EXTRACTION OF METHAMIDOPHOS RESIDUES FROM VEGETABLES WITH SUPERCRITICAL-FLUID CARBON-DIOXIDE

A simple supercritical fluid extraction (SFE) method has been develope d to efficiently extract incurred residues of methamidophos (a very po lar pesticide) from fresh vegetable samples by using commercial SFE eq uipment and moderate SFE conditions. Vegetable samples were mixed with anhydrous magnesium sulfate and extracted with supercritical carbon d ioxide at 300 atm and 50 degrees C with methanol as static modifier an d a few milliliters of ethyl acetate as trapping system. Methamidophos recoveries were >70% from 33 pepper, cucumber, and tomato samples at incurred levels ranging from 0.1 to 2.2 mg/kg. Triplicate analysis fro m 2 replicates at an incurred level of 0.53 mg/kg gave a coefficient o f variation of 14%. Results for incurred residues of chlorpyrifos, end osulfan, and procymidone in some samples show that the SFE technique c ould be used as a multiresidue method.