Simultaneous Determination of Aldicarb, Ethiofencarb, Methiocarb and Their Oxidized Metabolites in Grains, Fruits and Vegetables by High Performance Liquid Chromatography

Abstract

Three carbamate pesticides, aldicarb (A0), ethiofencarb (E0), methiocarb (M0) and six of their oxidized metabolites, sulphoxides (A1, E1, M1) and sulphones (A2, E2, M2) were simultaneously determined. Five grams of a sample were homogenized with acetone, and then treated with dichloromethane-hexane mixture (1:1) and sodium chloride (NaCl), homogenized and centrifuged. The organic layer was removed and the aqueous residue was reextracted a second time with dichloromethane - hexane mixture. The combined organic extracts were evaporated in vacuo. The residue was dissolved in dichloromethane and charged on a Sep-Pak® aminopropyl cartridge. Carbamates were eluted from the cartridge with 1% methanol in dichloromethane. The eluate was evaporated to dryness and 0.5 ml of methanol and 1.5 ml of 0.001 N-hydrochloric acid (HCl) solution were added. Individual carbamates were separated by gradient elution high performance liquid chromatography (HPLC) using octyldecylsaline (ODS) column. Derivatization of separated carbamates to fluorescent derivatives was achieved in-line. Recovery of pesticides and their oxidized metabolites from rice, apple, cabbage and other foods ranged from 60 to 103% following fortification at 20 ppb. Detection limits were 1 ppb for A1, A2, E1, E2, 2 ppb for A0, E0, M1 and 4 ppb for M0 and M2 (S/N>3).