A solid-contact ion-selective electrode for thallium(III) based on its complex with new complexone N,N'-) into a polymeric membrane is described. The ion-to-electron transducer used as the solid contact electrode was polyaniline which was electrochemically polymerized on a Pt wire. The plasticized poly(vinyl chloride) membrane incorporate ion-associate of [Tl(DOEDDSA)] À with N,N,N-trihexadecyl-N-methylammonium cation as electroactive material for ionometric sensor controls. The best performance in terms of slope (56 AE 2 mV per decade) and response time (15 s) is displayed. The sensor shows a Nernstian response for [Tl(DOEDDSA)]À ions over a wide concentration range of 6.4 Â 10 À7 to 10 À2 M, with a detection limit of thallium complexonate 8.2 Â 10 À8 M. The sensor can be used for more than three months without any considerable divergence in potentials. The selectivity is also good towards the most common univalent and divalent anions and the signal is constant in the pH range 4.7 -9.0. An application to thallium determination in a mineral sample proved to be a success, and it was employed as an indicator electrode in direct potentiometry.

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