LC-NMR and Other Hyphenated NMR Techniques: Overview and Applications

Abbreviations, Symbols, and Units xv

1. Basic Concepts of NMR Spectroscopy 1

1.1 Introduction / 1

1.2 Basic Knowledge Regarding the Physics of NMR Spectroscopy / 2

1.3 Basic Parameters for NMR Interpretation / 7

1.3.1 Chemical Shift / 8

1.3.2 Spin–Spin Coupling Constants / 13

1.3.3 Spin Systems / 20

1.3.4 Signal Intensities / 21

1.3.5 Bond Correlations / 23

1.3.6 Spatial Correlations / 27

1.3.7 Other Topics / 30

1.4 Conclusions / 35

References / 36

2. Historical Development of NMR and LC-NMR 39

2.1 Introduction / 39

2.2 Historical Development of NMR / 39

2.3 Historical Development of LC-NMR / 46

2.4 Historical Development of Other Analytical Techniques Hyphenated with NMR / 49

2.5 Current Trends / 52

References / 52

3. Basic Technical Aspects and Operation of LC-NMR and LC-MS-NMR 59

3.1 Introduction / 59

3.2 Technical Considerations Regarding LC-NMR / 59

3.2.1 Solvent Compatibility / 60

3.2.2 Solvent Suppression / 61

3.2.3 NMR Flow Cell / 62

3.2.4 LC-NMR Sensitivity / 64

3.3 Technical Considerations Regarding LC-MS-NMR / 65

3.3.1 Deuterated Solvents / 66

3.4 Modes of Operation of LC-NMR / 66

3.4.1 On-Flow Mode / 67

3.4.2 Stop-Flow Mode / 67

3.4.3 Time-Sliced Mode / 77

3.4.4 Loop Collection Mode / 77

3.5 Modes of Operation of LC-MS-NMR / 77

3.5.1 On-Flow Mode / 80

3.5.2 Stop-Flow Mode / 87

3.6 Other Modes of Operation / 87

3.7 Challenging Considerations / 89

3.7.1 Air Bubbles / 89

3.7.2 Carryover with and Without an Autosampler / 90

3.7.3 Sample Solubility and Precipitation / 90

3.7.4 Flow Cell and System Cleaning / 91

3.7.5 Flow Rate and Magnetic Susceptibility / 91

3.7.6 Quantitation / 92

3.8 Conclusions / 92

References / 93

4. Applications of LC-NMR 95

4.1 Introduction / 95

4.2 Applications of LC-NMR / 96

4.2.1 Natural Products / 96

4.2.2 Drug Metabolism / 102

4.2.3 Drug Discovery / 108

4.2.4 Impurity Characterization / 111

4.2.5 Degradation Products / 112

4.2.6 Food Analysis / 115

4.2.7 Polymers / 118

4.2.8 Metabolomics and Metabonomics / 118

4.2.9 Isomers, Tautomers, and Chiral Compounds / 119

4.2.10 Others Areas / 120

4.3 Conclusions and Future Trends / 120

References / 121

5. Applications of LC-MS-NMR 131

5.1 Introduction / 131

5.2 Applications of LC-MS-NMR / 132

5.2.1 Natural Products / 132

5.2.2 Drug Metabolism / 134

5.2.3 Drug Discovery and Development / 135

5.2.4 Metabolomics and Metabonomics / 136

5.2.5 Others Areas / 139

5.3 Conclusions and Future Trends / 139

References / 140

6. Hyphenation of NMR with Other Analytical Separation Techniques 143

6.1 Introduction / 143

6.2 GC-NMR / 144

6.3 GPC-NMR / 144

6.4 SEC-NMR / 145

6.5 SFC-NMR / 146

6.6 SFE-NMR / 147

6.7 CE-NMR / 147

6.8 CEC-NMR / 149

6.9 CZE-NMR / 150

6.10 cITP-NMR / 150

6.11 CapLC-NMR / 152

6.12 SPE-NMR / 154

6.13 SPE-MS-NMR / 159

6.14 Conclusions and Future Trends / 167

References / 168

7. Special Topics and Applications Related to LC-NMR 179

7.1 Introduction / 179

7.2 Off-Line Versus Online NMR for Structural Elucidation / 180

7.2.1 Cases Solved Off-Line / 180

7.2.2 Cases Solved Online / 186

7.3 Analysis of Chiral Molecules by NMR / 188

7.3.1 Classical Approach: Off-Line / 189

7.3.2 Nonclassical Approach: Online / 190

7.4 Monitoring Chemical Reactions In Situ / 190

7.4.1 Classical Approach: Off-Line / 191

7.4.2 Nonclassical Approach: Online / 194

7.5 Analysis of Mixtures Off-Line, Online, and by Other NMR Methodologies / 196

7.5.1 Traditional Analysis of Mixtures by Off-Line HPLC and NMR / 196

7.5.2 Online NMR Analysis of Mixtures / 203

7.5.3 Other NMR Methodologies That Mimic LC-NMR Separation / 208

7.6 Current Trends / 210

References / 211

Index 217