PH meter measurement electrode and its selection method
The antimony measuring electrode is a semi metal with a pure antimony active surface. The antimony contact of the electrode undergoes a chemical reaction to produce a hydrogen oxide layer. The reason why antimony electrodes can respond to pH like other electrodes is because this oxide layer can sense pH. However, antimony electrodes are not as good as glass or ion sensitive field-effect transistor (ISFET) electrodes for measurement, as their response to pH and temperature is nonlinear. Its standard temperature is limited to 0-80~C, and the standard pH range is 2-11. Oxidation or deformation reactions can interrupt the measurement of antimony electrodes. For example, oxidation or deformation caused by the presence of chlorine or sulfite. Because antimony contacts may respond to possible oxidation or deformation. Antimony electrodes are now rarely used for pH measurement, only in processes containing hydrofluoric acid solutions. Because a hydrofluoric acid solution with a pH value ≤ 4 can quickly damage the glass or ion sensitive field-effect transistor (ISFET) electrodes. However, the use of antimony electrodes in hydrofluoric acid solutions is also limited, as it is difficult to achieve measurement results when the pH value is ≤ 2.
The glass measuring electrode includes a special mechanism glass that can emit an mV signal that changes with pH. Glass electrodes typically exhibit a very linear mV response to pH values ranging from 1 to 12. Manufacturers of glass electrodes generally provide electrodes of different thicknesses to suit various temperature conditions. For example, glass electrodes with temperatures ranging from 0 to 80~C or 20 to 110~(2) are suitable. Even so, thick glass electrodes are still fragile and prone to breakage or breakage. Using glass electrodes in solutions with a pH ≥ 11 can result in sodium errors, as compared to solutions with lower hydrogen concentrations, glass electrodes are usually more responsive to solutions with higher sodium concentrations. Other solutions, such as potassium, are also prone to this reaction. pH measurement readings lower than the true value generally occur at pH 0. 1 to 0. 3. High pH solutions can also corrode the electrode. High temperature and high pH solutions can affect the response of glass electrodes to pH and shorten their lifespan. Thicker glass electrodes are used for high pH solutions. In contrast, in low pH solutions, such as pH ≤ 1, the glass electrode will produce an acid error. Because the ratio of acid to water is high in the solution, both the glass film and electrode response will be affected. In addition, solutions with high acid concentrations may affect accuracy, and it is also important to note that hydrofluoric acid can corrode and ultimately damage the glass electrode. A common rule is that hydrofluoric acid or solutions with pH ≤ 4 will shorten the lifespan of glass electrodes. A more accurate explanation is that glass electrodes are unstable and can corrode when measured in 10 mol/L hydrofluoric acid. Compared to glass electrodes, antimony measuring electrodes have much stronger resistance to hydrofluoric acid corrosion.
3 The ion sensitive field effect transistor (ISFET) measuring electrode has been used as a sensor since the 1970s, but it has only recently been used in industrial measurement. The main reason is that the design of the ISFET electrode often produces measurement errors and needs to be calibrated frequently every day. The ion sensitive field effect transistor (ISFET performance. Compared with glass electrodes, it has no sodium error and the acid error is much smaller in low pH solutions than glass electrodes. The oxidation/deformation reaction will not interrupt the pH response of ion sensitive field-effect transistors. In fact, so far it has not been found to be interrupted by any circumstances. Ion sensitive field-effect transistor electrodes can provide the correct linear mV response from pH 0-14. However, glass electrodes can only respond within the pH range of l2, and antimony electrodes can only respond within the pH range of 1l. Moreover, it is inherently very sturdy, while glass electrodes are fragile. In many measurement environments, the pH electrode of ion sensitive field-effect transistors is less susceptible to chemical corrosion, probe contamination, and general damage than antimony or glass electrodes. However, the current design still has flaws. It is more susceptible to high-temperature corrosive solutions than glass electrodes, although it can maintain measurement accuracy better than glass or antimony electrodes. Hydrofluoric acid can also quickly damage it. In addition, some chemical corrosion actually causes more severe corrosion of ion sensitive field-effect transistor electrodes than glass or antimony electrodes
