Further Characterization and Refinement of an HPLC Post-Column Fluorometric Labeling Technique for the Determination of Carbamate Insecticides

Abstract

HPLC-fluorescence parameters have been refined for the determination of nanogram amounts of five carbamate insecticides (carbaryl, carbofuran, methiocarb, methomyl, and propoxur) and two metabolites (3-hydroxycarbofuran and α-naphthol). The compounds are separated on a μBondapak C₁₈ HPLC column, using a methanol-water gradient mobile phase at a flow rate of 1.5 ml/minute. A solution of 0.05N NaOH is added to the column effluent at 0.5 ml/minute to hydrolyze the carbamates in line to methylamine, using a 16 second reaction at 100°C. A solution containing 0.5 mg o-phthalaldehyde and 1 μl 2-mercaptoethanol/ml is added at 0.5 ml/minute to react with the carbamate hydrolysis product, methylamine. The resulting fluorophore is monitored with a fluorescence detector containing a 10 pi cell. Using the above parameters, the following amounts (ng) produced 50% full scale deflection (FSD): carbaryl, 26; carbofuran, 42; 3-hydroxycarbofuran, 30; methiocarb, 51; methomyl, 12; α-naphthol, 52; and propoxur, 36. Detector responses are linear from 5 to 90% FSD for these compounds. In a sevenday system stability study, relative standard deviations in peak height responses and peak retention times for the seven compounds were 3.5 and 1.0%, respectively. The overall performance demonstrates that this system has the sensitivity, linearity, and stability desired in a pesticide residue determinative technique.