How Much Does Temperature Affect pH Accuracy Measurements?
For pH electrodes, temperature affects each pH by 0.003pH/°C. For example, a 0.2-grade pH meter is calibrated in a 30°C pH buffer and then tested at 60°C (assuming the pH of the solution ranges from pH 6 to 8) There is a difference between pH7.00 and pH7.00 by one pH unit), then the maximum error affected by temperature is 30×0.003=0.09pH. If it is 3 pH units (within the pH range of 4-10), the maximum error is 0.27pH, from which it can be seen that the temperature has a great influence on the pH. 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:
(1) Try to select a buffer solution close to the pH value of the solution to be measured to calibrate the pH meter.
(2) Try to make the temperature of the calibration solution consistent with or close to the temperature of the measured solution.
(3) A pH meter with temperature compensation should be selected.
pH meters with an accuracy higher than 0.1pH 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 0.1pH and precision 0.1pH. Even in terms of one pH unit, the pH error at a distance of 60°C is 0.003×60=0.18pH. Therefore, the highest accuracy of a pH meter without temperature compensation is only 0.2pH.
