SIMULTANEOUS DETERMINATION OF ALDICARB, ETHIOFENCARB, METHIOCARB AND THEIR OXIDIZED METABOLITES IN GRAINS, FRUITS AND VEGETABLES BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Three carbamate pesticides, aldicarb (A0), ethiofencarb (E0), methioca rb (M0) and six of their oxidized metabolites, sulphoxides (A1, E1, M1 ) and sulphones (A2, E2, M2) were simultaneously determined. Five gram s of a sample were homogenized with acetone, and then treated with dic hloromethane-hexane mixture (1:1) and sodium chloride (NaCl), homogeni zed and centrifuged. The organic layer was removed and the aqueous res idue was reextracted a second time with dichloromethane - hexane mixtu re. The combined organic extracts were evaporated in vacuo. The residu e was dissolved in dichloromethane and charged on a Sep-Pak(R) aminopr opyl cartridge. Carbamates were eluted from the cartridge with 1% meth anol 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 h igh performance liquid chromatography (HPLC) using octyldecylsaline (O DS) column, Derivatization of separated carbamates to fluorescent deri vatives was achieved in-line. Recovery of pesticides and their oxidize d metabolites from rice, apple, cabbage and other foods ranged from 60 to 103% following fortification at 20 ppb. Detection limits were 1 pp b for Al, A2, E1, E2, 2 ppb for A0 E0 M1 and 4 ppb for M0 and M2 (S/N> 3).