Carbon-13 Cpmas NMR and Ftir Spectroscopic-Studies of Humic Acids

Carbon-13 NMR spectra, acquired with cross-polarization and magic angle sample spinning (CPMAS), and Fourier-transform infrared (FTIR) spectra were obtained on solid humic acids (HAs) extracted from material sampled at four selected stages in a large municipal waste treatment process. The complexity of the spectra manifests the compositional diversity of these substances. 13C-′H solid-state NMR interrupted-decoupling spectroscopy aided in the examination of aromatic groups and of organic functional groups with no C-H bonds, which are typically only poorly resolved in normal 13C solid state NMR spectra of such systems. Data measured with this pulse sequence also indicate that certain moieties, such as methyl groups, are quite mobile even in the solid state. NMR and FTIR spectra combined with quantitative elemental analyses allow a comparison of both differences and similarities among the HAs considered here.