C-13 NMR spectral editing of humic material

The spectral-editing method introduced by Wu, Burns and Zilm (J. Magn. Reso n. A, ill (1994) 29) based on a prescribed combination of C-13 CP-MAS (cros s-polarization with magic-angle spinning) experiments that include suitably chosen depolarization periods, polarization inversion periods and either s hort or long CP periods, has been applied to a humic acid that was isolated from the Uncompahgre National Forest. The separate spectra derived on the basis of CHn multiplicity (n = 0, 1,2, 3) for CH groups, CH2 groups and CH3 + drop C drop (no directly attached hydrogen) groups confirm and advance p revious structural interpretations based on chemical shift arguments. This work demonstrates that, while very time consuming, these spectral-editing t echniques based on C-13 CP-MAS techniques, are practicable for complex soil -derived samples. (C) 2000 Elsevier Science B.V. All rights reserved.