Modern Supercritical Fluid Chromatography

Preface xiii 1 Historical Development of SFC 1 1.1 Physical Properties of Supercritical Fluids 1 1.2 Discovery of Supercritical Fluids (1822–1892) 6 1.3 Supercritical Fluid Chromatography (1962–1980) 8 1.4 SFC with Open Tubular Columns (1980–1992) 15 1.5 Rediscovery of pcSFC (1992–2005) 19 1.6 Modern Packed Column SFC 22 References 24 2 Carbon Dioxide as the Mobile Phase 29 2.1 Introduction to Carbon Dioxide 29 2.2 Supercritical Carbon Dioxide 32 2.3 Solvating Power of Supercritical CO2 35 2.4 Solvating Power of Modified CO2 45 2.5 Clustering of CO2 49 References 52 3 Instrumentation for Analytical Scale Packed Column SFC 55 3.1 Introduction 56 3.2 Safety Considerations 56 3.3 Fluid Supply 58 3.3.1 Carbon Dioxide and Other Compressed Gases 58 3.3.2 Mobile Phase “Modifiers” and “Additives” 59 3.4 Fluid Delivery – Pumps and Pumping Considerations 60 3.4.1 Pump Thermostating 60 3.4.2 Fluid Pressurization and Metering 60 3.4.3 Modifier Fluid Pumping 61 3.4.4 Pressure and Flow Ranges 62 3.4.5 Fluid Mixing 62 3.5 Sample Injection and Autosamplers 62 3.6 Tubing and Connections 64 3.6.1 Tubing 64 3.6.1.1 Stainless Steel Tubing 64 3.6.1.2 Polymeric Tubing 65 3.6.2 Connections 66 3.7 Column and Mobile Phase Temperature Control 66 3.8 Chromatographic Column Materials of Construction 67 3.9 Backpressure Regulation 68 3.9.1 Passive Flow Restriction 69 3.9.2 Active Backpressure Regulation 70 3.10 Waste Disposal 72 3.11 Conclusion 72 References 72 4 Detection in Packed Column SFC 77 4.1 Introduction 78 4.2 Predecompression Detection (Condensed‐Fluid‐Phase Detection) 78 4.2.1 UV/VIS Absorbance 78 4.2.2 Fluorescence Detection 81 4.2.3 Electrochemical Detection 82 4.2.4 Other Less Common Condensed Phase Detectors 83 4.2.4.1 Flow‐Cell Fourier Transform Infra‐Red Absorbance (FTIR) Detection 83 4.2.4.2 Online Nuclear Magnetic Resonance (NMR) Detection 84 4.2.4.3 Refractive Index (RI) Detection 85 4.3 Postdecompression Detection (Gas/Droplet Phase Detection) – Interfacing Approaches 85 4.3.1 Pre-BPR Flow Splitting 86 4.3.2 Total Flow Introduction (Post-BPR Detection) 88 4.3.2.1 BPR Requirements for Total‐Flow Introduction Detection 88 4.3.2.2 Total Flow Introduction with Mechanical BPR 89 4.3.2.3 Total Flow Introduction – Pressure‐Regulating‐Fluid (PRF) Interface 89 4.3.2.4 Total Flow Introduction without Active Backpressure Regulation 91 4.4 Postdecompression Detection 93 4.4.1 Flame‐Based Detectors 93 4.4.2 Evaporative Light Scattering Detection (ELSD) and Charged Aerosol Detection (Corona CAD) 97 4.4.3 Mass Spectrometric Detection 98 4.4.3.1 Interfacing and Ionization Approaches 99 4.4.3.2 Atmospheric Pressure Chemical Ionization (APCI) 100 4.4.3.3 Pneumatically Assisted Electrospray Ionization (ESI) 101 4.4.3.4 Atmospheric Pressure Photoionization (APPI) 103 4.4.4 Postdecompression Detection Using Less Common Approaches – Deposition IR 103 4.5 Concluding Remarks 103 References 104 5 Chiral Analytical Scale SFC – Method Development, Stationary Phases, and Mobile Phases 117 5.1 Introduction 117 5.2 Chiral Stationary Phases for SFC 119 5.3 Chiral SFC vs. Chiral HPLC 128 5.4 Method Development Approaches 130 5.4.1 Modifiers for Chiral SFC 132 5.4.2 Additives for Chiral SFC 133 5.4.3 Nontraditional Modifiers 135 5.4.4 Method Development Approaches 137 5.5 High Throughput Method Development 139 5.6 Summary 141 References 142 6 Achiral Analytical Scale SFC – Method Development, Stationary Phases, and Mobile Phases 147 6.1 Introduction 147 6.2 The Mixture to Be Separated 148 6.2.1 Molecular Interactions 148 6.2.2 Molecular “Handles” 149 6.3 Achiral SFC Stationary Phases 150 6.3.1 Column Safety and Compatibility 150 6.3.2 Efficiency 150 6.3.3 Retention 153 6.3.4 Selectivity 156 6.4 Mobile‐Phase Choices 157 6.4.1 Primary Mobile‐Phase Component 158 6.4.2 Secondary Mobile‐Phase Component – The “Modifier” 159 6.4.3 Tertiary Mobile‐Phase Component – “Additives” 163 6.5 Influence of Column Temperature on Efficiency and Selectivity 170 6.6 Where Do I Go from Here? Method Development Decision Tree and Summary 172 References 174 7 Instrumentation for Preparative Scale Packed Column SFC 183 7.1 Introduction 183 7.2 Safety Considerations 184 7.3 Fluid Supply 185 7.3.1 Carbon Dioxide 185 7.3.2 Mobile Phase Modifiers and Additives 187 7.3.3 Carbon Dioxide Recycling 188 7.4 Pumps and Pumping Considerations 189 7.4.1 CO2 and Modifier Fluid Pumping 189 7.4.2 Pressures and Flow Ranges 189 7.5 Sample Injection 190 7.5.1 Injection of Solutions 190 7.5.2 Extraction Type Injection 190 7.6 Chromatographic Columns 192 7.7 Detection 192 7.8 Back Pressure Regulation 193 7.9 Fraction Collection 193 7.9.1 Cyclone Collection 194 7.9.2 Open‐Bed Collection 195 7.10 Conclusion 197 References 197 8 Preparative Achiral and Chiral SFC – Method Development, Stationary Phases, and Mobile Phases 199 8.1 Introduction 200 8.1.1 Advantages and Disadvantages of SFC vs. HPLC for Purification 201 8.1.2 Cost Comparison: Preparative HPLC vs. SFC 202 8.2 Safety Considerations 202 8.3 Developing Preparative Separations 203 8.3.1 Linear Scale‐Up Calculations 209 8.3.2 Scaling Rule in Supercritical Fluid Chromatography 210 8.3.3 Metrics for Preparative Separations 213 8.3.4 Options for Increasing Purification Productivity 214 8.3.4.1 Closed‐Loop Recycling 214 8.3.4.2 Stacked Injections 214 8.3.5 Importance of Solubility on Preparative Separations 214 8.3.6 Preparative SFC Injection Options 217 8.4 Preparative Chiral SFC Purifications 220 8.4.1 Chiral Stationary Phases (CSPs) for Preparative SFC 220 8.4.2 Method Development for Chiral Purifications 222 8.4.3 Preparative SFC Examples 223 8.4.3.1 Milligram Scale Chiral Purification 223 8.4.3.2 Gram Scale Chiral Purification 224 8.4.4 Impact of Solubility on Productivity 226 8.4.5 Use of Immobilized Chiral Stationary Phase (CCP) for Solubility‐Challenged Samples 227 8.4.5.1 Immobilized CSP Example #1 227 8.4.5.2 Immobilized CSP Example #2 228 8.4.6 Coupling of Chiral and Achiral Columns for SFC Purifications 229 8.5 Preparative Achiral SFC Purifications 231 8.5.1 Introduction to Achiral SFC Purifications 231 8.5.2 Stationary Phases for Achiral Preparative SFC 232 8.5.3 Method Development for Achiral Purifications 232 8.5.4 Achiral SFC Purification Examples 234 8.5.4.1 Achiral Purification Example #1 234 8.5.4.2 Achiral Purification Example #2 234 8.5.5 Purifications Using Mass‐Directed SFC 236 8.5.6 Impurity Isolation Using Preparative SFC 237 8.5.6.1 Impurity Isolation Example 240 8.5.7 SFC as Alternative to Flash Purification 241 8.6 Best Practices for Successful SFC Purifications 244 8.6.1 Sample Filtration and Inlet Filters 244 8.6.2 Sample Purity 246 8.6.3 Salt vs. Free Base 247 8.6.4 Primary Amine Protection to Improve Enantiomer Resolution 250 8.6.5 Evaluation of Alternate Synthetic Intermediates to Improve SFC Purification Productivity 250 8.7 Summary 254 References 254 9 Impact and Promise of SFC in the Pharmaceutical Industry 267 9.1 Introduction to Pharmaceutical Industry 267 9.2 SFC in Pharmaceutical Discovery 268 9.2.1 Early Discovery Support 268 9.2.2 SFC in Medicinal Chemistry 269 9.2.2.1 Analytical SFC 270 9.2.2.2 Preparative SFC 271 9.2.3 Physiochemical Measurement by SFC 273 9.2.4 Use of SFC for Pharmacokinetic and Drug Metabolism Studies 274 9.3 SFC in Development and Manufacturing 276 9.3.1 Analytical SFC Analysis of Drug Substances and Drug Products 276 9.3.2 Preparative SFC in Development and Manufacturing 282 9.3.3 Metabolite/PKDM Studies in Development 283 9.3.4 SFC in Chemical Process Development 283 9.4 SFC for Analysis of Illegal Drugs 284 9.5 Summary 286 References 286 10 Impact of SFC in the Petroleum Industry 297 10.1 Petroleum Chemistry 297 10.1.1 Crude Refining Processes 297 10.1.2 Petrochemical Processes 298 10.2 Introduction to Petroleum Analysis 299 10.3 Historical Perspective 301 10.3.1 Hydrocarbon Analysis via FIA 301 10.3.2 SFC Replaces FIA 301 10.3.3 Hydrocarbon SFC Analysis via ASTM 5186‐91 302 10.4 Early Petroleum Applications of SFC 304 10.4.1 Samples with Broad Polymer Distribution 304 10.4.2 SFC Purification of Polycyclic Aromatic Hydrocarbons 305 10.4.3 Coal Tar Pitch 305 10.4.4 Enhanced SFC Performance 305 10.4.5 Sulfur Detection in a Petroleum Matrix 307 10.5 SFC Replacement for GC and LC 308 10.5.1 Simulated Distillation 308 10.5.2 Hydrocarbon Group‐Type Separations – PIONA Analysis 310 10.6 Biodiesel Purification 311 10.7 Multidimensional Separations 314 10.7.1 Comprehensive Two‐Dimensional SFC 314 10.7.2 SFC‐GC × GC 315 10.7.3 Comprehensive – SFC‐Twin‐Two‐Dimensional (GC × GC) 316 References 317 11 Selected SFC Applications in the Food, Polymer, and Personal Care Industries 321 11.1 Introduction 321 11.2 Selected Applications in the Foods Industry 322 11.2.1 Fats, Oils, and Fatty Acids 322 11.2.2 Tocopherols 325 11.2.3 Other Vitamins 327 11.2.4 Food Preservatives (Other Antioxidants and Antimicrobials) 330 11.2.5 Coloring Agents 330 11.2.6 Sugars 331 11.3 Selected Applications in the Field of Synthetic Polymers 332 11.3.1 Molecular Weight Distribution 332 11.3.2 Structural Characterization 334 11.3.3 “Critical Condition” Group/Block Separations of Complex Polymers Using CO2‐containing Mobile Phases 334 11.3.4 Polymer Additives 335 11.4 Selected Applications in the Personal Care Industry 337 11.4.1 Lipophilic Components of Cosmetics 337 11.4.2 Surfactants in Cleaning Mixtures 337 11.4.3 Emulsifiers in Personal Care Products 337 11.4.4 Preservatives 338 11.5 Conclusions 340 References 340 12 Analysis of Cannabis Products by Supercritical Fluid Chromatography 347 12.1 Introduction 347 12.1.1 Cannabis History 348 12.2 Analytical SFC 351 12.2.1 Introduction 351 12.2.2 Early SFC of Cannabis Products 352 12.2.3 Achiral SFC 353 12.2.4 Chiral SFC 354 12.2.5 Metabolite Analysis 357 12.3 Preparative SFC 357 12.4 Summary 360 References 361 13 The Future of SFC 365 13.1 Introduction 365 13.2 SFC Publication Record 366 13.3 SFC Research in Academia 368 13.4 SFC Conferences 368 13.5 Anticipated Technical Advances 369 13.6 Limits to SFC Expansion 370 13.7 Summary 372 References 373 Index 377