bluuebunny/crossref_metadata_2025 huggingface dataset:
Pattern recognition analysis of near‐infrared spectra by robust distance method
Authors: Cho Junghwan , Gemperline Paul J.
Published: May 2005

A method for pattern recognition analysis of near‐infrared spectra has been developed using robust distances determined by minimum volume ellipsoid (MVE) estimators of multivariate location and scatter. Classical methods such as the Mahalanobis distance method often fail in the presence of a moderate number of outliers in a training data set, while robust distance methods can tolerate a considerably larger proportion of outliers in a training data set Outliers can be detected by their relatively large robust distances and can be excluded from a training set without a priori knowledge of the nature of the data set. In this paper the properties of a robust distance method are examined using near‐infrared spectra of sulfamethoxazole and mixtures with its major degradation products, sulfanilic acid and sulfanilamide. The robust distance method successfully detected unacceptable samples (71.4%–89.3% (α = 0.05) or 78.6%–92.9% (α = 0.10)) even when they were inadvertently included in the training data set.
Some theoretical results on second‐order calibration methods for data with and without rank overlap
Authors: Kiers Henk A. L. , Smilde Age K.
Published: May 2005

GRAM, a method for second‐order calibration, has been introduced by Sanchez and Kowalski and later modified by Wilson, Sanchez and Kowalski. The methods are based on the claim that, in cases without measurement error they yield correct estimates for the concentration ratios and profiles of (rank‐one) analytes present in sample and mixture. This claim has not been proven rigorously. In the present paper, rigorous proofs are given for situations where the claims are valid indeed. In addition, it is shown that PARAFAC, an alternative method for second‐order calibration, can be used to obtain the same results. Next it is shown that the claims do not hold in cases with ‘rank overlap’ (partly overlapping profiles) and it is proven that a procedure by Wang et al. can still be used to assess some of the concentration ratios. A general framework is provided for a variety of second‐order calibration problems and the extent to which quantitative and qualitative information can be expected is given.
A review of robust process design approaches
Authors: Grize Yves L.
Published: May 2005

The aim of this paper is to present a simple structured review of the different approaches to robust process design to clarify their similarities and dissimilarities. It is primarily written for practitioners who wish to understand and compare the main ideas of each approach and to apply them to their work. Two examples are used to illustrate the different approaches and their corresponding data analysis strategies: the first one is a constructed example on a pigment kneading process and the second one is real example dealing with the validation of an HPLC method. A comparison of the different approaches is provided and some practical recommendations are formulated.
Algorithm for finding an interpretable simple neural network solution using PLS
Authors: Bro Rasmus
Published: May 2005

This communication describes the combination of a feedforward neural network (NN) with one hidden neuron and partial least squares (PLS) regression. Through training of the neural network with an algorithm that is a combination of a modified simplex, PLS and certain numerical restrictions, one gains an NN solution that has several feasible properties: (i) as in PLS the solution is qualitatively interpretable; (ii) it works faster than or comparably with ordinary training algorithms for neural networks; (iii) it contains the linear solution as a limiting case. Another very important aspect of this training algorithm is the fact that outlier detection as in ordinary PLS is possible through loadings, scores and residuals. The algorithm is used on a simple non‐linear problem concerning fluorescence spectra of white sugar solutions.
Optimization in organic synthesis. Sequential response surface modelling for obtaining kinetic information. Part 2: An experimental study of the williamson ether synthesis
Authors: Axelsson Anna‐Karin , Nordahl Åke , Carlson Rolf
Published: May 2005

In this work the utility of a new method for determining kinetic parameters by sequential response surface modelling, previously described (Part 1), is shown by applying it to an experimental study of a reaction with known kinetics. The nucleophilic substitution reaction between ethoxide and benzyl chloride, the Williamson ether synthesis, was selected as a model reaction. This reaction is known to proceed with second‐order kinetics. The method gives access to estimates of initial reaction rate which can be further used to obtain estimates of activation energy and reaction order of reactants. The results obtained are in good agreement with the estimated values of these parameters obtained with conventional kinetic experiments.
Robust non‐linear regression analysis
Authors: Roy Tapon
Published: May 2005

Several robust regression methods, including a new proposal, are described and their properties discussed. Resistance to various types of outliers and non‐normality is demonstrated. The techniques are applied to non‐linear regression models from chemical kinetics and calibration. Optimization of the types of objective functions encountered when applying robust regression is considered.
The deposition of aluminum thin films by CVD using a novel adduct of dimethylaluminum hydride
Authors: Jones Anthony C. , Houlton David J. , Rushwarth Simon A. , Flanagan Julia A. , Brown Juliette R. , Critchlow Gary W.
Published: May 2005

Thin films of aluminum have an important application in the metallization of silicon devices in very large scale integration technology. In this communication a new precursor, NMe2AlH(NMe2Et)2 has been used for the CVD of high purity aluminum in the temperature range 250–350 °C. In contrast to currently available precursors it is a free flowing and non‐pyrophoric liquid, making it less hazardous and more convenient for use in CVD.

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The deposition of platinum‐containing tin oxide thin films by metal‐organic CVD
Authors: Houlton David J. , Jones Anthony C. , Haycock Peter W. , Williams Edward W. , Bull John , Critchlow Gary W.
Published: May 2005

The metal oxide semiconductor SnO2 has a range of important applications, such as in transparent and conducting coatings on glass, and in gas‐sensing devices. CVD has a number of advantages as the technique of choice for the deposition of SnO2 thin films but development has in the past been hampered by the high toxicity of the available precursors and the necessity of adding an oxidant such as O2 or H2O. Here, SnO2 deposition from the relatively non‐toxic tetra‐t‐butoxide tin in the absence of added oxidant is reported. Platinum doping of the material is also discussed.
Novel, convenient, low cost alternative method for film fabrication: Titanium nitride thin films on alumina substrates for automotive applications from a molecular precursor, (CH3)3SiNHTiCl3
Authors: Narula Chaitanya K. , Czubarow Pawel , Seyferth Dietmar
Published: May 2005

The deposition of titanium nitride films on ceramic substrates from tetra‐ hydrofuran solutions of the title precursor is reported. It is demonstrated that the process, which involves a single dip‐coat—fire sequence, is a viable alternative to the CVD processes currently used, and that it is an economically feasible route for the mass production of porous TiN electrodes.

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A heat‐resisting acid catalyst: Thermal stability and acidity of a thin silica layer on alumina calcined at 1493 K
Authors: Katada Naonobu , Ishiguro Hideaki , Muto Koh‐ichi , Niwa Miki
Published: May 2005

The chemical vapor deposition of a thin layer of silica on alumina is shown to improve the thermal stability of alumina with respect to sintering and to reduce the loss of surface area of alumina during heating. Benzaldehyde‐ammonia titration showed that samples with high stability were almost completely covered by silica. These observations suggest that an ultrathin silica layer, probably a monolayer, thermally stabilizes the surface. Brønsted acidity was observed even after calcination at 1493 K: it was initially diminished by this calcination, but readily recovered on exposure to a humid atmosphere, whereas conventional solid‐acid catalysts are irreversibly deactivated by complete sintering.
Photo‐assisted chemical vapor deposition of gallium sulfide thin films
Authors: Pernot Patrick J. , Barron Andrew R.
Published: May 2005

Polycrystalline films of gallium sulfide may be deposited from [(tBu)GaS], (see Fig.) by photo‐assisted CVD at temperatures lower than by thermal CVD. It is found that the stoichiometry of the films is dependent on the wavelength window. The films are however found to be of the thermo‐dynamic hexagonal phase rather than the metastable cubic phase produced by thermal CVD.

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A study of the transition between growth of stoichiometric and silicon‐excess silicon carbide by CVD in the system MTS/H2
Authors: Josiek Andrei , Langlais Francis , Bourrat Xavier
Published: May 2005

Under conditions of medium decomposition of MTS (10–90 %), a transition between region A (growth of nearly stoichiometric SiC) and region B (Si‐excess SiC deposition) may be induced by the variations of total flow rate, total pressure or temperature in relatively small intervals. After the modification of one of these parameters, the growth rate reaches rapidly a new stationary value unless the modification leads to a transition from B to A. In this case, the growth rate increases during a transient stage before reaching the steady‐state mode. A growth model is presented which explains these observations. A TEM study confirms a prediction of this model.
Eurocvd 10—A nostalgic retrospect
Authors: Aylett Bernard J.
Published: May 2005

La Dolce CVD Vita!

Professor Aylett captures the flavor of the feast of scientific contributions and the culinary and alcoholic delights enjoyed by delegates at EUROCVD 10 in Lido di Jesolo. This highly successful meeting was the latest in the biennial series and it showed the breadth and depth of the CVD community in the European arena. In particular, the wide range of applications of CVD presented both in lectures and on posters, illustrated the extensive variety of practical targets for CVD workers to aim at in the future.
Atomic force microscopy on (001) surfaces of GaAs MOVPE layers
Authors: Pietzonka Ines , Hirsch Dietmar , Gottschalch Volker , Schwabe Reinhard , Franzheld Reiner , Bente Klaus , Bigl Frieder
Published: May 2005

Low dimensional materials are widely used in novel opto‐ and/or microelectronic devices. Therefore it is of great importance and fundamental interest to determine the correlation between variations of the crystal surface during growth and in situ development of microstructures. This paper reports on multistep formation of MOVPE GaAs analyzed by AFM, presenting and discussing images and cross‐section measurements of GaAs layers grown under various conditions.
Gas‐Phase Pyrolysis Mechanisms in Organometallic CVD
Authors: Russell Douglas K.
Published: May 2005

An overall CVD process is very complex, with contributions from steps which include gas‐phase reactions, mass transport, surface‐mediated chemistry, and nucleation. Traditional empirical optimization of growth parameters is now being replaced by more rational approaches to understanding the contributions of individual steps to the overall process. Mechanisms of gas‐phase pyrolysis of organometallic CVD precursors and their influences on deposition are reviewed here. Examples given show that spectroscopic techniques can provide valuable clues to factors which affect layer quality.
Thermodynamic approach to the OMCVD of titanium carbide from titanocene dichloride
Authors: Slifirski Joël , Teyssandier Francis
Published: May 2005

The deposition of TiC on steel at low temperatures is desirable. It can be achieved using readily decomposable precursor molecules, e.g., organometallics. However, this often results in excess carbon in a coating—the Figure shows the effect of precursor composition on the temperature of occurrence of excess carbon—and a deterioration in mechanical properties. This paper examines the theoretical influences of temperature, pressure, and hydrogen dilution on equilibrium carbon incorporation.

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Anisotropic materials prepared by OCVD: Organic molecular conductors
Authors: Caro Jaume , Garelik Susana , Figueras Albert
Published: May 2005

Organic compounds may play useful roles in future electronic devices. The preparation of thin films of molecular organic conductors will be an important step towards the development of organic‐based systems. This article reports on the preparation and characterization of TTF‐TCNQ layers grown by organic CVD (OCVD), which is based on classical thermal CVD. Highly oriented layers are deposited on glass substrates and the electrical properties are similar to those previously reported for films prepared under rather more complex high vacuum conditions.
Analysis and modeling of SIPOS deposition in a hot wall tubular reactor. Part I: Review of previous work and experimental study
Authors: Fayolle Francine , Couderc Jean‐Pierre , Duverneuil Patrick
Published: May 2005

LPCVD reactors, as illustrated in the Figure, are widely used in semiconductor manufacture. Modeling of these reactors has previously been restricted to relatively simple processes such as polysilicon deposition. This paper now examines the deposition of SIPOS (SiOx) by reviewing previous work, by identifying possible homogeneous and heterogeneous reactions, and by presenting new experimental results to complement existing data.

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Metal‐organic CVD of the high‐Tc superconductor YBa2Cu3O7−δ
Authors: Watson Ian M.
Published: May 2005

The great bulk of CVD effort on superconducting oxide materials has concerned MOCVD of the 93 K superconductor YBa2Cu3O7−δ. Most current work involves growth of triaxially oriented YBa2Cu3O7−δ films a few hundred nanometers in thickness on monocrystalline metal oxide substrates at 650–8500C. Optimized MOCVD processes now produce YBa2Cu3O7−δ films with crystallographic quality and electrical properties comparable to the best films prepared by physical vapor deposition techniques, and offer especially attractive opportunities for large‐area growth. Nevertheless, the metal δ‐diketonate precursors used in YBa2Cu3O7−δ MOCVD have limited volatility and other drawbacks, which have motivated extensive background research on barium sources in particular. Non‐traditional methods for delivering precursors to the deposition zone of a reactor, such as aerosol injection and flash vaporization techniques, have also been developed in response to these problems. A diverse range of YBa2Cu3O7−δ MOCVD processes, some involving plasma‐ or photo‐assisted deposition, are in current use. These have been optimized by largely empirical means, although thermodynamic analyses and mechanistic studies offer the prospect of controlling film deposition on a more scientific basis. Unique features of MOCVD in comparison with physical vapor deposition methods include the possibility of controlling film orientation through photochemical effects, and exploitation of the high surface mobility of adsorbed molecular precursors to grow YBa2Cu3O7−δ below 600°C. With reference to potential uses for MOCVD films, near‐term applications in passive microwave devices are considered in greatest detail.
Growth of Copper Films by Metal Organic Vapor Deposition Using (Pyrazolylborate)copper(I) Compounds
Authors: Plappert Elisabeth‐Charlotte , Stumm Thomas , van den Bergh Herbert , Hauert Roland , Dahmen Klaus‐Hermann
Published: May 2005

CuCl reacts with Na[HB(R3R5pz)3] and phosphine (PR3) or isonitrile (CNR) to yield volatile (pyrazolylborate)copper(I) complexes. These compounds were evaluated as MOCVD precursors. Using [{HB(pz)3}Cu(PEt3)] and [{HB(pz)3}Cu(PMe3)], thin copper films were grown by thermal metal organic chemical vapor deposition in a low pressure reactor in the temperature range 150–350°C. Polycrystalline Cu‐phases were obtained at temperatures as low as 150°C. The metallic films were characterized by four‐point‐probe resistivity measurements, AES, and XPS, as well as AFM and SEM. Selective deposition on metal‐seeded surface sites was observed on Pt, Au, Al, and W versus SiO2. Anti‐selective deposition was found to occur on Pd‐seeded samples.
The Kinetics of the Catalyzed CVD of Monocrystalline α‐Silicon Nitride Filaments
Authors: Guggenberger Michael A. , Hüttinger Klaus J.
Published: May 2005

Catalyzed chemical vapor deposition of α‐silicon nitride filaments from silicon subhydrides and ammonia was studied using calculation of nitrogen solubility in selected catalysts (silicon‐containing iron alloys), both in the solid and liquid‐state, by filament deposition experiments with catalysts of various composition and size, and by variation of the flow rates and partial pressures of precursor gases, the silicon subhydrides and ammonia. The results show that neither nitrogen solubility in, nor nitrogen diffusion through the catalyst plays a determining role in the deposition kinetics, as has been previously suggested. Instead, the deposition rate is determined by the partial dissociation of ammonia, which can be accelerated by adding diluent gases with a sufficiently high collision cross section. The catalyst material has an additional, strongly accelerating effect. The present state of research suggests that nitrogen is the preferred diluent gas and chromium an optimum alloying element.
Structural Properties of Yttria‐Stabilized Zirconia Films Grown on Silicon (001) Using MOCVD
Authors: Garcia Gemma , Casado Juan , Llibre Joan , Cifre Joan , Figueras Albert , Galí Salvador , Bassas Josep
Published: May 2005

Layers of yttria‐stabilized zirconia with different yttria content were prepared using MOCVD. The variation of the crystallographic parameters of the cell, as well as the residual stress of the deposits have been studied by XRD as a function of yttria content. The maximum value of the stress has been correlated with a deformation of the cell, in the cubic domain, due to an intrinsic structural modification of the crystals.
Growth of Iron, Nickel, and Permalloy Thin Films by MOCVD for Use in Magnetoresistive Sensors
Authors: Lane Penelope A. , Wright Peter J. , Oliver Peter E. , Reeves Christopher L. , Pitt Anthony D. , Keen John M. , Ward Michael C. L. , Tilsley Matthew E. G. , Smith Nigel A. , Cockayne Brian , Harris I. Rex
Published: May 2005

Thin films of elemental iron and nickel, plus a wide composition range of iron‐nickel alloys, have been deposited by atmospheric pressure metal organic chemical vapor deposition at a growth temperature of 200°C, using iron pentacarbonyl and nickel tetracarbonyl as the source precursors. Detailed magnetoresistance measurements of the permalloy layers showed that the maximum value of magnetoresistance occurred at a composition of approximately 90 % Ni10 % Fe, and the maximum sensitivity occurred at approximately 80 % Ni20 % Fe, in accordance with literature values. In addition, both the application of an 80 mT magnetic field during deposition and the annealing of samples at temperatures higher than the growth temperature of 200°C improved the magnetic properties.
A new approach to coulometry for flow‐through systems
Authors: Bao L. Y. , Tian Z. W.
Published: May 2005

A new method of flow‐through coulometry is presented. The fundamental principle is different from that in the conventional method. Two working electrodes are involved in the coulometric cell. An electrolysis efficiency of only 20 to 30% is required for the measurement. From the response coulombs (Q1 and Q2) of the two working electrodes, the charge (Qc) calculated by using Equation 4 correspond to an electrolysis efficiency of 100% and is independent of the temperature and flow rate.
Characterization of the voltammetric response at intracellular carbon ring electrodes
Authors: Lau Yau Yi , Chien Jennifer B. , Wong Danny K. Y. , Ewing Andrew G.
Published: May 2005

The intracellular response of ultrasmall carbon ring electrodes has been investigated. Adsorption of high molecular weight species (e.g., proteins, lipids, sugars) on the electrode surface appears to result in deterioration of the amperometric signal, making in vivo voltammetric measurements difficult. Assuming a linear dependence between the degree of electrode fouling and the number of scans taken in the neuronal microenvironment, an analytical method based on both pre‐ and postcalibration data is presented to evaluate the response obtained at deteriorating ultrasmall carbon ring electrodes during intracellular voltammetry. Additionally, poly(ester sulfonic acid)‐coated carbon ring electrodes have been used in an attempt to increase selectivity in intracellular voltammetry and to reduce the effects of electrode fouling. In vitro results obtained in solutions of dopamine, dihydroxyphenylacetic acid, and ascorbic acid indicate some exclusion of anionic species from the electrode by the negatively charged polymer film. Moreover, use of polymer‐coated electrodes in vivo result in such a decrease in the percentage of electrode fouling that the degradation of the response is only 45%. This leads to a more reproducible response and better detection limits compared to results from naked electrodes.
Use of EXAFS to probe electrode–solution interfaces
Authors: Dewald Howard D.
Published: May 2005

A review of the development and application of extended X‐ray absorption fine structure (EXAFS) spectroscopy for in situ structural characterization of chemical processes at he electrode surface is presented. The designs of the in situ electrochemical cells developed to date are shown. Applications are presented from the areas of metal passivation, spectroelectrochemistry, modified electrodes, underpotential deposition, and adsorption.
Highly sensitive and selective voltammetric detection of dopamine with vertically separated interdigitated array electrodes
Authors: Niwa Osamu , Morita Masao , Tabei Hisao
Published: May 2005

Highly sensitive (10−8 mol/dm3) and selective voltammetric detection of dopamine can be carried out with a closely spaced planar interdigitated array (IDA) or vertically separated new IDA electrodes. The sensitivity of dopamine was improved up to 10−8 mol/dm3 as a result of high collection efficiency and redox cycling, because twin electrodes with a very small gap make it possible to collect most of the active species oxidized at adjacent electrodes and then to return them to dopamine by reverse reduction before the chemical reaction has terminated. The influence of L‐ascorbic acid, which interferes with the detection of catecholamines, may be removed by oxidizing it at one electrode, because the oxidized acid converts rapidly to an electrochemically inactive species and is not detected at the other electrode. Dopamine was detected quantitatively in the presence of 10‐fold excess of L‐ascorbic acid in the same solution.
An electrochemical immunoassay for Clostridium perfringens phosholipase C
Authors: Cardosi Marco , Birch Stephen , Talbot Jane , Phillips Anthony
Published: May 2005

A sensitive two‐site, enzyme‐linked immunoassay utilizing electrochemical detection has been developed for Clostridium perfringens phospholipase C (α toxin). Alkaline phosphatase conjugated to a mouse monoclonal antibody is used as the enzyme label. The enzyme activity is measured using 1‐naphthyl phosphate as the enzyme substrate. The enzyme‐generated naphthol is detected amperometrically in a thin‐layer cell at a glassy carbon electrode after chromatography on a 50 mm C8 reverse phase column. Two assay formats are described, based on either microtiter plates or polydispersed polymeric microbeads. The limits of detection of the two assay formats were 67.1 and 13.0 ng/mL, respectively, with a total assay time of less than one hour. The performance characteristics of three possible substrates for the alkaline phosphatase catalyzed reaction are also described.
Homogeneous light‐induced electron transfer between 9,10‐anthracenedione and sodium tetraphenylborate: A channel electrode study
Authors: Compton Richard G. , Fisher Adrian C. , Wellington R. Geoffrey , Bethell Donald
Published: May 2005

The electron transfer between excited‐state 9,10‐anthracenedione (325 nm) and sodium tetraphenylborate (tetraphenylboron sodium) in acetonitrile solution is shown to form the radical anion of 9,10‐anthracenedione together with the BPh radical. The latter is known to decompose to biphenyl and other Products. A new channel electrode methodology is developed and characterized to deduce the mechanism of the reaction and to quantify its kinetics.
An XPS investigation of the influence of bromide and iodide solutions on the surface of silver chloride coated ion‐selective electrodes
Authors: Strydom C. A. , van Staden J. F. , Strydom H. J.
Published: May 2005

X‐Ray photoelectron spectroscopic (XPS) data of AgCl‐coated, ion‐selective electrodes exposed to solutions containing high concentrations of bromide and iodide ions revealed that the surface properties of the original electrode changed. The mixed phases, AgBrsCl1–s and AgIsCl1–s, seem to form initially on the electrode surface, with the existence of the AgICl phase much shorter than that of the AgBrCl phase. This indicates that the formation of the Agl surface layer is kinetically faster than the formation of the AgBr layer. In both cases XPS data showed the ultimate formation of AgBr and AgI layers on top of the original AgCl‐coated, ion‐selective electrode surface after being subjected to solutions containing either bromide or iodide ions. The conversion of the crystalline‐coated, chloride‐selective electrode surfaces to AgBr and AgI layers, however, transformed the chloride‐selective electrodes into bromide‐ or iodide‐selective electrodes with electrode properties different from those of the original electrode.
Flow injection analysis of myoglobin and hemoglobin at toluidine blue chemically modified electrode
Authors: Zhou Jianxun , Wang Erkang
Published: May 2005

Electrodeposition of the phenothiazine mediator titrant toluidine blue onto a glassy carbon substrate at an appropriate potential was used to construct a toluidine blue chemically modified electrode (CME) exhibiting electrocatalytic reduction for myoglobin and hemoglobin. The CME catalyzed the hemoprotein electroreduction at the reduction potential of the mediator molecule. When the CME as used as a detector for flow injection analysis at a constant applied potential of −0.30 V vs. a saturated calomel electrode, it gave detection limits of 20 and 50 ng (1.2 and 0.78 pmol) injected myoglobin and hemoglobin, respectively, with a dynamic linear concentration range over 2 orders of magnitude. After a brief equilibration period, the CME retained nearly 90% of its initial myoglobin response over 8 hours of continuous exposure to the flow‐through system.
Peroxidase–ferrocene modified carbon paste electrode as an amperometric sensor for the hydrogen peroxide assay
Authors: Sánchez Pilar Domínguez , Ordieres Arturo José Miranda , García Agustín Costa , Blanco Paulino Tuñón
Published: May 2005

A new enzymatic amperometric sensor for hydrogen peroxide based on a modified carbon paste electrode is described. Horseradish peroxidase and ferrocene mediator were immobilized by dissolution or dispersion in a graphite–paraffin oil paste. To prevent losses of immobilized chemicals under operational conditions, the electrode surface was coated with a Nafion membrane. The device exhibits a relatively fast response time (42 s for 95% of the steady‐state response) and yields currents linearly related to the hydrogen peroxide concentration over the 10−7 to 10−5 mol/L range in both static and flow injection operations. The slope of the calibration plot remained constant for more than 20 days. Flow injection assays of hydrogen peroxide at a sampling rate of about 70 injections per hour, with a relative standard deviation of 1.4%, are possible. An easy and low cost preparation procedure is described.
Voltammetric study of cadmium(II) ion in the presence of polysaccharides
Authors: Nadaly Anna M. , Ariño Cristina , Esteban Miquel , Casassas Enric
Published: May 2005

Complex formation of Cd(II) with alginic and polygalacturonic acids is studied by normal pulse (NPP), reverse pulse (RPP), and differential pulse polarography (DPP), as well as by cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). Titrations of Cd(II) with partially neutralized alginic or polygalacturonic acids, at different ionic strengths, by DPP and DPASV allow the precise determination of the apparent formation constant K of both systems. The systems appear to be labile on the different time scales of the various techniques. Adsorption of both polysaccharides, and the further induced adsorption of Cd(II), is evidenced clearly by NPP. On the other hand, the induced adsorption of Cd(II) is minimized under the conditions of RPP. The reversibility of the redox couple Cd2+/Cd(Hg) is not strongly affected by the presence of polysaccharides. Dependence of the apparent formation constants on the total ionic strength is reported.
Study of the radial and axial distribution of heavy metals in oak growth rings by stripping voltammetry
Authors: Queirolo F. , Valenta P. , Stegen S. , Sanchez A. M.
Published: May 2005

The concentrations of the heavy metals (Cd, Pb, Cu, and Zn) have been determined in oak growth rings from the polluted region of Königstein, Germany, by differential pulse anodic stripping voltammetry and compared to those in soil. The radial distribution was found to be the same for all four metals studied and features a distinct increase in the recent growth rings and a marginal increase in the transition zone between sapwood and heartwood. The toxic metals cadmium and lead are preferentially bound to lower parts of the tree, whereas for essential metals copper and zinc, monotonous axial distribution has been found in the range 0–5 m. This points to different degrees of mobility of heavy metal complexes in wood material.
Theoretical model of the response of pH‐based enzyme sensors
Authors: Głab Stanisław , Koncki Robert , Hulanicki Adam
Published: May 2005

A theoretical kinetic model of a pH‐based enzymatic sensor has been developed. The transport phenomena of substrates and products of enzymatic reactions as well as of buffer components were taken into account. Protolytic equilibria were described by dissociation constants. It was also assumed that the kinetics of the enzymatic reaction is described by the Michaelis–Menten equation. The final equation for the steady‐state response of an enzyme‐based pH sensor describes the form of the calibration curve for this type of biosensor. This equation takes into account sample pH and buffer concentration, as well as kinetic parameters (Vmax, KM) of the enzymatic reaction. The proposed model is particularly useful for describing pH‐based enzyme sensors with thin enzymatic membranes.
Dissociation constants of sore anti‐inflammatory agents (α‐phenylpropionic acids) in lsopropyl and tert‐butyl alcohol media
Authors: Bosch Elisabeth , Rodés Carles , Rosés Martí
Published: May 2005

The pKa of several α‐phenylcarboxilic anti‐inflammatory drugs in both isopropyl and tert‐butyl alcohols have been determined by means of potentiometry. The dissociation constant values of their tetrabutylammonium salts, which are necessary for computation of the acidity constants, have been determined conductometrically. The results show that both the drug acid strength resolution and the pH break in titration curves are greater in tert‐butyl than in isopropyl alcohol, but both alcohols can be used in everyday titrations. Titrations in one commercial pharmaceutical preparation have been carried out successfully.
Assessment of sodium‐selective ion‐selective electrodes based on methyl ketone derivative of p‐tert‐butylcalix[4]arene
Authors: Telting‐Diaz Martin , Diamond Dermot , Smyth Malcolm R. , Seward Eileen M. , McKervey Anthony M.
Published: May 2005

The performance of a newly synthesized tetramethyl ketone calyx [4]arene ionophore in ion‐selective electrodes has been investigated. Optimization of the plasticized polyvinyl chloride membrane composition has produced electrodes that exhibit a Nernstian response for sodium ions. The best general characteristics exhibited by the electrodes were found when the ionophore mixed with 2‐nitrophenyl octyl ether as plasticizing agent, and potassium tetrakis (p‐chlorophenyl) rate as ion exchanger. Selectivity studies carried out with the electrode have shown excellent discrimination for sodium against potassium and lithium ions. In addition, the electrode displays a rapid response time, a detection limit be low 10−6 M for sodium, and a working life of at least 4 months. Determinations of sodium in plasma patient samples have been performed and the results obtained compared to those from flame photometry and two commercial clinical analyzers.
Amperometric glucose sensor using silicon oxide deposited gold electrodes
Authors: Yokoyama Kenji , Tamiya Eiichi , Karube Isao
Published: May 2005

Glucose oxidase (GOD) immobilized electrodes using silicon oxide, were fabricated and their characteristics were evaluated. Silicon oxide deposited gold band (200 μm wide) and disk (1 mm diameter) electrodes were fabricated by vapor deposition of silicon monoxide. Alkylaminosilan and glutaraldehyde treatments were performed on the silicon oxide surface, followed by GOD immobilization. The GOD‐immobilized band electrode treated with 3‐aminopropyltriethoxysilane was characterized in a flow injection system. Hydrogen peroxide produced by the enzyme reaction was measured, resulting in a good response capable of high glucose concentration determination. The calibration curve was linear in the range between 1 to 200 mM. The GOD‐immobilized disk electrode treated with 3‐aminopropyldimethylethoxysilane was examined using electron transfer mediators. The effect of the thickness of silicon oxide on the response to glucose was investigated, leading to the highest, response at the electrode with the silicon oxide film that was 400 nm thick. In addition, a numerical analysis was performed, suggesting that immobilized GOD was located mainly in the vicinity of the silicon oxide surface.
Highly sensitive determination of L‐lactate and pyruvate by liquid chromatography and amperometric detection with lactate oxidase‐lactate dehydrogenase coimmobilized reactor involving amplification by substrate recycling
Authors: Yao Toshio , Kobayashi Naokazu , Wasa Tamotsu
Published: May 2005

An amperometric flow injection system with a lactate oxidase–lactate dehydrogenase coimmobilized reactor involving amplification by substrate recycling is used as a specific postcolumn detector system in liquid chromatography, to detect L‐lactate and pyruvate with high sensitivity. Both components are separated at a reversed phase column and are recycled enzymatically during the passage through the enzyme reactor in the presence of reduced nicotinamide adenine dinucleotide (NADH) and oxygen in the carrier stream. As a result of this recycling reaction, a large amount of hydrogen peroxidase is generated in the enzyme reactor which is detected amperometrically at a flow‐through peroxidase electrode in the presence of hexacyanoferrate(II) as a mediator. Linear determination range is 0.2–200 pmol for both L lactate and pyruvate. The detection limit is 0.02 pmol. The relative standard deviation obtained for this system at 2 pmol L‐lactate and pyruvate (n=5)is about 3.8%.
Synthesis and potentiometric selectivity study of acyclic formazanes
Authors: Attiyat A. S. , Badawy M. A. , Barsoum B. N. , Hanna H. R. , Ibrahim Y. A. , Christian G. D.
Published: May 2005

Seven compounds of a new class of ionophores, acyclic formazanes, were synthesized and tested for the potentiometric selectivity for lithium ion, in polyvinyl chloride (PVC) membrane electrodes. Four different plasticizers were studied: o‐nitrophenyloctyl ether (NPOE), o nitrophenylphenyl ether (NPPE), o‐nitrophenylbutyl ether (NPBE), and o‐nitrophenylbenzyl ether (NPBnE), as was the addition of trioctylphosphine oxide (TOPO). The ionophore, 1, 5‐bis‐(o‐butoxyphenyl)−3‐cyanoformazane (IIB) exhibited sodium–lithium selectivity, KpotLi, Na, of 6.2 × 10−3 by the matched potential method in the presence of 1% TOPO using NPPE plasticizer. The presence of TOPO generally causes a substantial increase in the lithium selectivity. Selectivities with respect to the lithium ion are reported for sodium, potassium, ammonium, barium, and calcium ions.
Deoxycholate‐sensitive PVC membrane electrode
Authors: Gyimesi János , Kovács Barna
Published: May 2005

A deoxycholate‐sensitive membrane electrode has been developed using cetyltrimethylammonium deoxycholate as the sensor material. The electrode can be used for the potentiometric determination of sodium deoxycholate.
Electrochemical and spectroscopic monitoring of the interaction between hydrogen peroxide and tungstophosphate heteropolyanion in homogeneous phase and in a polymer matrix
Authors: Keita Bineta , Bouaziz Djemai , Nadjo Louis
Published: May 2005

Cyclic voltammetry and UV‐visible spectroscopy have‐been used to monitor the reaction of tungstophosphate anion (PW12O3−40, abbreviated PW12 with hydrogen peroxide. The structures of some of the resulting peroxy complexes were also studied by IR spectroscopy. Depending on the experimental conditions, two different series of peroxy compounds are obtained as major products. It is also Shown that these species are easily extracted into a poly(4‐vinylpyridinium) film (PVP). Alternatively, the synthesis of, the peroxy, compounds has been performed directly by contacting a PVP film containing PW12 with an H2O2 solution. The facile entrapping of this series of peroxides in an appropriate polymer matrix creates new assemblies, stable and useful in the detection and study of the true catalytic species in oxygen transfer processes based on heteropolyanion/H2O2 systems.
Computerized potentiometric determination of stability constants of metal ion‐crown complexes by the method of corresponding solutions
Authors: Grabarić B. S. , Tkalčec M. , Merzel V. , Filipović I.
Published: May 2005

Two computerized potentiometric methods have been used to determine the stability constants of Na+, K+, and NH+4 complexes with 18‐crown‐6 in methanol‐water solutions (70% volume fraction of methanol) at 25.0 ± 01°C, and at constant ionic strength I = 0.1 M, adjusted with tetrabutylammonium iodide (TBAI). One method assumes a single complex equilibrium, while the method of corresponding solutions assumes the presence of simultaneous multiequilibria. It has been shown using the second method that K+ ion, even with 18‐crown‐6 ligand, can form both ML and sandwich‐type ML2 complexes, found so far only with smaller crown rings. The other two cations investigated form only ML complexes, as was confirmed by both methods.
Tomato seed‐based amperometric sensor for the determination of alcohols
Authors: Ozsoz Mehmet , Wang Joseph
Published: May 2005

The use of tomato seeds as a source for alcohol dehydrogenase (ADH) for the determination of alcohols is described. The unique reactivity pattern of the tomato ADH is coupled with the speed and sensitivity of the mixed tissue/carbon paste configuration. The effect of experimental variables, such as pH, cofactor concentration, applied potential, or paste composition, is explored. In accordance to the substrate specificity, the lowest detection limits (in the micromolar level) are obtained for allyl alcohol and ethanol.
Complexing properties of polycrownethers: I. Complexation of Na+ and K+ by tribenzo‐15 crown‐5 in MeOH‐DMF Medium
Authors: Lhermet Claude , Morel Jean‐Pierre , Angley Lysiane , Simonet Jacques
Published: May 2005

The complexation of Na+ and K+ cations by the polycyclic ligand tribenzo‐15 crown‐5 is studied in a methanol–dimethylformamide mixture. As opposed to the monomer benzo‐15 crown‐5, this trimer shows a marked selectivity for K+ with respect to Na+. This selectivity is due to the existence of associated farms of the K+ complexes in solution; at high concentration a salt precipitates, which presents a polymeric structure of stoichiometry 3 K+/ 2 trimers.
Adsorptive stripping voltammetry of cobalt and nickel in flow systems at wall‐jet electrodes
Authors: Brett Christopher M. A. , Oliveira Brett Ana Maria C. F. , Pereira Jorge L. C.
Published: May 2005

Adsorptive stripping voltammetry of cobalt and nickel in flow systems at wall‐jet mercury thin‐film electrodes has been investigated and assessed. A HEPES biological buffer with sodium perchlorate electrolyte was employed with excess nioxime, or dimethylglyoxime, ligand, and the accumulated complex on the mercury film surface determined by differential pulse reduction. Concentrations down to 1 nM can be routinely measured. Results at the wall‐jet electrode, supported by evidence from LSV and impedance measurements at rotating and stationary electrodes respectively, show the viability of the method.
Adsorption and electrochemical transformations of diphenylcarbazide and diphenylcarbazone on graphite electrodes
Authors: Malakhova Natalia A. , Chernysheva Albina V. , Brainina Khiena Z.
Published: May 2005

Potential dependences of the Current and differential double‐layer capacity were used to investigate the processes that take place on a graphite electrode in acidic media containing 1, 5‐diphenylcarbazide (DPCI) and 1, 5‐diphenylcarbazide (DPCO). It is shown that adsorption of the enol form of these compounds on the electrode surface is observed over the potential range of +0.2 to −1.0 V. Over the range of +0.2 to +0.4 V, the adsorbed enol form of the reagents is oxidized, involving formation of radicals to tetrazole salts, which are reduced irreversibly to the starting reagents at a potential lower than −0.2 V. The keto form of diphenylcarbazide is oxidized, omitting the adsorption stage. As the keto form of diphenylcarbazide is oxidized, an uncharged compound (probably a radical or a biradical) is formed.
Vanadium(V) determination through a catalytic polarographic method
Authors: Barrado Enrique , Alvarez Vicente , Pardo Rafael , Batanero Pedro Sánchez
Published: May 2005

A method for determining trace level of vanadium(V) has been developed. The reaction is the polarographic reduction of the bromate, catalyzed by this metal ion, in the presence of cupferron, in acetic‐acetate medium. The peak current obtained is proportional to the vanadium(V) concentration between 2.10−8 and 3.10−7 M, with a detection limit of 6.10−9 M. The procedure is very selective and has been successfully applied to a certified steel sample after extraction of iron wit ethyl ether.
Software for interfacing electrochemical instruments to a personal computer
Authors: David FrançOis , Papadopoulos Nikolaos
Published: May 2005

A potentiostat and a drop knocker have been interfaced to a Macintosh2 computer, using Labview2 for the programming of the interface. The whole system can perform the functions of a pulse polarograph. Digital storage of the experimental data permits baseline substraction and digital filtering at the end of the experiment.
Soybean meal tissue based membrane bioelectrode for urea
Authors: Deng Jiaqi , Fang Yao , Cai Ronghui
Published: May 2005

Novel potentiometric membrane electrodes with high selectivity to urea over the 1.3 × 10−4 − 1.1 × 10−2 M and 4.0 × 10−4 − 1.0 × 10−2 M concentration range were constructed by immobilized soybean meal at a NH3 or CO2 gas‐sensing electrode. The sensor does not require fresh bean tissue so it is not limited by the season of the year. The influence of some experimental parameters, including buffer composition, pH, and immobilization techniques are discussed. The resulting electrode is found to be a viable alternative to the enzyme‐based electrode.
Effects of alternating electric fields on transport through ion exchange membranes
Authors: Irgum Knut , Genborg ÅSa , Glad BÖRje , Gupta Syamasri , Dasgupta Purnendu K.
Published: May 2005

Transport of permitted and Donnas‐forbidden ions as well as neutral solutes through ion exchange membranes have been investigated in continuous flow‐through configurations in the presence and absence of an alternating electrical field (0.05–100 kHz, 0–40 V p‐p). There is no discernible effect on the transport rate of forbidden ions and neutral solutes but very significant increases in steady state transmembrane transport occur for permitted ions. At least for cation exchangers, an increase in effective ion exchange capacity also appears to occur in the presence of the field. These effects are ascribed to the greater kinetic energy of the ions exposed to the alternating field and thus to the higher effective thermodynamic temperature the ions experience.
Adsorptive stripping voltammetry of chromium 1,5‐diphenylcarbazonate
Authors: Malakhova Natalia A. , Chernysheva Albina V. , Brainina Khiena Z.
Published: May 2005

Electrochemical transformations of chromium 1,5‐diphenylcarbazonate (the complex), absorbed on the surface of a graphite electrode from a solution of 0.15 M sulfuric acid, were studied. The complex was synthesized by mixing acetone solutions of CrCl3·6H2O and diphenylcarbazone, as well as aqueous solutions of K2Cr2O7 and aqueous acetone solutions of diphenylcarbazide. The complex is absorbed on the electrode over the potential interval 0.55–0.30 V when the circuit is open. In the presence of diphenylcarbazide this interval narrows considerably as a result of competing absorption. Electrochemical reduction of the complex proceeds in stages, with formation of a chromium‐containing radical as an intermediate product that is subsequently reduced to diphenylcarbazide, with chromium(III) released to the solution. Absorbed complex is electrochemically oxidized in one stage mainly, with diphenylcarbadiazone formed as the main product.
Electroanalytical studies of chlorophylls and their determination
Authors: Wang Naixing , Di Pingping , Yu Tangdi , Chen Jianmin , Deng Jiaqi
Published: May 2005

The differential pulse polarographic behavior and quantitation of chlorophylls have been investigated. The detection limit is 2.4 × 10−7 M. The kinetics of the photolytic reaction of chlorophylls has been explored. Some kinetic parameters of the reaction system and the possibilities of a path for the photolytic reaction of chlorophylls have been measured and established. This reaction shows zero order kinetics with a rate constant of 3.3 × 10−6 mol · dm−3 · hr−1; with the help of the Arrnhenius relation, the activation energies of this reaction were determined. The method was successfully applied to the determination of chlorophylls in toothpaste and several kinds of green leaves.
Improved method for the determination of surfactants in fresh waters based on suppression of polarographic oxygen maximum
Authors: Bednarkiewicz Ewa
Published: May 2005

Measurements of the first kind of polarographic maximum current as a function of DME drop time allowed determination of the surfactants activity in natural fresh waters by means of standard addition techniques. In this way, the results of determination became independent of sample composition changes (over a reasonable range). The reported method expands an upper detection limit of determinations of surfactants, without dilution of the sample, up to 1 mg dm−3. Samples with higher content of surfactants were diluted with 0.001 mol dm−3 KCl solution of small and known amounts of surface active contaminants. The optimum range of electrical conductivity of the solution for recording the well‐developed oxygen maximum is attained because of dilution. It was found that surfactant activity for three types of drinking waters varied from 1 to 4 mg dm−3.