Oxidación electroquímica de captopril

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Captopril Electrochemical Oxidation on Fluorine-Doped SnO2 Electrodes and Their Determination in Pharmaceutical Preparations
Francisco Armijo,* Ignacio Torres, Ricardo Tapia, Leonard Molero, Mónica AntilØn, Rodrigo del Río, Ma AngØlica del Valle, Galo Ramírez
Facultad de Química, Pontificia Universidad Católica de Chile, Av. VicuÇa Mackenna 4860, Casilla 306, Correo 22, Santiago,Chile tel.: + 56-2-6864389; fax: + 56-2-6864744 *e-mail: jarmijom@uc.cl Received: April 13, 2010; & Accepted: May 18, 2010 Abstract A novel application of fluorine-doped tin oxide (FTO) electrodes is reported in the present work. To this end, the captopril electrochemical oxidation mechanism on FTO electrodes at various pH and its determination in pharmaceutical preparations was investigated.Captopril oxidation on FTO proceeds at pH between 2.0 and 4.0. The study revealed that interferences for captopril determination in pharmaceutical samples was totally suppressed using these electrode materials. Voltammetric survey showed an anodic peak at about 0.375 V (Ag j AgCl) for captopril oxidation, that takes place through an EC process at pH interval 2.0–4.0. The investigation demonstratedthat captopril oxidation occurs through protonated species and these electroactive species interact by adsorption on FTO electrodes, with a large heterogeneous rate constant and a mechanism involving 1H + /1eÀ in the global reaction. Moreover, a captopril sensor based upon FTO electrodes, with a linear range miliMolar, is proposed. These electrodes are promising candidates for the efficientelectrochemical determination of captopril in pharmaceutical preparations. Keywords: Fluor-doped tin oxide electrode, Captopril determination, Thiol

DOI: 10.1002/elan.201000257

1. Introduction
S-Captopril 1-((2S)-3-mercapto-2-methyl-propionyl)S(L)-proline, whose structure is illustrated in Figure 1, is an active angiotensin II-converting enzyme (ACE) inhibitor [1, 2]. It is widely utilized in thetreatment of hypertension, congestive heart failure and heart attack in both mono- and combination therapy [3, 4]. Nearly 50 % is metabolized through the liver being oxidized to the corresponding bisulfide, the rest is unchanged excreted in the urine [5]. Owing to it current pharmacotherapeutics importance, different methods have been reported for captopril

Fig. 1. Captopril(1-((2S)-3-mercapto-2-methyl-propionyl)-S(L)proline) chemical structure.
Electroanalysis 2010, 22, No. &, 1 – 8

(CAP) determination in a variety of pharmaceutical and biological samples, e.g., high performance liquid chromatography [6–9], FT-Raman spectrometry [10], headspace solid phase microextraction based on polypyrrole film coupled to ion mobility spectrometry [11], gas chromatography [12, 13], luminescence,[14–16], sequential injection analysis using electrochemical detection [17], atomic absorption spectrometry [18], and UV-vis spectroscopy [19, 20]. These techniques possess some drawbacks, such as cost, sampling time, complexity, and interferences, e.g., Fe2 + , Fe3 + , NO2À , ascorbic acid. Electrochemical techniques such as amperometry [21– 23], potentiometry [24–26], stripping voltammetry [27,28], voltammetric methods [29–32], and square-wave voltammetry [33] have also been utilized with the same purpose. The mercury electrode is one of the most commonly utilized for the electrochemical determination of CAP, but because it is contaminated by intermediates from the oxidation, presents problems for voltammetric determinations [28, 29, 33]. Other electrodes have also been proposed, e.g.,borondoped diamond and platinum electrodes characterized by a wide potential window, low impedance, low limit of detection, chemical stability, and high sensitivity and reproducibility. The major drawback is the cost of both electrodes [27, 30]. Thus the need to investigate new electrode &1&

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