Abstract: To develop an analytical method for the determination of 20 veterinary drugs residues in milk by UPLC-MS/MS. The milk samples were extracted with acetonitrile,and cleaned up with Oasis PRiME HLB solid phase extraction column. The elution was gathered together and then concentrated under nitrogen gas flow. The target components were separated in a gradient elution mode using an ACQUITY UPLC ® HSS T3 column as stationary phase and 0.2% formic solution-0.2% formic acetonitrile as mobile phase,then identified and externally quantified by UPLC-MS/MS with electrospray ion source （ESI） under multi-reaction ion monitoring （MRM） mode. Results showed that the 20 veterinary drugs had good relationship in their respective linear ranges of 0.5~10.0 ng/mL,with correlation coefficients（R²）higher than 0.991. The limit of detection for this method were between 0.02 μg/kg and 0.4 μg/kg,and the limit of quantification for which were between 0.05 μg/kg and 1.2 μg/kg. The method was validated at spiked levels of 2.0 μg/kg and 10.0 μg/kg,with overall recoveries in ranges of 60.6%~90.4% and 64.8%~93.2%. The method was simple and convenient,efficient,accurate and sensitive,which could meet the requirements of screening and quantification for the 20 veterinary drugs used widely in milk.

Key words: milk, veterinary drug residues, UPLC–MS/MS