Temperature plays a significant role on pH measurement. This is a well-know fact for most users of pH test equipment. However, the temperature affects not only your sensor but also your sample. All solutions will change their pH value with temperature. This is a result of the shifting of the chemical equilibrium of the components, mainly of dissociation.
The automatic temperature compensation (ATC) in a pH meter corrects for the change in mV per pH unit generated by the glass electrode as defined by the Nernst equation.
The pH change with temperature is not an error. It is the true pH of the
solution at the new temperature. At the table above you can see typical
pH values for solutions at different temperatures. The conclusion that
we can draw is that the effect of temperature is greatest for highly
A common mistake is when you take a sample from a process tank and make the pH measurement at the laboratory. You are probably not measuring at the same temperature (?), and this means that you do not have the same pH value.
How big the difference is between the two pH values, depends, of course, on your measured solution.
If you want to compare
pH values measured at different temperatures you need to use a function
called solution temperature compensation. Solution temperature
compensation converts the pH at the measurement temperature to the pH at
a reference temperature. The reference temperature is almost always
Do not confuse solution temperature compensation with the automatic temperature compensation used to correct the pH electrode, see at the beginning of this page.
The change in pH with temperature is called the solution temperature coefficient (pH/°C). For example, if a solution has a temperature coefficient of -0.035 [pH/°C], the pH decreases 0.035 units for every °C increase in temperature. Usually the temperature coefficient must be determined empirically.
• The pH value of a solution depends on the temperature.
• A pH value without a temperature value is meaningless.
• Solution temperature compensation converts measured pH to the pH at 25°C.
• Only pH values taken at the same temperature or converted using solution temperature compensation can be compared to each other.
To achieve highest accuracy, calibrate and measure at the same temperature.
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