Composition of size exclusion fractions of swamp water humic and fulvic acids as measured by solid state NMR and pyrolysis-gas chromatography-mass spectrometry

Organics from Neranie swamp water, collected from the Myall lakes district. New South Wales, Australia, have been fractionated by gel permeation chromatography and analysed by ¹³C nuclear magnetic resonance (NMR) spectroscopy and pyrolysis gas chromatography mass spectrometry (py GC MS). The results from these techniques demonstrate that: (1) low (M₁₁ < 5220 daltons) and high (M₁₁ > 74,830 daltons) weight average molecular weight humic acid fractions have aliphatic chains which are relatively unbranched compared to those humic acids fractions of intermediate molecular weight. (2) Alcoholic carbon, mainly as carbohydrates, is more predominant in the highest weight average molecular weight material, and carboxylic carbon is more predominant in molecules with M₁₁ 2800 8270 daltons. (3) If it is assumed that CP/MAS NMR data are at least semi-quantitative, polyoxyethers or unsaturated ethers account for as much as one half of the oxygen in humic low molecular weight (M₁₁ < 2900 daltons) materials. (4) Lignin related components of the fractions concentrate in the region M₁₁ = 74,830 27,930 daltons. If there are not multiple lignin sources, these data indicate that lignin degradation is somewhat selective about weak links. (5) The fulvic acids are more homogeneous, with different molecular weight fractions having similar structures.