Potentiometric determination of the standard potential of the As(V)/As(III) couple

The potential of the As(V)/As(III) half-cell was measured at 25 degrees with a glass electrode as reference electrode in order to eliminate the liquid-junction potential. Rapid and reproducible values could be obtained only in the presence of iodide, which increases the rate of electron-exchange between the two oxidation states of arsenic, but only at hydrogen-ion concentrations higher than about 0.5M. Extrapolation to zero ionic strength was therefore required to obtain the standard potential. A value of 573 +/- 2 mV was calculated for the half-reaction AsO(OH)(3) + 2e(-) + 2H(+) right harpoon over left harpoon As(OH)(3) + H(2)O.     

Photometric titration of total iodine at trace levels in concetrated chloride solutions

The method is based on reduction of total iodine (10^?7?10^?5 M), to iodide with sulphite in acidic solution. The excess of sulphur dioxide is removed by bubbling with nitrogen, and the resulting solution is titrated spectrophotometrically with a standard solution of iodate, the absorbance being measured at 230 nm. Some Italian table salts, iodized or common, were analyzed for their iodide and total iodine content.     

Sorption of proton and heavy metal ions on a macroporous chelating resin with an iminodiacetate active group as a function of temperature

A macroporous resin containing iminodiacetic groups (Lewatit) was investigated for its sorption properties towards proton and nickel(II) and cadmium(II). Different compositions of the aqueous phase, and different temperatures were examined. The stoichiometry, the exchange coefficients and the intrinsic constants of the sorption equilibria were obtained from the experimental data by using the Gibbs-Donnan model for the ion exchange resin. The intrinsic constants were found to be independent of the composition of the solution, so that they were used for characterizing the sorption equilibria. While the first intrinsic protonation constant of the active groups in the resin was found to depend on the temperature, the second one was independent. The sorption equilibrium of nickel in the resin was different from that of cadmium, being ascribable respectively to the formation of the complexes NiL and Cd(HL)(2). inside the resin. Their intrinsic complexation constants were found to be 10(-1.84) and 10(-3.64) at 25 degrees C. Compared to those of another resin with the same active groups, but not macroporous, they are higher. The dependence of the intrinsic constant on the temperature was also different for the two metals, allowing to evaluate a DeltaH degrees of +30.9 and of +13.7 kJ mol(-1) respectively. When a comparison is possible, these values are near to those in aqueous solution for the complexation with ligands of similar structure. These results can be used to achieve metal ion separation based on temperature variations.     

Solid phase extraction of copper(II) by fixed bed procedure on cation exchange complexing resins

The efficiency of the metal ion recovery by solid phase extraction (SPE) in complexing resins columns is predicted by a simple model based on two parameters reflecting the sorption equilibria and kinetics of the metal ion on the considered resin. The parameter related to the adsorption equilibria was evaluated by the Gibbs–Donnan model, and that related to the kinetics by assuming that the ion exchange is the adsorption rate determining step. The predicted parameters make it possible to evaluate the breakthrough volume of the considered metal ion, Cu(II), from different kinds of complexing resins, and at different conditions, such as acidity and ionic composition.     

Differentiation of Vitis vinifera varieties by MALDI-MS analysis of the grape seed proteins

Until now the study of pathogenic related proteins in grape juice and wine, performed by ESI-MS, LC/ESI-MS, and MALDI/MS, has been proposed for differentiation of varieties. In fact, chitinases and thaumatin-like proteins persist through the vinification process and cause hazes and sediments in bottled wines. An additional instrument, potentially suitable for the grape varieties differentiation, has been developed by MALDI/MS for the grape seed protein analysis. The hydrosoluble protein profiles of seeds extract from three different Vitis vinifera grape (red and white) varieties were analyzed and compared. In order to evaluate the environmental conditions and harvest effects, the seed protein profiles of one grape variety from different locations and harvests were studied.     

Modeling of cementitious materials exposed to isothermal calcium leaching,considering process kinetics and advective water flow. Part 2: Numerical solution

The second part of the paper presents numerical solutions of the mathematical model of hydro-chemo-mechanical behavior of cementitious materials exposed to contact with deionized water of part 1. The model defines kinetics of the calcium leaching process instead of a direct application of a curve describing equilibrium between solid calcium in the material skeleton and the calcium dissolved in the pore solution. It further takes into account the advective flux of calcium ions. Both aspects are new as compared to previous models. The weak form of the governing equations of the model is derived first using the Galerkin method. Then, the equations are discretized in space with finite elements and in time domain with finite differences, and finally the procedures used for numerical solution of their discretized form are presented. Three numerical examples are solved to test the numerical solution procedure proposed and demonstrate its robustness for solution of 1D and 2D problems concerning fast and slow leaching of cement-based materials. The effect of various factors on the results concerning chemical degradation of structures made of cementitious materials is analyzed as well.