Fractionation and characterization of humic acid from a lake sediment

Abstract

Humic acid from a lake sediment was divided into five fractions by extraction with chloroform (Fr. 1), methyl ethyl ketone (Fr. 2), methanol (Fr. 3) dimethyl formamide (Fr. 4) and extraction residue (Fr. 5). The amount of each fraction is 2, 3, 7, 21 and 67 per cent, respectively. Each fraction was characterized by elementary composition, IR and NMR spectra. From Fr. 1 to Fr. 5, methylene, methyl and carboxyl bonds decrease, and ketone or quinone groups increase. Proteinous and carbohydrate-like organic substances are present in Frs. 3, 4 and 5. There is a linear relationship between color intensity of the fractions and their H/C ratio. These results suggest that the humic acid is composed of many intermediates of "humification" of plankton bodies. No direct evidence could be obtained for the presence of aromatic hydrogen in the fractions.