Currently, I am working on the experiment which need a water with zero percent of dissolved oxygen. To remove the dissolved oxygen, I boiled the water in open beaker for 30 minutes. After that the the water poured into another conical flask. The flask sealed with rubber cork having two glass tubes. One glass tube was blocked with rubber septum while other connected to vacuum line to remove extra gases from the beaker.
After 30 minutes of vacuum treatment, the pure nitrogen gas used for nitrogen sparging for 30 minutes. I haven't measured the exact flow rate of gas but the nitrogen gas pass through the water vigorously.
The rubber cork was replaced with the rubber septa. Syringe with long needle was used to take the deoxygenated water from the flask.
Even after all these treatment/precaution, I got similar results for the normal and deoxygenated water. The time required for our experiment was ~ 1 hour.
It might be possible that due to some air present in the experimental flask, the deoxygenated water came in contact with air or atmospheric oxygen. However, I don't know the time required to dissolved the atmospheric oxygen in steady water present in the flask.
If someone provide me a reference/paper about oxygen dissolution time then it would be great help.
Thanks in advance