Electrode Radius Research Articles

Ultra High Resolution Linear Ion Trap Orbitrap Mass Spectrometer (Orbitrap Elite) Facilitates Top Down LC MS/MS and Versatile Peptide Fragmentation Modes

Although only a few years old, the combination of a linear ion trap with an Orbitrap analyzer has become one of the standard mass spectrometers to characterize proteins and proteomes. Here we describe a novel version of this instrument family, the Orbitrap Elite, which is improved in three main areas. The ion transfer optics has an ion path that blocks the line of sight to achieve more robust operation. The tandem MS acquisition speed of the dual cell linear ion trap now exceeds 12 Hz. Most importantly, the resolving power of the Orbitrap analyzer has been increased twofold for the same transient length by employing a compact, high-field Orbitrap analyzer that almost doubles the observed frequencies. An enhanced Fourier Transform algorithm—incorporating phase information—further doubles the resolving power to 240,000 at m/z 400 for a 768 ms transient. For top-down experiments, we combine a survey scan with a selected ion monitoring scan of the charge state of the protein to be fragmented and with several HCD microscans. Despite the 120,000 resolving power for SIM and HCD scans, the total cycle time is within several seconds and therefore suitable for liquid chromatography tandem MS. For bottom-up proteomics, we combined survey scans at 240,000 resolving power with data-dependent collision-induced dissociation of the 20 most abundant precursors in a total cycle time of 2.5 s—increasing protein identifications in complex mixtures by about 30%. The speed of the Orbitrap Elite furthermore allows scan modes in which complementary dissociation mechanisms are routinely obtained of all fragmented peptides.

Engineering the tube size for an inner surface modification by plasma-based ion implantation

In order to apply the inner surface modification of the tube component by plasma-based ion implantation (PBII) technique, the tube size has been characterized by introducing a characteristic parameter – the critical radius of tube (CRT) to optimize the process parameters of a grid-enhanced PBII technique for the nitrogen ion implantation onto the inner surface of an Fe–Cr–Ni stainless steel tube under the process conditions, including the plasma density of central plasma source, the steady pulse voltage, the grid electrode radius, and the processing pressure. The temporal sheath dynamics of the ion matrix sheath on the inner surface of the tube component modified by PBII were demonstrated by the collisional fluid model using the equations of ion continuity and ion motion, Poisson’s equation, and Boltzmann’s relationship of electron to determine the effective range of the process parameters. The optimum process parameters were found by the effect factors of the CRT which was bounded by the two important process parameters, i.e. the ion implantation dose and the processing time, for the engineering practice due to the available dependence on the surface modification effect in suitable costs.

Achieving Nanometer Scale Tip-to-Substrate Gaps with Micrometer-Size Ultramicroelectrodes in Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) tips with rounded glass insulation around the metal wire (radius a = 5 μm) were fabricated (apparent RG < 1.1, where RG is the ratio of the radius of the insulation sheath divided by the electrode radius), and their SECM feedback approach curves were studied in solutions of tris(2,2'-bipyridine)ruthenium(2+) (Rubpy) in acetonitrile and ferrocenemethanol in water with a platinum disk as the substrate electrode (radius a(s) = 1 mm). Considerable enhancement of the normalized feedback current, I(T)(L) = i(T)/i(T,∞), where L = d/a and d is the distance traveled by the SECM tip, was observed in both systems (e.g., I(T)(L) = 15 in organic solutions and I(T)(L) = 30 in aqueous solutions) with good electrode alignment. This shows that tip-to-substrate gaps of ca. d = 110 nm can be achieved. To account for any deviations from the usual disk UME behavior and currents caused by possible changes in the tip electrode geometry, simulations of the feedback response were performed for a 2D axisymmetric environment. All simulated results match in a point-to-point comparison with experimental values (average relative standard deviation (RSD) = 0.01 ± 0.005).

Localized Electron Transfer and the Effect of Tunneling on the Rates of Ru(bpy)32+ Oxidation and Reduction As Measured by Scanning Electrochemical Microscopy

The kinetics of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)) oxidation and reduction in acetonitrile were investigated by steady-state voltammetry using scanning electrochemical microscopy (SECM). The SECM setup was placed inside a drybox for carrying out experiments in an anhydrous atmosphere and in the absence of oxygen. The standard rate constant, k°, for Ru(bpy) oxidation at a Pt electrode (radius, a = 5 μm) was 0.7 ± 0.1 cm/s, which is smaller than k° for Ru(bpy) reduction measured under the same conditions (≥3 cm/s). This is attributed to the 2,2'-bipyridine ligands having an electron-transfer (ET) blocking effect on the oxidation of the ruthenium(II) center, as opposed to the reduction, which involves ET to the exposed ligands. Thus, tunneling effects may be important in considering the ET in this molecule.

A comparison of Marcus–Hush vs. Butler–Volmer electrode kinetics using potential pulse voltammetric techniques

Simulated voltammograms obtained by employing Butler–Volmer (BV) and Marcus–Hush (MH) models to describe the electrode kinetics are compared for commonly used potential pulse techniques: chronoamperometry, Normal Pulse Voltammetry, Differential Multi Pulse Voltammetry, Square Wave Voltammetry and Reverse Pulse Voltammetry. A comparison between both approaches is made as a function of the heterogeneous rate constant, the electrode size, the applied potential and the electrochemical method, establishing the conditions in which possible differences might be observed. The effect of these differences in the extraction of kinetic parameters, diffusion coefficients and electrode radii are examined, and criteria are given to detect possible deviations of the experimental system from Butler–Volmer kinetics from the behaviour of the chronoamperometric limiting current. The Butler–Volmer model predicts the appearance of an anodic peak in Reverse Pulse Voltammetry for irreversible processes and a peak split of differential pulse voltammograms for quasireversible processes with a value of the transfer coefficient very different from 0.5 (smaller than 0.3 for a reduction process). These striking phenomena are studied by using the Marcus–Hush approach, which also predicts the anodic peak for slow electrode reactions in Reverse Pulse Voltammetry but not the split of the curve in differential pulse techniques.

A numerical model of Trichel pulses in air; the effect of pressure

In this paper a three-species two-dimensional numerical model is used for the simulation of the Trichel pulse regime of corona discharge in air in a point-plane configuration. The effect of air pressure on Trichel pulse characteristics is investigated and the numerical results are compared with the available experimental data. The effect of corona electrode radius of curvature on charge per pulse and the relation between charge per pulse and the average charge per pulse is also studied, and compared with the experimental data reported by Atten et al.

Grounding Resistance of Electrode for Electrical Landfill Leakage Detection

The grounding resistance of power electrode plays a decisive role on the source current in landfill leakage detection using electrical method. A model of grounding resistance for cylindrical electrode was set up in this paper. The corresponding resistance expression was derived, and the main influence factors were also analyzed. The results show that: 1) the electrode grounding resistance is mainly determined by the resistivity of surrounding soil; 2) as the buried depth and the diameter increase, the electrode grounding resistance reduces. When the buried depth exceeds 40cm, the electrode grounding resistance is slightly influenced by the buried depth. Therefore, the buried depth and radius of power electrode should be as large as possible in practice. In addition, the soil around the power electrode should be watered to reduce the grounding resistance. Experiments validate the conclusions.

Development of an Automated Electrostatic Sampler (AES) for Bioaerosol Detection

In this study, an automated bioaerosol collection and output system was developed using a new electrostatic sampling method. The electrostatic sampler was designed using a half-ball shape steel electrode (radius is 45 mm) with three aerosol inlets (radius is 3.5 mm) on the top and a copper plate electrode (6 and 16 mm in diameter) suited inside a circular plastic support. Above the plate electrode, a plastic cylindrical reservoir (14 mm in diameter and 1 mm in height) was built with liquid inlet and outlet made of copper (2 mm in diameter). These outlets are connected to a peristaltic pump for liquid delivery. Next to the reservoir, there are two aerosol outlets (radius is 2.5 mm) connected to a vacuum pump. The physical collection efficiencies of the system were investigated when collecting indoor particles using an optical particle counter under different experimental conditions. The system was also tested when sampling indoor and outdoor bacterial aerosols. Experimental data showed that the system could collect 70%–90% of indoor particles of 0.3–2 μm at a low sampling flow rate of 1.2 L/min when a 20 kV voltage and a particle charger (1.5 V) were applied. Increasing sampling flow rate was observed to lead to the decrease of the collection efficiency. When a particle charger was applied, use of larger plate electrode (16 mm in diameter) was shown to significantly improve the collection efficiency close to two times than that of 6 mm. When operated for sampling environmental bacterial aerosols, the system obtained a similar magnitude of bacterial aerosol concentration levels compared to a mixed cellulose ester (MCE) filter. The integration of the automated electrostatic sampler (AES) sampler developed here with a biosensor device could offer a promising platform for the automated bioaerosol sensing.

Atomic and molecular spectra of normal liquid 4He excited by corona discharges

Liquid 4He at 4.2 K and different pressures up to 8 MPa is excited by positive and negative corona discharges. Emission of He I atomic lines and He2 molecular bands is observed. In negative corona, the line spectrum has distinct blue-shift and broadening, which becomes stronger with increasing pressure. The rotational structure of the molecular bands is resolved at pressures of 0.1–0.2 MPa. A blue shift of the Q-branch maximum with pressure is observed. A rotational temperature of 900 K is estimated from the d3Σu+ − b3Πg molecular band emission. Positive corona was produced on a point anode with smaller electrode radius and higher voltages than for the negative corona. The electric currents for the negative and positive corona are similar. The radiation from the positive corona discharges has spectral features which differ qualitatively from the negative corona discharges. The spectra with a positive corona have marked asymmetries with greater intensities in the longer wavelength (red) wings.

Effect of dimensions and geometry of co-field and co-linear pulsed electric field treatment chambers on electric field strength and energy utilisation

Approximations of the electric field strength and specific energy input of continuous pulsed electric field (PEF) systems often assume parallel plate configurations. However, it is known that actual electric field strengths and specific energy inputs can be significantly different from this simplistic approach. A systematic study of more than 150 dimensions and various insulator geometries of pilot-scale PEF treatment chambers with co-linear electrode configuration was performed. A reduction of the inner diameter of the insulator and its shape changes the distribution and (average) intensity of the electric field. Both, the average electric field strength of the PEF treatment zone and the actual specific energy input, were significantly lower than the expected values derived from dividing the applied voltage by the electrode gap. The difference between theoretical and actual values generally increased with increasing electrode radius and decreasing electrode gap. The relative ratios of theoretical electric field strength or specific energy input to actual (average) electric field strength or specific energy input showed a linear dependency on the ratio of electrode radius and gap. The determined relationships of specific energy input and treatment chamber dimensions and geometry were experimentally validated in four different PEF treatment chambers.

Analytical expressions for transient diffusion layer thicknesses at non uniformly accessible electrodes

Explicit analytical expressions for the diffusion layer thicknesses of disk and band electrodes of any size, under transient conditions have been deduced. We have applied these expressions to constant potential chronoamperometry and Linear Sweep Voltammetry (LSV). The analysis of the diffusion layer thickness and concentration profiles of electroactive species corresponding to the application of a constant potential have allowed us to characterise the evolution of the mass transport from linear (high sizes) to radial (microelectrodes). The influence of the time pulse, scan rate and the electrode radius has been analyzed, with limiting expressions corresponding to E ≫ E 0 and E ≪ E 0 were also deduced. The conditions required to attain a stationary state are discussed.

Additive Differential Pulse Voltammetry for the Study of Slow Charge Transfer Processes at Spherical Electrodes

The application of additive differential pulse voltammetry to the study of the kinetics of a charge transfer process is studied. A simple analytical solution is presented, valid for spherical electrodes of any size and for electrode processes of any reversibility. From this solution, valuable diagnostic criteria for the elucidation of the electrochemical reversibility are established based on the variation of the ADPV signal with the duration of the potential pulses, the electrode radius and the pulse height. Working curves for the determination of the kinetic parameters are also given. The value of the ADPV technique is experimentally demonstrated by studying the kinetics of the reduction of 3-nitrophenolate− and europium3+ at mercury hemispherical microelectrodes.

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, R ad + C sol ⇌ k _ k O ad + D sol , 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 r 0, from planar electrodes ( r 0 → ∞), to ultramicroelectrodes ( r 0 → 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.

Combination of Scanning Electron Microscopy in the Characterization of a Nanometer-Sized Electrode and Current Fluctuation Observed at a Nanometer-Sized Electrode

To what extent the effective radius of a nanometer-sized electrode matches its geometric radius is a concern because it is believed that the continuum assumptions of the Nernst−Planck equation do not work when the diameter of the electrode is less than 100 nm. In our research, high-resolution scanning electron microscopy images have been employed to characterize the electrodes whose effective radii have been obtained from electrochemical methods. Thus, electrode geometric and effective dimensions could be compared. Our results show that the geometric radius matches the effective radius very well when the effective radius is larger than 20 nm. There is a significant difference between the effective and the geometric electrode radii when the effective electrode radius is smaller than 20 nm. Current fluctuation can be observed on a 1.6 nm radius electrode at slow scan rates. Possible reasons for the current fluctuation on the electrode are discussed.

The zero-field approximation for weakly supported voltammetry: A critical evaluation

Voltammetry under weakly supported conditions can be modelled using the zero-field approximation [1], which accurately reproduces experiment for a range of systems with electrodes larger than nanoscale. We examine this approximation critically to justify its use, and consider when it may be inapplicable. A lower limit is placed on the radius of electrode for which the double layer and the diffusion layer are effectively decoupled. The success of the zero-field approximation is shown to be dependent on the site where electron transfer really takes place; only if electron transfer is infinitely fast is the approximation blind to these effects.

Effects of Mechanical Tolerances on QMF Performance for Operation in the Third Stability Zone

Our previously reported method of accurately simulating the performance of a quadrupole mass filter (QMF) has been applied to the investigation of the effects of electrode positional tolerance on the performance of a QMF when operated in stability zone 3 ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> ≈ 3.16 and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> ≈ 3.23). Simulations for single- and dual-electrode positional errors have been undertaken. Single-axis errors produced changes in mass peak shape that are similar to those previously reported for zone 1. Compound errors produce changes in mass peak shape that are approximately a summation of the effects obtained from individual single-axis errors. Our results show that the direction of the electrode displacement, not the electrode, is the important factor in determining the effect on QMF performance. We also show that the effects of an individual electrode radius tolerance result in changes to the mass peak shape that are similar to those produced by individual electrode positional errors. Simulations also show the suitability of unbalanced excitation voltages as a method of compensating for mechanical tolerance when operating in zone 3. From these results, we are able to provide suitable limits for the voltage accuracy and stability when employing this method of compensation.

Implications of Marcus−Hush Theory for Steady-State Heterogeneous Electron Transfer at an Inlaid Disk Electrode

For an outer-sphere heterogeneous electron transfer, Ox + e = Red, between an electrode and a redox couple, the Butler-Volmer formalism predicts that the operative heterogeneous rate constant, k(red) (cm s(-1)) for reduction (or k(ox) for oxidation) increases without limit as an exponential function of -alpha (E - E(0)) for reduction (or (1 - alpha)(E - E(0)) for oxidation), where E is the applied electrode potential, alpha (~1/2) is the transfer coefficient and E(0) is the formal potential. The Marcus-Hush formalism, as exposited by Chidsey (Chidsey, C. E. D. Science 1991, 215, 919), predicts that the value of k(red) or k(ox) limits at sufficiently large values of -(E - E(0)) or (E - E(0)). The steady-state currents at an inlaid disk electrode obtained for a redox species in solution were computed using both formalisms with the Oldham-Zoski approximation (Oldham, K. B.; Zoski, C. G. J. Electroanal. Chem. 1988, 256, 11). Significant differences are noted for the two formalisms. When k(0)r(0)/D is sufficiently small (k(0) is the standard rate constant, r(0) is the radius of the disk electrode, and D is the diffusion coefficient of the redox species), the Marcus-Hush formalism effects a limiting current that can be significantly smaller than the mass transport limited current. This is easily explained in terms of the limiting values of k(red) and k(ox) predicted by the Marcus-Hush formalism. The experimental conditions that must be met to effect significant differences in behavior are discussed; experimental conditions that effect virtually identical behavior are also discussed. As a caveat for experimentalists, applications of the Butler-Volmer formalism to systems that are more properly described using the Marcus-Hush formalism are shown to yield incorrect values of k(0) and meaningless values of alpha, which serves only as a fitting parameter.

Electrode geometry and Hopf instability

The method of impedance spectroscopy was used to study the effect of the electrode geometry and size on the appearance of spontaneous oscillations in the model electrochemical system of the N-NDR type, when the region of negative differential resistance is observed in the steady-state polarization curve. It is shown that in the case of the spherical and cylindrical electrodes, the potential region in which Hopf instability is observed becomes more narrow at a decrease in the electrode radius. However, this region will be wider in the latter case.

Transitions between corona, glow, and spark regimes of nanosecond repetitively pulsed discharges in air at atmospheric pressure

In atmospheric pressure air preheated from 300 to 1000 K, the nanosecond repetitively pulsed (NRP) method has been used to generate corona, glow, and spark discharges. Experiments have been performed to determine the parameter space (applied voltage, pulse repetition frequency, ambient gas temperature, and interelectrode gap distance) of each discharge regime. In particular, the experimental conditions necessary for the glow regime of NRP discharges have been determined, with the notable result that there exists a minimum and maximum gap distance for its existence at a given ambient gas temperature. The minimum gap distance increases with decreasing gas temperature, whereas the maximum does not vary appreciably. To explain the experimental results, an analytical model is developed to explain the corona-to-glow (C-G) and glow-to-spark (G-S) transitions. The C-G transition is analyzed in terms of the avalanche-to-streamer transition and the breakdown field during the conduction phase following the establishment of a conducting channel across the discharge gap. The G-S transition is determined by the thermal ionization instability, and we show analytically that this transition occurs at a certain reduced electric field for the NRP discharges studied here. This model shows that the electrode geometry plays an important role in the existence of the NRP glow regime at a given gas temperature. We derive a criterion for the existence of the NRP glow regime as a function of the ambient gas temperature, pulse repetition frequency, electrode radius of curvature, and interelectrode gap distance.

Characterization of slow charge transfer processes in differential pulse voltammetry at spherical electrodes and microelectrodes

Abstract The use of differential pulse voltammetry at spherical electrodes for the study of the kinetic of charge transfer processes is analyzed. An analytical solution is presented, valid for any value of the electrode radius, the heterogeneous rate constant and the transfer coefficient. Several reversibility criteria are established based on the variation of DPV peak with the duration of the potential pulses and the electrode radius. Moreover, general working curves for extraction of kinetic parameters from DPV experiments are given. The anomalous shape of DPV curves for quasireversible processes with small values of the transfer coefficient is reported. The effect of the presence of both electroactive species on DPV curves for quasireversible and irreversible systems is also studied.