Chromatography Forum

Hi, I am trying to use GC(Agilent 7890A) to detect He (ca. 1%)-CO2 (ca. 1%)-N2-CH4 mixture. The column used is a Carboxen-1000, length 15 ft, 1/8 in. OD and 2 mm ID and the detector is TCD. I was wondering if it is possible to use Ar as carrier gas instead of H2?
I did some tests using Ar as carrier gas and it seemed the retention time of CO2 was quiet long and CH4 was not detected. The Agilent ChemStation does not allow to chose Ar as reference and makeup flow so I chosed N2 in the software (but Ar in the pipe). Can anyone tell me if it is right?

Thanks in advance.

I think - problem is in Ar as career gas. Sencitivity of TCD is more lower compare with H2 or He. What is the CH4 concentration? Can you insert chromatogram and work mode? For information: https://www.sigmaaldrich.com/technical- ... -0114.html
Regards

frank2009,

You cannot detect He (low concentration) with H2 carrier. You can detect He with argon carrier but you might not see the CO2 (1%) in that scenario. You might need to explore two column/two detector configuration for this application.

You can choose Ar/Me as the reference and it should get you pretty close.

Best regards,

AICMM

I think - problem is in Ar as career gas. Sencitivity of TCD is more lower compare with H2 or He. What is the CH4 concentration? Can you insert chromatogram and work mode? For information: https://www.sigmaaldrich.com/technical- ... -0114.html
Regards

Hello nipe,
I just tried the single gas CH4, not the mixture of He, CO2, N2 and CH4. I'm working on to get a chromatogram and will insert one as soon as possible. I have read the article before and the carrier gas is helium.
Best regards.

frank2009,

You cannot detect He (low concentration) with H2 carrier. You can detect He with argon carrier but you might not see the CO2 (1%) in that scenario. You might need to explore two column/two detector configuration for this application.

You can choose Ar/Me as the reference and it should get you pretty close.

Best regards,

AICMM

Hello AICMM,
thank you for your advice. I'm also worrying about detecting He with H2 carrier. The firm Restek has some chromatograms regarding this issue, e.g. https://www.restek.com/chromatogram/view/GC_PC1182 (sample concentration 1% in H2).
However, I would prefer to use Ar carrier due to the safty reason. Is it possible that you can show one chromatogram with the conditions similar to mine (TCD, Ar carrier, sample composition)? I'm not sure about the Ar/Me as the reference since my sample has CH4.
Best regards.

The problem with measuring helium using hydrogen carrier gas is at low concentrations. If you plot a linearity curve you will find that at the low end the plot will look like a 'hockey stick', that means for two different concentrations you get the same signal. Chromatograms from column suppliers do not always tell the full story...……….

Gasman