The ion adsorption effect on selectivity of liquid state, O,O '-didecylodithiophosphate chelate based ion-selective electrodes

Ion-selective electrodes with liquid membranes including O,O'-didecylo-dith iophosphate complexes of TI(I), Pb(II), Cd(II) and Ni(II) are characterised and results of the study on their selectivity are reported. A short review of problems related to determination and interpretation of selectivity coe fficients of ion-selective electrodes is presented with particular emphasis on the drawbacks of the hitherto used methods. A new method is proposed, w hich in the experimental part is close to that of mixed solutions recommend ed by IUPAC but can be applied also when the latter is of no use. The metho d proposed for determination of selectivity coefficients simultaneously all ows concluding about the mechanism of potential generation. A few examples of relations between selectivity coefficients of the electrodes and concent rations of disturbing ions in solutions, are given. An interpretation of th e above relations as results of the processes of ion adsorption at the inte rface of the electrode membrane and water solution is proposed. The results obtained have confirmed the hypothesis given by Pungor, according to which the main role in the mechanism of generation of ion-selective electrodes p otential is played by the processes of ion chemisorption at the interface o f the membrane and water solution. (C) 2000 Elsevier Science B.V. All right s reserved.