bluuebunny/crossref_metadata_2025 huggingface dataset:
MOCVD Route to Chromium Carbonitride Thin Films Using Cr(NEt2)4 as Single‐Source Precursor: Growth and Mechanism
Authors: Ossola Franco , Maury Francis
Published: May 2005

Chromium carbonitride coatings with a low nitrogen content were deposited by low pressure MOCVD in the temperature range 573–793 K using Cr(NEt2)4 as single‐source precursor. As‐deposited films are amorphous and crystallize upon annealing at 873 K to form an orthorhombic ternary phase. They exhibit a high hardness and their resistivity decreases by increasing the growth temperature. This dependence has been correlated to their microstructure. Quantitative 1H NMR analysis of the by‐products of the MOCVD reaction has been performed. The quasi‐equimolecular ratio of the by‐products EtN=CHMe and HNEt2 suggests that most of the NEt2 ligands are removed by a stepwise mechanism, which is discussed.
Du CVD et d'Autres Choses
Authors: Hitchman Michael
Published: May 2005

Parlez‐vous franglais? C'est un morceau de gâteau for those attending the truly international meeting in Paris, which will bring together for the first time EUROCVD 11 and CVD XIV. The background to this meeting is given here together with a short review of the aims and objectives of CVD. There is clearly a strong overlap of cVD interests between the journal and the meeting and we can look forward to some interesting synergism arising from the happy confluence of the two. II sera un bon'appening!
Volatile Metal β‐Diketonates: ALE and CVD precursors for electroluminescent device thin films
Authors: Tiitta Marja , Niinistou Lauri
Published: May 2005

The use of volatile β‐diketonate chelates as precursors for the deposition of thin films for electroluminescent devices is reviewed. Alternating current thin film electroluminescent (ACTFEL) devices consist of an emitting layer sandwiched between two dielectric layers, together with conducting and buffer layers. Besides various physical deposition techniques, the commonly applied methods for preparing thin films are chemical vapor deposition (CVD) and its particular variant atomic layer epitaxy (ALE). Alkaline earth β‐diketonates are used as precursors for deposition of the semiconducting alkaline earth sulfide and thiogallate films that provide the matrix in emissive layers, while β‐diketonates of lanthanides and a few other metals (Mn, Na, K) are precursors for dopants and codopants producing colors. β‐Diketonate precursors can also be used for the preparation of dielectric alkaline earth titanate and oxide layers. Current research on thin film electroluminescent materials is focused on improving the blue color produced by cerium doping of alkaline earth sulfide and thiogallate matrices. The synthesis and properties of β‐diketonate chelates and the growth and characterization of the thin films obtained with them are presented and discussed. This review of precursors for TFEL materials is also relevant for other materials, including oxide superconductors.
Epitaxial BaTiO3 films grown by aerosol MOCVD
Authors: Gorbenko Oleg Y. U. , Kaul Andrey R. , Wahl Georg
Published: May 2005

BaTiO3 tin films are promising for electronic and optoelectronic devices. Current growth techniques give rather low deposition rates for practical applications. Here epitaxial growth rates over 100 times higher have been achieved using aerosol CVD with surface diffusion enhancement in the presence of Bio‐containing vapor. The AFM image shows a typical layer with an rms roughness of 12 nm.

magnified image
Photochemical Vapor Deposition of Wide Bandgap III‐V Materials: Influence of Photochemically Generated Radicals on the Growth of Aluminum Nitride and Gallium Nitride Films
Authors: Alwan James J. , Eden J. Gary
Published: May 2005

Aluminum nitride and gallium nitride films have been grown on the 1120, 0001, 1010, and 1102 (A, C, M, and R, respectively) planes of sapphire by laser photochemical vapor deposition and MOCVD at temperatures ranging from 600 to 950°C and a total reactor pressure of 1–5 Torr. For the molecular precursors triethylgallium (TEGa) and ammonia. GaN film growth directly onto sapphire or on AIN buffer layers ranging from ∼50 to 500 Å in thickness has been investigated under conventional MOCVD growth conditions and compared to the growth rates and structure for films produced when 193 and 248 nm (ArF, hω = 6.4eV, and KrF, hω = 5.0eV, respectively) photons are introduced into the reactor. Kinetic modeling of the growth rate dependence on laser pulse energy suggests that the dominant photolytically produced species is the amidogen radical, NH2. The presence of 193 nm photons also promotes the growth of (1120)‐oriented GaN films, which provides an example of the ability of photochemistry in the gas phase to drive surface kinetics.
Plasma‐assisted CVD of cubic boron nitride
Authors: Konyashin Igor , Bill Joachim , Aldinger Fritz
Published: May 2005

Single‐phase cubic boron nitride films of high quality might be of great importance as superhard wear‐resistant coatings and semiconductive materials. This paper reviews deposition techniques, precursors, deposition parameters and substrates employed in plasma‐assisted CHEMICAL VAPOR DEPOSITION (PACVD) of cubic boron nitride (c‐BN) as well as procedures applied for the characterization of c‐BN‐containing films. Mechanisms of the formation of sp3‐hybridized boron nitride during PACVD by use of either high‐energy nitrogen and argon ions or hydrogen plasmas are discussed. All experimental results on PACVD of c‐BN are thought to fit either “physical” or “chemical” routes for c‐BN low‐pressure synthesis, which are based on principles of c‐BN physical vapor deposition or diamond CVD.
Palladium thin films grown by CVD from (1,1,1,5,5,5‐hexafluoro‐2,4‐pentanedionato) palladium(II)
Authors: Bhaskaran Vijay , Hampden‐Smith Mark J. , Kodas Toivo T.
Published: May 2005

The precursor (1,1,1,5,5,5‐hexafluoro‐2,4‐pentanedionato) palladium(II) [Pd(hfac)2] was used to deposit high‐purity, polycrystalline palladium films under low‐pressure CVD conditions at high growth rates (1000–4000 Å/min) over a substrate temperature range of 80–200°C in the presence of H2. Mixing of the precursor and H2 streams near the substrate was required to avoid reactions of the precursor with H2 at locations other than the substrate surface. Auger electron spectroscopy (AES) showed that the films were impurity free when sufficient H2 was used. Resistivity values of 20 μΩ were obtained at the higher deposition temperatures (∼200 °C) while high values of 50 μω were observed at the lower deposition temperatures (∼90 °C). The deposition rate was feed‐rate limited even at the lowest deposition temperatures and highest precursor delivery rates, suggesting that even higher deposition rates could be obtained with higher feed rates. A high precursor conversion of 50–60 % was observed. The high surface reaction probability of Pd(hfac)2 in the presence of H2 was reflected qualitatively by trench fill studies which showed a greater film thickness on the top of sub‐micrometer trenches than in the bottom.
Silica gel modified carbon composite electrodes
Authors: Kopanica Miloslav , Stará Vĕra
Published: May 2005

Carbon composite electrodes modified with silica gel exhibit properties analogous to those of an ultramicroelectrode array in voltammetric measurements. The limiting current in linear scan voltammetry is independent of the potential scan rate in certain scan rate regions. The possibility of using high potential scan rates is advantageous analytically, both in direct voltammetric determinations and in analyses involving accumulation of the analyte on the surface of the working electrode.
A thin‐layer electrode cell for fluorescence. Measurements on electrogenerated intermediates
Authors: Compton Richard G. , Fisher Adrian C. , Wellington R. Geoffrey
Published: May 2005

A new methodology for the study of luminescence from photoexcited electrogenerated species is presented. A suitable optically transparent thin‐layer electrode compatible with fluorescence spectrometer was developed, and this was used to study luminescence from the radical cation of tris(4‐methylphenyl)amine and the radical anion of 9,10‐anthracenedione electrogenerated in situ.
Comparison of the adsorptive voltammetric behavior of avidin and streptavidin
Authors: Buckley Eileen , Alvarez Jose M. Fernández , Smyth Malcolm R. , O'Kennedy Richard
Published: May 2005

The adsorptive voltammetric behavior of the binding proteins avidin and streptavidin was investigated at a stationary mercury drop electrode. It is demonstrated that, although streptavidin contains no disulfide linkages or sulfur‐containing amino acids, it gives rise to voltammetric behavior similar to avidin, which is a glycoprotein containing two cysteine residues per subunit and one interchain disulfide linkage. The adsorptive accumulation of both proteins was investigated both at open circuit and under electrolytic conditions. It is shown that avidin shows preferential adsorption characteristics under open circuit conditions, and under electrolytic conditions when the potential of the electrode was held at positive potentials. Streptavidin, on the other hand, shows preferential adsorption characteristics when accumulation is carried out at open circuit. This behavior is explained by considering the charged nature of the proteins under the experimental conditions used in this study. It would appear, therefore, that the voltammetric peaks obtained for globular and other proteins not containing prosthetic groups are due in part to processes other than the simple reduction of the disulfide linkage.
Disposable amperometric CO2 sensor employing bacteria and a miniature oxygen electrode
Authors: Suzuki Hiroaki , Tamiya Eiichi , Karube Isao
Published: May 2005

We have developed a disposable bacterial CO2 sensor employing a miniature Clark‐type oxygen electrode and autotrophic bacteria. To make the sensitive area less vulnerable to stress, to facilitate CO2 diffusion through the sensitive area, and to make the application to biosensors easier, the sensor structure was simplified by immobilizing the bacteria in an oxygen electrode cell along with a 0.1 M KCl electrolyte solution. We developed a novel process that allows immobilization of bacteria in a small sensitive area, thereby improving the response time. The response time of this CO2 sensor ranged from 1 to 3 minutes. A linear relationship was obtained for NaHCO3 concentrations between 0.5 and 3.5 mM (at 32°C and pH 5.5). The CO2 sensor can be used up to 10 times before disposal.
Catalytic adsorptive stripping voltammetric determination of cobalt as an α‐benzil dioxime complex in the presence of an extremely large excess of zinc
Authors: Bobrowski Andrzej , Bond Alan M.
Published: May 2005

There is considerable interest in determining trace amounts of cobalt in highly concentrated zinc solutions. Existing commonly used voltammetric methods such as those based on formation of dimethlyglyoxime complexes and adsorptive stripping voltammetry, while very sensitive for the determination of cobalt, do not always provide the necessary discrimination against the zinc (and nickel) processes. In the present work a recently described method, based on the formation and adsorption of a cobalt–α‐benzil dioxime complex and catalyzed by nitrite, has been optimized so at a 106 to 107 M concentration excess of zinc can be tolerated. Since the method is also relatively insensitive to nickel, it can be applied to highly purified zinc electrolytes.
Electrocatalytic oxidation of ascorbic acid at chemically modified electrodes
Authors: Kulys Juozas , Drungiliene Alms
Published: May 2005

Electrocatalytic oxidation of ascorbic acid (AA) in aqueous buffer solution at the p‐tetracyanoquinodimethane (TCNQ)‐, ferrocene (Fc)‐, 1,1′‐dimethylferrocene (DMFc)‐, and tetrathiafulvalene (TTF)‐modified graphite electrodes is carried out at each modifier's redox potentials. Over the linear range of current dependence on AA concentration, the sensitivity of the electrocatalytic systems corresponds to up to 0.1 A/M. At pH 6.5–8.0 a change in the electrocatalytic process rate is less evident (for TCNQ, TTF) or is increased by a factor of 4.9 (DMFc). The electrocatalytic current is only slightly dependent on electrode rotation speed. The electrodes retain about 80% of their initial response over a 2‐month period of operation.
Flow injection determination of methionine with amperometric detection at a stable modified electrode
Authors: Cox James A. , Dabek‐Zlotorzynska Ewa
Published: May 2005

A glassy carbon electrode that is modified by electrodeposition of a film comprising mixed valence ruthenium oxide stabilized by cyano crosslinlks catalyzes the oxidation of methionine at 0.92 V vs. Ag/AgCl. A linear calibration curve is obtained for flow injection amperometry over the range 0.6–180 μM with a 0.2 M K2SO4 carrier at pH 2, a 7.5 μL sample volume, and a 1.0 mL/min flow rate. The sensitivity is 20 ± 0.3 nA/μM at a 0.07 cm2 electrode. With a single surface preparation, the sensitivity of the method remains constant over more than 3 weeks with daily use. The method also was used with carriers of the composition of common liquid chromatographic eluents such as various citrate–phosphate mixtures and a 0.1 M chloroacetic acid solution at pH 3.0 in 1% acetonitrile.
Polarographic identification and determination of synthetic coloring matter in corks
Authors: Barros Aquiles Araújo , Rodrigues José António M.
Published: May 2005

In the final treatment of corks a certain amount of coloring matter must be added to restore the natural color that is lost during manufacturing. The coloring matter most widely used is Sunset Yellow FCF. Another food coloring matter, Orange II, which is not permitted for use, is often incorporated. Unfortunately both dyes exhibit similar polarographic behavior, making it almost impossible to differentiate between them. This work describes a polarographic procedure that allows one to distinguish between the two coloring materials. An application of the method to the analysis of corks is described, including the quantitation of the coloring matter identified. Detection limits less than 100 ppb. were obtained, corresponding to an amount of coloring matter of about 2 μg per cork.
Modified electrodes for electrochemical sensors
Authors: Wang Joseph
Published: May 2005

Chemically modified electrodes exhibit unique behavior that can greatly benefit electrochemical sensing. In this article we review the development and applications of modified electrodes for chemical sensing. After a general introduction, different strategies for surface modification, as employed in chemical sensing, are discussed in detail. Special attention is given to permselective coatings, which offer controlled access at the sensor surface or the surface immobilization of biological entities that specifically recognize the analyte. Better, understanding of these modified electrodes is achieved by using high resolution surface characterization techniques. Future prospects are evaluated.
Signal shapes and single‐boundary measurements in flow injection analysis with amperometric detection
Authors: Fogg Arnold G. , Zhao Rui
Published: May 2005

The shapes of normal and reverse flow injection (nFI and rFI) signals have been studied using single‐channel manifolds, amperometric and visible spectrophotometric detection, and small and large (> 1.5 mL) injection volumes. The shapes of nFI and rFI signals are fundamentally different because in rFI the sample, being the carrier stream, is present in essentially infinite volume. For this reason, rFI signals are broader and are prone to double‐peak formation at lower injection volumes than are nFI signals. Contributions to the final signal from dispersion at the front and rear boundaries of the injected bolus frequently are, or appear to be, unequal. With loop injection, the rear boundary travels further than the front boundary and is dispersed more: injection by stream switching removes this factor. With spectrophotometric detection, correction for large and opposite refractive index effects at the two boundaries may be required. In amperometric detection, differences in acidity of carrier stream and injectate can cause significant changes in background current on switching and can distort the signal at low concentrations of monitorand. When these factors are eliminated, however, other factors causing peak height and peak shape differences remain: differences in dispersion rates of reactants, and of reaction rates, appear to be the major factors.
Comparative studies between ion‐selective field effect transistors and ion‐selective electrodes with polymeric membranes
Authors: Miyahara Yuji , Simon Wilhelm
Published: May 2005

Characteristics of ion‐selective field effect transistors (ISFETs) and ion‐selective electrodes (ISEs) with solvent polymeric membranes were compared for slope, selectivity, drift, and hysteresis. Drift and hysteresis of ISFETs were significantly inferior to those of analogous ISEs. Experiments using conventional ISEs with internal electrolyte solutions and ion‐selective liquid membranes of different kinds indicate that both primary ion and ionophore are necessary in the internal electrolyte solution and the ion‐selective membrane, respectively, to achieve small drift and small hysteresis. It is, therefore, concluded that to realize highly reliable membrane‐solid contact devices, the interface between the membrane and the solid in membrane–solid contact devices like ISFETs and coated wire electrodes (CWEs) should be electrochemically defined.
Determination of some metal ions using lichen‐modified carbon paste electrodes
Authors: Connor Michelle , Dempsey Eithne , Smyth Malcolm R. , Richardson David H. S.
Published: May 2005

Lichens have long been used as biomonitors of environmental pollution. We therefore investigated the application of lichen‐modified carbon paste electrodes (CPEs) for the determination of lead(II) and copper(II) using differential pulse anodic stripping voltammetry. These electrochemical biosensors incorporate the biological selectivity of lichen species such as Cladonia portentosa and Lobaria pulmonaria, and the genus Roccella, with the sensitivity of electrochemical detection. As such, they may offer new reactivity patterns that could be exploited in the determination of trace metal ions in environmental samples and in speciation studies. The voltammetric responses were evaluated with respect to pH of accumulation (carried out under open circuit conditions), pH of electrolyte, solution, metal ion concentration, percentage lichen loading in the carbon paste, interferences, and surface renewal.
Comparison of adsorptive stripping voltammetry at mercury and carbon paste electrodes for the determination of ciprofloxacin in urine
Authors: O'Dea Philip , Garcíc Agustín Costa , Ordieres Arturo J. Miranda , Blanco Paulino Tuñón , Smyth Malcolm R.
Published: May 2005

We compared hanging mercury drop electrodes (HMDEs) and carbon paste electrodes (CPEs) for the determination by adsorptive stripping voltammetry (AdSV) of the antibiotic ciprofloxacin in urine. The antibiotic compound could be preconcentrated at both electrode surfaces, with carbon paste electrode yielding a better performance. These electrodes could be used to determine between 6 × 10−7 and 4 × 10−6 M ciprofloxacin in urine. A cleanup procedure (with 81% recovery), utilizing a C18 Sep Pak cartridge, was required to separate ciprofloxacin from the biological matrix prior to adsorptive stripping analysis. The method was applied to the determination of ciprofloxacin in spiked urine samples with a relative standard deviation of 4.1%.
Coated wire electrodes in the analysis of surfactants of various types: An overview
Authors: Vytřas Karel
Published: May 2005

Simple ion‐selective electrodes of the coated wire type were prepared using an ordinary aluminum wire conductor, coating the central wire with the membrane formed by plasticized poly vinyl chloride. These simple and inexpensive electrodes can be used advantageously as sensors in ion pair formation‐based titrations of surfactants of various types. Cationic surfactants are titrated using sodium tetraphenylborate titrant yielding titration curves with sharp potential breaks. For the determination of nonionic surfactants containing poly oxyalkylene chains, the method used was based on the precipitation of ternary compounds with sodium tetraphenylborate in the presence of bivalent metal ion with an ionic radius higher than 100 pm. Also ampholytic surfactants can be titrated directly with tetraphenylborate in acidic solutions, in which they are cationic; but for the determination of some of them, back‐titration is more convenient. Anionic surfactants are titrated using lipophilic cationic titrants such as quaternary ammonium or pyridinium salts. Some mixed systems can also be analyzed. Several examples are given.
Study of the adsorptive stripping square‐wave voltammetry of bovine serum albumin
Authors: Flores J. Rodríguez , Marín C. , Gonzalez E. , Pariente F. , Lorenzo E.
Published: May 2005

The adsorptive stripping square‐wave voltammetric behavior of bovine serum albumin (BSA) is described. Conditions were optimized for the determination of this protein with respect to accumulation potential, accumulation time, drop size, scan rate, frequency value, and electrolyte concentration. Under these optimum conditions for the determination of BSA, two calibration plots were obtained. For an accumulation time of 60 seconds, the plot was linear in the range 0.25–1.25 μg/mL of BSA (r = 0.997); for an accumulation time of 180 seconds, the linear range was 0.10–1.25 μg/mL of BSA (r = 0.997). The square‐wave procedure offers the advantages of speed, higher sensitivity for the determination of BSA, and the discrimination against background currents. This method was applied successfully for the determination of total protein in fetal calf serum.
Electrochemical study and determination of todralazine by adsorptive stripping voltammetry
Authors: de Balugera Z. Gomez , Barrio R. J. , Goicolea A. , Arranz J. F.
Published: May 2005

The electrochemical reduction and adsorption of todralazine on the hanging mercury drop electrode are explored. These properties allow the development of a sensitive adsorptive stripping voltammetric procedure, with a detection limit of 3.2 × 10−9 mol L−1. A method is proposed for rapid determination in commercial preparations and human serum.
Electrochemical detection of todralazine in high‐performance liquid chromatography
Authors: Barrio R. J. , de Balugera Z. Gomez , Arranz J. F. , Goicolea A.
Published: May 2005

The electrochemical behavior of todralazine was studied by cyclic voltammetry on a glassy carbon electrode at different pH values. The results obtained were used in the electrochemical detection of todralazine in chromatographic effluents. The optimum detection potential was 0.90 V (vs. SCE). The limit of detection was 0.36 μg/L and the limit of determination 4.8 μg/L. The method can be applied to the determination of todralazine in human serum It offers significant advantages in sensitivity, specificity, and accuracy with respect to other reported methods.
Electrochemical behavior of tizanidine at the mercury electrode I. Reduction mechanism and surface state study
Authors: Quarin G. , Viré J.‐C. , Patriarche G. J. , Ruiz B. Lope , Christian G. D.
Published: May 2005

The electrochemical behavior of Tizanidine has been studied using dc, ac, and pulse polarographic techniques. Reduction of the compound occurs through an electrochemical mechanism involving a six‐electron transfer. Autoinhibition of the process resulting from the adsorption of species affects the reduction rate constants. At the electrode surface, adsorption proceeds through a competition between the oxidized and reduced forms.
Amperometric operation of porous flow‐through electrodes at very low conversion efficiencies in flow stream detectors
Authors: Zhu Caobin , Curran David J.
Published: May 2005

The limiting current equation for a porous flow‐through electrode operated amperometrically at low conversion efficiencies can be expressed in the same general format as that for amperometric detectors of other types. The equation shows that a critical dimension for the porous electrode is the pore diameter, the limiting current being inversely proportional to the two‐thirds, power of the pore radius. Experimental verification was obtained using reticulated vitreous carbon (RVC) electrodes.
Anodic stripping voltammetry in highly‐resistive media by electrodes supported on ion‐exchange membranes
Authors: Schiavon Gilberto , Zotti Gianni , Toniolo Rosanw , Bontempelli Gino
Published: May 2005

An electroanalytical device is described that is suitable for trace metal analysis by anodic stripping voltammetry (ASV) in highly‐resistive media in the absence of supporting electrolytes. It consists of a thin mercury film electrodeposited at the glassy carbon‐ion‐exchange membrane interface obtained by clamping a glassy carbon ring to one surface of a perfluorinated ion‐exchange membrane (cationic, Nafion 117, or anionic, Tosflex IE SA48). The inner surface of the membrane is in contact with an electrolyte solution (0.01 M HClO4), containing the counter and reference electrodes. The ion‐exchange membrane replaces a conventional supporting electrolyte dissolved in the analyte sample and can be regarded as a solid polymer electrolyte (SPE) confined to the near neighborhood of the working electrode. This device has been used to perform differential pulse anodic stripping voltammetric (DPASV) analyses of electrolyte‐free aqueous synthetic samples containing copper and lead ions. Better results are found at glassy carbon‐supported mercury electrodes facing anionic Tosflex membranes, since similar devices assembled with cationic Nafion membranes experience a memory effect associated with blockage of metal ions, due to cation‐exchange processes that occur during the stripping redissolution step, even though these processes are able, at the same time, to lead to an increase of DPASV peaks due to metal ion accumulation near the electrode surface. Approximate detection limits of 3.5 × 10−10 M (0.02 ppb) for Cu2+ and 3 × 10−10 M (0.05 ppb) for Pb2+ are estimated at Tosflex‐equipped devices for a signal‐to‐noise ratio of 3. Possible modifications aimed at improving the performance of such a device are discussed.
A Potentiometric approach to the study of the antagonism between acetazolamide and I‐carnitine congeners on carbonic anhydrase activity
Authors: Botré Claudio , Botré Francesco , Pranzoni Cinzia
Published: May 2005

The in vitro interactions among carbonic anhydrase (CA), acetazolamide (ACTZ), and some short chain acylcarnitines (l‐ and d‐isomers) were studied by means of a recently developed potentiometric method of analysis, based on a pCO2 sensor. The l‐ and d‐isomers of carnitine (C), acetylcarnitine (AC), propionylcarnitine (PC), and isobutyrrylcarnitine (iBC) were found not to affect CA catalytic activity in the absence of other compounds. Upon testing in the presence of ACTZ, the i‐isomers of the carnitine congeners were shown to antagonize the chemical inhibition of carbonic anhydrase II from bovine erythrocytes, whereas in this case the d‐isomers did not show any effect. The results obtained in these experiments, carried out at 25 and at 37°C, confirm the high reliability of this new approach and highlight the positive effect of l‐carnitine congeners on CA catalytic activity. The potentiometric method should be suitable for monitoring the interaction of other enzymes and CA.
Electrochemical transducers for in vivo monitoring
Authors: Vadgama Pankaj , Desai Mohamed , Crump Paul
Published: May 2005

Electrochemical sensors have seen extensive development in recent years, particularly with regard to their use in biological fluids. Their facility for near‐reagentless assay, together with an ability to generate a continuous signal, has made them an ideal choice for in vivo monitoring. Both Amperometric and potentiometric devices have been fabricated for practical monitoring. Ions, gases, and metabolites have been assayed, thereby providing useful biological and clinical insights. This view provides a description of the major types of electrochemical sensors used in vivo, together with some of the problems associated with their biological interfacing for both extracorporeal and invasive monitoring.
The voltammetric response of ethanolamine at gold electrodes in alkaline media
Authors: Jackson Warren A. , Lacourse William R. , Dobberpuhl David , Johnson Dennis C.
Published: May 2005

Voltammetric data are described that were obtained at Au electrodes in 0.1 M NaOH for ethanolamine and related compounds using a rotated disk electrode (RDE) and a thin‐layer electrochemical cell (TLEC). The anodic signal for the alcohol group of ethanolamine is much greater than for ethanol at the same concentration. This is attributed to the benefit of pre‐adsorption by the amine group of ethanolamine on the Au surface. Oxidation of the alcohol group of ethanolamine is terminated by formation of surface oxide. However, oxide formation appears to catalyze oxidation of the amine groups of ethanolamine and ethylamine. A value of n = ca. 4.6 eq mol−1 was determined for oxidation of the alcohol group of ethanolamine by exhaustive electrolysis in the TLEC. Glycine is tentatively concluded to be an oxidation product on the basis of n and the result of a chromatographic analysis of the contents of the TLEC following electrolysis at 0.0 V vs. SCE.
A redox‐active polymer film mediated enzyme electrode for amperometric determination of free cholesterol
Authors: Oyama Noboru , Ikeda Shin , Suzuki Mikiko , Ohsaka Takeo
Published: May 2005

A new amperometric sensor for determination of free cholesterol based on a bilayer‐film coating has been fabricated and its sensor characteristics have been examined by cyclic voltammetry and under steady‐state conditions. The electrode substrate was coated with two kinds of polymeric films in a bilayer state, i.e., first with the redox‐active cobalt tetrakis(o‐aminophenyl)prophyrin polymer (poly‐CoTAPP), and then with the enzyme film consisting of bovine serum albumin and cholesterol oxidase (CHOx). In this sensor system for assay of free cholesterol, oxygen consumption could be monitored by measuring the current for oxygen reduction electrocatalyzed by the inner poly‐CoTAPP film according to the following reaction sequence:magnified imagewhere reactions 1, 2, and 3 correspond to the cholesterol–cholesterol oxidase enzymatic‐reaction, the electrocatalytic reduction of O2 by the poly‐CoTAPP film, and the electrode reaction of Co(III/II)TAPP couple in the poly‐CoTAPP film, respectively. The reproducible relationship between concentration of free cholesterol and sensor output was obtained. The sensitivity and the dynamic range were found to depend on the amount of CHOx confined in the enzyme film.
Lead ion sensitive electrode based on a supported BLM system
Authors: Salamon Zdzislaw , Ti Tien H.
Published: May 2005

The lead ion sensitivity of a solid‐supported BLM system containing TCNQ (7, 7, 8, 8‐tetracy‐anoquinodimethan) as an electron mediator in 4, 4′‐n‐octyl‐cyanobiphenyl (8CB) dissolved in squalene, with a teflon coated platinum wire as a solid support, has been investigated with cyclic voltammetry. The results have shown that TCNQ in a cyanobiphenyl bilayer membrane produces a unique System that increases by three orders of magnitude the lead ion sensitivity of the platinum electrode. Cyclic voltammograms have also shown that a charge‐transfer complex between liquid crystal and TCNQ molecules is created and participates in redox reactions.
Amperometric detection of sugars in food at a nafion‐copper modified electrode
Authors: Mannino Saverio , Rossi Margherita , Ratti Simona
Published: May 2005

The characteristics and applicability of a Nafion‐copper modified electrode for the determination of some sugars in food samples are described. Coating with a Nafion membrane and subsequent immersion in a copper solution provides a good barrier against many electroactive hydroxyacids commonly found in food samples. The Nafion modified electrode is stable, can be easily renewed, and shows reproducible results. The analytical utility of the polymer‐coated electrode is demonstrated by application to wine and milk samples.
Enzyme‐modified carbon paste: Tetrathiafulvalene electrodes for the determination of acetylcholine
Authors: Hale P. D. , Liu L.‐F. , Skotheim T. A.
Published: May 2005

The response characteristics of a new sensor for determining acetylcholine are reported. The sensor is based on a carbon paste electrode containing the enzymes acetylcholinesterase and choline oxidase and the electron transfer mediator tetrathiafulvalene (TTF). TTF is shown to efficiently reoxidize the reduced flavin adenine dinucleotide centers of choline oxidase. Acetylcholine calibration graphs are obtained in the range 10−6 to 10−3 M in pH 7.0 phosphate buffer, and the sensors are shown to operate efficiently at low applied potentials, where electrochemical interference due to oxidation of ascorbic acid is minimized.
Langmuir–blodgett films of doxyl‐stearic acids: Cyclic voltammetry
Authors: Richardson T. , Roberts G. G. , Barghout R. , Compton R. G. , Riley D. J.
Published: May 2005

The electrochemical oxidation of Langmuir–Blodgett films of n‐doxyl‐stearates (n = 5, 7, 12, 16; present as their cadmium salts) on indium tin oxide electrodes has been studied. The n = 12 species gives cyclic voltammograms (CVs) that reveal split peaks consistent with the formation of an ordered partially oxidized layer with a structure controlled by interactions of longer range than nearest neighbor.
Batch injection analysis with the rotating disk electrode
Authors: Chen Liang , Wang Joseph , Angnes Lucio
Published: May 2005

The use of the rotating disk electrode (RDE) for batch injection analysis (BIA) is illustrated. The technique involves injections of microliter samples into a large‐volume blank solution, at a fixed location below the disk center. Transient response peaks—similar to those of flow injection analysis—are observed, reflecting the transport of the sample plug toward and away from the RDE. The effects of various experimental variables on the BIA/RDE operation are described. Injection rates of several thousand samples per hour can be achieved, with relative standard deviations of 1–3%, and detection limits at the micromolar (ng) level.
Separation and identification of isoflavones with on‐line liquid chromatography‐electrochemistry‐thermospray mass spectrometry
Authors: Dewald Howard D. , Worst Sue Anne , Butcher Jared A. , Saulinskas Elaine F.
Published: May 2005

The on‐line high‐performance liquid chromatography‐electrochemistry‐thermospray mass spectrometry (LCEC‐LC/MS) for separation and identification of the phenolic isoflavones genistein, formononetin, and Biochanin A is described. The isoflavones are separated on a C‐18 reversed phase column with methanol: 0.1 M ammonium acetate pH (70:30 v/v) as eluent, which is compatible for both LCEC and LC/MS detection. Low ng detection is achieved with a conventional glassy carbon thin‐layer electrochemical cell at 1.3 V vs. Ag/AgCl. Selected ion monitoring (SIM) mode LCMS results in detection levels at the 20–50 ng range, and the compounds are positively identified. In the on‐line detection, the electrochemical cell is connected to the thermospray and the column effluent flows from the working electrode into the heated thermospray capillary tube. The results show that on‐line coupling between a thin‐layer LCEC and a thermospray‐LC/MS can be used to characterize analytical systems.
Trace determination of antimony and bismuth in snow and water samples by stripping voltammetry
Authors: Postupolski Andrzej , Golimowski Jerzy
Published: May 2005

Simultaneous determination of antimony and bismuth was performed from 0.5 M HCl solution that contained 0.1 M hydrazine, using the hanging mercury electrode by differential pulse anodic stripping voltammetry with very slow potential scan rate and small pulse amplitude. The influence of HCl and chloride concentrations on the peak shape of Bi and Sb and the influence of other ions and organic substances were investigated. For the determination of antimony and bismuth in water and snow samples, the UV irradiation and the reduction of Sb(V) to SE(III) by hydrazine in boiling solution were applied. The detection limit for Bi and Sb is 20 ng L−1.
An XPS investigation of silver bromide‐coated ion‐selective electrodes
Authors: Strydom C. A. , Van Staden J. F. , Strydom H. J.
Published: May 2005

XPS data of AgBr‐coated ion‐selective electrodes exposed to high concentrations of Ag+, Cl−, Br−, I−, and NH3revealed a change in the surface properties of the original electrode. A 40 min to one week exposure of the silver bromide ion‐selective electrode surface to solutions containing high concentrations of chloride ions leads to the formation of a mixed halide layer, as the chloride ions are incorporated in the surface. Exposure to high concentrations of iodide‐containing solutions results in a new silver iodide layer on top of the original silver bromide laver. Silver ions diffuse to the newly formed layers. NH3results in the rapid degradation of the AgBr surface as the diamine complex, Ag(NH3)+2, is formed.
Spectroelectrochemistry of phenylnitromethane on gold and silver electrodes
Authors: Holze Rudolf
Published: May 2005

The spectroelectrochemical behavior of phenylnitromethane (nitromethylbenzene) dissolved in neutral and acidic electrolyte solutions at gold and silver electrodes is described. Observed cyclovoltammetric peaks are attributed to the reduction of the nitro group. Surface Enhanced Raman spectra (SERS) of adsorbed molecules are interpreted based on an assignment of the Raman band of the free PNM using literature data. A coordination via the oxygen atoms of the nitro‐group and consequently a tilted or perpendicular orientation of the adsorbed molecule with respect to the electrode surface are concluded.
Adsorptive stripping voltammetry for determination of trace amounts of aluminum with calmagite
Authors: Stryjewska Ewa , Rubel Stanislaw
Published: May 2005

Experimental parameters for determination of aluminum (up to 15 ppb) were evaluated in acetate (pH = 4.2) and borate (pH = 8.9) buffer solutions. Because the reaction of Calmagite in acetate buffer requires heating (10 min, 90°C) the total analysis time is relatively long. This inconvenience is circumvented by using a borate buffer. The complexation reaction is nonspecific in both media. Iron(III) should be reduced using hydroxylamine hydrochloride, whereas copper(II) and some other metals may be eliminated by electrolysis. The developed method was used for aluminum determination in reference material—flour V‐8 (IAEA‐Vienna), tap water, and commercial 4% acetic acid before and after boiling in an aluminum pot.
Determination of glutamine in serum using an amperometric enzyme electrode
Authors: Villarta Rhodora L. , Palleschi Giuseppe , Suleiman Ahmad , Guilbault George G.
Published: May 2005

An amperometric enzyme electrode for the determination of L‐glutamine was developed. The probe consisted of a platinum electrode that senses hydrogen peroxide produced from the reactions catalyzed by glutaminase and glutamate oxidase, which are co‐immobilized on a preactivated Immobilon‐AV Affinity membrane. Protective membranes eliminated interferences from L‐glutamate and most compounds electroactive at a similar potential. The response of the probe was linear over the concentration range 1 × 10−6 M to 7.5 × 10−4 M. L‐Glutamine in serum samples obtained from healthy volunteers was determined using the probe, and the results correlated well with previously reported values.
Blank response at glassy carbon electrodes in a flow injection system
Authors: Xu Yan , Halsall H. Brian , Heineman William R.
Published: May 2005

The blank response at glassy carbon electrodes in a flow injection system consists of a transient component and a steady state (residual current) component. The transient response is attributed to nonfaradaic current and faradaic current from the oxidation‐reduction of electroactive surface functional groups on glassy carbon. The magnitude of the transient response was dependent on the potential applied to the electrode, temperature, ionic strength and pH of the injected sample solution, and independent of the flow rate. A linear relationship exists between the transient response and the difference in concentration of ionic species or pH between injected sample and the carrier. A differnce of 0.01 M ionic concentration or 0.04 pH unit between carrier and injected sample could change the transient charge by ca. 0.038 μC/cm2. The shape of the transient response due to pH difference at high positive potential indicates that some changes occur on glassy carbon surface in this potential region.
Cyclic voltammetric study of some calcium antagonist dihydropyridines in aqueous medium
Authors: El Jammal A. , Vire J‐C. , Patriarche G. J. , Palmeiro O. Nieto
Published: May 2005

The electrochemical behavior of several calcium antagonists of the dihydropyridine family has been investigated in aqueous buffered solution using a glassy carbon electrode. Both oxidation of the dihydropyridine ring and the reduction of the nitro or benzoxadiazole moiety are observed using cyclic voltammetry and the shape of the voltammograms depending on the initial scan direction. Each process may interfere with the other. The single reduction peak corresponds to a four‐electron transfer giving rise to the hydroxylamine. Reversing the scan leads to the nitroso derivative, its reversibility depends on the 2‐ or 3‐position of the nitro group. Oxidation of the dihydropyridine ring proceeds through a two‐electron exchange. However, nicardipine, which possesses a dialkylbenzylamine side chain, exhibits two additional peaks; the first due to the methoxylation of the side chain, and the second attributed to the oxidative chlorination of this moiety. Potentials are pH dependent. A general EC mechanism is proposed for the overall process.
Voltammetric detection and analysis of the behavior of diethylstilbestrol oxidation products
Authors: Séquaris Jean‐Marie , Fritz Joan
Published: May 2005

Peroxidase‐mediated oxidation of diethylstibestrol (DES), a synthetic estrogen, has been proposed as a pathway in DES‐induced carcinogenicity. However, the transient nature of the DES oxidation product, DES‐quinone (DES‐Q), requires a rapid method such as cyclic voltammetry to study its stability and reactivity. Thus, the irreversible tautomerization of DES‐Q into dienstrol form (Z, Z‐DIES) is described by a two step mechanism. Tautomerization kinetics are studied as a function of pH and temperature. A significant descrease of half‐life for DES‐Q is observed in the presence of the glutathione thiolate form. Furthermore, voltammetric investigations were performed in dimethylformamide to detect the semiquinone radical of DES‐Q, a suspected genotoxic product.
Electro‐oxidative decarboxylation of D‐gluconic acid to D‐arabinose on graphite electrodes
Authors: Pezzatini Giovanni , Wei He , Guidelli Rolando , Pergola Francesco
Published: May 2005

A voltammetric investigation of the direct electro‐oxidative decarboxylation of D‐gluconate ion to D‐arabinose on spectroscopic graphite electrode from methanol–water mixtures as well as from aqueous solutions is described. Practically a 100% yield in D‐arabinose and and 80% yield in current were realized. The kinetic behavior points to a rate‐determining release of the first transferring electron from the gluconate anion to the electrode, followed by a cleavage of the C‐1–C‐2 bond and by the resulting decarboxylation.
Theoretical equations for electrochemical processes preceded by concurrent first‐order chemical reactions in DC polarography: Application to the study of the interaction between guanine and diacetyl
Authors: Mellado José Miguel Rodríguez , Montoya Mercedes Ruiz , Galvín Rafael Marín
Published: May 2005

Theoretical expressions are derived for electrochemical processes preceded by two concurent first‐order chemical reactions in dc polarography by using both the approximation of convective diffusion under the steady state conditions and the dimensionless differential equations of the Nernst diffusion layer approximation. These equations are formally identical to those obtained for CE and CEC processes, with differences only in the kinetic terms. Study of the interaction between guanine and diacetyl shows the usefulness of these equations. A value of 7 × 104 M is obtained for the formation constant of the adduct guaninediacetyl at 25°C.
Amount adsorbed in adsorption voltammetry. Part 1. Amount adsorbed in the adsorptive accumulation at a symmetric spherical electrode in a stirred solution
Authors: Jin Wenrui , Hou Yongchun , Yan Changtai , Wang Jianyan , Sun Changlin
Published: May 2005

The equation for the amount adsorbed during an adsorptive accumulation at a symmetric spherical electrode in a stirred solution has been derived and discussed under the condition of strong adsorption. When the angular velocity of the solution, ω0, is larger than 64 rad/s and the preconcentration time, ta, is more than 30 s, the equation can be simplified as Γ′(ta) = 4 πkD2/3 r ν−1/6 ω ta c*. The equation has been verified experimentally.
Biosensor for detection of organophosphate and carbamate insecticides
Authors: Marty J‐L , Sode K. , Karube I.
Published: May 2005

An enzyme sensor for the determination of organophosphate and carbamate insecticides is described. The mechanism is based on the coimmobilization and sequential enzymatic reactions of acetylcholinesterase and choline oxidase. The inhibition of acetylcholinesterase is measured as decreased formation of hydrogen peroxide (H2O2) as monitored by a H2O2 sensor. As low as 10 nM paraoxon can be determined with this technique. The long‐term stability of the sensor is two months, when stored at 4°C in phosphate buffer, and one year in a dry state.
A novel batch electrode design for use in stripping potentiometry facilitating medium exchange
Authors: Jagner Daniel , Renman Lars , Wang Yudong
Published: May 2005

Medium exchange between electrolysis and stripping steps affords numerous advantages in both voltammetric and potentiometric stripping techniques. A new electrode design for batch mode stripping analysis that allows simple medium exchange under potentiostatic control is described. This is achieved by adherence of a drop of sample to a glass tube containing a glassy‐carbon disc working electrode and a porous ceramic plug, which is in liquid contact with the inner solution in which the reference and counter electrodes are situated. The electrode can be used both for manual operation and for an automated system with a sample changer. Its use is demonstrated in the constant‐current stripping potentiometry determination of the dimethylglyoxime complexes of nickel(II) and cobalt(II) after medium exchange with stripping in 5 M CaCl2, thus avoiding interferences from dissolved oxygen and excessive amounts of zinc(II).
Considerations of the pH dependence of hydrous oxide films formed on iridium by voltammetric cycling
Authors: Hitchman Michael L. , Ramanathan Subramaniam
Published: May 2005

The electrochemical behavior and the analytical utility of hydrous oxide films, formed on iridium by voltammetric cycling, have been studied by evaluating the dependence of the apparent Standard Electrode Potential (E°′) and the ratio of protons to electrons (p/e) participating in the potential determining equilibria on the charge storage capacity. A model based on electron exchange involving protons in solution and conductive sites on the hydrous oxide surface is proposed and it is shown that an increase in population of the conductive sites can be correlated with an enhancement in proton exchange capacity. The influence of the pretreatment is shown to be an important factor in determining both E°′ and p/e. The implications of these results for the use of hydrous iridium oxide electrodes as potentiometric pH sensors are considered.