Why should the pH meter electrode be soaked? How to soak properly?
The pH electrode must be soaked before use, because the pH bulb is a special glass membrane with a thin hydrated gel layer on the surface of the glass membrane, which can respond well to the H+ ions in the solution only when it is fully wet. At the same time, the glass electrode is soaked, which can greatly reduce the asymmetric potential and tend to be stable.
The pH glass electrode can generally be soaked in distilled water or pH4 buffer solution. Usually it is better to use pH4 buffer solution, and the soaking time is 8 hours to 24 hours or longer, depending on the thickness of the bulb glass membrane and the aging degree of the electrode. At the same time, the liquid junction of the reference electrode also needs to be soaked. Because if the liquid junction dries up, the potential of the liquid junction will increase or become unstable. The soaking solution of the reference electrode must be consistent with the external reference solution of the reference electrode, that is, 3.3mol/L KCl solution or saturated KCl solution, and the soaking time is generally A few hours will do.
Therefore, for the pH composite electrode, it must be immersed in the pH4 buffer solution containing KCl, so that it can act on the glass bulb and the liquid junction at the same time. Special attention should be paid here, because in the past, people used to use a single pH glass electrode to be soaked in deionized water or pH4 buffer solution. The direct consequence of using this soaking method when using a pH composite electrode later is that the performance of a single pH glass electrode will be reduced. A good pH composite electrode becomes an electrode with slow response and poor precision, and the longer the immersion time, the worse the performance, because after a long time immersion, the KCl concentration inside the liquid junction (such as inside the sand core) has been greatly reduced , so that the liquid junction potential increases and becomes unstable. Of course, the electrodes will recover with just a few hours of re-soaking in the correct soaking solution.
In addition, the pH electrode should not be soaked in neutral or alkaline buffer solutions. Long-term immersion in such solutions will cause the pH glass membrane to respond sluggishly. Preparation of the correct pH electrode soaking solution: take a pack of pH4.00 buffer (250ml), dissolve it in 250ml of pure water, add 56 grams of analytically pure KCl, heat properly, and stir until completely dissolved. How to clean the pH electrode? After the bulb and liquid junction are polluted, they should be cleaned with the following solvents, then washed with deionized water to remove the solvent, and then immersed in the soaking solution to activate the electrodes.
