Página 1 dos resultados de 272 itens digitais encontrados em 0.012 segundos

Construção e avaliação de eletrodos de Nióbio/Óxido de Nióbio para determinações potenciométricas; Construction and evalution of Niobium/Niobium Oxide electrodes for potentiometric determination

Jardim, Wolney de Jesus
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 17/10/2008 PT
Relevância na Pesquisa
27.024263%
A construção de sensor potenciométrico, utilizando Nióbio acoplado a eletrodo de referência de prata/cloreto de prata num mesmo instrumento, possibilita o acompanhamento da variação de potencial que ocorre durante uma reação ácido-base em meio aquoso. Foi utilizado eletrodo de vidro combinado, cuja membrana de vidro foi danificada fisicamente, porém com sua referência interna em pleno funcionamento. O eletrodo de Nióbio foi confeccionado com metal polido ou então com a superfície modificada com óxido eletrodepositado. O crescimento de óxido sobre o Nióbio foi obtido por eletrólise em meio a H3PO4 diluído. O metal ou o par metal/óxido foi fixado no eletrodo de vidro contendo uma solução eletrolítica. O eletrodo de Nióbio não apresenta boa sensibilidade quando utilizado como indicador em potenciometria direta, mas é sensível às variações de potenciais que ocorrem em titulações ácido-base. O eletrodo de Nióbio metálico pode substituir o eletrodo de vidro combinado na determinação do teor de acidez de vinagres.; The construction of potentiometric sensors, using Niobium combined with the reference electrode silver / silver chloride in a single instrument, allows the variation of potential monitoring that occurs during an acid-base reaction in aqueous media. It was used a combined electrode glass...

Construção e otimização de um eletrodo de pasta de carbono modificado com óxido de manganês tipo espinélio dopado com cobalto (III) para determinação potenciométrica de íons lítio; Cosntruction and optimization of a carbon paste electrode modified with spinel type manganese oxide doped with cobalt (III) to potentiometric determination of lithium ions

Silva, Larissa Santos
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 19/09/2014 PT
Relevância na Pesquisa
27.024263%
Os efeitos terapêuticos dos sais de lítio são comprovados no tratamento de pacientes com depressão, certos tipos de câncer e transtornos bipolares de humor. A dosagem de lítio deve ser cuidadosamente controlada em cada paciente já que excessos na dosagem podem conduzir a danos irreversíveis no sistema nervoso e nos rins. Sendo assim é interessante produzir métodos de baixo custo, simples e rápidos que permitam o monitoramento desse íon. Portanto no presente trabalho foi estudado o desempenho potenciométrico de um eletrodo compósito de pasta de carbono modificado com óxido de manganês tipo espinélio dopado com cobalto (III). O eletrodo de pasta de carbono modificado foi preparado pela mistura de 55% (m/m) de pó de grafite, 20% (m/m) de aglutinante (óleo mineral) e 25% (m/m) de óxido de manganês dopado com cobalto (III) (Li1,05Co0,02Mn1,98O4.). O desempenho eletroquímico do eletrodo foi estudado através de voltametria cíclica (etapa de ativação) e cronopotenciometria (i=0) (etapas de estabilização e adição de padrão). Na caracterização eletroquímica do eletrodo estudou-se a melhor concentração de íons lítio para ativação do sensor, bem como a melhor velocidade de varredura, tempo de estabilização...

Estudio de la pasivacion de la aleacion Co-Cr-Mo en suero fisiologico

Ramires, I.; Rocha, L.; Codaro, E. N.; Guastaldi, A. C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 61-65
SPA
Relevância na Pesquisa
27.024263%
Results are presented on the mechanism of passivation of Co-Cr-Mo biological implant alloys in physiological serum using open circuit potentiometry, potentiodynamic curves, and electrochemical impedance spectroscopy. The potential dependence of impedance data and the analysis of the parameters obtained indicate a progressive diminution of the initial layer thickness and the simultaneous formation of a second higher resistive layer. In more severe conditions than the existent in human body, the metallographic examination of the alloy surface shows localized corrosion in interdendritric regions. Elemental analysis of the surface reveals the presence of higher chromium content in these regions. The presence of chlorine was not detected, which suggested that during preferential attack, soluble species are also formed.

Análise quantitativa de fluoretos nos alginatos para uso odontológico

Braga, A. S.; Catirse, Alma B. C. Elizaur B.; Vaz, L. G.; Polizello, A. C M; Spadaro, A. C C
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 181-188
POR
Relevância na Pesquisa
27.024263%
In this study, the aim was to measure the concentration of fluoride ions in dental alginates and the quantity released from alginate molds immersed in milliQ water, 0.1N hydrochloric acid and artificial saliva. Two separate lots of each of seven brands of alginate commercially available in Brazil were analyzed: Avagel, Deguprint, Hydrogum, Orthoprint, Jeltrate, Jeltrate Plus and Jeltrate Chromatic. Fluoride was measured in each sample by direct potentiometry, using the combined fluoride-ion selective electrode. The brands with the highest fluoride concentrations were Hydrogum (7052.87 μg/g), Jeltrate Plus (6519.68 μg/g) and Orthoprint (6218.18 μg/g). Only in Hydrogum and Jeltrate were different fluoride concentrations found in lots one and two. The various materials showed differences in the amount of fluoride released from the molds into the immersion medium, the mean concentration being highest in Hydrogum and Orthoprint, in all three media. The immersion medium also influenced the release of fluoride, which was lower in saliva than in water and highest in acid. Considering that the concentrations of fluoride found in the alginates tested were high and that various sources of exposure to fluoride exist, there is a need for constant monitoring of alginates intended for dental use.; Este trabalho teve como proposta analisar quantitativamente o conteúdo de fluoretos nos alginatos para uso odontológico e a liberação de fluoretos de moldes desses alginatos em água milliQ...

Emprego do sal di-sódico de edta como padrão no preparo de soluções

Silva,Paulo H. Pereira da; Oliveira,Andrea; Medeiros,Lívia Soman de; Neves,Eduardo F. de Almeida
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2007 PT
Relevância na Pesquisa
27.024263%
The hydrated sodium salt of EDTA, Na2H2Y·2H2O, cannot be used as a primary standard for titrations due to uncertainties in the water content. An alkalimetric titration of the homogenized solid in the presence of a small excess of BaCl2·2H2O allows one to titrate quantitatively the released two hydrogen cations with end-point indication by phenolphthalein or potentiometry. This leads one to calculate the average molar mass of the reagent and its water content, allowing to use it to prepare EDTA standard solutions. One titrated sample led to the formula Na2H2Y·1.876 H2O, and 370.01 g.mol-1 for the average molar mass.

Controle da qualidade na determinação potenciométrica de sulfetos volatilizáveis por acidificação (SVA) utilizando adições de padrão

Fagnani,Enelton; Guimarães,José Roberto; Grassi,Marco Tadeu; Fadini,Pedro Sérgio
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 PT
Relevância na Pesquisa
27.313442%
This paper presents a quality assurance and quality control protocol in order to ensure the reliability of analytical results for the determination of acid volatile sulfides in environmental samples by potentiometry. The monitoring of the ion selective sensor readings must be realized continually and particularly in this situation where the analyte is susceptible to transformation and volatilization. Potentiometry with the standard addition was presented as a rapid, accurate, precise, feasible as well as a low cost technique. Concentrations of the analyte in the range of 0.49 to 1.02 mg L-1 were tested with percentage recoveries varying from 89 to 113%.

Kinetic modeling of the biosorption of Cd2+ ions from aqueous solutions onto Eichhornia crassipes roots using potentiometry: low-cost alternative to conventional methods

Martínez-Sánchez,Carolina; Torres-Rodríguez,Luz María; García de la Cruz,Ramón Fernando
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 EN
Relevância na Pesquisa
27.024263%
This work presents the use of potentiometric measurements for kinetic studies of biosorption of Cd2+ ions from aqueous solutions on Eichhornia crassipes roots. The open circuit potential of the Cd/Cd2+ electrode of the first kind was measured during the bioadsorption process. The amount of Cd2+ ions accumulated was determined in real time. The data were fit to different models, with the pseudo-second-order model proving to be the best in describing the data. The advantages and limitations of the methodology proposed relative to the traditional method are discussed.

Uses of nitrate ion sensitive electrodes

DEL TÓRO DÉNIZ,Rubén; PEÓN ESPINOSA,Ana María; DANDIE MARSHALLECK,Hubert; BROCAR ESTEVEZ,Andres
Fonte: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP Publicador: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/1997 EN
Relevância na Pesquisa
27.024263%
Some models of ion-selective electrodes (ISE) and other methods have been elaborated, to quantify nitrate levels in environmental samples (water, fruits, vegetables and others), using direct potentiometry

Modern directions for potentiometric sensors

Bakker,Eric; Chumbimuni-Torres,Karin
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 EN
Relevância na Pesquisa
27.313442%
This paper gives an overview of the newest developments of polymeric membrane ion-selective electrodes. A short essence of the underlying theory is given, emphasizing how the electromotive force may be used to assess binding constants of the ionophore, and how the selectivity and detection limit are related to the basic membrane processes. The recent developments in lowering the detection limits of ISEs are described, including recent approaches of developing all solid state ISEs, and breakthroughs in detecting ultra-small quantities of ions at low concentrations. These developments have paved the way to use potentiometric sensors as in ultra-sensitive affinity bioanalysis in conjunction with nanoparticle labels. Recent results establish that potentiometry compares favorably to electrochemical stripping analysis. Other new developments with ion-selective electrodes are also described, including the concept of backside calibration potentiometry, controlled current coulometry, pulsed chronopotentiometry, and localized flash titration with ion-selective membranes to design sensors for the direct detection of total acidity without net sample perturbation. These developments have further opened the field for exciting new possibilities and applications.

Determination of pKa values of some auxins in methanol-water mixtures by reversed phase liquid chromatography and potentiometric methods

Kelen,Mustafa; Sanli,Nurullah
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
Relevância na Pesquisa
27.024263%
Plant hormones are of vital importance for the normal functioning of plants. Auxins are a class of phytohormones involved in many aspects of plant growth. Indole-3-acetic acid, (IAA), indole-3-pyruvic acid (IPA) and indole-3-lactic acid (ILA) are auxins with biological functions stimulating growth processes such as cell elongation and division. In this study, the pKa values of IAA, IPA and ILA in 30%, 40% and 50% (v/v) methanol-water mixtures were determined using potentiometry, liquid chromatography (LC) and LC-DAD methodology. Also, the pKa values in water predicted by the SPARC on-line calculator have been investigated.

Determination of protonation constants of some tetracycline antibiotics by potentiometry and lc methods in water and acetonitrile-water binary mixtures

Şanli,Senem; Şanli,Nurullah; Alsancak,Güleren
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
Relevância na Pesquisa
27.024263%
An accurate estimation of dissociation constants of tetracycline antibiotics in acetonitrile-water binary mixtures is very important for several separation techniques such as liquid chromatography and capillary electrophoresis that use these solvent mixtures. In this study, the pKa values of five tetracyclines (tetracycline, oxytetracycline, chlortetracycline, doxycycline and metacycline), have been determined in water and acetonitrile-water binary mixtures (10%, 20% and 30% (v/v)) by potentiometry and liquid chromatography (LC). The obtained results show a similar trend for the pKa1 values of five tetracycline antibiotics as they increase with increasing concentration of organic modifier, which allows a linear relationship between pKa1 values and mole fraction of acetonitrile to be obtained. The pKa values obtained in aqueous medium have been compared with the values predicted by the SPARC on-line pKa calculator.

Beyond potentiometry: robust electrochemical ion sensor concepts in view of remote chemical sensing

Bakker, Eric; Bhakthavatsalam, Vishnupriya; Gemene, Kebede L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.491401%
For about one hundred years, potentiometry with ion-selective electrodes has been one of the dominating electroanalytical techniques. While great advances in terms of selective chemistries and materials have been achieved in recent years, the basic manner in which ion-selective membranes are used has not fundamentally changed. The potential readings are directly co-dependent on the potential at the reference electrode, which requires maintenance and for which very few accepted alternatives have been proposed. Fouling or clogging of the exposed electrode surfaces will lead to changes in the observed potential. At the same time, the Nernst equation predicts quite small potential changes, on the order of millivolts for concentration changes on the order of a factor two, making frequent recalibration, accurate temperature control and electrode maintenance key requirements of routine analytical measurements. While the relatively advanced selective materials developed for ion-selective sensors would be highly attractive for low power remote sensing application, one should consider solutions beyond classical potentiometry to make this technology practically feasible. This paper evaluates some recent examples that may be attractive solutions to the stated problems that face potentiometric measurements. These include high amplitude sensing approaches...

Modern Potentiometry**

Bakker, Eric; Pretsch, Ernö
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
27.313442%
For most chemists, potentiometry with ion-selective electrodes (ISEs) probably just means pH measurements with a glass electrode. Only those interested in clinical analysis might know that ISEs, routinely used for the determination of blood electrolytes, have a market size comparable to that of glass electrodes. It is even less known that potentiometry went through a silent revolution during the last decade. The lower detection limit and the discrimination of interfering ions (the selectivity coefficients) have been improved in many cases by a factor of up to 106 and 1010, respectively. This opens up new fields of application including environmental trace analysis and potentiometric biosensing. Another important novel application covered in this review is the determination of complex formation constants between lipophilic hosts and ionic guests.

Automatic system for the determination of metals by anodic stripping potentiometry in non-deaerated samples

Cladera, A.; Estela, J. M.; Cerdá, V.
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em //1990 EN
Relevância na Pesquisa
27.024263%
An automatic system for the determination of Zn, Cd, Pb and Cu by anodic stripping potentiometry using the oxygen dissolved in the sample as oxidant is reported. The system relies on the use of a PC-compatible computer for instrumental control and data acquisition and processing.

High Temperature Potentiometry: Modulated Response of Ion-Selective Electrodes During Heat Pulses

Chumbimuni-Torres, Karin Y.; Thammakhet, Chongdee; Galik, Michal; Calvo-Marzal, Percy; Wu, Jie; Bakker, Eric; Flechsig, Gerd-Uwe; Wang, Joseph
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/12/2009 EN
Relevância na Pesquisa
27.024263%
The concept of locally heated polymeric membrane potentiometric sensors is introduced here for the first time. This is accomplished in an all solid state sensor configuration, utilizing poly(3-octylthiophene) as intermediate layer between the ion-selective membrane and underlying substrate that integrates the heating circuitry. Temperature pulse potentiometry (TPP) gives convenient peak-shaped analytical signals and affords an additional dimension with these sensors. Numerous advances are envisioned that will benefit the field. The heating step is shown to give an increase in the slope of the copper-selective electrode from 31 mV to 43 mV per 10-fold activity change, with a reproducibility of the heated potential pulses of 1% at 10 µM copper levels and a potential drift of 0.2 mV/h. Importantly, the magnitude of the potential pulse upon heating the electrode changes as a function of the copper activity, suggesting an attractive way for differential measurement of these devices. The heat pulse is also shown to decrease the detection limit by half an order of magnitude.

Backside Calibration Potentiometry: Ion Activity Measurements with Selective Supported Liquid Membranes by Calibrating from the Inner Side of the Membrane

Malon, Adam; Bakker, Eric; Pretsch, Ernö
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/01/2007 EN
Relevância na Pesquisa
27.611953%
In direct potentiometry, the magnitude of the measured potentials is used to determine the composition of the sample. While this places rather formidable demands on the required reproducibility of the associated potential measurements, typically on the order of microvolts, in vitro clinical analyses of blood samples are today successfully performed with direct potentiometry using ion-selective electrodes (ISEs). Unfortunately, most other analytical situations do not permit the sensor to be recalibrated every few minutes, as in environmental monitoring or in vivo measurements, and direct potentiometry is often bound to fail as an accurate method in these circumstances. This paper introduces a novel direction for potentiometric sensing, termed backside calibration potentiometry. Chemical asymmetries across thin supported liquid ISE membranes are assessed by determining the direction of potential drift upon changing the stirring rate on either side of the membrane. Disappearance of this drift indicates the disappearance of concentration gradients across the membrane and is used to determine the sample composition if the solution composition at the backside of the membrane and the interfering ion concentration in the sample are known. For practical determinations...

Sensitivity and Working Range of Backside Calibration Potentiometry

Ngeontae, Wittaya; Xu, Yida; Xu, Chao; Aeungmaitrepirom, Wanlapa; Tuntulani, Thawatchai; Pretsch, Ernö; Bakker, Eric
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.024263%
A new direction in potentiometric sensing, termed backside calibration potentiometry, was recently introduced. It makes use of the fact that the stir effect disappears in absence of ion-ionophore complex concentration gradient across supported liquid membrane ion-selective membranes. This method is especially suitable for measurements in which recalibration in the sample is not feasible, such as in remote monitoring applications. Here, a theoretical model is established to predict the working concentration range of the method. Lead(II)-selective Celgard membranes were used here with H+ as the dominant interfering ions. The emf difference for stirred and unstirred solutions was measured and the magnitude of this emf change as a function of the sample Pb2+ concentration was found to exhibit a bell shape that spans about three orders of magnitude. The concentration of interfering ions and the selectivity of the membrane were demonstrated to be important factors that affect the working range. Smaller ratios of primary ion concentrations at both aqueous sides of the membrane gave smaller emf difference values, and emf changes could still be observed with a logarithmic concentration ratio of 0.05. All experimental results correlated satisfactorily with the theoretical model.

Label-Free Potentiometry for Detecting DNA Hybridization Using Peptide Nucleic Acid and DNA Probes

Goda, Tatsuro; Singi, Ankit Balram; Maeda, Yasuhiro; Matsumoto, Akira; Torimura, Masaki; Aoki, Hiroshi; Miyahara, Yuji
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 07/02/2013 EN
Relevância na Pesquisa
27.024263%
Peptide nucleic acid (PNA) has outstanding affinity over DNA for complementary nucleic acid sequences by forming a PNA-DNA heterodimer upon hybridization via Watson-Crick base-pairing. To verify whether PNA probes on an electrode surface enhance sensitivity for potentiometric DNA detection or not, we conducted a comparative study on the hybridization of PNA and DNA probes on the surface of a 10-channel gold electrodes microarray. Changes in the charge density as a result of hybridization at the solution/electrode interface on the self-assembled monolayer (SAM)-formed microelectrodes were directly transformed into potentiometric signals using a high input impedance electrometer. The charge readout allows label-free, reagent-less, and multi-parallel detection of target oligonucleotides without any optical assistance. The differences in the probe lengths between 15- to 22-mer dramatically influenced on the sensitivity of the PNA and DNA sensors. Molecular type of the capturing probe did not affect the degree of potential shift. Theoretical model for charged rod-like duplex using the Gouy-Chapman equation indicates the dominant effect of electrostatic attractive forces between anionic DNA and underlying electrode at the electrolyte/electrode interface in the potentiometry.

NO2 Detection Using Microcantilever Based Potentiometry

Qazi, Muhammad; Koley, Goutam
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 12/11/2008 EN
Relevância na Pesquisa
27.024263%
A highly sensitive and novel sensor platform for gases and volatile chemicals using microcantilever based potentiometry is reported. A resonant cantilever is used to detect the changes in surface work functions of functionalized substrates caused by adsorption of target gas molecules. Surface work function (SWF) changes were measured for different functionalization layers made of transition metal oxide thin films with the flow of NO2. The rate of change in SWF for In2O3 and SnO2 were found to be ∼80 and ∼100 μV/sec, respectively, for 70 ppm NO2. A sensitivity of 64 μV/sec for SWF change was also found for 70 ppm NO2 concentration for isolated clusters of ZnO nanowires, indicating that this technique is applicable even for nano-clusters of sensing materials where amperometric detection is impossible due to material discontinuity. NO2 detection as low as 400 ppb was possible using highly insulating In2O3 and SnO2 thin films (resistivity > 1 TΩ/□. Two different forms of nano scale graphite were compared with the transition oxide based functionalization layer for sensing sub-ppm NO2 sensing. It was observed that nanostructured graphite (NG) shows much higher sensitivity and lower response time than transition metal oxides.

Scanning tunneling potentiometry implemented into a multi-tip setup by software

Lüpke, F.; Korte, S.; Cherepanov, V.; Voigtländer, B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.313442%
We present a multi-tip scanning tunneling potentiometry technique that can be implemented into existing multi-tip scanning tunneling microscopes without hardware changes. The resulting setup allows flexible in situ contacting of samples under UHV conditions and subsequent measurement of the sample topography and local electric potential with resolution down to \AA\ and \mu V, respectively. The performance of the potentiometry feedback is demonstrated by thermovoltage measurements on the Ag/Si$(111)-(\sqrt3\times\sqrt3)\rm R30^{\circ}$ surface by resolving a standing wave pattern. Subsequently, the ability to map the local transport field as a result of a lateral current through the sample surface is shown on Ag/Si$(111)-(\sqrt3\times\sqrt3)\rm R30^{\circ}$ and Si$(111)-(7\times7)$ surfaces.