Anodic stripping voltammetry in highly-resistive media by electrodes supported on ion-exchange membranes

An electroanalytical device is described that is suitable for trace metal analyses by anodic stripping voltammetry (ASV) in highly-resistive media in the absence of supporting electrolytes. It consists of a thin mercury film electrodeposited at the glassy carbon-ion-exchange membrane interface obtained by clamping a glassy carbon ring to one surface of a perfluorinated ion-exchange membrane (cationic, Nafion 117, or anionic, Tosflex IE SA48). The inner surface of the membrane is in contact with an electrolyte solution (0.01 M HClO4), containing the counter and reference electrodes. The ion-exchange membrane replaces a conventional supporting electrolyte dissolved in the analyte sample and can be regarded as a solid polymer electrolyte (SPE) confined to the near neighborhood of the working electrode. This device has been used to perform differential pulse anodic stripping voltammetric (DPASV) analyses of electrolyte-free aqueous synthetic samples containing copper and lead ions. Better results are found at glassy carbon-supported mercury electrodes facing anionic Tosflex membranes, since similar devices assembled with cationic Nafion membranes experience a memory effect associated with blockage of metal ions, due to cation-exchange processes that occur during the stripping redissolution step, even though these processes are able, at the same time, to lead to an increase of DPASV peaks due to metal ion accumulation near the electrode surface. Approximate detection limits of 3.5 x 10(-10) M (0.02 ppb) for Cu2+ and 3 x 10(-10) M (0.05 ppb) for Pb2+ are estimated at Tosflex-equipped devices for a signal-to-noise ratio of 3. Possible modifications aimed at improving the performance of such a device are discussed.