Analysis of colistin A and B in fishery products by ultra performance liquid chromatography with positive electrospray ionization tandem mass spectrometry.

A rapid and simple method for the determination of colistin A and B in fishery products by reversed phase ultra performance liquid chromatography with positive electrospray ionization tandem spectrometry (UPLC-ESI-MS/MS) method was described. The samples were extracted with 1.0 mol/L of hydrochloric acid in methanol-water and then purified on the PLS solid phase extraction columns. Then the eluate was evaporated to less than 1 mL under a gentle stream of nitrogen at 40 °C and formic acid-acetonitrile-water (0.2/10/90, v/v/v) was added to adjust volume to 1 mL final volume. An aliquot (10 µL) was injected onto the LC column for analysis with the mobile phase of 0.2% formic acid in acetonitrile and 0.2% formic acid in water at 0.20 mL min⁻¹. Multiple reaction monitoring was performed using precursor-product ion combinations. Calibration curves were linear from 200 ng/mL to 2000 ng/mL for colistin A and B. Mean recoveries were between 72.9% and 82.9%. The LOD was 10.0 µg/kg and LOQ was 40.0 µg/kg. The intra-day assay precision values for QC samples were between 2.17% and 9.00%, and inter-day values were between 2.80% and 6.97%. The method has merits of simplicity, sensitivity and rapidity, and it can be used for the determination of colistin A and B in fishery products.