Potentiometric titrations with ion-exchanging membrane electrodes : Part II. A theoretical treatment of the effect of membrane selectivity

The possible influence of the selectivity of the membrane used in an indicating electrode with potentiometric titrations was investigated by introducing some simple modifications in the calculations performed earlier. The influence of the selectivity is visible only before the equivalence point when the counter-ion is precipitated initially from the titrated solution. When the co-ion is precipitated initially, the shape of the titration curve is altered only after the equivalence point. The reliability of the determination of the equivalence point can be either advantageously or disadvantageously influenced by the selectivity, depending on the value of the selectivity coeffcient and the ratio of the diffusion coefficients.