Spectrophotometric study and analytical applications of the complexes of copper(II) and zinc(II) with some sulphonated azo dyes

Abstract

The complexing ability of some water-soluble azo dyes towards copper(II) and zinc(II) were studied in 0.1 M sodium perchlorate and perchloric acid solutions, at 25.0 °C. Solutions with C_M≫C_L, where C_M is the concentration of metal and C_L the concentration of ligand, and C_L≫C_M(C_M up to 10^–3M, C_L up to 2 × 10^–4M and pH up to the precipitation of metal hydroxides) were investigated spectrophotometrically.

The ligands T-azo-C and 3,6-disulpho-TAN are able to complex both copper(II) and zinc(II), but amaranth only copper(II). Besides the usual complexes having 1:1 metal to ligand molar ratios, a 2:1 complex has been detected in the system copper(II)- T-azo-C. The results are compared with others obtained previously. The copper(II) complexes are much more stable than those of zinc(II) and those of many other metal ions. Therefore, a method is proposed for the spectrophotometric determination of copper(II), which is almost free from interferences.