Paramagnetic Effects on Solid State Carbon-13 Nuclear Magnetic Resonance Spectra of Soil Organic Matter

ABSTRACT can result in the loss of carbon as water-soluble material once the clay minerals have been removed (Dai andThe effects of paramagnetic species on solid state 13C nuclear mag-Johnson, 1999).netic resonance (NMR) spectra were quantified in a series of doping experiments. The degree of signal loss caused by paramagnetic metals In this paper, we present an overview of our recent was shown to depend not only on the quantity, but also on the nature work on the effects of paramagnetic species on solid of the paramagnetic species, as well as the intimacy of contact with state 13C NMR spectroscopy of soil organic matter the organic substrate and the type of NMR experiment. Two mecha- (Smernik and Oades, 1999, 2000a–c; Smernik et al., nisms of signal loss were distinguished—signal loss via loss of magnetic 2000). We explore the various mechanisms through field homogeneity, which affects all 13C nuclei in a sample, and signal which paramagnetic materials affect solid state 13C NMR loss via interaction between electronic and nuclear spins, the effects spectra, in particular with respect to the effects on quan-of which were localized to the close environment of the paramagnetic titation. We also describe a number of experiments inspecies. Loss of field homogeneity is important for manganese species, which paramagnetic effects are actually turned to advan-but not for copper species, and is equally important for both cross tage, providing additional information on the structurepolarization and Bloch decay experiments. The interaction between electronic and nuclear spins is highly dependent on the spin-lattice of soil organic matter