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Abstract
Because of the well-known molecular complexity and heterogeneity of natural organic
matter (NOM), an aquatic bulk NOM was fractionated into well-defined polyphenolic-rich
and carbohydrate-rich subfractions. These fractions were systematically characterized
by fluorescence emission, three dimensional excitation-emission matrices, and synchronous-scan
excitation spectroscopy in comparison with those of the reference International Humic
Substances Society soil humic acid and Suwannee River fulvic acid. Results indicate
that fluorescence spectroscopy can be useful to qualitatively differentiate not only
NOM compounds from varying origins but also NOM subcomponents with varying compositions
and functional properties. The polyphenolic-rich NOM-PP fraction exhibited a much
more intense fluorescence and a red shift of peak position in comparison with the
carbohydrate-rich NOM-CH fraction. Results also indicate that synchronous excitation
spectra were able to provide improved peak resolution and structural signatures such
as peak positioning, shift, and intensity among various NOM components as compared
with those of the emission and excitation spectra. In particular, the synchronous
spectral peak intensity and its red shift in the region of about 450-480 nm may be
used to indicate the presence or absence of high molecular weight and polycondensed
humic organic components, or the multicomponent nature of NOM or NOM subcomponents.