We have used a 2.5mm CPMAS probe on our 300 instrument since 2006. We have
used the probe with both MAS II and MAS III controllers. The lowest spinning
speed I start with is 12 kHz since slower spinning is unstable. The highest
speed I typically use is 28.5 kHz.
The rotors must be inspected under a microscope carefully before insertion,
paying particular attention to fully seated caps and rotors, integrity of
the fins and ensuring nothing is present along the sides of the rotor.
We had trouble ejecting samples about 6 years ago and it turned out the
insertion tube needed to be replaced (not sure why - maybe it became slightly
bent).
We have had Bruker Service inspect and repair the probe at least once and they
did a great job bringing it up to spec.
My suggestions for you are to send the probe to Bruker Probe service and try
a new insertion tube.
Good luck!
Vernon
Vernon Russell
vrussell_at_wlgore.com
W. L. Gore & Associates, Inc.
Together, improving life
501 Vieve's Way, P.O. Box 1320
Elkton, MD 21922-1320
USA
gore.com
> From: main_at_ammrl.groups.io On Behalf Of Fares, Christophe
> Sent: Friday, April 26, 2024 6:30 AM
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] MAS VTN 500WB BL2.5mm Probleme
Dear solids-ammrlers,
we have a MAS VTN 500WB BL2.5mm (13C-31P/1H) probehead from Bruker. It was
installed in 2000.
I don't know much about its history before my time in the lab... only that
it was rarely used. But in 2 years I have never had any success with this
probe, and each time I put it in, I run into major problems. For one, a
majority of samples that I prepare do not rotate stably. The bearing/drive
regulation from our MAS Unit does not seem to be able to find the right
pressure for a given desired MAS rate. Very often it oscillates from too
fast to too slow and eventually crashes the rotor (we hear the rotor rubbing
the side). I have tried several rotors now, including brand new ones. The
second issue is that it is very difficult to eject the sample and require
several attempts.
I should however mention that, with a bit of patience and after a few tries,
I am able to get my adamantane and KBr test-rotors to rotate stably up to
25kHz (I don't dare go faster at this point).
I am running out of ideas and I wonder what you recommend for me to try at
this point? Should we first clean the stator? How do I do this? Or should
we even send the probehead in for testing/repair? On the other hand, perhaps
it is the regulation which is faulty. We are still using an old MAS II unit
(H13000 EC:04.01 1057) which works flawlessly with all our 4mm and 7mm MAS
probeheads.
I also heard that 2.5mm is an awful size to work with in the first place
(bigger or smaller give better results). Is this a widespread opinion?
Looking forward to your suggestions.
Best regards
---------------------------------------------------
Christophe Farès, Ph.D.
---------------------------------------------------
NMR Department/NMR Abteilung
Max-Planck Institut für Kohlenforschung
Kaiser-Wilhelm Platz 1
45470 Mülheim an der Ruhr
Tel: +49 208 306 2130
E-mail: fares [a] mpi-muelheim [.] mpg [.] de
https://www.kofo.mpg.de/en/research/services/nmr
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Received on Fri Apr 26 2024 - 06:18:45 MST