Several important questions about pH meter measurement
pH measurement of colloids and turbid liquids
In this type of sample, the glass electrode can generally respond normally. If the glass electrode is contaminated, it can be handled according to the glass electrode cleaning and maintenance methods. The problem often occurs at the liquid junction end of the reference electrode, where charged micelles or particles are easily If the potential of the liquid junction is unstable, two methods are generally used to solve it:
Increase the seepage speed of the salt bridge solution to reduce the impact of micelles and particles on the liquid junction.
pH measurement of highly alkaline and highly acidic samples
In alkaline solutions with pH>10, lithium glass electrodes should be used to reduce alkali errors. At present, the alkali errors of pH glass electrodes are generally small; when pH>12, the alkali errors increase because the electrodes are immersed in alkali for a long time. In the liquid, the electrode will experience potential drift, slow response, etc. At this time, the electrode should be rinsed with water and then immersed in 0.1mol/L HCL for 24 hours. After this treatment, the electrode performance can be restored.
In high-alkali solutions, the external reference liquid junction material, ceramic core, and asbestos filaments are easily corroded and damaged by the alkali solution.
In acidic solutions (pH<2), if acid errors occur, it is best to use lithium glass electrodes. If potential drift and other phenomena occur in acidic solutions, the electrodes can generally be restored after being immersed in distilled water.
When measuring alkalinity and acidity, the positioned standard solution should be as close to the pH value of the measured solution as possible to reduce the residual liquid junction potential.
When calibrating alkaline solutions, attention should be paid to the influence of CO2 in the air on the standard solution. After the pH=10 standard solution is in contact with the air for 12 hours, the pH changes by 0.22 units due to the influence of CO2, and the pH of the pH=9.18 standard solution changes by 0.02 units. Therefore, it is best to use a sealed container when calibrating an alkaline solution. Open it after use and cover it after use, and immerse the electrode in the solution.
pH measurement of solutions containing hydrofluoric acid (HF)
In acidic media, if the fluoride concentration is greater than 10-6mol/L, the glass electrode will be severely corroded. Generally, two methods are used:
(1) Measure quickly with a glass electrode.
(2) Use metal antimony electrodes. It is recommended to use the PHG8006 online pH meter and P8T3B hydrofluoric acid-resistant pH electrode from Shanghai Womao Instrument Technology Co., Ltd.
