Open tip glass microelectrodes: conduction through the wall at the tip.

Abstract

A theoretical and experimental study of the electrical resistance and the tip potential of open tip glass microelectrodes is presented. The main physico-chemica1l factors considered are the diffusion process of ions through the open tip, the ionic conduction in the bulk solutions, and the ionic conduction in the electrochemical double layers at the glass-electrolyte interface. In order to take into account possible conduction through the glass at the tip, a small part of the microtip is considered to be highly hydrated and its length is considered as an upper limit for the extent of hydration. Its longitudinal conduction is assumed to be much greater than in the remaining truncated cone. This lumped model, like a previous one which assumed a uniform distributed hydration, can be used to explain the electrical properties of open tip glass microelectrodes. It is concluded that end effects at the tip of a glass microelectrode are important and could explain in part their electrical properties.