Temperature dependence of response of a pH glass electrode for environmental measurement

During the continuous monitoring of pH in environmental water, the temperature of the environmental water changes at each moment. Coral reefs are likely to be strongly affected by ocean acidification, so accurate and continuous pH monitoring is important. On the other hands, the water temperature in coral reef areas varies greatly not only due to solar radiation but also due to the mixing of open ocean water and land water. This temperature variation affects the accurate pH measurement. Preparing calibration values for the pH electrodes at all water temperatures is impossible, but the monitoring accuracy could be improved by predicting the constituent values at the on-site water temperature from the electrode calibration results at one or two temperatures. Therefore, we calibrate the pH at one or two temperatures and use the result for estimating the calibration value at another temperature. For this purpose, we estimated the pH change of the internal liquid of the electrode (assumed as a phosphate buffer) under saturated and unsaturated conditions of the coexisting KCl in the buffer.