Bruker BioSpin Solid State NMR, User Manual

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116 (327) BRUKER BIOSPIN User Manual Version 002
Basic CP-MAS Experiments
Spectral Editing Sequences: CPPI, CPPISPI and CPPIRCP 7.5
These spectral editing sequences help to distinguish CH, CH
2
, CH
3
and quaterna-
ry carbons in
13
C spectra. Common to all are various polarization and depolariza-
tion times, which properly mixed and combined give a series of spectra, which can
be added and subtracted in order to obtain the various sub-spectra. All these se-
quences use constant-amplitude CP, which should be adjusted for maximum sig-
nal intensity. For the
CPPI and CPPISPI sequences, the only parameter needed
in addition to the CP parameters is
p16, for which a good starting value
is 40 µs
to give null signal for CH, negative signal for CH
2
, and positive signal for C and
CH
3
. If necessary, this value can be optimized on a sample similar to the sample
of interest for better editing.
p17,
for the repolarization step in the CPPIRCP ex-
periment, is about 10 – 20 µs.
For this experiment to succeed reliably, one should use moderate spinning
speeds around (up to) 10 kHz. At slow rotation rates, no advantage was found in
measuring the exact HH match. Running the experiment at constant amplitude
CP, optimized for maximum signal, proved to be sufficient.
References for these experiments:
1. X. Wu, K. Zilm, Complete Spectral Editing in CPMAS NMR , J. Magn. Reson. A 102, 205-213 (1993);
2. X. Wu, K. Zilm, Methylene-Only Subspectrum in CPMAS NMR , J. Magn. Reson. A 104, 119-122
(1993);
3. X. Wu, S.T. Burns, K. Zilm, Spectral Editing in CPMAS NMR. Generating Subspectra Based on Proton
Multiplicities , J. Magn. Reson. A 111, 29-36 (1994);
4. R. Sangill, N. Rastrup-Andersen, H. Bildsoe, H.J. Jakobsen, and N.C. Nielsen, Optimized Spectral
Editing of 13C MAS NMR Spectra of Rigid Solids Using Cross-Polarization Methods , J. Magn. Reson.
A 107, 67-78 (1994).
Figure 7.12. Block Diagram of the CPPI Experiment.
Typical pulse widths for the second part of the CP pulse with the phase inversion
are 40 µs.