Carrier gas for CO2/H2/methanol/CO/CH4 using TCD and FID

[JGUAN58]

Helium was used in our agilent 8860 GC system with a TCD and FID for CO2/H2/methanol/CO/CH4 detection. CO2/H2/CO/CH4 were detected by GS-carbonplot column to TCD. Methanol was in liquid phase and detected by a ALS to HP-5 to FID. Methanol and CO concentrations were relatively lower, CO2 and H2 concentrations were high.

Now we want to switch to N2 or Argon, would N2 be better than Ar? We also have HP-1, heavywax, MS4 columns.

Also, if we want to analyze CO2/H2/methanol/CO/CH4 all by gas phase in the future, do we need to connect the TCD and FID or still keep them separated?

Thank you!

[DR]

N2 should be cheaper and better than Ar, but either way, you'll be settling for broader peaks, longer run times and lower sensitivity. The larger/heavier the carrier gas, the lower the linear velocity needs to be to get similar separation efficiency.
Too bad H2 is on your analyte list. Otherwise it could actually be a better carrier than He.

[JGUAN58]

N2 should be cheaper and better than Ar, but either way, you'll be settling for broader peaks, longer run times and lower sensitivity. The larger/heavier the carrier gas, the lower the linear velocity needs to be to get similar separation efficiency.
Too bad H2 is on your analyte list. Otherwise it could actually be a better carrier than He.

Thank you DR!

I tried to use N2 as the carrier gas for the column and TCD to analyze a CO2/H2 mixture, but got two negative peaks...when using He, only H2 was negative.

And the CO2 peak is not shape but like you said broader and lower sensitivity, the H2 peak sensitivity is improved a lot...

[wss]

We use a MicroGC with PLOT and a couple of other columns for this sort of analysis, one channel plumbed with He and the others are all Ar. Never had a problem with argon, which seems to work quite well and we see positive peaks from the TCDs for these analytes (though maybe that's just how our DA method is set up).

[JGUAN58]

We use a MicroGC with PLOT and a couple of other columns for this sort of analysis, one channel plumbed with He and the others are all Ar. Never had a problem with argon, which seems to work quite well and we see positive peaks from the TCDs for these analytes (though maybe that's just how our DA method is set up).

Thank you! I have tried Ar, it seems our system is not able to separate H2 and CO peaks, CO2 and CH4 are fine. Maybe our CO concentration is too low.

[wss]

We use a MicroGC with PLOT and a couple of other columns for this sort of analysis, one channel plumbed with He and the others are all Ar. Never had a problem with argon, which seems to work quite well and we see positive peaks from the TCDs for these analytes (though maybe that's just how our DA method is set up).

Thank you! I have tried Ar, it seems our system is not able to separate H2 and CO peaks, CO2 and CH4 are fine. Maybe our CO concentration is too low.

You may also find the CO concentration low if the standard is quite old, I have noticed this happen in very old (>5 years) gas standards, the CO concentration/response drops over time presumably because it's the most reactive gas in there.

[JGUAN58]

N2 should be cheaper and better than Ar, but either way, you'll be settling for broader peaks, longer run times and lower sensitivity. The larger/heavier the carrier gas, the lower the linear velocity needs to be to get similar separation efficiency.
Too bad H2 is on your analyte list. Otherwise it could actually be a better carrier than He.

Hi DR,

I tried N2 and Ar but couldn't separate H2 and CO peaks, H2 peak is too strong and can cover the CO peak. May I ask is it possible to improve the separation efficiency by tuning the parameter rather than switching the column?

[DR]

Assuming your connections are sound, all you can really do is make sure you've optimized your flow and temp profile to make sure you're getting as much separation as you can. If that doesn't work, a longer column may help - otherwise, you need a different stationary phase and/or carrier.

[AICMM]

jguan58,

Not knowing the exact details of your configuration, have you considered using a methanizer? In particular a Jetanizer from Activated Research? Methanizer would see the CO, CO2, CH4 and methanol on the FID channel and then you would run the TCD with argon or nitrogen (I would use argon) for just the H2 peak. I have not run carbonPlot so I do not know where Meoh would come out but I still think this may be an attractive solution.

Best regards,

AICMM