Chromatography Forum

I am a research student new to GC.I have few questions regarding detection of hydrogen from head space of some bacterial culture bottles. The model of GC I am using is Agilent 7890A with Helium as carrier gas. When I calibrated using standard gas, the graph shows a negative peak for hydrogen gas. However,when I tested with my sample gas, the peak that I had was a positive peak for hydrogen gas. So, I was wondering is there anything wrong with my analysis? Thank you

I'm assuming you have a TCD for the detector. If this is the case, I would expect a negative peak for H2 if He is the carrier. Normally when H2 is the analyte of choice He is not used as a carrier because the thermo conductivity between the two gases is very similar yielding very low sensitivity toward H2. I would look at using Ar as you carrier.

What column are you using?

Thanks for your help. Yup,the supplier told me try not to use helium gas when gas sample contains hydrogen gas. But I have no other choices because my university is using helium gas as carrier for GC. The column is Porapak Q and molecular sieve. I am just curious why will my graph shows me a positive peak for hydrogen gas for my sample.

The different response depends upon the concentration of the hydrogen. Be aware the response is not linear even when the signal is positive.

As the concentration of H2 increases there is a point(6-8%) of concentration in the detector where the response becomes negative and a m or w shaped peak is produced.

If you want linearity you should use air or nitrogen as a carrier. Argon is also an option. Use MSieve if you can as a column, but a long porous polymer column will also work (3-6 meters)

good luck

Rod

If you use air as a carrier and are using a hot wire detector, not a thermister, you can burn out the detector easily and quickly. Use a very low temperature or expect a quick failure and an expensive repair.

FYI

Rod

A perfect application for an HID. (I know, I know, I know, I have a strong bias here since I make an HID but this really is an excellent example.) Especially since you know the next question is going to be "What about CO and CO2 sensitivity when I switched to Argon carrier?"

Jac88, nothing personal here at all, it is just that this question keeps popping up these days and I believe the old solutions are not as effective as the new solution.

Best regards,

AICMM

FID sensitivity for H2 !

Ain't that neat?

Go for it if you can.

AICMM has a point and a nice product.

best wishes

Rod

I wonder if HID could be an efficient soft ionization source for a mass spec...

willnatalie,

People have used Argon as a soft ionization source (I'll see if I can find a citation for the instrument I am thinking of.) I suspect that helium would work as well but have not seen anything in the literature (yet.) Pumping issues certainly come into play here but hey, people do MS at atmospheric so I can't see that being a show stopper. Advantage to using helium would be the higher ionization potential over argon so you would be able to ionize more but argon is much cheaper and probably covers a great deal of the constituents of interest.

I don't have any MS's to play with so I just continue to play just in the realm of GC's.

Best regards,

AICMM

Quick question, I am trying to detect hydrogen with a TCD and a helium carrier gas. I am in the 5% range and using a Carboxene 1006-PLOT column. I know that a 1010-PLOT column should seperate it out with the 7-1 ratio of Hydrogen to helium. Does anyone know if the Carboxene 1006 separates it out as well?

Since hydrogen and helium can be separated even on a porous polymer column with much larger pores that any of the Carboxen supports my guess would be YES, a 1006 will separate Hydrogen and Helium.

best wishes,

ROd

I was able to see a clear hydrogen peak after I changed the carrier gas to argon.