Differential pulse voltammetric method for the individual and simultaneous determination of antihypertensive drug metoprolol and its association with hydrochlorothiazide in pharmaceutical dosage forms

The present study describes a convenient method for the individual determination of antihypertensive drug metoprolol (MTP) and its association with hydrochlorothiazide (HCTZ) using a cathodically pretreated boron-doped diamond (BDD) electrode and differential pulse voltammetry (DPV). Two very well-resolved and reproducible oxidative processes of HCTZ and MTP were found at 1.11 V and 1.32 V (vs Ag/AgCl (3.0 mol L−1 KCl)), respectively, in lactate buffer solution (pH 4.0). Under the optimum analytical experimental conditions, the voltammetric method exhibited linear response for individual determination of MTP in the concentration range 0.38–22 μmol L−1, with detection limit of 0.034 μmol L−1, while for a simultaneous determination of HCTZ and MTP, the concentrations range were 0.51–18.7 and 1.23–22.8 μmol L−1, with detection limit of 0.376 and 0.077 μmol L−1 for HCTZ and MTP, respectively. The individual and simultaneous methods were successfully applied in the determination of HCTZ and MTP content in several pharmaceutical formulations, whose accuracy was attested by good agreement of the results (paired t-test at a 95% confidence level) with those obtained using high performance liquid chromatography. In order to indicate that the method is of potential application in biological fluids adequate recovery results were obtained for the determination of HCTZ and MTP in urine samples.