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A procedure based on solid-phase extraction (SPE) has been developed for the simultaneous preconcentration of three widely used herbicides and seven of their most common degradation products. The compounds studied were atrazine and its metabolites, desethylatrazine, desethyldesisopropylatrazine (DEDIA), 2-hydroxyatrazine, desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine (DIHA), terbutryne and its metabolite 2-hydroxyterbutylazine, and chlorotoluron and its metabolite 3-chloro-4-methylphenylurea. A HPLC system with diode array detection was used for the separation, identification and quantification of all these analytes. In the SPE preconcentration step, different types of sorbent were studied: C-18 on silica and polymeric sorbents (Oasis and LiChrolut EN), the best results being obtained with the styrene-divinylbenzene cartridge and when the elution was performed with methanol and ethyl acetate. The detection limits obtained were between 0.1 mug l(-1) for DIHA and DEDIA and 0.02 mug l(-1) for the other analytes. The method used permitted the determination of these herbicides in drinking water at the concentration levels demanded by current legislation. The proposed method was used to evaluate the presence and evolution with time of these herbicides and their degradation products in samples of surface and ground waters from agricultural zones of the provinces of Salamanca and Zamora (basins of the Rivers Guarena and Almar), Spain. (C) 2002 Elsevier Science B.V. All rights reserved.