Determination of coumaphos and its oxygen analog in eggs and milk by using a multiresidue method with liquid chromatographic quantitation and capillary gas chromatographic/mass spectrometric confirmation.

A multiresidue method for carbamate insecticides was adapted for the determination of coumaphos and its oxygen analog in eggs and milk. Eggs were extracted with acetonitrile and milk was extracted with acetone. Co-extractives were removed using liquid partitioning and charcoal column procedures described in the carbamate method. Coumaphos and its oxygen analog were determined by using a high performance liquid chromatograph equipped with a fluorescence detector. Recovery studies were performed for the 2 compounds at levels of 0.01 and 0.10 ppm in eggs and 0.01 and 0.02 ppm in milk. Overall average recovery was 100% (range 95-109%). In a trial of the method by another laboratory, the recovery of coumaphos and its oxygen analog from milk averaged 87 and 96%, respectively. Data are presented on the capillary gas chromatographic/mass spectrometric confirmation of coumaphos residues.