Matrix solid-phase dispersion method for the determination of macrolide antibiotics in sheep’s milk

A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed for the simultaneous cleaning-up and quantitative extraction of macrolide antibiotics (erythromycin, oleandomycin, roxithromycin, josamycin, spiramycin, tylosin and ivermectin) from manchega sheep milk samples. Solid support, defatting and elution solvents were evaluated thoroughly to find the optimal MSPD conditions. The best results were obtained using washed sea sand as dispersant sorbent, hexane as defatting agent and a mixture methanol/ethyl actetate (50:50) as elution solvent. Quantitative analyses were performed by liquid chromatography (LC) with diode-array ultraviolet detector (DAD-UV). The chromatographic separation was performed on a Hypersil ODS column (5 μm, 250 × 4.6) with a gradient system of KH2PO4 25 mM (pH = 7) and acetonitrile as the mobile phase at the flow rate of 1.2–1.5 mL min−1 and 60 °C of temperature. Under these conditions antibiotics recoveries were between 74% and 97% and relative standard deviations ranging from 1.6% to 9.0%. The analytical figures of merit of the optimised method have been performed using spiked milk samples at two different concentration levels (96.5 and 482.6 μg kg−1). The proposed method has been successfully applied to the determination of macrolides on milk samples.