ELECTROCHEMICAL OXIDATION OF THE LOOP DIURETIC TORASEMIDE

The oxidative behaviour of -[4-(3-methylphenylamino)-3-pyridinesulfony l]urea, torasemide, was studied at a glassy carbon electrode in methan ol-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. The voltammetric methods were developed at pH 8.0 (Britton-Robinson buffer) for the determination of torasemide using two different techniques: differential-pulse voltamm etry (DPV) and square-wave voltammetry (SWV). The peak current varied linearly with torasemide concentration in the range 2.6 x 10(-6)-4.8 x 10(-5) mol l(-1) (DPV) and 2.3 x 10(-6)-5.5 x 10(-5) mol l(-1) (SWV) with a detection limit of 115 ppb (3.3 x 10(-7) mol l(-1)) (DPV) and 4 0 ppb (1.15 x 10(-7) mol l(-1)) (SWV). The reproducibility, in terms o f relative standard deviation for ten determinations of 1.1 x 10(-5) m ol l(-1) torasemide, was 3.5% (DPV) and 3.8% (SWV). The method was app lied to urine samples spiked with torasemide, giving a recovery of 99. 2 +/- 5.3%.