Analytica Chimica Acta 583 (2007) 340–348 Schiff bases as cadmium(II) selective ionophores in polymeric membrane electrodes V.K. Gupta ∗ , A.K. Singh, Barkha Gupta Department of Chemistry, Indian Institute of Technology-Roorkee, Roorkee 247667, India Received 29 August 2006; received in revised form 16 October 2006; accepted 26 October 2006 Available online 6 November 2006 Abstract The construction and performance characteristics of polymeric membrane electrodes based on two neutral ionophores, N,N ′ -[bis(pyridin-2- yl)formylidene]butane-1,4-diamine (S 1 ) and N-(2-pyridinylmethylene)-1,2-benzenediamine (S 2 ) for quantification of cadmium ions, are described. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w) of (S 1 ) (2.15%):PVC (32.2%):o- NPOE (64.5%):KTpClPB (1.07%). The proposed electrode exhibits Nernstian response in the concentration range of 7.9 × 10 -8 to 1.0 × 10 -1 M Cd 2+ with limit of detection 5.0 × 10 -8 M, performs satisfactorily over wide pH range (2.0–8.0) with a fast response time (10 s). The sensor has been found to work satisfactorily in partially non-aqueous media up to 30% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 2 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of cadmium in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants. © 2006 Elsevier B.V. All rights reserved. Keywords: Cadmium selective electrode; Poly(vinylchloride) membranes; Schiff base; Potentiometry and ion-selective electrodes 1. Introduction Cadmium represents one of the important toxic metals and the effect of its acute poisoning is manifested in a variety of symptoms, including high blood pressure, kidney damage, anemia, hypertension, bone marrow disorders, cancer and tox- icity to aquatic biota. The provisional tolerable weekly input for cadmium recommended by the WHO on food additives is 0.4–5.0 mg based on a tolerable intake of 1 g kg -1 of body weight per day [1]. It is released into the atmosphere from smelters and the disposal of Cd bearing products. It enters natural water through industrial discharges from metal plating indus- tries, nickel–cadmium batteries, phosphate fertilizers, mining, pigments, stabilizers and alloys. The permissible limits of cad- mium discharge in wastewater and drinking water are 0.1 and 0.05 mg L -1 , respectively. Cadmium forms many binary and more complex alloys of commercial applications as well as its ∗ Corresponding author. Tel.: +91 1332 285801; fax: +91 1332 273560. E-mail address: vinodfcy@iitr.ernet.in (V.K. Gupta). salts are used as stabilizers in plastics, phosphors for televi- sion sets, scintillation counters and X-rays screens in storage, semiconductors and ceramic glazes [2]. Because of the increasing industrial use of Cd, on one hand, and its serious hazardous effect of human health, on the other, extensive studies have been carried out on the development of methods for Cd determination. Although sophisticated ana- lytical techniques, viz. graphite furnace-AAS, Flame atomic absorption spectrometry, spectrophotometry, ET-AAS, strip- ping chronopotentiometry have been employed for trace level determination, they are disadvantageous in terms of cost and unsuitability for routine analysis. So there is critical need for the development of selective, portable, inexpensive diagnos- tic tools for determination of cadmium. Analytical methods based on potentiometric detection with ion-selective electrodes (ISEs), can be considered as an advantageous alternative because they are eco-friendly techniques, provide easy construction and manipulation, present good selectivity in a wide concentration range of operatability, relatively low detection limit, show a fast response and non-destructive analysis. This has led to an increasing interest of our research group in the development and 0003-2670/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2006.10.039