The third point to calibrate the pH meter
No matter what kind of acidity meter is, the point of pH=7 should be corrected, and the point of pH=7 should be corrected first when calibrating two points. When doing calibration, starting from 7.0, the optional standard solution is related to the pH value of the solution to be tested, so that the pH value of the solution can fall within the calibration pH range. Generally two points can meet the requirements. If the requirements are high, the third point will be considered. Some instruments can be calibrated at three points, and there are optional modes that can be used directly. Some are not. Generally, two-point proofreading is used, that is, proofreading twice. The correction made by 7.004.01, if the third point is needed again, should I use 9.21 or 10.01, 9.18, 12.46, 1.68 and other buffers? How to be sure?
1. In fact, what is the third correction of pH, mainly depends on your sample situation. As you said, there are many kinds of calibration solutions ranging from PH 1.68 to 12.46. Choose the appropriate calibration solution according to the final pH range of the sample. We generally use 4.00, 6.86, and 9.18. If your sample is more basic, you will need 9.18, 10.01, and 12.46. Depending on the instrument, the calibration sequence is also different. Some require sequential calibration, some do not. The instrument will be recognized automatically, so please refer to the relevant instrument instruction manual.
2. No matter what kind of acidity meter, the point of pH=7 needs to be corrected. When calibrating two points, the point of pH=7 should be corrected first. During the calibration process, starting from 7.0, the selected standard solution is related to the pH value of the solution to be tested, so that the pH value of the solution can fall within the calibrated pH range. Generally two points can meet the requirements. If the requirements are high, the third point will be considered. Some instruments can be calibrated at three points, and there are optional modes that can be used directly. Some are not. Generally, two-point proofreading is used, that is, proofreading twice.
