Extraction of methamidophos residues from vegetables with supercritical fluid carbon dioxide

A simple supercritical fluid extraction (SFE) method has been developed to efficiently extract incurred residues of methamidophos (a very polar pesticide) from fresh vegetable samples by using commercial SFE equipment and moderate SFE conditions. Vegetable samples were mixed with anhydrous magnesium sulfate and extracted with supercritical carbon dioxide at 300 atm and 50 degrees C with methanol as static modifier and 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 from 2 replicates at an incurred level of 0.53 mg/kg gave a coefficient of variation of 14%. Results for incurred residues of chlorpyrifos, endosulfan, and procymidone in some samples show that the SFE technique could be used as a multiresidue method.