Chromatography Forum

I am not sure about N2 but I am hearing lots of stuff regarding H2
30% loss of sensitivity on MSD
Chemical ionization effects in EI spectra
H2 acts like a scubber driving out contaminants that have long been present in your gas lines
hydrogenation of unsaturated hydrocarbons

So , can someone comment on the benefits of using He vs N2 as carrier gas nowdays with today's prices, and in regards to sensitivity and noise?

I am sorry. I meant MAKEUP gas.

He vs N2 as makeup gas.

Nitrogen every time - much cheaper and the same performance. Also you can get nitrogen generators. If you come up with a helium generator count me in as an early investor !!

Peter

I always got BETTER performance with N2 makeup. Care must be taken not to lean the flame TOO much.

But cost is less than He as Peter states, even can use a generator instead of cylinders.

best wishes,

Rod

Hi Rod

The improved performance that you got with nitrogen is very interesting. I had heard of a similar thing, but I could never find any literature. It might be related to the diffusion kinetics in the flame - one of the theories about how an FID actually works is that atomic hydrogen diffuses upstream from the flame and hydrogenates all the analytes before they hit the combustion zone. The rate of diffusion would be different with different make-up gasses. What would happen with argon I wonder ?

Peter

I have found this to be true on Agilent and Varian GCs, as well as with process control GCs.

Improvements of detection limits ranged generally, from 30% to 50%, depending upon the analyte in question.

My understanding of the FID is that only a tiny fraction of the analyte molecules are ionized in the best of hydrogen flames and electrodes. Is it not likely that helium makes a better insulator of any possible tiny current than nitrogen?

Fortunately, we can use the improved results without having a good understanding of it, although said understanding might help us to increase the effect and improve performance.

Happy research,

Rod

An improvement of between 30 and 50% with a change in conditions that saves money ! Sounds good to me. And since this was detection limits, not just peak size the noise was not increasing in relation to the extra signal.

Peter

Baselines showed no difference. Just keep your electrodes and all electrical pathways clean and clear.

If you have issues not seen before due to the lower sensitivity of the FID, improving the response CAN disclose them where they were hidden previously.

No reason at all to use helium for makeup.

(Only if you are using a helium ionization detector instead of an FID)

best wishes,

Rod