High-performance liquid chromatographic determination of aryl N-methylcarbamate residues using post-column hydrolysis electrochemical detection.

A high-performance liquid chromatographic technique is reported which selectively detects the phenolic moiety of aryl N-methylcarbamates at low nanogram levels. The carbamates are separated on a C-8 column using an acetonitrile-water gradient mobile phase. The eluted carbamates are hydrolyzed in-line by post-column addition of base, which also serves as electrolyte in the electrochemical (coulometric) detection of the resulting phenols. The technique was tested with six carbamates (bufencarb, carbaryl, carbofuran, 3-hydroxycarbofuran, isoprocarb and methiocarb) and four crops (apples, cabbage, grapes and tomatoes). Optimum detector responses and stability for the carbamates were attained at 0.60 V. Detector response to the carbamates in the presence of crop coextractives was 99% of theoretical with a standard deviation of 2.8% at the 0.05- to 0.1-ppm fortification level. The lower limit of quantitation is 0.01 ppm. Other electrochemical detectors were evaluated for suitability for this work.