Several important issues regarding pH meter measurement:
1. pH measurement at high temperatures
The high temperature of aqueous solution generally refers to temperatures above 60 ℃. Under these conditions, the erosion effect of the solution on glass electrodes is particularly severe, especially in the alkaline pH range. This erosion effect causes a drift in the potential of the glass electrode, leading to performance degradation.
In industries such as pharmaceuticals, fermentation, and food, microbial breeding tanks require glass electrodes to withstand high temperatures of 120-130 ℃ for pH measurement, which means that the electrodes must be able to withstand the corrosive effects of high-temperature solutions.
Another issue that needs to be addressed in high-temperature measurement is the stability of the reference electrode.
To prevent the dissolution of AgCl at high temperatures, a thickened AgCl layer is used, and solid AgCl is added to the electrode solution or AgCl single crystal is used as a reference electrode; The reference electrode can also be connected outside the high-temperature zone through a salt bridge.
2. pH measurement at low temperatures
At low temperatures, the internal resistance of glass electrodes increases sharply, so low resistance pH glass electrodes should be selected. Adding organic solvents to the solution inside the electrode can lower the freezing point.
PH measurement of colloids and turbid liquids
In such samples, the glass electrode generally responds normally. If the glass electrode is contaminated, it can be cleaned and maintained according to the glass electrode cleaning and maintenance methods. The problem often occurs at the liquid junction end face of the reference electrode, where charged micelles or particles can easily cause unstable liquid junction potential. Generally, two methods are used to solve the problem:
Increase the exudation rate of salt bridge solution to reduce the influence of micelles and particles on the liquid interface.
PH measurement of high alkali and high acid samples
In alkaline solutions with pH>10, lithium glass electrodes should be used to reduce alkali errors. Currently, pH glass electrodes generally have smaller alkali errors; When pH>12, the alkaline error increases. Due to the electrode being immersed in alkaline solution for a long time, the electrode may experience potential drift and slow response. At this time, the electrode should be washed with water and then immersed in 0.1mol/L HCl for 24 hours. After this treatment, the electrode performance can be restored.
