The structural characterization of humic acids (HAs) is a focal point in understanding and establishing a relationship between their structure and biological properties. However, the complexity of HAs seriously limits the application of a single analytical technique. For a better understanding of HAs role in the environment, it is necessary to develop methods which can provide a complete characterization of HA structure. Humic acid extracted from the A horizon of a Chernozem (Boroll, USDA Soil Taxonomy) soil and their fractions (A, B and C+D) with different molecular size (MS) obtained by coupling size exclusion chromatography and polyacrylamide gel electrophoresis (SEC-PAGE) were investigated using thermal (TG-DTA), spectroscopic (DRIFT) and isotopic ( d 13C) analyses. Moreover, the molecular structure of the high temperature stable fraction (residues obtained by stopping the heating of the sample in TG-DTA apparatus at 400°C) was studied by DRIFT spectroscopy. The highest MS fraction (A) were characterized by the highest contents of aliphatic, carboxyl groups, carbohydrates and amino acids than the B and C+D fractions. Instead, the C+D fraction, that was 36% of HA (w/w), seems to be characterized by a higher content in aromatic compounds, in particular in benzoic derivatives, than the other fractions. A shift of δ 13C to more negative values was observed in the lowest MS fractions (B and C+D). The aromatic structure of A and B residues seems to be more complex than that of C+D residue.
Thermal and Spectroscopic Analyses applied to the study of different molecular size humic acids
MONTECCHIO, DANIELA;CAVANI, LUCIANO;GIOACCHINI, PAOLA;FRANCIOSO, ORNELLA;CIAVATTA, CLAUDIO
2009
Abstract
The structural characterization of humic acids (HAs) is a focal point in understanding and establishing a relationship between their structure and biological properties. However, the complexity of HAs seriously limits the application of a single analytical technique. For a better understanding of HAs role in the environment, it is necessary to develop methods which can provide a complete characterization of HA structure. Humic acid extracted from the A horizon of a Chernozem (Boroll, USDA Soil Taxonomy) soil and their fractions (A, B and C+D) with different molecular size (MS) obtained by coupling size exclusion chromatography and polyacrylamide gel electrophoresis (SEC-PAGE) were investigated using thermal (TG-DTA), spectroscopic (DRIFT) and isotopic ( d 13C) analyses. Moreover, the molecular structure of the high temperature stable fraction (residues obtained by stopping the heating of the sample in TG-DTA apparatus at 400°C) was studied by DRIFT spectroscopy. The highest MS fraction (A) were characterized by the highest contents of aliphatic, carboxyl groups, carbohydrates and amino acids than the B and C+D fractions. Instead, the C+D fraction, that was 36% of HA (w/w), seems to be characterized by a higher content in aromatic compounds, in particular in benzoic derivatives, than the other fractions. A shift of δ 13C to more negative values was observed in the lowest MS fractions (B and C+D). The aromatic structure of A and B residues seems to be more complex than that of C+D residue.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
