Alternating-current Polarography Research Articles

Catalytic-adsorptive determination of vanadium in solutions of 2,3-dihydroxybenzaldehide and bromate-ions

The influence of bromate-ions on polarographic behavior of the complex of vanadium with 2,3-dihydroxybenzaldehide in acetate buffer solutions with pH 4.7–5.5 has been examined. Using alternating-current polarography, chronovoltammetry with linear sweep of potential, square-wave voltammetry it has been demonstrated, that the electrode process is complicated by adsorption of ligand and formed complexes of vanadium with ligand. In the presence of bromate-ions the analytical signal increases more than one order. A sensitive catalytic-adsorptive method has been developed for determination of vanadium. The vanadium complex accumulation has been carried out at the potential −0.2 V (saturated calomel electrode (SCE) – a reference electrode) in a solution with pH 5.4 in the presence of 5 × 10 −5 М 2,3-dihydroxybenzaldehide and 0.1 М KBrO 3. The detection limit for the accumulation time of 30 s is 2 × 10 −10 М and the reduction current of vanadium complex is linear from 5 × 10 −8 M to 5 × 10 −10 М (the calibration graph is y = 1.5533 x + 39.371 with correlation coefficient of 0.9998). The proposed method has been successfully applied to determination of vanadium in water samples of the Prut River (Republic of Moldova).

Determination of complex formation constants by phase sensitive alternating current polarography: Cadmium–polymethacrylic acid and cadmium–polygalacturonic acid

The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. −10° for Cd–PMA and ca. −15° for Cd–PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents.

Phase Sensitive Alternating Current Polarography: A Chemometric Approach for the Selection of Phase Angles

AbstractA method based on the combined use of multivariate curve resolution by alternating least squares (MCR‐ALS) with phase sensitive alternating current polarography (ACP) is proposed to evaluate the phase angle where capacitive current is minimized in a much more accurate way than the visual inspection of ACP signals. The method allows, through the analysis of series of AC polarograms measured at different phase angles out the potential, to distinguish between faradaic and capacitive contributions. Then the angle at which the capacitive current is negligible can be shown and, in some cases, the influence of adsorption on measured currents minimized.

Minimization of Electrode Adsorption Effects: The Cadmium–Humic Acid System Studied by Phase Sensitive Alternating Current Polarography

AbstractThe use of phase‐sensitive Alternating Current Polarography (ACP) is investigated for the minimization of adsorption effects in metal‐ligand systems with induced metal adsorption onto the electrode. When ACP is applied to obtain information on metal complexation in bulk, some problems arise from the faradaic contribution of adsorbed species. This effect can be corrected by using the capacitive current measured in the potential region of the faradaic peak. Using this correction, ACP produces similar results to those from Reverse Pulse Polarography (RPP), a technique that minimizes electrode adsorption effects on the measured currents. The method proposed is applied to the study of the Cd–humic acid system that has been investigated by ACP, RPP and Differential Pulse Polarography (DPP).

Alternating Current Tensammetry of Tetraphenylborate (TPB) and its Application for Potassium Determination

AbstractAlternating‐current polarography of tetraphenylborate ion (TPB) in acetate buffer (pH 4 to 5) or 0.1 to 0.5 M NaCl produces a characteristic tensammetric (pseudocapacitive) peak at −0.95 V (vs. SCE). Within a limited range (till about 0.2 mM), the tensammetric peak current is proportional to the TPB concentration but it levels off at higher concentration. TPB concentration can also be determined within 5 to 50 μM by measuring the capacity current at −0.4 V or the differential pulse polarographic peak current at −0.85 V. The tensammetric peak current was used to determine the solubility of potassium tetraphenylborate in acetate buffer and sodium chloride solutions. Also, a method for amperometric back‐titration of potassium ion was worked out and applied to the analysis of mineral water.

Electrosorption of sodium cellulose sulfates with different substitution patterns

Various types of sodium cellulose sulfate (SCS), dissolved in a 1M LiCl solution, were investigated by alternating current (AC)polarography. The SCS samples differed in the degree of substitution (DS), thedistribution of substituents within the anhydroglucose unit (AGU), and alongthechain, due to the method of synthesis. The goal was to study theelectrosorptionbehavior, characterized by the shape of the desorption wave in the polarogram,as a function of the chemical structure of the SCS samples. The shape of thedesorption wave reflects domains of different substitution. A superimpositionofparameters like DS and pattern of substitution on the electrosorption behaviorwas observed. The AC polarography method described can be used as a tool todistinguish between an even or uneven distribution of substituents along thecellulose chain.

Polarographic Behavior of Eriochrome Red B and Its Complexes with Rare-Earth Ions

The polarographic behavior of Eriochrome Red B (ERB) and its complexes with rare-earth element (REE) ions in wide ranges of pH and concentrations was investigated by alternating-current polarography and cyclic linear-sweep voltammetry. A new polarographic method was proposed for the determination of heavy REEs and yttrium. The detection limit for REE(III) is 6 × 10–7M. The method proposed was used for determining REE(III) in single crystals with valuable optical properties and in intermetallic compounds of the Tb–Al system.

Determination of Barium by Classical and Alternating-Current Polarography

The behavior of barium(II) in 0.1–5.0 M CaCl2 solutions was studied by classical and alternating-current polarography. The kinetic parameters of barium(II) reduction and the diffusion coefficients were determined. A procedure for the determination of barium in calcium salts was proposed.

Investigation of the kinetic behaviour of captopril followed by A.C. polarography

This paper clarifies the adsorption mechanism of 1-[(2S)-3-mercapto-2-methyl-1-oxopropyl]-L-proline (CPT) on DME. Some characteristic features of CPT adsorption, previously followed by cyclic voltammetry (CV), have been investigated to give more precise information about some electrochemical constants by alternating current polarography (ACP). The first harmonic ACP was considered a suitable tool for obtaining electrochemical parameters of surface-confined reactions. The entity and sign of the molecular interaction parameter (g), the thermodynamic constant of adsorption (Kads), the extrapolated apparent electron rate constant (Kextsh), the saturation concentration (Co), maximum surface density (Γt)etc. have been determined. The values of some of these electrochemical parameters, found in a previous paper, were confirmed.

Polarographic determination of flutamide

The polarographic reduction of flutamide was investigated by direct current polarography (DCP), alternating current polarography (ACP), normal pulse polarography (NPP) and differential pulse polarography (DPP). The supporting solution was phosphate buffer containing 5% of 95% ethanol. The reduction process at the dropping mercury electrode was diffusion controlled and irreversible. Extraction with 95% ethanol followed by polarographic reduction was selected as the basis of a method for the determination of flutamide as a pure compound and in tablets.

Effect of methyl viologen on the electrochemical behavior of denatured cytochrome c at mercury and solid electrodes

Denatured cytochrome c has been studied in 9.5 M urea medium in the presence of methyl viologen, using differential pulse polarography (DPP) and voltammetry (DPV), alternating current polarography (ACP) and cyclic voltammetry (CV). The DPP and CV curves exhibit an additional peak, which is assigned to the catalytic reduction of denatured cytochrome c.

Cathodic stripping voltammetry of 2-mercaptoethanol

The behaviour of 2-mercaptoethanol at a hanging mercury drop electrode by cathodic stripping voltammetry (c.s.v.) is studied. The stripping curves are recorded by three scanning modes: rapid-scan direct-current, differential-pulse and fundamental harmonic alternating-current polarography. Under the recommended conditions, pre-electrolysis is done at a potential of 0.0 V vs. Ag/AgCl for 3 min in a medium of pH 6.7 or 8 (Britton-Robinson buffer). Then after 1 min, stripping is done at a scan rate of 6.6 mV s −1 preferably in the differential-pulse mode. The stripping peak at about −0.4 V is used to determine 2-mercaptoethanol within the concentration range 3 × 10 −8/2-8 × 10 −7 mol l −1. Calibration functions are reported; the standard additions method is preferred near the limit of detection. The interferences of several organic compounds are described.

Adsorption of deoxyribonucleic acid at mercury electrodes from alkaline solutions of higher ionic strength

Adsorption of double-stranded, thermally denatured DNAs and degradation products of DNA at mercury electrodes from alkaline solutions of higher ionic strength (0.5) has been studied with the aid of phase-sensitive alternating current (AC) and linear sweep voltammetry at the H.M.D.E. and phase-selective AC polarography (at the D.M.E.). It was found that the addition of DNA to the supporting electrolyte lowered the out-of-phase component of AC around the potential of zero charge. At potentials more negative than ca. - 1.0 V nucleic acids yielded nonfaradaic peaks on voltammetric or polarographic curves. The model of adsorption of DNA at the mercury electrode from alkaline solution of higher ionic strength that fits best with the experimental data to date is proposed.

Indirect amplification method for determining peroxydisulphate by alternating-current polarography

The first page of this article is displayed as the abstract.

The Alternating Current Electrode Processes

AbstractThis paper reviews the fundamentals of the alternating current (AC) electrochemical processes. The topics include: the faradaic impedance, the faradaic rectification, AC polarography, AC corrosion and the AC electrolytic methods currently being used in the industry.

Fundamental Comments On Cell Polarography According To Velázquez And Rosado

Some fundamental comments are made on cell polarography according to Velázquez and Rosado (Fertil Steril 23:562, 1972). The results which they have obtained cannot be reliable because fundamental mistakes are made against the principles of the electroanalytic techniques used. We comment upon the conductometry, the amperometric titrations, and the alternating-current polarography as carried out by Velázquez and Rosado.

Comparative Study of the Alternating and Direct Current Polarography of Several Δ4-3-Ketosteroids

A study was undertaken to compare alternating current polarography with direct current polarography as a method of analysis of testosterone, methyltestosterone, and progesterone. A solution consisting of 50 per cent ethanol, buffer (pH 1.3), and tetrabutylammonium iodide was used as the sample medium. Results showed that the lowest practical concentrations of detection for both a.c. and d.c. polarography was 3.3 × 10 −5 M . However, a.c. polarography gave greater precision than did the d.c. method.

Determination of Tetracycline Antibiotics by Alternating-Current Polarography

A method for the analysis of tetracycline, chlortetracycline, and oxytetracycline by alternating-current polarography was developed. The method agrees favorably with microbiological assays and was shown to be applicable to medicinals containing these antibiotics. It was more sensitive and faster than direct-current polarography. Qualitative and quantitative determination of oxytetracycline in the presence of chlortetracycline appears to be possible. The effect of pH and degradation of these antibiotics on polarographic response in comparison to biological activity are discussed. A method for the analysis of tetracycline, chlortetracycline, and oxytetracycline by alternating-current polarography was developed. The method agrees favorably with microbiological assays and was shown to be applicable to medicinals containing these antibiotics. It was more sensitive and faster than direct-current polarography. Qualitative and quantitative determination of oxytetracycline in the presence of chlortetracycline appears to be possible. The effect of pH and degradation of these antibiotics on polarographic response in comparison to biological activity are discussed.

The use of the rotated dropping mercury electrode in polarographic analyses and amperometric titrations of micromolar solution

The applicability of the rotated dropping mercury electrode in conventional direct current polarography, alternate current polarography, and amperometric titrations, has been investigated. The direct current polarographic method was applied to the determination of minute quantities of lead contained in high-purity electrolytic zinc, the lowest content of lead determined being 0.0001 %. It was confirmed that the rotation of the electrode has no advantage in alternating current polarography. Some characteristics of the electrode, revealed by the measurement of current-time curves, are also presented and discussed.

Alternating current polarography of organic compounds. III. Chloranilic acid

The behaviour of chloranilic acid at the dropping mercury electrode has been techniques of ordinary and of alternating current polarography. A new type of tensammetric wave has been encountered, which is probably an outcome either of multilayer adsorption and/or of a change in state of the adsorbed film. At the same time, a new tensammetric phenomenon, the exchange of one species of surface-active molecules against another, has been observed. Alternating current polarography can be used for estimating chloranilic acid at concentrations as low as 10-7M, whereas conventional polarography does not permit analysis at concentrations below 10-5M.