A highly selective thallium(I) electrode based on a thia substituted macrocyclic ionophore

A new highly Tl(I)-selective PVC membrane electrode based on tetrathia macrocycle 6,7: 14,15-dibenzo-5,8,13,16-tetraoxo-1,4,9,12-tetrathiacyclohexadecane Bz₂O₄(16)aneS₄] (I) as membrane carrier, o-nitrophenyloctyl ether (o-NPOE) as solvent mediator and potassium tetrakis(p-chlorophenyl)borate (KTpClPB) as lipophilic additive has been developed. The best performance was given by the membrane of macrocycle (I) with composition 3:120:1.5:50 (I:o-NPOE:KTpClPB:PVC). This electrode exhibits a Nernstian response to Tl(I) ions in the concentration range 1.0 × 10⁻¹-2.23 × 10⁻⁶ M with a slope of 58.2 mV/decade of concentration and a detection limit of 1.58 × 10⁻⁶ M. The response time of the sensor is 12 s and can be used over a period of 4 months with good reproducibility. The proposed electrode revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals. The electrode works well over a pH range of 3.2-11.5 and in partially non-aqueous medium with up to 30% organic content. The sensor was also used as an indicator electrode in potentiometric titration of Tl(I) ions with KI solution.