Chromatography Forum

As a novice to the chromatography world could someone help me out,
When/why is it advantageous to use a silicone/teflon septa?
Why can't we just use a plain teflon septa?

Thanks,
Doug

Doug,

The best thing to do is to use the manufacturer's recommendations for their autosampler.

Some instruments may not allow for use of the teflon/silicon septa; the needle may not be able to handle a thick septum. Some instruments even require the teflon septum to be pre-scored (pre-split).

A silicon/teflon septum offers a good seal and prevents evaporation loss. This is useful in a GMP lab were you may need to make investigations using re-injections or in the case where you just want to save the solution in the vial for a few days (manufactuers usually say its good for 2-3 days).

It has been noted that the silicon/teflon septum may provide too good a seal for some autosamplers. A kind of "vapor-lock" occurs and you get injection reproducibility/accuracy errors when more than one injection per vial is made. Again, check with the manufacturer's recommendations.

The teflon septum will allow for the solution to be kept for 1-2 days without evaporation losses becoming a concern.

I have been in a pharmaceutical analytical lab for a number of years and have used autosamplers from a number vendors. My best recommendation is to go with the manufaturer's recommendations, they know what is right for their instruments and I haven't had problems when I used what they recommend.

Regards,
Dan