Septum peaks are target compounds

Normally the cyclic siloxanes only come off at very high temperatures or by prolonged contact with solvents or solvent vapours, especially DMSO, DMF, THF, and others more aggressive solvents; not with a single injection from a headspace vial under classical conditions. And they very often do not come from your vial septum, but the GC inlet septum.

You can try to use a PTFE/butyl rubber disk/septum like 8010-0140 for the vials and if you still see the peaks, it is from the inlet septum.

I planned to try the PTFE/Butyl septa (8010-0140 | Agilent) received but it did not go as expected.

The metal housing of the fiber got bent, when using a CTC, destroying the SPME fiber assembly.

The septum is way too hard to be pierced by the blunt tip of the SPME. The fiber installed was new.

I even tried by hand with a cone-tip 10 mL syringe and I could feel the difference when compared to a PTFE/Silicone septum.

Because SPME fibers are not cheap, I will not try again.

I did not find anything on the page of Agilent about tip compatibility with this septum.

We are using SPME fibers from Supelco (ref.: 57319).

If you are not happy with butyl rubber, pre-pierced septa, we would always advise Merlin Microseal.

Thank you for the answer but the injector's septum was not the problem.

I was talking about the product you suggested: PTFE/butyl rubber disk/septum (8010-0140 | Agilent).

The septum is too hard for the SPME housing.

Here is a picture of what happened.

Then the septum was to strongly crimped. If you use an electric crimper please see the article about how to crimp perfectly.

It is a screw cap.

It might have been too tightly screwed. I don't know.

However, I have done more than 1500 SPME injections with screw caps and PTFE/Silicone septa and I never had this problem happening.

The PTFE/butyl rubber septum just feel harder that the PTFE/Silicone one.

Their compressibility is different from silicone septa.

BTW you never mentioned the solvent and the incubation time and temperature? As I said earlier D4 to D7 only form in quantifyable amount at high temperature or by leaching a silicone septum for a long time.

The peaks observed were from a blank injection (empty vial). No solvent.

Incubation temperature: 90ºC

Incubation time: 1,5 hours

It is a method established long before I started working with the equipment for trace analysis of headspace of polyols.

I'm using it as well to analyze the headspace of solid samples.