Pyrolysis gas chromatography - mass spectrometry of humic substances extracted from Canadian lake sediments

Humic substances (HS) were extracted with the aid of 0.1 M Na sub(4)P sub(2)O sub(7) and 0.5 M NaOH solutions from the sediments of four lakes located in the Sudbury area in Ontario, Canada, namely, Tilton, Clearwater, Silver and Ramsey Lake. The humic acid (HA) and fulvic acid (FA) extracts, purified and characterized using classical methods i.e., elemental analysis, FTIR spectroscopy, and CPMAS super(13)C NMR (see N. Belzile, H.A. Joly, and H. Li. (1997)), were submitted to pyrolysis - gas chromatography - mass spectrometry (Py-GC-MS). The pyrolysates of the HA and FA extracts were found to be complex mixtures of at least 200 compounds. Results based on statistical analysis of the abundances of pyrolysis products (of known origin) revealed trends similar to those obtained from the classical bulk characterization techniques. The Py-GC-MS technique supported the observation, obtained from classical methods, that the chemical composition of HA extracts varied less significantly among the four lake sediments than for the FA extracts. The abundances of lignin and carbohydrate pyrolysates showed the highest variation among the FA extracts. Pyrolysis products originating from lignin, carbohydrates, proteins, and fatty acids were identified.Original Abstract: On a extrait des substances humiques (SH) a laide de solutions de Na sub(4)P sub(2)O sub(7) 0,1 M et de NaOH 0,5 M, a partir des sediments de quatre lacs situes dans la region de Sudbury, en Ontario, Canada, a savoir, des lacs Tilton, Clearwater, Silver et Ramsey. Les acides humiques (AH) et fulviques (AF) isoles ont ete purifies et caracterises a laide de methodes classiques, comme lanalyse elementaire, la spectroscopie IR a TF, et la RMN du super(13)C a langle magique (A" CPMAS A") (voir: N. Belzile, H.A. Joly et H. Li. (1997)) avant detre soumis a une pyrolyse couplee a de la chromatographie gazeuse et a de la spectrometrie de masse (Py-CG-SM). On a trouve que les pyrolysats des AH et AF extraits sont des melanges complexes formes dau moins 200 composes. Des resultats qui reposent sur une analyse statistique des abondances des produits de pyrolyse (dorigine connue) mettent en evidence des tendances semblables a celles obtenues a partir de techniques de caracterisation classique de la masse. Les resultats obtenus a laide de la technique de la Py-CG-SM sont en accord avec ceux obtenus a laide de methodes classiques, selon lesquels la variation dans la composition chimique des AH extraits est moins importan