Simple analytical method for organophosphorus pesticide residues in milk

A simple method for determination of organophosphorus pesticide residues at the parts per million level in milk was developed. Pesticide residues were extracted with acetonitrile added to aqueous milk, fat was removed by zinc acetate addition and dichloromethane partition, and analytes were concentrated and analyzed by wide-bore capillary column gas chromatography. Recoveries of 6 pesticides spiked in milk samples at levels of 0.1 and 1.0 micrograms/mL were 82.1-93.8% and 79.7-96.6%, respectively. Triplicate samples spiked with 6 pesticides at 1 microgram/mL were analyzed independently by 3 laboratories. Average recoveries were greater than 80%, and the mean coefficients of variation for the complete study were 2.9% for diazinon, 5.4% for dimethoate, 4.6% for malathion, 4.6% for parathion, 4.9% for EPN, and 6.1% for phosalone.