Response of an Iridium Oxide pH-Sensor in Nonaqueous Solutions. Comparison with Other pH-Sensors

The response of an iridium oxide (IrO2) pH-sensor (nonaqueous version of METOX, TOA Electronics Ltd.) was studied in various dipolar aprotic solvents. From the potential measurements in picric acid-picrate solutions, it was confirmed to respond in a Nernstian way to the pH in all the solvents studied. The response speed of the IrO2 pH-sensor was compared with that of the glass electrode as well as those of the Si3N4- and Ta2O5-type pH-ISFETs, carrying out acid-base titrations at various speeds of titrant addition. The response speed of the IrO2 pH-sensor was much higher than that of the glass electrode, though it was somewhat lower than those of the pH-ISFETs. The IrO2 pH-sensor responded in a wide pH range, gave reproducible results, needed no pretreatment, and was durable over a year. It is promising for pH measurements in various nonaqueous solutions free from redox systems.