VOC determination - charcoal problems

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

3 posts Page 1 of 1
First of all as I'm new here, I want to say hi!

I work in an accredited environmental agency in my country and my coworker and I are trying to validate a method for VOC determination but we have an unusual specific problem.

We're using a GC 7890A with an 5975C MSD in case it's a relevant information.

Anyway to the important things, we don't have a thermal desorption unit so our method is by extraction with carbon disulfide, putting it all in the 2mL vials, shaking it for at least 30 minutes and then injecting the samples with the (again Agilent's) 7693A autoinjector.
So here's the problem, when we inject the extract/sample into the GC, what happens is that charcoal/carbon starts building up on the gold plated split/splitless seal disk (Agilent 5182-9652).
Just after even something as 20 injections the disk turns black and as a consequence it causes a drop in sensitivity and repeatability as well as an increase in baseline. Obviously it prevents us from being able to validate the method. The seal disks usually lasted us for a year without any need to change them if at all but this makes it necessary to clean (if that is even an option) or replace them.

We honestly have no idea why that's happening because it seems to not happen to anyone else in the world. In fact we checked a whole bunch of articles, standards etc. and no one ever mentioned having this problem.
We tried using a centrifuge after shaking at around 4000rpm for 20mins, it's only slightly better but still the same problem.
Because of the compounds in question and not having a TDU, only charcoal as sorbent and CS2 as solvent comes into play.
We tried filtrating just to try what happens but we noticed that CS2 seemed to have reacted with the filter, the solution became blurry.

Does anyone have any experience with this sort of matter? Any ideas?
Syringe filters with PTFE membrane.
What injection port liner are you using?

Have you tried liners with glass wool in them to capture the charcoal before it contacts the bottom of the injection port?

Much simpler to replace a liner each day than the gold seal. Most of the volatile analytes are not ones you have to worry about breakdown with so if the glass wool will capture the carbon then you can simply remove the wool, rinse the liner and put in fresh wool and that liner is ready to use again. Keep a couple liners handy and just swap out each day.
The past is there to guide us into the future, not to dwell in.
3 posts Page 1 of 1

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