AUTOMATIC GAS-CHROMATOGRAPHIC DETERMINATION OF N-METHYLCARBAMATES IN MILK WITH ELECTRON-CAPTURE DETECTION

A new analytical method that combines on-line derivatization-extractio n and gas-liquid chromatography for the determination of N-methylcarba mates is reported. The hydrolysis products of N-methylcarbamates (phen ols) are derivatized and extracted in a continuous fashion using penta fluoropropionic anhydride (derivatizing reagent) in n-hexane as an ext ractant. The thermal instability of N-methylcarbamates is overcome by forming fluoro derivatives that can be identified and quantified at th e nanogram per milliliter level with an ECD detector. Application of t he proposed method to six mixtures of N-methylcarbamates yielded detec tion limits between 2 and 20 ng/mL and a relative standard deviation o f 2.35-3.70%. Average recoveries of N-methylcarbamates added to cow's milk at concentrations between 50 ng/mL and 2 mug/mL ranged from 93.7 to 100.8%.