Automatic gas chromatographic determination of N-methylcarbamates in milk with electron capture detection.

A new analytical method that combines on-line derivatization-extraction and gas-liquid chromatography for the determination of N-methylcarbamates is reported. The hydrolysis products of N-methylcarbamates (phenols) are derivatized and extracted in a continuous fashion using pentafluoropropionic anhydride (derivatizing reagent) in n-hexane as an extractant. The thermal instability of N-methylcarbamates is overcome by forming fluoro derivatives that can be identified and quantified at the nanogram per milliliter level with an ECD detector. Application of the proposed method to six mixtures of N-methylcarbamates yielded detection limits between 2 and 20 ng/mL and a relative standard deviation of 2.35-3.70%. Average recoveries of N-methylcarbamates added to cow's milk at concentrations between 50 ng/mL and 2 micrograms/mL ranged from 93.7 to 100.8%.