Abstract

A composite adsorbent hydrogel bead was developed by coating zinc oxide and magnetite nanoparticles on a molecularly imprinted polymer embedded in alginate (ZnO/Fe<inf>3</inf>O<inf>4</inf>@SiO<inf>2</inf>-NH<inf>2</inf>/MIP/alginate). The adsorbent was fabricated and applied to extract and enrich trace sulfonamides in milk for determination by high-performance liquid chromatography (HPLC). Zinc oxide improved the adsorption efficiency of sulfonamides via hydrogen bonding. The magnetite nanoparticles enabled the simple and rapid separation of the adsorbent from the sample solution after extraction and desorption. The molecularly imprinted polymer increased selectivity toward the target analytes. Under optimum conditions, the developed method provided linearity from 0.20 to 1000 μg L⁻¹ for sulfamethazine (SMT) and from 0.10 to 1000 μg L⁻¹ for sulfadimethoxine (SDM) with R² greater than 0.995. The limits of detection (LODs) were 0.06 and 0.03 μg L⁻¹ for SMT and SDM respectively. The developed method was utilized to extract the two sulfonamides from milk samples, and a trace SDM concentration of 0.65 μg L⁻¹ was found in one sample. Relative recoveries were achieved in the range of 87.0 to 98.5% with RSDs lower than 6%. The advantages of the proposed adsorbent are simplicity, good selectivity, high extraction efficiency and accuracy.