Static Headspace-Gas Chromatography

Preface xi

Preface to the First Edition xv

List of Acronyms and Symbols xix

1 General Introduction 1

1.1 Principles of Headspace Analysis 1

1.2 Types of Headspace Analysis 3

1.2.1 Principles of Static HS-GC 4

1.2.2 Principles of Dynamic HS-GC 5

1.2.2.1 The Trap 5

1.2.2.2 The Water Problem 7

1.2.2.3 The Flow Problem 7

1.2.2.4 The Time Problem 8

1.2.2.5 Comparison of Static HS-GC with P&T 9

1.3 The Evolution of the HS-GC Methods 10

1.4 HS-GS Literature 12

1.5 Regulatory Methods Utilizing (Static) HS-GC 13

References 15

2 Theoretical Background of HS-GC and Its Applications 19

2.1 Basic Theory of Headspace Analysis 19

2.2 Basic Physicochemical Relationships 23

2.3 Headspace Sensitivity 25

2.3.1 Influence of Temperature on Vapor Pressure and Partition Coefficient 26

2.3.1.1 Enhancement of Lower Boiling Compounds 28

2.3.2 Influence of Temperature on Headspace Sensitivity for Compounds with Differing Partition Coefficients 29

2.3.3 Influence of Sample Volume on Headspace Sensitivity for Compounds with Differing Partition Coefficients 34

2.3.3.1 Sample-to-Sample Reproducibility 36

2.3.4 Changing the Sample Matrix by Varying the Activity Coefficient 37

2.4 Headspace Linearity 42

2.5 Duplicate Analyses 43

2.6 Multiple Headspace Extraction (MHE) 45

2.6.1 Principles of MHE 45

2.6.2 Theoretical Background of MHE 46

2.6.3 Simplified MHE Calculation 49

References 49

3 The Technique of HS-GC 51

3.1 Sample Vials 53

3.1.1 Vial Types 53

3.1.2 Selection of the Vial Volume 54

3.1.3 Vial Cleaning 55

3.1.4 Wall Adsorption Effects 55

3.2 Caps 56

3.2.1 Pressure on Caps 58

3.2.2 Safety Closures 58

3.3 Septa 58

3.3.1 Septa Types 58

3.3.2 Septum Blank 60

3.3.3 Should a Septum Be Pierced Twice? 62

3.3.3.1 Closed-Vial versus Open-Vial Sample Introduction Technique 65

3.4 Thermostatting 66

3.4.1 Influence of Temperature 66

3.4.2 Working Modes 69

3.5 The Fundamental Principles of Headspace Sampling Systems 70

3.5.1 Systems Using Gas Syringes 70

3.5.2 Solid Phase Microextraction (SPME) 73

3.5.2.1 Comparison of the Sensitivities in HS-SPME and Direct Static HS-GC 80

3.5.3 Balanced Pressure Sampling Systems 81

3.5.4 Pressure/Loop Systems 83

3.5.5 Conditions for Pressurization Systems 84

3.5.6 Volume of the Headspace Gas Sample 86

3.5.6.1 Sample Volume with Gas Syringes 87

3.5.6.2 Sample Volume with Loop Systems 87

3.5.6.3 Sample Volume with the Balanced Pressure System 88

3.6 Use of Open-Tubular (Capillary) Columns 89

3.6.1 Properties of Open-Tubular Columns for Gas Samples 89

3.6.2 Headspace Sampling with Split or Splitless Introduction 90

3.6.3 Comparison of Split and Splitless Headspace Sampling 93

3.6.4 Band Broadening During Sample Introduction 96

3.6.5 Influence of Temperature on Band Broadening 99

3.6.5.1 Conclusions 101

3.6.6 The Combination of Different Columns and Detectors 101

3.7 Enrichment Techniques in HS-GC 105

3.7.1 Systems for Cryogenic Trapping 108

3.7.1.1 Trapping by Cryogenic Condensation 109

3.7.1.2 Trapping by Cryogenic Focusing 110

3.7.1.3 Influence of Temperature on Cryogenic Focusing 118

3.7.1.4 Comparison of the Various Techniques of Cryogenic Trapping 122

3.7.2 Influence of Water in Cryogenic HS-GC 124

3.7.2.1 Water Removal in Static HS-GC 127

3.7.2.2 Applications 129

3.7.3 Enrichment by Adsorption 134

3.7.3.1 Water Removal from an Adsorption Trap 134

3.8 Special Techniques with the Balanced Pressure Systems 139

3.8.1 Instrumentation for MHE 139

3.8.2 Backflushing 140

3.9 Reaction HS-GC 143

3.9.1 Derivatization in the Headspace Vial 145

3.9.1.1 Methylation 146

3.9.1.2 Esterification 146

3.9.1.3 Transesterification 148

3.9.1.4 Acetylation 149

3.9.1.5 Carbonyl Compounds 149

3.9.2 Subtraction HS-GC 149

3.9.3 Special Reactions 153

3.9.4 HS-GC Analysis of Volatile Derivatives from Inorganic Compounds 158

References 160

4 Sample Handling in HS-GC 165

4.1 Equilibration 166

4.1.1 Gas Samples 167

4.1.2 Liquid Samples 168

4.1.2.1 General Properties 168

4.1.2.2 Reduction of the Equilibration Time for Liquid Samples 169

4.1.3 Solid Samples 171

4.2 Solution Approach 174

4.3 Sample Handling and Sample Introduction 177

4.3.1 Gas Samples 177

4.3.2 Liquid Samples 179

4.3.3 Solid Samples 180

4.4 Preparation of Standard Solutions 181

4.4.1 Preparation of a Standard Solution from a Liquid or Solid Substance 182

4.4.2 Preparation of a Standard Solution from a Gaseous Compound 184

4.5 Influence of the Matrix 186

4.5.1 Clean Matrix is Available 187

4.5.2 Matrix Effect Can Be Eliminated 187

4.5.3 Artificial Matrix Can Be Prepared 189

4.6 Methods Aiming at Complete Evaporation of the Analyte 189

4.6.1 The Total Vaporization Technique (TVT) 190

4.6.2 The Full Evaporation Technique (FET) 191

4.6.3 Calculation of the Extraction Yield in FET 194

4.6.4 Comparison of Headspace Sensitivities 195

References 195

5 Headspace Methods for Quantitative Analysis 197

5.1 Internal Normalization 199

5.2 Internal Standard Method 202

5.2.1 Blood Alcohol Determination 207

5.3 External Standard Method 207

5.4 Standard Addition Method 213

5.4.1 Single Addition 213

5.4.2 Handling of the Added Standard 214

5.4.3 Determination by Multiple Additions 218

5.5 Multiple Headspace Extraction (MHE) 221

5.5.1 Principles of MHE 221

5.5.2 Calibration in MHE 222

5.5.2.1 External Standard 222

5.5.2.2 Internal Standard 226

5.5.2.3 Standard Addition 226

5.5.3 The Use of Gaseous External Standards in MHE 227

5.5.3.1 Correction for Sample Volume 228

5.5.4 The Role of Quotient Q 229

5.5.4.1 Relationship between Q and Pressures 229

5.5.4.2 Value of Q in the Case of Total Vaporization 230

5.5.4.3 The Relative Position of the MHE Plots as a Function of Q 232

5.5.5 The Correlation Coefficient r 234

5.5.6 Evaluation of the Shape of the Regression Plot 234

5.5.7 Influence of K/ß 236

5.6 Analysis of Solid Samples (Adsorption Systems) 237

5.6.1 Suspension Approach 238

5.6.2 Surface-Modification Techniques 244

5.6.3 Highly Adsorptive Solid Samples 250

5.7 Calibration Techniques with Headspace Samples of Varying Volumes 252

5.8 Analysis of Gas Samples 253

References 255

6 Method Development in HS-GC 257

6.1 General Guidelines 258

6.2 Determination of the Residual Monomer Content of Polystyrene Pellets 259

6.2.1 First Approach: Use of Internal Standard with MHE 259

6.2.2 Second Approach: Single Determination with Internal Standard 262

6.2.3 Third Approach: Use of External Standard with MHE 263

6.2.4 Fourth Approach: Use of the Solution Approach 263

6.3 Determination of Residual Solvents in a Printed Plastic Film 263

6.3.1 First Approach: Use of External Standard with MHE 265

6.3.2 Second Approach: Use of Standard Addition with MHE 266

6.3.3 Third Approach: Use of Internal Standard 267

6.3.4 Fourth Approach: Use of Standard Addition 267

6.4 Determination of the Volatile Constituents of a Cathodic Electrolytic Plating Bath 268

6.4.1 First Approach: Use of External Standard with MHE 268

6.4.2 Second Approach: Dilution and Use of External Standard 269

7 Nonequilibrium Static Headspace Analysis 271

7.1 Accelerated Analysis 272

7.2 Heat-Sensitive Samples 274

References 277

8 Qualitative Analysis by HS-GC 279

8.1 The Use of HS-GC in "Fingerprinting" 282

8.2 The Use of Headspace Sampling in Hyphenated Systems 282

8.3 The Use of HS-GC in Microbiology 286

References 291

9 Special Measurements 293

9.1 Determination of Vapor Pressures 294

9.2 Determination of Activity Coefficients 299

9.3 Determination of Related Physicochemical Functions 302

9.4 Determination of Phase Distribution (Partition Coefficient) 303

9.4.1 The Vapor-Phase Calibration (VPC) Method 305

9.4.2 The Phase Ratio Variation (PRV) Method 308

9.4.2.1 Principles 309

9.4.2.2 Limitation of the PRV Method 311

9.4.3 MHE Methods for the Determination of the Partition Coefficient 312

9.4.3.1 VPC/MHE Method 313

9.4.3.2 PRV/MHE Method 316

9.5 Reaction Constant Measurements 316

9.6 Determination of Solute Solubility by MHE 319

9.7 Gas-Solid Systems 320

9.7.1 Determination of Adsorption Isotherms 320

9.7.2 Determination of the Rate of Release of a Volatile Analyte 321

9.8 Validation of Headspace Instrumentation: Investigation of Detector Linearity and Detection Limit 324

9.8.1 Definitions 325

9.8.2 Linear Range of the Detector 326

9.8.3 Precision of the Range 330

9.8.4 Minimum Detectability 330

References 332

Index 335