Francisco Rey

Influence of the concentration on the conductimetric properties of a fulvic acid system

Abstract The influence of the concentration on the behaviour of a soil fulvic acid is analyzed by conductimetric titrations. The values obtained (variation of molar conductivity between ca. 134 to 82 and variation of the degree of coverage between 0.31 to 0.16 when the concentration of fulvic acid rises from 20 to 100 mg l −1 ) are explained by the counterion condensation theory and parameters derivated are calculated. The influence of small quantities of an organic solvent is also analyzed.

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

Abstract 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.

Conductimetric analysis of the ion binding properties of three leaf extracts of chestnut (Castanea sativa), Eucalyptus (Eucalyptus globulus) and oak (Quercus robur).

Humic materials extracted from tree leaves of chestnut (Castanea sativa), eucalyptus (Eucalyptus globulus) and oak (Quercus robur) were analyzed by performing conductimetric titrations. Values between about 84 and 236 muS cm(-1) for the molar conductivity and between 0.42 and 0.74 for the charge distribution parameter were obtained when the concentrations of the extract are increased from 40 to 100 mg 1(-1). These variations were explained by using the counterion condensation theory, and the distance between the charged groups of the polyions, the volume of the counterion condensation and the Debye-Hückel potential were also calculated.

Conductimetric analysis of the interaction of Cu(II) ions and a humic-like natural polyelectrolyte (Laurel, Laurus nobilis) mixture

Abstract The influence of the ligand and metal ion concentrations on the conductimetric behavior of humic-like laurel extract–Cu(II) mixtures are analyzed by conductimetric titrations. The results obtained show that the extracts can be considered as polyelectrolytic molecules in the presence of heavy cations, forming complexes whose stability (related to the slope of a conductimetric excess function versus added Cu(II) plots) is low when compared to stronger ligands such as humic acids. The influence of ligand concentration and degree of neutralization is discussed.