Foreword

The growing concern about the quality and safety of our environment has led the European Union, the Environmental Protection Agency and affiliated regulatory bodies to compile lists of priority pollutants and to establish a number of rules and regulations for their control. As a consequence, there has been a rapid increase in demand for the determination of a wide variety of micropollutants in water. With many laboratories now focusing on the analysis of drinking, surface, ground, rain and waste water, aspects such as cost-effectiveness, high sample throughput, enhanced analyte detectability and identification potential, otherwise stated as speed, sensitivity, and selectivity, have become vital factors in micropollutant analysis. Of concern, especially in this age of environmental awareness, is also the amount of solvent used in performing an analysis and state-of-the-art procedures should be designed to reduce the consumption of organic solvents.

In general, the use of state-of-the-art procedures and the development of new and novel approaches to analytical problem solving requires an adequate knowledge of the existing literature. Unfortunately, many workers in the field of trace-level environmental analysis do not have easy access to the vast amounts of books, reviews, scientific papers, reports, and directives published today. By compre­hensively describing in their book the most modern methodologies for the determination of organic micropollutants included in the European List of Priority Pollutants, the authors provide their readers the means to critically assess the merits of their current procedures compared to alternatives provided.

The authors should be congratulated for their laudable attempt to persuade laboratories to move towards performance-based methods. Aiming to meet the above objectives, Water Analysis - Organic Micropollutants provides readers with fast, sensitive and selective methods of analysis - a helpful and practical guide for any person working in the field of environmental testing, and especially useful to those involved in water analysis.

Preface

One of our planet's most remarkable and precious resources is undoubtedly its natural water cycle, blessed and worshipped throughout the ages and recognized today as the regulator of various energy processes essential to man's existence. Mankind's pollution of lakes, rivers and seas may have started somewhere in Mesopotamia and has been increasing ever since, to the point where the whole planet is now affected. In the past, this was mainly microbial contamination but more recently, industrialization and the intensive use of agricultural chemicals have resulted in an unforeseen and drastic deterioration, with contamination sometimes persisting for years after a source of pollution has been identified and remedied. For example, triazines (until recently extensively and aggressively used as a herbicide in maize production) can still be detected in ground, surface and drinking water today.

Growing public awareness has led to increased concern about the environment and more particularly about water quality. For more than a century, industrialized areas such as North America, Western Europe and Japan have been successfully dealing with the crucial issues of microbial pollution before facing eutrophication, acidification and nitrate pollution problems. During the last decade consensus has been reached on the hazards of organic micropollutants and various authorities are presently focused on dealing with this problem. In 1982, the European Community adopted the EC Priority Pollutants List (often referred to as the 'black list') , coincidentally containing the same number of compounds as the US Environmental Protection Agency's list of 129 Priority Pollutants. Subsequently, 3 additional compounds were added to the European Community list. Unlike the EPA, the EC has not specified mandatory analytical methods for the determination of hazardous substances in various environmental matrices, stipulating that any validated method would be acknowledged. In some cases, maximum permissible concentration levels have been established, for example, 0.1 (xg/1 (0.1 ppb) per compound for pesticides and polynuclear aromatics in drinking water (European Community Drinking Water Regulation, July 15, 1980).

With regard to environmental testing, the lack of a united EC approach makes the present situation within the European Community member countries rather confusing. It is however undeniable that the European Community's numerous directives and local legislation on the subject have resulted in a far closer scrutiny of our environment. It has been established that no policy can be enforced without stringent measurement and analysis. The initial willingness to comply with regulations is often hindered by the absence of official methodologies, clear directives and a lack of specific knowledge of environmental analysis.

In writing this book, it was decided to focus on the substances on the EC Priority Pollutants List (Table 1) and to provide analytical solutions for the identification and measurement of most of the substances in various water matrices. The list has been divided into groups or families for which analytical procedures are described, the analytical method selection often being dictated by the availability of specific instrumentation and tools for sample preparation and clean-up. Table 1 therefore contains different solutions to a specific problem, for example, polyaromatic hydrocarbons in water (list number 99) can be enriched by liquid-liquid extraction, liquid-solid phase extraction or, in some instances, analysed by direct water injection. The chromatographic analysis may be performed by HPLC/fluorescence detection, CGC/mass spectroscopic detection in the ion monitoring mode or HPLC/diode-array detection. Several substances not on the EC Priority Pollutants List but nevertheless of considerable interest in Europe, are also included. Bearing in mind that some limits are very close to the analytical detection threshold (as low as 0.1 (xg/1), the complexities involved in trace level analysis of water pollutants generally require the use of the latest technological developments. Fortunately, the emergence of new analytical approaches based on hyphenated techniques are helping the analyst to solve the problems associated with organic pollutant analysis.

Besides causing major bottlenecks in environmental testing laboratories, sample preparation and clean-up are also the areas where the least amount of technical information exists. Because inappropriate methods could lead to erroneous results, we have attempted to provide clear and detailed instructions based on the 'preferred' sample preparation procedures used in our laboratories. This does not mean however, that successful analytical flow charts should be replaced by the methods described in this book. Traditionally, sample preparation and clean-up are laborious and time-consuming; we have therefore aimed to provide more acceptable and productive methods.

European Community Priority Pollutant List

LN	Compound	Class	AMI	AM2	AM3	SP 1	SP2	SP3
1	ALDRIN	OCP	CGC/ECD	CGC/MS	CGC/AED	L-L	SPE
2	2-AMINO-4-CHLOROPHENOL	CP	CGC/MS	HPLC/DAD	HPLC/MS	L-L	SPE	DER
3	ANTHRACENE	PAH	HPLC/FLD	CGC/MS	HPLC/DAD	L-L	SPE	DIRECT
4	ARSENIC	INORG
5	AZINPHOS ETHYL	OPP	CGC/MS	CGC/NPD	HPLC/MS	L-L	SPE
6	AZINPHOS METHYL	OPP	CGC/MS	CGC/NPD	HPLC/MS	L-L	SPE
7	BENZENE	VA	CGC/MS	CGC/FID	CGC/PID	P-T	L-L	HS
8	BENZIDINE	BD	HPLC/ECD	HPLC/MS	CGC/MS	L-L	SPE	DER
9	BENZYL CHLORIDE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	L-L	P-T	CLS
10	BENZYLIDENE CHLORIDE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	L-L	P-T	CLS
11	BIPHENYL	MISC	CGC/MS	CGC/PID	HPLC/DAD	L-L	SPE
12	CADMIUM	INORG
13	CARBON TETRACHLORIDE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
14	CHLORAL HYDRATE	СОН	CGC/MS			P-T	HS
15	CHLORDANE	OCP	CGC/ECD	CGC/MS	CGC/AED	L-L	SPE
16	CHLOROACETIC ACID	CCOOH	CGC/ECD	CGCA1S		L-L	SPE
17	2-CHLOROANILINE	CA	CGC/MS	HPLC/MS	CGC/NPD	L-L	SPE
18	3-CHLOROANILINE	CA	CGC/MS	HPLC/MS	CGC/NPD	L-L	SPE
19	4-CHLOROANILINE	CA	CGC/MS	HPLC/MS	CGC/NPD	L-L	SPE
20	CHLOROBENZENES	VHO	CGC/MS	CGC/ECD	CGC/ELCD	L-L	P-T	CLSA
21	l-CHLORO-2,4-DINITROBENZENE	CNB	CGC/MS	HPLC/MS	CGC/AED	L-L	SPE
22	2-CHLOROETHANOL	СОН	CGC/MS			L-L	P-T
23	CHLOROFORM	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
24	4-CHLORO- 3 -METHYLPHENOL	CP	CGC/MS	HPLC/DAD	HPLC/MS	L-L	SPE	DER
25	1 -CHLORONAPHTHALENE	SVHO	CGC/MS	CGC/ECD		L-L	SPE	CLSA
26	CHLORONAPHTHALENES	SVHO	CGC/MS	CGC/ECD		L-L	SPE	CLSA
27	4-CHLORO-2-NITROANILINE	CA	HPLC/MS	CGC/MS		L-L	SPE	DER
28	1 -CHLORO- 2 -NITROBENZENE	CNB	CGC/MS	HPLC/MS	CGC/AED	I^L	SPE
29	1 -CHLORO- 3 -NITROBENZENE	CNB	CGC/MS	HPLC/MS	CGC/AED	L-L	SPE
30	1 -CHLORO-4 -NITROBENZENE	CNB	CGC/MS	HPLC/MS	CGC/AED	L-L	SPE
31	4-CHLORO-2-NITROBENZENE	CNB	CGC/MS	HPLC/MS	CGC/AED	L-L	SPE
32	CHLORONITROTOLUENES	CNT	CGC/MS	HPLC/MS	CGC/AED	L-L	SPE

33	2-CHLOROPHENOL	CP	CGC/MS	HPLC/DAD	HPLC/MS	L-L	SPE	DER
34	3-CHLOROPHENOL	CP	CGC/MS	HPLC/DAD	HPLC/MS	L-L	SPE	DER
35	4-CHLOROPHENOL	CP	CGC/MS	HPLC/DAD	HPLC/MS	L-L	SPE	DER
36	CHLOROPRENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
37	3-CHLOROPRENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
38	2-CHLOROTOLUENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	L-L	P-T	CLSA
39	3-CHLOROTOLUENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	L-L	P-T	CLSA
40	4-CHLOROTOLUENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	L-L	P-T	CLSA
41	2 -CHLORO- 4 -TOLUIDINE	CT	CGC/MS	HPLC/MS		L-L	SPE
42	CHLOROTOLUIDINES	CT	CGC/MS	HPLC/MS		L-L	SPE
43	COUMAPHOS	OPP	CGC/MS	CGC/NPD	HPLC/MS	L-L	SPE
44	2,4,6,-TRICHLORO-l,3,5-TRIAZINE	TRIA	HPLC/DAD	CGC/MS	CGC/AED	SPE	L-L
45	2,4-D	PhAP	HPLC/DAD	CGC/MS	HPLC/MS	SPE	I^L	DER
46	DDT	OCP	CGC/ECD	CGC/MS	CGC/AED	L-L	SPE
47	DEMETON	OPP	CGC/MS	CGC/NPD	HPLC/MS	L-L	SPE
48	1,2 -DIBROMOETHANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
49	DIBUTYLTINDICHLORIDE	ORGSn	CGC/AED	CGC/MS	HPLC/MS	L-L	DER	SPE
50	DIBUTYLTINOXIDE	ORGSn	CGC/AED	CGC/MS	HPLC/MS	L-L	DER	SPE
51	DIBUTYLTINSALTS	ORGSn	CGC/AED	CGC/MS	HPLC/MS	L-L	DER	SPE
52	DICHLORO ANILINES	CA	CGC/MS	HPLC/MS	CGC/NPD	L-L	SPE
53	1,2-DICHLOROBENZENE	SVHO	CGC/MS	CGC/ECD		P-T	L-L	CLSA
54	1,3-DICHLOROBENZENE	S\T1O	CGC/MS	CGC/ECD		P-T	L-L	CLSA
55	1,4-DICHLOROBENZENE	SVHO	CGC/MS	CGC/ECD		P-T	L-L	CLSA
56	DICHLORO BENZIDIXES	BD	HPLC/ECD	HPLC/MS	CGC/MS	L-L	SPE	DER
57	DICHLORODIISOPROPYL ETHER	CE	CGC/MS			P-T	HS	CLSA
58	1,1 -DICHLOROETHANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
59	1,2-DICHLOROETHANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
60	1,1-DICHLOROETHYLENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
61	1,2 -DICHLOROETHYLENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
62	DICHLOROMETHANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
63	DICHLORO NITROBENZENES	CNB	CGC/MS	HPLC/MS	CGC/AED	L-L	SPE
64	2,4-DICHLOROPHENOL	CP	HPLC/DAD	CGC/MS	HPLC/MS	L-L	SPE	DER
65	1,2 -DICHLOROPROPANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS

European Community Priority Pollutant List

LN	Compound	Class	AMI	AM2	AM3	SP1	SP2	SP
66	l,3-DICHLOROPROPENE-2-OL	СОН	CGC/MS			L-L	P-T
67	1,3-DICHLOROPROPENE	VHO	CGCAIS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
68	2,3-DICHLOROPROPENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
69	DICHLORPROP	PhAP	HPLC/DAD	CGC/MS	HPLCAIS	SPE	L-L	DER
70	DICHLORVOS	OPP	CGC/MS	CGC/NPD	HPLCAIS	L-L	SPE
71	DIELDRIN	OCP	CGC/ECD	CGCAIS	CGC/AED	L-L	SPE
72	DIETHYLAMINE	A	CGC/MS			?	HS	SPE
73	DIMETHOATE	OPP	CGC/MS	CGC/NPD	HPLCAIS	L-L	SPE
74	DIMETHYLAMINE	A	CGC/MS			<?	HS	SPE
75	DISULFOTON	OPP	CGC/MS	CGC/NPD	HPLCAIS	L-L	SPE
76	ENDOSULFAN	OCP	CGC/ECD	CGCAIS	CGC/AED	L-L	SPE
77	ENDRIN	OCP	CGC/ECD	CGCAIS	CGC/AED	L-L	SPE
78	EPICHLOROHYDRIN	CE	CGC/MS			P-T	HS	CLSA
79	ETHYLBENZENE	VA	CGC/MS	CGC/HD	CGC/PID	P-T	L-L	HS
80	FENITROTHION	OPP	HPLC/MS	CGCAIS?		L-L	SPE
81	FENTHION	OPP	CGC/MS	CGC/NPD	HPLCAIS	L-L	SPE
82	HEPTACHLOR	OCP	CGC/ECD	CGCAIS	CGC/AED	L-L	SPE
83	HEXACHLOROBENZENE	OCP	CGC/ECD	CGCAIS	CGC/AED	L-L	SPE
84	HEXACHLOROBUTADIENE	SVHO	CGC/ECD	CGCAIS		P-T	L-L	CLSA
85	HEXACHLOROCYCLOHEXANE (LINDANE)		OCP	CGC/ECD	CGCAIS	CGC/AED	L-L	SPE
86	HEXACHLOROETHANE	SVHO	CGC/ECD	CGCAIS		P-T	L-L	CLSA
87	ISOPROPYLBENZENE	VA	CGC/MS	CGC/FID	CGC/PID	P-T	L-L	HS
88	UNURON	PU	HPLC/DAD	HPLCAIS		SPE	L-L
89	MALATHION	OPP	CGCAIS	CGC/NPD	HPLCAIS	L-L	SPE
90	MCPA	PhAP	HPLC/DAD	CGCAIS	HPLCAIS	SPE	L-L
91	MECOPROP	PhAP	HPLC/DAD	CGCAIS	HPLCAIS	SPE	L-L	DER
92	MERCURY	INORG
93	METHAiMIDOPHOS	OPP	CGC/MS?	HPLCAIS		L-L	SPE
94	MEVINPHOS	OPP	CGC/MS	CGC/NPD	HPLCAIS	L-L	SPE
95	MONOLINURON	PU	HPLC/DAD	HPLCAIS		SPE	L-L
96	NAPHTHALENE	PAH	HPLC/FLD	CGCAIS	HPLC/DAD	L-L	SPE	DIRE'
97	OMETHOATE	OPP	CGCAIS	CGC/NPD	HPLCAIS	L-L	SPE

98	OXYDEMETON METHYL	OPP	HPLA1S	CGC/MS?		L-L	SPE
99	PAH	PAH	HPLC/FLD	CGC/MS	HPLC/DAD	L-L	SPE	DIRE
100	PAEATHION	OPP	CGC/MS	CGC/NPD	HPLC/MS	L-L	SPE
101	PCB	PCB	CGC/ECD	CGCAIS		L-L	SPE
102	PENTACHLOROPHENOL	CP	HPLC/DAD	CGC/MS	HPLC/MS	L-L	SPE	DER
103	PHOXIM	OPP	HPLC/MS	CGCAIS?		L-L	SPE
104	PROPANIL	MISC	HPLC/MS	HPLC/DAD		SPE	L-L
105	PYKAZON	MISC	HPLC/MS	CGC/MS	HPLC/DAD	SPE	L-L
106	SIMAZINE	TRIA	HPLC/DAD	CGC/MS	CGC/AED	SPE	L-L
107	2,4,5-T	PhAP	HPLC/DAD	CGC/MS	HPLCAIS	SPE	L-L	DER
108	TETRABUTYLTIN	ORGSn	CGC/AED	CGC/MS	HPLCAIS	L-L	DER
109	1,2,4,5-TETRACHLOROBEXZENE	SVHO	CGC/ECD	CGC/MS		P-T	L-L	CLSA
110	1,1,2,2-TETRACHLOROETHANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
111	TETRACHLOROETHYLEXE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
112	TOLUENE	VA	CGC/MS	CGC/FID	CGC/PID	P-T	L-L	HS
113	TRIAZOPHOS	OPP	HPLC/MS	CGC/MS?		L-L	SPE
114	TRIBUTYLPHOSPHATE	misc	CGC/MS	CGC/NPD	CGC/AED	L-L	SPE
115	TRIBUTYLTIN OXIDE	ORGSn	CGC/AED	CGC/MS	HPLCAIS	L-L	DER
116	TRICHLORFON	OPP	HPLC/MS	CGC/MS?		L-L	SPE
117	TRICHLOROBEXZENE	SVHO	CGC/ECD	CGC/MS		L-L	SPE
118	1,2,4-TRICHLOROBENZENE	SVHO	CGC/ECD	CGC/MS		L-L	SPE	CLS
119	1,1,1 -TRICHLOROETHAXE	VHO	CGCAIS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
120	1,1,2-TRICHLOROETHANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
121	TRICHLOROETHYLENE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
122	TRICHLOROPHENOL	CP	HPLC/DAD	CGC/MS	HPLCAIS	L-L	SPE	DER
123	1,1,2 -TRICHLOROTRIFLUOROETHANE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
124	TRIFLURALIN	MISC	CGC/MS	CGC/NPD	CGC/AED	L-L	SPE
125	TRIPHENYLTIN ACETATE	ORGSn	CGC/AED	CGC/MS	HPLCAIS	L-L	DER
126	TRIPHENYLTIN CHLORIDE	ORGSn	CGC/AED	CGC/MS	HPLCAIS	L-L	DER
127	TRIPHENYLTIN HYDROXIDE	ORGSn	CGC/AED	CGC/MS	HPLCAIS	L-L	DER
128	VINYL CHLORIDE	VHO	CGC/MS	CGC/ECD	CGC/ELCD	P-T	L-L	HS
129	XYLENES	VA	CGC/MS	CGC/FID	CGC/PID	P-T	HS	HS
130	ISODRINE	OCP	CGC/ECD	CGC/MS	CGC/AED	L-L	SPE
131	ATRAZINE	TRIA	HPLC/DAD	CGCAIS	CGC/AED	SPE	L-L
132	BENTAZONE	MISC	HPLC/DAD	HPLCAIS	CGCAIS	SPE	L-L	DER

Table 1: The EC Priority Pollutants List

Acronyms used in Table 1:

LN	List Number of the EC priority pollutant
Compound	Nomenclature used by the EC
Class	Compound Class
OCP	Organochloro pesticides
CP	Chlorophenols
PAH	Polyaromatic hydrocarbons
INORG	Inorganics - metals
OPP	Organophosphorus pesticides
VA	Volatile aromatics
AA	Amino aromatics
VHO	Volatile halogenated organics
сон	Halogenated hydroxyl compounds
CCOOH	Halogenated carboxyl compounds
CA	Chloroanilines
CNB	Chloronitrobenzenes
SVHO	Semi-volatile halogenated organics
CNT	Chloronitrotoluenes
CT	Chlorotoluidines
TRIA	Triazines
PhAP	Phenoxy acid pesticides
ORGSn	Organotin compounds
BD	Benzidines
CE	Chloroethers
A	Amines
PU	Phenylurea compounds
MISC	Miscellaneous

AM	Analytical Methods
CGC	Capillary gas chromatography
ECD	Electron capture detection
NPD	Nitrogen phosphorus detection
PID	Photoionization detection
ELCD	Electolytic conductivity detection
MSD	Mass spectroscopic detection
AED	Atomic emission detection
HPLC	High performance liquid chromatography
DAD	Diode-array detection
FLD	Fluorescence detection
ECD	Electrochemical detection
MS	Mass spectroscopic detection
L-L	Liquid-liquid extraction
SPE	Solid phase extraction
DER	Derivatization
DIRECT	Direct injection of water sample
P-T	Purge and trap
CLSA	Closed loop stripping
HS	Headspace analysis

Analytical tools and techniques

1.1 Introduction

The basic task of monitoring water samples for organic micropollutants consists of detecting the suspected contaminants in a sample, elucidating their identity and measuring their concentration. This is of course an oversimplification. In practice, elaborate sample preparation techniques based around sophisticated analytical tools are required. Growing awareness, stringent legal requirements and the increasing number of pollutants have contributed to a significant rise in the number of analyses to be performed. Environmental laboratories must deal with a far wider range of compounds than just those included on the European Community or US Environmental Protection Agency Lists of Priority Pollutants. Productivity, rationalized labour and cost effectiveness are major concerns for environmental laboratory management that have direct repercussions on both the tools and techniques used. The development of automated, high productivity, integrated sample preparation — analytical systems is a clear illustration of this trend.

1.2 Sample preparation and clean-up procedures

In the analysis of environmental water samples, the first problem one generally encounters is sample preparation. Often too dilute or complex, samples need to undergo a chain of specific treatments to make them compatible with analytical techniques and to ensure effective separation and detection. Additionally, possible sources of interference must be discerned and eliminated so that the sample provides a representative picture of the situation at the time and place of collection. Clean-up procedures, designed to enhance column efficiency and lifetime, detector sensitivity and chromatographic peak resolution are conven­tionally tedious and time-consuming and often a major source of experimental error. While the dictum, "the best sample preparation is no sample preparation", is also true for water analysis, direct water injection is only applicable in some exceptional cases, notably, the determination of trihalomethanes in drinking water by capillary GC/ECD or the determination of PAHs in drinking water by HPLC with fluorescence detection. Several techniques for the enrichment and fractionation of organic pollutants from water matrices may be applied, the most important of which are discussed below.

1.2.1 Liquid-liquid extraction

The most commonly used sample preparation in water analysis, liquid-liquid extraction may be carried out manually by shaking the water sample with an organic solvent in a separation funnel or automatically, using a continuous liquid-liquid extractor. The liquid-liquid extractor recommended by the EPA for the enrichment of semi-volatiles (base-neutral/acid extractables) is illustrated in Figure 1.1. Depending on the conditions used, extracts can contain intermediate to low polarity, weakly volatile pollutants (universal extraction for neutral semi-volatiles) or acid and base compounds (selective extraction) by adjusting the pH.

1.2.2 Solid phase extraction

This innovative extraction procedure based on partitioning, adsorption, affinity or ion-exchange and also known as solid-phase extraction, is gaining wide acceptance, being much faster than most classic techniques. The principle of retention is analogous to high pressure liquid chromatography and is suitable for low, intermediate and high polarity pollutants, depending on the sorbent used. Large sample volumes can be handled using relatively small amounts of solid phase, which in turn require only small volumes of solvent for solid phase strip­ping, eliminating the need for an additional evaporation step and considerably reducing the risk of contamination. Depending on the sample throughput and the compounds to be analysed, the extraction may be performed either on car­tridges or on membranes disks. The recent introduction of high performance cartridges has contributed to the more efficient isolation of a larger number of pollutants, thus gaining favour in many environmental laboratories. Moreover, this approach allows a fair degree of flexibility in terms of automation as the extraction procedure is much simpler to execute. Recently, US EPA method 525, which originally stipulated liquid-liquid extraction for the analysis of semi-vola­tile organics in drinking water, has been modified to include solid phase extrac­tion. Liquid-solid partitioning, also known as solid phase partitioning is particu­larly suited to polar compounds. The pollutants are initially trapped and preconcentrated on macroreticular porous polymers called resins (e.g. Amberlite XAD), which are then dried, eluted with dichloromethane and the eluate concentrated prior to analysis. Thermal desorption may sometimes replace solvent elution, thus ensuring the highest degree of sample enrichment, its major drawback being the thermal instability of the polymers, which consi­derably narrows the range of applications.