Optimization, Automation, and Validation of the Solid-Phase Extraction Cleanup and On-Line Liquid Chromatographic Determination of N-Methylcarbamate Pesticides in Fruits and Vegetables

Abstract

A fully automated liquid chromatographic (LC) method was developed for the determination of 21 N-methylcarbamates and 12 of their metabolites. Our previously developed solid-phase extraction (SPE) cleanup method can now be performed using an automated SPE cleanup apparatus. The cleaned-up extract is injected on-line into the LC carbamate analysis system, which is based on a reversed- phase LC separation, postcolumn hydrolysis of the carbamates on a solid-phase catalyst, reaction of the methylamine formed with ophthalaldehyde reagent, and fluorescence detection of the derivatives. The optimized method was evaluated. Recovery and repeatability data were collected for 13 representative carbamates and 12 metabolites on 12 different food product types. The reliability of the method in routine analysis of fruit and vegetable samples is demonstrated. Registration of the analytical results of control samples in Shewhart charts during a year of routine analysis has demonstrated the excellent performance of this complete method. The limits of determination are in the 5-50 μg/kg (ppb) range. Sample throughput is about 20 per 24 h. Data are presented on real residues of N-methylcarbamates found in fruits and vegetables during 4 years of routinely applying this multiresidue method