Dear Christophe,
The stator bearings can be cleaned with 2-propanol. Hopefully, wiping the
bearing surface with q-tip soaked in IPA will do the job. If not the bearing
channels may be clogged.
You can manually switch on both the bearing and rotation gas valves to dry
the stator after cleaning.
Of course after some excess wear the cleaning wont help; the whole stator
has to be replaced.
When I was making solids I have always wiped the rotor with before inserting.
Also, with the 4mm I have opened the eject gas valve slightly to prevent free
falling of the rotor in the drop-tube.
If you are still using rotors which requires permanent marker I highly suggest
to switch to engraved rotors.
Szabolcs Balogh, PhD
XiMo Hungary Kft.
H-1045 Budapest, Berlini u. 47-49.
Building 5.
Mobile: (+36)-30-641-7546
> 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<mailto: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 - 07:11:51 MST