Showing papers on "Polarography published in 1992"
Patent•
03 Nov 1992
TL;DR: Disclosed as mentioned in this paper is a method of assaying a high concentration of a substance in a liquid sample with a polarographic cell, which includes an electrode assembly that includes a reference electrode and a hydrogen peroxide sensor electrode having a laminated membrane covering the liquid sample contacting face of the sensor.
Abstract: Disclosed is a method of assaying a high concentration of a substance in a liquid sample with a polarographic cell. The cell contains an electrode assembly that includes a reference electrode and a hydrogen peroxide sensor electrode having a laminated membrane covering the liquid sample contacting face of the sensor electrode. The laminated membrane includes an outer membrane permeable to the substance and oxygen, an inner membrane permeable to hydrogen peroxide and located adjacent the face of the sensor electrode, and an enzyme layer between the inner and outer membrane; the enzyme in the enzyme layer can oxidize the substance to generate hydrogen peroxide. The method includes contacting the outer membrane with the liquid sample; permitting the substance and oxygen in the liquid sample to pass through the outer membrane to contact the enzyme layer so that where the substance is oxidized to generate hydrogen peroxide; permitting the generated hydrogen peroxide to pass through the inner membrane to contact the sensor electrode; and ensuring that the supply of oxygen in the enzyme layer relative to the supply of glucose is sufficient to produce an equilibrium concentration of hydrogen peroxide, which generates a steady state response at the sensor electrode proportional to the concentration of the substance in the liquid sample.
139 citations
TL;DR: A kinetic study of the oxidation of 3,4-dihydroxyphenylalanine by tyrosinase using the oxygen electrode is shown to confirm the validity of the calibration method.
74 citations
TL;DR: In this article, the authors used sulfite to facilitate the removal of oxygen in the samples before they are analyzed, which reduced the time needed for the analysis of a sample for iodate and iodide to about 15 min and 5 min, respectively.
47 citations
TL;DR: In this article, a theoretical model for describing the reduction of a metal ion in the presence of a macromolecular ligand, including both the ligand adsorption and the induced adorption of the metal ion, was developed.
45 citations
TL;DR: In this paper, a ligand competition-anodic stripping voltammetric (ASV) technique was proposed for investigating copper complexation in sea water and the change in the stripping peak current was followed, which indicated that the naturally occurring non-labile copper fraction is bound to ligands having concentrations less than 5 × 10 −9 M and a conditional stability constant (log K ′ CuL ) of 13.1 ± 0.3
44 citations
TL;DR: In this article, a detailed mechanism of the ion transfer is proposed by considering branch diffusions of phen species from the interface to either bulk phase by which the Hphen + transfer producing the anodic wave is depressed.
28 citations
TL;DR: The yields and fate of the hydroxylamino derivative obtained in controlled potential electrolysis with a hanging mercury drop electrode (HMDE) differ from those in dc polarography, indicating the presence of different competing reactions.
27 citations
TL;DR: In this article, the authors used voltammetric or polarographic techniques to study the redox behavior of BESOD, a metallo-enzyme containing one Cu"-Zn" pair in each of the two subunits of the molecule.
27 citations
TL;DR: In this paper, a semi-empirical method is proposed for evaluating a parameter related to the hydrodynamic conditions during the pre-electrolysis step in anodic stripping voltammetry (ASV) measurements over metal-poly electrolyte systems.
23 citations
TL;DR: In this article, a new high-sensitivity procedure for the determination of molybdenum by adsorptive stripping voltammetry was developed, which is based on the reaction of MULE with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) to produce a complex which is absorbed onto mercury at −0.20 V (vs.
Abstract: Different polarographic and voltammetric techniques for the determination of molybdenum at the trace level have been investigated. As a result, a new high-sensitivity procedure for the determination of molybdenum by adsorptive stripping voltammetry was developed. The method is based on the reaction of molybdenum(VI) with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) to produce a complex which is absorbed onto mercury at −0.20 V (vs. Ag/AgCl, 3 mol/l KCl) from pH 2.7 solution. The cathodic stripping peak at −0.62 V can be used to determine molybdenum with a detection limit of 0.02 ng/ml after 5 min deposition time. The relative standard deviation for the determination of 0.1 ng/ml Mo after 5 min stirred collection was 6.6%. Interference from various inorganic ions and organic substances are reported. The method was applied to the determination of molybdenum traces in waters; interfering organic substances in polluted waters were destroyed by oxidative digestion in a microwave oven.
TL;DR: In this article, the authors derived theoretical expressions for pseudopolarography at a hemispherical mercury ultramicroelectrode and compared with experimental data at varying deposition times and low and high electrolyte concentrations and with previous theory for other electrodes.
Abstract: Trace heavy metals play a central role in many biogeochemical processes. Their toxicity and bioavailability in aqueous systems has been shown to be directly related to the chemical forms in which they exist, i.e., their chemical speciation. Especially promising in speciation studies has been an electrochemical technique referred to as pseudopolarography or stripping polarography. The theoretical expressions for pseudopolarography at a hemispherical mercury ultramicroelectrode are derived and compared with experimental data at varying deposition times and low and high electrolyte concentrations and with previous theory for other electrodes. It is shown that, even though several of the physical conditions are different, the behavior of both the pseudopolarographic half-wave potential and the limiting peak stripping current is similar to that for the HMDE. The fit between the theory and the experimental data was excellent. A correction term for the increase in the limiting peak stripping current with increasing negative deposition potentials seen in this and previous works is discussed and attributed to adsorption of trace organics on the mercury electrode surface. 21 refs., 4 figs., 1 tab.
TL;DR: The technique of differential pulse polarography is shown here for the first time to be applicable to monitoring directly the uptake of metal ions from solution by live bacteria in the chamber of the polarograph.
Abstract: The technique of differential pulse polarography is shown here for the first time to be applicable to monitoring directly the uptake of metal ions from solution by live bacteria in the chamber of the polarograph. The potential at which the polarographic current peak is observed is characteristic of the metal, whereas peak height is proportional to metal concentration. Adding solutions of Cd(II) or Zn(II) to a suspension of Pseudomonas cepacia in 50 mM Hepes buffer (pH 7.4) in the chamber gave polarographic peaks of lower amplitude than those observed when these metal solutions were added to buffer alone, due to metal binding or uptake by cells. Langmuir plots gave binding capacities of 0.13 and 0.20 mmol metal (Dd or Zn, respectively) per g (dry weight) biomass. Ni(II) uptake was biphasic. Metal uptake increased with pH. The value of polarography for rapid assessment of metal removal by cells and the ability to measure uptake from multi-metal solutions is demonstrated.
TL;DR: In this paper, the most reliable values of acid dissociation constants were found using spectrophotometry, potentiometry, changes in wave-heights and shifts in polarographic half-wave potentials.
TL;DR: In this paper, a sensitive adsorptive wave of antiepilepsirine was obtained in 2 M H 2 SO 4 by using linear-sweep polarography and the peak potential was −098 V vs SCE.
TL;DR: Anodic stripping voltammetry at the mercury film electrode as well as adsorptive stripping voltage at the hanging mercury drop electrode are applied in order to determine trace amounts of heavy and transition metals in alkaline and alkaline-earth metal salts.
Abstract: Anodic (cathodic) stripping voltammetry at the mercury film electrode as well as adsorptive stripping voltammetry at the hanging mercury drop electrode are applied in order to determine trace amounts of heavy and transition metals in alkaline and alkaline-earth metal salts. The procedures used are slightly modified versions of procedures known in sea water analysis. Examples of application include high purity potassium and sodium salts for optical purposes, etching solutions for silicon wafer production and sodium salts for the dialysis technique.
TL;DR: In this paper, the electrochemical oxidation reactions of α-, β- and γ-aminobutyric acid at a Pt electrode were investigated in aqueous solutions at pH 1 and pH 13 using steady-state current-potential measurements, cyclic voltammetry and open-circuit potential decay.
TL;DR: Polarographic and voltammetric results indicate that, from bromide solutions of cadmium(II), CdBr -3 can be extracted by the mercury surface, irrespective of the ionic strength.
TL;DR: In this article, the electroanalytical behavior of 2-aminocyclopentene-1-dithiocarboxylic acid and some of its derivatives has been investigated in aqueous or anorthogonal solutions at the mercury electrode, and it was shown that the current flowing in the main anodic wave is determined by the nature of the film of the particular insoluble mercury(II) products deposited on the electrode and varies with the substituent group on nitrogen.
Abstract: The electroanalytical behaviour of 2-aminocyclopentene-1-dithiocarboxylic acid and some of its derivatives has been investigated in aqueous or aqueous-ethanolic solutions at the mercury electrode. All the compounds studied give only one-electron anodic wave. The various adsorption phenomena are probably caused by varying orientation of the mercury compounds on the electrode surface. Although the overall electrode reaction mechanism is the same for all the derivatives, the current flowing in the main anodic wave is determined by the nature of the film of the particular insoluble mercury(II) products deposited on the electrode and varies with the substituent group on nitrogen.
TL;DR: In this paper, a single-sweep polarographic method was developed for the determination of estradiol or estriol in the urine of pregnant women, using a controlled nitration using 0.4 M sodium nitrite solution at 100°C in a water bath for 30 min.
TL;DR: In this paper, a polarographic study of organochlorine pesticides dieldrin, heptachlor, endosulfan, and sulfate in an emulsified medium formed with ethyl acetate and a mixture of two surfactants, Hyamine 2389 and Triton X-405, is reported.
Abstract: A polarographic study of the organochlorine pesticides dieldrin, heptachlor, endosulfan, and endosulfan sulfate in an emulsified medium formed with ethyl acetate and a mixture of two surfactants, Hyamine 2389 and Triton X-405, as emulsifying agent, is reported. Well-defined peaks were obtained by differential pulse polarography (dpp). Neither preceding acid-base equilibria nor mechanism changes are involved in the reduction processes. The characteristics of the electrode processes were examined at pH 8.0 for heptachlor and at pH 6.0 for the other pesticides. The diffusion coefficients were calculated as well as the kinetic parameters αna and k. The mechanisms of the polarographic reduction processes are proposed and the different behavior of heptachlor is discussed. Linear calibration plots were obtained using dpp over different concentration ranges; the analytical characteristics of the methods were determined. The effect of the presence of the other pesticides on the ip and Ep values of each one of the four pesticides was studied. Simultaneous determination of heptachlor and endosulfan sulfate was possible.
TL;DR: In this article, a simple, low cost, and versatile automatic mercury electrode, working as dropping (DME), hanging (HMDE), or static drop electrode (SMDE), is described.
Abstract: The construction and evaluation of a simple, low cost, and versatile automatic mercury electrode, working as dropping (DME), hanging (HMDE), or static drop electrode (SMDE), is described. Fast action of the needle valve is obtained with two solenoids, one for opening the valve and the other for closing it. The electrode can be controlled from a microcomputer or with a digital circuit. The performance of this electrode compares favorably with that of commercial ones in terms of area reproducibility (std. dev. < 0.05%), response time of the valve, current profile during potentiostatic extrusion of the drop, and flexibility of use.
TL;DR: In this paper, a 1, 4-dihydropyridine derivative, CRE-319, produces a cathodic polarographic peak due to the reduction of its nitro group according to the following well-known general pathway for the nitro groups: the electrode mechanism is strongly dependent on the pH of the solution and follows a similar behaviour to that previously reported for nitrobenzene.
Abstract: CRE-319, a novel 1, 4-dihydropyridine derivative, produces a cathodic polarographic peak due to the reduction of its nitro group according to the following well-known general pathway for the nitro group: The electrode mechanism is strongly dependent on the pH of the solution and follows a similar behaviour to that previously reported for nitrobenzene. The peak current shows a linear dependence with CRE-319 concentrations. This behaviour is used for analytical purposes in determining CRE-319 content in solution. In order to obtain comparative results, we have also developed a spectrophotomebic and an HPLC method for quantifying CRE-3 19.
TL;DR: In this paper, the polarographic behavior of spironolactone in buffers containing 40% methanol as a solubilizer was studied, and over the pH range 3-12 a cathodic wave was produced.
Abstract: The polarographic behaviour of spironolactone in Britton-Robinson buffers containing 40% methanol as a solubilizer was studied. Over the pH range 3-12 a cathodic wave was produced. The wave was characterized as irreversible, diffusion-controlled and partially affected by adsorption phenomena. The number of electrons involved in the reduction was found by coulometric measurements at a controlled potential. A method was developed for the determination of spironolactone in tablets and the results obtained were in agreement with those obtained by the B.P. 1988 method. The mechanism of the electrode reaction is discussed.
TL;DR: In this paper, the electrochemical reduction of solvatochromic and thermochromically mixed chelates of the type Ni(β-dik)(diam)+ was investigated at different temperatures in different solvents (DCE, An, Ac, DMF and DMSO).
Abstract: The electrochemical reduction of solvatochromic and thermochromic mixed chelates of the type Ni(β-dik)(diam)+, where β-dik represents a series of substituted β-diketonates and diam represents substituted diamines has been investigated at different temperatures in different solvents (DCE, An, Ac, DMF and DMSO). The observed polarographic two-electron reduction of Ni(II) on the Hg-electrode is irreversible in all solvents studied, Polarographic prewaves are observed which are interpreted in terms of kinetically and diffusion controlled electrode processes. E1,2 is shifted to more negative potentials by increasing donor number (DN), decreasing temperature and the presence of electron-donating substituents. The temperature dependence of the Ni reduction potentials yielded two groups of solvents. This is interpreted as being due to different electrode kinetics involving diffusion and kinetically controlled rate-determining steps. The two groups further refer to a different stereochemistry of the solva...
TL;DR: In this paper, the authors applied Matsuda's pulse polarization theory to the study of electrode processes under non-Nernstian conditions and coupled to very fast chemical steps by differential pulse polarography (reaction layer approximation).
TL;DR: In this article, a previously described expert system for the voltammetric determination of Cu, Zn, Cd, Pb, In, Ni, Co and Tl is enhanced by means of the addition of methods for Hg, V and Se (optionally also Te).
TL;DR: In this article, the incorporation of mercury into a conducting poly(3-methylthiophene) [P3MT] film results in an effective electrode for the analysis of lead in aqueous media.
Abstract: The incorporation of mercury into a conducting poly(3-methylthiophene) [P3MT] film results in an effective electrode for the analysis of lead in aqueous media. Mercury “films” were deposited electrochemically following the electropolymerization step. The resulting surfaces were characterized by cyclic voltammetry, scanning electron microscopy, and X-ray analysis techniques. The analytical performance of the electrode was examined for the determination of lead (II) ions in aqueous media. The differential pulse peak current, at −0.59 V, is ca 10-fold larger than the corresponding peak at the plain platinum electrode. Linear calibration curves are obtained for lead concentrations ranging from 0.1 to 0.8 ppm. The detection limit is 0.05 ppm. The relative standard deviation (at the 0.3 ppm level) is 2%. Interference effects were also studied. The new polymer modified electrode showed great promise toward resistance to surfactant fouling.