CONTENTS 4. 4.1. SPME Method Development for 4. 4.2. Choosing an SPME Fiber Coating 4.4.3. Optimizing Extraction Conditions 4. 4.4. Optimizing SPME-GC Injection 4.5. Liquid-Liquid Extraction with Large- Volume Injection 208 4.5.1. Large-Volume GC Injectic 08 4.5.2. Liquid-Liquid Extraction for Large-Volume Injection 46. Membrane extraction 212 4.6.1 Membranes and membrane 4.6.2 Membrane introduction mass Spectrometry 4.6.3. Membrane extraction with gas Chromatography 218 4.6.4. Optimization of Membrane Extraction 47. Conclusions 223 References CHAPTER 5 PREPARATION OF SAMPLES FOR METALS ANALYSIS 227 5.1. Introduction 5.2. Wet Digestion Methods Wet ash 5.2.2. Microwave Digestion 5.2.3. Comparison of Digestion Methods 235 5.2.4. Pressure Ashing 5.2.5. Wet Ashing for Soil S 5.3. Dry Ashing 5.3. 1. Organic Extraction of Metals 5.3.2. Extraction with Supercritical Fluids 244 5.3.3. Ultrasonic Sample Preparation 2454.4.1. SPME Method Development for Volatile Organics 201 4.4.2. Choosing an SPME Fiber Coating 204 4.4.3. Optimizing Extraction Conditions 206 4.4.4. Optimizing SPME–GC Injection 207 4.5. Liquid–Liquid Extraction with Large￾Volume Injection 208 4.5.1. Large-Volume GC Injection Techniques 208 4.5.2. Liquid–Liquid Extraction for Large-Volume Injection 211 4.6. Membrane Extraction 212 4.6.1. Membranes and Membrane Modules 215 4.6.2. Membrane Introduction Mass Spectrometry 217 4.6.3. Membrane Extraction with Gas Chromatography 218 4.6.4. Optimization of Membrane Extraction 222 4.7. Conclusions 223 References 223 CHAPTER 5 PREPARATION OF SAMPLES FOR METALS ANALYSIS 227 Barbara B. Kebbekus 5.1. Introduction 227 5.2. Wet Digestion Methods 230 5.2.1. Acid Digestion—Wet Ashing 231 5.2.2. Microwave Digestion 234 5.2.3. Comparison of Digestion Methods 235 5.2.4. Pressure Ashing 237 5.2.5. Wet Ashing for Soil Samples 237 5.3. Dry Ashing 240 5.3.1. Organic Extraction of Metals 241 5.3.2. Extraction with Supercritical Fluids 244 5.3.3. Ultrasonic Sample Preparation 245 contents xi