Download Solid State NMR: AVANCE Solids User Manual - Pascal-Man

CRAMPS 1D
Fine Tuning for Best Resolution
20.6
For fine tuning, the following parameters are important:
P9 sets the width of the observe window. The shorter it is, the better the resolution. 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 resonance, 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 –CH2- are in
equivalent in the solid state) should be below the 50% level.
Fine Tuning for Minimum Carrier Spike
20.7
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
20.8
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 between the two –CH2- peaks to 3.5 ppm, the NH3-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 acquisition parameter.
User Manual Version 001
BRUKER BIOSPIN
217 (261)