Pseudo-indicator behaviour of platinum electrode explored for the potentiometric estimation of non-redox systems Syed Raashid n , Oyais Ahmad Chat, Masood A. Rizvi, Mohsin Ahmad Bhat, Badruddin Khan Department of Chemistry, University of Kashmir, Srinagar 190006, India article info Available online 23 September 2012 Keywords: Platinum Pseudo-indicator Potentiometry Non-redox Spectroelectrochmical abstract A pseudo-indicator electrode based potentiometric method for estimation of non-redox metal ions is presented. In the proposed method, nature and concentration specific impact of analyte over the redox potential of ideally polarisable Pt/pregenerated-redox-couple interface forms the basis of quantifica- tion. Utility of the method in estimation of six non-redox metal ions viz. Zn 2 þ , Cu 2 þ , Ni 2 þ , Cd 2 þ , Pb 2 þ , Al 3 þ in the concentration range of 10 1 –10 3 moldm 3 , individually and as binary mixtures is also presented. Three types of potentiometric behaviours, which we ascribe to the nature specific thermodynamic and kinetic aspects of metal-EDTA binding, were observed. While Cu 2 þ , Ni 2 þ , Pb 2 þ and Al 3 þ were found to bind EDTA efficiently, without exchanging Fe 3 þ ; Zn 2 þ and Cd 2 þ were observed to replace Fe 3 þ from EDTA. In contrast, Ca 2 þ and Mg 2 þ were found to show no binding affinity to EDTA in the pH range employed in the present work. The proposed method was also used to explore the reversibility and the Nernestian behaviour of ferricyanide/ferrocyanide redox couple through spectro- electrochemical titration of Zn 2 þ with ferrocyanide. The presented method is presaged to be a reliable and low cost future replacement for costly and delicate ion selective electrodes (ISE) in the estimation of non-redox species like Zn 2 þ , Cu 2 þ , etc. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Potentiometric quantification of analyte concentration is based on the Nernstian type dependence of electromotive force (EMF) over the concentration of oxidised and reduced forms of analyte. Thus electron transfer is a prerequisite for such type of analysis [1,2]. This strategy has been explored for analytical monitoring of many industrial, pharmaceutical, biological and environmental samples [3–7]. In such methods, the electrode actually sensing the changes in the analyte concentration is regarded as indicator electrode and many a times, a simple redox electrode in the potentiometric setup acts as reliable and sensitive indicator electrode. Even after eighty years of its first reported use, platinum continues to be the most commonly used redox- indicator electrode, owing to its good surface characteristics, quick equilibration, well Nernstian behaviour, modest cost, easy storage and longer life [8–10]. However, there are a number of biologically [11,12] and environmentally [13,14] important species like Zn 2 þ , Cu 2 þ , Ni 2 þ , Cd 2 þ , Pb 2 þ ,Al 3 þ ,I  , Cl  , and Br  which being non-redox fail to generate a redox couple in vicinity of platinum contact in potentiometric cells and hence cannot be sensed through use of this metal contact in redox electrode. It is in this context that a good quantum of analytical work in recent past has been devoted to the development of alternate methods for estimation of such ionic species which include chemosensor based ion selective electrodes (ISE) [15–22] spectroflorescent probes (SFP) [23–25] and coated wire electrodes (CWE) [26–28]. ISE consist of macrocyclic and porphyrin type Schiff base adducts adsorbed over polyvinyl chloride material, with an appropriate pore size to bind a specific metal ion. SEP are made up of florescent type ligands which show change in spectral or fluor- escent properties on interaction with specific metal ions. CWE are the modified electrodes obtained by the electrodeposition of a chemosensor material over a bare platinum electrode. All these reported analytical techniques for the estimation of these impor- tant ionic species involve either a sophisticated instrumentation or costly ion selective electrodes. Moreover, poor shelf life and less chemical stability in various media associated to ISE have limited their general application in analytical chemistry. As of now to the best of our knowledge, there has been no attempt to make use of platinum electrode for the estimation of non-redox ions. The work presented in this report describes a novel indirect method for estimation of non-redox species like Zn 2 þ , Cu 2 þ , Ni 2 þ and Cd 2 þ over platinum by exploring their impact on redox potential of a pregenerated redox couple within the analyte solution. The non-redox cell reaction changes concentration of one of the two forms in the redox couple allowing potential to change and hence allows the quantitative monitoring of the Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta 0039-9140/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.talanta.2012.09.020 n Corresponding author. Tel.: þ91 99067 59925; fax: þ91 194 2421357. E-mail address: srm266@yahoo.in (S. Raashid). Talanta 101 (2012) 246–252