Introduction to commonly used electrodes in acidimeter (ph meter)
The acidometer mainly generates microvoltage through electrodes and solutions, so the electrode used is critical to the acidity value. The electrodes we commonly use to measure acidity meters mainly include the following types:
(1) Hydrogen electrode: The principle of hydrogen electrode is quite similar to that of metal electrode. But hydrogen is a gas and cannot be used directly as an electrode. Instead, a platinum electrode coated with platinum black is needed to absorb the hydrogen and act as a metal electrode. Its main advantage is that it is accurate and can be used to measure a wide pH range. However, when this kind of electrode generates other oxidized or reduced substances during the redox process, it will cause measurement errors and is inconvenient to operate. Therefore, this kind of electrode is generally only used as a standard electrode and is rarely used in actual measurements.
(2) Quinone-hydroquinone electrode: It is composed of inert metal platinum or gold immersed in a saturated solution of quinone-hydroquinone. It uses a quinone-hydroquinone pair to establish a potential balance on the inert electrode. The advantages of quinone-hydride electrode are fast potential stabilization and low internal resistance. But if the pH exceeds 8, hydroquinone, which is a weak acid, begins to dissociate or be oxidized into quinone, destroying the potential balance. In addition, other substances that can bind to quinone will affect pH measurement, such as proteins, borates, colloidal suspensions, etc.
(3) Antimony electrode: It is one of the metal oxide electrodes. The electrode of the antimony electrode occurs between the metal antimony and the oxide (produced on the surface of the antimony in contact with the air). Since the activity of the oxide is related to the OH ion activity in the solution, the potential of the antimony electrode is directly related to Depends on the pH value of the solution. The advantages of antimony electrodes are simple operation, strong and durable. However, the "standard" potential of this electrode is unstable, and there are other metal oxide electrodes that can also be used for pH measurements. For example: Bi electrode, the principle and structure are similar to the antimony electrode.
(4) Daily mercury electrode: The saturated calomel electrode is usually used, which is composed of metallic mercury, Hg2CI2 and saturated KC1 solution. There will be no polarization phenomenon and the stability of the electrode will not occur. Its electrode reaction is: Hg2CI2+2e= 2 Hg+ 2 C1 ˉ
(5) Glass electrode: Glass pH electrode is currently one of the most important methods of pH measurement. When it is immersed in the solution to be measured, the hydrogen in the solution to be measured is ionized and exchanged with the hydration layer on the surface of the electrode bulb, and the inner layer of the bulb also generates electrode potential. Since the hydrogen ionization of the inner layer remains unchanged, while the hydrogen ionization of the outer layer is changing, the potential difference between the inner and outer layers is also changing, and its size is determined by the hydrogen ionization concentration of the solution in the outer layer of the membrane. This testing method is simple, the results are accurate, and there are fewer interference factors.
(6) Composite electrode: Most currently use a type called composite electrode, which is an electrode that combines a glass electrode and a reference electrode into a single probe. It has the combined functions of a glass electrode and a reference electrode, making measurements more convenient, accurate, and reliable.
Maintenance of acidimeter (ph meter) instrument In addition to using the instrument correctly, you need to understand the maintenance of the instrument and the precautions when measuring.
