Home > Technical Articles > Permanent Gases
The terms “permanent, major, or fixed gases” refer to the gases N2, O2, Ar, CO2, and CO. Permanent gases are determined using gas chromatography (GC). Typically, the sample is attached to a sampling loop which can be evacuated. The sample is transferred into the loop, and then the contents of the loop are flushed onto the GC column using helium carrier gas. The GC column is a six foot by 1/8" steel column packed with a molecular sieve type of packing. The various gases are separated based on their molecular size, and then detected using a thermal conductivity detector (TCD). The TCD detects the individual compounds based on the difference between their thermal conductivity and that of the helium GC carrier gas. Click here to see a chromatogram of a gas standard.
Headspace analysis refers to analyzing the vapors present above a sample. One of the more common applications of this analysis is to verify that air-sensitive materials have been packaged under an inert atmosphere (usually nitrogen), and that the blanket of gas is intact. This is a critical step in many pharmaceutical packaging processes. To accomplish this, the sample container is attached to the sampling loop with a valve. With the valve closed, the loop is evacuated. The vacuum source is removed, and the valve opened, allowing the headspace to expand into the loop. The sample is then analyzed as described above. This type of analysis can detect oxygen present in a nitrogen-packaged container down to less than 0.1%, with a reproducibility of + 5% (relative).
Purity analysis can be used to confirm the purity of gases being used in inert gas packaging, incubators, compressed gas supplies, and many other important applications. We routinely analyze high purity nitrogen, oxygen and carbon dioxide to monitor for permanent gas impurities down to less than 0.1%. For a quotation...
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