Specific Response Characteristic of Ion-Selective Glass Electrodes and Its Applications to Potentiometric Titration

Abstract

Specific response characteristic of cation-selective glass electrodes and its applications to potentiometric titration have been investigated. The Na⁺-selective electrode, named by its most common ion species measurable, developed its electrode potential as the normal response approaching towards the new equilibrium potential when the electrode was exposed to changing concentrations of Na⁺, Ag⁺, and Li⁺, whereas the same electrode exhibited instantaneous transient response after the sudden change of concentrations of K⁺, Rb⁺, Cs⁺, NH4⁺ and most of the multivalent cations to which the electrode was practically nonresponsible at the equilibrium state. The transient response was numerically interpreted as sequential changes of the diffusion potentials in the two adjacent phases, i. e. the hydrated layer at the surface and the internal glass bulk of the membrane. The univalent-cation electrode made by different glass composition, however, gave no transient response presumably because of thicker hydrated layer where the diffusion potential was continuously developed within a finite time. The transient response with the former electrode was effectively employed for the end point detection during various potentiometric titrations by bivalent cations. Another type of titration was also feasible when the electrode was immersed in a sample solution containing a low level of sensing ion and titrated by another sensing ion. Either of the above titration curves marked a sharp inflection at the equivalence point.