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7 MQMAS METHOD
As seen in the above spectra, for the spectrum that cannot be analyzed using only the
MAS spectrum, measuring with MQMAS can obtain information on the three different
sites. Moreover, the MQMAS spectrum shows the MAS spectrum along the direct obser-
vation axis and the isotropic spectrum along the evolution (indirect observation) axis.
Therefore, various kinds of information can be obtained from the peak positions and the
line-shape analysis of the slice data in the MQMAS spectrum.
■ Points to notice on the MQMAS method
Although the MQMAS method is a technique with the ability to obtain various kinds of
information, some factors exist that influence the quality of the data.
a) High RF power required
b) The probe must withstand high voltage
c) High magnetic field required
High RF power is indispensable in the MQMAS method in order to cause the magnetiza-
tion transfer with multiple-quantum coherence. If the power weakens, the signal intensity
will decrease, and the peak may not be detected. Furthermore, an artifact signal may ap-
pear. Moreover, in order to use high RF power, the probe must be able to withstand high
voltage.
The greatest problem of MQMAS is the weak signal intensity, and the measurement time
is very long. Therefore, it is very effective to increase the signal intensity with a high
magnetic field and with high-speed spinning, and shorten the measurement time.
Furthermore, the quadrupolar interaction that causes the lines to broaden decreases with a
high magnetic field and high-speed spinning. Therefore, not only does the signal intensity
increase, but the resolution also improves markedly as a result of using a high magnetic
field and high-speed spinning.
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NMECAXS_V50-SLD-2
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