First, how to use the pH composite electrode correctly
(1) There should be no air bubbles at the front end of the bulb, such as the application of air bubbles.
(2) After the electrode is taken out of the soaking bottle, it should be shaken in deionized water and dried. Do not wipe the bulb with a paper towel. Otherwise, the electrostatic induction charge will be transferred to the glass film, which will prolong the potential stabilization time. A better method is Rinse the electrode with the solution being tested.
(3) After the pH composite electrode is inserted into the solution to be tested, it should be shaken a few times and then placed still, which will accelerate the response of the electrode. Especially when using a molded-shell pH composite electrode, the stirring sloshing is more severe, because there is a small cavity between the bulb and the molded shell. After the electrode is immersed in the solution, sometimes the gas in the cavity is too late to be eliminated, so that the bubble is generated. The bubble or liquid junction is in poor contact with the solution, so it is necessary to stir vigorously to remove air bubbles.
(4) After testing in a viscous sample, the electrode must be repeatedly rinsed with deionized water several times to remove the sample adhered to the glass film. Sometimes it is necessary to wash the sample with other solvents, then wash the solvent with water and immerse it in the soak solution to activate.
(5) Avoid contact with strong acid and alkali or corrosive solution. If testing such solution, minimize the immersion time and carefully clean it after use.
(6) Avoid use in dehydrating media such as absolute ethanol or concentrated sulfuric acid, which will damage the hydrated gel layer on the surface of the bulb.
(7) The shell material of the molded case pH composite electrode is polycarbonate plastic (PC), and the PC plastic is dissolved in some solvents, such as carbon tetrachloride, trichloroethylene, tetrahydrofuran, etc., if the test contains the above solvent, The electrode housing will be damaged. In this case, the pH composite electrode of the glass housing should be used instead.
Second, how to properly soak the pH composite electrode
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. It can only be well with the H+ ions in the solution under conditions of sufficient wetting. response. 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 soaking solution of the reference electrode must be the same as the external reference solution of the reference electrode, and the soaking time is generally several 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 used a single pH glass electrode to get used to soaking in deionized water or pH4 buffer. Later, when using a pH composite electrode, this soaking method is still used, even in some incorrect pH compounding. This error is also guided in the instructions for use of the electrode. The direct consequence of this erroneous immersion method is to make a good pH composite electrode into a slow-responding, poorly accurate electrode, and the longer the immersion time, the worse the performance, because after a long period of immersion, liquid connection The KCl concentration inside the boundary (for example, 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 properly, 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, and the electrode soaking liquid is built in. The electrode tip is soaked for a long time, and is pulled out when used. Wash it, it is very convenient. This method of preservation is not only convenient, but also very advantageous for prolonging the life of the electrode, but the soaking liquid in the plastic vial is not contaminated, so pay attention to replacement.
Third, the preparation method of PH electrode soaking liquid
1, short-term preservation:
PH electrode soaking liquid preparation method: a pack of PH4.00 buffer, dissolved in 250ML of pure water, plus 56g of analytically pure KCL, heated appropriately, stirred until completely dissolved.
2. Long-term preservation:
When the PH electrode is not used for a long time, the PH electrode should be immersed in a specially prepared protective solution and periodically replaced with a new protective solution for a maximum of 6 months. (Preparation method: a pack of PH4.00 buffer, soluble in In 250 ML pure water, add 56 g of analytically pure KCL and 0.5 g of thymol, heat appropriately, stir until completely dissolved.
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