Polyether ionophores residues in Minas Frescal cheese by UHPLC-MS/MS

An analytical method was developed and validated for the determination of three polyether ionophores (monensin, lasalocid, and salinomycin) in 60 samples of Brazilian Minas Frescal cheese by UHPLC-MS/MS. Linearity ranged from 1 to 8 μg kg^-1 for monensin and salinomycin, and from 0.50 to 4 μg kg^-1 for lasalocid. Limits of detection and quantitation were 0.50 μg kg^-1 and 1 μg kg^-1, respectively, for both monensin and salinomycin, and 0.25 μg kg^-1 and 0.50 μg kg^-1, respectively, for lasalocid. Recoveries were between 69% and 84% with coefficients of variation up to 16.28% for repeatability and 13.79% for intermediate precision. A total of 60 samples of Minas Frescal cheese were analysed and only monensin residues were found. Monensin was detected in 55% of the samples and quantified in 5 of them at mean levels varying from 1.00 to 1.73 μg kg^-1. The proposed method demonstrated the suitability for monitoring these substances in cheese.