Dear Christophe,
I have the same problem. But I have a procedure that allows me to rotate
the 2.5 mm rotors with my MAS II unit.
I start by rotating the rotor manually, using the MAS unit's screen
directly. At first I put in a lot of bearing (around 1600 mBars), then I
gradually increase the drive to 200 mB (the frequency should reach 10
kHz). Then I gradually increase the bearing and drive in parallel up to
a frequency of 15 kHz. From this point, I ask the Topsin's MAS interface
to set the frequency to the one I am at. Then, as far as I am concerned,
I can use Topspin's interface to continue increasing the frequency.
Good luck,
Yannick
Le 26/04/2024 à 12:29, Fares, Christophe a écrit :
>
> 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 Tue Apr 30 2024 - 04:01:33 MST