What is the proper method for soaking a pH combination electrode?
Soak in a pH 4 buffer solution containing KCL to simultaneously affect both the glass bulb and the liquid interface. Special attention should be paid here, because in the past, people used to soak single pH glass electrodes in deionized water or pH 4 buffer solution. Later, when using pH composite electrodes, this soaking method was still used, and even incorrect instructions were provided in the user manual of some incorrect pH composite electrodes.
The direct consequence of this incorrect soaking method is that it turns a pH composite electrode with good performance into an electrode with slow response and poor accuracy. Moreover, the longer the soaking time, the worse the performance, because after a long soaking time, the KCL concentration inside the liquid interface (such as inside the sand core) has greatly decreased, resulting in an increase and instability of the liquid interface potential. Of course, as long as the electrode is re soaked in the correct soaking solution for a few hours, it will still recover.
In addition, pH electrodes should not be immersed in neutral or alkaline buffer solutions, as prolonged immersion in such solutions can cause the pH glass film to respond slowly. The correct preparation of pH electrode soaking solution: Take a packet of pH 4.00 buffer (250ml), dissolve it in 250ml of pure water, add 56g of analytical grade KCl, heat appropriately, and stir until completely dissolved.
