Why does the PH electrode need to 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 with a very thin hydrated gel layer on the surface of the glass membrane. It can only have good interaction with the hydrogen ions in the solution under fully moist conditions. response. At the same time, the asymmetric potential of the glass electrode can be greatly reduced and stabilized after soaking. pH glass electrodes can generally be soaked in distilled water or pH4 buffer. 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 liquid junction potential will increase or become unstable. The soaking liquid of the reference electrode must be consistent with the external reference liquid of the reference electrode, that is, 3.3mol/L KCL solution or saturated KCL solution. The soaking time Usually a few hours is enough.
Therefore, the pH composite electrode must be soaked in a PH4 buffer 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 used to soak single pH glass electrodes in deionized water or pH4 buffer. Later, they still used this soaking method when using pH composite electrodes. 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 pure water, then add 56g of analytical grade KCL, heat appropriately, and stir until completely dissolved. In order to make the pH composite electrode more convenient to use, some imported pH composite electrodes and some domestic electrodes are equipped with a sealed plastic vial on the head of the pH composite electrode, which contains the electrode soaking liquid. The electrode head is soaked in it for a long time and is pulled out during use. Just wash it, very convenient. This storage method is not only convenient but also very useful in extending the life of the electrode. Just pay attention to the soaking solution in the plastic vial not to be contaminated and replace it.
