Complexes of Eriochrome Black T with Some Metals

Abstract

Spectroscopic studies were made on the complex formation of Eriochrome Black T with Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Mg²⁺, Ba²⁺, Sr²⁺, and Cr³⁺. The complex formation of these metallic ions is affected to a great extent by the pH and the measurements were carried out at pH 3.4, 5.9, 8.2, 10.0, and 13.5. Cu, Co, and Ni ions were found to form complex salts at any pH but Zn, Cd, and Mg ions formed complex salts only in the alkaline range and not in the acid range. Ba and Sr ions failed to form complex salts in the concentration of 3×10^-4 mole used in the present experiments. Cr ion did not form the complex in the alkaline range and formed a substance on the acid range but whether this is a complex salt or a simple sulfonate remains unclarified, though the absorption curve of the product was different from that of Eriochrome Black T. The composition of such complex salts were found to be in 1:4 molar ratio of Cu and Co ion with Eriochrome Black T, 1:2 molar ratio of Ni, Zn, and Cd ions with T, and 1:1 molar ratio of Mg with T, in a solution of pH 10.