Short Chain Fatty Acid - Standard Calibration

Discussions about GC and other "gas phase" separation techniques.

2 posts Page 1 of 1
Hello everyone,

I have a varian 450 GC with FID detector and auto sampler and have been using a ZB-FFAP column to detect short chain fatty acids.

I have a bubbler evaporation system that is used to bubble nitrogen gas through liquid phase acetic acid samples and generate a vapour which is used as a test gas for the calibration of VOC sensors.

http://www.mdpi.com/coatings/coatings-0 ... 4-g001.png

The bubbler system is similar to this.

I, however, would like to quantify the concentration of the generated test gas using my GC. I am curious if this is possible to do by collecting a sample of the test gas (acetic acid/humidity/nitrogen in a gas phase matrix) and directly injecting into the autosampler injection port, Are there matrix concerns when comparing against the liquid phase calibration standards I have used (acetic acid/h20 in a liquid phase matrix with nitrogen as the carrier gas used in the GC)?

Would titration (before bubbling and then some hours after) be a suitable alternative method of verifying the concentration of my test gas??
Even when sparging gas through a solution to evolve the acetic acid, you're still relying on the partitioning of the AA between the vapor phase and the condensed phase. Not knowing the partition coefficient for that process, makes it difficult to determine how much AA is actually in the gas phase. It's even more challenging for you because you are constantly sparging the liquid and changing the concentration of acetic acid in the liquid. You never really reach equilibrium because the AA is leaving your system all the time (if I understand your problem correctly).

You need a way to capture the AA from a known amount of gas and determine it another way. It could be trapping the AA from the gas in a liquid and titrating it.
It could be putting a known amount of the gas in a vessel with MeOH/BF3, make methyl acetate, and determine that by GC, etc. I have a thermal desorption system. I might try to aspirate a known volume of my gas through a Tenax trap and analyze for it that way using TD (fairly easy to create standards this way).

Once you reliably know what the AA concentration in the gas is under a given set of conditions, you can use it to calibrate your GC straightaway.
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