bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple and reliable fabrication of carbon fiber ultramicroelectrodes
Authors: Fernandez Avelino L. Suarez , Calzón Josefa A. Garcia , Garcia Agustin Costa , Blanco Paulino Tuñón
Published: May 2005

A simple method for the fabrication of carbon fiber ultramicroelectrodes, using easily available materials (micropipette tips, metal rod, mercury, low viscosity inert epoxy resin, and carbon fiber of 7.5 μm diameter) and with no requirement for specialized instrumentation, is described. A high success rate is reported.
Electrochemical behavior of nitrofurantoin and assay of its formulations
Authors: Sridevi C. , Reddy S. Jayarama
Published: May 2005

The electrochemical behavior of nitrofurantoin was studied by employing do polarography, cyclic voltammetry, and differential pulse polarography in universal buffers of pH 2.0–12.0. Kinetic parameters such as transfer coefficients, diffusion coefficients, and heterogeneous forward rate constant values were evaluated using these techniques. Differential pulse polarography was employed for the estimation of this drug in several pharmaceutical formulations.
Influence of the medium on the polarographic behavior of Cu(II)
Authors: Lurdes S. M. , Gonçalves Sim˜Es , Sigg Laura
Published: May 2005

The critical evaluation of the determination of copper, by pulse and stripping voltammetric methods in the presence of ligands occurring in natural waters was performed. The conditions under which Cu(I) can be detected, either due to its presence in solution or as an electrochemical intermediate, were investigated. The ligands Cl− and NH3 were considered and their effects in analytical determinations of Cu in natural waters are discussed. Concentrations of Cl− > 1.6 × 10−2 M and NH3 > 10−3 M lead to the reduction of Cu( II) in two steps with Cu(I) intermediates. We illustrate that the stability constants of complexes of Cu(I) can be determined by starting with the more stable solutions of copper(II) and electrochemically (in situ) producing Cu(I).
Determination of transition metals in natural waters by microprocessor‐controlled voltammetry in comparison with zeeman graphite furnace atomic absorption spectrometry
Authors: Buldini Pier Luigi , Ferri Donatella , Nobili Dario
Published: May 2005

Information on the transition metals content in natural waters is of great environmental interest. The procedures presented in this paper deal with the simultaneous determination of copper, cadmium, lead, and zinc in 0.05 M nitric acid (0.05 M HNO3 + 0.1 M CTRAc) 0.1 M citric acid by differential pulse anodic stripping voltammetry or differential pulse polarography; manganese, nickel, and cobalt were determined in ammonia/ammonium acetate buffer at pH 9.1 by differential pulse anodic or cathodic stripping voltammetry, titanium and relevant iron concentrations by pulse polarography in 0.2 M oxalic acid in the presence of 0.1 M potassium chlorate. The voltammetric schemes and response are critically compared to Zeeman graphite furnace atomic absorption spectrometry.
Potentiometric study of the nucleation of Cu2O after its formation from fehling solutions and reducing sugars
Authors: Nanos Christos G. , Konidari Constantina N. , Karayannis Miltiades I.
Published: May 2005

The oxidation of glucose by Fehling solution was followed by various solid‐state ion‐selective electrode. The shape of the recorded potential vs. time transient curves at three different electrodes (Cu2 + Ph2+, and Ag+/S2−) was explained on the basis of the known mechanisms of formation of precipitates, the growth of crystals, and adsorption/desorption phenomena. The curves are peculiar in shape, are very reproducible, and show three distinct parts. The potential changes of the electrodes are due to the consumption of OH− during the reaction, as well as to its adsorption and desorption on the Cu2O precipitate. The effects on the values of different curve parameters of the concentrations of glucose, OH−, and K, Na‐tartrate, as well as the temperature, were studied.
The wall‐jet ring‐disc electrode: The measurement of homogeneous rate constants from steady state ring currents
Authors: Brett Christopher M. A. , Oliveira Brett Ana Maria C. F. , Compton Richard G. , Fisher Adrian C. , Tyley Gwynfor P.
Published: May 2005

The wall‐jet ring‐disc electrode is shown to provide a convenient means determining homogeneous rate constants by means of ring current measurements as a function of disc currents and electrolyte flow rates. Theory is provided for the analysis of such “collection efficiency” experiments and applied to the specific case of the bromination of anisole, where good agreement with experiment is found. Advantages with respect to the rotating ring‐disc electrode are pointed out.
Enzyme electrodes for ADP/ATP with enhanced sensitivity due to chemical amplification and intermediate accumulation
Authors: Yang Xiurong , Johansson Gillis , Pfeiffer Dorothea , Scheller Frieder
Published: May 2005

Substrate recycling is used for making a highly sensitive enzyme electrode for the determination of ADP/ATP. A graphite electrode is modified with an adsorbed bis(benzophenoxazinyl) derivative of terephthaloic acid and covered with a gel containing entrapped glucose‐6‐phosphate dehydrogenase, pyruvate kinase, and hexokinase, all behind a dialysis membrane. The recycling produces NADH, which is detected by oxidation at the modified electrode. The cycle is driven by conversion of phosphoenolpyruvate to pyruvate and by phosphorylation of glucose to glucose‐6‐phosphate, which is oxidized to the corresponding gluconic acid with the simultaneous production of NADH. The calibration curves for ADP and ATP were linear to about 0.4 μM and the detection limit was 1 nM. A steady‐state response was obtained after 2–10 min. Sensitivity toward ADP can be increased further by the accumulation of ATP inside the membrane.
The effect of anodic surface treatment on the oxidation of catechols at ultrasmall carbon ring electrodes
Authors: Fishman Harvey A. , Ewing Andrew G.
Published: May 2005

Electrochemical anodic treatment at ultrasmall carbon ring electrodes appears to result in the formation of an oxide film that displays charge‐selective and pH‐dependent enhancements following treatment. Voltammetry after treatment in pH 7.4 citrate‐phosphate buffer is more Nernstian for dopamine (DA) and less Nernstian for 3,4‐dihydroxyphenylacetic acid (DOPAC). However, oxidation in pH 2.8 buffer gives rise to voltammetry that is less Nernstian for both DA and DOPAC. Extensive surface oxidation in potassium hydroxide apparently forms a thick layer that acts like a thin layer reservoir for adsorbed analyte. Voltammetry following extensive treatment is attenuated and peak shaped. Minimal surface oxidation in KOH results in more Nernstian sigmoidal voltammetry with only light current attenuation. The data suggest that an oxide layer formed following anodic treatment is non‐uniform and leaves sites of activated carbon exposed on the surface. Furthermore, it appears that this layer has cation‐exchange properties giving rise to charge transfer selectivity. A model of the surface formed following anodic oxidation is consistent with previous models involving both surface cleanliness and carbon structure orientation.
Determination of amalgam‐forming metals by anodic stripping voltammetry in solutions containing dissolved oxygen
Authors: Kopanica Miloslav , Stara Vera
Published: May 2005

Amalgam‐forming metals can be determined by anodic stripping voltammetry in solutions containing dissolved oxygen. The procedure uses a modified mercury film electrode prepared by deposition of mercury on the surface of a silica‐gel/carbon composite electrode. Between determinations the film is removed from the electrode surface either mechanically or by a potential pulse. Lead was determined over the concentration range from 0.01 to 250 μM, with relative standard deviation values not exceeding ± 5%. The method was applied for the determination of metals in used motor oil.
Stripping voltammetry of uranium based on adsorptive accumulation of its 4‐(2‐pyridylazo) resorcinol complex at the static mercury drop electrode
Authors: Farias Pércio A. M. , Ohara Aniy K.
Published: May 2005

A highly sensitive electrochemical stripping procedure for uranium is reported. Accumulation is achieved by controlled adsorption of the uranium/4‐(2‐pyridylazo) resorcinol complex on the static mercury drop electrode. The effect of various operational parameters on the stripping response is discussed. The detection limit is 0.2 nM with 10 min preconcentration. The response is linear over a 9.3 × 10−9−3.0 × 10−6 M concentration range, and the relative standard deviation (at the 24 μg·l−1 level) is 3%. Most cations and anions do not interfere in the determination of uranium; some interferences are eliminated by the addition of CDTA and EDTA. The applicability of the method to fresh water and seawater is demonstrated (the results obtained for uranium in reference seawater samples, NASS−2, were 2.95 μg·l−1 with standard deviations of 0.20 μg·l−1 (n = 5).
Correlation between the degree of activation by galvanostatic pretreatment and structure of biogenic amine compounds
Authors: Mattusch Jürgen , Werner Gerhard
Published: May 2005

The influence of steric and electronic effects of Biogenic compounds on their redox behavior at an electrochemically pretreated glassy carbon electrode in comparison to the polished electrode is elucidated by cyclic voltammetric data. The improvement of reversibility on a pretreated electrode increases mainly in order of carboxylic to amine substituent in position 1, acting by the I‐effect, and of unsymmetrical substituted compounds in positions 3 and 4, to symmetrical (dihydroxy‐) substituted compounds as attributed to steric hindrance of the electrode transfer.
Amalgam electrodes: Direct electrochemical generation of cadmium macrocyclic complexes
Authors: Boudon C. , Gisselbrecht J. P. , Gross M.
Published: May 2005

The electrochemical oxidation of cadmium amalgam was studied in the nonaqueous solvents CH2Cl2, 1,2‐C2H4Cl2 and propylene carbonate. Significant coordination effects were observed between the electrogenerated Cd(II) ions and 18‐membered macromonocyclic ligands, each containing six Lewis bases heteroatoms: 18‐O6, 18‐S6, 18‐N2O4, and 18‐N6. The stoichiometries and the stabilities of the resulting complexes were determined. These stabilities increase from 18‐O6 or 18‐S6 to 18‐N6.
Silicone‐based calcium‐selective electrode
Authors: Marrazza G. , Mascini M.
Published: May 2005

A silicone‐based calcium potentiometric sensor is described, with improved hemocompatibility, as desired for continuous monitoring of clinical samples. The favorable dynamic properties of the new electrode are illustrated in a flow operation.
Anodic stripping voltammetry at mercury “films” deposited on conducting poly(3‐methylthiophene) electrodes
Authors: Wang Zhi , Galal Ahmed , Zimmer Hans , Mark Harry B.
Published: May 2005

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.
A new polymeric mercury thin‐film electrode
Authors: Wallace G. G. , Imisides M. D.
Published: May 2005

A chemically modified mercury thin‐film electrode (MTFE) is presented that employs an electrochemically generated nonconducting polymer (poly‐N‐ethyltyramine), which has been derivatized with surface dithiocarbamate groups. Mercury is deposited chemically onto the electrode by complexation and, following electrochemical reduction of the mercury, is used as a substrate for anodic stripping voltammetry (ASV) of cadmium, lead, and copper. The properties of a conventional MTFE are compared with the modified electrode.
Determination of organochlorine pesticides by polarography in emulsified medium
Authors: Reviejo A. Julio , Samprón Arturo , Pingarrón José M. , Polo Luis M.
Published: May 2005

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.
Pulsed electrochemical detection at noble metal electrodes in liquid chromatography
Authors: Johnson Dennis C. , LaCourse William R.
Published: May 2005

The direct electrochemical detection of numerous polar aliphatic compounds is achieved at Au and Pt electrodes under the control of multistep potential‐time waveforms. In this technique, called “Pulsed Electrochemical Detection (PED),” the waveforms manage the sequential processes of sampling the faradaic signal, from the oxidation of analyte, followed by oxidative cleaning and reductive reactivation of the electrode surfaces. The response mechanisms in PED are strongly influenced by surface properties of the electrodes and, therefore, members of each chemical classification detected are observed to produce virtually identical voltammetric response. Consequently, applications of PED have their greatest analytical significance when coupled with Liquid Chromatography (LC) to achieve a priori resolution of complex mixtures. The basic concepts of PED are reviewed and LC‐PED results are presented for a variety of samples containing mixtures of alcohols, carbohydrates, alkanolamines, amines, and sulfur compounds.
A solid polymer electrolyte amperometric detector for FIA and HPLC with mobile phases of low conductivity
Authors: Loub Lukáš , Opekar František , Pacáková Věra , Štulík Karel
Published: May 2005

An amperometric cell with a small platinum wire working electrode, a submicroliter geometric volume, and a solid polymer electrolyte (Nafion) was constructed and tested. The cell permits sensitive and reliable detection even in mobile phases of negligible electric conductivity, (e.g., distilled water or nonpolar organic solvents). The sensitivity is substantially higher than that attained with similar cells containing large‐are working electrodes; typical limits of detection amount to analyte concentrations between 10−7 and 10−6 mol/dm3, corresponding to subnanogram amounts in common HPLC sample volumes. The detector response exhibits satisfactory linearity, a linear dynamic range of at least three concentration decades, and a good precision, with relative standard deviations of 1 to 5%. This cell substantially widens the possibilities of amperometric detection, permitting direct application, for example, to normal‐phase HPLC or to methods with programmed composition of the mobile phase (gradient elution).
Electrocatalytic oxidation and flow detection of hydrazine compounds in liquid chromatography at a vitamin B‐12 adsorbed glassy carbon electrode
Authors: Zhou Jianxun , Wang Erkang
Published: May 2005

A vitamin B‐12 chemically modified electrode (CME) was constructed by adsorption of vitamin B‐12 onto a glassy carbon surface. The electrode catalyzes the electrooxidation of hydrazine compounds over a wide pH range. The electrocatalytic behavior of hydrazines is elucidated with respect to the CME preparation conditions, solution pH, operating potential, mobile phase flow rate, and other variables. When applied to liquid chromatographic detection of the analytes, the vitamin B‐12 CME yielded a linear response range over 2 orders of magnitude, and detection limits at the picomole level. The vitamin B‐12 CME offers acceptable catalytic stability in both batch and flow systems.
Cross correlation with digital techniques in flow injection analysis and high performance liquid chromatography
Authors: Curran D. J. , McKeans R. E.
Published: May 2005

Digital techniques are implemented to demonstrate the use of cross correlation to improve the signal‐to‐noise ratio for measurements involving analog detectors in flowing stream analysis methods. Two examples are presented. The first involves amperometric detection of dopamine using flow injection analysis. The reference and analyte signals are digitized and cross correlation performed by software using the fast Fourier transform (FFT). The second example is the determination of a mixture of catecholamines by HPLC using a UV detector. Multiplication of the digitized reference and analyte signals was carried out in the time domain followed by low pass filtering. Improvement in the signal‐to‐noise ratio up to a factor of 35 was found, depending on the compound.
Cathodic behavior of 4,5‐dimethoxy‐2‐nitroamphetamine
Authors: Squella J. A. , Pezzani M. , Cassels Bruce K. , Aillon‐Torres Milton , Rezende Marcos C. , Nuñez‐Vergara L. J.
Published: May 2005

The amphetamine derivative 4,5‐dimethoxy‐2‐nitrophenyl‐2‐aminopropane, a positional isomer of the potent hallucinogen DON, was studied by cyclic voltammetry and polarography. The nitro compound was reduced to the corresponding hydroxylamine under the experimental conditions used.
Simultaneous polarographic determination of ascorbic acid and dipyrone in pharmaceutical preparations
Authors: Belal F.
Published: May 2005

A polarographic method is described for the simultaneous determination of ascorbic acid and dipyrone in dosage forms. The method is based on the anodic polarographic waves produced by both compounds in Walpole acetate buffer (pH 3.6). The separation of the two waves (>0.65 V) is sufficient to allow accurate measurements. The proposed method was successfully applied to the analysis of commercially available ampules, and the results obtained were of satisfactory accuracy and precision.
Electrochemical reduction of nitrofurazone and its determination in pharmaceutical dosage forms by differential pulse polarography
Authors: Reday C. Suresh , Reddy S. Jayarama
Published: May 2005

The electrochemical reduction behavior of nitrofurazone has been studied by employing dc polarography, cyclic voltammetry, and differential pulse polarography in the universal buffers of pH ranging from 2.0 to 12.0. A differential pulse polarographic method is described for the determination of nitrofurazone in its pharmaceutical formulations using the standard addition method. The kinetic parameters, such as diffusion coefficients (D) and heterogeneous forward rate constant (k) values are evaluated using these techniques.
Adsorption of lead (II) on mercury electrodes from chloride‐bromide mixtures of high ionic strength
Authors: Zelić Marina , Branica Marko
Published: May 2005

The adsorption of lead (II) from chloride‐bromide mixtures of a high ionic strength (I=4 mol/L) to mercury electrodes was studied using square wave voltammetry, differential, and normal pulse polarography. The presence of excess chloride ions in the solution prevents additional surface complexation of PbBr2 with previously adsorbed free bromide ions and the formation of PbBr3− at the mercury drop. Adsorption effects are highly pronounced, even when PbBr2o makes less than 1% of dissolved metal, indicating that a mixed‐ligand species could be attached to the electrode. It is possible to explain nearly all experimental results by the surface activity of both PbBr2o and a mixed‐ligand complex PbBr2Cl.
Isopolymolybdic acid‐poly(4‐vinyl)pyridine film modified electrode
Authors: Dong Shaojun , Song Fayi , Wang Baoxing , Liu Baifeng
Published: May 2005

Electrochemical polymerization of 4‐vinylpyridine produced a uniform poly(4‐vinyl)pyridine(PVP) film on the glassy carbon (GC) electrode surface. The isopolymolybdic acid‐PVP film‐modified electrode was prepared by soaking the PVP/GC electrode in the 0.05 M H2SO4 aqueous solution containing 0.005 M isopolymolybdic acid (H4Mo8O26). The latter (catalyst) is incorporated and held in the PVP film electrostatically. The electrochemical behavior and electrocatalytic properties of this H4Mo8O26–PVP/GC electrode was described. The results indicate that this modified electrode has good stability and electrocatalytic activity on the reduction of chlorate and bromate ions in aqueous solution. The catalytic process is regarded as an EC mechanism.
Anodic stripping voltammetry of selenium(IV) at a gold fiber working electrode
Authors: McLaughlin Kieran , Boyd Damien , Hua Chi , Smyth Malcolm R.
Published: May 2005

The anodic stripping voltammetry of selenium (IV) in a gold fiber electrochemical flow cell is described. The cell is simple to construct and flexible in its operation. The nonlinear diffusional mass transport characteristics of such small diameter electrodes influence the anodic stripping voltammetry of Se(IV) with the result that significant deposition of metal ions occurs during the scan period from the deposition potential to the peak potential. Therefore, an extremely short deposition period of the order of 20 seconds can be employed at the gold fiber electrode. The system described resulted in a linear working range from 0–15 ng/mL, a detection limit of 0.5 ng/mL Se(IV) and a relative standard deviation of 6% at 5 ng/mL (n = 7) in pure solution.
Electrochemical oxidation of 5‐hydroxytryptamine and 5‐hydroxyindoleacetic acid by integrated pulse linear scan voltammetry at ultrasmall gold ring electrodes
Authors: Lau Yau Yi , Wong Danny K. Y. , Luo Guoan , Ewing Andrew G.
Published: May 2005

Ultrasmall gold ring electrodes have been constructed by electrodeposition of gold onto carbon ring electrodes. Electrodes thus formed show similar adsorption/desorption peaks for oxygen in H2SO4 solution compared to those obtained at conventional‐sized electrodes. These electrodes have been used in conjunction with linear scan voltammetry and subsequent cleaning pulses to obtain repeatable quantitative results for the electochemical oxidation of 5‐hydroxytrptamine and 5‐hydroxyindoleacetic acid. This technique involves the use of a linearly scanned applied potential, followed by a large positive potential to clean the electrode oxidatively and negative potential for electrode activation. The result of the cleaning pulses is that oxidation products of 5‐hydroxytryptamine are cleaned off the electrode and reproducible voltammograms are obtained.
Stripping analysis on controlled‐growth mercury drop electrode
Authors: Kowalski Zygmunt , Migdalski Jan
Published: May 2005

In this study, special consideration is given to the “back‐diffusion effect” accompanying the process of electrochemical preconcentration and during the time between the end of this process and the initiation of stripping (that is, during the rest period). It is shown how far these effects can be eliminated when a Controlled‐Growth Mercury Drop Electrode (CGMDE), is applied. It has been demonstrated that controlled growth of the drop during preelectrolysis allows the formation of a homogeneous amalgamate of the deposited substances in the Hg drop and prevents the occurrence of the back‐diffusion effect. Quantitative relations between these factors and the back‐diffusion into the capillary thread of mercury are presented.
Insecticide determination with enzyme electrodes using different enzyme immobilization techniques
Authors: Kumaran Satish , Tran‐Minh C.
Published: May 2005

Three different techniques of immobilization of the enzyme butyrylcholinesterase (E.C. 3.1.1.8.) and their use in association with pH glass electrodes for the determination of certain insecticides (Carbofuran, Carbaryl, and Paraoxon) by inhibition of the enzyme, have been studied and the results obtained are compared. The immobilizations are done by cross‐linking a mixture of the enzyme and human serum albumin with glutaraldehyde onto nylon nets, by fixing the enzyme onto commercially available polyamide pre‐activated PALL™ membranes and by physically retaining the enzyme in a synthetic prepolymer of acrylamidemethacrylamide hydrazides which is cross‐linked with glyoxal. There are no significant differences with regard to the sensitivities or the detection limits among the sensors using the different membranes. The detection limits of the insecticides tested varied from 0.2 to 10 ppm. In terms of signal reproducibility, stability, and cost, the nylon net membranes appear most promising. Membranes prepared in lots show better sensor signal reproducibility compared to those prepared individually. For the development of “disposable” biosensors, both nylon net and PALL™ membranes are very apt, since these membranes are easily mass produced at low cost and maintain their original enzyme activities even after 3 years when stored dry.
Electrochemical analysis of arsenic compounds for veterinary use by two polarographic methods
Authors: Tzedakis T. , Comtat M.
Published: May 2005

Some compounds with the general formula magnified image (I) have an antiparasitic effect on animals and are used against heart disease induced by trypanosomes. A rapid, precise and selective analysis of species (I) and RNHC6H4AsO3H2 (II), RNHC6H4As  O (III), and R'SH (IV), appearing as intermediates, is necessary in order to regulate the synthesis processes if (I) and (II), to identify and measure the products before using them in the reactor, and to control their purity before scaling up. Tast polarography and differential pulse polarography convert quickly the concentration of these compounds into current intensity suitable for control of the process. The first method makes the assay in oxidation of (IV) possible, but the resolution is insufficient to obtain the species (III) and (I). The assay, in reduction of (II) is possible, but with interferences of (III). The second method, on the other hand, using oxidation of (I) in a basic medium provides sufficient resolution to analyze (I) and (III) with a precision on the order of 5%.
Logarithmic analysis of polarographic waves complicated by nonparallel initial and limiting currents
Authors: Lovrić Milivoj , Svetličić Vesna , Žutić Vera
Published: May 2005

A procedure for the logarithmic analysis of polarographic waves with nonparallel initial and limiting currents is developed and its application illustrated with two experimental systems: phosphine‐metriphonate reduction and methylene blue (MB) reduction and reoxidation. The procedure is based on the presumed identity of the wave function and the change of a double‐layer capacitance along the wave.
An X‐ray photoelectron spectroscopy investigation of silver iodide‐coated ion‐selective electrodes
Authors: Strydom C. A. , van Staden J. F. , Strydom H. J.
Published: May 2005

The AgI‐coated ion‐selective electrode surface is more stable than either the AgCl or AgBr surfaces if exposed to solutions containing ions such as Cl−, Br−, I−, Ag+, and NH3 for a week. A mixed AgClsI1− or AgBrsI1−s phase is formed upon a week's treatment of the AgI surface with either Cl− or Br−, with S much smaller than 1. After a week's treatment with high concentrations of the ions, no new surface layer consisting of only AgCl or AgBr is formed, as was observed in the case of AgCl and AgBr electrodes. Although AgI is much less soluble than either AgCl or AgBr, the absorption of chloride and bromide ions into the AgI surface nevertheless increases with time.
Cobalt(II, III)‐oxide chemically modified electrode as amperometric detector in flow injection systems
Authors: Mannino S. , Cosio M. S. , Ratti S.
Published: May 2005

A chemically modified electrode (CME) prepared by mixing cobalt(II, III) oxide and carbon paste, greatly reduces the overvoltage for the oxidation of various biologically important compounds, such as sugars, hydrogen peroxide, and cysteine. The new electrocatalytic surface facilitates the amperometric detection of these compounds in flowing streams. The modified electrode is very stable, can be easily renewed, and gives reproducible results. Application for the determination of hydrogen peroxide in milk is demonstrated.
An improved holder for the electrochemical quartz crystal microbalance and its cyclic voltammetry characteristics
Authors: Koh Wonyong , Kutner Wlodzimierz , Jones M. Thomas , Kadish Karl M.
Published: May 2005

The design and characteristics of a stationary, compact holder for an electrochemical quartz crystal microbalance (EQCM) are presented. A Au/quartz crystal oscillator is vertically mounted in a polytetrafluoroethylene body of the holder. The crystal is sealed with an O‐ring and is easily accessible for change. The performance of the holder was tested under cyclic voltammetry (CV) conditions with the Ag+ /Ag and Cu+ /Cu electrodeposition/electrodissolution processes. Frequency changes due to mass changes of the Au/quartz electrode were correlated with CV parameters. The holder was calibrated for a 5 MHz crystal oscillator by means of CV anodic stripping of silver. The mass sensitivity was 19.5 ± 0.1 ng Hz−1 cm−2. The concentration sensitivity was 14.2 ± 0.2 μM Hz−1 cm−2 at a potential scan rate of 0.01 V s−1 and 23.7 ± 0.3 μM Hz−1 cm−2 at a scan rate of 0.02 V s−1 for a potential of scan reversal which was 250 mV more negative than the electrodeposition peak potential.
Determination of copper(I) ion with a chemically modified carbon paste electrode based on di(2‐imino‐cyclopentylidine mercaptomethyl) disulfide
Authors: Won Mi‐Sook , Park Jin‐hyo , Shim Yoon‐Bo
Published: May 2005

A copper‐sensitive chemically modified electrode (CME) has been constructed by incorporating di(2‐imino‐cyclopentylidine mercaptomethyl) disulfide (didd) into the carbon paste composed of graphite powder and Nujol oil. Copper(I) ion was chemically deposited on the CME by immersing it in the Cu(I) solution. The resulting surfaces were characterized by cyclic and differential pulse voltammetry. The CME's surface could be regenerated by applying more positive potential than the stripping potential of the Cu(I) ion and then used for another deposition. After seven deposition/measurement/ regeneration cycles, the peak current of voltammograms of the analyte decreases slightly. The differential pulse technique was also applied to the above system. In this case, the detection limit for Cu(I) ion was 5 × 10−11 M for 30 minutes of deposition time. After reduction of Cu(II) ion to Cu(I) in the sample solution with hydroxylamine, satisfactory results were obtained for the determination of copper in certified standard urine reference material SRM's 2670 (trace elements in urine).
New electroanalytical method for determination of chloride ion at low concentrations
Authors: Sun Tianlin , Bai L. , Conway B. E.
Published: May 2005

A sensitive electroanalytical procedure is described for the detection of chloride ion down to micromolar concentration and over a wide linear range of (3.5) decades. The method is based on the blockage of a Pt anode caused by competitive adsorption of chloride ion, using cyclic voltammetry. The blocking effect is proportional to p[Cl−] over a wide concentration range; the significance of this relationship is discussed. The required conditions for this electroanalytical procedure are described and interferences from other anions are evaluated.

The new method is sensitive, accurate, and simple, and it is useful for analyzing trace chloride ion in nominally pure inorganic chemicals.
Voltammetric characterization of activated carbons in modified carbon paste electrodes
Authors: Kaplan Jeffrey D. , Marsh John H. , Orchard S. Walter
Published: May 2005

Carbon paste electrodes (CPEs), modified by the addition of small amounts of finely powdered activated carbon (AC) were studied using cyclic (CV) and square wave voltammetry (SWV). Cyclic voltammograms revealed the expected increase in surface area associated with the presence of the activated carbon but did not reveal any specific redox peaks. Square wave voltammograms of both the modified and unmodified electrodes obtained in acidic solution were characterized by well‐defined redox peaks whose behavior was consistent with that expected for couples of the quinone/hydroquinone type. The modified electrodes showed generally larger peaks than the unmodified ones. Regardless of the origin of the activated carbons, the square wave voltammetric response was fairly similar, and it was not possible to confidently differentiate between the different types on this basis.
Performance characteristics of a Labetalol‐H plus‐tetraphenylborate selective electrode
Authors: Voulgaropoulos Anastasios , Sofoniou Michalis , Kazakou Eleni
Published: May 2005

The construction and performance characteristics of an ion selective membrane electrode for labetalol drugs in protonated form, based on their ion‐pair complexes with sodium tetraphenylborate (TPB‐Na+) incorporated in a poly(vinyl chloride) matrix, are described. The Labetalol‐H+ selective electrode can be used practically for the determination of the pharmaceutical compound by direct potentiometry. The potentiometric sensor exhibits near‐Nernstian response from 10−2 M to about 10−5 M, with a slope of 55 mV/decade of concentration and detection limit of 4.46 × 10−6 M. The influence of changing the membrane characteristics, pH, and temperature of the test solution on the electrode potential are studied. The response time varies from a few seconds to several minutes, depending on labetalol concentration. The selectivity of the electrode for Lab‐H+ toward primary, secondary, tertiary, and quaternary amines is investigated. Determination of Lab‐H+ in pharmaceutical tablets is performed using the proposed membrane electrode. No interference from any excipients in the tablets was observed.
Application of adsorptive stripping voltammetry to trace measurements of molybdenum in plant materials
Authors: Karakaplan Mustafa , Henze GÜNter
Published: May 2005

A procedure is presented for quantifying molybdenum in dry ashed plant samples. The determination is made by adsorptive stripping voltammetry in the differential pulse mode (DPAdSV). It is based on the adsorptive accumulation of the Mo(VI)‐chloranilic acid complex on the surface of a hanging mercury drop, followed by the reduction of the adsorbed complex. Optimal conditions are stirred acidified supporting electrolyte solution (of pH 2–3), containing 10−3 mol/L chloranilic acid and an accumulation potential of −0.20 V (vs. Ag/AgCl, 3 mol/L KCl). The height of the cathodic stripping peak around −0.60 V depends linearly on the molybdenum concentration and accumulation time (over the ranges 0–12 ng/ml and 0–300 seconds, respectively). For an accumulation period of 5 minutes, the detection limit is 0.02 ng/ml. Possible interferences by other trace metals are investigated. The proposed procedure has been applied to the determination of molybdenum traces in a variety of plants with good accuracy and precision. The results are in good agreement with those obtained by atomic absorption spectrometry.
Amperometric detection after HPLC separation of selected polypeptides and proteins at an electrode modified by mixed valent ruthenium oxide crosslinked with cyanide
Authors: Przyjazny Andrzej , Cox James A.
Published: May 2005

An indicator electrode, in which a film containing Ru oxides with cyano‐crosslinks comprised the active surface, was used in an amperometric detector for ion‐exchange and reverse‐phase high‐performance liquid chromatography (HPLC). The latter used a C‐18 column and an eluent of 0.04 M citric acid, 0.1 M KH2PO4, 0.1% trifluoroacetic acid, and 20–80% acetonitrile. Oxytocin, isotocin, vasopressin, tocinoic acid, myoglobin, and ribonuclease A were separated and determined with detection limits at the 1–3 pmol level. The response to ribonuclease A, as a typical example, was linear over the range of 0.050‐2.5 μM, with a slope of 15 nA/μM at 0.94 V (vs. Ag/AgCl). A single preparation of the electrode was generally stable for 3 weeks, as long as the analyte concentrations were below 10 μM.
Polarography and stripping voltammetry of metal‐polycarboxylate complexes: The Cu(II)‐polyacrylate system
Authors: Díaz‐Cruz J. M. , Ariño C. , Esteban M. , Casassas E.
Published: May 2005

A systematic study of the voltammetric behavior of Cu(II) in the presence of polyacrylic acid (PAA) was carried out by means of sampled direct current polarography (DCP), normal pulse polarography (NPP), differential pulse polarography (DPP), reverse pulse polarography (RPP), cyclic voltammetry (CV), and differential pulse anodic stripping voltammetry (DPASV). Background currents due to PAA, and probably anodic oxidation of the Hg in this potential region, hinder the study of the Cu(II) reduction. Results obtained seem to indicate the lability of the Cu/PAA complex. Distorted DPASV signals are obtained for Cu(II) in the presence of PAA, which are explained on the basis of the change of the ligand‐to‐metal ratio during the different steps of the electrodic process. Titrations of Cu(II) with partially neutralized PAA allow the determination of the apparent formation constant K of the Cu/PAA complex system.
Electrooxidation of ascorbic acid at the bis(4‐pyridyl)disulfide modified gold electrode
Authors: Xie Yuanwu , Dong Shaojun
Published: May 2005

The electrooxidation of ascorbic acid (AA) at the bis(4‐pyridyl)disulfide (PySSPy) modified gold electrode was studied. The results showed that the oxidation process was pH‐dependent. It was mainly due to the static interaction between AA and the modified electrode surface. At pH < 5.5, the oxidation is controlled by diffusion and the electrode can be applied to the kinetic and mechanistic study. In the range of 5 × 10−6– 2 × 10−3 mole/L, the peak currents exhibit a good linear relationship with the concentration of AA. The modified electrode has greater stability and can be used in flow detection analysis.
Determination of arsenic by stripping potentiometry on gold electrodes using partial least‐squares (PLS) regression calibration
Authors: Jagner Daniel , Renman Lars , Stefansqottir Svana H.
Published: May 2005

Partial least‐squares (PLS) regression calibration was applied to the determination of arsenic by stripping potentiometry on gold electrodes. In a procedure involving the direct electrochemical reduction of arsenic (V), this allowed interferences from copper (II), due to formation of intermetallic compounds, and tin (IV), due to stripping peak overlaps, to be modeled. At levels of arsenic below 1 μg L−1, additional problems with the gold surface background, as well as copper interferences from a reagent blank, could be successfully modeled, and the prediction of sample concentrations could be accurately performed.
Studies on the electrocatalytic reduction of aliphatic aldehydes on palladium‐modified carbon paste electrodes
Authors: Cai Xiaohua , Kalcher Kurt
Published: May 2005

Carbon paste electrodes modified either by mixing palladium powder to the electrode material or by electrodepositing Pd via cycling the potential between 0.4 and −0.7 V (versus SCE) exhibited stable electrocatalytic response for aliphatic aldehydes and aliphatic alcohols. The aldehydes (e.g., formaldehyde) could be reduced to the corresponding alcohols (e.g., methanol), and the alcohols (e.g., methanol) could be oxidized to the corresponding aldehydes (e.g., formaldehyde) by direct current voltammetry (DCV). The electrocatalytic effect was attributed to the electrogenerated metallic palladium at the electrode surface. The cathodic current peak, the height of which was proportional to the aldehyde concentration, had negative values; it was ascribed to a desorption of the product of the electrode reaction from the surface of the electrode. This peak was used for quantitative analytical purposes.
A study of electrical double layer effects in the pretreatment of two‐electrode cells for enzyme electrodes
Authors: Higson Séamus P. J. , Vadgama Pankaj
Published: May 2005

The thermodynamics of the electrode/electrolyte interface have been described for a two‐electrode cell, using a classical Guhemian approach. The description has been related to a two‐electrode cell that frequently is employed for enzyme electrodes. Theoretical considerations of the electrical double layer have been correlated with conditioning pretreatment regimes for the preparation of enzyme electrode cells. Effects of electrolyte composition and effects of concentration have been described. Consequently, improved methodologies have evolved for the pretreatment of pseudo reference/secondary electrodes, allowing the equilibration and subsequent use of sensors within <5 minutes as compared with previous requirements for full equilibration from open circuit.
Surfactant modified carbon paste electrode: Part 1: Electrochemical and microscopic characterization
Authors: Digua K. , Kauffmann J.‐M. , Delplancke J.‐L.
Published: May 2005

The modification of the carbon paste electrode (CPE) with the amphiphile hexadecyl sulfonic acid (sodium salt) has permitted the development of a stable and analytically useful functionalized electrode. The electrochemical characterization of the modified electrode (potential range, background current, stability) has been investigated by cyclic voltammetry in aqueous media with different buffer compositions and in hydro‐organic media and the results compared favorably with the conventional carbon paste electrode. The characterization of the sulfonated functionalities and their influence in the electrode behavior has been pointed out using linear scan and adsorptive voltammetry by studying two model compounds: promethazine and ascorbic acid. The marked influence of the pH, ionic strength, and nature of the buffer cation on the shape (potential and intensity) of the voltammetric curves confirmed the structure of the modified electrode interface, i.e., electrode bearing strong cation exchange functionalities. Scanning electron microscopy and optical microscopic observations of the CPE and modified CPE showed a higher density of graphite particles not covered by liquid paraffin at the latter.
Performance test of voltammetric analyzers with a diode based dummy cell
Authors: Yarnitzky Ch. N.
Published: May 2005

An electrochemical dummy cell, consisting of the usual two resistors and a capacitor, and a combination of several diodes simulate diffusion currents in the case of direct current (DC) and differential current measurements. This dummy cell may be used as a qupck electrochemical analyzer tester to determine the electronic noise level and the operation of the different polarographic modes.
Square wave cathodic stripping voltammetric determination of selenium in small quantities of biological tissues
Authors: Prasad Pamidi V. A. , Arunachalam J. , Gangadharan S.
Published: May 2005

A sensitive procedure for the determination of selenium in small quantities of biological tissues (5 to 10 mg), using square wave cathodic stripping voltammetry with an in situ formation of Cu2Se on the HMDE, is described. Microwave digestion and clean‐room facilities have been used to prevent the loss of analyte and sample contamination. The method has been standardized through the analysis of NIST SRM 1577 bovine liver. The method offers a detection limit of 1 pg/mL. The average precision of determination at 150 pg/mL of Se is 1.8% RSD. This method is highly suitable for the determination of biopsy samples where the quantity available for the analysis is very limited.
Amperometric glucose biosensor based on a tetrathiafulvalene‐mediated epoxy‐graphite biocomposite
Authors: Céspedes F. , Martínez‐Fábregas E. , Alegret S.
Published: May 2005

An inexpensive, robust, and easily mechanized amperometric glucose senor based on a biocomposite material has been constructed. The biocomposite is made of graphite, a nonconductive epoxy resin, tetrathiafulvalene (TTF) as a redox mediator, and glucose oxidase (GOD). The enzyme retains its bioactivity on confinement in the rigid epoxy‐graphite matrix, with the oxidation current of the reduced mediator serving as the analytical signal (at 150 mV [vs. Ag/AgCl] in a pH 7.00 buffered solution featuring 0.1 M phosphate and 0.1 M KC1). The resulting biosensor shows a linear response in the 0.1 to 2 mM glucose range and produces a steady‐state signal within a few seconds (11 seconds for a 95% response). Simple polishing procedures can be used to regenerate a freshly bioactive transducer surface.
Galvanic sensor for determination of hydrogen sulfide
Authors: Jeroschewski Paul , Haase Karen , Trommer Andreas , Gründler Peter
Published: May 2005

A galvanic cell for trace determination of hydrogen sulfide in gases is presented. The cell covers the range from 30 ppb to some hundred ppm. It is characterized by simple construction. The use of ferricyanide/ferrocyanide ions as a redox mediator system ensures very low cross sensitivity. The sensor is well‐suited for mobile use.
The effect of hydrodynamic conditions on the speciation of copper at a chemically modified electrode
Authors: Labuda Ján , Vaníačková Mária
Published: May 2005

The determination of copper in the presence of humic acid and oxalic acid using anodic stripping voltammetry (ASV) at the graphite electrode modified with a copper complexing agents 1‐phenyl‐3‐methyl‐4‐octanoylpyrazol‐5‐on, and a Nafion film is described. The validity of voltammetric criteria for the metal speciation based on the diffusion‐layer thickness and complexing conditions, has been examined. In the copper‐humic acid system, the signal is controlled by diffusion, whereas in the system with oxalic acid, both the dissociation kinetics and diffusion have to be considered.
Detection of electroinactive ions using conducting polymer microelectrodes
Authors: Sadik Omowunmi A , Wallace Gordon G.
Published: May 2005

The detection of electroinactive ions using conducting polymers has been described previously. In this work, we show that the analytical performance of this method is greatly improved using microelectrodes. The use of microelectrodes overcomes the problems associated with the implementation of this detection scheme in low conductivity eluents.