Journal of Electroanalytical Chemistry 448 (1998) 33 – 39 A novel PVC membrane sensor for potentiometric determination of thallium(I) M.B. Saleh * Department of Chemistry, Faculty of Science, Minia Uniersity, Minia, Egypt Received 13 June 1997; received in revised form 24 September 1997 Abstract Several thallium(I) ion-selective electrodes based on quinoline-carbonitrile compounds as a novel class of sensors have been prepared and studied. The optimum thallium(I) ion-selective electrode is made from 2-cyclohexylthio-4-oxo-1(4H)quinoline-3-car- bonitrile as the electroactive material.This electrode exhibits a Nernstian response for 0.1 – 1.0 ×10 -5 M TlNO 3 with a slope of 56 mV decade -1 . The detection limit is 3.2 ×10 -6 M. The electrode shows a high selectivity, stability and reproducibility and can be used as a sensor in potentiometry. © 1998 Elsevier Science S.A. All rights reserved. Keywords: Thallium; PVC membrane sensor; Potentiometric sensor 1. Introduction From an environmental viewpoint, estimates of thal- lium-ion concentration have become a major interest because of their high toxicity. Ion-selective electrodes (ISE) are one of the most convenient and reliable analytical tools for estimating metal ion-concentrations. There have been only a few reports concerning thalli- um(I) liquid-membrane electrodes [1 – 5]. They need to be improved with regard to their low selectivities against alkali metal ions, linearity and pH-dependence. Poly(vinyl chloride) (PVC) membrane thallium(I) ion- selective electrodes based on bis(crown ether)s contain- ing the benzo-15-crown-5 moiety were described [6].These crown ether-based ISEs exhibited good slope and linearity of calibration plots and the electrode response was stable over a wide pH range. However, the Tl + selectivity against K + for one of the bis(15- crown-5)s (Bis-15) was fairly poor (log K Tl,K pot =- 0.52).Yamashoji et al. [7] found that Tl + -selective PVC membrane electrodes based on dibenzo-20-crown-6 (DB-20) and -22-crown-6 (DB-22) show higher selectiv- ities to Tl + than does symmetrical dibenzo-18-crown-6 (DB-18). The electrode based on DB-18, DB-20 or DB-22 showed a linear response to the Tl + activity over a range of 3.2 ×10 -5 to 1.0 ×10 -2 M TlNO 3 with a slope of 59 mV decade -1 . The log K Tl,K pot values for the electrodes based on DB-18, DB-20 and DB-22 are -0.15, -1.26 and -1.73, respectively. Recently, polythiamacrocycles (thia ethers) have been proposed as Tl + PVC-based ISEs [8]. The plasticizing agent was dioctyl phthalate (DOP) as opposed to the more fre- quently employed o -nitrophenyl octyl ether (o-NPOE). Moreover, the influence of membrane components such as the secondary ion exchanger [9], plasticizers [10] and the polymer base [11] on electrode performance has been examined in the literature. This paper reports a novel thallium ion-selective electrode incorporating the synthetic carriers quinoline-carbonitrile derivatives, which exhibit high selectivity and potential response stability and can be used in potentiometry. * Tel.: +20 86323011; fax: +20 86342601. 0022-0728/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0022-0728(97)00514-7