FLUORESCENCE EMISSION CHARACTERISTICS OF NATURALLY-OCCURRING ORGANIC-MATTER IN RELATION TO METAL COMPLEXATION STUDIES

The fluorescence properties of the Sep-Pak extractable marine organic matter (SPE-MOM) have been investigated by recording emission spectra varying the excitation wavelength (lambda(ex)) between 300 nm and 500 nm. Two different groups of fluorophores have been observed: the first emitting at wavelengths from 410 to 480 nm depending on lambda(ex), a nd a second group, lambda(ex) independent, with an emission maximum (l ambda(em)) close to 520 nm. Soil fulvic acid (SFA) and Sep-Pak extract able soil fulvic acid (SPE-SFA) exhibit two groups of fluorophores, wi th a distinctive dependence of lambda(em) on lambda(ex). Fluorescence quenching measurements of the copper complexation, performed at differ ent lambda(ex), permits an estimation of stability constants which ind icate the presence of a stronger binding site connected to the second group of fluorophores for SFA and SPE-SFA. SPE-MOM presents a higher r esidual fluorescence than SFA as well as a significant amount of non-f luorescent organic material indicating a possible competition between fluorescent and nonfluorescent ligands for the copper complexation in seawater.