Three different recently synthesized noncyclic crown ethers were used in polymeric ion-selective electrodes (ISEs) for thallium(I) sensing. The electrode based on a methyl-2-[2-(2-2- 2-(methoxycarbonyl) phenoxy] ethoxyethoxy) ethoxy] benzoate, L2, exhibited a near Nernstian response of 58.7 mV/decade to thallium ions over the activity range 1.2 9 10-7 to 3.0 9 10-2 M with a limit of detection 8.3 9 10-8 M. The response time to achieve a 95 % steady potential for Tl? concentration ranging from 1 9 10-6 to 1 9 10-3 M was \10 s. The potentiometric response of the electrode was independent of the pH of the test solution in the pH range 3.0–9.0. The sensor was also found to work satisfactorily in partially non-aqueous media up to 20 % (v/v) content of methanol, ethanol and acetone and could be used for a period of 3 months. The proposed sensor revealed fairly a good discriminating ability towards Tl? ion over alkali, alkaline earth and other heavy metal ions. Applications of this electrode for the determination of thallium in pollution in environmental waters, and as an indicator electrode for potentiometric titration of Tl? ions with NaI solution, were reported.

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