Hi everyone! I use the optical probe to measure dissolved oxygen in water in a glass bottle, read the results many times with different values. The dissolved oxygen value gradually decrease each time I repress "Measure" button. Can anyone please explain the cause and the way to fix it?
When you say "optical probe", I assume it does not consume any O2 in its measurement of O2. However, are you sure of that? Also, what is the possibility of leakage of O2 from the chamber? In my old days of working with Clark electrodes to measure O2 consumption, I saw both phenomenon.
Gordon L Warren I just realized that when I put the probe into the sample, there are a few air bubbles that form and stick to the membrane. Could it be the cause? My sample when measured without stirring, the results gradually decreased from about 0.7 ppm to 0.1 ppm after 3 measurements of the same sample. When I measured with magnetic stirrup, the result increased close to 1.0 ppm. Could you kindly give me some advice on this phenomenon?
If I understand correctly, PO2 is higher outside the chamber than inside the chamber. The behavior you observe when the stir bar is not stirring (i.e., PO2 goes down) is that I would expect if the probe was consuming oxygen. The PO2 is probably only going down right next to the probe. If your observation of PO2 going up when the stir bar begins stirring, again, it sounds to me like the probe is consuming oxygen. The stirring eliminates spatial heterogeneity in PO2. What kind of probe are you using?
You are right, sorry for my confusion (my lab has 2 types of probes, photochemical and electrochemical, the one I used is electrochemical). What should I do to get the accurate result, stirring or not stirring, how to prevent trapped air forming and sticking to the membrane. Thank You!
You definitely need to stir. Your probe consumes oxygen. Hopefully, your cells consume more oxygen than does the probe. You will probably need to measure oxygen consumption/leakage with and without cells. The difference between the two consumptions/leakages will be the true oxygen consumption of the cells.
Unfornaturely, I measure DO in a pharmaceutical sample that requires very low DO levels to prevent an oxidation reaction of the API. Thank you for helping me understand probes better. I think I should use optical probe instead of electrochemical probe, for more accurate results. Nice to talk to you.
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