Journal of Pharmaceutical and Biomedical Analysis 66 (2012) 116–125 Contents lists available at SciVerse ScienceDirect Journal of Pharmaceutical and Biomedical Analysis j ourna l ho me p a ge: www.elsevier.com/locate/jpba Voltammetric and RP-LC assay for determination of benidipine HCl Nurgul Karadas a,b , Senem Sanli c , Mehmet Gumustas a,b , Sibel A. Ozkan b,∗ a Hitit University, Faculty of Science and Arts, Dept. of Chemistry, Corum, Turkey b Ankara University, Faculty of Pharmacy, Dept. of Analytical Chemistry, 06100 Ankara, Turkey c Usak University, Faculty of Science and Arts, Dept. of Chemistry, Usak, Turkey a r t i c l e i n f o Article history: Received 11 January 2012 Received in revised form 13 March 2012 Accepted 14 March 2012 Available online 23 March 2012 Keywords: Benidipine Liquid chromatography pKa Voltammetry Stress conditions a b s t r a c t 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 voltam- metric 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 g mL -1 and 54.20 g mL -1 for GC and 1.08 g mL -1 and 54.20 g 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, rang- ing 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 g 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. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Benidipine HCl (BEN), (±)-(R’)-3-[(R’)-1-benzyl-3-piperidyl] methyl 1,4 dihydro-2,6-dimethyl-4-(m-nitrophenyl)-3,5- pyridenecarboxylate hydrochloride (Scheme 1), is a dihydropyridine-derived calcium channel blocker with gen- eral properties similar to those of nifedipine. It has relatively high vascular selectivity and is expected to show protective effects on vascular endothelial cells. It is used orally in the management of hypertension and angina pectoris [1,2]. For the time being, few methods have been reported for quan- tification of this compound such as gas chromatographic [3–5] and LC–MS methods [6]. These published methods are time consuming and might have some limitations such as expensive instru- mental set-up, and exact rigid experimental conditions like the amount of reagent, reaction temperature and time. So far, neither ∗ Corresponding author. Tel.: +90 312 223 82 43; fax: +90 312 223 82 43. E-mail address: ozkan@pharmacy.ankara.edu.tr (S.A. Ozkan). electroanalytical nor chromatographic report on quantitative determination of BEN in pharmaceutical formulations has been published. Also no information about the electrochemical redox properties, acid dissociation (pK a ) value, and degradation behav- ior of BEN by using LC method has been found in the literature. Moreover, no monograph of BEN has been published in the official pharmacopeias as of today. Electroanalytical methods have proved to be very sensitive, selective and rapid for the determination of active pharmaceu- tical ingredients (APIs) in their dosage forms. The advantage of experimental electrochemical techniques in the field of quanti- tative analysis of drugs arise from their simplicity, low cost and relatively short analysis time as compared with other techniques. Voltammetric techniques are most suitable for investigation of the redox properties of APIs, and these techniques can give insight into the metabolic fate, in vivo redox process or pharmaceutical activity [7,8]. Owing to the widespread use of LC–DAD method in routine analyses, it is important that specific and thoroughly validated LC methods are developed for the analysis of APIs in their dosage forms 0731-7085/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2012.03.025