Sensors and Actuators B 120 (2007) 455–461 A novel potentiometric membrane sensor for determination of Co 2+ based on 5-amino-3-methylisothiazole Ashok Kumar Singh ∗ , Sameena Mehtab, Puja Saxena Department of Chemistry, Indian Institute of Technology-Roorkee, Roorkee 247 667, India Received 5 November 2005; received in revised form 27 February 2006; accepted 27 February 2006 Available online 3 April 2006 Abstract A new poly(vinylchloride) (PVC) membrane electrode for trace level determination of Co 2+ ions has been developed based on 5-amino-3- methylisothiazole as an ionophore, o-nitrophenyloctylether as a plasticizer and oleic acid (OA) as a good lipophilic additive. The electrode exhibits a Nernstian slope of 29.5 ± 0.2 mV/decade in a linear range of 1.0 × 10 −1 to 6.3 × 10 −7 M for Co 2+ ions. The detection limit of this electrode is 3.9 × 10 −7 M. It has a fast response time of 12s and can be used for a period of 4 months without any divergence in potentials. The proposed electrode reveals a good selectivity for Co (II) over a wide variety of other tested cations and could be used in the pH range 3.3–9.0. The electrode was successfully applied as an indicator electrode for the potentiometric titration of cobalt ions with EDTA as well as for the direct determination of Co (II) in real samples. © 2006 Elsevier B.V. All rights reserved. Keywords: Potentiometry; Co (II) ion-selective electrode; 5-Amino-3-methylisothiazole; Poly(vinylchloride)membrane 1. Introduction An ion-selective electrode is useful tool for the potentio- metric measurement of the activity of an ion in the presence of other ions. Construction and application of an ion-selective electrode as a potentiometric sensor offers interesting advan- tage such as speed, fast response, simplicity, low cost and wide concentration range [1]. Specific metal–ligand interac- tions are important recognition mechanism that can be uti- lized in the development of potentiometric sensors [2]. Such interactions have been used in the development of cation- and anion-selective electrodes based on different ionophores [3]. Cobalt is an essential element for life and the central constitu- tion of Vitamin B 12 . It has been shown that animals deprived of cobalt show signs of retarded growth, anemia, loss of appetite, and decreased lactation [4]. In large doses cobalt and its salts can be toxic. The occupational exposure of it (>0.05 mg/m 3 ) causes irritant and allergic effects [5,6]. Currently, cobalt is mainly used in steel and variety of alloys, including high temperature ∗ Corresponding author. E-mail address: akscyfcy@iitr.ernet.in (A.K. Singh). steel alloys, magnetic alloys, abrasion-resistant glasses, ceram- ics, paints and batteries. Despite urgent need for a cobalt-responsible sensor for the potentiometric determination of Co 2+ in many industrial, clin- ical, pharmaceutical, plant, soil, and food samples, there have been only a few selective Co (II) sensors reported [7–16]. The most reported potentiometric sensors have not been very fruit- ful, because the developed ion-selective electrodes possess a narrow working concentration range, long response time and significant interferences from many cations. Thus, the fast, sim- ple, and accurate determination of cobalt in different samples is very important. Neutral carriers have characteristics of being uncharged, lipophilic, and undergoing reversible complexation with selected cations, and hence, of promoting cation transfers between the aqueous phase and the organic membrane phase [17–19] by means of carrier transport. In recent years, we have used a variety of ligands as ion carriers in the preparation of new ion-selective electrodes [20–23]. In this paper, we report a highly selective PVC membrane electrode for Co 2+ ions based on 5- amino-3-methylisothiazole (I) as a neutral carrier (ionophore). Thiazole derivatives have many applications as fertilizers, antibiotics, pesticides and neuroprotectors [24–28]. Thiazoles are aromatic compounds bearing coordinative sites of sulphur 0925-4005/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2006.02.038