Platinum Screen Research Articles

Reliable and inexpensive dissolved oxygen sensing materials

Bare, non-pretreated platinum wires and screen-printed platinum electrodes were used as both working and counter electrodes in the measurement of dissolved oxygen using a chronoamperometric method. The oxygen reduction current response in the diffusion state was used for a linear determination of air saturation. We evaluated the two different materials in general for their sensing performance such as conditioning time, accuracy, resolution and stability over 13 h of continuous mid-term measurement. A good performance was found for the wire electrodes in terms of accuracy with a current slope of 1.0–1.6 µA (% as)-1 and a resolution of 10–15 nA (Lowest Level of Detection = 0.1% as), but with an unstable current response result over the course of the measurement. The screen-printed electrodes have a resolution of 10–18 nA (Lowest Level of Detection = 0.6–0.8% as) and an accuracy of 620–660 nA (% as)-1 but they showed promising reproducibility and stability. Both materials require several hours of conditioning in the chronoamperometric method before a stable current response is achieved. For biotechnological applications, the platinum screen printed electrodes were evaluated in typical parameter settings (pH 4.0 and 7.4, salinity 0.1 to 10x phosphate buffered saline and temperature 12 to 42 °C) and showed correlations between the response time and stability and the temperature. No correlations were found between salinity, pH and the current response. In this paper, we present inexpensive electrode materials and a simple to implement chronoamperometric method for reliable direct measurement of dissolved oxygen in aqueous media.Graphical abstract

A two-membrane electrodialytic carbonate eluent generator for ion chromatography

A two-membrane electrodialytic carbonate eluent generator (EDG) for ion chromatography (IC) is described. It is in a sandwich-like configuration, in which the central eluent channel is spatially isolated from two outer regenerant channels by stacked cation exchange membranes (CEMs) and anion exchange membranes (AEMs). A platinum screen electrode is placed in each of two outer regenerant channels. The electrode at the CEMs side is set as an anode with respect to the electrode at the AEMs side being cathode. Potassium carbonate and/or bicarbonate solution is pumped into the regenerant channel as feed solution. The electromigration of carbonate and/or bicarbonate and potassium from feed solution respectively through AEMs and CEMs will form a gas-free eluent. With this configuration, ion transport behavior through AEMs was explored. The device demonstrated good reproducibility, as indicated by the relative standard deviation of retention time of less than 0.08%.

Online Gas-Free Electrodialytic KOH Eluent Generator for Ion Chromatography.

An online gas-free KOH electrodialytic eluent generator (EDG) with two-membrane configuration is described for ion chromatography (IC). A central eluent channel is separated from two outer regenerant channels bearing KOH solution (or one is water) by stacked cation-exchange membranes (sCEMs) and a bipolar membrane (BPM) plus stacked CEMs (BPM-sCEMs), in which the anion-exchange membrane (AEM) of BPM is facing the central channel (the anode direction). Independent fluid input or output ports address all channels. One platinum screen electrode is put in each outer channel, and the sCEM side is anode with respect to the cathode of the BPM-sCEM side. Under the electric field, enhanced water splitting at the intermediate layer of BPM will occur, offering hydroxide and hydronium; hydroxide electromigrates through AEM into the central channel, while the potassium of KOH feed solution at the anode migrates into the central channel to combine with hydroxide to form a solution of KOH. Because the central eluent channel is spatially isolated from both electrodes, the generated KOH solution is gas-free and no gas-removal device is required. More important, the AEM side of BPM is contactless with the alkaline solution, nearly avoiding possible AEM degradation when immersed into concentrated alkaline solution. This ensures long-term running stability of the EDG and high purity of the produced KOH solution (as indicated by the typical suppressed background conductance of 0.28 μS/cm). The EDG has a pressure tolerance (at least 21 MPa), and the produced KOH concentration is up to 101 μeq/min with near-unity faradaic efficiency. When operated in both isocratic and gradient modes, the EDG demonstrates excellent reproducibility, as indicated by the retention time of RSD ≤ 0.08% and the peak area of RSD ≤ 0.6%. To the best of our knowledge, this is the first description of gas-free EDG matched conventional IC system.

Potentiometric Method for Evaluating the Oxidant/Antioxidant Activity of Seminal and Follicular Fluids and Clinical Significance of this Parameter for Human Reproductive Function

Potentiometric method based on the sharp change of electrode potential for the ferricyanide/ferrocyanide mediator system after addition of the seminal or follicular fluid sample into the measuring electrochemical cell has been developed to enable the easy assessment of the oxidant/antioxidant status of these kind of biological fluids. Platinum screen printed electrode has been used as an indicator. Essential advantage of the proposed method is simultaneous use of the both forms of the ferricyanide/ferrocyanide mediator system (oxidized and reduced ones) that allows estimating oxidant and antioxidant components of the seminal or follicular fluids samples which were obtained, respectively, from 99 male and 27 female subjects. Oxidant activity of seminal fluids has been observed in pathology conditions of reproductive system of male studied subjects and related with possible male infertility symptoms.

Platinum screen printed electrodes for the electroanalytical sensing of hydrazine and hydrogen peroxide

We report the fabrication of platinum screen printed electrodes which are electrochemically characterised and evaluated as to their potential analytical application towards the sensing of hydrazine and hydrogen peroxide. In the case of hydrazine a linear range of 50 to 500 μM is possible with a limit of detection (3σ) of 0.15 μM achievable using cyclic voltammetry which can be reduced to 0.12 μM using chronoamperometry. The novelty of these platinum screen printed electrodes is highlighted in that the platinum on the screen printed electrode surface resides as an oxide, which is favourable for the electrochemical oxidation of hydrazine, which need to be formed via extensive potential cycling when using a traditional platinum electrode hence the platinum screen printed sensors alleviate these requirements. The electroanalytical reduction of hydrogen peroxide is shown to be feasible with a linear range over 100 and 1000 μM with a limit of detection (3σ) of 0.14 μM which is competitive with other reported analytical protocols.

Electrochemical generation of ozone at PbO2-loaded platinum screens

Ozone (O3) has been electrochemically generated on PbO2-loaded Pt screens (PbO2/Pts) at 25 °C from H2SO4 solutions. The PbO2/Pts electrodes were electrochemically and morphologically characterized by cyclic voltammetry and scanning electron microscopy (SEM), respectively. Different loadings of PbO2 and different acid concentrations (C acid) were used in this study. Higher efficiency (8%) for O3 electrogeneration was obtained at an applied potential of 1.8 V, higher C acid, and loading density of PbO2 ≥ 9.3 μmol cm−2 (of Pt screen) at room temperature. The stability of the prepared electrode was examined under the present experimental conditions. SEM images and current transients showed reasonable electrochemical and mechanical stability of the PbO2/Pts. The data were discussed in the light of results obtained on planar Pt electrode at similar conditions.

Electrolysis of Methyl-t-Butyl Ether in Aqueous Solutions using Electro-generated Persulfate

Aqueous sodium sulfate solutions containing dilute concentrations of methyl-t-butylmethylether (MTBE) were electrolyzed to destroy the MTBE. In this treatment, the sulfate / persulfate anion (S2O82-) redox couple servers as the mediator cycle to oxidize MTBE. The solution was circulated through the anode compartment of a two compartment cell, equipped with reticulated vitreous carbon electrodes with100 pores/inch and separated from the cathode compartment by a positively charged ion exchange membrane. The electrolysis successfully reduced the MTBE content of the solutions. The reaction proceeded best when the applied anode potentials were in the range 2 - 3 V vs SCE and the flow rates were 0.100 - 0.125 L/min. Graphite plate, gold screen and platinum screen anodes were briefly tested.

Preparação e avaliação de célula a combustível do tipo PaCOS unitária com ânodo a base de níquel e cobalto

Uma célula a combustível do tipo PACOS unitária foi preparada e avaliada na geração de energia elétrica, utilizando metano ou hidrogênio como combustível. O ânodo da célula foi sintetizado a partir do eletro-catalisador desenvolvido e testado nesse trabalho (CATAC). O CATAC foi preparado pela mistura mecânica da zircônia estabilizada com ítria (YSZ) com os precursores metálicos (nitrato de níquel e cobalto, em sua forma hexahidratado), adicionando-se 25% de ácido cítrico à massa total da mistura e por fim calcinado a 800°C por quatro horas em ar. O catalisador foi caracterizado por fluorescência de raios X (XRF) e espectroscopia foto-eletrônica de raios X (XPS), a qual não indicou interação eletrônica entre o cobalto e níquel; o teor metálico do CATAC foi de aproximadamente 35% em massa. O CATAC foi testado para a geração de hidrogênio a partir da reforma a vapor do metano, mostrando boa produtividade de hidrogênio a partir de 600ºC. A estrutura do ânodo/eletrólito/cátodo foi preparada por prensagem de uma camada de CATAC misturado com grafite, uma camada de YSZ puro, e uma camada de óxido misto de lantânio, estrôncio e manganês (LSM) e grafite. O conjunto foi então prensado e sinterizado a 1380°C por quatro horas. Nas superfícies do ânodo e cátodo foram fixadas telas de platina, com o auxílio de tinta de platina, sendo o conjunto aquecido a 1100°C. Todo o sistema foi colado a um reator de alumina utilizando cola cerâmica. Microscopias por MEV da estrutura mostraram eletrólito denso e eletrodos porosos, com um conjunto adequadamente sinterizado. A célula unitária foi testada utilizando metano ou hidrogênio como combustível, a três temperaturas de operação. A tensão variou inversamente proporcional com a corrente, quando o desempenho foi medido a 850 ou 950ºC e hidrogênio, mas manteve-se constante acima de cinco mV a 800ºC com metano. A célula unitária mostrou um desempenho satisfatório na geração de eletricidade tanto com metano quanto com hidrogênio como combustíveis.

Sensor and biosensor based on Prussian Blue modified gold and platinum screen printed electrodes

Gold (Au) and platinum (Pt) screen-printed electrodes were modified with Prussian Blue (PB) for the development of amperometric sensors selective for hydrogen peroxide detection. The sensors exhibited sensitivities towards H 2O 2 equal to 2 A M −1 cm −2 for Au and 1 A M −1 cm −2 for Pt electrodes. The sensors were also employed as the basis for construction of glucose biosensors through further modification with crystallised glucose oxidase immobilised in a Nafion membrane. In order to improve the operational stability of the modified electrodes a buffer solution containing tetrabutylammonium toluene-4-sulfonate was used. The long-term performance of the sensors and biosensors were evaluated by continuous monitoring of hydrogen peroxide and glucose solutions (50 μM and 1 mM, respectively) in the flow-injection mode for 10 h.

Voltammetric Studies of Electrodes in Contact with Ionomeric Membranes

Cyclic voltammetry studies were carried out on platinum and gold screen electrodes in contact with Nafion ionomeric membranes. In addition, experiments were carried out on multiple combinations of platinum screens with either graphite felt or gold screen electrodes, with only one of the electrodes in direct contact with the membrane. In the case of platinum and gold screens, it was found that the voltammograms were almost identical to that found for the same screens in acidic aqueous electrolytes. When two platinum screens were used, the adsorption charges on the platinum doubled. Obviously, adsorption can occur on sites remote from the membrane/electrode contact, provided the metal is wetted with water. In the case of platinum, a mechanism based on rapid mobility of adsorbed hydrogen and hydroxyl species is proposed. The implications of these findings regarding solid polymer electrolyte electrolyzers and fuel cells are discussed.

Potentiometric quantitation of glycerol using immobilized glycerol dehydrogenase

Glycerol dehydrogenase was immobilized in polyacrylamide gel layered over a small platinum screen and used to catalyze the oxidation of glycerol. In the presence of NAD(+) and potassium ferricyanide, the coupling reaction generated a measurable electrical potential which was found to be Nernstian with respect to the glycerol concentration range of 10(-4)M to 10(-1)M. The reproducibility of the measurement and the optimal conditions for glycerol determination were described.

432 — Potentiometric measurement of glucose concentration using a gel-immobilized glucose dehydrogenase electrode

Glucose dehydrogenase, a coenzyme-dependent oxidoreductase, was immobilized by a polyacrylamide gel matrix over the surface of a platinum screen to measure the glucose concentration in 0.1 M phosphate buffer, pH 7.4 at 25 and 37°C. The oxidation of β-D(+)-glucose in this enzyme reaction produced a zero-current potentiometric response over a limited range of glucose concentrations. The presence or absence of an electron mediator, ferricyanide, appears to have no observable effect on the electrode response. Concurrent spectrophotometric detection of NADH confirms that the zero-current potential produced was the result of the enzymatic coupled reactions. The temperature effects and the reusability of this immobilized GDH electrode in the mode of potentiometric measurement were investigated and described.

432 — Potentiometric measurement of glucose concentration using a gel-immobilized glucose dehydrogenase electrode

Glucose dehydrogenase, a coenzyme-dependent oxidoreductase, was immobilized by a polyacrylamide gel matrix over the surface of a platinum screen to measure the glucose concentration in 0.1 M phosphate buffer, pH 7.4 at 25 and 37°C. The oxidation of β-D(+)-glucose in this enzyme reaction produced a zero-current potentiometric response over a limited range of glucose concentrations. The presence or absence of an electron mediator, ferricyanide, appears to have no observable effect of the electrode response. Concurrent spectrophotometric detection of NADH confirms that the zero-current potential produced was the result of the enzymatic coupled reactions. The temperature effects and the reusability of this immobilized GDH electrode in the mode of potentiometric measurement were investigated and described.

Potentiometric measurement of glucose concentration using a gel-immobilized glucose dehydrogenase electrode

Abstract Glucose dehydrogenase, a coenzyme-dependent oxidoreductase, was immobilized by a polyacrylamide gel matrix over the surface of a platinum screen to measure the glucose concentration in 0.1 M phosphate buffer, pH 7.4 at 25 and 37°C. The oxidation of β-D(+)-glucose in this enzyme reaction produced a zero-current potentiometric response over a limited range of glucose concentrations. The presence or absence of an electron mediator, ferricyanide, appears to have no observable effect of the electrode response. Concurrent spectrophotometric detection of NADH confirms that the zero-current potential produced was the result of the enzymatic coupled reactions. The temperature effects and the reusability of this immobilized GDH electrode in the mode of potentiometric measurement were investigated and described.

An Engineering Model for Electro‐Organic Synthesis in Continuous Flow‐Through Porous Electrodes

Under controlled experimental conditions, 9–10 diphenylanthracene (DPA) was oxidized in a sectioned flow‐through porous electrode in order to study the relation between operating conditions and product yield. The DPA solution contained 0.2N tetraethylammonium perchlorate in acetonitrile. The electrode was fabricated from 100‐mesh platinum screens. The reaction rate distribution within the sectioned electrode was measured directly, and the reactor effluent was analyzed to obtain the concentrations of DPA and its cation radical (DPA+). Experimental data were compared with calculations based on flow‐through porous electrode theory with consideration of the multiple reaction sequence (EEC) under study. Literature values, where available, were used without adjustment in making theoretical calculations with use of a mathematical model of the reactor system. The model calculations predicted total currents which were within 4% of experimental data, and gave good agreement with current distribution data at various flow velocities and applied potentials.

Immobilized enzyme electrodes for the potentiometric measurement of glucose concentration: immobilization techniques and materials.

Glucose oxidase, catalase, and bovine serum albumin were co-immobilized with glutaraldehyde around a platinum screen or around a single platinum-iridium wire. The potential difference between this dual enzyme electrode and a Ag/AgCL reference electrode was proportional to the logarithm of the glucose concentration over the range from 10 to about 150 mg glucose per 100 ml in buffered solution at pH 7.4 and 37 degrees C. The enzyme electrode responded in serum only if coated with a semipermeable film, such as cellulose acetate, to exclude serum macromolecules. The potentiometric results were similar to those obtained with the two enzymes co-immobilized in polyacrylamide gel around a platinum screen or with only one of the enzymes, glucose oxidase, covalently coupled to a platinum screen. The results so far suggest that glucose for development of a continuous in vivo glucose sensor.

Evidence for production of the hydroxycarbonyl radical in the decomposition of formic acid on platinum

AbstractFormic acid molecules highly diluted in argon were passed through a clean platinum screen at 420–730 K and condensed onto an 8‐K CsI window. The well‐known decomposition products, CO2, CO, and H2O, were observed in the infrared spectra of the resulting matrices. In addition, new absorptions which are attributed to the OCOH free radical were also observed. Experiments with partially deuterated formic acids confirmed that the carbon‐hydrogen bond of the formic acid was lost in the formation of the new intermediate species. The activation energy for CO2 production, Ea = 3.5 ± 0.2 kcal/mol, was determined by monitoring its appearance rate at several different catalyst temperatures.

262 - Quantitation of glucose concentration using a glucose oxidase-catalase electrode by potentiometric measurement

Glucose oxidase and catalase were immobilized in polyacrylamide gel around a platinum screen and used to measure the concentration of glucose in 0.1 M phosphate buffer, pH 7.3, at 37°C. This enzyme electrode produced a direct potentiometric signal with reference to a standard Ag|AgCl electrode. The potential difference was linearly related to the logarithm of the concentration of glucose over the range of 3–40 cg/dm 3 (mg/dl). The electrode was stable for at least 32 hours at 37°C. Hydrogen peroxide, generated by the oxidation of glucose and depleted by decomposition and diffusion, was the apparent source of the potentiometric signal. Direct potentiometric measurement has the advantages of simple readout, continuous detection, and small electrode size, and does not require external polarising potential. This approach should be suitable for the continuous in vivo monitoring of blood glucose levels if the upper limit of specificity for glucose (presently 40 mg/dl) can be extended.

Quantitation of glucose concentration using a glucoseoxidase-catalase electrode by potentiometric measurement

Glucose oxidase and catalase were immobilized in polyacrylamidegel around a platinum screen and used to measure the concentration of glucose in 0.1 M phosphate buffer, pH 7.3, at 37°C. This enzyme electrode produced a direct potentiometric signal with reference to a standard Ag‖AgCl electrode. The potential difference was linearly related to the logarithm of the concentration of glucose over the range of 3–40 cg/dm3 (mg/dl). The electrode was stable for at least 32 hours at 37°C. Hydrogen peroxide, generated by the oxidation of glucose and depleted by decomposition and diffusion, was the apparent source of the potentiometric signal. Direct potentiometric measurement has the advantages of simple readout, continuous detection, and small electrode size, and does not require external polarising potential. This approach should be suitable for the continuous in vivo monitoring of blood glucose levels if the upper limit of specificity for glucose (presently 40 mg/dl) can be extended.

Criterion of completeness of electrolysis at flow porous electrodes

An equation is presented which allows the calculation of the critical solution flow velocity corresponding to complete reaction controlled by diffusion at flow porous electrodes. The equation has been experimentally confirmed with good accuracy for the mass transport-controlled reaction of the reduction of K3Fe(CN)6 at flow porous electrodes composed of fine platinum screens and of gilded graphite granules described in the literature. If the critical flow velocity can be determined experimentally, the equation may be used for the determination of the specific surface of the electrode or the diffusion coefficient of the process. In this way the specific surfaces of graphite electrodes have been determined, which also enabled the calculation of mass transfer coefficients and dimensionless correlations for the Sherwood Number andj D-factor.