Abstract
In conditions of monochromatic excitation (λexc=337.1), the spectral dependence of the efficiency of fluorescence quenching αλ of humic acids samples by Cd2+ and Cu2+ ions was studied. The difference of αλ dependencies for these ions was established. In the spectral range 350 - 650 nm, changes of the αλ for Cd2+ ion are markedly different from the magnitude for changes αλ, which occur for ion Cu2+. The interpretation of mismatch dependences obtained αλ ions Cd2+ and Cu2+ is carried out within the concept of the availability of different sites, due to the difference in ionic radii (0.108 nm and 0.08 nm for Cd2+ and Cu2+, respectively).
Highlights
Humic acids (HAs), regardless of their origin, are high nitrogen-containing organic acid molecules that contain aromatic groups
We obtained the following facts: First, in the spectral range 400 - 600 nm cadmium ion quenches the fluorescence weaker than the copper ion; second, in the spectral range 400 - 600 nm for the cadmium ion value ∆αλ is greater than for the copper ion; third, in the “blue” part of the spectrum of HA fluorescence the effective quenching by ions of both metals takes place; fourth; HA fluorescence quenching increases at λ > 600 nm upon adding cadmium ion; fifth, continuous growth values βλ with increasing λ was observed
1) The decrease of the effective quenching of cadmium ion can be explained by the low access to HA fluorophores by this ion due to its larger size compared to copper ion and, by the lower efficiency of forming the complex
Summary
Humic acids (HAs), regardless of their origin, are high nitrogen-containing organic acid molecules that contain aromatic groups. How to cite this paper: Lavrik, N.L. and Mulloev, N.U. Earlier [12], we proposed an original method for assessing the degree of polydispersity of the sample HA. This method is based on the excitation of the fluorescence by monochromatic illumination. This technique was able to detect the spectral dependence of the fluorescence quenching efficiency. The possibility of such approach has been demonstrated by fluorescence quenching of the standard sample HA by Cu2+ ion. Monotonic spectral dependence of the quenching constants was not received and results in the conclusion were made available at least three spectral components
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