Showing papers on "Reference electrode published in 2008"

Electrochemical Impedance Spectroscopy

Abstract: Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate properties of materials and electrode reactions. This Primer provides a guide to the use of EIS with a comparison to other electrochemical techniques. The analysis of impedance data for reduction of ferricyanide in a KCl supporting electrolyte is used to demonstrate the error structure for impedance measurements, the use of measurement and process models, as well as the sensitivity of impedance to the evolution of electrode properties. This Primer provides guidelines for experimental design, discusses the relevance of accuracy contour plots to wiring and instrumentation selection, and emphasizes the importance of the Kramers-Kronig relations to data validation and analysis. Applications of EIS to battery performance, metal and alloy corrosion, and electrochemical biosensors are highlighted. Electrochemical impedance measurements depend on both the mechanism under investigation and extrinsic parameters, such as the electrode geometry. Experimental complications are discussed, including the influence of nonstationary behaviour at low frequencies and the need for reference electrodes. Finally, emerging trends in experimental and interpretation approaches are also described.

Design of an Electrochemical Cell Making Syngas ( CO + H2 ) from CO2 and H2O Reduction at Room Temperature

Abstract: An electrolysis-cell design for simultaneous electrochemical reduction of CO 2 and H 2 O to make syngas (CO + H 2 ) at room temperature (25°C) was developed, based on a technology very close to that of proton-exchange-membrane fuel cells (PEMFC), i.e., based on the use of gas-diffusion electrodes so as to achieve high current densities. While a configuration involving a proton-exchange membrane (Nafion) as electrolyte was shown to be unfavorable for CO 2 reduction, a modified configuration based on the insertion of a pH-buffer layer (aqueous KHCO 3 ) between the silver-based cathode catalyst layer and the Nafion membrane allows for a great enhancement of the cathode selectivity for CO 2 reduction to CO [ca. 30 mA/cm 2 at a potential of -1.7 to -1.75 V vs SCE (saturated-calomel reference electrode)]. A CO/H 2 ratio of 1/2, suitable for methanol synthesis, is obtained at a potential of ca. -2 V vs SCE and a total current density of ca. 80 mA/cm 2 . An issue that has been identified is the change in product selectivity upon long-term electrolysis. Results obtained with two other cell designs are also presented and compared.

Ion-Selective Electrodes Using Carbon Nanotubes as Ion-to-Electron Transducers

Abstract: This study developed a new type of all-solid-state ion-selective electrode based on a transducing layer of a network of single-walled carbon nanotubes. The extraordinary capacity of carbon nanotubes to promote electron transfer between heterogeneous phases made the presence of electroactive polymers or any other ion-to-electron-transfer promoter unnecessary. The new transducer layer was characterized by environmental scanning electron microscopy and electrochemical impedance spectroscopy. The stability of the electrical potential of the new solid-contact electrode was examined by performing current-reversal chronopotentiometry, and the influence of the interfacial water film was assessed by the potentiometric water layer test. The performance of the new electrode was evaluated by determining K+ with an ion-selective membrane that contained the well-known valinomycin ion carrier. The new electrode had a Nernstian slope (58.4 mV/decade), dynamic ranges of four logarithmic units, and selectivities and limits...

Electrochemical detection of trace amount of arsenic(III) at glassy carbon electrode modified with cobalt oxide nanoparticles

Abstract: Novel cobalt oxide nanoparticles based sensor for the detection of trace amount of As3+ ion in aqueous solution has been developed. Cyclic voltammetry at potential range −1.1 to 1.1 V from aqueous buffer solution (pH 7) containing CoCl2 produced a well-defined cobalt oxide (CoOx) nanoparticles deposited on the surface of glassy carbon electrode. The resulting electrode surfaces and its morphology were examined with both cyclic voltammetry and scanning electron microscope (SEM) techniques. The modified electrode shows excellent catalytic activity toward arsenic oxidation at wide pH range, 5–11. The response to As3+ on the modified electrode was examined using cyclic voltammetry and hydrodynamic amperometry. The amperometric detection of arsenic is carried out at 0.75 V versus Ag/AgCl reference electrode in phosphate buffer solution with pH 7. The detection limit (S/N = 3) was 11 nM with linearity up to 4 orders of magnitude and sensitivity of 111.3 nA/μM. The response time of the electrode to achieve 95% of the steady-state current is

Environmentally friendly disposable sensors with microfabricated on-chip planar bismuth electrode for in situ heavy metal ions measurement

Abstract: This paper presents an environmentally friendly disposable heavy metal ion sensor for in situ and online monitoring in the nature and physiological systems. The miniaturized sensor chip consists of a non-toxic microfabricated bismuth (Bi) working electrode that replaces the conventional mercury electrodes, an integrated Ag/AgCl reference electrode, a gold counter electrode, and microfluidic channels. In this work, the electrochemical behavior of the Bi working electrode was characterized in several non-deaerated buffer solutions using cyclic voltammetry. The detection and quantification of Pb (II) and Cd (II) were statically performed using anodic stripping voltammetry inside the microchannels, in the Pb (II) concentration range of 25–400 ppb (R2 = 0.991) with limit of detection of 8 ppb for 60 s deposition, and in the Cd (II) concentration range of 28–280 ppb (R2 = 0.986) with limit of detection of 9.3 ppb for 90 s deposition. Particularly, the applications of this sensor chip have been reported with the examples of in situ measurement of Cd (II) concentration in soil pore and ground water and online direct measurement of Cd (II) concentration in cell culture media in its native environment.

Polymer Brush-Modified Electrode with Switchable and Tunable Redox Activity for Bioelectronic Applications

Abstract: A new signal-responsive interface with switchable/tunable redox properties based on a pH-responding polymer brush was studied. Poly(4-vinyl pyridine), P4VP, functionalized with Os-complex redox units was grafted to an indium tin oxide (ITO) conductive support in the form of a polymer brush. The modified electrode surface was responsive to the changes of the pH value of the electrolyte solution: at acidic pH = 4.0 the redox-polymer film demonstrated the reversible electrochemical process, E° = 0.29 V (vs Ag/AgCl), while at neutral pH > 6, the polymer was not electrochemically active. The reversible transformation between the active and the inactive state originated from the structural changes of the polymer support. The protonation of the pyridine units of the polymer backbone at the acidic pH resulted in the swelling of the polymer brush allowing quasi-diffusional translocation of the flexible polymer chains, thus providing direct contact of the polymer-bound redox units and the conducting electrode suppo...

Capacitance Measurements in a Series of Room-Temperature Ionic Liquids at Glassy Carbon and Gold Electrode Interfaces

Abstract: An extensive study has been done for the first time on the structure of the electrical double layer (EDL) at polarized glassy carbon (GC) and gold (Au) electrode interfaces in a series of room-temperature ionic liquids (RTILs) via the measurement of capacitance-potential curves. The parabolic capacitance-potential curves similar to those observed in high-temperature inorganic molten salts were obtained at GC electrode in all of the RTILs studied. Potential of zero charge (PZC) at GC electrode in imidazolium-based RTILs depends significantly on the electrochemical pretreatment of the electrode surface: Electrochemical oxidation pretreatment generates the oxide surface on GC electrode, which results in a favorable adsorption of positively charged imidazolium cations on the electrode surface and in turn shifts the PZC to the positive direction of potential, whereas at the electrochemically reduced GC electrode, on which the adsorption of the imidazolium cations is less favorable, PZC shifts to the negative d...

Lithium rechargeable cell with reference electrode for state of health monitoring

Abstract: A battery management system includes one or more lithium ion cells in electrical connection, each said cell comprising: first and second working electrodes and one or more reference electrodes, each reference electrode electronically isolated from the working electrodes and having a separate tab or current collector exiting the cell and providing an additional terminal for electrical measurement; and a battery management system comprising a battery state-of-charge monitor, said monitor being operable for receiving information relating to the potential difference of the working electrodes and the potential of one or more of the working electrodes versus the reference electrode.

Nanostructured NiO for electrochemical capacitors: synthesis and electrochemical properties

Abstract: A single phase nanostructured nickel oxide (NiO) crystalline product was synthesized via a simple solvothermal synthesis protocol by using nitrate–citrate precursor having Ni(NO3)2 as starting material. The thermal decomposition of the as-formed gel precursor leading to the formation of crystalline NiO was monitored by TG analysis under ambient conditions. The as-prepared product was subjected to thermal treatment at 400 °C for 1 h in air, exhibited a single phase cubic structure as confirmed by XRD and the nanostructure of the product was characterized by FE-SEM and HR-TEM/SAED analysis. It is thus confirmed that the particle size of the product was found to be within 7–15 nm range. The rate-dependent cyclic voltammetry reveals the pseudocapacitive behavior of the product when employed as working electrode in a three-electrode electrochemical cell containing 1 M KOH aqueous electrolyte with platinum (pt) and saturated calomel electrode (SCE) as counter and reference electrodes, respectively, yielding a capacitance of ~200 F g-1.

System and method for determining the point of hydration and proper time to apply potential to a glucose sensor

Abstract: According to an embodiment of the invention, a method of determining hydration of a sensor having a plurality of electrodes is disclosed. In particular embodiments, the method couples a sensor electronics device to the sensor and measures the open circuit potential between at least two of the plurality of electrodes. Then, the open circuit potential measurement is compared to a predetermined value. In some embodiments, the plurality of electrodes includes a working electrode, a reference electrode, and a counter electrode. In still further embodiments, the open circuit potential between the working electrode and the reference electrode is measured. In other embodiments, the open circuit potential between the working electrode and the counter electrode is measured. In still other embodiments, the open circuit potential between the counter electrode and the reference electrode is measured.

Studies of Local Degradation Phenomena in Composite Cathodes for Lithium-Ion Batteries

Abstract: Diagnostic Evaluation of Detrimental Phenomena in 13 C-labeled Composite Cathodes for Li-ion Batteries Marie Kerlau, Marek Marcinek, Robert Kostecki a Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA Abstract C-carbon black substituted composite LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes were tested in model electrochemical cells to monitor qualitatively and quantitatively carbon additive(s) distribution changes within tested cells and establish possible links with other detrimental phenomena. Raman qualitative and semi-quantitative analysis of 13 C in the cell components was carried out to trace the possible carbon rearrangement/movement in the cell. Small amounts of cathode carbon additives were found trapped in the separator, at the surface of Li-foil anode, in the electrolyte. The structure of the carried away carbon particles was highly amorphous unlike the original 12 C graphite and 13 C carbon black additives. The role of the carbon additive, the mechanism of carbon retreat in composite cathodes and its correlation with the increase of the cathode interfacial charge-transfer impedance, which accounts for the observed cell power and capacity loss is investigated and discussed. Introduction High-power Li-ion cells with graphite anodes and LiNi 0.8 Co 0.2 O 2 or LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes that were cycled and stored at elevated temperatures display significant impedance rise and capacity fade [1,2]. Impedance measurements of the cell components carried out with a Li-Sn reference electrode indicated that the composite cathode is primarily responsible for the observed cell power loss at elevated temperatures [3,4]. Electrochemical testing of LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes and graphite anodes removed from model pouch-type lithium- ion cells, which were cycled at C/2 over different ranges of DOD and at different temperatures, clearly showed that the cell capacity fade and impedance rise were strongly dependent on temperature, cycling potential limits, and number of charge/discharge cycles [5]. X-ray diffraction spectroscopy measurements failed to detect any noticeable changes in the bulk structure of tested LiNi 0.8 Co 0.2 O 2 and LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes [1,5]. Possible causes of the increase in cathode impedance and irreversible charge/discharge capacity loss include the formation of an electronic and/or ionic barrier at the cathode surface [6,7,8]. This is consistent with our earlier studies [9,10], in which we demonstrated that the non-uniform kinetic behavior of the individual oxide particles was attributed to the degradation of the electronically conducting matrix in the composite cathode upon testing. Carbon additive rearrangement in portions of the tested LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes and/or thin film formation on the surfaces of carbon and oxide particles is closely linked with the observed isolation of oxide active material. Because the composite cathodes typically consists of an active material, two types of carbon additive, and a binder, suitable instrumental techniques must be applied to obtain lateral resolution comparable to the size and morphology of electrode surface features. In situ and ex situ application of non-invasive and non-destructive microscopies and spectroscopies, including Raman, fluorescence spectroscopy, SEM, and AFM to characterize physico-chemical properties of the electrode/electrolyte interface at nanometer resolution provide unique insight into the mechanism of specific chemical a and electrochemical processes that may be responsible for the electrode and cell degradation. The extraordinary potential of Raman micro-spectroscopy was demonstrated by in situ acquisition of space- and time-resolved spectra of positive and carbon negative electrodes in Li-ion cells [4,9,11,12,13,14], single oxide or graphite particle in the composite electrode [10,15,16,17] or single graphite or LiMn 2 O 4 particle electrodes This work presents an example of this methodology used in post-test analysis of interfacial phenomena on the It describes a composite LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes. detailed Raman microscopy study of 13 C-carbon black substituted composite LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes which were tested in model electrochemical cells to monitor qualitatively and quantitatively carbon additive(s) distribution changes within tested cells and establish possible links with other detrimental phenomena. The role of the carbon additive in composite cathodes, the mechanism of carbon retreat in composite cathodes and its correlation with the increase of the cathode interfacial charge-transfer impedance, which accounts for the observed cell power and capacity loss is investigated and discussed. Experimental 99% pure 13 C soft carbon CLM-402 from Cambridge Isotope Laboratories, which emulates physico-chemical properties of acetylene black, was used to manufacture 13 C- enriched composite LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes. Prior to the electrode manufacturing the 13 C carbon powder was ball-milled for 6 hours to reduce the particle size and obtain powder morphology similar to a standard carbon black additive. The composite electrodes consisted of 84% of LiNi 0.8 Co 0.15 Al 0.05 O 2 , 4% 12 C graphite, 4% 13 C carbon black, and 4% PVDF binder. Freshly prepared electrodes were dried in an He-filled glove box antechamber vacuum oven at 120oC, 42 hours. After heat-treatment the electrodes were transferred immediately to a He-filled glove box. All the following tests and measurements were conducted in the same glove box i.e., the electrodes and cells were never exposed to the air. r_kostecki@lbl.gov

Electron transfer through molecules and assemblies at electrode surfaces.

Abstract: Chemically modified electrodes were first introduced to the scope of electrochemistry by Anson, Bard, Murray, Saveant, and others about three decades ago in an effort to provide selectivity to highly sensitive electrode surfaces. While electrochemical techniques had high sensitivity because of the availability of accurate current measurement techniques, the lack of any differential selectivity of electrodes for analytes over impurities complicated the analysis. A functionalized electrode however would and does give the opportunity to chemically modify the surface of an electrode, providing the means to make the surface much more chemically selective. In addition to the numerous contributions to the field of electrochemical biosensors (for example, in the field of electrochemical biosensing, the lock and key enzyme substrate relationship can be exploited by immobilizing an enzyme on the electrode surface to analyze a solution of the substrate even in the presence of impurities; major contributions in this field are presented in a recent review by Bakker and Qin), chemically modified electrodes opened up the possibility for electrochemists to be able to investigate electron transfer on electrode surfaces while side-stepping most of the mass transport problems (note that counterion diffusion and solvent rearrangement still have to take place). Once reliable techniques for modifying electrode surfaces were established, molecules with well positioned redox centers and with tunable redox potentials could be placed on electrode surfaces to be able to systematically vary and observe the effects of important parameters such as distance, and chemical environment, among others. For example, the work by Chidsey et. al describes long-range electron transfer making use of exquisite control over the placement of the redox active site relative to the electrode surface. In more recent work, Amatore et. al investigated the effects of chemical environment on electron transfer by making mixed monolayers of electroinactive alkanes with compounds with well-defined redox centers. Molecular electronics can also be dated to similar times as chemically modified electrodes. Though it has been argued that molecular electronics dates back to the days of Mulliken and his proposals of charge transfer salts, the general consensus is that the popularization of the field dates back to the cornerstone paper by Aviram and Ratner in 1974 in which they proposed a molecular structure that should act as a diode when electron transport was measured across it. They designed the molecule based on a donor-bridgeacceptor model and calculated the electron transport with a semi empirical INDO approach. A number of experimental methods have been proposed to measure conductance through molecules and molecular assemblies since then including scanned probe techniques, mercury drop electrodes, electrical or mechanical break junctions, sandwich electrodes, and others. The common concept in all of these methods is to be able to “wire” the molecules between two electrodes (generally metallic, though semiconductors are also employed in some rare cases) and measure current as a function of an applied potential. A third electrode (gate) coupled through an electronically insulating dielectric is generally used to modulate the electrostatics around the active material, changing, in a deliberate fashion, its electronic energy levels. If the device is immersed in an electrolyte solution, the gate electrode takes on the role of the more traditional reference electrode with identical function. In nearly all efforts related to measuring conductance across molecules and molecular assemblies, the experiments have been based on making a chemically modified electrode to establish the first electrode-molecule contact. The second electrode is then either brought into contact temporarily (scanned probe) or permanently (crossbar, sandwich) or the single electrode is broken into two (break junctions) to measure those molecules that are statistically trapped across the junction. The over three decades experience in modifying electrodes’ electronic and physical properties puts electrochemistry at center stage for the molecular electronics efforts along with nanofabrication. The experimental efforts on molecular electronics were pushed forward by two separate events. First, the development of scanning tunneling microscopy (STM) by Binnig and Rohrer in 1981, and second, the ever shrinking micro* To whom correspondence should be addressed. E-mail: hda1@cornell.edu. Chem. Rev. 2008, 108, 2721–2736 2721

Platinum as a Reference Electrode in Electrochemical Measurements

Abstract: The usefulness of platinum as an electrochemical reference electrode was investigated. Well known redox systems with one-electron single or multiple redox waves, and two-electron multiple redox waves were used as test regimes. The effects on electrode performance of variables such as the solvent, the physical state of the electrolyte and its temperature were investigated. Cyclic voltammetry (CV) was used to derive kinetic parameters for comparison with corresponding measurements on traditional reference electrodes. The results indicate that Pt can be used as a reference electrode under specific conditions in which traditional reference electrodes cannot be used.

The Influence of Electrode Porosity on Diffusional Cyclic Voltammetry

Abstract: A simple generic model to predict the influence of electrode porosity on the cyclic voltammetric response of an electrode is presented. The conditions under which deviation from the behavior of a perfectly flat, planar electrode can be expected are predicted. The scope for misinterpretation when conventional flat electrode theory is applied to porous electrodes is highlighted, especially in respect to the extraction of electrode kinetic parameters and the influence of ‘electrocatalysis’.

Electrochemical Synthesis of Zn−Al Layered Double Hydroxide (LDH) Films

Abstract: A new electrodeposition condition to produce Zn-Al LDH films was developed using nitrate solutions containing Zn (2+) and Al (3+) ions. Deposition was achieved by reducing nitrate ions to generate hydroxide ions on the working electrode. This elevates the local pH on the working electrode, resulting in precipitation of Zn-Al LDH films. The effect of deposition potential, pH of the plating solution, and the Zn (2+) to Al (3+) ratio in the plating solution on the purity and crystallinity of the LDH films deposited was systematically studied using X-ray diffraction and energy dispersive spectroscopy (EDS). The optimum deposition potential to deposit pure and well-ordered Zn-Al LDH films was E = -1.65V versus a Ag/AgCl in 4 M KCl reference electrode at room temperature using a solution containing 12.5 mM Zn(NO 3) 2.6H 2O and 7.5 mM Al(NO 3) 3.9H 2O with pH adjusted to 3.8. The resulting film contained 39 atomic %Al (3+) ions replacing Zn (2+) ions, leading to a composition of Zn 0.61Al 0.39(OH) 2(NO 3) 0.39. xH 2O. Increasing or decreasing the aluminum concentration in the plating solution resulted in the formation of aluminum- or zinc-containing impurities, respectively, instead of varying aluminum content incorporated into the LDH phase. Choosing an optimum deposition potential was important to obtain LDH as a pure phase in the film. When the potential more negative than the optimum potential is used, zinc metal or zinc hydroxide was deposited as a side product, whereas making the potential less negative than the optimum potential resulted in the formation of zinc oxide as the major phase. The pH condition of the plating solution was also critical, as increasing pH destabilizes the formation of the LDH phase while decreasing pH promoted deposition of other impurities.

Electrochemical charge transfer at a metallic electrode: a simulation study.

Abstract: The calculation of the Marcus free energy curves for electron transfer events between a redox species and a metallic electrode in an atomistic simulation designed to model the electrochemical interface with an ionic liquid is described. The calculation is performed on a system comprising a molten salt mixture confined between model metallic electrodes [Reed et al., J. Chem. Phys. 126, 084704 (2007)] which are maintained at a constant electrical potential. The calculation therefore includes a self-consistent description of the screening of the electrode potential by the liquid and the polarization of the electrode by the ions (image charge effects). The purpose of the study was to examine how the Marcus curves depend on the applied potential and on the distance of the redox species from an electrode. The pronounced oscillations in the mean electrical potential seen in molten salt systems in the "double-layer" region are not reflected in the reaction free energy for the electron transfer event. The reorganization energy depends markedly on the distance of the redox ion from the electrode surface because of image charge effects.

Electrocatalytic oxidation of aspirin and acetaminophen on a cobalt hydroxide nanoparticles modified glassy carbon electrode

Abstract: The electrocatalytic oxidation of aspirin and acetaminophen on nanoparticles of cobalt hydroxide electrodeposited on the surface of a glassy carbon electrode in alkaline solution was investigated. The process of oxidation and the kinetics have been investigated using cyclic voltammetry, chronoamperometry, and steady-state polarization measurements. Voltammetric studies have indicated that in the presence of drugs, the anodic peak current of low valence cobalt species increases, followed by a decrease in the corresponding cathodic current. This indicates that drugs are oxidized on the redox mediator which is immobilized on the electrode surface via an electrocatalytic mechanism. With the use of Laviron’s equation, the values of anodic and cathodic electron-transfer coefficients and charge-transfer rate constant for the immobilized redox species were determined as α s,a = 0.72, α s,c = 0.30, and k s = 0.22 s−1. The rate constant, the electron transfer coefficient, and the diffusion coefficient involved in the electrocatalytic oxidation of drugs were reported. It was shown that by using the modified electrode, aspirin and acetaminophen can be determined by amperometric technique with detection limits of 1.88 × 10−6 and 1.83 × 10−6 M, respectively. By analyzing the content of acetaminophen and aspirin in bulk forms using chronoamperometric and amperometric techniques, the analytical utility of the modified electrode was achieved. The method was also proven to be valid for analyzing these drugs in urine samples.

The superior performance of the electrochemically grown ZnO thin films as methane sensor

Abstract: Pd–Ag/ZnO/Zn and Rh/ZnO/Zn MIM (metal–insulator–metal) gas sensors were fabricated using nanoporous ZnO thin films, obtained by an electrochemical deposition method in the absence and presence of UV light. A high-purity Zn anode, a Pt cathode, a calomel reference electrode and a 0.3-M oxalic acid electrolyte were used for deposition. Pd–Ag (26%) and Rh were used separately as the catalytic metal electrodes to fabricate the two different types of MIM configurations. A gas response of the order of 3.85 ± 2, a response time of 5 ± 0.5 s and a recovery time of 16 ± 0.5 s were obtained with the Pd–Ag contact, while the Rh contact showed a response of the order of 4.82 ± 2, a response time of 24 ± 0.5 s and a recovery time of 72 ± 0.5 s, at the optimum temperature of 220 °C, which is the lowest temperature so far reported for metal oxide sensors to sense 1% methane in a N 2 carrier gas. The undoped zinc oxide thin films grown by UV-assisted electrochemical anodization of high-purity Zn demonstrated a better performance for methane sensing. The experiments were repeated in synthetic air and a somewhat reduced performance was observed. The selectivity in the presence of hydrogen and the stability of the sensors were studied.

Nanoporous organosilicas as preconcentration materials for the electrochemical detection of trinitrotoluene.

Abstract: We describe the use of nanoporous organosilicas for rapid preconcentration and extraction of trinitrotoluene (TNT) for electrochemical analysis and demonstrate the effect of template-directed molecular imprinting on TNT adsorption. The relative effects of the benzene (BENZ)- and diethylbenzene (DEB)-bridged organic−inorganic polymers, having narrow or broad pore size distributions, respectively, on electrochemical response and desorption behavior were examined. Sample volumes of 0.5−10 mL containing 5−1000 ppb TNT in a phosphate-buffered saline buffer were preconcentrated in-line before the detector using a microcolumn containing 10 mg of imprinted BENZ or DEB. Square-wave voltammetry was used to detect the first reduction peak of TNT in an electrochemical flow cell using a carbon working electrode and a Ag/AgCl reference electrode. Imprinted BENZ released TNT faster than imprinted DEB with considerably less peak tailing and displayed enhanced sensitivity and an improvement in the limit of detection (LOD)...

Electrocatalytic Determination of 6-Tioguanine at a p-Aminophenol Modified Carbon Paste Electrode

Abstract: A p-aminophenol modified carbon paste electrode (p-APMCPE) was constructed for determination of an anticancer drug 6-thioguanine (6-TG). The cyclic voltammogram showed that the electrocatalytic oxidation of 6-TG at the surface of p-APMCPE occurs at a potential about 840 mV less positive than at an unmodified electrode. Square-wave voltammetry results presented that the electrocatalytic oxidation peak currents of 6-TG in pH 9.0 had two linear dynamic ranges in the range of 0.2 to 8.0 and 8.0 to 350.0 μM 6-TG with a detection limit of 0.08 μM. The kinetic parameters such as electron transfer coefficient (α) and rate constant were determined for the chemical reaction between 6-TG and p-aminophenol. Finally, this method was evaluated for the determination of 6-TG in 6-thioguanine tablets and urine samples.