Browsing by Author "Benedetti, M. F."
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- Application of permeation liquid membrane and scanned stripping chronopotentiometry to metal speciation analysis of colloidal complexesPublication . Domingos, R. F.; Benedetti, M. F.; Pinheiro, J. P.The potential of permeation liquid membrane (PLM) to obtain dynamic metal speciation information for colloidal complexes is evaluated by measurements of lead(II) and copper(II) complexation by carboxyl modified latex nanospheres of different radii (15, 35, 40 and 65 nm). The results are compared with those obtained by a well characterized technique: stripping chronopotentiometry at scanned deposition potential (SSCP). Under the PLM conditions employed, and for large particles or macromolecular ligands, membrane diffusion is the rate-limiting step. That is, the flux is proportional to the free metal ion concentration with only a small contribution from labile complexes. In the absence of ligand aggregation in the PLM channels, good agreement was obtained between the stability constants determined by PLM and SSCP for both metals.
- Electrochemical methodology to study labile trace metal/natural organic matter complexation at low concentration levels in natural watersPublication . Domingos, R. F.; Benedetti, M. F.; Croué, J. P.; Pinheiro, J. P.A new electrochemical methodology to study labile trace metal/natural organic matter complexation at low concentration levels in natural waters is presented. This methodology consists of three steps: (i) an estimation of the complex diffusion coefficient (DML), (ii) determination at low pH of the total metal concentration initially present in the sample, (iii) a metal titration at the desired pH. The free and bound metal concentrations are determined for each point of the titration and modeled with the non-ideal competitive adsorption (NICA-Donnan) model in order to obtain the binding parameters. In this methodology, it is recommended to determine the hydrodynamic transport parameter, α, for each set of hydrodynamic conditions used in the voltammetric measurements. The methodology was tested using two fractions of natural organic matter (NOM) isolated from the Loire river, namely the hydrophobic organic matter (HPO) and the transphilic organic matter (TPI), and a well characterized fulvic acid (Laurentian fulvic acid, LFA). The complex diffusion coefficients obtained at pH 5 were 0.4 ± 0.2 for Pb and Cu/HPO, 1.8 ± 0.2 for Pb/TPI and (0.612 ± 0.009) × 10−10 m2 s−1 for Pb/LFA. NICA-Donnan parameters for lead binding were obtained for the HPO and TPI fractions. The new lead/LFA results were successfully predicted using parameters derived in our previous work.
- Field-flow fractionation characterization and binding properties of particulate and colloidal organic matter from the Rio Amazon and Rio NegroPublication . Benedetti, M. F.; Ranville, J. F.; Ponthieu, M.; Pinheiro, J. P.Colloidal and particulate natural organic matter was fractionated and concentrated from the Amazon and Rio Negro rivers using tangential-flow filtration (TFF). Flow field-flow fractionation, with UV absorbance detection, was used to investigate the molecular weight distributions of the organic colloids. To further characterize the nature of the Rio Negro colloids, the size distributions of the iron and aluminum concentrations were determined by off-line graphite furnace atomic absorption spectrometry analysis of fractions collected during the FFF separation. The size distributions obtained by FFF were considerably smaller than expected from the stated pore size of the TFF membranes. These results demonstrate that care must be taken in using TFF to classify the size distribution of organic colloids and associated elements present in rivers. Total metal complexing capacities (TMCC) of the colloids were determined by voltametry at various pH using lead as a probe. Total binding capacities were measured by automated proton titration of the particulate and the colloidal fractions. To describe Pb binding together with Al competition and the presence of mineral forms of Al in the particulate fraction, the NICA–Donnan approach was used. The fitted model lines agree reasonably well with the experimental results, suggesting that natural ligands behave like purified humic or fulvic acids. This result is surprising due to the extreme treatment humic substances are subjected to during purification. The only major difference between the binding constant values obtained for purified humic substances and the TFF fractions is a higher affinity constant value for the carboxylic groups of the latter. An interesting result is the agreement in the metal binding for the different fractions at pH 4 and 5, which implies that the type of groups present in these fractions are similar