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The behavior of U(IV) octahedral complexes [cation]2[UCl6], where the [cation]+ is [BuMeIm]+ and [MeBu3N]+, is studied using UV/visible spectroscopy, cyclic staircase voltammetry, and rotating disk electrode voltammetry in hydrophobic room-temperature ionic liquids (RTILs) [BuMeIm][Tf2N] and [MeBu3N][Tf2N], where BuMeIm+ and MeBu3N+ are 1-butyl-3-methylimidazolium and tri-n-butylmethylammonium cations, respectively, and Tf2N- is the bis(trifluoromethylsulfonyl)imide anion. The absorption spectra of [cation]2[UCl6] complexes in the RTIL solutions are similar to the diffuse solid-state reflectance spectra of the corresponding solid species, indicating that the octahedral complex UCl6(2-) is the predominant chemical form of U(IV) in Tf2N--based hydrophobic ionic liquids. Hexachloro complexes of U(IV) are stable to hydrolysis in the studied RTILs. Voltammograms of UCl(6)2- at the glassy carbon electrode in both RTILs and at the potential range of -2.5 to +1.0 V versus Ag/Ag(I) reveal the following electrochemical couples: UCl6-/UCl6(2-) (quasi-reversible system), UCl(6)2-/UCl6(3-) (quasi-reversible system), and UCl(6)2-/UCl6(Tf2N)x-3+x (irreversible reduction). The voltammetric half-wave potential, Ep/2, of the U(V)/U(IV) couple in [BuMeIm][Tf2N] is positively shifted by 80 mV compared with that in [MeBu3N][Tf2N]. The positive shift in the Ep/2 value for the quasi-reversible U(IV)/U(III) couple is much greater (250 mV) in [BuMeIm][Tf2N]. Presumably, the potential shift is due to the specific interaction of BuMeIm+ with the uranium-hexachloro complex in ionic liquid. Scanning the negative potential to -3.5 V in [MeBu3N][Tf2N] solutions of UCl6(2-) reveals the presence of an irreversible cathodic process at the peak potential equal to -3.12 V (at 100 mV/s and 60 degrees C), which could be attributed to the reduction of U(III) to U(0).

The selective extraction of Cs+ and Sr2+ from aqueous solutions by using the ionophores calix[4]arene-bis(tert-octylbenzo-crown-6) (BOBCalixC6) and dicyclohexano-18-crown-6 (DCH18C6), respectively, was demonstrated in the hydrophobic, room-temperature ionic liquid (RTIL), tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide (Tf2N−). The electrochemistry of Cs+ coordinated by BOBCalixC6 and Sr2+ coordinated by DCH18C6 was examined at a mercury film electrode (MFE) in this ionic liquid by using cyclic staircase voltammetry, sampled current voltammetry at a rotating electrode, and chronoamperometry. Both BOBCalixC6·2Cs+ and DCH18C6·Sr2+ exhibit well-defined reduction waves at approximately −2.4 and −2.9 V versus the ferrocene/ferrocenium (Fc/Fc+) couple, respectively, in which the coordinated ions are reduced to their respective amalgams, permitting the recycling of the ionophores. The diffusion coefficients of BOBCalixC6·2Cs+ and DCH18C6·Sr2+ are (2.7 ± 0.1) × 10−9 and (2.1 ± 0.1) × 10−9 cm2 s−1, respectively, at 30 °C. The coulometric efficiency for the reduction and stripping of Cs at mercury pool electrodes was about 90% and was independent of the deposition time, whereas the efficiency for Sr was slightly less than 90% at short times and decreased with the deposition time, probably due to the formation of a passive layer of Sr(Tf2N)2.

The electrochemistry of cesium was investigated at mercury electrodes in the tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide (Bu3MeN+Tf2N−) room-temperature ionic liquid (RTIL) by using cyclic staircase voltammetry, rotating disk electrode voltammetry, and chronoamperometry. The reduction of cesium ions at mercury exhibits quasireversible behavior with k0 = 9.8 × 10−5 cm s−1 and α = 0.36. The diffusion coefficient of Cs+ in this RTIL was 1.04 × 10−8 cm2 s−1 at 303 K. Bulk deposition/stripping experiments conducted at a rotating mercury film electrode gave an average recovery of 97% of the electrodeposited Cs. The density, absolute viscosity, and equivalent conductance of Bu3MeN+Tf2N− were measured over the range of temperatures from 298 to 353 K. A polynomial equation describing the temperature dependence of the density is presented. Both the viscosity and conductance exhibited the non-Arrhenius temperature dependence typical of glass-forming liquids. The ideal glass transition temperature and the activation energies for viscosity and conductance were obtained by fitting the Vogel–Tammann–Fulcher (VTF) equation to the experimental data for these transport properties.

Development of an in situ technique for measuring electrochemical impedance spectra in real time during an electrochemical experiment is described. The technique is based on staircase voltammetry with relatively large step heights, in which a series of increasing potential steps are applied to an electrochemical system, and the resulting currents are sampled. The first derivatives of the currents thus obtained are then converted to ac current signals in frequency domain, and impedances are computed from them. To demonstrate the technique as a tool for studying the electrode/electrolyte interface during the electrochemical reaction, we chose an electrochemical oxidation reaction of aniline, whose reaction products have been known to continuously change the electrode surface due to the polymer film growth on its surface, and report a number of observations that would not have been obtained without such in situ experiments. A suggestion is also made on the use of staircase voltammetry for mechanistic studies on complex electrochemical reactions by simply varying the sampling time.

Multivariate calibration of a single sensor for many mixed analytes is useful, but generating, validating and testing the calibration models requires large data sets which can be time consuming to collect, particularly when the number of analytes is large. In this paper, a solution to this problem is presented, in the form of an automated liquid handling system capable of producing mixtures and triggering an external analytical instrument to analyse them. As a case study, the electrochemical technique of dual pulse staircase voltammetry (DPSV) was used to collect data for three analytes (glucose, fructose and ethanol) mixed in varying concentrations. Artificial neural networks (ANNs), optimised using genetic algorithms were used to create the best possible multivariate calibration model. The liquid handling system performed 1668 experiments used in the study in approximately 60 h, compared to over 2 weeks that would be required to collect perform the experiments manually. The best calibration models produced from the data bettered those produced from previous manually collected data [1,2] for all the analytes concerned.

The electrochemical oxidation of H2O2 at a nickel rotating disc electrode was studied in 100 mM phosphate buffer at pH 7.26 over the temperature range 5–35°C, [H2O2] range 0 to 130 mM, rotation rates 630 to 10000 rpm and anodic potential + 364 to + 1068 mV s. Ag/AgCl using staircase voltammetry. These results were compared with those previously reported for platinum electrodes (S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim, Acta., 1998, 43, 579; ibid., 1998, 43, 2015; ibid., 1999, 44, 2455; ibid., 1999, 44, 4573; ibid., 2000, 45, 3573). The rate of oxidation of H2O2 on nickel is 15–20 times slower than on platinum. Modifications were made to the binding-site mechanism established for the reaction at platinum (S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim. Acta, 1999, 44, 2455) to account for the kinetics at nickel. These included removing the consideration of proton inhibition and constraining the rate of regeneration of the binding site to potential-invariance. Thermodynamic and kinetic parameters together with the pseudo-activation energy for the formation of the reduced binding site were evaluated.

A new sensor technology, an electronic tongue based on voltammetry has been developed at Linkoping University. Three different metallic working electrodes are used in combination with a set of voltage "pulses", a waveform, to separate different samples. In this paper, three different waveforms are investigated. This is done through a study with nine different teas. Multivariate data analysis ((MVDA), principal component analysis (PCA)) is used to evaluate the data (the recorded current responses). The waveforms are large amplitude pulse voltammetry (LAPV), small amplitude pulse voltammetry (SAPV), and staircase voltammetry. Each method discriminated between the tea samples to some extent, but differently from each other. Best discrimination is achieved when the combination LAPV and staircase are merged together. When SAPV is included in the combination a worse separation is observed. It is clearly the case that more waveforms do not automatically lead to more information. © 2001 Elsevier Science B.V.

In a previous paper we reported that by using artificial neural networks (ANNs) to interpret data acquired using dual pulse staircase voltammetry (DPSV), it is possible to determine the concentrations of aliphatic compounds in mixtures. This paper extends that work by probing the relationship between the DPSV response and mixture composition by fitting the acquired data to a proposed model, using a method based on multiple linear regression (MLR) and analysis of variance (ANOVA). The results of this suggest that the system is predominantly a linear function of the analyte concentrations, with additional contributions from a non-linear ethanol term and a fructose–ethanol interaction term. The common multivariate calibration techniques of MLR, principal component regression (PCR) and linear and non-linear partial least squares (PLS) were subsequently evaluated for the calibration of DPSV voltammograms. These approaches are compared with the previously published artificial neural network (ANN) results. ANNs are found to give the lowest prediction errors, although PLS and PCR are only slightly worse — this is assumed to be due to their inability to model the fructose–ethanol interaction and non-linearity of the ethanol response.

A flexible system has been constructed that allows impedance data to be rapidly measured over a range of frequencies (250 Hz–200 kHz) at each static potential applied to a working electrode during a staircase voltammetric scan. The data collected can be analysed in terms of a series of frequency-dependent ac voltammograms or a series of potential-dependent impedance diagrams. Preliminary tests of the instrument are reported. Ac voltammograms recorded with this instrument and with commercial equipment for a model reversible electrochemical reaction showed good agreement with each other and with theory. Keywords: Ac voltammetry, Impedance spectroscopy, Fourier transform

The success of improving the sensitivity in differential pulse anodic stripping voltammetry by exposure of low frequency sound has been reported in earlier papers. It has been found that audible sound in the low frequency range, of about 100 Hz or lower is very effective for this purpose, with an increase of the signal up to about 300%, without any significant increase of the corresponding noise level. It has been assumed that a similar effect will also appear with other modes of voltammetry. In this present paper this assumption is confirmed by use of low frequency sound in dc stripping and staircase voltammetry. Ordinary stirring or rotating has to be avoided during a voltammetric scanning due to the low reproducibility when this takes place. Sound exposure, however, can be performed during the entire measurement. The simplicity of using audible sound together with enhanced sensitivity and more reproducible analyses makes this method potentially attractive, especially for use in online instrume...

Dual pulse staircase voltammetry (DPSV)a combination of pulsed electrochemical detection and staircase voltammetryis investigated for the simultaneous determination of glucose, fructose, and ethano...

In this paper, a new coupled method of the B-spline wavelet and RLT filtration is presented. The B-spline wavelet is a new chemometrics technique to process signals. It is especially appropriate for processing nonstationary signal noise. RLT filtration can be used to remove extraneous currents from faradaic current, but it is not suitable for filtering random noise. The coupled application of these two methods in staircase voltammetry can filter not only random noise but also extraneous currents. Signals of S/N (signal-to-noise ratio)=0.8 can be filtered. The errors of the peak current are less than 5% and those of the peak potential are less than 1%. The processed results of experiment data are also satisfactory.

An easy, general analytical solution, applicable to any multipotential step technique for a catalytic process in planar and spherical electrodes (including ultramicrohemispheres), is presented. The solution has been deduced rigorously using the mathematical method described by Molina (A. Molina, J. Electroanal. Chem. 443 (1998) 163) based on the application of the superposition principle. In this paper it has been applied to multistep chronoamperometry, cyclic staircase voltammetry (CSCV) and cyclic linear sweep voltammetry (CLSV) by analysing the influence of the electrode radius and the equilibrium and rate chemical constants over the different I/t and I/E responses. Different voltammetric steady states (kinetic, microgeometrical and geometrical-kinetic) can be distinguished and methods for calculating the kinetic parameters of the chemical reaction are also proposed. In the case of an irreversible chemical reaction in linear sweep voltammetry our results are in agreement with those recently deduced by Diao and Zhang (G. Diao, Z. Zhang, J. Electroanal. Chem. 429 (1997) 67).

The general analytical solution corresponding to any multipotential step problem for a catalytic mechanism is presented. This deduction has been carried out rigorously without considering the reaction layer approximation. This solution is therefore applicable to any double and triple potential techniques, and also to any multipulse potential techniques, such as staircase voltammetry and square-wave voltammetry.

Square wave voltammetry (SWV) in the case of irreversible reactions has been studied systematically by digital simulation. A simple expression for the peak current and a method for the evaluation of the charge transfer coefficient are given. The height of the voltammograms increases greatly when pulses of large amplitude are used. In this case, it has been shown that the observed response essentially reflects the underlying potential staircase contribution. This indicates that, in the domain of low concentrations, the response in staircase voltammetry can present a better signal to noise ratio than that in SWV.

Cyclic voltammetry has become one of the most useful tools in modern electrochemistry, but the use of digital potentiostats should be treated with caution by users. Staircase Voltammetry utilizes some parameters to build up the potential ramp. However, for some electrochemical processes, the signal response can be different compared with that acquired using true linear sweep (analogic signal). In this work, the role of SCV parameters in current response during the hydrogen electrochemical adsorption/desorption reaction on a platinum surface was studied. In addition, the transient current in each step comprising the ramp was investigated. The results showed that with a step height of 2 mV, the SCV response matches that recorded by linear sweep voltammetry. From the transient current study, two kinds of capacity were identified: non-faradaic and faradaic charge.

Azobenzene solid particles have been mechanically attached to a graphite electrode and measured by cyclic staircase voltammetry. Well-developed and widely separated cathodic and anodic peaks were observed. Redox reaction is controlled by both the heterogeneous charge transfer kinetics and the mass transfer. Its mechanism is explained by the surface diffusion model. Reaction starts at the three-phase boundary, where electrons are transferred from the electrode surface to the attached azobenzene molecules. The electrons are then propagated over the surface of microcrystals by a series of exchange reactions between hydrazobenzene and azobenzene molecules, with the participation of proton donors from the solution. The apparent mass transfer occurs in this way. In the crystal lattice the transmission of protons is not possible, and consequently there is no propagation of electrons.

An equation is derived for the current in staircase voltammetry at any sampling time at a microdisk electrode for a reversible electrode reaction. On the basis of this equation, three differential staircase voltammetries are developed for the reversible case. Differential current equations of three methods have been derived for the same potential step and different time sampling current (SPDT), differential potential step and same time sampling current (DPST), and different potential step and different time sampling current (DPDT) respectively. Experimental results for the oxidation of K4[Fe(CN)6] in the presence of KCl at platinum ultramicrodisk electrodes were found to agree with theoretical predictions. The data obtained also demonstrate that the differential staircase voltammetry for DPDT is the most sensitive on the three methods.

Staircase voltammetry of surface redox reactions is characterized by a “quasireversible maximum”. The relationship between peak currents and scan rates is not linear, except for totally irreversible reactions, and the response may entirely vanish if the reaction is fast and reversible. For surface redox rections, the equivalence of staircase and linear sweep voltammetries can not he obtained by the variation of the current sampling fraction.

Rotating disk electrode (RDE) voltammetry with a mercury thin-film electrode on a glassy carbon substrate combined with anodic stripping voltammetry (ASV) using square-wave, differential-pulse, and staircase waveforms was applied to direct determination of Cu(II) and Pb(II) speciation in model solutions of Cu(II)−nitrilotriacetic acid and Pb(II)−nitrilotriacetic acid complexes and in snow samples. The dissociation rate constants of Cu(II) and Pb(II) complexes measured by square-wave voltammetry, differential-pulse voltammetry, and staircase voltammetry were found to be similar. Of the above three waveforms examined for their suitability for the study of Cu(II) and Pb(II) complexes in the above model solutions and in snow samples, staircase voltammetry gave the most satisfactory estimates of dissociation rate constants and diffusion coefficients of the metal complexes. However, the analytical sensitivity of square-wave voltammetry is 2 orders of magnitude higher than that of staircase voltammetry. Such hig...

Redox reaction volumes, obtained by high-pressure cyclic voltammetry, are reported for a selection tris(diimine), tris(diamine), hexaammine, and hexaaqua couples of Fe(III/II), Cr(III/II), Ru(III/II), and Co(III/II). Separation of the intrinsic and electrostrictive volume contributions for these couples has been achieved, some in both aqueous and acetonitrile solutions. For the Co(phen)(3)(3+/2+) system, the intrinsic volume change is estimated to be +15.3 +/- 2.1 cm(3) mol(-)(1) (based on measurements in water) and +16.5 +/- 2.0 cm(3) mol(-)(1) (in acetonitrile). For the Co(bipy)(3)(3+/2+) system, values are +12.7 +/- 1.4 cm(3) mol(-)(1) (in water) and +15.5 +/- 2.5 cm(3) mol(-)(1) (in acetonitrile). Using these experimentally determined intrinsic contributions, a simple structural model suggests that the intrinsic volume change for these reactions can be described using the change in effective volume of a sphere with radius close to that of the coordinating-atom-metal bond length. Electrostrictive volume changes for the 3+/2+ complex-ion couples are a function of solute size and coordinated ligands. For Ru(H(2)O)(6)(3+) and Fe(H(2)O)(6)(3+) reduction, volume behavior is significantly different from that of the other systems studied and can be rationalized in terms of possible H-bonding interactions with surrounding solvent which affect the electrostrictive volume changes but which are not available for the ammine and other complexes studied.

The current responses for staircase voltammetry might be very different from those of true linear sweep voltammetry. This is particularly true for data from surface reactions. The existing theories for linear sweep voltammetry may not be used to interpret staircase voltammetric data. In this paper, the frequency spectra of staircases ramp and linear sweep waveforms are analyzed. Two techniques were explored to make staircase voltammetry equivalent to linear sweep voltammetry. The first one involves shaping the output of a digital function generator by using a low-pass filter to convert the staircase ramp to linear potential sweep. The second technique involves filtering the current responses before ditizing. Both techniques are effective. When the filters are properly set, the voltammograms from staircase voltammetry match those obtained by linear sweep voltammetry

A new electroanalytical method, DPSV, employing dual pulses (0.7V and −0.8V) prior to anodic scan (using staircase voltammetry) is developed for simultaneous determination of glucose and fructose. The electrochemistry of both sugars was studied prior to optimizing the operational parameters. The linear ranges were found to be 0.01–2.0 mM for both sugars, precisions (mean = 0.10 mM and n = 8) 1.8% and 2.4% and detection limits (estimated by 3 times the standard deviation) 0.001 and 0.003 mM for glucose and fructose, respectively. To establish the reliability of the method, various food additives were tested and found to give no interference effect under normal concentrations. HPLC method was carried out in parallel with the method for analyzing food, drink and honey samples. No statistically significant difference in the results was obtained for methods.

A fast, sensitive method to determine Co (II) in unpurged ocean seawater is presented. The method combines high scan speed staircase voltammetry (HSACSV) and nitrite catalytic effect to enhance Co(II)-dimethylglyoxime reduction currents. The catalytic effect was magnified using high speed adsorptive cathodic stripping voltammetry and peak currents of ca. 0.1 μA were obtained for pM cobalt samples using 30-s deposition times. The effect of buffer, pH, nitrite concentration and scan speed on cobalt sensitivity was studied. Capacitance currents developed at high scan speeds were filtered by background subtraction. The same procedure was successfully applied to remove oxygen interference in unpurged solutions. Blank voltammograms were obtained in different ways yielding similar results without variation in peak reproducibility or accuracy. Nickel and zinc interferences were removed using a cleaning potential before the scan at −1.03 V. Ratios over 10 000 fold were eliminated using more negative cleaning potential steps. Nickel can also be measured by this method. Total analysis time of unpurged seawater (pM levels of cobalt) was decreased to reagents addition time, 30-s adsorption period and 10-s quiescence time. A detection limit of 5.9 pM Co was achieved in seawater. Short analysis time, sensitivity and portable hardware recommend this method for aboard determinations of cobalt. An oceanic profile of cobalt was measured at the Central East Atlantic Ocean.

Based on an electrolysis model and the analysis of the equivalent circuit, equations and procedures applicable to the correction of induced charging current for staircase voltammetry were derived. A system containing solutions of 0.25 mM ferrocene and 0.1 M tetraethylammonium tetrafluoroborate in acetonitrile was studied. The feasibility of the proposed procedures was confirmed by a linear plot of corrected peak currents obtained with different sampling periods (from 100 μs to 10 ms) versus the reciprocal of the square root of sampling time.

In this work a 50-channel characterisation system for PEMFCs is presented. The system is capable of traditional electrochemical measurements (e. g. staircase voltammetry, chronoamperometry and cyclic voltammetry), and concurrent EIS measurements. Unlike previous implementations, this system relies on dedicated potentiostats for current and voltage control, and independent frequency response analysers (FRAs) at each channel. Segmented fuel cell hardware is used to illustrate the system's flexibility and capabilities. The results here include steady-state data for cell characterisation under galvanostatic and potentiostatic control as well as spatially resolved impedance spectra.

Very simple explicit expressions for the diffusion layer thicknesses (δl) under transient conditions have been deduced for different geometries of the diffusion field. From these expressions we have completely quantified and characterized the variation of δl in normal pulse voltammetry, staircase voltammetry, and linear sweep voltammetry at planar, cylindrical, and spherical electrodes of any size. The influence of the time duration, the potential, the sweep rate, and the electrode radius has been analyzed, and interesting limit expressions for δl corresponding to E. E0 and E, E0 have also been deduced. The conditions required to attain stationary state are given. © 2010 American Chemical Society.

Because of the fact that real measurements are sometimes described in terms of the (formal) scan rate, the functional relationships between this parameter and the peak current in staircase (SCV) and square-wave voltammetry (SWV) were investigated theoretically for simple reversible and totally irreversible electrode reactions. The real SCV peak current is proportional to the square-root of the formal scan rate, v, and inversely proportional to ΔE0.0541: -ip = 0.1453nFScox*(D/π)½v½∆E-0.0541 where v = ΔE / τ. In SWV of a reversible electrode reaction the net peak current depends primarily on the frequency, while the influence of the formal scan rate is of minor importance: ∆ip = nFScox*D½(0.7339f½ + 0.0026∆E0.3118v½). On the other hand, in SWV of a totally irreversible electrode reaction, the real net peak current is a stronger function of the formal scan rate: ∆ip= 0.0942nFScox*D½∆E-0.11 v½ . Experimental results, obtained in perchlorate solutions of Eu3+, are in relatively good agreement with the theory.

The oxidation of As(OH) 3 at Pt is belleved to occur by an anodic oxygen-transfer mechanism that involves anodic discharge of H 2 O to form adsorbed hydroxyl radicals (PtOH); however, anodic conversion of PtOH to the inert oxide (PtO) results in severe passivation of the electrode surface. Hence, a transport-kimited response is not obtained at a Pt rotated-disk electrode by conventional linear scan or staircase voltammetry

Naflon-coated ultrasmall platinum ring electrodes have been implanted in the giant dopamine neuron of the pond snail Planorbis corneus, and the oxygen concentration inside these single neurons has been estimated. Experimental data suggest that the intracellular oxygen level in the identified dopamine neuron of P. corneus is approximately 0.032 mM. The oxygen concentration immediately outside the cell (ca. 10 microns away from the cell) is 0.041 mM. Furthermore, staircase voltammetry can be used to monitor dynamic changes in oxygen concentration inside the cell after bathing with Ringer's solution saturated with air/oxygen. Data obtained for intracellular oxygen concentrations suggest that intracellular oxygen consumption is increased following potassium chloride-induced stimulation of these cells.

High-pressure cyclic staircase voltammetry has been developed and used to measure the molar volume changes ΔV° of redox reactions. Design of the three-electrode high-pressure electrochemical cell, incorporating 1 mm gold or platinum disk working electrodes and an Ag/AgNO3 reference electrode, is outlined. The cyclic waveform is generated using a Forth microprocessor with serial communication to an Apple Macintosh system; the control of the experiment is achieved using a Hypercard graphic “instrument panel”. Successful testing of the cell has been carried out on a number of systems including the Fe(CN)63−/Fe(CN)64− redox couple in aqueous solution. An accurate and reproducible reaction molar volume change for the reaction Fe(CN)63− (aq) + Ag(s) → Ag+ (aq) + Fe(CN)64− (aq) is reported.

A portable, battery-operated electrochemical instrument which enables the method of staircase voltammetry to be implemented may be coupled with the method of abrasive stripping voltammetry for the direct identification of minerals in the field. Small amounts of solid mineral samples are mechanically transferred to a paraffin-impregnated graphite electrode by rubbing the electrode against the crushed mineral. The electrode is then transferred to a conventional electrochemical cell containing electrolyte, and experiments analogous to the well known method of stripping voltammetry are then completed to provide an “electrochemical spectrum” or fingerprint of the mineral. Since the technique can be applied directly with battery-operated equipment, the method can be used by geochemists and mineralogists undertaking field work in areas remote from sophisticated laboratories and mains-powered instruments normally used to characterize minerals. The method has been successfully applied to the identification of minerals such as galena, stibnite, cuprite, pyrite and chalcopyrite, although further work is required to investigate any limitations that might apply with complex mixtures or minerals, and, at the present stage of development, the method is qualitative rather than quantitative.

An electronic tongue based on pulsed voltammetry was designed in this paper. It included five electrodes, three working electrodes (gold, glassy carbon, platinum), an Ag/AgCL reference electrode, and a platinum auxiliary electrode, and these were arranged in a standard three-electrode configuration, adopted Staircase Voltammetry (SCV) to recognize of sulfate-reducing bacteria and iron bacteria in contrast to Normal Pulse Voltammetry (NPV). Using of principal component analysis (PCA) to deal with measurement data of each electrode, to ascertain the three working electrodes' different recognize ability. The result was that the discrimination of SCV is better. Finally it was found that the electronic tongue could differentiate the two bacteria.

The amounts of free ions and labile complexes of Pb, Zn and Cd have been determined in a complex organic growth medium by use of anodic stripping staircase voltammetry, ASSV. It was possible to determine the labile fractions of metals and to obtain good correlation with data on the toxicity of the metals to Tetrahymena when using a specific reduction potential ( E s ) for each element, - 600, - 800 and - 1200 mV vs . SCE for Pb, Zn and Cd, respectively. The labile fractions in the organic growth medium were less than 1% for Pb (Pb precipitated), 15% for Zn (as labile complexes) and 30–40% for Cd (as free ions) for total heavy metal concentrations of 0.5m M –2m M . The toxicity to Tetrahymena decreased in the order Cd⪢ Zn⪢ Pb. The effect of Pb was greater than predicted by ASSV, probably because Tetrahymena additionally ingests the lead-containing precipitate and therefore is exposed to concentrations of Pb exceeding those of the soluble species found in the medium. The results stress the importance of using different specific reduction potentials when different elements are compared, instead of one potential common to all elements. The use of a fixed potential may lead to erroneous conclusions regarding the concentrations of labile species in solution.

The previously described expert system has been extended: rules allowing the elucidation of a larger number of mechanisms have been added and automatic control of additional experimental parameters such as concentration and composition of the solution in the cell and the electrode size has been made possible. The new rules cover a number of mechanisms consisting of two electron transfer steps (ECE, EE, 'square' and triangle'' schemes) and simple mechanisms in which either the reactant or the product undergoes a fast, reversible adsorption. Previously used criteria for the detection of a net reaction in the system and for the determination of the type of the electron transfer were made more robust by combining results obtained with cyclic voltammetry and convolution voltammetry. With the present set of rules, the expert system is capable to evaluate 39 mechanisms and their variants. To validate this set, the system was run with a number of compounds for which reaction mechanisms have already been studied. In all cases, the mechanism found as the most probable was the correct one. The time of the elucidation depended on the number of experiments that had to be done and varied from 4 up to 6 h. During this time, the system worked practically without human supervision.

A significant depletion of the electroactive monoamines and their metabolites in the vicinity of a carbon fiber microelectrode may be induced by in vivo staircase voltammetry in the brain, even if the duration of the voltammetric scans is relatively short (≈5s). The variation of this depletion was determined in the extracellular fluid of the cat thalamus at different durations of the pauses separating consecutive measurements. Pauses not shorter than 5 min ensured a nearly full relaxation, so that at the beginning of each subsequent scan a virtually undisturbed environment surrounded the electrode. With pauses shorter than 5 min, it is still possible to monitor major changes in the monoamine concentration. Staircase scans separated with 45 s pauses, for example, were suitable to study the increase in monoamine levels after administration of reserpine, and release phenomena stimulated with KCl were monitored with frequently repeated voltammetric pulses. The electrochemically induced depletion, on the other hand, can be used for characterizing the dynamics of mass transport in the studied brain structure. This was demonstrated with staircase voltammetry alternated with pauses of 1–100s, and with quasi-chronoamperometry. In vivo brain voltammetry is generally used for monitoring extracellular monoamine (including dopamine) levels. These may be significantly altered by the voltammetric measurement itself through depletion in the vicinity of the electrode. This effect can be minimized with appropriate selection of sampling intervals and other parameters of staircase voltammetry. Conversely, depletion and the following relaxation can be used for determining dynamic characteristics of the studied brain structure which would be difficult to obtain otherwise.

The interfacial and redox behaviour of prazepam and chlorazepate was studied at a hanging mercury drop electrode (HMDE). The faradaic response in cyclic staircase voltammetry caused by the reduction of the adsorbed drug served to evaluate the adsorption parameters. The isotherms obtained showed a double-step adsorption, the first one being of Frumkin type for both compounds. The presence of prazepam and chlorazepate in urine can be determined at nanomolar levels by using adsorption as a preconcentration step prior to determination by differential pulse voltammetry in 0.20 and 0.08 M acetate buffer at pH 5.0 with accumulation potentials of − 0.60 and − 0.55 V, respectively. The influence of various operational conditions on the stripping response was examined. The method proposed is appropriate for the determination of the drugs in urine up to a level 350 ng ml − with short accumulation periods (10–80 s). The relative standard deviation for the 200 ng ml −1 level of the drugs in urine (50–60 s accumulation) was less then 4.6% for prazepam and 5.3% for chlorazepate.

Un calcul systematique de systemes electrochimiques reversibles du premier ordre, suivis ou precedes d'une reaction chimique catalytique, est entrepris par voltammetrie cyclique a vague carree afin de determiner les parametres de vitesse

Linear-scan staircase voltammetry and cyclic staircase voltammetry generate unsatisfactory current-voltage curves even for reversible electrode processes. A convolution method is described that converts such curves, obtained at spherical mercury electrodes, into the classical wave shape that is familiar from polarography

Inhibition of passivation during the anodic dissolution of copper by using organic additives was tested. The ability of four amino-acid chelating agents to delay the onset of passivation of copper anodes was evaluated using the galvanostatic method. Ethylenediaminetetracetic acid (EDTA) gave the most promising results and a more detailed study of this reagent was carried out by using both galvanostatic and staircase voltammetry techniques. The time before the potential of the working electrode exceeded 0.3 V vs. Hg, Hg 2 SO 4 /K 2 SO 4 saturated reference electrode for constant current experiments and the peak current characteristic for the staircase voltammetry, allowed the inhibition efficiency of each additive to be evaluated. The inhibition efficiency of each compound was very dependent on its concentration in the electrolyte. EDTA showed a maximum efficiency to delay copper anode passivation at a concentration of about 0.5% (w/w). Energy dispersive X-ray analysis carried out on samples electrolyzed in the presence and absence of EDTA revealed only metallic copper and/or copper oxide, in both cases. SEM observations showed that the surfaces of the above mentioned samples had different morphologies. No more than metallic copper was detected by X-ray diffraction analysis carried out on the same samples. Interpretations and some consequences of these observations are presented and discussed.

The study of the reversible reduction/oxidation molecules containing multiple interacting or noninteracting redox centers has been carried out using the multipotential step technique Differential Staircase Voltammetry (DSCV). Methods to obtain the formal potentials and other characteristic parameters of the process are proposed for any interaction degree between the centers, when using spherical electrodes of any size (from planar to ultramicrospherical electrodes) and, in particular, the advantages of microelectrodes are discussed. The theoretical predictions have been tested with two experimental systems: ethyl viologen in acetonitrile and pyrazine in aqueous acid media, finding an excellent agreement between the theory and experiments. Therefore, the formal potentials for these systems have been evaluated using DSCV.

A theory of the staircase voltammetry in a thin-layer cell is developed. The influence of the cell thickness and the redox reaction rate constant on the current and the peak potentials is analyzed. For moderately thick cells, the kinetic maximum is predicted. The relationship between peak currents and the square root of the scan rate is not linear and the response may entirely vanish if the redox reaction is fast, the cell is very thin and the scan rate is slow.

The sections in this article are Introduction Potential Step Single Potential Step Double Potential Step Potential Step Chronocoulometry Staircase Voltammetry Pulse Techniques Normal Pulse Voltammetry (NPV) Differential Pulse Voltammetry (DPV) Square Wave Voltammetry (SWV) Other Pulse Techniques Comparison between Potential Pulse Techniques Current Step and Chronopotentiometry Variation of Potential with Time Current Steps and Potentiometric Stripping Analysis Concluding Remarks

On spherical microelectrodes, cyclic staircase voltammograms of reversible redox reactions complicated by the reactant adsorption depend on lateral interactions in the monolayer. Attraction forces increase the separation between the main wave and the post-peak, while the repulsion prevents the resolution of responses of the surface and volume reactions. The theoretical relationships between the dimensionless responses and the dimensionless adsorption constant, the relative surface adsorption capacity, the Frumkin coefficient and the electrode sphericity are given.

The widely documented differences in behaviour of carbon fibre electrodes (CFEs) and carbon paste electrodes (CPEs) used for neurochemical analysis in vivo were investigated. Differential staircase voltammetry was used to study the electrooxidation of ascorbic acid (AA) at CFEs and CPEs in the presence of major constituents of brain tissue, viz., protein, lipid or a mixture of both. Both electrode types were poisoned by protein, reflected in positive shifts in the AA voltammetric peak potential, and also peak broadening, following exposure of the electrodes to protein solution. In contrast, CFEs and CPEs responded very differently to exposure to lipid suspension: CFEs exhibited poisoning whereas CPEs showed enhanced electron transfer kinetics for AA. This significant difference in the response of the two carbon materials to lipid was further demonstrated by showing that lipid could reverse the poisoning caused by protein for CPEs but not CFEs. It appears, therefore, that proteins adsorb on both CPEs and CFEs, hindering electron transfer from AA to the electrode surface. Surfactant lipid molecules, in contrast, have a cleaning effect on CPEs, removing pasting oil and adsorbed proteins from the CPE surface. These results provide an explanation for the stability of CPEs in brain tissue and for the contrasting instability of CFEs in the same environment. The data also suggest that a lipid–protein matrix represents a valuable in vitro chemical model of brain tissue that should allow a truer characterisation in vitro of new and existing in vivo sensors, reducing the need for animal experiments in these studies.

Differential staircase voltammetry is a technique which utilizes the measurements of the dc-component of differential pulse voltammetry. The analytical applicability of the method was estimated using some well-known electrochemical systems. It could be shown that the detection limits of differential staircase voltammetric determinations are almost equal those obtained with differential pulse voltammetry.

Solid microparticles of several different insoluble organic compounds were mechanically immobilized on the surface of graphite electrodes and immersed into a liquid electrolyte in order to study their electrochemical reactions. Cyclic staircase voltammetry and square-wave voltammetry were used. Quinhydrone was found to be a stable intermediate in the reversible redox reaction of solid quinone and hydroquinone on the electrode surface. The reaction occurs on the surface of the solid particle which is in contact with water. Indigo can be reduced to leucoindigo and oxidized to dehydroindigo in two separate reversible redox reactions. In strongly basic medium indigo dissolves in water upon electroreduction. A hydroacridine radical was detected as a stable intermediate in the electrochemically irreversible redox reaction of acridine and dihydroacridine. Famotidine can be electrooxidized and the product of this reaction can be electroreduced in two separate chemically irreversible reactions. Probucol is oxidized to a semiquinone radical which can be re-reduced in an electrochemically irreversible redox reaction. Propyl- thiouracil can be also oxidized to an unknown product which can be re-reduced in a chemically reversible, but slow solid state surface redox reaction. Reductions of solid thionicotinoylanilide and nicotinoylanilide are totally irreversible.