Shift and drift of electromotive forces of solid-state electrodes with ion-selective liquid membranes

The behavior of electromotive forces (EMFs) of solid-state ion sensors, in which the interface between the ion-selective liquid membrane and the silver-silver chloride electrode is modified with a hydrophilic intermediate layer containing various concentrations and various kinds of electrolyte salts, are described in this study. The EMF of this sensor is significantly dependent on the concentrations and kinds of electrolyte salts in the intermediate layer. The solid-state ion sensor shows a stable EMF only when the intermediate layer contains the primary ions and chloride ions. This indicates that an efficient ion exchange process is necessary at all interfaces involved, including a thin water layer, for a stable EMF of the solid-state ion sensor. The resistance measurement shows that mechanical deterioration of the ion-selective membranes in the solid-state ion sensor with the optimized intermediate layer does not take place due to the osmolality difference as long as the ion-selective membrane adheres to the sensor body tightly. The long term stability of the solid-state ion sensor with the optimized intermediate layer was found to be sufficient for practical use.