Screening and confirmation of 100 pesticides in food samples by liquid chromatography/tandem mass spectrometry

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An analytical method for screening, quantitation and confirmation of a group of 100 pesticides in vegetable and fruit samples was developed using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS). The pesticides studied belonged to different chemical families of herbicides, insecticides and fungicides; some degradation products were included as well. A thorough optimization was performed for each analyte to achieve individual optimum fragmentor and collision energy voltages. Two transitions per parent compound were monitored in a single chromatographic run containing two time segments. A small particle size C(18) column (1.8 microm) was used for the chromatographic separation of the mixture, providing very narrow peaks and allowing an excellent separation of all the analytes in a 30-min period for maximum peak capacity. The method was validated with blank matrices of green pepper, tomato and orange spiked from 0.1 to 100 microg/kg with the pesticide mix. Quantitation was carried out using matrix-matched standard calibration and linearity of response over 3 orders of magnitude was demonstrated (r > 0.99). Limits of detection based on two transitions and ion-ratio requirements ranged between 0.3 and 50 microg/kg. In general, the sensitivity obtained meets the maximum residue levels (MRLs) established by the European Union regulation for food monitoring programs. The analytical performance of the method was evaluated for different types of vegetables and fruits, showing little or no matrix effects, and examples of screening and confirmation of pesticides in these samples are shown here.