Interaction of fulvic acids with Al(III) studied by self-modeling curve resolution of second-derivative synchronous fluorescence spectra

The interaction of AI(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 synchro nous 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 AI(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 AI(III) coordination at pH 4 was 4.34(15).