Chromatography Forum

Hello,

I've been dealing with a problem for a little bit now with fronting after performing maintenance on my GC. This will occur in CCVs that I make AND my pre-made DFTPP standards, too. It also only seems to occur when I am running my 8270 SIM method on 2 different instruments, and not on the instruments using SCAN mode, but that might only be because it's not noticeable when I'm not looking at low levels. Sometime this will result in an entirely separate new peak on the front half of my expected peaks, and sometimes it is pretty minor and just occurs as you would expect for peak fronting. It will generally go away after a few blanks, but sometimes can occur again mid-run, as it did on my new curve from the other night.

The only thing I can think of was that a while back I started adding wool to my liners and soaking both in Sylon at the same time (an idea I got from a forum post here, which does wonders for phenols and other problem compounds for EPA 8270/625.1 by the way), but I have since decided to take out and replace that wool with unsoaked wool when inserting the liners for my 8270 SIM PAHs. I'm pretty confident that this is the problem since it looks to have started the same time I started this process, but since it is so helpful for my other analysis I'd love to avoid abandoning it.

GC is a HP 6890 series with a Agilent 5973 MS.

I've attached an extreme example of this (hopefully it works anyways, been a while since I used a forum):


Thanks

I don't have an answer (hopefully someone will!) but is it relevant that the retention time is so much earlier? Is that just the shift from clipping column?

I used to get similar looking fronting when I was running SCAN mode and used samples with too high of a concentration. I never used wool.

Could it be that the changes to the packing material are making it take longer to completely purge the inlet liner? Can you increase the inlet pressure (pulsed splitless) and/or just let it purge longer?

That looks very much like an effect of solvent condensing on the column - what solvent are you using, what volume do you inject, split or splitless, and what is that start temperature of the column programme?