AN “AVERAGE” STRUCTURE PROPOSED FOR SOIL FULVIC ACID AIDED BY DEPT/QUAT 13C NMR PULSE TECHNIQUES

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Abstract
A soil fulvic acid was extracted from topsoil of the Okchun Basin, Republic of Korea, and purified and characterized by chemical methods (elemental analysis, number averaged molecular weight) and by 13C and 1H NMR spectroscopy. An “average” structure of a soil fulvic acid has been developed by modifying one of the structural models proposed for Suwannee River fulvic acid, IHSS (International Humic Substances Society) reference sample, based on comparative chemical and NMR data. The assignment of the structural moieties was facilitated by the use of a set of 13C NMR subspectra of the CHn (n = 0 to 3) groups, obtained by distortionless enhancement by polarization transfer (DEPT) pulse sequence and the quaternary-only carbon spectra (QUAT) under quantitative conditions. The nature of metal binding sites on such soil fulvic acid molecule is discussed.