Quality Assurance in Environmental Monitoring Instrumental Methods

Edited by G. Subramanian

Weinheim - New York Base1 a Cambridge - Tokyo

This Page Intentionally Left Blank

Quality Assurance in Environmental Monitoring

Edited by G. Subramanian

This Page Intentionally Left Blank

Quality Assurance in Environmental Monitoring Instrumental Methods

Edited by G. Subramanian

Weinheim - New York Base1 a Cambridge - Tokyo

Other Important Titles for Quality Assurance:

Quevauviller, Ph. (ed.) Quality Assurance in Environmental Monitoring Sampling and Sample Pretreatment

1995. 306 pages. Hardcover. DM 178,-. ISBN 3-527-28724-8

W. Funk, V Dammann, G. Donnevert Quality Assurance in Analytical Chemistry

1995.238 pages with 87 figures. Hardcover. DM 125,-. ISBN 3-527-28668-3

0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim (Federal Republic of Germany), 1995

Distribution:

VCH, P. 0. Box 101161, D-69451 Weinheim (Federal Republic of Germany)

Switzerland: VCH, P. 0. Box, CH-4020 Basel (Switzerland)

United Kingdom and Ireland: VCH, 8 Wellington Court, Cambridge CBI 1HZ (United Kingdom)

USA and Canada: VCH, 220 East 23rd Street, New York, NY 10010-4606 (USA)

Japan: VCH, Eikow Building, 10-9 Hongo I-chome, Bunkyo-ku, Tokyo 113 (Japan)

ISBN 3-527-28682-9

Ganapathy Subramanian 60 B Jubilee Koad Littlebourne Canterbury Kent CT3 lTP, UK

This book was carefully produced. Nevertheless. authors, editor and publisher do not warraut the 111-

formation contained therein to be free of errors. Readcrs are advised to keep in mind that statements. data. illustrations, procedural details or other items may inadvertently be inaccurate.

Published jointly by VCH Verlagsgescllschaft, Weinheim (Fedcral Republic of Germany) VCH Publishers, New York. NY (USA)

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Die Deutsche Bibliothek - CIP-Einheitsaufnahine Quality assurance in environmental monitoring : instrumental methods I ed. by G . Subramanian. - Weinheim ; New York ; Basel ; Cambridge ; Tokyo : VCH, 1995

NE: Subramanian, Ganapathy [Hrsg.] ISBN 3-527-28682-9

0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim (Federal Republic of Germany), 1995

Printed on acid-free and low-chlorine paper

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form -by photoprinting, microfilm, or any other means - nor transmitted or trans- lated into a machine language without written permission from the publishers. Registcred names, tradc- marks, etc. used in this book, even when not specifically marked as such. are not to be considered unpro- tected by law. Composition: K + V Fotosatz GmbH, D-64743 Beerfelden Printing: betz-druck GmbH, D-64291 Darmstadt Bookbinding: Wilhelm Osswald + Co., D-67433 Neustadt Printed in the Federal Republic of Germany

Preface

Environmental Monitoring has focused great attention in many laboratories around the world. This is due to increased levels of legislation being enacted by various au- thorities such as environmental committees in Europe (EEC), the environmental pro- tection agency (EPA) in United States. Both of these, and the importance of public health awareness, place a great responsibility on all organisations to monitor the con- dition of the environment. This major task and the continuing changes in regulations have created a need for advanced instrumentation technology and analytical meth- ods which are capable of meeting the current and future requirements.

This book presents a balanced overview of selected instrumental developments and their application in environmental monitoring. Each chapter is essentially self- contained for those who wish to select a particular field of interest. The authors re- flect the considerable concern over the environmental analysis of a variety of sub- stances, describing in detail the technology of the instrumental principles and their successful application in monitoring pollutants. The coverage has been planned to report the current status of the subject to a wide range of readers who are actively involved in the field of environmental control. Graduates, postgraduates, chemical and biochemical engineers, biologists, researchers, industrial scientists, and consul- tants who require detailed information should all benefit from this book.

I am indebted to the international group of contributors who have shared their ex- perience and knowledge. Each chapter contains a balanced overview of the chosen topic. Chapter 1 gives an account of solid phase extraction in sample purification, its importance and application. Superfluid critical extraction in environmental anal- ysis is discussed in Chapter 2. Chapter 3 discuss the validation and environmental analysis by Atomic Absorption Spectrometry as applied to trace metals in environ- ment. The development of Inductively Coupled Plasma-Optical Emmission spec- trometry in environmental analysis is discussed in Chapter 4. Volatile Organic Chem- ical monitoring and the applications of GC-MS are covered in Chapters 5 and 6. CES in environmental monitoring is reviewed in Chapter 7. Development, design, and ap- plication of Field Flow analysis is discussed in Chapter 8. Chapter 9 presents the ap- plication of software in environmental auditing and quality control.

I wish to express my sincere thanks to Dr. Don Emerson and all the staff at VCH for their help in publishing this book.

Canterbury, Kent October, 1995

G. Subramanian

Contents

1 The Use of Solid Phase Extraction for Environmental Samples

1.1 1.2 1.3 1.3.1 1.3.2 1.3.3 1.3.4 1.4 1.5 1.5.1 1.5.2 1.5.3 1.6 1.6.1 1.6.2 1.6.3 1.7 1.7.1 1.7.2 1.7.3 1.7.4 1.8 1.8.1 1.8.2 1.8.3 1.8.4 1.9 1.10 1.11 1.12

Dean Rood

The Importance of Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . Introduction to Solid Phase Extraction ......................... 2 SPE Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Syringe Barrel or Cartridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Syringe Filter or Sep-paks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Choice of Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Using SPE Cartridges and Disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SPE Sorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Normal Phase Sorbents ...................................... 7 Reverse Phase Sorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Ion Exchange Sorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Sorbent and Solvent Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Normal Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Reverse Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Selecting the Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Conditioning Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Loading Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Rinsing Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Elution Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Solvent Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Solvent Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Solvent Miscibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Solvent Volatility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Solvent Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Selecting Cartridge Size ...................................... 16 Method Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Matrix Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Analysis Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1

Disks ...................................................... 5

6

Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

VIlI Contents

1.13 1.14

2

2.1 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.4

3

3.1 3.1.1

3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.2 3.2.1

Method Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Current Status of Supercritical Fluid Extraction in Environmental Analysis

Joseph M . Levy and Athos C . Rosselli

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What is Supercritical Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Applicable Environmental Analytes and Matrices . . . . . . . . . . . . . . . . Polynuclear Aromatic Hydrocarbons and Polychlorinated Biphenyls Total Petroleum Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SFE of Wet Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dibenzofurans/Dioxins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Validation and Quality Control with Atomic Absorption Spectrometry for Environmental Monitoring

Ian L . Shuttler

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of Atomic Absorption Spectrometry in Environmental Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Need for Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Importance of Consistent Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standardized/Reference Methods or Quality Control? . . . . . . . . . . . . The Degree of Analytical Quality Control ...................... Quality Control Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Method Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic Analytical Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.2.1 . 1 Preparation of Calibration/Standard Solutions . . . . . . . . . . . . . . . . . . 3.2.1.2 Use of Characteristic Concentration/Mass . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2.1 The Importance of Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2.2 Influence of the Blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2.3 Type of Calibration Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2.4 Linear or Non-Linear-Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2.5 Calibration by the Method of Analyte Additions . . . . . . . . . . . . . . . . 3.2.2.6 Calibration Quality Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Establishment of Performance Characteristics . . . . . . . . . . . . . . . . . . . 3.2.3.1 Assessment and Influence of Contamination . . . . . . . . . . . . . . . . . . . . 3.2.3.2 Estimation of Detection Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19 20

25 26 31 32 41 45 48 52 52

55

55 56 57 57 58 59 60 60 61 63 64 64 65 66 67 68 68 70 70 71

Contents IX

3.2.3.3 Recovery Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.2.3.4 Precision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

3.2.3.6 Analysis of Certified Reference Materials . . . . . . . . . . . . . . . . . . . . . . . 78 3.3 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

3.3.2 Preparation of In-house IQC Materials . . . . . . . . . . . . . . . . . . . . . . . . . 81

3.3.3 Use of Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 3.3.3.1 Defining a Quality Control Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.4 Systematic and Random Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 3.4 External Quality Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

3.2.3.5 Comparison with Alternative TechniquedMethods . . . . . . . . . . . . . . . 77

3.3.1 Frequency of Analysis and Choice of IQC Materials . . . . . . . . . . . . . 79

3.3.2.1 Establishment of IQC Target Values and Limits . . . . . . . . . . . . . . . . . 82

83

4 Application of ICP-OES Techniques in Environmental QC

Terry C . Dymott

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Theory of the ICP-OES Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Atomic Spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1.1 Principles of Atomic Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1.2 Plasma Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Instrumental Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Spectrometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 . 1 Polychromators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1.2 Monochromators ............................................ 4.3.2 Plasma Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 Sample Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.4 Detectors and Signal Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Monitoring of Environmental Pollution . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Pre-analysis Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Water Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.1 The Sample Collection Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.2 Sample Treatment Before Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.3 Instrument and Method Detection Limits ....................... 4.6.4 Pre-concentration Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.5 Analytical Conditions ........................................ 4.6.6 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Airborne Particulate Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.7.2 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.3 Analysis Conditions and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Analysis of Soils, Sludges and Sediments ....................... 4.8.1 Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.7.1 Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

95 96 96 96 98

100 101 101 102 103 104 106 108 110 112 112 113 113 114 116 117 118 120 121 122 123 123

x Contents

4.8.2 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.3 Analytical Conditions and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9 Plant and Biological Sample Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.1 Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.2 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.3 Analytical Conditions and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Practical Aspects of Monitoring Volatile Organics in Air

Elizabeth A . Woolfenden

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Transfer of Analytes to the Capillary GC System . . . . . . . . . . . . . . . . 5.2.1 Solvent Extraction or Thermal Desorption . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Focusing Trap Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Air Sampling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Whole Air Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Air Sampling Using Sorbent Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2.1 Minimizing Artifact Interference for Sorbent Tubes . . . . . . . 5.3.2.2 Pumped Air Sampling Onto Sorbent Tubes 5.3.2.3 Automating Pumped Tube Monitoring .......................... 5.3.2.4 Diffusive Sampling Onto Sorbent Tubes 5.3.3 On-Line Air Stream Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Moisture Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Permeable Membrane Dryers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 Desiccant Dryers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 Dry Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Analytical Instrumentation and System Calibration . . . . . . . . . . . . . .

5.5.2 Automation and Calibration of Sorbent Tube Analysis . . . . . . . . . . . 5.5.3 Calibrating Automatic On-Line Air Stream Analysis . . . . . . . . . . . . . 5.6 VOC Air Monitoring Applications ............................. 5.6.1 Workplace Air Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.1.1 Benefits of Diffusive Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.1.2 Pumped Monitoring Applications in Workplace Air . . . . . . . . . 5.6.1.3 On-Line Air Applications in Workplace Air Monitoring 5.6.1.4 Standard Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.1.5 Data Interpretation ........... ............................ 5.6.2 Industrial Emission Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.3 Mobile Emission Sources, ie, Vehicle Exhaust Testing . . . . . . . . . . . . . 5.6.4 Urban Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.4.1 Ozone Precursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.4.2 Air Toxics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.4.3 Roadside Air Concentrations of PAHs 5.6.5 Indoor Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .

........................

5.5.1 Automation and Calibration of Whole-Air Container Analysis . . . .

. . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

123 124 125 127 128 129

133 135 136 137 140 140 141 142 147 147 147 151 151 152 152 152 154 155 156 157 158 159 159 160 163 163 163 164 166 167 167 172 174 175

Con tents XI

5.6.5.1 Building Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 5.6.5.2 Building Materials Emission Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

5.6.6 Atmosphere Research Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 5.7 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

Appendix B . Calibration Calculation Methods . . . . . . . . . . . . . . . . . . . . . . . . . 187

5.6.5.3 Monitoring Polychlorinated Biphenyls (PCBs) . . . . . . . . . . . . . . . . . . 177

Appendix A . Diffusive Uptake Rates on Perkin-Elmer Sorbent Tubes . . . . . 183

6 Quality Control and Quality Assurance Aspects of Gas Chromatography-Mass Spectrometry for Environmental Analysis

Ray E . Clement and Carolyn J. Koester

6.1 6.2 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.4 6.4.1 6.4.2 6.4.3 6.5 6.6

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Use of GC-MS in Environmental Investigations . . . . . . . . . . . . QC/QA Aspects of GC-MS Instrument Operation . . . . . . . . . . . . . . Quality Control of GC-MS Instrumentation .................... Gas Chromatograph Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description of Various MS Instruments and Capabilities . . . . . . . . . QC Considerations for Qualitative and Quantitative Analysis . . . . . Quality Control for Qualitative GC-MS Analysis . . . . . . . . . . . . . . . Quality Control for Quantitative GC-MS Analysis . . . . . . . . . . . . . . Isotope Dilution GC-MS Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . QC/QA Considerations for Using GC-MS in Contracted Work . . .

Mass Spectrometer Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Summary and Conclusions ...................................

193 194 196 196 197 197 201 202 203 205 207 208 210

7 Application of Capillary Electrophoresis for Environmental Analysis

Saul M . Parry and Colin I;: Simpson

7.1 7.1.1 7.2 7.2.1 7.2.2 7.3 7.3.1 7.4 7.4.1 7.5 7.6 7.6.1 7.7

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Equipment Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Capillary Zone Electrophoresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Fundamentals of CZE Theory ................................ 214 Electroosmotic Flow (EOF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Additive Based CE Separations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 Micellar Electrokinetic Chromatography ....................... 218 Isotachophoresis (ITP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 ITP in the Presence of an Electroosmotic Flow . . . . . . . . . . . . . . . . . 220 Bi-Directional ITP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Sample Introduction Methods for CE . . . . . . . . . . . . . . . . . . . . . . . . . 226 Hydro-Dynamic and Electrokinetic Sample Introduction . . . . . . . . . 227 Novel Sample Introduction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 227

XI1 Contents

7.7.1 7.7.2 7.7.3 7.7.4 7.8 7.8.1 7.8.2 7.8.3 7.8.4 7.8.5 7.8.6 7.8.7 7.8.8 7.8.9 7.9 7.9.1 7.9.2 7.9.3 7.9.4 7.9.5 7.9.6 7.9.7 7.9.8 7.10 7.10.1 7.10.2 7.10.3 7.10.4 7.1 1 7.11.1 7.11.2 7.1 1.3 7.1 1.4 7.12

Electrical Sample Splitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rotary Valve Injector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slider Valve Sample Introduction . . . . . . . . . . . . . . . . . . . . .

Two-Dimensional Electrophoresis ........................

Membrane Sample Introduction . . . . . . . . . . . . . . . . . . . . Methods for Increased Sample Loading . . . . . . . . . . . . . . . . . . . . . . .

ITP-ITP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ITP-CZE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coupled Column ITP-CZE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Choice of Electrolyte System ITP-CZE . . . . . . . . . . . . . . . . . . . . On-Column ITP-CZE: Transient ITP and Sample Stacking . . . . . . Field Amplified Sample Injection (FASI) for CZE . . . . . . . . . . . . . . ITP-CZE With Applied Backpressure . . . . . . . . . . . . . . . . . . . . . . . . . Alternative Approaches to On-Line Preconcentration . . . . . . . . . . . . Detection Methods for CE . . . . . . . . . . . . . . . . . . . . . . . Indirect Optical Detection Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . Indirect Optical Detection for ITP . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indirect UV Detection for CZE . . . . . . . . . . . . . . Optimisation for Indirect UV Detection in CZE . . . . . Optimisation of Injection Method . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . .

Electrolyte System Optimisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Addition of Organic Solvents to Electrolyte System . . . . . . Addition of Complexing Reagents to Electrolyte System . . . . . . . . . Conductivity Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contactless Conductivity Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . In-Contact Conductivity Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Suppressed Conductivity Detection ............................ Mass Spectrometric Detection for CE

Combined Conductivity and UV Detection . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . The CE-MS Interface . . . . . . . . . . . . . . . . . . . . . . . . . . CZE-MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ITP-MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ITP-CZE-MS ........................... . . . . . . . . . . . . . . . . Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 Advances in Flow Analysis . Instrumentation and its Application in Environmental Analysis

Richard J Berman

8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Flow Analysis Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 Gas-Segmented Continuous-Flow Analysis (CFA) . . . . . . . . . . . . . . . 8.2.2 Flow Injection Analysis (FIA) ................................ 8.2.3 Sequential Injection Analysis (SIA) . . . . . . . . . . . . . . . . . . . . . . . . . . .

227 228 229 230 231 231 231 231 232 234 236 239 240 240 241 241 242 242 243 243 243 245 246 247 248 248 250 250 252 254 255 258 259 260

267 269 269 272 274

Conrents XI11

8.2.4 Comparison of Flow Analysis Techniques . . . . . . . . . . . . . . . . . . . . . . 8.2.4.1 Simple Chemistries: Fast Reactions and Few Reagents . . . . . . . . . . . 8.2.4.2 Complex Chemistries: Slow Reactions, Many Reagents. and

Heating Stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.4.3 Sample Dilution 8.2.4.4 Sample Preconcentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.4.5 Low Level Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.4.6 Sample Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.4.7 Precision 8.2.4.8 On-Line Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.4.9 Reagent Consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.4.10 Waste Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.5 Comparison of Flow Analysis with Other Techniques . . . . . . . . . . . 8.3 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . 8.3.2 Injection Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.3 Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.4 Analytical Manifold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.5 Heat Baths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.6 On-Line Distillation Baths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.7 Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.7.1 Improvements in Existing Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.7.2 Adaptation of New Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.8 Data Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Flow Analysis Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.2 Dilution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.3 Derivatization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.4 Stopped-Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.5 Solvent Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.6 Gas Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.7 Dialysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.8 Preconcentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.9 Removal of Interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.10 Digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 1 Combined CFA with FIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.12 Coupling with Other Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.13 Multicomponent Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Environmental Application of Flow Analysis . . . . . . . . . . . . . . . . . . . 8.5.1 Inorganic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1.1 Alkali and Alkaline-Earth Metals ............................. 8.5.1.2 Transition Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1.3 Nonmetals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1.4 Actinide Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1.5 Anions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1.6 Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

275 275

27 5 275 276 276 276 276 277 277 277 278 278 278 279 279 279 280 280 280 280 282 282 283 283 283 284 285 285 287 287 288 290 290 291 292 293 293 294 294 295 297 297 298 300

XIV Contents

8.5.2 Organic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 8.6 Quality Assurance Aspects of Flow Analysis . . . . . . . . . . . . . . . . . . . 301 8.6.1 Calibration Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 8.6.2 Initial and Continuing Calibration Verification . . . . . . . . . . . . . . . . . 302 8.6.3 Calibration Blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 8.6.4 Spikes and Duplicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 8.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

9 Application of Software in Environmental Auditing and Quality Control

Edward So0 and Miles Jack

9.1 9.2 9.2.1 9.2.2 9.3 9.4 9.4.1 9.4.2 9.4.3 9.4.4 9.4.5 9.4.6

Environmental Auditing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 The Mechanics of Auditing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Why Audit? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Implementing an Audit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 The Use of Computers in Auditing . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Coursafe . The Computer Based Auditing Program . . . . . . . . . . . . 315 The Heart of Coursafe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Using Coursafe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 Evaluation of Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 Multi-Audit Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 Implementing Coursafe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 Some Novel Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

Contributors

Richard J. Berman Wacker Siltronic Corporation P. 0. Box 83180 Portland, OR 97283-0180 USA (Chapter 8)

Ray E. Clement Ontario Ministry of Environment and Energy 125 Resources Road Ontario, Canada M9P 3V6 (Chapter 6 )

Terry C. Dymott AT1 Unicam York Street Cambridge CB1, 2PX United Kingdom (Chapter 4 )

Miles Jack Edward Alandale Associates Ltd. P.O. Box 20 Nuneaton Warwickshire CVlO 8RW United Kingdom (Chapter 9 )

Carolyn J. Koester Lawrence Livermore National Laboratory P.O. Box 808 Livermore, CA 94550 USA (Chapter 6 )

Joseph M. Levy ACCTA Inc. 521 6 Karrington Drive Gibsonia Drive, PA 15044 USA (Chapter 2)

Saul M. Parry Department of Chemistry Birbeck College 29 Gordon Square London WC 1 H OPP United Kingdom (Chapter 7)

Dean Rood J & W Scientific 91 Blue Ravine Road Folsom, CA 95630 USA (Chapter I )

Athos C. Rosselli Suprex Corporation 125 William Pitt Way Pittsburg, PA 15238 USA (Chapter 2)

Ian L. Shuttler Bodenseewerk Perkin Elmer GmbH Postfach 101761 D-88647 Uberlingen Germany (Chapter 3 )

XVI Contributors

Colin F. Simpson Department of Chemistry Birbeck College Gordon House 29 Gordon Square London WC 1 H OPP United Kingdom (Chapter 7)

Edward So0 Edward Alandale Associates Ltd. P.O. Box 20 Nuneaton Warwickshire CVIO 8RW United Kingdom (Chapter 9)

Elizabeth A. Woolfenden Perkin-Elmer 761 Main Avenue Norwalk, CT 06859-0001 USA (Chapter 5 )

1 The Use of Solid Phase Extraction for Environmental Samples

Dean Rood

1.1 The Importance of Sample Preparation

Nearly every sample needs some type of preparation before analysis. It is unusual when a sample collected from the environment can be injected directly into a chromatograph without detrimental consequences. The preparation may be neces- sary to remove or reduce sample components other than those of interest. These sample components may interfere with the analysis procedure and may reduce the ability to identify correctly and quantify the potential target analytes in the sample. In most cases, the sample is completely unsuitable for analysis without some type of preparation. Even if a sample was suitable for direct analysis, often the analyte concentrations are too low for detection. Sample preparation methods often result in substantial reductions in the sample volume, thus increasing the analyte concen- tration so that they can be more easily detected.

There are numerous sample preparation (also called extraction) methods for envi- ronmental samples. Environmental samples range from drinking water to solids such as sludge and soils. Sample preparation methods may be to accommodate a wide range of sample types. Column chromatography and liquid - liquid extractions are among the oldest and most frequently used preparation methods. One technique called solid phase extraction (SPE) is suitable for many environmental samples. SPE requires relatively simple equipment, can process multiple samples simultaneously, provides superior sample clean up to most liquid - liquid extraction methods, sub- stantially reduces solvent consumption, and reduces the time required to prepare samples for analysis. There are also robot SPE systems available that provide unat- tended and reliable sample preparation. The cost of materials per sample is equal, or in some cases lower, than for a corresponding liquid-liquid extraction. In nearly every aspect, SPE provides superior sample preparation to liquid - liquid extraction methods.

2 I The Use of Solid Phase Exfraction for Environmental Samples

1.2 Introduction to Solid Phase Extraction

Solid phase extraction (SPE) involves passing a sample that is dissolved in a solvent through a bed of small, adsorbent particles. This material is usually packed into small tubes resembling miniature liquid chromatography columns. Depending on the design of the tube, vacuum or pressure is used to force solvent containing the sample through the adsorbent. The adsorbent material, called the sorbent, will retain select compounds in the sample. Some or all of the retained compounds then can be wash- ed from the sorbent using an appropriate solvent. This solvent is collected for analy- sis or, if necessary, additional sample clean up.

The properties of the solvents and sorbent will determine the amount of com- pound retention and the ease of compound removal from the sorbent. By careful se- lection of the sorbent and solvents, isolation of the analytes of interest along with a minimal amount of other sample components can be achieved. By removing as many of the other sample components as possible, detection and identification of the target analytes are much easier and accurate. If the solvent containing the ex- tracted sample is evaporated and the remaining residue redissolved in a smaller vol- ume than the original sample, a concentration of the sample occurs. This allows the detection of very low levels of analytes not possible by direct analysis of the original sample. Also, a change in the sample solvent is possible which may be beneficial for the analysis procedure.

1.3 SPE Formats

There are several different designs for SPE devices. Each design has its advantages which are related to the sample type and volume, and the number of samples to be simultaneously extracted.

1.3.1 Syringe Barrel or Cartridges

The syringe barrel type of SPE tubes are referred to as cartridges (Fig. 1-1). The car- tridge bodies are usually made of serological grade polypropylene and terminates in a male h e r tip. Some barrels have a flared opening to accommodate robot gripper arms or large solvent volumes. Solvent reservoirs can be attached to the cartridges using coupling adapters to increase their volume. Frits are used to hold the adsorbent in place and to act as a particulate filter. Most frits are made from polyethylene and have 20 pm pores. Samples with large amounts of particulate material may block the frit and impede the flow of solvents through the cartridge. Glass or PTFE cartridge bodies and PTFE or stainless steel frits are available when very low contaminant

1.3 SPE Formats 3

Cartridge Fig. 1-1. Cartridge and sep-pak SPE

Sep-pak tubes.

levels are desired. The cost for these materials are substantially higher than for plas- tic cartridges and frits.

The most common sorbents are silica based materials. The particle shape can be irregular or spherical with irregular being the most common. The average particle diameter is 40 pm with 100- 120 A pores; however, larger particle sizes are not un- common. Other adsorbents such as Florisil, Alumina and resins are also available as SPE sorbents.

Solvent flow through a SPE cartridge is most often controlled by vaccum. A single cartridge can be processed using a side arm flask apparatus (Fig. 1-2). Multiple car- tridges can be simultaneously processed by using a vacuum manifold (Fig. 1-3). There are several different manifold designs, but they all function in the same basic manner and are primarily distinguished by their number of cartridge positions. Racks are used to hold collection tubes beneath each cartridge. A variety of racks are available to accommodate many different types and sizes of collection tubes.

Fig. 1-2. Side arm flask apparatus for SPE cartridges.

4 I The Use of Solid Phase Extraction for Environmental Samples

onnect to Fig. 1-3. Vacuum manifold for SPE vacuum source cartridges.

1.3.2 Syringe Filter or Sep-paks

The syringe filter type of SPE tubes are most commonly referred to as sep-paks (Fig. 1-1). The same type of materials are used for the frits and tube body as the car- tridge format. This type of SPE tube is designed to be placed on the end of a 5 - 50 mL her tip syringe (Fig. 1-4). Solvent is added to the syringe barrel and forced through the SPE sep-pak by the syringe plunger. This design is very convenient if only a few samples need to be processed, the SPE method is very simple, or a mini- mal amount of equipment is available. It is much easier to process a large number of samples with cartridge SPE tubes and a vacuum manifold. The sep-pak tube has to be removed from the end of the syringe or vented using an in-line stopcock before the syringe plunger can be safely removed from the syringe. For complex SPE meth- ods, a large number of different solvents are used. This may require a large number of inconvenient manipulations of the syringe and SPE sep-pak tube.

Fig. 1-4. Sep-pak tube and solvent syringe.

1.3 SPE Formats 5

1.3.3 Disks

The newest SPE format is the flexible disk. This format was introduced by 3 M and is referred by its brand name of EmporeTM disks. The 5 - 10 pm sorbent particles are intertwined with very fine threads of PTFE resulting in a disk about 0.5 mm thick and 47 - 70 mm in diameter. The disks resemble solvent filters. The disks are placed in a typical solvent filter apparatus and solvent is forced through the disk by vacuum (Fig. 1-5). A test tube is placed in the filter flask to collect the final extract. Multiple samples can be simultaneously extracted with a manifold setup (Fig. 1-6).

Fig. 1-5. SPE disk and filter apparatus (photo courtesy of 3M).

Fig. 1-6. Vacuum manifold for SPE disks (photo courtesy of 3M).

6 I The Use of Solid Phase Extraction for Environmental Samales

The thin sorbent bed and large surface area allows very rapid solvent flow rates through the disk. One liter of water can be passed through a disk in less than 10 min. Cartridge and syringe filter SPE tubes have a maximum flow rate of 5 - 10 mL min-'; faster rates result in poor sample extraction. Also large sample volumes are difficult to handle due to the limited volume and slower flow rates of cartridges and syringe filter SPE tubes.

1.3.4 Choice of Format

The choice of SPE format will primarily depend on the volume and type of samples to be extracted. Small to medium volume samples are easier to handle with the car- tridge or sep-pak type of SPE tube. A large number of samples is more easily han- dled with cartridge SPE tubes and a vacuum manifold; the sep-pak type of tube is best suited for a low number of samples or very simple methods. For large volume samples (ie, >50 mL) the disk format is best due to its high flow characteristics. Ex- cluding the sorbent, PTFE is the only material in the disk, thus impurities from the disk are virtually non-existent. Impurities from cartridge or sep-paks tubes and frits can sometimes be detected at low levels. Disk are susceptible to plugging by particu- lates in the sample. If the sample contains a high amount of solids, filter paper can be added to the top of the disk to minimize clogging problems. The cost of cartridge and sep-pak tubes are very similar, and are primarily related to the size and the amount of sorbent. Disks cost about 2-4 times more than cartridges or sep-paks.

1.4 Using SPE Cartridges and Disks

The methods and steps are the same for all of the SPE formats. There are four steps to most methods with each step fulfilling a specific function. Each step is distin- guished by the solvent, and the solvents used will depend on the characteristics of the sorbent and sample.

Condition Load

Fig. 1-7. Four steps of SPE methods.

o>:

Rinse Elute

1.5 SPE Sorbents 7

The four SPE method steps are conditioning, loading, rinsing and elution (Fig. 1-7). Conditioning creates a sorbent environment compatible with the sample and removes impurities from the cartridge. Loading is when the sample is added to the cartridge and forced through the sorbent; the analytes and other compounds in the sample are retained by the sorbent. Rinsing removes (elutes) some of the unwant- ed sample compounds without removing any of the analytes. Elution is the removal of the analytes from the sorbent with the minimal amount of other sample com- pounds. The sorbent and compounds will directly influence which solvents are used for each step. The relationships must be understood before methods can be success- fully developed or modified.

1.5 SPE Sorbents

The most common SPE sorbents can be placed into three classes - normal phase, reverse phase and ion exchange. The structure of the sorbent determines its classifica- tion and characteristics; however, some sorbents may actually belong to more than one class and exhibit several distinct characteristics.

The most common sorbents are based on silica. With the exception of unmodified silica, functional groups are bonded to the surface of the silica particle to alter its retentive properties. The structure of the bonded groups will determine the classifica- tion in which the sorbent belongs. There are several non-silica based sorbents in com- mon use. Florisil and Alumina are the best known examples of these types of sorbents.

1.5.1 Normal Phase Sorbents

Normal phase sorbents have polar functional groups bonded to the silica surface; unmodified silica, Florisil and Alumina are also included in this group (Fig.1-8). Due to this polar character, these sorbents have a stronger affinity for polar compounds than for non-polar compounds. Thus, a normal phase sorbent will retain polar com- pounds more strongly than non-polar compounds. The structure of the compounds and the sorbent will influence the strength of the retention. In general, normal phase sorbents are used to extract polar compounds, typically those with hydroxyl or amine groups. Phenols and nitrosoamines are examples of compounds strongly retained by normal phase sorbents.

1.5.2 Reverse Phase Sorbents

Reverse phase sorbents have non-polar functional groups bonded to the silica par- ticles (Fig. 1-9). These sorbents have a stronger affinity for non-polar compounds

8 1 The Use of Solid Phase Extraction for Environmental Samples

Sorbent Structure

Si Silica -Si-OH

CN Cyano -Si-CH,CH,CH,CN

NH2 Amino -Si-CH,CH2CH,NH,

20H Diol -Si-CH2CH,CH,0CH,-CH-CH

OH OH I I

Fig. 1-8. Normal phase sorbents.

than for polar compounds. Thus, a reverse phase sorbent will retain non-polar com- pounds more strongly than polar compounds. Like normal phase sorbents, the struc- ture of the compounds and sorbent will influence the strength of the retention. In general, reverse phase sorbents are used to extract non-polar compounds, typically

Sorbent Structure

C18 Octadecyl -Si-C,,H,,

C8 Octyl -Si-C,H,,

C4 Butyl -Si-C,H,

C2 Ethyl -Si-CH2CH,

C1 Methyl -Si-CH,

Ph Phenyl -si-Q

CH Cyclohexyl -Si-(J

Fig. 1-9. Reverse phase sorbents.

1.5 SPE Sorbents 9

those with substantial hydrocarbon character. Polynuclear aromatic hydrocarbons (PAH) and many pesticides are examples of compounds strongly retained by reverse phase sorbents.

1.5.3 Ion Exchange Sorbents

Ion exchange sorbents have either a cationic or anionic functional group bonded to the silica particle (Fig. 1-10). When in the ionized form, the phase will retain com- pounds of the opposite charge. Any compounds with the same charge as the sorbent or that are neutral will not be retained by the sorbent. Thus, sample components with the opposite charge as the sorbent will be retained. There are two groups of ion ex- change phases. Cation exchange phases will retain positively charged compounds (cations). Anion exchange phases will retain negatively charged compounds (anions). In general, ion exchange sorbents are used to extract ionic compounds typically those with a carboxylic acid or amine functional group. Triazine and phenoxyacid herbi- cides are example of suitable compounds for ion exchange sorbents.

Sorbent Structure

SCX Benzenesulfanic acid -Si-CH,CH, ' \ -SO;H' Q (strong cation exchange)

PRS Propylsulfonic acid -Si-CH,CH,CH,-SOy Na'

CBA Carboxylic acid -Si-CH,CH,COO-H'

SAX Quaternary amine -Si-CH,CH,CH,N'(CH,CH3),CI

(strong anion exchange)

DEA Diethylaminopropyl -Si-CH,CH,CH,N(CH,CHJ,

PSA Primarylsecondary arnine -Si-CH2CH,CH,NCH,CH,NH2

NH2 Amino -Si-CH,CH,CH,NH,

Fig. 1-10. Ion exchange sorbents.

10 I The Use of Solid Phase Extraction for Environmental Samples

1.6 Sorbent and Solvent Relationships

For normal and reverse phase sorbents, compound retention and elution will be con- trolled by the solvent selection. The polarity of the solvent will determine the strength of the solvent. A strong solvent can be simply defined as a solvent that elutes a compound from the sorbent in a smaller volume than a corresponding weak- er solvent. Thus, retention and elution of compounds is controlled by the polarity of the solvent passing through the sorbent. Ion exchange phases do not depend only on solvent polarity for retention and elution. Ion exchange phases depend primarily on the pH and the ionic species in solution for retention and elution.

1.6.1 Normal Phase

Table 3 - 1 lists solvents in order of increasing solvent strength for normal phase sorbents. Note that solvent strength increases as solvent polarity increases. For exam- ple, a smaller volume of methanol is needed to elute a compound completely from a normal phase sorbent than chloroform or that more retention is obtained with chloroform than methanol. Sometimes a solvent may be too strong while the next weaker solvent is too weak for a particular step. Solvent mixtures are often used to overcome this problem and to finely control retention and elution. Unfortunately, it is difficult to predict the exact amount of retention or elution change upon changing solvents or mixtures. The general direction of the change is predictable, but not the absolute amount of retention or elution change. Each compound and sorbent is affected differently by the change in solvent.

Table 1-1. Solvent strength for normal phase sorbents.

Table 1-2. Solvent strength for reverse phase sorbents.

WEAKEST hexane iso-octane toluene chloroform dichloromethane tetrahydrofuran (THF) ethyl ether ethyl acetate acetone acetonitrile iso-propyl alcohol

STRONGEST methanol

WEAKEST water methanol iso-propyl alcohol acetonitrile acetone ethyl acetate ethyl ether tetrahydrofuran (THF) dichloromethane chloroform toluene iso-octane

STRONGEST hexane

1.6 Sorbent and Solvent Relationships 11

1.6.2 Reverse Phase

Table 1-2 lists solvents in order of increasing solvent strength for reverse phase sorbents. Note that solvent strength increases as solvent polarity decreases. This sol- vent strength relationship is the opposite of normal phase sorbents. The solvents used with reverse phase sorbents are usually limited to water, methanol, iso-propanol and acetonitrile. Less polar solvents are often too strong for most reverse phase sorbents. As for normal phase, exact predictions about retention and elution changes with solvent changes are difficult.

1.6.3 Ion Exchange

There are three major factors that determines retention and elution for ion exchange sorbents. They are solvent and sample pH, ionic strength of the solvents and count- er-ion identity.

Regardless of the type of ion exchange phase, there is always a cation and anion pair. One is the sorbent and the other oppositely charged species is the analyte. For analyte retention to occur, the sample must be at least 2 pH units below the pK, of the cation (to maintain a positive charge) and 2 pH units above the pK, of the an- ion (to maintain a negative charge). At a pH/pK, difference of less than 2, reten- tion will suffer because the analyte or sorbent will be partially neutral instead of be- ing completely charged. This factor also requires that the p K , difference between the analyte and sorbent must be 4 or greater.

Elution of a retained analyte can be controlled by the pH of the elution solvent. If the solvent pH is at least 2 pH units above the p K , of the cation, significant elu- tion will occur since the cation becomes neutral. If the solvent pH is at least 2 p H units below the p K, of the anion, significant elution will also occur since the anion becomes neutral. As long as the sorbent or analyte is neutral, elution of the analyte from the sorbent will occur. The pK,s for the most common ion exchange phases are listed in Table 1-3.

Ionic strength is a measure of the total concentration of ionic species in solution. The retention and elution of analytes are a function of the solvent concentration of other ionic species with the same charge. These ions (called counter-ions) compete with the analytes for the limited number of binding sites on the sorbent. Low ionic strength solvents enhance retention since the analytes do not have to compete with a large number of counter-ions for the binding sites. High ionic strength solvents often inhibit retention since the high number of counter-ions may occupy most of the binding sites. High ionic strength solvents cause often elution of the analytes from the sorbent since the large number of counter-ions may displace the analytes from the sorbent.

Counter-ion strength is a measure of the affinity of the counter-ion for the sor- bent. High strength counter-ions have a greater ability to compete and bind to the sorbent than a weaker counter-ion. Relative counter-ion strengths are listed in

12 I The Use of Solid Phase Extraction for Environmental Samples

Table 1-3. Ion exchange phase pK,s.

Phase PK, a

SCX 2.2 -2.7 PRS 2.5 - 3.0 CBA 4.5 - 5.0 NH2 9.5 - 10.0 PSA DEA 10.5 - 11 .o SAX Always charged

10.0 - 10.5 ’, 10.7 - 11.2‘

a pK,s vary slightly by manufacturer, thus a range is given. ’ Primary amine.

Secondary amine.

Table 1-4. If there are ions present in the sorbent conditioning and load solvents, they should be weak counter-ions. The analyte has the best chance of displacing a weak counter-ion from the sorbent, thus enhancing retention. Solvents containing strong counter-ions will cause elution and poor retention since the counter-ions will easily displace the analyte from the sorbent.

Table 1-4. Counter-ion strengths.

Cation Relative strength Anion Relative strength

Li, H 0.5 OH, F, propionate 0.1 Na 1.5 Acetate, formate 0.2

K, Mg, Mn, Fe 2.5 CI, NO, 1 .o Cu(l), Zn, Co, Cd 3 .O HSO,, CN 1 .5

c u m 6.0 CIO, 4.5 Pb, Ag 8 s Citrate 9.5 Ba 10.0 Benzene sulfonate 10.0

For each ion category, the highest strength counter-ion was normalized to 10, thus the values are relative.

NH.4 2.0 HP,, HCO 0.4

Ca 4.5 NO3 4.0

1.7 Selecting the Solvents

The solvents for any SPE method depends on the analytes, sample and sorbent. A small amount of experimentation is usually needed to select the best solvents; however, it is often fairly easy to narrow the selections to a few possibilities.