Dear Brian and all,
I agree with you that the problem is the cap, not the septum.
While having the trouble with weak/soft/leaky caps I felt a real difference in their stiffness, and sometimes you could see a deformation (at 70 degrees) of the cap.
We had this problem only with white caps, but we only used white ones, so I cannot comment on other colored ones.
Von: Stable Isotope Geochemistry [[log in to unmask]]" im Auftrag von "Dana Biasatti [[log in to unmask]]
Gesendet: Dienstag, 10. März 2015 16:47
An: [log in to unmask]
Betreff: Re: [ISOGEOCHEM] Gasbench vial caps leaking
I have also been having problems with caps leaking/popping off on the 4.5ml vials. We have had caps pop off the larger vials as well, but reducing the helium flow into the vials during flushing (to ~100 ml/min) and also reducing the temperature of the gas bench heating block to 60 degrees C seems to have solved the problem with the 13ml vials. We have yet to solve the problem with the 4.5ml vials. I am not sure if the threads are different on the smaller vials, and that is the problem, but I would be interested in seeing if anyone on this thread has been able to successfully address this issue.
As far as the septa are concerned, I have had the best luck with tightening the cap just until there is a very slight dent in the septum. If the cap is turned too far, the septum will deform too much and the vial may leak. As you mentioned, some septa seem to deform without turning the cap too tight. In those cases, I just replace the cap with a different one. I was thinking that the actual plastic cap was the problem, rather than the septum, and that some caps require more turning than others, which causes the septum to deform.
I have found that both the blue and white caps have the same issues. There was a time, 4 or 5 years ago, before the cap threads were redesigned, that I found that the blue caps worked much better for me. That doesn't seem to be the case any more.
Date: Tue, 10 Mar 2015 15:15:55 +0000
From: [log in to unmask]
Subject: [ISOGEOCHEM] Gasbench vial caps leaking
To: [log in to unmask]
I'm polling to see if anyone has had a problem with the caps on 4.5 ml Gasbench vials leaking? We are using 4.5 ml vials to replicate Sebastian Breitenbach's small vial method for small carbonate analysis on the Gasbench.
I infer the caps are leaking because I get excellent internal standard deviation within vials, but every once and a while, and always later in the run than the first 10 vials, I get an NBS-19 that returns a value a few per mil light on d18O. I suspect atmospheric water leaking in and exchanging O with the CO2 in the vials as our water vapor is circa -8 for d18O around here. If I run with the large vials or the RK vials, I get excellent external precision (~0.06 per mil on d18O) between vials and no instances of light excursions on NBS-19. I can't help but conclude that my machine seems to be running fine and the caps on the small vials are leaking.
I've noticed some caps pop off on one side when they sit at temperature. I've tried reducing the temp to 40oC and it helps, but cap pops still occur. I've also noticed that the caps septa indent heavily on some caps. When I replace those caps with different caps on the same vial, I can always find some that don't indent on that vial. Is the septum deforming on some caps and not others?
I've tried 3 different batches of caps from Labco (3 different colors - white, blue, and pink) over the past 2 months and they all seem to leak occasionally. I had a few caps left over from Thermo on install and found that those sit tighter on the vial with little indentation of the septum I've read older threads where some people claimed different colors sealed better, but there was some disagreement about which color was best (green, blue, white?).
Am I down the rabbit hole here and going crazy or have others found a recent problem with labco caps on 4.5 ml vials?