Stationary and Time-Resolved Fluorescence Spectroscopy of Humic Acids

abstrakt

angličtina

Humic substances (HSs) play an important role in chemical, physical and geological processes occurring in natural waters and soils. Humic substances are natural organic compounds arising from microbial degradation of decaying plant and animal tissues and synthetic activity of microorganisms. HSs are among the most widely distributed organic materials on the Earth. They are found not only in soils, peat and brown coals (leonardites, lignites) but also in natural waters, sewage, compost, marine and lake sediments, carbonaceous shales and terrestrial sediments. HSs are known to be polydisperse macromolecules, which are made up to a large extend of aliphatic and aromatic carboxylic acids, phenols and also of higher condensed compounds. The major components of HSs are humic acids (HAs), fulvic acids (FAs) and humin (HU) which are defined on the basis of their solubilities in aqueous solution. HAs are soluble in solutions of pH>2, while FAs are soluble at all pH and HU is entirely insoluble. The relative quantities of the different constituents depend strongly on the origin and genesis of the HSs but also on the extraction method used. Humic acids (HAs) represent very important part of the organic matter (OM) in soils, compost and low-rank coal especially lignite. Object of our study were three samples HAs which were isolated from sandy soil (Arenosols), compost and South-Moravian lignite from the mine Mír in Mikulčice, Czech Republic. Isolation of HAs was performed according to the procedure recommended by the IHSS. All samples of HAs were characterized by elemental analysis, ultraviolet-visible spectroscopy, infrared spectroscopy, steady-state fluorescence spectroscopy and time-resolved fluorescence spectroscopy (TRES, TRANES). Absorption coefficients of HAs were calculated from the absorbance of HAs in UV-VIS spectral range. Infrared spectroscopy with Fourier transform is a useful technique in characterization of structure, functional groups and formation modes of HAs. Steady-state (emission, excitation and excitation-emission fluorescence spectra) and time-resolved fluorescence methods (TRES – Time Resolved Emission Spectra, TRANES – Time Resolved Area Normalized Emission Spectra) were applied to investigate the fluorescence properties of HAs of different origins. For the fluorescence experiments the final concentration of the HAs was adjusted to 10 mg/dm3. The pH-value of the samples was adjusted to seven using a standard phosphate buffer.

humic acids, absorption and fluorescence indexes, stationary and time-resolved fluorescence spectroscopy, time-resolved emission spectra, chemical composition and functional groups

ENEV, V.; KLUČÁKOVÁ, M.

15. 9. 2013

European Association of Organic Geochemists

Costa Adeje, Tenerife, Spain

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