Last 3 PAH peaks disappeared

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

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I haven't seen this happen in over 20 years. I ran a 36 PAH standard at 50ng/ml after a lot of tweaking/adjusting settings to increase peak areas, and replacing all of the inlet consumables.
I thought I was home free, but when I ran the 250 ng/ml standard, the last the peaks are gone (dba,icp,bgp).
How is this even possible?
I mean the 50 is diluted from the 250.
chronomag wrote:
when I ran the 250 ng/ml standard, the last the peaks are gone (dba,icp,bgp)...

Please clarify for all if THE SAME vial of standard mix gave decent results before you did all the changes to the GC.
Also, what inlet parameters changed?
Thanks Steve, your question is spot on. The problem was the standard. None of the standards gave a good result before I did the maintenance.
After the maintenance the only standard with the last 3 peaks missing was the highest standard 250ng/ml, which is bizarre.
It looks like those 3 compounds came out of solution only for that one vial. I remade the 250 ng/ml standard and the peaks are back.

The injection vol increased from 3ul to 4ul...the solvent volume still checks out ok for the liner since it is a pulsed splitless injection.
chronomag wrote:
Thanks Steve, you're question is spot on. The problem was the standard. None of the standards gave a good result before I did the maintenance.
After the maintenance the only standard with the last 3 peaks missing was the highest standard 250ng/ml, which is bizarre.
It looks like those 3 compounds came out of solution only for that one vial. I remade the 250 ng/ml standard and the peaks are back.

The injection vol increased from 3ul to 4ul...the solvent volume still checks out ok for the liner since it is a pulsed splitless injection.


If you store the standard in a freezer then at higher concentrations those can fall out of solution and require sonication to get them back into solution.

If it is just PAH compounds then I would store at a warmer temperature but away from direct light, they should be stable stored like that.

I also have this problem with Simazine herbicide, it will fall out of solution if frozen and is almost impossible to get dissolved again so we store at room temperature.
The past is there to guide us into the future, not to dwell in.
5 posts Page 1 of 1

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