Why I am getting H2 peak in TCD when only CO2 is injected?

[Ortega]

Hi,

I am using a 7890 GC with the following configuration: TCD -> Methanizer -> FID
The problem is that I detect hydrogen in the TCD when at no time do I inject hydrogen into the system, I'm just injecting CO2.
This problem doesn't happen to me if I inject just Argon.
Additionally, methanizer doesn't work properly because methanization is not taking place.
It's possible that H2 that feed the methanizer is leaking. Is that H2 what I am seeing in TCD?

Thanks!

[AICMM]

Ortega,

Three quick comments.

1) It is highly unlikely you are detecting H2 from the methanizer. H2 from the methanizer does not run through the column so it would not have a retention time. If H2 were to back diffuse to the TCD (not likely if you have sufficient flow) then what you would see is a change in the baseline signal of the TCD as the hydrogen would affect the conductivity of the gases through the detector.

2) What you don't say is what carrier/column you are using which would be helpful. Depending on carrier, the "H2" peak could simply be a baseline pertubation for example.

3) Shooting pure CO2 on most methanizers is not a great idea. They are meant for trace level and can get coked/contaminated by very high levels of hydrocarbons, CO or CO2.

Best regards,

aicmm