Determination of antibiotics from soil by pressurized liquid extraction and liquid chromatography–tandem mass spectrometry

A method for the analysis of several macrolide and ionophore antibiotics, as well as tiamulin, from soil was developed using pressurized liquid extraction (PLE), reversed-phase liquid chromatography and atmospheric pressure chemical ionisation (APCI) tandem mass spectrometry (LC–APCI+-MS–MS). The analytes were extracted from soil by PLE in 30 min and the extracts were cleaned up by solid-phase extraction (SPE) on a diol SPE cartridge. Liquid chromatographic (LC) separation of the antibiotics was achieved in 35 min. Recovery experiments were performed using spiked soil and concentrations varying from 1 to 2000 μg/kg. By using a macrolide internal standard the recovery rates for the macrolides erythromycin and roxithromycin ranged from 43 to 94% (RSD 20–23%), for the ionophore salinomycin the recovery rate was 76% (RSD 29%), while the pleuromutilin tiamulin was completely recovered. The limits of detection ranged from 0.2 to 1.6 μg/kg. In soil samples a maximum concentration of 0.7 μg/kg tiamulin was found.