ИСТИНА

Chromophoric dissolved organic matter (CDOM) is present in all types of natural water and plays a significant role in their biogeochemistry and optical properties. The main fluorescence characteristics like an excitation/emission maximum wavelengths and fluorescence quantum yield (QY) can provide the key information about CDOM structure and sources. The objective of this work was to study correlation between fluorescence QY and excitation wavelength for Suwannee River (SR) whole CDOM and its fractions A, B and C+D, obtained by size exclusion chromatography–polyacrylamide gel electrophoresis setup for which the nominal molecular size (NMS) varied in the order A>B>C+D>10kDa. Fraction with NMS<10kDa was lost during fraction purification and did not used for analysis. Fluorescence emission spectra were registered for different excitation wavelengths in the range 270 – 600 nm with the step 10 nm. The fluorescence QY was determined using a solution of sulphate quinine as a fluorescence QY reference. Our studies revealed that fluorescence quantum yield of SR CDOM depends on excitation wavelength: increase from QY=1,3% at wavelength excitation 270 nm to a maximum QY=2,5% at wavelength excitation 350 nm and decrease monotonically thereafter. The behavior of the fluorescence QY of SR CDOM fractions was found similar, but the fraction with the smallest molecular size (C+D fraction) had the highest value of QY. It was shown that the protein-like fluorescence was almost exclusively located in high molecular size fraction A and medium molecular size fraction B with the smaller value of QY. The work has been supported by Russian Foundation for Basic Research (project 15-04-00525-a).