PROPERTIES OF ELECTROLYTE-FILLED GLASS MICROELECTRODES - AN EXPERIMENTAL-STUDY

The electrochemical and electrical properties of geometrically defined electrolyte-filled microelectrodes were studied at various transelect rode current passages, using radiotracer (Cl-98 and K-42) and electric al techniques. Geometrically, the electrodes were defined by their tip properties that, for standard (single-barrelled, 3.0 M KCl-filled, ap proximate to 10 M Omega) electrodes implied a tip opening radius of 0. 135 mu m and a tip taper of 0.0215 mu/mu m in the most distal (0-150 m u m), and of 0.0105 mu/mu m in the next most distal (150-1000 mu m) ti p regions. From the radiotracer studies it followed that (a) in the ab sence of transelectrode current passage, K+ and Cl- are leaking from t he electrode tip in amounts corresponding to currents of +/-3.8 nA, an d (b) in the presence of transelectrode current passage, the flow of K + and Cl- through the electrode tip changes with the transelectrode cu rrent in a statistically linear fashion so that K+ carries about 80% a nd Cl- about 20% of any electrode-injected current. From the electrica l measurements it appeared that the standard electrodes are characteri zed by (a) a tip potential of -2.6 mV, and (b) a resistance that chang es from an instantaneous, non-rectifying type to a steady state, outwa rdly rectifying type, within tenths of a second of constant current fl ow. The outward current rectification was seen to be reduced by raisin g [KCl] in the immersing solution, or by lowering it in the filling so lution. Together, the observed electrode properties are consistent wit h the electrode electrolyte's solute and solvent turnover being govern ed by electro-osmotic as well as by electrodiffusion laws. (C) 1997 El sevier Science B.V.