SCANNING ELECTROCHEMICAL MICROSCOPY .19. ION-SELECTIVE POTENTIOMETRICMICROSCOPY

Potentiometric pH selective tips for scanning electrochemical microsco py (SECM) have been developed and used to image local pH changes in a variety of model chemical systems. Images of pH profiles around a plat inum microelectrode during water reduction, a corroding disk of silver iodide in aqueous potassium cyanide, a disk of immobilized urease hyd rolyzing urea, and a disk of immobilized yeast cells in glucose soluti on were obtained. A simple method for fabricating antimony microdisk e lectrodes suitable for use in SECM is described. The general theory fo r SECM with potentiometric ion selective tips is also presented, assum ing that the tip is a purely passive sensor. Reasonable agreement with theory was observed for relatively large tip to surface separations. The deviations observed at small separations were due to shielding of the surface by the tip and, consequently, were found to be much less s ignificant for smaller tips.