Comparison of degradation state and stability of different humic acids by means of chemolysis with tetramethylammonium hydroxide.
In the chemolysis products of extracted humic acids (HAs) and tetramethylammonium hydroxide, different compounds can be identified which allow a description of the sources of soil organic matter (SOM). It is possible to draw conclusions concerning stability, degree of intramolecular cross-linking and degradation of aliphatic and lignin components from the distinctive product ratios. The ratio of lignin derived acidic phenolic derivatives and their analogous aldehydes and the ratio of phenylpropenoic acids and analogous benzoic acids provide comparably good parameters for the characterization of the state of degradation of lignin compounds to relatively stable HA building blocks. Regarding the aliphatic chemolysis products, alpha,omega-dicarboxylic acid and methoxy fatty acid contents indicate an intramolecular cross-linking state within the HA molecules and the degree of stable aliphatic constituent parts. High contents of unsaturated fatty acids can be considered as an indicator of an easy degradable humic skeleton because with their double bonds they represent active sites for further transformations. The suitability of the carbon preference index as an indicator of a biogenic carbon source can be confirmed. It is remarkable how the results obtained from extracted humic acids are in accordance with the expectations for the different SOMs derived from land use.
Institute of Physical Chemistry and Theoretical Chemistry, University of Potsdam, Am Neuen Palais, Germany.
M
M
Grote
S
S
Klinnert
W
W
Bechmann
D005227:Fatty Acids / Q000378:metabolism; D005731:Ganglionic Stimulants / Q000494:pharmacology*; D006812:Humic Substances / Q000378:metabolism* / Q000493:pharmacokinetics; D008031:Lignin / Q000378:metabolism; D009930:Organic Chemicals / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D012989:Soil Pollutants / Q000378:metabolism* / Q000493:pharmacokinetics
D005227:Fatty Acids; D005731:Ganglionic Stimulants; D006812:Humic Substances; D009930:Organic Chemicals; D000644:Quaternary Ammonium Compounds; D012989:Soil Pollutants; D008031:Lignin; C027917:tetramethylammonium