Basics of Environmental Sampling and Analysis 11 2.1 Essential Analytical and Organic Chemistry 11 2.1.1 Concentration Units 11 2.1.2 Common Organic Pollutants and Their Properties 14 2.
Trang 2of Environmental
Sampling and Analysis
Trang 4of Environmental
Sampling and Analysis
Chunlong (Carl) Zhang
University of Houston-Clear Lake
WILEY-INTERSCIENCE
A John Wiley & Sons, Inc., Publication
Trang 5Copyright ß 2007 by John Wiley & Sons, Inc All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
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Wiley Bicentennial Logo: Richard J Pacifico
Library of Congress Cataloging-in-Publication Data:
Fundamentals of environmental sampling and analysis / Chunlong Carl Zhang.
Trang 6My Parents
To My Wife Sue and Two Sons Richard and Arnold
Trang 81.2.1 Scope of Environmental Sampling 5
1.2.2 Where, When, What, How, and How Many 6
1.3 Environmental Analysis 6
1.3.1 Uniqueness of Modern Environmental Analysis 7
1.3.2 Classical and Modern Analytical and Monitoring Techniques 7
Questions and Problems 10
2 Basics of Environmental Sampling and Analysis 11
2.1 Essential Analytical and Organic Chemistry 11
2.1.1 Concentration Units 11
2.1.2 Common Organic Pollutants and Their Properties 14
2.1.3 Analytical Precision, Accuracy, and Recovery 16
2.1.4 Detection Limit and Quantitation Limit 17
2.1.5 Standard Calibration Curve 18
2.2 Essential Environmental Statistics 20
2.2.1 Measurements of Central Tendency and Dispersion 20
2.2.2 Understanding Probability Distributions 21
2.2.3 Type I and II Errors: False Positive and False Negative 25
vii
Trang 92.2.4 Detection of Outliers 26
2.2.5 Analysis of Censored Data 28
2.2.6 Analysis of Spatial and Time Series Data 29
2.3 Essential Hydrology and Geology 30
2.3.1 Stream Water Flow and Measurement 30
2.3.2 Groundwater Flow in Aquifers 31
2.3.3 Groundwater Wells 32
2.4 Essential Knowledge of Environmental Regulations 35
2.4.1 Major Regulations Administrated by the U.S EPA 352.4.2 Other Important Environmental Regulations 35
References 37
Questions and Problems 39
3 Environmental Sampling Design 45
3.1 Planning and Sampling Protocols 45
3.1.1 Data Quality Objectives 46
3.1.2 Basic Considerations of Sampling Plan 48
3.2 Sampling Environmental Population 49
3.2.1 Where (Space) and When (Time) to Sample 49
3.2.2 Obtain Representative Samples from Various Matrices 49
3.3 Environmental Sampling Approaches: Where and When 52
3.3.1 Judgmental Sampling 52
3.3.2 Simple Random Sampling 53
3.3.3 Stratified Random Sampling 54
3.3.4 Systematic Sampling 56
3.3.5 Other Sampling Designs 57
3.4 Estimating Sample Numbers: How Many Samples are Required 61
References 63
Questions and Problems 63
4 Environmental Sampling Techniques 69
4.1 General Guidelines of Environmental Sampling Techniques 69
4.1.1 Sequence of Sampling Matrices and Analytes 70
viii Contents
Trang 104.1.2 Sample Amount 70
4.1.3 Sample Preservation and Storage 71
4.1.4 Selection of Sample Containers 74
4.1.5 Selection of Sampling Equipment 76
4.2 Techniques for Sampling Various Media:
Practical Approaches and Tips 83
4.2.1 Surface Water and Wastewater Sampling 84
4.2.2 Groundwater Sampling 86
4.2.3 Soil and Sediment Sampling 89
4.2.4 Hazardous Waste Sampling 90
4.2.5 Biological Sampling 92
4.2.6 Air and Stack Emission Sampling 92
References 93
Questions and Problems 94
5 Methodology and Quality Assurance/Quality Control
of Environmental Analysis 97
5.1 Overview on Standard Methodologies 98
5.1.1 The U.S EPA Methods for Air, Water, Wastewater,
and Hazardous Waste 98
5.1.2 Other Applicable Methods:
5.2 Selection of Standard Methods 108
5.2.1 Methods for Sample Preparation 109
5.2.2 Methods for Physical, Biological, and General
Chemical Parameters 111
5.2.3 Methods for Volatile Organic Compounds (VOCs) 112
5.2.4 Methods for Semivolatile Organic Compounds (SVOCs) 113
5.2.5 Methods for Other Pollutants and Compounds
of Emerging Environmental Concerns 113
5.3 Field Quality Assurance/Quality Control (QA/QC) 115
5.3.1 Types of Field QA/QC Samples 116
5.3.2 Numbers of Field QA/QC Samples 118
5.4 Analytical Quality Assurance/Quality Control 118
5.4.1 Quality Control Procedures for Sample Preparation 118
5.4.2 Quality Control Procedures During Analysis 119
Contents ix
Trang 11References 122
Questions and Problems 123
6 Common Operations and Wet Chemical Methods
in Environmental Laboratories 127
6.1 Basic Operations in Environmental Laboratories 128
6.1.1 Labware Cleaning Protocols for Trace Analysis 128
6.1.2 Chemical Reagent Purity, Standard, and Reference Materials 129
6.1.3 Volumetric Glassware and Calibration 132
6.1.4 Laboratory Health, Safety, and Emergency First Aid 134
6.1.5 Waste Handling and Disposal 136
6.2 Wet Chemical Methods and Common Techniques
in Environmental Analysis 137
6.2.1 Gravimetric and Volumetric Wet Chemical Methods 137
6.2.2 Common Laboratory Techniques 138
6.3 Analytical Principles for Common Wet Chemical Methods 141
6.3.1 Moisture in Solid and Biological Samples 141
6.3.2 Solids in Water, Wastewater,
and Sludge (TS, TSS, TDS, VS) 141
6.3.3 Acidity, Alkalinity, and Hardness of Waters 142
6.3.4 Oxygen Demand in Water and Wastewater
6.3.5 Oil and Grease in Water and Wastewater 148
6.3.6 Residual Chlorine and Chloride in Drinking Water 149
6.3.7 Ammonia in Wastewater 152
6.3.8 Cyanide in Water, Wastewater and Soil Extract 153
6.3.9 Sulfide in Water and Waste 154
References 155
Questions and Problems 155
7 Fundamentals of Sample Preparation for
Environmental Analysis 159
7.1 Overview on Sample Preparation 160
7.1.1 Purpose of Sample Preparation 160
7.1.2 Types of Sample Preparation 161
x Contents
Trang 127.2 Sample Preparation for Metal Analysis 162
7.2.1 Various Forms of Metals and Preparation Methods 162
7.2.2 Principles of Acid Digestion and Selection of Acid 163
7.2.3 Alkaline Digestion and Other Extraction Methods 165
7.3 Extraction for SVOC and Non-VOC from Liquid or
Solid Samples 168
7.3.1 Separatory Funnel and Continuous Liquid–Liquid
Extraction (LLE) 168
7.3.2 Solid Phase Extraction 171
7.3.3 Solid Phase Microextraction 173
7.3.4 Soxhlet and Automatic Soxhlet Extraction (Soxtec) 174
7.3.5 Ultrasonic Extraction 176
7.3.6 Pressured Fluid Extraction 177
7.3.7 Supercritical Fluid Extraction 177
7.3.8 Comparison and Selection of Organic Extraction Methods 178
7.4 Post-Extraction Clean-up of Organic Compounds 179
7.4.1 Theories and Operation Principles of Various
Clean-up Methods 179
7.4.2 Recommended Clean-up Method for Selected
7.5 Derivatization of Non-VOC for Gas Phase Analysis 182
7.6 Sample Preparation for VOC, Air and Stack Gas Emission 183
7.6.1 Dynamic Headspace Extraction (Purge-and-Trap) 183
7.6.2 Static Headspace Extraction 184
7.6.3 Azeotropic and Vacuum Distillation 185
7.6.4 Volatile Organic Sampling Train 186
References 187
Questions and Problems 187
8 UV-Visible and Infrared Spectroscopic Methods in
Environmental Analysis 190
8.1 Introduction to the Principles of Spectroscopy 191
8.1.1 Understanding the Interactions of Various Radiations
with Matter 191
8.1.2 Origins of Absorption in Relation to Molecular
Orbital Theories 193
Contents xi
Trang 138.1.3 Molecular Structure and UV-Visible/Infrared Spectra 200
8.1.4 Quantitative Analysis with Beer-Lambert’s Law 204
8.2 UV-Visible Spectroscopy 206
8.2.1 UV-Visible Instrumentation 206
8.2.2 UV-VIS as a Workhorse in Environmental Analysis 208
8.3 Infrared Spectroscopy 211
8.3.1 Fourier Transform Infrared Spectrometers (FTIR) 211
8.3.2 Dispersive Infrared Instruments (DIR) 213
8.3.3 Nondispersive Infrared Instruments (NDIR) 214
8.3.4 Applications in Industrial Hygiene and Air Pollution
Monitoring 214
8.4 Practical Aspects of UV-Visible and Infrared Spectrometry 215
8.4.1 Common Tips for UV-Visible Spectroscopic Analysis 215
8.4.2 Sample Preparation for Infrared Spectroscopic Analysis 216
References 217
Questions and Problems 218
9 Atomic Spectroscopy for Metal Analysis 220
9.1 Introduction to the Principles of Atomic Spectroscopy 221
9.1.1 Flame and Flameless Atomic Absorption 221
9.1.2 Inductively Coupled Plasma Atomic Emission 225
9.1.3 Atomic X-ray Fluorescence 227
9.2 Instruments for Atomic Spectroscopy 227
9.2.1 Flame and Flameless Atomic Absorption 227
9.2.2 Cold Vapor and Hydride Generation Atomic Absorption 229
9.2.3 Inductively Coupled Plasma Atomic Emission 232
9.2.4 Atomic X-ray Fluorescence 233
9.3 Selection of the Proper Atomic Spectroscopic Techniques 235
9.3.1 Comparison of Detection Limits and Working Range 235
9.3.2 Comparison of Interferences and Other Considerations 236
9.4 Practical Tips to Sampling, Sample Preparation,
and Metal Analysis 240
References 243
Questions and Problems 243
xii Contents
Trang 1410 Chromatographic Methods for Environmental Analysis 246
10.1 Introduction to Chromatography 247
10.1.1 Types of Chromatography and Separation Columns 247
10.1.2 Common Stationary Phases: The Key to Separation 249
10.1.3 Other Parameters Important to Compound Separation 251
10.1.4 Terms and Theories of Chromatogram 254
10.1.5 Use of Chromatograms for Qualitative
and Quantitative Analysis 258
10.2 Instruments of Chromatographic Methods 258
10.2.1 Gas Chromatography 258
10.2.2 High Performance Liquid Chromatography (HPLC) 260
10.2.3 Ion Chromatography 264
10.2.4 Supercritical Fluid Chromatography 265
10.3 Common Detectors for Chromatography 266
10.3.1 Detectors for Gas Chromatography 267
10.3.2 Detectors for High Performance Liquid
10.3.3 Detectors for Ion Chromatography 274
10.4 Applications of Chromatographic Methods
in Environmental Analysis 275
10.4.1 Gases, Volatile, and Semivolatile Organics with GC 27610.4.2 Semivolatile and Nonvolatile Organics with HPLC 278
10.4.3 Ionic Species with IC 278
10.5 Practical Tips to Chromatographic Methods 279
10.5.1 What Can and Cannot be Done with GC and HPLC 279
10.5.2 Development for GC and HPLC Methods 280
10.5.3 Overview on Maintenance and Troubleshooting 281
References 284
Questions and Problems 285
11 Electrochemical Methods for Environmental Analysis 289
11.1 Introduction to Electrochemical Theories 290
11.1.1 Review of Redox Chemistry and Electrochemical Cells 290
11.1.2 General Principles of Electroanalytical Methods 292
11.1.3 Types of Electrodes and Notations
for Electrochemical Cells 295
Contents xiii
Trang 1511.2 Potentiometric Applications in Environmental Analysis 296
11.2.1 Measurement of pH 296
11.2.2 Measurement of Ions by Ion Selective Electrodes (ISEs) 298
11.2.3 Potentiometric Titration (Indirect Potentiometry) 299
11.3 Voltammetric Applications in Environmental Analysis 300
11.3.1 Measurement of Dissolved Oxygen 300
11.3.2 Measurement of Anions by Amperometric Titration 302
11.3.3 Measurement of Metals by Anodic Stripping
Voltammetry (ASV) 303
References 305
Questions and Problems 306
12 Other Instrumental Methods in Environmental Analysis 309
12.1 Hyphenated Mass Spectrometric Methods and Applications 310
12.1.1 Atomic Mass Spectrometry (ICP-MS) 310
12.1.2 Molecular Mass Spectrometry (GC-MS and LC-MS) 313
12.1.3 Mass Spectrometric Applications
in Environmental Analysis 320
12.2 Nuclear Magnetic Resonance Spectroscopy (NMR) 322
12.2.1 NMR Spectrometers and the Origin of NMR Signals 32212.2.2 Molecular Structures and NMR Spectra 325
12.2.3 Applications of NMR in Environmental Analysis 329
12.3 Miscellaneous Methods 329
12.3.1 Radiochemical Analysis 329
12.3.2 Surface and Interface Analysis 333
12.3.3 Screening Methods Using Immunoassay 334
References 335
Questions and Problems 336
Experiment 1 Data Analysis and Statistical Treatment: A Case
Study on Ozone Concentrations in Cities ofHouston-Galveston Area 340
xiv Contents
Trang 16Experiment 2 Collection and Preservation of Surface Water and Sediment
Samples and Field Measurement of SeveralWater Quality Parameters 344
Experiment 3 Gravimetric Analysis of Solids and Titrimetric
Measurement of Alkalinity of Streamsand Lakes 348
Experiment 4 Determination of Dissolved Oxygen (DO) by Titrimetric
Winkler Method 352
Experiment 5 Determination of Chemical Oxygen Demand (COD) in
Water and Wastewater 357
Experiment 6 Determination of Nitrate and Nitrite in Water by
UV-Visible Spectrometry 362
Experiment 7 Determination of Anionic Surfactant (Detergent) by
Liquid-Liquid Extraction Followed byColorimetric Methods 366
Experiment 8 Determination of Hexavalent and Trivalent Chromium
(Cr6þand Cr3þ) in Water by Visible Spectrometry 370
Experiment 9 Determination of Greenhouse Gases by Fourier Transform
Infrared Spectrometer 374
Experiment 10 Determination of Metals in Soil–Acid Digestion
and Inductively Coupled Plasma–Optical EmissionSpectroscopy (ICP-OES) 378
Experiment 11 Determination of Explosives Compounds in a
Contaminated Soil by High Performance LiquidChromatography (HPLC) 382
Experiment 12 Measurement of Headspace Chloroethylene by Gas
Chromatography with Flame IonizationDetector (GC-FID) 386
Experiment 13 Determination of Chloroethylene by Gas Chromatography
with Electron Capture Detector (GC-ECD) 390
Experiment 14 Use of Ion Selective Electrode to Determine
Trace Level of Fluoride in Drinkingand Natural Water 392
Experiment 15 Identification of BTEX and Chlorobenzene Compounds
by Gas Chromatography-Mass Spectrometry
Contents xv
Trang 17Appendices 402
A Common Abbreviations and Acronyms 402
B Structures and Properties of Important Organic Pollutants 407
C1 Standard Normal Cumulative Probabilities 417
C2 Percentiles of t-Distribution 418
C3 Critical Values for the F-Distribution 419
D Required Containers, Preservation Techniques, and Holding Times 420
xvi Contents
Trang 18The acquisition of reliable and defensible environmental data through propersampling and analytical technique is often an essential part of the careers for manyenvironmental professionals However, there is currently a very diverse and diffusesource of literature in the field of environmental sampling and analysis The nature
of the literature often makes beginners and even skilled environmental professionalsfind it very difficult to comprehend the needed contents The overall objective of thistext is to introduce a comprehensive overview on the fundamentals of environmentalsampling and analysis for students in environmental science and engineering as well
as environmental professionals who are involved in various stages of sampling andanalytical work
Two unique features are evident in this book First, this book presents a ‘‘knowwhy’’ rather than a ‘‘know how’’ strategy It is not intended to be a cookbook thatpresents the step-by-step details Rather, fundamentals of sampling, selection ofstandard methods, chemical and instrumental principles, and method applications toparticular contaminants are detailed Second, the book gives an integratedintroduction to sampling and analysis—both are essential to quality environmentaldata For example, contrary to other books that introduce a specific area of samplingand analysis, this text provides a balanced mix of field sampling and laboratoryanalysis, essential knowledge in chemistry, statistics, hydrology, wet chemicalmethods for conventional chemicals, as well as various modern instrumentaltechniques for contaminants of emerging concerns
Chapter 1 starts with an overview on the framework of environmental samplingand analysis and the importance for the acquisition of scientifically reliable andlegally defensible data Chapter 2 provides some background information necessaryfor the readers to better understand the subsequent chapters, such as review onanalytical and organic chemistry, statistics for data analysis, hydrogeology, andenvironmental regulations relevant to sampling and analysis The following twochapters introduce the fundamentals of environmental sampling—where and when
to take samples, how many, how much, and how to take samples from air, liquid, andsolid media
Chapter 5 introduces the standard methodologies by the US EPA and otheragencies Their structures, method classifications, and cross references amongvarious standards are presented to aid readers in selecting the proper methods.Quality assurance and quality control (QA/QC) for both sampling and analysis arealso included in this chapter as a part of the standard methodology Chapter 6provides some typical operations in environmental laboratories and details thechemical principles of wet chemical methods most commonly used in environmental
xvii
Trang 19analysis Prior to the introduction to instrumental analysis and applications inenvironmental analysis in Chapters 8–12, various sample preparation methods arediscussed and compared in Chapter 7.
In Chapter 8, the theories of absorption spectroscopy for qualitative andquantitative analysis are presented UV-visible spectroscopy is the main focus of thischapter because nowadays it is still the workhorse in many of the environmentallaboratories Chapter 9 is devoted to metal analysis using various atomic absorptionand emission spectrometric methods Chapter 10 focuses on the instrumentalprinciples of the three most important chromatographic methods in environmentalanalysis, i.e., gas chromatography (GC), high performance liquid chromatography(HPLC), and ion chromatography (IC) Chapter 11 introduces the electrochemicalprinciples and instrumentations for some common environmental analysis, such as
pH, potential titrations, dissolved oxygen, ion selective electrodes, conductivity, andmetal analysis using anodic stripping voltammetry Chapter 12 introduces severalanalytical techniques that are becoming increasingly important to meet today’schallenge in environmental analysis, such as various hyphenated mass spectro-metries using ICP/MS, GS/MS and LC/MS This last chapter concludes with a briefintroduction to nuclear magnetic resonance spectroscopy (less commonly used inquantitative analysis but important to structural identifications in environmentalresearch) and specific instrumentations including radiochemical analysis, electronscanning microscopes, and immunoassays
The selections of the above topics are based on my own teaching and practicalexperience and the philosophy that sampling and analysis are equally important asboth are an integral part of reliable data An understanding of the principles ofsampling, chemical analysis, and instrumentation is more important than knowing
‘‘specific how.’’ It is not uncommon to witness how time and resources are wasted bymany beginners in sampling and analysis This occurs when samplers and analystsused improper sampling and analytical protocols This occurs also when properprocedures from ‘‘step-by-step’’ cookbook were followed, but the samplers oranalysts did not make proper modifications without understanding the fundamentals.Even skilled professionals are not immune to errors or unnecessary expenses duringsampling, sample preparation and analytical processes if underlying fundamentalsare either neglected or misinterpreted
WHOM THIS BOOK IS WRITTEN FOR
This book is primarily targeted to beginners, such as students in environmentalscience and engineering as well as environmental professionals who are directlyinvolved in sampling and analytical work or indirectly use and interpretenvironmental data for various purposes It is, therefore, written as a textbook forsenior undergraduates and graduate students as well as a reference book for generalaudiences
Several approaches are used to enhance the book for such a wide usage (1)Theories and principles will be introduced first in place of specific protocolsxviii Preface
Trang 20followed by examples to promote logical thinking by orienting these principles tospecific project applications Questions and exercise problems are included in eachchapter to help to understand these concepts (2) Suggested readings are given at theend of each chapter for those who need further information or specific details fromstandard handbooks (EPA, ASTM, OSHA, etc.) or journal articles This list ofreferences is intended to provide an up-to-date single source information describingthe details that readers will find for their particular needs (3) Practical tips are given
in most chapters for those who want to advance in this field (4) A total of 15experiments covering data analysis, sampling, sample preparation, and chemical/instrumental analysis are provided for use as a supplemental lab manual
TO THE INSTRUCTOR
This 12-chapter book contains chapters of sampling (Chapters 2–4), standardmethods and QA/QC (Chapter 5), wet analysis (Chapter 6), sample preparation(Chapter 7), and instrumental analysis (Chapters 8–12) It is designed to have morematerials than needed for a one-semester course Depending on your course focus(e.g., sampling vs analysis) and the level of students, you can select topics mostrelevant to your course These 12-chapters are better served in a lecture course but itcan be used as a supplemental textbook for a lab-based course Even though somechapter may not be covered in details for your particular course, the book cancertainly be used as a valuable reference
EXPERIMENTS
There are 15 experiments included in the book covering various sampling andanalysis techniques, such as computer-based data analysis, field sampling, labo-ratory wet chemical techniques, and instrumental analysis These 15 experimentsalone should be suited to an instruction manual for a lab-based course Several exp-eriments require more advanced instruments such as IR, HPLC, GC, and GC-MS
If such resources are limited, the Instructor can select proper labs from the list,which can be based entirely on gravimetric, volumetric, and UV-visible spectro-scopic analysis using analytical balance, burette, visible spectrometer, and pHmeters Each experiment can be completed during a 2–3 h lab session Many of theselab procedures have been tested in author’s lab with various TAs during the lastseveral years They have been debugged and are shown to be workable
ACKNOWLEDGMENTS
Materials of this book have been used in several lecture and lab-based courses at theUniversity of Houston I first would like to thank my students for their comments,suggestions, and encouragement These feedbacks are typically not technicallydetailed, but help me immeasurably to improve its readability Certainly I would like
Preface xix
Trang 21to thank several technical reviewers (including several anonymous) from the review
of the book proposal at the beginning to the review of the final draft Thanks are due
to Professors Todd Anderson (Texas Tech University), Joceline Boucher (MainMaritime Academy), and Kalliat Valsaraj (Louisiana State University) I have alsoinvited several individuals to proofread all chapters in their expert areas, including
Dr Dennis Casserly (Associate Professor, University of Houston – Clear Lake),
Dr Dean Muirhead (Senior Project Engineer, NASA-JSC), Dr Xiaodong Song(Principle Scientist, Pfizer Corporation), Mr Jay Gandhi (Senior DevelopmentChemist, Metrohm – Peak Inc.), and my thanks to them all
Special thanks to Wiley’s Executive Editor Bob Esposito for his vision of thisproject Senior Editorial Assistant Jonathan Rose has been extremely helpful ininsuring me the right format of this writing even from the beginning of this project
My sincere thanks to several other members of Wiley’s editorial and productionteam, including Brendan Sullivan, Danielle Lacourciere, and Ekta Handa It hasbeen a pleasant experience in working with this editorial team of high professionalstandards and experience
This book would not be accomplished without the support and love of my wifeSue and the joys I have shared with my two sons, Richard and Arnold Even duringmany hours of my absence in the past two years for this project, I felt the drive andinspiration This book is written as a return for their love and devotion With that, Ifelt at some points the obligation of fulfilling and delivering what is beyond mycapability
ABOUT THE AUTHOR
Dr Zhang is currently an associate professor in environmental science andenvironmental chemistry at the University of Houston-Clear Lake He lecturesextensively in the area of environmental sampling and analysis With over twodecades of various experience in academia, industries, and consulting, his expertise
in environmental sampling and analysis covers a variety of first-hand practicalexperience both in the field and in the lab His field and analytical work has includedmultimedia sampling (air, water, soil, sediment, plant, and waste materials) andanalysis of various environmental chemicals with an array of classical chemicalmethods as well as modern instrumental techniques
The author will be happy to receive comments and suggestions about this book
at his e-mail address: zhang@uhcl.edu
Houston, TexasAugust 2006
xx Preface
Trang 22Chapter 1
Introduction to Environmental Data Acquisition
1.1 INTRODUCTION
1.2 ENVIRONMENTAL SAMPLING
1.3 ENVIRONMENTAL ANALYSIS
REFERENCES
QUESTIONS AND PROBLEMS
This introductory chapter will give readers a brief overview of the purposes andscopes of environmental sampling and analysis Sampling and analysis, apparentlythe independent steps during data acquisition, are in fact the integrated parts toobtain quality data—the type of data that are expected to sustain scientific and legalchallenges The importance of environmental sampling and the uniqueness ofenvironmental analysis as opposed to traditional analytical chemistry are discussed
A brief history of classical to modern instrumental analysis is also introduced in thischapter
The objectives of environmental sampling and analysis may vary depending on thespecific project (task), including regulatory enforcement, regulatory compliance,routine monitoring, emergency response, and scientific research The examples are
as follows:
1 To determine how much pollutant enters into environment through stackemission, wastewater discharge, and so forth in order to comply with aregulatory requirement
Fundamentals of Environmental Sampling and Analysis, by Chunlong Zhang
Copyright # 2007 John Wiley & Sons, Inc.
1
Trang 232 To measure ambient background concentration and assess the degree ofpollution and to identify the short- and long-term trends.
3 To detect accidental releases and evaluate the risk and toxicity to human andbiota
4 To study the fate and transport of contaminants and evaluate the efficiency
of remediation systems
This introductory chapter briefly discusses the basic process of environmental dataacquisition and errors associated with field sampling and laboratory analysis Aunique feature of this text is to treat sampling and analysis as an entity This is to saythat sampling and analysis are closely related and dependent on each other The dataquality depends on the good work of both sampler and analyst
The importance of sampling is obvious If a sample is not collected properly, if itdoes not represent the system we are trying to analyze, then all our careful lab work
is useless! A bad sampler will by no means generate good reliable data In somecases, even if sampling protocols are properly followed, the design of sampling iscritical, particularly when the analytical work is so costly
Then what will be the data quality after a right sample is submitted for a labanalysis? The results now depend on the chemist who further performs the labanalysis The importance of sample analysis is also evident If the analyst is unable
to define an inherent level of analytical error (precision, accuracy, recovery, and soforth), such data are also useless The analyst must also know the complex nature of
a sample matrix for better results The analyst needs to communicate well with thefield sampler for proper sample preservation and storage protocols
and Legally Defensible Data
All environmental data should be scientifically reliable Scientific reliability meansthat proper procedures for sampling and analysis are followed so that the resultsaccurately reflect the content of the sample If the result does not reflect the sample,there is no claim of validity Scientifically defective data may be a result ofunintentional or deliberate efforts The examples include the following:
An incorrect sampling protocol (bad sampler)
An incorrect analytical protocol (bad analyst)
The lack of a good laboratory practice (GLP)
The falsification of test results
Good laboratory practice (GLP) is a quality system concerned with theorganizational process and the conditions under which studies are planned,performed, monitored, recorded, archived, and reported The term ‘‘defensible’’means ‘‘the ability to withstand any reasonable challenge related to the veracity,integrity, or quality of the logical, technical, or scientific approach taken in a
2 Chapter 1 Introduction to Environmental Data Acquisition
Trang 24decision-making process.’’ As scientific reliability must be established for allenvironmental data, legal defensibility may not be needed in all cases such as the one
in most academic research projects Legal defensibility is critical in many othercircumstances such as in most of the industrial and governmental settings.Components of legally defensible data include, but are not limited to:
Custody or Control
Documentation
Traceability
Custody or Control: To be defensible in court, sample integrity must be maintained
to remove any doubts of sample tampering/alteration A chain-of-custody formcan be used to prove evidence purity The chain-of-custody form is designed toidentify all persons who had possession of the sample for all periods of time, as it ismoved from the point of collection to the point of final analytical results ‘‘Control’’over the sample is established by the following situations: (1) It is placed in adesignated secure area (2) It is in the field investigator’s or the transferee’sactual possession (3) It is in the field investigator’s or the transferee’s physicalpossession and then he/she secures it to prevent tampering (4) It is in the fieldinvestigator’s or the transferee’s view, after being in his/her physical possession(Berger et al., 1996)
Documentation: Documentation is something used to certify, prove, ate, or support something else In a civil proceeding, documentation is anything thathelps to establish the foundation, authenticity, or relevance leading to the truth of amatter It may become evidence itself Photos, notes, reports, computer printouts,and analyst records are all examples of documentation The chain-of-custody form isone such piece of very important type of document Documentary evidence is thewritten material that ‘‘speaks for itself.’’
substanti-Traceability: Traceability, otherwise known as a ‘‘paper trail,’’ is used todescribe the ability to exactly determine from the documentation that which reagentsand standards were used in the analysis and where they came from Traceability isparticularly important with regard to the standards that are used to calibrate theanalytical instruments The accuracy of the standards is a determining factor onthe accuracy of the sample results Thus, each set of standards used in the lab should
be traceable to the specific certificate of analysis (Berger et al., 1996)
Similar to the components of scientifically defective data, legally weak datamay be a result of unintentional or deliberate efforts In the case of misconduct, theperson involved will be subjected to the same punishment as those who commitcriminal acts, such as those frequently reported (Margasak, 2003) Misconducts inenvironmental sampling and analysis can be a result of the following:
Outside labs oftentimes work for the people who hired them
Poor training of employees in nongovernmental or private labs
Ineffective ethics programs
Shrinking markets and efforts to cut costs
1.1 Introduction 3
Trang 25This text will not discuss the nontechnical or legal aspects of sampling and analysis,but the reader should be cautious about its importance in environmental dataacquisition The legal objective can influence the sampling and analytical effort byspecifying where to sample, defining the method of sampling and analysis, addingadditional requirements to a valid technical sampling design for evidentiaryreasons, and determining whether the data are confidential (Keith, 1996) Samplingand analytical protocols must meet legal requirements for the introduction ofevidence in a court, and the results of a technically valid sampling and analyticalscheme might not be admissible evidence in a courtroom if the legal goal is notrecognized early on in the presampling phase A brief introduction to importantenvironmental regulations will be presented in Chapter 2.
Practical tips
In governmental and industrial settings, lab notebooks are the legal ments In most of the research institutions, the rules about notebooks areloosely defined In any case, date and signature are part of the GLP
docu- Do not remove any pages and erase previous writings Write contactinformation on the cover page in case of loss A typical life of a laboratorynotebook ranges from 10 to 25 years (Dunnivant, 2004)
Data Acquisition
During data acquisition, errors can occur anytime throughout the sampling andanalytical processes—from sampling, sample preservation, sample transportation,sample preparation, sample analysis, or data analysis (Fig 1.1) Errors of environ-mental data can be approximately divided into sampling error and analytical error Ingeneral, these errors are of two types: (1) Determinate errors (systematic errors) arethe errors that can be traced to their sources, such as improper sampling andanalytical protocols, faulty instrumentation, or mistakes by operators Measurementsresulting from determinate error can be theoretically discarded (2) Indeterminateerrors(random errors) are random fluctuations and cannot be identified or correctedfor Random errors are dealt with by applying statistics to the data
The quality of data depends on the integrity of each step shown in Figure 1.1.Although errors are sometimes unpredictable, a general consensus is that most errorscome from the sampling process rather than sample analysis As estimated, 90% ormore is due to sampling variability as a direct consequence of the heterogeneity ofenvironmental matrices It is therefore of utmost importance that right samples arecollected to be representative of the feature(s) of the parent material being inves-tigated A misrepresentative sample produces misleading information Criticalelements of a sample’s representativeness may include the sample’s physical dimen-sions, its location, and the timing of collection If representativeness cannot beestablished, the quality of the chemical analysis is irrelevant (Crumbling et al., 2001)
4 Chapter 1 Introduction to Environmental Data Acquisition
Trang 26Unfortunately, there is a general misconception among many environmentalprofessionals that the quality of data pertaining to a contaminated site is primarilydetermined by the nature of analytical methods used to acquire data Thisassumption, which underestimates the importance of sampling uncertainties, canlead to a pronounced, negative impact on the cost-effective remediation of acontaminated site In fact, it is of little use by placing an emphasis only on analyticaluncertainty when sampling uncertainty is large and not addressed (Crumbling
et al., 2001)
Errors in environmental data acquisition can be minimized through the properdesign and implementation of a quality program Two main parts of a qualityprogram are quality control (QC) and quality assurance (QA) QC is generally asystem of technical activities aimed at controlling the quality of data so that itmeets the need of data users QC procedures should be specified to measure theprecisions and bias of the data A QA program is a management system that ensuresthe QC is working as intended QA/QC programs are implemented not only tominimize errors from both sampling and analysis, but many are designed to quantifythe errors in the measurement Details on QA/QC will be presented in Chapter 5
The scope of environmental sampling can be illustrated by a sample’s life with thefollowing seven consecutive steps (Popek, 2003) Since these steps are irreversible, amistake can be detrimental These seven steps of a sample’s life are as follows: (1) asample is planned (‘‘conceived’’); (2) a sampling point is identified; (3) the sample is
Sampling plan/design (Chapter 3)
Sampling techniques (Chapter 4)
Sample preparation (Chapter 7)
Sampling analysis (Chapter 6,8,9,10,11,12)
Data analysis (Chapter 2)
QA/QC (Chapter 5)
Methodology
(Chapter 5)
Figure 1.1 Environmental data acquisition process
1.2 Environmental Sampling 5
Trang 27collected (‘‘born’’); (4) the sample is transferred to the laboratory; (5) the sample
is analyzed; (6) the sample expires and is discarded; and (7) the sample reincarnates
as a chemical data point Simply, the scope of environmental sampling addressed inthis book will include the following aspects related to sampling:
Where to take samples
When to take samples
How to take samples
How many samples to take
How often samples will be taken
How much sample is needed
How to preserve samples
How long the sample will be stable
What to take (air, soil, water)
What to analyze (physical, chemical, biological)
Who will take samples (sample custody)?
Many think of field sampling as simply going out to the field and getting somematerial, then bringing it back to a lab for analysis Although such ‘‘random’’sampling is often suggested as the basis of a sampling design, it is rarely the mostappropriate approach, particularly when there is already some knowledge of thenature of the sample source and the characteristics of the variable being monitored.The choice of where (spatially) and when (temporally) to take samples generallyshould be based on sound statistics (simple random sampling, stratified randomsampling, systematic sampling, composite sampling, as given in Chapter 3).Although guidelines exists (detailed in Chapters 3 and 4), there is no set ruleregarding the number, the amount, and the frequency of samples/sampling Forinstance, the optimum number of samples to collect is nearly always limited by theamount of resources available However, it is possible to calculate the number ofsamples required to estimate population size with a particular degree of accuracy.The best sample number is the largest sample number possible But one should keep
in mind that no sample number will compensate for a poor sampling design In otherwords, quantity should not be increased at the expense of quality Data in a poorquality will have more inherent error and, therefore, make the statistics less powerful
Whereas some of the environmental analyses are conducted in the field, the majority
of the work is conducted in the laboratory Depending on the data objectives,
6 Chapter 1 Introduction to Environmental Data Acquisition
Trang 28standard analytical methods should be consulted This in turn depends on the analyteconcentration, available instruments, and many other factors Method selections arediscussed in Chapter 5 This is followed by the common wet chemical analysis(Chapter 6) and instrumental methods (Chapters 8–12) Chapter 7 is devoted tosample preparation that is very critical to most of the complicated environmentalsamples.
Environmental analyses are very different from the traditional chemical analysisentailed in analytical chemistry Regardless, the majority of environmentalanalytical work has been traditionally and currently, are still, performed by themajority of analytical chemists In the early days, this presented challenges toanalytical chemists largely due to the complex nature of environmental samples andthe analyses of trace concentrations of a wide variety of compounds in a verycomplex matrix As Dunnivant (2004) stated, ‘‘my most vivid memory of my firstprofessional job is the sheer horror and ineptitude that I felt when I was asked toanalyze a hazardous waste sample for an analyte that had no standard protocol Suchwas a life in the early days of environmental monitoring, when chemists trained inthe isolated walls of a laboratory were thrown into the real world of sediment, soil,and industrial waste samples.’’
Today’s analytical chemists, however, are better prepared for environmentalanalyses because a wealth of information is available to help them to conductsampling and analysis Nevertheless, professionals who are not specifically trained
in this area need to be aware of the uniqueness of modern environmental analysislisted below (Fifield and Haines, 2000):
There are numerous environmental chemicals, and the costs for analysis arehigh
There are numerous samples that require instrument automation
Sample matrices (water, air, soil, waste, living organisms) are complex, andmatrix interferences are variable and not always predictable
Chemical concentrations are usually very low, requiring reliable instrumentsable to detect contaminants at ppm, ppb, ppt, or even lower levels
Some analyses have to be done on-site (field) on a continuous basis
Analysts need not only the technical competency but also the knowledge ofregulations for regulatory compliance and enforcement purposes
and Monitoring Techniques
Environmental analyses are achieved by various ‘‘classical’’ and ‘‘modern’’ ques The difference between ‘‘classical’’ and ‘‘modern’’ analytical and monitoring
techni-1.3 Environmental Analysis 7
Trang 29techniques is a little arbitrary and ever changing as technology advances and manyinstruments continue to be modernized For example, the analytical balance was, for along time, considered to be the sophisticated instrument With today’s standards,however, those early balances were rather crude Many of such yesterday’s sop-histicated instruments have become today’s routine analytical tools They are essentialand continued to be improved and modernized (Rouessac and Rouessac, 1992).Table 1.1 is a chronological listing of selected analytical instrumentations Ingeneral, volumetric and gravimetric methods (wet chemicals) are the classicalmethods Spectrometric, electrometric, and chromatographic methods are goodexamples of modern analytical instrumentation Today’s environmental analysesrely heavily on modern instrumentations This, however, does not imply thatclassical methods will be vanished anytime soon As can be seen, analyticalinstrumentations have become increasingly sophisticated to meet the analyticalchallenge The advancement has made it possible to detect what would not had beendetected in the past.
In the 1950s gravimetric methods were primarily used to estimate analyte’smass and concentration by precipitation, infiltration, drying, and/or combustion.Although gravimetric methods were sufficient, colorimetric and spectroscopicmethods offered a greater precision Wet-chemistry-based methods were developedthat altered the spectroscopic properties of chemicals such as DDT and made these
Table 1.1 Selected milestones for analytical instrumentations
1870 First aluminum beam analytical balance by Florenz Sartorius
1935 First commercial pH meter invented by Arnold O Beckman
1941 First UV-VIS spectrophotometer (Model DU) by Arnold O Beckman
1944 First commercial IR instrument (Model 12) by Perkin-Elmer
1954 Bausch and Lomb introduced the Spectronic 20 (still used today in teaching)
1955 First commercial GC produced by the Burrell Corp (Kromo-Tog),
Perkin-Elmer (Model 154), and Podbielniak (Chromagraphette)
1956 First spectrofluorometer by Robert Bowman
1956 First commercial GC/MS using time-of-flight (Model 12-101) by Bendix Corp
1963 First commercially successful AA (Model 303 AA) by Perkin-Elmer
1963 First commercial NMR from a German company Bruker
1965 First true HPLC was built by Csaba Horva´th at Yale University
1969 First commercially available FI-IR (FTS-14) introduced by Digilab
1970 First commercial graphite furnace AA by Perkin-Elmer
1974 First ICP-OES became commercially available
1977 First commercial LC–MS produced by Finnigan (now Thermo Finnigan)
1983 First commercial ICP–MS (Elan 250) by MDS Scix
AA ¼ atomic absorption spectroscopy; ICP ¼ inductively coupled plasma; OES ¼ optical emission spectroscopy; IR ¼ infrared spectroscopy; FT-IR ¼ fourier transform infrared spectroscopy;
NMR ¼ nuclear magnetic resonance spectroscopy See also Appendix A for a more detailed list of abbreviations and acronyms used in this text.
8 Chapter 1 Introduction to Environmental Data Acquisition
Trang 30chemicals suitable for colorimetric determinations These methods offered someadvantages, but were still tedious and imprecise.
Soon, chromatographic methods made inroads into resolving separatecomponents from a mixed solution Chromatography is a physical method ofseparation that relies on the interaction of substances within a mixture when they areexposed to both a stationary and a mobile phase Early thin-layer chromatography(TLC) and paper chromatography (PC) techniques used in the 1950s and 1960sseparated compounds that were detected by measuring their intensity usingultraviolet and visible (UV-VIS) spectroscopy techniques
Gas chromatography (GC) and high performance liquid chromatography(HPLC) were developed in the 1960s, becoming the methods of choice for residueanalysis and replacing TLC and PC in the 1970s GC and HPLC techniquesefficiently ‘‘resolve’’ individual components from a complex mixture and canaccurately quantify how much of an individual substance is present in the mixedcomponent sample The primary difference between GC and HPLC is that theformer relies on resolution of substances being swept through a chromatographycolumn in the gas phase at elevated temperatures, while the latter relies on thesubstance in a solution being chromatographically separated when in contact with asolid stationary phase
Mass spectroscopy(MS) developments in the 1980s dramatically enhanced thescope of detection to include most semi- to nonpolar, and thermally-stablecompounds The first generation combined GC–MS relied on electron impact (EI)ionization to fragment the molecule into an array of positive mass ions Continuedrefinement in GC–MS and maturation of HPLC-mass spectrometry has resulted inincreasingly sensitive detections at even lower levels Overall, the advances ininstrumentation and technology have provided analysts with powerful tools torapidly and accurately measure extremely low levels Advanced analyticalinstrumentations tend to detect small quantities of almost anything
*C LEAVES KS, L ESNEY MS (2005), Capitalizing on Chromatography: LC and GC have been key to the central science, Enterprise of the Chemical Sciences, 75–82 (http://pubs.acs.org/supplements/chem- chronical2/075.pdf).
*C RUMBLING DM, G ROENJES C, L ESNIK B, L YNCH K, S HOCKLEY J, V AN E E J, H OWE R, K EITH L, M C K ENNA
J (2001), Managing uncertainty in environmental decisions, Environ Sci Technol., 35(19):404A–409A.
D UNNIVANT FM (2004), Environmental Laboratory Excises for Instrumental Analysis and Environmental Chemistry, John Wiley & Sons, Hoboken, NJ pp xi–xii
* Suggested Readings
References 9
Trang 31E RICKSON B (1999), GC at a standstill Has the market peaked out at $1 billion? Anal Chem., 71(7):271A–276A.
E TTRE LS (2002), Fifty years of gas chromatography—The pioneers I knew, Part I LCGC North America, 20(2):128–140 (http://www.chromatographyonline.com).
E TTRE LS (2002), Fifty years of gas chromatography—The pioneers I knew, Part II LCGC North America, 20(5):452–462 (http://www.chromatographyonline.com).
F IFIELD FW, H AINES PJ (2000), Environmental Analytical Chemistry, 2nd Edition, Blackwell Science, Malden, MA, pp 1–11.
*F ILMORE D (2005), Seeing spectroscopy: Instrumental ‘‘eyes’’ give chemistry a window on the world, Enterprise of the Chemical Sciences, 87–91 (http://pubs.acs.org/supplements/chemchronical2/087.pdf).
K EITH LH (1996), Principles of Environmental Sampling, 2nd Edition, American Chemical Society Washington, DC.
M ARGASAK L (2003), Labs Falsifying Environmental Tests, Houston Chronicle, January 22, 2003.
P OPEK EP (2003), Sampling and Analysis of Environmental Chemical Pollutants: A Complete Guide, Academic Press San Diego, CA, pp 1–10.
R OUESSAC F, R OUESSAC A (2000), Chemical Analysis: Modern Instrumentation Methods and Techniques, John Wiley & Sons West Sussex, England, p xiii.
S KOOG DA, H OLLER FJ, N IEMAN TA (1992), Principles of Instrumental Analysis, 5th Edition, Saunders College Publishing Orlando, FL, pp 1–15.
QUESTIONS AND PROBLEMS
1 Give examples of practice that will cause data to be scientifically defective or legallynondefensible
2 Define and give examples of determinate errors and random errors
3 Describe scopes of environmental sampling
4 Why sampling and analysis are an integral part of data quality? Between sampling andanalysis, which one often generates more errors? Why?
5 Describe how errors in environmental data acquisition can be minimized and quantified?
6 How does environmental analysis differs from traditional analytical chemistry?
7 Describe the difference between ‘‘classical’’ and ‘‘modern’’ analysis
8 A chemist is arguing that sampling is not as important as analysis His concern iswhether there is a need for a sampling course in an environmental curriculum His mainrationale is that most employers and governmental agencies already have their owntraining courses and very specific and detailed procedures Another consultant, on thecontrary, argues that sampling should be given more weight than analysis His mainrationale is that a company always sends samples to commercial laboratories foranalyses, and you do not become an analytical chemist by taking one course For each
of these two arguments, specify whether you agree or disagree and clearly state yoursupporting argument why you agree or disagree
10 Chapter 1 Introduction to Environmental Data Acquisition
Trang 32Chapter 2
Basics of Environmental
Sampling and Analysis
2.1 ESSENTIAL ANALYTICAL AND ORGANIC CHEMISTRY
2.2 ESSENTIAL ENVIRONMENTAL STATISTICS
2.3 ESSENTIAL HYDROLOGY AND GEOLOGY
2.4 ESSENTIAL KNOWLEDGE OF ENVIRONMENTAL REGULATIONSREFERENCES
QUESTIONS AND PROBLEMS
In the real world, environmental sampling and analysis are performed by a group ofpeople with different areas of expertise This might be very different from smallprojects or research work in academic settings, where the sampler and analyst may
be the same person In any case, a basic knowledge of environmental sampling andanalysis is essential for all individuals As illustrated in this chapter, environmentalsampling and analysis is an interdisciplinary field including chemistry, statistics,geology, hydrology, and law to name just a few It is the purpose of this chapter tointroduce readers to some of the relevant environmental sampling and analysisbasics An in-depth and detailed knowledge on particular topics is beyond the scope
of this text and readers are referred to the suggested readings for further details
CHEMISTRY
Proper concentration units are important in environmental reporting Althoughchemists prefer to use units such as percentage (% in m/v or v/v) or molarity (M) forchemical concentrations, these units are too large for common environmental
Fundamentals of Environmental Sampling and Analysis, by Chunlong Zhang
Copyright # 2007 John Wiley & Sons, Inc.
11
Trang 33contaminants that have low concentrations Concentration units also vary with thetypes of environmental media (air, liquid, or solid) as described below.
Chemicals in Liquid Samples
For chemicals in liquid samples (water, blood, or urine), the mass/volume (m/v) unit
is the most common Depending on the numerical value, the concentration isexpressed as mg/L, mg/L, or ng/L For freshwater or liquids with density equal to1.0 g/mL, the following units are equivalent The units will not be equivalent if seawater, and denser or lighter liquids are concerned
Chemicals in Solid Samples
For chemicals in solid samples (soil, sediment, sludge, or biological tissue), theconcentration unit is mass/mass (m/m) rather than mass/volume Units such as mg/L
or mg/L should not be used to express contaminant concentration in solid samples.The following two sets of units are equivalent:
1 mg=kg¼ 1 ppm 1 mg=kg¼ 1 ppb 1 ng=kg¼ 1 ppt ð2:2Þ
In reporting such mass/mass units in solid samples, it should specify whether themass is on a wet basis or on a dry basis A dry basis is commonly adopted forcomparison purposes when such samples have a large variation in moisture contents
A subsample should always be collected for the determination of the moisturecontent in addition to concentration measurement Use the following to convert fromwet basis to dry basis:
mg=kg on dry basis¼ mg=kg on wet basis=ð1 % moistureÞ ð2:3ÞChemicals in Gaseous Samples
For chemicals in air, both sets of mass/volume (mg/m3, mg/m3, and ng/m3) andvolume/volume (ppmv, ppbv, pptv) are used, but they are not equivalent:
Trang 34Practical tips
Report concentrations with the right unit and right significant figures Usecommon sense in reporting when to choose mg/L, mg/L, ng/L; or mg/kg, mg/kg,ng/kg; or even % if the concentration is high Avoid very large or very smallnumbers
It is a good practice to use mass/volume (mg/L), mass/mass (mg/kg), andmass/volume (mg/m3) for contaminants in water, soil, and air, respectively.Avoid using ppm, ppb, and ppt because they can be ambiguous If chemicals
in air are concerned, use ppmv, ppbv, and pptvto denote that the chemicalconcentration in air is based on the volume ratio
There are many other contaminant specific units, such as mg/m3 for spheric particulate matter (PM2.5or PM10) and lead (here ppm is an invalidunit because PM and lead cannot be expressed in volume); mg/L as CaCO3for water hardness, acidity, and alkalinity; nephelometric turbidity units(NTU) for turbidity; mS/m for conductivity; and pCi/L for radionuclides.The salinity unit is parts per thousands (ppt or %), which should not beconfused with parts per trillion (ppt)
atmo-EXAMPLE 2.1 Maximum contaminant level (MCL) according to the U.S EPA for 2,3,7,8-TCDD (dioxin) in drinking water is 0.00000003 mg/L Convert this concentration to pptand molarity (M) What is the equivalent number of dioxin molecules per liter of water? Themolecular weight of dioxin is 322 g/mol
SOLUTION:
0:00000003 mg=L¼ 0:00000003 mg=L 1 mg=L1 ppm 10
6ppt
1 ppm ¼ 0:03 ppt0:00000003 mg=L¼ 0:00000003mgL 101 g3mg1 mol322 g¼ 9:32 1014molL
2.1 Essential Analytical and Organic Chemistry 13
Trang 352.1.2 Common Organic Pollutants
and Their Properties
There are an estimated total of 7 million chemicals with approximately 100,000present in the environment The number of chemicals commonly considered asimportant environmental pollutants, however, is likely a few hundred Among them,few are routinely measured in environmental laboratories A smaller list of
‘‘priority’’ chemicals has been established by various organizations based onselected factors such as quantity, persistence, bioaccumulation, potential fortransport to distant locations, toxicity, and other adverse effects (Mackay, 2001).Such chemicals receive intense scrutiny and analytical protocols are alwaysavailable
The Stockholm Convention, signed by more than 90 countries in Sweden inMay 2001, listed 12 key persistent organic pollutants (POPs) Commonly known as
‘‘the dirty dozen’’, the POPs are aldrin, chlordane, DDT, dieldrin, endrin, heptachlor,hexachlorobenzene, mirex, toxaphene, PCBs, dioxins, and furans Most of the 12key POPs are no longer produced in the United States, and their uses in developingcountries have also declined Of the 12 chemicals, 10 were intentionally produced byindustries and 9 were produced as insecticides or fungicides Only two of the 12chemicals, dioxins and furans, are unintentionally produced in combustionprocesses (Girard, 2005)
The U.S EPA published 129 priority pollutants (114 organic and 15 inorganic)
in water Many other countries have similar priority pollutant lists reflecting theirpollution sources and monitoring priorities, such as the black and grey list by theEuropean Union in 1975 and the black list by China (58 organic and 10 inorganic).The lists should be regarded as dynamic For instance, the number of drinking watercontaminants regulated by the U.S EPA has increased from about five in 1940 tomore than 150 in 1999 (Weiner, 2000) Appendix B is a list of 114 organic pollutants
on the U.S EPA priority list Their chemical structures, molecular weights, andaqueous solubilities are also provided in this appendix
Important chemical pollutants can be divided into nine categories basedprimarily on their chemical characteristics Figure 2.1 lists the structure of severalimportant organic compounds by their functional groups
1 Element: Metals (Cu, Zn, Pb, Cd, Ni, Hg, Cr) and metalloids (As, Se)
2 Inorganic compounds: Cyanide, CO, NOx, asbestos
3 Organo-metallic and metalloid compounds: Tetraethyl lead and tributyl tin
4 Hydrocarbons: Saturated and unsaturated aliphatic and aromatic bons including BTEX compounds (benzene, toluene, ethylbenzene, andxylene) and polycyclic aromatic hydrocarbons (PAHs)
hydrocar-5 Oxygenated compounds: Alcohol, aldehyde, ether, organic acid, ester,ketone, and phenol
6 Nitrogen compounds: Amine, amide, nitroaromatic hydrocarbons, andnitrosamines
14 Chapter 2 Basics of Environmental Sampling and Analysis
Trang 367 Halogenated hydrocarbons: Aliphatic and aromatic halogenated bon, polychlorinated biphenyls (PCBs), and dioxins
hydrocar-8 Organosulfur compounds: Thiols, thiophenes, mercaptans, and many pesticides
9 Phosphorus compounds: Many pesticides to replace organo-chlorine pesticides
Cl
Cl Cl
OH C
R R C O R C R'
O
OH C R O
O C
R R' R N R'
R''
NH2C
R
O
CN
R R N N O
A = Hydrocarbon (BTEX Series)
B = Polycyclic aromatic hydrocarbon (PAHs)
C = Halogenated aliphatic hydrocarbons
Figure 2.1 Structure of several important organic compounds by their functional groups (where R,
R 0 , R 00 are alkyl groups and X can be either a chlorine or a hydrogen) (1) benzene, (2) toluene, (3) ethylbenzene, (4) o-xylene, (5) m-xylene, (6) p-xylene, (7) naphthalene, (8) phenanthrene, (9) pyrene, (10) tetrachloroethylene, (11) trichloroethylene, (12) dichloroethylene, (13) vinyl chloride,
(14) polychlorinated biphenyl, (15) alcohol, (16) aldehyde, (17) ketone, (18) acid, (19) ester, (20) ether, (21) phenol, (22) primary amine, (23) secondary amine, (24) tertiary amine, (25) amide, (26) nitrile, (27) nitrosamine
2.1 Essential Analytical and Organic Chemistry 15
Trang 37Chemicals are sometimes categorized by one of their properties or by their analyticalprocedures (the so-called analytical definition) Examples include those looselydefined compound categories based on the following:
1 Density: Heavy metals are elements of generally higher atomic weight withspecific gravities greater than five and especially those toxic to organismssuch as Cu, Zn, Pb, Cd, Ni, Hg, Cr and the metalloid (As)
2 Volatility: Volatile organic compounds (VOCs) are group of compounds thatvaporize at a relatively low (room) temperature VOCs have boiling pointsbelow 200C Examples of VOCs include trichloroethane, trichloethylene,and BTEXs Semi-volatile organic compounds (SVOCs) evaporate slowly atnormal room temperature and are operationally defined as a group oforganic compounds that are solvent-extractable and can be determined bychromatography including phenols, phthalates, PAHs, and PCBs Volatility
as defined by Henry’s law constant will be introduced in Chapter 7
3 Extractability: Extraction with methylene chloride initially under basicconditions to isolate the base/neutral fraction (B/N) and then acid condition
to obtain the acidic fraction (mostly phenolic compounds)
Accuracyis the degree of agreement of a measured value with the true or expectedvalue Accuracy is measured and expressed as % recovery and calculated according to:
% Recovery¼ Analytical value 100=True value ð2:5ÞThe true value (concentration) is rarely known for environmental samples Thus,accuracy is typically determined by spiking a sample with a known quantity of astandard:
% Recovery on spike¼Spiked sample value Sample value
An accurate test method should achieve a percentage recovery close to 100% Todetermine percentage recovery, the amount of spiking chemical should be close to(0.5 2 times) the analytical concentration In no case should the amount spikedexceed three times the concentration of the analyte
Precisionis the degree of mutual agreement among individual measurements
ðx1; x2; xnÞ as the result of repeated applications under the same condition.Precision measures the variation among measurements and may be expressed indifferent terms The first term is standard deviation (s), which is defined as followsfor a finite set of analytical data (generally n< 30):
Trang 38Two other terms are relative standard deviation (RSD) and relative percentdifference(RPD):
where CV denotes coefficient of variationðCV ¼ s=xx) and RPD is the differencebetween the duplicate values (A and B) divided by the average of the dupli-cate values and multiplied by 100 RSD is used for the evaluation of multiplereplicate measurements, whereas RPD is used for measuring precision between twoduplicate measurements
Precision and Accuracy along with three other qualitative descriptors(Representativeness, Comparability, and Completeness), or PARCC, are termeddata quality indicators(DQIs) The PARCC parameters enable us to determine thevalidity of environmental data
Both accuracy and precision are needed to determine the data quality in aquantitative way In an analogy, accuracy is how close you get to the bull’s-eye,whereas precision is how close the repetitive shots are to one another Hence, a goodprecision does not guarantee an accurate analysis On the contrary, it is nearlyimpossible to have a good accuracy without a good precision
The method detection limit is one of the secondary DQIs The U.S EPA definesmethod detection limit (MDL) as ‘‘the minimum concentration that can be measuredand reported with 99% confidence that the analyte concentration is greater thanzero’’ (EPA, 1984) To determine MDL, an analyte-free matrix (reagent water orlaboratory-grade sand) is spiked with the target analyte at a concentration that is 3–5times the estimated MDLs This sample is then measured at a minimum of seventimes From these measurements, a standard deviation (s) is calculated (Eq 2.7), andthe MDL is calculated according to the formula:
where t is obtained from ‘‘Student’s t value Table’’ (Appendix C2), corresponding to
t0.98and degree of freedom df ¼ n 1, where n is the number of measurements Forexample if n¼ 7 (i.e., df ¼ 6), then t ¼ 3:143 at a 99% confidence level
The MDLs are specific to a given matrix, method, instrument, and analyticaltechnique The MDL, however, is not the lowest concentration we can accuratelymeasure during a routine laboratory analysis EPA, therefore, uses another term,practical quantitation limit(PQL), and defines it as ‘‘the lowest concentration thatcan be reliably achieved within specified limits of precision and accuracy duringroutine operating condition’’ (EPA, 1996) Typically, laboratories choose PQL value
at 2–10 times its MDLs Therefore, the PQL may be also defined as ‘‘a concentrationthat is 2–10 times greater than the MDL and that represents the lowest point on the
2.1 Essential Analytical and Organic Chemistry 17
Trang 39calibration curve during routine laboratory operation’’ (Popek, 2003) Sample PQLsare highly matrix dependent For example, in measuring polynuclear aromatichydrocarbons (EPA Method 8310), the matrix factor ranges from 10 (groundwater)
to 10,000 (high level soil/sludge by sonication)
The calibration curve or standard curve is a plot of instrumental response(absorbance, electrical signal, peak area, etc.) vs the concentrations of the chemical
of interest Five or more standard solutions of known concentrations are firstprepared to obtain the calibration curve – normally a linear regression equation:
To obtain the regression equation (y¼ a x þ b), one should be familiar with aspreadsheet program such as Excel Procedures for the regression analysis usingExcel are as follows:
Select Tools|Data Analysis
Select Regression from Analysis Tool list box in the Data Analysis dialogbox Click the OK button
In the Regression dialog box
Enter data cell numbers in Input Y Range and Input X Range
Select Label if the first data cells in both ranges contain labels
Enter Confidence Level for regression coefficient (default is 95%)
Select Output Range and enter the cell number for regression output
Select Linear Fit Plots and/or others if needed
Click the OK button
In the regression output, r2, slope (a) and intercept (b) can be readilyidentified
Figure 2.2 illustrates several common outcomes when the calibration curve isplotted The calibration curve (a) is ideal due to its good linearity and the sufficientnumber of data points Curve (b) is nonlinear, which is less favorable and
18 Chapter 2 Basics of Environmental Sampling and Analysis
Trang 40effort should be made to improve it prior to use Data in (c) are too scattered, andyou should redo to correct the errors The curve in (d) does not have enough datapoints (five is normally the minimum) The concentration range for curve (e) isnot correct, either the sample has to be diluted or a wider range of concentrationsshould be used Calibration curve (f) does not run through the origin, implying thepresence of some systematic errors such as positive or negative matrix interference(Meyer, 1997).
Practical tips
It is always a good laboratory practice to run the calibration curve along withsamples in the same batch, particularly when there is a considerableinstrument drift It takes more time to prepare and run, but it will improvethe data validity and you can probably save time at the end
When a dilution is made and sample (injection) volume is different from thestandard solution, corrections are needed to calculate sample concentration
In this case, a plot of instrument response vs analyte mass (rather thanconcentration) is more appropriate
Figure 2.2 Correct and incorrect calibration curves: (a) Ideal, (b) Poor linearity, (c) Data too scattered, (d) Insufficient data points, (e) Incorrect concentration range, and (f) Systematic error (Meyer, VR, 1997, Reproduced with Permission, John Wiley & Sons Limited)
2.1 Essential Analytical and Organic Chemistry 19