Indirect electrochemical detection of cations with cerium(III) in the mobile phase

Cerium(III) has been used in the mobile phase for indirect electrochemical chromatography of cations. Lithium, sodium, ammonium, and potassium ions have been separated within 4 min and detected with both glassy carbon and Kel-F wax carbon paste electrodes. With a Kel-F wax/graphite electrode at 0.7 V, the detection limit for sodium, ammonium, and potassium ions are 1.5, 1.1, and 2.0 ppm, respectively.     

Evaluation of kel-f—graphite electrodes as detectors for continuous flow systems

A new electrode material, fabricated from Kel-F powder and graphite powder by pressing at 250°C and 1000 p.s.i., is applied as a detector in a thin-layer, flow-through cell, for applications to continuous flow streams. The detector is useful in a wide range of solvents for a wide range of species. Applications are described for 1,1'-bis(hydroxymethyl) ferrocene (BHMF), ascorbic acid, ferrocene, phenol, and hydroquinone, using various aqueous and methanolic solvent/electrolyte compositions. Detection limits range from 800 pg for BHMF to less than 20 pg for phenol. Background current fluctuations are used to estimate flow rate stability, which is the dominant factor in setting detection limits.     

Fabrication of Sn–C composite electrodes by electrodeposition and their cycle performance for Li-ion batteries

To improve the cycle performance of the thick Sn electrode of 10 μm thickness, the Sn–C composite electrodes were fabricated by co-electrodeposition with two kinds of carbon particles which were the graphite and the acetylene black. The acetylene black particles were well dispersed in the Sn matrix more than the graphite particles. The carbon content in the Sn–C composite electrodes was measured about 12% of the graphite and 16% of the acetylene black particles. Even though carbon content of the Sn–acetylene black electrode was not significantly higher than that of the Sn–graphite electrode, the cycle performance of the Sn–acetylene black electrode was much higher than that of the Sn–graphite electrode. This demonstrates that the ‘buffering effects’ of well dispersed acetylene black particles was larger than that of the graphite particles. The cycle performance of the Sn–acetylene black electrode was significantly improved by the aging treatment.     

Graphite multi-micro-disc based mercury film electrode: Comparison of experimental and theoretical anodic stripping results

an ensemble of properly distanced micro mercury film electrodes (MMFE) was used in cyclic and anodic stripping voltammetry. the experimental results were compared with the anodic stripping theory, and the agreement was found to be satisfactory. The MMFE peaks (calculated per unit area) were higher, thinner and shifted towards more negative potentials compared with the large area mercury film electrode (LAMFE) peaks.The initial graphite electrode consisted of 65 independent micro-discs forming a circle, and was prepared from carbon fibres 4.66 μm in radius. The graphite multi-micro-disc electrode was quantitatively checked in a Fe(CN)₆^3? solution under both chronoamperometric and voltammetric conditions. The deposition and oxidation of mercury is discussed also.     

Three‐Electrode‐Integrated Sensor into a Micropipette Tip

This work describes the construction, characterization, and application of a three‐electrode‐integrated sensor into a micropipette tip. The three electrodes (working, pseudoreference and counter) are positioned at the end of a micropipette tip. The working electrode (graphite composite or gold microfiber) is placed inside the micropipette tip and the pseudo‐reference and counter electrodes outside (diametrically opposed sides). This approach is candidate for portable applications and allows the analysis and studies in low‐volume solutions (ca. 10 µL) which are useful for waste minimization and development of clean analytical methods. In addition, the three‐electrode‐integrated sensor can be easy used as detector in flow injection system through its direct joining at the end of polyethylene tubing of the FIA system.     

Development and characterization of a new conducting carbon composite electrode

A new conducting composite flexible material prepared from cellulose acetate (CA) polymer and graphite has been developed and used for the fabrication of electrodes, which were then characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) was used to provide information concerning the morphology of the composite electrode surface. The potential window, background currents and capacitance were evaluated by cyclic voltammetry in the pH range from 4.6 to 8.2. The voltammetry of model electroactive species demonstrates a close to reversible electrochemical behaviour, under linear diffusion control. The electroactive area of the composite electrodes increases after appropriate electrode polishing and electrochemical pre-treatment. The electrodes were used as substrate for the electropolymerisation of the phenazine dye neutral red, for future use as redox mediator in electrochemical biosensors. The composite electrodes were also successfully used for the amperometric detection of ascorbate at 0.0 V vs. SCE, and applied to the measurement of ascorbate in Vitamin C tablets; the sensor exhibits high sensitivity and a low detection limit of 7.7 μM. Perspectives for use as a versatile, mechanically flexible and robust composite electrode of easily adaptable dimensions are indicated.     

Microchip Capillary Electrophoresis‐Electrochemistry with Rigid Graphite‐Epoxy Composite Detector

A new rigid graphite‐epoxy composite electrode for electrochemical detection in microchip electrophoresis is described. The end‐column wall‐jet detection design relying on tubular rigid composite working electrode shows favorably low noise level and high signal‐to‐noise ratio when compared to glassy carbon detector. The performance of rigid graphite‐epoxy composite detector was compared to glassy carbon detector using dopamine and catechol as model analytes. The various parameters of the microchip electrophoresis‐rigid graphite‐epoxy composite detector were optimized.     

Electron transfer kinetics on composite diamond (sp3)–graphite (sp2) electrodes

The concept of non-diamond sp² impurity states as charge transfer mediators on boron-doped diamond (BDD) surface was suggested as an explanation for the electrochemical behavior of synthetic diamond based electrodes. In order to verify this concept, graphite particles (sp²) were deposited on diamond electrodes (sp³) by mechanical abrasion. The behavior of the so prepared diamond–graphite composite electrodes were compared with those of as-grown (BDD_ag) and those after mild anodic polarization (BDD_mild).Outer-sphere electron transfer processes such as ferri/ferrocyanide (Fe(CN)₆III/II) and inner-sphere charge transfer reactions such as 1,4-benzoquinone/hydroquinone (Q/H₂Q) were chosen in order to investigate the electrochemical properties of these composite electrodes. Both redox systems became more reversible as the graphite (sp²) loading increased. A strong analogy existed between as-grown diamond electrodes and diamond–graphite composite electrodes.Finally a model is proposed which describes the BDD electrode surface as a diamond matrix in which non-diamond (sp²) impurity states are dispersed. These non-diamond sp² states on BDD surface acts as charge mediators for both inner-sphere and outer-sphere reactions.     

Graphite-silicone rubber composite electrode: Preparation and possibilities of analytical application

Composite electrodes were prepared using graphite powder and silicone rubber in different compositions. The use of such hydrophopic materials interned to diminish the swallowing observed in other cases when the electrodes are used in aqueous solutions for a long time. The composite was characterized for the response reproducibility, ohmic resistance, thermal behavior and active area. The voltammetric response in relation to analytes with known voltammetric behavior was also evaluated, always in comparison with the glassy carbon. The 70% (graphite, w/w) composite electrode was used in the quantitative determination of hydroquinone (HQ) in a DPV procedure in which a detection limit of 5.1x10(-8)molL(-1) was observed. HQ was determined in a photographic developer sample with errors lower then 1% in relation to the label value.     

Reason analysis for Graphite-Si/SiOx/C composite anode cycle fading and cycle improvement with PI binder

Designed Graphite-Si/SiO_x/C composite electrodes for rechargeable lithium-ion batteries are prepared with different binder of carboxymethyl cellulose-styrene butadiene rubber (CMC-SBR) and polyimide (PI). Electrode performance of composites highly depends on the selection of binder. The Si-based/graphite composite electrode containing PI binder shows very stable cycle stability with the retention higher than 95 % after 30 cycles; however, the capacity of composite electrode with CMC-SBR binder fades to less than 80 % after 20 cycles. The improvement mechanism of PI binder is characterized by SEM, EDS mapping, adhesive strength test, and electric performance test. The surface of anode film does not show crack after several cycles, and the SEI on the surface of Si/SiO_x/C particle is characterized. It is found that anode film peeing off strength matches well with the composite cycle stability. This result is further supported with cell disassembly result. We believe that improvement of anode film adhesion strength is an effective way to get stable long cycle life.     

Electrochemical detector based on sol-gel-derived carbon composite material for capillary electrophoresis microchips

An on-chip disk electrode based on sol-gel-derived carbon composite material could be easily and reproducibly fabricated. Unlike other carbon-based electrodes reported previously, this detector is rigid, convenient to fabricate, and amenable to chemical modifications. Based on the stable and reproducible characters of this detector, a copper particle-modified detector was developed for the detection of carbohydrates which extends the application of the carbon-based electrode. In our experiments, the performance of the new integrated detector for rapid on-chip measurement of epinephrine and glucose was illustrated. Experimental procedures including the fabrication of this detector, the configuration of separation channel outlet and electrode verge, and the performance characteristics of this new electrochemical detector were investigated.     

石墨烯包覆天然球形石墨作为锂离子电池的负极材料，是否需要乙炔黑导电剂？

我们通过包覆炭化的方法制备得到了石墨烯包覆的天然球形石墨(G/SG)材料,并使用扫描电子显微镜、X射线衍射仪以及多种电化学测试手段考察了不同石墨烯含量的复合材料的形貌结构及电化学性能。我们发现,在不添加乙炔黑(AB)的情况下,G/SG复合材料表现出较高的首次库伦效率,很好的循环稳定性和高倍率性能。当石墨烯包覆量为1%时,材料50次循环后的可逆容量可与添加10%AB的天然石墨电极(SG)等同;当石墨烯包覆量为2.5%时,材料的比容量完全高于添加10%AB的石墨电极。材料电化学性能的改善归因于石墨烯的包覆。一方面,石墨烯的柔软可变性可以保证天然石墨颗粒在充放电过程中的结构完整性,从而有效改善材料的循环稳定性;另一方面,石墨烯的存在提高了电极的导电性,促进更好导电网络的形成。因此,石墨烯包覆天然球形石墨材料中,石墨烯不仅是活性物质,也发挥导电剂的作用。当添加5%的乙炔黑时,在50 mA·g^-1电流循环50次后,5%G/SG电极的可逆容量从381.1 mAh·g^-1提高到404.5 mAh·g^-1,在1 A·g^-1电流时可逆容量从82.5 mAh·g^-1提高到101.9 mAh·g^-1,这表明G/SG电极仍然需要乙炔黑导电剂。乙炔黑颗粒填充在复合材料的空隙中,通过点接触的形式连接到G/SG颗粒,与石墨烯协同作用形成了更加有效的导电网络。尽管石墨烯包覆和乙炔黑添加对天然石墨电极具有积极的影响,例如增加了天然石墨电极的导电性和储锂性能(包括可逆容量,倍率性能和循环性能),但随着石墨烯或乙炔黑的增加,电极密度通常会降低。因此,在实际应用中应考虑石墨负极材料的质量和体积容量的平衡。这些结果对天然石墨的进一步商业应用具有重要意义。我们的工作为天然石墨电极在锂电池中的电化学行为提供了一种新的认识,并且有助于制备更高性能的负极材料。     

Electrooxidation of carbon monoxide on gold nanoparticle ensemble electrodes: effects of particle coverage

Gold nanoparticles were attached to amine-functionalized indium tin oxide substrate to form particle ensemble electrodes with controlled particle coverage. Electrooxidation of carbon monoxide (CO) on these particle ensemble electrodes was studied in CO-saturated alkaline solutions by means of cyclic voltammetry, with an emphasis on the effects of particle coverage. CO oxidation half-wave potential was found to decrease with increasing particle density. However, the current density was significantly larger at lower particle coverage electrodes. On the basis of a model for electron transfer on a partially covered electrode, the observations were explained in terms of the change in reactant mass transport pattern with varying particle coverages: CO diffusion is predominantly mixed spherical and linear at low particle coverages and changes to mostly linear at high particle coverages. The possibility of contributions from particle agglomeration is also briefly discussed.     

Screen-printable sol-gel ceramic carbon composite pH sensor with a receptor zeolite

A screen-printable method is proposed to prepare a ceramic carbon composite sensor for pH determination. The pH-sensing membrane of the sensor is prepared by sol-gel, graphite powder and zeolite, in which zeolite is used as a receptor of proton. The fabrication of this ceramic carbon sensor includes three steps: preparing electrode slides, making a pH-sensing composite ink and screen-printing the ink on electrode slides. Optimum conditions for the ceramic carbon composite film are established, and characters of the pH electrode (stability, reproducibility, lifetime and conductivity) are examined comparing with glass pH electrodes. The Nernst response to pH of the sensor is in the range of pH 1-12 with a slope of 60 mV per pH. The sensor has been applied to pH measurements of samples and satisfactory results were obtained with R.S.D. of 0.18-1.25%.     

Amperometric sensor for detection of bisphenol A using a pencil graphite electrode modified with polyaniline nanorods and multiwalled carbon nanotubes

We report on a simple and highly sensitive amperometric method for the determination of bisphenol A (BPA) using pencil graphite electrodes modified with polyaniline nanorods and multiwalled carbon nanotubes. The modified electrodes display enhanced electroactivity for the oxidation of BPA compared to the unmodified pencil graphite electrode. Under optimized conditions, the sensor has a linear response to BPA in the 1.0 and 400?μM concentration range, with a limit of detection of 10?nM (at S/N?=?3). The modified electrode also has a remarkably stable response, and up to 95 injections are possible with a relative standard deviation of 4.2% at 100?μM of BPA. Recoveries range from 86 to 102% for boiling water spiked with BPA from four brands of baby bottles.

Electrochemically Treated Pencil Graphite Electrodes Prepared in One Step for the Electrochemical Determination of Paracetamol

This article reports the electrochemical determination of paracetamol (PC) in the presence of ascorbic acid (AA) and caffeine (CF) using an electrochemically treated pencil graphite electrode. In this study, we describe the use of an electrode prepared by overoxidation between 0.0 and +2.1 V for paracetamol determination. The electrochemically treated pencil graphite electrodes (ETPGEs) were prepared using a cyclic voltammetric method. The electrode was characterized by Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Resonance Raman Spectroscopy. The differences in oxidation peak potentials were large enough to determine PC in the presence of AA and CF. The electroactive areas of the bare electrode and 10 scan-ETPGE in 0.5 M H₂SO₄ were calculated to be 0.0031 and 0.0341 cm², respectively. The sensor (10 scan-ETPGE in 0.5 M H₂SO₄) was sensitive to the PC with 1.74 × 10^–7 M limits of detection (S/N = 3). Finally, the developed method and the prepared electrodes were used for determination of PC in the pharmaceutical samples.

     

Stacked graphene nanofibers doped polypyrrole nanocomposites for electrochemical sensing

This publication shows a single-step electropolymerization which has been carried out by the incorporation of an anionic stacked graphene nanofiber (SGNF) dopant into a polypyrrole (PPy) film, at a disposable screen-printed electrode. The incorporation of the SGNFs into the polymer does not affect their electrochemical properties, shown through cyclic voltammetry by the earlier oxidation of guanine, when compared with that at the graphite doped PPy electrode. The SGNF/PPy composite shows a high selectivity when used in the oxidation of guanine and hydrogen peroxide, both of which are important biomarkers used for biosensing. Disposable screen-printed electrodes provide an inexpensive, sensitive and portable substitute to glassy carbon electrodes, while giving a reproducible surface; qualities essential for effective bionsensing. The production of this single-step disposable SGNF/PPy composite electrode allows for further applications in the detection of biomedically important compounds and DNA sensing.     

Preparation and characterization of superporous agarose-reticulated vitreous carbon electrodes as platforms for electrochemical bioassays

Three-dimensional flow-through electrodes were fabricated using superporous agarose (SPA) and reticulated vitreous carbon (RVC) composite materials that were suitable as a platform for sandwich assays. These SPA-RVC composite electrodes were fabricated by fitting a SPA-RVC composite cylinder inside a graphite tube and subsequently fixing the graphite tube onto a polypropylene micropipette tip. The electrode design allows for ease in reagent/washing steps involved in sandwich assay protocols and could easily be made portable. The electrode materials were characterized with respect to pore-size distribution, total free volume, ligament and bulk densities of the RVC, and physical structural characteristics. Coulometric detection of redox molecules such as K(3)Fe(CN)(6) and 4-aminophenol was possible using SPA-RVC electrodes by the trapping of these redox molecules inside the SPA-RVC electrodes. Avidin affinity molecules were covalently immobilized onto the SPA matrix inside the RVC electrodes by periodate-activation followed by reductive amination. The amount of avidin immobilized inside the SPA-RVC electrodes was (5+/-0.06)x10(-11) mol, which was determined by saturating the avidin sites with biotinylated fluorescein (b-fluo) and subsequently determining the amount of immobilized b-fluo via a standard addition method using fluorescence spectroscopy. Non-specific binding of labeled enzymes such as biotinylated alkaline phosphatase (b-ALP) onto the SPA-RVC electrodes without avidin capture sites was determined to be less than 1% compared to the specific binding of b-ALP on avidinylated SPA-RVC electrodes.     

Hydrodynamic voltammetry at an interdigitated electrode array in a flow channel: Part I. Numerical simulation

This paper describes the numerical simulation of convective diffusion at an interdigitated electrode array, consisting of multiple pairs of microelectrodes held at alternating applied potentials on one wall of a flow channel. The downstream microelectrode of each pair detects species generated at the upstream microelectrode. Concentration profiles in the channel, amperometric response, and signal-to-noise ratios for the detector electrodes are calculated. The simple backward implicit finite difference (BIFD) simulation approach is applicable for a wide range of channel conditions. The upper number of electrode pairs treatable is limited only by computational time. The agreement of the simulation with previous results for a single pair of electrodes under comparable conditions is very good. Substantial improvements in signal-to-noise ratio are predicted for the multi-electrode interdigitated electrode array relative to a single generator-detector pair of equal overall area. Electrode dimensions are discussed for optimum signal/noise ratio. Relative enhancement increases significantly with the number of generator-detector pairs.     

Covalent immobilization of an enzyme (glucose oxidase) onto a carbon sol-gel silicate composite surface as a biosensing platform

A porous organic-inorganic hybrid sol-gel carbon composite has been developed and used for surface covalent bonding of an enzyme for biosensing applications, illustrated by glucose oxidase (GOD). The composite comprises graphite powder, ferrocene, and an amino- and methyl-silicate backbone. The graphite powder provides the conductivity for the electrode and ferrocene acts as the mediator for signal transduction from the active center of the enzyme to the electron conductive surface. The presence of amine groups in the sol-gel silicate network allows for the covalent bonding sites for the enzyme via the carbodiimide reaction. The hydrophobicity and hydrophilicity properties of the electrode surface are controlled by the amine and methyl groups of the silicate network. Systematic optimization of the composite composition has been carried out and the performance of the glucose biosensor has been investigated. The optimal electrode gives a linear response range of 0.1-27 mM glucose with a sensitivity of 1.30 μA mM⁻¹ and detection limit (S/N = 3) of 26 μM.