Sample Preparation Techniques in Analytical Chemistry CHEMICAL ANALYSIS A SERIES OF MONOGRAPHS ON ANALYTICAL CHEMISTRY AND ITS APPLICATIONS Editor J. D. WINEFORDNER VOLUME 162 Acompletelistofthetitlesinthisseriesappearsattheendofthisvolume. Sample Preparation Techniques in Analytical Chemistry Editedby SOMENATH MITRA DepartmentofChemistryandEnvironmentalScience NewJerseyInstituteofTechnology A JOHN WILEY & SONS, INC., PUBLICATION Copyright62003byJohnWiley&Sons,Inc.Allrightsreserved. PublishedbyJohnWiley&Sons,Inc.,Hoboken,NewJersey. PublishedsimultaneouslyinCanada. 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LibraryofCongressCataloging-in-PublicationData: Samplepreparationtechniquesinanalyticalchemistry/editedbySomenathMitra. p. cm.—(Chemicalanalysis;v.162) Includesindex. ISBN0-471-32845-6(cloth:acid-freepaper) 1.Sampling. 2.Chemistry,Analytic—Methodology. I.Mitra,S. (Somenath),1959– II.Series. QD75.4.S24S26 2003 543—dc21 2003001379 PrintedintheUnitedStatesofAmerica 10 9 8 7 6 5 4 3 2 1 To the hands inthelaboratory and the heads seeking information CONTENTS CONTRIBUTORS xvii PREFACE xix CHAPTER 1 SAMPLE PREPARATION: AN ANALYTICAL PERSPECTIVE 1 SomenathMitraandRomanBrukh 1.1. The Measurement Process 1 1.1.1. Qualitative and Quantitative Analysis 3 1.1.2. Methods of Quantitation 4 1.2. Errors in Quantitative Analysis: Accuracy and Precision 6 1.2.1. Accuracy 6 1.2.2. Precision 6 1.2.3. Statistical Aspects ofSample Preparation 10 1.3. Method Performance and Method Validation 12 1.3.1. Sensitivity 13 1.3.2. Detection Limit 14 1.3.3. Range of Quantitation 15 1.3.4. Other ImportantParameters 15 1.3.5. Method Validation 16 1.4. Preservationof Samples 17 1.4.1. Volatilization 19 1.4.2. Choice of Proper Containers 19 1.4.3. Absorption of Gases fromthe Atmosphere 20 1.4.4. Chemical Changes 20 1.4.5. Preservation of Unstable Solids 20 vii viii contents 1.5. PostextractionProcedures 21 1.5.1. Concentrationof SampleExtracts 21 1.5.2. Sample Cleanup 22 1.6. QualityAssurance and QualityControl during Sample Preparation 25 1.6.1. Determinationof Accuracy and Precision 28 1.6.2. Statistical Control 29 1.6.3. Matrix Control 31 1.6.4. Contamination Control 32 References 35 SECTION A EXTRACTION AND ENRICHMENT IN SAMPLE PREPARATION CHAPTER 2 PRINCIPLES OF EXTRACTION AND THE EXTRACTION OF SEMIVOLATILE ORGANICS FROM LIQUIDS 37 MarthaJ.M.Wells 2.1. Principles of Extraction 37 2.1.1. Volatilization 38 2.1.2. Hydrophobicity 43 2.1.3. Acid–Base Equilibria 50 2.1.4. Distribution of Hydrophobic Ionogenic OrganicCompounds 57 2.2. Liquid–Liquid Extraction 57 2.2.1. Recovery 60 2.2.2. Methodology 66 2.2.3. Procedures 68 2.2.4. RecentAdvancesin Techniques 72 2.3. Liquid–Solid Extraction 74 2.3.1. Sorption 75 2.4. Solid-Phase Extraction 78 2.4.1. Sorbents inSPE 81 2.4.2. Sorbent Selection 96 2.4.3. Recovery 99 2.4.4. Methodology 108 contents ix 2.4.5. Procedures 111 2.4.6. Recent Advances in SPE 113 2.5. Solid-Phase Microextraction 113 2.5.1. Sorbents 116 2.5.2. Sorbent Selection 118 2.5.3. Methodology 119 2.5.4. Recent Advances in Techniques 124 2.6. Stir Bar Sorptive Extraction 125 2.6.1. Sorbent and Analyte Recovery 125 2.6.2. Methodology 127 2.6.3. Recent Advances in Techniques 129 2.7. Method Comparison 130 References 131 CHAPTER 3 EXTRACTION OF SEMIVOLATILE ORGANIC COMPOUNDS FROM SOLID MATRICES 139 DawenKouandSomenathMitra 3.1. Introduction 139 3.1.1. ExtractionMechanism 140 3.1.2. Preextraction Procedures 141 3.1.3. Postextraction Procedures 141 3.2. Soxhletand Automated Soxhlet 142 3.2.1. SoxhletExtraction 142 3.2.2. Automated Soxhlet Extraction 143 3.2.3. Comparison between Soxtec and Soxhlet 145 3.3. UltrasonicExtraction 145 3.3.1. Selected Applications and Comparison with Soxhlet 147 3.4. Supercritical Fluid Extraction 148 3.4.1. Theoretical Considerations 148 3.4.2. Instrumentation 152 3.4.3. Operational Procedures 153 3.4.4. Advantages/Disadvantages and Applications of SFE 154 3.5. Accelerated Solvent Extraction 155 x contents 3.5.1. Theoretical Considerations 155 3.5.2. Instrumentation 156 3.5.3. Operational Procedures 158 3.5.4. Process Parameters 159 3.5.5. Advantages and Applications of ASE 161 3.6. Microwave-Assisted Extraction 163 3.6.1. Theoretical Considerations 163 3.6.2. Instrumentation 164 3.6.3. Procedures and Advantages/ Disadvantages 170 3.6.4. Process Parameters 170 3.6.5. Applicationsof MAE 173 3.7. Comparison of theVarious Extraction Techniques 173 References 178 CHAPTER 4 EXTRACTION OF VOLATILE ORGANIC COMPOUNDS FROM SOLIDS AND LIQUIDS 183 GregoryC.Slack,NicholasH.Snow,andDawenKou 4.1. Volatile Organicsand Their Analysis 183 4.2. Static Headspace Extraction 184 4.2.1. Sample Preparation for Static Headspace Extraction 186 4.2.2. Optimizing Static Headspace Extraction E‰ciency and Quantitation 187 4.2.3. Quantitative Techniques in Static Headspace Extraction 190 4.3. Dynamic HeadspaceExtraction or Purge and Trap 194 4.3.1. Instrumentation 194 4.3.2. Operational Procedures in Purge and Trap 199 4.3.3. Interfacing Purge and Trap with GC 199 4.4. Solid-Phase Microextraction 200 contents xi 4.4.1. SPME MethodDevelopment for Volatile Organics 201 4.4.2. Choosingan SPME Fiber Coating 204 4.4.3. Optimizing ExtractionConditions 206 4.4.4. Optimizing SPME–GC Injection 207 4.5. Liquid–Liquid Extractionwith Large- VolumeInjection 208 4.5.1. Large-Volume GC Injection Techniques 208 4.5.2. Liquid–Liquid Extractionfor Large-Volume Injection 211 4.6. MembraneExtraction 212 4.6.1. Membranes and Membrane Modules 215 4.6.2. Membrane Introduction Mass Spectrometry 217 4.6.3. Membrane Extractionwith 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 BarbaraB.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. DryAshing 240 5.3.1. Organic Extraction of Metals 241 5.3.2. ExtractionwithSupercritical Fluids 244 5.3.3. Ultrasonic Sample Preparation 245