Quantitative Determination Method for Residual Colistin A/B in Edible Meats and Milk by Liquid Chromatography-Tandem Mass Spectrometry

Abstract Background Colistin is a polypeptide antibiotic serving as a crucial “last-resort” agent against multidrug-resistant Gram-negative bacteria. Objective This study aimed to develop a reliable analytical method for the determination of colistin A and B residues in food matrices using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Method Test portions were extracted with methanol–water (1:1) under hydrochloric acid–acidified conditions, followed by a secondary extraction with 0.1 mol/L hydrochloric acid. The extracts were cleaned using a weak cation-exchange cartridge, and chromatographic separation was performed on a biphenyl column with gradient elution, followed by LC–MS/MS. Result The developed method produced sharp and symmetrical peaks for colistin A and B, with no significant matrix effects. Recoveries ranged from 81.0% to 105.9% across all analytes and matrices, and both repeatability and reproducibility met the target criteria specified in the Japanese guidelines for method validation. The limits of quantification were 20 ng/g in bovine and swine muscles for colistin A and 10 ng/g for others. Conclusion An LC–MS/MS method was established for quantitative determination of colistin A and B residues in food matrices. The validation results met all performance criteria of the Japanese guidelines, confirming that the method provides reliable and precise measurements suitable for food residue monitoring. Highlights Reliable quantification of colistin residues was achieved using three distinct retention modes, enabling reliable monitoring of residues in foods.