ABSTRACT
The interpretation of the NMR spectra of humic materials in solution is complicated by the presence of broad lines in the spectra, and by the free radical content of the materials. These two problems are probably interrelated, because localized free radicals can cause paramagnetic broadening of NMR lines. The seemingly innocent act of phasing and base line correction of solution spectra also can change relative integral intensities significantly. This problem is particularly severe in spectra with broad lines. In solid-state NMR all of the problems discussed for solution spectra occur, along with added complications airsing from the cross-polarization. The two most important experimental parameters in the cross-polarization experiment are the contact-time and pulse delay.
