Determination of avermectins in feeds by liquid chromatography-mass spectrometry

An analytical method of avermectins(avermectin,dormectin,eprinomectin and ivermectin) was established by LC-MS.4 kinds of avermectins were simply extracted with acetonitrile from feeds.Then,the extraction was diluted with water and pH was adjusted with triethylamine.Target compounds were selectively concentrated by C18 SPE cartridge.They were determined by LC-MS.The average recoveries for 4 avermectins were ranged from 91.3% to 99.8%.The coefficients of variation were in the range of 2.9%～15%(n=4).The limits of detections were 10 μg/kg and the quantitative limits were 20 μg/kg for complete feeds,concentrated feeds and premixed feeds.The method can be used for confirmation of the detection of avermectin residues in feeds.