ABSTRACT
To determine the residue of 14 sulfonamides in milk, a high performance liquid chromatography-tandem mass spectrometry ( HPLC-MS/MS ) method with on-line soild phase extraction ( SPE ) in cation exchange mode was established. 5 g of milk was extracted with 15 mL acetonitrile. Then the extraction was evaporated by 50 ℃ nitrogen and dissolved by 1. 00 mL 0. 2% formic acid. The dissolution was enriched and purified by MS/MS cation exchange on-line SPE column on a double ternary liquid chromatography, and eluted by the mixed solution of 2% ammonia methanol and 0. 2% formic acid (50:50, V/V). The compounds were separated by an octadecyl silica bonded column and determined by the tandem mass spectrometry. The results showed that the linearity of 14 sulfonamides was good in the range of 0 . 1–10 μg/kg ( r≥0 . 9995 ) . The LOD of the method was 0. 05 μg/kg, while the LOQ was 0. 1 μg/kg. The recoveries of the 14 sulfonamides were in the range of 60 %-90 %, while the inter-batch and intra-batch RSDs were all lower than 10%. The method was proved to be more convenient, economical and stable than the traditional SPE column method.