Why should the pH electrode be soaked? How to soak the pH composite electrode correctly?
The pH electrode must be soaked before use, because the pH bulb is a special glass membrane, and there is a very thin gel layer on the surface of the glass membrane. Influence. 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 buffer solution with pH=4. Usually it is better to soak in pH=4 buffer solution, and the soaking time is 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 immersion 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, The soaking time is generally a few hours.
Therefore, for the pH composite electrode, it must be soaked in the pH=4 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 pH=4 group flushing solution. Later, when using a pH composite electrode, this soaking method was still used, even in some incorrect conditions. This kind of erroneous guidance will also be carried out in the instruction manual of the pH combination electrode. The direct consequence of this wrong immersion method is that a pH composite electrode with good performance 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 liquid junction The KCl concentration inside (for example, inside the sand core) has been greatly reduced, increasing and destabilizing the liquid junction potential. 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 solution. Long-term immersion in such solution will make the pH glass membrane slow in response.
Preparation of the correct pH electrode soaking solution: Take a pack of pH=4.00 buffer (250mL), dissolve it in 250mL pure water, add 56 grams of analytically pure KCl, heat properly, and stir until completely dissolved.
