Study of the mass spectrometric behaviour of phthalocyanine and azo dyes using electrospray ionisation and matrix-assisted laser desorption/ionisation

The negative ion MALDI-MS and ESI-MS behaviour of sulphonated. copper phtha locyanine dyes has shown the presence of both anionic and radical anionic s pecies. Substituent groups such as sulphonates and linker arms, as are pres ent in commercial dyes such as Remazol TB and Everzol TB, are found to be l abile and the dyes undergo in-source fragmentation in both MALDI-MS and ESI -MS. Ions corresponding to sodium salts can be formed. It appears that Cu i s firmly bound in the phthalocyanine structure, unlike the corresponding Mg and Al chelates that can undergo demetallation. The application of ESI-MS' confirmed that these labile groups can be fragmented from the dye molecule s and, in addition, SO2 losses are observed as for EI-MS. Hydrolysed commer cial azo dyes such as Remazol Black B (I) and Remazol Red RB (III) showed b oth singly and doubly charged molecular anion species as well as sodium sal ts using negative ion ESI-MS, but did not desulphonate like the copper phth alocyanine dyes. The application of ESI-MSn revealed fragmentation of the d ye molecules with the loss of entities such as HOCH2CH2SO2C6H4N2 (for both dyes) and SO2 (for Remazol Black B). MALDI-MS, ESI-MS and ESI-MSn can there fore be used for the characterisation of such dyes by exploiting these frag mentation processes, and some structural information can be obtained for th e dyes whose structures are not in the public domain. Copyright (C) 2001 Jo hn Wiley & Sons, Ltd.