MQ-MAS: Sensitivity Enhancement
User Manual Version 002 BRUKER BIOSPIN 239 (327)
For both sequences, TD in F1 determines the number of FID’s to be accumulated
in the indirect dimension. This value is determined by the line width and resolution
that can be expected and which depend on the properties of the sample. In crys
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talline material fairly narrow peaks can be expected so that a maximum acquisi-
tion time in F1 of 2 to 5 ms is expected. In disordered material where the line width
is broader and determined by distribution a total acquisition time in F1 up to may
be 1 ms may be sufficient. The total acquisition time aq in F1 equals (TD/
2)*IN_010. For rotor synchronized experiments IN_010 = 1/spinning frequency so
will typically be between 100 µs (10 kHz spinning) and 28.5 µs (35 kHz spinning),
so only 100 to 250 experiments might be required. The rotor synchronization im
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mediately means that the spectral range in F1 is limited. Dependent on chemical
shift range, spinning frequency, and quadrupole interactions the positions of the
peaks may fall outside this range. In such a case care must be taken when inter
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preting the spectrum. Acquisition with half-rotor synchronization to double the
spectral window in F1 may help. However, in this situation one set of spinning
sidebands appears and it must be avoided that the spinning side bands of one
peak fall on top of other peaks. Some sort of rotor synchronization is always rec
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ommended because spinning side bands in the indirect dimension extend over a
very wide range, which cannot be truncated by e.g. filtering. Therefore, rotor syn
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chronization together with States or States-TPPI phase sensitive acquisition helps
to fold spinning sidebands from outside back onto centre bands or other side
bands.
Table 18.2. Parameters for 2D Data Acquisition of 3-pulse Shifted Echo Experiment mp3qdfs.av.
Parameter Value Comments
pulprog mp3qdfs.av
F1 parameters: In eda.
FnMode QF Acquisition mode for 2D.
TD see text Number of FID’s to be acquired.
ND_010 1 There is only one d0 delay in the sequence.
SWH “masr” Equals spinning frequency for rotor synchronization, from this in0 is
calculated correctly, if ND_010 must be set first.
NUC1 Select the same nucleus as for F2 so that transmitter frequency off-
set is set the same in both dimensions (essential for referencing).
pulse program
parameters:
In ased.
D10 0
IN10 =IN0*7/9
0
For spin I = 3/2,
for all other spin I.
D11 0
IN11 0
=IN0*19/12
=IN0*101/45
=IN0*91/36
For spin I = 3/2,
For spin I = 5/2,
For spin I = 7/2,
For spin I = 9/2.
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