SAGE-Hindawi Access to Research International Journal of Electrochemistry Volume 2011, Article ID 864358, 6 pages doi:10.4061/2011/864358 Research Article Voltammetric Determination of Captopril Using Chlorpromazine as a Homogeneous Mediator Hossein Bahramipur and Fahimeh Jalali Department of Chemistry, Razi University, Bagh Abrisham, Kermanshah 67149-67346, Iran Correspondence should be addressed to Fahimeh Jalali, fahimehjalali@yahoo.com Received 6 August 2011; Accepted 22 August 2011 Academic Editor: Jay D. Wadhawan Copyright © 2011 H. Bahramipur and F. Jalali. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Chlorpromazine was used as a homogeneous electrocatalyst in the oxidation of captopril. The anodic peak current of chlorpromazine was increased substantially in the presence of low concentrations of captopril (pH 4). Cyclic voltammetry and chronoamperometry were used to study the kinetics of the catalytic electron transfer reaction. The values of electron transfer coefficient (α) and catalytic rate constant (k cat ) were estimated to be 0.34 and 8.48 × 10 2 M −1 sec −1 , respectively. Linear sweep voltammetry was used for the determination of captopril in the presence of chlorpromazine. A linear calibration curve was obtained in the concentration range of captopril of 10.0–300.0 μM, with a limit of detection of 3.65 μM. The relative standard deviation (RSD%) for 5 replicate measurements of captopril (100 μM) was 1.96%. The method was applied to the determination of captopril in pharmaceutical formulations and blood serum samples with satisfactory results. 1. Introduction Captopril (CAP), 1-(3-mercapto-2-D-methyl-1-oxopropyl) proline (Scheme 1(a)), is an oral drug and a member of a class of drugs called angiotensin-converting enzyme (ACE) inhibitors. CAP has been widely used as antihypertensive drug and to moderate heart failure [1]. It normally works by lowering blood levels of angiotensin enzyme, to help relax the blood vessels and lower blood pressure. Relaxing the arteries, and as a consequence lowering of blood pressure, improves the pumping efficiency of a failing heart and improves cardiac output in patients with heart failure [2]. CAP with a thiol functional group may also act as a scavenger of free radicals in living systems [3–5]. Several methods have been applied to the determination of CAP, including high-performance liquid chromatography [6–9], gas chromatography [10, 11], spectrophotometry [12, 13], fluorimetry [14–16], radioimmunoassay [17], chemilu- minescence [18–20], atomic absorption spectrophotometry [21], Raman spectroscopy [22], capillary electrophoresis [23, 24], and electrochemical methods [25–30]. Direct electrochemical determination of pharmaceutical compounds has a number of limitations, such as low sen- sitivity and reproducibility, slow electron transfer kinetics, and high overpotentials. The chemical modifications with redox active materials (homogenous and heterogeneous catalysts) offer significant advantages in the design and devel- opment of electrochemical sensors. During the reaction, the mediator shuttles electrons between the analyte and the electrode with significant reduction in the activation overpotential. In this study, chlorpromazine (CPZ, Scheme 1(b)), an antipsychotic drug, was used as a suitable homogeneous mediator in the electrooxidation of CAP. The proposed method was fast, selective, sensitive, and successful in the determination of CAP in real samples. Cyclic voltammetry (CV) and chronoamperometry were used to characterize the electrochemical properties of CPZ and to investigate its electrocatalytic effect on the CAP oxidation. Kinetic parameters such as electron transfer coefficient and the rate constant of catalytic reaction were estimated.