Abstract: A novel magnetic surface molecularly imprinted adsorbent is described. Fe₃O₄@SiO₂, tilmicosin, and methacrylic acid were chosen as the support substrate, template molecule, and functional monomer, respectively. 3-Methacryloxypropyltrimethoxysilane was chemically bonded onto the surface of Fe₃O₄@SiO₂ via a silanization reaction and used as the crosslinking agent in the subsequent reaction. The obtained magnetic surface molecularly imprinted polymer (MS-MIP) showed high selectivity and high enrichment capacity towards macrolide antibiotics (MACs), as indicated by the 212-, 275-, 675-, and 293-fold enrichment factors for spiramycin, josamycin, tilmicosin, and tylosin tartrate, separately. Because of the marked cavities onto the surface of the MS-MIP, the time required to reach adsorption equilibrium (30 min) was shorter than that for traditional MIP sorbents. Moreover, the adsorbent could be reused at least 6 times. Finally, the MS-MIP was used in combination with high performance liquid chromatography-ultraviolet detection (HPLC-UV) for the extraction and enrichment of four MACs in milk powder samples. The limits of detection (LODs) and limits of quantitation (LOQs) for the four MACs were in the range of 0.58-1.36 μg/kg and 1.92-4.55 μg/kg, respectively. The interday (n=5) and intraday (n=3) recoveries were in the range of 83.2%-123.0% at three spiked levels of 80, 200, and 500 μg/kg, under all the experimental conditions employed, and the relative standard deviations were less than 12.2%.

Key words: high performance liquid chromatography (HPLC), macrolide antibiotics, magnetic solid phase extraction, milk powder, surface molecularly imprinted polymer