Competitive Spectrophotometric Study of Copper, Zinc and Cadmium With 18C6 Using TAR as a Colorimetric Complexing Agent in Methanol

Abstract

<em>A Competitive spectrophotometric method has been used for the study of complexation between Cu²⁺, Zn²⁺ and Cd²⁺ (M) and 18-crown-6(18C6, B) in methanol using 4-(2-thiazolylazo) resorcinol (TAR, HL) as the colorimetric complexant. Absorption spectra of the species in the M-TAR-18 C6 system at a various concentrations of 18C6 showed no formation of ternary complex, MLB, and the stoichiometry of the resulting complexes was found to be 1:1 under the condition used. The formation constants of both types of complexes (ML and MB) were determined using the conditional formation constant of ML complexes at constant acidity in the absence (K</em>_ML'<em>) and presence (K</em>_M''L'<em>) of 18C6. The results showed that the K_MB values increased in the order of Cu²⁺<Zn²⁺<Cd²⁺, the K_MB values were comparable with those reported previously.</em>