Photometric and chromaticity characteristics of 4-(2-pyridylazo)resorcinates of rare-earth elements

The best conditions for the complexation of 4-(2-pyridylazo)resorcinol (PAR ) with La, Nd, Sm, Tb, Dy, Ho, Er, and Yb ions were found. It was shown tha t two types of complexes differing in the ionic state of the para-hydroxyl group in PAR can form, depending on pH. Molar absorptivities of complexes t hat form in weakly alkaline solutions and their chromaticity characteristic s were determined. Correlation equations were derived that relate the chrom aticity characteristics with the concentrations of rare-earth elements in t he range 10-50 mu g per 25 mL of solution. It was found that such chromatic ity characteristics as chromaticity coordinates, yellowness, and color tint most strongly depend on the concentration of rare-earth elements. The use of these characteristics can improve the sensitivity of determining rare-ea rth elements with PAR by 35-50 times compared to photometry.