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 phthalocyanine dyes has shown the presence of both anionic and radical anionic species. Substituent groups such as sulphonates and linker arms, as are present in commercial dyes such as Remazol TB and Everzol TB, are found to be labile 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 is 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 molecules and, in addition, SO2 losses are observed as for EI-MS. Hydrolysed commercial azo dyes such as Remazol Black B (I) and Remazol Red RB (III) showed both singly and doubly charged molecular anion species as well as sodium salts using negative ion ESI-MS, but did not desulphonate like the copper phthalocyanine dyes. The application of ESI-MSn revealed fragmentation of the dye 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 therefore be used for the characterisation of such dyes by exploiting these fragmentation processes, and some structural information can be obtained for the dyes whose structures are not in the public domain. Copyright (C) 2001 John Wiley & Sons, Ltd.