Ion-Pair Chromatography and Related Techniques Book

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

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 61

Chapter 6 Developments in Column Technology and Fast IPC 71

6.1 Ultrahigh Performance Liquid Chromatography (U-HPLC) 71

6.2 Monolithic Columns75

References 76

Chapter 7 Ion-Pair Reagents (IPR) 19

7.1 Traditional IPRs 19

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

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

Chapter 16 Non-Separative Applications of IPC 189

References 191

Chapter 17 Conclusions and Future Research Needs 193

Index 195