Abstract:

A method using liquid-liquid extraction (LLE) followed by clean-up steps of centrifugation, freezing and dispersive solid phase extraction (D-SPE)and ultra-performance liquid chromatography (UPLC) coupled with tandem mass spectrometry (MS/MS) has been developed for the determination of trace levels of 104 pesticides in vegetable oils. LLE has been optimized to extract these pesticide residues from oils to obtain the highest recoveries of pesticides and the lowest co-extract fat residue in the final extract. In addition, the centrifugation and freezing steps as well as D-SPE with primary secondary amine (PSA), graphite carbon black (GCB) and C18 were used as the clean-up steps to minimize the co-extract fat. The recoveries obtained ranged from 55% to 121% and the relative standard deviations (RSDs) ranged from 0.47% to 19.2% at the spiked levels of 0.01, 0.02 and 0.05 mg/kg. This method, combining with accurate and sensitive detection, allowed quantification and confirmation at levels as low as 1 μg/kg for 80% of the analytes. The limits of quantification (LOQs) of the most compounds were below the maximum residue limits (MRLs) established by the Chinese legislations for oils. The proposed method was applied successfully for the residue determination of the selected pesticides in oils.

Key words: dispersive solid phase extraction (D-SPE), liquid-liquid extraction (LLE), pesticides, residues, tandem mass spectrometry (MS/MS), ultra-performance liquid chromatography (UPLC), vegetable oils