The qualitative and quantitative determination of pesticides in aqueous samples is usually performed by liquid-liquid extraction (LLE) or solid phase extraction (SPE)(2-4) methods. These
two procedures require several steps for sample preparation and extraction of the analytes of interest. To achieve the required limits of detection, a concentration step (solvent evaporation) is included. It is at this stage in the analysis that the potential for loss of analytes or contamination of
samples is the greatest. Although this step is less aggressive in SPE methods, where the amounts of solvent used are smaller than those used for LLE methods, volatile analytes may still be lost during the evaporation step, adsorption to vial walls can occur and trace impurities present in solvents can also become concentrated. It is therefore desirable to limit the number of sample handling steps involved in any analytical method.