Multi-method study of the characteristic chemical nature of aquatic humic substances isolated from the Han River, Korea

Natural organic matter (NOM) from the Han River, Korea was fractionated into humic and non-humic fractions by absorbing onto XAD-7HP, and these fractions were analyzed using UV-absorption, and for dissolved organic C (DOC). The humic fraction (i.e. humic substances; HS) was extracted and its characteristics were compared to commercial humic materials using various spectroscopic methods such as Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR) and fluorescence spectroscopy. The humic fraction as organic C was 47.0% on the average, however, a rainfall event brought a higher humic fraction into Han River water. The molar ratios of H/C and O/C in the HS from Han River water (HRHS) were 1.40 and 0.76, respectively, and the ratio of aliphatic to aromatic protons in the HS (PAl/PAr ratio) was 5.8. Aromaticity and humification degree (i.e., degree of condensation) of HRHS were relatively lower than those from other humic materials, while the portion of oxygenated functional groups was relatively higher. FT-IR, 1H-NMR and fluorescence spectroscopy showed distinct differences between HRHS and the commercial humic materials. Commercial humic materials are not representative of HS extracted from Han River water. The fluorescence spectra, relatively simple measurements, were found to be most useful as fingerprints for humic materials from particular sources.