Analytical pyrolysis as a tool for the characterization of natural organic matter -: A comparison of different approaches

A substantial fraction of natural organic matter (NOM) consists of complex mixtures of macromolecular compounds. As a result, high-molecular weight fragments liberated during the pyrolysis of NOM often carry the most significant structural information. Their diagnostic value, however, is commonly limited by the preferential transfer of lower-boiling pyrolysis products to the GC column, compared to larger fragments. Non-discriminating pyrolysis is a technique that minimizes transfer losses of larger fragments, which is the problem with most conventional pyrolyzers. It allows a range of sample sizes from similar to 15 mg for the study of samples of low organic carbon content to estimated sub-microgram sizes for bacterial biomass. In this study, the performance of the non-discriminating pyrolysis system in the characterization of natural organic matter (NOM) was compared to the performance of a conventional Pt-filament pyrolyzer. In addition, a more limited comparison was carried out with a Curie-point system. A variety of organic materials were selected to serve as NOM models: chitin, peat, and organic matter isolated from tertiary sands. Nondiscriminating pyrolysis-GC/MS allowed for the observation of larger molecular fragments, such as traces of cholesterol in the pyrolysis of chitin. Also, the distribution of the homologous series such as that observed for alkyl benzenes was shifted towards higher molecular weight fragments with the non-discriminating system. Overall, the macromolecular structures within NOM were more pronounced when using non-discriminating pyrolysis, as shown by the higher abundance in the pyrograms of higher molecular weight fragments of various polyaromatic and long-chain aliphatic compounds. Characterization of NOM using non-discriminating Py-GC/MS reduces the ambiguity caused by mass discrimination against higher mass fragments compared to other pyrolysis approaches. This provides a better fingerprint of the organic material present in different sample types, including soils and sediments. (C) 2006 Elsevier B.V. All rights reserved.