Maintenance Shimming and Testing Procedures

Frequency

Every two months on each liquid state instrument, book half a day as “maintenance” to perform shimming on the default probe only. Perform signal-to-noise test every four months.

As often as not, probe changes will occur more frequently than this and extensive shimming will accompany the probe change. There is no need to perform an extra maintenance shimming and testing session within a two month period after if the shimming that accompanies the probe change is to the same level as the maintenance procedure.

For non-default probes, maintenance shimming should accompany the probe change only,

Default Probes:

• 600: 5mm TBI-Z
• 500: 5mm TBI-Z
• Flip 300: 5mm BBI-Z
• Gyro 300: 5mm QNP-Z

Shim Files

The objective is to write two shim files, one for acetone solvent (lineshape sample) and one for chloroform solvent (signal to noise sample)

e.g.,

The name should reflect the probe as appropriate.

Samples to use

Only use Bruker test samples that are new as they tend to degrade, especially the signal to noise samples

Methods

General procedure is:

1. Do the lineshape sample first. Goal is to shim, non spinning, to the manufacturers specifications. If this happens in less than 1 hour, stop, write, print and store the shim file (SHIMXXX.ACME). If after 1 hour or more spec has not been achieved, stop and write the shim file when the shimming becomes no worse than 50% more than specs at 50/0.55 and 0.11%. e.g., if spec is 0.4/5/10 Hz shim to at least 0.6/7.5/15 Hz. If this point has not been reached after 2 hours, stop, write your best shim file and consult GB.
2. Switch to the signal to noise sample and give it a 15-30 minute shim to modify the shims for CDCl3 solvent. Stop, write, print and store the shim file (SHIMXXX)
3. Tune as well as you can, measure the 90º pulse length and note in the book. Run a signal to noise test on the 0.1% ethyl benzene in CDCl3 sample. If it’s more than 90% of the spec, it should be OK – no need to waste days pretending we’re installing a new instrument! Inform GB if 90º pulse length is more the 15% out compared to the normal value or if S/N can’t be achieved.

Method Details

600, 500:

If you are shimming immediately after a probe change or VT experiment, let probe sit at 298K for at least one preferably two hours before commencing.

Put lineshape sample in the magnet. Tune 1H, lock, adjust lock phase

rsh SHIMTBI.ACME – start with the last time this file was written, unless it is known that for hardware reasons this is no longer valid.

Shim using the method of your choice. However, it is recommended to

1. spin the sample and use a 2H gradient shimming optimization on Z-Z5 (use i1_z15_20 or i1_z15_22) (see gradshim notes)
2. stop spinning, do a rough manual shim on X,Y,XZ,YZ.
3. use an auto shimming routine such as “tune mondooffaxis” for big changes on offaxis/3D shims up to 3rd order

Steps a,b and c can be cycled through. High order (4th order off axis/3D shims) shims may also require some manual adjustment (non spinning) when shims are quite good. Z,Z2,Z3 can be tweaked manually at the end usually.

Only write SHIMTBI.ACME if the shimming is no worse than 50% worse than specs. Otherwise, just write the temporary file shimtbi.010206

If you can do better than this in less than 1 hour of shimming, continue up to point that the spec is reached or the hour is passed.

300s:

The 300’s are not capable of 2H gradient shimming. So, there are two options:

1. Use 1H gradient shimming on a sample of 80:20 acetone/acetone-d6 (i.e., a protonated version of the test sample) prior to inserting the real lineshape sample.
   To run 1H gradient shimming, you need a large, single proton peak in your spectrum. The sample should be as close possible in length to the real lineshape sample.
2. Just shim manually on the 2H lock signal of the lineshape sample.
1. Spin the sample and use a 2H shimming optimization e.g., tunez1z2z3 or a simplex optimization such as “xau simplex simplexzz4” (takes ~0.5-1 hour)
2. Stop spinning, do a rough manual shim on X,Y,XZ,YZ.
3. Use an auto shimming routine such as “tune mondooffaxis” for big changes on offaxis/3D shims up to 3rd order

This needs to be done whether or not step 1 is completed.

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