Theoretical and experimental investigation of steady-state voltammetry for quasi-reversible heterogeneous electron transfer on a mercury oblate spheroidal microelectrode.

A mercury microelectrode formed by electroreduction of mercury on an inlaid gold microdisk is experimentally shown to be well modeled by oblate spheroidal geometry when the ratio of the semiminor axis to the semimajor axis of the protruding drop is less than 1. The validity of the geometry is established by comparison of the experimentally determined coefficient in the steady-state diffusion current equation with the theoretical value for oblate spheroidal geometry. Spherical cap geometry is also shown to be an equally valid geometric model; however, theoretical treatment for this system is more difficult. The theory of a quasi-reversible electrode process is developed and applied to the determination of the electrode parameters of the RuIII(NH3)6/RuII(NH3)6 electrode reaction on a mercury oblate spheroidal microelectrode. Results agree well with others found in the literature for the same process on a mercury electrode.     

Apparent Formation of an Oxidant by Electrochemical Reduction in the Mercury(0,I,II) Chloride System

The paradoxical appearance of a cathodic reaction sometimes observed in anodic stripping voltammetry and stripping potentiometry when using mercury film electrodes in chloride media containing mercury(II) has been investigated by systematically varying relevant chemical and electrochemical parameters and comparing the results with thermodynamic equilibrium calculations. Microscopic observations of morphological changes on the electrode surface caused by potential variations were made possible by using a novel electrode design. Three conditions have to be fulfilled for the cathodic reaction to occur: (a) formation of calomel by reaction between elemental mercury on the electrode surface and mercury(II) in solution, (b) subsequent reduction of mercury(II) to elemental mercury on the calomelized electrode surface, and (c) a chloride concentration in the range 0.001-3.5 M. Different ways of avoiding the interference from the cathodic reaction in stripping voltammetry and stripping potentiometry are experimentally demonstrated, and a mechanism for the appearance of the cathodic reaction is proposed.     

Effect of Electrode Size on the Performances of Micro-EDM

Understanding the effect of processing parameters on the tool electrode wear during micro-electrical discharge machining (micro-EDM) is helpful to predict and compensate the electrode wear, so as to improve the machining precision. In this paper, experiments are carried out and the influences of tool electrode diameter on the micro-EDM process are discussed based on the skin effect and area effect. It is demonstrated that the machining speed, tool wear, and taper rate are different with the increase of tool electrode diameter. Due to the skin effect and area effect, larger electrode diameter results in higher material removal rate along with higher tool wear rate. The electrode material removal increment is more than the workpiece material removal increment with the increase of tool electrode diameter, which leads to the increase of relative tool wear ratio. Discharge energy is concentrated on the tool surface which enhances the possibility of discharge on the side face and the corner of the tool electrode during the micro-EDM, especially when drilling with a larger tool electrode. As a result, a tool electrode with larger diameter results in a higher taper rate.     

Electrochemical and spectroscopic investigation of the reduction of dimethylglyoxime at mercury electrodes in the presence of cobalt and nickel

Voltammograms (polarograms) obtained from solutions of cobalt and nickel containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals. Detailed electrochemical and spectroscopic studies on the reduction process observed in the analytically important ammonia buffer media at mercury dropping, hanging, and pool electrodes are all consistent with an overall 10-electron reduction process, in which both the dmgH(2) ligand and cobalt ions are reduced in the adsorbed state: Co(II) + 2dmgH(2) ? (solution) [Co(II)(dmgH)(2)] + 2H(+); [Co(II)(dmgH)(2)] + Hg ? (electrode) [Co(II)(dmgH)(2)](ads)Hg; and [Co(II)(dmgH)(2)](ads)Hg + 10e(-) + 10H(+) → Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubility of the nickel complex in aqueous media restricts the range of studies that can be undertaken with this system, but an analogous mechanism is believed to occur. Low-temperature voltammetric studies in dichloromethane at a frozen hanging mercury drop electrode and in situ electron spin resonance electrochemical measurements on more soluble analogues of the dimethylglyoxime complexes are consistent with an initial one-electron reduction step being available in the absence of water. Deliberate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examined. The results of the present study are compared with the wide range of mechanisms proposed in other studies.     

超高纯度硝酸银制备工艺原理的探讨

照相用超高纯度硝酸银可用于生产高感光度的黑白与彩色感光材料。在超高纯度硝酸银中的各种杂质含量应限止在（ng)纳克级。特别是其中的（Hg)汞杂质的活性将严重地损害到卤化银颗粒的感光中心，以及影响到产品的稳定性与保存性。为此，笔者对于2000年以前有关照相用硝酸银制备的历史文献约为150篇参考文献做了系统的检索以后，根据（Hg)汞元素与汞盐的化学物理特性，在本文中探讨几种消除（Hg)汞杂质的不同生产工艺原理与方法。同时，又对于大批量工业生产装置的发展历史进行研究以后，再提出一些改进意见，包括：待申请的专利技术。     

Use of DNA repair enzymes in electrochemical detection of damage to DNA bases in vitro and in cells

Electrochemical measurements at mercury or solid amalgam electrodes offer a highly sensitive detection of DNA strand breaks. On the other hand, electrochemical detection of damage to DNA bases at any electrode is usually much less sensitive. In this paper, we propose a new voltammetric method for the detection of the DNA base damage based on enzymatic conversion of the damaged DNA bases to single-strand breaks (ssb), single-stranded (ss) DNA regions, or both. Supercoiled DNA exposed to UV light was specifically cleaved by T4 endonuclease V, an enzyme recognizing pyrimidine dimers, the major products of photochemical DNA damage. Apurinic sites (formed in dimethyl sulfate-modified DNA) were determined after treating the DNA with E. coli exonuclease III, an enzyme introducing ssb at the abasic sites and degrading one of the DNA strands. The ssb or ssDNA regions, or both, were detected by adsorptive transfer stripping alternating current voltammetry at the mercury electrode. This technique offers much better sensitivity and selectivity of DNA base damage detection than any other electrochemical method. It is not limited to DNA damage in vitro, but it can detect also DNA base damage induced in living bacterial cells.     

Spectroelectrochemical sensing based on attenuated total internal reflectance stripping voltammetry. 2. Determination of mercury and lead

Detection of lead and mercury by attenuated total internal reflectance spectroscopy coupled to stripping voltammetry is demonstrated. Changes in attenuation of light passing through an indium tin oxide optically transparent electrode (ITO-OTE) accompany the electrodeposition and stripping of lead and mercury on the electrode surface. The change in absorbance during stripping of electrodeposited metal constitutes the analytical response that enables detection over a range of 2.5 x 10(-7)-5 x 10(-5) and 5 x 10(-8)-5 x 10(-5) M for mercury and lead, respectively. The spectroelectrochemical responses of mercury and lead on the ITO surface are characterized and optimized with respect to solution conditions, the potential excitation signals used for deposition and stripping, and wavelength for detection. The deposited metals were examined by environmental scanning electron miscroscopy, and the electrodeposition pattern of lead and mercury was found to influence the optical response.     

Method of obtaining gallium from aluminate solution by electrolysis

Abstract

Gallium is an increasingly important material in the fields of semiconductors and energy transfer. A prime source of gallium is the aluminate solution that remains after the purification of bauxite. The authors have sought a way of reclaiming gallium economically by electrolysis of a laboratory aluminate solution without having to use a cathode of mercury – an environmental pollutant. Cathodes of copper, indium, 70In–30Ga, Wood's alloy, and mercury (for comparison) were used with a wide range of anodes. The study accounted for the effects of electrode material, temperature, current density, and initial gallium concentration on the yield, energy consumption, and utilization of both current and electrode. The best results were obtained with indium or In–Ga cathodes and with platinum, Pt–Ti, or stainless steel anodes, at 75°C and a current density of ~100 Am^?2. Electrolysis was more efficient the higher the gallium concentration, demonstrating that commercial–scale electrolysis of aluminate solution is unlikely to be economically viable without prior concentration of gallium.

MST/305     

Antimony film electrode for electrochemical stripping analysis

In this work, an antimony film electrode (SbFE) is reported for the first time as a possible alternative for electrochemical stripping analysis of trace heavy metals. The SbFE was prepared in situ on a glassy carbon substrate electrode and employed in combination with either anodic stripping voltammetry or stripping chronopotentiometry in nondeaerated solutions of 0.01 M hydrochloric acid (pH 2). Several key operational parameters influencing the electroanalytical response of SbFE were examined and optimized, such as deposition potential, deposition time, and composition of the measurement solution. The SbFE exhibited well-defined and separated stripping signals for both model metal ions, Cd(II) and Pb(II), surrounded with low background contribution and a relatively large negative potential range. The electrode revealed good linear behavior in the examined concentration range from 20 to 140 microg L-1 for both test metal ions, with a limit of detection (3sigma) of 0.7 microg L-1 for Cd(II) and 0.9 microg L-1 for Pb(II) obtained after a 120 s deposition step, and good reproducibility, with a relative standard deviation (RSD) of +/-3.6% for Cd(II) and +/-6.2% for Pb(II) (60 microg L-1, n = 12). When comparing the SbFE with the commonly used mercury film electrode and recently introduced bismuth film electrode, the newly proposed electrode offers a remarkable performance in more acidic solutions (pH < or = 2), which can be advantageous in electrochemical analysis of trace heavy metals, hence contributing to the wider applicability of electrochemical stripping techniques in connection with "mercury-free" electrodes.     

Probing mercury species-DNA interactions by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection

The interactions of inorganic mercury Hg(II), methylmercury (MeHg(I)), ethylmercury (EtHg(I)), and phenylmercury (PhHg(I)) with DNA have been probed by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection (CE-ETAAS) in combination with circular dichroism and Fourier transform infrared spectroscopy. The CE-ETAAS assay allows sensitive probing of the level of DNA damage by mercury species, extraction of thermodynamic and kinetic information on the interactions of mercury species with DNA, and provides direct evidence for the formation of mercury species-DNA adducts. The binding affinity of mercury species to DNA increases in order of Hg(II) < EtHg(I) approximately PhHg(I) approximately MeHg(I). The interactions of mercury species with DNA follow a first-order kinetics for mercury species and zero-order kinetics for DNA. Mercury highly covalently coordinates to endocyclic and exocyclic N sites of DNA bases. However, the interactions of DNA with mercuric species cause no transition of the DNA original conformation. The results reveal that organomercuric species exhibit stronger affinity and faster binding to DNA and show more potential damage to DNA than Hg(II) in view of the kinetic and thermodynamic evaluations. Moreover, MeHg(I) exhibits the fastest binding to DNA, suggesting that MeHg(I) enjoys superiority over the other mercuric species for rapid formation of a stable complex with DNA, whereas Hg(II) shows the slowest binding to DNA. The present study provides new evidence and understanding of the binding modality of mercuric species to DNA.     

Digital pulse ac voltammetry for the simultaneous analysis of electroactive and electrosorptive species in flow systems

A digital two-step and three-step pulse potential ac voltammetry system was proposed and applied for the simultaneous analysis of electrosorptive and electroactive species in flow systems. To perform the ac polarography function, a PC was interfaced to a potentiostat to mimic all the necessary hardware functions of an analog ac polarograph. From the measurement of the change of phase-selective charging current and the zero-order current, I(3)(-), Br(-) specifically adsorbed and Cd(2+), Pb(2+) reduced at a hanging mercury drop electrode can be determined simultaneously in a FIA and IC system. With the digital pulse ac voltammetry-coupled IC, detection limits as low as 5.0 microM and linear dynamic ranges from 5.0 to 100 or 200 microM with linear correlation coefficients better than 0.9990 were found for the analysis of I(3)(-), Br(-), and S(2)O(3)(2)(-).     

Determination of selenium(IV) by a photooxidized 3,3'-diaminobenzidine/perfluorinated polymer mercury film electrode

A new, and easily fabricated, chemically modified electrode for the determination of selenium(IV) was examined by cathodic square-wave stripping voltammetry. This new electrode consisted of an anion-exchange perfluorinated polymer (Tosflex) coated thin mercury film electrode containing photooxidized 3,3'-diaminobenzidine (ODAB). The coating solution of Tosflex and ODAB was spin-coated on a glassy carbon electrode followed by electroplating of a thin film of mercury. During the preconcentration, ODAB was reduced electrochemically and selenium was accumulated simultaneously onto the electrode by interacting with the reduced ODAB. After a 5-min preconcentration period, linear response was observed from 0.5 to 50 ppb selenium, and the detection limit was 0.1 ppb. The proposed method does not require a darkened room, which was required in many of the previous methods involving 3,3'-diaminobenzidine. In addition, the resistance to interference from surface-active compounds was improved by incorporating Tosflex in the film.     

Removal of mercury species with dithiocarbamate-anchored polymer/organosmectite composites

Mercury is one of the most toxic heavy metals found in solid and liquid waste disposed by chloro-alkali, paint, paper/pulp, battery, pharmaceutical, oil refinery and mining companies. Any form of mercury introduced to nature through any means is converted into a more toxic form such as methylmercury chloride (as produced by aquatic organisms) which usually accumulates in the tissue of fish and birds.

The primary aim of this study was to investigate performance of dithiocarbamate-anchored polymer/organosmectite composites as sorbents for removal of mercury from aqueous solution. The modified smectite nanocomposites then were reacted with carbondisulfide to incorporate dithiocarbamate functional groups into the nanolayer of the organoclay. These dithiocarbamate-anchored composites were used for the removal of mercury species [Hg(II), CH₃Hg(I) and C₆H₅Hg(I)]. Mercury adsorption was found to be dependent on the solution pH, mercury concentration and the type of mercury species to be adsorbed. The maximum adsorption capacities were equal to 157.3 mg g⁻¹ (782.5 μmol g⁻¹) for Hg(II); 214.6 mg g⁻¹ (993.9 μmol g⁻¹) for CH₃Hg(I); 90.3 mg g⁻¹ (325 μmol g⁻¹) for C₆H₅Hg(I). The competitive adsorption capacities (i.e. adsorption capacities based on solutions containing all three mercuric ions) are 7.7 mg g^−l (38.3 μmol g⁻¹), 9.2 mg g^−l (42.6 μmol g⁻¹) and 12.7 mg g⁻¹ (45.7 μmol g⁻¹) for Hg(II), CH₃Hg(I) and C₆H₅Hg(I), respectively, at 10 ppm initial concentration. The adsorption capacities on molar basis were in order of C₆H₅Hg(I) > CH₃Hg(I) > Hg(II).     

Adsorptive behaviour of mercury on algal biomass: competition with divalent cations and organic compounds

Biosorption processes constitute an effective technique for mercury elimination.Sorption properties of native and acid-treated Sargassum muticum have been studied. Effect of pH, initial mercury concentration and contact time studies provided fundamental information about the sorption process. This information was used as the reference values to analyse mercury sorption under competition conditions. Saline effect has shown little influence in sorption, when only electrostatic modifications took place upon salt addition. On the contrary, if mercury speciation dramatically changed owing to the addition of an electrolyte, such as in the case of chloride salt, very large modifications in mercury sorption were observed. Competition with other divalent cations or organic compounds has shown little or none effect on mercury, indicating that a different mechanism is taking place during the removal of these pollutants.Finally, continuous flow experiments have clearly shown that a reduction process is also taking place during mercury removal. This fact is not obvious to elucidate under batch sorption experiments. Scanning Electron Microscopy analysis of the surface of the materials show deposits of mercury(I) and metallic mercury which is indicative of the reduction process proposed.     

Design and synthesis of a more highly selective ammonium ionophore than nonactin and its application as an ion-sensing component for an ion-selective electrode

A novel ammonium ionophore, which exhibits superior NH4+ selectivity compared with that of the natural antibiotic nonactin, was successfully designed and synthesized based on a 19-membered crown compound (TD19C6) having three decalino subunits in the macrocyclic system. This bulky decalino subunit is effective for (1) increasing the structural rigidity of the cyclic compound, (2) introducing the "block-wall effect", which prevents forming a complex with a large ion, and (3) increasing the lipophilicity of the ionophore molecule. In the ammonium ionophore design, the first factor contributes to increasing the NH4+ selectivity relative to smaller ions such as Li+, Na+, or even the closest size, K+, and the second factor increases the NH4+ selectivity over larger ions such as Rb+ and Cs+. The X-ray structural analysis proved that TD19C6 forms a size-fit complexwith NH4+ in its crown ring cavity. As an application of this ionophore, an ion sensor (ion-selective electrode) was prepared, which exhibited NH4+ to K+ and Na+ selectivity of 10 and 3,000 times, respectively. This electrode showed a better performance compared to the electrode based on nonactin, which is the only ammonium ionophore presently used in practical applications.     

Charge injection engineering of ambipolar field-effect transistors for high-performance organic complementary circuits

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (～4.1 eV) compared to that of a pristine Au electrode (～4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ～0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ～0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain >50 and high noise margin >75% of ideal value) and ring oscillators (oscillation frequency ～12 kHz) based on a solution-processed ambipolar polymer are demonstrated.     

Measurement of association and dissociation rate constants for lead(II)/18-crown-6 using square wave voltammetry at a glassy carbon mercury film electrode

Understanding the rate parameters of metal ion-ligand complexes is necessary for sensing, separations, and responsive materials. The complexation between 18-crown-6 and lead(II) is of particular interest due to the potential use of this chemistry in sensors and separations. We have applied square wave voltammetry at a glassy carbon mercury film electrode to this problem. Lead(II) in aqueous solution containing an excess of 18-crown-6, studied with different experimental time scales, yields stoichiometry, binding constants, and rate constants (25 degrees C). For pulse times longer than 10 ms, the glassy carbon mercury film electrode acts as a planar electrode. For shorter pulse times, a roughness correction factor must be used to calculate dimensionless current because of the increase in effective area due to the droplike nature of the adsorbed mercury. Lead(II) forms a 1:1 complex with 18-crown-6 in both nitrate and perchlorate media. Log K for the complex with the nitrate counterion is 4.13 +/- 0.09 (SEM); in the presence of perchlorate it is 4.35 +/- 0.09 (SEM). The formation rate constants, kf, for the nitrate and perchlorate systems are (3.82 +/- 0.89) x 107 and (5.92 +/- 1.97) x 106 M-1 s-1, respectively. The dissociation rate constants, kd, are (2.83 +/- 0.66) x 103 s-1 with nitrate as the counterion and (2.64 +/- 0.88) x 102 s-1 with perchlorate as the counterion. The significant difference in rate constants for the two anions is probably caused by the ion pairing that occurs with lead(II) nitrate.     

Classification of simple amalgams

Taking into account the type of phase diagram of metal-mercury, solubility, heat of dissolution process, activity and diffusion coefficient of a metal in mercury as well as the kinetics of electroreduction of metallic aquo-cation on a mercury electrode with an amalgam formation, a general classification of simple amalgams into four groups is proposed. On this basis some experimentally unknown amalgam properties may be predicted which have significant meaning in technical and chemical applications.     

一种薄膜材料电阻率测试用环形电极设计

针对航天器用高电阻率薄膜材料的电阻率测试问题进行了研究。通过对现有高阻值电阻率测试环形电极设计方法进行仿真理论分析,结合数学模型推导,提出了一种环形电极有效测试宽度及尺寸设计取值方法,并制成薄膜材料测试用环形电极装置。通过实验实现了航天器用薄膜材料表面电阻率和体电阻率测量,相对示值误差可控制在9%范围内;该装置可应用于体积电阻率在105~1018Ω·cm的航天器用复合材料电阻率的测试。     

Fabrication of an optoelectrochemical microring array

In this paper, we describe a novel approach for fabricating an optoelectrochemical microring array. The array was fabricated by coating individual optical fibers of 25-microm diameter with a 1-microm layer of gold nanoparticles via electroless gold deposition. A SAM layer around the individual gold-coated imaging fibers prevented electrical contact with neighboring ring electrodes. To achieve better mechanical stability and to make the device more practical, the electrode/fiber bundle comprising approximately 600 individual gold-coated optical fibers was dipped into epoxy. By polishing the ends of such a device, a ring microelectrode array comprising 600 individual and insulated ring electrodes was formed. To limit diffusional overlap of current, only 20-30% of the microring fiber/electrodes were wired. The inner diameter of the ring electrode is fixed by the diameter of the individual optical fibers (25 microm), while the outer radius is determined by the thickness of the deposited gold. The array was characterized using ferrocyanide in aqueous solution as a model electroactive species to demonstrate that this microelectrode array format exhibits steady-state currents at short response times. In addition, cyclic voltammetry experiments were performed using conventional potentiostats due to the amplification of current inherent in the array format. Finally, electrochemiluminescence at the ring electrode array was demonstrated through the oxidation of Ru(bpy)3(2+) in tri-n-propylamide in a pH 7 phosphate buffer solution, where the light generated was collected and detected via the fiber bundle.