A fast and reliable method for the quantitative determination of benzimidazoles and metabolites in milk by LC-MS/MS with on-line sample treatment.

This work reports the development of a simple, reliable and automated method based on LC-MS/MS for the quantitative determination of benzimidazole residues and some of their metabolites in milk. The method involves the use of an extraction cartridge coupled on-line to the chromatographic system for the clean-up of the milk samples, efficiently eliminating matrix macromolecules and providing appropriate selectivity for the determination of such compounds. In the online method developed here, only a reduced manual sample manipulation was required (protein precipitation and filtration) prior to injection into the chromatographic system. The limits of detection of the target anthelmintics ranged from 0.1 to 0.8 ng mL(-1) in milk samples, these values being below the maximum residue limit established for these compounds. The whole method developed was validated in real samples according to the requirements set by the Commission Decision 2002/657/EC. The optimized method was successfully applied to commercial and raw milk samples of different origin demonstrating that the proposed method may find application in routine laboratory analyses of food control safety.