Abstract: A confirmative method to determine 9 cephalosporin residues in beef by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed. The sample was homogenized and extracted with acetonitrile and water for 1 min at 14000 r/min, centrifuged at 10000 r/min and 4 ℃ for 10 min. A total of 2 mL saturated sodium chloride solution was added to avoid foaming during the acetonitrile evaporation, the acetonitrile was evaporated below 37 ℃ using a rotary evaporator, and then cleaned up on an Oasis HLB(500 mg, 6 mL) SPE column by washing with 5 mL water and eluting with acetonitrile-water (7:3, v/v). The eluate was blown to dryness under a stream of nitrogen and adjusted to 3.0 mL with water. The separation was carried out on an ACQUITY UPLCTM BEH C18 column within 5 min, analyzed by UPLC-MS/MS system with external standard method. The limits of quantification (LOQs) of cefuroxime, ceftiofur and cefalonium were 10, 0.5 and 0.5 μg/kg, respectively; the LOQs of other cephalosporins were 1.0 μg/kg. The recoveries of cephalosporins ranged from 74.2% to 119% and the relative standard deviations (RSDs) ranged from 2.9% to 15% for the spiked beef sample. The method is quick, easy, very sensitive and suitable for the determination of cephalosporin residues in beef.

Key words: beef , cephalosporin, ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)