What is the liquid junction industry? Why use high concentration KCI?
In the pH measurement process, the reference electrode is used, in most cases the reference electrode is provided with a salt bridge solution. The reference electrode is connected with the solution to be measured through the salt bridge solution, so that a liquid junction is formed between the solution under test and the reference salt bridge solution. Ions in the solutions on both sides of the liquid junction continue to diffuse across the interface to the opposite side, Each ion diffusion rate is different, leaving the liquid junction with opposite signs on both sides of the charge, resulting in potential difference, which is called liquid junction potential, also known as the diffusion potential, which will affect the electrode measurement accuracy. In order to reduce the potential difference between liquid junction or to make it stable and reproducible, it is necessary to use a high concentration of KCI solution (≥3.3mol / L) as the electrode external reference salt bridge solution, which has a sufficiently high ionic strength, than The maximum possible ionic strength of the measured medium is also 5 to 10 times larger, so that at the liquid junction interface, K + and Cl- are always diffused outwards, whereas due to the mobility of K + and Cl- Speed) are nearly equal and the positive and negative charge distributions are substantially uniform, thus forming a smaller liquid junction potential, which is why the external reference solution in the reference electrode must use a high concentration of KCI solution.