[en] The present paper describes the uranium controlled potential coulometric titration technique in sulfuric acid media using two different electrodes: the mercury and the platinum electrode. The platinum electrode presents several important practical advantages compared to that of mercury. Using the platinum electrode, the uranium coulometric oxidation from state IV to VI is feasible and the couples of iron (III) and uranium (IV) or plutonium (IV) and uranium (IV) determination can be realised with the same electrode and the same solution the uranium and iron or plutonium quantity which reacted is calculated using coulombs number necessary to obtain either the total oxidation or reduction of the elements of interest

[en] The use of a thin mercury film wax-impregnated graphite electrode for the simultaneous determination of cadmium, lead and zinc in an acetate buffer by differential pulse anodic stripping voltammetry is described. Optimal instrumental parameters for maximum resolution and sensitivity for simultaneous analysis of these three elements in natural waters are discussed. The interference of copper with the determination of zinc is investigated in detail. An optimal mercury film thickness for this electrode is suggested. A method utilizing differential pulse polarography for the determination of chromium (VI) in natural water is described. Additions of 0.62 μg Cu(II) ml^-1 and 0.55 μg Fe(III) ml^-1 did not interfere with the determination of 0.050 μg Cr(VI) ml^-1. The natural water samples containing Cr(VI) were buffered to approximately pH 7 with 0.1 M ammonium acetate and 0.005 M ethylenediamine and analyzed. Natural water samples of chromium from 0.035 μg to 2.0 μg.ml^-1 may be analyzed directly without further preparation. The detection limit is 0.010 μg.ml^-1. A novel, highly efficient cell with integral stirrer for controlled potential coulometry is described. This cell was used to demonstrate the feasibility of determining uranium (VI) by predictive coulometry. A PDP 8/I minicomputer was used to predict the coulometric endpoint with high accuracy within 2.5 minutes in a titration which normally takes about 10 minutes. This technique was shown to yield acceptable results even in the presence of an interfering phosphate matrix

[en] Oxidation of glucose oxidase by ferrocenecarboxylic acid in the presence of glucose was examined by comparing experimental catalytic efficiencies from cyclic voltammetry with those digitally simulated by the general program ELEC. The program permitted consideration of individual diffusion coefficients of enzyme and mediator, the second-order nature of the initial electron-transfer event and the follow-up reaction of oxidized enzyme with glucose. A rate constant of 1.06x10⁵ 1 mol^-1 s^-1 was found by analysis with such simulations for the accepted two-electron EC'C pathway. This was nearly half the approximate value found by a previously used pseudo-first-order EC' model assuming equal diffusion coefficients. (author). 15 refs.; 3 figs.; 1 tab

No abstract available

[en] The development method for uranyl ion determination by the optimization of chemical reaction and instrumental parameters is shown. This method is based on preconcentration stage, where in adsorptive accumulation of metallic complex in a static electrode is presented. (author)

[en] The electrochemical reduction of uranyl ion at the dropping mercury electrode and/or mercury microelectrode has been studied in popanediol-1,2-carbonate(PDC) by voltammetric techniques. The position of the peak potentials, the nature of the limiting currents, their dependency on the temperature and on the concentrations, reversibility or irreversibility of the electrode reactions, and influence of phenol are described. The influence of PDC in aqueous solution of uranyl ion was also described. The values of kinetic parameters, viz. transfer coefficient, formalrate constant for the electrode reactions have been determined by Kouteck's method as extended by Meites and Israel. The values of ΔH, ΔG, and ΔS have been calculated. (Author)

[en] The equilibrium oxygen partial pressure over nonstoichiometric V₂O_5-x and the related two-phase mixture has been measured by coulometric titration using yttria-stabilized zirconia (YSZ) as the solid electrolyte at temperatures between 880 and 936 K. The nonstoichiometry (x) is observed up to 0.055 at 920 K and is related to the oxygen partial pressure (P_O2) as x∝P_O2^-1/4 in the region of x<0.017. This fact suggests the formation of the defect associate between an oxygen vacancy and a tetravalent vanadium ion. The equilibrium oxygen partial pressure over the coexisting mixture of V₂O₅ and V₄O₉ and the standard free energy change of the reaction, 4V₂O₅→2V₄O₉+O₂ at temperatures between 880 and 936 K are determined. 24 refs.; 8 figs.; 1 table

[en] A simple experiment with mercury showed that solid-liquid transition in metals may be utilized for a thermal formation of a current-voltage characteristic of N-type as well as for the switching from a state of lower to a state of higher resistance. As a measure for the switching effectiveness a factor q appears, defined as a ratio of conductivities of the metal in liquid and solid state. The lower its magnitude the better are the switching characteristics. In pure metals q is rather large but smaller values may be expected in alloys. Empirical rules governing design of such alloys are discussed

[en] Conditions for electrochemical generation of cerium(IV) at glassy carbon in acetic acid in the presence of alkali-metal acetates and sodium perchlorate, respectively, were investigated. A high current efficiency was achieved in anodic oxidation of cerium(III) in acetate supporting electrolytes. Coulometric titration methods for the determination of reducing substances with the generated oxidant were also developed. The end-points were determined by the biamperometric and bipotentiometric methods. The error of the determinations was less than ± 2%

[en] An alizarin-modified electrode for the voltammetric determination of aluminium(III) is reported. The single-use modified electrode is simply prepared by dip-coating a high-density graphite electrode in an N,N-dimethylformamide solution of alizarin. Optimum experimental conditions for aluminium(III) determination include a solution pH of 8.4±0.2, an accumulation time of 1 min and use of the differential-pulse mode for measurement of the oxidation peak of the aluminium(III)-alizarin complex. The detection limit is 1.5x10^-7 M, the response is linear up to 1.0x10^-5 M and the relative standard deviation for replicate preparations of the electrode [at 7.5x10^-6 M Al(III)] is 3.8%. The determination of aluminium in soil samples is reported. (author). 14 refs.; 5 figs.; 2 tabs