Hi All,
On our Bruker DRX-500 (delivered 1997) with the BOSS II shim system we
normally use a 5 mm BB probe dating to about 1994. We frequently
(every few weeks to couple of months) find that the insert glass is
broken. So far we have not been able to find out why. On the other
spectrometers we use older type probes with inserts of twice the
thickness, thus they are expected to more durable. With tjhose, insert
life-time is years, not weeks or months.
One possible reason might be the use of J. Young tubes. The last insert
broke while a user lowered J. Young tube. The spectrum of the last sample
run just before looked very nice, so it is most unlikely that the insert
had already been broken.
The insert broke at the bottom, and the J. Young would not inject until the
user increased the air pressure sufficiently to launch it into low orbit.
(I learned about this after the fact, the exact details are a bit sketchy.)
My suspicions are that:
o J. Young tubes are too heavy for the sample lift, they will not slow
enough for a soft landing. Of course, using a ceramic spinner adds even
more weight.
If the tube is positioned too low in the spinner, the bottom
can hit the thermocouple, be deflected side-ways, and break the insert.
Given the minimal clearance, this seems to be a good possibility.
o Even if the positioning is correct, the tube might slide in the spinner
and hit the thermocouple and break the insert.
o Given the top-heavy design spinning might also be a possible cause. If
the tube has sufficient run-out it might eventually hit the insert
glass.
Having the glass-shop shorten the tubes from the original 180, or more,
mm to about 130 mm might help a bit.
I think that using a low-tech fishing line to lower and retrieve, and not
spinning the sample, should be a reasonable solution if our suspicions are
indeed correct. Before insisting that our users put up with the above,
I would appreciate getting facts and opinions aboutusing of J. Young tubes.
Basically, are other labs seeing similar problems? If so, does anyone know
of modifications to the sample lift to prevent these problems?
I will summarize responses. Apologies for the cross-posting, and thanks
for your help.
-- Rudi
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Rudi Nunlist Voice: (510) 642-6407 FAX: (510) 642-8369
University of California Email: nmrlab@purcell.cchem.berkeley.edu
College of Chemistry
NMR Facility
Berkeley, CA 94720-1460 Personal email: rnunlist@purcell.cchem.berkeley.edu
www.cchem.berkeley.edu/College/Facilities/nmr
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