Operating Instructions for the Third Point Calibration of pH Meters
During the audit of a certain pH meter user, the following issue was raised: the pH meter requires three points of calibration, and two points are not enough. So, for the calibration done with 7.00 and 4.01, if a third point is needed, should we use 9.21 buffer or 10.01, 9.18, 12.46, 1.68, or which other buffer? How to determine?
1. The amount of pH correction at the third point mainly depends on your sample situation. As mentioned earlier, there are many calibration solutions available from pH 1.68 to 12.46, and the appropriate calibration solution is chosen based on the final pH range of the sample. We commonly use 4.00, 6.86, and 9.18. If your sample is more alkaline, you need 9.18, 10.01, and 12.46. The calibration sequence varies depending on the situation of different instruments. Some require calibration in sequence, while others do not. The instrument will automatically recognize it and please refer to the relevant instrument user manual.
2. No matter what type of pH meter it is, the point of pH=7 must be corrected, and the point of pH=7 must be corrected first when calibrating at two points. Starting from 7.0, the selected standard solution is related to the pH value of the solution to be measured, so that the pH value of the solution can fall within the calibrated pH range. Generally, two points are sufficient to meet the requirements, and the third point is only considered if the requirements are high. Some instruments can calibrate three points and have a mode to choose from, which can be used directly. For some that are not available, it is generally done through two point and two point proofreading, which means proofreading twice.
3. We usually use a calibration sequence of 7,4,10. First calibrate the acidity and then calibrate the alkalinity.
So how do you activate and calibrate the pH meter that has been idle for a long time and the electrode is not in the protective solution? What should I pay attention to? How to prepare standard calibration solution? What details should I pay attention to when using a pH meter?
