Voltammetric determination of the metal complexing capacity in model solutions

Abstract

Determination of the metal complexing capacity (MCC) has been carried out in model solutions of 0.55 mol l −1 NaCl using anodic stripping voltammetry by two different working electrode assemblies: Static Mercury Drop Electrode (SMDE) and Thin Mercury Film Glassy Carbon Disk Electrode (TMFGCDE). The separation of the reduction potentials of free ions and labile copper(II) complexes vs. the inert one (Cu-EDTA) at SMDE is achieved by the addition of l mg l −1 of Triton-X-100. The appropriate deposition potential for copper complexing capacity (CuCC) determination has been established from the pseudopolarograms. TMFGCDE yields better separation of those reduction processes, when thinner film of mercury is applied without addition of surfactants. The determination limit of 10 −7 mol l −1 CuCC with SMDE was found. The results obtained with model solution show lower CuCC values than expected. This can be attributed to the partial dissociation of an inert Cu-EDTA complex during the transport through a rather thick diffusion layer formed with SMDE devices. The determination limit of 10 −8 mol l −1 MCC (Cd, Pb, Cu) with TMFGCDE was found. The MCC values obtained in the model solution were higher than expected due to the cell's ‘blank capacity’.