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

Emamectin, milbemectin, ivermectin and abamectin are similar macrocyclic lactone chemicals used as an acaricides or parasiticides. We developed a simultaneous analytical method for determining the residual amounts of these compounds and emamectin metabolites in crops. A sample extracted with acetone was cleaned up with Bond Elut C18 and NH2. The sample was then fluorescence-derivatized with trifluoroacetic anhydride and 1-methylimidazole in acetonitrile. The analyte was measured by HPLC with fluorescence detection using an octadecylsilyl column with 3 μm particle size and gradient elution. In most crops, their recoveries by the developed method were ca. 80–110%. The 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 commercial crops in Osaka, Japan. The result of the surveillance was that emamectin 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 confirmed 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 vegetables except for milbemectin.