ABSTRACT
Ion-selective microelectrodes are used to measure the concentration of a specific ion. Most ion-selective microelectrodes in current use are based on a ‘liquid membrane’ placed in the tip of a glass microelectrode. This liquid is permeable to a specific ion, but excludes other ions. In fact the ion-selective electrode measures changes in ion activity rather than concentration, but as long as the total ion activity remains relatively constant and the electrode is specific for only one ion then the electrode can be calibrated in relation to ion concentration rather than activity. Significant electrical coupling would result in an inability to accurately determine what proportion of the electrode response was due to changes in ion concentration and what proportion was due to changes in membrane potential, because any change in potential in one barrel would affect the potential recorded in the other barrel.
