The "blue shift" of emission maximum and the fluorescence quantum yield as quantitative spectral characteristics of dissolved humic substances|
Daria Shubina, Elena Fedoseeva, Olga Gorshkova, Svetlana Patsaeva, Vera Terekhova, Mikhail Timofeev, and Viktor Yuzhakov
Humic substances (HS) play important roles in a variety of biogeochemical
processes. Fluorescence spectra can be used for quantitative and qualitative
characterisation of water-soluble humic substances (HS)
and, in particular, of dissolved organic matter (DOM) in water. In this study,
we measured the fluorescence spectra of natural HS (riverine,
lake, marine water, and soil aqueous extractions) and commercial water-soluble
HS under excitation from 270 to 355 nm. Natural water samples were filtered in
two stages by micro- and ultra-filtration. After ultra-filtration, DOM was separated
into two fractions depending on the size of the particles, for which
fluorescence spectra were also obtained. The comparative analysis was made with
a focus on the so-called "blue shift" (emission maximum shifts towards shorter
wavelengths with increasing excitation wavelength) and the fluorescence quantum
yield (QY) of samples of different origin. The fluorescence quantum yield under
excitation at 355 nm for commercial HS (QY=0.008) was less than that for
natural water DOM (QY=0.028), but more than for soil HS (QY=0.003). The low
molecular weight fraction quantum yield was bigger than that for the colloidal
fraction by 20-30%. The fluorescence quantum yield for natural water and for
soil extractions HS increased with excitation wavelength, but the quantum yield
did not depend on the excitation wavelength for commercial HS samples.
Natural HS differed from commercial HS in higher
heterogeneity of fluorophore composition as evidenced
by the larger "blue shift" value and QY dependence on excitation wavelength.
Submitted: 1 July 2009
Revised: 20 Nov 2009
Accepted: 12 Feb 2010
Published: 12 Mar 2010
Responsible editor: Rainer Reuter
Shubina D, E Fedoseeva, O Gorshkova, S Patsaeva, V Terekhova, M Timofeev & V Yuzhakov, 2010.
The "blue shift" of emision maximum and the fluorescence quantum yield as quantitative spectral characteristics of dissolved humic substances.
EARSeL eProceedings, 9(1): 13-21