Interaction of Fulvic Acids with Al(III) Studied by Self-Modeling Curve Resolution of Second-Derivative Synchronous Fluorescence Spectra

Abstract

The interaction of Al(III) with two samples of fulvic acids (fua), extracted from materials present in a pinewood soil (fua2 from the upper soil horizon, or leaf litter, and fua3 from lower soil horizons), was followed by synchronous fluorescence (SyF) spectroscopy at pH 4. The variations observed in the inverted second-derivative spectral data were analyzed by SIMPLISMA, a self-modeling curve resolution technique. Three binding sites were detected for each fua sample, and their spectra and SyF intensity profiles were obtained. Conditional stability constants for coordination of one binding site of each fua and Al(III) were obtained (log values): fua2, 5.65(15); fua3, 4.64(2). The experimental and data analysis methodologies were validated by analysis of data obtained for salicylic acid under the same conditions. The log value found for its conditional stability constant for Al(III) coordination at pH 4 was 4.34(15).