Structural study of soil humic acids and humin using a new preparative thermochemolysis technique

Humic acids and humin from an acidic soil from Plateau de Millevaches in France were investigated in their ester and ether groups. A new preparative thermochemolysis technique was used, in comparison with a classical determination based on chemical degradation methods. This technique allows the treatment of a high quantity of product (similar to 2 g). Preparative TMAH thermochemolysis of humin and humic acids yields various hydrocarbons (alkene/alkane doublets, sterenes, hopenes and hopanes), methyl esters of linear and branched fatty acids, linear dicarboxylic acids, omega-methoxy fatty acids and 1-methoxyalkanes. These components are found to derive mainly from ester- and ether-bond cleavage, as demonstrated by specific chemical degradations. The results confirms that important structural differences do exist between totally insoluble humin and humic acids. (C) 1998 Elsevier Science B.V. All rights reserved.