Colorimetric investigation of the reaction between p-phenylendiamine and meta-substituted derivatives of benzene on a model support.

The aim of this work was the employment of colorimetric techniques in the analysis of the color formed, on a proteic substrate, by the reaction between p-phenylendiamine and some meta-substituted benzene derivatives in the presence of hydrogen peroxide and in media at different pH values. In particular we investigated the chromatic variations that take place on the substrate in dependence on different reaction conditions. The obtained results show that for each couple of reagents the colorimetric data, namely the reflectance of the formed color, change considerably with the pH of the reaction medium and demonstrate how this parameter can be considered a good descriptor of the composition of the formed pigment.