Abstract
The fluorescence properties of the Sep-Pak extractable marine organic matter (SPE-MOM) have been investigated by recording emission spectra varying the excitation wavelength ( Λ 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 Λ ex, and a second group, Λ ex independent, with an emission maximum ( Λ ex) close to 520 nm. Soil fulvic acid (SFA) and Sep-Pak extractable soil fulvic acid (SPE-SFA) exhibit two groups of fluorophores, with a distinctive dependence of Λ em on Λ ex. Fluorescence quenching measurements of the copper complexation, performed at different Λ ex, permits an estimation of stability constants which indicate the presence of a stronger binding site connected to the second group of fluorophores for SFA and SPE-SFA. SPE-MOM presents a higher residual fluorescence than SFA as well as a significant amount of non-fluorescent organic material indicating a possible competition between fluorescent and nonfluorescent ligands for the copper complexation in seawater.
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