Notes on pH Meter Measurement of Ultrapure Water
Due to the unique characteristics of ultrapure water, it is very difficult to measure the pH value online with a pH meter. In practice, it is difficult to obtain reproducible and stable measurement results in samples with low ionic strength. Low ion samples, i.e. low alkalinity, low ionic strength, or low conductivity (usually 0.056-10) with high impedance, such as deionized water. Due to the varying junction potentials generated in the reference junction, different pH values are produced when measuring deionized water, even with new, sealed electrodes, and well calibrated in buffered standard solutions.
Why is it necessary to use an online pH meter to measure the pH value of pure water.
In the production process of pure water, measuring pure water can serve as an indicator of process pollution. When air or carbon dioxide invades the pure water production or distribution system, it will cause pH drift.
2. How to choose an online pH meter pH electrode
Compared to traditional pH electrodes, more expensive double junction electrodes have many advantages. However, compared to single junction electrodes, there is no significant advantage in measuring ultrapure water. *A good choice is a refillable liquid reference pH electrode, specially made of low impedance glass. A liquidity reference junction has a relatively high flow rate, reducing the junction potential. The sealed electrode is usually filled with gel, and its major advantage is long life, because its reference solution has a very slow leakage rate. However, a faster leakage rate is very suitable for ultrapure water because the pH potential can quickly stabilize.
