Simultaneous determination of polyether ionophores, macrolides and lincosamides in hen eggs by liquid chromatography–electrospray ionization tandem mass spectrometry using a simple solvent extraction Original Research Article

A liquid chromatography–electrospray ionization tandem mass spectrometric (LC–ESI-MS/MS) method was developed and validated for the determination of residues of 6 polyether ionophores (lasalocid, maduramicin, monensin, narasin, salinomycin, semduramicin), 3 macrolides (erythromycin, tylosin, clarithromycin) and 1 lincosamide (lincomycin) in eggs. Nigericin was used as qualitative internal standard. Samples were deproteinizated/extracted with acetonitrile without pH adjustments. Aliquots of the extracts were evaporated and reconstituted for injection in the instrument operated in positive multiple reaction monitoring (MRM) mode. The stability of the antibiotics and the intensity of the formed ions were considered in order to select a suitable solvent for the reconstitution of the obtained dry extracts. No clean-up steps were required and matrix effects were controlled by sample dilution, selection of appropriate chromatographic conditions and reduced injection volume. Good within-laboratory reproducibility was obtained, with relative standard deviations (RSDR) from 4.0 (semduramicin at 5 μg kg−1) to 18.6 (erythromycin at 25 μg kg−1) for the ionophores and macrolides. Lincomycin showed the least precise results, with a maximum RSDR of 20.2% at 75 μg kg−1). Satisfactory decision limits (CCα) and detection capabilities (CCβ) were also attained. Method limits of detection (LODs) from 0.04 (salinomycin) to 1.6 μg kg−1 (lincomycin) were achieved. Method limits of quantification (LOQs) were from 0.14 to 5.3 μg kg−1 for the same drugs, respectively. All the LOQs, except that obtained for maduramicin were remarkably below the lowest validation level. The proposed method is suitable for routine application in commercial egg samples.