NMR CHARACTERIZATION OF HUMIC-ACID FRACTIONS FROM DIFFERENT PHILIPPINE SOILS AND SEDIMENTS

Humic acids from a peat soil, an agricultural soil and a lake sediment from the Philippines were fractioned by sorption chromatography on cross-linked dextran gels (Sephadex1 1 Use of tradenames is for identification purposes only, and does not constitute endorsement by the U.S. Geological Survey.). The NMR spectra of these fractions have sharp, well resolved bands which can be attributed to lignin-like structures, carbohydrates and aliphatic groups. Similar bands have been observed in the NMR spectra of humic acid fractions from other environments; however, the chemical shifts of some of the lines vary from one humic acid to another. These lines appear to arise from well defined, partially decomposed plant components and probably are diagnostic of the types of plants that decomposed into these humic acids. The lines in the carbohydrate region are the best resolved and may prove to be the most useful in identifying the plant precursors of any particular humic acid fraction. © 1990.