DETERMINATION OF SULFONAMIDES BY LIQUID-CHROMATOGRAPHY, ULTRAVIOLET DIODE-ARRAY DETECTION AND ION-SPRAY TANDEM MASS-SPECTROMETRY WITH APPLICATION TO CULTURED SALMON FLESH

Ion-spray mass spectrometry was investigated for the analysis of 21 antibacterial sulfonamide drugs. All of the sulfonamides analyzed gave positive ion mass spectra with abundant protonated molecules and no fragmentation. Tandem mass spectrometry (MS-MS) using collision-induced dissociation provided structural information, allowing the identification of common fragmentation pathways and the differentiation of isomeric and isobaric sulfonamides. A reversed-phase high-performance liquid chromatographic method was developed, using gradient elution and ultraviolet diode-array detection (DAD), enabling the separation of 16 of the sulfonamides. Combined liquid chromatography (LC) MS was accomplished using the ion-spray interface. Analyses of a mixture of sulfonamide standards were performed with gradient elution and the mass spectrometer configured for full-scan acquisition, selected-ion monitoring. or selected-reaction monitoring. Procedures for the analysis of sulfadimethoxine (SDM), a representative sulfonamide used in the aquaculture industry, are described. The presence of SDM in cultured salmon flesh was confirmed at levels as low as 25 ng/g by a combination of LC-DAD and LC-MS-MS.