Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Advances in Procedures for the Isolation and Fractionation of Humic Substances

Authors
item Clapp, Charles
item Hayes, Mhb - UNIVERSITY OF LIMERICK

Submitted to: International Humic Substances Society Conference
Publication Type: Proceedings
Publication Acceptance Date: October 23, 2000
Publication Date: N/A

Interpretive Summary: Organic materials in soils are made up of a combination of components in close association. Among individual components of the organic matter are the humic substances -humic acid, fulvic acid, and humin. These are especially important because they are the most active agents for binding soil particles (aggregation) and for transporting chemical pollutants (pesticides). Results using "finger-print" methods (NMR and FTIR) and naturally-occurring isotopes of carbon and nitrogen show differences in the humic substances as to plant or microbial origin. By isolating, fractionating, and characterizing these components, we are able to uncover the processes by which they carry out their activities. Impact from this research will be felt by scientists, farmers, environmentalists, and the general public, all who have a stake in preserving both environmental quality of agricultural ecosystems, and in maintaining profitable farming operations.

Technical Abstract: The classical procedures for the isolation of humic substances (HS) from soils use basic solutions and solutions of metal complexing agents, especially sodium pyrophosphate. Adaptations to soil HS of XAD-8 [(poly)methylmethacrylate] resin technology used for the isolation of HS from waters has led to procedures that remove saccharide and peptide components in the HS fractions, and the 'true' HS to be recovered. Meaningful studies of compositions and aspects of the structures of HS require that the components are fractionated. Charge density, molecular sizes, and polarity differences are effective properties on which to base separations procedures. Appropriate use is made of exhaustive sequential extraction processes, culminating in applications of dipolar aprotic solvents (containing acid). Our recent studies have shown that applications of a diversity of isolation and fractionation procedures can provide humic fractions that give compositional and structural data that are meaningful. By means of 2-D (solution state) NMR we have resolved some of the connectivities that are fundamental in humic structures. There will be little point in attempting to obtain a detailed resolution of structure, but it should be possible to get advanced information about the component molecules and connectivities that are fundamental to humic structures.

Last Modified: 10/22/2014