Indirect Determination of Microelectrode Geometry

Measurement of the electrical properties of living cell membranes often involves electrolyte filled glass capillary microelectrodes, the properties of which enter into the interpretation of the measurements. Since the tips of the electrodes are beyond the resolving power of the light microscope, we present here indirect methods for the determination of the tip geometry based on resistance measurements. A model consisting of a 2-parameter family of geometric shapes is selected to agree with observed resistances over a range of hydrostatic pressure heads and fluid conductivities. For a specific electrode the two defining parameters are evaluated from the resistances of the electrode when immersed successively in pools of two different conductivities.