Bruker BioSpin Solid State NMR, Руководство пользователя

Страница: 249 / 328

STMAS
User Manual Version 002 BRUKER BIOSPIN 249 (327)
ph4 = 0
receiver = ph3-ph1-ph2
Experiment Setup 19.3
Before the 2D experiment on your sample of interest can be started some setup
steps must be done as described in detail below. All setup steps should be done
on a sample with:
•
A known MAS spectrum,
•
With sufficiently good sensitivity to facilitate the set-up, and,
•
A 2
nd
order quadrupole interaction of the order of the one expected for your
sample of interest.
In a first step, a low power selective pulse must be calibrated in a single pulse ex-
periment. After this the STMAS experiment can be optimized using the 2D pulse
sequence for the first t
1
increment.
Setting Up the Experiment 19.3.1
Sample: There are a large number of crystalline compounds that can be used to
set-up the experiment. Please refer to
Table 19.2.
to select a suitable sample. For
the general procedure described here the spin I of the nucleus is not important, of
course the obtained pulse widths will depend on the spin I, and the Larmor fre-
quency. For the STMAS experiment, in contrast to MQMAS, it is advisable to use
a well-known sample for the setup because the accuracy of the magic angle set-
ting is extremely critical.
Table 19.2. Some Useful Samples for Some Nuclei with Half Integer Spin
Nucleus Spin
Spectrometer
frequency
*1 )
d1 [s]
*3 )
Sample Comments
17
O 5/2 67.78 2 NaPO
3
> 10% enriched
11
B 3/2 160.42 >5 H
3
BO
3
23
Na 3/2 132.29 10 Na
2
HPO
4
*2 )
27
Al 5/2 130.32 5 YAG
87
Rb 3/2 163.61 0.5 RbNO
3
93
Nb 9/2 122.25 1 LiNbO
3
*1)
In MHz at 11.7 T (i.e. 500.13 MHz proton frequency).
*2)
Alternatively Na
2
HPO
4
* 2H
2
O can be used. For anhydrous Na
2
HPO
4
the sample should be dried at 70° C for a
couple of hours before packing the rotor in order to eliminate crystal water completely.
*3)
Recycle delays at 11.7 T, longer delays may be required at higher fields.