Separation of structural components in soil organic matter by diffusion ordered spectroscopy.

Abstract

Diffusion ordered spectroscopy (DOSY) was applied to two extracts of organic matter from the surface horizon of an oak forest soil. It was possible to identify and confirm the presence of numerous aliphatic, aromatic, sugar, and amino acid components that could be separated on the basis of diffusion in DMSO-d6 and D2O. On average, sugar components were identified as the largest molecules in solution, with molecular masses up to approximately 1500 Da followed by the aliphatic and aromatic components. Amino acids with a range of molecular weights were also identified in the mixture. The summation of the individual slices from the DOSY experiment closely resembles the conventional 1H spectra of the material, indicating that the components identified with DOSY represent all the components present in the mixture. The separation of components in the mixture in organic solvent supports new findings that fulvic and humic acids are not cross-linked, high molecular weight macromolecules but are instead aggregates composed of relatively simple molecules that take on colloidal properties in the presence of metal ions in aqueous solution. Using the knowledge that these organic mixtures are combinations of relatively simple entities with well-documented reactivities and behavior will improve our ability to predict and model their interactions and fate under natural conditions.