Ultra Trace Copper Determination by Catalytic-Adsorptive Stripping Voltammetry Using an Alizarin Red S modified Graphite Electrode

A sensitive stripping voltammetric procedure for ultra trace copper determination is reported in this paper. A Catalytic-Adsorptive Stripping Voltammetric (CASV) mechanism is proposed to interpret the amplified sensitivity. The procedure is based on the interfacial preconcentration of copper(II) on an alizarin red S (ARS) modified graphite electrode through a surface coordination effect. The formed ultra trace surface copper complex, i.e. Cu(II)-ARS, can be reduced to Cu(I)-ARS at the preconcentration potential range of -0.35 V to -0.5 V (vs. SCE). Cu(I)-ARS displays a catalytic activity towards proton reduction to form H2, which is then stored in the space between the Cu-ARS layer and the electrode surface. This catalysis process could produce a considerable amount of H2, which is then catalytically oxidized back to protons during the stripping process thus producing a large stripping peak current. This peak current is proportional to the quantity of pre-concentrated copper on the electrode surface. The application of the procedure in ultra-purified water samples demonstrates that it is possible to determine Cu(II) at a level as low as 1.7×10-13 mol/L in real samples with a recovery of 103%, a standard deviation (triplicate measurements) of 4.7%, and a confidence level of 95%.