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

Diffusion ordered spectroscopy (DOSY) was applied to two extracts of organi c 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-d(6) and D2O. On average, sugar components were identified as the largest molecules in solution, with molecular masses up to similar to 1500 Da followed by the aliphatic and aromatic components. Amino acids with a ra nge of molecular weights were also identified in the mixture. The summation of the individual slices from the DOSY experiment closely resembles the co nventional H-1 spectra of the material, indicating that the components iden tified with DOSY represent all the components present in the mixture. The s eparation of components in the mixture in organic solvent supports new find ings that fulvic and humic acids are not cross-linked, high molecular weigh t macromolecules but are instead aggregates composed of relatively simple m olecules that take on colloidal properties in the presence of metal ions in aqueous solution. Using the knowledge that these organic mixtures are comb inations of relatively simple entities with well-documented reactivities an d behavior will improve our ability to predict and model their interactions and fate under natural conditions.