Table Of ContentIon-Pair Chromatography and
Related Techniques
ANALYTICAL CHEMISTRY SERIES
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Quality and Reliability in Analytical Chemistry, George E. Baiulescu, Raluca-Ioana Stefan,
Hassan Y. Aboul-Enein
HPLC: Practical and Industrial Applications, Second Edition, Joel K. Swadesh
Ionic Liquids in Chemical Analysis, edited by Mihkel Koel
Environmental Chemometrics: Principles and Modern Applications, Grady Hanrahan
Quality Assurance and Quality Control in the Analytical Chemical Laboratory:
A Practical Approach, Piotr Konieczka and Jacek Namie´snik
Analytical Measurements in Aquatic Environments, edited by Jacek Namie´snik
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Ion-Pair Chromatography and Related Techniques, Teresa Cecchi
ANALYTICAL CHEMISTRY SERIES
Ion-Pair Chromatography
and Related Techniques
Teresa Cecchi
Boca Raton London New York
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Library of Congress Cataloging-in-Publication Data
Cecchi, Teresa.
Ion-pair chromatography and related techniques / Teresa Cecchi.
p. cm. -- (Analytical chemistry series)
Includes bibliographical references and index.
ISBN 978-1-4398-0096-6 (hardcover : alk. paper)
1. Chromatographic analysis. I. Title. II. Series.
QD79.C4C35 2010
543’.8--dc22 2009031933
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Dedication
To Andrea, drop of fading eternity.
To Euridice and Gaia, life for my life.
Contents
Preface.......................................................................................................................xi
The Author .............................................................................................................xiii
Chapter 1 Introduction ..........................................................................................1
Reference ..............................................................................................2
Chapter 2 Electrolyte Solutions and Historical Concept of Ion-Pairing ...............3
2.1 Phenomenological Treatment ....................................................3
2.2 Ion–Solvent Interactions ............................................................4
2.3 Ion–Ion Aspecific Interactions ..................................................7
2.4 Interactions of Ions with Non-Electrolytes ................................9
2.5 Critical Review of History of Theoretical Treatments
of Ion-Pairing ..........................................................................12
2.5.1 From the Beginning to Bjerrum’s Model ...................12
2.5.2 Further Developments ................................................14
2.5.3 Hydrophobic Ion-Pairing Concept .............................16
2.6 Thermodynamic Properties of Ion-Pairs .................................18
2.7 Techniques for Studying Ion-Pairing.......................................19
2.7.1 Conductometry ...........................................................19
2.7.2 Potentiometry .............................................................19
2.7.3 Spectroscopic Methods ..............................................20
2.7.4 Activity Measurement ................................................20
2.7.5 Relaxation Methods ....................................................20
2.7.5.1 Dielectric Relaxation Spectroscopy
(DRS) ..........................................................20
2.7.5.2 Ultrasonic Relaxation (UR) ........................21
2.7.6 Separative Methods ....................................................21
References ..........................................................................................22
Chapter 3 Retention Modeling as Function of Mobile Phase Composition ........29
3.1 Theoretical Models of Ion-Pair Chromatography (IPC) .........29
3.1.1 Stoichiometric Models................................................30
3.1.2 Non-Stoichiometric Models .......................................32
3.2 Empirical Models of IPC .........................................................46
3.2.1 Chemometrical Optimization Methods ......................46
3.2.2 Artificial Neural Network (ANN) Models .................49
References ..........................................................................................51
vii
viii Contents
Chapter 4 Modeling of Retention as a Function of Analyte Nature ...................57
References ..........................................................................................59
Chapter 5 Stationary Phases ...............................................................................61
5.1 Reversed Phase IPC .................................................................62
5.1.1 Silica-Based Stationary Phases and Silanophilic
Interactions .................................................................62
5.1.2 Other Reversed Phase Stationary Phases ...................65
5.2 Normal Phase IPC and Other Stationary Phases ....................66
References ..........................................................................................67
Chapter 6 Developments in Column Technology and Fast IPC .........................71
6.1 Ultrahigh Performance Liquid Chromatography
(U-HPLC) ................................................................................71
6.2 Monolithic Columns ................................................................75
References ..........................................................................................76
Chapter 7 Ion-Pair Reagents (IPR) .....................................................................79
7.1 Traditional IPRs .......................................................................79
7.2 Volatile IPRs ............................................................................81
7.3 Chaotropic Salts .......................................................................82
7.4 Ionic Liquid-Based IPRs .........................................................84
7.5 Unusual IPRs ...........................................................................88
7.6 IPR Counter Ions .....................................................................88
7.7 Conclusions ..............................................................................90
References ..........................................................................................90
Chapter 8 Organic Modifiers ..............................................................................99
8.1 Organic Modifier Concentration in Eluent ..............................99
8.2 Nature of Organic Modifiers .................................................101
8.3 Gradient Elution ....................................................................102
References ........................................................................................103
Chapter 9 Role of Eluent pH in IPC ..................................................................109
9.1 IPC versus RP-HPLC ............................................................109
9.2 pH-Dependent Silanol Ionization ..........................................113
References ........................................................................................114
Chapter 10 Temperature ......................................................................................117
10.1 Influence of Temperature on Column Efficiency ..................117
10.2 Influence of Temperature on Selectivity under RP–HPLC
and IPC Conditions ...............................................................117
References ........................................................................................121
Contents ix
Chapter 11 Special IPC Modes and Variations ..................................................125
11.1 Mixture of Different IPRs in Mobile Phase ..........................125
11.2 Permanently Coated Columns ...............................................125
11.3 IPRs Added Only to Sample Solution and Ghost
Peaks .............................................................................127
11.4 Special Additives in Mobile Phase ........................................128
11.5 Modification of Eluent Ionic Strength at Constant IPR
Concentration ........................................................................128
References ........................................................................................131
Chapter 12 Detection and Hyphenation ..............................................................135
12.1 UV-Vis Detectors ...................................................................136
12.2 Fluorescence Detectors..........................................................140
12.3 Electrical Conductivity Detectors .........................................142
12.4 Electrochemical Detectors ....................................................142
12.5 Evaporative Light Scattering Detectors .................................145
12.6 Unusual Detectors .................................................................145
12.7 Hyphenation Techniques .......................................................146
12.7.1 IPC-MS.....................................................................146
12.7.2 IPC-ICP and Other Unusual Hyphenations ..............151
References ........................................................................................153
Chapter 13 Examples of Applications.................................................................161
13.1 Inorganic and Organometallic Species .................................161
13.2 Food Analysis ........................................................................163
13.3 Life Science and Medicine ....................................................163
13.4 Pharmaceutical, Toxicological, and Clinical Analysis ..........165
13.5 Environmental Analysis ........................................................166
13.6 Enantiomeric Separations ......................................................168
References ........................................................................................169
Chapter 14 IPC versus Competitive Techniques .................................................179
References ........................................................................................180
Chapter 15 Ion-Pairing in Different Analytical Techniques ...............................183
15.1 Capillary Electrophoresis (CE) and Related
Techniques .....................................................................183
15.2 Supercritical Fluid Chromatography (SFC) and Other
Techniques .............................................................................184
15.3 UV-Visible Spectrophotometry .............................................184
15.4 Extraction and Sample Preparation .......................................185
References ........................................................................................186
Description:Ion-Pair Chromatography (IPC) is a rapidly evolving method for difficult analyses of organic and inorganic ions and ionogenic, neutral, and zwitterionic compounds. The possibilities for this technology continue to grow as novel ion-pair reagents and strategies are introduced at an accelerated level.
