We recently found that a few groups in our area of the world are using
'disposable' 5mm, 300MHz Aldrich nmr tubes in our 500 MHz machines. One of
the problems with them is that they do not seem to be manufactured to a
very high precision and some will fit into the spinner tightly and some
fit with varying degrees of looseness (is that a word?). The 'fix' as far
as the users are concerned is to plug a small piece of Kimwipe into the
spinner along with the tube to tighten it up.
Needless to say, I'm not comfortable with this solution as Murphy's Law
says that eventually a piece of Kimwipe will work its way into the probe
and begin to cause problems. Also, a semi-snug fitting tube without a
piece of Kimwipe could potentially be moved in the spinner by an
autosampler arm as it is being loaded into the magnet and potentially
break as it bottoms out in the probe.
What I would like to know is have you encountered this type of
tube/spinner problem and the user's 'fix' for the problem and what have
you done about it? Do you require that your users use high-precision
tubes? Also, do you find that tubes rated for lower fields work
satisfactorily on higher field machines? By 'satisfactorily' I mean that
there is no major compromise to spectral quality as compared to high-field
related tubes. My understanding has been that the lower precision tubes
can be the source of shimming problems, especially on automated machines.
Thanks in advance for any replies. I'll post a summary of what I find
out.
Dr. Keith Brown
Department of Chemistry/
Saskatchewan Structural Sciences Center
University of Saskatchewan
Saskatoon, Saskatchewan
306-966-1725
http://chem4823.usask.ca/kbrown.html
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Received on Mon Jul 05 2010 - 06:12:20 MST