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Skinny solvent Peak on GC/FID: TPH/DRO Analysis
Posted: Thu Jan 26, 2006 7:16 pm
by semivoadude
I can't get an approriate size Methylene Chloride solvent Front.
Ive inspected the syringes, injector, column ends, column insertion distance and the detector jets.
Anyone have an idea? can I email you a chromatogram?
Thanks in advance
email me:
jeffo@eailabs.com
solvent
Posted: Thu Jan 26, 2006 8:26 pm
by chromatographer1
So where has your solvent gone?
split vent? backflash out the septum? FSOT column? Is it cracked somewhere? Are all your mechanical connections tight and non-leaking?
Is your detector amplifier set at the proper setting?
good luck,
Rod
Skinny solvent Peak on GC/FID: TPH/DRO Analysis
Posted: Thu Jan 26, 2006 9:04 pm
by semivoadude
The FID recognizes the solvent but gives a weak response. I expect the solvent front to be fat and large. The peak I am getting is skinny and thin.
i manually testes flow rates and they look OK:
Air: 400ml/min
He: 30ml/min
H2: 60ml/min
I run splitless injection mode. When I disconnect Detector end, I do have pressure (I place the colum detector end in a vial of Mecl2 and see "bubbles")
I cant find any leaks, the agilent j&W db-5 column is in good shape, Im pretty much baffled at this point.
Posted: Thu Jan 26, 2006 9:11 pm
by Schmitty
What type of GC are you using? Sometimes on the HP 5890s the splitless injection port will be set to split at 0.2/0.5/1 minute. Then, late in the run it needs to be told to close. If the runtime doesn't reach that set time, the next injection (and all subsequent injections) will be split.
It's a reach, but...
Schmitty- skinny peaks on GCFID
Posted: Thu Jan 26, 2006 9:21 pm
by semivoadude
I run a 5890. I open the split valve at 0.75 minutes, then it closes for the remainder of the run.
I wish I could post a chromatogram on this site, that would be cool.
Hey, Tom Jupille- can you help me out?
thanks
semivoadude
no leaks!
Posted: Thu Jan 26, 2006 9:48 pm
by chromatographer1
I suspect that Schmitty is right. You are injecting in the split mode and your splitter shut-off valve may not be working properly or your software is not set correctly.
Rod
methylene chloride solvent peak
Posted: Mon Feb 06, 2006 8:06 am
by Peter Apps
You do not say whether or not your analyte peaks are the expected size. If they are unexpectedly small, like the solvent peak, there is probably a problem with split timing.
If the analyte peaks are big enough you do not really have a problem.
An FID has a weak response to chlorinated solvents, and so you will always get a smaller solvent peak with methylene chloride than you would with the same volume of pentane or hexane. Sometimes chlorinated solvents quench the flame, which makes the peak even smaller.
If you are running a lot of samples in chlorinated solvents, soot will build up in the FID, which needs to be cleaned out.
Peter