MATRIX SELECTION FOR THE ANALYSIS OF HYDROPHILIC DYES BY FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

This paper summarizes and compares the negative ion fast atom bombardment (FAB) mass spectra of azo and anthraquinone acid, and direct dyes using thioglycerol, glycerol, diethanolamine and 3-nitrobenzyl alcohol as FAB matrices. The results show thioglycerol to be the best general matrix and the one to try first for mono-, di- and trisulfonated dyes having a molecular weight in the range m/z 300-700. Thioglycerol facilitated the formation of molecular ion species (M-., [M - H]- and [M - Na]-), as well as abundant fragment ions, due to cleavage of azo linkages or carbon-nitrogen bonds adjacent to the azo linkages. Diethanolamine and 3-nitrobenzyl alcohol were effective, but less so, in this molecular-weight range. For sulfonated dyes having a molecular weight of 700-900, glycerol, 3-nitrobenzyl alcohol and thioglycerol occasionally gave good results. However, no matrix investigated consistently afforded abundant sample ions for dyes having a molecular weight above 900.