Evaluation of the Hg2+ binding potential of fulvic acids from fluorescence excitation–emission matrices

ANDREA M. BERKOVIC; FERNANDO S. GARCÍA EINSCHLAG; MÓNICA C. GONZÁLEZ; REINALDO PIS DIEZ; DANIEL O. MÁRTIRE

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2013 vol. 12 p. 384 - 392

1474-905X

The effect of Hg2+ on the fluorescence intensity of three fulvic acids (Pahokee Peat, Pony Lake andSuwannee River) was studied. The fluorescence intensity decreased in the presence of added Hg2+, whilethe fluorescence lifetimes were independent of the concentration of Hg2+ in solution. These results areindicative 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 withthe Singular Value Decomposition (SVD) and Multivariate Curve Resolution – Alternating Least Squares(MCR-ALS) methods provided additional valuable information regarding the binding properties betweenHg2+ ions and specific fluorescence components of the fulvic acids. The three fulvic acids were shown tocontain the same three groups of fluorophores characterized by excitation/emission pairs in the follow-ing regions: (320–330 nm/425–450 nm), (370–375 nm/465–500 nm), (290–295 nm/370–395 nm). Thesepairs 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 bothwww.rsc.org/pps methods. The obtained log K values are in the range of 4.4 to 5.4.