Comparative study of two fractions of riverine dissolved organic matter using various analytical pyrolytic methods and a 13C CP/MAS NMR approach

Two fractions of dissolved organic matter (DOM) from a French river, the Gartempe, were obtained using the XAD resin fractionation procedure and were termed hydrophobic acid (HPOA) and transphilic acid (TPIA) according to this method. The composition of these two fractions was investigated with solid state CP/MAS C-13 NMR, Curie point pyrolysis at 650 degrees C, with and without tetramethylammonium hydroxide (TMAH), and off-line TMAH thermochemolysis at 250 degrees C. Separation and identification of the released compounds were performed using gas-chromatography/mass spectrometry (GC/MS). The combination of these techniques allowed determination of the molecular characteristics of each fraction and showed large differences in composition. Solid state CP/MAS C-13 NMR revealed a major contribution of lignin-derived units to the hydrophobic acid fraction and the predominance of cellulose in the transphilic acid fraction. Identification of specific molecular structures upon conventional on-line pyrolysis revealed a predominantly lignin type origin for the HPOA fraction and a cellulose one for the TPIA fraction, whereas on-line TMAH/pyrolysis confirmed the presence of acids, phenolic acids and aliphatic diacids, also indicated by solid state CP/MAS 13C NMR in both fractions. Off-line TMAH thermochemolysis was determinant for evidencing the presence of amino acids. (c) 2005 Elsevier Ltd. All rights reserved.