Discussion on the Influence of Temperature on the Accuracy of pH Measurement
For pH electrodes, the effect of temperature is 0.003 pH/°C for each pH. For example, a 0.2-grade pH meter is calibrated in a pH 7.00 buffer solution at 30°C, and then tested at 60°C (assuming the pH range of the solution is at pH 6 There is a difference between pH 7.0 and pH 7.0 by one pH unit), then the maximum error affected by temperature is 30×0.003=0.09 pH. If it is 3 pH units (in the range of pH 4~10), the maximum error is 0.27 pH, from which it can be seen that the influence of temperature on pH is very important. Of course, we can also draw conclusions from it. In order to reduce the error of temperature to pH measurement, we should pay attention to the following three points:
(a) Try to select a buffer solution 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 with 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 adjustments, while pH meters with a grade of 0.2 do not have temperature compensation. Some 0.2-grade pH meters also claim to have 0.1-grade accuracy. In fact, this is impossible. Some people confuse the two concepts of resolution 0.1 pH and accuracy 0.1 pH. Even in terms of one pH unit, the pH error at a distance of 60°C is 0.03×60=0.18 pH. Therefore, the highest accuracy of a pH meter without temperature compensation is only 0.2 pH.
