H(+)-selective electrodes based on neutral carriers: Specific features in behaviour and quantitative description of the electrode response.

The influence has been studied of the membrane and solution composition on the response of H(+)-ISEs with plasticized polymer and liquid membranes based on the neutral carriers N,N-dioctylaniline and tridecylamine in association with trioctyloxybenzene sulphonic acid. It is shown that the extraction processes at the membrane/solution interface exert the main effect on the response limits by inducing essential changes in the activity of potential-determining ions in the membrane. At low pH, the amine extraction of acids followed by neutralization (free amines binding in ion-pairs) is the relevant process, while at high Ph it is the extraction of metal cations with amine salts of a lipophilic acid, with the consequent displacement of amine from the salts. Equations are suggested to represent the interphase potential of the H(+)-ISE membranes with allowance for these extraction processes. The experimental electrode responses of both liquid and polymer membranes are shown to be well described by the equations for the interphase potential, thus indicating its dominant contribution to the membrane potential.