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排序方式: 共有138条查询结果,搜索用时 15 毫秒
51.
Alan M. Bond Terr L.E. Henderson Keith B. Oldham 《Journal of Electroanalytical Chemistry》1985,191(1):75-90
An efficient method is presented for analyzing electrochemical processes controlled by diffusion and by the kinetics of heterogeneous electron-transfer. The method is based on a three-dimensional concept and has the advantage of utilizing all the data available from a voltammetric experiment. The three-dimensional method provides a useful diagnosis of whether Butler-Volmer kinetics is appropriate and, if so, for calculating the standard heterogeneous charge transfer rate constant, reversible halfwave potential, diffusion coefficient and charge transfer coefficient. Experiments on the [Cr(CN)6]3?+e?[Cr(CN)6]4? reaction using cyclic voltammetry are reported and the parameters so determined are shown to agree with literature values. 相似文献
52.
A statistical study of the potential dependence of a transfer coefficient supports the Marcus theory
A.M. Bond P.J. Mahon E.A. Maxwell K.B. Oldham C.G. Zoski 《Journal of Electroanalytical Chemistry》1994,370(1-2)
Cyclic voltammograms for the reduction of 2-methyl-2-nitropropane at a mercury electrode in acetonitrile solvent have been analyzed carefully by the “global” method. The dependence of the logarithm of the heterogeneous rate constant on the potential is only mildly parabolic, but statistical analysis shows that the curvature is nonetheless genuine and cannot be explained by random errors. The sign of the curvature is that predicted by the Marcus theory and the magnitude of the effect is also compatible with theory. No trend with scan rate is observed in any of the measured kinetic, thermodynamic or transport parameters. 相似文献
53.
Keith B. Oldham 《Journal of Solid State Electrochemistry》1998,2(6):367-377
When insoluble insulating crystals adhere to an electrode, the three-phase junction – where electrolyte solution, electrode
and crystal meet – is the only feasible site for an electrochemical reaction. Moreover, sustained reaction is possible only
if ions from the electrolyte solution are able to enter the crystal through the three-phase junction and disperse within the
crystal. Here, order-of-magnitude calculations demonstrate that diffusion to the three-phase junction is well able to support
voltammetry under standard experimental conditions. A model is built for cases of adherent cubes of uniform size and thereby
the shapes of chronoamperograms, chronograviograms and cyclic voltammograms are predicted. The model assumes that the ion
concentration at the three-phase junction plays a crucial role in the voltammetry, being determined by quasi-steady-state
ion diffusion from the bulk, the thermodynamics of the electrode reaction, and the extent to which the crystal has already
undergone reaction. Depending on the crystal size and scan rate, cyclic voltammograms may mimic solution-phase voltammograms
from classical thin-layer experiments or from typical stripping experiments. The effect of size heterogeneity on cyclic voltammetry
is simulated for lognormal distributions.
Received: 5 January 1998 / Accepted: 17 April 1998 相似文献
54.
C. C. Hayward G. Oldham A. R. Ware 《Journal of Radioanalytical and Nuclear Chemistry》1971,7(2):341-346
The feasibility and advantages of fast neutron activation analysis in a non-aqueous flowing system, using economical irradiation
techniques are outlined. The application of the method to the determination in solution of elements producing isotopes with
half lives in the range 588—29.4 sec, the selection of the optimum flow rate to minimise interferences for each element, and
their limits of detection are also given. A method for the prediction of the optimum flow rate, on a given system, for the
determination of any element producing an isotope of known half life is also given. 相似文献
55.
The conventional method of measurement in 14 MeV activation analysis is to employ gamma-ray spectrometry. The method has the
advantage of good selectivity but this is at the expense of sensitivity. In order to improve sensitivity the authors have
employed Cerenkov counting techniques and by the careful use of absorbers in a specially designed cell together with double
decay procedures have still retained a considerable degree of selectivity. The method has been applied to neutron flux measurement
and to the majority of the elements in the periodic table. 相似文献
56.
57.
Schaaf O Jarvis AP van der Esch SA Giagnacovo G Oldham NJ 《Journal of chromatography. A》2000,886(1-2):89-97
Based on reversed-phase high-performance liquid chromatography (RP-HPLC) and atmospheric pressure chemical ionization (APCI) mass spectrometry, a HPLC-MS method was developed to permit the rapid qualitative and quantitative analysis of azadirachtin and related tetranortriterpenoids from seeds and tissue cultures of Neem (Azadirachta indica). APCI+ standard scanning mass spectra of the major Neem triterpenoids were recorded and utilized to select suitable ions for selected ion monitoring (SIM). Transitions for selective reaction monitoring (SRM) were based on MS-MS experiments. Using SIM, major Neem triterpenoids were detected in callus culture material and seed kernels of A. indica. The limit of detection for azadirachtin in extract samples (approximately 1 ng ml(-1) or 10 pg in SIM mode) was determined to be (with respect to injected absolute amounts) approximately 1000-times lower than values quoted in the literature for existing HPLC methods (approximately 200 ng ml(-1) or 10 ng). In addition to high sensitivity, the HPLC-MS method is able to tolerate minimal sample preparation and purification, dramatically reducing total analysis time. 相似文献
58.
59.
The effect of arsenate on phosphate determination by the malachite green spectrophotometric method was investigated. The molar absorptivities of the molybdophosphate and malachite green–molybdoarsenate species at 625 nm and a final acidity of 0.38 M were calculated as 10.4±0.13×104 and 7.2±0.17×104 l mol−1 cm−1 respectively, indicating that arsenate could interfere in phosphate measurement. Arsenate concentrations as low as 23 μg l−1 caused increase in colour development in phosphate solutions. However, the extent of colour development for both anions depended on the final acid concentration of the solution. An acidified sodium sulphite solution (0.83 M NaSO3, 0.83 M H2SO4) quantitatively prevented arsenate colour development up to 300 μg l−1 As(V). It was also demonstrated that the method removed As(V) interferences in mixed As/P solutions and therefore can be used to treat natural water samples with elevated arsenate concentrations before phosphate measurement. 相似文献
60.
Bowmaker GA Hanna JV Hahn FE Lipton AS Oldham CE Skelton BW Smith ME White AH 《Dalton transactions (Cambridge, England : 2003)》2008,(13):1710-1720
Single-crystal structural characterizations confirm the existence of the unusual 1 : 4 copper(I) halide : unidentate ligand adducts [Cu(CNt-Bu)4]X for X = Cl, Br (two forms), I (the chloride and one form of the bromide being solvated) with crystal packing dominated by stacks of interleaving cations. Cu-C range between 1.941(2) and 1.972(4) A. The structure of the 1 : 2 chloride complex is also recorded, being [ClCu(CNt-Bu)2], with the copper(I) atom environment trigonal planar, while CuCN : (CNt-Bu) (1 : 1) is a single-stranded polymer which spirals about a crystallographic 3-axis (CN scrambled), the ligands being pendant from the ...CuCNCuCN... string. The (5Cu static broadline NMR spectra of [Cu(CNt-Bu)4]I and [Cu(CNt-Bu)4]Br.H2O in the solid state exhibit dominant, narrow -1/2 <--> +1/2 central transition resonances and associated +/-1/2 <--> +/-3/2 satellite transition resonances which are characteristic of first-order quadrupole broadened systems, while associated high-resolution 65Cu MAS NMR data provide accurate measurement of the 65Cu isotropic chemical shifts. Both approaches provide complete data on the quadrupole and chemical shift interactions which contribute to these spectra. Far-IR spectra of products of reactions involving a range of CuX : t-BuNC ratios reveal the existence of 1 : 1.5 adducts for X = Br, I. Metal-carbon and metal-halogen bands are assigned in the far-IR spectra, which indicate a binuclear double halogen-bridged structure for the 1 : 1.5 complexes. 相似文献