STRUCTURAL STUDIES ON SOIL HUMIC ACIDS BY CURIE-POINT PYROLYSIS-GAS CHROMATOGRAPHY MASS-SPECTROMETRY

Humic acids (HAs) extracted from the Ap horizon of a Haplaquoll (Bainsville) and the Bh horizon of a Haplaquod (Armadale) were investigated by Curie-point pyrolysis (Cp Py)-gas chromatography (GC)/mass spectrometry (MS). More than 300 pyrolysis products, tentatively identified by conventional electron impact (EI) and field ionization (FI) MS, were common to both samples, although very different in their intensity distributions. Whereas the Armadale HA produced predominantly alkanes and olefins, the Bainsville HA yielded large quantities of phenol derivatives. Alkanes and olefins formed homologous series up to C30 and n-alkylbenzenes up to C-18. Of particular interest were the intense signals originating from aromatics and alkyl-substituted aromatics, especially phenol derivatives and methyl-substituted naphthalenes. In addition, heterocyclic compounds such as furans, pyrroles, and pyridines with and without alkyl substituents were also detected. Our data indicate the presence of aryl-alkyl structures in the HA network and contribute to a better understanding of the chemical composition and structure of soil organic matter (SOM).