FLASH PYROLYSIS AND IN-SITU METHYLATION OF HUMIC ACIDS FROM SOIL

Conventional flash pyrolysis-gas chromatography-mass spectrometry has traditionally been used for the characterization of complex geological substances such as humic materials, but the technique appears to provide a biased representation of the structural components of very polar materials such as humic substances, probably because the polar compounds have insufficient volatility to be analyzed efficiently by gas chromatography. A new technique of in situ methylation (ISM) with tetramethyl ammonium hydroxide, introduced for oxygenated polymers, is applied to humic substances and shown to yield methylated products believed to be more characteristic of the structural components of these polar macromolecules from soils than are data from conventional pyrolysis without methylation. The discovery of benzenecarboxylic acids and long-chain aliphatic acids as the predominant constituents of three humic acids in ISM pyrolysis indicates that a reevaluation of recent structural models of humic acids which are based on conventional pyrolysis studies is in order.