Hi Friends:
I asked questions about if we need antivibration legs/feet as we have
vibration (0.35-0.65 mm/s*s) at the site which we are going to put a magnet.
I would like to thank the following people for sharing their experiences.
Ian Whitcombe, UK
Benjamin G.M. Chew
Roger Kautz, NEU
Don Eldred
Laurie Galya, INCYTE
Raju Subramanian, Amgen
Paul Shin, CSUN
Charlie G. Fry, WISC
Patrick Wheeler, Pfizer
Jiejun Wu, J&J Pharmaceutical Research and Development
Strong vibration may affect the quality of 2D, especially NOESY, inverse
detect experiments (HSQC, HMBC,...), 1D NOEDIF, water suppression
experiments. It will be great to have legs if you have budget. Attached are
experiences from friends mentioned above. You can read them if you want to
know more.
Zhe Zhou, Ph.D.
Research Specialist (NMR)
Analytical Sciences, Dow Chemical Company
2301 N. Brazosport Blvd., B-1219
Freeport, TX 77541
Tel: 979-238-1387
Fax: 979-238-0752
Email: zzhou_at_dow.com
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We have an AV400 with a 5mm SEI probe. We recently fitted anti-vibration
mounts (not legs?) to our magnet. We saw immediate improvements to all
spectra. Those experiments that involve any difference/subtraction, for
example DPGSE NOE, are now beautifully clean. Beforehand I had to run some
experiments several times or schedule them for 'quiet' times until I got
clean spectra. You should ask if mounts would solve your vibration issues
since they can be retro-fitted after you have determined if the measured
level of vibration causes you any problems for the sort of work you want to
do.
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We have a Bruker 500. If I turn off the vibration legs, we see
wiggles/sidebands on every peak in the proton experiments, especially with
our BBI probe.
I don't have the data in tabular form, but just looking at the plots,
biggest peaks in the 0-40 Hz range are
Hz mm/s^2
32 0.65
All other freq peaks between 15 and 30 Hz are between 0.1 to 0.4 mm/s^2
My report says anything 0.1-0.7 mm/s^2 int he 0-40 Hz range may or may not
affect things depend on the system. Our system is higher field than yours,
but we also have vibration legs on our 300 and 400 Varian systems. On the
400, I can still tell when the legs get accidentally left off after a
cryogen fill.
If they recommend getting the legs, I would get them. Better to get them
now rather than have them retrofitted later.
We have air handlers on the other side of the floor in the basement. I can
actually feel the vibrations through my feet in certain areas of the lab. I
knew we were going to need the vibration legs before I had the analysis
done.
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I see sidebands, like spinning sidebands, near peaks. They are at about
the 1% level, which obscures analyte resonances near solvent resonances.
It's not prohibitive for routine work, but for e.g. NOESY we set them up to
run between midnight and 5 am, when the world is quiet.
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We have 4 Varian/Oxford magnets at our Midland location (400, 400, 400, and
300). By design our building is extremely immobile. As such, we have opted
to not equip any of our magnets at this facility with anti-vibration legs.
For the 400's this has never been an issue in any data we have acquired. The
300 on the other had has two issues which may or may not have
interrelationships. First, the magnet is an R2D2 type design. It is very
easy to rock the magnet several inches in a left to right direction. It is
easy to see the impacts of this "flimsy" design if you bump the magnet
roughly on sample insertion (rare) or when we do a cryogen fill. Second,
the magnet is positioned near to a door which closes harder than I care for.
The vibration from the door closing easily traverses the few feet from the
door to the magnet and is observed in our 1H spectra. The observation of
these external vibrations in our spectra typically results in peak
distortion at the baseline in very strong signals. The primary role of this
instrument is walk up, fast turn around 1H NMR. So typically this is not an
issue. When it is an issue we either signal average out the non-phase
coherent aberrations or we restrict access to the problematic door.
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With these kinds of vibrational intensities you may well see garbage at the
base of your peaks in 1D experiments as well as reduced intensity in 2D
experiments. I would recommend getting them installed when the magnet is
put up. It's not very easy to add them later and would probably require
taking the magnet down and then re-energizing. The cost of taking the
magnet back down and re-energizing is probably more than the cost of the
legs.
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I am dealing with some of the same issues at my site.
Vibrations can have important consequences in NMR experiments in a number of
ways. Amongst them: a. NOE difference experiments. b. Any water suppression
expts or for that matter, if you are detecting a small signal next to a very
large signal.
c. If you have small amounts of sample and are pushing sensitivity in your
experiments
I am assuming the numbers you quoted were for z-direction vibrations. Some
of them will also be dampened by the weight of the magnet. Managing/damping
signals in the 0 to 10 Hz range is very difficult. It would be helpful to
know more about the site where you are going to put this magnet. For
example: What floor level is it? What could be causing the vibrations? Is
there an elevator etc in the vicinity?.
I also suggest that you check for any radial (x/y drection) vibrations. If
you have any radial direction vibrations not much can be done about it other
than make changes at the vibration source or find a new site for the
magnet.
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You will only see what appear to be very small side bands (what look like
spinning side bands at 5 Hz that do not move with different spinning rates)
on the 1D proton experiments. If the non-spinning shims are done and
maintained well, then the smaller these 5 Hz side bands will be. You will
not likely see them at all on any 2D NMR experiment.
The "donuts" are great and will do the trick. I highly recommend turning
the air to them off before you cryogen fill and turn them back on when done.
I am a former Bruker applications engineer and sales rep and have done
these vibration tests myself. I currently have a DRX400 with these
antivibration donuts and they work great!
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All experiments that use phase cycling for cancellation will be seriously
affected. In particular, NOESY/NOESY1D. HMBC will also be affected, as
will others. If you are nearly exclusively running standard 1D's, it may
make no real difference.
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Any 2-D will be affected with much increased T1 noise. Carbon-12
cancellation in HMQC & HSQC type experiments will deteriorate. Water
suppression will be more difficult.
You will probably be much happier with the legs.
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You always want to have anti-vibration legs if $ is there. You can simply
lower it if you don't like it.
Last time we have to do some heavy-duty drilling near the magnet (building
reconstruction). I think w/o the legs we would have major concerns as
whether the magnet will quench, not to mention the spc will be very bad. But
we were fine w/ them.
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Received on Sat May 21 2005 - 15:13:32 MST