DETERMINATION OF THALLIUM(I) IN SOLUTIONS CONTAINING CATIONS INTERFERING IN POTENTIOMETRIC ION-PAIR FORMATION-BASED TITRATIONS

The possibility of the use of simple potentiometric coated-wire sensor s in the analysis of mixtures of ions, the determination of which is b ased on the ion-pairing principle, was studied. Attention was especial ly paid on the determination of thallium(I) in the presence of alkali metal ions, mercury(II), copper(II) and silver(I). It was found that t hallium(I) can selectively be titrated with sodium tetraphenylborate i n diluted solutions. Interferences of ions of the alkali metals are pr actically negligible if their concentrations are lower than 10(-3) mol dm-3. Interference of Cu(II) is minimized using EDTA as a masking age nt, Hg(II) and Ag(I) ions are sufficiently screened by additions of so dium cyanide. In mixtures containing higher concentrations of alkali m etals, thallium(I) can be oxidized to thallium(III) and selectively ti trated as TlCl4- with a cationic titrant.