According to the Nernst equation cell potential depends on the temperature. Thus when measuring pH temperature changes must be taken into account.
In most cases it is enough to take care about the temperature at the time of calibration. Temperature changes slope which is checked during the calibration process. There are two things to take into account:
- for best results measurements should be done in the same temperature calibration took place,
- pH of calibration buffers changes with temperature, so you can't assume - especially using warm and hot buffer solutions - that their pH is nominal. pH values of calibration buffers should be tabelarized by manufacturer.
Many commercially available pH meters, especially better ones, have built in temperature compensation. The temperature compensation may be either manual or automatic. With manual compensation, a separate temperature measurement is required, and the pH meter manual compensation control can be set with the approximate temperature value. With automatic temperature compensation (ATC), the signal from a separate temperature probe (sometimes built into the electrode) is fed into the pH meter, so that it can accurately determine pH value of the sample at that temperature.