Published Ryan Schonert on November 13, 2019

2 responses to “Tackling the Helium Shortage with GC-VUV, Part 1”

  1. I work on VUV spectrocopy and trying to do GC-MS along with VUV on molecules.
    A doubt regarding this comparison. Why not argon. Safe. Relatively cheap for 99.999 purity. Easy to procure and store. Inert like Helium (better than nitrogen which can react some of the molecules at high temperatures)). Run time will be high (compared to nitrogen). Why not varying sample delivery column diameter to length ratio to achieve lesser sample carrying gas times (Again per run any issue with amount of argon spent?cost factor?). Easy to pump (like nitrogen). No VUV lines in 125-225nm (like nitrogen)

    • Ryan Schonert says:

      Hi Dr. Rajasekhar,

      As you point out, argon doesn’t have any absorption in the VUV region like nitrogen does, so the VGA detector could handle argon with few issues. We’ve even tested it as an alternative makeup gas for nitrogen in our lab’s VGA detectors. However, I believe it would be difficult to use argon as a GC carrier gas. The run times necessary to achieve good chromatographic resolution would be dramatically increased, enough so that argon is very rarely ever used as a carrier gas. VUV’s spectral deconvolution would allow you to sacrifice some resolution for a shorter run time, but speeding up the run too much could push the spectral deconvolution past its limits. Also, most GC EPCs aren’t set up to run argon, so even if argon was used, it would take additional work to tune the flow settings properly on the GC. I’m not aware of anyone using argon for GC-MS, although I’d suspect that would have additional issues.

      Even though nitrogen does absorb in the VUV region, the absorption is small enough that it can still be used without trouble. At the start of a run, the VGA detector takes a reference scan which can be subtracted from the absorbance of sample compounds, so nitrogen in the flow cell is effectively ignored.

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