Popular names of crude drugs

Abstract

Molecular identification of aged black carbon (BC) is problematic owing to potential interference of non-charred aromatic organic matter and to a general lack of techniques that are capable of providing detailed chemistry of it. Pyrolysis-GC/MS is thought to be unsuitable for analysis of BC because the pyrolysis step itself causes molecular rearrangements that may interfere with the thermal modifications by natural burning, and because a significant fraction of BC is not pyrolysable.We optimised a coil probe pyrolysis method for BC by analysing both a lignin-rich peat sample and an aged legume-derived charcoal at various temperatures (400–1200 °C). Pyrolysis at 750 °C for 10 s combined acceptable thermal modifications to the pyrolysed peat with high-quality chromatograms from charcoal.Using this method we analysed 91 samples of up to >11,000 yrs old oak, birch and legume charcoal from a colluvial soil in NW Spain. The charcoal produced a large suite of aromatic compounds that can be considered characteristic of BC in this study: benzene, toluene, PAHs (naphthalene, biphenyl, fluorene and phenanthrene) and N- and O-containing (poly)aromatics (e.g. dibenzofuran and benzonitrile). A series of N-containing compounds that had not been previously reported in charcoal pyrolysates were found (C1-benzoxazole, benzene dicarbonitriles, 2-phenylpyridine, naphthalenecarbonitrile, 2-biphenylcarbonitrile). Small amounts of short-chain n-alkane/n-alkene pairs indicated some aliphatic material had survived the fire. Uncharred or weakly charred carbohydrate substances in the charcoal were identified as levoglucosan, levoglucosenone, furans and furaldehydes.Charcoal fragments from different plants produced similar pyrolysates. Markers of ‘thermolabile’ (non-charred or weakly charred) biomass disappeared as sample age increased. Nonetheless, signal intensity improved with age, suggesting that the pyrolysability of the relatively ‘thermostable’ (condensed) BC fraction increased. We postulate that gradual oxidation of the condensed aromatic backbone of BC enhanced its susceptibility to pyrolysis.