In Process Citation

The formation of a metal-complex of copper(II) with vancomycin, an antibiotic active towards Gram-positive bacteria, has been proved by spectrophotometric, polarographic and potentiometric methods. In particular, the half-wave reduction potentials and voltamperograms indicate the stoichiometry of the addition compound and the equilibrium constant. This complex has been used for determination of vancomycin by a continuous flow method with copper(II) and amperometric detection in a polarographic cell of thin-layer type.     

Reduction of disulfides in the milligram range with hypophosphorous acid and organic phosphites

A number of organic disulfides in the milligram range were reduced to the corresponding thiol by reaction with hypophosphorous acid at elevated temperatures in aqueous solvents. Reduction is extensive after several hours. Aromatic disulfides were reduced by triethyl phosphite and triphenyl phosphite at room temperature. Products were deterimned by polarographic and amperometric titration techniques.     

Determination of benzoyl bisulphide by desulphurisation and solvolysis

Benzoyl disulphide is rapidly and quantitatively desulphurised to the monosulphide by reaction with triphenylphosphine in aqueous methanol at 25 degrees . The monosulphide reacts with methanol to form thiobenzoic acid and methyl benzoate. Benzoyl disulphide also reacts with methanol in solutions containing ammonium acetate or sodium acetate yielding thiobenzoic acid, methyl benzoate and elemental sulphur. Benzoyl disulphide and sulphur were detected by their polarographic reduction waves. Thiobenzoic acid was detected by its polarographic oxidation wave and yields were determined by amperometric silver nitrate titrations.     

Studies of the mechanically generated noise in static mercury drop electrodes

The moving parts needed for the operation of a mechanized static mercury drop electrode were found to generate additional noise which affects measurement of the polarographic current. A Fourier transformation method was employed in analysis of experimental data giving information about the frequency, amplitude and decay characteristics of the noise. The dominant noise frequency was found to depend on the drop size. Drop formation at a potential where no electrolysis takes place combined with a waiting period long enough for the mechanical vibrations to decay improved the precision of the polarographic current measurement.     

An Amperometric Biosensor Based on the Coimmobilization of Horseradish Peroxidase and Methylene Blue on a Carbon Nanotubes Modified Electrode

A novel hydrogen peroxide biosensor has been constructed based on the characteristics of the carbon nanotube. The multiwall carbon nanotube (MWNT) was used as a coimmobilization matrix to incorporate horseradish peroxidase (HRP) and electron transfer mediator methylene blue (MB) onto a glassy carbon electrode surface. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of methylene blue as an electron carrier between the immobilized peroxidase and the surface of glassy carbon electrode. The amperometric response of this resulting biosensor to H₂O₂ shows a linear relation in the range from 4 μM to 2 mM. The detection limit was 1 μM when the signal to noise ratio is 3. The presence of dopamine and ascorbic acid hardly affects the sensitive determination of H₂O₂. This biosensor also possesses very good stability and reproducibility.     

Determination of Organic Peroxides by High Performance Liquid Chroma-Tography with Electrochemical Detection

Abstract

The application of electrochemical detection to the high performance liquid chromatographic determination of organic peroxides has been studied. The use of a buffered mobile phase was found to be critical to the successful analysis of samples containing hydroperoxides. Using amperometric detection, mixtures of peroxide containing compounds were readily determined. The sensitivity of the amperometric detector was in the one nanogram range for both benzoyl peroxide and cumene hydroperoxide. Polar-ographic detection was found to be a highly reproducible method for the analysis of samples containing peroxides as components of mixtures in the range of 5-2000 ng. The peroxide containing compounds determined in this manner were t-butyl hydroperoxide, cumene hydroperoxide, and 13-hydroperoxy-9(Z)-11(E)-octadecadien-oic acid. The polarographic detection system was used to obtain observed half-wave potentials for the peroxides under different chromatographic conditions. These observations correlated closely with literature results on the polarography of these compounds.     

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.     

Polarographisches Verhalten von 1,2,3-Cyclohexantrion-trioxim in sauren Lösungen

The deoximation kinetics of 1,2,3-cyclohexanetrione trioxime was studied polarographically in 0.5 and 1.0M-HClO₄ solutions. From the three vicinal oxime groups, that in position 2 is hydrolysed by protonisation, followed by water uptake and hydroxylamine loss. The probable mechanism of the deoximation was proved by the study of the polarographic behaviour of 1,2,3-cyclohexanetrione-1,3-dioxime and by means of amperometric determination of the unchanged trioxime with Ni(II)-salt.     

Polarographic behaviour of alizarincomplexan,anodic wave and its analytical applications

Summary Polarographic Behaviour of Alizarincomplexan, Anodic Wave and Its Analytical Applications The polarographic DPP and DC techniques have been utilized to carry out the study of the anodic wave of alizarincomplexan (AC) in aqueous medium. At pH>5.7 the anodic current is produced by the complex formed between the AC and Hg(II) proceeding from the dropping electrode. At pH=7.3 theE _1/2 of this anodic wave is 0.000 V vs. Ag/AgCl. The main characteristics of the wave have been studied, and the corresponding electrode mechanism process is proposed. Since Hg(II) forms a complex with AC, a method for the amperometric determination of Hg(II) is proposed. We have also studied the analytical possibilities for doubly charged ions which form complexes with the reagent, and an amperometric method for Co(II) determination is also proposed.     

Modeling the measurements of cellular fluxes in microbioreactor devices using thin enzyme electrodes

An analytic approach to the modeling of stop-flow amperometric measurements of cellular metabolism with thin glucose oxidase and lactate oxidase electrodes would provide a mechanistic understanding of the various factors that affect the measured signals. We divide the problem into two parts: (1) analytic formulas that provide the boundary conditions for the substrate and the hydrogen peroxide at the outer surface of the enzyme electrode layers and the electrode current expressed through these boundary conditions, and (2) a simple diffusion problem in the liquid compartment with the provided boundary conditions, which can be solved analytically or numerically, depending on the geometry of the compartment. The current in an amperometric stop-flow measurement of cellular glucose or lactate consumption/excretion is obtained analytically for two geometries, corresponding to devices developed at the Vanderbilt Institute for Integrative Biosystems Research and Education: a multianalyte nanophysiometer with effective one-dimensional diffusion and a multianalyte microphysiometer, for which plentiful data for metabolic changes in cells are available. The data are calibrated and fitted with the obtained time dependences to extract several cellular fluxes. We conclude that the analytical approach is applicable to a wide variety of measurement geometries and flow protocols.     

Ion amperometry at the interface between two immiscible electrolyte solutions in view of realizing the amperometric ion-selective electrode

This article reviews the development in ion amperometry at the interface between two immiscible electrolyte solutions (ITIES) in view of realizing the amperometric ion-selective electrode (ISE). The concept of polarizability of ITIES in a multi-ion system is outlined. Principle aspects of ion amperometry at ITIES are discussed including the use of amperometry as a tool for the clarification of the ion sensing mechanism, and for determining the concentrations of ions in the solution. The reference is made to recent amperometric measurements at the supported liquid membrane (SLM) and polymer composite liquid membranes (PCLM), which, together with the micro-hole supported ITIES, appear to be particularly suitable for realization of the amperometric ISE.     

Polarographic indication of the end-point in chelometric titrations with triethylenetetraminehexa-acetic acid

The application of d.c. and square-wave polarographic measurements for the indication of the end-point in titrations with triethylenetetraminehexa-acetic acid (TTHA) has been studied. TTHA has ten co-ordinating groups and forms complexes with metal to ligand ratios of either 1:1 or 2:1, depending on the metal and experimental conditions. The shape of the titration curves, determined by the dependence of the limiting current (peak current of the square-wave polarographic curve) or of the half-wave potential (peak potential) on the amount of TTHA added indicates the composition of the complex formed in the titration. The composition of this complex as determined from the studied titration curves agrees with that predicted by theory. Titrations with polarographic indication of the end-point were also applied for direct titrations of binary mixtures of metal ions. The resulting titration curves indicated the existence of mixed dinuclear complexes and also the kinetic factors involved in the reactions between two different metal ions and TTHA.     

A New Ultramicrosensor for Nitric Oxide Based on Electropolymerized Film of Nickel Salen

Abstract

A new amperometric ultramicrosensor for the determination of nitric oxide (NO) is described. The ultramicrosensor, which is based on an electropolymerized film of ethylenebis(salicylideneiminate) nickel [Ni(salen)] and Nafion, shows a low detection limit, high selectivity and sensitivity to NO determination. The oxidation current (measured by a differential pulse amperometric method) is linear with NO concentration ranging from 1.0x10^?8 to 4.0x10^?6 mol/L with a calculated detection limit, at a signal to noise ratio of three, equal to 5.0x10^?9 mol/L. Some endogenous electroactive substances in biological tissues, such as dopamine, 5-HT and nitrite do not interfere with NO determination at the concentrations higher than those in biological systems. The ultramicrosensor could be employed for in vivo measurements of NO. The mechanism of the response of the ultramicrosensor to NO is also studied.     

Highly sensitive differential pulse amperometric detection of second generation anti-tumor platinum compounds in HPLC effluents

Summary A highly sensitive on-line amperometric detection of platinum compounds in HPLC effluents was possible with the use of a polarographic detector. For TNO-1 (=cis-1,1-di(aminomethyl)-cyclohexane Pt(II)chloride) a linear dynamic range of at least three decades could be obtained (0.034–108g TNO-1/ml) with a detection limit of three times the noise signal at 0.7 ng TNO-1 (20ng Pt/ml). The sensitivity was 0.1 nA/ng TNO-1 (0.2nA/ng Pt). The within-day presicion was 1.1% at a concentration of 10.8g TNO-1/ml (n=10). With this system the compatibility was measured of TNO-6 with infusion fluids. In 0.15 M NaCl, TNO-6 (=cis-1,1-di(aminomethyl)-cyclohexanePt(II)sulphate) was converted into TNO-1 within 40 minutes. Molecular changes of TNO-6 were also observed in a 5% aqueous glucose solution.     

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

Alternating‐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.     

Gradient flow-injection amperometry based on induced retention by the detector coating

A novel approach for enhancing the selectivity of amperometric flow-injection systems is described. This strategy relies on the use of coated electrodes to induce longer residence times for the target analyte (within the detector) compared to the interfering species. Selective measurements of the analyte are thus performed on the tailing edge of its peak, after passage of the interfering species from the detector. Surface coatings with different permeability properties, including charge-exclusion Nafion or hydrophobic lipid and alkanethiol films are thus used to retain and selectively detect counterionic or nonpolar analytes, after the elution of co-ionic and polar interferences, respectively, from the detector.     

Quantification of noise sources for amperometric measurement of quantal exocytosis using microelectrodes

Electrochemical microelectrodes are commonly used to record amperometric spikes of current that result from oxidation of transmitter released from individual vesicles during exocytosis. Whereas the exquisite sensitivity of these measurements is well appreciated, a better understanding of the noise sources that limit the resolution of the technique is needed to guide the design of next-generation devices. We measured the current power spectral density (S(I)) of electrochemical microelectrodes to understand the physical basis of dominant noise sources and to determine how noise varies with the electrode material and geometry. We find that the current noise is thermal in origin in that S(I) is proportional to the real part of the admittance of the electrode. The admittance of microelectrodes is well described by a constant phase element model such that both the real and imaginary admittance increase with frequency raised to a power of 0.84-0.96. Our results demonstrate that the current standard deviation is proportional to the square root of the area of the working electrode, increases ～linearly with the bandwidth of the recording, and varies with the choice of the electrode material with Au ≈ carbon fiber > nitrogen-doped diamond-like carbon > indium-tin-oxide. Contact between a cell and a microelectrode does not appreciably increase noise. Surface-patterned microchip electrodes can have a noise performance that is superior to that of carbon-fiber microelectrodes of the same area.     

Multiwalled Carbon Nanotubes Resist Intercalation Whereas Pyrolytic Graphite Can Exfoliate in Propylene Carbonate: Electroanalysis Without the Deleterious Effects of Intercalation for the Detection of Ammonia

A generic approach is presented allowing the sensing of electroactive species at carbon based electrodes in otherwise potentially intercalating media. Graphite electrodes are known to suffer intercalation leading to exfoliation in propylene carbonate solution containing tetra‐n‐butylammonium perchlorate as supporting electrolyte. However, we report contrasting behaviour at bamboo multiwalled carbon nanotubes, where intercalation/exfoliation does not occur, so allowing useful electroanalytical measurements to be made, in particular for the amperometric determination of ammonia.     

A spectrophotometric and polarographic investigation of three new cyclohexene-substituted benzodiazepines

Three recently introduced benzodiazepine derivatives, tetrazepam (I), nortetrazepam (II) and menitrazepam (III) have been subjected to spectral and polarographic investigation. From the ultraviolet spectral data their pK(a)-values have been determined: 4.28 (I), 4.3 (II) and 3.5 (III). From the polarographic measurements it can be concluded that in I and II the 4,5 CN double bond is reduced with 2 electrons. For the first time for the benzodiazepine series it has been observed that in slightly alkaline solutions this process takes place in two separate 1-electron steps. In III, first the aromatic nitro group is reduced to a hydroxylamine group, then at more negative potentials the CN double bond is also reduced; its reduction wave mostly coalesces with that for the 6-electron reduction of the nitro group to an amino group. A differential pulse polarographic method is presented, for the determination of I, II, III at concentrations as low as 10(-7)M.     

Determination of Sulfide by Hematoxylin Multiwalled Carbon Nanotubes Modified Carbon Paste Electrode

This study investigates a new approach for the amperometric determination of sulfide using a hematoxylin multiwalled carbon nanotubes modified carbon paste electrode (HM‐MWCNTs/CPE). The experimental results show that HM‐MWCNTs/CPE significantly enhances the electrocatalytic activity towards sulfide oxidation. Cyclic voltammetric studies show that the peak potential of sulfide shifted from +400 mV at unmodified CPE to +175 mV at HM‐MWCNTs/CPE. The currents obtained from amperometric measurements at optimum conditions were linearly correlated with the concentration of sulfide. The calibration curve was obtained for sulfide concentrations in the range of 0.5–150×10^?6 mol L^?1. The detection limit was found to be 0.2×10^?6 mol L^?1 for the amperometric method. The proposed method was successfully applied to a river water sample in Pardubice, Czech Republic.