Liquid chromatographic determination of emamectin, milbemectin, ivermectinand abamectin in crops and confirmation by liquid chromatography-mass spectrometry

Emamectin, milbemectin, ivermectin and abamectin are similar macrocyclic la ctone chemicals used as an acaricides or parasiticides. We developed a simu ltaneous analytical method for determining the residual amounts of these co mpounds and emamectin metabolites in crops. A sample extracted with acetone was cleaned up with Bond Elut C-18 and NH2. The sample was then fluorescen ce-derivatized with trifluoroacetic anhydride and 1-methylimidazole in acet onitrile. The analyte was measured by HPLC with fluorescence detection usin g an octadecylsilyl column with 3 mum particle size and gradient elution. I n most crops, their recoveries by the developed method were ca. 80-110%. Th e detection limits of the analytes in vegetables were 0.1-0.3 ppt Using the developed method, we surveyed the residues of these compounds in 20 commer cial crops in Osaka, Japan. The result of the surveillance was that emamect in benzoate of 0.2-6.7 ppb was detected in nine cases and milbemectin of 16 .7-279.3 ppb was detected in four cases. The detected samples were confirme d by LC-electrospray ionization (ESI) MS. The limit of detection by LC-ESI- MS was similar to the fluorescence detection level of 0.1-0.3 ppt in vegeta bles except for milbemectin. (C) 2000 Elsevier Science B.V. All rights rese rved.