Showing papers on "Polarography published in 1989"

Polarographic-amperometric three-electrode sensor

Abstract: For a potentiostatically operable, polarographic-amperometric sensor, in particular for biomedical use, wherein a working electrode (5) and a reference electrode (4) are covered by an electrolyte layer (9) which is separated from the medium to be measured by a semipermeable membrane (8), the invention proposes to provide the counter electrode (6) in the form of an external electrode which - for example - can be an outer metal coating surrounding the sensor chip (2) in a three electrode system fabricated as micro-sensor with the integrated technique, and which can be made - for example - of a stainless steel material or of a conductive plastics material.

Simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations by differential-pulse voltammetry using a glassy carbon electrode

Abstract: A simple, rapid and accurate method for the simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations has been developed. Peak currents were measured with a glassy carbon electrode at +0.350, +0.618 and +1.425 V versus a saturated calomel electrode for ascorbic acid, paracetamol and caffeine, respectively. Perchloric acid (0.1 M) - methanol (1 + 1) was used both as a solvent and supporting electrolyte. The optimum modulation amplitude, pulse repeat time and scan rate of the polarographic analyser were found to be 50 mV, 0.5 s and 5 mV s-1, respectively and the linear calibration ranges for ascorbic acid, caffeine and paracetamol were 0-35, 0-50, and 0-55 micrograms ml-1, respectively. The relative standard deviations for 9.30 micrograms ml-1 of ascorbic acid, 8.50 micrograms ml-1 of caffeine and 7.30 micrograms ml-1 of paracetamol were 1.3, 2.5 and 0.7%, respectively. Results are reported for several commercially available drugs.

Electrochemistry, past and present

Abstract: Electrochemistry in Retrospect: An Overview Wollaston's Microtechniques for the Electrolysis of Water and Electrochemical Incandescence: A Pioneer in Miniaturization Michael Faraday's First Law of Electrochemistry: How Context Develops New Knowledge The Universal Agent of Power: James Prescott Joule, Electricity, and the Equivalent of Heat The Contribution of Electrochemistry to the Development of Chemical Kinetics A Reappraisal of Arrenhius' Theory of Partial Dissociation of Electrolytes Historical Highlights in Transference Number Research Genesis of the Nernst Equation The Choice of the Hydrogen Electrode as the Base for the Electromotive Series Pursuit of the Elusive Single Ion Activity Historical Development of the Understanding of Charge-Transfer Processes in Electrochemistry William Lash Miller History of Organic Electrosynthesis Anodic Electroorganic Chemistry and Natural Products Oxygen Electrode: History, Design, and Applications Bioelectrochemistry-Before and After Development of Electrochemical Instrumentation Development of the pH Meter Development of the Glass Electrode pH Glass Electrode and Its Mechanism Ion-Sensitive Electrodes: From Glasses to Crystals and Crowns Modification of Solid Electrodes in Electroanalytical Chemistry, 1978-1988 With the Drop of Mercury to the Nobel Prize Past and Future of the Dropping Electrode Development of Pulse Polarography and Voltammetry Fortuitous Experiments: Discoveries of Underpotential and of Quantitive Anodic Stripping Voltammetry Coulometric Titrimetry History of Electroanalytical Chemistry in Molten Salts Electrodeless Conductivity Spectroelectrochemistry Using Transparent Electrodes: An Anecdotal History of the Early Years Borrowing From Industry: Edgar Fahs Smith's Rotating Anode and Double Cup Mercury Cathode Henry J.S. Sand (1873-1944), A Well-Remembered Tutor Industrial Electrochemistry Industrial Diaphragrams and Membranes Gibbs, LeSeur, and Willson: Pioneers of Industrial Electrochemistry History of Electrochemistry in Mexico The Search for Portable Electricity: History of the High Energy Density Batteries Evolution of Electrochemical Reactor Systems for Metal Recovery and Pollution Control Electrochemical Machining: Development and Application

Polarographic methods for ultratrace cobalt determination based on adsorption-catalytic effects in cobalt (II)-dioxime-nitrite systems

Abstract: L'augmentation d'un facteur 3 ou 4 des courants continus (DC) et differentiels (DPP) dans les systemes Cobalt (II)-dioxime-NaNO 2 permet de doser le cobalt avec precision, selectivite et une tres grande sensibilite

Diffusion Coefficients for Copper (II) in Aqueous Cupric Sulfate‐Sulfuric Acid Solutions

Abstract: Diffusion coefficients for Cu(II), , were determined at 25°C in over the concentration range . The reported values of represent average values for the physical properties over the diffusion layer, and for the diffusing Cu(II) species, which consist of Cu++ ions and ion pairs. Thus, represents an effective value that is suitable for substitution into the various mass‐transfer equations derived by assuming constant properties. At low concentrations (0.4–6 mM) static mercury drop electrode (SMDE) polarography using a modified version of the Cottrell equation with a spherical correction term was used to determine . At higher concentrations was determined chronopotentiometrically using the Sand equation. The values of in 0.51M aqueous at 25°C were as follows,where is the stoichiometric concentration of (mol liter−1). At the higher concentrations estimates were made of the effects of migration on the measured values of . Transport number calculations, although nonrigorous, indicate that these effects are relatively minor.

Pentaammineruthenium(II), pentaammineosmium(II), and (N-(hydroxyethyl)ethylenediaminetriacetato)ruthenate(II) complexes of styrenes

Abstract: [M(NH 3 ) 5 (styrene) 2+ ] and [M(NH 3 ) 5 (olefin) 2+ ] (M=Ru II , Os II ) and the related Ru(hedta)(styrene) − and Ru(hedta)(olefin) − complexes have been prepared and characterized by 1 H and 13 C NMR spectroscopy and by cyclic voltammetry and differential-pulse polarography

A reliable and ultrasensitive voltammetric method for the determination of molybdenum

Abstract: The determination of molybdenum(VI) in aquatic media by polarography, voltammetry and adsorptive stripping voltammetry using the formation of a Mo-chlorate-mandalic acid complex at +100 mV (SCE) is described. The 3 sblank-detection limit is 0.1 nmol/l with differential pulse adsorptive stripping voltammetry (DPAdsSV, catalytic current). The calibration graphs are linear up to 200 nmol/l for the latter, 400 nmol/l for staircase voltammetry without accumulation time and 1 mg/l for staircase polarography. The accuracy of the DPAdsSV method was checked by analysis of a standard reference water material. The utility of differential pulse voltammetry was tested in different aquatic media, e.g., tap water, ground water, surface water.

Comparison of physicochemical speciation procedures with metal toxicity to chlorella pyrenoidosa copper complexation capacity

Abstract: A comparison was made of methods for measuring the copper complexation capacity of natural and synthetic organic ligands in freshwaters. Complexation capacity values close to theoretical were obtained for nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid, when the following separation or analysis methods were used to detect ionic copper: algal assay (Chlorella pyrenoidosa), an aluminum hydroxide resin, ion-selective electrode (ISE), and anodic stripping voltammetry (ASV) at the mercury film electrode (MFE) and Nafion-coated MFEs. No complexation capacity could be measured for Cu-NTA when the hanging mercury drop electrode (HMDE) was used. Results from the ISE and a resin with adsorbed aluminum hydroxide agreed closely with algal assay for the copper complexation capacity of solutions of fulvic acid and Fe-humic colloids. Analysis by ASV at the HMDE, MFE, and Nafion-coated MFE gave values-of more than an order of magnitude lower than the other techniques because these methods failed to detect the end point for partially labile complexes with a large complexation capacity. On the other hand, the use of differential pulse polarography (DPP) detected these labile copper complexes and yielded results comparable with those for algal assay. Comparable copper complexation capacities for pristine river water samples were obtained by algal assay (2.5–4.1 × 10−6 M Cu) and DPP (2.0–3.7 × 10−6 M Cu), with lower values for the aluminum hydroxide resin (0.8–1.1 × 10−6 M Cu). Because the ASV techniques gave much lower results (0.1–0.4 × 10−6 M Cu), they are clearly unsuitable for the determination of the complexation capacity of freshwaters.

Electrochemical speciation analysis of metals at membrane-coated electrodes

Abstract: Speciation of model Cu complexes on the basis of size and charge was achieved by anodic stripping voltammetry (ASV) at mercury film electrodes (MFE) coated with Nafion or cellulose acetate Nafion (CANMFE). The Nafion-coated MFE effectively excludes negatively charged Cu complexes, and evidence for the containment of the diffusion layer beneath the Nafion coating is provided. The CANMFE excludes complexes with molecular weights greater than 200, including the Cu-fulvic acid complex, which is of particular interest for speciation in natural waters. Complexation titrations of fulvic acid with Cu show the unsuitability of differential pulse ASV for providing a realistic estimate of the end point (complexation capacity). Differential pulse polarography, which provides results more comparable with bioassays, can be used for the determination of complexation capacity. Results for the speciation analysis of coastal seawater and polluted fresh water are presented. The CANMFE is insufficiently sensitive for seawater analysis, but in polluted fresh water its use indicates that organic and inorganic complexes with molecular weights greater than 200 dominate the speciation for Cd (72%), Pb (96%), and Cu (> 99.8%).

Electroanalytical chemistry of sulfur compounds for the new coal conversion technologies

Abstract: Polarographic methods are described “tailor-made” for the speciation and determination of sulfur contaminants in synfuels and coal gasification/liquefaction process streams. In samples containing the anions, S2− x, sulfidic sulfur was quantitated by anodic depolarization of the dropping mercury electrode, while polysulfidic sulfur was determined with the aid of an electroreduction process implicating 2(x-1) electrons. Polythionates were electroreduced to thiosulfate, sulfite, sulfide and/or mixtures thereof, under judiciously controlled experimental conditions. Thiosulfate and sulfite were quantitated by differential pulse polarography at dropping mercury anodes via reactions involving formation of thiosulfato- and sulfitomercurates.

Study of the conditions for the determination of metamitron by differential pulse polarography

Abstract: The electrochemical behaviour of the herbicide 4-amino-3-methyl-6-phenyl-1,2,4 triazine-5(4H)-on (Metamitron) is studied in aqueous medium using voltammetric techniques, with the ionic strength adjusted to 01 mol/l in sodium perchlorate and using a Britton-Robinson buffer Two reduction waves on the mercury drop electrode appear, at −049 V the first and the second folded at −095 V and −105 V The system is identified as irreversible and fundamentally controlled by diffusion Using differential pulse polarography the detection limit reached was 002 mg · l−1 for the first wave with an error of less than 2% Thus a method is proposed for the determination of Metamitron in soil, with a detection limit of up to 002 μg/g

Polarographic measurements of micellar diffusion coefficients: new results and implications of surfactant adsorption at the mercury-solution interface

Abstract: L'adsorption du dodecylsulfate de sodium et du bromure de tetradecyltrimethylammonium sur une electrode a goutte de mercure, est etudiee par polarographie et voltammetrie cyclique

Preliminary studies for the differential-pulse polarographic determination of a new class of herbicides: sulphonylureas

Abstract: The electrochemical behaviour of four sulphonylureas (chlorsulfuron, metsulfuron methyl, DPX-M6316 and chlorimuron ethyl) used as active compounds in commercial herbicides was studied. Methanol-water solutions of the compounds were analysed by differential-pulse polarography. The dependence of peak potentials and peak height on the pH is reported. Detection limits of the order of 10–8M were obtained, working at a pH of between 2 and 3. Attempts to use a mercury-coated glassy carbon electrode, in view of the possible applications to high-performance liquid chromatography with electrochemical detection, gave unsatisfactory results due to the interference from hydrogen ion reduction.

Process for dyeing keratinous fibres with a hydroxyindole in combination with a quinone derivative; and novel 1,4-benzoquinones

Abstract: Process for dyeing keratinous fibres, comprising the step of applying to these fibres at least one composition A containing, in a medium appropriate for dyeing, at least one mono- or di-hydroxyindole the application of the composition A being preceded or followed by the application of a composition B containing, in a medium appropriate for dyeing, at least one quinone derivative chosen from ortho- or para-benzoquinones, monoimines or diimines of ortho- or para-benzoquinones, 1,2- or 1,4-naphthoquinones, sulphonimides of ortho- or para-benzoquinones, α, ω-alkylene-bis-1,4-benzoquinones, or 1,2- or 1,4-naphthoquinone-monoimines or -diimines; the mono- or di-hydroxyindoles and the quinone derivatives being chosen such that the oxidation-reduction potential difference ΔE between the oxidation-reduction potential E i of the mono- or di-hydroxyindoles, determined at pH 7 in a phosphate medium on a vitreous carbon electrode by voltametry, and the oxidation-reduction potential E q of the quinone derivative determined at pH 7 in a phosphate medium by polarography on a mercury electrode and relative to a saturated calomel electrode is such that ΔE=E.sub.i -E.sub.q ≦320 mV.

Cathodic stripping voltammetry of pyridine-2-thiol and some related compounds

Abstract: The cathodic stripping voltammetric behaviour of pyridine-2-thiol and some related heterocyclic thiols has been studied at a static mercury drop electrode. The influence of substituents on the adsorption of these compounds on the mercury electrode, and the nature of the different thiolates responsible for the subsequent stripping signals have been investigated. Differential-pulse cathodic stripping voltammetry was used to establish linear calibration ranges for the compounds studied. The use of a pre-concentration time of 240 s in open circuit allowed a detection limit of 8.0 × 10–9M to be attained for pyridine-2-thiol.

Electrochemical characteristics of nitro-heterocyclic compounds of biological interest. II. Nitrosochloramphenicol.

Abstract: The electrochemical characteristics of nitrosochloramphenicol have been studied in aqueous buffer systems (pH 7.1) using direct current (d.c.) and differential pulse polarography, cyclic voltammetry and coulometric techniques. Up to 4 charge-transfer steps can be identified. The first reduction step is reversible both chemically and electrochemically, the charge-transfer product showing no tendency to undergo further reaction on the electrochemical time-scale. In contrast, the second reduction step is irreversible, with the product undergoing a fast following reaction to yield a redox-active species which was detected by cyclic voltammetry. From the data and by comparison with related systems, two reduction mechanisms are possible and are discussed.

1.5th-Differential polarographic determination of trace amounts of selenium(IV) and selenium(VI) in natural waters at a dropping mercury electrode

Abstract: This paper describes a polarographic method for the determination of trace amounts of SeIV and SeVI in natural waters using a dropping mercury electrode. In an HClO4-Na2SO3-NH3-NH4Cl-NH2OH.HCl-KlO3 system (pH 10), the selenium complex SeSO32– gave a peak potential at –0.57 V versus Ag. The peak current was directly proportional to Se in the concentration range 0.01–1 µg l–1. The limit of detection was 10 ng l–1. The proposed method is rapid, simple, sensitive and accurate. The recovery of Se from standard additions to samples of natural waters was between 93 and 105%.

Electroanalytical study of indomethacin

Abstract: The Polarographic behavior of indomethacin has been studied with the aim of developing a procedure for its determination in pharmaceutical tablets. In the study of the electrode process, linear-sweep voltammetry and controlled potential coulometry were also considered. The electrode reactions are shown to be strongly affected by variations in pH. Adsorption phenomena appear at certain pH values. Detection limits and sensitivity in the determination of indomethacin were obtained by using tast polarography (TP), differential pulse polarography (DPP), and pseudoderivative pulse polarography (NPP).