Properties of electrolyte-filled glass microelectrodes: an experimental study

Abstract

The electrochemical and electrical properties of geometrically defined electrolyte-filled microelectrodes were studied at various transelectrode current passages, using radiotracer ( 38Cl and 42K) and electrical techniques. Geometrically, the electrodes were defined by their tip properties that, for standard (single-barrelled, 3.0 M KCl-filled, ≈10 MΩ) electrodes implied a tip opening radius of 0.135 μm and a tip taper of 0.0215 μm/ μm in the most distal (0–150 μm), and of 0.0105 μm/ μm in the next most distal (150–1000 μm) tip regions. From the radiotracer studies it followed that (a) in the absence of transelectrode current passage, K + and Cl − are leaking from the electrode tip in amounts corresponding to currents of ±3.8 nA, and (b) in the presence of transelectrode current passage, the flow of K + and Cl − through the electrode tip changes with the transelectrode current in a statistically linear fashion so that K + carries about 80% and Cl − about 20% of any electrode-injected current. From the electrical measurements it appeared that the standard electrodes are characterized by (a) a tip potential of −2.6 mV, and (b) a resistance that changes from an instantaneous, non-rectifying type to a steady state, outwardly rectifying type, within tenths of a second of constant current flow. The outward current rectification was seen to be reduced by raising [KCl] in the immersing solution, or by lowering it in the filling solution. Together, the observed electrode properties are consistent with the electrode electrolyte's solute and solvent turnover being governed by electro-osmotic as well as by electrodiffusion laws.