ABSTRACT
Two types of ion-selective electrode will be described which will satisfy most of the requirements described above. One is a macro-electrode based on a dip-cast construction, the other is an ion-selective micro-electrode based on the intracellular micro-pipette used for recording intracellular potentials. The dip-cast electrode has dimensions of the order of one millimetre, has a relatively low resistance and is physically robust. It has thus been used in a variety of extracellular spaces some of which will be given as examples later. Ion-selective micro-electrodes are very small, with a tip diameter of the order of one micrometre or less and so have been used to make measurements in the intracellular space and regions inaccessible to larger ion-selective electrodes. The small size however increases their resistance thus limiting their speed of response, stability and selectivity.
