Surface complexation of copper(II) with alizarin red S adsorbed on a graphite electrode and its possible application in electroanalysis

Alizarin red S (ARS) has been used previously as a spectrophotometric reage nt for several metals. It has been also employed as an electrode modifier a gent for voltammetric analysis. With the purpose of studying the electroche mistry of the adsorbed ARS ligand and the surface ARS-copper(II) complex, o n the pyrolytic graphite electrode, cyclic voltammetric experiments were ca rried out in open and closed circuits. The results indicate that ARS is str ongly and irreversibly adsorbed on the electrode surface. This adsorption p rocess was employed to immobilize, by complexation, copper ions from the so lution, and for a possible application of the ARS modified electrode in tra ce copper electroanalysis are explored in this article. The optimization fo r trace copper determination in aqueous solution was accomplished by anodic stripping voltammetric technique (differential pulse mode); the preconcent ration potential was -0.40 V; pH was 5.3 and accumulation time was 2 minute s. Under these conditions, the detection limit was 1.7 x 10(-8) mol L-1, an d a linear range from 1.0 x 10(-7) to 4.0 x 10(-6) mol L-1.