| Abstract
| - Irradiation (UV/Vis λ > 290 nm) under nitrogen andoxygen atmosphere significantly affected the structure ofdissolved humic material (DHM). Photobleaching of theDHM solution occurred essentially under O2 atmosphere inconjunction with a decrease in average molecularweight and an increase in acidity due to the disaggregationand photooxidation processes. The structural changeswere followed by various separation and analytical methodsincluding capillary zone electrophoresis (CZE), gelpermeation chromatography (GPC), Fourier transformationinfrared (FTIR), and one- and two-dimensional nuclearmagnetic resonance spectroscopy (NMR) as well as pyrolysis-field ionization mass spectrometry (Py-FIMS). Thestructural investigations showed selective degradations ofDHM, especially under oxygen atmosphere. Structuresof lignic and lipidic origin were the most photolabile ascompared to carbohydrates, alkylbenzenes, or N-containingstructures that accumulated in the system. Undernitrogen atmosphere the acids remained fairly stable.Indirect photolysis seems to be the major pathway indegradation of DHM subjected to UV/Vis irradiation.
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