Surface and Volume Resistivity of Pyrex Glass Used for Liquid Membrane Ion-Sensitive Microelectrodes

Abstract

The essence of a liquid membrane ion-sensitive microelectrode is a column of sensor lodged in the tip of a glass micropipette. For it to function well, the electrical resistivity of the surface of the glass crmust be high, and so must the resistance through the wall of the pipette. The behavior of a fine-tipped microelectrode depends on many factors, and direct examination of electrode responses has led to conflicting ideas about leaks (e.g., [11, 17]). We have therefore made measurements of resistance on the most commonly used glass, Pyrex (Corning 7740), on samples of defined geometry (tubes), and with the atmospheric contamination of a typical physiological laboratory. In addition, we have drawn on literature describing the use of new analytical techniques for studying glass surfaces, much of this research having been done with a view to applications in capillary column chromatography or fiber optics. We will suggest that the physiologist’s problems are confined to the extreme tip of the microelectrode, that they are unlikely to be due to hydration of the glass, and that they might be partly due to cracks.