Surface partitioning studies of N-methylcarbamate-treated post-harvest crops using SFE-HPLC-postcolumn reaction-fluorescence

Abstract

The partitioning characteristics of selected carbamate insecticides (carbaryl, aldicarb, bendiocarb and pirimicarb) on five fruit and vegetable types were investigated. Post-harvest samples were surface-saturated with a methanolic–aqueous mixed carbamate spiking solution for a number of time periods. Samples were taken at 3, 7, 10 and 14 d, and extracted using supercritical CO₂ at pressure = 300 atm modified with 10% dimethyl sulfoxide. Extracts were analysed by HPLC-postcolumn reaction-fluorescence detection at λ_ex = 330 nm and λ_em = 450 nm for N-methylcarbamates and at λ_ex = 315 nm and λ_em = 380 nm for pirimicarb. The relative partitioning of each insecticide between sample skin and flesh was investigated. This included the determination of both half-life and normalised matrix metabolic rate studies with respect to each carbamate. Multilinear regression (MLR) was applied to a number of insecticide and matrix-based variables to develop regression models for carbamate partitioning for each matrix type studied. Experimentally derived carbamate half-lives ranged from 3.6 d (carbaryl in pear flesh) to 8.0 d (bendiocarb in banana skin). Determinations of normalised metabolic rates were based on calculating the time period from the point of sampling through to the point where carbamate concentration was reduced to 5% of its initial value. These values ranged from 16.2 d (bendiocarb in potato skin) to 34.7 d (bendiocarb in banana skin). Although no practicable MLR partitioning models were obtained, it was found that the models created indicated that carbamate solubility in water (and hence log P) and the number of days in contact with the spiking solution were the most important parameters in model construction.