Selection of pH Meter Acidity-Alkalinity Sensor Electrodes
1. Selection of shell material:
The pH electrode casing generally adopts two types: PC plastic (polycarbonate) casing and glass casing. The PC casing is resistant to collision and impact, but suitable for temperatures<80oC. It is also susceptible to corrosion in high alkaline solutions and some media. The glass shell is suitable for temperatures ranging from 0-150oC and is generally not corroded except by hydrofluoric acid solution, but it is prone to collision damage.
2. Selection of liquid interface:
The liquid interface is a connecting component that communicates the external reference solution and the measured solution, requiring stable and reproducible potential. General liquid interface materials include fiber materials, ceramic cores, glass grinding ports, and other media. Fiber materials are generally used in plastic shell electrodes, and their solution leakage rate is fast and not easily blocked; Ceramic cores have good corrosion resistance, and the stability and reproducibility of the liquid interface potential are also good. They can be used in high-temperature media and are widely used as liquid interface materials; The glass grinding interface has a large contact area and leakage rate with the solution, making it suitable for the determination of weak ionic strength, high viscosity, turbid liquids or colloidal solutions.
3. Selection of pH sensitive glass film:
PH sensitive glass film is made by melting and blowing lithium glass with hydrogen function, generally spherical in shape. Most electrodes use conventional sensitive glass films, but there are also sensitive glass films for high-temperature media, high-temperature strong acid media, high-temperature vapor (130oC), and low resistance sensitive glass films (used for pure water determination), which should be selected according to different situations.
4. Selection of reference electrode:
Ag/AgCl reference electrodes are commonly used, but general Ag/AgCl reference electrodes are prone to dissolution at high temperatures and have unstable potentials. On the other hand, capillary structured Ag/AgCl reference electrodes have very stable reference potentials and are suitable for use under high temperature and long-term continuous testing conditions.
5. Selection of electrode socket:
The commonly used socket for pH electrodes is BNC type (also known as Q9 type), and there are various other forms depending on the matching of the corresponding instrument. The last letter of the electrode model indicates the socket type.
