Multiresidue method for the analysis of multiclass pesticides in agricultural products by gas chromatography-tandem mass spectrometry

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Abstract
A multiresidue method is described for determining 55 organophosphorus and organochlorinated compounds and pyrethroids commonly used in crop protection. Pesticide residues are extracted from samples with a mixture of ethyl acetate and sodium sulfate, obtaining a final preconcentration of 1 mg sample (ml extract)−1. No additional clean-up steps are necessary. Analysis is performed by gas chromatography by using a combination of positive chemical ionisation (PCI) and electron impact (EI) ionisation modes and tandem mass spectrometry (GC-PCI/EI-MS-MS). Good sensitivity and selectivity of the method are obtained with limits of detection (LODs) ranging from 0.07 to 4.21 μg kg−1 in all the cases, except for methamidophos, permethrin, cypermethrin and difenconazol. Average recoveries between 52 and 114% are obtained and good linearity is observed in the studied ranges (r 0.994). The RSD values are ⩽29% in all the cases. The method has been applied to the analysis of 178 vegetable samples, as a part of the monitoring programme of the Association of Producers and Exporters of Fruits and Vegetables of Almería (COEXPHAL) and quality control systems applied during the assays have demonstrated a good performance and stability with time.

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