IONOPHORE/IONOMER FILMS ON GLASSY-CARBON ELECTRODES FOR ACCUMULATION VOLTAMMETRY - INVESTIGATION OF A LEAD(II) IONOPHORE

The use of ionophores in voltammetry with modified glassy carbon (GC) electrodes is described. A lead(II) ionophore, methylenebis(N,N-diisobutyldithiocarbamate) was dissolved in a solution containing 0.1% Nafion, and this mixture was applied to the GC electrode. Solvent evaporation gave the GC-Nafion-ionophore modified electrode. The composition of the film coating was studied with respect to the mass of Nafion and amount of ionophore; the best composition was found to comprise 20 mu g Nafion and 10 nmol ionophore. Accumulation of lead(II) from 0.1 mol l(-1) acetate buffer (pH 4) followed by voltammetry gave a quasi-reversible reduction peak at about -0.85 V (versus SCE), with half-wave potential, E(1/2) = -0.57 V and peak-to-peak separation, Delta E(p) = 0.51 V. This reduction potential is 0.25 V more negative than the reduction potential in the absence of the ionophore where E(1/2) = -0.48 V and Delta E(p) = 0.14 V. Accumulation of 1 X 10(-5) mol l(-1) Iead(II) for 60 s at the GC-Nafion-ionophore modified electrode gave a lead(II) surface coverage of 1.3 X 10(-9) mol cm(-2). The film exhibited thin-film voltammetric behaviour. Detection of lead(II) down to 1 X 10(-7) mol l(-1) with a 600 s accumulation time was possible. The effects of preconcentration time and solution composition were evaluated. The accumulation process appears to consist of two steps: ion exchange followed by complexation in the film.