Effect of tautomerization on the fast-atom bombardment tandem mass spectra of azo dyes.

The effect of tautomerization on the collision-induced dissociation of negative ions produced from sulfonated azo dyes by fast-atom bombardment (FAB) was studied by analyzing the product ion spectra of several related compounds. The mechanisms by which azo dyes fragment were found to depend on the formation and stability of tautomers. The extent of tautomerization was affected by the number and location of hydroxy groups on the dye, as well as by the FAB matrix. Ions that retained a sodium were often inhibited from forming tautomers and gave different product ions. Substitution of deuterium for hydrogen on the hydroxy groups aided in the identification of ions having more than one possible structure and provided verification of proposed mechanisms. Mechanisms involving ions retaining a sodium were verified by substituting potassium for the sodium.