DETERMINATION OF N-METHYLCARBAMATE PESTICIDES IN ENVIRONMENTAL WATER SAMPLES USING AUTOMATED ONLINE TRACE ENRICHMENT WITH EXCHANGEABLE CARTRIDGES AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A fully automated high-performance liquid chromatographic (HPLC) method was developed for the determination of N-methylcarbamate pesticides and their polar metabolites in various types of water. Two different, commercially available, automated trace enrichment devices (OSP-2 and Prospekt) were investigated as to their performance. Low-carbon C-18-bonded silica (C-18/OH, 40 mu m particle size) was used, as a selective sorbent for solid-phase extraction and preconcentration of N-methylcarbamate pesticides from environmental water samples. PLRP-S (15-25 mu m), a styrene-divinylbenzene polymeric phase, was also evaluated as an alternative to extract N-methylcarbamates. After preconcentrating the N-methylcarbamates on an exchangeable cartridge, the analytes were eluted with the mobile phase gradient and transferred to the reversed-phase HPLC system. Detection was performed via post-column hydrolysis on a solid-phase catalyst (anion exchanger), derivatization of the methylamine formed with o-phthalaldehyde reagent, and fluorescence detection of the isoindole derivative. Both trace enrichment systems showed good quantitative results for the determination of N-methylcarbamates and their metabolites at the 0.1 mu g/l level. The repeatability was excellent with relative standard deviations in the range 2-10%. The method detection limits for surface water were between 30 and 50 ng/l. Sample throughput is about 30 samples per 24 h, unattended. The method proved to be suitable for monitoring N-methylcarbamate pesticides in environmental water samples.