Comparative Study of Basal-Plane Pyrolytic Graphite, Boron-Doped Diamond, and Amorphous Carbon Nitride Electrodes for the Voltammetric Determination of Furosemide in Pharmaceutical and Urine Samples

Sensitive and simple electroanalytical methods were developed for the determination of the loop diuretic furosemide (FUR) in pharmaceutical formulations and synthetic urine samples by coupling square-wave voltammetry (SWV) with polished basal-plane pyrolytic graphite (BPPG) or cathodically pretreated boron-doped diamond (BDD) and amorphous carbon nitride (a-CNx) as working electrodes. The analytical parameters obtained with the three methods were compared. With BPPG, best results were attained using 0.10 mol L−1 H2SO4 as supporting electrolyte, whereas with BDD and a-CNx, this was attained using a 0.040 mol L−1 BR buffer (pH 4.5). Cyclic voltammograms obtained for FUR evidenced an irreversible behavior (with two oxidation peaks), in agreement with the literature. On the BDD and a-CNx electrodes, the electrooxidation of FUR is a purely diffusion-controlled process, whereas on the BPPG electrode some degree of adsorption is also involved. The obtained linear response ranges (detection limits) for the BPPG, BDD, and a-CNx electrodes were 0.60-4.8 (0.47), 0.30-13 (0.30), and 0.50-99 (0.39) μmol L−1, respectively. The proposed methods were successfully applied in the determination of FUR in pharmaceutical formulations (tablets), with results similar to those obtained using a reference spectrophotometric method (at a confidence level of 95 %), and in the recovery of FUR in synthetic urine samples. The analytical conditions obtained with the novel SWV methods here reported are comparatively better than those for other electrochemical methods in the literature. As the pretreatment procedures are much simpler for BDD and a-CNx than for BPPG, one can conclude that the former two materials can be advantageously used to determine FUR with good sensitivity and selectivity.