66)
Beshon E-339 (brightener)
C18 Sep-Pak, dilution
10 mM sulfuric acid (15% ACN)
Direct spectrophot. at
76
Acidcopper plating baths
-
Plating bath brightener solution Metal finishing solution
Dilution
0.5 mumin 10 mM sulfuric acid (10%ACN) 1.O mVmin 5.0 rnM PIC-A (15% ACN) 1.1 mumin
254 nm
Brighteners
Watm Ulb-astyragel 750 x 3.9 rnrn ID Dionex MPICNS 1 separator
Benzamide (2,60), o-toluene sulfonamide (6.54), saccharin (11.61) Nickel ( 2 4 , zinc (3.3),cobalt (4.0), iron (11) (8.0). cadmium (12.4). manganese (18)
Dilution
Waters Nova Pak c18 150 x 3.9 mm ID Dionex CS-2 250 x 4.0 rnm ID
Direct
77
specwophot. at 254 nm Diren spectrophot. at 214 nrn
45
12 mM cimc acid,
Direct
78
40 mM tartaric acid,
spectrophot. at 520 nrn after post-column reaction with PAR
lithium hydroxide, pH 4.1 1.Omumin
See p . 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B (p. 745).
TABLE 20.2 ANALYSIS OF METALLURGICAL PROCESSING SOLUTIONS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride (2.2), chloride (3.3). sulfate (9.0), oxalate (13.1) Chloride (2.3), cyanide (2.8), sulfate (4.9, thiosulfate (5.8), thiocyanate (6.3)
Alumina mhydrate Gold process effluent
Aqueous leaching Dilution
Dionex AS-3
2.4 mM bicarbonate, 3.0 mM carbonate 0.5 mM benzenetricarboxylic acid, adjusted to pH 7.0 with THAM (2.5% n-butanol) 1.0 ml/min
Conductivity
79
Sulfide (5.8), thiosulfate (8.8), thiocyanate (1 1.O), copper cyano complex (12.8), tetrathionate (18.4)
Cyanide soh tions, wastewaten
2.0 mM tembutylammonium hydroxide, 0.5 mM bicarbonate, 0.5 mM carbonate (23% ACN) 0.9 ml/min 2.25 mM bicarbonate, 1.8 mM carbonate 6.0 mM carbonate 138 ml/hr
Direct 81 spectrophot. at 240 nm
2.0 mM bicarbonate, 2.0 mM carbonate 3.0 ml/min 3.0 mM bicarbonate, 2.4 mM carbonate 2.67 Wmin
Chloride (3.8), phosphate (6.5), Bayer liquors sulfate (11.8), oxalate (17.2) Chloride (5.3), sulfate (16.0), Bayer liquors oxalate (19.0)
Dilution in eluent Filtration
Supelcosil LC-18 coated with cetylpyridinium chloride 150 x 4.6 mm ID Dionex MPIC NS-1separator
Dionex AS-3 Dionex anion separator (x2) 500 x 3.0 mm ID YSP-2 anionexchanger
Fluoride (4.4), chloride (6.2), nitrate (14), sulfate (21)
Uranium !each solution
Fluoride, chloride, phosphate, nitrate, sulfate
Dionex anion Phosphate rock Sodium separator mining materials carbonate fusion, aqueous 500 x 3.0 mm ID leaching
i5
53
0;. Indirect 80 spectrophot. at 254 nm
Conductivity
79. 82
Conductivity
83
Conductivity
84
Conductivity
85
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendk B (p. 745).
B
$
g$. s
00. 0 W
8 P
TABLE 20.2 (CONTINUED). ANALYSIS OF METALLURGICAL PROCESSING SOLUTIONS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Fluoride, chloride, nitrate, arsenate, sulfate
Copper smelter leachate
-
86
Zinc, aluminium surfaces
Conductivity
87
Hydroxide (1.02), chloride (1.79), sulfate (6.09), arsenate (8.82) Arsenic (III) (0.88). arsenic (V) (4.17). sulfate (7.02)
Surface extraction with filter paper, dilution Dilution, cat-ex clean-up
0.25 g,4 sodium bicarbonate, 0.25 g/l sodium carbonate 1.5 mVmin 2.4 mh4 bicarbonate, 3.0 mh4 carbonate
Conductivity
Chloride, phosphate, nitrate, sulfate
Dionex anion separator 500 x 3.0 mm ID Dionex anion separator
Femc sulfate, sulfuric acid leaching media Metallurgical Dilution, cat-ex processing media clean-up
Dionex AS-4
3.5 mM carbonate, 1.0 mM hydroxide, pH 1 1 2.2 mVmin 2.8 mM bicarbonate, 2.25 mM carbonate, pH 10.4 2.2 d m i n
Conductivity
88, 89
Conductivity, amperometry at Pt electrode, +0.4V Indirect spectrophot.at 254 nm Direct spectrophot. at 205 nm Direct spectrophot. at 205 nm Indirect anodic detection at dropping mercury electrode
90, 88, 91
Separon H lo00 DIM 150 x 3.3 mm ID Separon H 300
Bicarbonate (3.3). chloride (3.7), sulfate (7.3), thiosulfate ( 1 3.2) Thiosulfate (2.5), trithionate (4.2), tetrathionate (9.3)
Carbonate leachatesof sulfide ores Carbonate leachates of sulfide ores Thiosulfate (2). trithionate (3, Carbonate tetrathionate (12), pentathionate leachates of sulfide ores (22) Hydroxide (1.7), sulfide (2.2), Coal solution sulfite (3.8), thiosulfate (7.5) (from desulfurization)
Dionex AS-4
DEAE
-
150 x 3.3 mm ID Separon H lo00 DEJA 150 x 3.3 mm ID Dionex AS-3
0.05 mM salicylic acid, pH 6.0 1.5 d m i n 25 mM perchlorate, 5 mM phosphate, pH 6.0 1.O mVmin 25 mM perchlorate, 5 rnM phosphate, pH 6.0 1.0 d m i n 5 mh4 sodium hydroxide, 0.2 M potassium nitrate 1.0 to 3.0 Wmin flowgradient
92 92 92 93
P R
-7
Seep. 487 for notes on the organization of this Table. Seep. 691for References. Abbreviations are listed in Appendix B (p. 745).
I\J
0
%
TABLE 20.2 (CONTINUED). ANALYSIS OF METALLURGICAL PROCESSING SOLUTIONS USING IC Solutes (min)
Sample
Sulfide (1.7). sulfite (2.3), thiosulfate (6.0)
Coal solution (from desulfurization)
Sulfate/sulfite (1.2), thiosulfate (4.7), sulfide (7.7)
Trithionate (5.7), teuathionate (9.0). pentathionate (1 1.4)
Coal plant process liquor
Coal plant process liquor
Carbonate (4.0), chloride (5.5). Steel surfaces nitrite (7.0) Chloride, sulfate
Steel surfaces
Sample Prep.
Column Dionex AS-3
Eluent
Detection
Ref
10 mM sodium hydroxide,
Indirectanodic detection at dropping mercury electrode Direct spectrophot. at 335 nm after Br postcolumn reduction, reaction with Fe(III) perchlorate Direct spectrophot. at 335 nm after Br postcolumn reduction, reaction with Fe(III) perchlorate Indirect spectrophot. at 254 nm
93
97.98
50 mM potassium niuate 1.1 d m i n
Dilution
vydac SAX 50 x 3.0 mm ID
(P
Water to 1.0 mM disodium hydrogen phosphate gradient 1.0 d m i n
Dilution
vydac SAX 300 x 2.0 m m I D
Water to 0.25 M perchlorate, 0.1 M borate gradient 1.0 d m i n
Aqueous sonication, filtration Aqueous sonication, preconcentration with post-flush
Wescan ion guard anioncamidge
1 mM benmic acid, pH 5.5 lmi/min
Vydac anion
2 mM phthalate. pH 7.0
Indirect
250 x 4.6 mm ID
2.0 d m i n
spectrophot. at 280 nm
Seep. 487 for notes on the organization of this Table. Seep. 691for References, Abbreviations are listed in Appendix B (p. 745).
L
&
P
$. 2 94
b
8z
ki
s 94
95,96
% 3
TABLE 20.2 (CONTINUED). ANALYSIS OF METALLURGICAL PROCESSING SOLUTIONS USING IC Solutes (min)
Sample
Sulfide (1.8). cyanide (2.3)
Fluoride, chloride
Column
Eluent
Detection
Ref
Metallurgical UV irradiation, process solutions neuaalization with hydroxide
Dionex Fast-Run Anion
Pyrolysis, sorption in carbonate, dilution Chloride, sulfate Cold mill rolling Extraction with coolants (steel ethanol, industry) petroleum ether and water Acetate, nitrite Temper rolling solution Phosphorus as phosphate (1.8) Copper-based Acid digestion, alloy dilution
Dionex 030170 anion separator 500 x 3.0 mm ID
Amperometry at Ag electrode, +0.15V Conductivity
99, 100
Tantalum metal
14.7 mM ethylenediamine, 1.0 mM carbonate, 10 mM sodium hydrogenborate 2.0 mumin 3.0 mM bicarbonate, 2.4 mM carbonate 150 mVhr
Conductivity
102
Conductivity
96
Phosphorus as phosphate
Home-packed activated alumina 50 x 2.0 mm ID Zorbax Cg 100 mm
1.42 mM gluconate, 5.82 mM boric acid, 0.25%glycerine, pH 8.5 1.O d m i n 5.0 mM phenol, pH 10.0 3.0 mVmin 50 mM oxalic acid, 95 mM sodium hydroxide, pH 4.8 1.O d m i n 1.5 mM sodium hydroxide 2.1 d m i n
Copper-based dOY
Sample Prep.
Acid digestion, dilution
Sulfate (7.0)
Lead acid battery Extraction with plates nitrilomacetic acid, Millex filtration
Sulfate
Steel surface trearment bath
Ag form cat-ex resin clean-up
Waters IC Pak A 50 x 4.6 mm ID SS-SAR 4.7 mm ID Dionex CS-5
Waters IC Pak A 50 x 4.6 mm ID
DC plasma emission spectrometry DCplasma emission spectrometry 5.0 mM octylamine-p-toiuene- Conductivity, indirect RI, sulfonate, pH 5.0 2.0 mVmin indirect spectmphot. at 254 nm 1.42 mM gluconate, 5.82 mM Conductivity boric acid, 0.25%glycerine, pH 8.5 (12% ACN) 1 .O d m i n
Seep. 487 for notes on the organization of this Table. Seep. 691for References. Abbreviationsare listed in Appendix B (p. 745).
101
103 103 104
102
TABLE 20.2 (CONTINUED). ANALYSIS OF METAUURGICAL PROCESSING SOLUTIONS USING IC ___
_ _ _ _ _ _ _ _ _ _
~
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Sulfate
Steel
Waters IC Pak A 50 x 4.6 mm ID
1.42 mM gluconate, 5.82 mM Conductivity boric acid, 0.25% glycerine, pH 8.5 1.0 d m i n
102
Sulfate
NBS steel
3.0 mM bicarbonate, 2.4 mM carbonate 138 rr@r 2.3 mM bicarbonate, 2.9 mM carbonate 3.0 ml/min
105
Coal solution (spent caustic from chemical cleaning) Metal cutting fluids
Dionex anion separator 500 x 3.0mm ID Dionex AS-3
Conductivity
Sulfate
Combustion, aqueous ammonia and peroxide sorption Combustion, sorption into eluent, peroxide Oxidation with acidified peroxide, dilution Centrifugation, dilution
Conductivity
106
107
Dilution, Clg Sep-Pak
3.0 mM bicarbonate, 2.4 mM carbonate 3.0 d m i n 5 mM sulfuric acid (40% MeOH)
Conductivity
Metal cutting fluid
Dionex anion separator 250 x 4.0 mm I D &&ax ODs 250 x 4.6 mm ID Dionex cation separator
5.0 mM hydrochloric acid
Dionex cation separator
0.5 mM hydrochloric acid, 2.5 mM m-phenylenediamine dihydrochloride
Conductivity
87
Interaction ION200
2.0 mM ethylene diammonium tartrate, pH 4.5 1.3 d m i n
Conductivity
109
Nitrite (4.1) Nitrite (4.4)
1.5 d m i n
Sodium,ammonium, potassium Zinc, aluminium Surface extraction with filter paper, dilution Zinc, aluminium Surface extraction with surfaces filter paper, dilution Sodium metal
surfaces Magnesium, calcium
Calcium
Detection
Ref
Direct 108 specmphot. at 214 nm Conductivity 87
See p . 487 for notes on the organization of this Table. Seep. 691for References. Abbreviations are listed in Appendix B (p. 745).
i2
TABLE 20.2 (CONTINUED). ANALYSIS OF METALLURGICAL PROCESSING SOLUTIONS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
Uranium solution Post-column addition of carbonate to prevent formation of uranium-PAR complex Copper (2), nickel (6). cobalt Acid digestion, Ni-Cr-Fe alloy (lo), iron (14), manganese (17) dilution
Aminex A5 100 x 4.0 mm ID
0.3 M to 0.5 M tartrate gradient, pH 3.5 1.Od m i n
Direct 110 spectmphot. at 540 nm after post-column reaction with PARjcahonate
Aminex A5 100 x 4.0 mm ID
0.2 M to 0.4 M tartrate gradient, pH 3.5 1.O mVmin
Cobalt (8), iron (14). manganese (22)
Steel samples
Acid digestion, dilution
Aminex A5 100 x 4.0 mm ID
1 mM to 1oOmMcitrate gradient, pH 4.8 1.5 d m i n
Copper (3.8), zinc (6.3)
Brass
Acid dissolution, dilution
C18 silica 250 x 4.6 mm ID
10 mM hexanesulfonate, 45 mM sodium m a t e ,
Direct 110 spectrophot. at 540 nm after post-column reaction with PAR Direct 110 spectrophot. at 540 nm after post-column reaction with PAR Direct 111 spectrophot. after postcolumn reaction with
Uranium (1.81, copper (3.7). zinc (7), lead (9), nickel (10). cobalt (12). iron (16). manganese (22)
pH 3.1 1.0 d m i n
PAR Nickel (4.4), iron (6.3)
Simulated steel digest solution
Masking of Fe(III) with sulfosalicylic acid
Home-packed cation-exchanger 350 x 2 mm ID
1.5 mM ethylenediamine, 2 m M tartrate, pH 4.2 0.85 d m i n
Conductivity
Seep. 487 for notes on the organization of this Table. Seep. 691for References. Abbreviations are listed in Appendix B (p. 745).
112
%
TABLE 20.2 (CONTINUED). ANALYSIS OF METALLURGICAL PROCESSING SOLUTIONS USING IC Solutes (min)
Sample
Aluminium (III) (2.40)
Aluminium (6.0)
Column
Eluent
Detection
Ref
Aluminium alloy Acid digestion
Waters IC Pak C 50 x 10 mm ID
Conductivity
1 13
Wescan 269-004 250 x 2.0 mm ID
Conductivity
114
Aluminium (1.8)
NBS standard alloy, aluminium solution Al alloy
8.23 mM p-phenylenediamine adjusted to pH 3.0 with perchloric acid 1.2d m i n 8.23 mMp-phenethylamine, pH 2.94 0.97 mllmin 0.1 M potassium sulfate, nitric acid, pH 3.0 1.0 mvmin
Cyano complexes-copper(6), silver (lo), iron (II) (17),cobalt (20), nickel (22), iron (III) (24), gold (1) (30) Cyanide complexes - copper (2.4), nickel (6.4),cobalt (8.0), iron (10.9), gold (12.8)
Gold metallurgical plant solutions, cyanide effluent Carbon-in-pulp (gold processing) solutions
2.0 mM tetrabutylammonium hydroxide, bicarbonate, carbonate buffer (28%ACN) 1.0 d m i n 5.0 mM tetramethyl ammonium hydroxide (23%ACN) 1.0 mvmin
Conductivity, 117 direct specaophot. at 240 nm Direct 118 spectrophot. at 214 nm
-
Cyano complexes copper
(5.3), silver (6.3). gold (26.0)
Sample Prep.
cb
Perchloric, nitric acid digest, dilution Nimc acid digest, dilution
Dionex CG-2 50 x 4.0 mm ID
Waters RCM Novapak C18 1OOx8mmID
-
Gold processing solutions
Dionex MPIC NS-1 separator Waters Nova Pak C18 150 x 3.9 mm ID
G-
8% n
is B a
Fluorescence at 115 360,512 nm after post Column addition of 8hydroxyquinoline 5sulfonate 2.5 mM PIC A (30% MeOH) Direct 116 1.0mvmin specmphot. at 210 nm
Seep. 487 for notes on the organization of this Table. Seep. 691for References. Abbreviations are listed in Appendix B (p. 745).
g 8.
h
TABLE 20.2 (CONTINUED). ANALYSIS OF METALLURGICAL PROCESSING SOLUTIONS USING IC Solutes (min)
Sample
Cyano complexes - silver (4.2), Gold processing gold (2 1.4) solutions Gold (I) cyano complex (9.6)
8
Sample Prep.
Column
Eluent
Detection
.
Waters Nova Pak CN 150 x 3.9 mm ID
5.0 mh4 tettamethyl ammonium hydroxide (8% ACN) 1.O mumin 5 mM low UV PIC A (20% ACN) switched to 5 mM low UV PIC A (30% ACN) 1 .O mVmin
Direct 118 specmphot. at 214 nm
5.0 mM t e r n e t h y l
Direct 121specmphot. at 123, 214 nm 119
Carbon-in-pulp Preconcentration Waters Nova Pak (gold processing) (2 ml) with c18 tailings solutions matrix elimina- 150 x 3.9 mm ID tion on C18 precolumn with "dynamic" coating Gold cyano complex (10.7) Carbon-in-pulp Preconcenuation Waters Nova Pak (gold processing) (2 ml) on CIS C I ~ tailings solutions pre-column with 150 x 3.9 mm ID "dynamic" coating Lutetium (4.0), ytterbium (4.7). Uranium leach Hydroxide ppt. Supelcosil LC-18 dissolution in thorium (5.2). thulium (5.9), 150 x 4.6 mm ID liquor uranium (6.5). erbium (6.6), hydrochloric acid, cat-ex holmium (7.3, ytmum ( K O ) , dysprosium (8.2), terbium clean-up (9.3), gadolinium (10.3), europium (10.7), samarium (11.7), neodymium (13.4), praseodymium (13.7), cerium (14.4). lanthanum (15.6)
ammonium hydroxide (32% ACN) 1 .O d m i n
0.05 to 0.4M hydroxyisobutyric acid gradient. 0.03 M Octane sulfonate, pH 4.6 (7.58 MeOH) 1.O mumin
Ref
Direct 119, specmphot. at 120 214 nm
Direct 124 specmophot. at 658 nm after post-column reaction with Arsenazo III
Seep. 487 for notes on the organization of this Table. Seep. 691 for References. Abbreviations are listed in Appendix B ( p . 745).
Metals and Metallurgical Applications
20.2 REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
Tanaka T., Hiiro K., Kawahara A. and Wakido S., Bunseki Kagaku, 32 (1983) 771. Waters IC Lab. Report No. 297. Nonomura M., Met. Fin., 85 (1987) 15. Jupille T..Togami D.W. and Burge D.E., Res. Dev., February (1983) 151. Smith R.E. and Smith C.H., LC, 3 (1985) 578. Wescan Application #128. Cuff D., CIJEMSA, 7 (1981) 11. Waters IC Lab. Report No. 259. Smith R.E., Tech. Report BDX-613-3104, 1984. Smith R.E. and Davis W.R., Plat. Sutf Finish, 71 (1984) 60. Waters IC Lab. Report No. 241B. Waters IC Lab. Report No. 241A. Waters Ion Brief No. 881 10. Dionex Application Note 26. Dionex Technical Note 24. Waters IC Lab. Report No. 273. Waters IC Lab. Report No. 290. Dionex Application Note 20R. Dionex Application Note 7R. Wescan Application #63. Ariga S., Tetsu-to-Hagane,66 (1980) S1055. Waters IC Lab. Report No. 241. Waters IC Lab. Report No. 250. Andrew B.E., J. HRC & CC, 10 (1987) 211. Sopok S., LC.GC, 7 (1989) 142. McCrory-Joy C., Anal. Chim. Acra, 181 (1986) 277. Dionex Application Update 110. Wong D., Jandik P., Jones W.R. and Hagenaars A., J . Chromutogr., 389 (1987) 279. Waters ILC Series Application Brief No. 5001. Dionex Application Note 40R. Haak K.K. and Franklin G.O., Annu. Tech. Conf. Proc.-Am. Electroplat. SOC.,70 (1983) 1. Wescan Application #7 1. Dionex Application Note 49. Wescan Application#196a. Wescan Application #288. Wescan Application#197a. Wescan Application#196c. Wescan Application#197b. Pohlandt C., Srh. Afr. J . Sci., 80 (1984) 208. Wescan Application#136a. Barthel P.J., Jr., Met. Fin., 84 (1986) 55. Wescan Application#136b.
69 1
692 43
Chapter 20 Dionex Application Update 115.
44 Dionex Application Update 116. 45 46 47 48 49 50 51 52 53
54 55 56 57 58 59
60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
Waters IC Lab. Report No. 275. Franklin G O . , Am. Lab., 17 (1985) 65. Wescan Application #2 11. Dionex Application Note 50. Wescan Application #208a. Wescan Application #180. Wescan Application #208b. Dionex Application Note 41. Memll R.M., Tech. Report SAND-82-1929, 1982. Wescan Application #119a. Wescan Application #196b. Korth W. and Ellis J., Talunza, 31 (1984) 467. Wescan Application #196d. Wescan Application #196e. Wescan Application #219. Wescan Application #119b. Waters IC Lab. Report No. 294. Wescan Application #295. Wescan Application #283. Dionex Application Note 28R. Wescan Application #233. Schaefer J., Burmicz J. and Palladino D., Am. Lab.,February (1989) 70. Dulski T.R., Anal. Chem., 51 (1979) 1439. Wescan Application #209. Dionex Application Note 42. Nonomura M. and Hobo T., J. Chromatogr., 465 (1989) 395. Tanaka K., Bunseki Kaguku, 32 (1983) 439. King J.N. and Fritz J.S., Aml. Chem., 59 (1987) 703. Crusberg T.C., Weathers P.J. and Cheetham R.D., in Jandik P. and Cassidy R.M. (Eds.), Advances in I o n Chromatography. VoI.I , Century International, Inc., Franklin, MA, p. 247. Tanaka T., Fres. Z. Anal. Chem., 320 (1985) 125. Waters IC Lab. Report No. 238. Waters IC Lab. Report No. 301. Dionex Application Update 111. Slingsby R.W. and Riviello J.M., LC, 1 (1983) 354. The K. and Roussel R.. tight Met. (Warrendale, PA), (1984) 115. Barkley D.J., Dahms T.E.and Villeneuve K.N., J. Chromarogr., 395 (1987) 631. Pohlandt-Watson C.,, Hemmings M.J., Barnes D.E. and Pansi G.W., MlNTEK Report No. M353, 1988. Jansen K.H., GlT Fachz. Lab., 22 (1979) 1062. Dionex Application Note 5. Liu K., Wang X., He B., Zhao W. and Jia X., Youkuangye, 2 (1983) 38. Kramer G.W. and Haynes B.W., Rep. Invest.-US. Bur. Mines R I 8661,1982. Steiber R. and Memll R., Anal. LRtt, 12 (1979) 273.
Merals and Metallurgical Applications 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104
693
Munier G.B.. Psota-Kelty L.A. and Sinclair J.D., Proc. Int. Symp. Atmos. Corros., 1982, p. 275. Tan L.K. and Dutrizac J.E., Anal. Chem., 57 (1985) 2615. Tan L.K. and Dutrizac J.E., Anal. Chem., 57 (1985) 1027. Tan L.K. and Duaizac J.E., Anal. Chem., 58 (1986) 1383. Tan L.K. and Dutrizac J.E., J. Chromatogr.,405 (1987) 247. Vins I. and Kabrt L., Coll. Czech. Chem. Commun., 52 (1987) 1167. Uddin Z., Markuszewski R. and Johnson D.C., Anal. Chim. Acta, 200 (1988) 115. Story J.N., J. Chromatogr. Sci., 21 (1983) 272. Andrew B.E.. J. HRC & CC, 10 (1984) 580. Andrew B.E., Proc. Corros. 88 Conf., 1988, paper no. 89. Andrew B.E.. Paperpresented at 7th Aust. Anal. Conf., Adelaide, August, 1983. Andrew B.E., Paperpresented atInr. Conk Corr. Inhib., Dallas, May, 1983. Pohlandt C., Sth. Afr. J . Chem.. 37 (1984) 133. Pohlandt C.. MINTEK Report No. M I 2 8 , 1984. Ishibashi W., Kikuchi R. and Yamamoto K., Bunseki Kagah, 30 (1981) 604. Tusset V. and Hancart J.. in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromatography,Vol.I , Century International, Inc., Franklin, MA, p. 421. Epstein M.S., Koch W.F., Epler K.S. and OHaver T.C., Anal. Chem.. 59 (1987) 2872. Dreux M., Lafosse M., Pequignot M., Morin-Allory L. andDouady M., J. HRC & CC, 7
(1984) 712. 105 Evans K.L., Tarter J.G. and Moore C.B., Anal. Chem., 53 (1981) 925. 106 Chriswell C.D., Mroch D.R. and Markuszewski R.. Anal. Chem., 58 (1986) 319. 107 Wu W.S., Arai D.K., Nazar M.A. and Leong D.K., Am. Ind. Hyg. Assoc. J., 43 (1982) 942. 108 Skelly N.E., Oomens A.C. and Schuurhuis F.G.. J. Chromatogr., 284 (1984) 503. 109 Sahasranaman S. and Bhat N.P., Trans. SAEST, 23 (1988) 13. 110 Cassidy R.M. and Elchuk S., J. Liq. Chromatogr..4 (1981) 379. 111 Schmidt G.J. and Scott R.P.W., Analyst (London). 109 (1984) 997. 112 Sevenich G.J. and Fritz J.S., J. Chromatogr.,347 (1985) 147. 113 Chaudry M.A., Noor-U1-Islam, Yasin Z., J. Radioanal.Nucl. Chem., 122 (1988) 43. 114 Fortier N.E. and Fritz J.S., Talanra,32 (1985) 1047. 115 Jones P., Ebdon L. and Williams T., Analyst (London), 113 (1988) 641. 116 Grigorova B.. Wright S.A. and Josephson M., J. Chromatogr..410 (1987) 419. 117 Pohlandt C., S. Afr. J. Chem., 38 (1985) 110. 118 Hilton D.F. and Haddad P.R., J. Chromatogr.,361 (1986) 141. 119 Haddad P.R. and Rochester N.E., J. Chromarogr.,439 (1988) 23. 120 Haddad P.R., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromatography, Vol. I, Century International, Inc., Franklin, MA, p. 473. 121 Jackson P.E., Rochester N.E., Haddad P.R. and Ruprecht U.. Proc. Equip. Min. Industry: Expl., Min. and Process. Conf.. 1987, paper no. 26. 122 Rochester N.E. and Haddad P.R.. Proc. 9th. Aust. Symp. Anal. Chem., 1987, p. 329. 123 Haddad P.R. and Rochester N.E., Anal. Chem., 60 (1988) 536. 124 Barkley D.J., Blanchette M., Cassidy R.M. and Elchuk S., Anal. Chem., 58 (1986) 2222.
This Page Intentionally Left Blank
695
Chapter 21 Analysis of Treated Waters 21.1 OVERVIEW The analysis of treated waters using IC is presented according to the scheme shown in Fig. 21.1.
ANALYSIS OF TREATED WATERS USING IC
Drinking waters (Table 21.1)
High purity waters (Table 21.2)
Fig. 21.1 Applications of IC in the analysis of treated waters.
TABLE21.1 ANALYSIS OF DRINKTNG WATER USING IC Solutes (min)
Sample Prep.
Column ~
Fluoride (2.7), chloride (3.3, phosphate (5.1), nitrate (7.11, sulfate (8.7) Fluoride (1.3), chloride (1.6). nimte (2.2), nitrate (3.6), sulfate (10.3) Silicate (1.55). fluoride (2.15). chloride (3.25), system peak (6.5), sulfate (18.8)
Degassing
Chloride (2.1), cyanate (2.9). chlorate (5.8), nitrate (5.8), sulfate (9.2) Chloride (2.3). cyanate (3.0). nitrate (4.3). sulfate (7.8) Bicarbonate (2.1), chloride (3.1). nitrate (5.4), sulfate (6.4)
Spiking, oxidation with hypochlorite Spiking, oxidation with chloramine-T
Bicarbonate (2.0), chloride (2.9), sulfate (3.7), nitrate (4.4)
Detection
Ref
Conductivity
1-8
~~
4.5 mM bicarbonate, 2.4 mM carbonate ll5myhr 2 mM phthalic acid, pH 5 (10%acetone) 70 mgA 2;Q-dihydroxybenzoic x-loo acid, pH 10.1 250 x 4.6 mm ID 3.0 Wmin Hamilton PRP-1 6 mM 4-hydroxybenzoic acid, (coated with 50 mg/l methyl green, adjusted methyl green) to pH 9.0 with hydroxide 125 x 4.6 mm ID 1.0 Wmin Dionex AS-4A 2.2 mM carbonate 1.5 td/min Dionex AS4A 2.2 mM carbonate 1.5 Wmin TSK gel IC1.2 mh4 phthalate, pH 7.5 Anion-PW 1.1 mflmin 50 x 4.6 mm ID TSK gel IC0.48 mh4 hemimellitate, Anion-PW pH 7.5 50x4.6mmID l.lml/min TSK gel IC0.4 mM mmellitate. pH 7.5 Anion-PW 1.1 mumin 50 x 4.6 mm ID
Dionex anion separator 250x6.0mmID Hydroxide addition, Hamilton PRP cat-ex pretreatment X- 100 Cat-ex pretreatment Hamilton PRP
Bicarbonate (3.4), chloride (3.8). nitrate (8.01,sulfate (9.0), system peak (14)
Bicarbonate (2.0), chloride (2.9), sulfate (4.2), nitrate (5.4)
Eluent ~
9 Conductivity, amperometry Indirect spectrophot. 10 at 312 nm
Indirect spectrophot. 11 at 31 1 nm Conductivity
12
Conductivity
13
Indirect spectrophot. 14 at 257 nm Indirect spectrophot. 14 at 250 nm Indirect spectrophot. 14 at 270 nm
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
L-. N
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
8
9 E;. Solutes (min) Chloride (2.9), nitrate (5.6), sulfate (8.4), bicarbonate (17.0) Fluoride (3.2), chloride (3.9, nitrate (5.8), sulfate (7.8) Chloride (15 sec), nitrate (23 sec), sulfate (32 sec), system peak (47 sec)
Sample Prep.
-
Silicate (6.3), chloride (10.0), nitrate (15.4), sulfate (30) Chloride, nilrate, sulfate, bicarbonate Bicarbonate, chloride, nitrate, sulfate
Large injection volume
Carbonate (2.7), chloride (3.3, nitrate (4.8)
-
Chloride (3.581, nitrate (7.15). sulfate (15.68)
Dilution
Column
Eluent
Wescan anion 3.0 mM phthalate, pH 5.0 250 x 4.6 mm ID 3.0 d m i n PE C18 silica 125 x 4.6 mm ID Wescan IonGuardAnion 30 x 4.6 mm ID TSK gel ICAnion-PW 50 x 4.6 mm ID zipax SAX 250 x 4.0 mm ID
1.0 mM tetrabutylammonium phthalate, pH 7.5 4.0 mM phthalate, pH 4.5 4.OmVmin 0.5 mM potassium hydroxide 1.2 d m i n
0.75 mM muconic acid, pH 4.40 2.5 ml/min Waters IC Pak A 0.32 g/l boric acid, 0.08 ml/i HC gluconic acid, 0.10 @Ilithium 150 x 4.6 mm ID hydroxide, 2 ml glycerine, pH 9.0 (12.5% ACN) 2.0 ml/min LiChrosorb RP- 5.0 mM octylamine salicylate 18 2.0 d m i n Waters IC Pak A 0.32 g/l boric acid, 0.08 mM 50 x 4.6 mm ID gluconic acid, 0.10 @Ilithium hydroxide, 2 ml glycerine, pH 9.0 (12.5% ACN) 1.2 Wmin
Detection
Ref
Indirect 7, 15spectrophot., 17 conductivity Indirect specaophot. 18 at 280 nm Conductivity 19,20
Indirect conductivity
2 1-23
Indirect spectrophot. 24 at 293 nm Conductivity, direct specaophot. at 214 nm
25
Indirect specaophot. 26 at254nm Conductivity 27.28
Seep. 487 for notes on the organization of this Table, Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
B
7
Q2 F
0
R
E:
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
Solutes (min)
Sample Prep.
Chloride (2.7), carbonate (4.4). sulfate (7.0) Chloride (6.5). bromide (8.2), nitrate (10.9) Chloride (3.2), sulfate (5.7), nitrate (9.0)
Dilution
Chloride (2.1), nitrate (2.5), sulfate (5.9)
-
Chloride (9). nitrate (1 l), sulfate (15) Chloride (3,nitrate (7), sulfate (10) Chloride (4.4), nimte (6.4), sulfate (9.1)
-
Chloride ( 5 . 3 , nitrate (8.6), sulfate (14)
-
Chloride (3), nitrate (6), sulfate (12)
Cat-ex pre-column clean-up
0
Column
Eluent
Detection
Ref
Home-packed agglomerated Dowex 2 resin 300 x 2.8 mm ID Vydac 302 IC 250 x 4.6 mm ID Home-made latex agglomerate 250 x 4 mm ID Home-packed anion-exchanger 500 x 2.0 mm ID Nucleosil 5 SB 150 x 4.6 mm ID vydac sc 500 x 3.0 mm ID SAX-4 125 x 5.0 mm ID
15 mM phenate 1.O mlfmin
Conductivity
29
0.02 M phosphate, pH 3.75 2.0 mumin 0.02 mM pyromellitate, pH 7.0 0.5 ml/min 0.4 mM phthalic acid, pH 5.6 0.93 mumin
Direct spectrophot. 30 at I80 nm Indirect spectrophot. 31 at 240 nm Conductivity
32, 33
0.03 M salicylate, pH 4.0 0.5 mlfmin 0.5 mM phthalate, pH 6.0 2.0 mumin 0.7 g/l citric acid, 0.05 g/l cemmide, pH 5.5 (30%MeOH) 1.0 mlfmin 1.0 mM phthalate, pH 4.1 l.Oml/min 0.2 mM Tiron 1.O mumin
Indirect RI
34, 7
Conductivity
35,33
Direct-indirect spectrophot. at 220
36
Zipax SAX 50x 2.1 mm ID TSK IC anion PW 50 x 4.6 mm ID
3
\D Dc
nm Indirect spectrophot. 37-40 at 264 nm 41 Conductivity, indirect spectrophot at 290 nm
Seep. 487 for notes on the organizationof this Table. Seep. 713for References. Abbreviations are listed in Appendix B ( p . 745).
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
Solutes (min)
Sample Prep.
Column
5 Eluent
Detection
Ref
%
7 2 (b
Chloride (3), nitrate (7),sulfate (15) Chloride, nitrate, sulfate
Filtration
Chloride (3), sulfate (15) Nitrite (1.7),nitrate (6.7) Nitrite, nitrate Nitrate (6.25)
Nitrate (9.5) Nitrate (7.4)
Fluoride (1 1 .O)
Large injection volume (10 ml)
Vydac 302 IC 250 x 4.6 mm ID Shimadzu Shimpack IC-A1 XAD-1 lo00 x 3.0 mm ID TSK-gel S A X Spherisorb
ODs-2 250 x 5.0 mm ID Vydac 302 IC 250 x 4.6 mm ID Home-packed anionexchanger 300 x 3.0 mm ID Lichrosorb RP-2 250 x 4.0 mm ID Wescan ion exclusion
1.0 mM phthalate, pH 5.0
Conductivity
5,42
2.5 mM phthalic acid, 2.4 mMTris buffer 0.05 mM citrate, pH 6.0 1.5 mvmin
Conductivity
43
conductivity
44
4.0 M chloride
Direct spectrophot. at 210 nm Direct specmphot. at 205 nm
45
5i
3
0.01 M cetyltrimethylammonium chloride (25%ACN) 1.5 Wmin 2.5 mM succinic acid, 10 mM sulfate, adjusted to pH 5.8 with tetraborate
0.03 M sodium sulfate, 0.01 M Tris buffer, pH 7.0 0.5% tricaprylylmethyl ammonium chloride (45%ACN)
2.0 rd/min 2.0 mM sulfuric acid
46
Fluorescence after 47 post-column reaction with Ce(IV), conductivity Direct spectrophot. 48 at 210 nm
Direct specmphot. at 205 nm
49
Conductivity, direct spectrophot. at 210
50
nm
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
0
w 2
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
Solutes (min)
Sample Prep.
Fluoride Fluoride
Column
Eluent
Detection
Ref
Dionex anion separator Home-packed AG50W-X4
2.5 mM disodium teuaborate
Conductivity
3
1 mM hydmhloric acid 1 ml/min
Conductivity
51
Conductivity
52
Graphite furnace atomic absorption Spec~scOPY Graphite furnace atomic absorption spectroscopy Graphite furnace atomic absorption spectroscopy
53
Conductivity
54,55
Direct spectrophot. at 365 nm
56, 57
300X9mmID
Bromide
Oxidation of mhalomethanes, preconcentration
Dionex anion and 3.0 mM bicarbonate, 2.4 mM carbonate trace anion 2.3 mI/min separators in series
Dimethylarsinate (14). methylarsonate (40). Spiking with arsenic LiChrosorb SAX 0.05 M sodium dihydrogen arsanilic acid (49) compounds 250 x 3.2 mm ID phosphate 0.5 mumin Spiking with arsenic Altex SCX 0.0375 M acetate, Arsenate (22), arsenite (35) 250 x 3.2 mm ID 0.0375 M acetic acid compounds 0.15 ml/min 5.0 mM tetrabutylammonium Spiking with arsenic Waters Arsenate (1I), arsenite (19) compounds pBondapak c18 phosphate, pH 7.3 300 x 4.0 mm ID (5% MeOH) 0.5 ml/min 2.5 mM bicarbonate, Arsenate (25) Re-injection Dionex AS-3 1.5 mM carbonate, pH 9.56 1.51 ml/min 20 mh4 nitric acid, Preconcentration Dionex AS-2 Chromate (6.0) 30 mM hydroxide (10 ml) 1.5 ml/min
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
53
53
BB b N
b
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
h
3. Solutes (min)
Sample Prep.
Column
Eluent
Spherisorb ODs 0.2 mM tewbutylammonium 120 x 4.6 mm ID chloride, 5.0 mM biacetyl, 2.0 mM phosphate buffer, pH 7.1 (5% ACN) 1.0 mvmin Selenate (27) Re-injection Dionex AS-3 3.0 mM bicarbonate, 2.4 mM carbonate, pH 9.72 1.51 mVmin Selenate (8.4) Dionex anion 3.0 mM carbonate tine 230 djh 500x3.0mmID Filmtion, Dionex anion 6.0 mM carbonate Molybdate (12.0) preconcenwtion separator 9omvhr on Chelex 100 250 x 3.0 mm ID Bicarbonate (7.5) XAD-1 0.1 mM benzoate, pH 6.25 500 x 2.0 mm ID 2.0 mumin Dilution Carbonic acid (5.0) TSK SCX Deionized water 100 x 7.5 mm ID 1.0 mvmin Boric acid (3.5) Pre-column addition TSK gel IC 0.2 M perchlorate, of chromotropic anion-PW 1 mM acetate buffer, pH 5.6 50 x 4.6 mm ID 1.0 ml/min acid, EDTA, octylaimethyl ammonium chloride Waters IC Pak C 2.0 mh4 nitric acid, Lithium (2.90), sodium (4.02), ammonium Dilution (5.17), potassium (7.42) 50 x 4.6 mm ID 0.05 mM disodium EDTA 1.2 mvmin Chromate (4.4)
Spiking
Detection
Ref
Quenched phosphorescence
58
Conductivity
54
Conductivity
59
Conductivity
60
Conductivity
33
Conductivity
61
Directspecmphot. at 350 nm
62
Indirect conductivity
28
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
B
3
-4
z
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
Solutes (min) Lithium (3.0), sodium (5.0),ammonium (8.3), potassium (1 1.3)
Sample Prep.
Column
Dionex CS-2 250 x 4.0mm ID Shimadzu ShimSodium (5.4),ammonium (8.3).potassium Filtration pack IC-Cl (10.0) Sodium (2), ammonium (3). potassium (4) Wescan 269024 cation/HS 50 x 3.0 mm ID Sodium (6). potassium (8) Home-packed Dilution cation-exchanger 340 x 2.0 mm ID Sodium (3.2), calcium (3.9). potassium Nucleosil-5-100PBDMA (4.5).magnesium (7.2) 125 x 4.5mm ID Sodium (2.3), potassium (4.3). magnesium Zipax SCX (12.6), calcium (20.0) 250 x 4.6 mm ID Interaction IONSodium (1.2). magnesium (4.0), calcium 210 (10.8) Nucleosil-5-100 Sodium (3.2). magnesium (8.5), calcium (PBDMA coated) (10.3) 125 x 4.5 mm ID Potassium (2), calcium (12) Softening, filtration Interaction ION210 100 x 3.2 mm ID
Eluent
Detection
Ref
8.0 mM hydrochloric acid 1.6 mumin 5.0 mM nitric acid
Conductivity
63, 64
43
3 mM nimc acid 1.5 mumin
Indirect conductivity Indirect conductivity
1.25 mM nitric acid 1.O W m i n
Indirect conductivity
66
3.75 mM pyridine-2,6-dicarboxylic acid 1.0 W m i n 2.5 mM copper sulfate 1.0 W m i n 0.1 mM cerium (HI) 1.O W m i n 0.01 M formic acid 1.0 mumin
Conductivity
67
Indirect spectrophot. at 220 nm Indirect spectrophot. at 254 nm Conductivity
68, 39, 69 70
0.15 mh4 cerium @I) 1.0 Wmin
65
71
Indirect spectrophot. 72 at 254 nm
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B ( p . 745).
TABLE 21.1 (CONTINUED).ANALYSIS OF DRINKING WATER USING IC
?
$ E;.
Solutes (min)
Sample Prep.
Home-packed 0.12 M perchloric acid cationexchanger 1.0 mumin 250 x 2.0 mm ID Dilution
Magnesium (18 sec), calcium (38 sec) Magnesium (2.89),calcium (5.04)
Dilution
Magnesium (2), calcium (4)
Dilution
Magnesium (3.3),calcium (6.0) Magnesium, calcium Aluminium (3.8),iron (II) (7.2)
Eluent
Detection
Ref
2
5
Magnesium (1.8), calcium (2.6)
Magnesium (2.5),calcium (4.1)
Column
B Y
Filtration
Home packed cation-exchanger 340 x 2.0 mm ID Wescan cation HS
1.0 mM EDTA, pH 6.1 1.O mVmin
Direct spectrophot. 73 at 590 nm after postcolumn reaction with Arsenaw-I Conductivity 66
1.0 mM ethylenediamine, Indirect pH 6.0 conductivity 8.0 mVmin Waters IC Pak C 0.05 mM disodium EDTA, Indirect 50 x 4.6 mmID nitric acid, pH 6.0 conductivity 1.2 mumin Wescan 269024 1 mM ethylenediamine, Conductivity cation/HS pH 6.1 50 x 3.0 mm ID 1.5 ml/min Hitachi custom 0.7 M sulfosalicylicacid, Direct spectrophot. cation exchanger 0.05 mM chlorophosfonazo 111 at 679 nm 150 x 2.6 mm ID 1.5 ml/min Shimadzu Shim- 4.0 mM tartaric acid, 2.0 mM Conductivity pack IC-C1 ethylenediamine Dionex CS-2 20 mM sulfosalicylate, 3.0 Direct spectrophot. 250 x 4.0 mm ID mM ethylenediamine,pH 5.0 after postcolumn 1.5 mVmin reaction
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviutionsare listed in Appendix B (p. 745).
74,20 28 75 76 43 77
E
3
Q
ii:
a
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
Solutes (min)
Sample Prep.
Aluminium (1.8)
Chloride (2.5), calcium ( 5 . 3 , nitrate (9.3, magnesium (13) sulfate ( 19)
-
Chloride (3.4), nitrate (5.0), calcium (7.4), magnesium (9.0), sulfate (14.2) Chloride (3.7), nitrate (5.7), sulfate (7.4), calcium (10.9, magnesium (13.9) Sodium (31, potassium (1 l), chloride (3). bromide (61, nitrate (7),sulfate (10) Magnesium (4), calcium (9), chloride (6). nitrate (25), sulfate (31)
-
-
i2
Column
Eluent
Detection
Dionex 03-2 50 x 4.0 mm ID
0.1 M potassium sulfate, adjusted to pH 3.0 with nitric acid 1.O mumin
Fluorescence at 78 360,5 12 nm after post column addition of 8-hydroxyquinoline 5-sulfonate Indirect specuophot. 79 at 290 nm
0.5 mM disodium copperMCI SCA-Ol anion-exchanger EDTA, 0.05 mM disodium 150x3.0mmID dihydrogen-EDTA 0.5 ml/min 1.0 mM EDTA, pH 6.0 TSK-gel IC1.0 ml/min Anion-SW 50 x 4.6 mm ID 1 mM diaminocyclohexaneNucleosil 10tetraacetic acid, pH 5.8 Anion II 250 x 4.6 mm ID 1.0 d m i n Dionex AS-3 and 1.6 mM lithium carbonate, 2.4 mM lithium acetate, CS-1 in series 150 x 4.0 mm ID pH 10.4 200 x 4.0 mm ID 1.5 ml/min 3.3 mM copper phthalate Vydac 302 IC and Dionex CS-1 1.5 ml/min in series 250 x 4.6 mm ID 200x4.0mmID
Ref
Directandindirect conductivity
80
Directandindirect spectmphot. at 205 nm Conductivity, inpotentiometry
81
Conductivity, indirect potentiometry
82
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
82
b
TABLE 21.1 (CONTINUED). ANALYSIS OF DRINKING WATER USING IC
3 0
P ~~~~
~~
Solutes (min)
Sample Prep.
Magnesium (3). calcium (4), chloride (3.3, nitrate (6),sulfate (14)
Column
Eluent
Detection
Waters IC Pak C and IC Pak A in series 50 x 4.6 mm ID 50 x 4.6 mm ID
2 mM ethylenediamine,3 mM Conductivity octanesulfonate, adjusted to pH 6.0 with octanesulfonic acid, 1.2 Wmin
~~
~
Ref
B t3 b
i3x P
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
83
0
2
2
rl
TABLE 21.2
0
m
ANALYSIS OF HIGH PURITY WATERS USING IC Solutes (min)
Sample
Sample Prep.
Column
Chloride (2.4), phosphate (4.2), Powerplant water Preconcentration Dionex anion nitrate (8.3), sulfate (11.6) separator 250 x 3.0 mm ID Fluoride (1.7), chloride (2.8). Semiconductor Preconcentration Waters IC Pak A nitrite (3.3, bromide (4.4). water, 50 x 4.6 mm ID nitrate (5.2), phosphate (10.2), powerplant water sulfate (14.1) Fluoride (1.7), chloride (2.), nitrite (3.3), bromide (4. l), nitrate (4.8) Chloride (2.66). nitrite (3.42), phosphate (6.64). nitrate (8.42), sulfate (13.90)
Semiconductor Preconcentration Waters IC Pak A 50 x 4.6 mm ID water, powerplant water Ultrapure water Preconcentration Dionex anion on Dionex AG-1 separator
Fluoride (2.0), glycolate (2.9), chloride (3.6), nimte (4.4), phosphate (6.2), bromide (10.0), sulfate (13.5)
Boiler feed water
Eluent
Detection
Ref
3.0 mM bicarbonate, 2.4 mM carbonate 138 mlhr 0.32 g/l boric acid, 0.08 mV1 gluconic acid, 0.08 g/l lithium hydroxide, 2 ml glycerine (12% ACN) 1.2 mVmin 0.75 g141 potassium hydroxide 1.2 mVmin 3.0 mM bicarbonate, 2.0 mM carbonate
Conductivity
84- 101
Conductivity
102, 103
Indirect conductivity
102
Conductivity
104112,88
Conductivity
113, 114
Conductivity
115-117
Conductivity
118
-
Dionex anion separator
Glycolate (2.6). chloride (3.3), Boiler blowsulfite (6.7), sulfate (9.4), down water phosphate (13.6)
-
Dionex anion 5.0 n M carbonate, separator 4.0 mM hydroxide 1000x2.8mmDD 115myhr
Chloride (3.60), nitrate (4.99), Boiler water sulfate (21.23), fluoride (6.80), (high pH) formate (8.88), acetate (lOSI), propionate (12.84)
Cat-ex clean-up, Waters fast fruit preconcentration juice (x2) and IC (32 ml) Pak A 150 x 7.8 mm ID 50 x 4.6 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 138 ml/hr
1.0 mM octanesulfonic acid and 3.0 mM octanesulfonate 1.O Wmin
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B ( p . 745).
f5
b
TABLE 21.2 (CONTINUED). ANALYSIS OF HIGH PURITY WATERS USING IC Solutes (min)
Sample
Sample Prep.
Column
a
Eluent
Detection
Ref
9 i;.
9 Boric acid (1.8), fluoride (2.4), acetate (2.7), formate (3.9), chloride (8.3) Formic (7.3, acetic (8.3), propionic (9.0),butyric (11.l), chloride (16.1) Chloride (2.92), bromide . (3.88), sulfate (11.69), fluoride (7.28)
Powerplant highpurity water, boratedwater Powerplant water
Reconcentration Dionex AS4A on Dionex AG4A Dionex anion separator 500X3mmID High-purity 500 p1 injection Waters fast fruit deionized water juice (x2) and IC Pak A 150x 7.8 mm ID 50 x 4.6 mm ID Borate (7). fluoride (8), silicate Ultra-pure water Beconcentration Wescan 269029 (9), chloride (15) (10 d) ani0ll.R 250 x 4.1 mm ID Dionex anion Chloride (4.0), phosphate (7.3), Demineralized, Filtration, boiler, preconcentration separator nitrate (9.8), sulfate (14.0) condensate and (10 ml) 500x3.0mmID cooling waters High-purity heconcentration Dionex AS-5 Chloride (2.0), nimte (2.4), nitrate (4.3), sulfate (12.3) water (15 d) 250 x 5.0 mm ID Chloride (4.3), sulfite (1 1.7), sulfate (19.0)
Boiler water
Chloride (2), nitrate ( 3 3 , sulfate (6.5)
Cooling tower water
Filtration
Dionex anion separator 500 x 3.0 mm ID Reconcentration Waters IC Pak A 50 x 4.6 mm ID
5 mM tetraborate
Y
Conductivity
119
5B
Q
0.1 mM hydroxide 2.3 d m i n
Conductivity
120
1.0 mM octanesulfonicacid and 4.0 mM octanesulfonate 1.O d m i n
Conductivity
121
5 mh4 hydroxide, 0.1 m M benzoate 2.0 Wmin 3.0 mM bicarbonate, 2.4 mM carbonate 138mVhr
Indirect conductivity
122
Conductivity
123126,4
3B
2
0.09 mM carbonate, Conductivity 8.0 mM hydroxide 2.0 Wmin Conductivity 1.0 mM hydroxide, 2.0 mM carbonate 138 mVhr 1.42 mM gluconate, 5.82 mM Conductivity boric acid, 0.25% glycerine, pH 8.5 (12% ACN) 1.2 d m i n
Seep. 487 for notes on the organizationof this Table. Seep. 713for References. Abbreviationsare listed in Appendix B (p. 745).
106, 104 123 127-130
-4
TABLE 21.2 (CONTMUED). ANALYSIS OF HIGH PURITY WATERS USING IC Solutes (min)
Sample
Sample Prep.
Chloride (4.4), nitrate (6.8), sulfate (19.4)
Deionized water
Preconcentration Waters 1C Pak A 50 x 4.6 mm ID (4 A)
Bromide (4.3, nitrite (LO), niuate (7.9)
Deionizedwater
-
Chloride (5). sulfate (14)
steam Preconcentration Home-packed condensate, (20.0 ml) XAD-1 150 x 3.0 mm ID boiler feed water Wescan 269001 Boiler feed water anion 250 x 4.6 mm ID Dionex AS-7 Boiler blowdown MPIC guard water column
Chloride (1.9), sulfate (7.8) EDTA (7.6). sulfate (8.4)
Silicate (8). chloride (14)
Boiler feed water -
Silicate (6), chloride (13)
Powerplant water -
Bicarbonate (2.0),chloride (2.9)
High-purity water
Large injection volume (2 ml)
Column
Parti~ilODs-3
3 Detection
3.5 mM p-toluenesulfonic acid, pH 6.0 1.0 d m i n 10mM octylamine, adjusted to pH 6.2 with phosphoric acid 2.0 d m i n 0.2 mM phthalate, pH 6.2 1.O mymin
Conductivity
Conductivity
133
9.1 mM phthalate, 0.9 mM phthalic acid 2.5 flmin 50 mM nitric acid 0.5 d m i n
Conductivity
134, 135
aniOn/R
3 mM hydroxide 1.7 d m i n
250 x 4.1 mm ID Waters IC Pak A 50 x 4.6 mm ID Zipax S A X 250 x 4.6 mm ID
Hydroxide 1.2 d m i n 0.2 mM phthalic acid, pH 6.8 2.0 d m i n
Wescan 269029
Ref
Eluent
131
132 Direct spectmphot. at 205 nm
136 Direct spectrophot. at 330 nm after post-column reaction with Fe(1II) perchlorate 137 Indirect conductivity Indirect 138 conductivity Indirect 139 spectrophot. at 231 nm
Seep. 487 for notes on the organizationof this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
BB tu
L,
TABLE 21.2 (CONTINUED). ANALYSIS OF HIGH PURITY WATERS USING IC Solutes (min)
Sample
Sample Prep.
Eluent
Detection
Chloride (4.0),nitrite (5.3)
High-purity water Distilled water
Reconcentration Dionex A S 4 (15 250 x 3.0 mm ID Large injection Wescan anion 250 x 4.6 mm ID volume (2ml)
1.2mM bicarbonate 1.5 d m i n
Conductivity
2.0 mM methanesulfonic acid, pH 5.0 2.0 d m i n
Direct 140 spectrophot. at 214 nm, conductivity
0.04 M sodiumperchlorate 2.0 d m i n
Direct
250 x 4.6 mm ID
Waters IC Pak A 50 x 4.6 mm ID Preconcentration Home-packed
Benzoic acid 1.2 d m i n 0.2 mM benzoate, pH 6.2 1.0 d m i n
Chloride (3.2)
Nuclear power water steam condensate, boiler feed water Deionizedwater
Chloride
Boilerwater
-
Silicate (5.1)
Boiler water
Chloride (4.7),nitrate (6.8)
Nitrite (3.6),nitrate (4.2) Fluoride (S),chloride (9) Chloride (7)
Deionized water
Millex iiltration
Column
Ionosphere A
Spiking
(8.4ml)
-
XAD-1 500x 3.0mm ID Vydac 302 IC 250 x 4.6 mm ID
2.0 mM phthalate, pH 4.96 2.5 d r n i n
Home-packed Zeo-Karb 225
100 ppm orthophosphate 0.3 d m i n
Waters IC Pak A HR
1.O mM lithium hydroxide
1.2 mlfmin
Ref
106
st
i;.
3
(b
B
141
spectrophot. at 190 nm 142 Conductivity Conductivity
133
Indirect 143 spectrophot. at 250 nm Potentiomtry 144 at silver wire electrodes Indirect 145 conductivity
75 x 4.6 mm ID
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in AppendixB (p. 745).
8
a
0
R
a
4.
TABLE 21.2 (CONTINUED). ANALYSIS OF HIGH PURITY WATERS USING IC Solutes (min)
Sample
Sample Rep.
Silica (3.2)
High-purity deionized water
Reconcentration Dionex AS-4A on Dionex AG-5
Sulfate (7) Sodium ( 5 . 9 , ammonium (7.8), potassium (9.5)
steam Reconcentration condensate, (24.7 ml) boiler feed water Deionized water, Reconcentration semiconductor device extracts
Column
Eluent
Detection
15 mM boric acid,
Direct 146 spectrophot. at 410 nm after post-column reaction with molybdate Conductivity 133
15 mM hydroxide
XAD-1
0.2 mM citrate, pH 6.0 1 .O mumin
500 x 3.0 mm ID Dionex cation separator 200 x 4.0 mm ID
5.0 mM hydrochloric acid
Home-packed
Lithium (3.9), sodium (5.8), ammonium (8.8),potassium (11.4) Sodium (3.8), ammonium (5.0). potassium (6.2), morpholine (9.4) Sodium (9.4), ammonium (13.4), morpholine (27)
Powerplant water Preconcentration Waters IC Pak C 50 x 4.6 mm ID
Steam water
Filtration
Sodium (5.88). potassium (11.24) Hydrazine (4.77)
Boiler water (high PHI Steam water
Cat-ex precolumn Filmtion
Dionex CS-3 250 x 4.0 mm ID
Synthetic powerplant water
i;
Dionex cation separator 200 x 4.0 mm ID Waters IC Pak C 50 x 4.6 mm ID Dionex cation separator 200 x 4.0 mm ID
Conductivity
Ref
86, 107.92, 85,
93, 94, 108 147, 102
2 mM nitric acid 1.2 mumin
Indirect conductivity
60 mM hydrochloric acid, 40 mM boric acid 1.5 mVmin 5.0 mM hydrochloric acid 2.3 mVmin
Conductivity
148
Conductivity
149, 126
5.0 mM nitric acid 1.2 mumin 3.0 mM hydrochloric acid, 2.5 mM L-lysine 0.77 d m i n
Indirect conductivity Amperornery
118
Seep. 487 for notes on the organizationof this Table. Seep. 713for References. Abbreviations are listed in Appendi-xB (p. 745).
149
TABLE 21.2 (CONTINUED). ANALYSIS OF HIGH PURITY WATERS USING IC Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Cyclohexylamine (8.2)
Steam water
Filtration
149
Synthetic powerplant water
Conductivity
148
Lead (lo), magnesium (19), calcium (21), strontium (33) Copper (2.7), zinc (6.7), lead (7.7), nickel (12.3), iron (16.3), manganese (23.4)
Distilled water
3.0 mhl hydrochloric acid, 2.5 mM L-lysine 1.3 d m i n 40 mM hydrochloric acid, 7 mM diaminopropionic acid monohydrochloride 1.5 d m i n 3.0 mM tartaric acid, 4.5 mM ethylenediamine 0.35 M to 0.5 M tartrate gradient, pH 3.5 1.O d m i n
Conductivity
Cyclohexylamine (3.3), magnesium (5.9), calcium (11.3)
Dionex cation separator 400 x 4.0 mm ID Dionex CS-3 250 x 4.0 mm ID
Conductivity
150
Large injection volume (1 ml) Deionized water, Preconcentration plantwater on Aminex A5
Silisorb C 150 x 0.7 mm ID Aminex A5 100 x 4.0 mm ID
Copper (2.1), cobalt (2.7), zinc Deionized water, Preconcenwtion Aminex A5 100 x 4.0 mm ID (3.2), lead (9.4), iron (14.3), plantwater on Aminex A5 manganese (21.9)
0.08 M to 0.2 M citrate gradient, pH 4.6 1.O d m i n
Iron (In) (2.0), copper (2.6), nickel (3.2), zinc (4.4), cobalt ( 5 . Q lead (8.5), iron (11) (14.3)
Citrate. oxalate
High-purity water
Preconcentration Dionex CS-2 (0.5-1.0 ml)
Ref
Direct 151 spectrophot. at 540 nm after post-column reaction with PAR Direct 152 spectrophot. at 540 nm after post-column reaction with PAR Direct 153 spectrophot. at 520 nm after post-column reaction with PAR
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
4
TABLE 21.2 (CONTINUED). ANALYSIS OF HIGH PURITY WATERS USING IC Solutes (min)
Sample
Sample Prep.
Copper (3.69), nickel (4.80), zinc (7.70), iron (I1 ) (12.29)
Boiler water
Reconcentration TSK Cation SW (48.75 ml) 50 x 4.6 mm ID
Iron (111) (5.8). copper (7.31, nickel (8.2). zinc (9.0)
Powerplant high- Preconcentration Dionex CS-5 purity water on Dionex CG2, acidification, Ntration
Copper (0.8), zinc (2.5)
Powerplant water Reconcentration (10 ml) on Dowex 50W-X8 Dithiocarbamate complexes-lead Deionized water Precolumn (11.7), cobalt (13.4), copper derivahtion (15.2) and preconcentration on c18 precolumn coated with CTABr-DTC
Column
Durmm DC4A cation exchanger 50 x 4.0 mm ID Spherisorb ODs 250 x 4.6 mm ID
I
N
Eluent
Detection
Ref
10mM cimc acid, 1.7 mM ethylenediamine 1.2 mumin 6 mM pyridine-2,6- dicarboxylic acid, 50 mM sodium acetate, 50 mM acetic acid, pH 4.5 1.O d m i n
Conductivity
reaction with
0.02 M tartrate, pH 4.0 0.62 mumin
Reversed-pulse 157 polarography
10 mM phosphate, 10 mh4 CTABr, pH 6.8 to 2 mM CTABr (75%ACN) gradient 0.4 d m i n
Direct 158 specmophot. at 254 nm
154, 155
Dins 156 spectrophot. at 520 nm after post-column
PAR
Seep. 487 for notes on the organization of this Table. Seep. 713for References. Abbreviations are listed in Appendix B (p. 745).
Analysis of Treated Waters
713
21.2 REFERENCES 1 2 3 4 5 6
Darimont T., Schulze G. and Sonneborn M., Fres. Z. Anal. Chem., 314 (1983) 383. Darimont T., Schulze G. and Sonneborn M., Fres. Z. Anal. Chem., 317 (1984) 400. Coggan C.E., Anal. Proc., December (1982) 567. Deister H. and Runge E.-A., Arch. Eisenhutrenwes., 54 (1983) 405. Girard J.E. and Glatz J.A., Am. Lab., 13 (1981) 26. Keuken M.P., Slanina J., Jongejan P.A.C. and Bakker F.P., J. Chromatogr., 439 (1988)
7 8 9 10 11 12 13 14
Rossner B. and Schwedt G., Fres. 2.Anal. Chem., 320 (1985) 566. Schwabe R., Darimont T., Mohlmann T., Pabel E. and Sonnebom M., Inter. J. Environ. Anal. Chem., 14 (1983) 169. Schaefer J., Burmicz J. and Palladino D., Am. Lab., February (1989) 70. Golombek R. and Schwedt G., J. Chromurogr.,367 (1986) 69. Golombek R. and Schwedt G., J. Chromatogr.,452 (1988) 283. Nonomura M., Anal. Chem., 59 (1987) 2073. Nonomura M. and Hobo T., J. Chromutogr.,465 (1989) 395. Motomizu S., Sawatani I., Hironaka T., Oshima M. and Toei K., Bumeki Kagaku, 36
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41
Yan D., Rossner B. and Schwedt G., Anal. Chim Acta, 162 (1984) 451. Jupille T., Burge D. and Togami D., Chromatographia,16 (1982) 312. Wescan Application #229a. Perrone P.A. and Grant J.R., Res. Do.,September (1984) 96. Jupille T., LC, 1 (1983) 26. Behnert J. and Behrend P., LaborPraris, 8 (1984) 1204. Okada T. and Kuwamoto T., Anal. Lett., 17 (1984) 1743. Waters Ion Brief No. 88111. Okada T. and Kuwamoto T., Anal. Chem., 57 (1985) 258. Brandt G. and Kettrup A., Fres. Z. Anal. Chem., 320 (1985) 485. Waters Ion Brief No. 88105. Gennaro M.C., J. Chromutogr.,449 (1988) 103. Waters IC Lab. Report No. 256. Waters IC Lab. Report No. 308. Small H., Stevens T.S. and Bauman W.C., Anal. Chem., 47 (1975) 1801. Genitse R.G. and Adeney J.A., J . Chromurogr.,347 (1985) 419. Miura Y.and Fritz J.S., J. Chromutogr.,482 (1989) 155. Barron R.E. and Fritz J.S., Reactive Polymers, 1 (1983) 215. Gjerde D.T., Schmuckler G. and Fritz J.S., J. Chromatogr., 187 (1980) 35. Buytenhuys F.A., J. Chromutogr.,218 (1981) 57. Gjerde D.T., Fritz J.S. and Schmuckler G., J. Chromutogr., 186 (1979) 509. Wheals B.B., J. Chromatogr.,262 (1983) 61. Cooke M.,Anal. Proc., 21 (1984) 321. Cooke M., J. HRC & CC, 6 (1983) 383. Hayakawa K., Ebina R. and Miyazaki M., Hokuriku Koshu Eisei Gakkaishi, 11 (1984) 38. Hayakawa K., Hiraki H. and Miyazaki M., Bunseki Kagaku, 34 (1985) T71. Sato H., Anal. Chim. Acta, 206 (1988) 281.
13.
(1986) 77.
714 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
60 hl 62 63
64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82
Chapter 2 I
Dogan S. and Haerdi W., Chimia, 35 (1981) 339. Stuurman H.W.. Int. Lab., July/August (1988) 20. Pohlandt C., S . Afr. J . Chem.. 33 (1980) 87. Okada T., Bunseki Kagaku, 36 (1987) 702. Mullins F.G.P. and Kirkbright G.F., Analyst (London), 109 (1984) 1217. Lee S.H. and Field L.R., Anal. Chem., 56 (1984) 2647. Gemtse R.G., J . Chromatogr., 171 (1979) 527. Mangia A. and Lugari M.T., Anal. Chim. Acta, 159 (1984) 349. Jupille T., Togami D.W. and Burge D.E., Res. Dev., February (1983) 151. Pohlandt C., NIM Report No. 2107, 1981. Morrow C.M. and Minear R.A., Wafer Res., 21 (1987) 41. Brinckman F.E., Jewett K.L., Iverson W.P., Irgolic K.J., Ehrhardt K.C. and Stockton R.A., J. Chromafogr., 191 (1980) 31. Hoover T.B. and Yager G.D., Anal. Chem., 56 (1984) 221. Hoover T.B. and Yager G.D., J . Chroniatogr. Sci.. 22 (1984) 435. Dionex Application Note 51, Dionex Application Note 26. Baumann R.A., Schreurs M., Gooijer C., Velthorst N.H. and Frei R.W., Can. J . Chem., 65 (1987) 965. Zolotov Y.A., Shpigun O.A. and Bubchikova L.A., Fres. Z. Anaf. Chem., 316 (1983) 8. Ficklin W.H., Anal. Len., 15 (1982) 865. Tanaka K. and Fritz J.S., Anal. Cheni.,59 (1987) 708. Juii 2..Oshiina M. and Motomizu S., Analysr (London), 113 (1988) 1631. Hoshika Y., Murayama N. and Muto G., Bunseki Kagaku, 36 (1987) 174. 'I'erabe S., Yamamoto K. and Ando T., Kenkyo Hokoku - Asahi Garasu Kogyo Gijufsu Shoreikai, 39 (1981) 131. Wescan Application #229b. Fritz J.S.,Gjerde D.T. and Becker R.M., Anal. Chem., 52 (1980) 1519. Kondratjonok B. and Schwedt G., Fres. 2. Anal. Clietn.,332 (1988) 333. Miyazaki M., IIayakawa K. and Choi S.-G., J . Chromatogr., 323 (1985) 443. Hayakawa K.. Hiraki I%, Choi B. and Miyazrcki G.,Hokuriku Koslui Eisei Gakkaishi, 10 (1983) 24. lnteraction Sepmtions # I , March, 1989. Kolla P., Kohler J. and Schomburg G., Chromatographia, 23 (1987) 1987. Sherman J.H. and Danielson N.D., Anal. Chem., 59 (1987) 490. Smith D.L. and Fritz J.S.,Anal. Chint. Acta, 203 (1988) 87. Behnert J., Behrend P. and Kipplinger A., Lahorfraxis, 9 (1985) 38. Wescan Application #229c. Zenki M., Anal. Chem.. 53 (198 1) 968. Yan D. and Schwedt G., Fres. 2. Anal. Chem., 320 (1985) 252. Jones P., Ebdon L. and Williams T., Analyst (London), 113 (1988) 641. Hayakawa K., Sawada T., Shimbo K. and Miyazaki M., Anal. Chem., 59 (1987) 2241. Yamamoto M..Yamarnoto H., Yamarnoto Y.,Matsushita S., Baba N. and Ikushige T., Anal. Chem., 56 (1984) 832. Schwcdt G. and Kondratjonok B., Fres. Z.And. Chem., 332 (1989) 855. Jones V.K. and Tarter J.G., fnt. Lab., November (1985) 36.
Analysis of Treated Waters 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
104 105 106 107 108
109
110 111 112
715
Jones W.R., Heckenberg A.L. and Jandik P., J. Anal. Pur., October (1986) 68. Cuff D., CHEMSA, 7 (1981) 11. Balconi M.L., Pascali R. and Sigon F., Anal. Chim. Acta, 179 (1986) 419. Blair C., Mullenix J., Barker J. and Angers L., Proc.-Int. Water Conf., Eng. SOC. West PA, 46th, 1985, p. 305. Borman S . , Anal. Chem., 52 (1980) 1409. Dionex Application Update 103. Fichte V.W. and Mohr G.,Maschinenschaden, 55 (1982) 81. Mansfield G.H., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. I I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 271. Pensenstadler D.F. and Fulmer M.A., Anal. Chem., 53 (1981) 859A. Pensenstadler D.F., Peterson S.H., Bellows J.C. and Hickham W.M., ASTM Spec. Tech. Publ., 742 (1981) 55. Peterson S.H., Bellows J.C., Pensenstadler D.F. and Hickam W.M., Proc. Int. Water Conf., Eng. SOC. West PA, 40th, 1979, p. 201. Peterson S.H., Pensenstadler D.F., Bellows J.C. and Hickham W.M., ASTM Spec. Tech. Publ., 742 (1981) 71. Rawa J.A., ASTM Spec. Tech. Publ., 742 (1981) 92. Robles M.N., Simpson J.L., Brobst G.,Alvi A. and Passel1 T.O., Water Chem. Nucl. React. Syst., 3 (1983) 339. Weiss J. and Gob1 M., Fres. Z . Anal. Chem., 320 (1985) 439. Resch G. and Grunschlager E., Vom Wasser, 62 (1984) 207. Mosko J.A., Anal. Chem., 56 (1984) 629. Haak K.K., Ultrapure Water, November/December (1985) 43. Rawa J.A. and Henn E L , Proc. Int. Water Conf., Eng. SOC. West PA, 4&h, 1979, p. 213. Waters IC Lab. Report No. 228. Stewart D.A., Brinklow A.J., Dymond G.A., Baker-Glen R. and Walker J.B., in Jandik P. and Cassidy R.M. (Eds.), Advances in Ion Chromaiography, Vol. I , Century International, Inc., Franklin, MA, 1989, p. 307. Brandt F. and Trost R., Vort.-VGB-Konf. "Chem Krafwerk", 1983, p. 24. Brandt F. and Trost R., VGB Kraftwerkrtech., 64 (1984) 74. Tretter H., Paul G.,Blum F., Schreck H., Fres. Z. Anal. Chem., 321 (1985) 650. Dionex Application Note 34. Fulmer M.A., Penkrot J. and Nadalin R.J., in Sawicki E. and Mulik J.D. (Us.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 381. Kapelner S.M., Trocciola J.C. and Freed M.S., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol.II, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 345. Takehara H., Bunseki Kagaku, 36 (1987) 457. Plechaty M.M., LC, 2 (1984) 684. Slanina J., Bakker F.P., Jongejan P.A.C., Van Lamoen L. and Mols J.J., Anal. Chim. Acta,
130 (1981) 1. 113 Rich W.E., Inst. Technol., 24 (1977) 47. 114 Rich W.E.,Anal. Inst., 15 (1977) 113. 115 Rich W.E., Tillotson J.A. and Chang C.C., in Sawicki E., Mulik J.D. and Wittgenstein E. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. I , Ann Arbor Sci. Publ., Ann Arbor, MI, 1978, p. 185.
7 16
chapter 21
116 117 118 119 120 121 122 123
Judy A. and Rosset R., Analusis, 7 (1979) 259. Stevens T.S.,Turkelson V.T. and Albe W.R., Anal. Chem., 49 (1977) 1176. Waters IC Lab. Report No. 279. Dionex Application Update 102. Ivanov A.A., Shpigun O.A. and Zolotov Y .A., Zh. Anal. Khim., 4 1 (1986) 134. Waters IC Lab. Report No. 293. Wescan Application #188. Rawa J.A., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. 11, Ann Arbor Sci. Publ., Ann Arbor, MI, 1979, p. 245. Westwell A., Anal. Proc., 21 (1984) 320. Law J.J., Power Eng., 85 (1981) 94. Simpson J.L., Robles M.N. and Passell T.O., ASTM Spec. Tech. Publ.. 742 (1981) 116. Waters ILC Series Application Brief No. 2001. Waters ILC Series Application Brief No. 2002. Waters ILC Series Application Brief No. 6001. Waters ILC Series Application Brief No. 6004. Jackson P.E. and Haddad P.R., J . Chromatogr., 439 (1988) 37. Skelly N.E., Anal. Chem., 54 (1982) 712. Roberts K.M., Gjerde D.T. and Fritz J.S., Anal. Chem.,53 (1981) 1691. Wescan Application #129b. Wescan Technical Note 7.8.85. Dionex Application Note 44R. Wescan Application #129a. Waters ILC Series Application Brief No. 2004. Brandt G., Matuschek G. and Ketuup A., Fres. Z. Anal. Chem., 321 (1985) 653. h e y J.P., J. Chromatogr., 267 (1983) 218. Eek L. and Femr N., J . Chromarogr.,322 (1985) 491. Waters ILC Series Application Brief No. 2003. Jenke D.R. and Raghavan N., J. Chromatogr.Sci.,23 (1985) 75. Franks M.C. and Pullen D.L., Analyst (London), 99 (1974) 503. Waters Ion Brief No. 88104. Dionex Application Update 113. Pecevich P..Res. Dev.. September (1985) 92. Potts M.E. and Stillian J.R., J . Chromatogr.Sci., 26 (1988) 315. Gilbert R., Rioux R. and Saheb S.E., Anal. Chem., 56 (1984) 106. Kourilova D., Thao N.T.P.and Krejci M., Inter. J . Environ. Anal. Chem., 31 (1987) 183. Cassidy R.M. and Elchuk S., J . Chromarogr.Sci., 19 (1981) 503. Cassidy R.M. and Elchuk S.. J. Chromarogr.Sci., 18 (1980) 217. Riviello J., Fitchett A. and Johnson E., Proc. Inr. Water Conf., Eng. SOC. West PA, 43rd, 1982. p. 458. Waters IC Lab. Report No. 303. Waters Ion Brief No. 88102. Dionex Application Update 101. Hsi T.and Johnson D.C., Anal. Chim. Acta, 175 (1985) 23. Irth H., De Jong G.J.. Brinkman U.A.T. and Frei R.W., Anal. Chem., 59 (1987) 98.
124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152
153 154 155 156 157 158
7 17
Chapter 22 Miscellaneous Applications 22.1 OVERVIEW
Miscellaneous applications of IC are presented according to the scheme shown in Fig. 22.1.
r MISCELLANEoUS APPLICATIONS OF IC
Chemicals, chemical products reaction mixtures (Table 22.1) Photographic solutions, explosives (Table 22.2)
L
Miscellaneous (Table 22.3)
Fig. 22.2 Miscellaneous applications of IC.
TABLE 22.1 ANALYSIS OF CHEMICALS, CHEMICAL PRODUCTS A N D REACTION MIXTURES USING 1C Eluent
Detection
Ref
Acid dissolution Aminex A-5 250 x 4.6 mm ID
0.5 mM sulfuric acid 0.2 mumin
Direct spectrophot. at 210 nm
1
By-products of C( 14)-labelled carbonates
Acid dissolution Ag 5OW-X12 250 x 4.6 m m ID
0.5 mM sulfuric acid 0.2 mumin
Direa
1
Molybdenum, sulfur reaction mixtures
Dilution
Dionex NS- 1 separator 200 x 4.0 mm ID
Polysulfide solution
Cyanolysis
TSK gel IC Anion-PW 50 x 4.6 m m ID
2.0 mM teuabutylammonium hydroxide, 1.0 mM carbonate (50% ACN) 1.0 mVnlin 1.3 mM gluconate, 1.3 mM boric acid, 1.3 mM tetraborate, 12% ACN, 3% I-butanol, 0.5% glycerin, pH 8.5 1.2 mumin 2.0 mM temabutylammonium hydroxide, 1.O mM carbonate, 25% to 75% ACN gradient 1.O mumin
Conductivity, direct spectrophot. at 254 nm Conductivity,
Solutes (min)
Sample
Sample Prep.
Oxalic (6.5). glyoxylic (9.0). glycolic (1 1S), formaldehyde (12.0), formic (13.5). acetic (15.0) Oxalic (7.3, glyoxylic (9.0), glycolic (10.5), formic (12.0). formaldehyde (12.0), acetic (14.5) Disulfido molybdenum complexes -12 x sulfide (9.0). 13 x sulfide (10.9). poly(thiomo1ybdate) (14.8) Cyanide (2.7), carbonate (3.2). sulfide (3.9), sulfite (13.8). sulfate (17.l), thiocyanate (22). thiosulfate (35)
By-products of C( l.l)-labelled carbonates
Dithiomolybdate (6.3). te~thiomolybdate(9.3). poly(thiomo1ybdate) (18)
Molybdenum, sulfur reaction mixtures
Dilution
Column
Dionex NS- 1 separator 200 x 4.0 mm ID
specuophot. at 210 nm 2
3
direst
specuophot. at 220 nm
Direct specuophot. at 254 nm
2
n
See p . 487 for notes on the organizationof this Table. Seep. 732for References. Abbreviationsare listed in Appendix B (p. 745).
h,
lu
TABLE 22.1 (CONTINUED). ANALYSIS OF CHEMICALS, CHEMICALPRODUCTS AND REACTION MIXTURES USING IC ~~
~
Solutes (min)
Sample
Sulfate (19.69),monosulfophenyl phosphonate (1 1.34), disulfophenyl phosphonate (19.34)
Chemical mcuon Dilution mixtures
Fluoride (2.0), chloride (3.4), phosphate (5.1), nitrate (9.2), sulfate (13.8) Acetate (1.23), chloride (1.71), sulfate (5.96), oxalate (7.94), phthalate (14.40)
3046 peroxide solution Chromium hydroxy salts
Sample Prep.
Decomposition with platinum
Column
Eluent
Detection
Waters IC Pak A 50 x 4.6 mm ID
Nimc acid gradient 1.2 d m i n
Diren
Dionex AS4
Aqueous Dionex AS4A solution, reflux with pyridinedicarboxylic acid, dilution Dilution, boiling Waters IC Pak A 50 x 4.6 mm ID
Bicarbonate (3.25).chloride (4.85),nitrate (11.30), sulfate (21.00)
Silver powder
Fluoride (1.48),chloride (2.92), nitrate (6.83), sulfate (12.48)
Colloidal silica
(5%)
Filtration, dilution
Chloride, phosphate, nitrate, sulfate
Concenhated electrolyte solutions
Neurralization of Dionex A S 4 matrix by dual ion-exchange
Waters IC Pak A 50 x 4.6 mm ID
2.8 mM bicarbonate, 2.2 mM carbonate 1.O mUmin 16 mM bicarbonate, 18 mM carbonate 1.6 d m i n
Ref
4 spectrophot. at 254 nm, direct spectrophot. at 340 nm after post-column reaction with Fe(1lI) perchlorate Conductivity, 5 potendometry at ISE Conductivity 6
1.42 mM gluconate, 5.82 mM Conductivity boric acid, 0.25%glycerine, pH 8.5 (12%ACN) 1.2 mumin 0.49 gll boric acid, 0.13 mV1 Conductivity gluconic acid, 0.14 g/l lithium hydroxide, 2 ml glycerine (12.5%ACN) 1.2 d m i n 3.0 mM bicarbonate, Conductivity 1.1 mM carbonate 2.0 mI/min
Seep. 487 for nores on the organization of this Table. Seep. 732for References. Abbreviations are listed in Appendix B (p. 745).
7
8
9
5 5 s i
Eb
n =: Q =.
E
-4
TABLE 22.1 (CONTINUED). ANALYSIS OF CHEMICALS, CHEMICAL PRODUCTS AND REACTION MIXRJRES USING IC Solutes (min)
Sample Prep.
Column
Eluent
Detection
Ref
Acetate (1.97), formate (2.42), Chromium hydroxy salts chloride (4.77)
Aqueous solution, reflux with pyridinedicarboxy lic acid, dilution
Dionex AS4A
6 mM tetraborate 1.6 mumin
Conductivity
6
Chloride (a), nitrate (1 l), sulfate (26)
309bperoxide solution
-
Wescan anion 250 x 4.6 mm ID
4 mM phthalate, pH 3.9 1 .O mumin
Conductivity
10
Chloride (2.5), nitrate (4), sulfate (8)
Chemical etching solutions
Waters IC Pak A 50 x 4.6 mm ID
11
Chloride (5.3), bromide (5.7). iodide (10.5)
Silver halides
Hydrazine reduction, filmtion
Dionex NS- 1 separator 250 x 4.0 mm ID
Bisulfite derivativesformaldehyde (2.13). acetaldehyde (2.64)
Chloride solutions
Wescan resin anion-exchanger 250 x 4.0 m m ID
Sulfite (6.0), sulfate (10.9)
Sodium sulfite
An-ex column treament, addition of bisulfite Dilution
1.42mM gluconate, 5.82 mM Conductivity boric acid, 0.25%glycerine, pH 8.5 (12%ACN) 1.2 ml/min 1.0mM tembutylammonium Conductivity hydroxide, 3.0 mM carbonate (15%ACN) 1.O ml/min 20 m M cimc acid, pH 2.6 Conductivity
Conductivity
14
Sulfate (l.O), citrate (5.8)
Calcium sulfate hemihydrate
Dionex AG-4 Hydrochloric acid dissolution, 50 x 4.0 mm ID
2.8 mM bicarbonate, 2.2 mM carbonate 2.3 mVmin 0.01 M carbonate 2.0 ml/min
Conductivity
15
dilution Aqueous dissolution
1.0 mM tartaric acid, pH 3.2 1.2 ml/min
Conductivity, radiation
16
Bromate (6.5), bromide (12.5)
Sample
8
Inadiated potassium bromide
Dionex AS-3
Toyo Soda ICanion-SW 50 x 4.6 mm ID
See p . 487 for notes on the organization of this Table. Seep. 732for RMerences. Abbreviations are listed in Appendix B (p. 745).
12
13
-%
TABLE 22.1 (CONTINUED). ANALYSIS OF CHEMICALS, CHEMICAL PRODUCTS AND REACTION MIXTURES USING IC
M.
Column
Eluent
Detection
Ref
B s
Carbonate and peroxide reflux, dilution Borate chemicals Hydrofluoric and sulfuric acid digestion, dilution Silver halides Hydrazine reduction, filtration AR grade sodium Dilution chloride
Dionex anion separator 500 x 3.0 mm ID Dionex anion separator (x2) 250 x 3.0 mrn ID 500 x 3.0 mm ID Dionex A S 4 250 x 4.0 mm ID
3.0 mM bicarbonate. 1.8 mM carbonate, pH 9.75 2.0 d m i n 3.0 mM bicarbonate 2.3 d m i n
Conductivity
17
P
Borate chemicals Aqueous dissolution
Dionex ion exclusion separator
0.1 M mannitoi, 1 mM hydrochloric acid
Dionex anion separator 250 x 3.0 mm ID Dionex AS4A
3.0 mM bicarbonate, 2.4 mM carbonate 184 mUhr 2.2 mM carbonate 1.5 d m i n 14.7 mM ethylenediamine, 10 mM boric acid, 1.0 mM carbonate, pH 11.0 2.5 ml/min
Solutes (rnin)
Sample
Chloride (3.8),sulfate (21.1)
Chloride-doped cadmium sulfide
Fluorosilicate (0.9),fluoride (1.4) Chloride (3.1), bromide (6.3) Chloride, bromide
Borate-mannitol complex (12)
Sample Prep.
Tetrafluoroborate (1 1)
Borate chemicals Aqueous dissolution
Cyanide (as cyanate) (3.0)
Metal cyanide complexes Cyanide complexes
Cyanide (2.3)
Oxidation with chloraxnine-T
Dionex AS-3
Dionex AS-4
0.7 mM bicarbonate, 0.56 mM carbonate 2.0 d m i n 2.0 mM sodium carbonate 2.5 d m i n
z
B=: c1
Conductivity
18
Conductivity
12
Arnperometry at Ag elecde, 4.3v Conductivity
19
20
Conductivity
20
Conductivity
21
Ampemmetry at Ag electrode, OV
19
55 muhr
Seep. 487 for notes on the organization of this Table. Seep. 732for References. Abbreviations are listed in Appendix B ( p . 745).
s.
8
4
TABLE 22.1 (CONTINUED). ANALYSIS OF CHEMICALS, CHEMICAL PRODUCTS AND REACTION MIXTURES USING IC Solutes (min)
Sample
Sulfate (9.0)
Hydrogen peroxide solution
Sulfate (1 1)
Chromium solution
Dilution, ascorbic acid addition
Chloride (4.3)
Nickel carbonate
-
Bromide (5.8)
Chloride solutions
Fluoride (7.8)
Stannous fluoride Dilution powder
Azide (8.9)
Tris buffer
Sodium (6.6), ammonium
Magnesium (7.5). potassium (9.5) chloride Sodium (4.7), ammonium (8.0) 30% peroxide solution Sodium (3.1), potassium (4.8) Chromium hydroxy salts
Sample Prep.
Dilution
Aqueous solution, reflux with pyridinedicarboxylic acid, dilution
L3
Column
Eluent
Detection
Ref
Dionex anion separator 500 x 3.0 mm ID Hamilton PRP-X 100
3.0 mM bicarbonate, 2.4 mM carbonate
Conductivity
22
2 mM phthalic acid, pH 5 (10%acetone)
Conductivity
23
Wescan 269013 anion/HS 100 x 4.6 mm ID Waters IC Pak A 50 x 4.6 mm ID
5 mM phthalic acid 1.7 mumin
Conductivity
24
5 mM sodium chloride 1.2 mlfmin
25
Waters fast fruit juice (x2) 150 x 7.8 mm ID Interaction ION310
1.0 mM sulfuric acid 1.O mlfmin
Direct spectrophot. at 214 nm Conductivity
Direct spectrophot. at 210 nm Indirect conductivity Indirect conductivity Conductivity
27
vydac sc 340 x 2.0 mm ID Wescan cation 250 x 2.0 mm ID Dionex CS-3
2 mM sulfuric acid 0.5 d m i n 1.5 mM nitric acid 0.72 mlfmin Nitric acid, pH 2.5 25 mM hydrochloric acid, 0.25 mM 2,3-diaminopropionic acid 1.0 d m i n
See p . 487 for notes on the organization of this Table. Seep. 732for References. Abbreviations are listed in Appendix B (p. 745).
26
28 10 6
P5
5
TABLE 22.1 (CONTINUED). ANALYSIS OF CHEMICALS, CHEMICALPRODUCTS AND REACTION MIXTURES USING IC Solutes (min)
Sample
Sodium (2.7), ammonium (4.6) Barium and strontium carbonates Uranyl nitrate Sodium (4.5)
Sample Prep.
Column
Eluent
Detection
Ref
Aqueous dissolution
Wescan 269024 cation/HS 50 x 3.0 mm ID Zipax SCX 5 0 ~ 2 . 1mmID SCX 1 250 x 4.6 mrn ID
3.2 mM nihic acid 2.5 mlJmin
Indirect conductivity
29
3.0 mM hydrochloric acid 1.5ml/min 2.0 mM ethylenediamine, 4.0 mM tartaric acid 2.0 d m i n
Indirect conductivity Conductivity
30
Home-packed cation-exchanger 350 x 2 nun ID Aminex A5 100 x 4.0 mm ID
1.5 mM ethylenediamine, 2 mM tartrate, pH 4.2 0.85 d m i n 0.3 M to 0.5 M tartrate gradient, pH 3.5 1 .O mumin
Conductivity
32
TSK silica cation 50 x 4.6 mrn ID
1.07 g/l cimc acid, 7.5 g/l tartaric acid, 120 pl/l ethylenediamine 1.0 ml/min
Aqueous leaching Solar salt Magnesium (2.9), calcium Aqueous (3.3, strontium (4.2), barium solution, filtration, (7.0) extraction Magnesium (3.3). manganese Copper solution Masking with (4.9, calcium (6.1) ninilomacetic acid Uranium (l), copper (3), zinc Uranium solution Post-column (7), lead (9), nickel (lo), cobalt masking of (12), iron (16), manganese (22) uranium PAR complex with carbonate Copper (7.7), nickel (8.4), zinc Silica chloride (12.3, cobalt (12.9) solution
Dilution, pH adjustment, filtration
Seep. 487 for notes on the organization of this Table. See p . 732for References. Abbreviations are listed in Appendix B (p. 745).
P 3
8
h
8 31
Direct 33 spectrophot. at 540 nm after post-column reaction with PAWcarbonate Direct 34 spectrophot. at 546 nm after post-column kaction with
PAR
5 --.
g g.
s
-1
TABLE 22.1 (CONTINUED). ANALYSIS OF CHEMICALS, CHEMICAL PRODUCTS AND REACTION MIXTURES USING IC
h)
P
Solutes (min)
Sample
Sample Rep.
Column
Dysprosium (2.3). terbium (2.61, gadolinium (3.01, europium (3.6), samarium (4.01, promethium (4.8), neodymium (5.2), praseodymium (5.7), cerium (6.3), lanthanum (7.5) Samarium (6.0), neodymium (7.3), praseodymium (7.8), cerium (8.4), lanthanum (9.4)
Mixed fission products
Clean-up on a coated C8 precolumn
Aminex A9 cation- Gradient from 0.65 M exchanger hydroxyisobutyric acid (pH 150 x 3.2 mm ID 3.6) to 0.95 M hydroxyisobutyric acid @H 4.8) 1.O d m i n
Lanthanide fission products
Acid digestion, dilution
Supelco LC 18 150 x 4.6 mm ID
Eluent
5 mM octanesulfonate, hydroxyisobutyric acid gradient, pH 4.6 2.0 d m i n
Detection
Ref
Sodium iodide 35 scintillation counter
Direct 36 spectrophot. at 653 nm after post-column reaction with
Arsenam III
Terbium (9). gadolinium (12)
Terbium doped Hydrochloric gadolinium oxide acid digest, dilution sulfide phosphors
Panisil 10 SCX 250 x 4.0 mm ID
Gradient from 0.03 to 0.07 M hydroxyisobutyricacid, pH 4.6 1.2 mVmin
Direct 37 specmphot. at 520 nm after post-column reaction with
PAR
See p . 487 for notes on the organizarion of this Table. Seep. 732for References. Abbreviations are listed in Appendix B (p. 745).
TABLE22.2 ANALYSIS OF PHOTOGRAPHIC SOLUTIONS AND EXPLOSIVES USING IC ~~~~
Solutes (min)
Sample
Chloride (lo), CD-3 (10). phosphate (12), sulfite (26), bromide (32),sulfate (75)
Photographic color developing solutions
MCI GEL mixed 4.2 mM bicarbonate, bed exchanger 3.4 m M carbonate 100 x 3.0mm ID 2.1 d m i n
Acetate (2.2), chloride (4), bromide (6).sulfite (13),sulfate (16),thiosulfate (49) Boric (2), acetic (2.2), sulfite (9), sulfate (19), thiosulfate (90)
Photographic fixing solutions
Home-prepared anion-ixchanger 500 x 3.0 mm ID Home-prepared anionexchanger 20 x 3.0 mm ID
Photographic processing solutions
Fixers and Formate ( 3 . Q acetate (6.0). sulfite-foxmalin adduct (8.3), photographic effluents chloride (12.2) Boric (2), sulfite (19). bromide Photographic (21),sulfate (50) processing solutions Sulfate (9), thiosulfate (13)
Photographic fixer
Thiosulfate
Photographic gelatin
Sample Prep.
Dilution
Column
Eluent
2.5 mM carbonate 4.2 Wmin
5.0 mM bicarbonate, 4.5 mM carbonate, 0.6 M mannitol 1.3 to 1.9 W m i n Dionex fast anion 1.0 mM bicarbonate, separator 0.2%(v/v) formalin 250 x 3.0mm ID ll0myhr Dilution Home-prepared 5.0 mM bicarbonate, anionexchanger 4.5 mM carbonate, 40 x 3.0 mm ID 0.6 M mannitol 1.5 mVmin Wescan 269013 4 mM phthalate. pH 3.8 anioniHS 2.7 ml/min 100 x 4.6 mm ID Dilution, Home-prepared 2.0 mM bicarbonate, pmncentration anion-exchanger 2.0 mM carbonate 180 x 3.0mm ID 2.0 ml/min
Detection
Ref
Conductivity.
38
direa spectmphot. at254nm Conductivity
39,40
Conductivity
41
Conductivity
42
Conductivity
41
Conductivity
43
Conductivity
44
Seep. 487 for notes on the organizationof this Table. Seep, 732for References. Abbreviations are listed in Appendix B (p. 74.5).
4
TABLE 22.2 (CONTINUED). ANALYSIS OF PHOTOGRAPHIC SOLUTIONS A N D EXPLOSIVES USING IC Eluent
h)
Q\
Solutes (min)
Sample
Sample Prep.
Column
Detection
Ref
Chloride (3.5). chlorate (4.7), sulfate (7.8), perchlorate (17)
Explosive residues
Chloride (2.8), nitrite (3.3). nitratdchlorate (6.8). sulfate (10.5) Ammonium (8.29). monoethanolamine (9.60). diethanolamine (13.20), triethanolamine (16.93) Sodium (4.0).ammonium (5.4). monomethylamine (6.4), potassium (6.9)
Explosive residues
Aqueous extraction, centrifugation, filtration Aqueous dissolution
Wescan 269-001 8.0 mM phthalate, pH 4.2 anion 6.0 d m i n 250 x 4.6 mm ID
Conductivity
45
Dionex anion separator 250 x 4.0 mm ID Waters 1C Pak TM
Conductivity, direct spectrophot. Indirect conductivity
46, 47
Hydroxylamine explosives
Aqueous extraction
Explosives
Sodium (1 2), ammonium (1 5). monomethylamine (17), potassium (23) Sodium (1 1.8), ammonium (14.3, monomethylamine and potassium (16.4) Sodium (S.l), ammonium (9.7), monomethylamine (13)
Explosives and exp1osive residues Explosives and explosive residues Water gel explosives
Sodium (10.0), potassium (17.2)
Explosive residues
0.1 mM diaminopropionic acid Conductivity dih ydrochloride, 25 mM hydrochloric acid (4%ACN) 1.O d m i n 10 mM hydrochloric acid Conductivity Homogenization Dionex cation and dilution, separator (40% MeOH) 250 x 6.0 mm ID 1.97 mVmin filtration Homogenization Dionex cation 10 mM hydrochloric acid Conductivity separator 1.53 d m i n and dilution, filtration 250 x 6.0 mm ID Wescan 269-004 3.9 mM nitric acid Indirect Nitric acid conductivity digest, dilution cation 1.8 d m i n 250 x 2.0 mm ID 10 mM hydrochloric acid Conductivity Dionex cation Aqueous dissolution separator (30% EtOH) 200 x 6.0 mm ID 3.0 d m i n
3.0 mM bicarbonate, 2.4 mM carbonate 3.0 d m i n 4.0 mM nitric acid (5% MeOH) 2.0 m h i n
Aqueous dilution Dionex CS-3
Seep. 487 for notes on the organization of this Table. Seep. 732for References. Abbreviations are listed in Appendix B ( p . 745).
48
49
47, 50 50, 47 51 46
h,
h,
TABLE 22.2 (CONTINUED). ANALYSIS OF PHOTOGRAPHIC SOLUTIONS AND EXPLOSIVES USING IC Solutes (min)
Sample
Sample Prep.
Calcium (7)
Explosives and explosive residues
calcium
Water gel explosives
2.5 mM hydrochloric acid, Homogenization Dionex cation and dilution, separator 2.5 mM phenylenediamine filtration 250 x 6.0 mm ID &hydrochloride 3.07 mumin Nitric acid Wescan 269-004 1.0 mM ethylenediamine digest, dilution cation adjusted to pH 6.1 with 250 x 2.0 mm ID nitric acid 1.5 rnl/min Aqueous Dionex CS-2 0.01 M sulfuric acid, extraction 0.2 M ammonium sulfate 1.0ml/min
Aluminium (4)
Explosive filler
Column
Eluent
Detection
Ref
Conductivity
47
Indirect
51
conductivity
Dirrxt 52 spectrophot. at 570 nm after post-column reaction with pyrocatechol violet
Seep. 487 for notes on the organizationof this Table. Seep. 732for Rderences. Abbreviations are listed in Appendir B (p. 74.5).
4
Y
4 00 h,
TABLE 22.3
MISCELLANEOUS APPLICATIONS OF IC Solutes (min)
Sample
Sample Prep.
Formate (8.4). acetate (10.3) and chloride (2.8). bromide (4.0).nitrate (4.7), sulfate (12.4)
Solder paste and flux
Dilution in Waters ion propanohater, exclusion and filtration, IC Pak A
Chloride (2). bromide (2.5). nitrate (3), sulfate (18)
Solder flux
Fluoride (2.0), chloride (3.4). phosphate (5.1), nitrate (9.2), sulfate (13.8) Fluoride (2.0), chloride (3.4). phosphate (5.1). sulfate (13.8)
Integrated &cut encapsulation material Polishing slurry
Eluent
Detection
Ref
1 .O mM octanesulfonicacid and 4.0 mM octanesulfonate 1 .O d m i n
Conductivity
53, 54
Conductivity
55
Conductivity, potentiomtry using an ISE Conductivity,
5
COlUmn
300x8mmID,
switching
50 x 4.6 mm ID 0.02 M phthalic acid Wescan 269001 anion 3.5 d m i n 250 x 4.6 mm ID Dionex A S 4 2.8 mM bicarbonate, 2.2 mM carbonate 1 .O mVmin 2.8 mM bicarbonate, Dionex AS-4 2.2 mM carbonate 1 .O d m i n Dionex anion 3.0 mM bicarbonate, 2.4 mM carbonate separator 500 x 3.0 mm ID 138 ml/hr
Aqueous extraction
Dilution
Chloride (3.8), bromide (7.8), nitrate (9.3, sulfate (12.5)
Combustion with sorption into carbonate solution, filmtion Printed wiring Aqueous aqueous extracts extraction
Fluoride, chloride, nitrate, sulfate
Contamination effluents
Chloride (3.1), phosphate (4.7), Airrraft ceiling panels, fabric sulfite (5.7). bromide (6.8), sulfate (8.9)
Column
Dionex anion separator 500 x 2.8 mm ID Preconcenmtion Waters IC Pak A (20 ml) 50 x 4.6 mm ID
3.0 mM bicarbonate, 2.4 mM carbonate 92 mVhr 3.5 mM p-toluenesulfonate, pH 6.0 1.2 mI/min
5
potentiometry using an ISE Conductivity
56,57
Conductivity
58.59
Conductivity
60.61
Seep, 487 for notes on the organizationof this Table. Seep. 73.2for References. Abbreviations are listed in Appendix B (p. 745).
%
TABLE 22.3 (CONTINUED). MISCELLANEOUS APPLICATIONS OF IC
F’
Solutes (min)
Sample
Sample Prep.
Column
Eluent
Detection
Ref
ii F
Chloride (3.7), chlorate (5.3). perchlorate (12.0)
Flame atomic
Aqueous sonication, filtration
Extech c 8 150 x 4.1 mm ID
1 mM tetrabutylammonium phthalate. pH 6.2 (15% MeOH) lml/min 0.5 mM octanesulfonic acid (5% 2-propanol) 1.0 mvmin Bicarbonate, carbonate buffer
Indirect spcctmphot. at 280 nm
62
H
Conductivity
64
1 mM salicylic acid, pH 5
Conductivity
23
5.0 mM hydroxide
Conductivity
65
1.O mM succinic acid 1.O ml/min
Conductivity
66
0.7 @ citricIacid, 0.05 g/l ceaimide, pH 5.5 (30%M d H ) 1.O mVmin 8.4 mM phthalate, 1.6 mM phthalic acid 2.5 Wmin 0.6 mM carbonate, 7 mM bicarbonate 2.0 mVmin
Direct 67 spectrophot. at
absorption accumulate
Nimc (5.0), hydrofluoric (7.4), Semiconductor acetic (9.2) acid etchant Fluoride, chloride. sulfate Chloride, bromide, iodide Fluoride, acetate, chloride Lactate, phosphate, chloride Phthalic acid u.9),isophthalic acid (15.0) Chloride (2.9). sulfate (8.5) Temfluoroborate (12), phosphate (28)
Dionex AS-1 ion exclusion 250 x 9.0 mm ID Dionex anion Domestic refuse Combustion, dilution separator Eluent exation Hamilton PRP-X Halogen lamps of broken 100 lamps, filtration Cloth Aqueous Dionex anion separator leaching 500 x 3.0 mm ID Paint bath Filtration, Hm-packed dilution XAD-1 solution 500 x 2.0 mm ID Hydrolysis with SAX-1 Paint resin methanolic 125 x 5.0 mm ID potassium hydroxide Wescan 269001 Dye anion 250 x 4.6 mm ID column Dionex AG-4 and BorophosphoAS-3 in series silicate glass film switching
138 mvhr
Conductivity
220 nm Conductivity
68.69
Conductivity
70
Seep. 487 for notes on the organization of this Table. Seep. 732for References, Abbreviations are listed in Appendix B (p. 745).
4
TABLE 22.3 (CONTINUED). MISCELLANEOUS APPLICATIONS OF IC Solutes (min)
Sample
Borate (18), fluoride (20)
NBS standard glass
Fluoride (16). formic (20) Teduoroborate (9) Chloride (9.4) Chloride (4.55)
Sulfate (6.0)
Sulfate (5)
Sodium (7.9, ammonium (ll.O), potassium (13.8)
Sample Prep.
Column
Wescan aniofl Hydroxide fusion, dilution, filtration,cat-ex clean-up Glass coating Wescan 269006 exclusion 300 x 7.8 mm ID Dionex anion Radioactive Hydrofluoric borosilicate glass acid dissolution, separator dilution Aqueous Dionex anion Printed wiring separator aqueous extracts extraction 500 x 2.8 mrn ID Nitric acid Waters IC Pak A Cement 50 x 4.6 m m ID digest, Ag ppt of chloride, redissolution in ammonia Dionex anion Aqueous Non-aqueous extraction separator media 250 x 3.0 mm ID Dionex AS-4 Alumina catalyst Hydrofluoric acid dissolution, supports evaporation Dionex cation Printed wiring Aqueous separator aqueous extracts extraction 250 x 6.0 mm ID
W
0
Eluent
Detection
Ref
0.6 gfl sodium hydroxide, 0.025 mM benzoate 0.5 mVmin
Conductivity
71
2 mM nitric acid 0.4 d m i n
Conductivity
72
Bicarbonate, carbonate buffer
Conductivity
73
2.5 mM bicarbonate 92 mUhr
Conductivity
58. 59
1.0 mM carbonate 1.2 mVmin
Conductivity
74
5.0 m M bicarbonate,
Conductivity
75
Conductivity
76
Conductivity
58,59
1.0 mM hydroxide 230 mVhr 3.0 mM bicarbonate, 2.4 mM carbonate 2.0 mVmin 6.0 mM nitric acid 230 ml/hr
Seep. 487 for notes on the organizationof this Table. See p . 732for References. Abbreviations are listed in Appendix B ( p . 745).
n
N
kl
Miscellaneous Applications
73 1
B
E
U
.9 c .y. r U
F
Chapter 22
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
Albanan G. and Collins C.H., J. Chromutogr.,395 (1987) 623. Weiss J., Mockel H.J.. Muller A., Diemann E. and Walberg H.-J., J. Chromurogr., 439 (1988) 93. Ikeda S., Satake H. and Segawa H., Nippon Kaguku Kaishi, 9 (1985) 1704. Waters IC Lab. Report No. 31 1. Talasek R.T., J. Chromurogr.,465 (1989) 1. Grasso G. and Bufalo G., J. Chromarogr.,454 (1988) 41 1. Waters IC Lab. Report No. 291. Waters IC Lab. Report No. 280. Cox J.A. and Tanaka N., Anal. Chem., 57 (1985) 383. Jupille T., Togami D.W. and Burge D.E., Res. Do.,February (1983) 151. Waters ILC Series Application Brief No. 6002. Gustafson F.J., Markell C.G. and Simpson S.M., Anal. Chem., 57 (1985) 621. DuVal D.L., Rogers M. and Fritz J.S., Anal. Chem., 57 (1985) 1583. Weiss J. and Gob1 M., Fres. Z . Anal. Chem., 320 (1985) 439. Matsui H., Amita K., Hashizume G., Adachi G. and Shiokawa J., Gypsum & Lime, 189 (1984) 69. Tamai T., Nishikawa S. and Tanaka Y., Annu. Rep. Res. Reactor Insr. Kyoto Univ., 17 (1984) 150. Koch W.F. and Stolz J.W., Anal. Chem., 54 (1982) 340. Wilshire J.P., LC, 1 (1983) 290. RocMin R.D. and Johnson E.L., A n d . Chem., 55 (1983) 4. Wilshire J.P. and Brown W.A., Anal. Chem., 54 (1982) 1647. Nonomura M. and Hobo T., J . Chromutogr., 465 (1989) 395. Lipski A.J. and Vairo C.J., Con. Res., 13 (1980) 45. Schaefer J., Burmicz J. and Palladino D., Am. Lab., February (1989) 70. Wescan Application # 1 0 . Waters Ion Brief No. 88112. Waters IC Lab. Report No. 267. Interaction Separations #1, 1989, March. Fritz J.S., Gjerde D.T. and Becker R.M., Anal. Chem., 52 (1980) 1519. Wescan Application # l a . Ahmad M. and Khan A.. The Nucleus, 18 (1981) 29. Sat0 K., Akama Y.,Tanaka S. and Nakai T., Bunseki Kagaku, 36 (1987) 552. Sevenich G.J.and Fritz J.S., J . Chromutogr., 347 (1985) 147. Cassidy R.M. and Elchuk S., J. Liq. Chromurogr.,4 (1981) 379. Waters IC Lab. Report No. 246. Baker J.D., Gehrke R.J., Greenwood R.C. and Meikrantz D.H., J. Radioanal. Chem., 74 (1982) 117. Knight C.H., Cassidy R.M., Recoskie B.M. and Green L.W., Anal. Chem., 56 (1984) 474. Mazzucotelli M., Dadone A., Frache R. and Baffi F., Chromatographia,15 (1982) 697. Ohno T., Kobayashi H. and Mizusawa S., J . Soc. Phorogr. Sci. Technol. Jpn., 47 (1984) 91. Karasawa F., Ohno T. and Mizusawa S., Nippon Shushin Gakkaishi, 44 (1981) 96.
Miscellaneous Applications 40 41 42 43 44
733
Karasawa F., Ohno T. and Mizusawa S., Nippon Shashin Gakkaishi, 43 (1980) 245. Ohno T., Kobayashi H. and Mizusawa S., Nihon Shashin Gakkai, 47 (1984) 108. McCormick M.J. and Dixon L.M., J. Chromatogr.. 322 (1985) 478. Wescan Application #72. Ohno T., Kamoi M., Karasawa F. and Mizusawa S., J . SOC.Photogr. Sci. Technol. Jpn., 43 (1980) 48.
66 67 68 69 70 71 72 73 74
Green M.J., LC, 3 (1985) 894. Rudolph T.L., Proc. Int. Symp. Anal. Detect. Explos., 1983, p. 213. Reutter D.J. and Buechele R.C., Proc. Int. Symp. Anal. Detect. Explos., 1983, p. 199. Waters IC Lab. Report No. 282. Dionex Application Update 121. Reutter D.J., Buechele R.C. and Rudolph T.L.. Anal. Chem., 55 (1983) 1468A. Barsotti D.J., Hoffman R.M. and Wenger R.F., Proc. Int. Symp. Anal. Detect. Explos., 1983. p. 209. Dionex Application Note 42. Dunn M.H., LC.GC, 7 (1989) 138. Waters IC Lab. Report No. 299. Wescan Application #290. Dionex Application Note 13. Speitel L.C., Spurgeon J.C. and Filipczak R.A., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of EnvironmentalPollutants, Vol.II, Ann Arbor Sci. hbl., Ann Arbor, MI, 1979, p. 75. Wargotz W.B., Surf. Contam: Genesis, Detect. Control, 4th. 2 (1979) 877. Wargotz W.B., Proc. Int. Symp. Contam. Control, 4th, 1978, p. 291. Bagchi R. and Haddad P.R., J. Chromatogr., 351 (1986) 541. Bagchi R. and Haddad P.R., Proc. 9th. Aust. Symp. Anal. Chem., 1987, p. 147. Andrew B.E., J. Anal. Atomic Spec., 3 (1988) 401. Rocklin R.D., Slingsby R.W. and Pohl C.A., J. Liq. Chromatogr., 9 (1986) 757. Henschel P., Keune H., Kressner R., Mohlmann T., Schwabe R. and Sonneborn M., Inter. J. Environ. Anal. Chem., 15 (1983) 19. Posner R.D. and Schoffman A., in Sawicki E. and Mulik J.D. (Eds.), Ion Chromatographic Analysis of Environmental Pollutants, Vol. 11, Ann Arbor Sci. hbl., Ann Arbor, MI, 1979, p. 51. Fritz J.S., DuVal D.L. and Barron R.E., Anal. Chem., 56 (1984) 1177. Wheals B.B., J. Chromatogr., 262 (1983) 61. Wescan Application #110. Wescan Application #137. Lai S.-T., Nishina M.M. and Sangermano L., J. HRC & CC, 7 (1984) 336. McCrory-Joy C., Anal. Chim. Acra, 181 (1986) 277. Wescan Application #108. Smith J.G., Proc. Con$ Anal. Chem. Energy Technol., 25th, 1982, p. 63. Bruins J., Hillebrecht B., Monien H. and Maurer W., Fres. Z . Anal. Chem., 331 (1988)
75 76 77
Dionex Application Note 1. Oquendo J. and Prieto H., Rev.Tec. Intevep., 5 (1985) 163. Wescan Application #297.
45 46 47 48 49 50 51 52 53 54 55 56 57
58 59
60 61 62 63
64 65
61 1.
This Page Intentionally Left Blank
735
Appendix A Statistical Information on Ion Chromatography Publications A1
INTRODUCTION
Since the introduction of IC in 1975, the field has expanded rapidly and a great deal of literature has been published on the topic. All of the references cited in the theory and the applications sections of this book have been used to compile a data base of over 1800 articles on IC. This data base contains an extensive coverage of all literature published on IC prior to the start of 1989 and includes monographs, chapters in monographs, journal articles, a wide variety of conference papers, technical reports and also the major manufacturers' application notes. Whilst no listing of references can be claimed to be thoroughly comprehensive, every effort has been made to locate all relevant literature. The primary source used was Chemical Abstracts, which was crossreferenced with bibliographies taken from pertinent books and review articles. In addition, all the major analytical and chromatographic journals were searched manually for articles relating to IC. This Appendix contains statistical information drawn from the data base.
220 1
Fig. AI Number of articles on IC (not including manufacturers' application notes) published each
year since 1975.
736
A2
Appendix A
TECHNIQUES IN ION CHROMATOGRAPHY
Annual output and source of IC articles Fig. A1 shows the annual output of articles on IC (excluding application notes), from 1975-1988. It can be noted that this output has remained relatively steady for the past 5 years. The distribution of these articles between the major scientific journals is shown in Fig. A2. It is apparent that Analytical Chemistry and Journal of Chromatography account for almost 50% of publications on IC. The 30% not shown in Fig. A2 is comprised of articles published in over 50 additional journals, none of which contained more than about 25 articles (in total) on IC. In fact, a surprising number of specialist journals contain articles on IC, with some of the more unusual including Phytopathology, Journal of Molluscan Studies and Kidney International. Of the non-English journals, those published in Japanese contain the most articles, followed by those in German. Apart from journal articles, the next best source of literature on IC is application notes and technical reports produced by the instrument manufacturers. More than 400 applications have been published by the Dionex Corporation, Millipore-Waters and Wescan Instruments. This is illustrated in Fig. A3, which contains the same information as Fig. A2, but also includes major instrument manufacturers' application notes and technical reports. Again, the missing percentage (approximately 25%) is made up of journals containing only a small number of articles on IC.
Fig. A2 Papers published (as a percentage of the total) in various journals. Manufacturers application notes are not included in the total.
Statistical In$ormarion on IC Publicarions
737
Fig. A 3 Papers published (as a percentage of the total) in various journals, including the major
manufacturers’ application notes. Separation and detection methods Fig. A4 shows the types of separation and detection methods used. The entry for ion interaction chromatography includes both the dynamic and permanent coating methods, with the former outnumbering the latter by around nine to one. All of the detection methods listed include both direct and indirect methods, with the exception of UV spectrophotometric detection. As would be expected from the original concept of IC, the most common method of ion analysis is the combination of an ion-exchange separation (either suppressed or non-suppressed) with conductivity detection. Solute types The frequency with which a particular solute has been determined by IC is illustrated in Fig. A5 (for anions), Fig. A6 (for carboxylic acids) and Fig. A7 (for cations). Fig. A5 shows that C1-, Sod2- and NO3- are the anions which are determined most frequently. These are normally quantitated together, along with Br-, N02-, F- and P043-. Of the solutes not included in Fig. A5, the order of incidence is ClO3-, BrO3-, Ioj, C104~-.C03~-,HCO3-,CN-. S2-and As0d3-. The frequency of analysis of carboxylic acids acids (quantitated either as the acid or the anion) appears in Fig. A6. Acetic and formic acids are the species determined most commonly, which may be due to the fact that these can separated readily by ionexchange, as well as by ion-exclusion. The relatively high number of oxalic acid analyses results primarily from the importance of this species in clinical applications.
5
Y 0-
k
CJ Y
P 1
s
L.
E
Y
C n, 0 1
1
Thiocyanate
Thiosulfate
Sulfite
Iodide
Phosphate
Fluoride
Nitrite
Bromide
Nitrate.
Sulfate
Chloride
Number of analyses
Conductivity Direct W Indirect w UV/post-column Amperomeay Potentiometry RI Fluorescence Atomic Spec
0
Others
Ion exclusion
Ion interaction
Nonsupp. ion-ex
Supp. ion-ex
z
g
g
g
6
s
g
:
p 0
” 0
Detection mode (% of analyses)
o
”
0
2
Separation mode (% of analyses) . l
00
w
6
0Y
A'
s
s
5.
Lead Manganese Cadmium Strontium Rubidium Barium Cesium Lanthanides
zinc Nickel Iron cobalt Lithium
copper
Sodium Potassium Ammonium Calcium Magnesium
0
3
z
-3 s
g
g
Number of analyses W
g
c
a
c C.
a
PJ
s -
Ei.
8.
0
Benzoic acid
Tartaric acid
Succinic acid
Citric acid
Propionic acid
Lactic acid
Oxalic acid
Formic acid
Acetic acid
0
z
s
Number of analyses
Appendix A
740
Cation determinations are shown in Fig. A7. from which it can be noted that the total number of determinations of these species is only about 25% of that for anions (see Fig. A5). This is a result of the fact that up to four discrete separations (alkali metals and ammonia, alkaline earths, transition metals, and lanthanides) are required to screen cations, so that analyses tend to be specific for one group of cations only. As might be expected, Na', K+ and N&+ are the most frequently determined cations. The importance of the determination of Ca2+ and Mg2+ in clinical samples is reflected in the high frequency of analysis for these two species. It can also be seen that IC has considerable usage for the determination of transition metal ions.
A3
APPLICATIONS OF ION CHROMATOGRAPHY
Overview The remainder of this Appendix details the frequency with which IC is applied in various application areas. Fig. A8 provides an overview of IC applications within the general classifications used in Part V of this book; viz. environmental, treated waters, foods and plants, clinical and pharmaceutical, metals and plating, industrial, and miscellaneous. A total of just under 1700 individual applications is shown in Fig. A8.
Environmental analysis Environmental analysis constitutes the largest single application area of IC. Fig. A9 shows the frequency with which various sample types have been analyzed. The analysis of air, aerosols and airborne particulates is by far the most common environmental application. The "River waters" category in Fig. A9 includes river, lake, pond and stream waters.
Fig. A 8 Number of analyses within the major application areas of IC.
e
l
c
B
9.
g e?. g 3 ‘d, 8
5’ a
s
0
PUlP/papeI Deterg./poly. Strong acids Process water Scrubber liquor Engine products Strong bases Sewage water Refinery water Indust. brines Niddenit water Other waters
Organic cpds.
Waste water
O
Z
S
!
=
2
&
Number of applications ~ 4
Z
2
i
F
e
B c
E i
B
z a
C
Rain water River waters soil SeawaterAxim Rocks/ore/coal Icelsnow Ground waters Well waters Misc. waters Misc. geoL
Aid~IOSOl
, ! s s s s g g
Number of applications
142
Appendix A
Fig. A l l Number and type of food, beverage and plant samples analyzed by IC.
applications. The “Engine products“ category incorporates fuels, oils, coolants, etc., while “Niqdenit water” represents water samples drawn from denitrification processes. Food and plant analysis Applications of IC in food and plant analysis, shown in Fig A1 1, are characterized by a great variety of sample types, with beer (and related samples such as wort and fermentation products) being the single most common application. Wine analysis is the next most frequent application, with beverage analyses in general being the largest sample group within this area. Clinical and pharmaceutical analysis In the area of clinical and pharmaceutical analysis, blood (together with serum and plasma) and urine account for approximately half of the applications, as shown in Fig. A12. Of the remaining application areas, pharmaceutical electrolytes (such as I.V. solutions, Ringers solutions, erc.), tablets/drugs, toothpaste and biological fluids (such as saliva, sweat, cerebrospinal fluid, etc.) show approximately equal frequency of analysis. Metals, metal plating and mineral processing Fig. A13 shows that IC is commonly applied to the analysis of metal plating solutions, particularly chrome plating solutions. In fact, metal plating solutions as a group comprise the largest single sample type to which IC is applied. It is interesting to note the usage of IC in mineral processing, which is an area dominated traditionally by spectroscopic methods of analysis.
Chrome plating Metal process Nickel plating Metals Copper plating Plating baths Plating wastes Gold plating Metal surfaces Leach solutions Plating acids Alumin. plating Brighteners Misc. plating Misc. metals
e
L
n
S
G
S
Number of applications G
G%
W
Y P;
a
=I (u
c
I .
2.
c.
s
B
Q
Y P
W
B
3
C
L.
I
Misc. Biol.
Misc. Pharm.
Contact solns.
Sterile s o h .
Vitamins
Tissue
Biol. fluids
Biol. products
Tabletddmgs Toothpaste
Blood/serum Urine Electrolytes
Number of applications
2 W
a
b
8
5
c
B
a.
r
3a.
744
Appendix A
Analysis of treated waters and miscellaneous applications More than 200 applications of IC are concerned with the analysis of treated waters (which include tap and drinking waters, and high-purity waters such as distilled, boiler, power-plant and deionized waters), but these samples are not sufficiently diverse in nature to warrant a separate Figure. In the Miscellaneous group, the analysis of chemicals (incorporating chemical products and reaction mixtures) is by far the most common, with almost 50 applications. Of the remaining miscellaneous applications, explosives and photographic solutions are the next most frequently analyzed samples.
745
Appendix B Abbreviations and Symbols
~A,B
A A-, A+ A A,
AAS ACN An-ex APDC
P BB-, B+ BO BHEDC BiPY C1. C2, efc.
c-
CE CL
CM CX Cat-ex CPBr CTABr CTMA d D D DA DCPAES, DCP DCTA DEAE DEDTC, DTC DEDTP
Fraction of a species present in the form designated by X Separation factor for solutes A and B Absorbance (p. 344) Solute ion (p. 16) Cross-sectional area of an electrode (p. 311) Number of free adsorption sites on the stationary phase Atomic absorption spectroscopy Acetonitrile Anion-exchanger
Ammoniumpyrrolidinedithiocarbamate Overall stability constant Borate (p. 91) Second solute ion Boric acid Bis(2-hydroxyethy1)dithiocarbamate 2 3 -bipyridine Constants Counter-anion Total eluent concentration Total concentration of the eluent ligand Total concentration of the solute, M Concentration of species X Cation-exchanger Cetylpyridinium bromide Cetyltrimethylammonium bromide Cetylvimethylammonium Flow-channel width in an electrochemical cell Diffusion coefficient (p. 3 11) Dynamic reserve (p. 353) Diffusion coefficient of solute A Direct current plasma atomic emission spectroscopy 1,2-diaminocyclohexanetetraaceticacid DiethylaminoethylDiethylthiocarbamate Diethyldithiophosphate
When the same symbol has been used more than once,page numbers are given in parentheses.
746
DMAE DME DMEA DMSO DTAC DTC DTPA e &
E-, E+ Ell2
EA EDDA EDTA F fm
rl G GT GFAAS h fI H2L r i2p
HBZ H D W HETP I IFAA HIBA IIMDE HP HPIC I IPLC I ITAC I I 10 1,
I, IE
Is IC ICE ICPAES, ICP
Appendix B
DimethylaminoethylDropping mercury electrode Dimethylethanolammonium Dimethylsulfoxide Dodecylmmethylammonium chloride Diethyldithiocarbamate Diethylenetriaminepentaaceticacid Electronic charge Molar absorptivity Eluent ion Half-wave potential Ethy lamine Ethylenediamine-N,N'-diacetate Ethylenediaminetetraaceticacid Faraday constant Fraction of time that a solute molecule spends in the mobile phase Viscosity Conductance Conductance at temperature T Graphite furnace atomic absorption spectroscopy Flow-channel thickness in an electrochemical cell Peak height Eluent ligand Neutral, dibasic eluent acid (e.g. phthalic acid) Benzoic acid Hexadecyltrimethy lammonium Height equivalent to a theoretical plate Hexafluoroacetylacetone ct-hydroxyisobutyric acid Hanging mercury drop electrode Singly charge eluent anions (e.g. hydrogen phthalate) High performance ion chromatography High performance liquid chromatography Hexadecyltrimethylammonium chloride Current (p. 245) Phosphorescence intensity (p. 374) initial phosphorescence intensity Anodic current Cathodic current Degree of ionization of the eluent Degree of ionization of the solute Ion chromatography Ion chromatography exclusion Inductively coupled plasma atomic emission spectroscopy
When the same symbol has been used nwre than once, page numbers are given in parentheses.
Abbreviations and Symbols
11R IPA ISE
k kA' K
KO Ka KA,E
Kb L A A0
hi, he,
x-
L2-
m (as subscript) MXf MA MDEA MeOH MlBK MPlC n N N NIOSH
ODS Oxine P2PA PAD PAR PBDMA PCR PDCA Phen PIC PIC A PS-DVR PTFE 4
Q Q' r
lon-interaction reagent lsopropyl alcohol Ion-selective electrode Conductivity or specific conductance Capacity factor for solute A Cell constant Sorption capacity Acid dissociation constant Ion-exchange selectivity coefficient for solute A and eluent E Base dissociation constant Length of the chromatographic column Equivalent conductance Limiting equivalent conductance Limiting equivalent ionic conductance Deprotonated eluent ligand Mobile or eluent phase Metal solute ion Methylamine Methyldiethanolammonium Methanol Methylisobutylketone Mobile phase ion chromatography Number of electrons in an electrode half-call Number of theoretical plates (p. 8) Detector noise (p. 353) National Institute for Occupational Safety and Health Octadecylsilane 8-hydrox yquinoline Doubly charged eluent anion (e.g. phthalate) Propy lamine Pulsed amperometric detection 4-(2-pyridylazo)-resorcinol Poly(butadiene-maleic acid) Post-column reaction Pyridine-2,6-dicarboxylic acid 1,lo-phenanthroline Paired-ion chromatography Tetrabutylammonium hydroxide Pol ystyrene-divinylbenzene Polytetrafluorethylene Phase ratio Ion-exchange capacity of the column Quaternary ammonium ion Ionic radius (p. 249)
When the same symbol has been used more than once,page numbers are given in parentheses.
747
748
r r (as subscript) P R R R R R RA
RC RCPVI RI RIC
RPLC Rs 0 02
SAX
scx SCE
SDS Spectrophot T TBA TEA THA TH'4M THF
TMA TOA
TPA b ? I
tR U
uv v V V Vi
VO
vm VR W
Appendix B
Resolution product (p. 471) Resin or stationmary phase Resistivity Slope of a gradient ramp (mM/min) (p. 150) Displacement ratio (p. 353) Resistance (p. 245) Radius of a working electrode (p. 312) Universal gas constant (p. 324) Ratio factor (anions) for spectrophotomeh-ic detection Ratio factor (cations) for spectrophotomemc detection Radial compression module Refractive index Replacement ion chromatography Reversed-phase liquid chromatography Resolution Standard deviation of a chromatographic peak Variance of a chromatographic peak Strong base anion-exchanger Strong acid cation-exchanger Saturated calomel electrode Sodium dodecylsulfate Spectrophotometry Temperature ' Tributylammonium Triethylammonium Trihexylammonium Tris(hydroxymethy1)aminomethane Tetrahydrofuran Trimethylammonium Trioctylammonium Tripropy lammonium Void time Triplet state lifetime Retention time Average linear velocity of the mobile phase Volume flow-rate Kinematic viscosity Volume of eluent pumped since start of a gradient (p. 150) Voltage (p. 245) Internal (occluded) volume Interstitial volume Volume of mobile phase Retention volume Weight of stationary phase
When the same symbol has been u e d more than once, page numbers are given in parentheses.
Abbreviations and Symbols w50 w4.4 WT X
XY z Zi
Width of a peak at 50%of height Width of a peak at 4.4%of height Width of a peak between tangents drawn to each side of the peak Charge on the solute anion or cation Solute anion Charge (or effective charge) on the eluent anion or cation Charge on a second solute anion or cation Number of charges on an ion
When the same symbol has been used more than once, page nwnbers are given In parentkses.
749
This Page Intentionally Left Blank
75 1
Index A Absorbing solutions 412(t), 422(t) AC conductance bridge 256,256 -,see also: conductivity detectors Acid-base indicators 403 Acid digestion of samples 418 Acid rain, analysis of 49O(t) -, see also: environmental applications Acids, analysis of 570(t) -,see also: industrial applications Active (Donnan) dialysis 426,428,430(t) Activity effects 133, 155 -,on equivalent conductance 247 Adsorbents for sample collection 413,423, 414(t) -,see also: sample handling methods Adsorber tubes 413, 423, 414(t) -,see also: sample handling methods Adsorption chromatography 5 Aerosols, analysis of 410, 41 l(t), 513(t) -,see also: sample handling methods -,see also: environmental applications Agglomerated ion-exchangers 56-66 -,characteristics60 -,synthesis 57 -, see also: ion-exchangers -,see also: environmental applications Air, analysis of 513(t) Airborne particulates, analysis of 513(t) -,see also: environmental applications Aircraft ceiling panels, analysis of 728(t) Aliphatic carboxylic acids (as eluents) 88,90 Aliphatic sulfonic acids (as eluents) 88,91(t) Alkali fusion of samples 418 Alkali metal ions (and ammonium), detection of -, direct conductivity 35,44,236, 253 -,indirect amperometry 300 -,indirect conductivity 32,254 -,indirect fluorescence 373,374(t) -,indirect refractive index 371(t), 372 -,indirect spectrophotornetry 65,202, 355(t),357,359 -,indirect spectroscopy 380
-,replacement IC 352,380 Alkali metal ions (and ammonium), separation of -,by ion-exchangechromatography -,-,typical retention times ZOO -,-,with aniline eluent 372 -,-,with benzylamine eluent 253 -,-,with Ce(1lI) eluent 202,373 -,-,with copper o-sulfobenzoate eluent 359 -,-,with [Cu(en)z]S04 eluent 202 -,-,with Cu(I1) eluent 34,65 -,-,with hydrochloric acid eluent 44 -,-,with methylbenzylamine eluent 357 -,-,with nitric acid eluent 32, 254,352, 380 -,-,with tartaric acid eluent 35, -,on crown ether stationary phases 236 -,simultaneously with anions 72-73 -,typical retention times 223 Alkaline earth ions, detection of -,direct conductivity 35,44,68 -,direct spectrophotometry349 -,indirect spectrophotometry 34,102, 355(t), 357 -,post-column reaction 404(t) Alkaline earth ions, separation of -,by ion-exchange -, -,with [Cu(en>2]SO4eluent 102 -,-,with Cu(1I) eluent 34 -,-,with EDTA eluent 96,349 -,-,with phenylenediamineeluent 44 -,-,with phenylethylamine eluent 357 -,-,with tartaric acid eluent 35 -,on silica 68 Alloys, analysis of 683(t) Almonds, analysis of 617(t) Alumina ion-exchangers 67 -,structure of 69 -,see also: ion-exchangers Aluminium alloys, analysis of 683(t) Aluminium anodizing solutions, analysis of 668(t) Amines, capacity factors for 98(t) Amino acids 404 Aminopolycarboxylic acids 395,396
Entries in boldface type rder to Figures,entries marked (t) refer to Tables.
752 Ammonium. separation and detection see:alkalimetal ions Amperometric detection -,comparison with other electrochemical methods 296 -,gradient elution 115 -,see also: electrochemical detection -, see also: pulsed amperometric detection Amphoteric ion-exchangers 66-70 Anesthetics, analysis of 65 l(t) Anion determinations, flowchart for 464 see also: methods development Anion-exchange -,definition 15 -,of complened cations 160 -,retention models 133-152 Anion-exchange materials see: ion-exchangers Anions - see: inorganic anions Annular denuder 4 15 Anthranilic acid 350 Antibiotics, analysis of 651(t) Antimicrobial solutions, analysis of 651(t) Antiperspirant, analysis of 651(t) Apple juice, analysis of 605(t) Applications -,beverages 605(t) -,chemicals and chemical products 7 18(t) -,clinical and phannaceutical 633-661 -,food and plant analysis 593-626 -,environmental 489-533 explosives 725(t) -, gas, aerosol and particulates 41 l(t) -,industrial 544-584 -,metals and metallurgical solutions, 667-690 -,rnkcellaneous 728(t) -,of atomic spectroscopicdetection, 378(t) -,of combustion methods for sample preparation 422(t) -,of conductivity detection 285 -, Of Coupled IC 480(t) -,of crown ether stationary phases 236 -,of diffusion denuders 417(t) -,of direct spectroscopicdetection, 346(t), 364 -, of disposable cartridge columns for sample cleanup 433(t) -,of electrochemical detection, 316(t) -,of indirect photoluminescence detection, 374(t) -,of indirect spectrophotomeuicdetection,
-.
-.
Index
355(t), 361, 364 -,of ion-exclusion chromatography 215-220,
216(t), 218(t) -,of ion-interaction chromatography 188,
189(t) -,of post-column reaction detection of anions 3990) -,of post-column reaction detection of cations 4wt)
-, of pre-column derivatization 434(t) -,ofrefractive index detection, 371(t) -,of reversed-phase HPLC of coordination compounds 226(t) -,of reversed-phaseHPLC of organometallic compounds 229(t) -,of sample cleanup using membranes 430(t) -,of UV visualizationdetection, 368(t) -,photographic solutions 725(t) -,treated waters 695-712 Aqueous infusions, analysis of 651(t) Aromatic bases (as eluents) 101(t), 356,357 Aromatic carboxylic acids (as eluents) 84.85 -,effective charge of 87 Aromatic sulfonic acids 88,91(t) Arsenazo I402 Arsenam 111 398 -,in detection of lanthanides 402,402 -,reactions with metal ions, 4W(t) -,see also: post-column reaction detection Arsenic speciation 377,379 -,by ion-exclusion 21 7,377 Atomic spectroscopic detection 376-380 -,applications, 378(t) -,atomic absorption spectroscopy 376,377 -,-,discrete sampling methods 376 -,-,flow-rate matching methods 376 -,-,indirect detection 377 -,atomic emission spectroscopy 378 -,-,applications, 378(t) -,-,plasma excitation 379 -,-,replacement IC 379,380 Aurocyanide, preconcentration of 450,455 Automation in IC 481 Auxiliary electrodes 292 -,see also: electrochemical detection
B Back-flush method 442 Background conductanceof eluent 249 Bacon, analysis of 594(t)
Entries in bold-fme type refer 10Figures, entries marked ( t )refer to Tables.
Index Badge samplers 410 Band broadening 8 -,factors affecting 10-12 -,in post-column reaction 392 Baseline balancing methods 121,122 Baseline noise in post-column reaction 389 Bases, analysis of 570(t) -,see also: industrial applications Bayer liquors, analysis of 683(t) Beer, analysis of 605(t) Benzenecarboxylic acid eluents 85 -,effective charge of 87 Benzo- 18-crown-6234 Benwic acid 85 -,variation of effective charge with pH 86, 87 Benzoquinone 299 Beverages, analysis of 605(t) Bi-functional ion-exchangers 73 Bile, analysis of 646(t) Biological samples, analysis of 646(t) Bipolar-pulse detectors 258 Bleach, analysis of 566(t) Blood, analysis of 634(t) -,see also: clinical applications Boiler water, analysis of 706(t) Borate, separation of 200,287 Boric acid 370 Borosilicate glass, analysis of 728(t) Brain tissue, analysis of 646(t) Brass, analysis of 683(t) Bread and bread products, analysis of 594(t) Brightener solutions, analysis of 668(t) Brines, analysis of 495(t), 55O(t) -,see also: environmental applications
C Calcium in brines 455 Calibration plots in suppressed IC 278-280 -,effect of suppression efficiency 280 Capacity factor 4 -,optimal range 469 Carbon electrodes 306 . -,see also: electrochemical detection Carbon-in-pulp processing solutions, analysis of 683(t) Carbonate, separation of -,ion-exchange chromatography 287 -,ion-exclusion chromatography 200 Carbohydrates 304,404
753 Carboxylic acid eluents 85-88 Carboxylic acids, detection of -,direct conductivity 200,232,481 -,direct potentiomeny 338 -,direct spectrophotomeny 200,209,215. 347 -,indirect potentiometry 339 -,UV visualization 368(t) Carboxylic acids, separation of -,applications 216(t) -,by multi-dimensional IC 479.480(t), 481 -,gradient elution 209,232 -,in urine 215 -,ion-exchange chromatography 338,339, 347 -,ion-exclusion chromatography 200,215 -,-,effect of organic modifiers 208 -,-,typical retention times 201 -,ion-suppression chromatography 230,232 Cartridge columns for sample cleanup 432 -,applications 433(t) -,modes of operation 432 -,practical aspects 433 -,stationary phases 432 -,see also: sample handling methods Cation determinations, flow-chart for 466 -,see also: methods development Cation-exchange -,definition 15 -,retention models 152-162 Cation-exchange materials see: ion-exchangers Cell constant 246 -,measurement 249 Cells -,for amperomemc detection 309,310,312, 314 -,for conductivity detection 257-261 -,-,see also: conductivity detectors -,for potentiometricdetection 333,333, 334,335 Cement, analysis of 728(t) Cerebrospinal fluid, analysis of 646(t) Cerium(II1) eluents 99 Cheese, analysis of 594(t) Chelates - see: coordination compounds Chelating stationary phases 232 Chelex 232 Chemical modification of the sample 424 see also: sample handling methods Chemical products, analysis of 718(t)
-.
Entries in bold-face type refer to Figures, entries marked (t) refer to Tables.
754 Chemicals, analysis of 7 18(t) Chloro-oxyanions,speciation of 286 Chloromethylation 45 Chocolate, analysis of %(I) Chromatogram 4 , 5 Chromatographic concepts 8- 12 Chromatographic efficiency 8 -, HETP 8 -, theoretical plates 8 Chromatographic process 2-4 -,classifications 5 -, schematic illustration 2 Chrome plating solutions, analysis of 668(t) Chromic acid, analysis of 668(t) Cinnamaldehyde 219,219 Cleanup of samples 423 -, filtration 423 -, ion-exchange resins 424,425(1) -, membranes 425 Clinical applications -,biological materials 646(t) -,blood 634(t) -,plasma 634(t) -, serum 634(t) urine 641(t) Cloth, analysis of 728(t) Coal desulfurization solutions, analysis of 683(t) Coastal vegetation, anions in 452 Coated-wire indicator elecvodes 328 -,see also: potentiometric detection Cocoa, analysis of 617(t) Coffee, analysis of 605(t) Cola, analysis of 605(t) Collection of samples in IC 409 -,see also: sample handling methods Colour additives, analysis of 594(t) Column fiits, contamination by 439 Column switching methods 476, 477,478 Columns 1 -, sizes 18 Combustion of samples 419-423,422(1) absorbing solutions 421,422(1) -, furnace combustion 412, 421 -, Pam oxygen bomb 420,420 -, Schoeniger flask 419,420 Competing ion 16 Complexation suppression 276 Complexing eluents 83,94, 101-105, 109 -, for transition metals 104 -,ion-exclusion chromatography 202
-.
- $
Index -,mechanism of operation 102,103 -,retention models 156-161 Composite criteria 471 -,see also: optimization of eluent composition Computer optimization 468-476 -,see also: optimization of eluent composition Concentrator column 443 -,characteristics449 -,ion-interactionChromatography and 449 Concentric-flow diffusion cell 335 Conductance 246 -,of eluent -,-,background 249,275 -,-,during sample elution 250, 254, 276 -,-,for various eluents, 255(t) Conductance cells - see: conductivity detectors Conductivity 246 Conductivity detection 245- 287 -,activity effects 247 advantages 245 -,applications 285-287 -,-,borate 287 -, -,divalent metal ions 287 -,speciation of anions 286 -,bipolar-pulse 258 -,calibration plots 277-281 -,cell constant 246 -,conductance 246 -,-,calculation of 248 -,-,with various eluents 255 -,conductivity 246 -,Debye-Huckel-Onsagereqn. 247 -,differential conductivity detection 260 -,-,chromatograms with 261 direct detection 252 -,-,examples 253 -, -,schematic representation 252 -,equivalent conductance 246 -,gradient elution 115-122 -,indirect detection 252 -,-,examples 254 -,-,schematic representation 252 -,injection peak in 283,283, 284 -,ion concentrations in 250 -,ion-exclusion chromatography and 265, 2 74 -, limiting equivalent conductance247 -,limiting equivalent ionic conductance 247, -, -,factors influencing 249 -, -,values for anions and cations 248(t)
-. -.
-.
Entries in bold-face type refer to Figures, entries marked (r) refer io Tables.
Index
-.-,principles post-suppressors 270 245 -,resistance 245 -,resistivity 246 -,Siemens 246 simultaneous direct and indirect detection 254 -,specific conductance246 -,suppressors for 261-277 -,-,see also: suppressors -,temperature effects 28 1,282 -, theory of detector response 249 -,-,background conductance 249 -,-,conductance during sample elution 251, 254 -,-,suppressed IC 275 -, without standards 282 Conductivity detectors 255-261 -,AC conductance bridge 256-258 -,-,equivalent circuit for 256 -,-,phenomena with 256 -,bipolar-pulse 258 -,cell constant 246 -,-,measurement 249 -,cell design 257-260 -,-,apparatus for four-electrodecell 259 -,-,circuit for four-electrode cell 259 -,-,differential conductivity detection 260 -,-,dual-cell configuration 260 -,-,four-electrode cell 258,260 -,-,two-electrode cell 257 -,electronic circuitry for 255 -,frequency effects 255 -,peak shape in suppressed IC 277.278 -,performance characteristics277 -,-,linearity of calibration plots 277, 278-280 -, suppressors for 261 -,-,see also: suppressors Contact lens solution, analysis of 651(t) contamination effects 435-441 -,from cartridge columns 436,437(t) -,from filtration devices 436,437(t) -,from hardware components 437 -,from metal ions 440,441 -,from organic species 440 -,from physical handling of the sample 435 -,from stainless steel components 437,439(1) -,of the column 440,442 Coolants, analysis of 582(t)
-.
755 Coordination compounds, separation 224 -,apparatus for automated formation 228 -,applications226(t) -,dithiocarbamate complexes225 -,formation of the chelate 225 -,ligand characteristics224 -,on-column complex formation 227 -,water-soluble complexes 227 Copper indicator electrode 329,337 -,see also: potentiometric detection Copper plating solutions, analysis of 668(t) Copper processing solutions, analysis of 683(t) Corned beef, analysis of 594(t) Cosmetics, analysis of 651(t) Coulometry 29 1,311 -,comparison with other electrochemical methods 296 -,see also: electrochemical detection Counter-ions 15 Coupled IC methods 476 -,see also: multi-dimensional IC Cream, analysis of 594(t) Cresolphthalein complexone 105 Cross-linking 24, 38 Crown ether stationary phases 233-237 -,applications 236 -,cavity size 235 -,chromatographic properties 235 -, gradient elution and 237,238 -,organic modifiers and 235 -,structures 234 -,synthesis 233 Crown ethers 233,234 -,nomenclature 233 -,structures 234 Cryptands 233,234, 237 Cyanidation process liquors, analysis of 455, 6830) Cyanide complexes, separation of 190 Cyanide waste solutions, analysis of 683(t) Cyclic polyethers see: crown ethers
-
D Dairy products, analysis of 594(t) Dead volume 11 Debye-Huckel-Onsager eqn. 247 DEDTC complexes, separation of 227 Deionized water, analysis of 706(t) Demineralized water, analysis of 706(t)
Entries in boldface type refer to Figures,entries marked ( I ) refer to Tables.
756 Denmfice sluny, analysis of 65 l(t) Denuders - see: diffusion denuders Derivative conductivity detection 261 Detection methods 245-404 conductivity detection 245-287 -, selection of 464,466, 467 -,-,see also: conductivity detection Detergents, analysis of 397. 576(t) -,see also: industrial applications Development of IC methods - see:methods development Dialysis 425 -,in mce enrichment 453 -,see also: sample handling methods Dichotomous sampler 410 Diesel fuel, analysis of 582(t) Diet cola, analysis of 605(t) Diethyldirhiocahamatecomplexes 225 -,automated formation of 228 -,separation of 227 Differential conductivity detection 260 Diffusion 10 Diffusion denuders 415, 415,416, 417(t) Diffusion scrubbers - see diffusion denuders Dionex resins - see: agglomerated ion-exchangers Direct detection, definition 252 -,in amperomebic detection 297 -,in atomic spectroscopic detection 376,377 -,in conductivity detection 252 -,in fluorescencedetection 37 1 -,in ion-exclusionchromatography 369 -, in ion-interactionchromatography 360, 362 -,in potentiometric detection 324,331,337, 338,339 -,in refractive index detection 369,370 -,in spectrophotometricdetection 343-350, 341,348,349 Displacement ratio 353 -,see also: spectrophotometric detection Disposable cartridge columns - see: camidge columns -, see also: sample handling methods Distilled water, analysis of 706(t) Distribution coefficient 3, 17 -,effect on solute distribution 3 in ion-exclusion chromatography 204(t) D i s u l f m 225 Dithiocarbamate complexes 225 -,automated formation of 228
-.
-.
Index -,in post-column reaction detection 403 -,onsolumn formation 230 -,pre-column formation 230
Dithimne 403 Dithizone silica gels 232,233 Divalent metal ions 287 Dominant equilibrium retention model 140 -,see also: ion-exchangeretention models Donnan dialysis 426. 427,428, 430(t) -,see also: sample handling methods Donnan exclusion 196,202,203 Donnan exclusion chromatography - see: ionexclusion chromatography Donnan potential 23 Drinking waters, analysis 696(t) Dual-electrodeampemmetric cells 314,318 Dual eluent species retention model 142 -,see also: ion-exchangeretention models Dual ion-exchange 429,43O(t), 453 Dyes, analysis of 728(t) Dynamic capacity 269 -,see also: suppressors Dynamic coating ion-interaction chromatography 173 -,ion-interactionreagents for 177(t) -,typical retention times for 179 Dynamic ion-exchange 168 -,see also: ion-interaction chromatography Dynamic reserve 353 -,see also: spectrophotometric detection
E Eddy diffusion 10 EDTA eluents 94,96 Effective charge retention model 140 -,see also: ion-exchangeretention models Effluents, analysis of 544(t) -, see also: industrial applications Electrical double-layer 168 Elecmactive solutes. 297(t) Electrochemical detection 291-319 -,amperometry 29 1 -,applications, 316(t) -,auxiliary electrode 292 -,basic principles, 296(t) -,co~lometry291 -,definitions 29 1 -,direct detection 297 -,electrode materials 304-309 -,carbon 306
-.
Entries in boldface type refer to Figures,entries marked (t) refer to Tables.
757
-,-,iodized platinum 308 -,-,mercury 306 -,-,potential ranges for 309 -,-,reference and auxiliary electrodes 304 -,-,selection criteria 308 -,-,silver, platinum, gold 307 -,-,working electrodes 305 -,flow-cells u)9-3 19 -,-,C O U ~ O U E ~297 ~~C -,-,design 309 -,-,dual working electrode types 314,318 -,-,flow-at type 309,312 -,-,flow-by type 309,320 -,-,flow-through type 309,311 -,-,multi-functional cells 313,325 -,-,polarographic cells 313,324 -,-,potentiometric 333,333,334 -,-,thin-layer 310,320 -,-,wall-jet 312,322 -,half-wave potential 293 -,hydrodynamic voltammogram 294 -,indirect amperometric detection 298 -,-,in non-suppressed IC 299 -,-, in suppressed IC 300 -,indirect coulometric detection 302 -,instrumentation 294 -,-,basic configuration 295 -,interrelationships between techniques 292 -,polamgraphy 291 -,potential window 292 -,-,for various electrode materials 309 -,pulsed amperometricdetection (PAD) 302 -,-,of carbohydrates 304 -,-,potential waveforms 303 -,reference electrode 292 -,response equations 311-312 -,reverse-pulse amperometry 303 -,-,detection of metal ions by 305 -,typical electroactive solutes, 297(t) -,usage patterns 295 -,voltammetry 291 -,voltammogram 292,293 -,working electrode 292 Electrochemical dialysis 431,431 Electrochemical suppression 27 1 -,see also: suppressors Electrodes for amperometry 304 -,see also: electrochemical detection Electrcdialysis - see: electrochemicaldialysis Electroless copper bath, analysis of 668(t) Electroless nickel bath, analysis of 668(t)
Electrolyte solutions, analysis of 7 18(t) Electroplating solutions, analysis of 668(t) Electroselectivity 23,52 Electrostatically-bound agglomerate resins 57 Elemental criteria 47 1 -,see also: optimization of eluent composition Eluent 17 -,characteristics in ion-exchange 19.79 -,complekation effects 83 -,contamination of 437 -,ion-exchange chromatography 79- 127 -,ion-exclusion chromatopphy 199-202 -,ion-interaction chromatography 171, I81 -,optimization of 468 -,pH effects 81 -,see also: ion-exchange eluents Elution chromatography 1.17 Engine products. analysis of 582(t) -,see also: industrial applications Environmental applications 489-533 -,acid rain 490(t) -,aerosols 5 13(t) -,air513(t) -,&borne particulates 513(t) -,brines 495(t) -,geological materials 529(t) -,lake water W t ) -,natural waters 506(t) -,pond water 500(t) -,rainwaters 490(t) -,river water Soo(t) -,seawater 495(t) -,soil extracts 523(t) -,soils 523(t) -,stream water 500(t) Equivalent conductance 246 Eriochrome Black T 403 Etchants. analysis of 668(t) Ethylenediamine 102 Ethyltin compounds, separation of 231 Explosives, analysis of 725(t) Extracolumn band broadening 11 Extraction of ionic species 417 -,see also: sample handling methods Eyewash, analysis of 651(t)
F Factorial design optimization 470 -,see also: optimization of eluent composition Faeces, analysis of 646(t)
Entries in bold-face rype refer to Figures, entries marked (t) refer to Tables.
758 Fermentation broths, analysis of 605(t) Fertilizer, analysis of 617(t) Filters for sample collection 410 Fish, analysis of 594(t) Fission products, analysis of 718(t) Fixed ions 15 Fixers (photographic),analysis of 725(t) Flame photomemc detection 378 Flue gas, analysis of 550(t) Fluorescence detection 371-374 -,applications, 374(t) -,direct detection 371 -, indirect detection 372,373 375 -, self-quenchingeffects 373 -,with postcolumn reaction 398 Food additives, analysis of 594(t) Foods, analysis of 594(t) -,see also: plants and plant products Form of an ion-exchangeresin 19 -,in ion-exclusionchromatography 210 Four-electrode conductivity cell 258.259, 260
Freeze dried food, analysis of 594(t) Frits, eluent contaminationby 439 Fruit juice, analysis of 605(t) Fuels, analysis of 582(t) -, see also: industrial applications Functional group 2 1 Functionalized silica ion-exchangers see: ion-exchangers -,performance 32 -, synthesis 3 1 Furnace combustion of samples 421,421, 422(t) Fusion of samples 41 8
G Gases, analysis of 410,41 I([) -,see also: sample handling methods Galvanizing solutions, analysis of 668(t) Gaussian peaks 9 Geological materials, analysis of 528(t) -, see also: environmental applications Germicide solutions, analysis of 651(t) Ghost peaks - see: system peaks Glass, analysis of 728(t) Glassy carbon 307 Gluconate-borateeluent 91-94 -,composition 94 Gold plating solutions, analysis of 668(t)
Index
Gold processing solutions. analysis of 683(t) Gradient capacity IC 237 Gradient elution 114-122 -,baseline balancing methods 121,122 -,conductivitydetection 115 -,high capacity suppressors 115, 118 -,i n ion-exclusion chromatography 209 -,in ion-suppressionchromatography 231 -,in micelle exclusion chromatography239 -,in potentiometric detection 115,336 -,isoconductive gradients 119. I20 -,macrocyclic stationary phases and 237 -, principles 114 -,retention model 149-152 -,with fluorescencedetection 372 -,with post-column reaction detection 397, 402 Grapefruitjuice, analysis of 605(t) Graphite furnace AAS 376,377
H Half-wavepotential 293 Halogen lamps, analysis of 728(t) Ham, analysis of 594(t) Hardware components 2 Height equivalent to a theoretical plate 8 Hetaeric Chromatography - see ion-interaction chromatography HEW 8 -,calculation 8,9 High purity water, analysis of 706(t) Hollow-fibre suppressors 264 -,see also: suppressors Hydraulic fluid, analysis of 583(t) Hydride generation AAS 376,377 Hydrodynamic voltammogram 294 Hydrogen ion effect in suppressed 1C 277 -,effect on peak shape 278 Hydrogen overpotential 306 Hydrophilic anions 465 Hydrophobic anions 465 Hydrophobic interactions -,ion-exclusion chromatography 206 Hydrophobically-bound agglomerate resins 59 Hydroponic nutrient solutions, analysis of 6170) Hydroquinone 299 Hydrous oxide ion-exchangers 66 Hydroxylamine explosives, analysis of 725(t)
Entries in boldface type refer to Figures, entries marked ( t ) refer to Tables.
Index
759
I Iminodiacetate 232 Immobilized ligands 232 Impingers 41 1, 412 -,absorbing solutions for 412(t) Indicator electrodes for potentiometric detection 323,325 -,see also: potentiometric detection Indirect detection, definition 252 -,in amperometric detection 298,299,300 -,in atomic absorption spectroscopic detection 377 -,in conductivity detection 252 -,in coulometric detection 302 -,in fluorescence detection 372,373 -,in ion-interaction chromatography 361, 362 -,in phosphorescence detection 374 in potentiometric detection 327, 338,339 -,in refractive index detection 369,372 -,in spectrophotometric detection 351,356 using pH changes 300, 327 Indirect photometric chromatography 35 1 -,see also: spectmphotometric detection Induced peaks 123, 363,367 Inductively coupled plasma detection 379 Industrial applications 544-584 -,acids and bases 570(t) -,detergents 576(t) -,effluents 544(t) -,engine products 582(t) -,fuels 582(t) -,industrial waters 550(t) -,oils 582(t) -,organic compounds 559(t) -,polymers 576(t) -,pulp and paper liquors 566(t) -, wastewaters 544(t) Industrial waters, analysis of 550(t) -,see also: industria1 applications Infant formula, analysis of 594(t) Injection peak 123, 124 -,characteristics 124 -,definition 4 -,dependence on solute concentration 283 for salts of the same anion 284 -,utilization in conductivity detection 283 Inorganic acid eluents 98 Inorganic anions, detection of -,atomic absorption spectroscopy 377,
-.
-.
-.
378(t)
-,direct amperometry 298,315 -,direct conductivity -,-,in gradient capacity IC 238 -,-,in gradient elution 120,238 -,-,in ion-interaction chromatography 170 -,with adipate eluent 34 -,-,with gluconate-borate eluent 49,253, 450,452 -,-,with nicotinic acid eluent 61 -,-,with octanesulfonate eluent 481 -,-,with p-hydroxybentoic acid eluent 49 -,-,with phosphate eluent 286 -,-,with phthalate eluent 32.54 -,-,with tartrate eluent 90,286 -,direct potentiometry 336,338,339 -,direct refractive index detection 370,37l(t) -,direct spectrophotometry 34,176,239, 346(t), 347,348,350,362, 364(t) -,first derivative conductivity detection 261 -,indirect amperometry 299,300 -,indirect conductivity detection 254 -,indirect fluorescence 373,374(t), 375 -,indirect phosphorescence 374(t) -,indirect potentiometry 339 -,indirect refractive index detection 371(t), 3 72 -,indirect spectrophotometry 32,65,355(t), 356,359,362, 364(t), 444,474 -,indirect spectroscopy 380 -,post-column reaction 97,396(t), 397, 399(t) -,replacement IC 350,380 -,suppressed conductivity -,-,in gradient elution 118,122 -,-,in ion-interaction chromatography 286 -,-,in multi-dimensional IC 479 -,-,with carbonate-bicarbonate eluent 61, 62,267,479 -,-,with K2EDDA eluent 112 -,-,with tyrosine eluent 112 -,UV visualization 368, 368(t) Inorganic anions, separation of -,by ion-exchange chromatography -,-,typical retention times 89 -,-,with acetate eluent 397 -,-,with adipate eluent 34 -,-,with carbonate-bicarbonate eluent 62, 62,247,380,472,473 -,-,with chloromethanesulfonic acid eluent 348
-.
Entries in bold-face type refer to Figures, entries marked (t) refer to Tables.
760
Index
-,-,with gluconate-borateeluent 49,253,
-,separation modes 7
450,452 -,-,with K2EDDA eluent I12 -,-,with nicotinic acid eluent 61 -,-,with nitric acid eluent 97 -* -,with octanesulfonate eluent 481 -,-,with p-hydroxybenzoic acid eluent 49 -, -, with perchlorate eluent 336 -,-,with phosphate eluent 286,347 -,-,with phthalate eluent 32.54.65.356, 372,444.474 -,-, with potassium hydroxide eluent 254 -,-,with salicylate eluent 299,373 -,-, with tartrate eluent 90,286,338,339 -, -,with tjrosine eluent 112 -,by ion-exclusion chromatography 217, 218(t) -,by ion-interaction chromatography Z70, 176,178,286,362,368,375 -,by micelle-exclusionchromatography239 -, by multi-dimensional IC 479,481 -, gradient elution 117(t). 118,120,122, 238,336 -,on alumina 70 -,on an amino column 34 -, on crown ether stationary phases 236,238 -, simultaneously with cations 71-73 -, speciation 286 -,with a hollow-fibre suppressor 267 -, with a packed-fibre suppressor 267 -,with micellar eluents 176 -, with preconcentration 450,452 Inorganic eluents for anion-exchange95, 970) 99 Inorganic species, separation by ionexclusion 217,218(t) Interpretive optimization methods 471,474 -,of phthalate eluents 474,475 -,see also: optimization of eluent composition Intravenous solutions, analysis of 651(t) Iodized platinum electrodes 308 kxtized salt, andysis of 594(t) Ion chromatography -,apparatus 1-2 -, components 1 -,background 1 -,classification of methods 24 -,definition 6-7 -,detection modes 7 -, historical aspects 6 -, non-suppressed 24
-,suppressed 25 -,types of Solutes 6 Ion-chromatography exclusion (ICE)- see ion-exclusion chromatography Ion-exchange -,affinity series for anions 23 -,affinity series for cations 23 -,classical methods 17,18 -,competing ion 19 -,coupled with ion-exclusion chromatography 477 478,479,480(t),481 -,h n n a n potential 23 -,eluent characteristics 19 -,eluent pH 19 -,ion concentrations in 250 -,intmduction 15-27 -,mixed mode 65 -,modem methods 18 -,open-column 17 -,principles 15-17 -.retention behaviour 137 -,retention models 133-161 -,-,anion-exchange 133-152 -,-,cation-exchange 152- 161 -,-,cation separation by anion exchange 160 -,-,complexing eluents 156-161 -,-,dominant equilibrium approach 140 -,-,dual eluent species model 142 -, -,effect of eluent charge 138 -,-,effect of solute charge 138 -,-,effective charge model 140 -, -,gradient elution 149 -,-,multiple eluent competing anions 140-
-.
149
-,-,single eluent competing anion 133-139 -,temperature effects 19 -,terminology 15 Ion-exchange capacity 21 -,in ion-exclusion chromatography 209,210 -,measurement of 21 Ion-exchange eluents 79-128 -,compatibility with detector 79 -,complexation effects 83 -,concentration of competing ion 80 -,effect of eluent strength 80,110 -,effect of pH 81.82 -,eluent characteristics 79 -,gradient elution 114-123 -, -,baseline balancing 121 -,-,conductivity detection 115
Entries in bold-jiie type refer to Figures,entries marked (t) refer to Tables.
Index
-,-,eluents used 117 -,-,high capacity suppressors 115 -,-,hydrolysis reactions in 117 -,-,isoconductive gradients 119 -,-,principles 114 -,-,retention model 149-152 -,nature of competing ion 80 -,non-suppressed IC 84-105 -,-,aliphatic carboxylic acids 88 -,-,aliphatic sulfonic acids 88,91(t) -,-,aromatic carboxylic acids 84-88 -,-,aromatic sulfonic acids 88.91(t) -,-,complexing eluents 101-105 -,-,EDTA 94 -,-,inorganic acids 98 -,-,inorganic eluents 95-101,97(t), I02 -,-,organic bases 98, lOl(t), 356,357 -,-,polyol-borate complexes 91-94 -,-,potassium hydroxide 90 -,-,push-pull effect 103,203 -,-,schematic classification 85 -,-,typical retention times 89,100 -,organic solvents 83,84 -,suppressed IC 106-113 -,-,amino acids 109 -, borate 108 -,-,carbonate-bicarbonate 108 -,-,complexing eluents 109 -,-,hydroxide 108, 118 -,-,inorganic acids 109 -,-,phenate 108, 118 -,-,suppressor requirements 106 -,-,typical eluent compositions 11l(t) -,-,typical retention times 110.113 -,suppressors for 261-281 -,system peaks 123-127 -,-,characteristics124, 126 -,-,non-suppressed IC 123 -,-,origin 125, 126 -,-,suppressed IC 126 -,typical retention times of anions 89 Ion-exchange screens 269 Ion-exchange selectivity 22,4842.63-66 -,agglomerated anion-exchangers 63-66 -,alumina 69 -,anions 23, 49-52,50 -,cations 23 -,effect of functional group 48-49,50,64 -,effect of substrate type 54,62 -,effect of "spacer-arm" length 51.51(t) -,electroselectivity 23,52
-.
761
-,factors infiuencing 23 -,hydrophobicity effects 52,6345 -,nature of the polymeric subshate 52 -,resin-based anion-exchangers 47-53 -,polarizability effects 24.51 -,water-structure induced ion-pairing 24,51 Ion-exchangers 20-24,29-74 -,agglomerated ion-exchangers 56-66 -,-,anion-exchangers57 -,-,cation-exchangers 57 -,-,characteristics 60 -,-,chromatographic efficiency 60 -,-,Commercially available packings 58(t) -,-,description 56 -,-,electrostatic binding 57,57 -,-,hydrophobic binding 59,59 -,-,mechanical binding 60.60 -,-,schematic representation 56-60 -,-,selectivity 63-66,64,65 -,-,simultanmus aniodcation-exchange ,6S-
66 -,-,stability 63 -,-,synthesis 57 -,-,typical separations 62,62 -,bi-functional exchangers 73 -,characteristics 21 -,classification 20,37 -,cross-linking 24.38 -,efficiencies 55(t) -,equilibration 19 -,form 19 -,functional groups 20,21(t). 45-46 -,hydrous oxide ion-exchangers 66-70 -,-,alumina 67,69,70 -,-,background 66 -,-,effect of pH 67.69 -,-,isoelectric point 66 -,-,mechanism of operation 66-68 -,-,selectivity 69 -,-,silica 67, 68 -,inorganic 20 -,mixed-bed ion-exchangers 72 -,organic 20 -,resin-based ion-exchangers 37-55 -,-,advantages and disadvantages 53 -,-,anion-exchange capacities 46 -,-,anion-exchange functional groups 46 -,-,cation-exchangers 40-45 -,-,centrally grafted makrials 48 -,-,characteristics 42,47,53-55 -,-,chromatographic efficiency 53
Entries in bold-fact +we rt$er to Figures, entries marked (t)refer to Tables.
762
Index
-,-,classification 37 -,-,column fouling 53 -, -,commercially available packings 43(t).
46(t) -, -,derivatization reactions 40,45 -, -,functional groups 45 -, -,isoporous 39 -,-,macroporous 39.40 -,-, macroreticular 39 -, -,microporous 39, 40 -, -,nature of the polymer 52 -,-,operating conditions 55 -, -,organic m d f i e r s 55 -,-,pH tolerance 53 -,-,polymerization reactions 38
-.-,-,retention pressure limitations 55 of metd ions on anion-,
exchangers 48 -,-,selectivity 48-53 -,-, sulfonation reactions 40.41 -, surface-aminated47 -,-,surface-sulfonated42 -,-, synthesis 40,45 -,silica 67 -,silica-based ion-exchangers 29-37 -, -,advantages and limitations 33 -,-,chromatographic efficiency 33 -,-,commercially available packings 33(t) -,-,“end-capping”36 -, -,functionalized 30 -,-,microparticulate 30 -,-,organic modifiers 33 -,-,pellicular 29 -,-, pH limitations -,-,polymer-coated 3 1 -,-,retention of metal ions on anionexchangers 36 -, -,sample size 37 -, -,synthesis 30, 31 -, types 29 -,strong and weak acid types 20 -,strong and weak base types 21 -,swelling effects 22 *, types 20-21 Ion-exclusion chromatography 195-220 -,alternative names 195 -,applications 215-220 -,-,biological materials 216 -,-,carboxytic acids 215 -, -, foods and beverages 216 -,inorganic acids and bases 216
-.
-.
-.
-,-,pharmaceuticals 216 -,water 218 -,columns 198(t) -,coupled with ion-exchange chromatography 477 478,479, 480(t), 481 -,distribution coefficients 204(t) -,eluents 199-202 -,acid eluents 199,200 -,-,complexing eluents 202 -,-,pH 205 -,-,water eluents 199, 200 -,gradient elution in 209 -,mechanism 196,196 -,principles 195 -,retention, factors influencing 202-212 -,-, eluent pH 205,206 -, -,hydrophobic interactions 206 -,-, ion-exchange capacity 209,220 -,-, ionic form of the resin 210 -,-,molecular size of the solute 205 -, -,organic modifiers 207,208 -,-,pKa of solute 203,204,205 -, -,solute ionization 202 -, -,summary 202.21 1 -, -,temperature 21 I , 212 -,retention model 212-215 -, -,verification of 214 -,stationary phases 197 -,suppression reactions for 273 -,typical retention times 201 Ion-exclusion effects in packed suppressors 2 63 Ion-exclusion partition chromatography see: ion-exclusion chromatography Ion-interaction chromatography 165-190 -,alternative names 165(t) -,applications 188, 189(t) -,counter-ion role 177 -,definition 165 -,dynamic coating 173 -, -,typical retention times 179 -, eluents 171, 179 -,-,dynamic coating method 173 -,-,guidelines for selection of 181 -,“permanent“coating method 175 -,-,summary of effects 179 -,mechanism 166, 267 -,-,dynamic ion-exchange model 168 -,for inorganic solutes 169 -,-,ion-interaction model 168 -,-,ion-pair model 166
-. -.
-.
-.
Entries in bold-face type refer to Figures, entries marked (r) refer to Tables.
Index
-,"permanent" coating 175 -,-,advantages 175 -,retention models 182-188 -,-,anion model 182 -,-,cation model 186 -,-,effect of counter-ion concentration 184 -,-,effect of IIR concentration 180, 184, 187,188 -,-,effect of sample size 183,285 -,stationary phases 170, 171 -,-,summary of effects 179 -,trends in solute retention 166 Ion-interactionreagent (IIR) 172-177 -,alkyl chain length of 173(t) -, alternativenames 165(t) -,effect of concentration of 180 -,requirements of 173 -,types for dynamic coating 172(t) -,types for permanent coating 177(t) Ion-interaction model 168 Ion-moderated partition chromatography see: ion-exclusion chromatography Ion-pairchromatography - see: ion-interaction chromatography Ion-pair model 166 Ion-selective electrodes 325 -,see also: potentiometric detection Ion-suppressionchromatography 230-232 -,gradient elution and 23 1 Iron(II1) perchlorate reagent 395,396(t), 397 Isocapacitive eluents I38 Isoconductive gradients 119,120 -,eluent strength 121 -,principles 119 Isoelectric point 66 Isoporous resins 39
K Kel-F 41, 46 Kidney stones, analysis of 646(t) Kraft liquors, analysis of 566(t) Kraft white liquor, analysis of 298,566(t)
L Lake water, analysis of 500(t) -,see also: environmental applicarions Lanthanide ions, detection of -,post-column reaction with Arsenazo 400(t), 402
763
-,post-column reaction with PAR Z74,239, 400(t) Lanthanide ions, separation of -,by anion-exchange 116 -,by dynamic coating ion-interaction chromatography 174,402 -,by micelle-exclusion chromatography239 -,gradient elution 116, 117(t), 239 Large injection volumes 442,43(t), 444 -,see also: sample handling methods Lead acid battery plates, analysis of 683(t) Ligands for HPLC ofmetal chelates 224 Limiting equivalent conductance 247 Limiting equivalent ionic conductance 247, 248(t) Liquid membrane electrodes 327 -,see also: potentiometric detection Liver tissue, analysis of 646(t) Longitudinal diffusion 10 Lubricants, analysis of 583(t)
M Macrocycle stationary phases - see: crown ether stationary phases Macroporous resins 39-40 Macroreticular resins 39 Magnesium in brines 455 Mannitol 122 Mass transfer 10 Matrix elimination 454 -,on-column methods 454,455 -,post-column methods 456, 457 Matrix normalization 428,453 -,see also: sample handling methods Meat and meat products, analysis of 594(t) Mechanically-bound agglomerate resins 60 Membrane diffusion denuder 416,416 Membrane reactor 393,393 -,see also: post-column reaction detection Mercury electrodes 306 -,see also: electrochemical detection Metal chelates - see: coordination compounds Metal cutting solutions, analysis of 683(t) Metal cyan0 complexes -,analysis of 668(t), 718(t) -, separation of 190 Metal finishing solutions, analysis of 668(t) Metal ion effective charge 155 Metal plating solutions, analysis of 668(t)
Entries in boldface type refer to Figures, entries marked ( t ) refer to Tables.
764 Metallic copper indicator electrode 329,337, 404 -,see also: potentiometric detection Metallurgical solutions, analysis of 668(t) Methods development 463-482 -,automation in IC 48 1 -,determination of anions, flowchart for 464 -,determination of cations, flow-chart for 466 -,multi-dimensional IC 476-481 -,-,column switching methods 476,477. 478 -,-, ion-exclusion / ion-exchange methods 477, 478,479.480(1), 481 -,optimization of eluent composition 468 -, -,computer optimization methods 468476 -, -,empirical methods 468 -, -,factorial design 472 -, -,interpretive methods 474,474 -,-,optimization criterion 471 -, -,optimization strategies 469 -,-,response surface 471 -, -,search area 469 -, -, Simplex methods 470, 470,472.473 -,-,window diagrams 475, 476 -,selection of chromatographicparameters 465 -,-,detection mode 467 -,-,eluent type 467 -,-,separation methods 465 Methyltin cc mounds, separation of 231 Mhos 246 Micellar chmnatography 237 Micellar eluents I76 Micelle exclusion chromatography 237-240 -, anions 238, 239 -, cations 239,240 -,eluents 238 -,gradient elution and 240 Milli-trap429 Micremembrane suppressor 267 -,see also: suppressors Microporous resins 39-40 Milk, analysis of 605(t) Milk powder, analysis of 605(t) Mine process liquors, analysis of 455 Mineral water, analysis of 605(t) Miscellaneous separation methods 223-240 -,overview 223 Mixed-bed ion-exchangers72
Index Mixed mode ion-exchange 65 Mixing chambers 391 -,see also: postcolumn reaction detection Mixing homogeneity in postcolumn reaction 392,394 Mobile phase ion chromatography (MPIC) 165 -,see ion-interactionchromatography Molecular size of the solute 205 Molybdenum blue 394 Mouthwash, analysis of 651(t) Multidimensional IC 476-481 -,applications of 480(t) -,column switching methods 476, 477,478 -,ion-exclusion / ion-exchange methods 477, 478,479,480(t), 481 Multiple eluent species model 142-149 -,see also: ionexchange retention models
N Natural waters, analysis of 506(t) -,see also: environmentalapplications Nickel plating solutions, analysis of 668(t) Nitrophenol 403 Noise in post column reaction detection 389 Non-linear calibration 277-280 -,calibration plots 278-280 -,effect of suppression efficiency 280 Non-suppressed IC 24 -,comparison with suppressed IC 26 -,definition 24 -,eluents 84-105 -, -,see also: ion-exchange eluents -, hardware 25 -,stationary phases - see: ion-exchangers -,system peaks 124 -,typical retention times of anions 89
0 Oils, analysis of 582(t) -,see also: industrial applications Oncolumn complex formation 227 On-line IC instruments 48 1 Optimization of eluent composition 468-476 computer optimization methods 468 -,-,factorial design 470 -, -,interpretive methods 471, 474 -,-,optimizationcriterion 471 -, -,principles 468 -,-,search area 469
-.
Entries in boldface type refer to Figures, entries marked ( t ) refer to Tables.
Index
-,-,Simplex 470, 470,472,473 -,-,window diagrams 475,476 -,empirical methods 468 -,in non-suppressed IC 474 -,in suppressed IC 472.473 Orange juice, analysis of 605(t) Organic bases as eluents 98 Organic compounds, analysis of 559(t) -,see also: industrial applications Organic modifiers -,in ion-exchange 83 -,in ion-exclusion 207,208 -,with crown ether stationary phases 235 Organomercury compounds, separation 231 Organometallic compounds, separation 228, 229(t). 232 Organotin compounds, separation of 231 Overpotential 306 Oxidizing anions, potentiometric detection 339
P Packed-bed post-column reaction 387,388 -,see also: post-column reaction detection Packed-column suppressors 262 -,see also: suppressors Packed-fibre suppressors 266 -,see also: suppressors Paint resin, analysis of 728(t) Paired-ion chromatography - see: ioninteraction chromatography PAR 398 -,in detection of transition metals 400,401 -,reaction with metal ions 4OO(t) ZnFDTA] reagent and 402 -,see also: post-column reaction detection Parr oxygen bomb combustion 420,420, 422(t) Particulates, analysis of 410,41l(t), 513(t) see also: environmental applications -,see also: sample handling methods Partition chromatography 4 Passivation of stainless steel 438 Passive dialysis 425.426,430(t) Passive sampling 410 PBDMA 31.35 PDCA 105 "Permanent" coating ion-interaction chromatography 175 -,ion-interaction reagents for 177(t)
-.
-.
765 Permselectivity 429 Peroxide solution, analysis of 718(t) Petroleum, analysis of 582(t) pH adjustment of samples 424 pH detection 326 -,see also: potentiometric detection pH effects in ion-exclusion chromatography 206 pH electrodes 326 Pharmaceuticals, analysisof 651(t) Phenylenediamine eluent 44 Phosphate rock, analysis of 683(t) Phosphating solutions, analysis of 668(t) Phosphorescence detection 374 Photographic solutions, analysis of 725(t) Phthalate 85 -,optimization of eluents 474,475 -,variation of effectivecharge with pH, 86.87 Phosphorus oxyanions, speciation of 286 -,atomic spectroscopic detection 379 -,ion-exclusion chromatography of 208 -,post-column reaction detection 394,395, 397 Photoluminescence detection 37 1 pKa of solute in ion-exclusion chromatography 203,204,205 Plant nutrients, analysis of 617(t) Plants and plant products, analysis of 617(t) Plasma, analysis of 634(t) -,see also: clinical applications Plastic, analysis of 559(t) Plate theory 8 Plating solutions, analysis of 668(t) Platinum plating solutions, analysis of 668(t) Pneumatic pumps for post-column reaction 390,391 Polarography 29 1,313 -,see also: electrochemical detection Polishing slurry, analysis of 728(t) Poly(butadiene-maleic acid) 3Z,35 Polymer-coated silica ion-excHhYigers - see: ion-exchangers -,PBDMA type 31 -,synthesis 31 Polymerization reactions for ion-exchangers 38-40 Polymers - see: ion-exchangers Polymers, analysis of 576(t) -,see also: industrial applications Polymethacrylate resins 38.39
Entries in boldface type refr to Figures,entries marked (t)refer to Tables.
766 Polyol-borateeluents 91 -,structure of active species in 92-93 -,see also: ion-exchange eluents Polyphosphates 394, 395 Polyphosphonates 370 Polystyrene-divinylbentene resins 38 Pond water, analysis of 500(t) -,see also: environmental applications Post-column matrix elimination 456,457 Post-column reaction (PCR)detection 387404 -, anions 394-398 -,-, aminopolycarboxylic acids 395,397 -,-,applications 399(t) -,-,molybdenum blue method 394 -, -, phosphorus 0x0-anions 394, 395,397 -,-,with iron0ll) perchlorate reagent 395, 396(t), 397 -,Arsenazo I11 398, 4OO(t), 402, 402 -, baseline noise 389.390 -,cations 398-403 -,-, applications, 404(t) -, -,choice of K R reagent 398 -, -,colour-forming reactions, 400(t) -, -,detection limits 401(t) -,-, lanthanides 402, 402 -, -,other metal ions 403 -, -, transition metals 400, 401 -,cell noise 389 -,detector noise 389 -,flow noise 389 -, gradient elution 396. 397,402 -, hardware 389-394 -,membrane reactors 393 -,mixing chambers 391-394 -,-,comparison of differcnt types 394 -,-,membrane reactors 393 -, -, tee-piece mixers 391.392 -, mixing noise 389 -,organic species 403 -,packed-bed PCR reactors 387,388 -, -,characteristics 389 -, PAR 398, 400, 4OO(t), 401, 401(t) -, -, with ZnlEDTA] reagent 401 pumps 389-391 -, -, pneumatic pumps 391 -, -,reciprocating piston pumps 389 -,-, syringe pumps 390 -,reactors 394 -,solution PCR 387, 388 -, -,characteristics 387
-.
Index -,sulfur-selectivedetection 398 -,tee-piece mixers 391,392 -,types 387 Post-suppression 118, 270,271 -, see also: suppressors Potassium hydroxide eluents 90 Potassium iodide tablets, analysis of 651(t) Potential window, in ampemmetry 292,309 Potentiometric detection -,applications 336-340, 34qt) -,-,cations 337 -,-,halides and pseudohalides 336 -, -,of metallic copper electrode 337,338,
339 -,-,weak acid anions 337 -,calibration plots 329 -,-,coated wire electrodes 330 -, -,metallic copper electrode 332 -,characteristics 323 -,direct detection 324,332 -,-, with metallic copper electrode 337.338, 33 9 -,flow-cells 333-336 -,-,concentric flow-diffusion cell 335 -,-,for cylindrical ISEs 333 -,-,for wire indicator electrodes 334 gradient elution 1 15,336 -,indicator electrodes 323,325 -,-,coated-wire electrodes 328 -,-,ion-selective electrodes 325 -,-,liquid membrane electrodes 327 -, -,metallic copper electrode 33 1 -, -,pH electrodes 326 -, -, solid-stateelectrodes 327 -, indirect detection 326. 327,332 -, -,with metallic copper electrode 338,339 -, instrumental considerations 324,325 -,Nernst equation 324 -,pH detection 326,327 -,principles 324 -,response equation 324 -,-,coated wire electrodes 328 -,-,metallic copper electrode 33 1 Power plant water, analysis of 706(t) Precipitation suppressors 276 Pre-column derivatization 434(t), 435 Preconcentration of samples 443-454 -,see also: sample handling methods -,see also: trace enrichment methods Process solutions, analysis of 550(t) Pseudo peaks - see: system peaks
-.
Entries in boldface t y e refer to Figiues. entries marked ( t ) refer to Tables.
Index Pulp and paper liquors, analysis of 566(t) -,see also: industrial applications Pulsed amperometric detection 301,303, 304 -,see also: electrochemical detection Pumps for post-column reaction detection 389 -,see also: post-column reaction detection Push-pull effect of eluent 103 Pyromellitic acid 85,356 -, variation of effective charge with pH, 86, 8 7
R Rain water, analysis of 490(t) -, see also: environmental applications Reaction mixtures, analysis of 7 18(t) Receiver electrolyte 428,430 Reciprocal ohms 246 Reference electrodes292 Refractive index detection 369 -,applications, 371(t) -,direct detection 369,370 -, indirect detection 370,372 Re-injection methods 477 "Re-launch" effect 442 Replacement IC 350 -,chariicteristics 350 of anions 350 -,of cations 351,352 -,with atomic spectroscopic detection 379, 380 Resins - see: ion-exchangers Resin-based ion-exchangers- see: ionexchangers Resistance 245 Resistivity 246 Resolution equation 469 Resolution factor 9,469 -,see also: methods development Response surface 471 Retention models -,activity effects 134, 155 -,anion-exchange 133 -,-,gradient elution 151 -,-,multiple eluent competing anion 142, 146,148 -,-,single eluent competing anion 133, 138, 139,141 ' -,cation-exchange 152, 154,155 -,complexation effects 156, 158, 159
-.
767
-,gradient elution 151 -,ion-exchange 133-161 -,ion-exclusion chromatography212-214, 214 -,ion-intemction chromatography 182-188 -,-,anions 182 -,-,cations 186 -,in interpretive optimization methods 471, 475 -,see also: ion-exchange retention models Retention time 4 Reversed-phase HPLC 224 -,separation of carboxylic acids 230-232 -, separation of coordination compounds 224228 -,separation of organometallic compounds 228-229 Reverse-osmosis water, anions in 450 Ringers solution, analysis of 651(t) River water, analysis of SOO(t) -,see also: environmental applications River water, cations in 452
S Saliva, analysis of 646(t) Salt, analysis of 594(t) Sample handling methods 409-457 -,cartridge columns 432-435 -,-,applications 433(t) -,-,ion-interaction methods 435 -,-,modes of operation 432 -,-,practical aspects 433 -,-,stationary phases 432 -,combustion methods 419-423 -,-,absorbing solution 421,422(t) -,-,applications 422(t) -,-,furnace 421,421 -,-,Pam oxygen bomb 420,420 -,-,pyrohydrolysis 421 -, -,Schoeniger flask 419,420 -,contamination effects 435-441 -,-,column frits 439 -, -,from cartridge columns 436,437(t) -,-,from chromatographic hardware 437, 439(t) -,-,from filtration devices 436,437(t) -,-,from physical handling of the sample 435 -,-,of column 440, 441 -, -,of eluents 437, 439(t) -,-,passivation 438
Entries in boldface ype refer to Figures, entries marked (t) refer to Tables.
768 -,dialysis 425-431
-, -, active - see: Donnan dialysis -,-,electrochemical 431,431 -,-,passive 425, 426 -,Donnan dialysis 426 -,-, apparatus 428,429 -, -,applications 430(t) -, dual ion-exchange 429 -,-,permselectivity 429 -,-,principles 426,427 -,-,selective addition of an ion 428,429 -, -,selective removal of an ion 429 -, dual ion-exchange 429 -, elecnodialysis 431, 431 -,extractior.of ionic species 417-423 -, -, acid digestion 418 -,-, alkali fusion 418 -, -,aqueous extraction 417 -, -,organic solvents 418 -,matrix elimination methods 454 -, on-column methods 454.455 -, -,post-column methods 456. 457 -,pre-column derivatization 434(t), 435 -, sample cleanup 423-435 -,-,dialytic methods 425.430(t) -,-,disposable cartridge columns 432,433(t) -,-,filtration 423 -, -,pre-column derivatization 434(t), 435 -, -,with ion-exchange resins 424 -,-,with membranes 425, 430(r) -,sample collection 409-417 -,-,diffusion denuders 415, 415, 417(t) -,-,filter media 410, 410 -,-, gases, aerosols, particulates 410, 41 I(t) -,-, impingers 411, 412(t), 412 -, -, membrane diffusion denuders 416.416, 417(t) -, -,solid adsorbents 413,413, 414(t) -,sample generator for calibration 414 -,sample preconcentration 443-453 -, -,anions 450 -, -, cations 451 -,-,choice of eluent 446 -,-,concentrator column characteristics449 -, -,dialytic 453 -,-,sample loading effects 449 -,-,samples of high ionic strength 452,452 -, samples of low ionic strength 451,450 -, -,single-valve system 444,445 -, -, two-valve system 445, 446,447 -,trace enrichment - see: sample
-.
-.
-.
Index preconcentration
-,ultra-trace analysis 441-454 -,-,dialytic methods 453 -,-,large injection volumes 442,443(t), 444 -,-,preconcentration columns 443-453 -,with ion-exchange resins 424,425(t) Sanitizing solution, analysis of 651(t) Saturated calomel electrode 304 Schoeniger flask combustion 419,420. 422(t) Scrubbing liquors, analysis of 55qt) Search area 469 -,see also: optimization of eluent composition Seawater, analysis of 495(t) -,see also: environmental applications Selectivity coefficient 16 Selectivityof ion-exchangers 22,48-54 -,see also: ion-exchangeselectivity Semiconductoretchant,analysisof 728(t) Semiconductorwater, analysis of 706(t) Separation method, selection of 464,465, 466 Serum, analysis of 634(t) -, see also: clinical applications Sewage, analysis of 550(t) Shellfish, analysis of 594(t) Siemens 246 Signal enhancement devices 273 -,see also: suppressors Silica-basedion-exchangers- see: ionexchangers Silver-silverchloride electrode 304 Simplex optimization 470 -, in separation of sulfur oxyanions 472 -, in suppressed IC 473 -,see also: optimization of eluent composition Simultaneousindirect detection of anions and cations 358,359 Simultaneous separation of alkali metals and alkaline earths 34,35,102 Simultaneousseparation of anions and cations 70-74, 71-73,96 -,bi-functional ion-exchangers73 -,mixed-bed ion-exchangers 72 -,tandem anion- and cation-exchange71 Size-exclusioneffects in ion-exclusion chromatography 205 Sodium gluconate - see:gluconate-borate eluent Soft drink, analysis of 605(t) Soil extracts, analysis of 523(t)
Entries in bold-face type refer to Figures, entries marked ( r) refer to Tables.
Index
-,see also: environmental applications Soils, analysis of 523(t) -,see also: environmental applications Solder flux, analysis of 728(t) Solid adsorbents for sample collection 413 Solid-stateion-selective electrodes 327 -,see also: potentioxnettic detection Solute size, in ion-exclusion chromatography 205 Solution post-column reaction 387,388 -,see also: post-column reaction detection Solvent peak 4 -,see also: injection peak Spacer-arm in anion-exchangeresins 51 Specific conductance 246 Spectrophotomehic detection 344-369 -,applications 346(t), 355(t), 361(t), 364(t), 3W) -,direct detection 345 -,-,effect of wavelength on sensitivity 347 -,-,of anions 347 -,-,of cations 348,349 -,-,replacement IC 350 -,-,schematic representation 345 -,-,typical applications 346(t) -,gradient elution 115 -,indirect detection 345,351 -,-,displacement ratio 353 -,-,dynamic reserve 353 -,-,of anions 354,356 -,-,of cations 356,357 -,-,schematic representation 345 -, sensitivity of 351 -,typical applications 355(t) -,-,without standards 360 -,in ion-exclusion chromatography 369 -,in ion-interaction chromatography 360 -, -,applications 364(t) -,-,dynamic coating methods 361,362 -,-,permanent coating methods 361(t) -,-,see also: UV visualization -,response equations 344 -,simultaneous indirect detection of anions and cations 358,359 -,UV visualization 363 -,-,applications 368(t) -,-,characteristics 365 -,-,of anions 36s' -,-,mechanism 365,367 Spectroscopic detection methods 343-380 -,direct and indirect detection 343
-.-.
769
-,types 343 -,see also: atomic spectroscopic detection -,see also: fluorescence detection -,see also: phosphorescence detection
-,see also: refractive index detection -,see also: spectrophotometric detection Stainless steel -,composition of 438(t) -,contamination by 439(t) -,passivation 438 Standard deviation of a peak 8 -,estimation 9 Stationary phases -,ionexchange chromatography 29-74 -,-,see also: ion-exchangers -,ion-exclusion chromatography 197 -,ion-interaction chromatography 171 Steam condensate, analysis of 706(t) Steel, analysis of 683(t) Sterilizing solution, analysis of 651(t) Stern-Volmerequation 374 Stream water, analysis of 500(t) -,see also: environmental applications Sugar products, analysis of 617(t) Sulfate in brine 454 Sulfite, amperometric detection of 298,472 Sulfite in peppers 217 Sulfonation 40,42(t) Sulfonic acid eluents 88 Sulfur dioxide denuder 416 Sulfur oxoanions, speciation of 286 Sulfur-selective detection 398 Sulfuric acid, chloride in 478 Suppressed IC 25 -,calibration plots 277,278-280 -,comparison with non-suppressed IC 26 -,definition 25 -,eluents 106-113 -,hardware 25 -,hydrogen ion effect 277 -,stationary phases - see: ion-exchangers -,system peaks 126 Suppressor reactions 106 Suppressors 25 -,chelation reactions and 276 efficiency 280 elechochemical suppressors 271 -,-,schematic designs for 272 -,eluent requirements for 106-113,108(t) -,function 106,261 -,gradient elution 115,118,122
-.-.
Entries in bold-facetype refer to Figures, entries marked (t) refer to Tables.
770
-,hollow-fibre suppressors 264 -,-, advantages 264 -,-,anion-exchange eluents 265 -, -, cationexchange eluents 265 -,design of 264 -,-,ion-exclusion eluents 265 -,-,ion-interaction eluents 265 -,-,principles 264 -,-,regenerants 266 -,hydrogen ion effect 277 -,-,effect on peak shape 278 -,ion-exclusion chromatography 273,274 -, linearity of calibration 277,278-280 -, micro-membranesuppressor 267-270 -, -,advantages 269 -,-, design 268 -, -,dynamic capacity 269 -, -,operating principles 269 -, packed-column suppressors 262 -,-,disadvantages 263 -, -, ion-exclusion effects with 263 -, packed-fibre suppressors 266 -, chromatographic efficiency 267 -,-,schematic design 266 -, post-suppressors 270-27 1 -,-, advantages 271 -, -,design 270,271 -,precipitation reactions and 276 -,response equation for 275 Surface-aminated anion-exchangers45 -,commercially available packings 47(t) -,efficiencies 55(t) -,functional groups 45, 46(t) -,ion-exchangecapacities 4qt) -, structure 48 -, synthesis 45 -, typical separations 49 -,see also; ion-exchangers Surface-sulfonated cation-exchangers42 -,commercially available packings 43(t) -, structure 42, 43 -,synthesis 40 -,typical separations 44 -,see also: ion-exchangers Surfactant chromatography - see ioninteraction chromatography Swear, analysis of 646(t) Swelling of resins 22 Syringe pumps for post-column reaction 390,
-.
-.
391
Index
System peaks 123-127, 354,440 -,in non-suppressed IC 124 -,in suppressed IC 127 -, model 125
T Tandem anion- and cation-exchange 71 Tartaric acid (as eluent) 90 Tee-piece mixers 39 1,392 -,see also: post-column reaction detection Temperature effects 19 -,in conductivity detection 281,282 -,in ion-exchange Chromatography 19 -,in ion-exclusion chromatography 21 I , 212 Theoretical plates 8 -,calculation 9 Thin-layer cells 3 10 -,see also: electrochemical detection Thiosulfate, amperometric detection of 298 Tissue extracts, analysis of 646(t) Tobacco, analysis of 617(t) Toothpaste, analysis of 651(t) Trace enrichment methods 443-454 -,anions 450,452 -,cations 451 -,choice of eluent 446 -,concentrator column characteristics449 -,dialytic methods 453 -,of samples of high ionic strength 452,452 -, of samples of low ionic strength 450,451 -,sample loading characteristics 449 -,single-valve system 444,445 -, two-valve system 445, 446,447 Transition metal ions, detection of -,direct spectrophotometry 349 -,indirect conductivity 104,287 -, indirect coulometry 302 -,indirect specuophotometry 174 -, post-column reaction with Arsenazo 400(t) -,post-column reaction with PAR 32,104, 178,233,239, 400(t), 401(t), 401, 451 -,reverse-pulse amperometry 305 Transition metal ions, separation of -,by anion-exchange 116 -,by dynamic coating ion-interaction chromatography 174,178,401 -, by ion-exchange chromatography -,as chloride complexes 349 -, -,with citrate-EDA eluent 104,287
-.
Entries in boldface type refer to Figures, entries marked (t) refer to Tables.
Index
-,-,with oxalate EDA eluent 32 -,-,with PDCA eluent 104 -,-,with tartrate eluent 104,302 -,-,with tartrate-Mg(IJ)eluent 305 -,by micelle-exclusionchromatography 239 -,gradient elution 117(t),239 -,on an anion-exchangecolumn 36 -,on dithizone silica gel 233 -,with preconcentration 451 Trimesic acid 85 -,variation of effective charge with pH, 86, 87 Type 304 stainless steel 437,438(t) Type 316 stainless steel 437,438(t)
U Uranium processing solutions, analysis of 683(t) Urine, analysis of 215, 641(t) -,see also: clinical applications UV visualization 363 -,see also: spectrophotometric detection
V Vacancy detection 35 1 -,see also: spectrophotometric detection Van Deemter plots 11 Variance of a peak 10 Vegetable juice, analysis of 605(t) Vegetables, analysis of 617(t) Vinegar, analysis of 605(t) Vitamin formulations,analysis of 651(t) Void time 4 Voltammetry 291 -,comparison with other electrochemical methods 296 -,see also: electrochemical detection Voltammogram 292,293
77 1
W Wall-jet cells 312 -,see also: electrochemical detection Waste waters, analysis of 544(t), 668(t) -,see also: industrial applications Water, analysis of -,boiler water 706(t) -,deionized water 706(t) -,demineralized water 706(t) -,distilled water 706(t) -,drinking water 696(t) -,lake water 500(t) -,rainwater 490(t) -,natural waters 506(t) -,power plant water 706(t) -,river water 500(t) -,seawater 495(t) -,semiconductor water 706(t) -,stream water 500(t) Water - separation of 218,219 Water dip 263 Water gel explosives,analysis of 725(t) Water-structure breaking effects 24,51 Window diagrams 475,476 -,see also: optimization of eluent composition Wine, analysis of 605(t) Working concentration ranges in IC 442 Working electrode 292.305 -,see also: electrochemical detection Wort, analysis of 605(t)
XAD-2 172 Yoghurt, analysis of 594(t) Zipax packings 3 1 Zone compression effect 442
Entries in boldface type refer to Figures, entries marked (t) refer to Tables.
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773
JOURNAL OF CHROMATOGRAPHY LIBRARY A Series of Books Devoted to Chromatographic and Electrophoretic Techniques and their Applications Although complementary to the Journal of Chromatography, each volume in the Library Series is an important and independent contribution in the field of chromatography and electrophoresis. The Library contains no material reprinted from the journal itself.
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Antibiotics. Isolation, Separation and Purification edited by M.J. Weinstein and G.H. Wagman
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Porous Silica. Its Properties and Use as Support in Column Liquid Chromatography by K.K. Unger
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75 Years of Chromatography - A Historical Dialogue edited by L.S. Ettre and A. Zlatkis
Volume 18A
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Chemical Derivatization in Gas Chromatography by J. Drozd
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Chromatography. Fundamentals and Applications of Chromatographic and Electrophoretic Methods. Part A: Fundamentals edited by E. Heftmann
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Chromatography of Alkaloids. P a r t A: Thin-Layer Chromatography by A. Baerheim Svendsen and R. Verpoorte
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chromatography of Alkaloids. P a r t B: Gas-Liquid Chromatography and High-Performance Liquid Chromatography by R. Verpoorte and A. Baerheim Svendsen
Volume 24
Chemical Methods in Gas Chromatography by V.G. Berezkin
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Modern Liquid Chromatography of Macromolecules by B.G. Belenkii and L.Z. Vilenchik
Volume 26
Chromatography of Antibiotics. Second, Completely Revised Edition by G.H. Wagman and M.J. Weinstein
Volume 27
Instrumental Liquid Chromatography. A Practical Manual on High-Performance Liquid Chromatographic Methods. Second, Completely Revised Edition by N.A. Parris
Volume 28
Microcolumn High-Performance Liquid Chromatography by P. Kucera
Volume 29
Quantitative Column Liquid Chromatography. A Survey of Chemometric Methods by S.T. Balke
775
Volume 30
Microcolumn Scparations. Columns, Instrumentation and Ancillary Techniques edited by M.V. Novotny and D. Ishii
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Gradient Elution in Column Liquid Chromatography. Theory and Practice by P. Jandera and J. Churatek
Volurne 32
The Science of chromatography. Lectures Presented at the A.J.P. Martin Honorary Symposium, Urbino, May 27-31,1985 edited by F. Rruner
Volumc 33
Liquid Chromatography Detectors. Second, Completely Revised Edition by K.P.W. Scott
Volume 34
Polymer Characterization by Liquid Chromatography by G. Gliickner
Volunie 35
Optimization of Chromatographic Selectivity. A Guide to Method Development by P. J. Schoenmakers
Volume36
Selective Gas Chromatographic Detectors by M. Dressler
Volume 37
chromatography of Lipids in Biomedical Research and Clinical Diagnosis etliledl~yA. Kuksis
Vo!unie 38
Preparative Liquid Chromatography edited by B.A. Bidlingnieyer
Volume 39A
Selective Sample Handling and Dctcction in High-Performance Liquid Chromatography. Part A edited by R.W. Frei and K. Zech
Volume 39B
Selective Sample Handling and Detection in High-Performance Liquid Chromatography. Part B edited liy K . Zech and R.W. Frei
Volume 40
Aqueous Size-Exclusion Chromatography edited by P.L. Dubin
Volume 41 A
High-Performance Liquid Chromatography of Biopolymers and Bio-oligomers. Part A.Principles, Materials and Techniques by 0.MikeS
Vol u nic 41 R
High-Performance Liquid Chromatography of Biopolymers and Bio-oligomers. Part B: Separation of Individual Compound Classes by 0.Mikeri
Volume 42
Quantitative Gas Chromatography for Laboratory Analyses and On-Line Process Control by G. Guiochon and C.1,. Guillemin
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Natural Products Isolation. Separation Melhods for Antimicrohials, Antivirals and Enzyme Inhibitors edited by G.H. Wagman and K.Cooper
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Analytical Artifacts. GC, MS, HPLC,TLC and PC by B.S. Middleditch
776
Volume 45A
Chromatography and Modification of Nucleosides. Part A: Analytical Methods for Major and Modified Nucleosides- HPLC, GC, MS, NMR, UV and FT-IR edited by C.W. Gehrke and K.C.T. Kuo
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Trace Metal Analysis and Speciation edited by I S . Krull
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Stationary Phases in Gas Chromatography by H. Rotzsche
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Hyphenated Techniques in Supercritical Fluid Chromatography and Extraction edited by K. Jinno
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Chromatography of Myocotcxins.Techniques and Applications. edited by V. Betina
