Talanta 63 (2004) 371–376 Potentiometric membrane sensors based on zirconyl(IV) phthalocyanine for detection of sulfosalicylic acid Saeed Shahrokhian ∗ , Abdollah Taghani, Ali Hamzehloei, S. Reza Mousavi Department of Chemistry, Sharif University of Technology, Tehran 11365-9516, Iran Received 12 July 2003; received in revised form 19 October 2003; accepted 5 November 2003 Abstract A metallophthalocyanine complex with zirconium(IV) ion in the center (as an oxo-zirconium, Zr=O, group) was used in poly vinyl chloride (PVC) membranes for the selective detection of 5-sulfosalicylic acid (SSA). The resulting electrodes demonstrate Nernstian responses over a wide range of sulfosalicylic acid concentration (10 −6 to 10 −1 mol dm −3 ) with a slope of about −29 mV per decade. The influence of lipophilic ion-exchanger sites on the response properties of the electrodes was investigated. The optimal potentiometric response was observed for the electrode in the presence of about 150 mol% of cationic additive (relative to ionophore) in the phase membrane. The electrodes have a fast response time, micromolar detection limit and good long-term stability (more than 2 months). The feasibility of the application of these sensors for the potentiometric titration of iron in solutions that were prepared from magnetite samples was investigated. © 2003 Elsevier B.V. All rights reserved. Keywords: Potentiometry; Ion selective electrodes; Zirconyl(IV) phthalocyanine; Sulfosalicylic acid 1. Introduction There is a perceived and increasing demand for simple, inexpensive and rapid analytical methods for selective detec- tion of biologically and chemically important compounds. Potentiometric sensors are particularly suited for these appli- cations and offer the advantageous of simple design and op- eration, wide linear dynamic range, relatively fast response, reasonable selectivity, and low cost. These characteristics have inevitably led to sensors for various ionic species, and the list of available ion-selective electrodes (ISEs) have grown over the past two decades [1,2]. A very interesting development of potentiometric sensors is in the construction of electrodes that respond selectively to ionic species. The wide use of ISEs in routine chemical and biological analysis has been accompanied by a search for ionophores that can chemically recognize specific ions and offer either new or improved selectivities for different ions.Although the majority of the approximately 60 ions for which carrier-based ion-selective membrane electrodes have been described up to now are cations [1], a series ∗ Corresponding author. Fax:+98-21-6012983. E-mailaddress: shahrokhian@sharif.edu (S. Shahrokhian). of new anion-selective electrodes [1,3,4] were introduced recently as a growing interest in host-guest chemistry of anions [5]. One of the important recognition elements that can be utilized in the development of ISEs involves specific metal–ligand interactions [6]. For the development of truly anion-selective electrodes, a strong interaction between the ionophore and the interested anion is required in order to complex the anion in a selective fashion. It is especially challenging to obtain a desirable and useful selectivity for the strongly hydrophilic anions, since their standard free energies of equilibrium exchange from sample to phase membrane of ISE must be overcompensated by strong and selective complexation [7]. Complexes of several metal ions with different ligand, such as phthalocyanines [8–12], por- phyrins [13–16], metallocenes [17], and schiff bases [18,19] have been observed to show such specific metal–ligand in- teractions and induce anion selectivities in the membranes thatdiffer somewhat from the classical anion exchangers (Hofmeister selectivity pattern). The propose of the present work has been the devel- opmentofapolymericmembranelectrodecontaining oxo-zirconium(IV) phthalocyanine (ZrOPc) for the detec- tion of 5-sulfosalicylic acid (SSA). In this work, we show that a strong hard–hard interaction between sulfosalicylate anion (as a hard and hydrophilic base) and zirconium(IV) 0039-9140/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2003.11.007