Abstract
The effect of Hg2+ on the fluorescence intensity of three fulvic acids (Pahokee Peat, Pony Lake and Suwannee River) was studied. The fluorescence intensity decreased in the presence of added Hg2+, while the fluorescence lifetimes were independent of the concentration of Hg2+ in solution. These results are indicative of ground-states association between the fulvic acids and Hg2+ with formation of stable non-fluorescent complexes (static quenching process). The analysis of the excitation–emission matrices with the Singular Value Decomposition (SVD) and Multivariate Curve Resolution–Alternating Least Squares (MCR-ALS) methods provided additional valuable information regarding the binding properties between Hg2+ ions and specific fluorescence components of the fulvic acids. The three fulvic acids were shown to contain the same three groups of fluorophores characterized by excitation/emission pairs in the following regions: (320–330 nm/425–450 nm), (370–375 nm/465–500 nm), (290–295 nm/370–395 nm). These pairs are almost not affected by the change of pH from 2.0 to 7.0. Ryan–Weber and modified Stern–Volmer methods were used to analyze the static fluorescence quenching of the individual components. Similar conditional stability constants of Hg2+ binding for the three components were found by both methods. The obtained log K values are in the range of 4.4 to 5.4.
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Abbreviations
- DOM:
-
Dissolved organic matter
- EEM:
-
Excitation–emission matrices
- FA:
-
Fulvic acid
- HA:
-
Humic acid
- HS:
-
Humic substances
- IHSS:
-
International Humic Substance Society
- M w:
-
Molecular weight
- MCR-ALS:
-
Multivariate Curve Resolution–Alternating Least Squares
- PP:
-
Pahokke Peat
- PARAFAC:
-
Parallel Factor Analysis
- PL:
-
Pony Lake
- SDV:
-
Singular Value Decomposition
- SR:
-
Suwannee River
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Berkovic, A.M., García Einschlag, F.S., Gonzalez, M.C. et al. Evaluation of the Hg2+ binding potential of fulvic acids from fluorescence excitation—emission matrices. Photochem Photobiol Sci 12, 384–392 (2013). https://doi.org/10.1039/c2pp25280e
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DOI: https://doi.org/10.1039/c2pp25280e