Acid-base characteristics of naphthazarin and solution equilibria of yttrium(III) chelates

摘要

The spectral absorption and acid-base characteristics of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone,NAZA) in ethanol water medium containing 50 (v/v) ethanol have been studied, and thepKavalues determined. Two equilibria are established in solution atpH2.5–11.5, based on the acid dissociation of the nonionized form of the reagent. The existence of these equilibria is confirmed by potentiometricpHtitrations and the precision of the equilibrium study is improved. The composition, molar absorptivities and stability constants of the chelates ofNAZAwith yttrium(III) have been determined spectrophotometrically under the conditions encountered in this study. The complexation equilibria existing in solution are discussed. The Y(NAZA) monoligand chelate formed atpH5.5 (ɛ=1.15×104lmol−1cm−1at 595 nm) allows the determination of 1.95–8.86 µg ml−1yttrium. Interferences and their elimination have