2.5 Adjusting Homogeneity
01-999162-00 C0402 VNMR 6.1C User Guide: Solid-State NMR
30
6. Attach the lock cable from lock preamp to the observe (OBS) connector on the
probe.
7. Lock the spectrometer and shim on the lock signal. The principle shims involved in
adjusting homogeneity when a magic angle spinning (MAS) probe is used are: Z1,
Z2, X, Y, XZ, YZ, XY, and X2Y2.
A typical procedure is:
a. adjust Z1, X, Y, and Z2
b. adjust XZ, YZ, XY, and X2Y2
c. readjust Z1 and Z2
d. adjust any other off-axis shims as necessary
8. To see how well the field homogeneity has been adjusted, do the following:
9. Turn the lock transmitter off by entering lockpower=0 lockgain=0
alock=’u’ su.
10. Disconnect the lock cable from the probe.
11. Connect the cables so that the observe (OBS) port of the probe is connected to the
observe connector on the magnet leg.
a. Acquire a deuterium spectrum using the deuterium parameter set. The
deuterium linewidth should be typically between 1 and 5 Hz.
b. Finer adjustment and evaluation of the homogeneity is possible using a
sample of solid adamantane (not available from Varian). A linewidth between
2 and 10 Hz is typically attainable, see the sample spectrum in Figure 5.
A solids probe is not locked during normal operation and Z0 must be adjusted
manually to put the lock on resonance when shimming. When the lock is on
resonance the spectrometer will correctly set the transmitter and decoupler
frequencies. It will be necessary to periodically reset z0 to compensate for
magnet drift whenever you shim. Between shimming sessions it is sufficient
to adjust reffrq, tof and dof.
12. Continue with section “Positioning the Probe and Shimming the D
2
O FID or
Spectrum,” page 30.
Positioning the Probe and Shimming the D
2
O FID or Spectrum
1. Enter lockpower=0 lockgain=0 rtp(‘/vnmr/parlib/xpolar1’).
2. Enter su.
3. Disconnect the lock cable from the probe.
System Connector
INOVAcpmas J5205
MERCURYcpmas LOCK PREAMP (J5202) or LOCK PROBE (J6002)
System Connector
INOVAcpmas J5311
MERCURYcpmas LO BAND Preamp (J5302) or FROM BB Probe (J6001)
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