Characterization of colored dissolved organic matter using high-energy laser fragmentation

A new approach combining high-energy laser fragmentation (HELF) with excitation-emission matrix spectroscopy (EEMS) was used to study colored dissolved organic material (CDOM) in rivers feeding the Tampa Bay Estuary, Results presented as difference spectra showed that fluorescent material destroyed had two distinct peaks for all samples at all degradation wavelengths of 320 nm or greater. All samples showed highest loss of UV-C (220-280 nm) stimulated fluorescence, even when irradiated at 390 nm, with lower loss of UV-B (280-320 nm) stimulated fluorescence centered around the wavelength used for degradation. In contrast to spectra for the initial and residual fingerprints, loss spectra showed the rounded contours expected for a pure organic fluorophore. These observations suggest that laser irradiation targets a specific fluorophore or restricted group of fluorophores in the original mixture, some of which have a double excitation maximum and single emission maximum. By varying the degradation wavelength, eight distinct fluorophore groups were identified in the sample set, some of which were unique to either river or estuarine samples and some of which were common to samples from both environments.