Dear Tim,
We have used the CHCl3 matched Shigemi tubes. They seem to work quite
well. The line shape is nearly as good as regular tubes with a larger
volume. I encountered two problems. (1) Beware of solvent evaporation if
you plan to do a long experiment. Parafilm is not adequate. Shigemi
suggested using the rubber cap that they supply and sealing it with a
small amount of five minute exoxy, top and bottom. When you are ready to
disassemble the tube heat the epoxy with a heat gun to soften it a
little, then the seal can be broken. We were able to do it without
breaking the tube. (2) This is kind of obvious, but bubbles are deadly
and can form a long time after the tube is assembled if the solvent is
not well degassed prior to use. Blowing off excess solvent with nitrogen
ensures that you will get bubbles. If you must remove excess solvent,
take the sample all the way to dryness, then add the correct amount of
degassed solvent. We have also had success by placing the assembled tube
in a bath 20 C or so above ambient, allowing the bubbles to form,
teasing them out, and repeating the process until no more bubbles form
within a few minutes.
If anyone else has practical tips for using Shigemi tubes, I would like
to know them, and probably others would too.
Charlie
--Charles L. Mayne University of Utah Dept. of Chemistry B103 HEB Salt Lake City, UT 84112 Voice: (801)581-7413 FAX: (801)581-4763 or 8433 E-mail: mayne@chemistry.utah.edu http://www.chem.utah.edu/atlas/facilities/nmr.html