EFFECT OF THE VARIOUS PARAMETERS GOVERNING SOLID-PHASE MICROEXTRACTION FOR THE TRACE-DETERMINATION OF PESTICIDES IN WATER

The parameters governing solid-phase microextraction (SPME) are invest igated, with emphasis on the determination of the partition coefficien ts, K, and their use to predict the selection of a fibre, depending on the respective characteristics of the fibres and the analytes. Film t hickness and stability of the compounds can interfere with the determi nation of K values. The time profile curves were determined for twelve pesticides having a wide range of water solubilities and polarities a nd using four fibres (polydimethylsiloxane, polydimethylsiloxane-divin ylbenzene, Carbowax-divinylbenzene and polyacrylate). Although the aff inity order was different for the four coatings, no correlation was fo und between the respective characteristics of the fibres and solutes. The two fibres containing divinylbenzene were shown to have the highes t affinities and the polydimethylsiloxane had the lowest affinity. The polyacrylate fibre which is the more polar commercial fibre did not p rovide the highest affinities for the more polar and water-soluble ana lytes. The important parameters for quantitative analysis have been ev aluated. The calibration curves were similar when one analyte of inter est was present on its own in a drinking water sample, or when eleven other pesticides were present at the same concentration or when much h igher concentrations of other analytes were present in the sample. Lin earity was obtained over a wide range of concentrations in drinking wa ter samples. Detection limits are in agreement with European regulator y levels in drinking water for most of the analytes using solid-phase microextraction-gas chromatography-nitrogen-phosphorus detection (SPME -GC-NPD). In contaminated surface water samples, the chromatograms are relatively clean and most of the compounds can be detected at levels lower than 0.5 mu g/l. (C) 1998 Elsevier Science B.V.