Chromatography Forum

Hi all,
We've run into problems with apparent "bleeding" on our GC-MS that we've identified as coming from the septa of vials we use (I know it's not column bleed, but for some reason that's what we call it in the lab). Anytime a vial is pierced we immediatedly need to change the septum, which is rather wasteful and still does not fully resolve the problem. We use red PTFE/Silicone from Supelco, and was wondering if anyone has better alternatives to use. We typically analyze hydrocarbons, FAMES, and TMS-alcohols with hexane or dichloromethane as a solvent.
And I suppose a secondary question would be: what's the consensus term for this type of vial septum "bleed"?
Cheers,
Robert

We've seen this problem with an FID, though not on the next injection, and found that the problem was better or worse depending on the septum supplier. Since you are used to dealing with Supelco, you might let them know about your problem and see if they have any alternatives. Another option is to check with other suppliers and see if they will give you any free samples to check. We were able to do that and found some that work well for our applications from National Scientific. Of course, with an MS your application is more demanding.

This is a problem with newer mass spectrometers since they are so much more sensitive than the older instruments. Are you changing the rinse vial solvent regularly? Always rinse out rinse vials with solvent before refilling, and never top off a rinse vial.

Other than that, you may have to try other suppliers to try to find a septum with lower bleed. I always call this septum bleed, not very accurate but it does point out the source.