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GC FID Leak
Posted: Mon Jul 21, 2008 5:33 pm
by tilly
I'm new to GC FID and have a question about the cause of high levels of baseline noise. Is it possible to attribute this to a leak in the carrier gas (helium) inlet? What contaminants would there be in atmosphere which would cause this or is it that the column is caused to degrade? Thanks for your replies.
Posted: Mon Jul 21, 2008 6:54 pm
by chromatographer1
Hi Tilly,
You posted in the less than a perfect match section but that is ok.
Oxygen will damage many phases used in GC and give you a lot of bleed from the column which may or may not be "noisy".
A dirty or contaminated flame tip can give you a lot of noise, or other parts in an flame detector. Cleaning is always a priority.
Contaminated air or hydrogen can also give you a lot of noise.
A broken column tip in the detector or a tip installed too deep in the detector body are other causes.
No leaks in your pneumatics. No broken or misinstalled columns. Gases and detector components that are uncomtaminated are all requirements for a quiet and sensitive detector.
best wishes,
Rod
Posted: Mon Jul 21, 2008 9:00 pm
by tilly
Hi Rod
Thanks for the reply. As the column is still installed, do you think it would be a good idea to 'bake' the column (to get rid of contaminants?) and then run a sample.
If the noise is reduced can we then say it was caused by the leak in the gas inlet line? Also, do you have any cleaning proceedures you would recommend? eg. solvents to use?
Posted: Tue Jul 22, 2008 3:05 am
by chromatographer1
If you have a leak you must fix it before your column is destroyed.
You should remove your column from the detector and cap the detector to see if your noise is eliminated or reduced.
Troubleshoot your problem before you raise the temperature of your column or you may cause great damage.
best wishes,
Rod
Posted: Tue Jul 22, 2008 4:57 pm
by Bigbear
Not to sound condesending ,but are your H2 and air flows correct? most FID's want 10X times air as hydrogen, (ie 40 cc/min H2 and 400-450 cc/min air). Are you using make up gas at the detector ( old style detectors were designed for carrier gas flows of 40-60 cc/min). If using "house air" are you filtering out oil and water?
Posted: Sat Jul 26, 2008 10:01 pm
by tilly
thank you all for your replies.
Since the leak from the gas inlet line was rectified, i ran a sequence and the S/N improved. I didn't change anything else except the wash bottle. In the first blank there were some peaks eluting. the second blank seemed clearer, and the third blank injection saw more peaks again. Do you have any ideas what this could be? If it was column bleed or solvent contamination would you expect it to be more constant? The blank runs are 90mins.