STRUCTURAL-ANALYSIS OF SULFONATED MONOAZO DYESTUFF INTERMEDIATES BY ELECTROSPRAY TANDEM MASS-SPECTROMETRY AND MATRIX-ASSISTED-LASER-DESORPTION IONIZATION POST-SOURCE DECAY MASS-SPECTROMETRY/

Sulfonated azo molecules containing hydroxy groups ortho- or para- to the azo linkage exhibit azo/hydrazone tautomerism, which affects their coloristic properties and also the fragmentation pathways observed in tandem mass spectrometry. Electrospray tandem MS and matrix-assisted laser desorption/ionization post-source decay are used in this work to study the fragmentation mechanisms of such molecules, The two techniq ues show closely matching product ion distributions, the predominant f ragmentation pathways depending on the extent of tautomerism in each m olecule. Evidence of tautomerism is afforded by comparing the product ions of the hydroxyazo molecules with their methoxyazo analogues where tautomerism is not possible. Keto-tautomers show cleavage of the sing le N-N bond whereas the azo forms dissociate via the azo C-N bonds, fo llowed in both cases by neutral losses of SO2, In addition, the simple introduction of a nitro group on a naphthyl group in an azo dye is sh own to have a marked influence on its observed fragmentation. (C) 1998 John Wiley & Sons, Ltd.