(A
PDF version of this page is available from the Handouts site)
MTR
Resources
This
page contains pertinent information to help you when a problem arises.
Please look through the list below to identify and find resolutions
to the most common problems at our facility. If your problem is not
listed, please contact the staff at 792 or leave a detailed voice
message at 386 (Kermit) or 387 (Dan). In addition, please fill out
our NMR incident report so that we may be better able to serve your
needs. The incident report should be used even if you are able to
fix the problem. Click here to
get the NMR Incident report. For specral problems, see NMR
Artifacts.
THIS MUST BE REPORTED AS SOON AS POSSIBLE
TO MINIMIZE DAMAGE TO THE PROBE. DO NOT ATTEMPT TO REMOVE SAMPLE! PLEASE
CONTACT NMR STAFF IMMEDIATELY (CALL 792, 386, OR 387). IF STAFF IS UNAVAILABLE,
LEAVE MESSAGE AT 386 OR 387. ALWAYS LOG-OFF OF THE INSTRUMENT AND HANG
A SIGN ON MONITOR STATING; 'BROKEN SAMPLE: DO NOT USE INSTRUMENT'.
Console is unresponsive to Commands:
1. With the right mouse button, click once on
the Solaris desktop background to reveal a menu. Click on Programs or
Tools,
then over to select
Terminal… A Terminal window will pop-up.
2. In the Terminal window, type ‘su acqproc’ and hit Return. You
will get a message indicating that acqproc is being ‘killed’. Also,
in the ACQUISITION STATUS window in VNMR, STATUS should now read “inactive”.
3. Proceed to the NMR console, which is the big grayish box. See below
for location of reset button for various instruments.
4. Push the
reset button.
LOCATION OF RESET BUTTON FOR EACH INSTRUMENT
Instrument (floor)
Reset
Button Location
Mut & Anubis: UnityPlus-500 (sb)
In the big grayish box to the right of the computer (left for Mut). Open
the left door and look for a large red button
on the middle right.
Ra: Inova-300 (sb)
In the grey box to the left of the computer, open the left door and
look for the hand written blue arrows to the middle left. The red button
below 'reset' at the far left where the blue arrows point is the button.
Hathor: G-300 (5th)
Open the door of the box to the right of the computer. Look for the
switch with the hand-written words,'reset'.
Maat & Imseti: UnityPlus-300 (2nd)
Open the left door of the console. Look for a large red button
on the middle right.
Khufu: Inova-300 (2nd)
Open the left door of the box on the wall with windows. Look at the
middle left and just above the blue plug. The small white button above
the letters RST is the button.
5. Wait for at least 40 seconds.
6. In the terminal window type su acqproc and hit Return. This
will take a few moments. Look at the ACQUISITION STATUS window
in VNMR. Wait for STATUS to read “idle”.
7. In the VNMR command line (i.e. where you usually type e), type su and
hit Return. The NMR should now be ready for use.
This can be caused by several
problems. Common reasons and their solutions are listed below:
Common Reasons for Inability to Lock
Cause
Result
Solution
No deuterated solvent
No deuterium signal to lock on.
Use a deuterated solvent like CDCl3.
Shimming is very poor
The signal is so broad that it is not well observed.
Type fixshims to get a good start.
Suspended particles
This causes line broadening, which makes the signal intensity weaker.
Filter your sample.
Too concentrated
There is little deuterated solvent to get a lock. Especially problematic
when using CDCl3.
Dilute your sample or use a solvent with more deuteriums (e.g. C6D6).
Improperly gauged
When injected, the sample is not in the coil.
Eject sample and ensure that the sample resides between the white lines
on the gauge.
Lockpower is too low
The sample is not receiving enough rf signal to flip the deuterium
spins.
Increase lockpower to 80% of max before trying to lock.
Lockpower is too high (for multi-resonance samples)
With solvents having more than one deuterium resonance (e.g. CD3OD,
THF-d8), high lock power will cause all resonances to be excited. This
makes locking on a single resonance difficult.
Reduce the lockpower by 20 and find the lock signal. If you see the
signal with 'bumps', reduce lockpower further.
Lockgain is too low
The signal from your sample is not amplified enough for you to see
the signal.
Increase Lockgain to maximum.
If the above table does not resolve your problem, try locking
on a pure sample of C6D6.
Once you are able to lock on the benzene-d6, shim as
well as you can.
Replace the benzene-d6 sample with your sample and attempt
to lock.
Still can't get a lock? Contact the staff at 792
I Can't Access a Workspace (e.g. exp1, exp2):
The usual message you will get is,'foreground
processing is active.'
A locked experiment is a result of improper
logging-off by a user. Remember to always exit VNMR prior to exiting the
User session!
To unlock and gain access to an experiment:
Type unlock(#,'force'), where # is the
number of the locked experiment. For example, I try to access exp1
by typing jexp1 and I get the 'foreground processing is active' message.
I would then type unlock(1,'force'). Exp1 is now available.
I Can't Eject my Sample:
This is usually a result of a failure in
the acquisition computer. You need to see if the acquisition computer is
active.
Look at the ACQUISITION STATUS window and
see if the Status is Idle, Acquiring, or Inactive.
If it is Acquiring, type aa. If
you get the message similar to,'no experiment is active', you will need
to reboot the acquisition computer. Use the procedure for a unresponsive
console. Click here to view reboot procedure.
If it is Inactive, you will need
to reboot the acquisition computer. Use the procedure for a unresponsive
console. Click here to view reboot procedure.
If it is Idle, try typing exit.
Wait about 1 minute. If you are not exited from the VNMR program, you
will
need to reboot the acquisition computer. Use the procedure for a unresponsive
console. Click here to view reboot procedure.
If you are exited, click on the VNMR icon and type su, then
try ejecting again. Still can't eject? Try to reboot the acquisition
computer. Use the procedure for a unresponsive console. Click here to
view reboot procedure.
If rebooting does not work, contact the
NMR staff at 792!
Poor Shimming: (Click
HERE to get a more detailed procedure for shimming. PDF format)
Poor shimming or more properly, poor lineshape,
can be a result of many factors. Below is a list of common causes and their
remedies:
Common
Reasons for Poor Shimming
Cause
Result
Solution
No deuterated solvent
No deuterium signal to lock on and, thus nothing to shim on.
Use a deuterated solvent like CDCl3.
Initial shimming is poor
Your peaks are very broad.
Type fixshims to get a good start.
Suspended particles
This causes line broadening, which makes the signal intensity weaker.
Filter your sample.
Too concentrated
Concentrated samples can be viscous, which will cause line broadening.
Dilute your sample.
Too little solvent
When injected, the sample is not properly positioned in the coil and
the liquid/air interface is 'seen' by the coil. This will make shimming
very difficult.
Add more solvent.
Improperly gauged
When injected, the sample is not properly positioned in the coil and
the liquid/air interface is 'seen' by the coil. This will make shimming
very difficult.
Eject sample and ensure that the sample resides between the white lines
on the gauge.
Cheap, old, or stored in hot oven NMR tube
Poor quality NMR tubes are either very slightly out-of-round and/or
have uneven wall thickness. This results in a flucuation in the field
and thus poor line shape.
Throw away the NMR tube and get a tube that is, at the very least,
rated for the field you are using. We recommend the Wilmad
528 series as a minimum.
If shimming problems are not resolved, contact
the NMR staff at 792.
Poor Signal/Noise:
Signal/Noise (S/N) improves as the square root of nt. Increasing
the number of scans will improve S/N up to a point. Maximum improvement
in S/N occurs early in the experiment. Diminishing returns are acheived
with larger number of scans.
Increasing concentration is an obvious fix if you have enough
sample. But be careful not to get too concentrated because linebroadening
will occur at higher concentration.
Many of the same problems with poor shimming result in poor
signal/noise. If you don't get better S/N after trying the shimming
procedures, contact the NMR staff.
If you are using either of the UnityPlus-500's, make sure
that the probe is tuned correctly. The tuning procedures are posted on
the magnets.
Some hints are listed below:
Tuning hints:
(tuning procedure for a Switchable BB probe is available here)
Be sure that you setup the correct experiment (e.g.
Setup=>C13,CDCl3 for
carbon) and type su after setup.
Be sure to carefully follow the instructions on
the magnet.
Do NOT force the tuning rods. They are FRAGILE.
If you feel resistance when turning the rod, you probably have
reached the end and should turn the rod in the opposite direction.
Always start tuning by turning the shorter rod (Red for Proton. Gold for Carbon).
In general, you need only turn the shorter of the
two rods for either Proton or Carbon.
If you need to turn both rods, start by turning
the shorter one until you get a minimum on the meter. Then,…
a. Turn the longer one (Blue for proton. Black for Carbon) in a direction opposite
to what you turned the short rod. Turn the long one to the minimum and continue
turning in the same direction until the meter reading goes up a bit (5 with the
lower knob set to 60).
b. Now turn the short rod to minimize the meter reading and continue turning
in the same direction until the meter reading goes up a bit.
c. Return to the long rod and turn to minimize. Turn past the minimum as before.
d. Repeat for both the short and long rod until the meter reading is minimized.
e. If this process does not lead to a minimum, try reversing the directions you
were turning the rods.
The Computer Screen is Blank:
Try moving the mouse to see if the screen
saver is activated.
Make sure the monitor is turned on.
Turn off the montor and turn it on again.
If this does not fix the problem, contact
the NMR staff at 792.
The Temperature is too High/Low:
Type vttype?. If the reponse is 'vttype =2', proceed
to next bullet. If not, type vttype=2 su.
Type temp=25 su. This will reset the temperature controller
to 25 degrees Celsius.
If this does not work, type temp, click RESET,
wait until VT controller has reset, and
set the temperature in the pop-up window by dragging the slider.
If this does not work, type temp='n' su. This should
turn off temperature control.
If the temperature is still incorrect, contact the NMR staff
at 792.
The VNMR Screen Colors are Terrible:
The odd colors for your VNMR interface are usually a result of having too
many windows/applications open. Since VNMR is generally the last to be opened,
it is given the last dregs of color available, which turn out to be pretty
awful. You should close all unnecessary applications prior to running VNMR.
TO FIX THE DISPLAY COLORS OF VNMR:
I. After logging-in to the session and prior to running VNMR, close all
windows that pop up (e.g. Netscape, Solaris Registration, Terminals, etc.).
a. If you have the Solaris Registration window open every time you log-in,
you can disable it by clicking More Information=>Never
Register=>Never
Register.
II. Click on the VNMR icon. The colors should be fine. If not or if you want
your own colors, do the following:
a. Type color. A color palette will appear.
b. Click on the button for the item you wish to change the color (e.g. background,
spectrum, etc.) and then click on the desired color.
c. When completed, enter a filename for the name color scheme and click save.
If you want this new scheme to be the default, save the file as DEFAULT.
My Sample is not Spinning:
Check to make sure that spin is turned on by clicking Acqi=>LOCK.
Check the spin setting at the bottom of the window. Adjust the spin rate
to 20. To the right of Spin:, click off,
then click on. If it still is not spinning, then...
The most common cause of this problem
is a dirty spinner or a improperly gauged sample.
Eject the sample and clean the spinner
with a Kim wipe and ispropanol. Make sure you clean the narrow portion
of the spinner.
Regauge the sample. IMPORTANT: Always hold the spinner
and sample at the fat part of the spinner. Holding the sample and not
the spinner may cause the spinner to slip, which will make shimming
difficult.
Insert the sample. If it still does not spin, contact
the NMR staff (792 or leave message at 386 or 387). Please fill out
a NMR Incident Report.
There are several possible causes of this problem:
Too high receiver gain can cause severe distortions
to the baseline that cannot be corrected. If this is the problem, you
should of seen the error message 'Reciever Overflow' or 'ADC Overflow'
during the experiment. The easiest fix is to enable autogain (default
setting) by typing gain='n' and rerunning the experiment.
Arrayed experments like pulse width determination or kinetics do not
allow autogain so you must set it manually. Type gain=gain-6 and
rerun the experiment (one scan will be sufficient to check for errors).
If errors still occur, reduce gain and repeat experiment. Continue
with command until no error is shown. If you've reduced the gain to
the minimum and still
get an
error,
reduce
the
pulse width
(e.g. type pw=pw/2).
If your spectral window is too narrow, peaks outside
that window will be 'folded' or aliased because they were not properly
sampled (they need to be sampled at twice their frequency, see Nyquist
theorem). These peaks will typically appear as out-of-phase peaks
folded into the opposite side of the spectrum. For example, my spectral
window is set for 10 ppm to 0 ppm and I have a carboxylic acid with
a peak at 13 ppm. Since the 13 ppm peak is outside my window it will
appear as a distorted peak at 3 ppm (0 ppm +(13 - 10 ppm). To correct
this, increase the spectral window by typing setsw(upper desired
ppm #,lower desired ppm #) [e.g. type setsw(15,0)].
A rolling baseline can be a result of improper phasing
due to a failure of autophasing (usually because the S/N is too low
for the automation to work properly). You should reset the phasing
parameters
and start over. Type lp=0
rp=0 to
return zero- and first-order phasing to their initial positions. Follow
the manual phasing procedure detailed here.
A crooked but flat baseline is due to a slight offset
in the quadrature detectors. To correct, type f full cdc dc.
This will make the edges of the spectrum horizontal. Do not use if you have a peak
at the edge of the spectrum. You'll need to increase the spectral width
and repeat the experiment.
Last Updated:
March 13, 2008
- WebMaster
URL: http://www.chemistry.msu.edu/facilities/nmr/Whatdoido.html
