title: 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, approximately 10 M[ohm]) electrodes implied a tip opening radius of 0.135 microm and a tip taper of 0.0215 microm/microm in the most distal (0-150 microm), and of 0.0105 microm/microm in the next most distal (150-1000 microm) 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.
authors.affiliation: Department of Physiology and Neuroscience, University of Lund, Sweden. christer.fahraeus@mphy.lu.se
authors.forename: C
authors.initials: C
authors.lastname: Fåhraeus
authors.forename: K
authors.initials: K
authors.lastname: Borglid
authors.forename: W
authors.initials: W
authors.lastname: Grampp
mesh_terms: D002712:Chlorides / Q000032:analysis*; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods; D004573:Electrolytes; D004867:Equipment Design; D008839:Microelectrodes; D011188:Potassium / Q000032:analysis*; D011197:Potassium Radioisotopes; D019275:Radiopharmaceuticals / Q000032:analysis; D012588:Scintillation Counting / Q000379:methods; D012680:Sensitivity and Specificity
chemical_list: D002712:Chlorides; D004573:Electrolytes; D011197:Potassium Radioisotopes; D019275:Radiopharmaceuticals; D011188:Potassium