Time-resolved laser fluorescence spectroscopy of organic ligands by europium: Fluorescence quenching and lifetime properties

Abstract

Time-resolved Laser Fluorescence Spectroscopy (TRLFS) has proved its usefulness in the fields of biophysics, life science and geochemistry to characterize the fluorescence probe molecule with its chemical environment. The purpose of this study is to demonstrate the applicability of this powerful technique combined with Steady-State (S-S) measurements. A multi-mode factor analysis, in particular CP/PARAFAC, was used to analyze the interaction between Europium (Eu) and Humic substances (HSs) extracted from Saint Lawrence Estuary in Canada. The Saint Lawrence system is a semi-enclosed water stream with connections to the Atlantic Ocean and is an excellent natural laboratory. CP/PARAFAC applied to fluorescence S-S data allows introspecting ligands-metal interactions and the one-site 1:1 modeling gives information about the stability constants. From the spectral signatures and decay lifetimes data given by TRLFS, one can deduce the fluorescence quenching which modifies the fluorescence and discuss its mechanisms. Results indicated a relatively strong binding ability between europium and humic substances samples (LogK value varies from 3.38 to 5.08 at pH 7.00). Using the Stern-Volmer plot, it has been concluded that static and dynamic quenching takes places in the case of salicylic acid and europium interaction while for HSs interaction only a static quenching is observed.

Modeling the quenching of fluorescence from organic matter in Amazonian soils

“…The excitation and emission slits were fixed at 10 nm, the integration was set at 500 scans min -1 , and the detector voltage was 700 V. The data were obtained with an open filter and excitation wavelength increases of 10 nm, giving 30 scans. The EEM obtained using this technique was treated using the mathematical method known as canonical polyadic/parallel factor analysis (CP/PARAFAC) (Bro, 1997;Mounier et al 2011;Luciani et al 2013;Nouhi et al 2018).…”

Humic-like acids from hydrochars: Study of the metal complexation properties compared with humic acids from anthropogenic soils using PARAFAC and time-resolved fluorescence

“…The fluorescence excitation emission matrix (EEM) has gained prominence in the characterization of organic matter and its interaction with metallic species (Elkins and Nelson, 2002). The analytical potential of fluorescence EEM spectra coupled with chemometric tools such as Parallel Factor Analysis (PARAFAC) has been successfully realized for this type of analysis (Mounier et al, 2011;Nouhi et al, 2018;Stedmon and Bro, 2008;Tadini et al, 2019;Yuan et al, 2015). Moreover, PARAFAC has also been used in the characterization of dissolved organic matter (DOM) of biochars produced with different biomass content (El-Naggar et al, 2020;Rajapaksha et al, 2019;Yang et al, 2019b).…”

“…Moreover, PARAFAC has also been used in the characterization of dissolved organic matter (DOM) of biochars produced with different biomass content (El-Naggar et al, 2020;Rajapaksha et al, 2019;Yang et al, 2019b). Further, because different chemical species have different fluorescence lifetimes, it is also possible to study organic matter-metal interaction through timeresolved fluorescence (TRF), particularly in complex samples such as HA and HLA (Nouhi et al, 2018).…”

Humic fractions from Amazon soils: Lifetime study and humification process by fluorescence spectroscopy

“…Fluorescence spectroscopy is frequently used in the literature to rapidly assess the structural and molecular characteristics of OM and their humic fractions (Senesi and D'Orzio, 2005;Tadini et al 2015Tadini et al , 2018Tadini et al , 2020Liu et al, 2020;Mohinuzzaman, et al 2020;Soares da Silva et al 2020;Mielnik et al 2021;Rinot et al 2021), recently highlighting the use of Time Resolved Laser Fluorescence Spectroscopy (TRLFS) (Nicolodelli et al 2017;Nouhi et al, 2018;Dos Santos et al, 2020a,b). This technique can measure the decay of the fluorescence intensity of a sample after excitation, allowing the determination of the fluorescence lifetime in sample fluorophores (Millar, 1996).…”