bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electroanalytical study of succinylsulfathiazole and phtalylsulfathiazole at a glassy carbon electrode
Authors: Carrazon J. M. Pingarron , Recio A. Dominguez , Diez L. M. Polo 
Published: February 2006

AbstractAn electroanalytical study of succinylsulfathiazole and phtalylsulfathiazole oxidation processes at a glassy carbon electrode using different voltammetric techniques was carried out. Results obtained at a rotating disk electrode allow the determination of the pKa values of the reduced and oxidized forms. Limiting currents are diffusion controlled in concentration ranges of 1.0 × 10−5 to 5.0 × 10−5 and 2.0 × 10−5 to 6.0 × 10−5 mol L−1 for Succinylsulfathiazole and phtalylsulfathiazole, respectively. Adsorption phenomena occur at higher concentrations, becoming stronger as the acidity of the medium increases. From differential pulse voltammetry at a stationary electrode, the limits of determination were 3.7 × 10−6 and 4.7 × 10−6 mol L−1 for succinylsulfathiazole and phtalylsulfathiazole, respectively. Interferences between the two sulfa drugs were studied. The application of differential pulse voltammetry at a stationary electrode gave good results for the determination of phtalylsulfathiazole in a commercial pharmaceutical preparation.
Simultaneous electrochemical and EPR studies of flavin radical equilibria
Authors: Male Roxanne , Samotowka Michael A. , Allendoerfer Robert D. 
Published: February 2006

AbstractThe comproportionation reaction of the oxidized and reduced forms of both riboflavin and lumiflavin to form their respective radicals is studied over a range of pHs in aqueous solution and in the aprotic solvent methylene chloride. The comproportionation equilibrium constant is reported for basic solutions reduced at an amalgamated Au electrode, where adsorption does not interfere with equilibrium measurements, with both Na+ and Ca2+ as the counterion. The basic and nonaqueous solution voltammetries of riboflavin and lumiflavin are shown to be similar by measuring the radical concentration by electron paramagnetic resonance (EPR) during an in situ electrolysis as a function of potential. In both solvent systems the first of the two reduction waves corresponds to a two‐electron reduction with the radical present formed by comproportionation.
The enhancement effect of surfactants in single‐sweep polarography of the palladium‐dimethylglyoxime complex
Authors: Zhao Zaofan , Gao Zhiqiang 
Published: February 2006

AbstractA rapid, sensitive, selective single‐sweep polarographic method for the determination of palladium based on the reduction of palladium(II) in the Pd(II)‐dimethylglyoxime (DMG) complex is described. In weakly acidic media, Pd(II) reacts with DMG and forms a yellow precipitate. After adding a low concentration of the anionic surfactant SDBS (sodium dodecylbenzenesulfonate), the solubility of the complex increases remarkably, and the sensitivity of the determination increases more than fivefold. The solution is stable for at least 3 hours. The complex is strongly adsorbed on the surface of the mercury electrode. The enhancement effect of the surfactant is ascribed to the “synergistic adsorption” of the complex and the surfactant. The current is caused by the reduction of palladium in the complex at −0.45 V (versus SCE). The method can be used to determine trace amounts of palladium over the range of 4 × 10−8 to 4 × 10−6. Assays of palladium catalysts and waste water samples are illustrated.
Liquid chromatography and electrochemical detection of alditols and acidic sugars at a cobalt phthalocyanine‐containing chemically modified electrode
Authors: Tolbert Andre M. , Baldwin Richard P. 
Published: February 2006

AbstractChemically modified carbon paste electrodes containing incorporated cobalt phthalocyanine (CoPC) were shown to exhibit an electrocatalytic response for the oxidation of carbohydrate derivatives from the alditol and aldonic, uronic, and aldaric acid families. The electrocatalysis, which is similar to that previously seen for simple carbohydrates, resulted in the electrolysis of these compounds between +0.4 and +0.6 V vs. Ag/AgCl where Co(II)PC is oxidized to Co(III)PC. The response was greatest for the alditols and decreased from the aldonic to the aldaric acids. When used to quantify these compounds following anion exchange chromatography, detection limits at +0.42 V ranged from 10 pmol for the alditols to the nanomole level for some of the aldaric acids.
Amperometric determination of lactose in human and cow's milk using a flow‐injection system with some immobilized enzyme reactors
Authors: Yao Toshio , Akasaka Reina , Wasa Tamotsu 
Published: February 2006

AbstractA bioelectrochemical flow‐injection system is proposed for the determination of lactose in milk from humans and cows. The system includes an amperometric flow‐through platinum electrode to measure hydrogen peroxide, which was enzymatically generated by injecting a 10‐μL sample into the packed‐bed reactors of immobilized β‐galactosidase and glucose oxidase that are incorporated in series in the flow line. Because the presence of glucose interfered with the measurement of lactose, a precolumn packed with coimmobilized glucose oxidase and catalase was positioned just before the two immobilized enzyme reactors to remove the glucose from the milk. The peak current was linearly related to the lactose concentration between 0.01 and 2.0 mM. The determinations of lactose in milk could be performed at a rate of 60 samples/h with satisfactory precision (less than 0.8% RSD) and no pretreatment except for the sample dilution.
Mediated enzyme/wall‐jet amperometric electrode in flow‐injection monitoring of glucose
Authors: Gunasingham Hari , Tan Chin‐Huat 
Published: February 2006

AbstractTetrathiafulvalene serves as a useful mediator for glucose oxidase in its application in second‐generation enzyme electrodes for monitoring glucose. Among its useful characteristics are a low redox potential, fast homogeneous electron exchange kinetics with glucose oxidase, high stability, and low solubility in aqueous solutions. The fabrication and characterization of tetrathiafulvalene‐glucose oxidase enzyme electrodes in flow‐injected and stopped‐flow analysis is described. One of the conclusions is that the homogeneous rate constant for tetrathiafulvalene is higher than that of dimethyl ferrocene. Tetrathiafulvalene is, however, more susceptible to pH variations. The characteristics and advantages of the mediated enzyme/wall‐jet amperometric detection are described.
Optimization of parameters for differential pulse voltammetry at the hanging mercury drop electrode
Authors: Pelzer Jürgen , Scholz Fritz , Henrion Günter , Nitschke Lutz 
Published: February 2006

AbstractThe detection limit of differential pulse voltammetry at a hanging mercury drop electrode is investigated. The most important result of this study is that very small pulse amplitudes considerably improve the signal‐to‐background ratio and lead to lower detection limits. Due to the fact that (in practice) the background current does not originate only from capacitive properties of the electrode, an optimal pulse duration also exists, which guarantees the highest signal‐to‐background ratio. It is shown that the background current consists of the capacitive current and a very noisy but, on average, constant component, presumably of a faradaic nature that originates from impurities. The effects of the prepulse time, the pulse amplitude, the pulse duration, the step height of the staircase ramp, and the duration of the current sampling time on the signal and background intensity and noise are described.
Ion transfer of barium and strontium across the liquid‐liquid interface facilitated by polyethylene glycol 400
Authors: Sun Zhisheng , Wang Erkang 
Published: February 2006

AbstractA mechanism of metal ion transfer for Ba2+ and Sr2+ at the liquid‐liquid interface, facilitated by polyethylene glycol 400 and based on complexation in aqueous and organic phases, is proposed. The interfacial half‐wave potential equations are deduced in terms both of the mechanism proposed and of the equilibria of distribution and dissociation in two phases and are verified experimentally. The effect of the polyoxyethylene structure on the selectivity of the facilitated transfer is discussed, and a useful way of improving the selectivity by selecting neutral carriers for practical analysis is suggested.
Preconcentration and determination of promethazine at lipid‐modified carbon paste electrodes
Authors: Khodari Mahmoud , Kauffmann Jean‐Michel , Patriarche Gaston J. , Ghandour Mahmoud A. 
Published: February 2006

AbstractLipid‐modified carbon paste electrodes were electrochemically characterized and their potential for drug analysis was compared with conventional carbon paste electrodes. The presence of lipids (phospholipids, fatty acids) in the paste matrix provided enhanced current responses with improved reproducibility. With 5 minutes of accumulation, phenothiazines exhibit a 40‐fold enhancement of the response compared to that obtained without accumulation. As a result, a detection limit of 1 × 10−9 M was attained. The response was characterized with respect to pH, preconcentration potential, accumulation time, paste composition, possible interferences, and other variables. The determination of the tranquilizer in serum and urine required no preliminary treatment other than dilution with phosphate buffer and medium exchange. Detection limits are 5 × 10−8 M in urine and 2 × 10−7 M in serum.
Electrochemical oxidation of dacarbazine and its major metabolite (AIC) on carbon electrodes
Authors: Rodriguez José R. Barreíra , Garcia Agustin Costa , Ordieres Arturo J. Miranda , Blanco Paulino Tuñón 
Published: February 2006

AbstractThe electrochemical behavior of the antitumor agent dacarbazine (DTIC) and its major metabolite, 5‐aminoimidazole‐4‐carboxamide (AIC), on carbon paste electrodes has been studied. Linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV) have been applied, showing that both molecules are active in oxidation. Both compounds are oxidized in a two‐electron process, presenting a charge transfer coefficients (β) of 0.44 ± 0.03 and 0.48 ± 0.03 for DTIC and AIC, respectively, which indicate slow processes. The oxidation mechanisms proposed for each of these compounds seem to yield the same final product, the 5‐hydroxyimidazol‐4‐carboxamide. DPV proved to be a valuable analytical technique that is suitable for distinguishing and analyzing both compounds when the most adequate medium (0.1 M HCIO4) and operating conditions are chosen.
UV‐visible and ESR spectroelectrochemical study of xylenol orange
Authors: Dong Shaojun , Song Shihua 
Published: February 2006

AbstractThe proposed first step in the electroreduction of xylenol orange (XO), a reversible electrode process coupled with a chemical reaction, is based on ultraviolet (UV)‐visible spectroelectrochemistry. Electrochemical excitation‐electron spin resonance (ESR) in situ measurements are used to observe the radical signal produced by the first step reduction of XO. The ESR spectra of the radical in solution at pH 4.0, 4.5, and 5.0 have the same characteristics: no observed hyperfine structure, a line width of 10.5 G, and a g value of 2.0034. The structure of the XO radical and its disproportionation reaction are elucidated.
The importance of adsorption in anodic surface‐catalyzed oxygen‐transfer reactions at gold electrodes
Authors: Vitt Joseph E. , Larew Larry A. , Johnson Dennis C. 
Published: February 2006

AbstractA large number of anodic oxygen‐transfer reactions were studied at Au electrodes in both acidic and alkaline media. Results of competitive adsorption studies are interpreted and support the conclusion that adsorption is a prerequisite to subsequent oxygen‐ and electron‐transfer steps. Many of these oxidation reactions gave the voltammetric appearance of reversible waves, even though the observed half‐wave potential values were shifted hundreds of millivolts positive of the thermodynamic potentials. A catalytic mechanism is proposed in which adsorbed hydroxyl radicals (AuOH) participate in the oxygen‐transfer step. The absence of pH effects on half‐wave potentials for several inorganic compounds suggests that the electron transfer precedes the deprotonation step for these reactants.
Linear sweep polarographic studies of trace gold in an N‐allyl‐N′‐(sodium‐p‐phenylsulphonate)thiourea medium
Authors: Zhao Zaofan , Jiang Mian , Liu Qing 
Published: February 2006

AbstractUsing linear sweep polarography (LSP) in an acidic solution (pH 2.8) containing Au(III) ions and N‐allyl‐N′‐(sodium‐p‐phenylsufonate)thiourea (NTu), the product of the reaction between Au(III) and NTu (NDF) is reducible at the mercury electrode with two waves at about −0.40 and −0.95 V [versus the saturated calomel electrode (SCE)]. In the presence of excess chloride, the potential of the first wave shifts positively to −0.35 V. This forms the basis of a highly selective and sensitive method for gold. The linear range for gold is from 1 × 10−7 to 3 × 10−M, and the detection limit is 5 × 10−8 M (9 ppb). This method has been used for the determination of gold in ore samples, and the results agree well with values obtained by accepted procedures. Various electrochemical techniques were used to study the mechanism of the redox process. The reaction mainly involves the formation of C,C′‐di‐N‐allyl‐N′‐ (sodium‐p‐phenysulfonate)dithiodiformamidine (NDF). Unlike some explanations reported in the literature about the reduction of formamidine derivatives (containing an SS bond) on an Hg electuode, the electrode process for the first wave (−0.40 V) is ascribed to the reduction of the HgS film, which is caused by the reaction of Hg with adsorbed NDF. In the presence of excess Cl‐ ions, the mixed precipitation film of HgS·xHg2Cl2 may be formed on the electrode surface and make the first wave shift to −0.35 V. The second wave (−0.95 V) is caused by the irreversible reduction of NDF.
Photomicroscopic measurement of the diffusion layer around mercury drop electrodes: Part I, description of the electrochemical system
Authors: Tercier M.‐L. , Bernard C. , Bujard F. , Rodak S. , Buffle J. 
Published: February 2006

AbstractA special electrochemical system has been developed to determine the optimum conditions for the stirred deposition step of anodic stripping voltammetric techniques with the sessile mercury drop electrode (SMDE) in order to get a reproducible flux that is predictable on sound theoretical grounds. The sessile Hg drop is formed at the upper part of a vertical capillary, which is placed coaxially below a rotating disc electrode that serves as both an auxilliary electrode and a stirrer. This system permits the visualization of the hydrodynamic flux, diffusion layer, and screening effects of the capillary around the mercury drop.
New bromide‐selective membrane electrodes based on a methyl methacrylate matrix and their use in drug analysis
Authors: Pastor Tibor J. , Pastor Milka M. , Kalajdžievski Krume 
Published: February 2006

AbstractA new, simple procedure for the preparation of methyl methacrylate‐based bromide ion‐selective membrane electrodes with an internal solid contact is described. The stability, response range, and slope as well as the selectivity and interference‐free pH range of these electrodes were found to be satisfactory. The electrodes were applied to the determination of low bromine levels in biologically active substances with direct potentiometry and potentiometric titration after their combustion in an oxygen atmosphere. The results obtained are accurate and reproducible.
Brucine, part 1: Electrochemistry of brucine
Authors: Nyasulu Frazier W. 
Published: February 2006

AbstractCyclic voltammetry and chronocoulometry were used to study the electrochemistry of brucine. The oxidation of brucine 0.9 V versus a saturated calomel electrode at a carbon paste electrode produces a compound that undergoes reversible electrochemical behavior at Eo′ = 0.47 V. The product formed on the oxidation of brucine undergoes a slow chemical reaction to produce a compound that shows reversible behavior at Eo′ = 0.27 V. The hexadecane content of the carbon paste plays an important role in the observed behavior. Electrodes with low hexadecane did show oxidation of brucine, but irreversible waves occurred at Eo′ = 0.47 and 0.27 V. These features were also displayed by a platinum electrode. Calcium oxalate incorporated into the carbon paste catalyzes the oxidation of brucine. Chronocoulometry was used to estimate the heterogenous rate constant for the oxidation of brucine at calcium oxalate‐modified and unmodified electrodes. The values found were 21.4 × 10−3 cm/s for the modified electrode and 6.1 × 10−3 cm/s for the unmodified electrode. Preliminary results on the use of brucine as a reagent for the determination of nitrate are given.
Amperometric determination of carbon dioxide using a gold electrode modified by the underpotential‐deposited cadmium
Authors: Shao Mei‐Jun , Xing Xue‐Kun , Liu Chung‐Chiun 
Published: February 2006

AbstractAn underpotential‐deposited cadmium layer formed on a gold electrode was used to amperometrically determine PCO2 in an aqueous medium. This electrode reduces nitrate anions in an aqueous solution. The reduction current produced can be related to the proton concentration. Thus, when dissolved CO2 is present in a nitrate solution it alters the proton concentration, which can then be measured amperometrically. Experimental investigation of this system and a Nafion coated gold electrode were both carried out. The effect of oxygen present in the system is also discussed.
Chemically modified carbon paste electrodes in voltammetric analysis
Authors: Kalcher Kurt 
Published: February 2006

AbstractA review of chemically modified carbon paste electrodes (CMCPEs) and their use in voltammetric analysis is presented. The different methods of modification as well as the types of interaction between substrate and modifier are discussed. In addition to a survey of the literature (173 references), the scope of and prospects in this field of electroanalysis are discussed briefly.
Dynamic response characteristics of an impinging‐jet amperometric detector
Authors: Powell Francis E. , Fogg Arnold G. 
Published: February 2006

AbstractA dynamic response experiment at an impinging‐jet detector indicated that laminar flow in the straight delivery tube was modified by mixing stages in the electrode channel and its connections. The response obtained, resulting from this final dispersion, defines an effective detection volume of 7 μL. In a practical flow injection line made from a number of connectors, coils, and so on, this small volume ensured that the detector described here, which incorporated a well‐activated glassy carbon electrode, would not be expected to contribute significantly to the overall dispersion.
Determination of the pesticide guthion by flow‐injection analysis with amperometric detection
Authors: Méndez J. Hernández , Martínez R. Carabias , Gonzalo E. Rodríguez , Trancon J. Pérez 
Published: February 2006

AbstractGuthion, a pesticide, was determined by flow‐injection analysis using single‐ and three‐channel systems with and without a chemical reaction. The experimental variables involved in each case were investigated and optimized, and the analytical features of the two procedures were compared. A method based on the oxidation of anthranilic acid yielded in the alkaline hydrolysis of the pesticide at a glassy carbon electrode is proposed for its determination. The detection limit is 4.1 × 10−7 M, and the relative standard deviation is 2.2% (n = 10) when the hydrolysis reaction takes place within the threeenamel manifold.
Electroanalytical study of pirimicarb by anodic voltammetry at a glassy carbon electrode in aqueous and acetonitrile media
Authors: Pingarrón José M. , González Araceli , Polo Luis M. 
Published: February 2006

AbstractAn electroanalytical study of the oxidation process of pirimicarb at a glassy carbon electrode using different voltammetric techniques was carried out. Two media were used: aqueous Britton‐Robinson buffer and acetonitrile (0.1 mol L−1 Bu4NClO4). Studies using linear sweep voltammetry (LSV) at a rotating disk electrode show that the limiting current becomes nondiffusion controlled at concentrations higher than 6.0 × 10−5 mol L−1. Cyclic voltammetry showed an irreversible electrode process. The best detection and determination limits were obtained by differential pulse voltammetry at a stationary electrode in an acetonitrile medium. The differential pulse mode in an aqueous medium was used to determine pirimicab in soil samples.
Composite electrodes for electroanalysis: Principles and applications
Authors: Tallman Dennis E. , Petersen Steven L. 
Published: February 2006

AbstractA composite electrode has a surface that consists of an ordered arrangement (array) or a random arrangement (ensemble) of conductor regions, typically micrometers in dimension, separated from one another by an insulator. These active regions (or microelectrodes) may themselves be of regular geometry and confined primarily to the surface, as with most array electrodes, or of irregular geometry and permeate the bulk of the material, as with most ensemble electrodes. In this review, we classify composite electrodes according to the distribution of a conductor and insulator within the material (or on the surface), survey a number of the fabrication schemes used to construct composite electrodes, discuss percolation theory as it applies to certain composite electrodes, examine the surface morphology of selected composite materials, discuss the origins of the enhancement in current density observed at many composite electrodes in both quiescent and flowing solutions, and provide a few examples illustrating the applications of composite electrodes to real analytical problems.
Pineapple‐tissue based bioelectrode for the determination of hydrogen peroxide
Authors: Lin Meng Shan , Tham Sock Ying , Rechnitz Garry A. 
Published: February 2006

AbstractA flow‐injection analysis (FIA) system for the determination of hydrogen peroxide was developed by utilizing a pineapple‐tissue‐based modified carbon paste electrode. Pineapple stem core tissue contains peroxidase, which is not available commercially in the pure isolated form. Hydrogen peroxide concentrations were determined in the presence of O‐phenylenediamine as a hydrogen donor at a potential of −200 mV. The detection limit (S/N = 3) for hydrogen peroxide using this tissue electrode is 2.1 μM with a relative standard deviation of 0.44% (n = 12). The tissue‐modified carbon paste electrode is stable for up to 20 days with no significant activity changes.
Amperometric amino acid electrodes
Authors: Pfeiffer Dorothea , Wollenberger Ulla , Makower Alexander , Scheller Frieder , Risinger Lars , Johansson Gillis 
Published: February 2006

AbstractSubstrate specificity, the linear measurement range, and the lifetime of monoenzyme electrodes were determined using L‐glutamate oxidase, L‐lysine oxidase, and tyrosinase immobilized in gelatin. These sensors were applied to the analysis of protein hydrolyzates. By coimmobilizing the three enzymes, an electrode responding to a group of amino acids was obtained. Its analytical performance was compared with that of an L‐amino acid oxidase sensor. The net charge of the immobilization matrix influenced the relative sensitivities of the amino acids.
Determination of the catalytic reaction rate constant of the ferrocyanide—aniline system using spectroelectrochemistry
Authors: Dong Shaojun , Xie Yuanwu 
Published: February 2006

AbstractThis work develops the theoretical equations for a single potential step—open circuit relaxation chronoabsorptometry for use in cases when the other species also displays absorption at the wavelength being observed for oxidation. A data analysis method is proposed to determine the rate constant of the catalytic reaction. The rate constants of ferrocyanide—aniline and ferrocyanide—antipyrine systems are determined by an optically transparent spectroelectrochemical method. The result coincides with the value determined by the electrochemical method.