Fabrication of anodically electrodeposited iridium oxide film pH microelectrodes for microenvironmental studies

A new method for fabrication of anodically electrodeposited iridium oxide film pH microelectrodes has been developed in this study. Novel for its tip size (3-10-μm tip diameter), the microelectrode is fabricated in a tapered glass micropipet filled with a low melting point alloy. The tapered end is recessed and platinized. Thereafter, iridium oxide is electrodeposited over the platinized end in the recessed part. The microelectrode has a very short response time (t₈₀ < 5 s) in the pH range of 0-12 with an accuracy of 0.05 pH unit. The pH microelectrode is not affected by most ions and complexing agents of relevance in environmental and biological studies; it can be used in fluids over wide ranges of stirring speeds (0-55 rpm) and temperatures (∼5-40 °C). Redox agents such as dissolved oxygen and hydrogen peroxide have no effect on the pH response while quinhydrone, ferro- and ferricyanide, and sodium sulfide have marked effects. However, the microelectrode can still be used in any sample when calibration is done in standards having similar redox characteristics.