7 MQMAS METHOD
7.1 OUTLINE OF MQMAS METHOD
The MQMAS method was proposed by Frydman and Harwood in 1995.
Reference: A.Medek, J.S.Harwood, and L.Frydman. JACS, 117, 12779-12787 (1995).
The MQMAS method has the advantage that it can eliminate quadrupolar interaction
without using a special probe in contrast to the DOR and DAS methods.
Moreover, since it can be adjusted comparatively easily, it can be generally used as the
measuring method.
■
Feature of theMQMAS method
For nuclei having a spin 1/2, information about how many sites exist can only be obtained
by the MAS spectrum. For nuclei having a half-integer spin, the site analysis is difficult
when you only use the MAS spectrum because of the influence of quadrupolar interac-
tions.
As an example, the
87
Rb MAS spectrum of rubidium nitrate (RbNO
3
) is shown below.
Fig. 7.1
87
Rb-MAS spectrum (300 MHz)
Although three different sites exist in rubidium nitrate, such information cannot be ob-
tained from the MAS spectrum. The following figure shows the spectrum measured by
the MQMAS method.
-10
-20
-30
-40
-50
-60
-70
ppm
-7
0
-6
5
-6
0
-5
5
-5
0
-4
5
-4
0
-3
5
-3
0
p
p
m
Fig. 7.2
87
Rb MQMAS spectrum (300 MHz)
NMECAXS_V50-SLD-2
7-1
