Voltammetric and RP-LC assay for determination of benidipine HCl.

The detailed electrooxidative behavior of benidipine (BEN) has been studied by using glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Using cyclic voltammetry, depending on the pH values and the working electrodes, BEN showed one or two sharp and irreversible oxidation responses. The voltammetric experiments on some model compounds allowed elucidation of the oxidation mechanism of BEN. Highly sensitive, selective, rapid, and fully validated voltammetric methods for the determination of BEN in tablet dosage form were also presented. Under optimized conditions, the peak current showed a linear dependence with concentration in the range between 3.25 μg mL(-1) and 54.20 μg mL(-1) for GC and 1.08 μg mL(-1) and 54.20 μg mL(-1) for BDD electrodes by using differential pulse (DPV) and square wave (SWV) voltammetric techniques. In this study, acid dissociation constant (pK(a)) value of BEN was determined by using the dependence of the retention factor on the pH of the mobile phase using reverse phase-liquid chromatographic (RP-LC) method. The effect of the composition of the mobile phase on the ionization constant was studied by measuring the pK(a) at different acetonitrile-water mixtures, ranging between 50 and 65% (v/v). Also simple, accurate, precise and fully validated RP-LC method for the assay of BEN in dosage form has been developed. XTerra RP-18 column at 25 °C with the mobile phase of acetonitrile:water 55:45 (v/v) adjusted to pH 3.0 with 15 mM o-phosphoric acid was used. Isocratic elution was performed in less than 5.0 min with a flow rate of 1.0 mL min(-1). The RP-LC method allowed quantitation over the 0.25-15.00 μg mL(-1) range for BEN. The proposed voltammetric and RP-LC methods allow a number of cost and time saving benefits. BEN was also exposed to thermal, photolytic, oxidative stress, acid-base catalyzed hydrolyses, and the stressed samples were detected by the proposed RP-LC method.