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Electrochemically
Terms modified by Electrochemically Selected AbstractsElectrochemically Induced Formation of Surface-Attached Temperature-Responsive Hydrogels.ELECTROANALYSIS, Issue 9 2010Amperometric Glucose Sensors with Tunable Sensor Characteristics Abstract Employing thermally responsive hydrogels, the design of an amperometric glucose sensor is proposed. The properties of the biosensor can be modulated upon changing the temperature. Homo- and copolymers of N -isopropylacrylamide (NIPAm) and oligo(ethylene glycol) methacrylate (OEGMA) were prepared by electrochemically induced polymerization thus yielding surface-attached hydrogels. The growth of the films as well as the change in the film thickness in dependence from the temperature were investigated by means of an electrochemical quartz crystal microbalance (EQCM). The layer thickness in the dry state ranged from 20 to 120,nm. The lower critical solution temperature (LCST) of the hydrogel increases with increasing content of the more hydrophilic OEGMA. Hence, the swelling in aqueous electrolyte is composition dependent and can be adjusted by selecting a specific NIPAm to OEGMA ratio. All homo- and copolymer films showed good biocompatibility and no fouling could be observed during exposing the surfaces to human serum albumin. For amperometric glucose detection, glucose oxidase was entrapped in the films during electrochemically-induced polymerization. Both the apparent Michaelis constant (K and the apparent maximum current (i as determined by amperometry could be adjusted both by the film composition as well as the operation temperature. [source] Electrochemically Induced Modulation of the Catalytic Activity of a Reversible Redoxsensitive RiboswitchELECTROANALYSIS, Issue 9 2008Denise Strohbach Abstract Over the past decade, RNA conformation has been shown to respond to external stimuli. Thus, dependent on the presence of a high affinity ligand, specifically designed ribozymes can be regulated in a classical allosteric way. In this scenario, a binding event in one part of the RNA structure induces conformational changes in a separated part, which constitutes the catalytic centre. As a result activity is switched on (positive regulation) or off (negative regulation). We have developed a hairpin aptazyme responding to flavine mononucleotide (FMN). Ribozyme activity is dependent on binding of FMN and thus is switched on in the presence of FMN in its oxidized form. Under reducing conditions, however, FMN changes its molecular geometry, which is associated with loss of binding and consequently down-regulation of ribozyme activity. While in previous experiments sodium dithionite was used for reduction of FMN, we now present an assay for electrochemically induced activity switching. We have developed an electrochemical microcell that allows for iterative cycles of reduction/oxidation of FMN in an oxygen free atmosphere and thus for reversible switching of ribozyme activity. The reaction proceeds in droplets of 3 to 10,,L at micro- to nanomolar concentrations of the reaction components. [source] Electrochemically Induced Iron Release of Adsorbed Horse Spleen Ferritin: Quantitation of Iron Using Long Optical Path Length Thin-Layer SpectroelectrochemistryELECTROANALYSIS, Issue 23 2007Abstract In this work, long optical path length thin-layer electrochemical cell was constructed using indium-tin oxide on glass as the electrode material. Iron release from ferritin adsorbed on the electrode was induced by applying a negative potential sweep in the presence of 1,10-phenanthroline. The usefulness of spectroelectrochemistry as a means of determining the quantity of iron released from an adsorbed layer of ferritin is demonstrated. [source] Electrochemically Initiated Catalytic Oxidation of 5-Thio-2-Nitrobenzoic Acid (TNBA) in the Presence of Thiols at a Boron Doped Diamond Electrode: Implications for Total Thiol DetectionELECTROANALYSIS, Issue 21 2003Olga Nekrassova Abstract The electrochemical response of 5,5-dithiobis(2-nitrobenzoic acid) (DTNB) to increasing additions of thiol species has been examined at a boron doped diamond electrode. A reaction has been shown to occur with a range of biologically relevant thiols and proceeds via a CECC' process. A total thiol detection methodology has been developed showing that the sensitivities of the standard addition plots are independent of the individual thiol species added to the solution. The analytical utility of the reaction process has been assessed using chronoamperometry with the corresponding data producing detection limits of 5.7,,M, 4.4,,M and 5.8,,M for the detection of cysteine, homocysteine and glutathione respectively. [source] Amperometric Ion Sensing Using Polypyrrole MembranesELECTROANALYSIS, Issue 5-6 2003Agata Michalska Abstract Oxidation/reduction of conducting polymers, coupled with ion exchange between the polymer and electrolyte solution can be utilized for amperometric ion sensing. Electrochemically deposited "model" polypyrrole membranes doped by chloride (PPyCl) and hexacyanoferrate (PPyFeCN) anions were studied from the point of view of their advantages and limits for amperometric determination of electroinactive anions and cations, respectively. Monotonous dependences of the current on electrolyte concentration were obtained for short reading times after potential step application (in the range of ms). The experimental conditions were optimized to obtain linear dependences: log (current) vs. log (KCl concentration) within the range 10,6,1,M. The advantages of the amperometric method over the potentiometric one are highlighted: much lower effect of redox and pH interferences, wider concentration range, elimination of long conditioning procedure. [source] Adsorptive Stripping Voltammetric Detection of Single-Stranded DNA at Electrochemically Modified Glassy Carbon ElectrodeELECTROANALYSIS, Issue 23 2002Huai-Sheng Wang Abstract Electrochemically modified glassy carbon electrode (GCE) was used to study the electrochemical oxidation and detection of denatured single-stranded (ss) DNA by means of adsorptive stripping voltammetry. The modification of GCE, by electrochemical oxidation at +1.75,V (vs.SCE) for 10,min and cyclic sweep between +0.3,V and ,1.3,V for 20,cycles in pH,5.0 phosphate buffer, results in 100-fold improvement in sensitivity for ssDNA detection. We speculated that the modified GCE has a high affinity to single-stranded DNA through hydrogen bond (specific static adsorption). Single-stranded DNA can accumulate at the GCE surface at open circuit and produce a well-defined oxidation peak corresponding to the guanine residues at about +0.80,V in pH,5.0 phosphate buffer, while the native DNA gives no signal under the same condition. The peak currents are proportional to the ssDNA concentration in the range of 0,18.0,,g,mL,1. The detection limit of denatured ssDNA is ca. 0.2,,g mL,1 when the accumulation time is 8,min at open circuit. The accumulation mechanism of ssDNA on the modified GCE was discussed. [source] Electrochemically Tuned Properties for Electrolyte-Free Carbon Nanotube SheetsADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Alexander A. Zakhidov Abstract Injecting high electronic charge densities can profoundly change the optical, electrical, and magnetic properties of materials. Such charge injection in bulk materials has traditionally involved either dopant intercalation or the maintained use of a contacting electrolyte. Tunable electrochemical charge injection and charge retention, in which neither volumetric intercalation of ions nor maintained electrolyte contact is needed, are demonstrated for carbon nanotube sheets in the absence of an applied field. The tunability of electrical conductivity and electron field emission in the subsequent material is presented. Application of this material to supercapacitors may extend their charge-storage times because they can retain charge after the removal of the electrolyte. [source] Alkyl side chain driven tunable red,yellow,green emission: Investigation on the new ,-conjugated polymers comprising of 2,7-carbazole unit and 2,1,3-benzo-thiadiazole units with different side chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008Junping Du Abstract Four new soluble polymers containing a 2,7-carbazole unit and a 2,1,3-benzothiadiazole unit in the main chain were synthesized by Suzuki polycondensation. Variation of the substituent groups (R) at 5-position of 2,1,3-benzothiadiazole unit resulted in different color emission of the copolymers. Thus, when R was CH3 (or H), the polymer showed yellow,green (or red) emission; whereas the polymers showed the emission from green to yellow,green, when R was CH2(CH2)5CH3 or CH2OCH(CH3)2. To investigate the nature of the color change, a Gaussian 03 program was used for estimation of the dihedral angles between a 5-R-2,1,3-benzothiadiazole unit and a 2,7-carbazole unit. The results showed that the different substituents at 5-position of 2,1,3-benzothiadiazole brought about different the dihedral angles, which gave the different conjugation levels to the polymers. Hence, the tunablity of emission color may be attributed to the different conjugation levels between 2,7-carbazole units and 5-R-2,1,3-benzothiadiazole units induced by simply changing substituent groups at 5-position of benzothiadiazole unit. Electrochemically, the copolymers exhibited a higher oxidation potential as well as the reversible reduction behavior bearing from 2,1,3-benzothiadiazole unit. To investigate the electroluminescent properties of the polymers, the nonoptimized devices were fabricated and the results showed that the electroluminescent emission wavelength was basically similar to that of the photoluminescent. All polymers showed good thermal stability with 5 wt % loss temperature of more than 296 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1376,1387, 2008 [source] Reactions of 4-Pentenoic Acid with Sulfenyl Cations Generated Electrochemically from Bisquinolinyl and Bispyridinyl Disulfides.CHEMINFORM, Issue 20 2006Krzysztof Marciniec Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Electrochemically Assisted Fabrication of Metal Atomic Wires and Molecular Junctions by MCBJ and STM-BJ Methods,CHEMPHYSCHEM, Issue 13 2010Dr. Jing-Hua Tian Abstract Atomic wires (point contacts) and molecular junctions are two fundamental units in the fields of nanoelectronics and devices. This Minireview introduces our recent approaches aiming to develop versatile methods to fabricate and characterize these unique metallic and molecular structures reliably. Electrochemical methods are coupled with mechanically controllable break junction (EC-MCBJ) or scanning tunneling microscopy (STM) break junction (EC-STMBJ) methods to fabricate metallic point contacts and metal/molecule/metal junctions. With the designed electrodeposition method, the metal of interest (e.g. Au, Cu, Fe or Pd) is deposited in a controlled way on the original electrode pair, on a chip for MCBJ or on the STM tip, to make the metallic contact. Then, various metal atomic wires and molecular junctions can be fabricated and characterized systematically. Herein, we measured the quantized conductance through the construction of histograms of these metal atomic point contacts and of single molecules including benzene-1,4-dithiol (BDT), ferrocene-bisvinylphenylmethyl dithiol (Fc-VPM), 4,4,-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA). Finally, we briefly discussed the future of EC-MCBJ and EC-STM for nanoelectronics and devices, for example, for the formation of heterogeneous metal-based atomic point contacts and molecular junctions. [source] Prussian Blue-Modified Titanate Nanotubes: A Novel Nanostructured Catalyst for Electrochemical Reduction of Hydrogen PeroxideELECTROANALYSIS, Issue 19 2010Damir Ivekovi Abstract Prussian blue (PB) modified titanate nanotubes (PB-TiNT) have been synthesized by the reaction of Fe2+ -modified TiNT with hexacyanoferrate(III) ions. The rate constant for heterogeneous catalytic reaction between PB-TiNT and H2O2 was found to be k=2×104,dm3,mol,1,s,1, which is an order of magnitude higher than the values of k reported for conventionally prepared, electrochemically deposited PB films. On the PB-TiNT modified electrode with subnanomolar surface concentration of PB (,(PB)=2.8×10,11,mol/cm2), a stable, reproducible and linear response towards H2O2 was obtained in the concentration range 0.02,4,mM, with the sensitivity of 0.10,AM,1,cm,2 at ,150,mV. [source] Electrochemically Induced Formation of Surface-Attached Temperature-Responsive Hydrogels.ELECTROANALYSIS, Issue 9 2010Amperometric Glucose Sensors with Tunable Sensor Characteristics Abstract Employing thermally responsive hydrogels, the design of an amperometric glucose sensor is proposed. The properties of the biosensor can be modulated upon changing the temperature. Homo- and copolymers of N -isopropylacrylamide (NIPAm) and oligo(ethylene glycol) methacrylate (OEGMA) were prepared by electrochemically induced polymerization thus yielding surface-attached hydrogels. The growth of the films as well as the change in the film thickness in dependence from the temperature were investigated by means of an electrochemical quartz crystal microbalance (EQCM). The layer thickness in the dry state ranged from 20 to 120,nm. The lower critical solution temperature (LCST) of the hydrogel increases with increasing content of the more hydrophilic OEGMA. Hence, the swelling in aqueous electrolyte is composition dependent and can be adjusted by selecting a specific NIPAm to OEGMA ratio. All homo- and copolymer films showed good biocompatibility and no fouling could be observed during exposing the surfaces to human serum albumin. For amperometric glucose detection, glucose oxidase was entrapped in the films during electrochemically-induced polymerization. Both the apparent Michaelis constant (K and the apparent maximum current (i as determined by amperometry could be adjusted both by the film composition as well as the operation temperature. [source] Silver Doped Poly(L -valine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Uric Acid, Ascorbic Acid and DopamineELECTROANALYSIS, Issue 5 2010Wenna Hu Abstract In this paper, a silver doped poly(L -valine) (Ag-PLV) modified glassy carbon electrode (GCE) was fabricated through electrochemical immobilization and was used to electrochemically detect uric acid (UA), dopamine (DA) and ascorbic acid (AA) by linear sweep voltammetry. In pH,4.0 PBS, at a scan rate of 100,mV/s, the modified electrode gave three separated oxidation peaks at 591,mV, 399,mV and 161,mV for UA, DA and AA, respectively. The peak potential differences were 238,mV and 192,mV. The electrochemical behaviors of them at the modified electrode were explored in detail with cyclic voltammetry. Under the optimum conditions, the linear ranges were 3.0×10,7 to 1.0×10,5,M for UA, 5.0×10,7 to 1.0×10,5,M for DA and 1.0×10,5 to 1.0×10,3,M for AA, respectively. The method was successfully applied for simultaneous determination of UA, DA and AA in human urine samples. [source] Voltammetric Determination of L -Dopa on Poly(3,4-ethylenedioxythiophene)-Single-Walled Carbon Nanotube Composite Modified MicroelectrodesELECTROANALYSIS, Issue 4 2010Jayaraman Mathiyarasu Abstract In the present communication, it is shown that platinum microelectrodes electrochemically coated with a composite of poly(3,4-)ethylenedioxythiophene and single-walled carbon nanotubes (PEDOT/SWNT) enable determinations of 3,4-dihydroxy- L -phenylalaines (L -dopa) in neutral phosphate buffer solutions containing an excess of ascorbic acid. The interpenetrated networked nanostructure of the composite was characterized by scanning electron microscope (SEM) and Raman spectroscopy. It is shown that the presence of the composite gives rise to an increase in the electroactive area of an order of magnitude in compared to the area for the bare microelectrodes. The composite film-coated microelectrode, which yielded reversible cyclic voltammograms for the ferro/ferricyanide redox couple for scan rates between 0.01 and 0.10,V s,1, also gave rise to two well-resolved oxidation peaks for L -dopa and ascorbic acid (AA). The latter effect, which was not seen in the absence of the composite, enabled differential pulse voltammetric determinations of L -dopa in the concentration range between 0.1 to 20,,M with a detection limit of 100,nM. [source] Lactate Biosensor Based on Hydrotalcite-Like Compounds: Performances and Application to Serum SamplesELECTROANALYSIS, Issue 22 2009Irene Carpani Abstract A lactate biosensor based on lactate oxidase supported onto a hydrotalcite, electrochemically deposited on a platinum surface, was developed for the first time. For the best electrode configuration, a linear response up to 0.8,mM, with a limit of detection of 14,,M and a sensitivity of 91,mA M,1,cm,2, was obtained. The influence of some interferents due to the oxidation of hydrogen peroxide (at +0.35,V vs. SCE) was also studied. By controlling carefully the experimental conditions, the determination of lactate in a commercial serum sample in the presence of interferents was successfully accomplished. [source] Solid Contact Micropipette Ion Selective Electrode II: Potassium Electrode for SECM and In Vivo ApplicationsELECTROANALYSIS, Issue 17-18 2009Gergely Gyetvai Abstract Micropipette ion selective electrodes are very small, but fragile, short-life time sensors with very high resistance. Their high resistance is a draw back considering application in scanning electrochemical microscopy (SECM) and in life sciences. New, low resistance potassium micropipette electrodes were prepared, and applied. The electrode contains solid internal contact made of a carbon fiber lowered down all the way close to the orifice of the micropipette. The internal contact potential was kept constant by applying a doped, electrochemically prepared PEDOT coating on the fiber surface. The electrode performed well in in vivo experiments both in plant and animal tissue without capacitance neutralization and in SECM. [source] Redox Couple of DNA on Multiwalled Carbon Nanotube Modified ElectrodeELECTROANALYSIS, Issue 14 2009Hongxia Luo Abstract It has been envisioned that carbon nanotubes could promote electron-transfer reactions when used as electrode materials in electrochemical cells. In the present study, calf thymus DNA was electrochemically oxidized at an electrode modified with multiwalled carbon nanotubes. The potentials for DNA oxidation at pH,7.0 were found to be 0.71 and 0.81,V versus SCE, corresponding to the oxidation of guanine and adenine residues, respectively. An initial oxidation of adenine was observed in the first scan, which was followed by a quasi-reversible redox process of the oxidation product in the subsequent scans. [source] Glucosinolate Amperometric Bienzyme Biosensor Based on Carbon Nanotubes-Gold Nanoparticles Composite ElectrodesELECTROANALYSIS, Issue 13 2009V. Serafín Abstract A novel electrochemical biosensor design for glucosinolate determination involving bulk-incorporation of the enzymes glucose oxidase and myrosinase into a colloidal gold - multiwalled carbon nanotubes composite electrode using Teflon as binder is reported. Myrosinase catalyzes the hydrolysis of glucosinolate forming glucose, which is enzymatically oxidized. The generated hydrogen peroxide was electrochemically detected without mediator at the nanostructured composite electrode at E=+0.5,V vs. Ag/AgCl. Under the optimized conditions, the bienzyme MYR/GOx-Aucoll -MWCNT-Teflon exhibited improved analytical characteristics for the glucosinolate sinigrin with respect to a biosensor constructed without gold nanoparticles, i.e. a MYR/GOx-MWCNT-Teflon electrode, as well as with respect to other glucosinolate biosensor designs reported in the literature. The biosensor exhibits good repeatability of the amperometric measurements and good interassay reproducibility. Furthermore, the biosensor exhibited a high selectivity with respect to various potential interferents. The usefulness of the biosensor was evaluated by the determination of glucosinolate in Brussel sprout seeds. [source] Kinetic Study of the Oxidation of Catechols in the Presence of Some Aza-crown Ethers by Digital Simulation of Cyclic VoltammogramsELECTROANALYSIS, Issue 9 2009Davood Nematollahi Abstract The electrochemical oxidation of catechols (1) have been studied in the presence of diaza-18-crown-6 (DA18C6) (3a), diaza-15-crown-5 (DA15C5) (3b), and aza-15-crown-5 (A15C5) (3c) as nucleophiles in aqueous solution, by means of cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of electrochemically generated o -benzoquinones (2) in Michael-type reaction with aza-crown ethers (3) to form the corresponding new o -benzoquinone-aza-crown ether adducts (5). Based on ECE mechanism, the observed homogeneous rate constants (kobs) of the reaction of o -bezoquinones (2) with aza-crown ethers (3) were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated observed homogeneous rate constants (kobs) was found to vary in the order DA18C6>DA15C5>A15C5. [source] Current-Free Deposition of Prussian Blue with Organic Polymers: Towards Improved Stability and Mass Production of the Advanced Hydrogen Peroxide TransducerELECTROANALYSIS, Issue 3-5 2009Anastasiya Abstract We report on a novel approach for open-circuit (current-free) deposition of Prussian blue. Synthesis of Prussian blue is carried out by reduction of ferric ferricyanide with organic molecules, which are known to form polymers upon oxidation. The proposed interfacial deposition is a result of the synthesis in the presence of electrode support due to preconcentration of precursors at the interface. The resulting modified electrodes displayed the dramatically improved operational stability in hydrogen peroxide continuous monitoring with no loss of either electrochemical or analytical performance characteristics compared to electrodes with electrochemically deposited Prussian blue. The shown possibility to deposit stable films with regular structure in the absence of any external voltage could open new horizons for sensor science. [source] Electrochemical Determination of Manganese Solubility in Mercury via Amalgamation and Stripping in the Room Temperature Ionic Liquid n -Hexyltriethylammonium Bis(trifluoromethanesulfonyl)imide, [N6,2,2,2][NTf2]ELECTROANALYSIS, Issue 24 2008Abstract The solubility of manganese in mercury was determined electrochemically via amalgamation and stripping in the room temperature ionic liquid n -hexyltriethylammonium bis(trifluoromethanesulfonyl)imide, [N6,2,2,2][NTf2]. A hemispherical mercury electrode was made by electrodepositing mercury onto a planar platinum microelectrode. Cyclic voltammetry of Mn2+ in [N6,2,2,2][NTf2] at the mercury microhemisphere electrode was investigated at temperatures of 298, 303 and 313,K. The solubility of Mn in Hg was determined on the basis of the charge under the reduction peak (Mn2+,Mn0) and the corresponding reoxidation. [source] Using Capsaicin Modified Multiwalled Carbon Nanotube Based Electrodes and p -Chloranil Modified Carbon Paste Electrodes for the Determination of Amines: Application to Benzocaine and LidocaineELECTROANALYSIS, Issue 23 2008Roohollah Abstract The utilization of the capsaicin modified carbon nanotube modified basal-plane pyrolytic graphite electrode or p -chloranil modified carbon paste electrodes are presented for the determination of pharmaceutical compounds containing amine functionality, such as benzocaine and lidocaine. In detection of benzocaine at a capsaicin modified electrode, the guaiacol functional group is irreversibly electrochemically oxidized to form the o -quinone derivative which then undergoes nucleophilic attack by the aromatic amine group in benzocaine via a 1,4-Michael addition mechanism forming a catechol-amine adduct. The electrochemically initiated formation of the capsaicin-benzocaine adduct causes a linear decrease in the voltammetric signal corresponding to capsaicin which correlates to the added concentration of benzocaine. [source] Electrochemically Induced Modulation of the Catalytic Activity of a Reversible Redoxsensitive RiboswitchELECTROANALYSIS, Issue 9 2008Denise Strohbach Abstract Over the past decade, RNA conformation has been shown to respond to external stimuli. Thus, dependent on the presence of a high affinity ligand, specifically designed ribozymes can be regulated in a classical allosteric way. In this scenario, a binding event in one part of the RNA structure induces conformational changes in a separated part, which constitutes the catalytic centre. As a result activity is switched on (positive regulation) or off (negative regulation). We have developed a hairpin aptazyme responding to flavine mononucleotide (FMN). Ribozyme activity is dependent on binding of FMN and thus is switched on in the presence of FMN in its oxidized form. Under reducing conditions, however, FMN changes its molecular geometry, which is associated with loss of binding and consequently down-regulation of ribozyme activity. While in previous experiments sodium dithionite was used for reduction of FMN, we now present an assay for electrochemically induced activity switching. We have developed an electrochemical microcell that allows for iterative cycles of reduction/oxidation of FMN in an oxygen free atmosphere and thus for reversible switching of ribozyme activity. The reaction proceeds in droplets of 3 to 10,,L at micro- to nanomolar concentrations of the reaction components. [source] Simulation of Redox-Cycling Phenomena at Interdigitated Array (IDA) Electrodes: Amplification and SelectivityELECTROANALYSIS, Issue 5 2008M. Odijk Abstract We present Finite Element Method (FEM) simulations of interdigitated array (IDA) electrode geometries to study and verify redox selectivity and redox cycling amplification factor. The simulations provide an adequate explanation of an earlier found, but poorly understood, high amplification factor (65×) in a 1,,m-spaced IDA microdevice. Moreover, using the FEM calculations we present selectivity measurements with IDA electrodes in a mixture of two redox species, as for example dopamine and ferricyanide. We show that it is possible to electrochemically detect dopamine in presence of the stronger reductor ferricyanide, which is impossible with direct amperometric detection, with the use of IDA electrodes with proper polarization potential of the collector electrode. Using our simulations, we show that a theoretical selectivity of dopamine over ferricyanide of 11 can be achieved. [source] Electrochemical Detection of Arsenic(III) in the Presence of Dissolved Organic Matter (DOM) by Adsorptive Square-Wave Cathodic Stripping Voltammetry (Ad-SWCSV)ELECTROANALYSIS, Issue 4 2008Tsanangurayi Tongesayi Abstract This study has demonstrated that As(III) can be electrochemically detected and quantified in the presence of fulvic acid (FA) and dissolved organic matter (DOM). This eliminates the need to remove DOM prior to measurement of As(III) in environmental samples. Apart from reducing analysis time and the cost of the analysis, this could be potentially useful for the development of electrochemical methods for the detection and measurement of As(III) onsite. Both synthetic samples in which FA was added and a real sample with 22.16,mg/L total organic carbon (TOC) were analyzed. [source] Voltammetry as an Alternative Tool for Trace Metal Detection in Peloid Marine SedimentsELECTROANALYSIS, Issue 13 2007Irena Ciglene Abstract Here was demonstrated for the first time a possible application of abrasive stripping voltammetry in the direct measurement of trace metals in anoxic, sulfidic marine sediments (peloid mud) from a small and shallow (0.2,1,m) marine lagoon in Central Dalmatia, Croatia. Trace amounts of sample compounds are transferred to the graphite electrode surface and electrochemical reduction or oxidation processes are followed by the cyclic voltammetry in seawater or 0.55,M NaCl as electrolyte. After a preelectrolysis at potentials ranging from ,1.0 to ,1.5,V (vs. SCE) a well-defined anodic stripping peak corresponding to the oxidation of metal deposits generated at deposition potentials is obtained around ,0.74,V (vs. SCE). The same samples were studied by anodic stripping voltammetry at the Hg electrode and inductively coupled plasma-mass spectrometer (ICP-MS). ICP-MS showed higher concentrations of trace metals such as Al, Fe, Mo, Mn. A relatively high concentration of reduced sulfur species (RSS) (10,3 M) is determined electrochemically in porewater of the peloid mud, indicating that the magnitude of metal enrichment in the sediments is probably controlled by precipitation with sulfide. [source] Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device.ELECTROANALYSIS, Issue 5 2007Abstract Quaternized poly(4-vinylpyridine) (QPVP) has been incorporated as an anion exchanger into sol-gel derived silica films for use in a spectroelectrochemical sensor. The preparation, characteristics and performance of these films are described. The films, which are spin-coated onto the surface of a planar optically transparent electrode, are optically transparent and uniform. Scanning electron microscopy and spectroscopic ellipsometry have been used to examine film structure, thickness and optical properties. These films have been shown both spectroscopically and electrochemically to preconcentrate ferrocyanide, a model analyte for the sensor. The films can be regenerated for multiple measurements by exposure to 1,M KNO3. The effects of polymer molecular weight and storage conditions on film performance are described. The overall response of this film is comparable to the poly(dimethyldiallylammonium chloride)-silica films previously used for this sensor. [source] Preparation of Tip-Protected Poly(oxyphenylene) Coated Carbon-Fiber UltramicroelectrodesELECTROANALYSIS, Issue 23 2006El-Deen Abstract A high-yield, reliable, and reproducible method has been successfully developed to fabricate poly(oxyphenylene)-coated carbon fiber ultramicroelectrodes (POCF UMEs) with tip radii r<2,,m. During the insulation process, the tip of the electrochemically etched electrode is protected by inserting it into an inert polymer while the remainder of the electrode is insulated by electrochemical deposition of a 1,3,,m thick poly(oxyphenylene) film. Optimum conditions for poly(oxyphenylene) deposition are developed and the resulting carbon fiber UMEs showed good cyclic voltammetric behavior even after storage for more than one year. These UMEs were tested for use as amperometric scanning electrochemical microscopy (SECM) tips and successfully imaged Au/Kel-F and Al/SiCp metal matrix composites. [source] Electrochemically Functionalized Single-Walled Carbon Nanotube Gas SensorELECTROANALYSIS, Issue 12 2006Ting Zhang Abstract We demonstrate a facile fabrication method to make chemical gas sensors using single-walled carbon nanotubes (SWNT) electrochemically functionalized with polyaniline (PANI). The potential advantage of this method is to enable targeted functionalization with different materials to allow for creation of high-density individually addressable nanosensor arrays. PANI-SWNT network based sensors were tested for on-line monitoring of ammonia gas. The results show a superior sensitivity of 2.44% ,R/R per ppmv NH3 (which is more than 60 times higher than intrinsic SWNT based sensors), a detection limit as low as 50,ppbv, and good reproducibility upon repeated exposure to 10,ppmv NH3. The typical response time of the sensors at room temperature is on the order of minutes and the recovery time is a few hours. Higher sensitivities were observed at lower temperatures. These results indicate that electrochemical functionalization of SWNTs provides a promising new method of creating highly advanced nanosensors with improved sensitivity, detection limit, and reproducibility. [source] Redox Active Two-Component Films of Palladium and Covalently Linked Zinc Porphyrin,Fullerene DyadELECTROANALYSIS, Issue 9 2006Marta Plonska Abstract Redox active films have been generated electrochemically by the reduction of dyads consisting of fullerene C60 covalently linked to zinc meso -tetraphenyloporphyrin, ZnPC60, and palladium acetate. The films are believed to consist of a polymeric network formed via covalent bonds between the palladium atoms and the fullerene moieties. In these films, the zinc porphyrin moiety is covalently linked to the polymeric chains through the pyrrolidine ring of the fullerene. The ZnPC60/Pt films are electrochemically active in both positive and negative potential excursions. At positive potentials, two oxidation steps for the zinc porphyrin are observed. In the negative potential range, electron transfer processes involving the zinc porphyrin and the fullerene entities are observed. Film formation is also accompanied by palladium deposition on the electrode surface. The presence of a metallic phase in the film influences its morphology, structure and electrochemical properties. [source] | |||||||||||||||||||||||||||||||||||||||||||