By polymerv on Friday, July 9, 2004 - 11:52 am:

I'm using a varian GC with an FID detector. I'm loooking for small hydrocarbons in water, but the flame keeps going out on the runs. ITs fine when I use a solvent for the compounds, but when I use water---flame out. Any suggestions?
H2- 30 ml, air 300ml, makeup/carrier He 28/2 ml.
35 C to 60 (4 C/min) 60 - 120 (10C/min) Inject--200, FID--225. HB 5 column 30M, 320 micron, split injector ~ 100:1

I really need to use water as the solvent for injects.

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By Anonymous on Friday, July 9, 2004 - 02:08 pm:

Use 0.5ul injections when using water (large expansion coefficient)

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By Jason Ellis on Friday, July 9, 2004 - 04:01 pm:

You might try using a retention gap (guard column) -- deactivated fused silica is more wettable to water than the nonpolar HP-5 phase is, and the retention cap may help spread out the water band so it elutes over a longer time rather than in a "bolus". I have heard some people have luck with this technique.

You might also want to try adjusing the H2:Air ratio on your FID -- richen the flame up a little as this sometimes helps as well.

Finally, the 0.5 uL injection is highly advised -- less water eluted to detector, also less potential for backflash in the inlet (better RSDs, less contamination of inlet).

Jason Ellis
Technical Support
Agilent Technologies

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By polymerv on Monday, July 12, 2004 - 09:51 am:

Thanks, I'll try all. I've been using 1 microL injections so far with a standard open insert.

Thanks

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By Ron on Monday, July 12, 2004 - 01:17 pm:

If you can start at a higher oven temperature that will also help. Starting at 50 instead of 35C will keep more water in the vapor phase and help keep the flame lit.

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By Ron on Wednesday, July 14, 2004 - 05:11 am:

I overlooked something in your post, you are already running a 100:1 split. That should reduce the amount of water on column enough to prevent flameouts, at least I have never had any trouble with FID flames running 20:1 split on Shimadzu or Agilent GCs. I'm wondering if your jet may be partially blocked or there is another detector problem that is causing this sensitivity to water.