Hydrolysis of Sulfonated Azo Dyes

Sulfonated azo dyes (reactive dyes) are widely used in the textile industry. Due to the simultaneous hydrolysis in the dyeing process, 15-60 % of the reactive dyes reach the waste water system. In addition, their use strongly increases with the colouring of natural fibres, and so a total of 60 % of all dyes emitted to the waste water are reactive materials. 

Whereas non-azo dyes are almost resistant to bacterial decolorization, azo dyes can be decolorized by bacteria under anaerobic conditions to form aromatic amines which show both toxic and carcinogenic potential [18]. Further aerobic mineralization can therefore only be initiated by additional chemical oxidation, for example, by partial ozonation, as reported by Krull et al. [19]. 

The most commonly used waste water treatment procedures are not sufficient to remove these dyes. Considerable efforts are therefore made to improve the efficiency of the physical, chemical and biological treatment procedures. However, in order to achieve this aim, reliable analytical methods for the identification and quantification of the azo dyes and their by- and degradation products are required. Since most of the dyes are non-volatile and thermally labile, LC-NMR and LC-MS are the methods of choice. 

The MS data (negative ESI mode) provide information on the molecular mass of the partially deuterated molecules due to the use of D20 in the eluent. The MS experiments, however, were carried out via flow injection analysis (FIA-MS) on peaks that were cut from a separate chromatographic run in which H20 was used instead of D20. In this way, in addition to the fragmentation, the 

Furthermore, components could already be detected in this mixture (peaks 2 and 3) which are assumed to be degradation products formed by the reductive cleavage of the azo linkage. 

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