Enhanced analysis of sulfonated azo dyes using liquid chromatography/thermospray mass spectrometry

Modifications to a thermospray vaporizer probe and ion source have been made that enhance ion evaporation resulting in increased sample ion current. These modifications include restricting the thermospray vaporizer exit orifice and the addition of a needle-tip repeller electrode to the thermospray ion source. The interaction and effect of probe-tip size, repeller voltage, and flow rate on sulfonated azo dye detection are reported. An increase in signal response for sulfonated azo dyes was observed. An efficient chromatographic separation procedure for sulfonated azo dyes, which is compatible with thermospray mass spectrometric detection, is also presented. Five disulfonated azo dyes were separated and detected by using selected ion monitoring. Mass spectra of disulfonated dyes show a number of molecular ions and adduct ions that provide unequivocal molecular weight information.