The adsorption of tetraethylammonium ions at a mercury electrode from perchlorate solutions

The adsorption of tetraethylammonium ions at the mercury-perchlorate solution interphase has been studied. Solutions at constant perchloric acid activity have been prepared and the use of several perchloric acid activities allows us to calculate the simultaneous adsorption of both ions: tetraethylammonium and perchlorate. An interphase model is described to explain co-adsorption of both ions.     

Electrode reaction of zinc ions at a dropping mercury electrode in ammonium sulphate solutions

The electrode reaction of Zn(II) at a DME in aqueous solutions of (NH₄)₂SO₄ has been studied by d.c. and square-wave polarography at 25.0±0.1°C. The electrochemical kinetic parameters for the reaction are determined. The appearance of the second wave in the square-wave polarogram has been attributed to the low values of the rate parameter and the transfer coefficient.     

Berberine adsorption at a mercury electrode

The adsorption of berberine and canadine was measured by a.c. polarography. For berberine three different superficial structures were observed: the ions lying flat, the mixed layer of flat and perpendicular ions and the condensed film of perpendicular ions which incorporates anions of the supporting electrolyte. The boundaries between these structures are diffuse. The condensation is an instantaneous nucleation and two-dimensional film growth process. The adsorption of canadine is similar, but its condensed film is very stable and the exchange rate between the adsorbed canadine and the dissolved berberinium ions is very low. Different structures of the adsorbed berberine result in different faradaic square-wave responses.     

Residual photocurrent at a mercury electrode

The residual photocurrent observed at negative potentials with mercury in contact with slightly alkaline 1 M KCl solution has been reinvestigated and found to be caused partly by the reaction of e^?_aq with traces of unidentified electron acceptors and partly by reaction with the solvent. Such a solution can be freed from electron-accepting impurities by irradiation with light of shorter wavelength than 270 nm if SO^2?₃ is present at low concentration. The time constant for the homogeneous decay of e^?_aq at pH ca. 8.8 is then raised to about 400 μs. This slow decay is due to reaction with the solvent as the decay time constant can be increased considerably by raising the pH of the solution. In unsteady state experiments with purified 1 M KCl solutions of high pH containing no added scavenger for e^?_aq the current connected with electron emission and e^?_aq diffusion towards the electrode and the bulk of the solution, is cancelled out at ca. ?1.4 V vs. SCE by a thermal non-faradaic current component when 360 nm light is employed. When CO₂ is present at high concentration a similar cancellation is observed at lower pH at ca. ?1.1 V vs. SCE, suggesting a value for the diffusion coefficient of the radical-ion CO^?₂ about 3.3 times smaller than that of e^?_aq.     

Electrochemical study of potassium isobutyl xanthate at a mercury electrode.

Polarographic studies of potassium isobutyl xanthate at a mercury electrode reveal that the product of an anodic reaction is strongly adsorbed at the mercury surface, as indicated by a prewave. The adsorbed film greatly affects the characteristics of the anodic wave of xanthate in an aqeous medium. The current of total wave is proportional to the concentration of xanthate from 0.32 to 1.6 mM.     

Voltammetry of resazurin at a mercury electrode

Electrochemical behavior of resazurin on HMDE in Britton-Robinson (B-R) buffers (pH 2.0–10.0) was studied using the square-wave voltammetry (SWV), square-wave adsorptive stripping voltammetry (SWAdSV), and cyclic voltammetry (CV) techniques. The voltammogram of resazurin in B-R buffer at pH < 4.0 exhibited two cathodic reduction peaks. The voltammetric peaks were obtained at −0.144 V (reversible) and −1.250 V (irreversible) at pH 3.2, and correspond to the reduction of resorufin to dihydroresorufin and to the catalytic hydrogen wave, respectively. At pH > 4.0, a new irreversible cathodic reduction peak, assigned to the protonation of N-oxide on the phenoxazin ring, was observed. Electrochemical parameters (I _p/E _p, I _p/v, I _p/pH, I _p/t _acc) of the compound were determined. From the voltammetric data, electrochemical reduction mechanisms for all peaks have been suggested. Maximum peak current for the reversible peak was obtained at pH 4.1. A linear relationship between the current and concentration was determined, and also the lowest detection limit was found as 3.25 × 10⁻⁸ mol L⁻¹ and 1.98 × 10⁻¹⁰ mol L⁻¹ for SWV and SWAdSV, respectively.     

Reduction of complexes in unbuffered solutions a unified treatment of the reduction of complexes at a stationary planar electrode or at an expanding mercury electrode

A general treatment is given of an electrode reaction connected with complexation at low ligand concentrations in unbuffered media. The reduction of the simple or complex metal ions occurs at an electrode expanding in accord with some power law; the stationary (solid or mercury) electrode and the dropping mercury electrode are special cases. The ligand is added to the solution as a j-protic acid. Linear semi-infinite diffusion is regarded as the sole mode of transport of all dissolved substances.The solution found, being of a very wide generality, was applied to the case of a potentiostatic regime of electrolysis on a dropping mercury electrode, as well as to the case of a galvanostatic regime on a stationary electrode. The voltammetric relationships obtained embrace all known equations of polarographic and chronopotentiometric reduction of simple and complex metal ions.The theoretical polarographic I—E curves in buffered and unbuffered solutions are presented graphically and compared. Apparently, the changes in the surface proton concentration cause a stretching of the wave.     

A simple model for the electrochemical oscillations on a stationary mercury electrode in bromate solutions

A simple model for the electrochemical oscillations on a stationary mercury electrode in bromate solutions has been proposed and its mathematical simulation carried out on a qualitative level. We believe it can be added to the simplest mathematical models of chemical oscillators, since it consists of only four reaction components.

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Anodic stripping voltammetry at a micro-disc mercury film electrode: Theory of the reversible case

For p=(ar²/D_O)^1/2<0.12 and H=al²/D_R<0.14, simple theoretical equations are proposed to characterize the reversible anodic stripping voltammetric peaks of amalgams obtained with a micro-disc mercury film electrode. The calculated, normalized peaks were higher, thinner and shifted towards more negative potentials compared with the peaks described for the regular size mercury film electrodes. The ADI method was used in calculations.     

Electrochemical studies of technetium at a mercury electrode

The electrochemistry of technetium was studied by polarography, cyclic voltammetry and coulometry in chloride and sulfate media as a function of pH in the range 1.5–13. Compounds of Tc(III) and Tc(IV) are produced by reduction of pertechnetate, and the system Tc(III)/Tc(IV) was investigated in acidic media. The potential—acidity diagram of technetium is described for two total pertechnetate concentrations. Evidence for the dismutation of Tc(III) below pH 4 is discussed.     

Convolutive forecasting at a hanging mercury drop electrode

Convolutive forecasting is a procedure which converts a non-steady-state voltammogram into a steady-state voltammogram. The procedure was found to be successful on a range of sphericities generated by varying the size of a hanging mercury drop and the potential sweep rate in a series of cyclic voltammetric experiments. Both theoretical and experimental analyses on a reversible electrochemical system were considered. An expression establishing the relationship between the radius of a spherical electrode and the potential sweep rate was developed to define the limits of the convolutive forecasting algorithm which was used.     

Anodic stripping coulometry at a thin-film mercury electrode

Primary coulometric versions of d.c. anodic stripping voltammetry, performed in a microcell at a mercury-plated rotating glassy carbon electrode, are applied to the determination of cadmium and lead. With exhaustive preelectrolysis of the sample solution, 5–100 ng of the metal can be determined from the charge contained in the stripping signal; precision and accuracy are in the 5% range. An extrapolation procedure that requires only partial metal deposition is evaluated.     

Amperometric titration of mercury with a stationary platinum electrode in stirred solutions

Amperometric titration of mercury (in the range of 0-4 to 3.5 mg) has been carried out with 2-mercaptobenzoxazole with a stationary electrode in stirred solution in a sodium acetate-acetic acid medium.     

Voltammetric study of the behaviour of N-acetyl-p-aminophenol in aqueous solutions at a platinum electrode

The electrochemical oxidation of N-acetyl-p-aminophenol (PAR) was investigated at a Pt electrode with the application of cyclic (CV) and differential pulse (DPV) voltammetry methods. An effect of scan rate, substrate concentration and pH on electrode reactions was determined. The parameters of substrate electro-oxidation, i.e. heterogeneous rate constant, charge transfer coefficient, and diffusion coefficient, were calculated. Our investigation's results prove the exchange of two electrons and one proton in the first step, followed by a chemical reaction. PAR electro-oxidation occurs according to an EC mechanism.     

Anodic behaviour of 2-mercaptoethanol at a mercury electrode

The anodic processes which occur at the mercury electrode in 2-mercaptoethanol solutions are studied by various polarographic techniques (d.c., a.c. and differential pulse), controlled-potential coulometry, cyclic voltammetry and differential capacity curves. Two steps are distinguished in the process: a one-electron charge transfer and a dismutation step leading to the formation of a mercury(II) mercaptide. The final product is isolated and analyzed. Differential-pulse polarography can be used to determine ?10^?4 M 2-mercaptoethanol with a limit of M.     

Theory of cyclic voltammetry at the mercury film electrode: Reversible case with substrate initially present in the mercury phase

The theory of cyclic voltammetry has been developed for a case describing the behaviour of a reversible system at the mercury film electrode with a metal present initially in the mercury phase. Theoretical results are presented in the form of a simple equation coupled with a set of the calculated current function values. In addition, several simple relationships are given for the parameters characterizing the cyclic curves. The rapid exhaustion of the metal from the mercury film and the generation of the metal ions into the solution free of metal ions offer better conditions for the resolution of adjacent peaks than those existing in cyclic voltammetry at the HMDE and at the MFE with substrate present initially in solution. Theoretical predictions were compared with experimental results obtained for lead and thallium at the silver-based mercury film electrode.     

Electrochemical determination of 2,4-D at a mercury electrode

An indirect electrochemical determination of 2,4-dichlorophenoxyacetic acid (2,4-D), has been presented. The method is based on the adsorption and desorption of 2,4-D on mercury electrode. Also, the electrochemical behavior of 2,4-D in aqueous solutions at different pH values and different 2,4-D concentrations were studied. A simple and rapid method has been developed for its extraction from water and soil. The subsequent determination was carried out by a tensammetric method. Three calibration curves could be obtained from different parts of voltammogram. Under the optimum conditions (pH = 2.3; E_acc = −1100 mV; t_acc = 60 s; alternative current mode; ν = 40 mV s⁻¹; pulse height = 20 mV; modulation frequency = 60 Hz; phase angle = 90°) the limit of detection was 50 μg L⁻¹. The proposed method was applied to the determination of 2,4-D in real samples such as soil and water.