Why should the pH electrode be soaked, and how to soak the pH composite electrode correctly?
The pH meter is a common small tool in our laboratory, and it is also the basis of various experimental projects. We not only need to measure the pH of the sample but also the pH of the mobile phase, so we should not underestimate it. The small body has great effects, and we want to maintain it Well what should it do? look down. . .
The pH electrode must be soaked before use, because the pH bulb is a special glass membrane, and there is a very thin hydrated gel layer on the surface of the glass membrane, which can have a good interaction with the hydrogen ions in the solution only under fully wet conditions response. At the same time, the glass electrode can greatly reduce the asymmetric potential and tend to be stable after soaking. 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 surface dries up, the liquid junction potential 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. Usually a few hours.
Therefore, for the pH composite electrode, it must be soaked 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 soak in deionized water or pH4 buffer solution, and later used this soaking method when using a pH composite electrode. The direct consequence of this wrong immersion method is to turn a pH composite electrode with good performance into 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 concentration of KCL inside the boundary (such as inside the sand core) has been greatly reduced, making the potential of the liquid junction increase and 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 solution. Long-term immersion in such solution will make the pH glass membrane unresponsive. Preparation of the correct pH electrode soaking solution: Take a pack of pH4.00 buffer (250ml), dissolve it in 250ml pure water, then add 56g of analytically pure KCL, heat properly, 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 at the head of the pH composite electrode, which contains electrode soaking solution. Just wash it off, very convenient. This storage method is not only convenient but also very useful for prolonging the life of the electrode, just pay attention to the soaking solution in the plastic vial not to be polluted, and pay attention to replacement.
