Question about ghost peaks

Discussions about GC and other "gas phase" separation techniques.

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Hello everybody,

I have a question about ghost peaks in a solvent blank which only appear in one single run (so far) and are relatively sharp. Can I reasonably believe that they are very late eluting compounds from previous samples rather than some kind of contamination upstream of the column?

I have attached the chromatogram where it appeared (in blue).

The solvent blanks are MTBE, analytes are volatile fatty acids, samples are wastewater after liquid liquid extraction into MTBE. Injection volume 1 uL splitless, inlet temp 240C, detector is FID.

None of the samples ran after that one had any ghost peaks. The ghost peaks came out after all analyte peaks and they came out at the maximum isothermal temperature of the column (Restek Stabilwax-DA with a polar deactivated guard column).

I did previously attempt water injections on the same instrument but never exceeded the liner volume and all liner/o-ring/septum have been changed since then.

Please let me know whether this could be a problem or just carry over from late eluting compounds! Thank you!

Image
I'd just make a second method identical to the first, except that it holds at the final temperature for an extra half hour (or whatever the runtime of your method is). Then rerun the sample that was before the one with the ghost peaks, and see if something similar shows up after the run normally ends.
MichaelVW wrote:
I'd just make a second method identical to the first, except that it holds at the final temperature for an extra half hour (or whatever the runtime of your method is). Then rerun the sample that was before the one with the ghost peaks, and see if something similar shows up after the run normally ends.

HI MichaelVW, thanks for the idea, I'll test it the next time I use the GC. But the sample before the one with ghost peaks is a solvent blank which was also the first injection of the day. The last actual "sample" was 3 samples ago. So I assume I'll need to extend the run time to 4 samples worth (100 min) when I try it?
If I am looking at the rights ones, they look too sharp to be leftovers from a couple of runs prior.
Run the sample you think is causing the ghost peaks, follow this with a no injection run (I remove my syringe from the auto sampler). If no ghost peaks I would suspect inlet contamination.
For your sample prep, do you "dry" the extracts prior to injection? You most likely have entrapped water in your MTBE.
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