Advanced Operation
26 Z33085_2_002
6. The definition of the selectivity for selective excitation is entered next. This depends on the
difference of the chemical shift of the field lock solvent to the next closest signal of the
thermometer compound. As an example, a selectivity of 0.5 ppm is sufficient for chemical
shift difference of 1ppm. For larger shift differences a selectivity of 1 ppm shall be used:
7. The T
1
relaxation time of the shim nucleus is used to define the repetition time for the shim
procedure. Typical values for the T
1
relaxation time are about 1 sec. for D
2
O, 3 sec for C
6
D
6
and 5 sec. for acetone-d
6
.
8. In a final step the optimization parameter has to be defined. There are three options:
• ss: Shims will be optimized for solvent suppression
• ls: Shims will be optimized for the line shape
• lshump: Shims will be optimized for narrow hump.
In the example shown here, solvents suppression has been selected:
Further details of the setup of a new solvent for shimming can be found in the Topshim
reference manual which can be accessed with the command help topshim in TopSpin.
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