Study of the interaction of a soil fulvic acid with UO2 2+ by self-modelling mixture analysis of synchronous molecular fluorescence spectra

Abstract

The interactions between UO22+ and fulvic acids (FUA) were studied by a methodology that involves synchronous molecular fluorescence spectroscopy, to monitor the quenching of the intrinsic fluorescence of FUA by UO22+, and a self-modelling mixture analysis method (SIMPLISMA), to treat spectroscopic data. This methodology was applied to the analysis of the interaction of UO22+ with salicylic acid at pH 3.5 and with a soil FUA at pH 3.5 and 7.0, in this case in the presence of various concentrations of carbonate ion (10–5, 10–4 and 10–3 mol l–1). From the calculated quenching fluorescence intensity profiles, using either the Stern–Volmer relationship or a non-linear least-squares method, mean conditional stability constants (log values with standard deviations in parentheses) were estimated for salicylic acid [respectively 2.72(4) and 2.77(6)], for FUA at pH 3.5 [3.93(2) and 4.4(1)] and pH 7.0 [4.06 and 4.1 (average values for the various concentrations of carbonate ion)]. The non-linear least-squares method also allowed the estimation of the number of binding sites that exist in FUA (0.11 and 0.24 mol g–1 at pH 3.5 and 7.0, respectively).