Thin-layer chromatographic separation of noble metals on ECTEOLA-cellulose in hydrochloric acid and aqueous chloride solutions

Summary The thin-layer chromatographic behaviour of the noble metals on ECTEOLA-cellulose has been examined in HCl and aqueous chloride solutions of Li, Na, Mg, Ca, Sr and Al. The R_f-values decrease in the order Ir(III) Rh(III) > Ru(III) > Pd(II) > Pt(IV) > Ir(IV) > Au(III) in all of the media of higher chloride concentrations (3M to 5M), in which there are sufficiently large differences in R_f-values of adjacent metals to resolve them clearly. Especially, the HCl solutions with or without H₂O₂ are very suitable for multi-component separations of the noble metals.

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DC-Trennung von Edelmetallen auf ECTEOLA-Cellulose in salzsauren und wäßrigen Chloridlösungen

Zusammenfassung Das Verhalten von Edelmetallen wurde in salzsauren Lösungen sowie in Lösungen der Chloride von Li, Na, Mg, Ca, Sr und Al geprüft. Die R_f-Werte nehmen in allen Medien mit höherer Chlorid-konzentration (3M bis 5M) in folgender Reihenfolge ab: Ir(III) Rh(III) > Ru(III) > Pd(II) > Pt(IV) > Ir(IV) > Au(III). Die Unterschiede in den R_f-Werten sind groß genug, um eine deutliche Trennung zu gewährleisten. Salzsaure Lösungen mit oder ohne H₂O₂-Zusatz sind besonders gut für die Trennung von Vielkomponenten-Gemischen geeignet.

     

Electrochemical behavior of mesidine in aqueous solutions

The electrochemical oxidation of mesidine has been investigated in the pH range 0.7–11 at a platinum electrode with periodical renewal of the diffusion layer and at a stationary carbon paste electrode. A E_1/2/pH relation for the platinum electrode has been derived in the pH range 0–7. It has been indicated that the only oxidation products of mesidine are 2,6-dimethylbenzoquinone-4-(2′,4′,6′-trimethyl)-anil at pH <8 and 2,4,6,2′,4′,6′-hexamethylazoxybenzene at pH>8. Oxidation mechanisms consistent with the kinetic parameters and the oxidation products are discussed.     

Electrochemical behavior of tartaric acid at solid electrodes in aqueous and mixed solutions

Electrochemical behavior of D-tartaric acid at the Pt-, Cu-, Ta-, Cu-Hg-electrodes and the Cd-alloys with Sn, Ni, Hg, and In in aqueous and mixed solutions (water mixtures with acetone, ethanol, dimethylformamide, and pyridine) is studied by voltammetry. It is shown that the tartaric acid voltammograms always show waves related to the hydrogen ion discharge. A method recently suggested by authors allowed calculating the dissociation degrees at different stages, the concentrations of ionized and not ionized forms in dilute solutions of stereoisomers: DL-tartaric, L-tartaric, D-tartaric, and meso-tartaric acids. Simple empiric equations are suggested for the approximate calculating of some dissociation parameters for these acids.     

Application of radioisotope XRF for the determination of noble metals in aqueous solutions

Radiometric methods of determination of platium and palladium (0.1 to 5% of Pt and 0.1 to 2% of Pd), gold and indium (0.01 to 1% of Au and 1 to 4 g In/l) and of platinum and rhodium (0.1 to 9% of Pt and 0.05 to 1% of Rh) in aqueous solution has been worked out. A suitable measuring device has been designed and constructed. The methods are based on the measurement of characteristic radiation of the L_α line for gold and platinum and of the K-series for indium, palladium and rhodium, as well as on the measurement of scattered radiation from a²³⁸Pu source. The r.m.s. error of the determination varies from 0.01 to 0.10% of Pt, 0.002 to 0.01% of Au and 0.01 to 0.15% of Pd depending on the concentration. In the case of Rh and In the errors are 0.008% and 0.04 g In/l, respectively.     

Electrochemical oxidation of formic acid at noble metals: Catalytic effects of foreign metal monolayers

The catalytic effects of a submonolayer of lead on noble metals have been shown and discussed in terms of a previously published model. A theoretical analysis of these effects is presented. It was demonstrated that foreign metal monolayers allow a determination of the true catalytic activity of electrodes in the case of self-poisoning reactions. A volcano-shaped curve for oxidation of formic acid on noble metal electrodes was obtained.     

Electrochemical behavior of benzenepolycarboxylic acids on solid electrodes in aqueous and mixed solutions

Electrochemical behavior of biologically active benzenepolycarboxylic (trimellitic, trimesic, pyromellitic, mellitic) acids is studied by a voltammetry method on Pt, Cu, Ta, and Cu-Hg in aqueous media and water mixtures with ethanol and pyridine. In all cases, voltammograms for the acids display waves corresponding to the discharge of hydrogen ions. In the case of Cu-Hg, voltammograms for trimellitic, trimesic, and pyromellitic acids additionally exhibit poorly pronounced prewaves. Concentrations of ionized and non-ionized forms in dilute solutions of the acids are calculated. Apparent dissociation constants K _a ^II and K _a ^III for mellitic acid are calculated from the voltammetry data.     

Electrochemical and complexation behavior of neptunium in aqueous perchlorate and nitrate solutions

Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption, and Np L(III)-edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo structural rearrangement from spherical coordinating ions (Np(3+) and Np(4+)) to transdioxoneptunyl ions (NpO2(n+), n = 1 for Np(V) and 2 for Np(VI)). The redox reaction of the Np(V)/Np(VI) couple involves no structural rearrangement on their equatorial planes in acidic perchlorate and nitrate solutions. A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H2O)10](4+) in 1.0 M HClO4, while Np(V) and Np(VI) exist dominantly as pentaaquoneptunyl complexes, [NpO2(H2O)5](n+) (n = 1 for Np(V) and 2 for Np(VI)). A systematic change is observed on the Fourier transforms of the EXAFS spectra for all of the Np oxidation states as the nitrate concentration is increased in the sample, revealing that the hydrate water molecules are replaced by bidentate-coordinating nitrate ions on the primary coordination sphere of Np.     

Electrochemical amination. Dilute aqueous organic solutions of sulfuric acid

The electrochemical process of anisole amination is studied in 1.5–9 M H₂SO₄ solutions containing acetonitrile or acetic acid. It is shown that the synthesis of aromatic monoamino compounds is better performed in moderately acidic media with high concentrations of organic solvents. Due to the chain mechanism of the electrochemical process, the current efficiency of amines can exceed 150% under these conditions.     

Electrochemical procedure for express evaluation of the corrosion effect of aqueous glycol solutions on metals

Electrochemical procedure for express evaluation of the corrosion effect of aqueous glycol solutions on the metallic construction materials for cooling systems was studied. This procedure was used to develop new coolant formulations.     

A critical review of neutron activation and tracer methods for the determination of the noble metals

Neutron activation methods for the seven noble metals are critically reviewed up to December, 1965. The methods deal with the determination of trace impurities in each noble metal as well as traces of noble metals in media such as organic material, fission product and other solutions, ores, alloys, minerals, silica and base metals. The need for confirmatory evidence in the case of such complex materials as ores is emphasized.     

Electrochemical behavior of C-(60) modified electrode in aqueous solutions

The construction of adsorptive type C60 modified electrode and its electrochemical reduction and oxidation behavior in aqueous solutions are described in this report. Four pairs of one-electron transfer reduction and oxidation cyclic voltammetry is obtained in aqueous solution containing 30% CH3CN and 2% (C2H5)4NOH. It is reported in this paper that the C60 modified electrode also catalyzes the electrochemical reduction of dissolved oxygen in 40% DMF and 2% (C2H5)4NOH aqueous solution and this might open a new field for the potential applications of C60 in electrochemistry and electroaualytical chemistry.     

Electrochemical behavior of 3-amino-pyridine, 2,3-diamino-pyridine and 2,6-diamino-pyridine in aqueous solutions

The electrochemical behavior of 3-amino-pyridine, 2,3-diamino-pyridine and 2,6-diaminopyridine has been investigated in the pH range 0.7–13 at platinum and carbon paste solid electrodes with periodical renewal of the diffusion layer. Electrolysis at controlled potential of 3-amino-pyridine and 2,3-diamino-pyridine have been carried out in the pH range 0.7–13. The formation, among the oxidation products of 3-amino-pyridine, in alkaline solutions, of 3,3′-azopyridine has been pointed out and the percentages of this compound at changing pH were reported.     

Electrochemical behavior of high-molecular-weight poly(ferrocenylsilane) films in aqueous electrolyte solutions

The electrochemical behavior of high-molecular-weight poly(ferrocenyldimethylsilane) films and poly(ferrocenylmethylphenylsilane) films, which contained about 2.8 × 10⁻⁶ mol cm⁻² ferrocene sites in eight kinds of aqueous electrolyte solutions, was investigated with cyclic voltammetry (CV). In some aqueous electrolyte solutions, the CV peak currents diminished gradually with an increase in the scanning times, whereas in other aqueous electrolyte solutions, stable and repeated cyclic voltammograms were obtained. The polymer films were poor-solvent-swollen in aqueous electrolyte solutions, and this resulted in a high resistivity of mass transfer and a slow rate of electrode reaction; therefore; quasireversible or irreversible CV processes were obtained. The kinetic parameters of the film-electrode processes, such as the surface transfer coefficient, the apparent diffusion coefficient, and the standard rate constant for electron transfer, for the two films in aqueous LiClO₄ solutions were measured, and the electrode process mechanism of the films was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2245–2253, 2004     

Electrochemical properties of aqueous solutions of fullerenol-d

Dependence of the pH value on the concentration of fullerenol solutions was studied by means of pH-potentiometry, and the apparent degree of dissociation and the dissociation constant of fullerenol were calculated. The dependence of the electrical conductivity of fullerenol solutions on their concentration was examined. The molar electrical conductivity and also the apparent degree of dissociation and the dissociation constant of fullerenol were calculated.     

Preparation of colloidal solutions of noble metals stabilized by polyoxometalates and supported catalysts based on these solutions

Conditions for the preparation of stable aqueous monometallic and bimetallic colloidal solutions (sols) of noble metals (Ru, Rh, Pd, Pt, Ir, Ag, and Au) in the presence of polyoxometalates containing W, Mo, V, and Nb were found. The stability of sols against coagulation at room temperature was studied. The metal/C samples prepared by metal adsorption from sols were studied by powder X-ray diffraction analysis and transmission electron microscopy. The following factors of importance for the preparation of a stable sol are discussed: (1) the formation of a sol of a metal polyhydroxo complex stabilized by a polyoxometalate (preliminary stage) and (2) the formation of polyoxometalate-metal clusters in the course of reduction of polyhydroxo complexes.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 921–929.Original Russian Text Copyright © 2004 by Maksimova, Chuvilin, Moroz, Likholobov, Matveev.     

Nitrate ion reorientation in aqueous calciuim nitrate solutions: new evidence for ion association

The spectrum of nitrate ion reorientational motion in dilute calcium nitrate solutions has been obtained from the line-shape of depolarised Rayleigh scattering determined by Fabry—Pérot interferometry. The results show the presence of at least two lorentzian components. For a solution 0.9 mol dm^?3, broad and narrow bands can be resolved which correspond to relaxation times of 3.8 and 50 ps. The former is assigned to reorientation of NO^?₃ similar to that observed previously for dilute alkali-metal nitrate solutions. The slow relaxation probably results from reorientation of NO^?₃ in associated ion pairs or similar structures.     

Electrochemical behavior of aluminum alloy AA2024 in aqueous solutions in the presence of caffeine

The influence of the presence of caffeine (CFN) on the electrochemical behavior of aluminum alloy AA2024 in aqueous solutions was studied. The interaction between the metal surface and the organic compound is potential dependent as well as time dependent. The anodic currents, responsible for the metal dissolution, decreases in the presence of caffeine even adding chloride anion as contaminant. The EIS data obtained at the open-circuit potential clearly demonstrated that the adsorption of CFN on the surface of the AA 2024 electrode is favored allowing the film defects to be repaired. The protective action of CFN is considerably improved on increasing the adsorption time due to a sealing process which enhances the film stability.     

Contact corrosion of metals in aqueous and aqueous-glycolic solutions

Corrosion behavior of aluminum, steel, and cast iron both without contact and in short-circuited aluminum-steel, aluminum-cast iron, steel-cast iron, and aluminum-steel-cast iron systems in fresh water, ethylene glycol, and its aqueous solutions of various compositions containing 5 to 95 vol % fresh water was studied.