Varian Solid-State NMR - Page 36

2.7 Calibrating the CP/MAS Probe
01-999162-00 C0402 VNMR 6.1C User Guide: Solid-State NMR 36
Calibrating Decoupler Power
Using the previously determined pw, calibrate decoupler power (γB
2
) as follows.
1. Recall the parameters used in the previous test.
2. Set pw, tpwr, and tpwrm to the values obtained for the
13
C 90
o
pulse width
specification in “Calibrating
13
C Nucleus Pulse Width,” page 35.
3. Enter dof=5e4,-5e4 d1=10 xpol=’n’.
4. Enter at=0.05.
5. Set the following parameter values according to the spectrometer used.
6. Enter ga.
7. When acquisition is finished, measure the reduced coupling on each of the two
spectra.
8. Enter h2cal to calculate
γB
2
.
This is the maximum decoupler power,
γB
2
Max. Record this value. If the value of
γB
2
Max fails to meet specifications, remove some of the attenuation from the input
to the highband amplifier and repeat the
γB
2
Max calibration.
9. Calculate the
γB
2
CP (
1
H cross polarization field):
a.
γB
2
CP=1.0/(4.0*
13
Cpw90) where
13
Cpw90 is the value determined in the
previous section.
b. Adjust dipolr and enter ga.
c. Repeat step 6 and 7.
d. Adjust the value of dipolr until the value for
γB
2
measured in 7 equals the
value calculated in step 8a.
e. Record the values of dipolr and
γB
2
CP. These values will be used in the
next section.
10. Continue with “Adjusting the Hartmann-Hahn Match,” this page.
Adjusting the Hartmann-Hahn Match
Hartmann-Hahn matching can be readily accomplished by using a sample of
hexamethylbenzene, HMB.
1. Load a rotor with HMB, insert it in the probe, and spin it at about 2500 Hz.
2. Recall the test parameters by entering rt('/vnmr/parlib/xpolar1').
3. Enter xpol='y'.
4. Set pw, and tpwr to the values obtained for the
13
C pw90 in “Calibrating
13
C
Nucleus Pulse Width,” page 35.
5. Enter dpwr dipolr and dof values determined in “Calibrating Decoupler
Power,” page 36.
Use the second set of values for the
1
H cross polarization field.
Parameter INOVAcpmas
INOVAcpmas
(1 kW amplifier)
MERCURYcpmas
dpwr 63 55 63
dipolar 4095 4095 255