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 - 03:40:28 MST