Magnetic solid phase extraction followed by high-performance liquid chromatography for the determination of sulphonamides in milk samples

A simple and effective method based on magnetic solid-phase extraction combined with high performance liquid chromatography was used for the determination of nine sulphonamides in milk samples. The extraction and cleanup via silica-based magnetic adsorbent dispersion in milk samples followed by the magnetic isolation and desorption of the analytes using NaOH–methanol. Three different magnetic phenyl silica adsorbents were synthesized by varying the molar ratio of phenyltrimethylsilane and tetramethylorthosilicate; these adsorbents were evaluated for sulphonamides retention in terms of their pH and degree of hydrophobicity. The optimal conditions were a pH of 6.0 and a magnetic:sorbent ratio of 2:1. Under optimal conditions, limits of detection ranging from 7 to 14 μg L−1 were obtained. The method was validated according with the European Commision Decision 2002/657/EC. The proposed method was applied to analyse sulphonamides in 27 milk samples of different brands. Thirteen samples tested were positive for the presence of sulphonamides.