Table 1.

Proposed composition of humic acid fractions separated using rapid fractionation technique (adapted from Buchanan et al. [9]).

Fraction	Organic compounds
Hydrophobic (VHA and SHA)
Acid	Soil fulvic acids, C5–C9 aliphatic carboxylic acids,1- and 2-ring aromatic carboxylic acids, 1- and 2-ring phenols
Base	1- and 2-ring aromatics (except pyridine), proteinaceoussubstances
Neutral	Mixture of hydrocarbons, >C5 aliphatic alcohols, amides, aldehydes, ketones, esters, >C9 aliphaticcarboxylic acids and amines, >3 ring aromatic carboxylic acids and amines
Hydrophilic (CHA and NEU)
Acid	Mixtures of hydroxy acids, C5 aliphatic carboxylic acids, Polyfunctional carboxylic acids
Base	Pyridine, amphoteric proteinaceous material (i.e., aliphatic amino acids, amino sugars, C9 aliphatic amines, peptides, and proteins)
Neutral	<C5 aliphatic alcohols, polyfunctional alcohols, short-chain aliphatic amines, amides, aldehydes, ketones, esters; cyclic amides, polysaccharides, and carbohydrates