SPECTRAL EDITING IN CPMAS NMR - GENERATING SUBSPECTRA BASED ON PROTON MULTIPLICITIES

A new approach to spectral editing of CPMAS C-13 spectra is presented that combines depolarization and polarization inversion of the rare C-13 spins. Four different spectra have been obtained in which the intensities of the nonprotonated C-13, (CH)-C-13, (CH2)-C-13, and (CH3)-C-13 groups are affected in a predictable fashion. A proper combination of these spectra yields a (CH2)-C-13-only subspectrum, a (CH)-C-13-only subspectrum, and a spectrum with (CH3)-C-13 and nonprotonated C-13 only. If the (CH3)-C-13 and quaternary carbons can be distinguished by their chemical shifts, intensity-corrected (CH3)-C-13-only and quaternary-C-13-only subspectra can also be generated. In this case the individual proton-multiplicity-selected subspectra can be added to yield a synthetic CPMAS spectrum. Differences between the synthetic CPMAS spectra and the corresponding normal CPMAS spectra are found to be quite small for a number of model compounds, indicating that the method is fairly robust. Applications to complex solid mixtures such as whole coals are also presented. (C) 1994 Academic Press, Inc.