Determination of organophosphorus pesticides and metabolites in crops by solid-phase extraction followed by Liquid Chromatography/Diode Array Detection.

A multiresidue method for the analysis of 28 common organophosphorus pesticides and 3 of their main metabolites (paraoxon-ethyl, paraoxon-methyl and malaoxon) in a variety of crop samples has been developed. An aliquot of the chopped sample is homogenized with an organic solvent. The efficiency of extraction methods using methanol, acetone and acetonitrile was evaluated. The acetonitrile gives higher recoveries and minimizes co-extractives from the samples matrix. The resulting aqueous acetonitrile extract is filtered and cleaned by solid phase extraction (SPE). For SPE three different types of adsorption materials (Carbograph 1, LiChrolut-EN and Amberchrom CG-161m) were compared. The cleaned-up extract is injected into the LC system. Three different analytical columns were tested in conjunction with two mobile phase compositions of different polarity. The use of LC-DAD techniques allowed the identification of bath organophosphorus pesticides and metabolites by means of standard and spectral comparison, respectively. The accuracy of the quantitative determination measured in terms of average percentage recovery of 31 compounds in crop samples was 61-96% with a relative standard deviation of 5-10%.