Development and validation of a multi-residue liquid chromatography-tandem mass spectrometry confirmatory method for eleven coccidiostats in eggs

A confirmatory method for the determination of residues of eleven coccidiostats including ionophore antibiotics: lasalocid, maduramycin, monensin, narasin, salinomycin, semduramycin and chemical coccidiostats: decoquinate, diclazuril, halofuginone, nicarbazin and robenidine in poultry eggs was developed and validated. The sample was extracted with acetonitrile, defatted with hexane and cleaned-up on a silica SPE cartridge. The analytes were identified and quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The method performance characteristics required by Commission Decision 2002/657/EC were estimated adopting a more flexible and simple validation design. In this alternative approach the experimental study focuses on a larger dynamic range with progressively increasing validation levels. Each of them presents equal concentrations of all the analytes. On the contrary the classical Decision plan investigates a restricted concentration range necessarily different for each analyte being determined by the individual permitted limit (0.5-1.5 times the permitted limit). As a consequence each validation level involves the simultaneous fortification with complex mixtures containing different concentrations of each analyte. Adopting this alternative strategy the validation of several substances with significantly different permitted limits is considerably simplified and a deeper knowledge of the method is achieved. The results proved that the method enables the confirmation of regulated coccidiostats in eggs at the levels required in the official control of residues (CCα in the range of 2.2-174 μg kg(-1), depending on the coccidiostat). The repeatability (CV(r) in the range of 1.1-19%) and within-laboratory reproducibility (CV(Rw) in the range of 1.8-30%) are also acceptable. The procedure was successfully verified in the proficiency test and implemented in the national residue control plan.