Reconstruction of hydrodynamic flow profiles in a rectangular channel using electrochemical methods of analysis

We propose a theoretical method for reconstructing the shape of a hydrodynamic flow profile occurring locally within a rectangular microfluidic channel based on experimental currents measured at double microband electrodes embedded in one channel wall and operating in the generator-collector regime. The ranges of geometrical and flow parameters providing best conditions for the flow profile determination are indicated. The solution of convection-diffusion equation (direct problem) is achieved through the application of the specifically designed conformal mapping of spatial coordinates and an exponentially expanding time grid for obtaining accurate concentration and current distributions. The inverse problem (the problem of flow profile determination) is approached using a variational formulation whose solution is obtained by the Ritz's method. The method may be extended for any number of electrodes in the channel and/or different operating regimes of the system (e.g. generator-generator).     

Studies on film potentiometric stripping analysis: effects of electrochemical parameters

Film potentiometric stripping analysis (PSA) is a novel method for concentrating the test ion directly on a glassy carbon electrode with subsequent stripping by a chemical oxidant, the redissolution step being followed by a chronopotentiometric sequence. The electrochemical parameters governing both preconcentration and redissolution steps are studied on a rotating disk electrode: experimental results are compared with the theoretical developments recently published. Except for the influence of rde rotation rates on each step and on analytical parameters, experiments and theory are in agreement. Discrepancies concerning the rotation rate effects are studied by potentiostatic coulometry and voltammetry measurements in regard to the preconcentration step: the rotation rate effects are based on the physical behaviour of the rde. Routine analysis is carried out using film PSA, Pb(II) as the test ion and Fe(III) as oxidizing agent, in perchlorate medium.     

The electrochemical behavior of erythromycin A on a gold electrode

The reactivity of erythromycin (pure) was investigated on a gold electrode in neutral electrolyte by cyclic voltammetry. The resulting structural changes were observed with HPLC and FTIR spectroscopy by analyzing the bulk electrolyte after the electrochemical reactions. The results were compared with those previously obtained for azithromycin and clarithromycin under the same experimental conditions. It was found that the electrochemical behavior of erythromycin A differs from that of azithromycin dihydrate. Comparison with the electrochemical activity of basic clarithromycin suggests that the electrochemical activity of erythromycin is similar but more pronounced than that of clarithromycin.HPLC analysis confirmed these observations and showed that during the electrochemical oxidation of erythromycin A, the amount of starting macrolide decreased while the amount of starting impurities increased. Also some new products were observed. FTIR spectroscopy confirmed that erythromycin A is more reactive than clarithromycin, although similar changes in their molecular structures were observed.     

Powdered activated carbon and carbon paste electrodes: comparison of electrochemical behaviour

Commercial activated carbon (Norit R3ex), de-mineralised with conc. HF and HCl, was oxidised (conc. HNO₃) and heat-treated at various temperatures (180, 300 and 420 °C). The physicochemical properties of the samples obtained were characterised by selective neutralisation and pH-metric titration of surface functional groups (acid–base properties), thermogravimetry (thermal stability—TG), FTIR spectroscopy (chemical structure) and low-temperature nitrogen adsorption (BET surface area). Thermal treatment of the carbon materials caused the surface functional groups to decompose; in consequence, the chemical properties of the carbon surfaces changed. Cyclic voltammetric studies were carried out on all samples using a powdered activated carbon electrode (PACE) and a carbon paste electrode (CPE), as were electrochemical measurements in aqueous electrolyte solutions (0.1 M HNO₃ or NaNO₃) in the presence of Cu²⁺ ions acting as a depolariser. The shapes of the cyclic voltammograms varied according to the form of the electrodes (powder or paste) and to the changes in the surface chemical structure of the carbons. The electrochemical behaviour of the carbons depended on the presence of oxygen-containing surface functional groups. The peak potentials and their charge for the redox reactions of copper ions depended on their interaction with the carbon surface.     

Photoelectrocatalytic determination of NADH in a flow injection system with electropolymerized methylene blue

It was firstly described that a glassy carbon electrode electropolymerized with methylene blue shows an efficient photoelectrocatalytic activity towards NADH oxidation in a phosphate buffer solution (pH 7.0). In order to perform the photoelectrocatalytic determination of NADH in a flow injection analysis (FIA) system, a home-made flow electrochemical cell with a suitable transparent window for the irradiation of the electrode surface was constructed. The currents obtained from the photoamperometric measurements in the FIA system at optimum conditions (flow rate of carrier solution, 1.3 mL min⁻¹; transmission tubing length, 10 cm; injection volume, 100 μL; and constant applied potential, +150 mV vs. Ag/AgCl) were linearly dependent on the NADH concentration and linear calibration curves were obtained in the range of 1.0 × 10⁻⁷–2.0 × 10⁻⁴ M. The detection limit was found to be 4.0 × 10⁻⁸ M for photoamperometric determination of NADH.     

Electroless immobilization and electrochemical characteristics of nickel hexacyanoruthenate film at an aluminum substrate

The surface of an aluminum (Al) electrode was modified with a thin film of nickel hexacyanoruthenate (NiHCR) as a novel electrode material. The modification procedure of Al surface, includes two consecutive procedures: (i) the electroless deposition of metallic nickel on the Al electrode surface from NiCl₂ solution, and (ii) the chemical transformation of deposited nickel to nickel hexacyanoruthenate films in solution of 20 mM K₃[Ru(CN)₆] + 0.5 M KNO₃. Cyclic voltammogram of the modified Al electrode showed a well-defined redox reaction due to [Ni^IIRu^III/II(CN)₆]^1−/2− system. The effects of different supporting electrolytes and solution pH were studied on the electrochemical characteristics of the modified electrode. The diffusion coefficients of K⁺ and Na⁺ cations in the film (D), the transfer coefficient (α), and the charge transfer rate constant at the modifying film/electrode interface (k_s), were calculated in the presence of both K⁺ and Na⁺ cations. The stability of the modified electrode was investigated under various experimental conditions.     

Amperometric detection of acetaminophen by an electrochemical sensor based on cobalt oxide nanoparticles in a flow injection system

This paper reports the use of a carbon ceramic electrode as a highly-porous substrate for the electrochemical formation of cobalt oxide nanoparticles. The electrocatalyst was characterized by energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry techniques, and it was used in a homemade flow injection analysis (FIA) system for acetaminophen determination using 0.1 M KOH as the carrier solution. The rate constant (k_s) and charge transfer coefficient (α) were calculated for the electron exchange reaction of the modified film. The kinetic parameters and the mechanism of acetaminophen electrooxidation at the electrode surface were studied by cyclic voltammetry and chronoamperometry. The effects of working potential and flow rate on the performance of the FIA system were studied. Under optimized conditions, the electrode response due to the electrocatalytic oxidation of acetaminophen at 450 mV (vs. SCE) is proportional to the concentration of acetaminophen over a 5-35 μM range with an associated detection limit (S/N = 3) of 0.37 μM and a sensitivity of 0.0296 μA/μM. The relative standard deviation (RSD) was 1.6% for eight replicate measurements. The modified electrode was used to determine the acetaminophen content in tablet samples.     

Theory of linear sweep/cyclic voltammetry for the electrochemical reaction mechanism involving a redox catalyst couple attached to a spherical electrode

The catalytic mechanism O_ad + ne⁻ ? R_ad, , involving a redox couple (O_ad, R_ad) attached to the electrode, and soluble species (C_sol, D_sol), is a precursor for many contemporary electrocatalytic reaction models. The theory of cyclic voltammetry for this mechanism was presented long ago for planar electrodes. Analogous rigorous theory for spherical electrodes has not been available thus far, despite the fact that the use of spherical microelectrodes for kinetic studies is often advantageous. By adopting the integral equation formalism, combined with the recently developed adaptive Huber method for integral equations, we obtain such a rigorous theory. The theory is applicable for any value of the electrode radius r₀, from planar electrodes (r₀ → ∞), to ultramicroelectrodes (r₀ → 0). With the decreasing electrode radii the current functions increase, gradually approaching steady-state sigmoidal waves. Equations for the dependences of the forward peak potentials on dimensionless model parameters, and equations for steady-state voltammograms, obtained in this work, can be used for model verification and parameter estimation.     

电化学还原脱氯用GC负载Pd-Ni电极的制备及表征

通过电沉积法在玻碳板（GC）电极上负载钯镍双金属颗粒,并利用正交实验对其进行循环伏安（CV）研究,得到Pd-Ni/GC电极的最佳制备条件为：Ni²⁺=8.5 mmol·L^-1,Pd²⁺=3 mmol·L^-1,pH=7.0,J_k=15 mA·cm^-2,T=30 min。可以在-500 mV（以Hg/Hg₂SO₄为参比电极）左右获得-24.83 mA的氢吸附峰。用聚吡咯(PPy)修饰GC制备Pd-Ni/PPy/GC电极,CV结果表明,Pd-Ni/PPy/GC电极具有比Pd-Ni/GC电极更大的氢吸附峰值,可以在-500 mV（以Hg/Hg₂SO₄为参比电极）左右获得-32.33 mA的氢吸附峰。扫描电镜（SEM）分析表明,聚吡咯的修饰明显改变了Pd-Ni颗粒的沉积形态,使其沉积粒径更小,分散度更高。     

Pb~(2+)在掺硼金刚石膜电极上的电化学行为

为了充分发挥掺硼金刚石膜(BDD)电极在分析检测工业废水中重金属离子的优势,利用BDD电极作为工作电极,采用线性扫描阳极溶出伏安法测定水溶液中的铅离子,考察了硝酸、硫酸、高氯酸、盐酸4种酸体系对铅离子分析测试的影响。结果发现,在实验室条件下检测铅离子最优的支持电解质体系是硫酸,并且与其他3种酸(硝酸、盐酸、高氯酸)相比,硫酸更加稳定,不具挥发性。     

Glassy carbon electrodes modified with a film of nanodiamond-graphite/chitosan: Application to the highly sensitive electrochemical determination of Azathioprine

A novel modified glassy carbon electrode with a film of nanodiamond-graphite/chitosan is constructed and used for the sensitive voltammetric determination of azathioprine (Aza). The surface morphology and thickness of the film modifier are characterized using atomic force microscopy. The electrochemical response characteristics of the electrode toward Aza are investigated by means of cyclic voltammetry. The modified electrode showed an efficient catalytic role for the electrochemical reduction of Aza, leading to a remarkable decrease in reduction overpotential and enhancement of the kinetics of the electrode reaction with a significant increase of peak current. The effects of experimental variables, such as the deposited amount of modifier suspension, the pH of the supporting electrolyte, the accumulation potential and time were investigated. Under optimal conditions, the modified electrode showed a wide linear response to the concentration of Aza in the range of 0.2-100 μM with a detection limit of 65 nM. The prepared modified electrode showed several advantages: simple preparation method, high stability and uniformity in the composite film, high sensitivity, excellent catalytic activity in physiological conditions and good reproducibility. The modified electrode can be successfully applied to the accurate determination of trace amounts of Aza in pharmaceutical and clinical preparations.     

Influence of anion and pH on the electrochemical behaviour of polypyrrole synthesised in alkaline media

The electrochemical behaviour of conducting polypyrrole films electrosynthesised on vitreous carbon electrodes in alkaline solutions has been investigated by means of cyclic voltammetry and open circuit potentiometric measurements. The shape and evolution of the voltammograms during cycling depend strongly on the kind of anion and solution pH used. From these results, anion and cation participation in the redox process of the polymer has been analysed. The transport of anions like NO₃⁻ or Cl⁻ is dominant, while the transport of OH⁻ is the most important contribution when the polymer is cycled in the presence of anions that cannot be incorporated into the polymer matrix. The incorporation of Na⁺ also takes place and its contribution is more significant as deposition charge increases. The characteristics of the films are compared with those obtained in acid media. The polymerisation efficiency is similar in both cases. Films electrodeposited in alkaline solution can be doped and undoped in acid solution without loosing its redox behaviour.     

Influence of experimental conditions on electrochemical behavior of Prussian blue type nickel hexacyanoferrate film

Electrochemical properties of thin films and microcrystalline precipitates of nickel(II) hexacyanoferrate(II, III), NiHCNFe, are strongly dependent on the method of their preparation and experimental conditions of their investigation. The films have been generated on both inert (gold) and parent metal (nickel) substrates. Interpretation of voltammetric responses of nickel hexacyanoferrate microstructures on electrodes is supported with the data of elemental analysis estimations obtained using atomic absorption and surface examination based on X-ray energy dispersive spectroscopy. Both electrodeposited films and mechanically-attached precipitates of nickel hexacyanoferrate constitute mixed structures in which the relative ratios of K and Ni to Fe reflect composition of a solution for modification, choice of the deposition potential and time, and the time and potential limits of exposure of the system to voltammetric potential cycling in potassium salt supporting electrolyte. We demonstrate here that the more positive set of peaks of nickel hexacyanoferrate is related to the electroactivity of the form containing relatively larger amount of potassium and smaller of nickel. On the other hand, the more negative set of the system’s peaks shall be attributed to the form that is largely potassium depleted and containing more nickel relative to iron. In this context, the use of the previously proposed approximate formulas, K₂Ni[Fe^II(CN)₆] and KNi_1.5[Fe^II(CN)₆], for the predominant nickel hexacyanoferrate (reduced) forms is justified.     

Characterization of a stirred tank electrochemical cell for water disinfection processes

Laboratory experiments were performed to characterize the behaviour of an electrochemical cell equipped with boron-doped diamond anodes and to verify its effectiveness in water disinfection. The hydrodynamic regime was determined when the cell worked either in batch or in continuous mode. Galvanostatic electrolyses of aqueous 1 mM Na₂SO₄ solutions were performed to investigate on the oxidant production in different experimental conditions. The same solutions contaminated by E. coli, enterococci and coliforms were used as test media to verify the effectiveness of the system in the disinfection process. Experimental results indicated that the major inactivation mechanism of bacteria in the electrochemical cell is a disinfection by electrochemically generated oxidants, however a cooperative effect of superficial reaction has to be taken into account. The great capability of BDD anode to produce reactive oxygen species (ROS) and other oxidizing species during the electrolysis allows to establish a chlorine-free disinfection process.     

Nanostructured polyaniline counter electrode for dye-sensitised solar cells: Fabrication and investigation of its electrochemical formation mechanism

Nanostructured polyaniline films with controlled thickness have been successfully grown on fluorine-doped tin oxide (FTO) glass substrates using the cyclic voltammetry (CV) method at room temperature. The formation mechanism of the polyaniline film is monitored by CV techniques, alternating current (AC) impedance spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). It is found that the accumulation of nanostructured polyaniline (>70 nm) on both the scattered and compact layers simultaneously increased the reactive interface, which supports charge transfer at the interface and resistance that hinders electronic transport in the film. By optimising the preparation conditions, the short-circuit photocurrent density of a dye-sensitised solar cell (DSSC) with a PANI counter electrode (CE) increased by 11.6% in comparison to a DSSC with an electrodeposited platinum CE.     

Microscopic and electrochemical characterization of lead film electrode applied in adsorptive stripping analysis

Lead film electrodes (PbFEs) deposited in situ on glassy carbon or carbon paste supports have recently found application in adsorptive stripping voltammetric determination of inorganic ions and organic substances. In this work, the PbFE, prepared in ammonia buffer solutions, was investigated using scanning electron microscopy, atomic force microscopy and various voltammetric techniques. The microscopic images of the lead films deposited on the glassy carbon substrate showed a considerable variability in microstructure and compactness of the deposited layer depending on the selected experimental conditions, such as the concentration of Pb(II) species, the nucleation and deposition potential, and the time applied. The catalytic adsorptive systems of cobalt and nickel in a solution containing 0.1 ammonia buffer, 2.5 × 10⁻⁵ M nioxime and 0.25 M NaNO₂ were employed to investigate the electrochemical characteristics and utility of the in situ prepared lead films.The optimal parameters, i.e. the lead concentration in the solution, the procedure of film removal, and the time and potential of lead nucleation and film deposition for the adsorptive determination of metal traces, were selected, resulting in the very good reproducibility (RSD = 4.2% for 35 scans) of recorded signals. The voltammetric utility of the lead film electrode was compared to that of glassy carbon, mercury film and bismuth film electrodes, and was subsequently evaluated as superior.     

The use of silver solid amalgam electrode for voltammetric and amperometric determination of nitroquinolines

Solid amalgam electrodes represent a suitable alternative to mercury electrodes due to their similar electrochemical properties and non-toxicity of the amalgam material. Nitro derivatives of quinoline have been proven to be genotoxic, thus their presence in environmental samples is a legitimate cause for concern.In this contribution, meniscus modified silver solid amalgam electrode (m-AgSAE) was employed for the batch voltammetric determination and amperometric determination in connection with flow injection analysis of 5-nitroquinoline and 6-nitroquinoline (5-NQ, 6-NQ). Their electrochemical behavior was characterized by cyclic voltammetry, for their determination direct current voltammetry and differential pulse voltammetry were used. Linear calibration curves in the concentration range of 2 × 10⁻⁷ to 1 × 10⁻⁴ mol L⁻¹ were obtained. These results are comparable with results obtained for polarographic determination of the same substances using mercury electrodes. Further, the meniscus modified silver solid amalgam electrode was employed in amperometric detection cell in “wall jet” arrangement for determination of 5-NQ in flow injection analysis. Under optimized conditions (run buffer 0.05 mol L⁻¹ borate buffer, pH 9.0; flow rate 4 mL min⁻¹; detection potential −1.6 V; injection volume 0.1 mL), the limit of quantitation of ∼4 × 10⁻⁶ mol L⁻¹ was achieved. The repeatability of the detector response is satisfactory (relative standard deviation ∼2.15% for c(5-NQ) = 1 × 10⁻⁴ mol L⁻¹). Practical applicability of the method was verified for the determination of micromolar concentrations of 5-NQ in drinking and river water model samples.     

Analysis of experimental constraints and variables for time resolved detection of Fourier transform electrochemical impedance spectra

By using the Fourier transform (FT) technique, it is possible to perform electrochemical impedance spectroscopy in real time during the occurrence of DC voltage controlled surface reactions. The data obtained in this approach, a series of Nyquist plots as functions of DC control variables, can provide a wealth of time resolved information about surface kinetics. We discuss in detail the theoretical and experimental considerations for such time resolved experiments. We focus primarily on the constraints and criteria of measurements in the context of new data acquisition electronics that became available during the last few years. We also present sample experimental results for a gold electrode.     

Synthesis and electrochemical characterisation of benzylmercapto and dodecylmercapto tetra substituted cobalt, iron, and zinc phthalocyanines complexes

The work reports on cyclic voltammetry (CV), square wave voltammetry and spectroelectrochemistry of the following complexes: tetrakis (benzylmercapto) phthalocyanine complexes of Zn(II) (ZnTBMPc, 4a), Co(II) (CoTBMPc, 5a), and Fe(II) (FeTBMPc 6a); tetrakis (dodecylmercapto) phthalocyanine complexes of Zn(II) (ZnTDMPc, 4b), Co(II) (CoTDMPc, 5b), and Fe(II) (FeTDMPc, 6b). More reversible CV couples were observed for complexes 4a, 5a, and 6a containing thiol phenyl ring substituents. Complexes 4b, 5b, and 6b containing long chain thiol substituents showed less reversible couples. Complexes 6a and 6b showed a relatively large number of redox processes (5 for 6a and 6 for 6b) within the potential window employed in this work. The processes for FePc derivatives (6a) are assigned to Fe^IIIPc⁻¹/Fe^IIIPc⁻², Fe^IIIPc⁻²/Fe^IIPc⁻², Fe^IIPc⁻²/Fe^IPc⁻², Fe^IPc⁻²/Fe^IPc⁻³, and Fe^IPc⁻³/Fe^IPc⁻⁴ and for the CoPc derivative (5a) to Co^IIIPc⁻¹/Co^IIIPc⁻², Co^IIIPc⁻²/Co^IIPc⁻², Co^IIPc⁻²/Co^IPc⁻², and Co^IPc⁻²/Co^IPc⁻³.