Characterization of sulfonamides by flow injection and liquid chromatography-electrospray ionization-mass...

The online photochemical identification of six sulfa compounds, sulfadiazine, sulfamerazine, sulfamethoxazole, sulfaisoxazole (SIX), sulfamoxole (SMX), and sulfamethizole, are investigated using flow injection and liquid chromatography (LC)-electrospray ionization-mass spectrometry (MS). Although the identification of some of the mentioned sulfonamides can be performed by recognizing their respected protonated molecules, more positive MS identification of many of these compounds is possible because they undergo various phototransformation processes to produce different product profiles. The LC separation and online photolysis of a mixture containing the geometric isomers SIX and SMX is such an example. With no photolysis, the MS spectra for SIX and SMX are virtually identical, showing primarily the sodiated molecule at m/z 290 with a relative abundance of 100% in addition to a few small peaks caused by fragments. With photolysis, SMX is found to form multiple major ions from 100 to 241 amu. However, SIX follows a similar fragmentation pathway either with or without photolysis. Online photochemistry should be a viable approach to extend the capabilities of LC instruments interfaced to a single quadrupole MS detector.