Raising baseline with HP GC-FID

Chromatography Forum: GC Archives: Raising baseline with HP GC-FID
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Y. Hardi on Wednesday, December 13, 2000 - 04:18 pm:

Hi folks !
Can anyone explain the symptom of a strong
raising baseline, no, not the "nornal" column
bleed starting at a certain high temperature.
The baseline raising increases at the same
time and temperature as the ordinary column
bleed but with a much higher intensity. It
started with one of our GCs without any
reason. I already tried to heat possible
contaminants out of the column by setting a
longer temperature program on an analytical
run with only a solvent being injected. We use
a HP 5 in a GC/FID 5890 II with a Cool
On-Column injector.
Thanks in advance for any suggestions or
help regarding this problem.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, December 18, 2000 - 07:19 am:

Since the baseline starts at a certain temperature, it would seem to rule out the detector. This narrows it down to the inlet or the column itself. One way to see if it's the column is to replace with a new, conditioned column of the same type. It could also be something from the inlet that starts eluting once the temperature gets high enough, routine inlet cleaning/maintenance is very worthwhile.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Ron on Monday, December 18, 2000 - 09:17 am:

Try a systematic approach. First remove the column from the detector and block the column inlet with a plug. Re-ignite the detector and run the temperature program to determine if the baseline rise still occurs. If so, the detector base is the most likely source of the contamination. If the baseline rise is gone, install a different, known good column and repeat the experiment. If the rise is gone, the column was bad. If the rise is still there, clean the inlet thoroughly and try again. Verify that any traps are still good, and replace if they are too old.

The fact that your baseline rise starts at the same temperature as the normal column bleed makes me suspect that the stationary phase has been seriously damaged. This can be from an air leak, column overheating, or could be from the samples. For example, elemental sulfur which occurs in some petrochemical samples will rapidly cause irreversible phase damage and high levels of column bleed.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By jclark on Monday, December 18, 2000 - 10:10 am:

The likelihood is that it's coming from the cool on-column injector. Some non-volatile material is/has probably been deposited in the injector and when the oven heats up, it volatilizes some of this material from the injector at a predictable temperature with each injection.
Alternatively, the column may have been damaged by oxygen-containing)carrier gas and an exhausted purifier. You should have an oxygen "getterer" immediately upstream from each instrument.


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