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 front the Myall Lakes dis trict, New South Wales, Australia, have been fractionated by gel perme ation chromatography and analysed by C-13 nuclear magnetic resonance ( NMR) spectroscopy and pyrolysis-gas chromatography-mass spectrometry ( py-GC-MS). The results from these techniques demonstrate that: (1) low (<(M)over bar (w)> < 5220 daltons) and high (<(M)over bar (w)> > 74,8 30 daltons) weight average molecular weight humic acid fractions have aliphatic chains which are relatively unbranched compared to those hum ic acids fractions of intermediate molecular weight. (2) Alcoholic car bon, mainly as carbohydrates, is more predominant in the highest weigh t average molecular weight material, and carboxylic carbon is more pre dominant in molecules with <(M)over bar (w)> 2800-8270 daltons. (3) If it is assumed that CP/MAS NMR data are at least semi-quantitative, po lyoxyethers or unsaturated ethers account for as much as one half of t he oxygen in humic low molecular weight (<(M)over bar (w)> < 2900 dalt ons) materials. (4) Lignin related components of the fractions concent rate in the region <(M)over bar (w)> = 74,830-27,930 daltons. If there are not multiple lignin sources, these data indicate that lignin degr adation is somewhat selective about weak links. (5) The fulvic acids a re more homogeneous, with different molecular weight fractions having similar structures. Copyright (C) 1996 Elsevier Science Ltd