Tips on Locking and Shimming

1. Turn the lock OFF. If the lock display not flat, change Z0 until the lock is flat. Consult the solvent list posted near the spectrometer for an approximate Z0 value for your solvent. (The Z0 values listed for various solvents are RELATIVE to the current Z0 value of chloroform on that spectrometer. Therefore, first consult the shim card posted at the spectrometr for the current Z0 value for chloroform; then add this value to the Z0 value listed for your solvent in the Z0-solvent list).
2. If you can't see the lock signal,
   • increase the lock power. You may have to increase lock power to the maximum.
   • The lock gain should always be a maximum, excpet on the Gem300. The lock gain on the Gem300 should be set at 20 (a value of 30 makes the lock too noisy on this spectrometer).
   • Once you have a flat lock display, set the lock to ON; on the VXR400, set the lock to AUTO.
   • If the lock signal is greater than ths display range, decrease lock power until you can see the lock display.
3. Shim on Z1C and Z2C ONLY.
   • If the lock intensity "bounces" up and down, decrease lock power.
   • If the lock signal is very low, the shims may be off by a large amount. Be sure that the shim values match closely with the values on the shim card posted at the spectrometer.
4. Change the lock phase until the lock signal is a maximum.
5. Record a spectrum. If the peak is assymetrical or there are spinning sidebands, return to the shim display. Verify that the shim values (except Z1C and Z2C) match the shim card at the spectrometer. Verify that Z1C and Z2C are properly set for a maximum lock signal. If the shims are OK and the spectral lines are not symmetrical, they are unusually broad, or there are large spinning sidebands, then:
   • Shim Z3 and Z4. Then Shim Z1C and Z2C again. Record a new spectrum.
   • OR contact a NMR Facility staff member.

6. Once you are finished with the spectrometer put the standard ethylbenzene sample in the magnet and lock and shim the magnet. Readjust any parameters you changed so that you leave the instrument as you found it.

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   Last updated: April 2nd, 1998
   URL: http://nmr.chem.indiana.edu/NMRguide/operation/lockshim.html
   Copyright 1996, The Trustees of Indiana University