Why is the PH meter electrode soaked in how to properly soak Shanghai Sujing

The pH electrode must be immersed before use because the pH bulb is a special glass membrane with a very thin layer of hydrated gel on the surface of the glass membrane that is only sufficiently wet to respond well to the H+ ions in the solution. At the same time, the glass electrode is soaked, so that the asymmetric potential is greatly reduced and tends to be stable.

The pH glass electrode can generally be soaked in distilled water or a pH 4 buffer solution. It is generally preferred to use a pH 4 buffer, and the soaking time is 8 hours to 24 hours or longer, depending on the thickness of the bulb glass film and the degree of electrode aging. At the same time, the liquid junction of the reference electrode also needs to be immersed. Because if the liquid junction is dry, the liquid junction potential will increase or be unstable, the reference electrode soaking solution must be the same as the reference electrode's external reference solution, ie 3.3mol/L KCl solution or saturated KCl solution, the soaking time is generally It can be a few hours.

Therefore, for a pH composite electrode, it must be immersed in a pH 4 buffer containing KCl in order to simultaneously act on both the glass bulb and the liquid junction. Special attention should be paid here, because in the past, people using a single pH glass electrode have been accustomed to soaking in deionized water or pH4 buffer, and the direct consequence of using such a soaking method when using a pH composite electrode is to make a performance. A good pH composite electrode becomes a slow-responding, poorly-precision electrode, and the longer the immersion time, the worse the performance, because after a long period of immersion, the KCl concentration inside the liquid junction (such as inside the sand core) has been greatly reduced. , making the liquid junction potential increase and unstable. Of course, the electrode will recover as long as it is re-soaked for a few hours in the correct soaking solution.

In addition, the pH electrode can not be immersed in a neutral or alkaline buffer solution, and long-term immersion in such a solution will make the pH glass film unresponsive. Preparation of the correct pH electrode soaking solution: Take a package of pH 4.00 buffer (250ml), dissolve in 250ml of pure water, add 56g of analytically pure KCl, heat it appropriately, stir until completely dissolved. How to clean the pH electrode? After the bulb and liquid junction are contaminated, wash it with the following solvent, then wash the solvent with deionized water, and immerse the electrode in the soak solution to activate.

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