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Made available in DSpace on 2018-12-11T16:43:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-01-01 Electropolymerization of a π-conjugated polymer from [N,N′-bis(salicylidene)-o-phenylenediamine]nickel(II) complex ([Ni(salophen)]) on the surface of indium-tin-oxide (ITO) was studied. Two structures of the polymer have been proposed based on the theorem of molecular columns. The highlighted structures are the molecular column of the central aromatic rings (MCCAR) and molecular column of the side aromatic rings (MCSAR). The molecular structures were obtained by control of the potential scan rate in the electropolymerization step. The MCCAR structures are stable and structurally compact, whereas the MCSAR structures are less compact. Electrochemical measurements, atomic force microscopy (AFM), UV–Vis spectroscopy, FTIR Raman spectroscopy and optical microscopy support the formation of the multiblock π-conjugated polymer. Department of Chemistry and Biochemistry Faculty of Science and Technology São Paulo State University (UNESP), Rua Roberto Simonsen 305 São Carlos Institute of Chemistry University of São Paulo (USP) Department of Chemistry Faculty of Science and Technology University of Coimbra Department of Chemistry and Biochemistry Faculty of Science and Technology São Paulo State University (UNESP), Rua Roberto Simonsen 305 more...

Made available in DSpace on 2018-12-11T16:44:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-01-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) This work reports on the sol-gel synthesis of barium- and europium-doped silica xerogel and its use as an electrocatalytic sensor. Barium was chosen to assist the network framing and europium to provide electronic properties, including the Eu2+/Eu3+ redox process. The results from different molecular and structural techniques indicated that this xerogel is a composite material that combines a non-crystalline polymeric silica network with a high level of agglomeration and a low degree of reticulation formed by the hydrolysis and condensation of TEOS and M-O bonds (M = Ba2+ and/or Eu3+), whereas the oxygen atoms belong to the xerogel phase. The electrochemical behavior of the silica xerogel:Ba2+,Eu3+ with different amounts of Eu3+ under several different conditions was investigated. The electrochemical sensing platform showed a well-defined redox coupling with a formal potential of 0.06 V, assigned to europium redox sites in silicate. Electrocatalytic activity was observed with an increasing anodic peak current to the isoniazid oxidation, indicating that the electrochemical sensing platform designed here was successfully achieved. Faculdade de Ciências e Tecnologia UNESP Univ Estadual Paulista, Rua Roberto Simonsen, 305 Instituto de Biociências Letras e Ciências Exatas UNESP Univ Estadual Paulista, Rua Cristóvão Colombo, 2265 Instituto de Química de São Carlos Universidade de São Paulo-USP Faculdade de Ciências e Tecnologia UNESP Univ Estadual Paulista, Rua Roberto Simonsen, 305 Instituto de Biociências Letras e Ciências Exatas UNESP Univ Estadual Paulista, Rua Cristóvão Colombo, 2265 more...

The preparation and electrochemical characterization of a nickel hydroxide modified nickel electrode as well as its behavior as electrocatalyst toward the oxidation of hydrochlorothiazide (HCTZ) were investigated. The electrochemical behavior of the modified electrode and the electrooxidation of HCTZ were explored using cyclic voltammetry. The voltammetric response of the modified electrode in the detection of HCTZ is based on the electrochemical oxidation of the Ni(II)/Ni(III) and a chemical redox process. The analytical parameters for the electrooxidation of HCTZ by the nickel hydroxide modified nickel electrode were obtained in NaOH solution, in which the linear voltammetric response was in the concentration range from 1.39 × 10−5 to 1.67 × 10−4 mol L−1 with a limit of detection of 7.92 × 10−6 mol L−1 and a sensitivity of 0.138 μA L mmol−1. Tafel analysis was used to elucidate the kinetics and mechanism of HCTZ oxidation by the modified electrode. more...

The supramolecular building blocks from a nickel(II) bisalphen-type complex have been reported. The conjugations through the bridge provide flexibility of the monomer in the electropolymerization stage. Thus, different structures can be obtained with the variation of electrochemical parameters used in the electropolymerization. The structural characterization and the electrochemical behavior in aqueous solution was also evaluated, which demonstrated that the electropolymerization mechanism was similar to that observed for the classical salen polymers, but the molecular organization onto the conductor substrate was different. The supramolecular structure of the polymeric film allows observation of the NiI/NiII and NiII/NiIII redox couples by differential pulse voltammetry. Thus, the comproportionation constant and Gibbs energy were calculated for the NiI/NiII redox couple. These characteristics make these polymers versatile materials in the field of supramolecular chemistry and materials science, in particular in applications as sensors, in electrocatalysts and for energy storage. more...

The preparation and electrochemical characterization of hausmannite-type manganese oxide to use as a sensing material for sodium ion is described. This paper reports a new via synthetic to obtain of the hausmannite-type manganese oxide and its application in the construction of modified electrode as a voltammetric sensor. The electrochemical activity of hausmannite-type manganese oxide is controlled by intercalation/deintercalation of the sodium ions within the oxide lattice. The detection is based on the measurement of anodic current generated by oxidation of Mn III –Mn IV at electrode surface. The best electrochemical response was obtained for a sensor composition of 20% (w/w) hausmannite oxide in the paste, a TRIS buffer solution of pH 6.0–7.0 and a scan rate of 50 mV s −1 . A sensitive linear voltammetric response for sodium ions was obtained in the concentration range of 2.01 × 10 −5 –2.09 × 10 −4 mol L −1 with a slope of 355 μA L mmol −1 and a detection limit of 7.50 × 10 −6 mol L −1 using cyclic voltammetry. The use of hausmannite has significantly improved the selectivity of the sensor compared to the birnessite-type manganese oxide modified electrode. Under the working conditions, the proposed method was successfully applied to determination of sodium ions in urine samples. more...

An amperometric oxygen sensor based on a polymeric nickel– salen ( salen = N , N ′-ethylene bis (salicylideneiminato)) film coated platinum electrode was developed. The sensor was constructed by electropolymerization of nickel– salen complex at platinum electrode in acetonitrile/tetrabutylammonium perchlorate by cyclic voltammetry. The voltammetric behavior of the sensor was investigated in 0.5 mol L −1 KCl solution in the absence and presence of molecular oxygen. Thus, with the addition of oxygen to the solution, the increase of cathodic peak current (at −0.25 V vs. saturated calomel electrode (SCE)) of the modified electrode was observed. This result shows that the nickel– salen film on electrode surface promotes the reduction of oxygen. The reaction can be brought about electrochemically, where the nickel(II) complex is first reduced to a nickel(I) complex at the electrode surface. The nickel(I) complex then undergoes a catalytic oxidation by the molecular oxygen in solution back to the nickel(II) complex, which can then be electrochemically re-reduced to produce an enhancement of the cathodic current. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the oxygen reduction. A plot of the cathodic current vs. the dissolved oxygen concentration for chronoamperometry (fixed potential = −0.25 V vs. SCE) at the sensor was linear in the 3.95–9.20 mg L −1 concentration range and the concentration limit was 0.17 mg L −1 O 2 . The proposed electrode is useful for the quality control and routine analysis of dissolved oxygen in commercial samples and environmental water. The results obtained for the levels of dissolved oxygen are in agreement with the results obtained with a commercial O 2 sensor. more...

In the present work, we investigated the immobilization and electrochemical behavior of Reactive Blue 4 dye on 3-aminopropyl-functionalized silica. The electrochemical behavior of the modified electrode and the electro-oxidation of dipyrone were studied by cyclic voltammetry. The modified electrode showed a well-defined redox coupling with a formal potential of 0.45 V (vs. saturated calomel reference electrode) assigned to anthraquinone/anthrahydroquinone redox process (pH = 2). The modified electrode also demonstrated electrocatalytic activity and an increased peak current towards the oxidation of dipyrone at a reduced overall potential. The electrocatalytic process was found to be highly dependent on the pH of the supporting electrolyte. The voltammetric responses for dipyrone were linear in the concentration range of 49.9 to 440 μmol L−1 at a pH of 2.0 with a detection limit and sensitivity of 22.0 μmol L−1 and 0.0278 μA mmol L−1, respectively. more...

The electrochemical behavior of a carbon paste electrode modified (CPEM) with nickel-doped potassium strontium niobate (KSr 2 Ni 0.75 Nb 4.25 O 15− δ ) of tetragonal tungsten bronze (TTB)-type structure was investigated as a new sensor for dipyrone. The optimum conditions were found in an electrode composition (in mass) of 20% KSr 2 Ni 0.75 Nb 4.25 O 15− δ , 65% graphite and 15% mineral oil in 0.5 mol L −1 KCl solution at pH 6.0. The electrode exhibits reversible electrochemical behavior in a wide potential range (0.1–0.7 V vs. SCE), high conductivity, and stability/durability electrode in 0.50 mol L −1 KCl solution. The estimated surface concentration was found to equal 1.08 × 10 −9 mol cm −2 . The oxidation of dipyrone was performed at carbon paste electrode unmodified at +0.54 V vs. SCE and carbon paste electrode modified with KSr 2 Ni 0.75 Nb 4.25 O 15− δ at +0.45 V vs. SCE. This result shows that the nickel-doped potassium strontium niobate on electrode surface promotes the oxidation of dipyrone. The reaction can be brought about electrochemically, where the niobium(IV) is first oxidation to a niobium(IV) oxide at the electrode surface. The niobium(IV) then undergoes a catalytic reduction by the dipyrone in solution back to the niobium(III), which can then be electrochemically re-oxidized to produce an enhancement of the anodic current. The identification of the oxidation product of dipyrone was made by mass spectrometry for elucidation of response mechanism of the sensor. Anodic peak current ( I pa ) vs. dipyrone concentration for amperometric method at the modified electrode was linear in the 3.5 × 10 −5 and 3.1 × 10 −4 mol L −1 concentration range and the detection limit was 5.1 × 10 −6 mol L −1 dipyrone. At higher concentrations (>3.1 × 10 −4 mol L −1 ), deviation from linearity occurs. Under this condition, an electrocatalytic reaction takes place and proceeds through a mechanism similar to the Michaelis–Menten model. more...

Electrochemical behavior of oxo-bridged dinuclear ruthenium(III) complex ([(bpy)2(H2O)RuIII-O-RuIII(H2O)(bpy)2]4+) has been studied in aqueous solution (KCl 0.5 mol L−1) by both cyclic and rotating disk electrode (RDE) voltammetry in order to identify and elucidate the reaction mechanism. Modified electrode containing the oxo-bridged ruthenium complex incorporated into a cation-exchange polymeric film deposited onto platinum electrode surface was studied. Cyclic voltammetry at the modified electrode in KCl solution showed a single-electron reduction/oxidation of the couple RuIII-O-RuIII/RuIII-O-RuIV. The modified electrode exhibited electrocatalytic property toward hydrogen peroxide oxidation in KCl solution with a decrease of the overpotential of 340 mV compared with the platinum electrode. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the hydrogen peroxide oxidation. The first at low overpotential region there is no significant change in the Tafel slope (∼0.130 V dec−1) with varying peroxide concentration. The second region at higher overpotential the slope values (0.91–0.47 V dec−1) were depended on the peroxide concentration. The apparent reaction order for H2O2 varies from 0.16 to 0.50 in function of the applied potential. The apparent reaction order (at constant potential) with respect to H+ concentration of 10−5 to 10−1 mol L−1 was 0.25. A plot of the anodic current vs. the H2O2 concentration for chronoamperometry (potential fixed = +0.61 V) at the modified electrode was linear in the 1.0 × 10−5 to 2.5 × 10−4 mol L−1 concentration range. more...

Made available in DSpace on 2013-09-27T14:53:52Z (GMT). No. of bitstreams: 1 WOS000288227800090.pdf: 442251 bytes, checksum: b5dc8c3fb00f96f187e4b8aba1393341 (MD5) Previous issue date: 2011-02-01 Made available in DSpace on 2013-09-30T18:09:39Z (GMT). No. of bitstreams: 1 WOS000288227800090.pdf: 442251 bytes, checksum: b5dc8c3fb00f96f187e4b8aba1393341 (MD5) Previous issue date: 2011-02-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:23:13Z No. of bitstreams: 1 WOS000288227800090.pdf: 442251 bytes, checksum: b5dc8c3fb00f96f187e4b8aba1393341 (MD5) Made available in DSpace on 2014-05-20T13:23:13Z (GMT). No. of bitstreams: 1 WOS000288227800090.pdf: 442251 bytes, checksum: b5dc8c3fb00f96f187e4b8aba1393341 (MD5) Previous issue date: 2011-02-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. This paper describes the amperometric determination of lithium ions using carbon-paste electrode modified with spinel manganese(IV) oxide under flow conditions. Systematic investigations were made to optimize the experimental parameters for lithium sensor by flow injection analysis. The detection was based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the lithium ions extraction into the spinel structure. An operating potential of 0.50 V (vs. Ag/AgCl/3 KCl mol/L) was exploited for amperometric monitoring. The amperometric signal was linearly dependent on the lithium ions concentration over the range 4.0 x 10(-5) to 1.0 x 10(-3) mol L-1. The equilibrium constant of insertion/extraction of the lithium ion in the spine! structure, apparent Gibbs energy of insertion, and surface coverage of the electrode with manganese oxide, were calculated by peak charge (Q) in different concentration under flow conditions. Considering selectivity, the peak charge of the sensor was found to be linearly dependent on the ionic radius of the alkaline and earth-alkaline cations. (C) 2010 Elsevier Ltd. All rights reserved. Univ State São Paulo UNESP, Fac Sci & Technol, Dept Phys Chem & Biol, BR-19060900 Presidente Prudente, SP, Brazil Universidade Federal do Paraná (UFPR), Dept Quim, BR-80060000 Curitiba, Parana, Brazil Universidade Federal de São Carlos (UFSCar), Dept Quim, BR-13560 São Carlos, SP, Brazil Univ State São Paulo UNESP, Fac Sci & Technol, Dept Phys Chem & Biol, BR-19060900 Presidente Prudente, SP, Brazil FAPESP: 08/07298-7 FAPESP: 09/11079-1 CNPq: 474367/2004-5 more...

In this paper, we studied the development of a selective lithium ion sensor constituted of a carbon paste electrode modified (CPEM) with an aluminum-doped spinel-type manganese oxide (Li 1.05 Al 0.02 Mn 1.98 O 4 ) for investigating the influence of a doping ion in the sensor response. Experimental parameters, such as influence of the lithium concentration in the activation of the sensor by cyclic voltammetry, pH of the carrier solution and selectivity for Li + against other alkali and alkaline-earth ions were investigated. The sensor response to lithium ions was linear in the concentration range 5.62 × 10 −5 to 1.62 × 10 −3 mol L −1 with a slope 100.1 mV/decade over a wide pH 10 (Tris buffer) and detection limit of 2.75 × 10 −5 mol L −1 , without interference of other alkali and alkaline-earth metals, demonstrating that the Al 3+ doping increases the structure stability and improves the potentiometric response and sensitivity of the sensor. The super-Nernstian response of the sensor in pH 10 can be explained by mixed potential arising from two equilibria (redox and ion-exchange) in the spinel-type manganese oxide. more...

The preparation and electrochemical characterization of a carbon paste electrode modified with layered birnessite-type manganese oxide for use as a sodium sensor is described. The effects of powder synthesis process (sol–gel and redox precipitation) for birnessite on the electrochemical activity of the sensor was investigated by cyclic voltammetry. The carbon paste electrode modified with birnessite-type manganese oxide that was synthesized by the sol–gel method showed a best electrochemical for sodium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the sodium ions extraction into the birnessite structure. The best voltammetric response was obtained for an electrode composition of 15% (w/w) birnessite oxide in the paste, a TRIS buffer solution of pH 8.0 and a scan rate of 50 mV s −1 . A sensitive linear voltammetric response for sodium ions was obtained in the concentration range of 7.89 × 10 −5 to 3.49 × 10 −4 mol L −1 with a slope of 37.5 μA L mmol −1 and a detection limit (3 σ /slope) of 3.43 × 10 −5 mol L −1 using cyclic voltammetry. Under the working conditions, the proposed method was successfully applied to determination of sodium ions in urine samples. more...

Copper(II) hexacyanoferrate(III) (CuHCF) modified carbon paste electrode was used for the electroanalytical determination of dipyrone and acetaminophen in pharmaceutical preparations by cyclic voltammetry. Several parameters were investigated for the optimization of the sensor such as composition of the electrode, electrolytic solution, effect of pH, scan rate of potential and interference. The best conditions were found for an electrode composition in mass of 20% CuHCF, 55% graphite and 25% mineral oil in acetate buffer containing 0.05 mol L -1 of NaCl. The analytical curve was linear in the dipyrone and acetaminophen concentration ranged from 1.25 x 10 -5 mol L -1 to 1.23 x 10 -3 and 2.84 x 10 -4 to 2.59 x 10 -3 mol L -1 respectively, being successfully applied to the determination of dipyrone and acetaminophen in phar- maceutical preparations. The CuHCF modified carbon paste electrode presented comparable results to those obtained us- ing iodimetry and ultraviolet spectrophotometry methods, respectively. more...

Made available in DSpace on 2013-09-27T14:53:53Z (GMT). No. of bitstreams: 1 WOS000275995600210.pdf: 171567 bytes, checksum: 8603747737628bbd5ef1b702ec0f6a96 (MD5) Previous issue date: 2009-01-01 Made available in DSpace on 2013-09-30T18:09:38Z (GMT). No. of bitstreams: 1 WOS000275995600210.pdf: 171567 bytes, checksum: 8603747737628bbd5ef1b702ec0f6a96 (MD5) Previous issue date: 2009-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:23:13Z No. of bitstreams: 1 WOS000275995600210.pdf: 171567 bytes, checksum: 8603747737628bbd5ef1b702ec0f6a96 (MD5) Made available in DSpace on 2014-05-20T13:23:13Z (GMT). No. of bitstreams: 1 WOS000275995600210.pdf: 171567 bytes, checksum: 8603747737628bbd5ef1b702ec0f6a96 (MD5) Previous issue date: 2009-01-01 An amperometric dipyrone sensor based on a polymeric nickel-salen (salen = N,N'-ethylenebis(salicydeneiminato)) film coated platinum electrode was developed. The sensor was constructed by electropolymerization of nickel-salen complex at a platinum electrode in acetonitrile/tetrabuthylamonium perchlorate by cyclic voltammetry. After cycling the modified electrode in a 0.50 mol L-1 KCl solution, the estimated surface concentration was found to be equal to 1.29 x 10(-9) mol cm(-2). This is a typical behavior of an electrode surface immobilized with a redox couple that can usually be considered as a reversible single-electron reduction/oxidation of the nickel(II)/nickel(III) couple. A plot of the anodic current versus the dipyrone concentration for chronoamperometry (potential fixed = +0.50 V) at the sensor was linear in the 4.7 x 10(-6) to 1.1 x 10(-4) mol L-1 concentration range and the concentration limit was 1.2 x 10(-6) mol L-1. The proposed electrode is useful for the quality control and routine analysis of dipyrone in pharmaceutical formulations. Univ State São Paulo UNESP, Dept Phys Chem & Biol, Fac Sci & Technol, Presidente Prudente, SP, Brazil Univ State São Paulo UNESP, Dept Phys Chem & Biol, Fac Sci & Technol, Presidente Prudente, SP, Brazil more...

Made available in DSpace on 2013-08-28T14:10:25Z (GMT). No. of bitstreams: 1 WOS000270213300002.pdf: 658881 bytes, checksum: 1f5c5299c22dcb801bcf602d01e6372e (MD5) Made available in DSpace on 2013-09-30T18:09:28Z (GMT). No. of bitstreams: 2 WOS000270213300002.pdf: 658881 bytes, checksum: 1f5c5299c22dcb801bcf602d01e6372e (MD5) WOS000270213300002.pdf.txt: 32167 bytes, checksum: b40a80e74296d8f79f86715cebe81471 (MD5) Previous issue date: 2009-09-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:23:09Z No. of bitstreams: 2 WOS000270213300002.pdf: 658881 bytes, checksum: 1f5c5299c22dcb801bcf602d01e6372e (MD5) WOS000270213300002.pdf.txt: 32167 bytes, checksum: b40a80e74296d8f79f86715cebe81471 (MD5) Made available in DSpace on 2014-05-20T13:23:09Z (GMT). No. of bitstreams: 2 WOS000270213300002.pdf: 658881 bytes, checksum: 1f5c5299c22dcb801bcf602d01e6372e (MD5) WOS000270213300002.pdf.txt: 32167 bytes, checksum: b40a80e74296d8f79f86715cebe81471 (MD5) Previous issue date: 2009-09-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. A sensor based on a nanostructured hollandite-type manganese oxide was investigated for voltammetric detection of potassium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and the subsequent extraction of the potassium ions into the hollandite structure. In this work, an amperometric procedure at an operating potential of 0.80 V (versus SCE) is exploited for amperometric monitoring. The current signals are linearly proportional to potassium ion concentration in the range 4.97 x 10(-5) to 9.05 x 10(-4) mol L(-1), with a correlation coefficient of 0.9997. Univ State São Paulo, UNESP, Fac Sci & Technol, Dept Phys Chem & Biol, BR-19060900 Presidente Prudente, SP, Brazil Univ Fed Sao Carlos, Dept Quim, BR-13560 Sao Carlos, SP, Brazil Univ State São Paulo, UNESP, Fac Sci & Technol, Dept Phys Chem & Biol, BR-19060900 Presidente Prudente, SP, Brazil CNPq: 372010/2006-7 more...

The electrochemical preparation described herein involved the electrocatalytic oxidation of sulfite on a platinum electrode modified with nanostructured copper salen (salen = N , N ′-ethylene bis (salicylideneiminato)) polymer films. The complex was prepared and electropolymerized at a platinum electrode in a 0.1 mol L −1 solution of tetrabutylammonium perchlorate in acetonitrile by cyclic voltammetry between 0 and 1.4 V vs . SCE. After cycling the modified electrode in a 0.50 mol L −1 KCl solution, the estimated surface concentration was found to be equal to 2.2 × 10 −9 mol cm −2 . This is a typical behavior of an electrode surface immobilized with a redox couple that can usually be considered as a reversible single-electron reduction/oxidation of the copper(II)/copper(III) couple. The potential peaks of the modified electrode in the electrolyte solution (aqueous) containing the different anions increase with the decrease of the ionic radius, demonstrating that the counter-ions influence the voltammetric behavior of the sensor. The potential peak was found to be linearly dependent upon the ratio [ionic charge]/[ionic radius]. The oxidation of the sulfite anion was performed at the platinum electrode at +0.9 V vs . SCE. However, a significant decrease in the overpotential (+0.45 V) was obtained while using the sensor, which minimized the effect of oxidizable interferences. A plot of the anodic current vs . the sulfite concentration for chronoamperometry (potential fixed = +0.45 V) at the sensor was linear in the 4.0 × 10 −6 to 6.9 × 10 −5 mol L −1 concentration range and the concentration limit was 1.2 × 10 −6 mol L −1 . The reaction order with respect to sulfite was determined by the slope of the logarithm of the current vs . the logarithm of the sulfite concentration. more...

A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater. The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l−1 COD with detection limit of 20.3 mg l−1 COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate) COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end products do not contain toxic metals. more...

A general view of the electroanalytical applications of metal‐salen complexes is discussed in this review. The family of Schiff bases derived from ethylenediamine and ortho‐phenolic aldehydes (N,N′‐ethylenebis(salicylideneiminato)—salen) and their complexes of various transition metals, such as Al, Ce, Co, Cu, Cr, Fe, Ga, Hg, Mn, Mo, Ni, and V have been used in many fields of chemical research for a wide range of applications such as catalysts for the oxygenation of organic molecules, epoxidation of alkenes, oxidation of hydrocarbons and many other catalyzed reactions; as electrocatalyst for novel sensors development; and mimicking the catalytic functions of enzymes. A brief history of the synthesis and reactivity of metal‐salen complexes will be presented. The potentialities and possibilities of metal‐Salen complexes modified electrodes in the development of electrochemical sensors as well as other types of sensors, their construction and methods of fabrication, and the potential application of ... more...

Made available in DSpace on 2018-12-11T16:38:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-06-25 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Abstract This paper describes the development of a selective lithium ion sensor based on spinel-type manganese oxide doped with gallium and anions (Ga0.02Mn1.98O3.98X0.02, where X = S2- and F-). Investigation was made of the influence of cationic and/or anionic doping agents on the potentiometric response of the sensor. Experimental parameters evaluated included the effect of the lithium concentration on activation of the sensor by cyclic voltammetry, the pH of the electrolyte solution, and the selectivity towards Li+ compared to other alkali and alkaline-earth metal ions. There was an important influence of the unit cell size of the material on the linear range, detection limit, and selectivity of the sensor. Reduction in the size of the tunnel for insertion of the lithium in the porous structure of the oxide directly affected the potentiometric performance of the electrode. Sensor performance increased in the order: Ga0.02Mn1.98O4 > Ga0.02Mn1.98O3.98S0.02 > Ga0.02Mn1.98O3.98F0.02. The observed super-Nernstian response could be explained by a mixed potential arising from two equilibria (redox and ion exchange) in the spinel-type manganese oxide. Sensitivity and the influence of pH on the electrode response were directly related to the doping agents present in the oxide structure. Faculty of Science and Technology, São Paulo State University (UNESP) Department of Chemistry, Federal University of Sao Carlos Faculty of Science and Technology, São Paulo State University (UNESP) FAPESP: 2005/01296-4 FAPESP: 474367/2004-5 more...

A simple and rapid flow‐injection spectrophotometric method is reported for the determination of dipyrone in pharmaceutical formulations. The method is based on the reaction of dipyrone with ammonium molybdate in acidic medium to produce blue molybdenum, which was detected spectrophotometrically at 620 nm. The analyte was determined in a single‐line flow system. The calibration curve obtained was linear in the range of 5×10−4 to 8×10−3 mol L–1 for dipyrone concentration and the precision (s r=1.7%) was satisfactory. The method proved to be selective and adequately sensitive. Application of the method to the analysis of pharmaceutical samples resulted in excellent accuracy; the percent mean recoveries were in the range 95.3%–101% and relative errors less than 5.0% for five pharmaceutical formulations were found. more...

The electrochemical behavior of a carbon paste electrode modified (CPEM) with N,N′-ethylenebis(salicylideneiminato)oxovanadium(IV) complex ([VIVO(Salen)]) was investigated as a new sensor for cysteine. Cyclic voltammetry at the modified electrode in 0.1 mol L−1 KCl solution (pH 5.0) showed a single-electron reduction/oxidation of the couple VO3+/VO2+. The CPEM with [VO(Salen)] presented good electrochemical stability in a wide pH range (4.0–10.0) and an ability to electrooxidate cysteine at 0.65 V versus SCE. These results demonstrate the viability of the use of this modified electrode as an amperometric sensor for cysteine determination. more...

The preparation and electrochemical characterization of a carbon paste electrode modified with N,N'-ethylenebis(salicylideneiminato)oxovanadium(IV) complex ([VO(Salen)]) as well as its behavior as electrocatalyst toward the oxidation of dipyrone were investigated. The electrochemical behavior of the modified electrode and the electrooxidation of dipyrone were explored using cyclic voltammetry. The voltammetric response of the modified electrode is based on two reactions. One electrochemical related to the oxidation of the metallic center of the [VO(Salen)] and the other involving the chemical redox process involving the oxidized form of the complex and the reduced form of dipyrone. The best voltammetric response was observed for a paste composition of 25% (m/m) [VO(Salen)], KCl solution pH from 5.5 to 8.0 as the electrolyte and potential scan rate of 10 mV s-1 in the presence of dipyrone. A linear voltammetric response for dipyrone was obtained in the concentration range from 9.9 x 10-6 to 2.8 x 10-3 mol L-1, with a detection limit of 7.2 x 10-6 mol L-1. Among of several compounds tested as potential interference, only ascorbic acid presented some interference. The proposed electrode is useful for the quality control and routine analysis of dipyrone in pharmaceutical formulations. A preparação e a caracterização eletroquímica de um eletrodo de pasta de carbono modificado com o complexo N,N´-etilenobis(salicilidenoaminato) de oxovanádio(IV) ([VO(Salen)]), como também o seu comportamento eletrocatalítico na oxidação da dipirona foi investigado. O comportamento eletroquímico do eletrodo modificado e a eletrooxidação da dipirona foram estudados usando a voltametria cíclica. A resposta voltamétrica do eletrodo modificado é baseada em duas reações. Uma relacionada com a oxidação eletroquímica do centro metálico do complexo [VO(Salen)] e a outra que envolve o processo redox entre centro metálico do complexo oxidado e a dipirona. A melhor resposta voltamétrica foi observada para uma composição do eletrodo de 25% (m/m) [VO(Salen)] em solução eletrolítica de KCl para pH entre 5,5 a 8,0 e uma velocidade de varredura de 10 mV s-1 na presença de dipirona. Uma resposta voltamétrica linear para dipirona foi obtida no intervalo de concentração de 9,9 x 10-6 a 2,8 x 10-4 mol L-1, com um limite de detecção de 7,2 x 10-6 mol L-1. Entre os diversos compostos testados como interferente, somente o ácido ascórbico apresentou alguma interferência. O eletrodo proposto é útil para o controle de qualidade e a análise rotineira de dipirona em formulações farmacêuticas. more...

The electroanalytical determination of isoprenaline in pharmaceutical preparations of a homemade carbon paste electrode modified with copper(II) hexacyanoferrate(III) (CuHCF) was studied by cyclic voltammetry. Several parameters were studied for the optimization of the sensor such as electrode composition, electrolytic solution, pH effect, potential scan rate and interferences in potential. The optimum conditions were found in an electrode composition (in mass) of 15% CuHCF, 60% graphite and 25% mineral oil in 0.5 mol l −1 acetate buffer solution at pH 6.0. The analytical curve for isoprenaline was linear in the concentration range from 1.96×10 −4 to 1.07×10 −3 mol l −1 with a detection limit of 8.0×10 −5 mol l −1 . The relative standard deviation was 1.2% for 1.96×10 −4 mol l −1 isoprenaline solution ( n =5). The procedure was successfully applied to the determination of isoprenaline in pharmaceutical preparations; the CuHCF modified carbon paste electrode gave comparable results to those results obtained using a UV spectrophotometric method. more...

A potentiometric sensor constructed from a mixture of 25% (m/m) spinel-type manganese oxide (lambda-MnO2), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li against other alkali and alkaline-earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6 10 5 ± 1.0 10 2 mol L 1 1 more...

The use of selective pre-concentration and differential pulse anodic stripping voltammetry (DPASV) using a carbon paste electrode modified (CPEM) with spinel-type manganese oxide has been proposed for the determination of lithium ions content in natural waters. The new procedure is based on the effective pre-concentration of lithium ions on the electrode surface containing spinel-type Mn(IV) oxide with the reduction of Mn(IV) to Mn(III) and consequently the lithium ions intercalation (insertion) into the spinel structure. The best DPASV response was reached for an electrode composition of 25% (m/m) spinel-type MnO(2) in the paste, 0.1moll(-1) tris(hydroxymethyl)aminomethane (TRIS) buffer solution of pH 8.3, scan rate of 5mVs(-1), accumulation potential of 0.3V versus saturated calomel reference electrode (SCE), pre-concentration time of 30s and potential pulse amplitude of 50mV. In these experimental conditions, the proposed methodology responds to lithium ions in the concentration range of 2.8x10(-6) to 2.0x10(-3)moll(-1) with a detection limit of 5.6x10(-7)moll(-1). The determination of the lithium ions content in different samples of natural waters samples using the proposed methodology and atomic absorption spectrophotometry are in agreement at the 95% confidence level and within an acceptable range of error. more...

The construction and analytical evaluation of a pH sensor based in a matrix containing 20% of [(Mg6Si8O20)](OH)4, a magnesium silicate, talc and 30% graphite dispersed in an epoxy resin (50%) is described. The data obtained from various acid–base titrations were compared with those using a glass electrode in the same conditions. The proposed electrode presented a linear response in the 1–12 pH range with a slope of � 39.9F0.3 mV/pH (at 25 jC) and ca. 15 s of response time. The lifetime of this electrode was higher than 8 months (ca. 1500 determinations) and it showed a good performance for pH determination and end-point indication in the potentiometric titrations of acids and bases. more...

The use of the differential pulse voltammetry for the determination of lithium ions in pharmaceutical samples using a carbon paste electrode modified with spinel-type manganese oxide has been examined. The best voltammetric response was reached for a modified electrode in borate buffer solution of pH 9.0 and submitted to a scan rate of 5 mV s(-1) and a pulse amplitude of 50 mV. This electroanalytical procedure was able to determine lithium ions in the concentration range of 8.0 x 10(-5)-1.0 x 10(-2) mol l(-1) even in the presence of several alkali metals (1.0 x 10(-3) mol l(-1)) with a detection limit of 7.1 x 10(-7) mol l(-1). Rapidity, precise and good selectivity were also found for the determination of lithium ions in pharmaceutical formulations. more...

A copper(II) hexacyanoferrate(III) (CuHCF) modified carbon paste electrode was used for the electroanalytical determination of pyridoxine (vitamin B6) in pharmaceutical preparations, using cyclic voltammetry. Diverse parameters were investigated for the optimization of the sensor response, such as composition of the electrode, electrolytic solution, effect of pH, scan rate of potential and interferences. The optimum conditions were found at an electrode composition of 20% CuHCF, 55% graphite and 25% mineral oil (m/m) in an acetate buffer (pH 5.5) containing 0.05 mol L-1 of NaCl. The range of determination of pyridoxine was from 1.2 x 10-6 to 6.9 x 10-4 mol L-1. The procedure was successfully applied to the determination of vitamin B6 in formulation preparations. The CuHCF modified carbon paste electrode gave results comparable to those obtained using spectrophotometry. Um eletrodo de pasta de carbono modificado com o complexo de hexacianoferrato(III) de cobre(II) (CuHCF) foi utilizado na determinação eletroanalítica de piridoxina (vitamina B6) em formulações farmacêuticas usando voltametria cíclica. Diversos parâmetros, tais como: composição do eletrodo, melhor solução eletrolítica, efeito do pH, velocidade de varredura de potenciais e interferentes sobre a resposta do eletrodo modificado, foram estudados. As melhores condições foram encontrados para uma composição de eletrodo de 20% de CuHCF (m/m), 55% de grafite (m/m) e 25% óleo mineral (m/m) em tampão acetato (pH 5,5) contendo 0,05 mol L-1 de NaCl. O intervalo de concentração para determinação de piridoxina foi 1,2 x 10-6 a 6,9 x 10-4 mol L-1. O procedimento foi aplicado na determinação de vitamina B6 em formulações farmacêuticas e os resultados obtidos com o eletrodo de pasta de carbono modificado com CuHCF foram comparados com os de espectrofotometria. more...

A sensitive and selective λ-MnO 2 -modified carbon-paste electrode is proposed for voltammetric determination of lithium ions in pharmaceutical formulation. The various parameters that can influence the voltammetric response of the proposed electrode (carbon-paste composition, pH electrolyte, potential scan rate and interference of several ions) were investigated. The best voltammetric response was reached for an electrode composition of 25% (m/m) λ-MnO 2 in the paste, borate buffer solution of pH 9.0 and scan rate of 5 mV s −1 in the voltammetric measurements. The proposed electrode responds to lithium ions in the concentration range from 8.0×10 −5 to 2.2×10 −2 mol l −1 with a detection limit of 3.6×10 −5 mol l −1 . The concentrations of lithium ions in a pharmaceutical formulation (tablet) using the proposed electrode and atomic absorption spectrophotometry are in agreement at the 95% confidence level and within an acceptable range of error. more...

The potentiometric response of a λ-MnO2-based graphite–epoxy electrode for the determination of lithium ions was examined. The electrode response to lithium ions was linear in the concentration range 10−6–3.3×10−2 mol/l with a slope of 58.2 mV/decade (at 25°C) over a wide pH range (4–10); no such linear response was found for the ions of other alkali metals or alkaline-earth metals. The logarithm of the selectivity coefficients for Li+ against Na+, K+, Cs+, Mg2+, Ca2+, Sr2+and Ba2+ was found to be −1.5, −2.0, −2.2, −2.0, −2.0, −2.1 and −2.1, respectively. The response time of the proposed electrode was lower than 30 s and its lifetime greater than 6 months. more...

The potentiometric response of a novel λ-MnO 2 -based graphite–epoxy electrode for the determination of acids and bases was examined. The electrode was prepared by the incorporation of manganese (IV) oxide in a graphite–epoxy matrix. The data obtained in various acid–base titrations were compared with those using a glass electrode in the same conditions. The proposed electrode presented a linear response in the pH range 2 to 13 with a slope of −53.6±0.5 mV/pH (at 25°C) and a response time of ca. 10 s. The lifetime of this electrode was higher than 3 months (ca. 1500 determinations) and it showed an excellent performance for pH determination and end-point indication potentiometric titrations in the determination of acids and bases. The miniaturization of the proposed electrode is also possible. more...

A coated graphite-epoxy iron(III) ion-selective electrode, based on the ion-pair between [Fe(oxalate)3]3− anion and tricaprylylmethylammonium cation (Aliquat 336) in a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) in PVC was deposited directly onto a PerspexR tube containing a graphite-epoxy conductor substrate attached to the end of a glass tube. The effect of membrane composition (ion pair, DBPh and PVC), oxalate concentration, pH and some cations and anions upon the electrode response is investigated. The electrode shows a linear anionic response to E vs. log[Fe3+] in the iron(III) concentration range from 2.9×10−6 to 10−2 mol/L, and a slope of −18.7±0.5 mV/dec, at pH working range 2-8 and 0.3 mol/L oxalate concentration. Variation in the potential of about ±2 mV was observed during a working day of 7-8 h. The response time was less than 5 sec and the lifetime of this electrode was superior to one year (over 1500 determinations ... more...

The preparation and electrochemical characterization of a carbon paste electrode modified with the N , N -ethylene- bis (salicyllideneiminato)oxovanadium (IV) complex ([VO(salen)]) as well as its application for ranitidine determination are described. The electrochemical behavior of the modified electrode for the electroreduction of ranitidine was investigated using cyclic voltammetry, and analytical curves were obtained for ranitidine using linear sweep voltammetry (LSV) under optimized conditions. The best voltammetric response was obtained for an electrode composition of 20% (m/m) [VO(salen)] in the paste, 0.10 mol L − 1 of KCl solution (pH 5.5 adjusted with HCl) as supporting electrolyte and scan rate of 25 mV s − 1 . A sensitive linear voltammetric response for ranitidine was obtained in the concentration range from 9.9 × 10 − 5 to 1.0 × 10 − 3 mol L − 1 , with a detection limit of 6.6 × 10 − 5 mol L − 1 using linear sweep voltammetry. These results demonstrated the viability of this modified electrode as a sensor for determination, quality control and routine analysis of ranitidine in pharmaceutical formulations. more...

Made available in DSpace on 2013-09-27T14:53:53Z (GMT). No. of bitstreams: 1 WOS000275995600209.pdf: 196067 bytes, checksum: 28e9cc15bcb9ac9fa20cb6cbf7be20c2 (MD5) Previous issue date: 2009-01-01 Made available in DSpace on 2013-09-30T18:09:38Z (GMT). No. of bitstreams: 1 WOS000275995600209.pdf: 196067 bytes, checksum: 28e9cc15bcb9ac9fa20cb6cbf7be20c2 (MD5) Previous issue date: 2009-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:23:13Z No. of bitstreams: 1 WOS000275995600209.pdf: 196067 bytes, checksum: 28e9cc15bcb9ac9fa20cb6cbf7be20c2 (MD5) Made available in DSpace on 2014-05-20T13:23:13Z (GMT). No. of bitstreams: 1 WOS000275995600209.pdf: 196067 bytes, checksum: 28e9cc15bcb9ac9fa20cb6cbf7be20c2 (MD5) Previous issue date: 2009-01-01 In the work described by this paper, we studied the development of a selective potassium ion sensor constituted of a carbon paste electrode modified (CPEM) with a novel KSr(2)Nb(2)O(15). The material KSr(2)Nb(2)O(15) is an oxide with the tetragonal tungsten bronze structure (TTB) type are in forefront both in the area of research as well as in industrial applications. The sensor response to potassium ions was linear in the concentration range 1.26 x 10(-5) at 1.62 x 10(-3) mol L(-1) (E (mV) = 32.7 + 51.1 log [K(+)]). The sensor based KSr(2)Nb(2)O(15), of the TTB-type presented very good potentiometric response, with a slope of 51.1 mV/dec (at 25 degrees C) and detection limit for the potassium ions of 7.27 x 10(-5) mol.L(-1) Univ State São Paulo UNESP, Dept Phys Chem & Biol, Fac Sci & Technol, Presidente Prudente, SP, Brazil Univ State São Paulo UNESP, Dept Phys Chem & Biol, Fac Sci & Technol, Presidente Prudente, SP, Brazil more...

Direct detection of amoxicillin (AMX) was achieved at a carbon paste electrode modified with [N,N'-ethylenebis(salicylideneaminato)]oxovanadium(IV), [VO(Salen)]. It was observed that the current of the [V IV O(Salen)]/ [V V O(Salen)] redox couple at the electrode surface increases proportionally to the log of AMX concentration. The electrochemical behavior of the modified electrode was characterized by cyclic voltammetry and analytical curves were obtained for AMX using linear sweep (LSV), differential pulse (DPV), and square-wave voltammetry (SWV) under optimized conditions. Limits of detection at 24.8, 16.6, and 8.49 μmol L -1 were observed in LSV, DPV and SWV, respectively. The SWV method using the modified electrode was applied in the determination of AMX in pharmaceutical formulations (tablets) and compared with the iodimetric method. more...

The [Mn4IVO5(terpy)4(H2O)2]6+ complex, show great potential for electrode modification by electropolymerization using cyclic voltammetry. The voltammetric behavior both in and after electropolymerization process were also discussed, where the best condition of electropolymerization was observed for low scan rate and 50 potential cycles. A study in glass electrode for better characterization of polymer was also performed. Electrocatalytic process by metal centers of the conducting polymer in H2O2 presence with an increase of anodic current at 0.85 V vs. SCE can-5 -4 -1 be observed. The sensor showed great response from 9.9 x 10to 6.4 x 10 mol Lconcentration range with a -5 -1 detection limit of 8.8 x 10 mol L, where the electrocatalytic mechanism was based on oxidation of H2O2 to H2O IV IIIIII IV with consequently reduction of Mnto Mn. After, the Mnions are oxidized electrochemically to Mnions. more...

An amperometric oxygen sensor based on a polymeric nickel-salen (salen = N, Ń -ethylene bis (salicydeneiminato)) film coated platinum electrode was developed. The sensor was constructed by electropolymerization of nickel- salen complex at a platinum electrode in acetonitrile/tetrabuthylamonium perchlorate by cyclic voltammetry. The voltammetric behavior of the modified electrode was investigated in 0.5 mol L -1 KCl solution in the absence and presende of molecular oxygen. A significant increased of cathodic peak current (at -0.20 vs. SCE) of the modified electrode with addition of oxygen to the solution was observed. This result shows that the nickel- salen film on the surface of the electrode promotes the reduction of oxygen. The reaction can be brought about electrochemically where in the nickel(II) complex is first reduced to a nickel(I) complex at the electrode surface. The nickel(I) complex then undergoes a catalytic oxidation by the oxygen molecular in solution back to the nickel(II) complex, which can then be electrochemically re-reduced to produce an enhancement of the cathodic current. The plot of the cathodic current versus the dissolved oxygen concentration for chronoamperometry (potential fixed = -0.20 V) at the sensor was linear in the concentration range of 3.95 to 9.20 mg L -1 with concentration limit of 0.17 mg L -1 O 2 . The modified electrode proposed is useful for the quality control and routine analysis of dissolved oxygen in commercial water and environmental water samples. The results obtained for the levels of dissolved oxygen are in agreement with the results obtained with an O 2 commercial sensor. more...