Chromatography Forum

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!

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