Kresoxim-methyl and its two thermolabile metabolites, BF 490-2 and BF 490-9, were analyzed in pear using a pepper leaf matrix protection to maintain the metabolites inside the gas chromatography system. Samples were extracted with a mixture of ethyl acetate and n-hexane (1:1, v/v) and purified and/or separated using a solid phase extraction procedure. The pepper leaf matrix was added and optimized with cleaned pear extract to enhance metabolite sensitivity. Matrix matched calibration was used for kresoxim-methyl in the pear matrix and for metabolites in the pear mixed with pepper leaf matrix. Good linearity was obtained for all analytes with a coefficient of determination, r (2) ⩾ 0.992. Limits of detection (LOD) and quantification (LOQ) were 0.006 and 0.02 mg kg(-1) and 0.02 and 0.065 mg kg(-1) for kresoxim-methyl and the metabolites, respectively. Recoveries were carried out at two concentration levels and were 85.6-97.9% with a relative standard deviation <2.5%. The method was successfully applied to field incurred pear samples, and only kresoxim-methyl was detected at a concentration of 0.03 mg kg(-1).
Keywords: Gas chromatography; Kresoxim-methyl; Matrix effect; Metabolites; Pear.