Determination of N-methylcarbamate pesticides in liver by liquid chromatography

A liquid chromatographic (LC) method using a 2-step purification technique for the simultaneous determination of 10 carbamates in bovine, swine, and duck livers has been developed. Carbamates are extracted from liver samples with methylene chloride. After evaporation, the residues from the extract are dissolved in methylene chloride-cyclohexane (1 + 1) and cleaned up by gel permeation chromatography. The eluate containing carbamate residues is evaporated to dryness, reconstituted in methylene chloride, further purified by passing it through an aminopropyl Bond Elut extraction cartridge, and analyzed by liquid chromatography using post-column derivatization with orthophthalaldehyde and fluorescence detection. Excitation and emission are set at 340 and 418 nm, respectively. Liver samples for beef, pork, and duck were fortified with 5, 10, and 20 ppb of mixed carbamate standards. The average of 10 recoveries of 10 carbamates at all 3 levels of fortification was greater than 80% with coefficients of variation less than 17%.