Contribution à l'étude structurale par PY/CG-SM de la matière organique liée aux particules fines (0-50 µm) dans quelques sols sous formations naturelles de longue durée au Burkina Faso

Contribution to the study by PY/GC-MS of organic matter linked to fine particles (0-50 µm) in some soils under long-term natural formations in Burkina Faso. The study aims to enhance the knowledge on organic matter of Arenosols, Ferralsols, and Cambisols in Burkina Faso. It deals with the distribution of C and N in three particles size fractions and is focused on the structures of organic matter linked to the (0-50 µm) fraction. The results showed that total organic matter was lower than 2% in all soil units. More than 70% of total carbon were held by the finest fraction. The main products released by PY/GC-MS technique of the (0-50 µm) fraction were lignin derived compounds, non lignin derived aromatic compounds, carbohydrates derived compounds, fatty acids methyl esters and nitrogen derived compounds. The aliphatic compounds ranged from C12 to C18, C16 being the dominant one. The aliphatic compounds were negatively correlated with the aromatic compounds. A positive correlation was observed between the nitrogen derived compounds and the amounts of clay. On the other hand, the carbohydrates derived compounds were negatively correlated with clay particles. Furthermore, the study pointed out some different structures of lignin such as syringyl, guaiacyl, and p.hydrophenyl. Depending on the nature of wood (hard wood, soft wood and grasses), they reflected the composition of vegetation on the studied sites. Therefore, PY/GC-MS technique was efficient for structural characterization of low amounts of soil organic matter

Structural characterization of humic acids, extracted from sewage sludge during composting, by thermochemolysis–gas chromatography–mass spectrometry

Thermochemolysis coupled with gas chromatography and mass spectrometry were applied to determine the structure of humic acids (HA) extracted from a sewage sludge and straw mixture at different steps of composting. The HA extracted from sludge mixture released various compounds, such as mono-, di-, tri-methoxy (alkyl) benzene and (alkyl) benzoic acids, which originated from lignin like derivatives of phydroxyphenyl, guiaicyl and syringyl units. In addition, other aromatic non-lignin derived structures were found along with series of branched C15, linear C16, C18 fatty acid methyl esters. The follow-up of various lignin-derived units during composting shows a decrease in phydroxyphenyl type-compounds (C) after the stabilisation phase. In parallel the more oxidized units, derived from guaiacyl (G) and syringyl (S) units, corresponding mainly to methylated derivatives of cafeic acids, protocatechuic acids, gallic acids and aldehydes, significantly increased in comparison with the other aromatic structures. Various ratios commonly used as parameters to determine the degree of lignin decomposition during humification were followed to monitor the chemical structure changes of the HA extracted from sludge mixture during composting. In the present case, the S/G ratio did not present significant changes during composting. The acid/aldehyde ratio was supervised using the ratio of gallic acids to gallic aldehyde methylated derivatives and showed an increase from 0.73 to 2.13 after the stabilisation phase but a decrease to 0.93 at the end of composting. This evolution may be explained by the increase of acid-containing derivatives following the intense oxidation of lignin side-chains during the stabilisation phase. But, the decrease of the acid/aldehyde ratio during the maturation phase could be attributed to a decrease in acid units by polymerisation of benzoic acid type-compounds through ester/ether linkages. The follow up of six families of compounds of similar chemical structures during composting showed a decrease of lignin-type compounds C6–C3 and that C6–C1 units predominated in the humic acid isolated from end compost sludge. The fatty acid methyl esters showed an increase in the intermediate phase of composting probably originating from the activities and tissues of microorganisms, which are numerous during the process. The final decrease in the amount of fatty acids may be explained by the death of most of the microbial population at the end of composting typified by a low respiratory rate. The index of Shannon-Weaver (Ish) remained constant at about 3 in course of composting indicating the neoformation of HA from subunits of similar chemical nature. A similitude index (Sij, S0 i j) showed a split between 30 and 90 days of composting indicating a change in the rate of neoformation of HA after a stabilisation phase. Afterwards, the rate of HA neoformation varied linearly with the duration of composting

Structural characterization of fulvic acids, extracted from sewage sludge during composting, by thermochemolysis–gas chromatography–mass spectrometry

Thermochemolysis coupled with gas chromatography and mass spectrometry were applied to determine the chemical structure of fulvic acids (FA) extracted from a sewage sludge and straw mixture at different steps of composting. The FA starting structures were composed mainly of mono-, di- and tri-methoxy (alkyl) benzoic acids representing lignin derivatives in an advanced stage of oxidation, as well as of methylated polyphenols and a series of fatty acids saturated C15, C16, C18, unsaturated and branched C18:1. Besides, there are many unidentified structures suspected to be N-containing compounds. During the composting process, the fate of the three structural typical monomer units of lignin was followed. The p-hydroxyphenyl units showed a strong relative decrease especially at the beginning of composting. The guiaicyl units showed a steady increase in course of composting. A relative decrease of syringyl units was noted at the beginning of composting, but they then relatively increased towards the end of composting. These changes support the formation during composting of more oxidized units. All subunits composing the fulvic acid structures have been subdivided into main five groups of similar chemical structure. The lignin-like C6–C3 subunits showed a relative decrease during composting attributed to microbial oxidation, but there was a relative increase during the intermediate step of composting related probably of an enhancing of lignin solubility. The C6–C1 subunits were reduced at the beginning of composting, which mainly attributed to the oxidation of 4-methoxybenzaldehyde to hydroquinones derivatives under the composting conditions. Although, the relative increase of these subunits (C6–C1) at the end of composting originates from oxidation of C6–C3 lignin side-chains or could be partly attributed to microbial neosynthesis. The unidentified N-containing compounds increased strongly during course of composting. The rise in the level of fatty acids at the beginning of composting is attributed to an increase of branched-chain fatty acids such as C18:1 commonly used as bacterial biomarkers. Their amounts were greatly reduced at the end of composting. Both the Shannon–Weaver and similitude indices show a relative increase in structural diversity at the start of composting conditions following the appearance of hydroquinone derivatives and unidentified nitrogen compounds in the FA network. But, the produced FA structure reaches a certain level of homogeneity at the end of composting through self-polycondensation or recombination of C6–C1 subunits and hydroquinones derivatives with N-containing compounds

Tetramethylammonium hydroxide thermochemolysis for the analysis of cellulose and free carbohydrates in a peatbog

International audienceWe have compared TMAH thermochemolysis with the classical method using acid hydrolysis for carbohydrates analysis in a peat core. Even if TMAH thermochemolysis does not analyse hemicellulosic carbohydrates and discriminate each individual carbohydrate sensu stricto, it allows the analysis of a cellulose pool hidden to acid hydrolysis and the specific analysis of free and terminal carbohydrates. Simple direct comparisons of thermochemolysis data with data generated from acid hydrolysis cannot be done because of the different mechanisms involved in each process. TMAH thermochemolysis must be viewed and used as a pertinent and complementary method for the analysis of carbohydrates protected and trapped by the organic matter in complex environmental systems

Micromorphological and chemical investigation of late-Viking age grave fills at Hofstaðir, Iceland

Grave fills from seven human burials from a late-Viking age - early medieval cemetery at Hofstaðir, Mývatnssveit (Iceland) were examined by soil micromorphology and organic chemical analysis. Detailed analysis of the weathering of the mineral constituents of the grave fills demonstrates a relationship between the extent of weathering of volcanic silicates within the fills and the presence of buried human remains. Gas chromatography-mass spectrometry (GC–MS) of extracts from the fills and controls of two graves revealed organic signatures dominated by plant-derived organic matter, with no evidence of degradation products of the body tissues. Transformation of n-alkanes into n-alkan-2-ones provides evidence for microbial activity within the fills. GC–MS analysis of the organic extract from under one of the skulls and pyrolysis gas chromatography of wood fragments found in that grave provide compelling evidence for the former presence of a conifer wood coffin. The use of this non-native wood in the burial provides evidence for either the import of foreign lumber or the utilisation of driftwood, most likely originating from Russia/Siberia