Quantitative comparison of the nitrogen-containing pyrolysis products and amino acid composition of soil humic acids

Pyrrole and acetonitrile, major pyrolysis products of soil humic substances, vary characteristically in abundance with the degree of humification of the organic matter in the soil. Their origin, however, is uncertain because of the large amount of unidentifiable soil nitrogen. A quantitative relationship between amino acid composition and pyrrole and acetonitrile abundances has been established by Curie-point pyrolysis-gas chromatography of a group of test proteins, using polystyrene as an internal standard. The pyrolysis yields of these products from three humic acids extracted from the surface horizons of Scottish brown forest soils (Cambisols or Ochrepts) were entirely accounted for by the known hydrolysable amino acid content and composition, and the products were related to individual amino acids. The peptide amino acid was also found to be the overall source of the aromatic pyrolysis products toluene, phenol and p-cresol.