Oxygen humic acid fraction

Spectra of fulvic acids must be interpreted carefully purification of this fraction leads to losses that can reach 50%. Comparison of spectra of different humic fractions of the same sample, such as a sediment from the Oman Sea (Fig. 6) illustrates several differences. Oxygenated functional groups are more important in fulvic and humic acids than in stable residues. Particularly important are the absorption bands at 3400 cm (OH from alcohols, acids, etc.), 1710 cm (C==0 from quinones, ketones, carboxylic acids), 1250 cm (C—O from alcohols, esters, ethers) and 1050 cm (C—O from carbohydrates). Absorption at 1050 cm is nearly absent in stable residues. Aliphatic content increases from fulvic acids to humic acids and stable residues (bands between 2870 and 2960 cm ) and the shape of the aliphatic bands (2900-2950 1450 1375) indicates that fulvic acids contain mainly CH groups. 

The third stage is incorporation into the sediment. Once these substances are incorporated into sediment and buried, oxygen and biota are no longer present. Fulvic acid, the smallest and most soluble fraction, decreases due to diffusion and mineralization. Humic acid undergoes insolubilization by defunctionalization and evolves with humin into the kerogen of ancient sediments. 

Rashid, M. A. and King, L. H. (1970). Major oxygen-containing functional groups present in humic and fulvic acid fractions isolated from contrasting marine environments. Geochim. Cosmochim. Acta 34, 193-201. 

Although widely ranging values for carboxyl content in humic substances have been reported, there is a general trend for fulvic acid fractions to have higher concentrations than humic acids. This is consistent with their higher oxygen content and greater water solubility. 

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