Drevenkar_1983_Int.J.Environ.Anal.Chem_14_215

On-column transesterification with methanol was applied for the gas chromatographic determination of N-methylcarbamates extracted from human urine. Transesterification conversion efficiencies of N-methylcarbamates dioxacarb, carbofuran and OMS-22, calculated from the amount of the on-column produced O-methyl-N-methylcarbamate (DMC), were 96, 77 and 76% with detection limits of 8, 10 and 10 ng, respectively. In the investigated concentration range of 0.2-3 micrograms/ml of urine the extraction efficiencies with methylene chloride were independent of the initial concentration of N-methylcarbamate added to urine samples of non-exposed persons. The recoveries and rel. S.D. were 74 +/- 11, 64 +/- 8 and 79 +/- 12% for dioxacarb, carbofuran and OMS-22, respectively. The procedure was applied for the gas chromatographic determination of carbofuran and its metabolites containing the N-methylcarbamic group extracted from urine samples of occupationally exposed persons in a pesticide formulating plant. The level of extracted N-methylcarbamates and the concentration of degradation products of organophosphorus pesticides detected in the urine of the same persons were correlated with the blood and plasma cholinesterase activities. Although the determination of DMC includes only a smaller part of the excreted N-methylcarbamate, a simultaneous determination of both carbamates and organophosphorus residues made it possible to distinguish the cause of depression in cholinesterase activity, indicating early and specifically the exposure to a particular group of agents hazardous to health.