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Cathode
Kinds of Cathode Terms modified by Cathode Selected AbstractsEffect of Cathode and Anode Voltage on an Ion Sheath Thickness in a Magnetically Confined Diffusion PlasmaCONTRIBUTIONS TO PLASMA PHYSICS, Issue 10 2007M. Kr. Abstract This article reports about the ion sheath thickness variation occurring in front of a negatively biased plate immersed in the target plasma region of a double plasma device. The target plasma is produced due to the local ionization of neutral gas by the high energetic electrons coming from the source region (main discharge region). It is observed that for an increase in cathode voltage (filament bias voltage) in the source region, the ion flux into the plate increases. As a result, the sheath at the plate contracts. Again, for an increase in source anode voltage (magnetic cage bias), the ion flux to the plate decreases. As a result, the sheath expands at the plate. The ion sheath formed at the separation grid of the device is found to expand for an increase in cathode voltage and it contracts for an increase in the anode voltage of the main discharge region. One important observation is that the applied anode bias can control the Bohm speed of the ions towards the separation grid. Furthermore, it is observed that the ion current collected by the separation grid is independent of changes in plasma density in the diffusion region but is highly dependent on the source plasma parameters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-Performance Carbon-LiMnPO4 Nanocomposite Cathode for Lithium BatteriesADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Seung-Min Oh Abstract A cathode material of an electrically conducting carbon-LiMnPO4 nanocomposite is synthesized by ultrasonic spray pyrolysis followed by ball milling. The effect of the carbon content on the physicochemical and electrochemical properties of this material is extensively studied. A LiMnPO4 electrode with 30 wt% acetylene black (AB) carbon exhibits an excellent rate capability and good cycle life in cell tests at 55 and 25 °C. This electrode delivers a discharge capacity of 158 mAh g,1 at 1/20 C, 126 mAh g,1 at 1 C, and 107 mAh g,1 at 2 C rate, which are the highest capacities reported so far for this type of electrode. Transmission electron microscopy and Mn dissolution results confirm that the carbon particles surrounding the LiMnPO4 protect the electrode from HF attack, and thus lead to a reduction of the Mn dissolution that usually occurs with this electrode. The improved electrochemical properties of the C-LiMnPO4 electrode are also verified by electrochemical impedance spectroscopy. [source] Intermediate Temperature Anode-Supported Fuel Cell Based on BaCe0.9Y0.1O3 Electrolyte with Novel Pr2NiO4 CathodeFUEL CELLS, Issue 1 2010G. Taillades Abstract A proton conducting ceramic fuel cell (PCFC) operating at intermediate temperature has been developed that incorporates electrolyte and electrode materials prepared by flash combustion (yttrium-doped barium cerate) and auto-ignition (praseodymium nickelate) methods. The fuel cell components were assembled using an anode-support approach, with the anode and proton ceramic layers prepared by co-pressing and co-firing, and subsequent deposition of the cathode by screen-printing onto the proton ceramic surface. When the fuel cell was fed with moist hydrogen and air, a high Open Circuit Voltage (OCV,>,1.1,V) was observed at T,>,550,°C, which was stable for 300,h (end of test), indicating excellent gas-tightness of the proton ceramic layer. The power density of the fuel cell increased with temperature of operation, providing more than 130,mW,cm,2 at 650,°C. Symmetric cells incorporating Ni-BCY10 cermet and BCY10 electrolyte on the one hand, and Pr2NiO4,+,, and BCY10 electrolyte on the other hand, were also characterised and area specific resistances of 0.06,,,cm2 for the anode material and 1,2,,,cm2 for the cathode material were obtained at 600,°C. [source] Optimisation and Evaluation of La0.6Sr0.4CoO3,,,, Cathode for Intermediate Temperature Solid Oxide Fuel CellsFUEL CELLS, Issue 5 2009Youkun Tao Abstract In this work, La0.6Sr0.4CoO3,,,,/Ce1,,xGdxO2,,,, (LSC/GDC) composite cathodes are investigated for SOFC application at intermediate temperatures, especially below 700,°C. The symmetrical cells are prepared by spraying LSC/GDC composite cathodes on a GDC tape, and the lowest polarisation resistance (Rp) of 0.11,,,cm2 at 700,°C is obtained for the cathode containing 30,wt.-% GDC. For the application on YSZ electrolyte, symmetrical LSC cathodes are fabricated on a YSZ tape coated on a GDC interlayer. The impact of the sintering temperature on the microstructure and electrochemical properties is investigated. The optimum temperature is determined to be 950,°C; the corresponding Rp of 0.24,,,cm2 at 600,°C and 0.06,,,cm2 at 700,°C are achieved, respectively. An YSZ-based anode-supported solid oxide fuel cell is fabricated by employing LSC/GDC composite cathode sintered at 950,°C. The cell with an active electrode area of 4,×,4,cm2 exhibits the maximum power density of 0.42,W,cm,2 at 650,°C and 0.54,W,cm,2 at 700,°C. More than 300,h operating at 650,°C is carried out for an estimate of performance and degradation of a single cell. Despite a decline at the beginning, the stable performance during the later term suggests a potential application. [source] Combined First-Principle Calculations and Experimental Study on Multi-Component Olivine Cathode for Lithium Rechargeable BatteriesADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Hyeokjo Gwon Abstract The electrochemical properties and phase stability of the multi-component olivine compound LiMn1/3Fe1/3Co1/3PO4 are studied experimentally and with first-principles calculation. The formation of a solid solution between LiMnPO4, LiFePO4, and LiCoPO4 at this composition is confirmed by XRD patterns and the calculated energy. The experimental and first-principle results indicate that there are three distinct regions in the electrochemical profile at quasi-open-circuit potentials of ,3.5,V, ,4.1,V, and ,4.7,V, which are attributed to Fe3+/Fe2+, Mn3+/Mn2+, and Co3+/Co2+ redox couples, respectively. However, exceptionally large polarization is observed only for the region near 4.1,V of Mn3+/Mn2+ redox couples, implying an intrinsic charge transfer problem. An ex situ XRD study reveals that the reversible one-phase reaction of Li extraction/insertion mechanism prevails, unexpectedly, for all lithium compositions of LixMn1/3Fe1/3Co1/3PO4 (0,,,x,,,1) at room temperature. This is the first demonstration that the well-ordered, non-nanocrystalline (less than 1% Li,M disorder and a few hundred nanometer size particle) olivine electrode can be operated solely in a one-phase mode. [source] Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Tae-Woo Lee Abstract The short device lifetime of blue polymer light-emitting diodes (PLEDs) is still a bottleneck for commercialization of self-emissive full-color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three-layer (BaF2/Ca/Al) cathode compared with conventional two-layer cathodes (BaF2/Al and Ba/Al). Therefore, the roles of the BaF2 and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF2 layer should be deposited to the thickness of at least one monolayer (,3,nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF2 and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer. [source] An Ethanol/O2 Biofuel Cell Based on an Electropolymerized Bilirubin Oxidase/Pt Nanoparticle Bioelectrocatalytic O2 -Reduction CathodeADVANCED MATERIALS, Issue 42 2009Yi-Ming Yan An effective O2 -reducing bioelectrocatalytic electrode is prepared by the electrochemical crosslinking of thioaniline-modified Pt nanoparticles (NPs) and thioaniline-functionalized bilirubin oxidase (BOD). An O2/ethanol biofuel cell element is constructed by integrating the Pt NP/BOD cathode and an electrically contacted alcohol dehydrogenase (AlcDH)-based anode. [source] Electrochemical Behavior of Gel-Derived Lanthanum Calcium Cobalt Ferrite Cathode in Contact with LAMOX ElectrolyteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Tsu-Yung Jin The electrochemical performance and structural features of (La1,yCay)(CoxFe1,x)O3 cathode prepared via a citrate acid gel route are studied when it is interfaced with the (La1.8Dy0.2)(Mo2,zWz)O9 electrolyte. The resistance and chemical capacitance of a low-frequency arc are extracted from the impedance results to evaluate its catalytic activity in oxygen reduction reaction (ORR). (La0.75Ca0.25)(Co0.8Fe0.2)O3 cathode exhibits the minimum area-specific resistance of 0.9 , cm2 and maximum capacitance of 5.7 mF/cm2 at 800°C among the compositions of x=0.1,0.9 and y=0.25. As the Co content increases, the decrease in resistance outweighs the increase in capacitance so that the product of resistance and capacitance (RC time constant) decreases. In contrast, when varying the Ca content of the A-site, the changes in resistance and the capacitance compensate each other; hence the RC time constant is virtually unchanged with respect to the calcium content. Thus, Co is a more influential element than Ca on the ORR catalytic activity. The pore structure study reveals a small amount of Mo diffuses from the electrolyte into the cathode, and its quantity is reduced when interfaced to an electrolyte of high W content. [source] ChemInform Abstract: B Cation Ordered Double Perovskite Ba2CoMo0.5Nb0.5O6-, as a Potential SOFC Cathode.CHEMINFORM, Issue 4 2010Z. Q. Deng Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Template-Free Synthesis of Li[Ni0.25Li0.15Mn0.6]O2 Nanowires for High Performance Lithium Battery Cathode.CHEMINFORM, Issue 15 2009Min Gyu Kim Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Efficient Electrochemical Dicarboxylations of Arylacetylenes with Carbon Dioxide Using Nickel as the Cathode.CHEMINFORM, Issue 42 2008Gao-Qing Yuan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Characterization of GdBaCo2O5+, Cathode for IT-SOFCs.CHEMINFORM, Issue 29 2008Na Li Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Synthesis of Pinacols Through Electrochemical Reduction of Carbonyl Compounds at Platinum Cathode in Non-aqueous Weakly Acidic Medium.CHEMINFORM, Issue 14 2005K. L. Yadava Abstract For Abstract see ChemInform Abstract in Full Text. [source] A High-Performance Cathode for the Next Generation of Solid-Oxide Fuel Cells.CHEMINFORM, Issue 47 2004Zongping Shao Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: A Novel Concept for the Synthesis of an Improved LiFePO4 Lithium Battery Cathode.CHEMINFORM, Issue 21 2002F. Croce Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Enhancement of Methanol Tolerance in DMFC Cathode: Addition of Chloride IonsCHEMPHYSCHEM, Issue 10 2008Sunghyun Uhm Dr. Abstract In the operation of a direct methanol fuel cell, the modification by chloride ions on the surface of a Pt cathode can facilitate the extraordinary increase of power performance and long-term stability. Analyzing the results of cyclic voltammograms and electrochemical impedance spectroscopy, the positive shift of Pt oxidation onset potential and the depression of oxidation current are observed, which results from the role of chloride as surface inhibitor. In addition, O2 temperature-programmed desorption and X-ray photoelectron spectroscopy also reveal that the suppression of Pt surface oxide can be best understood in terms of lower binding of oxygen species by the alteration of electronic state of Pt atoms. Such a reduced surface oxide formation not only provides more efficient proton adsorption sites with high selectivity but also decreases the mixed potential by crossover methanol, resulting in higher performance and stability even under high voltage long-term operation. [source] Electrochemical Reduction of 4,4,-(2,2,2-Trichloroethane-1,1-diyl)- bis(chlorobenzene) (DDT) and 4,4,-(2,2-Dichloroethane-1,1-diyl)- bis(chlorobenzene) (DDD) at Carbon Cathodes in DimethylformamideELECTROANALYSIS, Issue 4 2006Mohammad Abstract In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4,-(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4,-(2,2-dichloroethane-1,1-diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4,-(ethene-1,1-diyl)bis(chlorobenzene) (DDNU) as principal product (67,94%), together with 4,4,-(2-chloroethene-1,1-diyl)bis(chlorobenzene) (DDMU), 1-chloro-4-styrylbenzene, and traces of both 1,1-diphenylethane and 4,4,-(ethane-1,1-diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D2O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon,chlorine bonds of DDT is a two-electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products. [source] Low-Temperature Ionic-Liquid-Based Synthesis of Nanostructured Iron-Based Fluoride Cathodes for Lithium BatteriesADVANCED MATERIALS, Issue 33 2010Chilin Li A mesoporous iron-based fluoride cathode for lithium batteries is fabricated by a novel low-temperature non-aqueous synthesis based on ionic liquid medium. The hydration-water-induced microstructural optimization and morphological decoration are expected to contribute positively to both the large reversible Li-storage capacity and the high reactive voltage of carbon-free FeF3 · 0.33H2O at room temperature. [source] High-Performance SOFC Cathodes Prepared by InfiltrationADVANCED MATERIALS, Issue 9 2009John M. Vohs Abstract Improved cathodes are required for low-temperature operation of solid-oxide fuel cells (SOFCs). Recent work has shown that electrode fabrication and modification by infiltration of active components into a porous scaffold can result in outstanding electrochemical performance. In this paper we review the literature on this new approach for cathode preparation and discuss the insights that this work has provided for understanding the relationships between the materials properties, electrochemical performance, and electrode stability. [source] Conducting-Polymer/Iron-Redox- Couple Composite Cathodes for Lithium Secondary Batteries,ADVANCED MATERIALS, Issue 6 2007K.-S. Park Physically or chemically attaching an FeIII/FeIIredox couple to the backbone of a conducting polymer leads to stabilization of the charge/discharge characteristics and higher electrode capacities. Composite cathodes made from LiFePO4 particles bound to polypyrrole show enhanced electrode capacities and better rate capabilities, as shown in the figure. Chemically attaching ferrocene to the pyrrole backbone not only stabilizes the charge,discharge curves but also leads to higher capacity. [source] TiO2(B) Nanowires as an Improved Anode Material for Lithium-Ion Batteries Containing LiFePO4 or LiNi0.5Mn1.5O4 Cathodes and a Polymer Electrolyte,ADVANCED MATERIALS, Issue 19 2006G. Armstrong Rechargeable lithium-ion batteries have been constructed with a TiO2(B) nanowire anode, a gel electrolyte, and either a LiFePO4 or LiNi0.5Mn1.5O4 cathode. Cycling stability is very good as is rate capability (see figure), with 80% of the low-rate capacity being retained at C/5. [source] Pt Thin Film Collectors Prepared by Liquid-Delivery Metal,Organic CVD Using Pt(C2H5C5H4)(CH3)3 for LiCoO2 Thin Film Cathodes,CHEMICAL VAPOR DEPOSITION, Issue 6 2003W.-G. Choi Abstract Platinum thin film collectors were deposited onto p-type Si(100) planar and trench substrates by liquid-delivery metal,organic (LD-MO) CVD using Pt(EtCp)Me3, Pt(C2H5C5H4)(CH3)3, for microbatteries. The resistivity and root-mean-square (rms) roughness of Pt thin films with (111) preferred orientation increased with the increase of both deposition temperature and system pressure. The deposition of Pt thin films was controlled by a gas-phase mass-transfer mechanism and Pt thin films deposited at 350,°C showed the lowest resistivity, rms roughness, and the highest step coverage, 57,%, in trench structure. The LiCoO2 cathode films (step coverage,=,51,%) deposited on the trench Pt collector showed an increase in discharge capacity of approximately two and half times that of the planar Pt collector. Platinum thin films deposited by LD-MOCVD have a possible application as collector materials for LiCoO2 thin film cathodes. [source] ChemInform Abstract: Synthesis of Nanowire and Hollow LiFePO4 Cathodes for High-Performance Lithium Batteries.CHEMINFORM, Issue 43 2008Sunhye Lim Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Interactions Between Extracellular Stimuli and Excitation Waves in an Atrial Reentrant LoopJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 10 2003CHAD R. JOHNSON B.S.E. Introduction: The interactions between extracellular stimuli and excitation waves propagating in a reentrant loop are a complex function of stimulus parameters, structural properties, membrane state, and timing. Here the goal was a comprehensive understanding of the mechanisms and frequencies of the major interactions between the advancing excitation wave and a single extracellular stimulus, separated from issues of anatomic or geometric complexity. Methods and Results: A modernized computer model of a thin ring of uniform tissue that included a pair of extracellular stimulus electrodes (anode/cathode) was used to model one-dimensional cardiac reentry. Questions and results included the following: (1) What are the major interactions between a stimulus and the reentrant propagation wave, and are they induced near the cathode or near the anode; and, for each interaction, what are the initiating amplitude range and timing interval? At the cathode, the well-known mechanism of retrograde excitation terminated reentry; changes in timing or amplitude produced double-wave reentry or phase reset. At the anode, termination occurred at different cells depending on stimulus amplitude. (2) Relatively how often did termination occur at the anode? For most stimulus amplitudes, termination occurred more often at the anode than at the cathode, although not always at the same cell. (3) With random timing, what is the probability of terminating reentry? Stimulation for 5 msec terminated reentry with a probability from 0% to approximately 10%, as a function of increasing stimulus amplitude. Conclusion: A single extracellular stimulus can initiate major changes in reentrant excitation via multiple mechanisms, even in a simple geometry. Termination of reentry, phase shifts, or double-wave reentry each occurs over well-defined ranges of stimulus amplitude and timing. (J Cardiovasc Electrophysiol, Vol. 14, pp. ***-***, October 2003) [source] Stochastic and Relaxation Processes in Argon by Measurements of Dynamic Breakdown VoltagesCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7 2005V. Lj. Abstract Statistically based measurements of breakdown voltages Ub and breakdown delay times td and their variations in transient regimes of establishment and relaxation of discharges are a convenient method to study stochastic processes of electrical breakdown of gases, as well as relaxation kinetics in afterglow. In this paper the measurements and statistical analysis of the dynamic breakdown voltages Ub for linearly rising (ramp) pulses in argon at 1.33 mbar and the rates of voltage rise k up to 800 V s,1 are presented. It was found that electrical breakdowns by linearly rising (ramp) pulses is an inhomogeneous Poisson process caused by primary and secondary ionization coefficients , , , and electron yield Y variations on the voltage (time). The experimental breakdown voltage distributions were fitted by theoretical distributions by applying approximate analytical and numerical models. The afterglow kinetics in argon was studied based on the dependence of the initial electron yield on the relaxation time Y0 (, ) derived from fitting of distributions. The space charge decay was explained by the surface recombination of nitrogen atoms present as impurities. The afterglow kinetics and the surface recombination coefficients on the gas tube and cathode were determined from a gas-phase model. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study on Glucose Biofuel Cells Using an Electrochemical Noise DeviceELECTROANALYSIS, Issue 14 2008Yueming Tan Abstract An electrochemical noise (ECN) device was utilized for the first time to study and characterize a glucose/O2 membraneless biofuel cell (BFC) and a monopolar glucose BFC. In the glucose/O2 membraneless BFC, ferrocene (Fc) and glucose oxidase (GOD) were immobilized on a multiwalled carbon nanotubes (MWCNTs)/Au electrode with a gelatin film at the anode; and laccase (Lac) and an electron mediator, 2,2,-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS), were immobilized on a MWCNTs/Au electrode with polypyrrole at the cathode. This BFC was performed in a stirred acetate buffer solution (pH,5.0) containing 40,mmol/L glucose in air, with a maximum power density of 8,,W/cm2, an open-circuit cell voltage of 0.29,V, and a short-circuit current density of 85,,A/cm2, respectively. The cell current at the load of 100,k, retained 78.9% of the initial value after continuous discharging for 15,h in a stirred acetate buffer solution (pH,5.0) containing 40,mmol/L glucose in air. The performance decrease of the BFC resulted mainly from the leakage of the ABTS mediator immobilized at the cathode, as revealed by the two-channel quartz crystal microbalance technique. In addition, a monopolar glucose BFC was performed with the same anode as that in the glucose/O2 membraneless BFC in a stirred phosphate buffer solution (pH,7.0) containing 40,mmol/L glucose, and a carbon cathode in Nafion-membrane-isolated acidic KMnO4, with a maximum power density of 115,,W/cm2, an open-circuit cell voltage of 1.24,V, and a short-circuit current density of 202,,A/cm2, respectively, which are superior to those of the glucose/O2 membraneless BFC. A modification of the anode with MWCNTs for the monopolar glucose BFC increased the maximum power density by a factor of 1.8. The ECN device is highly recommended as a convenient, real-time and sensitive technique for BFC studies. [source] Application of Bacterial Biocathodes in Microbial Fuel CellsELECTROANALYSIS, Issue 19-20 2006Zhen He Abstract This review addresses the development and experimental progress of biocathodes in microbial fuel cells (MFCs). Conventional MFCs consist of biological anodes and abiotic cathodes. The abiotic cathode usually requires a catalyst or an electron mediator to achieve high electron transfer, increasing the cost and lowering the operational sustainability. Such disadvantages can be overcome by biocathodes, which use microorganisms to assist cathodic reactions. Biocathodes are feasible in potentiostat-poised half cells, but only very few studies have investigated them in complete MFCs. The classification of biocathodes is based on which terminal electron acceptor is available. For aerobic biocathodes with oxygen as the terminal electron acceptor, electron mediators, such as iron and manganese, are first reduced by the cathode (abiotically) and then reoxidized by bacteria. Anaerobic biocathodes directly reduce terminal electron acceptors, such as nitrate and sulfate, by accepting electrons from a cathode electrode through microbial metabolism. Biocathodes are promising in MFCs, and we anticipate a successful application after several breakthroughs are made. [source] Application of CE with novel dynamic coatings and field-amplified sample injection to the sensitive determination of isomeric benzoic acids in atmospheric aerosols and vehicular emissionELECTROPHORESIS, Issue 19 2007Ewa Dabek-Zlotorzynska Dr. Abstract A simple and reliable CE method with direct UV detection has been developed to separate eight isomeric benzoic acids in atmospheric aerosols and vehicular emission without complex sample pretreatment. Optimal electrophoretic conditions, with migration times under 5,min, were obtained by using a 50,mM acetate buffer (pH,4.7) containing a dynamic surface coating EOTrolÔ LN (0.005% w/v). The separations were carried out in a cathode to anode direction (,30,kV) allowing the low cathodal EOF (,1×10,9,m2V,1s,1) to extend the effective separation by slowing the movement of the studied aromatic acids. Moreover, the sensitivity of the method at 200,nm was enhanced by using a field-amplified sample injection (FASI) with electrokinetic (EK) sample injection (,2,kV, 60,s). Prior to sample injection, a short water plug (3,s at 0.5,psi) was introduced. Under these conditions, the method was capable of detecting the analytes in deionized water with LODs (S/N,=,3) as low as 0.1,,g/L for most of the studied acids. In the presence of 10,mg/L of sulphate (added to simulate a sample matrix), LODs ranged from 0.26 to 0.62,,g/L. The validation of the method has proven an excellent separation performance and accuracy for the determination of isomeric benzoic acids in the studied matrices. [source] Characterization of hydroxyaromatic compounds in vegetable oils by capillary electrophoresis with direct injection in an oil-miscible KOH/propanol/methanol mediumELECTROPHORESIS, Issue 17 2005Carla R. B. Mendonça Abstract The separation of hydroxyaromatic compounds in vegetable oils, including synthetic antioxidants (3- tert -butyl-4-hydroxyanisol and 2,6-di- tert -butyl-4-hydroxytoluene), E-vitamers and other natural oil components, by nonaqueous capillary electrophoresis in an oil-miscible background electrolyte (BGE) was investigated. The BGE contained 40,mM KOH in a methanol/1-propanol (PrOH) mixture (15:85 v/v). The oil samples were 1:1 diluted with PrOH and directly injected in the capillary. Under negative polarity (cathode at the injection end), the anionic solutes moved faster than the electroosmotic flow, being well-resolved among them and from the triacylglycerols. Using virgin palm, extra virgin olive, wheat germ, virgin soybean and other oils, the capability of the procedure to quickly yield a characteristic profile of the biophenols present in the sample was demonstrated. The , -, (,,+,,)- (as unresolved pair) and , -tocopherols of a soybean oil sample were quantified. [source] Treatment of Process Water Containing Heavy Metals with a Two-Stage Electrolysis Procedure in a Membrane Electrolysis CellENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 2 2005R. Fischer Abstract The capability of a two-stage electrochemical treatment for the regeneration of acidic heavy-metal containing process water was examined. The process water came from sediment bioleaching and was characterized by a wide spectrum of dissolved metals, a high sulfate content, and a pH of about 3. In the modular laboratory model cell used, the anode chamber and the cathode chamber were separated by a central chamber fitted with an ion exchanger membrane on either side. The experiments were carried out applying a platinum anode and a graphite cathode at a current density of 0.1,A/cm2. The circulation flow of the process water in the batch process amounted to 35,L/h, the electrolysis duration was 5.5,h at maximum and the total electrolysis current was about 1,A. In the first stage, the acidic process water containing metals passed through the cathode chamber. In the second stage, the cathodically pretreated process water was electrolyzed anodically. In the cathode chamber the main load of dissolved Cu, Zn, Cr and Pb was eliminated. The sulfuric acid surplus of 3,4,g/L decreased to about 1,g/L, the pH rose from initially 3.0 to 4,5, but the desired pH of 9,10 was not achieved. Precipitation in the proximity to the cathode evidently takes place at a higher pH than farther away. The dominant process in the anode chamber was the precipitation of amorphous MnO2 owing to the oxidation of dissolved Mn(II). The further depletion of the remaining heavy metals in the cathodically pretreated process water by subsequent anodic treatment was nearly exhaustive, more than 99,% of Cd, Cr, Cu, Mn, Ni, Pb, and Zn were removed from the leachate. The high depletion of heavy metals might be due to both the sorption on MnO2 precipitates and/or basic ferrous sulfate formed anodically, and the migration of metal ions through the cation exchanger membrane via the middle chamber into the cathode chamber. In the anode chamber, the sulfuric acid content increased to 6,7,g/L and the pH sank to 1.7. All heavy metals contained, with the exception of Zn, were removed to levels below the German limits for discharging industrial wastewaters into the receiving water. Moreover, the metal-depleted and acid-enriched process waters could be returned to the leaching process, hence reducing the output of wastewater. The results indicated that heavy metals could be removed from acidic process waters by two-stage electrochemical treatment to a large extent. However, to improve the efficiency of metal removal and to establish the electrochemical treatment in practice, further work is necessary to optimize the operation of the process with respect to current density, energy consumption, discharging of metal precipitates deposited in the electrode chambers and preventing membrane clogging. [source] | ||||||||||||||||||||||||||||||||||||||||