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‣ Fabrication of carbon paste electrode containing a new inorganic–organic hybrid based on [SiW12O40]4− polyoxoanion and Nile blue and its electrocatalytic activity toward nitrite reduction

Kakhki, Somayeh; Shams, Esmaeil; Barsan, Madalina M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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In this study, a new inorganic–organic hybrid compound consisting of a Keggin type polyoxometalate, H4SiW12O40 (SiW12), and Nile blue (NB) was synthesized and characterized. The (NB)2H2SiW12O40 (NB2SiW12) hybrid compound was characterized by Fourier transform infrared (FT-IR), elemental (CHNS) analysis, UV–Vis and thermogravimetry techniques, and used as a bulk modifier to fabricate a chemically modified carbon paste electrode (CPE) by direct mixing. The electrochemical behavior of the newly NB2SiW12 composite CPE was analyzed by cyclic voltammetry, and the electrode was applied for nitrite reduction, exhibiting high electrocatalytic activity. Determination of nitrite by fixed potential amperometry was done under various experimental conditions and, at the optimum conditions, the linear response ranged from 5 to 1200 μM with a high sensitivity of and a low detection limit. The electrode has the remarkable advantage of surface renewal owing to bulk modification, as well as simple preparation, good mechanical and chemical stability and reproducibility. No noticeable interferences from other ionic species usually found in natural water were observed. The new developed electrode has been successfully applied for detection of nitrite in real water samples.

‣ Grafite funcionalizada em condições de Friedel-Crafts mediada por radiação de microondas: novo material para construção de eletrodos de pasta de carbono; Graphite Functionalized in Conditions of Friedel-Crafts Reaction mediated by Radiation of Microwave: New Material for Construction of Electrodes of Carbon Paste

Nascimento, Leandro Fontanetti do
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/03/2007 Português
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A modificação e/ou a funcionalização de eletrodos têm por objetivos o desenvolvimento de métodos eficazes para a preparação de eletrodos quimicamente modificados (EQMs) que possam aliar melhorias em sua sensibilidade, seletividade e reatividade em relação aos eletrodos base. Entretanto, a estabilidade e a reprodutibilidade dos EQMs quanto ao processo de lixiviação dos modificadores precisam ser melhorados para que se possam obter eletrodos mais robustos com longo tempo de análise. Uma das possibilidades para se obter eletrodos mais estáveis é por meio de uma ligação estável do tipo covalente entre o eletrodo base e o modificador. Desta forma este trabalho tem por objetivo a funcionalização da grafite por meio de uma reação covalente entre os modificadores cloreto de 4-nitrobenzoíla (4-NB), cloreto de 3,4-dihidroxibenzoíla (3,4-DHB) e do cloreto de 2,2?-bipiridina 4,4?-dicarbonílico (2,2-BP) por meio de uma reação de acilação de Friedel-Crafts assistida por radiação de microondas. O material de síntese foi caracterizado por voltametria cíclica, espectroscopia de infravermelho, curvas termogravimétricas e térmicas diferenciais e espectroscopia de impedância eletroquímica em comparação com a mistura física entre a grafite e os modificadores. Além disso...

‣ Aplicações analíticas de eletrodos quimicamente modificados por espécies de interesse biológico; Analytical applications of chemically modified electrode of biological species interest

Silva, Robson Pinho da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 14/09/2007 Português
Relevância na Pesquisa
68.36981%
O trabalho apresentado nesta Dissertação de Mestrado descreve o desenvolvimento e aplicação de eletrodos de pasta de carbono modificados eletroquimicamente em soluções de guanina e de eletrodos de grafite pirolítico modificados em soluções de dopamina. Estes eletrodos foram empregados na detecção e, a quantificação, por voltametria de pulso diferencial (VPD), de alguns compostos de importância biológicas tais como NADH, NADPH, 8-oxo-guanina, ácido úrico (AU), ácido ascórbico (AA), dopamina (DA) e xantina (XA). No primeiro caso, os eletrodos de pasta de carbono foram modificados em solução de guanina por aplicação de um potencial de 1,1 V (vs Ag/AgCl, KClsat) ao eletrodo de trabalho por 12 minutos sob sat agitação constante. Com estes eletrodos detectaram-se NADH, NADPH, 8-oxo-guanina e AU, com limites de detecção de 3,3, 3,7, 2,0 e 6,6 x 10-6 mol L-1 respectivamente, na faixa de concentração de 7,5 x 10-6 a 8,1 x 10-4 mol L-1 . No segundo caso, eletrodos de grafite pirolítico, previamente tratados em solução de NaOH, foram modificados eletroquimicamente em solução de DA por aplicação de um potencial 1,5 V (vs Ag/AgCl, KClsat ) ao eletrodo de trabalho durante 2 minutos. Com estes eletrodos foi possível a determinação simultânea de AA...

‣ Desenvolvimento e aplicação de eletrodos quimicamente modificados com hexacianoferratos dos metais Fe, Ni e Co; Development and application of chemically modified electrodes with hexacyanoferrate of Fe, Co and Ni

Carvalho, Sâmea Eulles Quixaba de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/06/2011 Português
Relevância na Pesquisa
68.54998%
O presente trabalho descreve o uso de eletrodos de carbono vítreo como eletrodo-base para modificação com hexacianoferratos de Fe (FeHCF), Co (CoHCF) e Ni (NiHCF) por meio da adsorção destes complexos utilizando a técnica de voltametria cíclica. Os eletrodos quimicamente modificados (EQMs) preparados por este método apresentam características diferenciadas tais como robustez e estabilidade ao longo das medidas eletroquímicas, além de boas propriedades redox. Os EQMs com FeHCF e NiHCF foram avaliados em função da sua atividade eletrocatalítica para a reação de oxidação do Ácido Ascórbico em solução de KCl 0,1 mol L-1 (pH 6,6). O EQM com CoHCF foi avaliado nas mesmas condições dos outros filmes, porém não apresentou uma diminuição no sobrepotencial de oxidação do Ácido Ascórbico. Embora não tenha apresentado uma resposta semelhante aos EQMs com FeHCF e NiHCF, o EQM com CoHCF apresentou a melhor sensibilidade da resposta de corrente de pico quando comparado aos demais. A fim de proporcionar a renovação da superfície do eletrodo foi avaliada a utilização de eletrodos de pasta de carbono modificada com FeHCF, CoHCF ou NiHCF. Os parâmetros de composição da pasta, o eletrólito suporte e o pH foram avaliados utilizando o EPCM com FeHCF por meio da técnica de voltametria cíclica e os parâmetros otimizados foram aplicados no uso dos EPCM com CoHCF e NiHCF. Para avaliar a sensibilidade na deteccção da L-Cisteína...

‣ Eletrodos quimicamente modificados com Poli (benzil viologênio): comportamento eletroquímico de fármacos nitroderivados.; Chemically modified electrodes with Poly (benzyl viologen): electrochemical behavior of nitro derivative drugs.

Deliberto, Laíla Aparecida
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/03/2013 Português
Relevância na Pesquisa
68.32861%
Na área da saúde, destacam-se alguns fármacos amplamente administrados, os quais possuem grupamentos nitro em suas moléculas, como o Clonazepam (CNZ), Nitrazepam (NTZ) e Nimesulida (Nimes). O CNZ e o NTZ são utilizados ilicitamente em coquetéis entorpecentes, fragilizando vítimas. A Nimes é anti-inflamatório amplamente administrado e frequentemente usado sem prescrição médica. As metodologias de detecção e quantificação destes fármacos são, na sua maioria, dispendiosas, desenvolvidas por HPLC, GC, etc. Poucos trabalhos utilizam determinação eletroanalítica e dentre eles, menos ainda utilizam eletrodos quimicamente modificados (EQMs). Os EQMs melhoram a seletividade e sensibilidade das análises. Dentre as formas de modificação, a metodologia de filmes poliméricos é muito versátil e possibilita o desenvolvimento de eletrodos específicos. Uma classe importante de polímeros é a dos derivados de viologênio, como o Poli (benzil viologênio) (PBV). Este polímero é empregado com diferentes finalidades. Possui três estados de oxidação, um deles; o PBV+ atua como mediador redox. E, a partir de experimentos prévios em nosso laboratório demonstrou ainda a possibilidade de atuar na redução de nitrocompostos. Neste sentido...

‣ Stripping voltammetry of mercury(II) with a chemically modified carbon paste electrode containing silica gel functionalized with 2,5-dimercapto-1,3,4-thiadiazole

Dias, N. L.; do Carmo, D. R.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 1540-1546
Português
Relevância na Pesquisa
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The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2,5-dimercapto-1,3,4-thiadiazole (DTTPSG-CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range -0.2 to +0.8 V (vs. Ag/AgCl), (0.02 mol L-1 KNO3; nu=20 mV s(-1)) show two peaks one at about 0.0 V and other at 0.31 V. However, the cathodic wave peak, around 0.0 V, is irregular and changes its form in each cycle. This peak at about 0.0 V is the reduction current for mercury(II) accumulated in the DTTPSG-CPE. The anodic wave peak at 0.31 V is well-defined and does not change during the cycles. The resultant material was characterized by cyclic and differential pulse anodic stripping voltammetry performed with the electrode in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. The precision for six determinations (n=6) of 0.05 and 0.20 mg (L)-(1) Hg(II) was 2.8 and 2.2% (relative standard deviation), respectively. The method was satisfactory and used to determine the concentration of mercury(II) in natural waters contaminated by this metal.

‣ Prepararion of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury

Dias, N. L.; do Carmo, D. R.; Gessner, F.; Rosa, A. H.
Fonte: Japan Soc Analytical Chemistry Publicador: Japan Soc Analytical Chemistry
Tipo: Artigo de Revista Científica Formato: 1309-1316
Português
Relevância na Pesquisa
58.536377%
A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg2+, Pb2+, Cd2+, CU2+, and Zn2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0,25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 mu g L-1. The precision of determination was satisfactory for the respective concentration level.

‣ Electrochemical study of o-toluidine blue impregnated in mesoporous silica channels

Utrera Martines, Marco Antonio; do Carmo, Devaney Ribeiro; de Castro, Gustavo Rocha; Caetano, Laercio
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 188-193
Português
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); This paper reports an electrochemical study of ordered mesoporous silica impregnated with a cationic dye (o-toluidine blue), prepared with a non-ionic surfactant as the structure-directing agent. O-toluidine blue was chosen because of its utility as an electron transfer mediator (redox catalyst). O-toluidine blue impregnated mesoporous silica was characterized by nitrogen sorption porosimetry, small angle X-ray scattering, infrared spectroscopy, scanning electron microscopy and cyclic voltammetry using chemically modified carbon paste electrodes. Results indicate that the dye is located within the ordered mesopores of micron-sized silica spheres.

‣ DEVELOPMENT OF A CHEMICALLY MODIFIED ELECTRODE BASED ON CARBON PASTE AND FUNCTIONALIZED SILICA-GEL FOR PRECONCENTRATION AND VOLTAMMETRIC DETERMINATION OF MERCURY(II)

Aleixo, L. M.; Souza, MDB; Godinho, OES; Neto, G. D.; Gushikem, Y.; Moreira, J. C.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 143-148
Português
Relevância na Pesquisa
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A mercury-sensitive chemically modified electrode (CME) based on modified silica gel-containing carbon paste was developed. The functional group attached to the silica gel surface was 3-(2-thiobenzimidazolyl)propyl, which is able to complex mercury ions. This electrode was applied to the determination of mercury(II) ions in aqueous solution. The mercury was chemically preconcentrated on the CME prior to voltammetric determination by anodic stripping in the differential-pulse mode. A calibration graph covering the concentration range from 0.08 to 2 mg l-1 was constructed. The precision for six determinations of 0.122 and 0.312 mg l-1 Hg(II) was 3.2 and 2.9% (relative standard deviation), respectively. The detection limit for a 5-min preconcentration period was 0.013 mg l-1. A study for foreign ions was also made.

‣ Study of an organically modified clay: Selective adsorption of heavy metal ions and voltammetric determination of mercury(II)

Dias, N. L.; do Carmo, D. R.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 919-927
Português
Relevância na Pesquisa
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In this work, a hydrophilic clay, Na-montmorillonite from Wyoming, USA, was rendered organophilic by exchanging the inorganic interlayer cations for hexaclecyltrimethylammonium ions (HDTA), with the formulae of [(CH3)(3)N(C16H33)](+) ion. Based on fact that organo-clay has high affinities for non-ionic organic molecules, 1,3,4-thiadiazole-2,5-dithiol was loaded oil the HDTA-montmorillonite surface, resulting in the 1,3,4-thiadiazole-2,5-dithiol-HDTA-montmorillonite complex (TDD-organo-clay).The following properties of TDD-organo-clay are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II).The main point of this paper is the construction of a selective sensor, a carbon paste electrode modified with TDD-organo-clay, its properties and its application to the determination of mercury(II) ions, as this element belongs to the most toxic metals. The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. (c) 2005 Elsevier B.V. All rights reserved.

‣ Determination of nickel in fuel ethanol using a carbon paste modified electrode containing dimethylglyoxime

Oliveira Tartarotti, Fernando; Firmino de Oliveira, Marcelo; Roberto Balbo, Valdir; Ramos Stradiotto, Nelson
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 397-401
Português
Relevância na Pesquisa
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A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 x 10(-9) to 5.0 x10(-7) mol(-1) was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 x 10 mol(-1) and 5.2 x 10(8) mu A mol(-1) L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 x 10(-8) to 6.9 x 10(-8) mol(-1). A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.

‣ Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury

Dias Filho, Newton L.; Do Carmo, Devaney R.; Gessner, Fergus; Rosa, André H.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1309-1316
Português
Relevância na Pesquisa
68.634116%
A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg 2+, Pb 2+, Cd 2+, Cu 2+, and Zn 2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO 3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 μg L -1. The precision of determination was satisfactory for the respective concentration level. 2005 © The Japan Society for Analytical Chemistry.

‣ Preparation of a silica gel modified with 2-amino-1,3,4-thiadiazole for adsorption of metal ions and electroanalytical application

Dias Filho, Newton L.; Caetano, Laércio; Do Carmo, Devaney R.; Rosa, André H.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 473-481
Português
Relevância na Pesquisa
58.632773%
Silica gel with a specific area of 382 m2 g-1 and an average pore diameter of 60 Å was chemically modified with 2-amino-1,3,4-thiadiazole, for the purpose of selective adsorption of heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). The following properties of this functionalized silica gel are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II). The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. ©2006 Sociedade Brasileira de Química.

‣ Voltammetry of mercury (II) based on an organo-clay modified graphite electrode

Dias Filho, Newton L.; Okajima, Giovana L.; Pires, Geovanna; Costa, Reginaldo M.; Do Carmo, Devaney R.; Rosa, André H.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 163-179
Português
Relevância na Pesquisa
57.89377%
Organo-clay complex of ligand-hexadecyltrimethylammonium with montmorillonite was made for the purpose of application as a preconcentration agent in a chemically modified carbon paste electrode for determination of mercury (II) in aqueous solution. It was found out that the adsorption of Hg(II) by organo-clay complex is independent of the pH of the solution. It was also found out that the adsorption of the remaining metals Cd(II), Ps(II), Cu(II), Zn(II), and Ni(II) was dependent on the changes in pH solutions and increased when it varies from 1 to 8. The resultant material was characterized by cyclic and differential pulse anodic voltammetry using a modified graphite paste electrode in different supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, possible interferences and other variables.

‣ Voltammetric determination of ethyl acetate in ethanol fuel using a Fe 3+/Nafion®-coated glassy carbon electrode

Caetano, Lahys G.; Takeuchi, Regina M.; Santos, André L.; De Oliveira, Marcelo F.; Stradiotto, Nelson R.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 837-842
Português
Relevância na Pesquisa
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A voltammetric method for the determination of ethyl acetate in ethanol fuel using a Fe3+/Nafion®-coated glassy carbon electrode (GCE) is proposed. The ethyl acetate present in the ethanol fuel was previously converted to acetohydroxamic acid via pretreatment with hydroxylamine chloride. The acetohydroxamic acid promptly reacted with the iron (III) present in the film, producing iron (III) acetohydroxamate, which presents a well-defined voltammetric peak current at -0.02 V. Optimization of the voltammetric parameters for the cyclic, linear sweep, square wave, and differential pulse modalities was carried out for this chemically-modified electrode. Square wave voltammetry afforded the best response for acetohydroxamic acid detection. The analytical curve for this species was linear from 9 to 100 μmol L 1 according to the following equation: ip (μA) = 0.27 + 2.55Cacetohydroxamic acid (μmol L 1), with linear correlation coefficient equal to 0.993. The technique presented limit of detection equal to 5.3 μmol L 1 and quantification limit of 17.6 μmol L 1. The proposed method was compared to the official method of ethyl acetate analysis (Gas Chromatography), and a satisfactory correlation was found between these techniques. © 2012 Elsevier Ltd. All rights reserved.

‣ Preparation of a silica gel modified with 2-amino-1,3,4-thiadiazole for adsorption of metal ions and electroanalytical application

Dias Filho,Newton L.; Caetano,Laércio; Carmo,Devaney R. do; Rosa,André H.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 Português
Relevância na Pesquisa
58.632773%
Silica gel with a specific area of 382 m² g-1 and an average pore diameter of 60 Å was chemically modified with 2-amino-1,3,4-thiadiazole, for the purpose of selective adsorption of heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). The following properties of this functionalized silica gel are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II). The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination.

‣ Chemically Functionalized Carbon Nanotubes as Substrates for Neuronal Growth

Hu, Hui; Ni, Yingchun; Montana, Vedrana; Haddon, Robert C.; Parpura, Vladimir
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/2004 Português
Relevância na Pesquisa
58.08542%
We report the use of chemically modified carbon nanotubes as a substrate for cultured neurons. The morphological features of neurons that directly reflect their potential capability in synaptic transmission are characterized. The chemical properties of carbon nanotubes are systematically varied by attaching different functional groups that confer known characteristics to the substrate. By manipulating the charge carried by functionalized carbon nanotubes we are able to control the outgrowth and branching pattern of neuronal processes.

‣ Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury

Dias Filho, Newton L.; Carmo, Devaney R. do; Gessner, Fergus; Rosa, André H.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1309-1316
Português
Relevância na Pesquisa
68.634116%
A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg 2+, Pb 2+, Cd 2+, Cu 2+, and Zn 2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO 3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 μg L -1. The precision of determination was satisfactory for the respective concentration level. 2005 © The Japan Society for Analytical Chemistry.

‣ Chemically Modified Carbon Paste Electrodes for Ascorbic Acid Determination in Soft Drinks by Flow Injection Amperometric Analysis

Sales,M. Goreti F.; Castanheira,M.S.A.; Ferreira,Rosa M.S.; Vaz,M. Carmo V.F.; Delerue-Matos,Cristina
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 Português
Relevância na Pesquisa
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Simple, rapid and precise amperometric methods for quantification of ascorbic acid (AA) are presented. Glassy carbon (GC), carbon paste (CP) and modified carbon paste (MCP) electrodes are used for this purpose. MCP electrodes are of CP with 10 % vanadate (V). All electrodes are inserted in a wall-jet device with an Ag/AgCl reference electrode and a platinum auxiliary electrode. This device is coupled to a flow injection analysis (FIA) set-up. Hydrodynamic and amperometric parameters are optimized unvaryingly. GC electrodes present slopes of 4.75 ´ 10(5) nA L mol-1 (± 6.4 %) under optimum conditions. CP and MCP electrodes show higher sensitivity, with slopes of 6.37 ´ 10(5) nA L mol-1 (± 6.6 %) and 7.32 ´ 10(5) nA L mol-1 (± 4.4 %). Linear responses range (1.0-2.0) ´ 10-6 to (0.8-1.0) ´ 10-5 mol L-1. Correlation coefficients were > 0.994 and about 48 samples are analysed per hour. Application of the proposed method to the analysis of soft drinks is presented.

‣ Voltammetry of Mercury(II) Based on an Organo-Clay Modified Graphite Electrode

Filho,Newton L. Dias; Okajima,Giovana L.; Pires,Geovanna; Costa,Reginaldo M.; Carmo,Devaney R. do; Rosa,André H.
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 Português
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Organo-clay complex of ligand-hexadecyltrimethylammonium with montmorillonite was made for the purpose of application as a preconcentration agent in a chemically modified carbon paste electrode for determination of mercury (II) in aqueous solution. It was found out that the adsorption of Hg(II) by organo-clay complex is independent of the pH of the solution. It was also found out that the adsorption of the remaining metals Cd(II), Pb(II), Cu(II), Zn(II), and Ni(II) was dependent on the changes in pH solutions and increased when it varies from 1 to 8. The resultant material was characterized by cyclic and differential pulse anodic voltammetry using a modified graphite paste electrode in different supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, possible interferences and other variables.