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Search Results: 1 - 10 of 3475 matches for " Modified Electrode "
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Eletrodo modificado em filme de paládio para a determina??o voltamétrica de fosfito
Ito, Helenice Akemi;Oliveira, Marcelo Firmino de;Gomes Neto, José Anchieta;Stradiotto, Nelson Ramos;
Eclética Química , 2002, DOI: 10.1590/S0100-46702002000200014
Abstract: phosphite ions constitute an important inorganic component as phosphorus source in soil fertilization, showing a large number of advantages in relation to phosphate. the determination of this compound in fertilizing products is realized by classical methods of analysis as gravimetry, in the form of magnesium pyrophosphate or by mercurous chloride formation. however, there are some disadvantages in these methods as the necessity of high times of digestion and possible toxic residue production. so, this work has the objective to propose an alternative electrochemical method for phosphite determination. electrochemical modification on electrode surface by electrodeposition of palladium has exhibited catalytic effect for oxidation of phosphite to phosphate ions in 1,0mol.l-1 sulfuric acid aqueous medium, being obtained a linear dependence in relation to phosphite concentration from 5,0x10-6 to 5,0x10-4 mol.l-1 with an amperometric sensibility of 8,5x104 ma.mol-1.l and a detection limit of 3.67x10-6 mol.l-1. in the absence of palladium film on platinum electrode no anodic peak current is observed for phosphite oxidation.
Eletrodos quimicamente modificados aplicados à eletroanálise: uma breve abordagem
Souza, Maria de Fátima Brito;
Química Nova , 1997, DOI: 10.1590/S0100-40421997000200011
Abstract: chemically modified electrodes (cmes) have been subject of considerable attention since its inception about 23 years ago. cmes result of a deliberate immobilization of a modifier agent onto the electrode surface obtained through chemical reactions, chemisorption, composite formation or polymer coating. this immobilization seeks transfer the physicochemical properties of the modifier to the electrode surface and thus to dictate and control the behavior of the electrode/solution interface. in recent years the interest in cmes has increased particularly to enhance the sensitivity and/or the selectivity of electroanalytical techniques. in general higher sensitivity and/or selectivity may be achieved by exploiting one or more of the following phenomena: electrocatalysis, preconcentration and interferents exclusion. this paper deals with the application of cmes in electroanalysis, including a brief presentation of the more general procedures that have been employed for the modification of electrode surfaces.
Chemically Modified Carbon Paste Electrode for Determination of Cesium Ion by Potentiometric Method  [PDF]
Refat F. Aglan, Gehad G. Mohamed, Hala A. Mohamed
American Journal of Analytical Chemistry (AJAC) , 2012, DOI: 10.4236/ajac.2012.38076
Abstract: A new chemically modified carbon paste electrode for cesium(I) ion determination based on potassium zinc hexacyan-oferrate (PZHCF) as an ionophore was prepared. The electrode exhibits a Nernstian response for Cs(I) ions over a wide concentration range from 1 × 10-6 to 1 × 10-1 mol·L-1 with a slope of 58 ± 0.5 mV·decade-1. It has a response time of about 35 s and can be used for a period of 3 months with good reproducibility. Detection limit obtained in the optimal conditions was 3 × 10-7 mol·L-1. The potentiometric response is independent of the pH of the solution in the pH range 4.0 - 8.0. The electrode possesses the advantages of low resistance, fast response over a variety of other cations. The proposed electrode is applied as a sensor for the determination of Cs(I) ion concentration in different samples solutions. The results showed a good correlation with the data obtained by atomic absorption spectrometric method.
Sensitive Voltammetric Determination of Mitoxantrone by Using CS-Dispersed Graphene Modified Glassy Carbon Electrodes  [PDF]
Bin Hong, Qiong Cheng
Advances in Chemical Engineering and Science (ACES) , 2012, DOI: 10.4236/aces.2012.24055
Abstract: A novel CS-dispersed graphene modified glassy carbon electrode was fabricated. Study electrochemical characteristics of mitoxantrone in the CS-dispersed graphene modified electrode by cyclic voltammetry and other methods, by selecting and optimizing the various parameters to create a new electrochemical method for the determination of mitoxantrone. The linear range of the oxidation peak current is from 6×10–10 to 1 ×10–6 mol/l in this method, after 2.5 mins open-circuit accumulation, the limit of detection is 2×10–10 mol/l. After 10 parallel determinations, the relative standard deviation was 3.7% that the concentration of mitoxantrone was 1×10–8 mol/l. The modified electrode has been successfully applied for the assay of mitoxantrone in human urine samples.
Electrocatalytic and Sensors Properties of Natural Smectite Type Clay towards the Detection of Paraquat Using a Film-Modified Electrode  [PDF]
H. L. Tcheumi, I. K. Tonle, A. Walcarius, E. Ngameni
American Journal of Analytical Chemistry (AJAC) , 2012, DOI: 10.4236/ajac.2012.311099
Abstract: In this study, a low-cost and sensitive voltammetric method was developed for the determination of paraquat (PQ2+). This was achieved by coating a glassy carbon electrode with a purified fraction of a smectite-type clay, which was then used to accumulate paraquat by an ion exchange process. The electronanalytical procedure involves two steps: the chemical preconcentration of paraquat under open-circuit conditions in an aqueous medium, followed by the voltammetric detection of the preconcentrated pollutant in a medium containing permanganate ions which significantly improved through its catalytic action the electrode response. A systematic study of the experimental conditions (pH of the accumulation and detection media, permanganate concentration in the detection medium, clay content of the coating, potential and duration of the electrolysis step) on the stripping response were examined in detail. After optimization, a linear calibration curve for paraquat was obtained in the concentration range from 1.6 to 2.8 μM, leading to a detection limit of 3.8 × 10–9 mol·L–1 (S/N = 3). The proposed method was successfully applied to the determination of paraquat in spring water.
Electrochemical determination of catechol in tea samples using anthraquinone modified carbon paste electrode  [PDF]
Fekadu Melak, Mesfin Redi, Merid Tessema, Esayas Alemayehu
Natural Science (NS) , 2013, DOI: 10.4236/ns.2013.58107
Abstract:

Electrochemical investigation of catechol using square wave voltammetry with anthraquinone modified carbon paste electrode was found to be very sensitive. Compared with the unmodified carbon paste electrode, the anthraquinone modified electrode remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Two varieties of tea, namely green, and black variety: Wush Wush tea, from Ethiopia, known by its brand name were investigated. Responses for the extracts using ethanol: water (1:4) % v/v showed green tea to be superior in catechol content. Optimization of different variables such as pH of working solution, modifier composition and square wave parameters such as frequency, amplitude and step potential were made to improve the method efficiency during the experiment. The reproducibility for the nine repeated analysis of 80 μmol·L-1 of catechol gave a relative standard deviation of 3.65% and linear calibration plots were obtained in the range 6 to 80 μmol·L-1 with (R = 0.998) and the detection limit with (S/N = 3) was as low as 2.155 x 10-7 mol·L-1.

Preparation and characterization of carbon paste electrode modified with tin and hexacyanoferrate ions
REZA E. SABZI,ALL HASANZADEH,KHOSROW GHASEMLU,PARVANEH HERAVI
Journal of the Serbian Chemical Society , 2007,
Abstract: A carbon paste electrode was modified chemically using Sn(II) or Sn(IV) chlorides and hexacyanoferrate(II) or hexacyanoferrate(III). The electrochemical behavior of such SnHCF carbon paste electrodes was studied by cyclic voltammetry. The study revealed that Sn(IV) and hexacyanoferrate(II) yield the best results. This electrode showed one pair of peaks: the anodic and cathodic peak at the potentials of 0.195 and 0.154 V vs. SCE, respectively, at a scan rate of 20 mV s-1 in a 0.5 M phosphate buffer as the supporting electrolyte. The SnHCF modified electrodes were very stable under potential scanning. The effects of pH and alkali metal cations of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied. The results showed that cations have a considerable effect on the electrochemical behavior of the modified electrode. The diffusion coefficients of hydrated K+ and Na+ in the film, the transfer coefficient and the electron transfer rate constant were determined.
Eletrodos de pasta de carbono modificados com ácidos húmicos: estudo e determina??o de metais em meio aquoso
Crespilho, Frank Nelson;Rezende, Maria Olímpia Oliveira;
Química Nova , 2004, DOI: 10.1590/S0100-40422004000600022
Abstract: since 1992, the carbon paste electrodes modified with humic acids have been used for studying the behavior of metals in aqueous solutions. many parameters influence the performance of the electrodes, such as the humic acid ratio, the nature of the humic acid, the accumulation time, the ph, the scan rate, and the preparation of the electrodes itself. there are various methos of preparing the electrodes. the goal of this paper is to review some of them. the advantages of using electrodes modified with humic acids as electrochemical sensors for evaluating metals in aqueous solution are stressed.
Eletrodos de pasta de carbono modificados com ácidos húmicos: estudo e determina o de metais em meio aquoso
Crespilho Frank Nelson,Rezende Maria Olímpia Oliveira
Química Nova , 2004,
Abstract: Since 1992, the carbon paste electrodes modified with humic acids have been used for studying the behavior of metals in aqueous solutions. Many parameters influence the performance of the electrodes, such as the humic acid ratio, the nature of the humic acid, the accumulation time, the pH, the scan rate, and the preparation of the electrodes itself. There are various methos of preparing the electrodes. The goal of this paper is to review some of them. The advantages of using electrodes modified with humic acids as electrochemical sensors for evaluating metals in aqueous solution are stressed.
Electrooxidation and Determination of Dopamine Using a Nafion?-Cobalt Hexacyanoferrate Film Modified Electrode
Suely S. L. Castro,Roger J. Mortimer,Marcelo F. De Oliveira,Nelson R. Stradiotto
Sensors , 2008, DOI: 10.3390/s8031950
Abstract: The electrocatalysis of dopamine has been studied using a cobalt hexacyanoferrate film (CoHCFe)-modified glassy carbon electrode. Using a rotating disk CoHCFe-modified electrode, the reaction rate constant for dopamine was found to be 3.5 × 105 cm3 mol-1 s-1 at a concentration of 5.0 × 10-5 mol L-1. When a Nafion? film is applied to the CoHCFe-modified electrode surface a high selectivity for the determination of dopamine over ascorbic acid was obtained. The analytical curve for dopamine presented linear dependence over the concentration range from 1.2 × 10-5 to 5.0 × 10-4 mol L-1 with a slope of 23.5 mA mol-1 L and a linear correlation coefficient of 0.999. The detection limit of this method was 8.9 × 10-6 mol L-1 and the relative standard deviation for five measurements of 2.5 × 10-4 mol L-1 dopamine was 0.58%.
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