What substances can affect the accuracy of online pH analyzers
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Are there any substances that can affect the accuracy of online pH analyzers? During one driving session, the system’s pH would not rise no matter what; the amount of alkali added was already twice the normal level, yet the pH still did not increase. Multiple calibrations using the online meter showed no problems, but it seemed possible that too much alkali had been added (one possible cause). Offline analysis indicated that the acid content was not high. Eventually, the pH gradually improved, and the system functioned properly again. Is it possible that some substance is affecting the accuracy of the online pH analyzer, such as being identified by the electrode as hydrogen ions or directly influencing the electrode potential value? Is there such a possibility? What type of substance?
Troubles using the Mettler-Toledo_M400 PH online analyzer? https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1986195&shareuid=398787 I recommend you take a look; it will give you a good understanding of the requirements for using online meters.
What are the operating conditions, and how is the salt content of the medium determined? There may be an issue with instrument matching as mentioned by Teacher Q in the link on the second floor. Either too pure water quality or too high salt content can affect pH measurement.
This post was last edited by Yang Qing on 2020-9-23 at 10:13. I’m able to access it here; I’ve copied the relevant information for your reference: Issue: This facility is equipped with a Mettler-Toledo_M400PH online analysis instrument. No feed material is being supplied to the system; only a water circulation process is in operation, using deoxygenated water with a pH level of around 7.8. However, since the system started operating, the readings from the online instrument have been decreasing continuously. The relevant pipelines have been checked, and actual water samples have also been tested on-site; test strips indicate that the pH is around 7, whereas the instrument shows a value of less than 3.8! The water sample flow was interrupted, and tests were conducted using backwash water (fresh water with a pH of around 6.8). It was found that the measurement values remained within this range and were quite stable, with no downward trend observed! Reply: Based on the information you provided, your process medium should be pure water (water that has undergone strict deionization). Such water has an extremely low conductivity. The pH measurement system you have ordered is a regular pH meter, not one designed for measuring the pH of pure water; this results in significant drift in the measurement values. Another reason for drift is that the measurement electrode system is affected by nearby stray electromagnetic signals. The water I use for backwashing is likely the regular water used in the process equipment, that is, municipal supply water; its conductivity falls within the range measurable by ordinary pH electrodes, so the measurement values are normal again. The Mettler family should have pH systems for pure water measurement, which generally consist of a pH electrode designed for use with pure water and a special flow cell for pure water; there are also certain technical considerations involved in their installation. If no suitable product from Mettler is available, Yokogawa, Hach, E+H, and DKK also offer similar products. Comment on liaifeng: It has to be said that the senior is truly an expert in this field! The reasons you analyzed are the same ones I learned from the supplier yesterday; they’re not very different from what you said! In other words, the current operating conditions and water quality are not those for which the online table applies; especially regarding water quality, the supplier assured me that it is on a downward trend. For more details, please reply. Posted on 2018-5-16 20:47