How should the third point calibration of the pH meter be calibrated?
How should the third point calibration of the pH meter be calibrated? Customer question: Our PH meter user unit audited the following questions: The PH meter needs three-point calibration, and two points are not enough. May I ask everyone, our company uses 7.004.01 for calibration. If the third point is needed, should we use 9.21 buffer or 10.01, 9.18, 12.46, 1.68 and other buffers? How to determine? answer:
1. In fact, the pH correction at the third point mainly depends on your sample conditions. As you said, there are many kinds of calibration solutions ranging from pH 1.68 to 12.46, and the appropriate calibration solution should be selected according to the final pH range of the sample. We commonly use 4.00, 6.86, 9.18, if your sample is more alkaline, you need 9.18, 10.01, 12.46. Calibration sequence is also different according to different instruments. Some require calibration in order, while others do not. The instrument will automatically recognize it. You need to refer to the relevant instrument manual.
2. No matter what kind of pH meter, the point of pH=7 must be calibrated, and the point of pH=7 must be calibrated first when the two points are calibrated. When doing calibration, start from 7.0, and 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 can be used to meet the requirements. If the requirements are very high, the third point should be considered. Some instruments can calibrate three points, and there is an optional mode, which can be used directly. For some that don't, two-point two-point proofreading is generally used, that is, proofreading twice.
3. We usually use the calibration sequence of 7, 4, 10. Check the acid first and then the base.
