Chromatography Forum

I'm currently in the process of selecting gas mixtures to calibrate a gas chromatograph (Agilent 7890B). One of the gas mixtures I'm interested in has the following composition by percent volume:

methane (CH4): 95%
carbon dioxide (CO2): 1%
butane (C4H10): 1%
acetylene (C2H2): 1%
nitrogen (N2): 2%

The gas cylinder pressure is 1345 psig. I plan on calibrating the gas chromatograph at room temperature (24 C) and need to ensure that all compounds in the cylinder are in gas phase. I know that the CH4 and N2 will be in gas phase since their critical temperatures are well below room temperature. However, I'm unsure about whether the CO2, butane, and acetylene are in liquid or gas phase. For example, CO2 has a critical point of ~ 31 C and 1070 psi. Since the gas cylinder will be pressurized above this at 24 C, will it be in liquid phase? Am I approaching this problem the right way?

Interesting problem - but before we all hurt ourselves thinking about it, take into consideration 1) the ideal gas law and 2) the low percentages of all but CH4. It should all be in "solution" and thus in the same phase (gas).

Then take the pragmatic approach and check with the gas test mix vendor or website thereof to confirm that it's fine at your temp...

I realized that I wasn't applying the ideal gas law properly. According to the ideal gas law, each gas in a mixture behaves independently and has its own partial pressure. So CO2, butane, and acetylene each have a partial pressure of 13.45 psig (28.14 psia). I looked up the vapor pressures of these compounds and realized that they were all higher than 28.14 psia, which means they should all be in gas phase.

I also contacted the gas vendor and they confirmed that all the contents were in gas phase.