Thermochemolysis of genetically different soil humic acids and their fractions obtained by tandem size exclusion chromatography–polyacrylamide gel electrophoresis

Humic acids (HA) from soils of very different origin and bioclimatic conditions (podzoluvisol, phasozem, chernozem, and ferralsol) were fractionated by coupling size-exclusion chromatography and polyacrylamide gel electrophoresis (tandem SEC–PAGE). From each HA, three fractions—A, B, and C+D, with different molecular sizes and electrophoretic mobilities—were obtained and analysed by thermochemolysis, the products being identified subsequently by gas chromatography/mass spectrometry. Regardless of HA origin, fraction A contained considerably more n-fatty acids and n-alkanes derived from plant waxes than did fractions B and C+D. Lignins accumulated mainly in fractions B and C+D. These results show that tandem SEC–PAGE allowed the separation of soil HA into fractions enriched in different structural components whose distribution was independent of HA genesis.