Chromatography Forum

Hello. I was wondering what the best type of septa for screw top vials is for a 26s gauge cone tip agilent needle? We get them from ChromSys LLC:

Types of septa available for your vial caps (Prices include 100 caps, septa and 10/20 ml headspace vials)

* 1803 2063-10/20mL : Ultraclean Silicone/PTFE layer. $110
Slit (only in silicone layer) septa for longer SPME fiber lifetime. (See image below).
* 1803 1414-10/20mL : Ultraclean Silicone/Blue PTFE. $110
* 1803 1309-10/20mL : Natural Silcone/White PTFE. $110
* 1803 1874-10/20mL : White Silicone/Aluminum Foil. $110
* 1803 1416-10/20mL : Butyl rubber/PTFE. Low cost septa for headspace. $70

The current ones we use are the red PTFE and we have a hard time piercing through it, to the point where we just take the cap off to use it and then re-blanket it with nitrogen before re-sealing.

I should clarify that we are using strong solvents like heptane and pyridine.

Second question: when you cap the column for service/maintenance, can you re-use the caps that came with the column or should you buy new ones and use new ones each time?

You are doing headspace analysis.

If you are pressurizing (or heating) the vials then I would suggest you NOT use the septa that are split.

If you are doing SPME then use the split septa.

Depending upon the analytes I would stay with the silicone septa, the second listing preferred.

If you are doing headspace I would NOT use pyridine as a solvent due to partition issues.

Good luck,

Rodney George
consultant

Is this for headspace analysis, liquid samples in an autosampler, SPME or for storage ?

If for storage you need a solid cap with a PTFE-silicone liner.

For headspace either of the unsplit PTFE silicones shold be OK ( butyl rubber gets hard and grippy at lower HS temperatures (say below about 60C) and aluminium foil is difficult to get to seal).

For liquid samples, conventional injection; silicone-PTFE.

For SPME; slit silicone but you can get specialised thin SPME septa also.

Peter

Something you might want to consider is the use of a 23 gauge needle instead of the 26 gauge needle. The 23 gauge is much more rugged than the 26 gauge needle.