Picking up on a thread from the "Precision requirements for GC" query above relating to the difficulty in sealing the magnetic crimp caps.
I first became aware of the problem when we gave some magnetic caps, seals and vials to a customer to prepare and seal their own samples. When they were returned we checked for tightness of the seal (rotation test) and they seemed fine. Then we noticed that the seals had been put in upside down! On recapping with the seals the correct way around I found that I could not crimp them enough to get a decent seal.
I have since tried a variety of inserts and found that using a 3mm teflon faced silicone seal together with a 1mm teflon faced silicone seal I can successfully hand crimp a headspace vial. I have not yet checked whether there are any penetration problems with an SPME needle on the CTC autosampler.
I also note that Chromocol supply a composite magnetic cap with an aluminium skirt for easier crimping and decrimping.
By Ron on Thursday, August 14, 2003 - 07:22 am:
I've used the composite cap, and it is easier to do consistently than the steel. The penetration depth of the SPME needle and fiber on the CTC are adjustable, so I would not expect issues there with septum penetration.
I found that the brand of crimper was also important for proper sealing of the steel seals. Microliter is a good source of supplies for the CTC autosampler, and I found there crimper worked better than most others for the steel seals.
By Anonymous on Monday, August 18, 2003 - 06:11 am:
Thanks for that
By Dirk Judas on Thursday, August 28, 2003 - 03:35 am:
We know that problem too. We're not able to get the vials tight. I ordered a free sample of the chromacol-caps, but it is still not working. I noticed that we use vials with a beveled top. which type of vials do you use?
I would really appreciate your help.
Dirk from Germany