Determination of colistin in animal tissues, egg, milk, and feed by ultra-high performance liquid chromatography-tandem mass spectrometry

•An UHPLC-MS/MS method was developed suitable for a variety of matrices.•The fragmentation pathway of the product ion at m/z 101 was investigated.•The proposed method was demonstrated in real samples from surveillance program. A confirmatory method for the determination of colistin in animal tissues, egg, milk, and feed was developed and validated. Colistin A and colistin B were extracted from samples with the mixture of 10% trichloroacetic acid-acetonitrile and isolated with mixed-mode weak cation exchange cartridge. Analytes were separated from matrix components using ultra-high performance liquid chromatography, and detected with electrospray ionization on a triple quadrupole mass spectrometer. Mean recoveries ranged from 78.0% to 115.6% with intra-day and inter-day relative standard deviation lower than 8.4% and 12.4%, respectively. The quantitation limits for different matrices were between 5 and 30 μg/kg, which was satisfactory for surveillance monitoring. The developed method was applied to the analysis of real samples collected from different provinces of China, and 19 out of 348 samples were found to be contaminated, with the highest concentration of approximately 12,000 μg/kg colistin A and 10,000 μg/kg colistin B in feed.