Why do pH electrodes need to be soaked? How to soak correctly?

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The PH electrode must be soaked before use, as the pH bulb is a special type of glass membrane with a very thin layer of hydrated gel on its surface; it can respond properly to H+ ions in the solution only when it is fully moistened. At the same time, soaking the glass electrode can **reduce and stabilize** the asymmetry potential. A pH glass electrode can generally be soaked in distilled water or a pH 4 buffer solution. It is generally better to use a pH 4 buffer, with an immersion time of 8 hours to 24 hours or longer, depending on the thickness of the bulb glass membrane and the degree of electrode aging. At the same time, the liquid junction of the reference electrode also needs to be immersed. Because drying out of the liquid junction can increase or destabilize the liquid junction potential, the immersion solution of the reference electrode must be identical to the external reference solution of the electrode, namely a 3.3 mol/L KCl solution or a saturated KCl solution; the immersion time is usually just a few hours. Therefore, for a pH composite electrode, it must be immersed in a pH 4 buffer containing KCl in order to act on both the glass bulb and the liquid junction. It is important to note here that in the past, people using single pH glass electrodes were accustomed to soaking them in deionized water or pH 4 buffer solution. When they later started using combined pH electrodes, they continued to use this same soaking method. The direct consequence of this was that a combined pH electrode with good performance became an electrode with slow response and poor accuracy. Moreover, the longer the soaking time, the worse its performance would be. This is because prolonged soaking reduces the concentration of KCl inside the liquid junction (e.g., within the porous ceramic element), thereby increasing and destabilizing the liquid junction potential. Of course, the electrode will recover as long as it is soaked in the correct soaking solution for a few hours again. Furthermore, pH electrodes should not be immersed in neutral or alkaline buffer solutions either; prolonged immersion in such solutions will cause the pH glass membrane to become less responsive. Proper preparation of the pH electrode immersion solution: Take one packet of pH 4.00 buffer (250 ml), dissolve it in 250 ml of pure water, then add 56 grams of analytically pure KCl. Heat gently and stir until everything is completely dissolved.