gc maintenance questions

[ece]

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?

[chromatographer1]

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

[Peter Apps]

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

[Ron]

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.