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Pressurized liquid extraction (PLE) was applied to the simultaneous extraction of a wide range of pesticides from food commodities. Extractions were performed by mixing 4 g of sample with 4 g of Hydromatrix and (after optimization) a mixture of ethyl acetate:acetone (3:1, v/v) as extraction solvent, a temperature of 100 degrees C, a pressure of 1000 psi and a static extraction time of 5 min. After extraction, the more polar compounds were analyzed by liquid chromatography (LC), and the apolar and semipolar pesticides by gas chromatography (GC); in both cases LC and GC were coupled with mass spectrometry in tandem (MS/MS) mode. The overall method (including the PLE step) was validated in GC and LC according to the criteria of the SANCO Document of the European Commission. The average extraction recoveries (at two concentration levels) for most of the analytes were in the range 70-80%, with precision values usually lower than 15%. Limits of quantification (LOQ) were low enough to determine the pesticide residues at concentrations below or equal to the maximum residue levels (MRL) specified by legislation. In order to assess its applicability to the analysis of real samples, aliquots of 15 vegetable samples were processed using a conventional extraction method with dichloromethane, and the results obtained were compared with the proposed PLE method; differences lower than 0.01 mg kg(-1) were found.

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Residue levels and degradation rates of five benzoylphenylurea insecticides were studied in zucchinis and peppers grown in experimental greenhouses in Almería (Spain). Benzoylphenylurea residues were analyzed by HPLC using on-line post-elution photoirradiation with fluorescence detection. Mathematically defined decline curves were established by determining optimal relationships between benzoylphenylurea residues and time, using different models. The models that best fitted the experimental data were those of first-order for diflubenzuron, triflumuron, hexaflumuron and flufenoxuron in zucchini and RF first-order models for the five insecticides in peppers and for lufenuron in zucchini. Half-life times for the residues on the two vegetables were estimated from the optimal models. In order to guarantee safe consumption of the two vegetables, we have estimated suitable pre-harvest intervals complying with the maximum residue levels established by the Spanish Government. In all cases, such pre-harvest intervals were shorter than those specified by the manufacturers of commercial formulates. Experimental data for the five insecticides in peppers and for lufenuron in zucchini were also fitted to a first-order model. Even though this function was legitimized statistically, estimations of decline times (T/2) and pre-harvest intervals were quite different from those provided by the optimal model.

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