Chromatography Forum

Hi all.

Can anyone please explain the difference between PTFE/rubber and PTFE/silicone vial septa? Rubber is substantially cheaper than silicone but I'm not familiar with the differences between the two.

Any help is appreciated.

It depends on your analysis. If you are using a 'very' non-polar solvent, components from rubber may leach out and give you 'strange' peaks in your chromatogram. Contamination will always a concern.

If you are using a polar solvent like water, this will not be a concern.

PTFE is a form of Teflon.

Hi

To expand on HPLC chemist's reply

As far as I am aware and to answer your query

The septa are formed from 2 layers
The PTFE is on the lower side that faces your sample in the vial and is relatively inert to solvents

The top side is red coloured rubber or a silicone that helps to make the seal with the cap on crimping.

In general the Rubber/PTFE septum is fine for general use for 1 or 2 injections within a short space of time

Bear in mind HPLC chemist's reply - with a Rubber/PTFE septum - if left for a while after piercing , both polar and non polar solvents can leach out unwanted contaminants from the rubber

Silicone/PTFE septa will suffer less from this

There is unlikely to be any significant cost difference

Does that help?

Regards

Ralph

If you are talking about headspace vial septa you will find that the rubber ones tend to grip the sampling needle, making the septum more difficult to penetrate. This is not a problem with valve and loop samples that have short, strong needles but it can bend needles on syringes.

Peter

Thank you all for the replies.

I am only performing one injection for each sample, so I think rubber will be suitable.

Is there any difference in how these two septa store when refrigerated? Can vials with rubber/PTFE septa be archived for long periods in a fridge?

Hi Cene

From my experience an unpunctured PTFE faced rubber septum, whether crimp sealed or screw capped, stored well for a few months in the fridge if securely sealed.
It worked for a variety of analytes in different commonly used solvents

Regards

Ralph

To expand on the topic of PTFE/rubber and PTFE/silicone:

Depending on what type of rubber septa is being used, some rubber can only withstand temperature of 100 C while some can withstand up to 250 C. That also applies to silicone. Rubber septa are generally not recommended when chlorinated solvents are in use. I would check to see which type of PTFE/rubber or PTFE/silicone you are using. Hope that helps.