Surface Complexation of Copper(II) with Alizarin Red S Adsorbed on a Graphite Electrode and Its Possible Application in Electroanalysis

Abstract

Alizarin red S (ARS) has been used previously as a spectrophotometric reagent for several metals. It has been also employed as an electrode modifier agent for voltammetric analysis. With the purpose of studying the electrochemistry of the adsorbed ARS ligand and the surface ARS-copper(II) complex, on the pyrolytic graphite electrode, cyclic voltammetric experiments were carried out in open and closed circuits. The results indicate that ARS is strongly and irreversibly adsorbed on the electrode surface. This adsorption process was employed to immobilize, by complexation, copper ions from the solution, and for a possible application of the ARS modified electrode in trace copper electroanalysis are explored in this article. The optimization for trace copper determination in aqueous solution was accomplished by anodic stripping voltammetric technique (differential pulse mode); the preconcentration potential was –0.40 V; pH was 5.3 and accumulation time was 2 minutes. Under these conditions, the detection limit was 1.7×10–8 mol L–1, and a linear range from 1.0×10–7 to 4.0×10–6 mol L–1.