yes, I remember that I had a bit of trouble with one batch of Labco caps. They would do ok if unheated, but get soft and leaky when heated.
We got a new batch from Labco after reporting this problem and since then had no such troubles anymore.
Use only the old caps, else you might also compare new and old (bad and good) - we found you can distinguish them: the notches at the lower rim are different, but its hard to describe, just check with known bad and good ones, you'll see the difference. Btw, you dont need standoffs to keep the caps from the block, as long as they do not get soft, I never had trouble (except with some of the bad batch, which cost me some precious samples).
Pls let me know if this solves your troubles.
all the best,
Von: Stable Isotope Geochemistry [[log in to unmask]]" im Auftrag von "Brian Frappier [[log in to unmask]]
Gesendet: Dienstag, 10. März 2015 16:15
An: [log in to unmask]
Betreff: [ISOGEOCHEM] Gasbench vial caps leaking
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?