Looking to use alternative carrier gas from Helium


I am putting together a proposal for the owner of the company I work for to make flavors. I cannot purchase the GC/MS system until I can determine if I can use an alternative carrier gas with good resolution,selectivity, etc. We are looking at buying 7890A GC with a 5975C msd as a detector. In the past at another company I used same equipment with helium as a carrier gas and built a mass spec library including retention times, etc. Using the column - DB-5ms 40m x 0.18mm x 0.18um. Now that Helium is difficult to get, when we buy this equipment from Agilent I want to start off using a carrier gas that is in constant supply. I understand I will have to update retention times for thousands of peaks so I need to know what you guys think I should use as a carrier gas other than helium. Should I not use Nitrogen? I remember reading in the Agilent class books from classes I took a few years ago that nitrogen will give some overlapping peaks at some point in the column depending on phase.Is it still not a good alternative to helium now that we may not be able to get helium at times. Is hydrogen ok to use with mass spec using a hydrogen generator? Could I use a combination of two gases?


Also, is there a newer method translation software so I could translate the old method and column to using a new type of column and carrier gas that may keep retention times somewhat close to original method. If I have to start over on the retention times then that is fine.

Thank you,

Dan Lingo

  • 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.




  • 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



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