Abstract: A poly(methacrylic acid-co-ethylene dimethacrylate) polymer (poly(MAA-co-EDMA)) was prepared via in-situ polymerization on the outside surface of vial glass insert and used as stir rod sorptive extraction (SRSE) coating. The extraction performance of the polymer coating toward four sulfonamides (SAs) was investigated. The effects of several parameters to SRSE, such as the pH value, inorganic salt and organic phase concentrations of the sample matrix, were investigated. It demonstrated that the sulfonamides were captured on the poly(MAA-co-EDMA) coating mainly through cation-exchange and hydrophobic interactions. A novel approach is presented for the determination of four sulfonamide antibacterial residues in milk samples by coupling SRSE to liquid chromatography and electrospray ionization mass spectrometry (SRSE/LC-ESI-MS). In this method, the detection limits (S/N=3) of 0.11~0.52 μg/L and quantification limits (S/N=10) of 0.35~1.72 μg/L were obtained. The method showed good linearity in the range of 1~500 μg/L. Good method reproducibility was also found by intra- and inter-day precisions, yielding the relative standard deviations (RSDs) less than 11.3%. The results demonstrated that the proposed method is simple, sensitive, low cost and suitable for the determination of sulfonamides in milk samples.

Key words: milk, poly(methacrylic acid-co-ethylene dimethacrylate) (poly(MAA-co-EDMA)), sulfonamides (SAs), stir rod sorptive extraction (SRSE)