A novel method for the determination of some pesticides in vegetable oils based on dissociation extraction followed by gas chromatography-mass spectrometry.

The distribution of 40 pesticides of basic nature in different extraction systems was studied at 20 ± 1°C. The distribution constants (P) and distribution ratios (D) between n-hexane and polar phases are calculated. It was found that the studied pesticides are most fully and selectively extracted from hexane and vegetable oils by solutions of perchloric acid in acetonitrile. In particular, the acidification of acetonitrile decreases the D-value of fenpropimorph by 29,000 times. This phenomenon was used for the development of an improved technique for the quantitative analysis of widely used pesticides of basic nature in rapeseed, linseed, sunflower and olive oils by GC-MS. The proposed approach allows obtaining much purer sample extracts, compared with the use of standard solvent extraction with further purification by the freezing-out technique. This approach expands the range of pesticides (flutriafol, fenpropidine, metazachlor, cyprodinil and others) that can be determined by GC-MS. The recovery values of the studied pesticides from vegetable oils were between 85% and 115% with RSD values below 10%. The obtained limits of detection ranged from 0.001 to 0.1 mg kg(-)(1), and are below or equal to the maximum residue levels (MRLs) set by the European Union for the corresponding pesticides.