Simultaneous determination of three sulfonamide residues in modified milk by ultra performance liquid chromatography-tandem mass spectrometry

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/ MS) method for the residue determination of sulfadiazine, sulfamerazine and sulfamethazine in modified milk was established. The modified milk samples were extracted and their protein precipitated with water (containing 1% (v/v) acetic acid) and methanol. Then they were purified with an HLB solid phase extraction cartridge. The separation was performed on an ACQUITY UPLC HSS T3 column (100 mm x 2.1 mm, 1.8 µm) with a gradient system of water (containing 0.1% (v/v) formic acid) and acetonitrile as mobile phases at a flow rate of 0.3 mL/min, and detected by the MS in ESI+ mode. Standard curves were drawn by using matrix standard addition method, and the external standard method was used for quantitative analysis. The limits of quantification were 1 µg/kg. The calibration curves for the three sulfa drugs were linear in the mass concentration range of 1-100 µg/L with R2 ≥ 0.998. The recoveries at the levels of 1, 2, 10 µg/kg fortified samples ranged from 76.5% to 101.9% with the relative standard deviations of 1.2%-12.4%. The method is simple, rapid, accurate, and its performance can meet the requirements of the domestic and international legislations. It is suitable for the detection of sulfonamide residues in modified milk.