I have two thoughts about this--it does sound like the probe would definitely
benefit from going in for inspection/repair. I'm not sure how much
cleaning you can actually do on a 2.5mm probe without disassembling things
to a higher degree than you probably want to. The sample eject difficulty
is also suspicious--it just sounds like overall things don't quite work right
and it would benefit from a good going-over.
And the MAS/2 with that size probe likely won't regulate well at "low" speeds.
So if your first test is at 5kHz I suspect it's not going to regulate well.
The MAS/2 doesn't have the fine adjustment capability of the newer MAS/3 so for rotors
smaller than 3.2mm it tends to have problems regulating well at "lower" spinning speeds.
It could also depend on the firmware on the MAS/2. Newer versions of the
firmware might have better regulation profiles for the smaller rotors but it is likely
not trivial to update.
Cheers,Mike
On Friday, April 26, 2024 at 04:40:35 AM MDT, Fares, Christophe wrote:
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 - 06:01:03 MST