Objective: A high performance liquid chromatography-tandem mass spectrometric method was established for determination of 7 penicilins (cloxacillin, nafcillin, oxacillin, penicillin V, amoxicillin, penicillin G, ampicillin) and their penicilloic acids (cloxacilloic acid, nafcilloic acid, oxacilloic acid, penicilloic acid V, amoxicilloic acid, penicilloic acid G and ampicilloic acid) in milk products. And the 7 penicilins and penicilloic acids in milk products were surveyed.
Methods: The 7 penicilins and penicilloic acids in milk products were extracted by water in super-sonic instrument , precipitated proteins by acetonitrile and degreased fat by n-hexane with liquid-liquid extraction, then the purified solution was concentrated by nitrogen, dissolved with acetonitrile-water (10 + 90, V/V) and cleaned by 0.22 µm millipore filter. The filtrate was detected by high performance liquid chromatography-tandem mass spectrometry, identified by electrospray ionization (ESI) in positive mode using multiple reaction monitoring, and quantified with external standards.
Results: The calibration curves of 7 penicilins and penicilloic acids showed good linearity in the range of 1.0-200 µg/kg with correlation coefficients were above 0.9992. The detection limits of the method were from 0.03 µg/kg to 0.15 µg/kg. The recoveries of three spiking levels ranged from 80.0% to 110.0%, and RSDs of 7.06% or less were obtained.
Conclusion: The method for determination of 7 penicilins and penicilloic acids in milk products by HPLC-MS/MS was of operation convenience, less interference from impurities and good accuracy, which could meet the requirements for the determination of 7 penicilins and penicilloic acids residues in milk products.