Cyclic staircase voltammetry

The use of cyclic staircase voltammetry was investigated in order to study kinetic mechanisms at low concentration levels. The reversible case for c.s.c.v. was studied along with two common kinetic cases: e.c. and catalytic mechanism. For both the e.c. and catalytic case, it was possible to correlate the peak current ratio with the rate constant with one working curve regardless of the step size, the step time or the time in the step in which the current was measured. For the catalytic mechanism, the increase in the peak current of the forward peak can also be correlated with the rate constant, once again regardless of the experimental parameters. Using this technique, high sensitivity can be obtained at low concentrations and fast scan rates as was shown by comparing c.s.c.v. with cyclic voltammetry for micromolar cadmium solutions. The use of staircase voltammetry for the study of the catalytic reaction between iron (III)-triethanolamine and hydroxylamine was demonstrated and a rate constant of 180 M^?1 s^?1 was obtained, which is consistent with previous work.     

Cyclic voltammetry and differential pulse voltammetry of rescinnamine

Two redox processes can be4 observed for rescinnamine by cyclic voltammetry. The electroactive group is identified as the 3,4,5-trimethoxycinnamic. A mechanism including a homogenous dimerization reacyion following the electron transfer is proposed for the redoz process which occurs at less negative potentials, and the rate constant for the homogenous reactions is calculated. Differential pulse voltammetry is proved to be a suitable method for quantitative determination of the alkaloid.     

Cyclic voltammetry at microstructured electrodes

We present the theoretical treatment of cyclic voltammograms at microstructured electrodes. Calculations of voltammograms permit the determination of electrochemical parameters of redox systems in a single cell in parallel with the determinations of the spectroscopic parameters. The structural parameters of the electrode can be determined using the theoretical treatment presented if the electrochemical parameters of the redox system are known. Furthermore, lithographic-galvanic (LIGA) structures can be used as a model for microporous electrodes. Regression analysis was used to compare experimental and calculated cyclic voltammograms as well as to determine the electrochemical and spectroscopic parameters. A modified Randles-Sevčik equation has been derived to described the peak current dependence of cyclic voltammograms at micro-structured electrodes for both reversible and quasi-reversible charge transfer.     

Cyclic voltammetry studies on pure lead

A potentiometric study of complex formation between gallium and L-serine, L-tyrosine, L-methionine shows the existence of the complexes Ga(L₀)³⁺ and Ga(L_?)²⁺. In the case of L-cysteine, the complex Ga(L_2?)⁺ exists also. L₀, L_?, L_2? designate respectively the zwitterion and the mono- and divalent anions of amino acid. The stability constants of the complexes have been determined.     

Cyclic voltammetry of copper in sodium hydroxide solutions

The cyclic voltammograms of the Cu electrode were, obtained in NaOH solution as a function of the voltage scanning rate, electrolyte concentration and voltage range. A correlation was made between three well-defined anodic peaks and their corresponding cathodic ones. The anodic peaks were found to correspond successively to the formation of a monolayer of Cu₂O, formation of a thick multilayer film of CuO and finally Cu₂O₃ upon which O₂ is evolved. It is suggested that CuO is formed from the oxidation of Cu₂O and/or direct oxidation of metallic copper.Below 0.1 M NaOH the ratio of anodic to cathodic charges was found to be about unity, indicating the quantitative reduction of solid oxidation products, while at higher alkali concentrations higher charge ratios were obtained due to increasing proportions of soluble reaction products.The behaviour of the copper electrode in NaOH was found to be quite complicated. Thus, no simple relations were found between the voltage scanning rate and both the peak current and peak potential or between the peak current and the alkali, concentration. Further work is needed to obtain a definitive explanation of this behaviour.     

Cyclic voltammetry of iron dimine complexes in acetonitrile

The electrochemical behavior of iron diimine complexes, (H₃C?N=C(R)?C(R′)=N?CH₃)₃Fe(II) (R, R′=H,H;H, CH₃; CH₃, CH₃), and (C₅H₄N?C(R₁)=N(R₂))₃Fe(II) (R₁, R₂=H, CH₃; CH₃, CH₃) on a platinum working electrode in acetonitrile is described, and compared to that of the parent aromatic complex, tris-(2,2′-bipyridine)Fe(II). One-electron reversible oxidations were found for all the compounds studied. The electrochemical reductions show 2–3 reduction waves in the potential range studied. Only for the complexes of mixed diimine ligands or 2,2′-bipyridine, a pre-adsorption wave is also observed. It is possible to stabilize low valence states with all ligands studied. A formal iron(I) state is described for the first time for all aliphatic diimine complexes, thus showing that the acceptor properties of the diimine complexes do not depend on the presence of the aromatic rings, but on the iron-diimine chromophore.     

Cyclic voltammetry of silyl- and stannyl-tricobalt cluster compounds

The electrochemical behavior of the clusters PhM′Co₃(CO)_n (M′ = Si, n = 11 and M′ = Sn, n = 12) has been examined via cyclic voltammetry in CH₂Cl₂ solution. In both cases the radical anions PhM′Co₃(CO)_n? are unstable, rearranging to Co(CO)₄ and other products. However, for the silicon compound, where there is one formal cobalt—cobalt bond, the radical anion is sufficiently stable to allow for detection of anion reoxidation at medium scan speeds. The half-life of PhSiCo₃(CO)₁₁? has been calculated as 2.3 s at 25°C.     

Cyclic voltammetry and theoretical calculations of silyl-substituted 1,4-benzoquinones

Cyclic voltammograms of 2,3,5,6-tetrakis(trimethylsilyl)-1,4-benzoquinone (1a), 2,3,5,6-tetrakis(dimethylvinylsilyl)-1,4-benzoquinone (1b), 2,3,5,6-tetrakis(dimethylsilyl)-1,4-benzoquinone (1c), 4,4,6,6,10,10,12,12-octamethyl-4,6,10,12-tetrasilatricyclo[7.3.0.0^3,7]dodeca-1(9),3(7)-diene-2,8-dione (1d), and 5-t-butyl-2-(pentamethyldisilanyl)-1,4-benzoquinone (5h) showed that the first reduction step was reversible and that the second step was irreversible. The first half-wave reduction potentials of 1a, 1b, 1c, and 1d shifted negatively relative to 1,4-benzoquinone by −0.31, −0.24, −0.03, and −0.18 V, respectively. These results demonstrated that the electron-accepting ability of the chair-form quinones 1a and 1b was lower than that of the planar quinones 1c and 1d. The of 5h (−0.93 V vs. Ag/Ag⁺) was quite similar to that of 5-t-butyl-2-trimethylsilyl-1,4-benzoquinone (5a, −0.94 V). A cyclic voltammogram of dimethylsilylene-bridged 1,4-benzoquinone dimer 7 showed two kinds of (−0.76 and −0.94 V). The electrochemical behavior of 7 would be interpreted in terms of near-neighbor interactions between reduced and non-reduced quinone units. Theoretical calculations of the silyl-1,4-benzoquinones reproduced well the solid state structures of the compounds. Also, the computed vibrational frequencies of the silyl-1,4-benzoquinones were in good agreement with the IR absorption frequencies of the CO units in the compounds. The LUMO energy levels of the silyl-1,4-benzoquinones were quantitatively proportional to the .     

Cyclic voltammetry of nucleic acids and determination of submicrogram quantities of deoxyribonucleic acids by adsorptive stripping voltammetry

In cyclic voltammetry (at a mercury drop electrode) guanine residues in the polynucleotide chain give a characteristic anodic peak at potentials close to ?0.3 V (vs. saturated calomel electrode). At low concentrations of polynucleotide, this peak can be enhanced substantially if the potential scan is preceded by adsorptive preconcentration of the polynucleotide at the hanging mercury drop electrode. With accumulation times shorter than 10 min at pH 6.8, the limit of detection of a single-stranded polynucleotide is < 0.1 μg ml^?1. The peak of double-helical deoxyribonucleic acid (DNA) is considerably lower than that of single-stranded DNA under the same conditions, which can be exploited to determine low concentrations of single-stranded DNA in the presence of double-stranded DNA.     

Cyclic voltammetry responses of metastable gold electrodes in aqueous media

Ohne Zusammenfassung     

Cyclic voltammetry determination of epinephrine with a carbon fiber ultramicroelectrode

A carbon fiber ultramicroelectrode was used for the electroanalytical determination of epinephrine in biological fluids (urine) by cyclic voltammetry. The ultramicroelectrode was subjected to an electrochemical pretreatment in order to improve the epinephrine adsorption on the electrode surface. With this preconcetration step, detection limits of 7.8 ng ml(-1) and determination limits of 27.6 ng ml(-1) can be reached. The method was contrasted with native fluorescence determination-similar results were obtained.     

Cyclic voltammetry and bulk electronic properties of soluble carbon nanotubes

The bulk electronic properties of pyrrolidine-functionalized nanotubes are obtained from cyclic voltammetry measurements and discussed in the light of quantum chemical calculations. The functionalization is found to preserve the metallic character and to hardly affect the average density of electronic states.     

Cyclic voltammetry of biopolymer heparin at PVC plasticized liquid membrane

Cyclic voltammetry is used to study the charge transfer reaction of the biopolymer heparin at the PVC plasticized 1,6-dichlorohexane membrane–solution interface. Several unique feature of the reaction are demonstrated including the apparent diffusion control and the specific interaction of heparin with the cation of the membrane phase, which probably acts as the heparin carrier (ionophore). Voltammetric behaviour corresponds to the interfacial transfer of a mixture of polyanions with a relatively high content of polyanions carrying a low charge. Amperometry appears to be a suitable method for the quantification of heparin in various preparations with the sensitivity of ca. 1 U mL⁻¹ (S/N=3).     

Cyclic voltammetry and chronoamperometry of lead ions at carbon fibre electrodes

Cyclic voltammetry of reversible redox couples. e.g., hexacyanoferrate (III)/(II), at carbon fibre electrodes yields sigmoidal anodic and cathodic scans that are almost superimposed. However, the cyclic voltammogram of lead (II) ions was markedly different. The voltammogram, and results from chronoamperometric measurements, can be interpreted on the basis of lead nucleation.     

Cyclic voltammetry of highly hydrophilic ions at a supported liquid membrane

Cyclic voltammetry has been used to study the coupling of ion transfer reactions at a liquid membrane. The liquids are either supported by a porous hydrophobic membrane (polyvinylidene difluoride, PVDF) when the organic solvent is non-volatile (o-nitrophenyloctylether) or are merely a free standing organic solvent layer such as 1,2-dichloroethane comprised between two hydrophilic dialysis membranes supporting the adjacent aqueous phases. The passage of current across the liquid membrane is associated with two ion transfer reactions across the two polarised liquid liquid interfaces in series. It is shown that it is possible to study the transfer of highly hydrophilic ions at one interface by limiting the mass transfer of the other ion transfer reaction at the other interface. Indeed, for systems comprising an ion M in one aqueous phase and a reference ion R partitioned between the membrane and the other aqueous phase, the observed and simulated cyclic voltammograms have a half-wave potential determined by the Gibbs energy of transfer of M transferring at one interface and by the limiting mass transfer of R at the other interface. This new methodology opens a way to measure the Gibbs energy of transfer of highly hydrophilic or hydrophobic ions, which usually limits the potential window at single liquid liquid interfaces (ITIES).     

Cyclic voltammetry of nitronyl- and iminonitroxyls detected by electron spin resonance

The combined cyclic voltammetry method (cyclic voltammetry detected by electron spin resonance, CVA-DESR CVA) was applied to study the electrochemical reactions of nitronyl- and iminonitroxyls (NN and IN) and to estimate the diffusion and absorption characteristics of their products. The ESR method yielded the hyperfine structure constants, including ¹³C. Even if exposed to lower temperature, all the studied NN were shown to spontaneously lose oxygen and to convert gradually into the relevant IN. For each specific NN, the combined CVA-DESR CVA experiments found the reduction potential value at which it can be virtually completely converted into the relevant IN.     

Spectroelectrochemistry on electroactive self-assembled monolayers: Cyclic voltammetry coupled to spectrophotometry

We present a spectroelectrochemical bench involving an electrochemical/spectrophotometric coupling dedicated to probe electroactive self-assembled monolayers (SAMs). This bench is validated by the study of the oxidation of a 5,5′-disubstituted-2,2′-bithiophene immobilized on Au substrate, producing a reversible dimerization of the radical cation (i.e. EC_Dim process) leading to a dimer. A direct comparison between thin layer spectroelectrochemistry in solution and spectroelectrochemistry on SAMs shows that a SAM could be viewed as a highly concentrated solution.     

Determination of phenol by differential pulse voltammetry with a sepiolite-modified carbon paste electrode

Summary The determinations of phenol is studied by means of a carbon paste electrode modified with 10% sepiolite using DPV. A 10 min preconcentration step was performed at pH 1.5 under open circuit conditions. Measurements were made in another cell by DPV with E=100 mV (sweep rate = 40 mV/s) in 0.02 mol/l KNO₃ medium at pH 2. Detection limits (3 ) of 30 ng/ml were achieved for determinations in orange, lemon and cola drinks.

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Phenolbestimmung durch Differentialpuls-Voltammetrie mit einer Sepiolit-modifizierten Kohlepaste-Elektrode