bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of a large assembly of microelectrodes to the study of cytochrome‐c and other redox proteins
Authors: Bianco Pierre , Haladjian Jean , Fletcher Stephen
Published: May 2005

A novel microelectrode assembly containing more than 1000 carbon microdisks has been used to study the interfacial electron transfer kinetics of cytochrome c and several other redox proteins. It is demonstrated that near‐steady‐state current–voltage curves can be obtained without solution stirring, and without significant mains interference or capacitive charging currents. In addition, it is demonstrated that concentrations of redox proteins as low as 1 μM can be detected in solution. Finally, it is shown that the surfaces of carbon microdisk assemblies can be successfully coated with thin films of poly(ester sulfonic acid), which allows reactants to be studied in a membrane‐like environment.
Response of the jalpaite membrane copper(II) ion‐selective electrode in marine waters
Authors: De Marco Roland , Mackey Denis J. , Zirino Alberto
Published: May 2005

The response of the Orion 94‐29 CuII ion‐selective electrode (ISE) [employing a jalpaite membrane] in seawater has been related to levels of free CuII yielding results for the Derwent River and San Diego Bay that are 2 to 3 orders of magnitude higher than those for the Pacific Ocean. Response data for the electrode in acidified seawater at pH 2 are internally consistent with total CuII levels determined using differential pulse anodic stripping voltammetry (DPASV) and graphite furnace atomic absorption spectrometry (GFAAS). It has been found that, even in acidified seawater, the organic ligands influence the response of the electrode, and this effect can be compensated successfully by either analyzing UV‐photooxidized seawater and/or using a standard addition technique. The assigned ISE results for total CuII in acidified seawater fall within ± (0.1–0.5) pCu unit of values determined using GFAAS. Electrode drift in seawater can be minimized by using a polished electrode that has been conditioned in seawater for 24 h. The improved response rate of a conditioned ISE minimizes electrode soaking times and sample contamination through membrane corrosion.
Arrays of gold microelectrodes made from split integrated circuit chips
Authors: Nascimento Valberes B. , Augelli Márcio A. , Pedrotti Jairo J. , Gutz Ivano G. R. , Angnes LúCio
Published: May 2005

A simple and inexpensive way to fabricate arrays of gold microelectrodes is proposed. Integrated circuit chips are sawed through their middle, normal to the longest axis, leading to destruction of the silicon circuit and rupture of the gold wires that interconnect it with the external terminals. Polishing the resulting rough surface converts the tips of the wires embedded in the chip halves into arrays of gold microdisks of about 25 μm diameter. The number of active microelectrodes (MEs), of an array depends on the number of pins in the chip, n, being typically (n/2)‐4. These MEs can be used individually or externally interconnected in any combination. X‐ray images of the chips and micrographs of the resulting surface of the polished arrays have revealed variable distances between neighbor MEs, which are however, larger than 10 times the radius of the disks. This feature of the MEs prevents diffusional cross‐talk between electrodes. The use of these microdisk electrodes for analytical purposes exhibits sigmoidal voltammograms, and chronoamperometric experiments confirm the nonlinear i vs. t1/2 plots, typical for processes where radial diffusion prevails, Satisfactory uniformity was observed for the response of each electrode of an array, indicating similarity of geometry and disk areas. The potentialities of these MEs were demonstrated by the determination of cadmium at ppb levels using square wave voltammetry with preconcentration. Due to the relative ease with which these MEs can be manufactured and their good performance in (chemical) analysis, wide applications in electrochemistry and electroanalysis is envisioned.
Quantification of the adsorption of methyl viologen on pyrex glass using a renewable perfluorosulfonated ionomer carbon paste electrode
Authors: Pailleret Alain , Rapicault Stéphane , Degrand Chantal
Published: May 2005

Square wave voltammograms of methyl viologen (MV2+) were recorded at a renewable Nafion‐loaded carbon paste electrode immersed in 20 mL of phosphate buffer solution (pH 7.4) contained in a beaker‐type electrochemical cell (Pyrex glass; contact area = 33 cm2). From the calibration plot obtained in the concentration range 0.01–2.4 μM, it could be concluded that the maximum surface excess of MV2+ adsorbed on Pyrex glass (0.24 nmol cm−2) was reached at concentrations above 1.4 μM. The adsorption isotherm presented a sigmoidal shape characteristic of attractive interaction. From this plot, it was evaluated that the maximum depletion of MV2+ in solution (28%) did not occur at the lowest concentrations, but in nearly micromolar solutions. This result emphasizes the unavoidable and random errors which are involved when MV2+ solutions are purposely diluted in Pyrex glassware. The MV2+ adsorption proceeds to a less extent on Duran borosilicate glass and/or in acid or alkaline medium.
Potentiometric stripping analysis and anodic stripping voltammetry for measurement of copper(II) and lead(II) complexation by fulvic acid: A comparative study
Authors: Town Raewyn M.
Published: May 2005

The utility of potentiometric stripping analysis (PSA) for studying the interaction of fulvic acid with CuII and PbII at pH 1.8 and 4.8 was assessed. The impact of fulvic acid on both the deposition and stripping steps was considered. In contrast to results obtained by anodic stripping voltammetry, fulvic acid influenced both these steps in PSA, and to different degrees. Surface active substances have been claimed to have self‐compensatory effects in PSA; this work shows that this is not valid for heterogenous natural complexants such as fulvic acid.
Nickel determination in osteoblast‐like cell culture medium by adsorptive cathodic stripping voltammetry with a mercury microelectrode
Authors: Morais Simone , Carvalho Graça Simões , Sousa João Paulo
Published: May 2005

The purpose of this study is to investigate the influence of nickel, which is an alloying element in commonly used metallic biomaterials, on the biomaterials mineralization process. An electrochemical method was developed to quantify this metal ion in osteoblast‐like cell culture medium (OST) by performing adsorptive cathodic stripping voltammetry (CSV) with dimethylglyoxime (DMG) at a mercury film microelectrode (MFM). The optimized analytical conditions and the square‐wave CSV parameters for the analysis are: DMG concentration: 5.00 × 10−4 mol L−1; ammonium chloride buffer: 0.10 mol L−1 (pH 9.2); frequency: 50 Hz, amplitude 20 mV; step: 2 mV; adsorption time: 10 s, deposition potential: −0.70 V and reduction potential: −1.20 V. The limit of detection was 7.70 × 10−9 mol L−1 for an adsorption time of 10 s. The results achieved by CSV using the MFM were compared to those obtained by atomic absorption spectrometry (AAS) to ensure the reliability of the electrochemical method. The mineralization process was evaluated by biochemical and histochemical assays.
Electrochemical detection of herbicides and plant growth regulators at membrane glassy carbon electrodes
Authors: Bianco Pierre , Aghroud Nadia
Published: May 2005

Membrane glassy carbon electrodes modified with cation‐exchangers (Eastman AQ‐29D, laponite, or polystyrene sulfonate) entrapped between the membrane and the carbon surface were used to study the electrochemical behavior of herbicides and plant growth regulators from the quaternary ammonium family. Cations are shown to incorporate in the entrapped solutions containing negatively charged cation‐exchangers, because of favorable electrostatic interactions. In the case of nonelectroactive cations, collection of mepiquat, chlormequat and difenzoquat from the bulk solution is assessed from the competition in ion‐exchange equilibrium between one of the above‐mentioned cations and the electroactive diquat cation. An attractive property results from the use of spinach ferredoxin as cation‐exchanger inside the membrane electrode. Promotion of ferredoxin is shown to be evidenced as a result of the collection of nonelectroactive cations from the bulk solution. Prospects of such modified membrane electrodes in the environmental field are discussed.
Voltammetric behavior and determination of bismuth on sodium humate modified carbon paste electrode
Authors: Wang Chunming , Sun Qiaoyu , Li Hulin
Published: May 2005

The preconcentration and voltammetric behavior of BiIII on a sodium humate modified carbon paste electrode was studied by means of cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). The proposed measurement involves an initial nonelectrolytic preconcentration step in which BiIII is complexed by the surface modifier in a solution of 0.05 M KNO3‐0.0106 M HNO3 (pH 2.0) and a subsequent electrochemical scan step in which the preconcentrated BiIII was reduced and then oxidized promptly in supporting electrolyte of 0.5 M HNO3. The resulting DPSV anodic current was proportional to the concentration of BiIII ion over the range of 4.78 × 10−8–1.44 × 10−5 M. The detection limit was 4.78 × 10−8 M. The proposed method was used to determine bismuth in various samples. Various factors affecting the electrode behavior were also investigated at the same time.
Controlling the selectivity of glassy carbon flow detectors using covalently attached monolayers
Authors: Downard Alison J. , Roddick Alisa D.
Published: May 2005

Significant improvements in selectivity for amperometric detection in flow analysis are achieved at covalently modified glassy carbon electrodes. Flow detectors modified with p‐alkylbenzene (alkyl = methyl, decyl) and p‐phenylacetate monolayers demonstrate how selectivity may be obtained on the basis of solute hydrophobicity and charge. The modified electrodes are stable under hydrodynamic conditions and in aqueous and mixed aqueous/organic carrier streams.
Adsorptive stripping voltammetry of anionic surfactants on a carbon paste electrode using ferrocenyl cationic surfactant as an analytical electrochemical probe
Authors: Hattori Toshiaki , Kato Masanao , Tanaka Shunitz , Hara Minoru
Published: May 2005

Adsorption stripping voltammetry (AdSV) for anionic surfactants was examined, based on ion association with an electroactive ferrocenyl cationic surfactant. The ion association complex between an anionic surfactant and a ferrocenyl cationic surfactant accumulated on the carbon paste electrode (CPE) in the absence of an applied potential. The concentration of anionic surfactant was indirectly evaluated from the oxidation wave of the ferrocenyl cationic surfactant. By means of AdSV, levels of anionic surfactants of 10−7 mol dm−3 could be measured with good selectivity. The role of pasting liquids on the accumulation behavior of ferrocenyl TMA were examined by a comparison of two pasting liquids. The first, 2‐nitrophenyl octyl ether (NPOE) was capable of extracting the ferrocenyl TMA salt, while the other, di‐n‐octylphthalate (DOP) was not. The voltammograms of ferrocenyl TMA varied considerably with the pasting liquids. In particular, the peak potentials at NPOE‐CPE gradually shifted with time, as a result of the extraction of the ferrocenyl TMA salt into the CPE. However, the peak potential at DOP‐CPE remained constant.
Electrochemical study of methylene blue immobilized in zirconium phosphate
Authors: Pessôa Christiana A. , Gushikem Yoshitaka , Kubota Lauro T.
Published: May 2005

Methylene Blue (MB) was adsorbed in zirconium(IV) phosphate by means of an ion exchange reaction. The dye is strongly retained and not easily leached from the matrix. The material with the adsorbed dye was incorporated into a carbon paste electrode and by means of cyclic voltammetry and amperometry, the electrochemical property was investigated. In various electrolyte solutions and changing the pH between 2.5 and 6, the midpoint potential remained practically constant, i.e., 0.15 ± 0.01 V. This is not the usual behavior of MB, since it is known in solution phase that its midpoint potential changes considerably as the pH changed. It appears that the Methylene Blue is a guest molecule in the lamellar structure of the zirconium phosphate. The electrode made with this material was used to study the electrochemical oxidation of ascorbic acid.
Prediction and characterization of the charge/size exclusion properties of over‐oxidized poly(pyrrole) films
Authors: Farrington Amiel M. , Slater Jonathan M.
Published: May 2005

Over‐oxidation of poly(pyrrole) films has been shown to result in permselective films favoring cation transport and excluding anions. The exclusion principal depends on both the size of the analyte and electrostatic interactions between the analyte and the polymer film. The size of the polymer dopant anion and hence the resulting pore size of the polymer has been varied and the size exclusion studied. Molecules just larger than the size of the original dopant anion can pass through the membrane, thought to be due to solvation of the incorporated anion in the initial polymer preparation. The pH of the sample analyte has been varied to test the permselective properties of the prepared polymer. A range of substituted pyrroles were polymerized, over‐oxidized and compared for selectivity. The nature and position of substituents on the pyrrole monomer were observed to change the morphological structure of the polymer and hence the resulting selectivity of the membrane. Molecular modeling of both the analytes and the dopant ions has allowed size/charge density profiles of the analytes to be compared with the predicted size of the polymer pores.
Hydrodynamic microelectrodes. The microdisk electrode: Theory and experiment
Authors: Fisher Adrian C. , Davies C. W. , Fulian Q. , Walters M.
Published: May 2005

A computationally efficient fully implicit approach to the simulation of linear sweep and potential step voltammetry at a channel microdisk electrode is derived. The generality of the method is illustrated with reference to the simple case of a reversible one electron transfer reaction. The influence of flow rate and the effects of axial, lateral and normal diffusion upon the electrolysis current are quantified. Scan rate and electrode geometry dependences are established and the requirements for measurement of true steady state hydrodynamic voltammograms defined.
A new membrane sensor for UO ions based on 2‐hydroxyacetophenoneoxime‐thiourea‐trioxane resin
Authors: Jain A. K. , Gupta V. K. , Khurana U. , Singh Lok P.
Published: May 2005

Poly(vinylchloride) (PVC) and polystyrene based uranyl ion‐selective electrodes have been constructed using 2‐hydroxyacetophenoneoxime‐thiourea‐trioxane resin as electroactive material. For PVC based membranes dibutylphthalate (DBP) and dioctylphthalate (DOP) were used as plasticizing solvent mediators. These membrane electrodes work in the concentration range of ca. 10−5–10−1 M with a response time as fast as 30 s. The useful working pH range is 2.5–3.5 and the electrodes perform satisfactorily up to 20 % (v./v.) partially nonaqueous content. The electrodes were used over a period of 4 months with good reproducibility (standard deviation = 0.5 mV). Further, the selectivity coefficient values of the order 0.1 for mono‐ and bivalent ions indicate moderate selectivity for UO ions over the interfering ions.
Electroanalytical determination of styrene in acrylonitrile‐butadiene‐styrene copolymers
Authors: Geraldo M. Dulce , Montenegro M. Irene
Published: May 2005

The analysis of residual styrene in terpolymers of acrylonitrile, butadiene and styrene (ABS) by a rapid electroanalytical method is described. The sample is simply dissolved in N, N‐dimethylformamide containing an excess of electrolyte and analysed by square wave voltammetry on a gold microdisk electrode; the styrene content is determined using the standard addition technique.
XPS analysis of hydroxide ion surface reactions on reactions on CeF3 and LaF3 fluoride ion‐selective electrodes
Authors: Shen W. , Wang X. D. , Cattrall R. W. , Nyberg G. L. , Liesegang J.
Published: May 2005

Lanthanum fluoride and cerium fluoride single crystals, used as the sensing membranes of the fluoride ion‐selective electrode (F‐ISE), were investigated for their hydroxide interference and surface reactions with OH− in high pH conditions. While these membranes show fast response and excellent Nernstian behavior over a wide concertration range in buffered F− solutions, they deviate from the theoretical slope at high pH. CeF3, in particular, exhibits a much larger deviation from the Nernstian slope and a substantially slower response to a F− activity change compared to LaF3. This larger deviation is due to more extensive and faster formation of hydroxo‐complexes, with the release of a greater amount of the fluoride ion into the hydrated gel layer. The slower response of the CeF3 membrane after contact with OH− is due to the formation of CeIV oxide on the surface, which acts as a blocking layer to the exchange of F−.
A graphite silver(I) hexacyanoferrate(III) composite electrode for the determination of iron (III) ions
Authors: Kahlert Heike , Scholz Fritz
Published: May 2005

A reactive electrode (reactrode) made of silver(i) hexacyanoferrate(III) (Ag‐hcf), graphite and paraffin has been developed for the determination of iron(III) ions in solutions down to a concentration of 0.12 mg L−1. Silver ions are reduced to Ag0 and the liberated hecacyanoferrate ions react with iron(III) ions from the solution to form Prussian blue. After this preconcentration step, the iron ions can be determined electrochemically by the characteristic signals of Prussian blue in differential pulse voltammetry. A nonlinear calibration plot is obtained which has a standard deviation of 13%. Pb2+, Cu2+ and Ni2+ interfere when they are at the same concentration as iron(III), whereas Cd2+ does not interfere even at higher concentrations. The incorporation of an active reagent into the electrode material remarkably facilitates the analytical procedure and makes the use of a mercury electrode unnecessary.
The electrochemical determination of N‐nitrosamines at polymer modified electrodes via an adsorptive stripping voltammetric regime
Authors: Collyer Stuart D. , Butler Alastair J. , Higson Séamus P. J.
Published: May 2005

An adsorptive linear sweep stripping voltammetric method has been developed for the determination of nitrosamines at polymer modified gold electrodes. N‐nitroso‐N‐butyl‐N‐propylamine has been quantified over a 10−10 M to 10−6 M concentration range at Nafion modified electrodes. CA coatings inhibited the determination of N‐nitroso‐N‐butyl‐N‐propylamine, while small enhancements were observed at CAB modified electrodes. This improvement may be due to the anionic butyrate groups within the CAB polymer facilitating nitrosamine sorption. It is postulated, that the insulating effect of the polymer and the incorporation of anionic moieties compete to give either a net enhancement or depreciation of analytical sensitivity.
Peroxidase‐glucose oxidase‐poly(amphiphilic pyrrole) bioelectrode for selectively mediated amperometric detection of glucose
Authors: Popescu Ionel C. , Cosnier Serge , Labbé Pierre
Published: May 2005

Monoenzyme (HRP) and bilyer/monolayer bienzyme (HRP‐GOX) bioelectrodes were realized by the oxidative electropolymerization of amphiphilic pyrrole monomer 1 enzyme(s) mixtures, previously adsorbed on the surface of a glassy carbon electrode. Cyclic voltammetry measurements, carried out on poly 1‐HRP modified electrodes showed that the electrocatalytical reduction of H2O2, in the presence of K4Fe(CN)6 as mediator, occurs at applied potentials well placed in the optimal potential range for amperometric detection. An optimization study concerning the mediator concentration, the amount of the immobilized enzyme(s), the electrode material and the matrix structure (mono‐ or bilayer) was performed in order to obtain the glucose biosensor. At an applied potential of −0.1 V (vs. SCE), batch amperometric response to H2O2 for the HRP modified electrodes gave a sensitivity of ca. 280 mA M−1 cm−2 (up to 0.65 mM). For monolayer biosensor the sensitivity to glucose was ca. 170 mA M−1 cm−2 (up to 1.9 mM). The interference of ascorbate, urate and acetaminophen was found almost negligible.
Rotating disk electrode voltammetry/anodic stripping voltammetry for chemical speciation of lead and cadmium in freshwaters containing dissolved organic matter
Authors: Lam Michael T. , Chakrabarti C. L. , Cheng J. , Pavski V
Published: May 2005

Rotating disk electrode voltammetry (RDEV) in conjunction with anodic stripping voltammetry (ASV) with a thin mercury film electrode (TMFE) or with a Nafion‐coated thin mercury film electrode (NCTMFE) has been evaluated for the direct determination (i.e., without preconcentration) of lead and cadmium speciation in aqueous solutions containing dissolved organic matter. The RDEV technique has been used to estimate dissociation rate constants and diffusion coefficients; pseudopolarograms have indicated the identity of the metal complexes undergoing electrode reductions at the corresponding plateaus of the pseudopolarograms in a number of model solutions containing Cd or Pb and known amounts of fulvic acid. It has been found that the effect of dissolved organic material is measurable when the concentrations of fulvic acid are equal to or less than 20 μg/mL (which is below the concentration of naturally occurring dissolved organic carbon in most freshwaters). The effective electrode surface area has been found to be considerably less than the geometric surface area, and if this fact is not explicitly taken into consideration, the result would be an erroneous estimation of dissociation rate constants and diffusion coefficients. Pseudopolarograms of aqueous samples containing Cd or Pb and fulvic acid and samples of Rideau river surface water clearly show that NCTMFEs effectively block the transport of large inert metal‐FA complexes to the electrode surface, resulting in interference‐free determination, and giving well‐defined pseudopolarograms, and yet do not hinder the transport of small metal‐FA complexes to the electrode surface. It is concluded that RDEV/ASV offers promise of being a valuable technique for determining chemical speciation of lead and cadmium in river surface waters.
Carbon packed‐bed upstream electrode in combination with a downstream thin‐layer cell for dual electrode applications in microbore liquid chromatography and flow injection analysis
Authors: Jayaratna H. G. , Yang Liu , Huang T. , Bruntlett C. S. , Kissinger P. T.
Published: May 2005

A flow‐through electrode with a high conversion efficiency has been developed for chromatographic detection as well as other on‐line electrochemical applications. A small length of reticulated vitreous carbon material of high pore density permits excellent conversion of so ne organic compounds. This can easily be employed in dual electrode applications with radial or cross flow thin‐layer detectors. When used as a generator electrode, it can improve selectivity for electrochemically active compounds in chromatographic detection and microdialysis/biosensor combinations.
Immobilization of methylene blue using α‐zirconium phosphate and its application within a reagentless amperometric hydrogen peroxide biosensor
Authors: Ruan Chuanmin , Yang Feng , Xu Jinsuo , Lei Chengheng , Deng Jiaqi
Published: May 2005

A novel H2O2 sensor was constructed by employing methylene blue (MB) incorporated in α‐zirconium phosphate as an electron transfer mediator. Methylene blue was intercalated into a α‐zirconium phosphate modified horseradish peroxidase (HRP) immobilization matrix cross‐linked on a glassy carbon electrode surface via bovine serum albumin (BSA)‐glutaraldehyde. Such a coimmobilization matrix of the mediator and enzyme was formed from α‐zirconium phosphate‐MB inclusion colloid in which horseradish peroxidase was dissolved. Intercalation of methylene blue in layered α‐zirconium phosphate was investigated by X‐ray power diffraction (XRD), IR spectra and electrochemical measurements. Methylene blue immobilized in this way underwent a quasi‐reversible electrochemical redox reaction. Cyclic voltammetry and amperometric measurements demonstrated that methylene blue coimmobilized with HRP displayed good stability and efficiently shuttled electrons between HRP and the electrode. The sensor responded rapidly and linearly to H2O2 over the range from 2.0 × 10−6 to 5.0 × 10−3 mol/L, with a detection limit of 3.0 × 10−7 mol/L.
Electrocatalytic oxidation and flow amperometric detection of hydrazine at an electropolymerized 4‐vinylpyridine/palladium film electrode
Authors: Li Tao , Wang Erkang
Published: May 2005

A poly(4‐vinyl)pyridine (PVP)/Pd film electrode was constructed for the electrocatalytic detection of hydrazine. The preparation of the PVP/GC electrode was performed by electropolymerization of the monomer 4‐vinylpyridine onto the surface of a glassy carbon electrode. Subsequently, palladium is electrodeposited onto the polymer modified electrode surface. The ion‐exchange function of PVP polymer is helpful to this process in view of the tetrachlorapalladate anion. Compared with the Pd/GC electrode, the modified electrode displays a better mechanical stability in a flowing stream. The PVP/Pd film electrode exhibits higher sensitivity when detecting hydrazine with a detection limit of 0.026 ng (S/N=3).
Time differential surface plasmon resonance measurements applied for electrochemical analysis
Authors: Iwasaki Yuzuru , Horiuchi Tsutomu , Morita Masao , Niwa Osamu
Published: May 2005

The processes of oxide film formation and ion adsorption on gold electrodes were monitored by the simultaneous measurement of electrochemical potential scanning voltammetry and surface plasmon resonance (SPR) condition. The time differential of the SPR incident angle was used for the analysis of the surface reactions of the gold electrode. Each stage of oxide film formation on the sputtered gold electrodes and anion adsorption/desorption was clearly detected by this method and directly correlated to the current. SPR is sensitive to the surface adsorbate while the electrode current reflects the overall electrochemical process. This difference was used to separate adsorption from the diffusion process under different hydrodynamic conditions.
Alkylated cyclodextrin‐based potentiometric and amperometric electrodes applied to the measurement of tricyclic antidepressants
Authors: Kataky Ritu , Palmer Simon , Parker David , Spurling Dominic
Published: May 2005

Alkylated α, β and γ cyclodextrins have been incorporated in ion‐selective electrodes as neutral ionophores and used for the detection of the tricyclic antidepressants imipramine, desipramine and trimipramine as their hydrochloride salts. Nernstian response and excellent potentiometric limits of detection were observed with each of the three alkylated cyclodextrins examined. Interference from ‘serum’ levels of Na+, K+ and Ca2+ ions was very low. Interference from organic molecules such as glycine, L‐histidine and nicotinamide was also low in most cases (see text for exceptions). Electrodes suitable for amperometric measurements were assembled by depositing alkylated cyclodextrins on screen printed electrode substrates. Inclusion of the tricyclic antidepressants in the cyclodextrin cavity aided by controlled potential electrolysis, allowed subnanomolar levels of the analyte to be monitored by square wave voltammetry. Mechanistic studies indicated that, by preconditioning the modified electrodes at approximately +0.6 V in phosphate buffer, the appropriate radical cation was formed, which, on further conditioning at approximately −0.2 V rapidly formed the dimer which possessed a lower oxidation potential of approximately +0.18 V. Monitoring the redox wave at 0.18 V afforded a powerful analytical handle for trace analysis of these tricyclic antidepressants. This redox wave is observable only in the presence of aqueous phosphate which may be attributed to the formation of a hydrogen‐bonded surface ion‐pair including the substrate and a phosphate counterion.
Characteristics of copper(II) ion‐selective electrode based on aquatic humic substances
Authors: Lu Xiaoqiao , Yang Xinhao , Chen Zuliang
Published: May 2005

A carbon rod electrode coated with a poly(vinyl chloride) (PVC) membrane containing aquatic humic substances (HS) isolated from swamp water was constructed for the detection of copper(II) ion. The electrode exhibits a linear response with a slope of 60.1 ± 2.0 mV/decade in concentration range from 10−5 mol L−1 to 10−2 mol L−1. The detection limit for the copper(II) ion was estimated to be of 1 × 10−5 mol L−1. Electron spin resonance spectroscopy (ESR) and pH titration results indicated that the humic substances interact with copper(II) ions to form complexes. These results confirm that the potential response of the membrane electrode with good sensitivity, selectivity except for Pb2+ and Hg2+, and response to copper(II) ion is due to the formation of stable complexes occurring at the electrode surface.
Solid‐state sodium‐selective sensors based on screen‐printed Ag/AgCl reference electrodes
Authors: Walsh S. , Diamond Dermot , McLaughlin J. , McAdams E. , Woolfson D. , Jones D. , Bonner M.
Published: May 2005

The potentiometric and AC impedance characteristics of all solid‐state sodium‐selective electrodes based on planar screen‐printed Ag/AgCl electrodes are described. Two solid‐state designs have been investigated. The first was based on the deposition of a sodium‐selective PVC membrane directly on top of a screen‐printed Ag/AgCl electrode. The second design included a NaCl doped hydrogel layer, between the PVC and Ag/AgCl layers. The hydrogel provides a mechanism to relieve any blockage to charge transfer occurring when PVC membranes are used directly on top of Ag/AgCl and also improves adhesion between the two layers. Results suggest the electrodes display fast ion exchange kinetics, low noise and drift. The performance compares favorably to that of a conventional ion‐selective electrode with internal filling solution.
Derivative adsorption chronopotentiometric determination of aluminum in natural and drinking waters using the AlIII‐1,2‐dihydroxyanthraquinone‐3‐sulfonic acid system
Authors: Bi Shuping , Yu Jiong
Published: May 2005

An absorptive chronopotentiometric method was developed for the determination of trace aluminum. The method relies on the adsorptive accumulation of a AlIII‐1,2‐dihydroxyanthraquinone‐3‐sulfonic acid complex on the surface of a hanging mercury drop electrode. The optimum experimental conditions with respect to pH. preconcentration potential, preconcentration time and concentration of 1,2‐dihydroxyanthraquinone‐3‐sulfonic acid have been investigated. The suggested procedure has been used for the determination of aluminum in natural and drinking water samples and the accuracy investigated by comparison with results obtained by atomic absorption spectrometry.
Differential pulse adsorptive anodic stripping voltammetric determination of pipemidic acid in tablets at a carbon fiber microdisk electrode
Authors: He Ya‐Nan , Chen Hong‐Yuan
Published: May 2005

An adsorptive anodic stripping voltammetric determination of pipemidic acid (PPA) in tablets with a carbon fiber microdisk electrode is presented. A sensitive differential pulse adsorptive anodic stripping peak of PPA was found at 1.06 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solutions. Under the optimal conditions (buffer solution: pH 7.0 0.20 mol/L PBS, accumulation time: 30s, accumulation potential: 0.10V, pulse height: 80 mV, pulse width: 80ms) the height of the peak linearly increased with the concentration of PPA in the range of 2.8 × 10−7–1.2 × 10−6 mol/L. The method is not affected by oxygen, no extraction was required before the voltammetric analysis, and the excipients present in the PPA tablets show no interference with the analysis. The method was used for the determination of PPA in tablets with satisfactory results.
Protein kinase C subspecies distinguish major cell types in rat hippocampus: An immunocytochemical and in situ hybridization histochemical study
Authors: McGinty Jacqueline F. , Couce Marta E. , Bohler William T. , Ways D. Kirk
Published: May 2005

This study compares the distribution of protein kinase C (PKC) α and β with the distribution of PKC ∈ in the hippocampal formation of rats by immunocytochemistry and in situ hybridization histochemistry. Alpha and PKC β are members of the group A PKC genes that were first described; PKC ∈ is a member of the group B PKC genes that were more recently identified by molecular cloning. A combination of all three gene products and their mRNAs overlapped in their distributions in dentate granule cells and pyramidal and nonpyramidal neurons. However, each subspecies predominated in one of the major cell types. PKC α‐immunoreactivity and mRNA were most intense in CA2‐3 pyramidal cells and dendrites, whereas PKC β‐immunoreactivity and mRNA were most intense in CA1 pyramidal cells and dendrites. PKC ∈‐immunoreactivity and mRNA were concentrated in dentate granule cells and CA3 pyramidal cells. Furthermore, PKC ∈‐immunoreactivity was detectable in mossy fibers. Each subspecies labeled different kinds of interneurons that were particularly numerous in, but not restricted to, the hilus. These data support the contention that different subtypes of hippocampal neurons are distinguished by the expression of different combinations of PKC subspecies under resting conditions.
Equivalent impairment of spatial and nonspatial memory following damage to the human hippocampus
Authors: Cave Carolyn Backer , Squire Larry R.
Published: May 2005

The hippocampus has sometimes been proposed to function as a cognitive map, a memory system that stores information about allocentric space. Work with experimental animals and memory‐impaired patients has raised difficulties with this view by showing that the hippocampus is not performing an exclusively spatial function. However, the possibility has remained that the hippocampus plays a special role in spatial memory or a disproportionately large role in spatial memory compared to other kinds of memory. This study compared spatial and nonspatial memory in amnesic patients with lesions of the hippocampal formation or diencephalon. Subjects studied an array of 16 toy objects and were subsequently tested for object recall, object recognition, and memory for the location of the objects. Control subjects were tested after long retention intervals in order to equate their object memory performance with that of the patients. The main finding was that, when the performance of amnesic patients on the object memory tests was matched to the object memory performance of control subjects, spatial memory performance of the amnesic patients also matched the spatial memory performance of the control subjects. The results were the same for the two groups of patients. These findings suggest that the hippocampus is not especially involved in spatial memory. Spatial memory is simply one instance of a broader category of memory that requires the hippocampus. While cognitive mapping in its most abstract sense may describe hippocampal function, our results support alternative formulations, suggesting that the hippocampus is necessary for the rapid acquisition of relational, configural, or declarative (as opposed to purely spatial) information.
Intragranular mossy fibers in rats and gerbils from synapses with the somata and proximal dendrites of basket cells in the dentate gyrus
Authors: Ribak Charles E. , Peterson Gary M.
Published: May 2005

Intragranular and supragranular mossy fibers arise from granule cells and are present in the dentate gyrus of hippocampi from kindled and epileptic animals. The intragranular fibers often appear as fibers perpendicular to the long axis of the granule cell layer at periodic intervals. Rats and gerbils were analyzed to determine whether such mossy fibers are also associated with nongranule cells (including the basket cells), which send their apical dendrites through this layer with a periodicity similar to that of mossy fibers. The results for rats and both epileptic and nonepileptic gerbils show that many intragranular mossy fibers are apposed to the surfaces of the somata and apical dendrites of basket cells where they form asymmetric synapses. This plexus of mossy fiber axons appears to follow the dendrites of these neurons into the inner molecular layer. Based on previous data indicating that basket cells are GABAergic inhibitory neurons, the present findings in normal rats and both types of gerbils suggest that intragranular and supragranular mossy fibers provide additional circuitry for feedback inhibition to granule cells. It is possible that under pathological conditions, such as denervation or kindling, these fibers sprout and form synapses with granule cells.
The effects of reversible inactivations of the hippocampus on exploratory activity and spatial memory
Authors: Thinus‐Blanc C. , Save E. , Poucet B. , Buhot M.‐C.
Published: May 2005

This study was aimed at testing the effects of a reversible inactivation of the ventral hippocampus on behavior in response to a change, following a period of habituation with a hippocampus that functions normally. A new dishabituation paradigm was used, which allowed the testing of visuospatial memory. A salient stimulus was placed under the glass floor of the apparatus during initial exploration and was removed during the test session. The time spent above the zone where the stimulus was initially located indicated the rats' reaction to the change. Unlike the control rats who reacted to the removal of the salient stimulus by reexploring its previous location, lidocaine‐injected subjects did not display any similar searching behavior. Experiment 2 examined the hypothesis that landmarks located under the floor could help hippocampus‐inactivated animals to accurately react to the change. Two objects were located either close to the stimulus or some distance away from it. Even when the objects were closely associated to the stimulus, the same failure to react to the removal of the stimulus was found in lidocaine‐injected rats. However, these animals displayed a higher activity level measured by the time spent on a “neutral” zone. This behaioral pattern suggests a specific localization deficit. The method of reversible inactivation appears to be a promising approach to the study of the time course of memory process with short‐term experimental paradigms such as those used in the present study.
Factors governing the potentiation of NMDA receptor‐mediated responses in Hippocampus
Authors: Muller Dominique , Arai Amy , Lynch Gary
Published: May 2005

A modified medium containing an AMPA receptor antagonist and low concentrations of magnesium was used to investigate the factors governing the potentiation of synaptic responses mediated by NMDA receptors. When long‐term potentiation (LTP) was induced in standard medium and NMDA responses were analyzed by changing to the modified medium, no statistically significant differences were observed between potentiated and control pathways. Returning the slices to the standard medium showed that LTP was still present, indicating that the potentiation effect was not reversed by the modified medium. High‐frequency stimulation applied in the modified medium produced an enhancement of synaptic responses, but this was not occluded by prior potentiation in standard medium. The degree of potentiation induced in the modified medium and expressed by NMDA responses was larger in the presence than in the absence of inhibition and, unlike LTP, was proportionately larger when recorded in the stratum pyramidale than in the stratum radiatum. These results indicate that the potentiation of NMDA receptor‐mediated responses triggered by high‐frequency stimulation applied in modified medium differs in several respects from the LTP induced in standard conditions. They confirm that LTP is expressed to a markedly different degree by NMDA and non‐NMDA receptors and suggest that events that do not necessarily accompany LTP affect the potentiation of NMDA receptordependent synaptic responses.
Receptor changes and LTP: An analysis using aniracetam, a drug that reversibly modifies glutamate (AMPA) receptors
Authors: Staubli Ursula , Ambros‐Ingerson José , Lynch Gary
Published: May 2005

The hypothesis that long‐term potentiation (LTP) involves receptor modifications was tested with aniracetam, a nootropic drug that selectively increases currents mediated by the AMPA subclass of glutamate receptors. Aniracetam had different effects on the waveform of synaptic potentials in hippocampus before and after induction of LTP: (1) the drug caused a slight reduction (or delay) of the initial segment of the response after LTP; and (2) the facilitatory effects of aniracetam occurred at a later time point in the response after LTP than before. The interactions between LTP and aniracetam were still present when synaptic responses were greatly reduced by partial blockade of postsynaptic receptors and were not reproduced by increasing release or the number of stimulated synapses. A mathematical treatment of synaptic currents produced the following results: (1) if aniracetam facilitates AMPA receptor currents simply by reducing desensitization, then its complex interaction with LTP emerges when potentiation changes the kinetic and conductance properties of receptor channels; (2) if aniracetam also significantly increases conductance, then the experimental data can be reproduced by modeling LTP as an increase in channel conductance alone.
Spontaneous recovery of deficits in spatial memory and cholinergic potentiation of NMDA in CA1 neurons during chronic lithium treatment
Authors: Richter‐Levin Gal , Markram Henry , Segal Menahem
Published: May 2005

The therapeutic action of lithium in affective disorders is still unclear. One effect lithium is to deplete membrane inositol and consequently to exhaust the phosphoinositide (PI) pathway. Under chronic lithium treatment, rats showed persistent performance deficits in an active avoidance task and in a visually cued maze. The same treatment, however, resulted in only a transient deficit in the performance of rats in a spatial memory task. Lithium treatment caused a similarly transient deficit in the ability of acetylcholine to potentiate responses to N‐methyl‐D‐aspartate (NMDA) in neurons of the hippocampal slice. The authors propose that the development of compensatory mechanisms may account for the lack of severe memory impairments during lithium treatment. It is suggested that the effects of lithium on the PI pathway are not sufficient to explain the behavioral consequences of chronic lithium treatment.
Spatial responsiveness of monkey hippocampal neurons to various visual and auditory stimuli
Authors: Tamura Ryoi , Ono Taketoshi , Fukuda Masaji , Nakamura Kiyomi
Published: May 2005

To investigate involvement of the hippocampal formation in spatial information processing, activity of neurons in the hippocampal formation of the conscious monkey was recorded during presentation of various visual and auditory stimuli from several directions around the monkey. Of 1,047 neurons recorded, 106 (10.1%) responded to some stimuli from one or more directions. Of these 106 neurons with directionally differentiating responsiveness, 49 responded to visual stimulation, 35 to auditory stimulation, and 22 to both. Among 81 neurons, each tested with more than 10 differnt stimuli, one type responded independent of the nature of the stimulus (nonselective, n = 39), and responses of the other type depended on the nature of the stimulus (selective, n = 42). To investigate effects of change in spatial relations between test stimuli and background stimuli fixed on the monkey or fixed in the environment, 59 of 106 neurons were tested while the experimental apparatus holding the stimulus was moved relative to the monkey. Of these 59 neurons, 36 changed their responsiveness; 7 maintained the magnitude of their responses but changed the response direction with the movement of the apparatus, 5 changed direction regardless of the movement, and 24 did not change direction, but decresed or extinguished responses from the preferred direction. Thirty‐two of 106 neurons were also tested by rotating the monkey. The directionally differentiating responsiveness of 11 neurons followed the monkey (egocentric neurons), that of 9 remained in place in the environment (allocentric neurons), and responses of 12 were reversibly extinguished when the monkey was rotated. The results suggest that these hippocampal neurons may be involved in identification of relations among various kinds of stimuli in different spatial frameworks (egocentric or allocentric) and this identification may be developed from multiple sensory modalities.
Neuronal activity in the hippocampus during delayed non‐match to sample performance in rats: Evidence for hippocampal processing in recognition memory
Authors: Otto Tim , Eichenbaum Howard
Published: May 2005

Neuronal activity in the CA1 of rats was explored with regard to functional correlates of performance in an odor‐guided continuous delayed non‐match to sample task. Although different CA1 cells fired in association with each identifiable trial event, these analyses focused on cells that fired selectively during the period of odor cue sampling and response generation. The firing patterns of many of these cells reflected the match or non‐match comparison between current and previous odor cues independent of the particular stimuli that composed those comparisons. Such cells were more prevalent in sessions when performance was highly accurate. Hippocampal cells did not demonstrate stimulus‐evoked firing that persisted through the memory delay, nor did they fire differentially to session‐novel vs. repeated odor presentations. These results suggest that the hippocampus contributes to recognition memory by processing comparisons between current information and representations of previous stimuli stored in parahippocampal and neocortical structures.
Mossy cell axonal projections to the dentate gyrus molecular layer in the rat hippocampal slice
Authors: Buckmaster Paul S. , Strowbridge Ben W. , Kunkel Dennis D. , Schmiege Donna L. , Schwartzkroin Philip A.
Published: May 2005

The ipsilateral associational pathway connects different septotemporal levels of the dentate gyrus. Neurons of the dentate hilus project hundreds of micrometers from the cells of origin to the inner molecular layer. The authors hypothesized that mossy cells, the major cell type of the hilus, also project locally to the inner molecular layer. Within a 400 μm slice, mossy cells were (1) recorded intracellularly while the inner molecular layer was stimulated to test for antidromic responses, and (2) labeled with biocytin and examined with light and electron microscopy for axonal projections into the molecular layer. The authors found that mossy cells can be antidromically activated by inner molecular layer stimulation and that axonal projections to the molecular layer can be visualized within a 400 μm hippocampal slice. In 13 of 19 intracellularly labeled and electrophysiologically characterized mossy cells, collaterals could be traced into the molecular layer. These results suggest that mossy cells contribute to the ipsilateral associational pathway and also participate in local recurrent circuitry to influence granule cell activity.