Calibration of PH meter and configuration of standard buffer solution
1. What is the standard buffer solution of pH meter?
The pH buffer solution is a solution that can keep the pH value stable. If a small amount of acid or alkali is added to this solution, or a small amount of acid or alkali is produced by chemical reaction in the solution, and the solution is properly diluted, the pH value of this solution is basically stable. This solution can resist a small amount of acid or alkali or dilution, so that the pH value is not easily changed is called a pH buffer solution.
The standard buffer solution of pH meter has the following characteristics:
(1) The pH value of the standard solution is known and reaches the specified accuracy;
(2) The pH value of the standard solution has good reproducibility and stability, and has a large buffer capacity, a small dilution value and a small temperature coefficient;
(3) the preparation method of the solution is simple;
2. For PH meter, what is the main function of pH buffer solution?
(1) Calibrate the pH meter before pH measurement.
⑵ Used to verify the accuracy of the pH meter. For example, after calibrating the pH meter with pH6.86 and pH4.00, insert the pH electrode into the pH9.18 solution to check whether the displayed value of the instrument is consistent with the pHs value of the standard solution;
⑶ Check whether the pH meter needs to be recalibrated during general accuracy measurement. After the pH meter is calibrated and used, it may drift or change. Therefore, before testing, insert the electrode into the standard buffer which is close to the solution to be tested, and determine whether it is necessary to calibrate again according to the error.
⑷ Test the performance of pH electrode.
3. How to prepare pH standard buffer solution?
For general pH measurement, a complete set of pH buffer reagents (250ml can be prepared) can be used. When preparing the solution, deionized water should be used and boiled for 15 ~ 30 minutes in advance to remove dissolved carbon dioxide. Cut open the plastic bag, pour the reagent into a beaker, dissolve it with proper amount of deionized water, rinse the packaging bag, pour it into a 250ml volumetric flask, dilute it to scale, and shake it well.
4. How to correctly store and use pH buffer solution;
After the buffer solution is prepared, it should be packed in glass bottles or polyethylene bottles (alkaline pH buffers, such as pH9.18, pH10.01 and pH12.46, should be packed in polyethylene bottles). The bottle cap should be tightly closed and stored in the refrigerator at a low temperature (5 ~ 10℃). Generally, it can be used for about two months. If turbidity, mildew or precipitation are found, it can not be used any more. When using, several 50ml polyethylene vials should be prepared, and the buffer solution in the large vial should be poured into the vial, and left at ambient temperature for 1-2 hours before use. After use, the buffer solution in the vial can be used for 2 ~ 3 days under the environmental conditions of > 10℃. Generally, the use time of the three solutions of pH7.00, pH6.86 and pH4.00 can be longer, and the pH value of the solutions of pH9.18 and pH10.01 is relatively easy to change because of absorbing CO2 in the air.
