Chapter 4. CRAMPS/Multipulse Module Operation
61
VNMR 6.1C User Guide: Solid-State NMR 01-999162-00 C0402
Configure the Spectrometer
1. Connect the preamplifier and cable that are used for
1
H detection to the
1
H port of
the probe to be used.
If this is a tune-up for
1
H decoupling instead of CRAMPS, the preamplifier must
remain in line during the decoupling experiment.
2. The presence or absence of the preamplifier in the circuit will make a significant
difference in pulse widths. A Solids preamplifier that is suitable for CRAMPS can
also remain in line during decoupling. Do not use the standard T/R switch in a
decoupling circuit unless you know it has been specified for solids.
Adjust the Homogeneity and Determine an Approximate 90
o
Pulse
1. Collect a single pulse
1
H spectrum of the sample.
2. Shim for a minimum line width (<50 Hz).
3. Roughly measure the 90
o
pulse and place the signal on resonance.
It is convenient but not mandatory to use Z0 to place the signal on resonance with
tof=0.0. Be sure the receiver gain is low so as to avoid overload (gain<20) and
d1 is set to insure full recovery of the signal.
Calibrate the Exact 90
o
Pulse Width (FLIPFLIP or XX)
This procedure is accomplished by retuning the probe or amplifier while observing
a repeating cycle of alternating X and -X pulses. The procedures for tune-up are as
follows:
1. Enter the macro flipflop.
2. Set the following permeates according to the system in use:
3. Acquire a FID and enter df to display both the real and imaginary points.
Obtain the imaginary trace with the imaginary menu button. Adjust the phase to
minimize the imaginary channel. If this is not possible, check to be sure the FID is
on resonance.
Parameter
UNITY
INOVA or
UNITYplus
UNITY or
VXR-S
Comments
d1 1.0 sec 1.0 sec Longer for samples with no relaxation agent
rof1 1.5 µsec 1.5 µsec
rof2 0.2 µsec 0.2 µsec
pw <1.5µsec <1.5µsec 1.5 usec is optimal for CRAMPS
tau 7.0 µsec 7.0 µsec add pulse width in excess of 1.5 µsec the value
base value, e.g. is pw =2.5 then tau = 8.0 usec
phase1 00
phase2 00
phfid 00
nt 11
trig ‘n’ ‘y’ Rotor sync. module is required to set
trig=’y’
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