Polarographic and cathodic stripping voltammetric determination of tipredane

Abstract

The electroreduction of tipredane has been investigated by direct current and differential pulse polarography and by cyclic voltammetry at a hanging mercury drop electrode. In Britton-Robinson (B-R) buffer, pH 2.0–5.0, the drug is reduced in a single well-defined step: this reduction process has been shown to involve a preceding protonation step. At pH 12 also there is only a single step, this time involving reduction of the unprotonated species followed by a chemical step involving dimerisation. At intermediate pH values both peaks are present, peak 1 being at a less negative potential; studies of the mechanisms here are complicated by adsorption processes. Tipredane can be determined by differential pulse polarography at a pH of 7.0 or pH 2.0 using the first reduction peak over the concentration range 1.0 × 10 −5 to 8.0 × 10 −5 M or 1.0 × 10 −6 to 8.0 × 1010 −5 M, respectively. In B-R buffer at pH 4.5 two cathodic stripping peaks are obtained. The first peak, not present in the polarograms, is due to the accumulation and subsequent reduction of a mercury salt from tipredane. The second peak, which corresponds with the first polarographic peak, is recommended for use in the determination of tipredane by cathodic stripping voltammetry in the range 1 × 10 −8-5 × 10 −7 M with preconcentration for 2–3 min at 0 V. The detection limit was calculated to be 5 × 10 −10 M. The relative standard deviation determined from seven determinations at the 1 × 10 −7 M level was 1.3%.