Applications of inverse chromatography in organic geochemistry—I. Characterization of polar solute-soil organic matter interactions by high performance liquid chromatography

In order to more fully understand the role of soil and sedimentary organic matter (SOM) in the migration and fate of organic pollutants in aquatic systems, a fast and accurate liquid chromatography method has been developed for the determination of sorption isotherms. The method is a modified Frontal Analysis by Characteristic Point (FACP) technique which accounts for hydrodynamic dispersion and which uses conventional HPLC equipment coupled with commercially available chromatography software. We have used this technique to generate sorption isotherms for various fractions of the total SOM. Isotherms are then fit to the Freundlich equation, from which water-organic carbon distribution coefficients (Koc values) can be calculated. In this presentation we report on our studies of the roles played by various fractions of soil organic matter (lipids, humic/fulvic acids and humin) in the overall sorption process. By using solute probes which interact with solid phases in well-defined ways, we have been able to determine the contributions of acidic, basic and dipolar sites in the various SOM fractions as well as the contribution of nonspecific hydrophobic partitioning, in the sorption of nonionic, polar organic solutes. It appears that these solutes interact with soil organic matter primarily through specific interactions with active sites in the humin fraction of the organic matrix, although there is some hydrophobic partitioning into the lipid fraction as well.