Application of surfactant modified zeolite membrane electrode towards potentiometric determination of perchlorate Alireza Nezamzadeh-Ejhieh ⇑ , Atefeh Badri Department of Chemistry, Shahreza Branch, Islamic Azad University, P.O. Box 311-86145, Shahreza, Isfahan, Iran article info Article history: Received 22 November 2010 Received in revised form 12 May 2011 Accepted 3 June 2011 Available online 12 June 2011 Keywords: Perchlorate Surfactant modified zeolite (SMZ) Potentiometry Ion selective membrane electrode Poly vinyl chloride (PVC) abstract Potentiometric electrodes based on the incorporation of surfactant-modified zeolite Y (SMZ) particles into poly vinyl chloride (PVC) membranes were described. The electrode characteristics were evaluated regarding the response towards perchlorate ions. PVC membranes plasticized with dioctyl phthalate and without lipophilic additives (co-exchanger) are used throughout this study. The influence of membrane composition on the electrode response was studied. The electrode exhibited a Nernstian response towards perchlorate in the concentration range of 7.9  10 6 –8.0  10 2 M with a slope of 59.7 ± 0.9 mV per decade of perchlorate concentration with a working pH range of 1.7–9.5 with a fast response time of 610 s. The lower and upper detection limits were 4.07  10 7 and 0.13 M, respectively. The elec- trode response to perchlorate remains constant in the temperature range of 20–40 °C and in the presence of 2.5  10 6 –1  10 2 M NaNO 3 . The selectivity coefficients for perchlorate anion as test species with respect to other anions were determined. The proposed modified zeolite-PVC electrode can be used for at least 30 days without any considerable divergence in potential. It was applied as indicator electrode in water samples with satisfactory results. The results of this study and our previous work show HDTMA plays different roles according to the zeolite type and matrix, as HDTMA-zeolite Y in a carbon paste matrix showed a good Nernstian behavior towards phosphate anion. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The introduction of new ion-selective electrodes (ISEs) pro- moted fundamental developments in potentiometry over the past few decades [1,2]. Solvent polymeric membranes based on ISEs to- gether with the incorporation of new ion carriers proved to be a very useful tool for chemical, clinical, and environmental analysis as well as for process monitoring [3,4]. The incorporation of zeolites into electrochemical systems re- ceived increasing attention during recent years and advances in the modification of electrode surfaces with zeolites were exten- sively reviewed in [5–7]. Zeolites, due to their precisely uniform crystal lattice with pores of molecular dimension into which guest molecules can penetrate, possess outstanding potentialities for use in electroanalytical measurements. The unique properties of zeolites were utilized for developing zeolite modified voltammetric/amperometric electrodes exhibiting enhanced selectivity [8,9]. On the other hand, the ion exchange properties of zeolites makes them inevitable candidates for prepar- ing ion-selective membranes for the potentiometric cation sensing. For this purpose, many different matrices were employed [10–13]. Zeolites possess permanent negative charges in their crystal struc- tures making them suitable cation exchangers. This negative charge is also suitable for surface modification of zeolites using cationic surfactants such as hexadecyltrimethyl ammonium (HDTMA) cation. At surfactant concentrations greater than the crit- ical micelle concentration (CMC) and when sufficient surfactant is present, the sorbed surfactant molecules primarily form a bilayer on the zeolite external surface [14]. This bilayer formation results in a charge reversal on the external zeolite surface, providing sites where anions will be retained and cations repelled, while neutral species can partition into the hydrophobic cores. Recent studies indicate that surfactant-modified zeolites (SMZ) are effective sor- bents for multiple types of contaminants and a review in this mat- ter was published by Bowman [15]. The design of anion receptors is far less developed than the field of cation receptors and this is reflected by the fact that majority of polymeric membrane based ISEs has been described for determina- tion of cations [13,16,17]. The development of selective and sensitive liquid polymeric membrane electrodes for anions is of increasing interest for clinical, industrial, as well as environmental applications. The traditional anion-selective membrane electrodes based on ion exchangers always display a Hofmeister selectivity sequence, as follows; perchlorate > thiocyanate > iodide  salicy- late > nitrate > bromide > nitrite > chloride > sulfate, in which a membrane selectivity is controlled by the free energy of hydration of the ions involved, and recent studies have been more concerning 1572-6657/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2011.06.007 ⇑ Corresponding author. Tel.: +98 321 3292515; fax: +98 321 3291018. E-mail address: arnezamzadeh@iaush.ac.ir (A. Nezamzadeh-Ejhieh). Journal of Electroanalytical Chemistry 660 (2011) 71–79 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem