Effect of Temperature on pH Measurement Accuracy
mple, a 0.2 level pH meter is calibrated in a pH 7.00 buffer solution at 30 ℃, and then tested in a solution at 60 ℃ (assuming the pH range of the solution is between pH 6-8, which differs from pH 7.0 by one pH unit). The maximum error of temperature effect is 30 × 0.003=0.09 pH. If there are 3 pH units (within the pH range of 4-10), the maximum error is 0.27 pH, indicating that temperature has a significant impact on pH. Of course, we can also draw the conclusion that in order to reduce the error of temperature on pH measurement, we should pay attention to the following three points:
(a) Try to choose a buffer solution that is close to the pH value of the measured solution to calibrate the pH meter;
(b) Try to make the temperature of the calibration solution consistent or close to the temperature of the measured solution;
(c) A pH meter with temperature compensation should be selected.
PH meters with an accuracy higher than 0.1 pH have temperature compensation adjustment, while pH meters with a 0.2 level do not have temperature compensation. Some pH meters at 0.2 level also claim to have an accuracy of 0.1 level, but this is actually impossible. Some people have confused the concepts of resolution 0.1 pH and accuracy 0.1 pH. Even in terms of a pH unit, the pH error separated by 60 ℃ is 0.03 × 60=0.18 pH. Therefore, without temperature compensation, the highest accuracy of a pH meter is only 0.2 pH.
