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On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

SALAZAR-BANDA, Giancarlo R.; CARVALHO, Adriana E. de; ANDRADE, Leonardo S.; ROCHA-FILHO, Romeu C.; AVACA, Luis A.
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.96%
The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to -14000 C cm(-2) in steps of -600 C cm(-2) using -1 A cm(-2) caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: -9 C cm(-2), passed at -1 A cm(-2). This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq; CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Simultaneous Differential Pulse Voltammetric Determination of Ascorbic Acid and Caffeine in Pharmaceutical Formulations Using a Boron-Doped Diamond Electrode

LOURENCAO, Bruna Claudia; MEDEIROS, Roberta Antigo; ROCHA-FILHO, Romeu C.; FATIBELLO-FILHO, Orlando
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.1%
A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry Linear calibration curves (r = 0 999) were obtained from 1 9 x 10(-5) to 2 I x 10(-4) mol L(-1) for AA and from 9 7 x 10(-6) to 1 1 x 10-4 mol L(-1) for CAF. with detection limits of 19 wool L(-1) and 7 0 mu nol L(-1). respectively This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations. with results equal to those obtained using a HPLC reference method; FAPESP[2007/05894-9]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES

Caffeine Determination at a Carbon Fiber Ultramicroelectrodes by Fast-Scan Cyclic Voltammetry

Nunes, Ronaldo S.; Cavalheiro, Eder Tadeu Gomes
Fonte: SOC BRASILEIRA QUIMICA; SAO PAULO Publicador: SOC BRASILEIRA QUIMICA; SAO PAULO
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
26.27%
Caffeine determination using a fast-scan voltammetric procedure at a carbon fiber ultramicroelectrode (CF-UME) is described. The CF-UME was submitted to electrochemical pretreatment. Parameters such as number of acquisition cycles, scan rate, potential window, and the electrochemical surface pretreatment were optimized. Using the optimized conditions, it was possible to achieve a LDR from 10.0 up to 200 mu mol L-1, with a LOD of 3.33 mu mol L-1. The method has been applied in the determination of caffeine in commercial samples, with errors of 1.0-3.5% in relation to the label values and recoveries of 97-114% within the linear range.; FAPESP/Brazil; ; CAPES;

Desenvolvimento de eletrodo modificado com polímero de azul de metileno para a determinação eletroanalítica de glifosato; Development of poly (methylene blue) modified electrode for the determination eletroanalítica of glyphosate

Marinho, Maria Inês da Costa
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 11/11/2010 PT
Relevância na Pesquisa
16.1%
O presente trabalho descreve o preparo, a caracterização e o uso de eletrodo modificado com polímero de azul de metileno (PMB) imobilizado sobre a superfície de eletrodo de carbono vítreo (GCE-PMB) na análise do herbicida glifosato. O método utilizado para a preparação dos filmes do PMB foi a eletropolimerização. Os filmes preparados por este método apresentam características diferenciadas tais como robustez, estabilidade e propriedade redox satisfatória. As condições experimentais otimizadas foram a velocidade de varredura (50 mV s-1), o intervalo de potencial (-0,4 a +1,2 V), o número de ciclos (30) e o pH da solução do eletrólito suporte (pH 8). A solução de eletrólito suporte foi preparada a partir das soluções de tampão fosfato (0,05 mol L-1) e NaNO3 (0,1 mol L-1), pH 8. A mesma foi utilizada no preparo da solução de azul de metileno (MB) (0,25 x 10-3 mol L-1), no pré-tratamento do eletrodo de carbono vítreo (GC) por voltametria cíclica (CV) e no preparo de soluções para os estudos iniciais com o GCE-PMB. O pré-tratamento da superfície do eletrodo de GC foi realizado aplicando + 0,9 V por 240 s seguido de várias varreduras cíclicas de -0,4 a +1,0 V com velocidade de varredura de 50 mV s-1 até obter um perfil estável do voltamograma do eletrodo. Após o preparo do GCE-PMB...

Filmes híbridos obtidos a partir de precursores alcoóxidos para proteção contra corrosão em aço estrutural

Baggio, Tamara Francisca
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
16.1%
A necessidade de construções com maior tempo de vida útil, as preocupações com segurança e com o meio ambiente, levam cada vez mais ao desenvolvimento de materiais que associem meio ambiente, custo, praticidade e durabilidade. A corrosão de armadura é uma das causas mais significativas de deterioração das estruturas de concreto armado. Diferentes processos vêm sendo propostos com o objetivo de evitar esse tipo de corrosão, como por exemplo: proteção catódica, revestimentos da armadura com zinco, revestimento da armadura com resina epóxi. Revestimentos com resina epóxi apresentam-se como uma excelente alternativa promovendo a formação de uma barreira entre o metal e o meio. Contudo, esse tipo de revestimento tem comprometido a ancoragem armadura/concreto e não deve conter descontinuidades, pois isso pode favorecer corrosão localizada da armadura. Nesse contexto, o presente trabalho tem por objetivo elaborar e caracterizar filmes híbridos aplicados sobre aço AISI 1020 e aço estrutural CA50. Os filmes híbridos vêm sendo largamente estudados para proteção contra corrosão nos mais diferentes metais. Além disso, esses filmes apresentam baixa espessura, o que diminuiria o comprimento de ancoragem armadura/concreto. A adição de elementos de terras raras como inibidores de corrosão promove o efeito autocicatrizante ao filme...

Stripping voltammetric methods for determination of the antiparasitic drug nitazoxanide in bulk form, pharmaceutical formulation and human serum

El-Desoky,Hanaa S.; Ghoneim,Mohamed M.; Abdel-Galeil,Mohamed M.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
16.48%
Cyclic voltammograms of nitazoxanide recorded at the hanging mercury drop electrode in the Britton-Robinson universal buffer of pH values 2 to 11 containing 20% (v/v) ethanol exhibited a single 4-electron irreversible cathodic peak corresponding to the reduction of its NO2 group to the hydroxylamine stage. Nitazoxanide was found to adsorb onto surface of the mercury electrode in a monolayer surface coverage of 3.16×10-10 mol cm-2 in which each adsorbed molecule occupies an area of 0.525 nm². Based on its adsorption behavior onto the mercury electrode surface, validated linear sweep (LS), differential pulse (DP) and square wave (SW) adsorptive cathodic stripping voltammetric methods were described for determination of bulk nitazoxanide. Limits of detection of 1.5×10-10, 2.4×10-10 and 3.0×10-11 mol L-1 and limits of quantification of 5.0×10-10, 8.0×10-10 and 1.0×10-10 mol L-1 nitazoxanide in the bulk form were achieved by means of the described LS, DP and SW adsorptive cathodic stripping voltammetric methods, respectively. The described methods were successfully applied for determination of nitazoxanide in its pharmaceutical formulation (Cryptonaz powder) and in spiked human serum without the necessity for sample pretreatment...

Voltammetry of irbesartan drug in pharmaceutical formulations and human blood: quantification and pharmacokinetic studies

El-Desoky,Hanaa S; Ghoneim,Mohamed M; Habazy,Allia. D
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2011 EN
Relevância na Pesquisa
16.48%
Cyclic voltammograms of irbesartan at the hanging mercury dropping electrode in the Britton-Robinson buffer of pH values lower than 4.5 exhibited a single 2-electron irreversible cathodic peak corresponding to the reduction-saturation of the C=N double bond of its tetrazolyl moiety. Over the pH range 4.5-5.5, the voltammograms exhibited two irreversible cathodic peaks (1st and 2nd peaks) of lower peak current but of relatively equal heights which were attributed to reduction of the C=N group of the acidic and basic forms of irbesartan, respectively. A validated square-wave adsorptive cathodic stripping voltammetric method was developed for quantification of irbesartan in the bulk form. The developed stripping voltammetric method was successfully applied for quantitation of irbesartan in pharmaceutical formulations and spiked human serum, without the necessity for samples pretreatment and/or time-consuming extraction steps prior to the analysis. Insignificant interferences from its active ingredient "hydrochlorothiazide", excipients, common metal ions and co-administrated drugs were obtained during the analysis. Limits of detection of 9.0x10-10 and 2.1x10-9 mol L-1 and limits of quantitation of 3.0x10-9 and 7.0x10-9 mol L-1 irbesartan in the bulk form and in spiked human serum were achieved...

Determination of propylthiouracil in pharmaceuticals by differential pulse voltammetry using a cathodically pretreated boron-doped diamond electrode

Sartori,Elen Romão; Trench,Aline Barrios; Rocha-Filho,Romeu C.; Fatibello-Filho,Orlando
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2013 EN
Relevância na Pesquisa
26.1%
A simple procedure is described for the determination of propylthiouracil (PTU) by differential pulse voltammetry (DPV) using a cathodically pretreated boron-doped diamond (BDD) electrode. Cyclic voltammetry studies indicate that the oxidation of PTU is irreversible at a peak potential of 1.42 V (vs. Ag/AgCl (3.0 mol L-1 KCl)) in a Britton-Robinson (BR) buffer solution (pH 2.0). Under optimized conditions, the obtained analytical curve was linear (r = 0.9985) for the PTU concentration range of 1.0 to 29.1 mmol L-1 in a BR buffer solution (pH 2.0), with a detection limit of 0.90 mmol L-1. The proposed method was successfully applied in the determination of PTU in pharmaceutical samples, with results in agreement at a 95% confidence level with those obtained using an official titration method.

Lithium Inhibition of the Thigmomorphogenetic Response in Bryonia dioica1

Boyer, Nicole; Chapelle, Brigitte; Gaspar, Thomas
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1979 EN
Relevância na Pesquisa
16.1%
Pretreatment of young Bryonia dioica plants with lithium prevents the inhibition of elongation due to rubbing. Lithium treatment also suppresses the appearance of a specific cathodic isoperoxidase characteristic of rubbed plants.

Electrochemical Activation of Diamond Microelectrodes: Implications for the In Vitro Measurement of Serotonin in the Bowel

Duran, Boris; Brocenschi, Ricardo F.; France, Marion; Galligan, James J.; Swain, Greg M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27%
The electrochemical pretreatment of diamond microelectrodes was investigated for the purpose of learning how an anodic, cathodic or a combined anodic + cathodic polarization affects the charge-transfer kinetics for two surface-sensitive redox systems: ferri/ferrocyanide and serotonin (5-hydroxytryptamine, 5-HT). The pretreatments were performed in 0.5 mol L−1 H2SO4. The anodic pretreatment was performed galvanically for 30 s at 250 mA cm−2. The 10 cathodic pretreatment was performed for 180 s at −250 mA cm−2. The combined pretreatment involved application of the anodic step first followed by the cathodic step. The results clearly demonstrate that the best performance for both redox systems is obtained after the cathodic polarization, which presumably activates the electrode by cleaning the surface and removing site-blocking surface carbon-oxygen functionalities. The cathodic pretreatment was found to be effective at activating a fouled microelectrode in situ. This observation has important implication for the measurement of 5-HT in the bowel.

Direct Electrochemistry of Glucose Oxidase on Novel Free-Standing Nitrogen-Doped Carbon Nanospheres@Carbon Nanofibers Composite Film

Zhang, Xueping; Liu, Dong; Li, Libo; You, Tianyan
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 06/05/2015 EN
Relevância na Pesquisa
16.1%
We have proposed a novel free-standing nitrogen-doped carbon nanospheres@carbon nanofibers (NCNSs@CNFs) composite film with high processability for the investigation of the direct electron transfer (DET) of glucose oxidase (GOx) and the DET-based glucose biosensing. The composites were simply prepared by controlled thermal treatment of electrospun polypyrrole nanospheres doped polyacrylonitrile nanofibers (PPyNSs@PAN NFs). Without any pretreatment, the as-prepared material can directly serve as a platform for GOx immobilization. The cyclic voltammetry of immobilized GOx showed a pair of well-defined redox peaks in O2-free solution, indicating the DET of GOx. With the addition of glucose, the anodic peak current increased, while the cathodic peak current decreased, which demonstrated the DET-based bioelectrocatalysis. The detection of glucose based on the DET of GOx was achieved, which displayed high sensitivity, stability and selectivity, with a low detection limit of 2 μM and wide linear range of 12–1000 μM. These results demonstrate that the as-obtained NCNSs@CNFs can serve as an ideal platform for the construction of the third-generation glucose biosensor.

Electrochemical characterization of parylene-embedded carbon nanotube nanoelectrode arrays

Miserendino, Scott; Yoo, Juhwan; Cassell, Alan; Tai, Yu-Chong
Fonte: Institute of Physics Publicador: Institute of Physics
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 28/02/2006
Relevância na Pesquisa
16.1%
A novel parylene-embedded carbon nanotube nanoelectrode array is presented for use as an electrochemical detector working electrode material. The fabrication process is compatible with standard microfluidic and other MEMS processing without requiring chemical mechanical polishing. Electrochemical studies of the nanoelectrodes showed that they perform comparably to platinum. Electrochemical pretreatment for short periods of time was found to further improve performance as measured by cathodic and anodic peak separation of K3Fe(CN)6. A lower detection limit below 0.1 µM was measured and with further fabrication improvements detection limits between 100 pM and 10 nM are possible. This makes the nanoelectrode arrays particularly suitable for trace electrochemical analysis.