Hi all,
Thanks so much for you multitudinous responses! (40 of them!) This
insight was extremely helpful.
Consensus is that spinning is allowed, and is often the default, at
most institutions. However, most of those who allow spinning have also
spent many years building up a culture in which baking NMR tubes is
not acceptable.
Several mentioned that the people who are most vocal about needing to
spin are often the least likely to benefit from spinning. Their
samples frequently are too short, are in substandard tubes, have heaps
of particulates in them, and store their tubes in an oven.
Modern shimming methods have done a lot to obviate the need for
spinning. Bruker's Topshim routine gets high marks for producing great
lineshapes with little effort or time. Regularly performing 3D
Topshimming is a great way of keeping nonspinning shims close enough
to optimal that only minor touching up of X and Y is required to meet
spec. I'll note that I've personally had great success keeping things
good for organic samples by regularly applying 3D Topshim to a Gd-
doped ASTM standard (40/60 dioxane/benzene-d6); thanks to Bruker
engineer Jason Clark for that. Varian's 3D gradshimming has done
wonders to improve our nonspinning shims on an old Inova 500 here, and
Christine Hofstetter at Varian was very helpful in helping us with that.
Many responded to say that users should bear the costs of repairing
probed damaged by spinning bent tubes, but this poses a subtle
difficulty. If threatened with having to pay, many students will
simply stop reporting damage. The facility at NU used to regularly
discover broken probes and samples by sheer accident - someone would
break it and not report it, then the next user would put their, have a
bad experience and go on to another spectrometer without telling
anyone, and the next users would do the same, and it took a long time
before problems were discovered. We've tried hard to get our
researchers to report problems to us, and considering all accidental
damage to be "no fault" has been important for improving the
relationship and recovering from damage quickly.
For now, I think we're going to continue to disallow spinning and
touch up our shims every week, but also launch an awareness initiative
to improve NMR tube quality and care. A visit to all the labs with a
stack of Wilmad's guides to care and cleaning, and placing their NMR
tube tester at every spectrometer should help. Now the challenge will
be to get the less conscientious users to test their tubes. Perhaps if
we can be assured that our users' tubes are safe for a multiuser
facility, we'll allow them to spin and see whether it really helps them.
Thanks for all your help!
- Josh
Wilmad's NMR tube cleaning guide:
http://www.wilmad-labglass.com/services/NMR_010.jsp
Wilmad's NMR tube straightness tester:
http://www.wilmad-labglass.com/group/2099
COMPENDIUM OF RESPONSES:
*****
Spin the tube, but only if they pass a spinning test. Get an NMR tube
tester from Wilmad (a glass tube just larger than the tube). It'll sniff
out the bent tubes.
****
We had similar problems (broken inserts regularly) but fixed it in a
different way. Replace all the NMR tubes in the place (we use cheap-
ish Norell 502-7 tubes but re-use). We haven't replaced an insert in 4
years (except one which had a tube mashed inside it - long story).
If we find NMR tubes in ovens we toss them out - not a popular move,
but I offered to send them the bill for the inserts instead.....
****
I don't yet have a fixed policy in place, but I train my users to not
spin when using the 500 MHz instruments. Similar to your facility, I
keep a set of standard shims that everyone is trained to load before
the shim their sample. I usually couch this training in the context
of 2D NMR, i.e. it's simply better to never spin than to forget to
turn off spinning and get more t1 noise.
However, for the undergraduate students who use our 300 MHz in an
organic lab, I typically instruct them to spin because they are
purchasing new NMR tubes and don't have the experience or time to play
with the non-spin shims. I may move towards no spinning in this lab
as well as I plan to introduce some 2D NMR into the labs.
****
we let them spin. It was necessary on a previous spectrometer; it
would be heck to implement a new policy and we have enough trouble
teaching the chemists to shim even with spinning.
We have never seen a broken tube. I do threaten them that this could
happen if they don't let the sample spin down before ejecting it. But
I don't think anyone here has ever picked up the bad habit of baking
tubes to bananify them. I do allow disposables (Wilmad HIP tubes).
But I agree spinning is optional on a well-tuned spectrometer and I
would disconnect the spinner air if I had to replace an insert a
second time.
****
Bruker probes pass most specs nonspin. With vt the gradient is always
minimized by spin. All 2D should be done non spin.
Your prior users worries about probe damage are real.
****
We have two Bruker DPXs and two Bruker DRXs and I have permitted sample
spinning for the last 6 years that I have been here. Thus far, we have
suffered no significant probe damage as a result of sample spinning (I
hope
I'm not jinxing myself). Occasionally a sample will slip thru the
spinner
and grab the lower shield on the inside of the insert and pull it up
such
that some of the active volume is blocked and tuning/matching becomes
impossible, but that doesn't really have anything to do with spinning.
One of our DPX will not spin anyway. I've replaced the o-ring in the
upper
shim stack and ensured that all the air holes on the lower spinner
turbine
are free flowing but it still won't spin in the magnet but no one
complains.
****
Most of our users are organic people, and they just don't want to
spend time shimming the magnet...an unfortunate reality . To
accomodate these people, the spinner in our spectrometer is turned on
by default once sample is loaded. So far we have not got any problems.
****
We have been spinning 5mm NMR samples in our 200, 400 and 600 MHz
for more than 15 years and so far no problems. The only time we had a
broken insert is about 16 years ago, when someone left a broken NMR
tube in
the probe. The subsequent user, no knowing there is broken glass inside
tries to put in another NMR tube. This causes the broken glass to go
sideways breaking the probe insert. Since we have a policy encouraging
students to tell us when something unusual is happening without any
repercussion, things has been running smoothly.
****
We almost always spin. We only had a problem with lots of broken
inserts on one particular spectrometer for a long time; then it quit.
We
generally presume that some user was using strange tubes, perhaps J
Young
tubes they had the glass blower fix or something like that. We also
figure
that person has gone now because the problem went away. We are back to
rarely needing to change inserts.
Having said that, it sounds like your staff spend adequate time
on the
off-axis shims such that you are getting along fine without spinning.
It
may be that it's a matter of "but we've always done it this way" on
the part
of the users. Do you have good gradient shimming available on all
spectrometers? Topshim in Topspin is excellent. I have considered
the idea
of at least not suggesting that people spin when we finally get rid of
our
thousand year old spectrometers on which I can't run Topspin and don't
have
gradients.
****
I suppose this inquiry is with regards to 1D 1H spectra
only. I don't know how you can keep people from not spinning-
unless you remove the spinner-air line to the shim stack. How about
having
your machine shop make a 'tube gauge'? It needs to be about 5"
long, and reamed out to 5mm. If the tube fits EASILY into gauge,
it should be OK to spin. Of course, you still have to trust your
users to actually use the gauge, and then not use the tube if
it does not pass the test. It's an ongoing struggle.
I would be interested in hearing other responses.
****
Interesting question! I have always been of the opinion that samples
should be spun and then the x-y shims almost never need touching. I
also do a number of variable temperature runs this alters the shimming
so it would be a pain to have to shim the x-y at each temperature as
well as the z’s.
I’ve never had a problem – if the tube is bent it just will not spin
at least on the instruments I use (all Bruker). Often at very low
temperature the tubes stop spinning again without any problems (except
the resolution goes).
That said I have a few users who insist on no spinning so they get
their wish.
****
If a user here uses a substandard tube and the insert breaks they have
to pay for repair , this usually gets them to use a tube tester before
putting the sample in a magnet and spinning. They have been warned
about baking nmr tubes unless they are pyrex .
****
In our facility, we require that only the highest quality NMR tubes
are used so they fit properly in the spinner. We've never had problems
with deformation and if there is such a problem, then we would insist
on disposal of the tube. Also, double check that the o-rings in
spinners are properly positioned in the slits in the spinner if there
is 'slippage' of the tube.
Spinning samples is advantageous to improve homogeneity of the
magnetic field, as I'm sure you are aware. But every magnet is
different - some facilities get away without spinning there samples
without huge loss of resolution, but others, not so much. So, I guess
you would have to make the call on whether spinning improves NMR
results or not.
Spinning your sample is a big issue and I'm sure most solution NMR
users spin their samples for standard 1D experiments. Insist on only
using high-grade NMR tubes and also may help to cover the magnet bore
to prevent dust particles from entering which can cause problems when
spinning.
****
We have Varian instruments and we ran all of our samples spinning as
we use gradient auto shimming. I started here at XXX about a year ago
and none of the students here know how to manually shim and with a few
instruments connected to sample changers we had no choice.
What I have done to minimize the negative effects on the probes is to
set the sample depth gauges so that the NMR tubes do not touch the
bottom of the probes in addition to using the tube straightness tester
test. I had also met with the faculty in the department emphasizing
the importance of users not drying their NMR tubes in the oven at all.
I hope that this will help minimize the wear and tear on the probes
for sample spinning but only time will tell.
****
This has never been an issue here. We spin routinely for all
experiments
except those where you don't want to spin,,, 2D, T2, etc......
I do provide guidance to new users on cleaning tubes but no special
enforcement. My experience has been, if tube it THAT bad, it won't
spin,
and sort of self regulating in that sense. Not sure what probes you
have
but, hard to believe the tubes could cause that much damage
consistently,
but I'll take your word for it.
****
I've fought this battle many times, but no matter what I do the organic
chemists feel that they can't acquire if the sample isn't spinning.
Since
keeping a Varian spinning reliably is a full-time job, I often get "my
sample won't spin" reported by the user as a fatal error that must be
fixed
before they acquire their data. On my 300 (Bruker AVANCE-III) the
homogeneity is so good that it is almost impossible to tell the
difference
between spinning and non-spinning (I have proof posted on the wall, in
the
form of an overlay plot). But they still think they have to spin to
do NMR.
I have to admit that With complex, small molecules, one can usually
see the
difference way down near the baseline between spinning and non-
spinning, no
matter how well you optimize the non-spinning shims. Of course this is
only with 1D proton when working in the extreme-narrowing regime.
Bottom line, I don't have the authority here to forbid them from
spinning.
In the minds of many of my user-faculty, I'm the "caretaker" of the
instrument, and can't tell them what to do. I make very strong
"suggestions", and I rant on about proper NMR tube care, and "require"
high-precision tubes (which I also can't enforce), and I hope the probe
doesn't break. If it does, then I have to fix it. We also never spin
> 16
Hz, and I strongly discourage spinning with valved NMR tubes (i.e. J-
Young
valves).
Most of my users are pretty good about following my suggestions, but
eventually probe-inserts break, and we have to fix/replace them.
****
I don’t believe spinning increases the possibility of insert breakage
over that of using warped tubes. If the tube is warped enough to
break the insert, then it will break the insert even if not spinning,
IMO.
We allow spinning. User education regarding sample tube drying and
storage conditions is our work-around for your problem. It’s a simple
rule, easy to follow – No Drying Ovens. We have not had a broken
insert in quite some time, but do see sample tube breakage at least
once or twice a year. Whenever we have a broken NMR tube inside a
probe, we remind users of the rule.
****
We routinely employ sample spinning (Brukrer Avance 400 for some 5 odd
years) with no problems whatsoever and before the Avance 400 on a
Bruker AC-300, again nary a problem during 8 years or so.
****
My guess is that you're already doing this-
Tell users that if they use any of your approved tubes and make
their samples to your volume standard, it will save them large amounts
of time and give them much better results. Show them. (I know you're
already doing this). Provide good shim sets for them. This applies even
to 13C and 31P spectroscopy. Students are really happy to save shimming
time. To convince some of the thicker-headed faculty, take a demo
spectrum to their office or have them come down to see a demo. This is
the carrot.
For the stick, can you have a deity of some kind send a letter that
groups using the spinner take on financial liability for probe damage?
****
We spin each sample on our Bruker systems. When we train our users we
stress that the NMR tubes must NOT be dried in the oven with T above
60C. The insert broke sometimes but not frequently, may be once every
three years on the room temp probes.
We don't spin on the Varian system because the spinner has scratch
marks on it when we spin, besides spinning is not necessary on this
system because we usually run multidimensional experiments on it.
****
We spin samples regularly on all our spectrometers, ranging from
AC-300s to Varian 500 and 600s. Nearly 100% of spectra on the 300s
are taken spinning, maybe 25 to 50% (nearly all standard 1Ds) on the
500s, and occasionally on the 600.
We've seen very few insert breaks due to spinning. We've had two
occasions (over 17 yrs) where a group was drying tubes improperly and
their warped tubes were etching the insert. But we observed the
etching (by line shape degradation) well before the insert broke.
These were on older Bruker probes, however; not sure if Varian probes
might be more sensitive to warped tubes (perhaps). Varian probes are
certainly more expensive and down-time-involved to fix than our older
Bruker probes (where we can replace the glass insert in-house).
In my 15+ yrs here, we've had very few insert breaks on Varian probes
(thankfully!). None to my knowledge were due to sample spinning
issues. We've had more breaks on our Bruker probes, but most of those
have been associated with sample drop problems (drop is too fast;
probe assembly too tight; sample dropped in without lift air; etc.).
We work hard to educate users as to proper drying techniques, by
referencing a Wilmad tech note in training, and regularly outside of
training.
> See Wilmad’s NMR-010 technical note at their web site
> (www.wilmad.com) for suggestions on
> how to correctly clean and dry tubes. In particular, the following
> is from that note:
>
> Drying tubes at elevated temperatures can reshape and ruin precision
> NMR tubes. If you
> dry tubes in an oven, WILMAD recommends placing tubes on a perfectly
> flat tray at
> 125° C for only 30-45 minutes. Better is the use of a vacuum oven
> that will remove water
> at lower temperatures. In a flat position, tubes that do reshape
> could be out-of-round and
> may not fit the spinner turbine as well. But they'll not affect the
> spectrometer probe
> adversely. Tubes placed in an oven in a beaker, flask, or tube rack
> can bend, increasing
> Camber (lack of straightness)1. Bent tubes may still fit the spinner
> turbine, but can
> damage or break the NMR probe insert, a costly repair with many
> probes.
My general observations about spinning are the following:
Spinning definitely improves line shape for small organic compounds,
most noticeably at lower field strength (300 MHz). But even at 500
MHz, line shape can often be noticeably improved with spinning. These
comments do not extend to biochemical samples--e.g., peptides or
proteins where 1H relaxation typically limits linewidths to >= 1 Hz.
I often find bio-oriented people are surprised that we spin samples
here.
I've wondered if part of my knowledge on this subject is aged, due to
our older equipment (in particular, the older RT shim sets on our
ACs). But on our 500s, with reasonably modern (Oxford 28-channel)
shim sets, sample spinning regularly improves line shape for proton
spectra of small organic compounds. Spinning definitely improves 1H
line shape on our Varian Mercury-300, as well as our older Bruker
AC-300 spectrometers. [We regularly shim, and most probes shim to
much better than line shape spec; spinning sidebands are < 0.5%, often
not detectable; all experiment setups start with reading in facility
shim files.]
If we got to a spot where a spectrometer was going down twice (or
more) per year with long (>1wk) repairs costing multiple thousands of
$, and the cause was sample spinning, I would strongly consider
eliminating spinning on that spectrometer, and perhaps throughout the
facility. My guess is that many groups here would be strongly
resistance to such a change, so I've been glad that this hasn't
happened here (yet).
****
I understand your concerns. And I'm sure there are many people in
SpinLand who could tell us horror stories. However, at the University
of ZZZ, we spin the sample on all spectrometers. To my knowledge
there has been no spinning-related probe damage. Three comments.
#1) Our 500 has a cryoprobe and an autosampler and we (the staff) load
samples and set up the queues (students don't touch this instrument).
We always use that wilmad tool for testing the straightness of the
tube. And in 1.5 years of doing this only 1 or 2 tubes have failed.
I would have guessed a lot more tubes would have failed. The
storeroom here carries cheap norrell tubes, so I guess the conclusions
it that those tubes are pretty good. Also, several faculty are well-
versed in NMR tube handling procedure and don't let their students
bake their tubes.
#2) Keeping the PID feedback circuit for spins well calibrated can
help protect your probe from damage caused by spinning. On our
instruments, we routinely (~monthly) recalibrate the PID. As you
know, when it is miscalibrated, the spin rate doesn't increase
steadily to the desired frequency, but jumps way past the mark and
then slows down. I would wager a beer that the inserts on your probe
were damaged because of both a badly misshapen tube and miscalibrated
spins.
#3) Having said all of this, I come from a protein NMR background and,
hence, I never spin samples. I don't like the sidebands and like you
said it doesn't make much of a difference. If you've trained people
to touch up x and y and people are getting good results, then why rock
the boat. If I had my druthers I would stop spinning here, but it is
so entrenched in the culture that it would take a lot more energy to
convince people not to spin than it would to keep calibrating the PID
circuit, etc.
****
I suppose there is a real advantage on earlier limited shim sets
(twenty or less) but rarely matters anymore. Often the students that
want to spin have the worst samples and use the worst nmr tubes -
probably part of the reason they want to spin.
Some spectrometers allow you to control this with software (e.g.,
spinmax) otherwise just disconnect and defeat the spin air.
****
We do not spin our samples; period. First of all, gradient shimming
is not spun. Second, 2D spectra are never spun. Third, spinning
sidebands and other spinning anomalies don't show up non-spinning.
Fourth, lineshape is just as good non-spinning as spinning. So, the
proton experiment on our instruments is customized to not spin; ever.
Also, spinning causes all the things you mentioned and more. Just not
worth it except to tweak up the non-spins with the lineshape test
sample.
Once you have laid down the policy of never spinning, then lay down
the law on never heating NMR tubes to dry them. I learned that from
an old NMR pro early on. Do these people pay for the repairs to the
probe? Do they have to account for the NMR being down? I think not.
By the way, we use disposable NMR tubes.
****
nitial training I show the researcher the guts of a probe and the
clearance between the NMR tube and the insert and explain why I
discourage spinning. Seeing less than a mm clearance the point
becomes obvious. It also demonstrates the need for the outside of the
tube to be clean...("you will see whatever is on the outside of your
tube and so will everyone else for quite a while") I also explain why
'defective' tubes should not be used ( baked chipped etc ) which not
only could cause loss of sample or a stuck tube but messes with center
of mass. ("what is the difference between a $1 tube and a $40 tube
and a 5 cent test tube - hint its not the glass material and how do
you turn a $15 tube into worse than a $1 tube?" - "dry your tube with
nitrogen or argon and if you're paranoid about protons hanging onto
your tube for dear life just put a few drops of deuterated solvent and
blow again ". - "now if youvabsolutely must insist on drying your
tubes with heat use less than 60 C") I explain bad tubes waste time
( more shimming required) and you will not be able to correct for
distortions. I make the analogy between NMR tubes and an audiophiles
speakers and also camera lens. Bad tube is like a phone camera lens
with fingerprint smudge and scratch. Good tube is like SLR lens.
You've got light getting distorted in a lens you've got magnetic field
getting distorted by tube glass
Even with a good tube but if the cap is not square can cause wobble
when spinning. I explain why we spin ( some researchers actually come
in believing that it is a requirement for acquisition ) and explain
the tradeoffs of spin vs non-spinning. In addition Spininng improves
apparent homogenity of shims but also can couple with vibrations (or
magnet sway) and effectively amplify it. I tell them if they must
spin what to look out for ( undtavle lock signal) Then there is all
that banging against inserts which if they even slightly damaged will
affect spectra. They shim z1 to z3 and I tell them that if they want a
little improvement they can use x and y which is usually more than
enough.
Hey wake up you want to use the instrument don't you. Yeah I devote a
good piece of time on tubes and this subject.
I also set up the software so that whenever a researcher has finished
spin is auomatically turned off so that only those that really want to
spin has to turn spin on - so default is always spin off.
While I keep some spare inserts handy (Bruker probes) I've rarely had
to change them. Either I've been very lucky or what Ive been telling
them at training works.
****
Oh yeah keeping a set of " standard shims" is an excellent idea. I do
that but with a twist: I have a macro which performs the function of
reading in the stadard shims so the user doesn't have to explore and
always gets it right. This shim file has the probe ID as part of it's
name so it's a no brainer if the probe is changed. Part of SOP is the
strong recommedation that the researcher will read in this file at
least once before starting samples. After all you never know what the
last person did with the shims or his tube.
Every so often I will save a copy with the date in case the main one
gets corrupted -but now with gradient shim it's fairly easy to redo
all the shims anyway. So now I have a macro which goes through all the
shiiming required with a h2o d2o sample and stores results
automatically.
****
We have a 600 MHz. We rarely spin because the spectra are better
without. As
a result our spinning does not work particularly well and we can't
achieve
the full spin rate. Every now and then we clean out the bore and regain
spinning capability. We've never had a problem with broken inserts. We
do
take extraordinary care of our NMR tubes to ensure homogeneity and
prevent
such problems. No baking is allowed. The cleaning protocol is strict and
calls for 40 C under vacuum at the end to prevent any deformation.
In your case I would require new NMR tubes appropriate to the
spectrometer
and your own cleaning protocol before I'd allow any spinning. You could
require the tubes be bought from you to assure the right quality and to
reduce the number of people who spin unnecessarily (due to the added
cost).
****
We allow user to spin but discourage it because: spinning changes the
tuning thus 90s may be 87s on different acquisitions which is important
with poor SNR samples, creates SSB that might be misinterpreted and in
your experience may do damage. You can demonstrate the tuning change by
observing the tuning spinning vs not spinning. I convinced several
hardcore spinners this way.
At my place I teach users to clean tube using the following:
NEVER allow anyone else to use your tubes thus you maintain quality
buy high quality tube > ~$9/tube,
use short tubes 7" thus less wobble if spun
clean tubes as usual
rinse several time with dH2O as final rinse
use thin polyethylene tubing to aspirate water on the inside
wipe tubes dry on the outside
put all tubes batches into a graduated cylinder longer then the tubes
lay the cylinder ~ flat in a drying oven
heat no higher than 90 C over night
remove, cool and store flat or vertical until used.
tube holders are cleaned and o-rings occasionally replaced spin rate
=20 Hz
I'm lucky only RRC staff change probes. I learned that probes NEVER
break
for a user, always for the next user. That is an amazing coincidence.
****
On our open access Bruker Avance NMR all the users are measuring 1D
spectra with the probe spinning (at speed 20 rps for 5mm samples) and we
had no big problems with the breakage of probe inserts. Some years ago
was
a insert breakage, but it is not clear to date what caused this. We have
not using susceptibility plugs, but from time to time are using
capillary
tubes in 5mm samples for an external referencing for a some nucley. The
tubes used are usually Norell or Wilmad 507... quality class ones.
****
We operate a JEOL 600 MHz instrument since 2008 and a Varian Mercury
300 MHz before that since 1999, and I have had not problems with
spinning at all. Spinning does help to further increase the resolution
in the spectrum beyond well-adjusted X/Y-shims, which we also adjust
every 2-3 weeks.
There may be pulse sequences for which the manufacturer recommends NOT
to spin the sample, but this has rather to do with data collection and
artefacts from hard or soft pulses specific for this particular
experiment where spinning artefacts are not completely removed and
affect the spectra quality. For example, on our instrument, I run HMBC
and NOE experiments often without spinning.
The physical consequence that you experienced sound indeed
frightening. They might have to do with low-quality NMR tubes whose
concentricity is not very good and that (consequently) "wobble" while
spinning. You call them banana tubes. "Baking" NMR tubes is defintiely
not good. Drying at 30-40C is not a problem as far as I can tell from
my experience. Best is drying with a gentle stream of air at rt on an
inverted glass pipet. What about the age of the spinner head that
holds the sample? Is it new and is the rubber O-ring tight when it
holds the tube in place? Does the tube slip easily? It might be time
to replace the spinner and/or O-ring. At what ferquency do you spin?
Were the broken samples spun at high frequency, e.g. during a
paramagnetic shift experiment? It could also be a problem of the probe
head itself. Have you had the probe head checked? Of course it is all
a financial question...
****
In 50 years of running personally, or overseeing nmr systems from Varian
HR40 to Bruker Avance 600 I have never broken or had a probe broken by
users
due to spinning. MAS is another matter - having lost a probe once.
****
Tell everyone the NMR are dispossable glass since you can now buy 600
MHz quality tubes for $1/tube from the Bruker store - and the bonus is
that spinning will probably not be required with the better quality
tube.
****
We don't allow spinning at 600 MHz. At 500, most students spin, but
I've warned people about underfilling tubes.
At 400, about half of the samples are run spinning. At 300, the photo-
optic has problems, so spinning isn't regulated.
I check shim files regularly, but for the most part even X and Y don't
need shimming. I'm slowly moving the population to
automated shimming, which fails only when X and Y are out.
****
We allow spinning on our Varian system but not the Bruker with the
BACS sample changer. I've been told that the turbines Bruker provides
may or may not be rated for spinning; they carry different prices.
They have a "type A" which the the Bruker store says is for 500 MHz
and above. I'd be interested in the difference between type a and
regular POM spinner turbines. I have noticed that the spinning
(Varian) lineshape is better than the (Bruker) non-spinning lineshape.
We do 3D shimming to touch up the shims regularly on both systems.
We too have issues with baked tubes, which we try to enforce by
removing obviously baked tubes from the sample changer racks. This has
lead to some issues with the faculty however, so it may not be
possible at some places.
****
our systems are constantly spinning. The spectra are just better
resolved with spinning...
I have very little problem with tubes breaking, maybe 3-4 times/per
year. It typically only happens when the spinner loses the "grip" and
the tube does not stay tight. Or someone makes a bad mistake.
I constantly tell students not to bake tubes and for the most part
they don't. They are afraid of losing their NMR access ;-)
Sorry, but fear of not being able to use the NMR usually works well!!!
****
Within 1 year after the delivery of our Mercury consoles in 2000,
users had
contaminated the white spots on the rotor to the point where the
spinning
rate would not work. I spent ~ 1/2 a day cleaning the bore and
remarking the
turbine, only to have it failure within 1 week. Afterwards, I turned
spinning off and have not had problems with resolution (polymer
linewidths
are fairly broad).
****
the only sample that spins here (Bruker AVANCE 500) is the standard
1H lineshape sample, for me to meet and maintain spec. We run this
system
via automation and the software (ICON-NMR) allows me to disable
spinning and
so there is no "policing" required. Approximately every month, I
insert a
standard sample in CDCl3 (the most common solvent) and touch up all
shims,
using the resolution of the Si-29 satellites of TMS (static sample) as a
guide to how good the shimming is. This is saved to a shim file which
gets
read in on every sample changeover in automation. Every 3 months, I I
look
at the actual lineshape sample and meet spec static and spinning.
Bruker's
topshim module has been very valuable for this in terms of timesaving!
I have been following this protocol for years and there are no
complaints/problems from the users.
****
I have one of those Wilmad testers by each instrument, and stress to
users that tubes should not be placed in ovens.
We tend to spin samples on two out of four systems, those with the
oldest magnets. Currently I would guess I replace inserts about evry
two years on those systems.
****
We spin almost everything, with no ill effects. I'm sure most of our
users bake their tubes.
We do end up cleaning upper stacks quite often as dirt builds up and
prevents spinning.
Samples don't break very often, and even less now that we require
users to turn off the spin air when they eject.
****
****
ORIGINAL POST:
I'd appreciate your insight into an institutional policy matter:
whether to allow sample spinning.
I am told that, for years in our facility before I arrived, probe
inserts were being broken every few months, resulting in considerable
downtime and repair costs. Then the lab forbade users from spinning
their samples, and we haven't had a probe needing such repair since
the rule was implemented. We try to compensate for spinning's
lineshape benefit by ensuring that spinning isn't necessary; every
week someone touches up the nonspinning shims (X, Y, ...) and saves
the shims to a filename everyone knows about. On standard samples, the
differences we observe between spinning and nonspinning lineshapes is
not functionally significant for routine samples.
We now have a number of users who wish to spin their samples. While
several among this set would benefit slightly, we have a sizeable
number of less careful users who bake their NMR tubes to dry them,
sometimes resulting in banana tubes that would damage probes if they
were spun. I've observed some samples here that fail the Wilmad tube-
straightness-tester test (
http://www.wilmad-labglass.com/group/2099).
How is spinning handled at your facility? Does it pose problems for
you? How do you manage risk to your probes?
Josh Kurutz, Ph.D.
Instructor and Senior Scientist for NMR
IMSERC, Chemistry Department
Northwestern University
2145 Sheridan Rd.
Evanston, IL 60208-3113
847-467-1949
fax: 208-978-2599
Facility: www.chem.northwestern.edu/imserc
NMR Blog: www.imserc-nmr.org
Twitter feed: twitter.com/imserc_nmr
Other: www.joshkurutz.com
Received on Thu Jul 29 2010 - 03:43:37 MST