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.
By Anonymous on Friday, July 9, 2004 - 02:08 pm:
Use 0.5ul injections when using water (large expansion coefficient)
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).
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.
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.
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.