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 that 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 that form in weakly alkaline solutions and their chromaticity characteristics were determined. Correlation equations were derived that relate the chromaticity characteristics with the concentrations of rare-earth elements in the range 10-50 mu g per 25 mL of solution. It was found that such chromaticity 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-earth elements with PAR by 35-50 times compared to photometry.