Alain Castetbon

Determination of trace metal speciation parameters by using screen-printed electrodes in stripping chronopotentiometry without deaerating

The objective of this study was to exploit the advantages of stripping chronopotentiometry (SCP) and stripping chronopotentiometry at scanned deposition potential (SSCP) for trace metal speciation analyses by using thin-film mercury screen-printed electrodes (TMF-SPE). At first, the SCP parameters were optimised for TMF-SPE, in order to reach the complete depletion regime. It has been shown that a stripping current higher than or equal to 10 μA allows this regime to be attained without removing oxygen from the solution. Then, these analytical conditions were used for the construction of SSCP curves for Cd-PDCA and Cd-NTA. When the concentration of free ligand in solution was known, the knowledge of the model describing the SSCP curves in absence and presence of a complex and the use of an effective fitting tool enabled estimating the stability constant and the rate constants for complexation. Further studies with complexes of restricted mobility are however necessary to assess the usefulness of this procedure to also estimate the diffusion coefficient of the complexes. Besides, this study showed that this approach was valid even when ligands were not in excess at the electrode during stripping.

Pollution d'eaux de ruissellement par les metaux lourds en zone urbaine. Premiere partie: Metal total

Abstract The metallic content (Cd, Cu, Pb, Zn) of urban runoff waters has been studied after phase separation by 0,45 μm filtration, as well as global parameters. Sequential sampling has been performed during seven important rainfalls in a single residential area in 1991 and 1992. A minor first flush effect has been noted. The better part of the metallic pollutants was in the particulates at quite high concentrations (Cd 5 μg g‐1; Cu 400 μg g‐1; Pb 700 μg g‐1 and Zn 2000 μg g‐1). A study of the multiparameter correlations evidenced strong links between COD, BODg, Suspended Solids and Cu and Pb concentrations in the particulate phase. Conductivity was not correlated to any parameter.

Free Zn2+ determination in natural freshwater of the Pyrenees: towards on-site measurements with AGNES

An on-site methodology has been developed for the direct determination of free Zn2+ with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) in freshwaters. This implementation includes: (i) the use of screen-printed electrodes, which provide good limits of detection and easy transportation and deployment; (ii) no need for sample purging; (iii) a calibration in a synthetic river solution that reproduces the speciation changes of the natural samples well and allows oxygen interference to be minimised; (iv) the addition of a background electrolyte up to 0.01 mol L–1 in both the calibration and freshwater samples; (v) chemical stripping chronopotentiometry as the quantification stage of AGNES. This procedure minimises the effects of working at low ionic strength and in the presence of dissolved oxygen. In the laboratory, the methodology was checked with different natural samples taken from rivers Garonne, Gave de Cauterets and Gave de Pau in the Pyrenees. Results appeared in good agreement with theoretical estimations computed from Visual Minteq. On-site measurements were performed for the first time with AGNES in the Gave de Cauterets in Soulom (France) and the results were corroborated with purged measurements performed in the laboratory.

Pollution d'eaux de ruissellement par les metaux lourds en zone urbaine. Deuxieme partie: Speciatton

Abstract The speciation of cadmium, copper, lead and zinc has been studied in the particulate and the dissolved fractions of urban runoff waters. Sequential sampling has been performed during seven important rainfalls in a same residential area in 1991 and 1992. In the dissolved fraction cadmium is essentially labile, copper is present as very stable complex species, lead in stable slowly labile compounds whereas the lability of zinc species depends on the concentration of suspended solids. Particulate cadmium belongs to the “exchangeable”; fraction, copper is linked to the organic and residual fractions, lead to organic matter and “exchangeable”; fraction. Particulate zinc is shared between all fractions.

Determination of the correlation between physical measurements of roughness, optical properties, and perception of frosted glass surfaces.

Chemical frosting is used as a surface decorating method by many glass package producers. After immersion in an acid frosting bath, glass items present the desired frosted effect. The perception of this particular effect is due to the formation of a microscopic crystalline pattern on the glass surface, which scatters light passing through the glass surface. The chemical composition of the frosting bath influences these properties by modifying the surface roughness, the depth, and the average slopes of the crystalline pattern. Perception of the final aspect can be modified according to the chemical composition of the frosting bath. Different correlations between all these parameters exist and have been quantified.

Mesure de la capacite complexante de solutions aqueuses d'acides humiques par titrage au cuivre et D.P.A.S.V. en tampon acetate

Abstract D.P.A.S.V. evaluation of the complexing capacity of aqueous solutions of humic acids by copper titration has been studied in non complexing solutions and in acetate buffers. Some difficulties have been evidenced due to the necessity of controlling pH and interferences from the buffers. A method using dilute buffer solutions and a semi empirical integration of the voltamperometric peaks is proposed.