ELECTROCHEMICAL DETERMINATION OF THE LOOP DIURETICS PIRETANIDE AND FUROSEMIDE IN PHARMACEUTICAL FORMULATIONS AND URINE

The oxidation of the loop diuretics 4-phenoxy-3-(1-pyrrolidinyl)-5-sul phamoylbenzoic acid (piretanide) and 4-chloro-2-furfurylamino-5-sulpha moylbenzoic acid (furosemide) was studied in methanol-water (10:90) in the pH range 0.3-13 (piretanide) and 0.5-13 (furosemide), with 0.04 m ol/l Britton-Robinson buffers as supporting electrolytes and 0.5 mol/l KCl as ionic medium at a glassy carbon electrode. Oxidation processes have shown to be irreversible and predominantly diffusion controlled over the whole pH range studied for both diuretics. Voltammetric metho ds have been developed for the determination of piretanide at pH 5.0 a nd furosemide at pH 4.5 using differential pulse and square wave volta mmetry. The peak current showed a linear relationship with concentrati on up to 25 mg/l (6.9 x 10(-5) mol/l for piretanide and 5.5 x 10(-5) m ol/l for furosemide) with a reproducibility in terms of standard devia tion (n = 10) lower than 5.6%. A detection limit of 50 ng/l was obtain ed (1.38 x 10(-7) mol/l piretanide and 1.51 x 10(-7) mol/l furosemide) for both electroanalytical techniques. Methods proposed were applied to pharmaceuticals and spiked urine samples.