Measuring Ethylene in 7890A

Do you have a valve configuration on your GC similar to that shown on page 2 of the application note?  If the columns are simply connected in series to the inlet, you may not see anything more than the O2 and N2 peaks, as the other components would be trapped by the Molesieve PLOT column (19095P-MS0).

Indeed, as mentioned above the ethylene needs to bypass the molsieve column otherwise it gets stuck, so to check for the correct switching moment of the valve; set the valve in the bypass mode, run a sample over the porabond Q column to the TCD, you will see 2 peaks, 1 for Ar+N2 and the 2nd for ethylene, then you define the time inbetween those peaks as the switching time for the bypass valve and run with the Ar+N2 peak going to the molsieve, switch the ethylene to the bypass and back to the molsieve after that peak has reached the TCD, so the Ar and N2 peaks can elute from the molsieve. Important to have a needle valve restriction in the bypass which gives the same restriction as the molsieve column, so you can keep the expected retention when switching the valve.

I think we do this at my lab but not with a valve.  We use a plot column and anayze headspace  above a water sample.  We test for methane ethane ethene and propane useing an FID.  The integrated gastight syringe with a valve in it from Fisher helps. We use air stamdards to cslibrate