bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical study of cadmium complexes with folic acid and its related compounds
Authors: El‐Maali Nagwa Abo , Ghandour Mahmoud A. , Vire Jean‐Claude , Patriarche Gaston J. 
Published: February 2006

AbstractDifferential pulse polarography and cyclic voltammetry have been used to elucidate the complexation reaction between folic acid (vitamin B9) and cadmium(II) in unbuffered solutions. In order to follow this mechanism, the interaction of compounds related to folic acid (pterin, pterin‐6‐carboxylic acid, pteroic acid, and glutamic acid) with cadmium ions has been investigated using the same conditions. It appears that no complexation occurs between cadmium(II) and glutamic acid and that the complexation is very weak with pterin. One complex is formed with pterin‐6‐carboxylic acid with log β1 = 6.72, two complexes are formed with pteroic acid with log β1 = 5.0 and log β2 = 10.88, and three complexes appear with folic acid with log β1 = 5.56, log β2 = 10.40, and log β3 = 16.63. The mechanism of complexation is also considered.
A study of the anodic oxidation of thiophosphate at a gold electrode in 0.10 M sodium hydroxide by double‐potential‐step chronocoulometry in a thin‐layer cell
Authors: Ngoviwatchai Aporn , Johnson Dennis C. 
Published: February 2006

AbstractThe oxidation of adsorbed SPO33− during the positive potential scan at a gold electrode is a major contributor to the total anodic signal that is catalyzed by formation of surface oxide. The number of electrons for oxidation of SPO33− in both the adsorbed (nads) and solution (nsoln) states was determined to be 6 equiv mol−1 on the basis of double‐step chronocoulometry in a thin‐layer cell. The products are concluded to be PO32− and SO43− on the basis of these n values, 31P NMR spectra, and a positive BaCl2 test for sulfate. The adsorption of SPO33− on Au is concluded to be consistent with the Langmuir isotherm to a coverage of θ = ca. 0.9, which is achieved for 0.6 mM Na3SPO3.
Enzyme electrode‐based differential potentiometric cell with enhanced substrate sensitivity
Authors: Cha Geun Sig , Meyerhoff Mark E. 
Published: February 2006

AbstractA novel approach for enhancing the substrate sensitivity of ion‐selective electrode‐based enzyme probes is described. The concept involves the use of two working enzyme electrodes in a differential potentiometric cell arrangement. One of the enzyme probes is prepared by immobilizing a suitable enzyme or enzymes at the surface of a cation‐selective electrode, while the second working electrode contains the same or different enzymes immobilized on an appropriate anion‐selective electrode. Enzymatic substrate conversion at the surface of each electrode yields a detectable cation and anion, respectively. Since each sensor selectively responds to the same substrate, but in opposite directions, the potential difference between the two working enzyme electrodes is greater than that obtained when each enzyme probe is measured alone versus a standard reference electrode. As examples, differential cells for measuring urea and arginine are reported in which urease or urease plus arginase is immobilized on the surfaces of ammonium‐ and carbonate‐selective electrodes prepared with asymmetric cellulose acetate membranes.
Simultaneous measurements of trace metals by adsorptive stripping voltammetry
Authors: Wang Joseph , Mahmoud Jawad , Zadeii Javad 
Published: February 2006

AbstractSimultaneous measurements of trace metals, based on adsorptive stripping voltammetry of their chelates with dihydroxyazo dyes, are demonstrated. Variables affecting the resolution between neighboring chelate peaks, including the ligand and its concentration, pH, adsorption time and potential, concentration ratio, and scan rate, are assessed. Adequate resolution is demonstrated for more than 10 pairs of metals, present at the ppb level. Possible changes in peak heights, associated with competition for the complexing ligand and/or coadsorption effects, are explored. Different concentration ratios of the mixture components can be tolerated. Applicability to seawater analysis is illustrated.
An ultraviolet‐cured, pH‐sensitive membrane electrode for use in flow injection analysis
Authors: del Mundo Florian R. , Cardwell Terence J. , Cattrall Robert W. , Iles Peter J. , Hamilton Ian C. 
Published: February 2006

AbstractThe preparation of an epoxyacrylate, UV‐cured polymer membrane electrode for determining pH is described. This is based on the neutral carrier, tridodecylamine, and shows Nernstian behavior from pH 5 to 10. Interferences from cations in this range are negligible. The response of the electrode is very fast, reaching more than 90% of the equilibrium value in less than 1 second, which makes it very suitable for use in flow injection analysis (FIA). The application of the electrode to the determination of pH in flow injection analysis using a miniature flow cell is described, and the influence of the buffer capacity and pH of the carrier on the accuracy of the pH measurement is discussed. The FIA system has been applied to the determination of the acidity of some soil samples.
Electrode reactions of 3,4‐dihydroxyphenylacetic acid (DOPAC) at glassy carbon, graphite‐reinforcement carbon, and carbon fiber electrodes
Authors: Sujaritvanichpong Surasak , Aoki Koichi 
Published: February 2006

AbstractThe voltammetric behavior of 3,4‐dihydroxyphenylacetic acid (DOPAC) in a phosphate buffer solution (pH 7.4) was investigated at untreated and electrochemically treated glassy carbon (GC), graphite reinforcement carbon (GRC), and carbon fiber (CF) electrodes. Except for the pretreated GRC, all of the electrodes exhibit a well‐defined anodic wave (Aa) at approximately 0.25–0.5 V vs. SCE. The untreated and the pretreated GC electrodes yielded irreproducible behavior compared to the GRC electrode. Transfer coefficients and the charge transfer rate constant were evaluated from variations of the peak potential with the potential sweep rate. The peak current was controlled by both diffusion and the sluggish charge transfer process. Similar results were obtained at weakly pretreated CF electrodes. As the level of the pretreatment for the CF electrode was raised up by applying more anodic potential, wave Aa decreased and new anodic and cathodic waves, B and C, appeared at 0.1 and 0.27 V, respectively, versus SCE. Wave B was ascribed to the adsorption of DOPAC. Amounts of the adsorbed species increased with the time the electrode was immersed in the solution and then tended to the steady‐state value. They were subjected to the Langmuir adsorption isotherm. A value of the saturated adsorption was 0.89 × 10−9 mol/cm2 and the adsorption coefficient was 1.63/mmol/dm3.
Pretreatment of glassy carbon electrodes by anodic galvanostatic pulses with a large amplitude
Authors: Mattusch Jürgen , Hallmeier Karl‐Heinz , Štulík Karel , Pacáková Věra 
Published: February 2006

AbstractGlassy carbon electrodes (GCEs) can be activated by the passage of large‐amplitude (for example, 20‐mA) anodic galvanostatic pulses with durations shorter than 1 second. The increased activity stems from an increase in the rate of charge‐transfer reactions and from the adsorption accumulation of the analytes on the electrode surface, which is demonstrated for catecholamines and ascorbic acid. As demonstrated by X‐ray photoelectron and fast‐atom‐bombardment mass spectrometry, the galvanostatic treatment leads to an increase in the amount of chemisorbed oxygen. Scanning electron microscopy shows very small mechanical changes of the electrode surface. The activation effect depends on the composition of the test solution and the character of the analytes. There is an optimal electric charge that produces the highest electrode activity and lowers the limits of determination for catecholamines by approximately two orders of magnitude; on further increase in the charge, the electrode activity decreases (due to the formation of a thick layer of graphite oxide). The activation effects are less pronounced in flow‐through measurements. The method can be readily implemented for the periodic, automated reactivation of glassy carbon electrodes, but the optimal conditions must be found experimentally for various systems.
Application of second harmonic alternating current anodic stripping voltammetry in the simultaneous trace and ultra trace metal determination of a multicomponent system
Authors: Fagioli Francesco , Locatelli Clinio , Landi Silvio , Vecchietti Roberto 
Published: February 2006

AbstractSecond harmonic alternating current voltammetry coupled with anodic stripping techniques has been used for the simultaneous determination of lead(II), tin(II), and thallium(I) (elements which, in common supporting electrolytes exhibit similar half‐wave potentials). The supporting electrolyte was 0.1 M HClO4 for the Pb‐Tl couple with the subsequent addition of EDTA (0.02 M) for measuring the tin ion. Once conditions for the experimental measurements were optimized, calculation was done for the various concentration ratios for which one could determine one element in the presence of the other two; the maximum experimental error was 5%. These concentration (c) ratios were as follows: CSn : CPb = 43:1; CSn : CTl = 32:1 (HClO40.1 M)and CTl:CSn = 45:1; Ctl:CPb = 156:1 (HClO4 0.1 M plus EDTA 0.02 M). Precision and accuracy data (3–5%) are also reported and expressed, respectively, as the relative standard deviation and relative error. The detection limit for each element proved to be around 10−8 M. The standard addition technique improved the resolution of the alteranting current voltammetric method, even in the case of very high concentration ratios.
Mn(III)—porphyrin‐based thiocyanate‐selective membrane electrodes: Characterization and application in flow injection determination of thiocyanate in saliva
Authors: Brown D. V. , Chaniotakis N. A. , Lee I. H. , Ma S. C. , Park S. B. , Meyerhoff M. E. , Nick R. J. , Groves J. T. 
Published: February 2006

AbstractThe response properties of a new thiocyanate‐selective solvent‐polymeric membrane electrode are reported. The membrane contains (5,10,15,20‐tetrakis(2,4,6‐triphenylphenyl)porphyrinato)manganese(III) chloride (Mn[TPPP]CI) in a plasticized polyvinyl chloride matrix. The electrode deviates from the Hofmeister selectivity pattern by responding to thiocyanate preferentially over inorganic anions (perchlorate, chloride, iodide, and bromide) and several organic anions often present in biological samples (ascorbate, citrate, urate, and salicylate). The performance of this electrode as an ion‐selective detector in a low‐dispersion, flow‐injection system is also evaluated. While selectivity in such a nonequilibrium flow arrangement is found to be somewhat different than that observed under equilibrium conditions, the electrode's response and selectivity is still adequate to allow for measurement of thiocyanate in biological samples. This application is demonstrated via the flow‐injection analysis (FIA) detection of thiocyanate in 22 human saliva samples with good correlation to a classical colorimetric method (r = 0.981).
Electrochemical speciation analysis of metals at membrane‐coated electrodes
Authors: Morrison Gregory M. P. , Florence T. Mark 
Published: February 2006

AbstractSpeciation 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%).
Electrocatalysis and determination of hydrazine compounds at glassy carbon electrodes coated with mixed‐valent ruthenium(III, II) cyanide films
Authors: Wang Joseph , Lu Ziling 
Published: February 2006

AbstractChemically modified electrodes, which were constructed by anodizing glassy carbon electrodes in a RuCl3/K4Ru(CN)6 solution, are shown to catalyze the electrooxidation of hydrazine compounds in acidic and neutral media. The mixed‐valent ruthenium cyanide film offers improved stability and a broader operational pH range compared to previously described phthalocyanine‐catalytic surfaces. The catalytic response of hydrazine, methylhydrazine, and dimethylhydrazine is evaluated with respect to the film preparation conditions, solution pH, potential scan rate, concentration dependence, and other variables. Highly stable and sensitive flow injection measurements [with a relative standard deviation (RSD) of 1.4% (n = 30) and a detection limit of 0.13 ng] are described. A composite film prepared by the codeposition of polyaniline offers additional advantages.
Cyclic voltammetry of metal/polyelectrolyte complexes: Complexes of cadmium and lead with deoxyribonucleic acid
Authors: Séquaris J.‐M. , Esteban M. 
Published: February 2006

AbstractCyclic voltammetry was used for the determination of the association constants of Pb2+and Cd2+with deoxyribonucleic acid. The adsorption of the biological polyelectrolyte at the mercury electrode surface was controlled by the alternating current voltammetric method, which permits corrective factors to be introduced in the evaluation of cyclic voltammetric responses. The results are based on the analysis of the labile complexation of the slow‐diffusing DNA by studying the current intensity peak as well as the peak potential shift of Pb2+and Cd2+. The association constants (β) obtained from the two treatments are in satisfactory agreement. The dependence of the conditional association constant (β1) for the Cd‐DNA system on the monovalent ion (Na+) concentration is also reported.
Electrochemical investigations of thiocinnamide
Authors: Bǎnicǎ F. G. , Florea M. , Diacu Elena 
Published: February 2006

AbstractThe electrochemical behavior of thiocinnamamide in aqueous solutions with 5% (v/v) ethanol was studied by dc and ac polarography and cyclic voltammetry. In acidic media, the reduction of thiocinna mamide occurs in the adsorbed state, giving a single dc wave. In alkaline solutions, the reduction starts at the negative limit of the adsorption potential range and produces two poorly separated dc waves. The first corresponds to the reduction of the adsorbed molecules with a strong dependence of the adsorption coefficient on the electrode potential. The second is due to the irreversible reduction of nonadsorbed molecules. This reaction involves a slow chemical step. The reduction results in the fission of the carbon‐sulfur bond. Another reaction is the hydrolysis of adsorbed molecules (in the absence of any charge‐transfer step), giving the nitrile of cinnamic acid. This compound is also formed in the range of the anodic wave of thiocinnamamide.
Enhanced voltammetric waves of iron(III)—EDTA at a chitin‐containing carbon paste electrode and its analytical application
Authors: Bai Zhu‐Ping , Nakamura Toshio , Izutsu Kosuke 
Published: February 2006

AbstractA chitin‐containing carbon paste electrode was found to give highly sensitive voltammetric waves for Fe(III)‐EDTA chelate both in cyclic voltammetry (CV) and in differential pulse voltammetry (DPV). Various conditions for the determination of trace Fe(III) were studied. The optimum chitin content in the carbon paste (graphite powder: mineral oil = 2:1) was 6% (by weight). In a solution of 0.01 M KCl and 3 × 10−4 M EDTA (pH 3.0), the DPV peak potential for the reduction of Fe(III)‐EDTA was −0.05 V vs. Ag/AgCl. The peak current was proportional to the Fe(III) concentration between 2 × 10−7 and 6.5 × 10−6 M; the relative standard deviation for 2 × 10−6 M Fe(III) was 2.6%. The method was fairly free from interference and could be applied to the determination of iron in both river and tap water.
Photomicroscopic measurement of the diffusion layer around mercury drop electrodes: Part II, choice of the optimal conditions
Authors: Tercier M.‐L , Buffle J. 
Published: February 2006

AbstractThe special electrochemical system described in Part I was employed to determine the optimum conditions for the deposition step of anodic stripping voltammetric techniques with a sessile Hg drop electrode. Much care was taken to obtain a reproducible reduction flux that is predictable on sound theoretical grounds and, in particular, to minimize the screening effects of the capillary. This article illustrates how this can be achieved by coupling optical microscopy, photography, and video recording with computer‐controlled voltammetry. This set up allows to simultaneously observe the dynamic movement of the water flux around a Hg drop electrode, observe and determine the diffusion layer thickness during the reduction, and record the chronopotentiometric current‐time curves as a function of the stirring rate and geometric conditions of the cell. The best conditions for obtaining a reproducible reduction flux at the electrode are given for a sessile Hg drop. The system described here, however, can be applied for the determination of diffusion and hydrodynamic conditions around electrodes having other configurations.
Single‐sweep polarographic determination of ammonia by its reaction with 1‐naphthol and hypochlorite
Authors: Zhao Zaofan , Mo Jianwei 
Published: February 2006

AbstractA polarographic procedure is described for the determination of ammonia at concentration levels below 10−4 M that is based on its reaction with 1‐naphthol and hypochlorite in a strongly alkaline medium whose (1,4‐indonapthol) product is polarographically active. The polarographic behavior of the compound and the electrode process has been studied by several electrochemical methods. The experimental results showed that it is an EC process involving the formation of a radical as the electrode product that is followed by a disproportionation reaction of the radical. The rate constant (kf) of the coupled following chemical reaction was found to be 0.228 s−1. The wave height at −0.47 V [versus the standard calomel electrode (SCE)] on the dropping mercury electrode (DME) is directly proportional to the concentration of ammonia from 1 × 10−7 to 5 ×−5 M, and the detection limit is 5 × 10−8 M. A mercury film electrode can also be used for the determination of ammonia. The method has been applied to the analysis of water and serum samples.
Theory of stationary current—potential curves at interdigitated microarray electrodes for quasi‐reversible and totally irreversible electrode reactions
Authors: Aoki Koichi 
Published: February 2006

AbstractAnalytical equations for steady‐state current‐potential curves at interdigitated microarray electrodes (IDA) were derived by the conformal mapping of the complex variable theory when the electrode reaction was quasi‐reversible and totally irreversible. In this technique, curved current lines in the IDA could be transformed into a set of parallel lines, as in a thin‐layer cell at a faced twin electrode. The current‐potential curves were a function of ko(we + wg)/D and were almost independent of the geometrical parameter, wg/(we + wg), where ko is the reaction rate constant, we is the common width of each microband anode or cathode, wg is the width of the gap between the anode and the cathode, and D is the diffusion coefficient. The quasi‐reversible domain was 0.2 < ko(we + wg)/D < 10. A polaro‐graphic log plot for the current‐potential curve did not fall on a straight line except for the reversible wave. A modified log‐plot method is presented in which the current‐potential curve can be transformed into a straight line. The transfer coefficient and ko can be evaluated from this technique.
An experimental study of phase‐sensitive ac voltammetry in continuous‐flow streams—reversible systems
Authors: Kingsley Edward D. , Curran David J. 
Published: February 2006

AbstractFundamental harmonic ac voltammetry at flow‐by wall electrodes was found experimentally to be independent of the flow rate for rates from 0 to 2.1 L/min. Measurements were made with phase‐sensitive instrumentation. The ac peak current dependence on the concentration, the frequency and amplitude of the applied ac voltage, and the dc scan rate was the same in flowing or stationary solutions. The shape of the ac voltammogram was also not influenced by the flow rate. These results are general for experimental conditions that produce unrestricted diffusion and that maintain simple, reversible electron‐transfer mechanisms.
HPLC separation and square‐wave adsorptive‐stripping detection of human immunoglobulin G and A
Authors: Zhang Li Qun , Sturrock Peter E. 
Published: February 2006

AbstractHuman immunoglobulin G and A (IgG and IgA) were studied with square‐wave voltammetry. For IgG, three reduction peaks (HIGG1, HIGG2, and HIGG3) were observed under different conditions. HIGG1 and HIGG3 are strongly related to the pH of the buffer solution. In pH 7.5 phosphate buffer, the peak potential of HIGG2 is −0.58 V (vs. Ag/AgCl). A linear response holds for human IgG below 3.3 × 10−8 M (5 ppm). As little as 1.1 × 10−10 M (16 ppb) of human IgG is detectable after only 20 seconds of adsorptive accumulation in static solution.IgA has two flat adsorptive‐stripping responses (HIGA1 and HIGA2). The sensitivity of IgA is much poorer compared to IgG. HIGA2 at −0.44 V can be observed throughout the tested pH range with the maximum response between pH 6.0–6.2. In a static solution, a linear calibration graph can be obtained for 0.8–16.8 ppm IgA.IgG and IgA can be separated from each other by using HPLC with an AB × column. The response of 32 ppb IgG can be observed clearly. This research indicates the possibility of direct separation and detection of immunoglobulins from a real sample (e.g., human serum) by simply applying HPLC‐adsorptive‐stripping analysis.
Mechanism of electrochemical oxidation of trimethoprim at pyrolytic graphite electrode
Authors: Goyal R. N. , Kumar Anoop 
Published: February 2006

AbstractThe electrochemical oxidation behavior of trimethoprim has been investigated at a pyrolytic graphite electrode over a wide pH range (1.35–10.71). Below pH 3.2, trimethoprim is electrooxidized in two well‐defined steps, each involving 4e, 4H+. Only one well‐defined oxidation peak was observed above pH 3.5 however. Products corresponding to each peak have been separated and characterized by thin‐layer chromatography (TLC), infra red (IR), and mass spectra. A tentative mechanism associated with the voltammetric oxidation has been proposed to account for the observed experimental behavior. The same product has also been observed during the metabolic oxidation of trimethoprim in albino rats.