<title>Absorption and fluorescence spectroscopic investigations of PAC/humic substance-interactions in water</title>

Abstract

Time-resolved emission spectra of humic substances of different origin have been recorded in order to extend our previous spectroscopic characterization of humic and fulvic acids in aqueous solution with stationary UV/Vis-absorption and fluorescence measurements. Instead of applying a fitting procedure, decay times are introduced as simple and robust experimental parameters for the quantitative description of fluorescence decays. The analysis of time-resolved emission spectra indicates a wavelength dependence of the fluorescence investigations of the interactions between pyrene and various humic substances in water. For all humic substances the quenching of pyrene fluorescence is dominated by a static quenching process, i.e. by a ground-state complexation. A significant influence of pH on the fluorescence quenching efficiencies is found, whereas no long-term changes of the interaction between pyrene and a humic substance are discernible. Time-resolved triplet- triplet absorption measurements reveal a decrease of chrysene triplet lifetime due to the presence of humic substances.