Voltammetry and controlled-potential coulometry with boron carbide electrodes

With the boron carbide electrode, E_{p$\text{p}\text{2}$} values were determined for the reduction of the following ions: Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II), Ru(IV), Sb(V), and U(VI). The linear dependence of peak current on concentration is demonstrated for the U(VI) → U(IV) and Fe(III) → Fe(II) reductions at the boron carbide electrode. The suitability of the electrode for the controlled-potential coulometric ti trations of Fe(II) → Fe(III), Fe(III) → Fe(II), and U(VI) → U(IV) was studied; the results were inconclusive because of the small surface area that could be used conveniently and the possibility of oxygen leaks in the cell.     

Coulometric determination of uranium in presence of iron/plutonium using a platinum working electrode

A controlled potential coulometric method for the determination of uranium in the presence of iron or plutonium using a platinum working electrode has been developed. The method consists of reduction of uranium in 8M H₂SO₄ by Ti(III) followed by destruction of excess Ti(III) and selective oxidation of Fe(II) or Pu(III) to Fe(III) or Pu(IV), respectively, by sodium nitrite. The U(IV) is subsequently determined by electrolytic oxidation at Pt electrode using Fe(III) as an intermediate. The method was employed for the determination of uranium in synthetic mixtures of U+Fe and U+Pu containing varying ratios of U/Fe or U/Pu. The precision obtained for uranium results was ±0.25%.     

Note on a theoretical interpretation of the isotopic ratio vOH/vOD versus vOH in isotopically diluted HDO molecules in solid hydrates

A simple intra- and inter-molecular potential for water molecules engaged in hydrogen bonding has been used in a one-dimensional approximation for a theoretical interpretation of the experimental correlation $\text{v}$_OH/$\text{v}$_OD versus $\text{v}$_OH in solid hydrates. The variation in the equilibrium OH(D) distance has also been considered.     

Crystal structure and properties of the uranium chalcogenides α-US2 and α-USe2

The uranium chalcogenides α-US₂ and α-USe₂ crystallize in the tetragonal space group $\text{P4}\text{ncc}$ and not $\text{I4}\text{mcm}$ as previously reported. Their crystal structures have been determined from single-crystal X-ray diffraction data and refined to R = 0.041 and R = 0.034, respectively. Uranium atoms occupy two crystallographic sites: U(1) in (8f) and U(2) in (4c). The fourfold position, U(2), is incompletely filled with three uranium atoms which show a significant uniaxial delocalization. Properties are discussed in relation to this new crystal structure.     

Electrode processes of uranium ions and electrodeposition of uranium in molten LiCl-KCl

In the first part, LiCl-KCl-UCl₃ and LiCl-KCl-UCl₃-UCl₄ molten salts were prepared, which were studied employing cyclic voltammetry and chronopotentiometry techniques, respectively. It was determined that the reduction of U(IV) to uranium metal takes two steps. Firstly, U(IV) is reduced to U(III). Then, the reduction of U(III) to uranium metal occurs in a step with a global exchange of three electrons. Cyclic voltammetry studies indicated that at low sweep rates, the reduction of U(III) to uranium is reversible. However, a mixed control of both diffusion and electrontransfer is observed as the sweep rate increases. The diffusion coefficient of U(III) and the formal potential of U(III)/U versus Ag/AgCl reference electrode in these two salt systems were calculated respectively. In second part, based on the data of the electrode processes of uranium ions, electrodeposition of uranium metal was carried out. Uranium deposits were prepared adopting a 304 stainless steel electrode in the molten LiCl-KCl-UCl₃ and LiCl-KCl-UCl₃-UCl₄, respectively by employing suitable electrolytic techniques. The morphology of the deposits and the cross-section of the cathode were investigated by SEM. It was determined that at the beginning of the deposition process, uranium product alloys with stainless steel and forms a thin layer, and then uranium begins to grow adhering to the layer.     

The formation of tris(2-methyl-8-hydroxyquinolinato)-aluminum(III)

The compound Al(C₁₀H₃ON)₃ can be precipitated from a 20 % ($\text{v}\text{v}$) acetone—water medium in the absence of auxiliary complexing agents. Precipitation from an initially acidic solution yields a product containing hydrolyzed forms of aluminum(III) but precipitation from an initially basic solution results in the pure tris compound. Under appropriate conditions, solid-phase aluminum hydroxide can be completely converted to Al(C₁₀H₃ON)₃. Stability constants for the formation of aluminum(III) complexes of 2-methyl-8-hydroxyquinoline are given.     

Selective formation of peroxy-p-quinolato Co(III) complexes in the oxygenation of 4-alkyl-2,6-di-t-butylphenols with Co(II)-Schiff's base complexes

The oxygenation of 4-alkyl-2,6-di-$\text{t}$-butylphenols ($\text{2}$) with Co(II)-Schiff's base complexes in aprotic solvents such as CH₂Cl₂, THF, Py, and DMF leads to highly selective formation of the corresponding peroxy-$\text{p}$-quinolato Co(III) complexes. The reaction proceeds by mechanism involving a rate determining hydrogen abstraction by superoxo Co(III) species from $\text{2}$ giving phenoxy radical, rapid step of electron transfer from Co(II) complex to the phenoxy radical, and dioxygen incorporation into phenolato Co(III) complex thus formed.     

Determination of experimental parameters in the Fe(III)/Fe(II) system in 1 M H2SO4, with a polycrystalline gold electrode, taking advantage of its non-linear behaviour

In this work, the values of the heterogeneous standard rate constant and the transfer coefficient of the electrochemical system Fe(III)/Fe(II) in 1 M H₂SO₄ at a polycrystalline gold electrode were determined. The response spectrum to an ac potential of such amplitude as to make the behaviour of the electrode process non-linear was analysed. The experimental study was complemented by a theoretical study of the Fe(III)/Fe(II) system using numerical methods. Comparison of the experimental and theoretical data enabled the kinetic parameters of this electrode process to be determined.     

A new coated-wire cobalt(II)-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair

A cobalt-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair is described. The response is Nemstian (slope 29.3 $\text{mV}\text{pCo}$) in the cobalt concentration range 10^-1–10^-4 M in solutions with a constant ionic strength of 3.0 M made up with KSCN at 25°C. The electrode is suitable for end-point detection in titrations of cobalt(II) with EDTA as well as for direct potentiometric determinations of cobalt(II), even in the presence of large amounts of several metal ions (Ni²⁺, Fe²⁺, Mn²⁺, Mg²⁺, Ca²⁺, Ba²⁺) and anions (HCO₃^-, Br^-, I^-, NO₃^-, SO₄^2-).     

Étude du comportement polarographique de Ge(IV)

A reduction wave of Ge(IV) is observed at pH valvest greater than 7. The study of the wave has shown that the reduction is irreversible and occurs from Ge⁺⁴ to Ge° and that its height is strongly dependend on the pH. We have shown that the second wave observed by Das Gupta and Nair in the medium NH₄CI-NH₄OH cannot be ascribed to Ge. From an analytical point of view, it should be operated in the pH-regiXXXn. from 8 to 9, wliere the height of the wave can be considered as constant ; the diffusion current constant equals 6.82. In the KCl 0.05M medium, we have measured D = 0.79.1O^-5 cm²/sec and E$\text{1}\text{2}$ = —1.50 volt v/SCE; where as NH₄Cl-NH₄OH, medium. D = 0.89–10^-5 cm²/sec and E$\text{1}\text{2}$ = —1.56 volt v/SCE,     

Infrared chemiluminescence in the reactions of 0.45 eV hydrogen atoms with Cl2, SCl2 and PCl3

Infrared chemiluminescence from HCl has been observed in “arrested relaxation” experiments to yield vibrational and rotational distributions from the reactions $\text{H}$+Cl₂, SCl₂ and PCl₃, where $\text{H}$ denotes hydrogen atoms with translational energy of 0.45 eV. The following relative populations were determined: N_v-1: N_v-2: N_v-3: N_v-4: N_v-5: N_v-6 = 0.89:1.00:0.84:0.47:0.26:0.11 for $\text{H}$+Cl₂: N_v-1: N_v-2: N_v-3: N_v-4: N_v-5: N_v-6 = 0.80:1.00:0.72:0.48:0.24:0.10 for $\text{H}$+SCl₂: N_v-1: N_v-2: N_v-3: N_v-4: N_v-5 = 0.79:1.00:0.88:0.36:0.14 for H+PCl₃. In all three reaction systems the chemiluminescence was attributed to the primary chlorine abstraction. Comparison with the results of the thermal processes (0.04 eV hydrogen atoms) led to the following conclusions: for H+Cl₂ the excess of translational energy is transformed into translational product energy and rotational energy of the molecule HCl; for H+SCl₂ the excess of translational energy is transformed mainly into translational energy of the products and perhaps internal energy of SCl; for H+PCl₃ the excess of translational energy allows the observation of the primary abstraction reaction, which could in earlier experiments at 300 K not be separated from secondary chemiluminescent processes. Bimodal rotational distributions were confirmed for several vibrational states of HCl formed in the systems $\text{H}$+Cl₂, and $\text{H}$+SCl₂. Bimodal rotational distributions were also detected in the chemiluminescent reaction H(0.04 eV)+CH₃SCl → HCl(v ? 5)+CH₃S.     

Determination of seven trace elements in natural waters after separation by solvent extraction and anion-exchange chromatography

A method is described for the determination of cadmium, cobalt, copper, manganese, lead, uranium, and zinc in samples of natural waters. After acidification with hydrochloric acid the water sample is filtered and the diethyldithiocarbamates of the trace elements are isolated by extraction with acetone—chloroform (2:5) at pH 5. Following this preconcentration step the metal ions are adsorbed on a column of the strongly basic anion-exchange resin Dowex 1-X8 (chloride form) using as sorption solution a mixture (5:4:1, $\text{v}\text{v}$) of tetrahydrofuran, methyl glycol and 6 M hydrochloric acid. Successive elution is effected with 6 M hydrochloric acid (Co, Cu, Mn and Pb), 1 M hydrochloric acid (U) and 2 M nitric acid (Cd and Zn); the metal ions in the eluates are determined by atomic absorption spectrophotometry (except uranium, which is determined fluorimetrically). The procedure was used to determine the trace-metals in water and snow samples collected in Austria and to analyse a sample of sea water from the Adriatic Sea.     

Coulometric titration of salts of strong mineral acids in acetic anhydride by application of a hydrogen/palladium electrode

The application of H₂/Pd electrodes as generator and indicator electrodes is described for coulometric titrations of alkali metal halides and trivalent metal sulphates in acetic anhydride with potentiometric end-point detection. In acetic anhydride, sodium fluoride is a strong enough base to be titrated directly with H⁺ ions obtained by anodic oxidation of hydrogen dissolved in palladium. Other halides (NaCl, KCl, LiCl, KBr and NaBr) can be determined, after reaction of halides with mercury (II) acetate, by coulometric titration of the liberated base. Potentiometric end-point detection with a H₂/Pd-mercury(I) acetate electrode pair is satisfactory. Sulphates of Fe(III), Cr(III) and Al(III) are determined by back-titrating the excess of barium acetate after precipitation of barium sulphate. The errors in these determinations are < 1% for concentrations ranging from 0.001 to 0.003 M.     

Oxygenation of p-nitrophenylhydrazones with Co(II)-schiff base complexes

$\text{p}$-Nitrophenylhydrazones, unsusceptible to autoxidation, are readily oxygenated in the presence of a five-coordinate cobalt(II)-Schiff base complex, Co(II)(MeOSalen) (Py) leading to quantitative formation of novel 1-($\text{p}$-nitrophenylazo)-1-peroxy Co(III) complexes 2, which were isolated as crystals. A plausible mechanism involving hydrogen abstraction by Co(III)(O₂^?.) from the substrate followed by formation of a substrate anion Co(III) complex intermediate is proposed.     

Determination of sulfate in waters

Determination of sulfate in industrial waters is performed by shaking with Dowex 50-X8 resin (removing of metal ion interferences) and titration of aqueous acetone ($\text{1}\text{1}\text{,}\text{v}\text{v}$) solution with barium perchlorate employing Dimethylsulfonazo III as indicator. Only phosphate and arsenate interfere.     

Analytical applications of triethylenetetraminehexaacetic acid : Part I. the influence of TTHA on the polarographic reduction of some metal ions

The influence of triethylenetetraminehexaacetic acid (TTHA) on the d.c. and square-wave polarographic curves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), Zn(II), Fe(III), Bi(III), Sb(III), As(III) and In(III) has been investigated in several supporting electrolytes over the pH range 1–13. The E_{$\text{1}\text{2}$} and E_p values with and without a 10-fold excess of TTHA are compared. Some analytical applications are suggested.     

Etude polarographique du rhodium(III) en milieu thiocyanate. Application au dosage microanalytique de composes organometalliques: Polarographie study of rhodium(III) in thiocyanate media. Application to the microanalysis of organometallic compounds.

Polarographie study of rhodium(III) in thiocyanate media. Application to the microanalysis of organometallic compounds.Reduction of rhodium(III) at the dropping mercury electrode is performed in thiocyanate media by classical a.c. and pulse polarography, and linear sweep voltammetry. The reduction (E$\text{1}\text{2}$ = —0.5 V vs. SCE) is shown to be a 3e irreversible transfer. Coulometric investigation confirms this result and rhodium gives a dark grey deposit at the mercury surface. This explains the i—t curves even in the presence of gelatin as maximum suppressor and the anomalous slope of log [i/(i_d - i)] at potentials more cathodic than the E$\text{1}\text{2}$ value. A.c. and differential pulse polarography are suitable for analysis down to the 0.1-ppm level. Palladium and platinum do not interfere although there is enhancement of the base line, but ruthenium affects the end of the polarogram, probably because of catalytic hydrogen evolution. Applications to organometallic compounds and industrial catalytic bimetallic grids show good agreement with the predicted compositions.     

Studies on the coulometric determination of uranium and plutonium employing a graphite electrode

Summary Graphite has been employed as a working electrode in the controlled potential coulometric determination of uranium and plutonium. The couples U(VI)/U(IV) and Pu(IV)/Pu(III) employed for analysis have diverse redox potentials and commonly the working electrodes employed are mercury and platinum. A graphite electrode in the shape of a beaker showed satisfactory performance for the quantitative reduction of U(VI) to U(IV) and Pu(IV) to Pu(III) and also for quantitative oxidation of Pu(III) to Pu(IV). Studies on the levels of the background current, blank values and their reproducible behaviour in acid media have been carried out with a view to achieve good precision and accuracy. A software-based predictive evaluation technique of end-point charge has been investigated. The results have shown that the graphite electrode can be used for the determination of both uranium and plutonium in the presence of each other with a precision and accuracy of better than ±0.5%.     

The effect of pH on some outer-sphere electrode reactions at carbon electrodes

The apparent heterogeneous rate constant, k°_app, for three couples known to undergo outer-sphere electron transfer reactions has been investigated at carbon, gold, and platinum electrodes as a function of solution pH. The rates are found to be pH dependent at two different types of glassy carbon and at carbon paste but not at metallic electrodes. The rate is found to decrease with increasing pH for Fe(CN)^{$\text{3?}\text{4?}$}₆ and IrCl^{$\text{2?}\text{3?}$}₆, and the opposite effect is observed for the Ru(NH₃)^{$\text{3+}\text{2+}$}₆ couple. For the three compounds examined, the magnitude of the pH dependent rate changes can be associated with a change in the magnitude of the potential of the reaction layer induced by a change in surface charge of ～ 2 × 10^?7 C cm^?2. The pH dependence of the observed rate constant at glassy carbon can be attenuated by heat treatment, chemical reduction, or esterification of the surface. This behaviour is consistent with the theory that the pH dependence of k°_app arises from the presence of functional groups on the carbon surface.     

Voltamperometric determination of uranium and plutonium in alkaline solutions

The simultaneous determination of U(VI), Pu(VI), Pu(V) in 0.5–4.0 M NaOH has been elaborated by means of classical and differential pulse voltamperometry. U(VI) is determined with a dropping mercury electrode (DME) at the half-wave potential of E_1/2=–0.89 V vs. Ag/AgCl reference electrode due to reduction to U(V). The limiting current or peak heights are proportional to uranium(VI) concentration in the range of 1.3.10^–7–3·10^–4 M U(VI). Deviation from proportionality is observed for higher concentrations due to polymerization of uranates. Pu(VI) and Pu(V) are determined with a platinum rotating electrode at E_1/2=–0.02 V due to the reaction Pu(VI)+e^–»Pu(V) and with DME at E_1/2=–1.1 V due to the reduction to Pu(III). The limiting currents of both Pu(VI) and Pu(V) are proportional to their concentrations in the range of 4·10^–6–1.2·10^–3 M Pu. The determination of U(VI), Pu(VI), Pu(V) is not interfered by the presence of the following salts: 2M NaNO₃, 2M NaNO₂, 1.5M NaAlO₂, 0.5M NaF and ions of Mo(VI), W(VI), V(V), Cu(II). The presence of CrO ₄ ^2– and FeO ₂ ^– ions disturbs the determination of U(VI) in 1–4M NaOH, however, contribution of the reaction Fe(III)+e^–»Fe(II) to uranium reduction peak can be calculated from the height of the second peak Fe(II)+2 e^–»Fe(0).