Holger,
We had a same problem a year ago when we switched from high quality tubes
to economy tubes. We doubled up the o-ring on the bottom part of the
holder and took care of the problem. All our sample holders are very old
(~15 years). O-rings from Wilmad are expensive. We found the o-ring
568-109 from Grainger (cat#2KAK9) works just fine (only $7 for a pack of
50).
Katherine Wu, PhD
Albemarle Co.
holger_at_uwm.edu
07/06/2011 02:26 PM
To
ammrl_at_ammrl.org
cc
Subject
AMMRL:NMR tubes loose in sample holder
AMMRLers,
for the last months or so I had an increasing number of NMR tubes show up
in our lab which
are too loose in the sample holders. My first suspicion was that our
sample holders (Bruker
Kel-F spinners, 13 years old) were worn out, so I replaced the O-rings on
all of them. But
that seems not have solved the problem.
Many of the bad tubes have no markings or markings I can not trace to a
particular
manufacturer. In one case the tube turned out to be a Wilmad Economy
>400MHz tube. I
have so far always trusted Wilmad tubes, but I usually purchased their
precision line, which
so far has not given me any of those problems .
I was wondering whether anybody else has encountered similar problems and
are there
certain brands or types of tubes you ban from your labs ? I so far
required tubes to be rated
300+ MHz, but have not enforced certain brands or banned economy tubes.
Is it conceivable that the problem still could be caused by the age of the
sample holders,
despite the O-ring replacement, and that it is time to invest in new
sample holders rather than
harrass my users about their tubes ?
I apprechiate any feedback and will post a summary.
Thanks
Holger Foersterling
Received on Wed Jul 13 2011 - 08:04:25 MST