NMR spectra of oriented 2,2,2-trifluoroethanol (CF3CH2OH)

Photolysis of hydrogen sulphide in argon, nitrogen and carbon monoxide matrices at 20 K produces HS radicals and S atoms. On warming the matrix, H₂S₂ and S₂ molecules are formed as a result of recombination reactions. The latter are identified by a blue-purple emission observed during warm-up of the matrix.     

Binary electrocatalysts for organic oxidations

The electro-oxidation of formaldehyde and methanol has been studied on a number of binary platinum electrocatalysts. These comprised mixed electro-deposits of Pt with Sb, As, Bi, Hg, Re, Te or Sn and a range of homogeneous Pt-Rh alloys of different, known, surface composition. These systems were found to exhibit an enhanced activity over that of platinum alone, and this behaviour was correlated with the ease of adsorption of oxygen on the added metal. The activities for organic oxidation were compared with predictions of a model involving reaction between adsorbed oxygen and organic species on the metal surface. The proposed mechanism accounts for the behaviour of both homogeneous and heterogeneous alloy systems.     

Ring-disk electrode studies of the formation,growth and transformation of iodine films formed during the anodic oxidation of iodide on platinum

The kinetics and mechanism of the formation, growth and dissolution of iodine films on platinum during the electrooxidation of iodide have been investigated using rotating-disk and ring-disk techniques. The dissolution-precipitation mechanism of film formation and a linear growth law for film growth has been confirmed. The iodine film on platinum is believed to be made up of an ionically insulating barrier layer covered by a porous overlayer. The oxidation behavior of iodide and ferrous species shows that the iodine film is predominantly an iodide-ion conductor. Also, a film transformation, responsible for the transient features observed during iodide oxidation has been confirmed. This transformation changes the mechanism of iodide transport through the film from a partly “pore”-type to a Grotthus-type mechanism. The ring current maximum, which occurs at the same instant as the disk current minimum, reveals the mechanism of dissolution of iodine film during the transient period as involving complexation with iodide. Evidence for the mass-transport-controlled component of the potentiostatic transient response has been obtained from the sinusoidal hydrodynamic modulation response.     

Fundamentals of lead acid cells part V. The oxidation of porous PbSO4/PbO2 on a pure lead base in sulphuric acid

Potentiostatic experiments are described in which porous electrodes of PbO₂ containing PbSO₄ are oxidised to PbO₂ in 5 M H₂SO₄. The process is analogous to the constant potential recharging of a lead acid cell. The form of the current transient depends upon the balance of PbSO₄ and PbO₂. For relatively small amounts of PbSO₄ a simple falling transient is obtained. For larger amounts the transient becomes more complicated and may be deconvoluted using a novel computer technique. Processes corresponding to various modes of electrocrystallisation are identified. The behaviour of newly prepared electrodes is compared and contrasted with the behaviour of electrodes stabilised by repeated cycling in 5 M H₂SO₄.     

Electrolyte—formamide interactions studied by raman spectroscopy

The effects of dissolved electrolytes on the structure of liquid formamide have been investigated by Raman spectroscopy. The spectral features are dependent on the concentration and nature of the dissolved electrolyte and are discussed in terms of direct electrolyte formamide interactions. Two vN—H bands, arising from ion—formamide species, have been observed superimposed on the spectrum of residual liquid formamide. The results lend further support to the interaction model for electrolytes in liquid formamide previously proposed by us on the basis of nuclear magnetic resonance and infrared spectral data.     

Calculation of the spectral distribution of absorption coefficients in vibrational spectra of complicated molecules,polymers and molecular crystals

The interpretation of vibrational spectra of complicated systems is necessary for the subsequent use of these spectra in the analysis of the structure and physical properties of complicated molecules, polymers and molecular crystals.This interpretation is accomplished with the aid of various methods including calculations of frequencies and in certain cases use of the intensities of absorption bands.     

An electron diffraction study of the molecular structure of gaseous allyl silane

The molecular structure of allyl silane has been studied by gas-phase electron diffraction. The experimental radial distribution curve has only four prominent peaks, resulting in serious resolution problems in the structure determination. A single conformer whose dimensions resemble those of related molecules fits the diffraction data. The torsion angle φ_siccc is102 ± 1°, measured from the conformation having Si-C and CC eclipsed.     

Glassy-carbon amperometric transducers as electrochemical detectors in liquid chromatography The influence of oxygen

The electrochemical behaviour of oxygen on glassy-carbon electrodes and the suitability of this electrode material for electroreduction of organic compounds have been investigated. The observed oxygen overpotential on a glassy-carbon electrode was more negative than that on an amalgamated gold electrode, thus allowing the determination of easily reducible compounds such as polynitro-aromatics and quinones without the need for exhaustive removal of dissolved oxygen. The detection limits (3sigma) were about 0.2, 0.8, and 2.5 pmole for polynitro-aromatics, mononitro-aromatics and quinones, respectively. Though the glassy-carbon material has a negative-potential limit about 250 mV more positive than that for the amalgamated gold electrode, and requires a longer equilibration time before use, it is more convenient for routine use.     

Iron(III)-titanium(IV)-oxide electrodes: Their structural,electrochemical and photoelectrochemical properties

Iron(III)-titanium(IV)-oxides of the general composition Fe_xTi_1-xO_y were prepared in the composition range x=0–0.9 by thermal decomposition of the corresponding metal salt solutions. For a medium range of composition, 0.1≤x≤0.7, amorphous oxides were formed under the given conditions of preparation. Electrochemical properties such as reduction and re-oxidation of the oxide, electrode capacity behaviour, oxygen evolution and reduction and the redox reaction, Fe²⁺/Fe³⁺, were investigated. Photoelectrochemical properties were obtained from photocurrent spectra and the dependence on potential of the photocurrent. Annealing experiments showed that crystallization yields lower photocurrents and a shift of the photocurrents spectra to shorter wavelengths. Thus, amorphous semiconductors seem worth being investigated for a possible application in electrochemical solar cells. An attempt is made to describe the impact of non-crystallinity on the photoelectrochemical behaviour of semiconductors. A model of the oxide is proposed to explain the electrochemical and photoelectrochemical properties of the oxides Fe_xTi_1-xO_y.     

Sensor System for Simultaneous Measurement of Oxygen and Hydrogen Peroxide Concentration During Glucose Oxidase Activity

An amperometric sensor system, based on a repetitive double step potential method at a glassy carbon electrode, has been developed for the simultaneous measurement of hydrogen peroxide and oxygen concentrations. The current measured at a potential of –1 V (vs. Ag/AgCl/saturated Cl^–) corresponds to the sum of the reduction currents of hydrogen peroxide and dissolved oxygen. The current measured at –0.55 V (vs. Ag/AgCl/saturated Cl^–) is due to the reduction of dissolved oxygen to hydrogen peroxide. Alternatively, the concentration of dissolved oxygen can also be determined using a Clark electrode. The concentration of hydrogen peroxide and dissolved oxygen during enzymatic conversion of glucose can be followed on line and be used to control the process.     

Charge-transfer properties of the hydrogen bond: Part 6. Charge-transfer theory and dipole moments of hydrogen-bonded complexes

The enhancement of the dipole moments of hydrogen-bonded complexes are discussed using Mulliken's charge-transfer theory.A linear relation is found between the ratio a/b and the ionization potential of the donor, I^V_D. This behaviour is similar to that previously found for halogen charge-transfer complexes [6].     

Theoretical investigation of the peroxidase-oxidase chemical oscillator for quantitative enzyme analysis

The theoretical basis for quantitative enzyme determinations by using the features of chemical oscillations is developed. An existing model of the peroxidase-oxidase chemical oscillator, consisting of the enzyme horseradish peroxidase, oxygen and reduced nicotinamide adenine dinucleotide (NADH), is modified to include a competing (analyte) reaction. The competitive effect between the analyte and the peroxidase on the observed periodic and chaotic oscillations forms the basis of the modified model. Corresponding differential equations are numerically integrated to produce plots of dissolved oxygen concentration vs. time. The calculated oscillatory oxygen transient shows a sensitive dependence on the analyte concentration. Utilizing the property of period doubling, a theoretical calibration graph can be generated for the determination of an analyte enzyme concentration. Special properties of the technique offer a potential combination of wide dynamic range and selectable precision. This demonstrates that the oscillator should prove experimentally useful for quantitative analysis.     

苯酚抑制条件下亚硫酸盐氧化的本征反应动力学

亚硫酸盐的氧化是湿法烟气脱硫工艺中的重要过程. 利用间歇式反应装置, 研究了苯酚抑制条件下亚硫酸盐氧化的本征反应动力学. 结果表明, 该复杂的反应过程分两个阶段进行, 即富氧区的快速反应和贫氧区的慢速反应. 在富氧区, 苯酚、亚硫酸盐和溶解氧的分级数分别为－0.5, 1.0和2.0, 反应的表观活化能为99.2 kJ•mol－1; 在贫氧区, 苯酚、亚硫酸盐和溶解氧的分级数分别为－0.5, 1.5和0, 反应的表观活化能为 129.7 kJ•mol－1. 结合实验结果, 对苯酚抑制条件下亚硫酸盐氧化的宏观反应动力学过程进行了推断.     

Hydrodynamic voltammetry at channel electrodes: Part VII. Current transients at double channel electrodes

Expressions for the transient current at the downstream electrode in response to galvanostatic electrolysis at the upstream electrode in the channel flow cell were derived by applying double Laplace transformation when the electrode reaction at the upstream electrode is kinetically controlled. The ratio of the transient current to the steady state current or the transient collection efficiency was calculated as a function of electrode geometry and θ

, where U_m is the mean flow velocity in the channel cell, D the diffusion coefficient of the electroactive species, b the half height of the channel, x₁ the length of the upstream electrode and t the time elapsed since the beginning of the galvanostatic electrolysis at the upstream electrode. Curves for the transient collection efficiency can be applied to evaluating the amount of adsorption at the upstream electrode when metal at the electrode is anodically dissolved in solution. Digital simulation was carried out. Transient curves, obtained analytically, were in good agreement with those evaluated from the digital simulation. In order to allow one to draw transient curves readily, we derived a simple approximate equation.     

Interferences from oxygen reduction reactions in bioelectroanalytical measurements: the case study of nitrate and nitrite biosensors

Bioelectroanalytical procedures based on cathodic processes are often subject to interference from dissolved oxygen. At the potentials applied for analyte detection, oxygen reduction may occur directly at the electrode or may be catalyzed by the electron mediators or the sensing enzyme of the biosensor. These processes affect the background current and may thus result in erroneous analyte quantification. In this review, current strategies to circumvent these oxygen interferences are presented and critically assessed with respect to their compatibility for on-site monitoring with amperometric biosensing devices operating at low potential. The main strategies consist in (1) use of oxygen scavenging systems to remove dissolved oxygen from the sample, (2) design of bioelectroanalytical approaches to shift the applied potential for analyte detection to more positive values, and (3) development of electrode materials to increase the overpotential for the oxygen reduction reaction. The latest developments in these approaches have recently led to the first biosensing devices based on reductases fully compatible with on-site monitoring requirements and this opens up possibilities for their widespread application.     

Molecular emission cavity analysis13-a new flame analytical technique : Part II.The determination of selenium and tellurium

The determination of 0.4–4 μg of selenium by molecular emission cavity analysis is described. Selenium in organic compounds is determined after oxygen flask combustion. Metal ion interferences are eliminated by reduction of selenium to the element, filtration onto a glass-fibre paper, and direct incorporation of the filter into the cavity. Applications to the determination of selenium in inorganic and organic compounds are described. The determination of μg-amounts of tellurium is also outlined.     

A new kind of iron-nitric oxide complex: the radical Fe(No)3CO

Photolysis of Fe(CO)₅ in non-polar solvents containing dissolved NO results in the generation of an EPR spectrum which is assigned to the free radical Fe(NO)₃CO.     

Flotation of traces of heavy metals coprecipitated with aluminum hydroxide from water and sea water

Microgram quantities of heavy metals in 1-l samples of water and sea water are quantitatively coprecipitated with aluminum hydroxide at pH 9.5. The precipitate is floated with the aid of sodium oleate and small nitrogen bubbles, separated and dissolved in 2 M nitric acid, and the heavy metals are determined by atomic-absorption spectrometry. The method is rapid and applicable to 9 heavy metals at the low p.p.b. level.     

还原态聚苯胺的光电化学研究

本文研究了还原态聚苯胺修饰电极的光电化学。通过不同基底电极、饱和气氛、温度、扰动方法（光照电极、电极旋转、气体鼓泡搅拌溶液、顺电极表面向电解池滴加电解液等）对还原态聚苯胺电流响应的影响及光谱分析，首次发现还原态聚苯胺的光电流响应并不是由于其吸收可见或近红外光激发而引起的，光的作作是通过扰动电极表面，促进电解质溶液中溶解的氧气对聚苯胺的氧化，仪器为了维持恒电位将氧化了的聚苯肢再还原而产生光电流响应。