Available online at www.sciencedirect.com Talanta 74 (2008) 806–814 Polymeric membrane sensors based on Cd(II) Schiff base complexes for selective iodide determination in environmental and medicinal samples Ashok Kumar Singh ∗ , Sameena Mehtab Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India Received 9 June 2007; received in revised form 12 July 2007; accepted 13 July 2007 Available online 25 July 2007 Abstract The two cadmium chelates of schiff bases, N,N ′ -bis(salicylidene)-1,4-diaminobutane, (Cd-S 1 ) and N,N ′ -bis(salicylidene)-3,4-diaminotoluene (Cd-S 2 ), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to iodide(I) ion. Potentiometric investigations indicate high affinity of these receptors for iodide ion. Polyvinyl chloride (PVC)-based membranes of Cd-S 1 and Cd-S 2 using as hexadecyltrimethylammonium bromide (HTAB) cation discriminator and o-nitrophenyloctyl ether (o-NPOE), dibutylphthalate (DBP), acetophe- none (AP) and tributylphosphate (TBP) as plasticizing solvent mediators were prepared and investigated as iodide-selective sensors. The best performance was shown by the membrane of composition (w/w) of (Cd-S 1 ) (7%):PVC (31%):DBP (60%):HTAB (2%). The sensor works well over a wide concentration range 5.3 × 10 -7 to 1.0 × 10 -2 M with Nernstian compliance (59.2 mV decade -1 of activity) within pH range 2.5–9.0 with a response time of 11 s and showed good selectivity for iodide ion over a number of anions. The sensor exhibits adequate life (3 months) with good reproducibility (S.D. ± 0.24 mV) and could be used successfully for the determination of iodide content in environmental water samples and mouth wash samples. © 2007 Published by Elsevier B.V. Keywords: Iodide-selective electrode; Poly(vinyl chloride) membranes; Schiff bases; Potentiometric sensors 1. Introduction Iodine is an indispensable microelement to humans. Iodine is toxic and its vapors irritate the eyes and lungs. The maximum allowable concentration in air when working with iodine is just 1 mg m -3 [1]. Iodine-131 is one of the radionuclides involved in atmospheric testing of nuclear weapons. Iodine plays a key role in many biological activities such as brain functions, cell growth, neurological activities, metabolism and thyroid func- tions [2]. Iodide ions also present in the composition of various drugs. I - /I 3 - redox couple contributes to the high performance of dye-sensitized solar cells. Due to vital importance of iodide in environment, medicines and industry, determination of iodide ion is very important in clinical and chemical analysis [3,4]. Numerous analytical methods have been reported for its determination at low concentration levels. These include gas chromatography with mass spectrometry detection [5]; induc- ∗ Corresponding author. E-mail address: akscyfcy@iitr.ernet.in (A.K. Singh). tively coupled plasma atomic emission mass spectrometry [6]; neutron activation analysis [7]; chemiluminescence [8]; polarog- raphy [9]; pulse stripping analysis [10] and flow injection analysis [11]. These methods are time consuming, require large infrastructure backup, high operational cost and not very appro- priate for analysis of large number of samples. On the other hand potentiometric sensors offer an inexpensive and convenient method for fast analysis with high sensitivity and selectivity. Ion elective electrodes have emerged as one of the most promising tools for direct determination of various species in biological and industrial analysis. In view of such advantages, efforts have been made to make selective sensors for different anions. Anion sensing and recognition remains a challenging task because of the limited availability of suitable molecular hosts for anions. In order to have selective sensor for iodide, the most important requirement is to have an ionophore in the sensor which show high affinity towards iodide ion and poor for other anions. Thus, quest for new materials capable of specific and effective recognition of iodide is a topic of cur- rent interest. It has been shown that the anion selectivity of the membrane electrodes that are based on metal complexes 0039-9140/$ – see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.talanta.2007.07.016