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Ashwini K Srivastava - One of the best experts on this subject based on the ideXlab platform.

  • macrocyclic compounds based Chemically Modified Electrodes for voltammetric determination of l tryptophan using electrocatalytic oxidation
    Analytical Letters, 2010
    Co-Authors: Ashwini K Srivastava, Reena R Gaichore
    Abstract:

    The electrochemical behavior of L-tryptophan is studied at carbon paste electrode and Electrodes Modified with different macrocyclic compounds of which Dibenzo-18-crown-6 (DB18C6) showed better response for L-tryptophan at + 0.95 V vs. Ag/AgCl. Use of Ni2+ ions as electrocatalyst shows a further enhancement in peak current leading to a linear range of 1.96 × 10−6 − 1.01 × 10−3 M and a detection limit of 9.79 × 10−8 M by differential pulse voltammetry. Electrochemical impedance diagnosis reveals that L-tryptophan oxidation is kinetically facile on DB18C6 Modified electrode. The Modified electrode is used for L-tryptophan determination in real samples.

  • electrochemical behavior of folic acid at calixarene based Chemically Modified Electrodes and its determination by adsorptive stripping voltammetry
    Electrochimica Acta, 2007
    Co-Authors: Vishwanath D Vaze, Ashwini K Srivastava
    Abstract:

    Abstract Voltammetric behavior of folic acid at plain carbon paste electrode and electrode Modified with calixarenes has been studied. Two peaks for irreversible oxidation were observed. Out of the three calixarenes chosen for modification of the Electrodes, p - tert -butyl-calix[6]arene Modified electrode (CME-6) was found to have better sensitivity for folic acid. Chronocoulometric and differential pulse voltammetric studies reveal that folic acid can assemble at CME-6 to form a monolayer whose electron transfer rate is 0.00273 s −1 with 2-electron/2-proton transfer for the peak at +0.71 V against SCE. An adsorption equilibrium constant of 5 × 10 3  l/mol for maximum surface coverage of 2.89 × 10 −10  mol/cm 2 was obtained. The current is found to be rectilinear with concentration by differential pulse voltammetry. However, linearity in the lower range of concentration 8.79 × 10 −12  M to 1.93 × 10 −9  M with correlation coefficient of 0.9920 was achieved by adsorptive stripping voltammetry. The limit of detection obtained was found to be 1.24 × 10 −12  M. This method was used for the determination of folic acid in a variety of samples, viz. serum, asparagus, spinach, oranges and multivitamin preparations.

  • behavior of riboflavin on plain carbon paste and aza macrocycles based Chemically Modified Electrodes
    Sensors and Actuators B-chemical, 2007
    Co-Authors: Rahul M Kotkar, Purvi B Desai, Ashwini K Srivastava
    Abstract:

    Abstract The electrochemical behavior of riboflavin at a carbon paste electrode and Electrodes Modified with aza crown ethers have been studied using voltammetric techniques. The macrocycles used as modifiers were 1,4,8,11-tetraazacyclooctadecane; 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane; 1,4,7,10-tetraoxa-13-azacyclopentadecane and 1,4,7,10-tetratosyl-1,4,7,10-tetraazacyclooctadecane, out of which 1,4,8,11-tetraazacyclooctadecane showed better response for riboflavin. The interaction of riboflavin with 1,4,8,11-tetraazacyclooctadecane was confirmed by complexation study in 20% DMSO + water (log  K 5.58) using differential pulse polarography. The kinetic parameters viz. electron transfer coefficient and rate constant of electron transfer across the Modified electrode were found to be 0.708 and 5.5 s −1 , respectively. The surface coverage of the 1,4,8,11-tetraazacyclooctadecane Modified electrode was calculated to be 5 × 10 −10  mol cm −2 by cyclic voltammetry and chronocoulometry. A linear working range of 0.5 ng cm −3 to 70 μg cm −3 with a detection limit of 0.2 ng cm −3 has been obtained using 1,4,8,11-tetraazacyclooctadecane Modified electrode by square wave anodic stripping voltammetry. It was possible to determine riboflavin in presence of some organic molecules like thiamine hydrochloride, nicotinamide, pyridoxine hydrochloride, ascorbic acid, para -aminobenzoic acid and l -tryptophan. Also simultaneous and quantitative determinations were achieved for combination of some of these. The electrode could be used for estimation of riboflavin in pharmaceutical and food samples.

  • Chemically Modified Electrodes based on macrocyclic compounds for determination of vitamin c by electrocatalytic oxidation
    Analytica Chimica Acta, 2001
    Co-Authors: Vijaykumar S Ijeri, Priya V Jaiswal, Ashwini K Srivastava
    Abstract:

    The voltammetric behavior of Vitamin C (l-ascorbic acid) at carbon paste Electrodes and Electrodes Modified with aza macrocycles have been studied. The use of zinc complexes, formed in situ at the electrode surface reduced the overpotential for the oxidation of ascorbic acid by about 200 mV and enhanced the peak currents. Linearity was observed over the range of 0.6–500g/cm 3 with a detection limit of 0.1g/cm 3 by differential pulse voltammetry. The Modified electrode was used for the determination of Vitamin C in multivitamin–multimineral pharmaceutical preparations, fruit juices and wine samples. © 2001 Elsevier Science B.V. All rights reserved.

  • voltammetric determination of lead at Chemically Modified Electrodes based on crown ethers
    Analytical Sciences, 2001
    Co-Authors: Vijaykumar S Ijeri, Ashwini K Srivastava
    Abstract:

    The feasibility of fabricating lead-sensitive Chemically Modified Electrodes (CMEs) for trace analysis in aqueous and 40% (v/v) ethanol-water media was investigated. Carbon paste Electrodes Modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The thus-formed Electrodes were able to bind Pb(II) ions Chemically, and gave better voltammetric responses than unModified ones. The crown ethers studied and compared were 18-crown-6 and dibenzo-18-crown-6. With a 5% 18-crown-6 CME, Pb(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.02 ppm. It was possible to selectively pick up Pb(II) from a solution of several other ions at an open circuit through complexation. A simultaneous analysis of Cu(II) and Pb(II) was also attempted. By differential pulse anodic stripping voltammetry Pb(II) could be quantified over the range of 1 to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Ag(I), Fe(III), Ca(II) and Mg(II) was also studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.

Vairathevar Sivasamy Vasantha - One of the best experts on this subject based on the ideXlab platform.

  • electrochemical preparation of epinephrine nafion Chemically Modified Electrodes and their electrocatalytic oxidation of ascorbic acid and dopamine
    Electrochimica Acta, 2006
    Co-Authors: Shen-ming Chen, Jiyan Chen, Vairathevar Sivasamy Vasantha
    Abstract:

    Abstract Two types of epinephrine and cyclized epinephrine quinone films have been prepared using cyclic voltammetry from the epinephrine in the strong acidic solutions and neutral aqueous solutions over different scanning potential ranges. The cyclic voltammogram of the epinephrine film is characterized by one redox couple at about +0.5 V (versus Ag|AgCl) and cyclized epinephrine quinone film exhibits one redox couples at about −0.15 V (versus Ag|AgCl) .In addition to cyclic voltammetry and an electrochemical quartz crystal microbalance (EQCM) were used to study the growth mechanism of the epinephrine and cyclized epinephrine quinone molecules. The electrocatalytic oxidation of catecholamines (dopamine and norepinephrine) and also ascorbic acid were investigated in acidic aqueous solutions using epinephrine films. The rotating ring-disk electrode technique was used to investigate the mechanism of electrochemical oxidation of dopamine and ascorbic acid.

  • preparation and electrocatalytic properties of the tbo nafion Chemically Modified Electrodes
    Journal of Electroanalytical Chemistry, 2006
    Co-Authors: Shen-ming Chen, Ghenghsien Chuang, Vairathevar Sivasamy Vasantha
    Abstract:

    Abstract The glassy carbon electrode Modified with nafion and toluidine blue O (TBO) was prepared and their electrochemical properties were investigated. The TBO molecules were strongly and irreversibly adsorbed on the nafion-Modified glassy carbon surface. The electrochemical behavior and mechanism for interactions of the TBO molecules with the nafion film were investigated through cyclic voltammetric and UV–vis spectra methods. The electrocatalytic reductions of nitric oxide and oxygen were performed at this Modified electrode by cyclic voltammetry, rotating ring disk voltammetry and chronoamperometry as diagnostic techniques. The nafion membrane played a duel role as a matrix for the TBO immobilization and also helped to partitioning the NO from the solution phase. The diffusion coefficients of nitric oxide and oxygen at the TBO/nafion/GC Modified electrode were calculated using chronoamperometric technique and rotating ring disk voltammetry, respectively. The ‘ D ’ value for nitric oxide and oxygen obtained by the above methods were found as 1.2798 × 10 −6 and 1.4 × 10 −5  cm 2  s −1 , respectively. From the intercept value of the Koutecky–Levich plot, the catalytic reaction rate constant, k , was calculated for O 2 reduction and found as 6.6 × 10 4  M −1  S −1 .

Richard P Baldwin - One of the best experts on this subject based on the ideXlab platform.

  • selective oxidation of thiols to disulfides at polymeric cobalt phthalocyanine Chemically Modified Electrodes
    Journal of The Electrochemical Society, 1996
    Co-Authors: Richard P Baldwin
    Abstract:

    Cysteine, glutathione, and several other aliphatic and aromatic thiols were exhaustively oxidized at Chemically Modified reticulated vitreous carbon containing a polymer coating of cobalt phthalocyanine (CoPC). Coulometric measurements indicated that, for all thiols examined, the electro-oxidation was a one-electron process. Subsequent end product analysis by high performance liquid chromatography, polarimetry, and 13 C nuclear magnetic resonance spectrometry confirmed that, for cysteine and glutathione, the corresponding disulfide species were formed very cleanly with no evidence of further oxidation to the sulfinic or sulfonic acid. The polymeric CoPC Electrodes were compatible with a wide range of solvent and pH conditions. Unlike most conventional Electrodes, which are rapidly passivated upon attempted oxidation of organosulfur compounds, the CoPC Electrodes were extraordinarily durable, exhibiting turnover numbers of greater than 10 4 for each Co 2+ center with little or no loss of activity

  • Chemically Modified Electrodes in liquid chromatography detection a review
    Talanta, 1991
    Co-Authors: Richard P Baldwin, Karsten N Thomsen
    Abstract:

    Recent trends in the use of Chemically Modified Electrodes (CMEs) in electrochemical detection systems used in flow-injection analysis or high-performance liquid chromatography are reviewed, with the objective of indicating the most promising approaches for practical CME applications. Four specific application areas of CMEs are identified: (1) those using perm-selective coatings to enhance selectivity and inhibit surface fouling, (2) those using immobilized electron-transfer mediators to catalyse slow electrode reactions, (3) those using enzymes as modifiers to provide biological activity on the electrode surface and (4) those using ion-exchange coatings for the electrochemical detection of non-electroactive anions and cations. By virtue of these approaches, the judicious use of CMEs has already had a significant impact on the performance and scope of electrochemical detection in flow systems. The most important improvements have been in CME selectivity, which produces simpler assay procedures with less need for sample treatment, and increased usefulness for complex samples, and in CME reactivity, which expands the range of analytes amenable to electrochemical monitoring.

Nagaraj P Shetti - One of the best experts on this subject based on the ideXlab platform.

  • electrochemical behavior of flufenamic acid at amberlite xad 4 resin and silver doped titanium dioxide amberlite xad 4 resin Modified carbon Electrodes
    Colloids and Surfaces B: Biointerfaces, 2019
    Co-Authors: Nagaraj P Shetti, Deepti S Nayak, Shweta J Malode, Kakarla Raghava Reddy, Shyam S Shukla, Tejraj M Aminabhavi
    Abstract:

    Abstract Novel sensors based on carbon paste assorted with amberlite XAD-4 resin and silver-doped titanium dioxide/amberlite XAD-4 resin (Ag-TiO2/XAD) were designed and employed for sensitive detection of flufenamic acid (FFA). The main objective of this study is to develop novel electrochemical sensors for more sensitive and selective detection of FFA and to propose its oxidation mechanism. In this perspective, we have developed Modified Electrodes using amberlite XAD-4 matrix and Ag-TiO2/XAD-4 mixture. These sensors when used in conjunction with different voltammetric techniques to observe enhanced outcome on FFA electrode reaction in PBS of pH 7.0. Our data confirmed exceptional stability, sensitivity, and quick responses for FFA. The effect of modifier, analyte concentration, pH of buffer solution, pre-concentration time, and sweep rates on electrochemical behavior of FFA was investigated. The current intensities were linearly proportional to the concentration of FFA. From the calibration plot of different concentrations of FFA, the detection limit of 3.6 nM at XAD-CPE and 1.2 nM, respectively at AgTiO2/XAD-CPE were obtained. The estimation of FFA in biological as well as clinical samples was achieved using the Chemically Modified Electrodes.

Juozas Kulys - One of the best experts on this subject based on the ideXlab platform.

  • modelling amperometric biosensors based on Chemically Modified Electrodes
    Sensors, 2008
    Co-Authors: Romas Baronas, Juozas Kulys
    Abstract:

    The response of an amperometric biosensor based on a Chemically Modified electrode was modelled numerically. A mathematical model of the biosensor is based on a system of non-linear reaction-diffusion equations. The modelling biosensor comprises two compartments: an enzyme layer and an outer diffusion layer. In order to define the main governing parameters the corresponding dimensionless mathematical model was derived. The digital simulation was carried out using the finite difference technique. The adequacy of the model was evaluated using analytical solutions known for very specific cases of the model parameters. By changing model parameters the output results were numerically analyzed at transition and steady state conditions. The influence of the substrate and mediator concentrations as well as of the thicknesses of the enzyme and diffusion layers on the biosensor response was investigated. Calculations showed complex kinetics of the biosensor response, especially when the biosensor acts under a mixed limitation of the diffusion and the enzyme interaction with the substrate.

  • bienzyme sensors based on Chemically Modified Electrodes
    Biosensors and Bioelectronics, 1991
    Co-Authors: Juozas Kulys, Rolf D Schmid
    Abstract:

    Abstract Bienzyme sensors for alcohol, D-amino acid, L-aminoa cid, choline, and cholesterol determination were prepared based on peroxidase and the respective oxidases at graphite Electrodes Modified with 1,1′-dimethylferrocene, tetrathiafulvalene and tetracyanoquinonedimethane. Cholesterol was determined using a peroxidase sensor and soluble cholesterol oxidase. The response time of the alcohol oxidase/peroxidase biosensors was 30–40 s. Linear calibration of these Electrodes was achieved up to 0·6—1·2 mM or 9 mM depending on the immobilization technique used. Biosensors were operated at potentials from −0·2 to +0·2 was a saturated Ag/AgCl electrode. The biosensors showed the highest activity in the pH range 7—11. The substrate specificity of ethanol and D-amino acid biosensors was investigated. L-amino acid determination was possible using a trienzyme sensor based on peroxidase, D-amino acid oxidase and amino acid racemase.

  • Chemically Modified Electrodes for the determination of sulphydryl compounds
    Analytica Chimica Acta, 1991
    Co-Authors: Juozas Kulys, A Drungiliene
    Abstract:

    Abstract Under neutral conditions, the electrocatalytic oxidation of sulphydryl compounds at rotating graphite Electrodes Modified with tetracyano- p -quinodimethane, tetrathiafulvalene and 1,1′-dimethylferrocene proceeds at potentials higher than −0.1 V vs. SCE. The sensitivity of the Electrodes depends on the nature of both the modifier and the sulphydryl compounds, and in 0.1 M potassium phosphate buffer solution (pH 7) it reaches 0.16 A 1 mol −1 cm −2 . The electrode sensitivity is higher in a weakly alkaline medium. The sensitivity is only slightly dependent on the electrode rotation speed.