Extra peak when using hydrogen carrier gas from generator

[pacerlaser]

Hello, I am setting up to run AK101 analysis by GC-FID and I would like to get off of using helium so I am tring to use hydrogen as a carrier gas. Everything went great in terms on calibration but then I noticed an extra peak eluting right after my second surrogate, bromofluorobenzene. I've tried switching generators and I switched back to helium carrier and the peak goes away so I know that the generator is causing the peak. I have a general GC capillary trap installed at the back on the H2 generator but I'm wondering if I need more specific traps. The last thing I'm going to try is using a hydrogen cylinder and see if the peak goes away then I'll definitively know the generators are causing the peak. Any ideas would be great, thanks!

[Steve Reimer]

I don't know what your column is but on my DB-624 I get a siloxane peak that elutes just after BFB when my system sits for an extended period.

[pacerlaser]

That is interesting, I think I'll fill a summa canister straight from the hydrogen generator and run it via TO-15 and determine what peak I'm seeing. Its good to know that others are experiencing the same thing. Thanks for the input!

[AICMM]

pacerlaser,

I think you missed the point. I believe Mr. Reimer was saying that you create the siloxane in the column when you use hydrogen as the carrier rather than helium. Hydrogen is more reactive than helium so it is possible that at higher temperatures it is breaking down bonds within the column.

Therefore, you won't necessarily see anything with a Summa run.

Best regards,

AICMM

[James_Ball]

When I try to tune for mass spec volatiles (8260 or 624 methods)for BFB while running hydrogen I always get a high count for mass 96 versus mass 95. It seems to be adding a hydrogen in the source when fragmenting, but could it also be reacting in the injection port to give some product with BFB that you are seeing even on FID?

[Steve Reimer]

The plus one ion to give "excess" 96 is common when using hydrogen.
My comment about siloxane is that it is common and can come from the system itself. It may even be from some part in the hydrogen generator or a result of the hydrogen reacting in the inlet.

[pacerlaser]

I've discovered what was causing the extra peaks to appear. I had installed a two way valve on the back of the hydrogen generator and it was the culprit. As soon as I removed it, the peaks were gone. When using helium or nitrogen I never had a problem with the valve but hydrogen most definately reacted with it causing extra peaks to appear in the chromatogram.