ow to maintain a pH meter
The pH meter is a common small tool in our laboratory and 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 cannot underestimate 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 with a thin hydrated gel layer on the surface of the glass membrane. 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 pH4 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 the junction potential will increase or become unstable if the liquid junction surface dries up, the soaking 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, soaking time Usually a few hours.
Therefore, for the pH composite electrode, it must be immersed in a pH4 buffer 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 a single pH glass electrode to soak in deionized water or pH4 buffer solution, and this soaking method was still used when using a pH composite electrode later. 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 soaking, the liquid contact The KCl concentration inside the junction (eg, inside the sand core) has been greatly reduced, making the junction potential larger and unstable. Of course, the electrodes will recover as long as they are re-soaked in the correct soaking solution for a few hours.
In addition, the pH electrode should not be immersed in neutral or alkaline buffer solutions. Long-term immersion in such solutions will make the pH glass membrane unresponsive.
The correct preparation of pH electrode soaking solution: take a pack of pH4.00 buffer (250mL), dissolve it in 250mL pure water, add 56g analytical pure KCl, heat properly, and stir until it is completely dissolved. In order to make the pH compound electrode more convenient to use, some imported pH compound electrodes and some domestic electrodes are equipped with a sealed plastic vial on the head of the pH compound electrode, and the electrode soaking liquid is inside. The electrode head is immersed in it for a long time. It's very convenient to wash it off.
This storage method is not only convenient but also very useful for prolonging the life of the electrode, just be careful not to contaminate the soaking solution in the plastic vial, and pay attention to replacement.
