Use of Solid-Phase Microextraction for the Quantitative Determination of Herbicides in Soil and Water Samples Felix Hernandez,* Joaquim Beltran, Francisco J. Lopez, and Jose V. Gaspar Analytical Chemistry, Experimental Sciences Department, University Jaume I, P.O. Box 224, E-12080, Castellon, Spain An in-depth study of SPME optimization and application has been made, considering not only aqueous (surface water and groundwater samples) but also the more complex soil samples. Seven herbicides widely used in the area of study have been selected including five triazine herbicides (atrazine, simazine, terbumeton, terbuthyl- azine, terbutryn), molinate, and bromacil. Linearity range was between 0.1 and 1 0 ng/ mL and the repeatability below 1 0 % when applying the optimized SPME procedure to water samples. Reproducibility was found to be lower than 20% at the 1 ng/ mL level, and the limits of deter- mination in environmental water samples using GC/ MS (SIM mode) were well below 0.1 ng/ mL (values ranging from 10 to 60 ng/ L). Extraction of selected herbicides from soil was carried out by microwave-assisted solvent extraction using methanol in screw-capped vials, leading to recoveries over 80% in spiked soil samples at the 5 -2 0 0 ng/ g level. SPME application over methanolic soil extracts required a 1 0 -fold dilution with distilled water. The recommended procedure was found to be fully applicable for quantitative determination of selected her- bicides in soils containing low organic matter content with coefficients of variation below or around 1 0 % and limits of determination ranging from 1 to 10 ng/ g. Both proce- dures were applied to real-world surface water and soil samples where several pesticides were detected including atrazine, simazine, terbuthylazine, and molinate. The presence of pesticides in the environment is a problem that has caused great social and scientific concern in the last years as can be deduced from the restrictive legislation developed by various governments. As a result, both EPA regulations and EU legislation established a maximum pesticide residue level in water supply samples 1 that is in the range of low parts-per-billion. This has forced the scientific community to develop analytical proce- dures that can be used to determine not only the presence of pesticides in environmental samples but also their concentrations with a good accuracy. These methods have to be robust, precise, and sensitive to be used in regulatory situations. In most cases, determination of pesticide residues in water, or other environ- mental samples, relies on the use of liquid-liquid extraction, solid- phase extraction, or supercritical fluid extraction as described in many papers and as is referenced in several EPA methods. 2-7 These procedures are usually expensive and labor- and time- consuming because in most of cases typical environmental samples cannot be directly analyzed by the usual chromatographic methods applied. Sample matrixes range from relatively simple, as in groundwater, to more complex as in surface water, wastewater, or soil samples. Additionally, the concentration levels are too low to allow the determination without a preconcentration step. In this way, some papers have been published dealing with the trends and strategies in sample preparation for organic micropollutant determination in environmental samples. 8-10 It is widely accepted that, at the moment, a great number of research activities are oriented to develop simple (preferably in one step) sample preparation procedures that could be automated and coupled on-line with the final analytical measurement step. Sample treatment simplification accounts for several aspects related to cost saving (by reduction of time, laboratory staff, and solvent consumption) and ecological and toxicological concern (by dramatically decreasing solvent residues and by eliminating the use of highly toxic chlorinated solvents), taking profit from the amazing progress made in analytical instrumentation. As a result of the effort devoted in this research field of sample treatment reduction, Pawliszyn and co-workers developed in the early 1990s the solid-phase microextraction technique (SPME), 11,12 which provides a simple solvent-free approach for organic pollutant * Corresponding author: (fax) 34 964 72 80 66; (e-mail) hernandf@ exp.uji.es. (1) EC Drinking Water Guideline, 98/ 83/ CE, Brussels, November 1998. (2) DFG. Manual of Pesticide Residue Analysis; WCH: Weinheim, Germany, 1992; Vol. II. (3) Clesceri, L. S., Greenberg, A. E., Trussell, R. R., Eds. Standard Methods for the Examination of Water and Wastewater, 20th ed.; American Public Health Association, American Water Works Association, Water Environment Federation: Washington, DC, 1998. (4) Hernandez, F.; Morell, I.; Beltran, J.; Lopez, F. J. Chromatographia 1993 , 37, 303-312. (5) Beltran, J.; Lopez, F.; Forcada, M.; Hernandez, F. Anal. Chim. Acta 1997 , 356, 125-133. (6) Font, G.; Manes, J.; Molto, J. C.; Pico, Y. J . Chromatogr. 1993 , 642, 135- 161. (7) EPA Method 565.1. Determination of organic compounds in drinking-water by liquid solid extraction and capillary column GC/ MS. Revision 2.2, May 1991 , Environmental Monitoring System Laboratory, US EPA, Cincinnati, OH, 45268, 1991; p 323. (8) Balinova, A. J . Chromatogr., A 1996 , 754, 125-135. (9) Poole, C. F.; Poole, S. K. Anal.Commun. 1996 , 33, 11H-14H. (10) Hogendoorn, E. A.; Dijkman; E., Baumann, B.; Hidalgo, C.; Sancho, J. V.; Hernandez, F. Anal. Chem. 1999 , 71, 1111-1118. (11) Arthur, C. L.; Pawliszyn, J. Anal. Chem. 1990 , 62, 2145-2148. (12) Arthur, C. L.; Killam, L. M.; Buchholz, K. D.; Berg, J. R. Anal. Chem. 1992 , 64, 1960-1966. Anal. Chem. 2000, 72, 2313-2322 10.1021/ac991115s CCC: $19.00 © 2000 American Chemical Society Analytical Chemistry, Vol. 72, No. 10, May 15, 2000 2313 Published on Web 04/12/2000