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Microscopic Measurement of pH with Iridium Oxide Microelectrodes

David O. Wipf* and Fuyun Ge^†

Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762

Thomas W. Spaine^‡ and John E. Baur*

Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160

Anal. Chem., 2000, 72 (20), pp 4921–4927

DOI: 10.1021/ac000383j

Publication Date (Web): September 13, 2000

Corresponding authors. D.O.W.: (e-mail) wipf@ra.msstate.edu; (fax) (662) 325-1618. J.E.B.: (e-mail) jebaur@ilstu.edu; (fax) (309) 438-5538.

†

Present address: DBS Communications, Inc., 126 W. Center Court, Schaumburg, IL 60195.

‡

Present address: Department of Chemistry, Iowa State University, Ames, IA 50011.

Abstract

Microscopic pH electrodes were produced by deposition of hydrous iridium oxide onto carbon fiber microelectrodes. The electrodes exhibit two linear regions of potentiometric response between pH 2−6 and pH 6−12. The electrodes respond to pH changes within 50 ms, and an equilibrium value is reached within 30 s. By using these electrodes as probes in the scanning electrochemical microscope, dynamic pH changes occurring at or near a surface can be measured and pH maps of the surface can be generated. Vertical pH profiles and images of pH were obtained at substrates where electrochemical (oxidation and reduction of H₂O₂, hydrogen evolution) or enzymatic (glucose oxidase) reactions involving proton transfers occur.

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