Direct Chemical Characterization of Dissolved Organic Matter in Water by Pyrolysis-Field Ionization Mass Spectrometry

The chemical composition of dissolved organic matter (DOM) in the leachates of moder profiles under mixed pine and oak forests was investigated by temperature-resolved pyrolysis-field ionization mass spectrometry (Py-FIMS). The FI-mass spectra of the freeze-dried samples from the 35- and 140-year-old forests show dinstict differences. Temperature-resolved Py-FIMS indicates several steps of thermodesorption and thermal degradation of the organic materials due to free and chemically bound constituents. In the first step, these constituents are non-carbohydrate aliphatics volatilized between 100 and 200°C. In the following steps of thermal evolution, carbohydrates, amino acids/peptides/proteins, and glycolipids are observed between 200 and 350°C, followed by lignin subunits between 280 and 350°C. Finally aromatic degradation products are recorded between 350 and 630C.