ph meter calibration 3-point calibration procedure
With the calibration done with 7.004.01, if a third point is needed again should I use the 9.21 buffer or which of the other buffers such as 10.01, 9.18, 12.46, 1.68, etc.? How to determine?
1, Actually, how much the third point of pH picking calibration is depends largely on your sample situation. As you said, there are many kinds of calibration solutions from pH1.68~12.46, according to the final pH range of the sample to decide to choose the appropriate calibration solution. We commonly used are 4.00, 6.86, 9.18, if your sample is more alkaline, you need 9.18, 10.01, 12.46. calibration order according to the different instruments also varies, some require calibration in order, and some do not require, the instrument will be automatically recognised, you need to refer to the relevant instrument instruction manual.
2, no matter what kind of pH meter, pH = 7 this point must be corrected, and in the two-point calibration should be corrected first pH = 7 this point. Do the calibration from 7.0 to start, select the standard solution and to determine the pH value of the solution, so that the pH value of the solution can fall within the corrected pH range. Generally two points can be used to meet the requirements, if the requirements are very high, before considering the third point. Some instruments can calibrate three points, there are modes to choose, you can use the mode directly. Some do not have, generally two-point two-point calibration, that is, calibration twice.
3, we usually use 7, 4, 10 calibration order. First calibrate acid and then calibrate alkali.
