Gradient Shimming (Gradshim)

For (a lot) more details see the Bruker Gradient shimming brochure

The availability and type of gradient shimming depends upon the probe and sample you have:

Instruments/Probes permitting ¹H gradient shimming:

To run ¹H gradient shimming, you need a large, single proton peak in your spectrum, typically 90% H₂O:10%D₂O etc

Samples in fully deuterated solvents cannot use this method.

If you want to gradient shim on samples with more than one peak you probably need to setup selective excitation - see Facility staff.

Instruments/Probes permitting ²H gradient shimming:

You may use ²H gradient shimming on fully deuterated samples.

For more details see the Bruker Gradient shimming manual

Running Gradshim:

Remember to start with a decent shim file if possible!

The sample may be run either spinning or non spinning for 1D gradient shimming, but usually it is better to run with spinning even if you are going to run your sample non spinning later.

For 3D gradient shimming, do not spin the sample

Quick method for 2H gradient shimming:

On 500 or 600 with appropriate (default) probes, just type dshim in XWINNMR/TOPSPIN. This will do a quick optimization of z1 – z3 with no extra input required.

More detailed method:

Type gradshim to open the gradient shimming interface

Shimming Method: Choose ¹H for proton and ¹D²H for deuterium gradient shimming as appropriate

User: set this to whoever you are logged into the linux box as, e.g., iconnmr, hilda, bam etc. This may well be different from the name of the NMR data directory.

Shim iteration control: Typically use i1_z15_20 (code for one iteration, z1-z5 optimized) or deflt1d1h or ¹D proton or deflt1d2h for ¹D deuterium

Make your own iteration file with edit->iteration control if you wish

Alternate off axis with gradshim

Gradshim bugs:

The most common bug is if you try and start gradshim acquisition in a data set that belongs to a different owner, e.g., the default owner which is “gradshim” Gradshim will crash with “permission denied” errors. To avoid this:

• Make sure you are logged in with your usual linux login ID
• Make sure you set the user name to who you are logged in as before starting the acquisition

Off axis shims:

Remember the gradient shimming usually optimizes only the Z shims. You will still need to adjust the X,Y,XZ,YZ,…etc. shims. Very often typing tune and selecting an off axis shim file such as mondooffaxis will achieve this automatically if you are patient enough to wait for it.

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