Chemometric Models For Quantitative Analysis of Tautomeric Schiff Bases and Azo Dyes

The main problem in the quantitative analysis of tautomeric compounds is that the individual tautomers cannot be physically separated. As a result, quantitative analysis, which requires calibration, is in general impossible. This is a general problem for molecular spectroscopy and gives rise to many chemometric approaches for the treatment of existing spectral data, all of them developed to overcome the lack of individual spectral data for the pure, individual, tautomers. The reliability of these approaches depends strongly on the mathematical and spectral approximations used. Therefore the aim of the current review is to describe and compare critically the most frequently used methods for the processing of spectral data of tautomeric systems. Such data are usually obtained by absorption spectroscopy (UV-Vis, Fl and sometimes IR) and NMR in solution, but, in addition, some attempts for quantitative analysis in gas phase by mass spectrometry are considered.