Liquid chromatographic determination of abamectin in fruits and vegetables

A simplified extraction and cleanup procedure was developed for determining abamectin in fruits and vegetables. Abamectin is extracted from sample matrices by acetonitrile, and the acetonitrile phase is separated from the aqueous phase by saturating the extract with sodium chloride. Abamectin is then partitioned into hexane from the acetonitrile, and the hexane layer is cleaned up with an aminopropyl solid-phase extraction (SPE) system. The fluorescent abamectin derivative is formed by dehydration with trifluoroacetic anhydride-1-methylimidazole in dimethylformamide for 1 h at 30 degrees C and with methanolic ammonium hydroxide for another 30 min at 30 degrees C. The derivatized residues are separated from the reaction mixture by a silica SPE. The abamectin derivative is determined by reversed-phase liquid chromatography with a fluorescence detector. The method yields recoveries of 85-97% at fortification levels of 10 and 50 micrograms/kg for orange, pears, spinach, and celery.