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Spectrophotometric study of ternary complex forming systems of dysprosium(III) and holmium(III) with pyrogallol red in presence of cetylpyridinium bromide for microdetermination

A.S.Dhepe, A.B.Zade

With the growing applications of lanthanoids in science and technology, the study of coordination compounds of these elements has received great attention. A large number of chromogenic reagents form soluble colored complexes with rare earths. Pyrogallol red has been reported to form blue colored complexes with rare earths and has been used for microdetermination of thesemetal ions. The addition of cationic surfactant, cetylpyridinium bromide (CPB), sensitizes the color reactions of Dy(III) and Ho(III) with pyragallol red. The formation of awater soluble ternary complex of stoichiometric ratio 1:1:4 (e.g. Dy(III)-R-CPB) is responsible for the observed enhancement in molar absorptivity at shifted wavelength, when a surfactant is present. The ternary complexes exhibit absorptionmaxima at 584nmwith a bathochromic shift of about 35nm. BeerÂ’s Law obeyed between 0.5 to 6.30ppm. Effective photometric range and molar absorptivity of these ternary complexes have been calculated. The optimum reaction conditions and other analytical parameters were evaluated. The effects of interfering ions on determination of both the metal ions were studied. Asimple, rapid and highly sensitive method for the determination of Dy(III) and Ho(III) with pyragallol red is proposed.