Amperometric Mode Research Articles

A conductive ormosil encapsulated with ferrocene conjugate and multiwall carbon nanotubes for biosensing application

Highly non-toxic and conductive ormosil composite film was prepared using (3-aminopropyl)triethoxysilane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane by doping with ferrocenemonocarboxylic acid–bovine serum albumin (FMC–BSA) conjugate and multiwall carbon nanotubes (MWNTs). With glucose oxidase (GOD) as a model enzyme this film could be used to design an amperometric biosensor for glucose determination. The entrapped FMC–BSA conjugate performed excellent redox electrochemistry and the immobilized GOD was highly stable. Under optimal conditions this biosensor was able to detect glucose with a detection limit of 20 μ m ( S / N = 3 ) in the linear range of 0.05–20.0 m m in flow system, which was wider than the batch amperometric mode, with an analysis time of 25 s for each sample. The value of K M app was 6.6 m m. The proximity of these three components FMC–BSA, MWNTs and GOD enhanced the electron transfer between the film and electrode. This film could be used efficiently for the entrapment of other redox bioactive compounds and biosensing/bioelectrochemical applications.

The Analysis of Chlorinated Phenol Solutions by Capillary Electrophoresis Coupled with Direct and Indirect Amperometric Detection Using a Boron-Doped Diamond Microelectrode

Analysis of aqueous solutions containing chlorinated phenol pollutants was accomplished by capillary electrophoresis with direct and indirect amperometric detection using a boron-doped diamond microelectrode. The microelectrode was prepared by (i) coating a thin film of boron-doped polycrystalline diamond on a sharpened platinum wire (76-μm diameter) and (ii) sealing the coated wire in a polypropylene pipet tip. The diamond microelectrode, used in end-column detection, exhibited a low and stable background current with low peak-to-peak noise and good electrochemical activity for the pollutants without any conventional pretreatment. The electrode performance was evaluated in terms of the linear dynamic range, sensitivity, limit of quantitation, and response precision for the detection of several priority pollutants (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol). The diamond microelectrode gave good detection figures of merit for these contaminants in the direct amperometric mode with no evidence of any electrode fouling. As an example, the concentration limit of quantitation for 2-chlorophenol was 100 nM or 13 ppb (S/N=3) and the relative standard deviation of the peak height for 9 injections was 4.7±0.5% (est. 1.1 nL inj.). The separation efficiency was greater than 100 000 plates/m for all seven solutes. The microelectrode was also employed for the indirect detection of the chlorinated phenols. In this approach, which is useful for detecting electroinactive solutes, ferrocene carboxylic acid was added to the run buffer as the electrophore. Good detection figures of merit were also achieved for the separation and detection of 2-chlorophenol, 3-chlorophenol, and 2,4-dichlorophenol in this mode, although the linear dynamic range was not as wide and the limit of quantitation was not as low as in direct amperometry. For example, the concentration limit of quantitation for these pollutants was in the mid micromolar range (1–10 ppm) with excellent response reproducibility of 3.2±0.8%, or less.

Amperometric hydrocarbon sensor using La(Sr)Ga(Fe)O 3 solid electrolyte for monitoring in exhaust gas

Emission of hydrocarbon at low temperature, especially in the cold start condition of the automobile engine, has attracted attention these days. For the first time an electrochemical sensor based on LaGaO 3 with iron doping was demonstrated to have very high sensitivity to propene (C 3H 6) at low temperature (423–573 K). In the amperometric mode, the output current signal was found to increase linearly with the C 3H 6 concentration (500–2000 ppm) in logarithm scale. Effect of iron doping at the gallium site was found to influence the sensing properties greatly and the electrolyte composition La 0.7Sr 0.3Ga 0.7Fe 0.3O 3 showed the highest sensitivity of 976 μA/decade at 473 K. The sensors were fast, reproducible and highly selective to hydrocarbons.

Computer-controlled system for ISEs automatic calibration

The present work examines the problems encountered during the design, construction and testing of a fully computer-controlled system for automatic calibration of ion-selective electrodes (ISEs), based on two data acquisition boards, a home-made fast multifunction potentiostat, two peristaltic pumps and an injection valve. With few minor modifications, the experimental setup allows the using of batch and flow techniques for automatic calibration of ISEs, operated in potentiometric or amperometric mode. For flow measurements, a wall-jet cell (WJC) was designed, built and characterized. Using [Fe(CN) 6] 3−/[Fe(CN) 6] 4− as standard redox couple, the WJC amperometric response was examined in order to establish the dispersion factor as well as the hydrodynamic regime as a function of the flow rate and cell geometry. Finally, a Na +-selective electrode, based on a commercial NASICON (CERAMATEC™), was used to evaluate the electroanalytical performances of the experimental setup for potentiometric and amperometric calibration of ISEs using batch, steady-state flow and flow injection measurements.

Polyaniline biosensor for choline determination

Choline oxidase has been immobilized inside nanostructured polyaniline layers of a controlled porosity and a micrometer or nanometer thickness to form a choline sensor: polyaniline–choline oxidase (PChO) biosensor. Electrochemical techniques were used either, to prepare polyaniline films of a controlled thickness and to immobilize the enzyme molecules. The electrical response of a PChO sensor depends on choline concentration and its sensitivity reaches a value of 5 μA/mM in the amperometric mode and of 10 mV/mM in the potentiometric mode of measurements. The current response measured at a constant potential of +0.4 V is linear vs. choline concentration. No interference with ascorbic acid has been found. The storage stability is very satisfied: the sensors examined did not change essentially their electrical response even after a month of storage.

Development of a breath alcohol sensor using a copper electrode in an alkaline medium

A copper disc electrode working in alkaline solutions was demonstrated to act as a suitable amperometric sensor for ethanol determination at +0.6 V vs Ag | AgCl. The participation of a freely soluble Cu(III) species in the electrocatalytic process involving the anodic oxidation of ethanol has been demonstrated by rotating ring–disc electrode voltammetry. The influence of the pretreatment potential on the anodic signal was investigated and a correlation with the morphology of the electrode surface characterized by energy dispersive X-ray spectroscopy (EDS) indicated that the Cu(III) species originated from the oxidation of a CuO layer. Ethanol measurements were performed in the amperometric mode at 0.6 V (vs Ag | AgCl). The repeatability of the measurements for a 0.05% aqueous ethanol solution was estimated as 3%, and the detection and quantification limits were determined as 0.005% and 0.01%, respectively. Under the optimum experimental conditions, the amperometric sensor was used to monitor the concentration of ethanol in breath (BrAC), which was conveniently collected in a rubber air balloon (volume=3 l) and introduced to a 1 mol l −1 NaOH working solution (volume=10 ml). The sensor can measure a person's breath ethanol over the concentration range 0.26–130 ppm by operating it according to an established protocol, of which the analytical parameters are specified by the Brazilian legislation for BrAC measurements in drivers. The rate of ethanol degradation in the body was followed, and the results agree with predictions in the literature.

Chemical reversibility and stable low-potential NADH detection with nonconventional conducting polymer nanotubule modified glassy carbon electrodes.

Studies of the oxidation of beta-nicotinamide adenine dinucleotide (NADH) at glassy carbon (GCEs) electrode surfaces, modified with nonconventional conducting polymer nanotubules, are reported. In contrast to the situation with conventional carbon electrodes, chemical reversibility of the NADH oxidation reaction was achieved by means of poly(1,2-diaminobenzene) conducting nanotubule coatings. A Delta E(p) of 425 mV (vs Ag/AgCl; pH 7.0) was observed. The NADH amperometric response of the conducting nanotubule modified GCEs was shown to be extremely stable, with 98% of the initial response remaining after 48 h of stirring in the presence of 1 x 10(-4) M NADH solutions (compared to 14% at the poly(1,2-diaminobenzene) modified GCEs). The nonconventional conducting polymer nanotubule-coated electrodes, when tested in amperometric mode for NADH electrochemical oxidation at an applied potential of 450 mV, showed a sensitivity of 99 nA/mM, an operational stability for 2 days, a storage stability of 2 weeks at 4 degrees C, a linearity from 5 x 10(-5) to 1 x 10(-3) M, and good NADH chemical reversibility, all of which make them useful tools for dehydrogenase enzyme probe assembly.

Amperometric Solid-State Gas Sensor Using LaGaO3 Based Perovskite Oxide Electrolyte for Detecting Hydrocarbon in Exhaust Gas: II. Improvement of Inactive Electrode Performance

(LSGM) based solid electrolyte coupled with suitable electrodes was demonstrated to be a highly sensitive hydrocarbon sensor in the temperature range of 523-673 K. Sensors were studied in the amperometric mode. Keeping Pt as the active electrode, the various inactive electrode materials were studied. It was seen that (LSC 55) gave the best sensitivity among the studied catalysts. Furthermore, it was found that the performance of the sensor with (LSM 55) showed the highest sensitivity (≈600 μA/decade at 623 K) among all the investigated perovskite oxides for an inactive electrode. The sensitivity of all the sensors was fast, reversible, and the current linearly increased with increasing concentration. Over a broad range of oxygen concentration, the sensitivity was found unaltered. The thickness of the electrolyte played an important role for increasing the sensitivity. The measured value of the open circuit potential in the potentiometric mode was very small; but it confirmed the development of mixed potential between the two electrodes which palyed the key role for changing current in the present amperometric sensor. © 2004 The Electrochemical Society. All rights reserved.

A planar thick film sensor for hydrocarbon monitoring in exhaust gases

A miniaturised planar two-electrode cell with centro-symmetric diffusion geometry for detection of hydrocarbons in oxygen, nitrogen, hydrocarbon gas mixtures has been developed using thick film technology. As a model of hydrocarbon gas propene (C 3H 6) is chosen for sensor tests. The solid-state electrochemical cell based on yttria-stabilised zirconia (YSZ) operates in the amperometric mode. Oxygen is fairly pumped out at the Au/YSZ electrode and C 3H 6 is oxidised at the Pt/YSZ electrode. At a gas temperature of 600 °C, the sensitivity amounts 2 nA/ppm C 3H 6.

Characterisation of Prussian blue modified screen-printed electrodes for thiol detection

The electrocatalytic behaviour of Prussian blue towards thiol oxidation was thoroughly investigated. Cyclic voltammetry experiments performed in thiol solution showed the classical shape of a mediated redox system. The current due to thiol-mediated oxidation was then evaluated in batch amperometric mode at +200 mV vs. Ag|AgCl. Many thiocompounds were investigated and their different reactivities were discussed. Thiocholine and cysteamine were found to give the best results in terms of LOD (i.e., 5 × 10 −6, 10 −6 mol l −1, respectively) and linear range (5 × 10 −6–5 × 10 −4, 10 −6–10 −4 mol l −1, respectively). Two applications are also proposed, one involving the measurement of thiocholine as a mean for pesticide detection, and the other being an electrochemical alternative to Ellman’s test for total thiol estimation.

NASICON-based amperometric CO2 sensor using Na2CO3–BaCO3 auxiliary phase

An amperometric CO 2 sensor was fabricated using a Pt|NASICON (Na + conductor, Na 3 Zr 2 Si 2 PO 12 )|Pt cell and a porous Na 2 CO 3 –BaCO 3 (1:1.7 in molar ratio) auxiliary layer. The sensor with the Na 2 CO 3 –BaCO 3 layer showed a faster response than that with the Na 2 CO 3 layer, and the sensor signal was barely influenced by the humidity. When operated in an amperometric mode with an applied external electric field, the sensor could detect the CO 2 concentration stably and precisely without the need for a reference gas or a reference electrode material, and the sensor signal was constant for extended test periods (60 days). The sensing mechanism and the long-term stability is discussed in terms of the amperometric operation of the sensor.

NASICON-based amperometric CO2 sensor using Na2CO3–BaCO3 auxiliary phase

An amperometric CO2 sensor was fabricated using a Pt|NASICON (Na+ conductor, Na3Zr2Si2PO12)|Pt cell and a porous Na2CO3–BaCO3 (1:1.7 in molar ratio) auxiliary layer. The sensor with the Na2CO3–BaCO3 layer showed a faster response than that with the Na2CO3 layer, and the sensor signal was barely influenced by the humidity. When operated in an amperometric mode with an applied external electric field, the sensor could detect the CO2 concentration stably and precisely without the need for a reference gas or a reference electrode material, and the sensor signal was constant for extended test periods (60 days). The sensing mechanism and the long-term stability is discussed in terms of the amperometric operation of the sensor.

Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor

A mediator-less microbial fuel cell (MFC) was used as a biochemical oxygen demand (BOD) sensor in an amperometric mode for real-time wastewater monitoring. At a hydraulic retention time of 1.05 h, BOD values of up to 100 mg/l were measured based on a linear relationship, while higher BOD values were measured using a lower feeding rate. About 60 min was required to reach a new steady-state current after the MFCs had been fed with different strength artificial wastewaters (Aws). The current generated from the MFCs fed with AW with a BOD of 100 mg/l was compared to determine the repeatability, and the difference was less than 10%. When the MFC was starved, the original current value was regained with a varying recovery time depending on the length of the starvation. During starvation, the MFC generated a background level current, probably due to an endogenous metabolism.

Intracellular Patch Electrochemistry: Regulation of Cytosolic Catecholamines in Chromaffin Cells

Alterations in the cytosolic pool directly affect neurotransmitter synthesis and release and are suggested to be key factors in various neurodegenerative disorders. Although this cytosolic pool is the most metabolically active, it is miniscule compared with the amount of vesicular transmitter and has never been quantified separately. Here, we introduce intracellular patch electrochemistry (IPE), a technique that for the first time provides direct measurements of cytosolic oxidizable molecules in single mammalian cells. In amperometric mode, IPE detects total catechols, whereas in cyclic voltammetric mode, it preferentially measures catecholamines. In cultured chromaffin cells, the total cytosolic catechol concentration was 50-500 microm, of which approximately 10% were catecholamines. Reserpine, a vesicular monoamine transporter inhibitor, had no effect on the catecholamine pool but increased total catechols by fourfold to fivefold. Combined with pargyline, a monoamine oxidase inhibitor, reserpine increased catecholamine levels in the cytosol by approximately sixfold. Amphetamine induced a transient approximately fivefold accumulation of cytosolic catecholamines and a slow increase of total catechols. In cells incubated with 3,4-dihydroxy-L-phenylalanine (L-DOPA), catecholamines increased by approximately 2.5-fold and total catechols increased by approximately fourfold. Cytosolic catecholamines returned to control levels <or=10 min after L-DOPA withdrawal, whereas total catechols remained approximately twofold elevated even after a 1.5 hr incubation in L-DOPA-free media. Our data indicate that cytosolic catecholamines are strictly maintained at a defined level, and drug-induced increases in their concentrations lead to the accumulation of other catecholamine derivatives, such as DOPAC and 3,4-dihydroxyphenylethyleneglycol. These derivatives reside in the cytosol for hours after treatment and may be an underlying cause of drug-related cytotoxicity.

Polypyrrole Bilayers: Charge Trapping and Application for Amperometric Ions Sensing

AbstractBilayers composed of polypyrrole: doped by perchlorate ions (PPy(ClO4) – anion exchanging inner layer) and by dodecyl sulfate ions (PPy(DS) – cation exchanging outer layer) are very effective charge trapping systems that are usually not observed for other bilayers comprised of polypyrrole. Chronopotentiometric experiments carried out for oxidation and reduction showed that the trapping effect in the inner layer resulted from different ion exchange properties of the component polymers, leading to a low permeability of the reduced outer layer towards anions. Estimated diffusion coefficients of Cl− anions in the oxidized and reduced PPy(DS) are in the range of 10−9 and lower than 10−10 cm2 s−1, respectively. The presence of the outer layer limiting the ion transfer was found to be beneficial to improve the signal resolution in amperometric mode of ion sensing within wide KCl concentration range, from 10−5 M up to 3 M. The influence of experimental conditions (film thickness, response time) on optimization of this novel kind of polymeric bilayer ion sensors was studied.

Application of electrodes modified with ion-exchange polymers for the amperometric detection of non-redox cations and anions in combination to ion chromatography

An amperometric sensor for non-electroactive ions was designed, evaluated in flow injection analysis, and applied as a novel detector in suppressed ion chromatography. It consists of a carbon paste electrode modified with either a polycationic or a polyanionic polymer containing a suitable charge transfer mediator (Fe(CN) 6 3− or Cu 2+), operating in an indirect amperometric mode. The detection mechanism involves ion exchange between the non-redox ionic analyte and the electroactive mediator, in the polymer particles located at the electrode surface, followed by the electrochemical transformation of the mediator species leached out of the polymer at the electrode ∣ solution interface. As detection was achieved in the absence of added supporting electrolyte, the amperometric signal contains both faradic and capacitive components. Optimisation was performed to get the highest faradic signals, by varying various experimental parameters (i.e. applied potential, composition of the electrode). These systems were then successfully applied to the analysis of mixtures of cations (Li +, Na +, K +, NH 4 +, Ca 2+, Mg 2+) and anions (F −, Cl −, NO 2 −, NO 3 −, SO 4 2−, PO 4 3−) subsequent to chromatographic separation. Good operational stability was observed, with typically less than 5% signal loss for 50 successive measurements.

A Mercury Selective Electrode

ABSTRACTA novel mercury ion selective electrode has been constructed to have strongly coordinating macrocyclic ligand binding site covalently attached to polythiophene film using 1-1,4,10-trioxa-7,13-diazacyclopentadecane-1-thiophenylmethane (TDCD-thiophenylmethane) as a specific chelator. In amperometric mode, the current is proportional to mercury (II) concentrations down to 2 ppb. Reversible cyclic voltammetric waves show that both mercury (I) and mercury (II) are stabilized by the ligand. Monomethyl mercury and vapor phase elemental mercury are also electrochemically determined. Dissolved oxygen and heavy metal cations show no significant interference even at ten times the mercury concentration. The polymer surface shows robust performance for two years or longer. Fabrication strategies are being developed to optimize the probe performance. The variables under investigation include substrate surface roughness, the ratio of derivitized thiophene (TDCD-thiophenylmethane) to underivatized thiophene in the surface polymer, ratio of thiophene with two chelating rings to thiophene with only one, number and thickness of electrodeposited polymer layers, composition of polymer layers, and number of -CH2- units separating the chelating ring from the thiophene monomer units. The probe exhibits linear response to mercury concentration, and detects mercury in several forms.

A novel thick film sensor for simultaneous O 2 and NO monitoring in exhaust gases

A miniaturized two-electrode sensor for the simultaneous detection of oxygen and nitrogen monoxide in oxygen, nitrogen, NO gas mixtures has been developed by using thick film technology. The solid state electrochemical sensor, based on yttria-stabilized zirconia, operates in the amperometric mode. Oxygen concentrations ranging up to 5 vol.% and NO concentrations ranging up to 2500 ppm can be detected separately and simultaneously. The diffusion properties of the diffusion barrier of the sensor have been determined by the current dependence on the working temperature.

Progress in the development of zirconia gas sensors

The development of zirconia gas sensors, arising from work instigated by Brian Steele in 1983, is reviewed and progress reported. New oscillatory modes of operation of pump-gauge sensors are described with concomitant advantages including, in particular, tolerance to leakage due to deterioration of the seal. A double chamber sensor, which does not need the provision of a reference gas of fixed composition, has been developed allowing the excess-air and fuel-rich regions to be distinguished in a combustion system. Planar thick-film sensors have been prepared and tested which operate effectively in the amperometric mode. Reducing unit cost is a crucial factor in the commercialisation and widespread application of these sensors and associated instrumentation.

Fabrication and characterization of disposable type lactate oxidase sensors for dairy products and clinical analysis

Disposable transducers having a working electrode made of a polymer disk sputter-coated with platinum, a screen-printed graphite basal track and an aluminum foil as a contact pad were fabricated for the development of l-lactate oxidase biosensors. Uncoated electrodes were characterized by cyclic voltammetry. A mixture of lactate oxidase with polyethyleneimine (PEI) and poly(carbamoyl)sulphonate (PCS) hydrogel was used for enzyme immobilization onto the platinum disk of the transducers. A two-electrode configuration set up in an amperometric mode was used to measure the current generated due to the enzymatically generated hydrogen peroxide. The sensors capable of sensitive l-lactate determination were fabricated with different settings of Nafion® layers to exclude electroactive interferents. Lactate oxidase sensors were characterized with respect to linear range, sensitivity, response time and recovery time. The effects of ascorbic acid and temperature on the sensor performance were investigated. The continuous operation and the stability of sensors were also evaluated. The performance of sensors coated with larger numbers of small amounts of Nafion® was found to be more advantageous than that of sensors coated with fewer numbers of larger amounts of Nafion®. The sensors were also tested with diluted dairy products and human whole blood and serum. Good agreement was found between the results obtained by the newly developed disposable sensors and other well established analytical methods.