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Application of Py-Gc/Ms to Study Changes in the Organic Matter ff Macro- and Microaggregates of A Mediterranean Soil upon Heating

AuthorsCampo, Julián ; Cammeraat, E.; Andreu Pérez, V. ; Rubio, José Luis
Issue DateSep-2010
PublisherSociedad Española de Cromatografía y Técnicas Afines
Citation28th International Symposium on Chromatography (2010)
AbstractThe study of the changes in soil organic matter (SOM) composition has made great progress due to the use of techniques such as solid-state nuclear magnetic resonance (NMR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), thermally assisted hydrolysis and methylation (THM), etc. Field and laboratory studies applying 13C and 15N NMR indicate that the thermal modifications of organic matter duríng charring include dehydration, aromatization, loss of methoxylic and carboxylic functional groups, condensation of carbohydrates into furan-like structures and enrichment of heterocyclic aromatic N-compounds. In terms of spectroscopic properties, the effect of heating on SOM leads to the loss of the O-alkyl and di-O-alkyl structures that dominate wood and a large increase in aromatic C. The Py-GC/MS is an alternative approach that involves thermal degradation of organic molecules into small fragments that are analyzed by GC/MS. providing information related to their structure. According to some researchers. pyrolysis products released by unburned soils include a wide variety of molecules arising Irom carbohydrates. lignin, lipids and proteins. On the contrary, in soils affected by wildfires, most of the pyrolysis products present in unburned soils are absent and the dominance of charred >non-pyrolysable> refractory carbonaceous material is evident. The composition of a Mediterranean soil organic matter was studied in two different fractions (macro-and microaggregates) and in two environments (soil under canopy of Quercus coccilera and bare soil between plants). Samples were heated under laboratory conditions at different temperatures (220, 380 and 5000 C) to establish their effects on the SOM quality by comparison with unheated or control samples (250 C). The organic matter extracted with NaOH had a similar composition, as analyzed by Py-GC/MS, in macro-and microaggregates of control samples, both under canopy and on bare soil. Obtained pyrolysates were characterized by the presence of polyphenol and other aromatic pyrolysis products (lipids and some polysaccharides derivatives, proteins and lignin). Some of these products, together with the presence of black carbon (BC) markers, confirmed the occurrence of past wildfires in the study zone. The composition of the organic matter, extracted Irom the soils heated at 2200 C, was quite similar to that obtained from unheated soils. Changes in SOM characterization started at 3800 C when the products derived from polysaccharides and lignin, and some coming from polyphenols, were not detected in the pyrolysates suggesting that labile organic matter was likely destroyed by the high temperatures. The lower proportion of pyrolysed material detected at 380 and 5000 C could be partly due to selective enrichment of heat-resistant aromatic components.
DescriptionPonencia presentada en el 28th International Symposium on Chromatography celebrado en Valencia del 12 al 16 de septiembre de 2010
Appears in Collections:(CIDE) Comunicaciones congresos
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