bluuebunny/crossref_metadata_2025 huggingface dataset:
Microband electrodes of ideal and nonideal geometries: AC impedance spectroscopy
Authors: Alden John A. , Compton Richard G.
Published: May 2005

The AC impedance behavior of microband electrode geometries which deviate from the ideal is derived via numerical modelling of the chronoamperometric response under diffusion‐only conditions. Specifically attention is given to four electrode shapes in addition to the ideal microband geometry: elevated microband electrodes (with conducting supporting sides), recessed microband electrodes (with insulating pit walls), platform electrodes (with insulating supporting sides) and, for the purposes of comparison, a hypothetical line electrode without any support which permits diffusional mass transport to both sides of the infinitesimally thin electrode. Simple analytical expressions are established for the frequency dependence of the AC impedance in each case.
Derivative chronopotentiometric stripping analysis of insulin
Authors: Honeychurch Michael J. , Ridd Michael J.
Published: May 2005

Porcine insulin was analyzed in the presence of dissolved oxygen by constant current stripping analysis (CCSA) and potentiometric stripping analysis (PSA). The CCSA analysis involves the constant current reduction of mercuric insulin thiolate following its potentiostatic accumulation on a hanging mercury drop electrode. The CCSA response was quantitatively enhanced in the presence of dissolved oxygen. The PSA analysis involves the oxidation, by dissolved oxygen, of sulfhydryl groups in reduced insulin following its accumulation on the HMDE at −900mV (vs. SCE).
Anion selectivities of membranes based on HgII complexes of calix[4]arene derivatives
Authors: Wróblewski Wojciech , Malinowska Elżbieta , Brzózka Zbigniew
Published: May 2005

Anion selectivities of membranes based on cationic complexes of thioamide calix[4]arene derivatives are presented for the first time. HgII complexes of thioamide derivatives of calix[4]arene were applied to design perchlorate‐selective ISEs which show linear responses in the range 1–5 of pClO4 with a slope of 56.5mV decade −1. The highest selectivity over other anions (except iodides) and optimum performances of electrodes were obtained for a 0.01 M solution of HgII as an internal electrolyte.
The nature of voltammetric waves of copper complexes with dimethylglyoxime in ammonia and borate buffer solutions
Authors: Bobrowski Andrzej
Published: May 2005

The voltammetric and adsorptive characteristics of the Cu‐DMG complexes in a wide range of Cu concentration (from 5 × 10−8 M to 1 × 10−3 M) have been investigated in ammonia and borate buffer. Evaluation of the electrode process included the examination of the effect of Cu, DMG, buffers, ethanol and Triton X100 concentration, buffer capacity and ionic strength, pH and instrumental parameters. The adsorption phenomena were observed by direct current, linear scan, pulse and alternating current polarography and voltammetry. At high Cu concentration the additional effects such as spikes on the pulse and linear scan voltammetric curves as well as maxima and erratic behavior on the direct current polarograms were observed. From the voltammetric and the potentiostatic transient studies it has been found that these effects are caused by the nucleation and condensation processes. From the bulk electrolysis and microelectrolysis results it follows that the Cu‐DMG complex is reduced with participation of two electrons and no proof has been found that in the presence of a Cu‐DMG complex a catalytic hydrogen wave is formed. The adsorptive properties of the Cu‐DMG complex can be utilized for sensitive determination of Cu traces (from 1 × 10−7 M to ca. 1 × 10−5M Cu) or for simultaneous determination of Cu, Ni and Co by differential pulse polarography or linear fast sweep polarography.
Development and optimization of a solid composite tyrosinase biosensor for phenol detection in flow injection systems
Authors: Mareikelutz E. S. , Dominguez Elena
Published: May 2005

Bulk‐modified epoxy‐graphite tyrosinase biosensors were fabricated by four different procedures. The influence of these fabrication procedures on the analytical performance of the enzyme electrode in an amperometric wall‐jet flow cell has been studied. The bioprobe performance is assessed by cyclic voltammetry. Higher current densities and narrower peaks were obtained when the enzyme was introduced in the dry state into the epoxy‐graphite material, instead of introducing it previously dissolved in the buffer. In the F1 system responses of 11.79 μA cm−2 and 1.43 μA cm−2 are then obtained for catechol and phenol respectively for 50 μL injections of 20 μM solutions. Moreover, if gold/palladium is introduced into the epoxy‐graphite, a further increase in current is achieved resulting in 27.70μA cm−2 and 4.90μA cm−2for catechol and phenol, respectively. This biosensor can operate in aqueous as well as in mixed aqueous‐organic environments.
Amperometric determination of peroxides by glassy carbon electrodes modified with copper‐phenanthroline complexes
Authors: Toniolo Rosanna , Comisso Nicola , Bontempelli Gino , Schiavon Gilberto
Published: May 2005

An amperometric sensor is described for the determination of peroxides in both aqueous and organic media. It consists of a rotating glassy carbon electrode modified by coating first with a thin film of a perfluorinated anionic exchanger (Tosflex) and then by immobilizing on this substrate the mixed‐ligand copper complex [CuL2]2+ with 1, 10‐phenanthroline and bathophenanthroline (i.e., 1, 10‐phenanthroline containing two phenyl‐sulfonic groups as substituents in the positions 4 and 7), thanks to the bonds formed between the −NR+3 cationic groups of the Tosflex coating film and the −SO−3 anionic groups present in the latter ligand. The modified electrode, which is rather stable with time and can be easily restored, permits detection of peroxides by their reduction at less cathodic potentials than at an unmodified electrode surface. It shows enhanced sensitivity in a variety of media (water, ethanol and ethanol‐toluene 60/40 v./v.) which were investigated in view of their ability, on the whole, to dissolve peroxides originally present in different natural samples. Its satisfactory performance, which is unaffected by the presence of oxygen in the sample, in all the media studied is reported for hydrogen peroxide and tert‐butyl hydroperoxide in terms of detection limits, dynamic ranges and response time. Its application to the direct determination of peroxides in some cereal oils was also attempted and the results found are compared with those obtained by conventional methods.
Measurement of liquid junction potentials in strongly alkaline solutions
Authors: Norkus Eugenijus , Vaškelis Algirdas
Published: May 2005

The values of liquid junction potentials (Elj) between the saturated KCl solution in Ag/AgCl electrode and NaOH solutions (0.8–3.0 mol/L), as well as between NaOH solutions of different concentrations were determined at 20°C using Hg/HgO electrodes. The Elj value obtained can be as high as 20mV and its calculation by Henderson equation is not accurate enough.
A water‐soluble tetramethylbenzidine‐2‐hydroxypropyl‐β‐cyclodextrin inclusion complex as an efficient mediator for oxidoreductases
Authors: Cattaneo Maurice V. , Luong John H. T.
Published: May 2005

A water soluble 3,5,3′,5′‐tetramethylbenzidine‐2‐hydroxypropyl‐β‐cyclodextrin (TMB‐hpβCyD) inclusion complex was demonstrated for the first time as an efficient mediator for glucose oxidase, xanthine oxidase and glutamate dehydrogenase. At pH 5, the cyclic voltammogram of the TMB‐hpβCyD complex exhibited two reversible oxidation waves with potential peak values (Epa) of 384 mV (TMB → TMB+·) and 496mV (TMB+· → TMB2+) at a glassy carbon electrode (vs. Ag/AgCl). The Epa value of the former was pH‐independent, whereas that of the latter was strongly pH dependent. However, at pH 7 the inclusion complex exhibited only one reversible oxidation wave with Epa of 396 mV. Based on cyclic voltammetric measurements, the second rate constant (k) for the TMB+ (glucose oxidase) reaction was determined as 6.7 × 105 M−1s−1 which compares favorably with that of ferrocene (2.6 × 104 M−1s−1), one of the most common mediators. The inclusion complex was then investigated for bioelectrocatalysis at membrane electrodes of glucose oxidase and xanthine oxidase. The response of the hypoxanthine electrode was linear up to 40μM; its sensitivity was 2.8 μA mM−1 and a response time was smaller than 2 min. A similar response time was also observed for the glucose electrode, however, the linear range and sensitivity of the glucose electrode were 0–3 mM and 0.6 μA mM−1, respectively. The capability of TMB+˙ to oxidize NADH formed from a glutamate dehydrogenase:NAD/glutamate reaction, was also demonstrated, as illustrated by a well‐defined catalytic wave for NADH oxidation.
Flow injection amperometric detection of ammonia using a polypyrrole‐modified electrode and its application in urea and creatinine biosensors
Authors: Trojanowicz Marek , Lewenstam Andrzej , Krawczyk Tadeusz Krawczyński Vel , Lähdesmäki Ilkka , Szczepek Wojciech
Published: May 2005

The interaction of unprotonated ammonia molecules with polypyrrole (PPy) is employed for the amperometric detection of ammonia with the use of an anodically polarized platinum electrode modified with PPy as the working electrode. The polymer was obtained by electropolymerization in potentiostatic conditions from aqueous solutions. Chloride was found to be the most suitable dopant for PPy from several dopants studied. Satisfactory dynamic characteristics of detection permit its application to the determination of ammonia in a flow injection system up to 100 μM of analyte with a detection limit of 0.6 μM. Such a detector of ammonia was also employed as the internal detector in amperometric biosensors for urea and creatinine by the immoblization in a different way at the PPy surface of urease and creatinine iminohydrolase, respectively. An amperometric biosensor of very low sensitivity was obtained by urease entrapment in the PPy layer during the electropolymerization. The urea membrane biosensor was successfully applied in the determination of urea in human blood samples. On the basis of results of elemental analysis, UV and IR spectroscopy some suggestions are presented about the mechanism of the interaction between PPy and ammonia and about the anodic electrode process occurring in the amperometric detection of ammonia.
CuII‐poly (dithiooxamide) film coated anion selective electrode
Authors: Gong Young‐Tae , Won Mi‐Sook , Shim Yoon‐Bo , Park Su‐Moon
Published: May 2005

Electrochemical deposition of a solid state anion selective membrane for thiocyanate and thiosulfate ions has been made from a 0.050 M dithiooxamide solution in 0.10 M sulfuric acid on a copper coated platinum electrode and its performance evaluated. The solid state membrane electrode displays excellent linearities with slopes of 59.2 ± 0.5 and 98.6 ± 0.6mV/decade and detection limits of 7 × 10−7 and 4 × 10−6 M for SCN‐ and S2O, respectively, high selectivity over other anions, and response time of about 6 s. The optimum pH for the electrode is around 6 in an acetate buffer, although it is usable in a wide pH range. The electrode was shown to be rugged and stable for at least a month and give reproducible responses if stored in an inert atmosphere.
The derivative adsorption chronopotentiometry of flavin adenine dinucleotide
Authors: Honeychurch Michael J. , Ridd Michael J.
Published: May 2005

The flavin adenine dinucleotide (FAD), leucoflavin adenine dinucleotide (FADH2) couple was studied by derivative adsorption chronopotentiometry at a HMDE. The theory of an EE mechanism for adsorption chronopotentiometry was developed and the semiquinone formation constant determined. Constant current stripping results at pH 7.0 were consistent with previous reports that adsorbed FAD was reduced via a stable semiquinone intermediate in two reversible one‐electron transfers (EE mechanism). Potentiometric stripping analysis was also carried out in which the FAD was accumulated as FADH2 on the HMDE at a reducing potential. The FADH2 was subsequently oxidized by dissolved oxygen. This reaction was also found to fit the EE model.
Investigations in bioanalytical chemistry part VIII: Derivative adsorption chronopotentiometry of the CuII complex with adenine, adenosine and adenosine monophosphate
Authors: Zhao Xin , Jin Wenrui , Tang Jian
Published: May 2005

The derivative adsorption chronopotentiometric characteristic of the CuII complex with adenine, adenosine and adenosine monophosphate (AMP) is discussed. The optimum experimental conditions and the linear ranges were studied. The detection limits of adenine, adenosine and AMP were 2.2 × 10−9, 4.5 × 10−8 and 4.6 × 10−8 mol/L, respectively.
Determination of traces of RNA in submicrogram amounts of single‐ or double‐stranded DNAs by means of nucleic acid‐modified electrodes
Authors: Fojta Miroslav , Doftlková Renata , Palečhk Emil
Published: May 2005

Recently we have utilized the advantages of nucleic acid‐modified mercury electrodes to develop a method capable of determining RNA traces in samples of double‐stranded DNA [1]. It was, however, impossible to determine less than 10 % of RNA in a single‐stranded DNA sample. Here we show that the DNA voltammetric signals can be selectively suppressed by precipitation with [Co(NH3)6]3+ while the signal of any RNA digested with RNase A is not influenced. Following from our studies we proposed a voltammetric method for determination of less than 1% of RNA in microgram samples of single‐ and double‐stranded DNA.
Carbon film based ring‐disk and split‐disk dual electrodes as detectors for microbore liquid chromatography
Authors: Niwa Osumu , Morita Musao , Solomon Bruce P. , Kissinger Peter T.
Published: May 2005

The electrochemical properties of carbon film based ring‐disk and split‐disk electrodes in small active volume (0.24–2μL) radial flow cells were studied in order to employ them in conjunction with microbore liquid chromatography (LC) for determining catecholamines. The high conversion of dopamine (DA) at the disk of a ring‐disk electrode makes the DA limiting current lower than the theoretical value at a low flow rate. The collection efficiency (CE) increases with decreasing flow rate and cell thickness, which is different from previously reported results. A high CE of 0.96 was achieved because of the narrow gap of 5 μm.

On the other hand, a higher limiting current was observed with the split‐disk than with a commercially available dual‐disk electrode because of its efficient geometry for analyte collection. The cross talk of the DA after reacting at one of the electrode is only 2%. The ring‐disk and split‐disk electrodes were suitable as series and parallel electrochemical detectors for small bore LC. A detection limit of 103 fg was obtained for DA at the disk of the ring‐disk because of the high signal in the thin‐layer radial flow cell and the low noise level of the carbon film. In contrast, very slight interference was observed from neighboring electrodes when determining catecholamines at the split‐disk.
Enzymatic electrode for the determination of L‐lactate
Authors: Boujtita Mohamed , Chapleau Muriel , Murr Nabil El
Published: May 2005

An amperometric L‐lactate biosensor was constructed by confining lactate oxidase and a redox mediator in a carbon paste electrode. Conditions for optimal electrode response were determined by varying the modified carbon paste composition. Using hydroxymethyl ferrocene as a redox mediator resulted in an improvement of sensitivity and linearity range of the electrode. The sensor showed a repeatability and accuracy compatible with industrial use.
Polarographic study of the coordinated system ZnII‐alanine‐alaninate ion
Authors: González Manuel De La Cuesta , Sánchez Mariana Cuesta , Morales Juan C. Ruiz , Placeres Jesús C. Rodríguez
Published: May 2005

Polarography has been applied to the study of the mixed‐ligand system ZnII‐alanine‐alaninate, in aqueous medium, at I = 1.0 M NaClO4 and 25 ± 0.05°C. The study of the quasireversible waves characteristic of ZnII has been carried out by means of a new method of analysis, which is faster and more accurate than traditional methods. The stabilization of the coordinated species [ZnA]2+ (β10 = 1.8), [ZnA2]2+ (β20 = 0.52), [Zn(A−)]+ (β01 = 9.1 × 104), [Zn(A−)2] (β02 = 9.4 × 108) and [ZnA(A−)]+ (β11 = 6.2 × 104) has been established.
Voltammetric monitoring of photochemical reactions: Photo‐induced electron transfer to p‐chloronitrobenzene
Authors: Kumbhat Sunita , Webster Richard , Marken Frank , Eklund John C. , Compton Richard G.
Published: May 2005

Channel electrode voltammetry using an irradiated gold electrode is used to study the photolysis of p‐chloronitrobenzene in aqueous ethanolic solution in the presence of the hydroxide anion. The formation of the stable radical anion, [p‐CIC6H4NO2]•−, via light‐induced electron transfer is demonstrated and kinetic parameters are reported.
Electrochemically prepared and optimized membrane compositions for silver(I)‐responsive chalcogenide‐based ion‐selective electrodes
Authors: Neshkova Milka T. , Pancheva Elka M.
Published: May 2005

Through electrochemical modeling, an attempt has been made to correlate the composition, structure and stoichiometry of a number of thin electroplated silver chalcogenide (selenides and tellurides) all‐solid‐state membranes with their performance as Ag‐responsive ion‐selective electrodes. The conclusions drawn from the electrochemical membrane composition modeling could be of practical value to the pressed‐pellet technology as well. The results suggest that no binary silver chalcogenide, irrespective of its stoichiometry, could perform reliably in an all‐solid‐state configuration. On the contrary, hyperstoichiometric membranes featuring both intrinsic and extrinsic defects, e.g., Ag2+δSe1−xTex have proved to exhibit high sensitivity, potential reproducibility and selectivity (even to mercury) under both steady‐state and flow‐injection modes. The competitiveness of the newly developed electroplated membranes to conventional Ag2S pressed ones has been assessed.
The preparation and sensor application of poly(p‐aminophenol)
Authors: Ekinci Ergun , Karagözler A. Alev , Karagözler A. Ersin
Published: May 2005

An amperometric biosensor for glucose based on a novel polymeric matrix is described. The sensor was prepared by electrochemical polymerization of p‐aminophenol in the presence of glucose oxidase on Pt substrates in a KCl solution at a potential of 0.6 V (vs. Ag/AgCl). The chronoamperometric response of poly(p‐aminopheno1)‐glucose oxidase biosensor to hydrogen peroxide formed as the result of enzymatic reaction was measured at a potential of 0.7 V (vs. Ag/AgCl) in PBS solution. It was shown that a biosensor prepared by this one‐ step procedure has a linear range up to 6mM glucose, a response time less than 5 s and a lifetime around 15 days. The sensitivity of the electrode was superior to that of much publicized polypyrrole based glucose oxidase electrode. Also, the substrate selectivity of PAP/GOx electrode was tested for coexisting substances such as lactose, sucrose, urea, paracetamol, uric and ascorbic acid and no discernible anodic response was observed above the background current.
Automatic chemical current determination in coulometric stripping potentiometry facilitating calibration‐free trace metal determinations
Authors: Jagner Daniel , Wang Yudong , Ma Feng
Published: May 2005

The theory of an improved coulometric stripping potentiometry method, involving automatic determination of the chemical current for each sample, and thus suitable for calibration‐free determination of trace elements in microliter samples is described. The method has been applied to the determination of ZnII, CdII, PbII, TlI, CuII and BiIII by reductive in situ amalgamation and of AsV, SnIV and CuII by reductive in situ dissolution on a gold film followed by three consecutive constant current stripping potentiometry measurements permitting the determination of the chemical current. Quantitative reduction (≥99%) of the analyte ions was obtained after four minutes of vibrationally enhanced reductive electrolysis of the 12μL samples placed on top of an inverted glassy carbon disk electrode combined with Ag and Ag/ AgCl counter and reference electrodes. The concentration detection limits ranged from 11 nM for elements oxidized to the monovalent state to 3 nM for elements oxidized to the trivalent state. The mass detection limits ranged from 4.5 pg for ZnII to 28pg for TlI.
Conversion from electronic conducting phase to redox conducting phase of polypyrrole
Authors: Yang Chunhe , Dong Shaojun
Published: May 2005

Square‐wave voltommetry is used to study the oxidation of polypyrrole doped with dodecylsulfate. The net current curve in this experiment shows why the oxidation current does not display the capacitive‐like shape common in cyclic voltammetry. In cyclic voltammetry, the redox behavior of polypyrrole is attributed to the size of dodecylsulfate, irreversible incorporation and the complete consumption of dodecylsulfate. After the polypyrrole film was scanned in aqueous NaCl solution, square wave voltammetric measurements show different results, indicating the change of the polymer nature with regard to the charge transport. This is explained by anion replacement, exclusion and the change of the charge transport mechanism.
The application of abrasive stripping voltammetry for a simple and rapid screening of pesticides
Authors: Jayarama Reddy S. , Hermes Michael , Scholz Fritz
Published: May 2005

Abrasive stripping voltammetry has been employed to describe a simple and rapid solid‐state voltammetric procedure for the screening of pecticides. A particular case of chlorothion studied on cucumber and lettuce is discussed in this communication. The procedure described provides a semiquantitative assessment and obviates the need to bring the substrate into solution.
A peak current – scan rate relationship in staircase voltammetry of a surface redox reaction
Authors: Komorsky‐Lovrić Šebojka , Lovrić Milivoj
Published: May 2005

Staircase voltammetry of surface redox reactions is characterized by a “quasireversible maximum”. The relationship between peak currents and scan rates is not linear, except for totally irreversible reactions, and the response may entirely vanish if the reaction is fast and reversible. For surface redox rections, the equivalence of staircase and linear sweep voltammetries can not he obtained by the variation of the current sampling fraction.
Iodide sensitive sensor based on a supported bilayer lipid membrane containing a cluster form of carbon (fullerene C60)
Authors: Wang Lei‐Guang , Wang Xing , Ottova Angelica L. , Ti Tien H.
Published: May 2005

The iodide ion sensitivity of a solid‐supported bilayer lipid membrane (s‐BLM) containing buckminsterfullerene(C60) as an electron mediator has been investigated using the cyclic voltammetry technique. We have shown that C60 in a lipid bilayer environment produces a unique and simple system for the detection of iodide. The sensitivity of C60‐containing s‐BLM to I− is excellent with a linear response in the range from 10−8 to 10−2 M. The use of fullerene C60‐doped s‐BLMs as sensors and devices for detecting other species is proposed.
Direct electrochemistry of hemoglobin at a bare silver electrode promoted by cetyl pyridinium chloride and its application in analysis
Authors: Ye Baoxian , Zhou Xingyao
Published: May 2005

The electrochemical redox of hemoglobin at a bare silver electrode promoted by cetyl pyridinium chloride with the cyclic voltammetric technique has been studied. The electrode reaction exhibits such good stability that the peak currents change less than 8.5% (oxidation) and 10.2%(reduction) for a continuing scan of 30 min in a solution containing 1 × 10−7mol/L hemoglobin. The electrode reaction rate constant Ks is 0.0865s−1 with a single electron transfer. Moreover, both the oxidation currents and the reduction currents are linear with the concentration of hemoglobin over the range of 1 × 10 −8−5 × 10−7mol/L. So, it can be used as an analytical method of determining hemoglobin.
Catalytic voltammetric determination of molybdenum at a chemically modified carbon paste electrode
Authors: Gao Zhiqiang , Siow Kok Siong , Ng Adeline
Published: May 2005

Trace amounts of molybdenum can be determined in an acetate buffer solution (pH 2.6) containing chlorate, after the accumulation of molybdenum on a α‐benzoinoxime modified carbon paste electrode, coupled with the catalytic effect on the reduction of chlorate. Under optimized conditions, the catalytic voltammetric procedure gives a detection limit of 20 nmol L−1 molybdenum (60s accumulation). Most of the ions investigated did not interfere with the determination of molybdenum except for stannous ion. The catalytic peak current increases linearly with molybdenum concentration between 0.1 and 80 μmolL−1 with a correlation coefficient of 0.997 and a current sensitivity of 2.13 μA/μmol L−1. The chemically modified carbon paste electrode also displays good reproducibility with a relative standard deviation of 6.4 % for 20 repetitive determinations of 5.0 μmol L−1 molybdenum solutions.
Selectivity of liquid membrane ion‐selective electrodes
Authors: Bakker Eric
Published: May 2005

The current status of describing the selectivity of liquid membrane ion‐selective electrodes (ISEs) is reviewed. For ISEs that show Nernstian response toward all measured ions, the mixed ion response can often be described rigorously by a newly developed model that establishes required Nikolskii coefficients for a given target application. For ions of different charge, these obtained values are significantly different than predicted using the traditional Nikolskii–Eisenman equation. In contrast, for ISEs that show non‐Nernstian responses toward highly discriminated ions, two different procedures are recommended, depending on the scope of the experiment. Selectivities obtained with the so‐called matched potential method yield information about the apparent selectivity behavior of ISEs in real‐world samples, irrespective of theoretical expectations, but can, for the very same reason, generally not be used to predict the empirical selectivity for different analytical situations. On the other hand, experimental procedures are presented that allow for the determination of fundamental Nikolskii coefficients of such membranes, i.e., Nernstian slopes can now often be obtained by carefully adjusting the experimental conditions. Such values more closely reflect the ion extraction behavior of the membrane and can be used for characterization and optimization purposes. Each of the procedures has its validity and the respective values should preferably be reported simultaneously.
The use of ultrasound in the enhancement of the deposition and detection of metals in anodic stripping voltammetry
Authors: Marken Frank , Rebbitt Thomas O. , Booth Jonathan , Compton Richard G.
Published: May 2005

The fast electrochemical deposition of both mercury and amalgam films, a crucial step in analytical anodic stripping voltammetry, is demonstrated to occur in the presence of power ultrasound emitted from an immersion horn probe which was placed opposite the working electrode in a conventional three electrode cell. Due to considerably enhanced mass transport the rate of deposition is strongly increased compared to ‘silent’ conditions. The total amount of mercury adhering to a glassy carbon electrode surface, however, is limited to a ‘thin film’ of microscopically small droplets of mercury as shown by atomic force microscopy and voltammetry. Due to surface forces induced by ultrasound, abrasion of some of the deposit occurs and after a certain period of time the parallel electro‐deposition and abrasion processes reach a ‘steady state’.

The deposition of mercury in the presence of Pb2+ or Cu2+ results in the formation of an amalgam and well‐defined, very sharp ‘stripping’ responses for the oxidation process of the corresponding amalgam were detected. The merit of insonation in analytical electrode preconcentration techniques is dicussed.
Determination of thallium in environmental samples using potentiometric stripping analysis. Method development
Authors: Švancara Ivan , Ostapczuk Peter , Arunachalam Jayaraman , Emons Hendrik , Vytřas Karel
Published: May 2005

A method employing computerized potentiometric stripping analysis has been developed in order to determine trace levels of thallium in various environmental samples. The method is based on the preconcentration of T1 onto a mercury film electrode (formed in situ) with a subsequent reoxidation of amalgamated T1. A deaeration of the solution as well as the use of EDTA have resulted in a significant improvement of the sensitivity. In a supporting electrolyte containing 0.02–0.07 M HNO3 + 0.02 M CH3COONa + 0.001 M EDTA + 6 × 10−5 M HgCl2, the analytical signal versus concentration dependence is linear from 9 × 10−11 to 2.5 × 10−8 M T1 (preconcentration time from 5 to 30 min). A detection limit of about 5 × 10−11 M T1 (0.01 μg/L) is achieved when using preconcentration for 30 min. Despite a relatively high acidity of the supporting electrolyte used (pH 1.0–2.5), EDTA is capable to suppress the interferences from PbII ions up to a 500‐fold excess in concentration and from CdII and CuII up to their 100‐fold excess, respectively. Nitric acid has been incorporated into the supporting electrolyte as its constituent in order to determine T1 directly in the samples decomposed by means of high pressure ashing. The applicability of the method is demonstrated on various samples such as tap water (spiked), rain water, river sediment or sewage sludge. The results agree well with those obtained by isotope dilution‐mass spectrometry. The method has also been tested to determine T1 in digested biological samples (e.g., pine needles, poplar leaves and mussel tissues).
Study on diffusion of electroactive species in polyelectrolyte polyethylene glycol lithium perchlorate by chronoamperometry at a microdisk electrode
Authors: Zhou Huafang , Che Guangli , Dong Shaojun
Published: May 2005

The mass transport dynamics of ferrocene in polyelectrolyte polyethylene glycol lithium perchlorate (PEG · LiClO4) was studied by using chronoamperometry at a microdisk electrode. Chronoamperometry is a powerful method for the study of mass transport in polyelectrolyte, it has many advantages over the conventional methods at a microelectrode and the steady‐state method at an ultramicroelectrode. By using this method the apparent diffusion coefficient Dapp and concentration Ca of the electroactive species, can be estimated from a single experiment without previous knowledge of either one. We have estimated Dapp and Ca of ferrocene in PEG · LiClO4 polyelectrolyte from 25°C to 75°C. The dependence on the concentration of electroactive species was observed. The diffusion coefficients decrease with increasing ferrocene concentration and decreasing temperature. The mass transport mechanism is explained by using a free volume model.
Comparison of the voltammetric behavior of metronidazole at a DNA‐modified glassy carbon electrode, a mercury thin film electrode and a glassy carbon electrode
Authors: Brett Ana Maria Olivira , Serrano Silvia H. P. , Gutz Ivano G. R. , La‐Scalea Mauro A.
Published: May 2005

The electroanalytical performance at three electrodes: DNA‐modified galssy carbon electrode, mercury thin film electrode and glassy carbon electrode, for the study of the electrochemical reduction of metronidazole is compared. All three electrodes showed a similar trend in the reduction mechanism for metronidazole, depenent on pH in the acid and neutral region and independent in alkaline media, although there was a shift in the peak potentials to more negative values when a bare glassy carbon electrode was used compared to the other two. Besides the advantage of using a solid electrode for the reduction of metronidazole, the DNA‐modified galssy carbon electrode enables a lower detection limit of 1.0 μM owing to the preconecentration of the drug on the electrode surface, which is not the case for the mercury thin film or bare glassy carbon electrodes.
Amperometry and cyclic voltammetry of tyrosine and tryptophan‐containing oligopeptides at carbon fiber microelectrodes applied to single cell analysis
Authors: Paras Charina D. , Kennedy Robert T.
Published: May 2005

The amperometric and cyclic voltammetric detection of α‐melanocyte stimulating hormone (MSH), β‐endorphin, and corticotropin‐like intermediate lobe peptide (CLIP), all proopiocortin (POC) derived peptides secreted from melanocytes of the pituitary intermediate lobe, at carbon fiber microelectrodes was investigated. For amperometry, it was found that all of these peptides could be detected; however, fouling of the electrodes reduced the response of the electrode after successive application of the peptide in flow injection experiments. The fouling was apparently due to oxidation of tyrosine in the peptides as similar results were found for tyrosine but not tryptophan. The effect of fouling could be reversed if the electrode was electrochemically treated by scanning from −1.0 V to +1.0 V at 300 V/s for 2 min between application of the peptides. Using cyclic voltammtery at 800 V/s, it was possible to distinguish MSH, which had a peak shaped voltammogram, from the other POC peptides, which had relatively flat voltammetric waves at this scan rate. The scan rate dependence of the peak current for MSH revealed that the voltammetry was adsorption controlled. As a result, in a monitoring application, where voltammograms are continuously obtained with a fixed interval between them, decreasing the interval increases the temporal resolution but decreases the sensitivity for MSH. It was found that when monitoring the current in the potential range of 0.90 to 1.00 V, the temporal response to MSH was dependent upon the potential window used for scanning. Using high scan rates and a potential window 0 to 1.2 V, it was possible to monitor exocytosis from single melanocytes and use the voltammogram to demonstrate detection of MSH from the cells.
Electroanalytical determination of peroxidases and laccases on carbon paste electrodes
Authors: Kulys Juozas , Drungiliene Alma , Wollenberger Ulla , Krikstopaitis Kastis , Scheller Frieder
Published: May 2005

Electrocatalytical reduction of hydrogen peroxide and oxygen was performed by horseradish peroxidase, recombinant Coprinus cinereus peroxidase, Polyporus pinsitus laccase and Botrytis cinerea laccase on carbon paste electrodes containing a paraffin soluble mediator. The electrocatalytical process proceeded at 0.0V (vs Ag/AgCl; in situ electrode). The electrode responses had maximum values at pH 6.4 and 5.5 for the horseradish peroxidase and laccases catalyzed reactions, respectively. The sensitivity for horseradish peroxidase and recombinant Coprinus cinereus peroxidase was 23.4 and 5.4 μC nM−1 cm−2, respectively. A detection limit of 7.5 fmol horseradish peroxidase could thus be achieved. Systems based on laccases showed lower sensitivity. The model of electrocatalytical reduction of hydrogen peroxide and oxygen included a permanent liberation of mediator from the carbon paste and it's biocatalytical conversion in the diffusion layer. The model was analyzed by comparing kinetic data in homogeneous solution with the electrode response. Mass transport effects were studied by using rotating carbon paste electrodes.
Voltammetry study of zeatin in a carbon fiber ultramicroelectrode. Determination by adsorptive stripping
Authors: Hernández Pedro , Paton Fernando , Ballesteros Yolanda , Hernández Lucas
Published: May 2005

The adsorptive stripping voltammetric determination of zeatin at a carbon fiber electrode is optimized and characterized. Applicability to assays of vegetable extracts is illustrated.
Hexacyanoferrate‐anion exchanger‐modified carbon paste electrodes
Authors: Labuda Ján , Hudáková Monika
Published: May 2005

The preparation of carbon paste electrodes (CPEs) modified with the hexacyanoferrate ion attached to synthetic hydrotalcite, a solid anion exchange resin Wofatit SBW and a liquid anion exchanger tris‐octylamine (TOA) used as pasting liquid, is described. Stability of the electrodes and their electrocatalytic properties were investigated. The surface‐modified hexacyanoferrate‐TOA‐CPE can be prepared and renewed in a simple and reproducible manner. The sensor was applied to the determination of ascorbic acid in real samples using a mediator accumulation/chronoamperometric detection scheme.
Simultaneous FIA determination of two components with differential normal pulse voltammetric multidetection
Authors: Alpízar Jesús , Crespí Antonio , Cladera Andreu , Forteza Rafael , Cerdà Víctor
Published: May 2005

A flow injection method for the simultaneous determination of two components based on differential normal pulse voltammetric multidetection was developed. The method entails applying two sequential potential pulses to a 3‐electrode voltammetric system (with a carbon paste working electrode) connected to a flow‐through cell. The proposed method can be applied to other complex systems comprising more than two substances provided large differences in their peak potentials.
Analysis of the derivative chronopotentiometric peak shape for the reduction of adsorbed bovine serum albumin
Authors: Honeychurch Michael J. , Ridd Michael J.
Published: May 2005

The broad shape of the reduction peak of adsorbed proteins containing multiple electroactive disulfide bonds can be modeled by developing the existing theory used to describe the reduction peaks of proteins with multiple heme groups. This theory is developed and applied to the study of the derivative chronopotentiometric (DCP) reduction peak of adsorbed bovine serum albumin (BSA). For BSA adsorbed on mercury, six disulfide groups were found to be electroactive. It was found that the DCP peak shape could be deconvoluted into five electrochemically equivalent, non‐interacting disulfide groups with formal potentials (vs SCE) of −598 mV, −598 ± 17.8 mV and −598 ± 41.3 mV, and one electrochemically distinct group with a formal potential of −706 mV.
Activation of titanium electrodes for voltammetric detection of oxygen and hydrogen peroxide in alkaline media
Authors: Clark Theotis , Johnson Dennis C.
Published: May 2005

Bright, freshly‐polished Ti electrodes give minimal cathodic response for O2 and H2O2 in 1.0 M NaOH. However, the response is increased gradually by repeated application of a triangular waveform within the approximate potential limits of O2 response (ca. −1.5 to −0.7 V vs. SCE). This same voltammetric pretreatment applied for excessive periods results in formation of golden films on the Ti surfaces that are active for reduction of O2 and H2O2. Levich plots of cathodic current for O2 and H2O2 at rotated golden‐Ti disk electrodes in 1.0 M NaOH (−1.35 V) are linear over a large range of rotational velocity (42 to 513 rad s−1), a behavior considered to be indicative of fast heterogeneous kinetics. Ring‐disk data demonstrate that a small amount of H2O2 is produced throughout the potential region for O2 reduction and H2O2 is concluded to be an intermediate product in the O2‐reduction mechanism. These observations are consistent with those reported previously for single‐crystal TiO2 electrodes.
Critical comparison of metallized and mediator‐based carbon paste glucose biosensors
Authors: Wang Joseph , Chen Liang , Liu Jie
Published: May 2005

The performance of metallized carbon oxidase‐based biosensors is critically compared with that of mediator‐based enzyme electrodes. Dimethyl ferrocene and rhodium metal centers are used as model mediator and catalyst, respectively, in connection to carbon‐paste electrode transducers and assays of glucose. The rhodium‐containing bioelectrode displays enhanced selectivity (particularly improved discrimination against ascorbic acid), lower sensitivity, faster response time, greater oxygen dependence, and similar detection limit in comparison to the mediated electrode. In addition to assessing the relative merits of both strategies, the data offer useful insights into the behavior of these ‘first’‐ and ‘second‐generation’ oxidase amperometric electrodes.
Development of an ion‐sensitive field effect transistor based on PVC membrane technology with improved long‐term stability
Authors: Jiménez Cecilia , Bartroli Jordi
Published: May 2005

An NH ‐ISFET sensor based on PVC membrane technology with improved long‐term stability has been developed. As a new approach, the plasticizer (tetra‐n‐undecyl) 3,3′,4,4′ ‐benzhydroltetracarboxylate (ETH2112) was used in membrane preparation. Its lipophilic nature provides a restricted diffusion of the membrane components to the external solution and improves membrane adhesion to the gate area of the ISFET. The good performance of this plasticizer was confirmed by comparison with usual plasticizers applied in standard ISE technology. Moreover, the durability and stability of the sensor were enhanced by the application of a graphite‐epoxy layer as an internal reference between the gate area and the PVC membrane. This composite layer permits the reduction of the optical sensitivity and improves the adherence of the PVC membrane to the ISFET surface. Furthermore, this composite layer acts as a plug, preventing the entrance of water upon the encapsulant‐chip interface, thus protecting electrical connections from moisture. As a result, an NH ‐ISFET with a long‐term stability of three months and a sensitivity of −58.7 ± 2.3 mV decade−1 in a linear range of 10−5 −0.1 mol dm−3 has been developed. The application of this sensor to a continuous‐flow system has confirmed the feasibility of the technological approach proposed.
TTF‐TCNQ complex based printed biosensor for long‐term operation
Authors: Khan Golam Faruque
Published: May 2005

A printed amperometric glucose sensor based on glucose oxidase adsorbed on crystals of tetrathiafulvalene‐tetracyanoquinodimethane (TTF‐TCNQ) is described. The sensitivity and the stability of the sensor are affected by the binder and solvent used for the preparation of the GOD.TTF‐TCNQ paste. The sensors are continuously used in a flow injection analysis (FIA) system under continuous polarization at 0.15 V (vs Ag/AgCl) at 37°C. The developed sensors exhibit a large response current, an extended linear range and oxygen independence. The sensors can be used for more than 3 months. The GOD.TTF‐TCNQ paste is suitable for the preparation of planar sensor by screen printing method.
Development of a hypoxanthine biosensor based on immobilized xanthine oxidase chemically modified electrode
Authors: Hu Shengshui , Liu Chung‐Chiun
Published: May 2005

An amperometric biosensor for hypoxanthine determination has been developed. The sensor uses a Nafion‐paraquat chemically modified glassy‐carbon electrode. It detects the oxygen consumed by the enzymatic reaction catalyzed by xanthine oxidase which is immobilized on the electrode surface. The sensor responds linearly to hypoxanthine over the concentration range of 1 × 10−6 M −2 × 10−4 M. The biosensor can be reused for more than 100 times without significant deterioration in performance. After 32 days storage at 3–5°C, the sensor response remains at 68% of the initial level. The high sensitivity, selectivity and stability of this biosensor demonstrates its practical applicability for a simple, rapid and economical determination of hypoxanthine in fish samples.
pHh‐dependent permselectivity of the fibrinogen‐modified carbon paste electrode
Authors: El Rhazi Mama , Randriamahazaka Hyacinthe N. , Nigretto Jean‐Maxime
Published: May 2005

The modification of carbon paste matrices with fibrinogen is reported. The effect of the pH of the solution on the CV peak currents of positively or negatively charged redox analytes was examined at the fibrinogen‐modified carbon paste electrode. In the presence of the coating, pH‐dependent selectivity in electrochemical detection of charged species was demonstrated depending on the sign of the supported charge. Above the isoelectric pH attributed to the immobilized protein (5.5), the current response of anionic redox probes [Fe(CN)/Fe(CN)] was impeded while the response was almost totally restored below this pH. Opposite trends were observed with the Ru(NH3)/Ru(NH3) cationic redox analytes.
Electrochemil investigation of the photodecomposition of selected ferrocene derivatives
Authors: Davis James , Vaughan D. Huw , Cardosi Marco F.
Published: May 2005

The photostability of nine ferrocene derivatives of varying functionality was investigated using cyclic voltammetry. Derivatives with carbonyl groups (aldehyde or ketone) directly attached to the cyclopentadiene ring system were found to decompose in aqueous (pH 7.4) solution over a period of 10 min when exposed to light. The kinetics of the photodecomposition process were investigated and the relative values of the rate constants for the photodecomposition tabulated. The implications for biosensor applications are assessed.
Electrochemical oxidation and determination of heparin at electrodes modified with ruthenium oxide or copper oxide
Authors: Lewinski Krzysztof , Hu Yun , Griffin Charles C. , Cox James A.
Published: May 2005

The electrochemical oxidation of full‐size heparin (13–15 kDa) is demonstrated in 1 M H3PO4 at a glassy carbon electrode coated with a ruthenium oxide film. The pathway apparently is analogous to chemical oxidation by periodate. By comparison to currents from inorganic species, it is apparent that only about 2 electrons per mole are involved. Flow injection analysis (FIA) allowed determinations down to 2 μM heparin, but the calibration plot was nonlinear. Low molecular weight heparin (5–6 kDa) was not electroactive with this system. In basic solution at a glassy carbon electrode that is modified with a film of Cu2O, both full‐size and low molecular weight heparin are oxidized. The pathways involved oxidative desulfation and attack on saccharide units with evolution of CO2. Linear calibration plots which extended into the sub‐μM level were obtained by FIA. The detection limits, which were based on a value of 3 for the ratio of the signal to the standard deviation of replicates, were 9 nM for full‐size and 20–30 nM for various low molecular weight heparin samples.
An original electroenzymatic system: Flavin reductase‐riboflavin for the improvement of dehydrogenase‐based biosensors. Application to the amperometric detection of lactate
Authors: Cosnier Serge , Fontecave Marc , Innocent Christophe , Niviere Vincent
Published: May 2005

The electropolymerization of a flavin reductase (Fre) – amphiphilic pyrrole ammonium mixture previously adsorbed on the electrode surface provides an efficient bioelectrode for the amperometric detection of NADH and NADPH. The bioelectrode response was based on the oxidation at −;0.1 V vs. SCE of the enzymically generated dihydroriboflavin. The sensitivity and detection limit of the bioelectrode were 29 mAM−1 cm−2 and 0.2 μM for NADH and 15.8 mAM−1 cm−2 and 0.4 μM for NADPH. The coimmobilization of Fre and a lactate dehydrogenase leads to a dehydrogenase‐based bioelectrode for the determination of lactate in the presence of riboflavin and NAD+. With laponite additives into the polypyrrole host matrix, the sensitivity and the detection limit of the bioelectrode for lactate are 11.7 mAM−1 cm−2 and 1 μM respectively. Owing to the negative value of the applied potential for the oxidation of riboflavin, the response of the bienzyme electrode remains insensitive to interferents like ascorbate, urate and acetaminophen.