ON LINE PRECONCENTRATION AND GAS-CHROMATOGRAPHIC DETERMINATION OF N-METHYLCARBAMATES AND THEIR DEGRADATION PRODUCTS IN AQUEOUS SAMPLES

A continuous liquid-solid extraction system coupled to a gas chromatog raph for the preconcentration and determination of N-methylcarbamates and their corresponding phenols in water is reported. Various sorbent materials were assessed, of which XAD-2 provided the best results in t he preconcentration of propoxur, carbofuran, carbaryl, 2-isopropoxyphe nol, 3-hydroxycarbofuran, and l-naphthol. The proposed method is highl y sensitive to trace levels of the analytes; it features detection lim its between 0.7 and 1 mu g/L, which are substantially lower than those afforded by flame ionization detection. Changes in three river water samples containing only carbamate pesticides or phenols and pesticides plus their hydrolysis products (phenols) at the microgram per liter l evel were studied under natural conditions over a B-week period; the r ate of degradation was lower for the N-methylcarbamates than for their respective phenols. The proposed continuous system was evaluated for environmental samples without detectable residues of pesticides.