Fluorescence of soil humic acids and their fractions obtained by tandem size exclusion chromatography-polyacrylamide gel electrophoresis

Humic acids (HAs) extracted from soils of different origin (chernozem, ferralsol and ranker) and their fractions (A, B and C+D) obtained by tandem size exclusion chromatography–polyacrylamide gel electrophoresis were investigated by steady-state fluorescence spectroscopy in the emission mode. Independently of HA source, high molecular size fractions A and B are shown to be weakly fluorescent. The main fluorophores, especially those emitting at long wavelength (around 500–510 nm), are contained in the polar and low molecular size fractions C+D. As indicated by the observed pH effect, aromatic structures bearing carboxylate and OH substituents may be involved in these longer wavelength emissi…