Platinum Wire Electrodes Research Articles

Electrogeneration of hydrogen peroxide applied to the peroxide-mediated oxidation of (R)-limonene in organic media

Horse radish peroxidase (HRP) from Armoracia rusticana catalyses the oxidation of ( R )-limonene into the oxidized derivatives carveol and carvone. This study compares the direct addition (DA) of hydrogen peroxide with its continuous electrogeneration (EG) during the enzymatic oxidation of ( R )-limonene. Reaction mixtures containing HRP, ( R )-limonene as substrate, and hydrogen peroxide, added directly or electrogenerated, in 100 mM sodium-potassium phosphate buffer pH 7.0, at 25oC were studied. Two electrochemical systems for the hydrogen peroxide electrogeneration were evaluated, both containing as auxiliary electrode (AE) a platinum wire and saturated calomel electrode (SCE) as reference. Reticulated vitreous carbon foam (RVCF) and an electrolytic copper web (CW) were evaluated as working electrodes (WE). Results were compared in terms of hydrogen peroxide electrogeneration, ( R )-limonene residual concentration or conversion and product selectivity. Best results in terms of maximum H 2 O 2 concentration (1.2 mM) were obtained using the CW electrode at -620 mV SCE , and continuous aeration. Use of the EG system under optimized conditions, which included the use of acetone (30% v/v) as a cosolvent in a 3 hrs enzymatic reaction, lead to a 45% conversion of ( R )-limonene into carveol and carvone (2:1). In comparison to the results obtained with DA, the use of EG also improved the half-life of the enzyme.

Development of a membrane-based electrochemical immunosensor

A membrane-based electrochemical immunosensor sensitive towards proteins is described, based on nanoporous alumina-modified platinum wire electrodes. The sensing mechanism depends on the blocking of pore channels when the protein antigen molecules bind to antibody molecules attached to the channel walls, impeding the diffusion of redox probe, ferrocenemethanol, towards the sensing platinum wire overlaid by the nanoporous alumina film. The antibody and antigen used in this work were anti-glucose oxidase and glucose oxidase, respectively. The immunosensor showed a low limit of detection of 100 ng L −1 antigen concentration and was selective towards glucose oxidase protein in the presence of another protein, glucothione S-transferase.

Ambient Gas Influence on Electrospray Potential As Revealed by Potential Mapping within the Electrospray Capillary

The effect of ambient gas on potentials inside the electrospray (ES) capillary was investigated. Potential measurements and differential electrospray emitter potential (DEEP) maps were obtained with the help of a small, movable, disklike platinum wire electrode inserted into the ES capillary. Typical solvents used for electrospray mass spectrometry such as methanol and mixtures of methanol-water and chloroform/methanol have been tested. It was found that oxygen is readily adsorbed from the surrounding ambient gas into the spraying liquid. Following adsorption, it resides in, or near to, the Taylor cone, thereby affecting the electrochemical potential near the ES capillary exit, as well as the character of the inherent electrochemical reactions occurring during the ES process. The potentials measured in an air environment with reactive oxygen present are contrasted against those obtained in an inert nitrogen environment. The kinetics of oxygen admission have been found to be quite fast, i.e., occurring in a matter of seconds, but it takes far longer to purge the system of oxygen by changing the ambient atmosphere to nitrogen. The oxygen effect is present in negative and positive ion modes of ES, but the total ES current is not affected by the change of ambient gas. The magnitude of the oxygen effect owing to ambient air was compared to the effect caused by initially dissolving oxygen in the solution prior to the start of ES; it was found that the presence of oxygen in the ambient gas has a far greater consequence. These results indicate that the presence of reactive gases, such as molecular oxygen, in the region of the ES emitter may have unintended secondary effects on the ES process prior to mass spectrometric analysis.

Threshold suprachoroidal–transretinal stimulation current resulting in retinal damage in rabbits

The purpose of this study is to determine the threshold suprachoroidal–transretinal stimulation (STS) current that results in retinal damage in rabbits. Biphasic STS pulses (anodic first, frequency 20 Hz) were used to stimulate the retina of pigmented rabbits (n = 18) continuously for 1 h using a 100 µm diameter platinum wire electrode. The STS current that induced retinal damage after 1 h was determined by ophthalmoscopy or by fluorescein angiography (FA) independently. The effect of the pulse duration on the threshold current was investigated. Histological studies were performed after electrical stimulation experiments. The threshold for a safe current to the retina was 0.6 mA for a duration of 0.5 ms. The threshold for a safe charge increased approximately linearly with an increase of stimulus duration but the threshold for a safe current decreased logarithmically with an increase of duration. The threshold for a safe electrical energy remained almost constant for all durations. Histological examination showed severe retinal damage when the current exceeded the threshold, with more damage in the inner layers compared with the outer layers of the retina. The threshold for the safe current was higher than that reported for direct stimulation of neural tissues, suggesting that the STS method was safe and able to be used with a retinal prosthesis. Because the threshold for the safe charge was lower with shorter pulse durations, care should be taken using pulses of short durations.

A mediator-free amperometric hydrogen peroxide biosensor based on HRP immobilized on a nano-Au/poly 2,6-pyridinediamine-coated electrode

A mediator-free amperometric hydrogen peroxide biosensor was prepared by immobilizing horseradish peroxidase (HRP) enzyme on colloidal Au modified platinum (Pt) wire electrode, which was modified by poly 2,6-pyridinediamine (pPA). The modified process was characterized by electrochemical impedance spectroscopy (EIS), and the electrochemical characteristics of the biosensor were studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The biosensor displayed an excellent electrocatalytical response to reduction of H(2)O(2) without the aid of an electron mediator, the linear range was 4.2 x 10(-7)-1.5 x 10(-3) mol/L (r = 0.9977), with a detection limit of 1.4 x 10(-7) mol/L. Moreover, the performance and factors influencing the resulted biosensor were studied in detail. The studied biosensor exhibited permselectivity, good stability and good fabrication reproducibility.

Study of hydrogen nanobubbles in solution in the vicinity of a platinum wire electrode using double-potential step chronoamperometry

A solution supersaturated with hydrogen around a platinum wire electrode was studied by double-potential step chronoamperometry. The time–current curve at the hydrogen oxidation potential obtained with double-potential step increased with a shift of the hydrogen evolution potential to the cathodic potential. The initial slope of the chronoamperogram at the oxidation potential increased to zero with the shift from the hydrogen evolution potential to the cathodic potential. The increase was observed with increasing ionic strength and increasing cathodic current density. These phenomena were analyzed with numerical method using a number of assumptions.

Direct electrochemical immunoassay based on a silica nanoparticles/sol–gel composite architecture for encapsulation of immunoconjugate

A highly hydrophobic and non-toxic colloidal silica nanoparticle/polyvinyl butyral sol-gel composite membrane was prepared on a platinum wire electrode. With diphtheria-toxoid (D-Ag) as a model antigen and encapsulation of diphtheria antibody (D-Ab) in the composite architecture, this membrane could be used for reagentless electrochemical immunoassay. It displayed a porous and homogeneous composite architecture without the aggregation of the immobilized protein molecules. The formation of immunoconjugate by a simple one-step immunoreaction between D-Ag in sample solution and the immobilized D-Ab introduced the change in the potential. Under optimal conditions, the D-Ag analyte could be determined in the linear ranges from 10 to 800 ng ml(-1) with a relatively low detection limit of 2.3 ng ml(-1) at 3delta. The D-Ag immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy, and reproducibility. This composite membrane could be used efficiently for the entrapment of different biomarkers and clinical applications.

A coulometric flow cell for in-line generation of reagent, titrant or standard solutions

A universal and easily ON–OFF time operated coulometric flow cell for generation of chemicals is proposed. The cell can be used for generation of reagents, titrants or standard solutions, and can be coupled to analytical equipments in combination with flow systems for generation of micro-quantity amounts of chemicals in a wide concentration range. Platinum wire electrodes and other common laboratory available materials were employed in the cell assembly. The application of the cell for analytical purposes was illustrated by employing it for generating triiodide ions as a carrier in a flow injection analysis system applied to the analysis of dipyrone in pharmaceuticals, and as a titrant in a flow-batch analysis system applied for analysis of ascorbic acid in natural orange juice samples. Preliminary studies demonstrate that such a flow cell is suitable to allow the use of unstable reagents in analytical chemistry, since they can be generated in a closed system and promptly used in subsequent reactions. In addition, it offers advantages of saving chemicals, time and specially the laborious calibrating standard solutions preparation task of routine laboratories. Taking in account its analytical performance, the proposed cell promises to be an important tool in analytical chemistry with a great competition potential as compared to the other ones proposed in the literature.

Antiallodynic effects of acupuncture in neuropathic rats.

Peripheral nerve injury often results in abnormal neuropathic pain such as allodynia or hyperalgesia. Acupuncture, a traditional Oriental medicine, has been used to relieve pain and related symptoms. However, the efficiency of acupuncture in relieving neuropathic pain is not clear. The aim of this study was to investigate the anti-allodynic effects of acupuncture through behavioral and electrophysiological examinations. Male Sprague-Dawley rats were subjected to neuropathic surgery consisting of a tight ligation and transection of the left tibial and sural nerves, under pentobarbital anesthesia. The acupuncture experiment consisted of four different groups, one treated at each of three different acupoints (Zusanli (ST36), Yinlingquan (SP9), and a sham-acupoint) and a control group. Behavioral tests for mechanical allodynia and cold allodynia were performed for up to two weeks postoperatively. Extracellular electrophysiological recordings were made from the dorsal roots using platinum wire electrodes. Mechanical and cold allodynia were significantly reduced after acupuncture treatment at the Zusanli and Yinlingquan acupoints, respectively. Electrophysiological neural responses to von Frey and acetone tests were also reduced after acupuncture at the same two acupoints. These results suggest that acupuncture may be beneficial in relieving neuropathic pain.

Production Of Acetic Acid From Ethanol By Electrolysis (Electrosynthesis)

Production of acetic acid from ethanol by electrolysis (electrosynthesis) in alkaline (0.008 M KOH) and acidic (0.08 M HClO4) mediums has been carried out using platinum wire electrode. Besides that, the electrochemical study by cyclic voltammetry (CV) in different scan rates and electrolyte (alkaline and acidic mediums) also had been done. The study shows that the oxidation potential of ethanol ranges from 600-1065 mV in 0.008 M KOH and 700-1125 mV in 0.08 M HClO4. The electrooxidation products were analyzed using the High Performance Liquid Chromatography (HPLC). Keywords: Ethanol, acetic acid, electrolysis, electrosynthesis.

A Flow-Injection Biamperometric Method for Determination of Pantoprazole in Pharmaceutical Tablets

A flow-injection biamperometric method for determination of pantoprazole (PTZ) in pharmaceutical tablets is reported for the first time. The reversible redox couples Fe3+/Fe2+, Fe(CN)6(3-)/Fe(CN)6(4-), Ce4+/Ce3+, VO3(-)NO2+, and I2/I- were tested as indicating redox systems for biamperometric determination of PTZ in a flow-injection assembly with optimized flow parameters. The best results were obtained using V03(-)NO2+, which showed to be a selective and sensitive biamperometric indicating system for PTZ even in the presence of excipients and antioxidants that typically are found in drugs. The analytical graph was linear (r = 0.99945) in the range from 10 to 100 mg/L using 25 mmol/L VO3(-) as the reagent and water as the carrier stream and applying 100 mV between the 2 platinum wire electrodes. The limits of detection and quantitation were 200 and 667 microg/L, respectively, with a sensibility of calibration of 22.6 mV/mg/L. The proposed method was successfully applied to determine PTZ in commercial pharmaceutical tablets with a mean relative error of 1.60% (n = 5) and mean relative standard deviation of 3.10%. Recoveries close to 100% showed good agreement between the expected amount of PTZ in tablets (40 mg) and the results found by the application of the proposed method and demonstrated that the formulations used in the tablet compositions do not interfere in the PTZ analysis. The system had good stability, with a relative standard deviation of 3.80% for 9 sequential injections of a 60 mg/L PTZ solution. A sampling rate of about 100 samples/h was obtained.

Micro Electrochemical Machining of 3D Micro Structure Using Dilute Sulfuric Acid

Micro electrochemical machining (ECM) using ultra short pulses with tens of nanosecond duration is presented. 0.1 M sulfuric acid was used as electrolyte and 3D micro structures were machined on stainless steel. To prevent taper, a disk-type electrode was introduced. Using the disk-type electrode, taper could be eliminated. To improve productivity, multiple electrodes were applied and multiple structures were machined simultaneously. Since the wear of tool electrode is negligible in ECM, micro wire can be used as tool electrode. Using a platinum wire electrode with 10 urn diameter, various 3D features were machined on stainless steel plate.

Investigation of Electrolyte Stability Using Amperometric Sensors: Implications Concerning Electrode Polarization Measurements

Amperometric sensors with yttria-stabilized zirconia (YSZ) discs and YSZ cylinders were made with platinum electrodes applied on the YSZ disc, which served as working (inside) and counter (outside) electrodes, and a platinum wire electrode positioned along the circumference of the disc. Two sets of platinum electrodes were applied on the YSZ cylinder, one inside and the other outside. The YSZ cylinder was attached to the YSZ disc using a sealing glass. A YSZ disc with a tiny diffusion hole was glass-sealed on the other end of the YSZ cylinder. The amperometric sensor was tested at 800°C in air over an applied DC voltage range from zero to 2.5 V. The measured current over a voltage range from ∼0.4 to ∼1.6 V exhibited a plateau. For applied voltage ≥ 1.7 V, the measured current increased, with a rapid increase for applied voltage ≥1.9 V. This rapid rise is consistent with the development of nonstoichiometry or the occurrence of YSZ electrolyte decomposition. The voltage between the reference and the working electrodes was measured. Based on this information, the cathodic activity of the platinum working electrode was estimated. Implications concerning the use of the three electrode system for the study of electrode polarization are discussed.

鉄／白金系電極対を用いた養豚廃液の脱窒・脱リン処理

This research showed that the addition of KCI to piggery wastewater and the application of electrolytic treatment enables the removal of nitrogen together with phosphorus from that wastewater, which is something that previous biological treatment methods were unable to accomplish. It also showed that the addition of an aerobic treatment method employing and activated sludge as a first step prior to electrolytic treatment results in a more efficient system for the removal of nitrogen and phosphorus from piggery wastewater than electrolytic treatment alone. This research showed clearly that (1) polarity switching removes scale that forms on the iron electrode, making nitrate reduction also possible with piggery wastewater, (2) it is difficult to generate hypochlorous acid with the platinum-wire electrode for nitrogen removal even when using polarity switching due to the formation of stubborn scale, (3) electrolysis of piggery wastewater using polarity switching can reduce the amount of nitrogen and phosphorus in the wastewater to virtually zero if the frequency of the switching is optimized, and (4) the amount of electric power used to remove nitrogen and phosphorus from piggery wastewater can be reduced significantly by conducting electrolysis after biological treatment rather than just electrolysis alone.

Electrodynamic smooth muscle sphincter

Many authors have suggested that the activity of the enteric inhibitory nerves is important in regulating normal gastrointestinal motility and inducing smooth muscle relaxation. Hitherto, no experimental or clinical models exist that transfer these physiological aspects to creating an autologous artificial sphincter for the treatment of major incontinence. Therefore, this study was performed to determine the contractile and relaxant capacity of gastrointestinal muscle types and to investigate the efficiency of a novel smooth muscle sphincter, based on the non-adrenergic, non-cholinergic (NANC) receptive relaxation under electrical field stimulation (EFS). For the first step, the isometric tension from isolated circular porcine fundus and colon muscle strips was recorded during pharmacological stimulation (TTX, L-NNA and atropine) and EFS. As a result, a continent electrodynamic smooth muscle sphincter (ESMS) was created by wrapping a fundus muscle flap around an isolated segment of porcine distal colon. The EFS of the free nerve fibers of the flap was realized using a circular platinum wire electrode. Parameters such as threshold of continence, intra/preluminal pressure and fluid passage were analyzed in a newly designed in vitro stoma simulator. Electrical field stimulation produced a maximal and voltage-dependent fundus relaxation to --12.4 mN/mm(2) (frequency of 40 Hz, pulse duration, train duration and voltage of 5 ms, 1 s and 60 mA respectively), which were abolished by N-nitro-L -arginine (L-NNA; 10(-4) M) in a dose-dependent manner, confirming that relaxant responses were mediated by NANC nerves. The results of eight ESMS showed that circular electrical stimulation of the muscle flap caused muscle relaxation with a concomitant and effective reduction in the occlusion pressure. The NANC-induced relaxation mechanism of porcine fundus preparations could be transferred to an efficient smooth muscle sphincter with a high threshold of continence and electrically controlled defecation.

Direct stimulation of optic nerve by electrodes implanted in optic disc of rabbit eyes.

To determine whether wire microelectrodes implanted in the optic disc can be used to elicit cortical potentials. Two or four platinum wire electrodes of two types, viz., the cut-end type and the exposed-tip type, were inserted through the vitreous and fixed in the optic disc of 16 rabbit eyes. Electrically evoked potentials (EEPs) were recorded after bipolar electrical stimulation with the two wire electrodes and by different combinations of the four-electrode system. The optic discs were examined histologically after the experiment. The wire electrodes were successfully implanted and fixed into different positions of the optic disc without serious complications in all 16 eyes. EEPs could be elicited after bipolar electrical stimulation of the optic nerve using either the two-electrode system or different pairs of the four-electrode system. Threshold charge densities to elicit EEPs were 0.32-0.64 mC/cm(2) in eyes using the cut-end type of electrodes and 0.93-6.21 muC/cm(2) in eyes using the exposed-tip type. The amplitude of the EEPs increased with increasing electrical stimulus intensities. Histological evaluation revealed limited damage to the neural tissue adjacent to the electrode track. The visual cortex can be activated by direct microelectrical stimulation of the optic nerve. The acute implantation of the wire microelectrodes into the optic disc by a transvitreal approach is feasible and results in only limited damage to the optic nerve.

Vacuum electrolysis reactor technique for quantitation of 13-carbon isotope enrichment at the C1-position of formic acid and acetic acid.

A specialized vacuum electrolysis reactor was designed, constructed, and utilized for 13-carbon isotope analysis of formic acid-13C and acetic acid-13C, each highly enriched at the C1-position. This reusable reactor was equipped with two platinum wire electrodes, miniature stir bar, and sidearm reaction chamber. The associated technique developed for 13-carbon isotope analysis is based upon electrolytic generation of carbon dioxide into the preevacuated reactor followed by gas inlet mass spectrometry. It proved practical to degas and electrolyze 95% formic acid (without added electrolyte) due to adequate ionic conductivity. Formic acid-13C (nominally 99 at. % 13C) was measured by electrolytic CO2 generation to be 98.9 at. % 13C. To analyze various 13C-isotopic permutations of acetic acid, lithium and acid were separately added to reactor compartments, vacuum degassed, and stirred to produce an acidic solution. Thus, acetic acid-1-13C that was nominally 99 at. % 13C1 was determined by vacuum electrolysis to be 98.9 at. % 13C1. Further, acetic acid-2-13C that was isotope depleted at the C1-position (and known to be 99 at. % 13C at C2) gave 0.8 at. % 13C by mass spectrometry.

A flow injection method for biamperometric determination of dipyrone in pharmaceuticals

A flow-injection method for determination of dipyrone (novalgin, metamizol) in pharmaceutical tablets with biamperometric detection is described. Flow-parameters such as flow rate, coil length and sample injection volume were optimized. The calibration graph was linear ( r=0.9997) within the range of 10–50 mg l −1 in a 1-mmol l −1 HCl carrier solution for an applied potential of 100 mV between the two platinum wire electrodes. Two indicating redox systems were studied, namely Fe(III)/Fe(II) and I 2/I − . The former proved to be well suited as a selective and sensitive biamperometric indicating system for dipyrone in the presence of ingredients commonly accompanying the drug. The developed method was successfully applied to the determination of dipyrone in several commercial pharmaceutical preparations. The sampling rate was 71 samples per hour with a rsd of 1.6% (eight injections of a 14-mg l −1 dipyrone solution). Recoveries close to 100% demonstrated the reliability of the proposed method.

A flow injection method for biamperometric determination of dipyrone in pharmaceuticals

A flow-injection method for determination of dipyrone (novalgin, metamizol) in pharmaceutical tablets with biamperometric detection is described. Flow-parameters such as flow rate, coil length and sample injection volume were optimized. The calibration graph was linear ( r =0.9997) within the range of 10–50 mg l −1 in a 1-mmol l −1 HCl carrier solution for an applied potential of 100 mV between the two platinum wire electrodes. Two indicating redox systems were studied, namely Fe(III)/Fe(II) and I 2 /I − . The former proved to be well suited as a selective and sensitive biamperometric indicating system for dipyrone in the presence of ingredients commonly accompanying the drug. The developed method was successfully applied to the determination of dipyrone in several commercial pharmaceutical preparations. The sampling rate was 71 samples per hour with a rsd of 1.6% (eight injections of a 14-mg l −1 dipyrone solution). Recoveries close to 100% demonstrated the reliability of the proposed method.

Coated wire silver-ion selective electrode based on a N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene.

A novel membrane coated platinum-wire electrode (MCPWE) based on N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene (BTMD) for highly selective determination of Ag+ ion has been developed. The influences of membrane composition and pH on the potentiometric responses of electrode were investigated. The potentiometric responses are independent of the pH of the test solution in the range of 5.0 - 9.0. The electrode shows a linear response for Ag+ ion over the concentration range of 1.0 x 10(-60 to 1.0 x 10(-1) M with a lower detection limit of 6.0 x 10(-7) M. The electrode possesses a Nernstian slope of 59.7 mV decade(-1) and a fast response time of < or = 17 s and can be used for at least 2 months without any observable deviation. The proposed electrode displayed very good selectivity for Ag+ ion with respect to NH4+ and alkali, alkaline earth and some common transition metal ions. The practical utility of the electrode has been demonstrated by its use as the indicator electrode in the potentiometric titration of an AgNO3 solution with a NaI solution and in determination of the silver content of a developed radiological film.