Adsorptive stripping voltammetric behaviour of copper(II) at a hanging mercury drop electrode in the presence of excess of imidazole

Abstract

In the presence of excess of imidazole (1.0 × 10^–3 mol dm^–3), copper(II), at pH 8.5, adsorbs at a hanging mercury drop electrode to give two adsorptive stripping voltammetric peaks at –0.36 and –0.46 V. The peak at –0.36 V is only present at accumulation potentials more negative than –0.05 V versus Ag—AgCl: it increases in height as the accumulation potential becomes more negative up to and beyond –0.6 V, the voltammetric sweep being started at –0.20 V. This peak appears to be due to the adsorption of polymeric [Cu^II(lm)₂] or its reduced copper(I) form. The peak at –0.46 V is only present at high imidazole concentrations (>5.0 × 10^–4 mol dm^–3): the accumulation is uniform from 0.0 to –0.36 V but is negligible at potentials more negative than –0.46 V. This peak appears to be due to adsorption of [Cu(lm)₄]²⁺. On cycling between 0.0 and –0.6 V this latter complex is converted into the polymeric complex and only the peak at –0.36 V remains. Copper(II) can be determined by using the peak at –0.46 V after accumulation at 0.0 V, or at –0.36 V after accumulation at –0.6 V. The latter method is more sensitive: the detection limit is about 2.0 × 10^–9 mol dm^–3 after accumulation for 3 min.