Determination of Multi-Residues of Tetracyclines and Their Metabolites in Milk by High Performance Liquid Chromatography-Tandem Positive-ion Electrospray Ionization Mass Spectrometry

A high performance liquid chromatography-tandem mass spectrometric method was developed for the simultaneous determination of 7 antibiotics residues of tetracycline, chlortetracycline, oxytetracycline, doxycycline, demeclocycline, methacycline, minocycline, and 3 metabolites of 4-epitetracycline, 4-epichlortetracycline, 4-epioxytetracycline in milk. In the method, the reversed-phase column of Inertsil C8-3 (5 μm,150 mm×2.1 mm i.d), the EDTA-Mcllvaine buffer solution (pH 4.0), the HLB solid phase extraction column, and the methanol-0.01 M trifluoroacetic acid solution mobile phase with gradient elution were used. The flow rate was 0.3 ml/min, the detection mode was MRM with positive-ion electrospray ionization, and the injection volume was 30 μl. The limit of detection (LOD) was between 0.5 and 10.0 μg/kg, and the limit of quantitation (LOQ) was 50 μg/kg. The linear plots were obtained in the range of 50–1200 μg/kg. The overall recoveries were in the range of 74.4%–101% with RSD (n=10) ranging from 1.8% to 8.3%. The method is sensitive, accurate, convenient and rapid, and can be used to simultaneously confirm multi-residue of tetracyclines and their metabolites in milk.