Multiresidue method for the determination of organophosphorus pesticides in cereal matrixes

Our research was focused on a preliminary comparison of three cleanup procedures for the determination of 26 organophosphorus (OP) pesticide residues in cereal matrixes. The aim of the study was to reduce the analytical problems associated with the presence of high-molecular-weight compounds in these matrixes in order to improve the efficiency of the chromatographic separation. The method was based on the extraction of OP pesticides from the samples with the use of petroleum ether, acetone, and dichloromethane, and on three different cleanup procedures, followed by GC identification. The first procedure was carried out with a multicartridge system; the second procedure consisted of a low-temperature lipid precipitation; for the third procedure, acid and neutral alumina were used for cleanup of the extract. The use of deactivated acidic alumina as the adsorbent medium and the use of n-hexane-dichloromethane-ethyl acetate (6 + 3 + 1, v/v/v) as the eluting system were preferred. After purification, the residue was injected into a gas chromatograph for separation followed by nitrogen-phosphorus detection; the identities of the OP pesticides in positive samples were confirmed by GC/MS. The proposed method could be extended to the determination of other OP pesticides in various food matrixes in routine analysis.