Please cite this article in press as: Md.M. Hossain, et al., Voltammetric studies of hexachromic anion transfer reactions across micro-water/polyvinylchloride-2-nitrophenyloctylether gel interfaces for sensing applications, Electrochim. Acta (2012), http://dx.doi.org/10.1016/j.electacta.2012.03.127 ARTICLE IN PRESS G Model EA-18458; No. of Pages 7 Electrochimica Acta xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Voltammetric studies of hexachromic anion transfer reactions across micro-water/polyvinylchloride-2-nitrophenyloctylether gel interfaces for sensing applications Md. Mokarrom Hossain a , Sang Hyuk Lee a , Hubert H. Girault b , Valérie Devaud b , Hye Jin Lee a,∗ a Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu 702-701, Republic of Korea b Laboratoire d’Electrochimie Physique et Analytique, Station 6, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland a r t i c l e i n f o Article history: Received 2 December 2011 Received in revised form 22 March 2012 Accepted 24 March 2012 Available online xxx Keywords: Micro-liquid/gel interface Amperometric sensors Chromium(VI) Facilitated ion transfer Aliquat 336 a b s t r a c t The transfer reactions of various anionic hexavalent chromium species across a polarized water/polyvinylchloride-2-nitrophenyloctylether (PVC-NPOE) interface featuring a 66 microhole array are described for the development of selective and sensitive Cr(VI) sensors. The trans- fer of hydrophilic hexachromic anions across a liquid/liquid interface typically involves setting the potential window in a negative region. Therefore, a highly hydrophobic tetraoctylammonium tetrakis(pentafluorophenyl)borate (TOATB) salt was synthesized and incorporated into the PVC-NPOE gel phase as an organic supporting electrolyte to provide a larger potential window at the negative end. The transfer of different hexachromic anions across the microhole array interface between the aque- ous and PVC-NPOE gel phase containing TOATB was first characterized by voltammetric measurements. Since Cr(VI) ion species can hold different anionic forms such as Cr 2 O 7 2- , HCrO 4 - , and CrO 4 2- depending upon the pH and the Cr(VI) concentration, the effect of these two parameters on the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) responses was also investigated. In order to utilize the ion transfer reaction across the microhole array interface for the selective and sensitive detection of Cr(VI) ions, the assisted transfer of HCrO 4 - anion by an Aliquat 336 ionophore incorporated into the PVC-NPOE gel phase was investigated using CV and differential pulse stripping voltammetry (DPSV). An excellent detection limit of 0.5 M (26 ppb) with a wide linear dynamic range extending from 0.5 M to 10 M was achieved. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The analysis of various chromium species is of immense impor- tance due to their interesting physicochemical properties as well as their significant impact in environment and biochemical activity in human body. With several oxidation states possible for chromium, the two most common states present in an ambient environment are the Cr(III) and Cr(VI) ions. Trivalent chromium is considered as an essential trace element responsible for glucose and choles- terol metabolism in humans and other animals [1]. The Cr(VI) ion is known as a human respiratory carcinogen and is associ- ated with various skin diseases such as skin allergies, dermatitis, dermal necrosis and dermal corrosion [2,3]. Moreover, Cr(VI) ions have been reported to be 100–1000 times more toxic than Cr(III) ions [4] and the World Health Organization (WHO) has thus recom- mended a provisional upper limiting value of 0.05 mg L -1 (50 ppb) ∗ Corresponding author. E-mail addresses: hyejinlee@knu.ac.kr, leehyejin82@gmail.com (H.J. Lee). in groundwater [5,6]. Considering the different toxicities of the two valence states of Cr, rather than the total concentration of Cr, the development of a fast and sensitive detection method spe- cific to Cr(VI) ions in environmental samples could be powerfully employed to accurately assess pollution levels and help prevent further environmental contamination in industrial zones. Several methods have been introduced for the successful detec- tion and quantification of Cr(VI) in an aqueous phase such as atomic absorption spectrophotometry [7,8], high pressure liquid chromatography [9,10], X-ray fluorescence [11], inductively cou- pled plasma emission spectrometry [12] and optical sensors [13]. Although these methods offer reliable, accurate and reproducible analysis, some drawbacks remain such as being time-consuming, requiring sample pretreatment, high instrumentation costs as well as difficulty in clearly differentiating between different oxi- dation states [13]. Alternatively, electrochemical methods have attracted interest for Cr(VI) detection due to rapid and accurate analyses, great potentials for miniaturization as well as high sen- sitivities and selectivities [14]. A wide spectrum of solid metal electrodes [15], modified solid electrodes [16], gold and silver 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.03.127