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7 MQMAS METHOD
7.6
APPENDIX
This section describes special processing required in the MQMAS method.
7.6.1
Shearing process
Since the MQMAS method measures the echo, the top of the echo signal (the starting
point of FID) shifts along with the t1 evolution time. As an example, a two-dimensional
FID signal of the
If the Fourier transform is carried out by the usual method for such two-dimensional FID
data, it will become a tilted two-dimensional spectrum. Therefore, we must change it into
an ordinary spectrum by performing the shearing process.
After the Fourier transform of F2 axis, shearing conversion performs the phase correction
that increases the first order phase of the F1 axis linearly. Figure 7.7 shows the relation
between FID and the spectrum when the sampling starting position of an echo signal is
shifted.
7-12
23
Na nucleus in sodium sulfate (Na
Fig. 7.6 Two-dimensional FID signal of sodium sulfate (Na
Sampling
ｔ
Fig. 7.7 Relation between FID and the spectrum
when sampling start position is shifted
SO
) is shown below.
2
4
SO
2
ω
NMECAXS_V50-SLD-2
)
4
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