Precautions for selection of pH electrode and ORP electrode

Selection of pH electrode and ORP electrode 1. Selection of pH electrode: 1. Selection of shell material: PC plastic (polycarbonate) shell and glass shell are generally used for pH electrode shells. PC shells are resistant to collisions and impacts, but proper temperature<80oC. And it is susceptible to corrosion in high alkali solution and some media. The glass casing is suitable for a temperature of 0-150oC, and is generally not corroded except for hydrofluoric acid solution, but it is easy to be damaged by collision. 2. Selection of the liquid junction: The liquid junction is the connection part that communicates the external reference solution and the measured solution, and requires stable and reproducible potential. Generally, liquid junction materials include fiber material, ceramic core, glass grinding mouth and other media. Fiber material is generally used in plastic case electrodes, and the solution seeps out faster and is not easy to block; the ceramic core has good corrosion resistance, and the liquid junction potential The stability and reproducibility are good, and it can be used in high temperature medium. It is a widely used liquid junction material; the contact area between the glass grinding interface and the solution and the seepage speed are large, and it is suitable for the weak ionic strength. , Determination of high viscosity, turbid liquid or colloidal solution. 3. Selection of pH-sensitive glass membrane: pH-sensitive glass membrane is melt-blown from lithium glass with hydrogen function, generally in a spherical shape, and most electrodes use conventional sensitive glass membranes, but there are still sensitive ones for high-temperature media. Glass membranes, sensitive glass membranes for high-temperature strong acid media, sensitive glass membranes for high-temperature steam sterilization (130oC), and low-resistance sensitive glass membranes (for the determination of pure water), etc., should be selected according to different situations. 4. Selection of reference electrode: Ag/Agcl reference electrode is commonly used, but the general Ag/Agcl reference electrode is easy to dissolve at high temperature and the potential is unstable, while the Ag/Agcl reference electrode with capillary structure has Very stable reference potential, suitable for use under high temperature and long-term continuous testing conditions. 5. Selection of electrode socket: The most commonly used socket for pH electrodes is BNC type (also known as Q9 type), in addition to other types, it mainly depends on the matching of corresponding instruments. (The last letter of the electrode model indicates the socket type). 2. ORP electrode selection: 1. General selection requirements: Same as pH electrodes (except the sensitive membrane) 2. Selection of sensitive components: The selection of ORP electrode sensitive components mainly considers the properties of the measured medium. Generally, gold electrodes are used for Oxidizing media such as oxidation of cyanide, oxidation of nitrite, measurement of ozone, measurement of hydroperoxides. Platinum electrodes are used for reducing media, such as the reduction of chromate, chlorination of swimming pools, etc.
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