Solid-State NMR Experiment

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Instrument: JEOL 300 MHz solid-state
Probe: JEOL 3.2 mm MAS
Required Sample Tube: NM-05410ST32  (Zirconia, ZrO2)
Sample volume: 27-50 mm3

Updated 11/5/2024

Solid-State NMR Experiment

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Step 1. Achieve Working Speed in the Probe


Important Notes

NOTE 1

The sample tube must have been packed according to a standard procedure described in Packing of the JEOL sample tube where

  1. It has been spun at range of speeds on a benchtop including the maximum speed exceeding by 2 kHz the speed you intend to use in the probe; and
  2. It has demonstrated high stability at high speeds judged by permissible speed fluctuations given in a reference table.

NOTE 2

Even if your sample tube has been previously measured, it must still be tested in the benchtop spinner to confirm its stability at a speed that is 2,000 Hz higher than its intended working speed. This is because handling the tube might have disturbed its internal packing. Please follow the guidelines in the last section of the sample preparation protocol, but you don't have to let it spin for 5 minutes after each speed increment.

NOTE 3

If you see the speed stall in the 1000-1500 Hz speed range, YOUR MUST STOP SPINNING IMMEDIATELY. The tube is unbalanced and continuous spinning will lead to the tube and probe damage!

Important: The MASCONT software misinterprets the stall condition and overreacts by indiscriminately increasing Drive pressure until a speed increase is detected. This results in significant pressure overshoot, pushing the probe's spinning speed beyond safe operating range for the tube.

If the speed stalls: the tube is unbalanced and must be repacked even if it span correctly in the benchtop spinner. If stalling occurs again after repacking and a successful test on a benchtop spinner, contact NMR staff to deal with this problem!

NOTE 4:

Light adjustment is mandatory every time after you inserted a sample in either probe or benchtop spinner.

 


1.1 Put Sample in the Probe

  • Pull the probe out, place it on a floor, open the probe shield. Disconnect the temperature control cable TEMP
  • Tilt the probe back to about 45 degrees to make the probe bore vertical. Orient the sample tube with painted portion of the bottom cap facing up to have it also facing up when it is in the probe. Drop the sample tube into the probe.
  • Close the probe shield. Reconnect the temperature control cable.
  • Attach the gas supply lines.
  • Attach the spin control cable to the probe.
  • Rotate the light adjustment knob to the pen mark.
  • Close the shield on the benchtop spinner
  • Do not insert the probe at this time yet. We need to make certain that the sample can float.
  • In MASCONT:
    • Turn on "Probe Cooling"
    • Enter the File Name in the "Log" section as [Your initials]_[experiment ID]_probe, interval=20 sec, and click "Start" to start recording the spinning log
  • Check if the tube is floating:

    • Increase Bearing pressure to 150 kPa. You should see that the tube begins to rotate meaning it floats in the Bearing gas jet.
    • If it does not, set pressure to zero, take the tube out and put it back in making sure the painted strip faces up in the stator of the probe.
    • Re-try applying Bearing pressure. Several times might be needed to make some tubes "unstick".
    • If still does not float, check if the standard sample is floating in the same conditions.
  • When the tube demonstrated that it can float:

    • Stop spinning (hit Stop in MASCONT)
    • Insert the probe into the magnet.

 


1.2 Adjust Light Intensity for the Speed Measurement

Follow the same guidelines as for the light adjustment on the benchtop spinner.

 

1.3 Spin Up to the Working Speed of 10 kHz

GENERAL NOTE:

If you notice that

  • the tube makes buzzing oscillating noise and the speed stalls despite increasing Drive pressure or
  • the speed fluctuates in the 50-100 Hz range

STOP IMMEDIATELY!

The tube is unbalanced and must be repacked!

In the following step, the speed must increase to about 2000 without any hesitation around 1100-1500 Hz.

 If the speed stalls in this range, hit STOP immediately! 

 Stalling means that the tube touches the stator walls and slows down despite the Drive pressure. Both the spinner stator and the tube will be damaged by continued spinning. Report the issue to NMR staff.


Did the speed stall around 1100-1500? STOP immediately!
If the tube smoothly reached the speed around 2000 Hz with fluctuations no more than 10 Hz, proceed to Automatic mode.

Spin up in the Automatic mode:

NOTE 1: Watch for Drive pressure NOT to exceed what is expected in the spinning rate table by more than a few kPa.

NOTE 2: Watch for fluctuations to remain in the "permitted" range.

IMPORTANT: If your speed fluctuates > 10 Hz,  STOP and

If speed still fluctuates > 10 Hz, stop spinning and talk to NMR Director to adjust the light sensor in the Manual mode.


Step 2. Tuning and Matching the Probe


2.1  Quick Tuning and Matching with Reflection Meter

  • Display the experiment that contains nuclei that you want to use. For example, to tune proton and carbon, display 13C CPMAS experiment.
  • In Header tab, check auto_gain and force_tune
  • Click Submit Job
    • The low-frequency (broadband) channel is tuned first. Ignore tuning/matching settings shown on the Delta screen.
    • Find what capacitor stick you need for your heteronucleus in the probe parameters table attached to the top of the amplifier. Check what stick is currently inserted.

      NOTE: The capacitor stick is wobbly: if you accidentally touch it during subsequent tuning/matching, the probe might go out of tune.  Therefore, it is recommended to recheck tuning by resubmitting the job one more time after tuning/matching was completed.
    • Turn on the probe display and dial Tune and Match values for the nucleus from the table on the amp.
    • Verify that the amplification button on the amp is at 10x and the knob at the rightmost clockwise position.
    • Rotate Match and then Tune rods for the corresponding channel to get meter display down to <15 LED elements

      NOTE: Proton in proton-detected experiments does not tune better than 30 LEDs - this is OK. If you see the meter maxed out and need to push 1x button to see the signal, perform tuning with the frequency analyzer (next section).

      • If the FA is not available, the procedure to tune on the Reflection meter is as follows:
      Set amplification to 1x and turn the knob to have the signal in the middle of the meter display.
      1. Rotate Match in direction of reducing signal (smallest number of LEDs) and then past the minimum to increase by 1-2 LED. Note the direction that you were rotating the Match.
      2. Rotate Tune to further reduce number of LEDs; If you cannot reduce, go to (1) and rotate Match in the opposite direction.
      3. Rotate match again in the same direction till the signal is minimized and go past the minimum by 1-2 LEDs.
      4. Repeat tuning/matching steps 1-3 until you get the lowest possible signal. Make sure to increase amplification to 10x and turn the knob clockwise as you proceed. Keep checking the Delta screen: make sure that it did not time out! If it did you should abort the job and resubmit it to continue tuning.
      5. In the end, the amplification must be at 10x and the turn knob at the CW limit (maximum). You should see 10-15 lighted elements on the reflection meter (may be 20-30 in proton-detected expt).
  • When tuning/matching is satisfactory, click Done on the Delta screen. The software will automatically proceed to tuning the next channel. After you completed the second channel tuning, click Done and then abort the job (click red circle with X in the blue Activity section and confirm)

2.2 Tuning and Matching with Frequency Analyzer (FA)

  • Usually, only the proton channel requires using FA . However, it may be used on the broadband channel as well (pay attention to  set the correct center frequency for your nucleus!)
  • Attach black extender cord to the wall power and turn on the FA.
  • Disconnect the appropriate probe cable from the amp (for proton: with the deuterium filter)
  • Attach yellow cable to the probe cable using the adaptor.
  • Push TG button to see it light up and click [TG] next to the screen label
  • Set the center of spectrum to the desired frequency:
    • Look up the frequency for your nucleus in the table on the amp;
    • Hit TG:Freq: enter frequency on keypad, hit MHz unit key, and hit ENTER;
    • change spectral width as needed: TG:SPAN, enter the value and hit ENTER;
    • change amplitude of the spectrum display: TG:AMPT:Scale/Div;
    • change reference line : TG:AMPT:Reference and turn dial.
  • (Optional) Set a marker at the center frequency (to better see the tuning result)
  • Tune and match using appropriate Tune and Match wheels on the probe
    NOTE: For proton, optimize tuning but not worry about matching because matching will still have to be adjusted on the reflection meter display.
  • Once finished tuning on FA, reconnect the cable to the amp.
  • Check the resulting signal on the Reflection Meter; adjust Tune and Match as needed. 
    NOTE: Sometimes Delta tuning window times out and switches to the next channel or starts acqusition. Then - abort the job and Submit again.

 


Step 3. Acquisition

NOTE: Acquisition started automatically as soon as you clicked Done in the tuning window. .

  • Stop acquisition.
  • Re-submit to to check tuning on a tune interface one more time, because carbon channel may have detuned during proton tuning adjustment! Look at the tune interface and verify that number of LEDs remained the same as you recorded above.
  • Click on the actual job you intend to run. Submit.
  • As experiment is collected: see Monitor tab. Click Process and (Play) symbol to show frequency-domain data as they accumulate.
NOTE: If you have multiple experiments, uncheck force-tune, otherwise the job will be stuck every time it starts new experiment

Step 4. Processing

  • in Delta - only to view the data quality
  • Topspin and MNova are installed on the workstation to have a better view at the data if needed.
Copy the file with "-1.jdf" extension to a flash drive for analysis in TopSpin or MNova (on your computer)

 


Step 5. Finishing Your Work

  • Stop spinning: Click Stop on the MASCONT screen.
  • Stop loggin speed: Click Stop in the "Log" section. It is viewable in Desktop\Libraries\Documents\My Documents\MSCONT\Log
  • Remove any unfinished experiments from your queue

    • Click on Queue tab.

    • Click on gray X sign to delete any experiments still appearing in the queue.
      NOTE: If you don't clean up your queue, next user may not be able to start their own experiments because your experiments will be blocking the queue!
  • Take the probe out and remove your sample.
  • Close the probe head cover and insert the probe back into the magnet.
  • Re-insert a default stick A.
  • Close the benchtop spinner cover.
  • Turn off the frequency analyzer.
  • Put its cables around it (off the floor).
  • Disconnect black extender cord (for frequency analyzer) from the wall power socket.
  • Disconnect Delta software from the spectrometer.
  • Stop the Kiosk.
  • CLOSE GAS SUPPLY ON A WALL   (turn yellow handle to the vertical position)
  • Clean all the tools that you used for packing your sample.
  • Wipe off the sample prep bench if you used it.
  • Take all your chemicals and samples back to your lab.

 


Adjustment of the MAS Angle and Recording Chemical Shift Reference


MAS Angle Adjustment

The NMR signal is strongly dependent on the rotation angle matching the magic angle relatively to the static magnetic field. The angle adjustment must be checked periodically.

NOTE: The MAS angle adjustment screw is delicate. If you turn it counterclockwise (CCW) too much, it can slip off the adjustment rod, making further adjustments ineffective. You'll notice this when your screwdriver spins freely without resistance.

To fix this, slowly turn the screw clockwise (CW) until you feel a slight resistance. This means it's re-engaged with the rod and you can now adjust the MAS angle by turning the screw CW or CCW.

Important: Be careful not to over-tighten the screw. Excessive CW rotation can damage the adjustment rod. Stop turning as soon as you feel significant resistance.

It is advisable to add KBr directly to your sample so you will be able to check the magic angle directly with your sample without a need to insert AGK standard.

    • Spin up AGK sample at 10 kHz
    • Create a new job and pick experiment MAS_Adjust_KBr_Br79
    • Click "force-tune" , "auto-gain". See if 'repeat" is checked.
    • Submit experiment and tune Low Frequency channel to 79Br
    NOTE: Tuning to 13-C is also acceptable
      • insert stick A;
      • Take the settings for 79Br from the table on the amp;
      • Adjust Tune and Match to see 13-14 elements on the reflection meter;
      • Click Done on screen.
    • Turn on Processing and copy the peak center ppm value.
    • Stop experiment; Enter peak center value as offset frequency for the new experiment.
    • Re-submit acquisition.
    • Shift-2 to show imaginary fid as well.
    • Adjust Magic Angle adjustment screw while watching the screen. You need to have spinning sidebands extend to  4ms. Make very small adjustments and wait. The screw has a significant slack when changing the turning direction.

Chemical Shift Reference recording

Referencing is done by the low-field peak of adamantane at 37.77ppm. This AGK sample includes adamantane, therefore, referencing is most convenient to do at the same time with the MA adjustment on the AGK sample.

The spectrometer field gradually shifts, therefore, you have to record the reference sample close in time to your other samples (less than a week). When the spectrometer frequency had drifted too far (more than a ppm) it is adjusted by NMR staff with a corresponding notice to users. Yet, we strongly recommend to record AGK sample every time you measure your samples to have a reliable reference dataset.

To determine chemical shift correction for your spectra:

  • Record a decoupled single-pulse 13C.
  • Open this spectrum in Topspin
  • Set frequency of the low-field adamantane peak to 37.77ppm
  • Note the resulting ProcPar: SR parameter and copy it to your other experiments

 


Set up of Other Nuclei that are not in the Probe Spec Table

These steps are to be done by the NMR staff!

Not all nuclei are accessible on the JEOL MAS probe. The probe table (on the amp) contains the nuclei that have been already set up. It may be possible to add a similar-frequency nuclear spins to the probe setup. Ask NMR staff about this possibility.

  1. Create an experiment with this nuclear spin, set 1 scan, check force-tune and submit.
  2. Find the nuclear spin close in frequency to your desired nucleus and set probe to Tune/Match values from the probe table for that spin.
  3. Tune probe on the frequency analyzer
  4. Fine-tune on the tune interface (both matching and tuning will need to be adjusted).
  5. Record new Tune/Match values
  6. Determine 90-degree pulse time for the new nucleus.
  7. Make a parameter set in Delta for this nucleus