UV–visible-DAD and 1H-NMR spectroscopy data fusion for studying the photodegradation process of azo-dyes using MCR-ALS

The photodegradation process of three azo-dyes – Acid Orange 61, Acid Red 97 and Acid Brown 425 – was monitored simultaneously by ultraviolet–visible spectroscopy with diode array detector (UV–vis-DAD) and 1H-nuclear magnetic resonance (1H-NMR). Multivariate curve resolution-alternating least squares (MCR-ALS) was applied to obtain the concentration and spectral profile of the chemical compounds involved in the process. The analysis of the H-NMR data suggests there are more intermediate compounds than those obtained with the UV–vis-DAD data. The fusion of UV–vis-DAD and the 1H-NMR signal before the multivariate analysis provides better results than when only one of the two detector signals was used. It was concluded that three degradation products were present in the medium when the three azo-dyes had practically degraded. This study is the first application of UV–vis-DAD and 1H-NMR spectroscopy data fusion in this field and illustrates its potential as a quick method for evaluating the evolution of the azo-dye photodegradation process.