Response Time Of Electrode Research Articles

Electrochromic and photoconductive polymer nanoparticles

Abstract Electrochromic (EC) and photoconductive nanoparticles coated with a conducting polymer, poly(1,4-bis(2-[3′,4′-ethylenedioxy]thienyl)-2-methoxy-5-2‴-ethylethylhexyloxybenzene) (PBETH) were prepared. TiO 2 nanoparticles were employed as a nanotemplate for the preparation of conducting polymer capsules. The PBETH capsules showed blue to red transition by the applied potential showing electrochromic behavior. Electrochromic contrast, coloration efficiency and response time of the EC electrodes coated with PBETH/TiO 2 were significantly improved compared to the electrode coated with PBETH without TiO 2 . Having conductive polymer layer and photoactive TiO 2 particles, the polymer capsules showed photocurrent generation when exposed to a UV light.

Comparison of Polypyrrole-Conducting Polymer and Ag/AgCl Reference Electrodes Used for Ruthenium Dioxide pH Electrode

A laboratory-made conducting polymer reference electrode (CPRE) was developed using polypyrrole coated onto indium tin oxide by the electroplating technique and used as the miniaturized reference electrode (RE) for a ruthenium dioxide ion-selective electrode device in electrochemical hydrogen ion measurements. Ruthenium dioxide thin films were deposited by a radio frequency sputtering method, and the sensing characteristics of were measured with a CPRE and an Ag/AgCl RE. Subsequently, the selectivity coefficients (, , , , and ) of the ruthenium dioxide thin film with the CPRE were investigated. Furthermore, we also compared the sensing characteristics (such as: pH sensitivity, drift rate, hysteresis width, and response time) of the thin-film pH electrode with a commercial Ag/AgCl RE and the laboratory-made CPRE. The experimental results demonstrated that the sensing characteristics of the pH electrode measured with the laboratory-made CPRE are superior to the Ag/AgCl RE, and the size of the CPRE can be efficiently miniaturized compared to a commercial Ag/AgCl RE.

Development of a POA/DBS/GOx Biosensor for the Determination of Glucose

In the present work, a simple technique is described for constructing a poly(o-anisidine) (POA)-dodecylbenzene sulphonic acid (DBS)-glucose oxidase (GOx) (POA-DBS-GOx) electrode. The enzyme glucose oxidase (GOx) was immobilized by crosslinking via glutaraldehyde on the POA-DBS film. The POA-DBS films were synthesized electrochemically on platinum substrate. The synthesized films were characterized by using electrochemical technique, conductivity measurement, UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The conductivity of the polymer films was found to be about 7.61 × 10−2 S/cm. The crosslinking of enzyme and the porous morphology of the polymer film lead to good stability and good response time of the enzyme electrode. The stability and lifetime of the POA-DBS-GOx electrode have been studied. It shows very good stability and response for 3–4 weeks at 4°C. The results of this study reveal that a phosphate buffer gives better response than acetate buffer in amperometric measurements.

Impedance spectroscopy on porous materials: A general model and application to graphite electrodes of lithium-ion batteries

Electrochemical impedance spectroscopy (EIS) was applied to porous negative graphite electrodes for lithium-ion batteries in the EC:DMC, 1 M LiPF 6 electrolyte. The effect of porosity on the electrode response time was studied and a theoretical model was developed, based on free path of the current lines between subsequent reaction sites. The effect of porosity on the electrode response is evidenced by the impedance spectra in which the high frequency capacitive semicircle is distorted. Fresh electrodes (before the formation of the solid electrolyte interphase, SEI) and cycled electrodes have different shapes of the impedance spectra indicating a change of processes at the surface. In particular, the shape of the spectrum for a fresh electrode can be related to an adsorption process. Impedance spectra of fresh electrodes were fitted using a simple model that considers porosity and the assumed electrochemical processes, giving good agreement between model and data. A correlation was found between adsorption sites and irreversible charge capacity in the first cycle.

Naphthazarin modified carbon paste electrode for determination of copper(II)

A carbon paste electrode modified with naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) was fabricated as a copper(II) sensor. Voltammetric and potentiometric detections were investigated. Adsorptive stripping voltammetry offers better sensitivity but poorer repeatability than potentiometry. The applied potential and current passing in voltammetric detection cause irreversible electrode reactions and shortening of the lifetime of the electrode. Potentiometric determination in batch and flow injection using 3% (w/w) of naphthazarin in the paste exhibited linear response with supra-Nernstian slope to copper(II) over a wide concentration range of three orders of magnitude in 0.10 M ammonium acetate medium. The potentiometric detection limits were 1.5 × 10−6 and 3.0 × 10−5 M by batch and flow injection, respectively. The electrode shows a good selectivity for copper(II) over a wide variety of metal ions and was applied to the analysis of alloys. The electrode response time was 50 sec and it showed good reproducibility for at least 60 days.

Immobilization of GOD on Ppy–PVS Composite Film for Determination of Glucose: A Comparative Study of Phosphate and Acetate Buffers

The Polypyrrole-polyvinylsulphonate-glucose oxidase (Ppy–PVS–GOD) biosensor for determination of glucose has been described in the present investigation. The enzyme, glucose oxidase (GOD) was immobilized by crosslinking via glutaraldehyde on a polypyrrole–polyvinyl sulphonate (Ppy–PVS) composite film. The Ppy–PVS film was electrochemically synthesized on indium-tin-oxide (ITO)–coated glass plate. The synthesized composite films were characterized using galvanostatic electrochemical technique, electrical conductivity, UV-Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The crosslinking of enzyme and porous morphology of the polymer film leads to high enzyme loading and an increase in lifetime, stability, and fast response time of the enzyme electrode. Characterization of resulting amperometric biosensor for the estimation of glucose has been experimentally determined in terms of linear response range, optimum pH, applied potential, and shelf-life. These Ppy–PVS–GOD electrodes can be used for glucose estimation from 1 to 50 mM and have a shelf-life of about 5–6 weeks at 4°C. The sensitivity of Ppy–PVS–GOD electrode in phosphate and acetate buffer has been studied. It was found that the phosphate buffer gives fast response as compared to acetate buffer in amperometric measurements.

Enhanced charge-discharge characteristics of RuO2 supercapacitors on heat-treated TiO2 nanorods

Electrochemical capacitors based on RuO2 were prepared onto electrospun TiO2 nanorods. Further heat treatment of the TiO2 at 800°C under nitrogen was found to greatly improve the electrochemical performance of the RuO2 electrodes, especially at fast charge-discharge rates. The specific capacitance was found to decrease by only 33% when the scan rate increased from 10to1000mVs−1 (from 687to460Fg−1). The characteristic response time of the RuO2 electrode was found to be 0.15s when a heat-treated TiO2 substrate was used, which is 20 times better than that of the pristine TiO2 used.

Immobilization of GOD on electrochemically synthesized Ppy–PVS composite film by cross-linking via glutaraldehyde for determination of glucose

The Ppy–PVS-GOD biosensor for determination of glucose has been described. The enzyme, glucose oxidase (GOD) was immobilised by cross-linking via glutaraldehyde on a polypyrrole–polyvinyl sulphonate (Ppy–PVS) composite film. The Ppy–PVS film was electrochemically synthesized on indium–tin-oxide (ITO)-coated glass plate. We have synthesized Ppy–PVS film with 0.1 M pyrrole, 0.025 M PVS at 3.0 pH and 1 mA/cm 2 current density. The immobilization was done by cross-linking 2 mg/ml GOD via 0.1% glutaraldehyde at 0.1 M phosphate buffer with 7.0 pH. The synthesized composite films were characterized using galvanostatic electrochemical technique, electrical conductivity, UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The cross-linking of enzyme and porous morphology of the polymer film leads to high enzyme loading and an increase in lifetime, stability and fast response time of the enzyme electrode. Amperometric response was measured as a function of different concentration of glucose. It was observed that current increases with increasing glucose concentration in the range 1–50 mM.

A bromide selective polymeric membrane electrode based on Zn(II) macrocyclic complex

A novel bromide ion-selective PVC membrane sensor based on 2,3,10,11-tetraphenyl-1,4,9,12-tetraazacyclohexadeca-1,3,9,11-tetraene zinc(II)complex ( I) as carrier has been developed. The electrode exhibited wide working concentration range 2.2 × 10 −6 to 1.0 × 10 −1 M and a limit of detection as 1.4 × 10 −6 M with a Nernstian slope of 59.2 ± 0.5 mV per decade. The response time of electrode was 20 s over entire concentration range. The electrode possesses the advantages of low resistance, fast response and good selectivities for bromide over a variety of other anions and could be used in a pH range of 3.5–9.5. It was successfully used as an indicator electrode in the potentiometric titration of bromide ions with silver ion and also in the determination of bromide in real samples.

A selective modified carbon paste electrode for determination of cyanide using tetra-3,4-pyridinoporphyrazinatocobalt(II)

A chemically modified carbon paste electrode with 3,4-tetra pyridinoporphirazinatocobalt(II) (Co(3,4 tppa) was applied to the determination of free cyanide ion. The electrode has a linear range between 1.5 × 10 −5 M and 1.0 × 10 −2 M with a Nernstian slope of 60 ± 1.5 mV/decade and its detection limit is 9 × 10 −6 M. The response time of electrode is 5 min. The proposed electrode was applied successfully for the determination of cyanide in commercially available spring water. Some anions, such as SCN −, I −, Cl −, Br − and oxalate that are usually serious interfering species for most of cyanide selective electrodes, did not have any interfering effect for this proposed electrode.

Carbon paste electrodes of the mixed oxide SiO 2/Nb 2O 5 prepared by the sol–gel method: dissolved dioxygen sensor

A carbon paste of SiO 2/Nb 2O 5 material was used as the electrode in the development of a dissolved dioxygen sensor in 1.0 mol l −1 KCl solution at pH 6.2. The material was prepared by the sol–gel method. In the investigation of its electrochemical properties, linear and cyclic voltammetric and chronoamperometric techniques were employed. Dioxygen reduction, which was diffusion controlled, occurred at −280 mV vs. SCE by a two electron mechanism, producing peroxide. A linear response between the cathodic peak current intensity and the dissolved O 2 concentration was obtained for the region between 1.0 and 13.6 mg l −1. The stability proved to be very good over successive voltammetric cycles. The electrode response time was about 5 s. The electron transfer reactions were explained as being to an n-type semiconductor of niobia dispersed in the silica surface.

Model-based optimization of a conductive matrix enzyme electrode.

A mathematical model has been developed to describe the mechanism for internal mass transfer and enzyme reaction kinetics of an amperometric conductive matrix enzyme electrode. The model is simplified and solved analytically to arrive at a representation for the response slope in the linear range as well as for the response time. This is the first time that the response time of an enzyme electrode is described by a mathematical model. Simulations give information on how the design parameters influence the performance of the electrode for a glucose oxidase catalyzed sensing reaction process. Based on this information, several designs were constructed and tested showing suitable agreement with theoretical predictions. Finally, an optimized electrode was designed and validated.

Selective nitrate poly(vinylchloride) membrane electrode based on bis(2-hydroxyacetophenone)ethylenediimine vanadyl (IV)

The construction, performance, and applications of nitrate-selective electrode based on complex of bis(2-hydroxyacetophenone)ethylenediimine vanadyl (IV) as carrier, in plasticized poly(vinylchloride) (PVC) matrix are described. The electrode exhibited linear response with Nernstian slope of −58.5±1.0 mV per decade within the concentration range 5.0×10 −6 to 1.0 M nitrate ion. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration graph, was 1.0×10 −6 M. The response time of electrode was <25 s over the entire concentration range. This electrode could be used for at least 3 months without a considerable divergence in their potential. The electrode exhibited good selectivities for nitrate respect other anions. The electrode is suitable for use in real samples.

Electrocatalytic Oxidation of NADH by Oxidized s‐Adenosyl‐L‐Methionine (SAMe): Application to NADH and SAMe Determinations

Abstracts‐Adenosyl‐L‐methionine (SAMe) is an adenosine analogue with therapeutical activity against affective disorders and liver dysfunctions. It can be oxidized on graphite electrode yielding a strongly adsorbed electroactive oxidation product for which a quinone‐imine structure is proposed. This compound is capable of electrocatalyzing the NADH oxidation at low potentials, lowering the overvoltage by about 300 mV. An amperometric method for NADH determination at +0.1 V (Ag|AgCl|KClsat) is developed using an oxidized‐SAMe‐modified electrode in pH 9. Linear calibration plots were obtained with a detection limit of 2.4 nM. The electrode response time and the relative standard deviation of the slope of the calibration plot for 5 different modified electrodes were 12 s and 5.6% respectively. The catalytic scheme also provides the first method to determine SAMe itself by adsorptive differential pulse voltammetry. The linear range was found to be 42.4–424 nM with a reproducibility of 6.9%. The method was applied to SAMe determination in a pharmaceutical formulation.

Amperometric tyrosinase based biosensor using an electropolymerized PTS-doped polypyrrole film as an entrapment support

An amperometric biosensor was constructed by entrapment of enzyme, tyrosinase, also known as poly phenol oxidase (PPO) in an electrochemically prepared p-toluene sulfonate ion-doped polypyrrole film on a glassy carbon plate. The enzyme, tyrosinase, retains its bioactivity well within the polymer film. Phenolic compounds were quantitatively estimated in aqueous medium by the direct electrochemical reduction of enzymatically liberated quinone species at 0.05 V vs. Ag/AgCl. The results of amperometric response measurements conducted on enzyme electrode show sensitivity of 17.1, 70.2 and 24.3 μA/mM, and a linear response range of 3.3–220.3, 5.6–74.3 and 3.8–85.6 μM for phenol, catechol and p-chlorophenol, respectively. The limit of detection and a response time of the enzyme electrode are ranges from 0.8 to 2.4 μM and 40 to 75 s, respectively for these phenolic compounds. The enzyme electrode is stable for 3 months at about 4 °C.

Coated wire linear alkylbenzenesulfonate sensor based on polypyrrole and improvement of the selectivity behavior

The potentiometric behavior of coated wire electrodes based on dodecylbenzenesulfonate-doped polypyrrole (PPy-DBS) and hyamine as ion exchanger was investigated. The PPy-DBS was prepared electrochemically by anodic polymerization of pyrrole in the presence of DBS − ions in aqueous solution and used as ionophore for construction of the sensor. Two types of coated wire electrodes made of PVC-PPy-DBS and PVC-Hyamine-DBS, plasticized with ortho-nitrophenyloctylether ( o-NPOE) showed the Nernstian behavior (with respective calibration slopes of about 58 and 60 mV per decade) over the DBS − concentration range of 3.0×10 −6 to 1.1×10 −3 M and 5.0×10 −6 to 1.3×10 −3 M, respectively. The influence of membrane composition, type of plasticizer, and pH of test solution on the potentiometric responses of the two electrodes was investigated. The potentiometric response was independent of the pH of test solution in the range 3–10. The response time of electrodes was fast (10 s for both types of electrode), and they can be used for at least 3 months without any significant change in potential. The proposed electrodes revealed very good selectivity for DBS − ion over diverse inorganic and organic anions. The potentiometric selectivity coefficients for the PPy-DBS based electrode revealed a significant improvement as compared to the electrode made by conventional Hyamine-DBS (Hya-DBS) anion exchanger. The proposed electrode was used for determination of DBS − ion in some commercial detergents. The results of the potentiometric determinations were in satisfactory agreement with those obtained by a standard method (two-phase titration).

Cobalt(II) porphyrin complex immobilized on the binary oxide SiO 2/Sb 2O 3: electrochemical properties and dissolved oxygen reduction study

In this work, SiO 2/Sb 2O 3 prepared by the sol–gel processing method, having a specific surface area, S BET, of 790 m 2 g −1, an average pore diameter of 1.9 nm and 4.7 wt.% of Sb, was used as substrate base for immobilization of the 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21 H,23 H-porphine ion. Cobalt(II) ion was inserted into the porphyrin ring with a yield of complex bonded to the substrate surface of 59.4 μ mol g −1. A carbon paste electrode of this material was used to study, by linear sweeping voltammetric and chronoamperometric techniques, the electrocatalytic reduction of dissolved oxygen. The reduction, at the electrode solid–solution interface, occurred at −0.25 V versus SCE in 1.0 mol l −1 KCl solution, pH 5.5, by a four electron mechanism. The electrode response was invariant under various oxidation–reduction cycles showing that the system is chemically very stable. Such characteristics allowed the study of the electrode response towards various dissolved oxygen concentrations using the chronoamperometry technique. The cathodic peak current intensities plotted against O 2 concentrations, between 1.0 and 12.8 mg l −1, showed a linear correlation. The electrode response time was very fast, i.e. about 1 s. This study was extended using the electrode to determine the concentration of dissolved oxygen in sea water samples.

A method for cultivating plants under controlled redox intensities in hydroponics

An automated, low-cost hydroponic system was developed for growing single plants at controlled redox potentials (Eh) for extended periods. The system features a millivoltmeter with high and low set-point relays and offers the investigator full control of Eh within the entire redox potential range encountered in natural soils (−300 to +700 mV) with an accuracy of ±50 mV around the set-point value. Eh is lowered in the nutrient solution by adding the reducing agent titanium citrate. Conversely, Eh is elevated by bubbling the nutrient solution with air. The system’s ability to control Eh is demonstrated using data from a test experiment involving Phragmites australis plants grown at three redox levels (−150, +150 and +550 mV). Some frequently encountered factors that were potentially responsible for erroneous control are discussed. The buffer capacity and the relationship between pH and Eh were determined for the nutrient solution. These parameters, along with plant-mediated changes in pH, not only determine the time interval between pH adjustments, but also affect the Eh fluctuations in the continuously aerated experimental units. The variability and drift in readings from the platinum (Pt) electrodes, used to measure Eh, was investigated in order to relate electrode reliability to system performance. The variation in Eh readings for clean Pt electrodes was lower (S.E.=4.3 mV, n=23) than that of the calomel reference electrodes (S.E.=6.8 mV, n=23), the difference fixed across solutions of different poise. The response time (drift) of Pt electrodes in hydroponics (low-poised nutrient solution) was compared to pH-buffered quinhydrone (medium-poised) and flooded alluvial silt (well-poised). Drift increased from the low-poised nutrient solution, where Eh readings stabilized within minutes, to high-poised flooded soil, where Eh readings showed a downward drift for ca. 50 h. Overall, it is concluded that both the Pt electrodes and the calomel reference electrodes perform well in hydroponics. The extent to which the high NaCl salinity of titanium citrate (ca. 84‰) may limit the growth of plants is also discussed relative to the proportion of titanium citrate in the nutrient solution.

Coated wire ion-selective electrode for palladium(II) and its application to catalyst analysis

The construction, performance and application of polymeric membrane (PME) and coated wire (CWE) palladium(II)-selective electrodes based on the ion pair between tetra bromopalladate(II) and hexadecylpyridinium cation (HDP +) in a poly(vinyl chloride) matrix, plasticized with o-NPOE are described. The influence of membrane composition, bromide ion concentration and pH on the potentiometric responses of electrodes were investigated. Nernstian responses were obtained for the two type of electrodes with low limits of detection (1.0×10 −6 M for PME and 5.0×10 −8 M for CWE). The potentiometric responses are independent of the pH of test solution in the range 3–8. The response time of electrodes are fast (30 s for PME and 10 s for CWE), and they can be used for at least 3 months without any considerable divergence in potentials. The proposed electrodes revealed good selectivity for palladium(II) respect to different cations and anions. They were used to the direct potentiometric determination of palladium(II) in silicon-alumina catalysts.

Determination of potassium ions in pharmaceutical samples by FIA using a potentiometric electrode based on ionophore nonactin occluded in EVA membrane

A simple and rapid method was developed for the K + ions determination employing a flow injection system using a flow-through electrode based on the naturally-occurring antibiotic ionophore nonactin occluded in a polymeric membrane. The nonactin ionophore was trapped in poly(ethylene- co-vinyl acetate) (EVA) matrix (40% w/w in vinyl acetate) and dispersed on the surface of a graphite-epoxy tubular electrode. The plasticizer-free all-solid-state potassium-selective electrode showed a linear response for K + concentrations between 5.0×10 −5 and 5.0×10 −2 M ( r=0.9995) with a near-Nernstian slope of 51.5 mV per decade, when Tris–HCl buffer (pH 7.0;0,1 M) was employed as a carrier. The potentiometric-FIA system allows an analytical frequency of 120 samples per hour with a precision of 3.6%. The relative standard deviations (R.S.D.) for K + determination in pharmaceuticals samples, without any previous treatment, were lower than 4.0%, comparable to those obtained by flame photometry. Ammonium is the main analytical interference and the electrode response time was 5 s at 25 °C. The useful lifetime of the tubular sensor is longer than 3 months in continuous use.