Polarographic Current-time Curves Research Articles

Direct and Rapid Electrochemical Determination of Total Surfactants in Amniotic Fluid for Assessment of Foetal Lung Maturity

Abstract The characteristic response in the polarographic current-time curves, observed by the inhibition of the oxygen reduction process by adsorption of phospholipids at the mercury-solution interface, is used for the direct and rapid analysis of surfactants content in amniotic fluid samples. Good correlations were obtained between the described method and two well established routine methods used for estimation of foetal lung maturity in prenatal diagnosis of the respiratory distress syndrome.

404 - Potential induced compaction of adsorbed polyelectrolytes at electrode surfaces: Part II. A model for the π-state of DNA

At distinct potentials conformational transitions of adsorbed polynucleotides, especially double- and single-stranded DNA on the h.m.d.e. occur, recorded by a.c. polarographic current-time curves at the potential of peak 2. From the dependences of such fading reactions on potential, temperature, a.c. frequency, a.c. amplitude, ionic strength, pH value, complex formation and other effects, a coulombic model for DNA adsorption and compaction is established on the basis of current polyelectrolyte theory. The following steps are essential: 1. partial dehydration of adsorbed segments; 2. partial transition B → A form; 3. enhancement of fluctuation in base pairing; 4. compaction of neutralized DNA (π-state) by enhancement of cations in the vicinity of the electrode; 5. dissociation field effect on condensed counter ions in the attached parts of DNA; 6. direct and indirect (hopping mechanism) electron uptake, especially at lower pH values A.c-polarography (after Breyer) indicates certain transitions of tertiary structures, not only of adsorbed polynucleotides but also polyamino acids.

404 — Potential induced compaction of adsorbed polyelectrolytes at electrode surfaces Part II. A model for the π-state of DNA,

At distinct potentials conformational transitions of adsorbed polynucleotides, especially double- and single-stranded DNA on the h.m.d.e. occur, recorded by a.c. polarographic current-time curves at the potential of peak 2. From the dependences of such fading reactions on potential, temperature, a.c. frequency, a.c. amplitude, ionic strength, pH value, complex formation and other effects, a coulombic model for DNA adsorption and compaction is established on the basis of current polyelectrolyte theory. The following steps are essential: o (1) partial dehydration of adsorbed segments; (2) partial transition B→A form; (3) enhancement of fluctuation in base pairing; (4) compaction of neutralized DNA ( π -state) by enhancement of cations in the vicinity of the electrode; (5) dissociation field effect on condensed counter ions in the attached parts of DNA; (6) direct and indirect (hopping mechanism) electron uptake, especialy at lower pH values. A.c. -polarography (after Breyer) indicates certain transitions of tertiary structures, not only of adsorbed polynucleotides but also polyamino acids.

The influence of the adsorption of surface active substance on the rate constant of the electrode reaction

The electrode reaction of copper-EDTA complex was studied polarographically in the presence of polyvinylalcohol. The d.c. polarographic current-time curves were analyzed by using the equation given by Matsuda for the diffusion process of the depolarizer influenced by the adsorbates. The rate constants affected by the adsorption are assumed to be composed of two parts at relatively high coverage, i.e., one is the rate constant of the electrode reaction at free surface of DME and the other the rate constant of the electrode reaction through the adsorded layer. The rate constant at the uncovered surface was analyzed by a formula analogous to that proposed by Parsons and it was shown that one of the parameters involved in the formula depends on the electrode potential. On the other hand, it was shown that the electrode reaction at the covered surface is irreversible, and its cathodic rate constant depends on the electrode potential exponentially.

The influence of the adsorption of surface active substance on the rate constant of the electrode reaction

The electrode reaction of copper-EDTA complex was studied polarographically in the presence of polyvinylalcohol. The d.c. polarographic current-time curves were analyzed by using the equation given by Matsuda for the diffusion process of the depolarizer influenced by the adsorbates. The rate constants affected by the adsorption are assumed to be composed of two parts at relatively high coverage, i.e., one is the rate constant of the electrode reaction at free surface of DME and the other the rate constant of the electrode reaction through the adsorded layer. The rate constant at the uncovered surface was analyzed by a formula analogous to that proposed by Parsons and it was shown that one of the parameters involved in the formula depends on the electrode potential. On the other hand, it was shown that the electrode reaction at the covered surface is irreversible, and its cathodic rate constant depends on the electrode potential exponentially.

Electrode kinetics by analysis of polarographic current-time curves

The method, which enables the evaluation of the kinetic parameters of electrode reactions by analysing the polarographic current-time curve, is presented. As examples of the application of this method, the electrode reactions of the simple zinc ions and of the zinc-acetate complex ions were experimentally examined. For the former case the current-time curves were measured as a function of the electrode potential and the perchlorate concentration. It was found that the standard rate constant, corrected both for the increase of the activity coefficient of the zinc ion and for the Frumkin double-layer effect, has a constant value over the concentration range of perchlorate 0.6–4.0 M. For the latter case the current-time curves in the solution with constant ionic strength (4 M) are measured as a function of the electrode potential and of the acetate concentration. It was concluded that the potential-determining reaction of zinc-acetate complexes is referred only to the species Zn(Ac)2 over a range of acetate concentrations larger than 0.5 M.

Electrode kinetics by analysis of polarographic current-time curves

The method, which enables the evaluation of the kinetic parameters of electrode reactions by analysing the polarographic current-time curve, is presented. As examples of the application of this method, the electrode reactions of the simple zinc ions and of the zinc-acetate complex ions were experimentally examined. For the former case the current-time curves were measured as a function of the electrode potential and the perchlorate concentration. It was found that the standard rate constant, corrected both for the increase of the activity coefficient of the zinc ion and for the Frumkin double-layer effect, has a constant value over the concentration range of perchlorate 0.6–4.0 M. For the latter case the current-time curves in the solution with constant ionic strength (4 M) are measured as a function of the electrode potential and of the acetate concentration. It was concluded that the potential-determining reaction of zinc-acetate complexes is referred only to the species Zn(Ac)2 over a range of acetate concentrations larger than 0.5 M.

Electrochemical behaviour of natural and biosynthetic polynucleotides at the mercury electrode: Part II. Reduction of denatured DNA at stationary and dropping mercury electrodes

Summary The electrode process of denatured DNA has been studied at the DME and HMDE with several polarographic techniques under potentiostatic conditions, i.e. d.c. polarographic current-time curves, phase-sensitive a.c. polarography, polarography with saw-tooth single sweeps and repeated triangular sweeps and pulse polarography. A protonated form of denatured DNA is reduced from the adsorbed state in a totally irreversible electrode reaction to products also strongly adsorbed at the electrode, leading to blocking of the electrode surface and thus to a strong inhibition of the electrode process for longer polarisation times. In neutral media the protonation of DNA becomes rate-determining. A nonfaradaic current response observed in neutral and alkaline solutions was identified as caused by a rearrangement of the adsorbed DNA layer with subsequent slow desorption at more negative electrode potentials. Furthermore the action of double layer effects on the protonation of DNA could be detected and explained.

Effect of surfactants on polarographic current-time curves. Investigation of oxygen maximum and application to trace determination of cysteine.

Effect of surfactants on polarographic current-time curves. Investigation of oxygen maximum and application to trace determination of cysteine.

Polarographic behaviour of halide ions: I. Chloride

The wave obtained in the a.c. polarography of chloride is attributed mainly to the adsorption of chloride ion which results in a high differential capacity of the electrical double-layer. The alternating current at potentials more negative than the summit of this a.c. wave is non-faradaic in character since no faradaic direct current can be detected in this potential region. D.c. polarographic current-time curves indicate that discharge of chloride ion begins almost discontinuously at a potential corresponding to the summit of the a.c. wave.

Analysis of the Polarographic Current-time Curves due to the Reduction of Formaldehyde in Unbuffered Solutions

Analysis of the Polarographic Current-time Curves due to the Reduction of Formaldehyde in Unbuffered Solutions

Polarographic current-time curves and the Ilkovic Equation.

The Ilkovic equation for the limiting diffusion current obtained with a dropping mercury electrode predicts that the instantaneous current grows during the life of the mercury drop as the one-sixth power of the time, and that the ratio of the instantaneous current at the end of the drop life (the maximum current) to the average current is 1.17. McKenzie (1948) showed in a preliminary study that these relations are not obeyed. The present paper is concerned with a more detailed study of current-time curves for cadmium(II), lead(II), and thallium(I) ions and oxygen. Measurements are made both in the presence and absence of maximum suppressor (gelatin) in two supporting electrolytes (potassium chloride and potassium nitrate). It is found that the rate of growth of the instantaneous current is not in accordance with the Ilkovic equation. Also, it does not accurately follow the modified equations, such as the Lingane-Loveridge equation, particularly during the early stages of drop life. The ratio of maximum to average current varies for the different electroactive substances, but in all cases examined 1.23<imax./iav.<1.30. An interesting observation is also made on the current-time curves for cadmium(II) in potassium nitrate in the presence of gelatin. At pH values appreciably below the isoelectric point (?pH 5) the current-time curves and the current-voltage curves are distorted. The implications of these results in the measurement of polarographic waves, both in theoretical and analytical applications, are discussed.

Researches on the Polarographic Diffusion Current. I. Criticism of the Ilkoic Theory and Theoretical Revision of the Ilkovic Equation

Abstract The integral equation representing the thickness of the diffusion layer surrounding a spherical electrode is derived; upon solving this equation, the formula for the polarographic diffusion current is obtained. It becomes clear that the Ilkovic theory is not right because of its ignorance of the curvature of drop and that our revised equation can elucidate many oscillographic recordings of the polarographic current-time curves.

Additions and Corrections - Polarographic Current Time Curves

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdditions and Corrections - Polarographic Current Time CurvesHugh McKenzieCite this: J. Am. Chem. Soc. 1948, 70, 12, 4279Publication Date (Print):December 1, 1948Publication History Published online8 July 2002Published inissue 1 December 1948https://doi.org/10.1021/ja01192a647RIGHTS & PERMISSIONSArticle Views12Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (106 KB) Get e-Alerts Get e-Alerts