pH meter maintenance and solutions to common problems!
1. The pH values measured twice are different for the same sample?
Temperature changes or chemical reactions in the sample itself can cause changes in pH. Therefore, try to keep the temperature consistent and avoid chemical reactions.
2. The same sample is measured on two pH meters at the same time, but the readings are inconsistent?
Since the calibration conditions of the two pH meters are different (such as calibration done at different times), the measured values are different. Therefore, the pH meter must be calibrated with the same buffer at the same time, and then measured at the same time.
3. Why has the buffer deteriorated and cannot be used within the validity period?
The validity period of the buffer solution refers to the storage period in the unopened condition. Once opened and used, the buffer is prone to deterioration due to the action of various molds in the air.
Note: Never pour used buffer solution back into the original bottle!
4. How often do electrodes need to be calibrated?
The calibration frequency of the electrode depends on the specific conditions such as electrode use, maintenance, sample properties, and measurement accuracy. It is recommended to calibrate once a day and no more than once a week at most. When replacing electrodes or not using them for a long time, they must be calibrated before use.
5. How to maintain pH electrode?
After using the electrode for a period of time, if you find that the slope becomes lower and the response speed becomes slower, you can try the following methods:
① If the measurement sample contains protein, the electrode membrane can be cleaned with pepsin/hydrochloric acid washing solution.
② If the measurement sample is oily/organic liquid, it can be rinsed with acetone or ethanol.
③If the electrode junction is found to be dirty and black, you can use mercaptan cleaning solution to clean the junction.
④Activate the electrode film. Activation method: Soak in electrode regeneration solution for 30 seconds, then soak in 3mol/L KCl solution for 5 hours.
6. The sample temperature is 10°C. At this time, does the meter display the pH value at 10°C or 25°C?
The acidometer displays the pH value of the solution at the current temperature. If measured at 10°C, the meter displays the value of the solution at 10°C. If you need to obtain the pH value of 25°C, you must raise/lower the temperature of the solution to 25°C, and then Take measurements. The temperature compensation of the acidometer refers to compensating the effect of temperature on the pH electrode, but it cannot compensate the pH value at any temperature to 25°C.
7. Why does the electrode display 7.02 after calibration in pH 7.00 buffer?
At this time, the buffer temperature is around 20°C. Since the pH of a buffer changes slightly with temperature, 7.00 is only the value of the buffer at 25°C, while the value of the buffer at 20°C should be 7.02. The pH meter can automatically compensate for the effect of temperature on the buffer to ensure measurement accuracy.
