Showing papers on "Polarography published in 2010"

On the impedance of galvanic cells: VI Alternating current polarography in the complex impedance plane: General treatment

Abstract: The views developed in parts III and IV of this series are applied to alternating current polarography in the impedance plane. It is shown that from such polarograms a quantity q can be determined which is inversely proportional to concentration. The method covers a concentration range of 5.10−9/n2

History of Electroanalytical Methods

Abstract: There are many historical reviews on electrochemistry as well as on analytical chemistry, where-as hardly any survey of the history of electroanalytical methods exists. This contribution is an approach to provide a short overview on the development of the electroanalytical methods, electrodes and electrochemical sensors. Electrogravimetry belongs to the oldest quantitative procedures introduced 1864 by Wolcott Gibbs. Roots are even older and are represented by “voltameters”. Closely related to electrogravimetry is coulometry, which is also based on Faraday's laws; early applications comprise determinations of atomic masses and of thin metal layers. Conductivity measurements are also a rather old analytical method, applied (with direct current) in the 18th century already. The effective procedure was developed in the 1860s after the use of alternating current by Friedrich Kohlrausch. The Nernst equation (1889) was the base for direct potentiometry, e.g., determination of sparingly soluble electrolytes. Max Cremer is the inventor of the glass electrode (1906), which is the first electrochemical sensor. Potentiometric indication of titrations by Robert Behrend (1883) was the first instrumental indication in volumetric analysis. The invention of polarography by Jaroslav Heyrovský (1922) is the starting point of the electroanalysis with the dropping mercury electrode. The polarograph, developed in cooperation with Masuro Shikata, was the first automated analytical device. As a follow-up various methods (e.g., pulse and alternating current methods) as well as voltammetry including stripping analysis have gained importance. Further development of electroanalysis is characterized by new electrodes and electrode materials, e.g., stationary mercury electrodes, carbon-paste electrodes, chemically modified electrodes, and increased application of electrochemical sensors.

Preparation and Properties of Mercury Film Electrodes on Solid Amalgam Surface

Abstract: A simple apparatus (electrolyzer) and a reliable procedure were developed for the preparation of mercury films of exactly defined thickness on a silver solid amalgam substrate. Constant concentration of Hg(II) in the electrolyzer is ensured by dissolution of an anode from silver paste amalgam. Small volume of electrolyte, which can be used repeatedly many times, and paste amalgam preventing the spillage of liquid mercury substantially decrease the danger of environmental contamination with mercury. Parameters and behavior of mercury film electrodes on silver solid amalgam substrate (MF-AgSAE) were compared with polished silver solid amalgam electrode (p-AgSAE) which does not contain liquid mercury, with mercury meniscus modified silver solid amalgam electrode (m-AgSAE), and with hanging mercury drop electrode (HMDE). The height of anodic stripping voltammetric peaks divided by electrode area was highest for MF-AgSAE and the width of those peaks, which determines the resolution of the method, was minimal at MF-AgSAE. Available potential window of MF-AgSAE in different supporting electrolytes is comparable with that of HMDE.

The polarographic reduction of conjugated hydrocarbons: II. The reduction of 1,n‐diphenylpolyenes

Abstract: The current-voltage curves of some 1,n-diphenylpolyenes were measured in a 0.175 molar solution of tetrabutylammoniumiodide in 96% dioxanewater at 25° and 75° C. The experimental half-wave potentials and the roots a of the M.O. secular equation, corresponding to the lowest non-occupied π-electronic level of the conjugated systems, fit the linear equation: ϵ1/2 = a · γ − 1.05 Volts, discussed in part I, giving a mean value of y¯ = − 2.18 ± 0.04 ev (stand, dev.). The theoretical discussion of the course of the reduction of conjugated hydrocarbons has been extended, taking into account the effect of the methylene group on the π-electronic distribution in the intermediately formed radical ions. From a comparison between the results of these theoretical approximations and the experimental data some reasonable suppositions have been made about the behaviour of these polyenes and their partial reduction products at the dropping mercury electrode during electrolysis.

Electrochemical Study of the Pesticide Methidathion at a Mercury Electrode under Cathodic Stripping Mode

Abstract: Methidathion, a non-systemic organophosphorous insecticide and acaricide is studied at the hanging mercury drop electrode under cathodic stripping mode by means of cyclic and square-wave voltammetry (SWV). Its electrode reaction is analyzed in the light of recent theory of cathodic stripping processes of insoluble salts of SWV. Its complex electrode mechanism is described by an electrode reaction of a second order, complicated by adsorption of methidathion molecules on the electrode surface involving lateral interactions between each other. Moreover, under specific experimental conditions the electrode mechanism can be additionally complicated by multilayer formation on the electrode surface, as well as by a chemical transformation following the cathodic stripping process of the methidathion-mercury salt. Following the mechanistic study of the electrode reaction, a method for quantitative determination of methidathion is proposed applying SWV.

Electroanalytical Applications of Pulse Polarography and Voltammetry

Abstract: Some resent developments in the applications of pulse polarography and pulse voltammetry are discussed, with emphasis on techniques which avoid problems associated with the capacitative background current in pulse polarography.

On the impedance of galvanic cells: III. Applications to alternating current polarography

Abstract: The theory described in part I of this series 1 is applied to alternating current polarography by treating the complex cell impedance and cell admittance as functions of d.c. voltage. It is proposed to plot a.c. polarograms in the complex impedance or admittance plane. By this method it is possible to reduce the uncertainty in the height of the peak caused by the base current. An exactly linear relationship between the quantity measured and concentration can be obtained over a large range of concentrations by means of a simple construction. The measurements can be performed over a wide range of frequencies. Consequently, in some cases, a higher sensitivity can be obtained, because the most favourable frequency can be chosen. The method is not only suitable for analytical purposes, but also for the determination of the fundamental constants of electrode processes (rate constants, diffusion constants and double layer capacities).

Eu(III)-Anthracene-9-carboxylic Acid as a Responsive Luminescent Bioprobe and Its Electroanalytical Interactions with N-Acetyl Amino Acids, Nucleotides, and DNA

Abstract: The interaction of Eu(9-ANCA)3 (9-ANCA = anthracene-9-carboxylic acid) with DNA has been investigated by a fluorescence method. Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm−3 KNO3 for the interaction of Eu(III) and 9-ANCA with adenosine 5′-diphosphate (ADP), adenosine 5′-triphosphate (ATP), N-acetyl glutamic acid (Nc-Glu), N-acetyl leucine (Nc-Leu), and N-acetyl lysine (Nc-Lys) in a 1:1:1 ratio. The formation of various mixed ligand complexes was inferred from the potentiometric titration curves. The formation constants of the binary and ternary complexes have been refined with the SUPERQUAD computer program. The interaction of Eu(III)-(9-ANCA) with Nc-Glu, Nc-Leu, and Nc-Lys has been investigated by electroanalytical methods including cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon (GC) electrode.

Fluorescence and Electrochemical Probing of N-Acetylamino Acids, Nucleotides, and DNA by the Eu(III)−Bathophenanthroline Complex

Abstract: The solid complex Eu(III)−bathophenanthroline was synthesized and characterized by elemental analysis, IR spectra, and thermal analysis. The interaction of the Eu(III)−bathophenanthroline solid complex with calf-thymus DNA has been investigated by fluorescence and electrochemical methods including cyclic voltammetery and differential pulse polarography on a glassy carbon electrode. The formation of binary and ternary complexes of Eu(III) with nucleotides guanosine 5′- monophosphate (5′-GMP), adenosine 5′-monophosphate (5′-AMP), inosine 5′-monophosphate (5′-IMP), cytidine 5′-monophosphate (5′-CMP), or N-acetylamino acids (N-acetylaspartic acid, N-acetylhistidine, and N-acetylhistamine), and bathophenanthroline (BPhen) has been studied potentiometrically at (25.0 ± 0.1) °C and an ionic strength of I = 0.1 mol·dm−3 (KNO3) in 1.8 % v/v ethanol−water mixture solvent. The formation of the normal and protonated binary and ternary complexes is inferred from the corresponding titration curves. The experimental con...

Handheld Electrochemical Sensor

Abstract: A handheld sensor device is provided for measuring an ion concentration in a solution. The solution is in an electrochemical cell that includes a counter electrode, a working electrode, and a reference electrode. The sensor includes a control amplifier configured to provide a current through the counter electrode and the working electrode so as to maintain a predetermined voltage between the working electrode and the reference electrode. The sensor also includes a current amplifier configured to measure the current provided through the counter electrode and the working electrode. In one embodiment, the sensor also includes a direct digital frequency synthesizer (DDFS) including a phase accumulator. The DDFS is configured to selectively generate a waveform specified by an electrochemical technique such as square wave voltammetry, cyclic voltammetry, linear sweep voltammetry, differential-pulse polarography, normal-pulse polarography, or other known electrochemical techniques. An example microelectrode array usable with the handheld sensor is also provided.

Corrosion Behavior of As‐Received and Previously Cast Type III Gold Alloy

Abstract: Purpose: The rationale for using gold alloys is based largely upon their alleged ability to resist corrosion, but little information is available to determine the corrosion behavior of recast alloys. This study characterized the elemental composition of as-received and recast type III gold alloy and examined the in vitro corrosion behavior in two media using a potentiodynamic polarization technique. Materials and Methods: Seventy-eight disk-shaped specimens were prepared from a type III gold alloy under three casting protocols according to the proportion of as-received and recast gold alloy (n = 26). (1) Group as received (100% as-received metal), (2) group 50% to 50% (50% wt. new metal, 50% wt. once recast metal), and (3) group recast (100% once recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy, and their elemental compositions were determined using X-ray energy-dispersive spectroscopy. Further, the potentiodynamic cyclic polarization between −1000 and +1000 mV (SCE) were performed for six specimens from each casting protocol in 0.09% NaCl solution (n = 3) and Fusayama artificial saliva (n = 3) at 37°C. Zero-current potential and corrosion current density were determined. The data were analyzed with 1-way ANOVA and the Ryan–Einot–Gabriel–Welsch multiple-range test t (α= 0.05). Results: Elemental composition was significantly different among the casting groups (p 0.05); however, the difference between the electrolytes was significant (p < 0.001). Fusayama artificial saliva seemed to offer the most corrosive environment. Conclusions: Type III gold alloy in any casting protocol retained passivity under electrochemical conditions similar to the oral environment. Moreover, high-gold type III alloys from reputable manufacturers and recasting protocol tested should produce acceptable corrosion-resistant castings.

COOH+ ion implantation-modified indium tin oxide electrode for the direct electrochemistry of cytochrome c

Abstract: A COOH+ ion implantation-modified indium tin oxide (COOH/ITO) electrode was prepared and the existence of carboxyl group on the electrode was verified by X-ray photoelectron spectroscopy analysis The field emission-scanning electron microscope result showed that the ion implantation formed many active centers on the ITO surface The COOH/ITO electrode was applied for cytochrome c (cyt c) immobilization and the electrochemical behaviors of cyt c were evaluated by cyclic voltammetric techniques The results demonstrated that the immobilized cyt c retained its electrocatalytic activity to the reduction of H2O2 This ion implantation-modified electrode might be used in development of new biosensors and biofuel cells

Electrochemical Reduction Behaviour of Zileuton at a Dropping Mercury Electrode by Polarography

Abstract: Electrochemical behaviour of anticancer drug zileuton was investigated by direct current polarography (DCP) and differential pulse polarography using a dropping mercury electrode (DME) as working electrode and Ag/AgCl reference electrode in universal buffer of pH range from 2.0 to 12.0. The drug was extracted from the dosage forms in dimethyl formamide (DMF). Kinetic parameters such as diffusion co-efficient (D) and heterogeneous forward rate constants (k0f,h) are evaluated and reported. The differential pulse polarographic method has been developed for the determination of this drug in pharmaceutical formulations.

Studies on polarography: I ‐ Reduction of potassium permanganate at the dropping mercury electrode

Abstract: Reduction of the permanganate ion at the dropping mercury electrode is studied in acid, neutral, and alkaline solutions. As supporting electrolytes KCl, BaCl2, and Ba(NO3)2 together with the constituents of buffer solutions of pH 1, 3, 5, 7, 9, and 12 were used. The polarograms consist each of two waves; the first starts at zero potential and corresponds to the process Mn+7 Mn+2, except in the phosphate buffer of pH 12. In this phosphate buffer it proceeds as Mn+7 Mn+3. The second wave corresponding to the process Mn+3 Mn or Mn+2 Mn appears at ∼ pH 5 and higher. In alkaline solutions the first wave is split up into smaller waves, possibly corresponding to Mn+7 M+4, Mn+4 Mn+3, and Mn+3 Mn+2. In acid solutions the Mn+2 Mn wave disappears and is replaced by a hydrogen wave. Some irregularities observed in alkaline solutions are explained.

A study of the polarographic reduction of the acridizinium and phenanthridizinium ions

Abstract: The properties of acridizinium and phenanthridizinium at the dropping mercury electrode have been investigated, and a mechanism for reduction is proposed. Acridizinium is reduced in two one-electron stages at potentials of −0.807 volts and −1.022 volts in acid and neutral solutions, these values being independent of pH. In basic solution, these two reduction steps disappear and two other waves appear at potentials of approximately −1.5 volts and −2.1 volts (vs. saturated calomel electrode). This change in polarographic behavior has been linked with “pseudo-base” formation. Phenanthridizinium is reduced in a single two-electron step with a measured half-wave potential of −1.202 volts. The reduction potential is independent of pH.

Kinetics and mechanism of the cyclic‐hemiacetal ring opening in 2‐keto‐L‐gulonic acid. A polarographic study

Abstract: The occurrence of two consecutive cathodic waves, both with absolute rate control, in the case of the polarographic reduction of 2-keto-L-gulonic acid in a buffer solution of malonic acid (pH between 4.8 and 6.3) is described. The theory of this case is based on the assumption that 2-keto-gulonic acid or its anion predominantly exists in the cyclic-hemiacetal form, which is non-reducible, but which produces the free keto-acid or its anion by a very rapid reaction in the zone around the dropping mercury electrode. The latter substances are reducible, with different half wave potentials. Expressions in the relevant rate constants are derived for both the total current and the current of the first wave. This does not permit the calculation of all the rate constants involved. However, it could be shown that the wave heights are related to pH in the way predicted by the theory. Definite conclusions with respect to the relative magnitude of the rate constants could be drawn. The single wave in the lower pH range of 0.2 to 3.5 was also studied as a function of pH. The reaction mechanism is discussed on the basis of the relationships found and in connection with the expected influence of the ionization of the carboxyl group upon the reactivity of the catalytic species present. The process of ring closure or opening was shown to be second-order, rather than third.

The possibility of simultaneous voltammetric determination of desloratadine and 3-hydroxydesloratadine.

Abstract: The electrochemical behaviour of desloratadine (DLOR) and its derivative 3-hydroxydesloratadine (30H-DLOR) was investigated by direct current (DCP) polarography, cyclic (CV), differential pulse (DPV) and square-wave (SWV) voltammetry in Britton-Robinson (BR) buffer solutions (pH 4-11). Both compounds are reduced at mercury electrode in irreversible two electron reduction of the C=N bond of the pyridine ring in their molecules. The difference in their electrochemical behaviour was investigated, and the most pronounced distinction is observed at pH > 9, as a consequence of the deprotonation of the phenolic moiety in 30H-DLOR molecule, yielding significant change in their reduction potentials (E p DLOR = -1.48 V, and E p 3OH-DLOR = -1.6 V). The observed results correlate with calculated LUMO energy levels and Hammet substituent constants (σ). Based on the difference in the reduction potential for DLOR and 30H-DLOR, conditions for simultaneous determination these two molecules in alkaline medium were established. The best selectivity was achieved using SWV method at pH 10. The linearity of the calibration graphs were achieved in the concentration range from 1.5 x 10 -6 M - 1 × 10 -5 M for DLOR and 7.5 x 10 -6 M - 5 × 10 -5 M for 30H-DLOR with detection limits of 2.29 x 10 -7 M and 2.08 x 10 -6 M, and determination limits of 7.64 x 10 -7 M and 6.94 x 10 -6 M, for DLOR and 30H-DLOR, respectively. The method was checked in human plasma sample. Good response was obtained with LOD and LOQ values of 4.63 x 10 -7 M and 1.54 x 10 -6 M, for DLOR and 2.39 x 10 -6 M and 7.97 x 10 -6 M, 30H-DLOR, respectively.

Elektrochemisches Verhalten von 2,4‐Diamino‐1,3,5‐triazinen und ihren Photolyseprodukten

Abstract: 2,4-Diamino-1,3,5-triazines are widely applied as herbicides. These compounds are very stable which leads to a accumulation in soil and plants. To detect this group of compounds chromatographic methods (gas chromatography, HPLC, TLC) were employed in the past. The present work was done with the aim to determine electrochemically triazines in flowing systems like HPLC and FIA. Therefore the polarographic and voltammetric behaviour of these compounds was investigated. A sensitive detection was possible on a mercury electrode in the cathodic range and on a glassy carbon electrode pretreated by galvanostatic pulses in the anodic range. The sensitivity can be improved by photochemical derivatization of the triazines in 6-position to create phenol-like compounds. The photochemical response of simazine, prometryne, atrazine and ametryne depends on the substitutes in 2- and 4-position and also in 6-position. The degree of the photochemical conversion was measured with an amperometric detector in a FIA equipment.

Polarography with a stationary platinum plate electrode. Part II: The anodic waves of iodides and bromides

Abstract: Previous reports on the behaviour of iodide solutions when subjected to anodic oxidation are limited and not in agreement. This has been clarified by carrying out the oxidation in solutions of different pH values using the stationary platinum microelectrode and a special technique which applied the potential to the electrode intermittently. The anodic oxidation of the iodide ion produces two well defined waves. The first wave corresponds to a one electron process and is due to the formation of elementary iodine at its reversible potential. The wave height is proportional to the concentration of the iodide ion in solution. The second wave showed irregularities and corresponds to the irreversible formation of iodous acid HIO2. This was concluded from the fact that the height of the wave was roughly four times that of the first wave, and from its dependence on the pH value of the solution. At fairly positive potentials and prior to evolution of oxygen, the wave was found to lose a part of its height, and a minimum appeared in the current which was interpreted by the interaction between the diffusing iodide ion and hydroxyl radicals formed as intermediaries in the evolution of oxygen. Investigations on the bromide ion reveal that it is oxidised in a simple one electron wave to yield bromine. This took place with some overvoltage. The wave height was a linear function of the concentration of the bromide ion in solution.

Electrochemical study of spiramycin and its determination in pharmaceutical preparation

Abstract: Spiramycin (SPY) is a medium-spectrum antibiotic with high effectiveness against Gram-positive bacteria. The voltammetric behaviour of spiramycin was studied using differential pulse polarography (DPP) and square wave polarography (SWP). The drug in Britton-Robinson buffer (pH 11.5) is reduced at − 1.45 V, giving rise to a well-defined cathodic peak using hanging mercury drop electrode (HMDE) versus Ag/AgCl electrode. This peak is attributed to the reduction of the aldehyde group. The results proved that the reduction of SPY is an irreversible diffusion-controlled process. The diffusion current-concentration relationship was shown to be rectilinear over the range of 20–80 and 0.8–80 µg ml−1 using DPP and SWP modes, respectively, with detection limit of 8.5 µg ml−1 (1.01 × 10−5 M) and 0.46 µg ml−1 (5.46 × 10−7 M) for DPP and SWP modes, respectively. A mechanism is postulated for the reduction of SPY. The proposed techniques were successfully applied to the determination of the studied compound either in pure form or in its formulation. Copyright © 2010 John Wiley & Sons, Ltd.

Polarography of aldoximes in buffer solutions

Abstract: The polarographic reduction of both isomers of benzaldoxime and furfurald-oxime and the syn-oximes of vanillin, O-vanillin, p-dimethylaminobenzaldehyde and salicylaldehyde have been studied in various buffers. It is observed that wave heights decrease upto pH 8.0, and the half-wave potential shifts to more negative values. The reduction of the oxime possibly proceeds via the conjugate acid of the oxime(R-CH: N-OH) H+ at the electrode interface. The waves dis-appear at pH>8, owing probably to the decreasing concentrations of H+ ions with increasing pH values. The mechanism of the reduction has been discussed.