CRAMPS 1D
User Manual Version 002 BRUKER BIOSPIN 281 (327)
Fine Tuning for Best Resolution 22.6
For fine tuning, the following parameters are important:
P9 sets the width of the observe window. The shorter it is, the better the resolu-
tion. However, the natural limit is the size of the sampling period and the dead
time of the probe. Preamp and receiver play no significant role in the total dead
time. A CP/MAS probe usually has a fairly narrow bandwidth (long dead time), so
p9 <3µsec is only possible at frequencies 400 and higher. With l11 4-8, p9 can be
chosen shorter for better resolution, but at the cost of S/N. Sampling more data
points during d9=l11*0.1 µsec with larger values of l11, will increase S/N slightly
but requires more time within the window, may require a longer p9 and therefore
degrade resolution.
Since the decoupling bandwidths are not very large, o1 should be close to reso-
nance, especially for DUMBO. For PMLG, this is less critical. The power level for
the shapes should be adjusted in steps of 0.2 dB. The splitting of the two high field
lines (the protons in the –CH
2
- are in-equivalent in the solid state) should be be-
low the 50% level.
Fine Tuning for Minimum Carrier Spike 22.7
The tilt pulse p14 and its phase (cnst25) determine the size of the carrier spike.
Optimise both parameters alternately for minimum spike, and make sure the spike
does not overlap with a resonance by choosing o1 appropriately. N.B: changing
o1 will lead to different values for cnst25.
Correcting for Actual Spectral Width 22.8
Since the sampling rate is governed by the multi-pulse sequence repetition rate,
the foreground parameter swh has no real meaning. Once all tuning procedures
are done, calculate the real spectral width swh according to the formula given in
the parameter tables and run a new experiment. After FT, the spectrum should
have an approximately correct spectral width. Calibrate the middle position be
-
tween the two –CH
2
- peaks to 3.5 ppm, the NH
3
-peak should then be at about 7.5
ppm. Since the actual peak positions depend on the probe tuning, you will have to
recalibrate for your sample using one or more known chemical shifts. If the peak
separation is incorrect, change the status parameter swh by typing s swh and
scaling it appropriately. Some pulse programs are written such that upon ased,
the (approximately) correct sweep width is shown and can be set as an acquisi
-
tion parameter.
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