[Determination of levamisole residue in milk and milk powder by ultra performance liquid chromatography-tandem mass spectrometry].

A sensitive and selective method is presented for the determination of levamisole residues in milk and milk powder by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Levamisole in the test samples was extracted with ethyl acetate under alkaline condition, then transferred into dilute hydrochloric acid, and cleaned-up with a strong cation exchange (SCX) column to obtain an extract suitable for the analysis by UPLC-MS/MS. Levamisole was separated by a BEHC18 UPLC column and acetonitrile-1.0% formic acid (15:85, v/v) as mobile phase, and electrospray ionization was applied and operated in the positive ion mode. The calibration curve was good linear between the peak area and the mass concentration of levamisole from 2.0 to 100.0 microg/L with the correlation coefficient of 0.997. The average recoveries of levamisole spiked in milk and milk powder samples at the three concentrations ranged from 64.5% to 102.0% with the relative standard deviations less than 13.1%. The detection limits of levamisole were 0.4 microg/kg in milk and 2 microg/kg in milk powder.