This was such a counterintuitive-but-effective trick that I am compelled to
post it. (Tell me if I'm wasting bandwidth)
The gentlest way to lower a tube into our GE-Nicolet (GN-500) spectrometer
was to drop it down the stack with the eject air off, then immediately cup
your hand over the top of the stack, sealing it. The tolerance between the
spinner and the stack was so close that the sample glided down slower than
Alice in the rabbit-hole. I discovered this myself in a moment of panic;
it was also mentioned by Jerry Dallas, who did the training for GE. (Test
this in your spectrometer with a taped-over spinner, not a glass sample!)
I later did a lot of work using ceramic spinners in a Bruker AM-500. We
didn't always have enough air pressure to get them out. One solution was
connecting a hose barb at the top of the stack to an aspirator; with the
stack cover on. The vacuum got the sample moving; the available air
pressure was enough to float it the rest of the way out.
In the end, though, we settled on the "fishline" method. The final
refinement was to use a copper wire hook which we could remove after
lowering the sample, so we could spin. For removing the tubes there was an
art to making the end of the hook like a slightly-unwound spring, so by
turning the wire you could guide the NMR tube cap into its wire cradle.
Probably the right way to address Rudi's problem would be:
Adjust the insert air (does Bruker have a "slow-drop" valve?).
How do the Bruker spinners grip the tube? Can you insert new O-rings that
are either slightly tighter or stickier?
-- Roger
===========================================================
Roger Kautz, Staff Scientist, Ph.D.
Barnett Institute of Chemical and Biological Analysis
Room 341 Mugar Life Sciences Bldg.
Northeastern University, 360 Huntington Ave.
Boston, MA 02115
tel (617) 373 -8211
fax(617) 373-2804
email rkautz_at_lynx.neu.edu
Received on Fri Oct 13 2000 - 13:09:10 MST