Abstract: A method for the determination of five polyether ionophores in urban sewage sludge has been developed. The extraction of compounds was performed by pressurised liquid extraction using acetone, while florisil was used for in-cell clean-up to minimise the matrix effect in the sludge extracts. An amide polar-embedded reversed-phase column was used for the chromatographic separation with a rapid-resolution liquid chromatograph coupled to a tandem mass spectrometer. Moreover, several clean-up strategies such as in-cell and on-cell clean-up and solid-phase extraction clean-up, among others, were tested and their results are discussed in the present paper. Recoveries (10 and 250μg/kg in dry weight (d.w.), n =6) were close to 90%, repeatability and reproducibility (%RSD, 10 and 250μg/kg (d.w.), n =6) were less than 10% and12%, respectively. Limits of detection (LODs) and limits of quantification (LOQs) ranged between 0.5 and 1μg/kg (d.w.) and between 1 and 5μg/kg (d.w.), respectively. The method was applied to samples collected in five sewage treatment plants in Catalonia. Monensin and narasin were determined in some sludge samples at concentrations from