Natural organic matter (NOM) is a naturally occurring, complex and ubiquitous component of aqueous environments. While its structural characteristics are widely variable, all NOM can absorb light and relax down to the ground state via fluorescence. Changes to the fluorescence of NOM are caused by the presence of heavy atoms or the addition of metals, which can act as quenchers or enhancers of fluorescence. Metals have also been shown to alter the conformation of natural organic matter via the formation of complexes, affecting its photochemical properties. This work focuses on the how the additions of divalent and trivalent metals that are commonly present in seawater (Fe3+, Cu2+, Al3+ and Mg2+) influence the fluorescence of two natural organic matter samples by either quenching or enhancing it. For both Suwannee River and Nordic Reservoir NOM samples, we observe that both iron and copper quench fluorescence, with copper not as effective as iron within the same concentration range. We compare the metal concentration ranges over which quenching is linear with concentration of these two metals and attempt to unravel the static and dynamic quenching processes. By contrast, both aluminum (III) and magnesium (II) in solution give rise to a fluorescence enhancement of the NOM samples, albeit to different extents within the same concentration range. Given that metals can alter the conformation of organic matter, we attempt to link quenching and enhancement trends with changes to the fluorescence anisotropy of Suwannee River and Nordic Reservoir NOM samples in the presence of Fe3+, Cu2+, Al3+ and Mg2+. We report these results and our explorations of the mechanism(s) responsible.

Exploring the relationship between the conformation of NOM and fluorescence changes caused by the presence of metals

2019 Fall National Meeting

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