Shimming problem

I got a query about the troubleshooting for D2O shimming problem. Below is some of my summary.

Shimming problem is pretty common because of many factors.
In principle, magnet shims (+Z or -Z) are not optimized. So the shape of the peak is not distributed evenly. If so, it (the shape of the peak) will give you a hint as to which shims need adjustment. Two examples are as follows:

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Except peak shape, poor shimming can also affect the sensitivity of the magnet/instrument. If the spectrum shows a significant decrease in sensitivity, it needs to double check shims and other factors.

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Another factors can also affect shimming quality, e.g., sample volume (sample preparation and sample loading) problem (below).

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Below are some of examples to determine shimming is qualified or not. Once shimming goes to “good” and “acceptable”, shimming needs adjustment . If shimming is poor or even bad, shimming must be optimized.

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https://www.researchgate.net/publication/331370599_Optimizing_1D_1H-NMR_profiling_of_plant_samples_for_high_throughput_analysis_extract_preparation_standardization_automation_and_spectra_processing

1H line-shape test can be considered as a standard, to show the line width (in Hz). For example, 1H NMR spectrum of chloroform in acetone-d6 obtained at 400 MHz. The line width at 50%:0.55%:0.11% (maximum height)=0.4:4.4:12 Hz