Reaction contrast of some metal complexing with alizarin in dimethyl formation solutions

The absorption spectra of alizarin and its complexes with Cu, Co, Ni, La and Th in dimethyl formamide solutions at different pH values are studied. The spectra of alizarin anion forms are characterized by the presence of a wide asymmetrical band, conditioning the absorption in the range of 500-700 nm. The reaction contrast of complex formation, which is determined as the difference of the absorption band maxima of alizarin neutral molecule and the complex molecule has the following values: Cu - 120, C0 - 120, Ni - 160 at pH 9.5; Th - 120 at pH 5.0; La -140 at pH 7.0. The application of non-aqueous medium permits to achieve a great contrast of photometric reaction, at that, the metal hydrolysis is avoided