Looking to use alternative carrier gas from Helium

Hi danlingo,

You may want to check this thread. It has links to calculators and a hydrogen reference package.

https://community.agilent.com/message/5525-gc-and-helium-shortage

As far as using N2, I have had a couple of customers try, its not a supported carrier gas for GCMSD. Mass 28 does not aid in creating an efficient mean free path in the MSD.

Regards

James

Hydrogen should be fine, but with a couple of issues. It is harder to pump down to high vacuum, but you are using a 0.18 ID column which only needs about half the amount of carrier gas amount for the same results as a 0.25 column. H2 is potentially reactive with some analytes in a hot injector; but assuming that you are using split injection that would be less of a problem, as you would be injecting a larger amount of analyte, so it is less likely to be degraded. Low level splitless injections could be more of a problem. H2 can give slightly different mass spectra than He, so Library searches may not be as reliable, but I have not found that to be much of a problem. H2 is a more efficient carrier gas (Look at Van Deemter curves for He, H2 and N2) so you can get better separations in the same time for H2 compared with He, or shorter analysis times for the same resolution.

Hydrogen generators do have a number of advantages: they only generate relatively small amounts of hydrogen, so if you have a leak, they are much safer than a large cylinder; and they can generate hydrogen as pure as 99.99999% so you don’t need filters/purifiers in the gas line. However, the cost of ownership can be higher than using high purity H2 cylinders and purifiers.

If your instrument uses another carrier gas as well as hydrogen the instrument background can be very high for several days as hydrogen "strips" previous contamination from surfaces. I agree with James' post, N2 is not a good choice.

Regards,

Tim

Do you have to use a MS detector? If you could use a different detector then perhaps N2 is an option? I'm just remembering some old lab horror stories of GC's blowing up due to H2 leaks, although perhaps safety issues have been addressed in current systems. I've never had a problem ordering He cylinders. Perhaps an alternative is to always stock a minimum number of He cylinders to guard against temporary back order situations. (FYI, I'm in KS, USA, which may or may not effect my He availability.)

Nitrogen is not a very good GC carrier gas and is really poor inside the MS.  The only real alternative is hydrogen - but it has it's own set of issues as it is a very active chemical.   Hydrogen safety has been an Agilent concern forever and the GCs, Single Quad GCMS, and Tandem Quad GCMS systems are all tested for use with hydrogen (the QTOF cannot be used with hydrogen).   I just uploaded to this community the latest document with details about converting an Agilent GCMS system from Helium to Hydrogen. 

I will add a comment to Tim's post here. I would recommend gas trap especially with a H2 generator. I have had many issues through the years with H2 generators adding water and other impurity's to the background. Gas traps are cheap insurance against replacing an EPC module or two . 

Regards

James

HI,

Thank you all for replying and adding your input. It has all been helpful. I think I will stick with using He.

Could you guys give me a rough estimate on how long a 200 sq ft Helium tank lasts if it is in gas saver mode when not in use and if running 5~25 samples a day on a 0.18 ID column or similar? At first. I will be running the gc ms all day. I don't recall how long the tanks lasted when I used to run gc/msd setup. It seemed like sometimes we would go through a tank every 2mo. Also, what grade of helium do you use from say Airgas? I remember I need to use 99.9995%min purity but not sure if UPC grade is ok for running flavor raw materials. I could not find a purity for UPC grade listed.