Copper(II) interference by complexation in cathodic stripping voltammetry: accumulation of sulfachloropyridazine as its copper(I) complex to increase the sensitivity of its direct determination at a hanging mercury drop electrode and to overcome interference from copper(II)

Abstract

Sulfachloropyridazine adsorbs on a hanging mercury drop electrode and can be determined by direct reduction in acidic solution using cathodic stripping voltammetry. In pH 3–4 Britton–Robinson buffer [peak potential =–0.70 to –0.77 V versus Ag/AgCl (3 mol l–1 KCl)] about a three fold increase in signal size is obtained when accumulation is effected at –0.1 V in the presence of sufficient added copper(II). Studies of the effect of accumulation potential, accumulation on open circuit and the use of EDTA buffer indicate that the enhancement is due to accumulation of the copper(I) complex of sulfachloropyridazine. At pH values <3, where complex formation would be suppressed by protonation of the sulfonamide group, the peak height is not enhanced by copper(II). The enhancement by copper(II) at pH 3 reaches a limiting maximum at 5 × 10–7 mol l–1 and precise determination of sulfachloropyridazine (detection limit 1.7 × 10–9 mol l–1) can be made under these conditions. The present system serves as an example of a determinand which can accumulate in more than one form, in this case as sulfachloropyridazine and its copper(I) complex, with the possibility of errors and imprecision being created in the subsequent voltammetric determination. Copper(II) in the sample, or the de-ionized water supply, interferes in the determination of sulfachloropyridazine if sufficient copper(II) is not added.