Chapter 2. CP/MAS Solids Operation
35
VNMR 6.1C User Guide: Solid-State NMR 01-999162-00 C0402
2.7 Calibrating the CP/MAS Probe
Calibrating
13
C Nucleus Pulse Width
The following steps cover calibrating the pulse width.
1. Insert a rotor containing liquid-state p-dioxane and spin at 200-300Hz.
Do not spin faster than 200-300 Hz, or the p-dioxane will be forced out of the hole
in the rotor cap. The addition of a small amount of CrAcAc (not provided) to the
p-dioxane will allow you to use d1=1.0 in these tests.
2. Recall the parameters by entering rt('/vnmr/parlib/xpolar1’).
3. Enter tn=’C13’ reffrq=sfrq d1=10 nt=4 xpol='n' at=0.05
lb=10.
4. Set the following parameter values according to the spectrometer used:
5. Enter su.
6. Tune the probe to
13
C for p-dioxane.
See Getting Started for instructions on how to tune a probe.
7. Enter ga.
8. Place the cursor 500 Hz on low field side of the p-dioxane resonance and enter
movetof.
9. Enter sw=5000 ga.
10. Array pw from 0 to 5 times the 90
o
pulse width specification.
11. Increase tpwrm as necessary to achieve the 90
o
pulse width specification or desired
90
o
pulse width. Do not exceed the 90
o
pulse width specification.
If you cannot achieve the
13
C 90
o
pulse width specification with tpwrm set to full
value, you may need to remove any attenuation added to the lowband amplifier and
repeat the calibration.
12. Record the values of tpwr and tpwrm used to obtain the
13
C 90
o
pulse width
specification. Save the final data for reference.
Estimate the
13
C 90
o
pulse width using either use the maximum 90
o
or find the
difference between the 360
o
and 180
o
and divide by 2. The 180
o
is not a good
measurement of twice the 90
o
because of r.f. inhomogeneities of the coil.
13. Continue with “Calibrating Decoupler Power,” this page.
Parameter INOVAcpmas
INOVAcpmas
(1 kW amplifier)
MERCURYcpmas
gain 40 40 20
tpwr 63 54 63
tpwrm 1600 1600 100
dpwr 63 55 63
dipolar 1600 1600 100
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