Question: High error in determining benzene content in gas using gas chromatography
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Dear colleagues, I’ve encountered a problem recently: when using gas collection bags to collect gas samples and then applying gas chromatography to determine the benzene content in those gases, the results obtained from the same sample vary significantly. Could you please advise me on what exactly is going wrong in the testing process?
When I did this before, every time before taking a sample, I would squeeze the gas bag to mix the gas inside, and then take the sample. Wash the needle 2 times, and inject it for the third time. Three consecutive measurements, and the values are all pretty similar.
This situation may be caused by the low temperature of the gas pocket; some components with a slightly higher boiling point, due to their higher concentration, get adsorbed on the walls of the gas pocket or even condense into a liquid. Slightly warm the air bag with a hair dryer, then gently shake it before proceeding with the sampling analysis; this issue is usually resolved in such a way. This situation is generally rare in summer and only occurs when the weather is colder.
When collecting gas samples using a gas collection bag, replace the sampling bag several times and allow the gas to stay inside for a while before taking the sample, as the gas tends to adhere to both the sampling bag and the pipes. Once the sample is obtained, it should be analyzed immediately.
Thank you. Actually, what I mainly want to ask is how to take specific actions to avoid such problems, or during the analysis process, which mistakes can lead to significant errors in the analysis results. Could you please explain this in more detail?
Two methods: 1. Thoroughly knead and shake the air bag ； 2. Heat the sample container.