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4 ADJUSTMENT OF MEASUREMENT CONDITIONS AND PROCESSING CONDITIONS
4.4
SETTING WAITING TIME IN CP METHOD
For the CPMAS method, the optimum value of relaxation_delay is determined by the T
of
1
H. Theoretically, the accumulation efficiency (= signal-to-noise ratio/accumulation
time) becomes optimum, if relaxation_delay is about 1.2 times the T
shown in the following figure. For the sample whose T
change the relaxation_delay if necessary to improve the accumulation efficiency using
the following values as estimations:
• Approximately 2 to 5 s when the sample includes the methyl group as one of its main
components.
• Approximately 5 to 10 s for a polymer that contains almost no methyl groups.
• Approximately 5 to 60 s for a crystal that contains no methyl group.
Fig. 4.3 Accumulation efficiency and signal intensity versus the ratio of the
The accumulation efficiency becomes its maximum at relaxation_delay/T
Since the efficiency will decrease quickly if you set a shorter relaxation_delay, you
will need to set a slightly longer relaxation_delay.
4-4
)
waiting time (relaxation_delay) to the T
of
1
CP method
relaxation_delay/T
1
CP method
relaxation_delay/T
1
(relaxation time) of
1
value of
1
H as
1
1
H is difficult to measure,
1
H
= 1.2.
1
NMECAXS_V50-SLD-2
1
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