Classification of binding sites for Al(III) in fulvic acids extracted from leaf litters and soils by synchronous fluorescence spectroscopy and multidimensional chemometric analysis

The major binding sites for Al(III) in six samples of fulvic acids (fua) extracted form soils and leaf litters were investigated by synchronous fluorescence (SyF) spectroscopy. Two samples of fua from soil of an oak forest (two horizons, 0–5 cm, fuaol, and 5–15 cm, fuao2) and four fua like samples extracted from leaf litters (eucalyptus, fern, oak and chestnut coverture, respectively feu, fer, foa and fch) were studied. The SyF spectra of the mixtures of fua and increasing concentration of Al(III), at pH 4, were analyzed by evolving factor analysis (EFA), a self-modeling curve resolution method, to detect the number of major binding sites, their SyF spectra and SyF profiles as function of the Al(III) concentration. The overall set of calculated SyF spectra was analyzed by pattern recognition methods, such as cluster analysis and multidimensional scaling, to detect similarities and differences between them. Although there are differences in the intrinsic SyF properties of fua extracted from soils and leaf litters, the soil fua samples showing a more complex binding site composition, the most important binding site is common to all fua samples studied. The amount of this binding site was roughly estimated. It is approximately the same for all samples but for fuao2, in which the amount is twice the others.