Thermal release of nitrogen organics from natural organic matter using micro scale sealed vessel pyrolysis

Abstract

Characterisation of recent organic matter such as aquatic natural organic matter (NOM) can be aided by the artificial maturation provided by closed system, micro scale sealed vessel (MSSV) pyrolysis. Gas chromatography–mass spectrometry (GC–MS) analysis of the products released via MSSV pyrolysis of several NOM fractions showed complex and varied product distributions that included a range of nitrogen-containing organic products (N organics) such as pyrroles, pyridines, pyrazines, indoles and carbazoles. N organics were found in highest abundance in the products from the transphilic and colloid fractions of NOM. A larger number and great abundance of N organics were detected with MSSV pyrolysis than with flash pyrolysis of the same samples. To better understand the sources of N organic products detected with MSSV pyrolysis of NOM, the distinctive N pyrolysate distributions from several likely precursors (i.e. peptide, amino sugar, porphyrin and a cultured bacterium) of dissolved organic nitrogen are reported. A number of qualitative distinctions between these precursors were evident, such as high abundances of C 1–3 pyrroles from the amino sugar and C 4–5 pyrroles from the porphyrin. The thermal profile of the N organic products from the pentaglycine and porphyrin standards was established by analysing these samples using several different MSSV temperatures. The abundance of the N organics in most pyrolysates increased with temperature, but the relatively constant ratio of particular N organic product abundances (e.g. ethyl dimethyl pyrrole/diethyl methyl pyrrole) suggests these may be useful for source distinction across a broad range of thermal analytical conditions.