Electrochimica Acta 109 (2013) 818–822 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom ep age: www.elsevier.com/locate/elec tacta Square-wave voltammetric determination of pantoprazole using ex situ plated antimony-film electrode Biljana Nigovi ´ c a,∗ , Samo B. Hocevar b a Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovacica 1, 10000 Zagreb, Croatia b Analytical Chemistry Laboratory, National Institute of Chemistry, Hajdrihova 19, Sl-1000 Ljubljana, Slovenia a r t i c l e i n f o Article history: Received 11 June 2013 Received in revised form 20 July 2013 Accepted 21 July 2013 Available online 7 August 2013 Keywords: Antimony film electrode Direct voltammetry Pantoprazole a b s t r a c t The antimony film electrode (SbFE) was used for expedient measurement of pantoprazole, i.e. an impor- tant pharmaceutical substance. The SbFE was prepared ex situ on a supporting glassy carbon electrode and employed in direct square-wave voltammetric mode. After studying and optimizing several experimen- tal parameters, the electrode exhibited an auspicious electroanalytical performance in Britton–Robinson buffer solution with the calculated LOD of 9.1 × 10 -7 mol L -1 and an excellent reproducibility with the RSD of ±0.8%. Actual applicability of the SbFE in organic electroanalysis was demonstrated via measuring low concentration levels of pantoprazole in a real pharmaceutical dosage form. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Among working electrodes which can serve as conve- nient replacements for toxic mercury electrodes, bismuth- and antimony-based electrodes have attracted prodigious attention due to similar electroanalytical behavior compared to their mer- cury analogs [1]. In the year 2000, bismuth film electrode was introduced for anodic stripping voltammetric measurements of trace metal ions and soon after, its application has spread also toward organic analytes [2–5]. Following bismuth electrode, in the year 2007 the antimony film electrode (SbFE) was presented as another suitable alternative for mercury film electrode [6]. In parallel with bismuth electrode, which has been, by now, adopted in numerous electroanalytical laboratories [1], the SbFE allows measurements of low concentration levels of several metal ions in more acidic media with pH ≤ 2 in combination with advanced voltammetric or chronopotentiometric (stripping) pro- tocols [6,7]. Moreover, the antimony electrode exhibits some interesting electroanalytical attributes such as relatively wide operational potential window associated with favorably negative hydrogen evolution reaction and unexpectedly low re-oxidation signal for the antimony itself, i.e. the feature which can be ben- eficially exploited for measuring analytes with their re-oxidation potentials close to that of the antimony [6,8]. Another interest- ing feature is also a specific amorphous structure of antimony films compared to bismuth films which are primarily characterized ∗ Corresponding author. Tel.: +385 1 6394 453; fax: +385 1 4856 201. E-mail address: bnigovic@pharma.hr (B. Nigovi ´ c). by their (micro)crystalline structure. Up till now, several configu- rations of the antimony-based electrodes have been studied, i.e. in situ and ex situ prepared SbFE created on different supporting electrodes such as glassy carbon, carbon paste, carbon fiber and boron-doped diamond electrodes, sputtered antimony electrode, antimony powder carbon paste electrode and antimony oxide car- bon paste electrode [6–13]. However, due to its relatively recent emergence, the investigations toward the application of antimony electrode for measuring organic compounds are still in a very early stage [14]. Pantoprazole is a proton pump inhibitor drug used for treat- ing the acid-peptic diseases such as duodenal and gastric ulcers, reflux esophagitis and Helicobacter pylori eradication (Scheme 1). Pantoprazole controls gastric acid secretion by inhibition of gas- tric H + , K + -ATPase, i.e. the enzyme responsible for the final step in secretion of hydrochloric acid by gastric parietal cells [15]. The methods that have been applied for its assay in pharmaceutical formulations and in biological materials involve high-performance liquid chromatography [16–22], capillary electrophoresis [23], spectrophotometric methods [24–26] and electrochemical meth- ods using hanging mercury drop electrode (HMDE) [27,28]. The oxidation mechanism of pantoprazole and its voltammetric detec- tion (based on the oxidation of its amino group) at a glassy carbon and at a carbon paste electrode (CPE) have been described [29,30]. In addition, pantoprazole molecule contains a sulfoxide group which can undergo electrochemical reduction allowing its voltam- metric measurement also at more negative potentials. Namely, using a HMDE the reduction peak of pantoprazole molecule was observed at -1.18 V in Britton–Robinson buffer solution adjusted to pH 7 [27]. 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.07.173