Electrochemical oxidation of the loop diuretic torasemide

Abstract

The oxidative behaviour of 1-isopropyl-3-[4-(3-methylphenylamino)-3-pyridinesulfonyl]urea, torasemide, was studied at a glassy carbon electrode in methanol–water (10 + 90), using different ionic media. The oxidation process was shown to be irreversible over the entire pH range studied (3–11) and predominantly diffusion controlled. Two voltammetric methods were developed at pH 8.0 (Britton–Robinson buffer) for the determination of torasemide using two different techniques: differential-pulse voltammetry (DPV) and square-wave voltammetry (SWV). The peak current varied linearly with torasemide concentration in the range 2.6 × 10^–6–4.8 × 10^–5 mol l^–1(DPV) and 2.3 × 10^–6–5.5 × 10^–5 mol l^–1(SWV) with a detection limit of 115 ppb (3.3 × 10^–7 mol l^–1)(DPV) and 40 ppb (1.15 × 10^–7 mol l^–1)(SWV). The reproducibility, in terms of relative standard deviation for ten determinations of 1.1 × 10^–5 mol l^–1 torasemide, was 3.5%(DPV) and 3.8%(SWV). The method was applied to urine samples spiked with torasemide, giving a recovery of 99.2 ± 5.3%.