Abstract
Molecular weights of dyes and intermediates containing one to four sulphonic acid groups were determined by negative-ion electrospray mass spectrometry. Mass spectra of monosulphonated dyes exhibit an important ion that arises from the loss of a cation from a sulphonic group. Sulphonated dyes form molecular ions with different charges either by subsequent loss of protons, i.e. [M–xH]x−, or from adducts with sodium ions, i.e. [M–(x+y)H+yNa]x−. The maximum values of x or (x+y) are equal to the total number of sulphonic and carboxylic acid groups, where x is higher than y. This method is applicable to various types of poly-sulphonated dyes, including anthraquinone, azo or metal complex dyes. The HPLC/MS technique can be used for the analysis of mixtures of dyes and intermediates also.
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