Determination of chloramphenicol, enrofloxacin and 29 pesticides residues in bovine milk by liquid chromatography-tandem mass spectrometry.

A sensitive method for determination of chloramphenicol, enrofloxacin and 29 pesticides residues in bovine milk by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed. Residues of the targets were extracted from milk with acetonitrile, cleaned up by C(18)-SPE cartridge, and then determined by HPLC-MS/MS. The MS detection was operated in positive or negative ionization mode, depending on the compounds. For confirmation of each target compound, two precursor ion>product ion transitions were selected by multi-reaction monitoring mode (MRM). The method showed good linearity for all the tested compounds over the studied concentration range with correlation coefficient higher than 0.9910. Recoveries for the studied compounds at three spiked levels (0.05, 0.10, 0.19mgkg(-1)) in bovine milk were in the range of 71-107% with RSDs not larger than 13.7%, except that recoveries of trifluralin ranged between 62% and 70% at the spiked levels. Limits of quantitation for the analytes were estimated to range between 0.03×10(-3) and 14.5×10(-3)mgkg(-1). The proposed method was applied for the determination of the analytes residues in real samples. The found levels of the analytes in milk samples were lower than maximum residues levels (MRL).