Why do pH electrodes need to be soaked? How to properly soak the pH combination electrode?
Reason analysis: The pH electrode must be soaked before use because the pH bulb is a special glass membrane with a very thin hydrated gel layer on the surface of the glass membrane. It can only interact with H ions in the solution under fully moist conditions. There was a good response. At the same time, after soaking the glass electrode, the asymmetric potential can be greatly reduced and stabilized. pH glass electrodes can generally be soaked in distilled water or pH4 buffer solution. It is usually better to use pH 4 buffer, 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/LKCL solution or saturated KCL solution. The soaking time is generally Just a few hours.
Correctly soak the pH composite electrode: soak it in a pH4 buffer solution containing KCL, so that it can act on the glass bulb and liquid junction at the same time. Special attention should be paid here because in the past, people who used single pH glass electrodes were accustomed to soaking them in deionized water or pH4 buffer. Later, when using pH composite electrodes, they still used this soaking method, and even used some incorrect pH composite electrodes. This type of erroneous guidance can also be found in the electrode instruction manual. The direct consequence of this wrong soaking method is to turn a pH composite electrode with good performance into an electrode with slow response and poor accuracy, and the longer the soaking time, the worse the performance, because after a long soak, the liquid contact The KCL concentration inside the boundary (such as inside the sand core) has been greatly reduced, making the liquid junction potential increased and unstable. Of course, the electrode will recover as long as it is re-soaked in the correct soaking solution for a few hours.
In addition, the pH electrode cannot be immersed in neutral or alkaline buffer solutions. Long-term immersion in such solutions will cause the pH glass membrane to respond slowly. Preparation of the correct pH electrode soaking solution: Take a pack of pH 4.00 buffer (250ml), dissolve it in 250ml of pure water, then add 56 grams of analytical grade KCl, heat appropriately, and stir until completely dissolved.
