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A peculiar method used for particle separation device in microfluidics is hydrodynamic filtration. To achieve the filtration of sample fluid with particle, this is the technique which concedes two-input (with buffer inlet) sheath fluid to conflow at distinct velocity rates in a sifter-shaped microchannel network demonstrated. The objective is to assure the separation of particles based on size and mass in microflow network with grooves or rectangular cross section by hydrodynamic filtration. However, simulation is done to examine the particle tracing with mass by sifter-shaped microchannel network using COMSOL Multiphysics software. The size, mass and density of the particle are related to the properties of K. pneumoniae and blood particles samples. During the experiments, different networks were designed and simulated to acquire a better filtration effect and particle separation based on size and mass. After the simulation done for the networks, it resulted that sifter-shaped microchannel network shows a precise separation of K. pneumoniae particle. Analysis of a microchannel having distinct angles (90°, 15°, 25° and 35°) with individual inflow velocity for sample with particle and buffer inflow velocity without particle at 3000 µl/s and with various other flow rates for blood and 50 µl/s and with various other flow rates for water was performed, where sifter-shaped microchannel device consisting of 90° and 25° sifter structure provides a preferable separation through the targeted outlet 4 and outlet 1 of microchannel for a larger bioparticles and smaller particles (blood cells) through the other outlets of device.

Fourier-transformed large amplitude alternating current voltammetry (FTACV) provides a sensitive analytical tool for the discrimination of electrode reactions that are complicated by surface heterogeneity. In this paper, it is shown how the FTACV response at a dual-electrode system comprised of different electrode materials having different heterogeneous charge transfer (k01 and k02) can be resolved into its individual electrode kinetics components without prior knowledge of the electrode size ratio (θ1:θ2). This is possible when one process is reversible and the other is quasi-reversible; achievable by careful selection of the FTACV frequency. The applicability of the FTACV method over a wide range of electrode kinetic values and size ratios is considered for conditions under which numerical simulations based on a 1D diffusion model are adequate to describe the mass transport problem.

A conducting polymer-modified electrode was proposed in this article, which was fabricated by electropolymerization of 5-amino-1H-tetrazole (ATet) on a glassy carbon electrode. Electrochemical studies such as differential pulse voltammetry and chronoamperometry were performed for the evaluation of the rate constant of the catalytic reaction, the diffusion coefficient of the analyte dopamine, and the linear dynamic range of the analyte determination. The film modified electrode has superior resolving power in quantitative determination from the mixture of analytes and it was found to be an efficient functionalized electrode for its sensitivity and selectivity toward the analyte of interest.

Theory for cyclic square wave voltammetry of electrode reactions with coupled chemical reactions following the electron transfer is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics.

Separation micro-particles based on physical characteristics is important in numerous applications such as diagnostics, biological analyses, food industries and chemical processing. Microfluidic devices have emerged as a multifunctional and powerful platform for separation ranging from nano-micro sized particles to biological cells. This paper presents a simulation study for microparticle separation in a microfluidic channel based on hydrodynamic technique. By exploiting the hydrodynamic properties of the fluid flow and physical characteristics of microparticles, effective size-based separation is demonstrated. The objectives of the simulations are to obtain the appropriate channels’ angle to separate micro-particle. The analysis of effects of taper angle for microparticle separation was carried out using numerical solutions from the finite element ABAQUS-FEA software. The taper angles 20° and 25° are successfully separate the mixture of 1000 kgm−3 and 10000 kgm−3 density microparticle.

Cyclic voltammetry curves of two kinds of electrode reactions based on a simple E mechanism with unequal diffusion coefficients and the ECirre mechanism under convergent, linear and 'mixed' (convergent/linear) diffusion conditions are developed by numerical simulation. We show that these two types of distinct electrode reactions can respond almost identically under cyclic voltammetry and with similar variation with scan rate under mixed and linear diffusion conditions.

International audience; Electrochemical analysis of species known to passivate electrode surfaces remains challenging. We previously proposed a new method dealing with sampled-current voltammetry performed on an electrode array to mimic polarography at a dropping mercury electrode for the detection of copper. In this work, we study the effectiveness of this method to circumvent electrode fouling with the analysis of phenol solutions at high concentrations (10-2 mol L-1), known to polymerize on electrode surface during its oxidation. Electrode arrays well-adapted to the analysis with such system are prepared by photolithography and characterized by X-Ray photoelectron spectroscopy, X-ray diffraction and voltammetry. While analyses performed in conventional linear voltammetry or sampled-current voltammetry on a single electrode are considerably affected by electrode fouling, a linear calibration plot was achievable using our method. Modelling of the electrochemical signal showed that the current depends only on the applied potential and a parameter characteristic of the passivation phenomenon. It also underlined that sampled-current voltammetry on electrode array can circumvent the problem of passivation by a judicious choice of the sampling time.

Single cell analysis has emerged as a paradigm shift in cell biology to understand the heterogeneity of individual cells in a clone for pathological interrogation. Microfluidic droplet technology is a compelling platform to perform single cell analysis by encapsulating single cells inside picoliter-nanoliter (pL-nL) volume droplets. However, one of the primary challenges for droplet based single cell assays is single cell encapsulation in droplets, currently achieved either randomly, dictated by Poisson statistics, or by hydrodynamic techniques. In this paper, we present an interfacial hydrodynamic technique which initially traps the cells in micro-vortices, and later releases them one-to-one into the droplets, controlled by the width of the outer streamline that separates the vortex from the flow through the streaming passage adjacent to the aqueous-oil interface (dgap). One-to-one encapsulation is achieved at a dgap equal to the radius of the cell, whereas complete trapping of the cells is realized at a dgap smaller than the radius of the cell. The unique feature of this technique is that it can perform 1. high efficiency single cell encapsulations and 2. size-selective capturing of cells, at low cell loading densities. Here we demonstrate these two capabilities with a 50% single cell encapsulation efficiency and size selective separation of platelets, RBCs and WBCs from a 10× diluted blood sample (WBC capture efficiency at 70%). The results suggest a passive, hydrodynamic micro-vortex based technique capable of performing high-efficiency single cell encapsulation for cell based assays.

A theory of square wave voltammetry of three step electrode reaction of amalgam forming ions is developed for a thin mercury film electrode. It is assumed that the first and the second electron transfers are kinetically controlled while the third one is reversible and that the intermediates are thermodynamically unstable. The responses to the cathodic and anodic scan directions are analyzed.

There are several protecting techniques managing with contamination on optical surfaces of in-vessel diagnostic components in ITER. Analysis of impurity transport in narrow and curved gaps gave us the idea that it can’t be explained by convection flows. The proposed protecting construction, situated between plasma and irradiating laser mirror launcher, was analysed for effectiveness. The protecting ability of this construction is based on the principles of hydrodynamic, in particular on bevelled entrance, which provides redirection of polluting gas flow away from the optical components due to angling optical and geometrical channel axes. Several different numerical simulations were studied. The design, setting objectives as well as equations and parameters are under discussion. Results of 2D and 3D numerical simulations are provided.

The simultaneous perturbation of the disk and ring electrode potentials of an RRDE with time-varying controlling waveforms seems to be an effective way of carrying out high-sensitivity collection experiments. The method of dual cyclic voltammetry (i.e. applying dynamic potential programs to the disk and the ring electrodes of an RRDE simultaneously) has proven to be an especially promising method for studying the mechanisms of electrochemical processes. The new 3D representation of the data can be effectively used in order to reveal the formation of electroactive species in the disk electrode process. However, some issues concerning the application of this method may also arise. The “dual dynamic” perturbation of the electrodes can cause transients to appear in the current–potential characteristics of the two electrodes, which often results in electrical cross-talk effects. In this paper it is shown that the afore-mentioned cross-talk (experienced mainly when perturbations of a high rate are applied) is caused by the common resistance shared by the current paths of the two working electrodes. Numerical simulations as well as experiments with a simple model system have been carried out in order to study the cross-talk effects, and a method is suggested for their elimination.

Size exclusion chromatography (SEC) or gel filtration is a hydrodynamic technique that separates molecules in solution as a function of their size and shape. In the case of proteins, the hydrodynamic value that can be experimentally derived is the Stokes radius (R(s)), which is the radius of a sphere with the same hydrodynamic properties (i.e., frictional coefficient) as the biomolecule. Determination of R(s) by SEC has been widely used to monitor conformational changes induced by the binding of calcium (Ca(2+)) to many Ca(2+)-sensor proteins. For this class of proteins, SEC separation is based not just on the variation in protein size following Ca(2+) binding, but likely arises from changes in the hydration shell structure. This protocol aims to describe a gel filtration experiment on a prepacked column using a Fast Protein Liquid Chromatography (FPLC) system to determine the R(s) of proteins with some indications that are specific for Ca(2+) sensor proteins.

The theory of three step electrode reaction is developed for square wave voltammetry on stationary spherical electrodes. It was assumed that all electroactive species are solution soluble. The dependence of the response on the thermodynamic stability of intermediates, on the electrode radius and the scan direction is investigated for the fast and reversible electrode reactions. The criterion of reversibility is postulated. Furthermore, the influence of electrode kinetics on the response was calculated for the cathodic and anodic scan directions. The difference in responses caused by the variation of scan direction is an indication of multiple electron transfers. The method for the estimation of transfer coefficient is demonstrated. This work is licensed under a Creative Commons Attribution 4.0 International License.

Based on the cutting-edge technology provided by National Instruments' data acquisition cards and on the LabVIEW graphical programming language, a new electrochemical measuring system has been designed, developed, and presented in this paper. The main objective of the development was to design a workstation which is capable of conducting advanced rotating ring-disk electrode experiments that are based on the simultaneous dynamic potential control of both the disk and the ring electrodes. Our system provides great flexibility in defining the perturbing waveforms and visualizing the measured data. By the use of this system, several new experimental methods have been developed; for example, the construction of three dimensional maps of electrode reaction products has become possible.

There are several strategies for enhancing the sensitivity of electroanalytical methods. Usually, those strategies are based on the selection of the voltammetric technique, the inclusion of an accumulation step, and the eventual addition of a catalytic chemical reaction that regenerates the electroactive species. Square-wave voltammetry (SWV) is one of the most sensitive techniques. In the case of electroanalytical applications, it is typically preceded by an electrochemical or adsorptive pre-concentration step. In this manuscript, the theory of SWV for a quasi-reversible electrode process coupled to a catalytic chemical reaction between an adsorbed reagent and a soluble product is presented. The dependences of the dimensionless net peak current and its peak potential on the value of the standard charge transfer rate constant are described. The variation of the SWV parameters such as frequency and potential pulse amplitude are discussed. The effect of the chemical and electrochemical kinetics on the voltammetric profile is analyzed. Fil: Vettorelo, Sabrina Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

An apparatus for the measurement of steady-state microelectrode voltammetry at elevated temperatures is described. The scope of this experimental approach as a method for the determination of diffusion coefficients at variable temperatures in the case of simple one-electron processes is demonstrated. Diffusion coefficients over a range of temperatures are derived for N,N,N′N′-tetramethylphenylenediamine in both acetonitrile and water solvents, tris-4-bromophenylamine in acetonitrile, and ferrocene in acetonitrile and dimethylformamide from which activation energies for diffusion are obtained. Diffusion coefficient values are used to derive Stokes-Einstein radii for each species in solution. The electroreductions of o-bromonitrobenzene in dimethylformamide and 9-chloroanthracene in acetonitrile are studied as a function of temperature and activation energies estimated for carbon-halide bond cleavage in the corresponding radical anions.

A simple equation is presented which relates the diffusion layer thickness at a rotating disk electrode to the average diffusion layer thickness at a channel (or tubular) electrode, under the assumption that the hydrodynamic flow in both cases is laminar. It is demonstrated that, through the equation, the parameters characterising various possible electrode reaction mechanisms (ECE, DISP1, EC', CE,⋯) under transport-limited conditions at one of the two electrodes, are readily deduced once the corresponding mass transport problem has been rigorously solved at the other electrode. In addition, the relationship is shown to be equally successful when considering the chronoamperometric response at the two electrodes to a potential step, from a region in which no current flows to one corresponding, under steady-state conditions, to the passage of the transport-limited current, and also for the description of the general form of the current-potential curves for the two electrode geometries. The circumstances under which the transformation may be applied are critically assessed.

The theory of cyclic voltammetry at disc electrodes and microelectrodes is developed for a system where the electroactive reactant is regenerated in solution using a catalyst. This catalytic process is of wide importance, not least in chemical sensing, and it can be characterized by the resulting peak current which is always larger than that of a simple electrochemical reaction; in contrast the reverse peak is always relatively diminished in size. From the theoretical point of view, the problem involves a complex physical situation with two-dimensional mass transport and non-uniform surface gradients. Because of this complexity, hitherto the treatment of this problem has been tackled mainly by means of numerical methods and so no analytical expression was available for the transient response of the catalytic mechanism in cyclic voltammetry when disc electrodes, the most popular practical geometry, are used. In this work, this gap is filled by presenting an analytical solution for the application of any sequence of potential pulses and, in particular, for cyclic voltammetry. The induction principle is applied to demonstrate mathematically that the superposition principle applies whatever the geometry of the electrode, which enabled us to obtain an analytical equation valid whatever the electrode size and the kinetics of the catalytic reaction. The theoretical results obtained are applied to the experimental study of the electrocatalytic Fenton reaction, determining the rate constant of the reduction of hydrogen peroxide by iron(II).

Both the strongly implicit procedure and the alternating direction implicit finite difference (ADI) technique are used to simulate mass transport to a microdisc electrode located in a channel flow, taking account of diffusion in three dimensions and the parabolic laminar convective flow over the electrode surface. The effect of the latter on the shape of the disc diffusion layer is qualitatively identified. The flow rate dependence of the transport-limited disc current is predicted and shown to be in quantitative agreement with experiments conducted on the oxidation of ferrocene in acetonitrile solution. © 1995 American Chemical Society.

Epigenetic modifications have been associated by many studies with several types of diseases and metabolic dysfunctions. Specifically, N7-methyl modification of guanine (7-mG) is well established to be used as a biomarker for the detection and determination of DNA methylation. The use of an electrochemical sensor has the potential to provide a simpler and more economic sensing methodology for the determination of 7-mG compared to traditionally utilised laboratory based approaches. In this paper we demonstrate the feasibility of an electrochemical sensor which could potentially be easily applied towards the determination of 7-mG within biological samples, such as human urine. A practical electrochemical configuration was employed consisting of a boron-doped diamond electrode (BDD) as the working electrode and a screen-printed graphite electrode (SPE) providing the counter electrode and the reference electrode. With this new protocol, the electrochemical behaviour of 7-mG has been investigated via cyclic voltammetry (CV) and square wave voltammetry (SWV) using a BDD electrode with a simplified electrochemical set-up. The electrochemical behaviour of 7-mG within acetate buffer solutions at a BDD electrode has been compared and contrasted to a glassy carbon electrode with the following parameters studied: voltammetric scan rate, solution pH, 7-mG concentration and electrode surface pretreatment. The oxidative mechanism elucidation has been performed at controlled potential and such results have provided the dimer formation as the major product. The simultaneous electroanalytical identification of 7-mG together with the presence of guanine, adenine and 8-oxoguanine has been investigated under the optimum experimental conditions. Furthermore, the feasibility of using a BDD electrode for the detection of 7-mG is explored in a human urine sample. Authors would like to acknowledge funding throughout the University of Alicante. J. Iniesta thanks the programme Salvador de Madariaga from the Ministerio de Economía y Competitividad, grant number PRX14/00363.

The dual cyclic voltammetry technique and the electrochemical measuring system with rotating gold disk-gold ring electrodes have been tested in air-saturated and deaerated aqueous sulfuric acid solutions (selected as model systems). The oxygen reduction process has been chosen as model reaction. A new 3D representation of the data has been proposed which can be used to reveal the formation of electroactive species (intermediates or products) at the disk. Keywords: Dual cyclic voltammetry, Rotating ring-disk electrode, Oxygen reduction, 3D map

The basis for mass transport of the electroactive species in different diffusion fields is examined, pointing out important insights in relation to the value of the surface concentrations for the case of fast electrode processes. Moreover, a general analytical solution for the transient current is given for several geometries, when an arbitrary sequence of potentials pulses is applied to macroelectrodes (planar), spheres, cylinders, discs and bands. The results are particularized for Square Wave Voltammetry. Explicit solutions for the net current and the forward and backward components are given. The effects of frequency, pulse amplitude and electrode size or shape on the peak current are studied. Moreover, the conditions for the attainment of the steady state response are analyzed in the different geometries as well as the characteristics of this response. © Pleiades Publishing, Ltd., 2012.

Adsorption of colloidal particles at a solid/liquid interface leads to a spontaneous formation of a porous structure, which may have a strong effect on the ion transport from the bulk solution to the adsorption surface. This effect can be investigated by employing the cyclic voltammetry and rotating disk electrode techniques. We used the cyclic voltammetry method to characterize monolayers of 1 μm sulfate polystyrene particles. We conducted measurements of the limiting diffusion current in a 1 mM solution of potassium hexacyanoferrate(III) at various rotational speeds of the disk. Before each experiment the gold rotating disk electrode was carefully prepared by mechanical polishing to obtain a smooth, clear, and reproducible gold surface. The state of the gold surface was then examined using optical microscopy, atomic force microscopy and cyclic voltammetry measurements. We used a diffusion cell for particle deposition under barrierless conditions. We demonstrated a good agreement between the experimental results and theoretically predicted limiting diffusion current at medium and high surface coverages of the rotating disk electrode. Our results suggest that the voltammetric method can be used for the characterization of monolayer thickness and porosity, as well as for the determination of surface concentration of deposited colloidal particles.

Graphene modified electrodes have been fabricated by electrodeposition from an aqueous graphene oxide solution onto conducting Pt, Au, glassy carbon, and indium tin dioxide substrates. Detailed investigations of the electrochemistry of the [Ru(NH(3))(6)](3+/2+) and [Fe(CN)(6)](3-/4-) and hydroquinone and uric acid oxidation processes have been undertaken at glassy carbon and graphene modified glassy carbon electrodes using transient cyclic voltammetry at a stationary electrode and near steady-state voltammetry at a rotating disk electrode. Comparisons of the data with simulation suggest that the transient voltammetric characteristics at graphene modified electrodes contain a significant contribution from thin layer and surface confined processes. Consequently, interpretations based solely on mass transport by semi-infinite linear diffusion may result in incorrect conclusions on the activity of the graphene modified electrode. In contrast, steady-state voltammetry at a rotating disk electrode affords a much simpler method for the evaluation of the performance of graphene modified electrode since the relative importance of the thin layer and surface confined processes are substantially diminished and mass transport is dominated by convection. Application of the rotated electrode approach with carbon nanotube modified electrodes also should lead to simplification of data analysis in this environment.

Cyclic biamperometry was studied as an analytical method for use with commercially available, comb-type, coplanar microinterdigitated electrodes (μIDEs), using the ferri-/ferrocyanide redox couple as a model analyte. The μIDEs studied in this work were made of gold that had been deposited onto a Ti/W adhesion layer on borosilicate glass chips and had 5 and 10 μm bands with equal gap sizes. Close proximity of the two working electrodes, and their interdigitation, resulted in signal amplification by redox cycling. Results were compared with those obtained by cyclic voltammetry, where one of the two IDE electrodes was used as the working electrode and external reference and auxiliary electrodes were used. Amplification factors of almost 20 were achieved due to redox cycling. Attempts to apply cyclic voltammetry to the μIDEs, with one of the combs as the working and the other as the auxiliary electrode, were unsuccessful due to corrosion of the auxiliary electrode comb. Results of this study, and the electrochemically unique feature of biamperometry to probe but not change the net contents of the medium under examination, suggest the applicability of scanning biamperometry at μIDEs to the very small volumes and electrochemical cell dimensions that are now of great interest.

The use of single walled carbon nanotube (SWNT) band electrodes in a channel flow cell, for low concentration detection, with hydrodynamic voltammetry is reported. A two dimensional SWNT network electrode is combined with a one piece channel flow cell unit, fabricated by microstereolithography. This configuration provides well defined hydrodynamics over a wide range of volume flow rates (0.05–25 mL min−1). Limiting current measurements, from linear sweep voltammograms, are in good agreement with the channel electrode Levich equation, for the one electron oxidation of ferrocenylmethyl trimethylammonium (FcTMA+), over a wide concentration range, 1×10−8 M to 2.1×10−5 M, with a detection limit of 5 nM. At the highest flow rates, some influence of the slightly recessed electrode geometry arising from the SWNT electrode fabrication is noted. However, this can be accounted for by a full simulation of the hydrodynamics and solution of the resulting convection–diffusion equation. Application of this hydrodynamic configuration to the voltammetric detection of dopamine is also demonstrated. Keywords: Channel flow electrode, Hydrodynamic electrode, Single walled carbon nanotubes, Dopamine, Band electrode

An experimental and computational laboratory studying the linear sweep voltammetry (LSV) technique under stirred conditions using a rotating disk electrode (RDE) is discussed in this paper. Experimental analysis is conducted of one of the most well-researched systems in electrochemistry: reduction of Fe(CN) 6 3− species on Pt in an aqueous KNO 3 solution. In the computational portion, a comprehensive physicochemical model is presented to describe the electrode response of the system (i.e., current density vs. electrode potential), which is then solved using COMSOL™ Multiphysics software. Further insights into the system are obtained by computing variables that cannot be experimentally measured such as the surface concentrations and the concentration profiles. Information concerning the pedagogical goals, details of the system, experimental issues, mathematical modeling, results and feedback are provided to facilitate its implementation.

The electrochemical behaviour of Zn(II) ion as example of C rev E irr system was studied at hanging mercury drop electrode in aqueous solution in the presence of 1M KCl using cyclic voltammetry and convolutive voltammetry methods. Digital simulation technique was used to test the chemical and electrochemical parameters of Zn(II) ion estimated experimentally as well as verifying the proposed electrode mechanism. Keywords: Electrochemical behaviour, C rev E irr system, cyclic voltammetry, convolutive Voltammetry, digital simulation. introduction The electroreduction of Zn(II) has been extensively studied in aqueous and non-aqueous solutions and found to be controlled by both diffusion and charge transfer. 1-6 At mercury electrode different mechanisms have been proposed for electrode reduction of metal cations, e.g., a simple electron transfer process 7,8 , stepwise electron transfer 9 , a CE or CEE mechanism. 10,11 Several literature reports a possible validity of a mechanism involving two one-electron transfer has been discussed.

The numerical method for the simulation of linear scan voltammetry on the rotating disk electrode is adjusted to the problem of irreversible redox reaction between the adsorbed catalyst and the dissolved reactant under transient conditions. The response consists of the wave and the maximum. The peak current depends on the scan rate in linear scan voltammetry, while the limiting current of the wave depends on the rate of rotation of the working electrode. The rate constant of catalytic reaction is determined from the kinetic current under steady-state conditions.

The electrodeposition of tin, at a copper surface, from a tin sulphate (0˙014 mol dm–3) electrolyte containing methanesulphonic acid (12 ˙5 vol.-%) at 295 K has been studied. Cyclic voltammetry, using potential sweep rates of 8–128 mV s–1, at a stationary copper electrode provided information on the potential ranges for tin deposition and stripping. Linear sweep voltammetry, at a copper rotating disc electrode was used to evaluate the mass transport characteristics of the system under controlled, laminar flow conditions. The changes in the limiting current density with a Sn2+ concentration of 0˙006–0˙078 mol dm–3 and an electrode rotation rate of 200–4800 rev min–1 were quantified. Randles-Sevcik and Levich equations were used to give an averaged diffusion coefficient for Sn2+ of 5˙4 × 10–6 cm2 s–1.

In this study, we investigated the mechanism of polishing the inner wall of a tube utilizing a magnetic compound fluid (MCF) from a hydrodynamic viewpoint. We conducted polishing experiments by filling a tube with a MCF consisting of abrasive grains and applying a rotating magnetic field perpendicular to the tube axis. In addition, in order to clarify the polishing mechanism, we performed visualization experiments by observing the behavior of the abrasive grains and measuring the pressure distribution on the inside surface of the tube using a hydrodynamic technique. This study demonstrated that a magnetic field distribution for effective polishing should exist in the region furthest from the centerline between the magnetic poles in the tube. At this position, the abrasive grains are located on the sides of the walls of the inner tube of the clusters formed along the line of magnetic force and the pressure generated is effective for polishing. The pressure distribution has a flat valley profile. Therefore, the radial force of clusters formed near these locations is considered to impart a processing force to the abrasive grains.

As a complement to a previous contribution from us, the mass transport mechanisms of the electroactive species to and from the electrode in an uncomplicated electrode mechanism are considered. The electrode process as a whole is discussed, with emphasis to its reversibility degree, as results from the relevant responses in controlled potential techniques, such as chronoamperometry and current sampling voltammetry, linear sweep and cyclic voltammetry, and in rotating disk voltammetry. The electrode process as a whole, composed by charge transfer and mass transport steps that concur to condition the current flowing, is analysed on the basis of the relative rates of the two steps, as well of the time window within which the process is observed. The so-called ‘boundary value problem’ for uncomplicated charge transfers with different reversibility degrees is outlined. Supplementary Material is available, in which the simulated concentration profiles for reduced and oxidised species reacting at an electrode, at which a triangular potential waveform is applied, are linked to the corresponding current densities.

This work presents a low-cost microfluidic device with sensitive, in-channel electrochemical detection capabilities in microfluidic device. This is accomplished using in-channel gold microelectrodes. The detection unit is composed of (i) the working electrodes (WE) with (ii) a common pseudo-reference electrode (RE) in gold and (iii) a counter electrode (CE) made with indium tin oxide (ITO) on a glass substrate. A redox solution ferrocyanide/ferricyanide was flowed through the microfluidic channel in order to test sensing capabilities using cyclic voltammetry (CV). This solution was confined by an electrochemically inactive solution (ultra-pure water) in the same channel. The position of the interface between the redox solution and the confinement solution could be changed via the ratio between their volumetric flow rates. Cyclic voltammetry allowed the detection of electro active species with reduction current of 150 nA.

Theory for cyclic square wave voltammetry of electrode reactions with chemical reactions preceding the electron transfer is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics.

A novel form of hydrodynamic modulation voltammetry (HMV) is described, based on the periodic variation of mass transport in a microjet electrode (MJE) system, in combination with phase-sensitive detection techniques. In the configuration developed, a jet of solution is fired from a nozzle that is aligned directly over the surface of a dual disk Pt-Pt ultramicroelectrode (UME). The potential at each electrode is controlled separately. A rotating blade, positioned between the nozzle and the UME probe, is used to periodically interrupt flow to the electrode surface, resulting in modulation of the overall mass transfer rate between two defined extremes. The use of a dual disk UME enables two transport-limited current signals to be recorded simultaneously, one for the analyte of interest, and the other for a ‘reference species’ (oxygen for the studies described herein). The latter current response corresponds to the variation in mass transport rate in the chopped flow (CF) arrangement and is used as the signal for phase sensitive detection of the analyte current. Studies of potassium hexachloroiridate (III) [IrCl] oxidation in aqueous solution are used to demonstrate the capabilities of the technique. HMV in the CF-MJE arrangement allows quantitative concentration measurements, down to at least 5×10−7 M.

The voltammetry at three micro-mesh electrodes is explored. It is found that at sufficiently short experimental durations, the micro-mesh working electrode first behaves as an ensemble of microband electrodes, then follows the behaviour anticipated for an array of diffusion-independent micro-ring electrodes of the same perimeter as individual grid-squares within the mesh. During prolonged electrolysis, the micro-mesh electrode follows that behaviour anticipated theoretically for a cubically-packed partially-blocked electrode. Application of the micro-mesh electrode for the electrochemical determination of carbon dioxide in DMSO electrolyte solutions is further illustrated. Neste trabalho investigamos a voltametria em eletrodos do tipo micromesh. Em experimento de duração suficientemente curta, os eletrodods de trabalho micromesh se comportam primeiramente como uma rede de eletrodos de microbanda, seguido pelo comportamento esperado para um arranjo de eletrodos de micro-anel, independentes de difusão, com perímetro igual ao tamanho da grade. Durante eletrólise prolongada, o eletrodo apresentou o comportamento previsto para um eletrodo parcialmente bloqueado, com arranjo cúbico. A aplicação deste eletrodo micromesh na determinação eletroquímica de dióxido de carbono em soluções eletrolíticas de DMSO é descrita.

Hydrodynamic voltammetry is reported at the interface between two immiscible electrolyte solutions (ITIES), using a rotating diffusion cell configuration. The voltammetry arises from laminar flow, induced in the organic and aqueous phases of the ITIES separately. The ITIES has been stabilized by a polyester (PET) track-etched membrane material. The resultant voltammetry is shown to be in accord with the Koutecký-Levich equation for limiting currents at rotating electrodes. The technique is promising for the determination of reaction mechanisms and kinetic parameters for reactions involving immiscible liquid phases.

Rotating disk electrode voltammetry (RDEV) in conjunction with anodic stripping differential pulse voltammetry (ASDPV) with a special type of gold side disk electrode has been evaluated for the direct estimation of copper in natural water (i.e. river water and underground water) as well as in whole blood without any pretreatment. Copper is quantified with high reproducibility and reliability even below 5 ppb without any interference of the common ions or organic materials dissolved in the samples, i.e., natural water and blood. The voltammetric measurements were carried out using a conventional three electrodes cell (i.e., gold as working, platinum as auxiliary and Ag/AgCl as reference electrodes) and the acidified sample. The major problem due to hydrogen evolution at cathode during the deposition of copper ions specially in acidified blood sample is overcome with the help of special design of rotating side disk gold electrode. A new type of rotating side disk electrode was designed to avoid the problem of gas bubbles interference in the stripping voltammetry. The shape, position and the rotation speed of the side disk electrode were optimized as per the requirement in the mild acidic condition. A simultaneous estimation of the zinc, lead and copper is also performed in aqueous sample with KCl as supporting electrolyte. The special design of working electrode and the modified voltammetric conditions are enhanced the sensitivity and reproducibility of the copper estimation at low ppb level with negligible interference.

Cu-rich Cu-Ni alloys (containing 70–90% Cu) are shown to be excellent indicator electrode materials for voltammetric measurements at cathodic potentials. These electrodes have been characterised using a variety of methods: rotating disk voltammetry, amperometric measurements and sono-ring-disk voltammetry. The mechanism of electrochemical oxygen reduction at the Ni-30Cu alloy has been established. The results are compared with the surface study results.

Fast scan stripping voltammetry is applied to copper determination, using a rotating glassy carbon electrode as working electrode. Optimal conditions are determined by an experimental design where the current peak is chosen as response factor. The effects of different parameters (deposition potential, deposition time, electrode rotation rate and potential sweep) and their interdependence is optimized. A value of 2.8×10–10 M is obtained for the detection limit, with a relative standard deviation of 0.16 in four replicated assays. The method is applied to the determination of copper in tap water and in some chemicals (HClO4, HNO3, etc.).

Predictions have been made of how total withdrawal of supporting electrolyte affects the steady-state limiting current at a rotating disk electrode. Incorporating transport by diffusion, migration, and convection, the treatment is restricted to a three-ion system under the assumption that all the ions share the same diffusivity. The results predict qualitative, but not quantitative, agreement with similar studies relating to steady-state voltammetry at a hemispherical microelectrode. The experimental findings of Gao and White are discussed in the light of the new treatment.

Local, difficult-to-solve spatio-temporal structures such as extremely thin reaction layers at the electrodes, thin moving reaction fronts, fast transient variations, isolated temporal discontinuities in boundary conditions, edge effects, etc. are characteristic of the initial boundary value and boundary value problems occurring in electrochemical kinetic modelling. Further progress in the simulation methodology is hindered by the lack of automatic solution techniques for such problems. Based on a critical consideration of various adaptive grid strategies for partial differential equations reported in the scientific literature, a new finite-difference adaptive grid strategy has been formulated, that is especially designed for electrochemical kinetic simulations, and is currently limited to models in one-dimensional space geometry. The intention is to enable an automatic solution of the governing partial/ordinary differential equations to a prescribed accuracy, without any a priori knowledge about the spatio-temporal location of the emerging solution structures. In view of the importance of the solution (concentration) gradients for the electrochemical theory, simultaneous control of the spatial errors of the solutions and their spatial gradients is included in the strategy. Spatial grid adaptation is based on a local uniform grid refinement, using overlapping grid patches. Temporal step selection uses a recent control theoretic algorithm, combined with a simple method of detecting temporal discontinuities of the boundary conditions. A third-order accurate, implicit and L-stable Rosenbrock time-stepping scheme ROWDA3 is used to enable efficient and non-oscillatory temporal integration in the time intervals where a regular solution occurs. A second-order accurate Lawson–Morris–Gourlay extrapolation scheme is used to enable a reliable time-stepping at temporal discontinuities.

New theoretical and experimental results are presented for the response corresponding to a charge transfer reaction when cyclic voltammetry is applied to a dropping mercury electrode (DME). Amalgam formation for both reversible and slow electrode processes has also been considered. We show that sphericity and convective effects can be controlled experimentally so that it is easier to detect possible kinetic effects. Working curves for determining the rate constants of electrode reactions are also given.

The theory of normal pulse voltammetry (NPV) and cyclic potential sweep voltammetry (CV) of the amperometric ion-selective electrodes (AISEs) based on the ionophore-assisted transfer of ions across polarized organic solvent or oil ∣ water (O ∣ W) interfaces is discussed. The numerical solution of the resulting integral equations has been used to show how their voltammograms vary with the ratio of the concentration of analyte ion in the W phase, that is, the test solution, to that of ionophore in the O phase, that is, the ion-sensitive membrane. Generally, the current response of the AISEs at constant ionophore concentration is not linear with respect to the concentration of analyte ion when the ratio exceeds 0.01. In order to obtain a linear calibration curve in a wide range of analyte concentrations, up to a few molar of Na + ion, e.g. a new technique, called F-pulse amperometry, is proposed and experimentally verified, where a pulse voltage corresponding to the ‘foot-of-wave’ potential is applied and the current is sampled according to the NPV technique. When the concentration of analyte ion is very low, the stripping voltammetry technique is promising. Poly(oxyethylene)alkyl ether surfactants at ppb levels can be determined using the stripping voltammetry technique based on the electrochemical pre-concentration of the surfactants by ion-assisted transfer at the O-gel ∣ W interface.

An electrochemical sensor was fabricated by screen printing techniques. This sensor, coupled with stripping voltammetry, could provide a means for a relatively inexpensive on site detector for trace levels of heavy metals. The sensor consists of an electrode pair of graphite/carbon black working electrode and Ag/AgCl reference electrode printed onto a polycarbonate surface. Microscope observation of the working electrode shows considerable surface roughness. Cyclic voltammograms of ferricyanide and lead nitrate indicated that the electrochemical nature of the carbon working electrode and the reference electrode on the sensor were comparable to the performance of conventional glassy carbon and Ag/AgCl reference electrodes. Lead in the 10−6–10−9 M concentration range using linear scan anodic stripping voltammetry with identical deposition times resulted in a linear relationship between peak current and analyte concentration. Square-wave anodic stripping voltammetry is compared with alternative electroanalytical techniques and is shown to offer the advantage of rapid determination of lead in O2-containing solutions.

The kinetic equations for an electrochemical process consisting of a homogeneous first‐order chemical reaction followed by electron transfer at the electrode surface are solved numerically, for linear sweep voltammetry under hydrodynamical conditions in a tubular electrode. Models for both the cases involving reversible as well as irreversible electrode charge transfer reaction are investigated. The influence on current–potential voltammograms of the experimentally measurable parameters like the potential scan rate, axial flow rate and chemical equilibrium parameter is examined and depicted graphically.