Showing papers on "Reference electrode published in 2001"

Lead Phthalocyanine as a Selective Carrier for Preparation of a Cysteine-Selective Electrode

Abstract: A novel cysteine-selective electrode based on lead phthalocyanine (PbPc) as ionophore is described. The electrode was prepared by incorporating PbPc into a plasticized poly(vinyl chloride) (PVC) membrane, which was directly coated on the surface of a graphite electrode. This electrode shows high selectivity for the response to cysteine, as compared with many common inorganic anions, salicylate, and other kinds of amino acids. The influence of membrane composition, pH, and the effect of lipophilic cationic and anionic additives on the response characteristics of the electrode were investigated. The resulting sensor demonstrates nernstian response over a wide linear range of cysteine concentration (1 × 10-6 to 5 × 10-2 M). The electrode has a fast response time, micromolar detection limit (∼1 × 10-6 M), and good long-term stability (more than 1 month). The prepared electrode was used for determination of cysteine in a synthetic human serum sample, and very good recovery results were obtained over a wide con...

An Asymmetric Hybrid Nonaqueous Energy Storage Cell

Abstract: A nonaqueous asymmetric electrochemical cell technology is presented where the positive electrode stores charge through a reversible nonfaradaic or pseudocapacitive reaction of anions on the surface of an activated carbon positive electrode. The negative electrode is a crystalline intercalation compound which supports the fast reversible intercalation of lithium ions. Using a positive electrode material of activated carbon and newly developed negative electrode material of nanostructured Li 4 Ti 5 O 12 we obtain a cell which exhibits a sloping voltage profile from 3 to 1.5 V, 90% capacity utilization at 10C charge/discharge rates, and 10-15% capacity loss after 5000 cycles. Electrolyte oxidation on the activated carbon positive electrode was characterized in a Li metal asymmetric hybrid cell by cyclic voltammetry. Oxidation during the anodic scan was found to decrease significantly after surface passivation at high voltage and elevated temperatures. We also introduce the asymmetric hybrid technology in a bonded flat plate plastic cell configuration where packaged energy densities were calculated to be in excess of 20 Wh/kg. In addition, a practical method for three-electrode analysis of Li cells by use of a Ag quasi-reference electrode wire is discussed.

Multi-electrode catheter, system and method

Abstract: A system for detecting electrode-tissue contact comprises a multi-electrode catheter having a location sensor and a plurality of contact electrodes. The catheter preferably further comprises a reference electrode that is preferably protected from making contact with tissue. The system further comprises a signal generator to transmit test signals to each of the contact electrodes and to the reference electrode. Tissue contact is detected by comparing the signals across the tip electrode to a return electrode versus the signal across the reference electrode to a return electrode. Ablation energy may be delivered to the contact electrodes if contact of the electrode with tissue is detected.

System and method for detecting electrode-tissue contact

Abstract: A system for detecting electrode-tissue contact comprises a catheter having a location sensor and a distal tip electrode. The catheter preferably further comprises a reference electrode that is preferably protected from making contact with tissue. The system further comprises a signal generator to transmit test signals to the distal tip and reference electrodes. Tissue contact is detected by comparing the signals across the tip electrode to a return electrode versus the signal across the reference electrode to a return electrode. Ablation energy may be delivered to the distal tip electrode if contact of the electrode with tissue is detected.

A pH Electrode Based on Melt-Oxidized Iridium Oxide

Abstract: Fabrication and characterization of a novel potentiometric pH electrode based on melt-oxidized iridium oxide film is presented. The oxide film produced in a lithium carbonate melt has the composition of and shows high chemical stability. The electrode based on this oxide film exhibits very promising pH sensing performance, with an ideal Nernstian response in the tested pH range of 1 to 13. The potential response is fast, with a 90% response time obtained in less than 1 s for all pH changes. The open-circuit potential of the electrode is almost drift-free, with an average variation over time in a pH 6.6 solution as small as 0.1 mV/day. Furthermore, the potential/pH slopes and the apparent standard electrode potentials show excellent agreement among electrodes from the same batch. A comparison is made of the present electrode and those reported in the literature with respect to fabrication method and pH sensing characteristics. © 2001 The Electrochemical Society. All rights reserved.

Microchip reservoir devices and facilitated corrosion of electrodes

Abstract: Methods and devices are provided for enhancing corrosion of an electrode in a biocompatible fluid. The method comprises (1) placing a primary electrode and a counter electrode in an electroconductive biocompatible fluid to form an electrochemical cell; and (2) applying a time-varying potential, through the electrochemical cell, to the primary electrode. In a preferred embodiment, the primary electrode is metal and comprises a reservoir cap of a microchip device for the release of molecules or exposure of device reservoir contents. The potential preferably is characterized by a waveform having a maximum potential effectively anodic to meet or exceed the corrosion potential of the primary electrode. Also, the minimum potential preferably is effectively cathodic to be below the value where re-deposition of metal ions on the metal electrode can substantially occur, thereby corroding the metal electrode.

Investigation of the electrochemical windows of aprotic alkali metal (Li, Na, K) salt solutions

Abstract: This work is a comparative study of the electrochemical windows and the basic processes on gold electrodes in LiClO 4 , NaClO 4 , and KClO 4 solutions in propylene carbonate (PC). The analytical tools included cyclic voltammetry, electrochemical quartz crystal microbalance, surface-sensitive Fourier transform infrared spectroscopy (ex situ, external reflectance mode), and X-ray photoelectron spectroscopy. The apparent electrochemical windows of these systems are anodically limited at potentials above 1.3 V (vs. Ag pseudoreference electrode corresponding to 4.3 vs. Li/Li 1 ) due to solvent oxidation. The apparent cathodic side is limited due to the reversible bulk active metal deposition occurring at approximately -3 and < -2.7 V vs Ag pseudoreference electrode for Li and Na, respectively. In the case of the potassium salt solution, the electrochemical window is limited by a pronounced cathodic process below -2 V (vs Ag reference electrode), which is attributed to irreversible reduction of solution species. Irreversible potassium deposition occurs at potentials below - 2.5 V. This process cannot be separated from the reduction processes of the solution starting below -2 V. The study revealed that irreversible trace O 2 , trace H 2 O. and PC reduction form passivating surface films on these electrodes, These films act as a solid electrolyte interphase, i.e., they allow transport of the alkali metal ions through them. The study also found that the major constituent in the surface films is the PC reduction product CH 3 CH(OCO 2 M)CH 2 OCO 2 M. In general, the surface films formed on the noble metal electrodes in the Li and K salt solutions are more stable than those formed in the Na salt solutions, because the sodium oxides, hydroxide, and carbonates thus formed are more soluble in PC than the corresponding Li and K compounds.

Development of Reliable Three-Electrode Impedance Measurements in Plastic Li-Ion Batteries

Abstract: AC impedance experiments have been performed on three-electrode plastic LiCoO 2 /graphite batteries using a thin reference electrode. Various shapes, positions, and types of reference electrodes have been tested to select the most reliable and accurate configuration, Once biphasic lithium insertion materials, such as Li 4 Ti 5 O 12 , were identified as the optimum material for the reference electrode, the evolution of the Nyquist plots for each electrode of the battery was followed as a function of the cycle number or storage time. An analysis of the impedance diagrams for each electrode allowed us to determine the interface responsible for the capacity loss during cycling or storage in plastic Li-ion cells.

Rapid response glucose sensor

Abstract: A disposable electrochemical sensor for the detection of an analyte such as glucose in a liquid sample is formed with a working electrode and a reference electrode disposed within a sample-receiving cavity, and a reagent layer disposed within the sample-receiving cavity and over the working electrode. The reagent layer contains at least an enzyme for producing an electrochemical signal in the presence of the analyte. The sample-receiving cavity has a volume of less than 1.5 νl, and such that the sensor provides a measurement which correlates with the amount of analyte in a period of 10 seconds or less. The sensor is used in combination with a meter for detection of the analyte in a liquid sample. A suitable meter has a timing circuit for controlling the measurement of current indicative of analyte in the sample following detection of sample application to a test strip inserted in the meter. This timing circuit causes the measurement of current to occur at a time 15 seconds or less after the detection of sample application.

Device and method for determining the concentration of a substrate

Abstract: A method for determining the concentration of a substrate in a sample solution using an electrode system comprising a working electrode and a counter electrode, both being formed on an electrically insulating base plate, and a reaction layer which contains at least an oxidoreductase and an electron mediator and is formed on the electrode system to electrochemically measure a reduced amount of the electron mediator resulting from enzyme reaction in the reaction layer, wherein a third electrode is formed as an interfering substance detecting electrode somewhere apart from the reaction layer to detect supply of the sample solution on the basis of an electrical change between the counter electrode and the third electrode. A current flowing between the counter electrode and the third electrode is measured which is taken as a positive error. Subsequently, voltage application between the counter electrode and the third electrode is released and a voltage for oxidizing the reduced form electron mediator is applied between the working electrode and the counter electrode to measure a current flowing between the two electrodes. Influences of any interfering substance such as easy-to-oxidize substance are reduced, whereby a highly reliable value of substrate determination can be obtained.

Auto-compensating capacitive level sensor

Abstract: A capacitive sensor array is adapted to be disposed in a reservoir containing fluid or material along an axis of measurement of the fluid or material to determine the level of fluid or material contained within the reservoir. The sensor array includes a plurality of reference electrodes, wherein the capacitance of each of the electrodes varies in accordance both with the extent of the array's immersion in the fluid or material and the dielectric constant of the fluid or material. The plurality of reference electrodes preferably includes a lower electrode adapted to be immersed within the fluid or material in the reservoir and whose capacitance provides an estimate of the dielectric constant of the fluid or material contained within the reservoir. The reference electrodes also include an upper electrode adapted to be positioned above the fluid or material level that provides an estimate of the dielectric constant above the level of the fluid or material in the reservoir, and a middle electrode whose capacitance varies from a calibrated initial value to a value that is dependent on the level of and the dielectric constant of the fluid or material contained within the reservoir as determined from the capacitance of the lower electrode.

Electrochemical determination of dopamine using a poly(2-picolinic acid) modified glassy carbon electrode.

Abstract: A poly(2-picolinic acid) chemically modified electrode (CME) for the determination of dopamine (DA) by cyclic voltammetry is described. Compared with a bare glassy carbon electrode, the CME exhibits a 200 mV shift of the oxidation potential of DA in the cathodic direction and a marked enhancement of the current response. In pH 7.0 buffer solution, a linear calibration graph is obtained over the range from 2.5 ×10−7 to 1.0 × 10−5 mol dm−3 with a correlation coefficient of 0.998. The detection limit is 3.0 × 10−8 mol dm−3. The modified electrode eliminated efficiently the interference from ascorbic acid (AA) when present in a 150-fold concentration ratio. It also showed excellent stability and reproducibility.

Chemical sensing apparatus and methods

Abstract: In an improved amperometric gas sensor, the structure, composition, and electrode potential are adjusted so as to prevent or minimize any unwanted reactivity at the counter and/or reference electrode of any analyte or interfering component of the matrix that may cross over thereto. The sensor is preferably structured so that the product of the analyte reaction at a first working electrode can be reconverted to the original analyte at a counter electrode or at a second working electrode and then reacted again at the first working electrode, with such back-and-forth reactions repeating many times, so as to yield an amplification of the analyte signal.

Electrode Work Function and Absolute Potential Scale in Solid-State Electrochemistry

Abstract: A two-Kelvin-probe arrangement was used to measure, for the first time in situ, the work functions, Φ, of the gas-exposed surfaces of porous Pt, Au, and Ag working and reference electrodes exposed to O 2 -He, H 2 -He and O 2 -H 2 mixtures, and deposited on 8% Y 2 O 3 -stabilized ZrO 2 IYSZ) in a three-electrode solid electrolyte cell. It was found that at temperatures above 600 K the potential difference, U WR , between the working (W) and reference (R) electrode reflects the difference in the actual, spillover, and adsorption-modified work functions, Φ W and Φ R of the two electrodes cU WR = Φ W - Φ R [1] This equation, typically valid over 0.8-1 V wide U WR ranges, was found to hold for any combination of the Pt, Au, and Ag electrodes. It is consistent with the previously reported equation eΔU WR = ΔΦ W [2] which is also confirmed here, and allows for the definition of a natural absolute electrode potential U O (abs) in solid-state electrochemistry from U O2 (abs) = Φ/e [3] where Φ is the work function of the gas-exposed electrode surface of the metal (any metal) electrode in contact with the YSZ solid electrolyte. It expresses the energy of solvation of an electron from vacuum to the Fermi level of the solid electrolyte. The value U O2 0 (abs) = 5.14 ± 0.05 V was determined as the standard U O2 (abs) value at p O , = I bar and T = 673 K.

Electrochemical cell having multiplate electrodes with differing discharge rate regions

Abstract: An electrochemical cell comprising a medium rate electrode region intended to be discharged under a substantially constant drain and a high rate electrode region intended to be pulse discharged, is described. Both electrode regions share a common anode and are activated with the same electrolyte.

Electrochemical cell having an electrode with a carbonate additive in the electrode active mixture

Abstract: An electrochemical cell of either a primary or a secondary chemistry, is described. In either case, the cell has a negative electrode of lithium or of an anode material which is capable of intercalating and de-intercalating lithium coupled with a positive electrode of a cathode active material. A nitrite compound is mixed with either the anode material or the cathode active material prior to contact with its current collector. The resulting electrode couple is activated by a non-aqueous electrolyte. The electrolyte flows into and throughout the electrodes causing the nitrite compound to dissolve in the electrolyte. The nitrite solute is then able to contact the lithium to provide an electrically insulating and ionically conducting passivation layer thereon.

Gas component sensor for gas sulfur oxides

Abstract: The present invention is a gas component sensor comprising novel electrolyte compositions. The electrolyte compositions in bulk, sintered or thin film embodiments are capable of forming with different-metal sensing and reference electrodes a highly stable gas oxide sensors. The novel electrolyte composition changes electrochemical reactions at the sensing and reference electrodes and the overall reaction of the electrodes and electrolyte. The novel electrolyte compositions have: (1) excellent chemical stability and thermal compatibility as to the electrodes and a preferred ceramic substrate, (2) excellent chemical stability with the environment as to the reference and sensing electrodes, which need not be sealed against the atmosphere to be sensed, (3) effective adherence to the substrate and electrode metals.

Biological fluid analysis device

Abstract: A biological fluid analysis device (100) including a biosensor (50) comprising an electrochemical-enzymatic sensor including a working electrode (51) and a reference electrode (52), is disclosed.

High impedance electrode assembly

Abstract: A lead having an electrode assembly has a high impedance electrode. The high impedance electrode includes a partially insulated sleeve electrode or a wire filament. The high impedance electrode includes an exposed surface of less than 1.2 mm2. One or more eluting drugs are disposed adjacent to the high impedance electrode.