TuP-22
GC-MS DETERMINATION OF NON-POLYMERIC HUMIC ACID COMPONENTS
Michael Susic
Australian Institute of Marine Science, P.M.B. No.3, Townsville M.C., Qld 4810
Humic acid properties depend on their composition, which can be very complex, and includes small molecules amenable to GC analysis. When formed by humic acid degradation, these small molecules can give vital clues about humic acid structures. MS detection is essential to discriminate coeluted components and to positively identify individual components. Humic acids extracted from soils, plants, fungi and seagrasses contained minor amounts (<1% w/w) of aromatic and aliphatic acids. Mild oxidation of humic acids with hydrogen peroxide in dilute sodium hydroxide gave mainly oxalic, malonic, succinic, maleic, fumaric and malic acids, indicating that humic acids are aliphatic polymers. Samples from lignin-containing sources contained p-hydroxy benzoic, vanillic and syringic acids, lignin oxidation products. Samples from non-lignin-containing sources did not contain these aromatic acids, but had numerous dicarboxylic and long-chain fatty acids. The dicarboxylic acids result from the oxidation of humic acids, either at their source or during the esterification step for GC analysis. Small amounts of levulinic acid (derived from glucose oxidation), glycerol (derived from lipid hydrolysis), benzyl alcohol, citric acid and 3-hydroxy-3-methyl-glutaric acid were also detected.