Fernández E, García-Río L, Mejuto J C, Parajó M
Departamento de Química Física, Facultad de Química, Universidade de Santiago, 15782 Santiago, Spain.
Spectrochim Acta A Mol Biomol Spectrosc. 2007 Apr;66(4-5):1102-6. doi: 10.1016/j.saa.2006.05.019. Epub 2006 May 26.
The influence of acidity upon the pyridine-2-azo-p-dimethylaniline (PADA) absorption spectrum has been studied. The obtained results allowed us to calculate the acidity constants of PADA. The spectra resolution method has been used to determinate the constants. The absorption spectrum was decomposed in two sub-bands for the neutral form of the indicator, one for the monoprotonated molecule and another more for the diprotonated structure. The quantitative analysis of relative areas variation with the medium acidity allows us to obtain the equilibrium constants of PADA prolongation. The obtained values are in good agreement with the values reported in the literature.
