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GC of FAME problem
Basic questions from students; resources for projects and reports.
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New to GC and setting up a system from scratch. It is an Agilent 7890A with FID and I have installed a Supelco 2380 column. I am running a qualitative PUFAME standard at 10mg/mL in hexane with all of my method parameters set as indicated in the certificate of composition leaflet that came with the standard. I am getting a solvent peak but nothing else. I have triple checked my dilutions, reduced the split from 100:1 to 10:1, and even ran the standard at 100mg/mL. Any ideas on what could be going wrong here? I will be more than happy to answer any questions that may arise regarding my methods if anyone would be willing to help me out. Thank you!
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Is the electrometer or the computer setup using the correct parameters?
Did you 'condition' the column before you used it?
(I hope not)
best wishes,
Rod
Did you 'condition' the column before you used it?
(I hope not)
best wishes,
Rod
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The default display setting may be to put the biggest peak on scale. So the software shows you the solvent peak just touching the top of the chromatogram and the other peaks that are 100 times smaller are invisible blips on the baseline. Try using the zoom functions on the on-screen chromatogram, and changing the scale parameters for the reports.
Peter
Peter
Peter Apps
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Agreed with the first two gentlemen. Sounds like something is amiss with the FID as the data comes out of the data system--not with the detector itself. You could try to inject butane mix for recharging a cigarette lighter to see if this affords a signal--should elute near the void time for the column, just like the solvent for the FAME standard mix.
Wouldn't make sense that you'd be getting "flame-outs" every injection...and you likely did check for leaks in your column installation and at the injector nut? A massive leak in the septum might explain the trouble, too...enough solvent that you see a response for it, but not the analytes.
Wouldn't make sense that you'd be getting "flame-outs" every injection...and you likely did check for leaks in your column installation and at the injector nut? A massive leak in the septum might explain the trouble, too...enough solvent that you see a response for it, but not the analytes.
MattM
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That is a good suggestion MattM.
A blown out detector is less likely as that column is narrow bore and is unlikely to get enough solvent through to affect the flame very much.
Another preparation of a known concentration would be a good idea. Just to confirm the std you have is made correctly (accidents do happen).
I still have my momey on the display parameters or the data collection paramaters being mischosen.
Let us know your solution when you find it.
Rod
A blown out detector is less likely as that column is narrow bore and is unlikely to get enough solvent through to affect the flame very much.
Another preparation of a known concentration would be a good idea. Just to confirm the std you have is made correctly (accidents do happen).
I still have my momey on the display parameters or the data collection paramaters being mischosen.
Let us know your solution when you find it.
Rod
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Thanks all very much for the suggestions. I discovered the problem and you won't believe what it was. The autosampler was not attached to the syringe plunger, so I sat for two days racking my brain and was never even injecting any sample! My peak came from whatever small residual amount of solvent was on the tip of the needle. Many thanks again and I'm sure I will be back with future questions as I am just getting started with GC.
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The moral of the story: don't trust autosamplers.
Peter
Peter
Peter Apps
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The other moral:
trust, but verify.
Rod
trust, but verify.
Rod
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Well, it's been a while since I've done GC work...but holey-moley! I'll file this observation away...one time I do remember not getting any peaks at all in GC-FID (Thermo Trace GC) and I went to the lab and saw a needle the shape of an accordion...autosampler assembly and needle weren't properly lined up to the injector. One might have thought the autosampler would have been smart enough to "realize" that it wasn't aligned to the injection port (at least, I would have)...was an interesting sight at the time.
MattM
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The nut in front of the machine is usually the cause of the problem
Good judgment comes from bad experience, and a lot of that comes from bad judgment.
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Humph !
I resemble that remark. (my apologoies to Rodney Dangerfield)
Rod
I resemble that remark. (my apologoies to Rodney Dangerfield)
Rod
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Well...if you've not broken some eggs...how could you make a superior omelet?
Eggs, or egg-like products sold in a carton, Do Not Count.
Eggs, or egg-like products sold in a carton, Do Not Count.
MattM
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