Use Of Electrochemical Sensors Research Articles

Electrochemical Sensor for Organophosphate Pesticides and Nerve Agents Using Zirconia Nanoparticles as Selective Sorbents

An electrochemical sensor for detection of organophosphate (OP) pesticides and nerve agents using zirconia (ZrO2) nanoparticles as selective sorbents is presented. Zirconia nanoparticles were electrodynamically deposited onto the polycrystalline gold electrode by cyclic voltammetry. Because of the strong affinity of zirconia for the phosphoric group, nitroaromatic OPs strongly bind to the ZrO2 nanoparticle surface. The electrochemical characterization and anodic stripping voltammetric performance of bound OPs were evaluated using cyclic voltammetric and square-wave voltammetric (SWV) analysis. SWV was used to monitor the amount of bound OPs and provide simple, fast, and facile quantitative methods for nitroaromatic OP compounds. The sensor surface can be regenerated by successively running SWV scanning. Operational parameters, including the amount of nanoparticles, adsorption time, and pH of the reaction medium have been optimized. The stripping voltammetric response is highly linear over the 5-100 ng/mL (ppb) methyl parathion range examined (2-min adsorption), with a detection limit of 3 ng/mL and good precision (RSD = 5.3%, n = 10). The detection limit was improved to 1 ng/mL by using 10-min adsorption time. The promising stripping voltammetric performances open new opportunities for fast, simple, and sensitive analysis of OPs in environmental and biological samples. These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.

Electrochemical stripping analysis of organophosphate pesticides and nerve agents

A sensitive electrochemical stripping voltammetric method for analyzing organophosphate (OP) compounds was developed using a carbon paste electrochemical (CPE) transducer. OPs strongly adsorb on a CPE surface and provide facile electrochemical quantitative methods for electroactive OP compounds. Operational parameters have been optimized, and the stripping voltammetric performance has been studied using square wave voltammetry. The adsorptive stripping voltammetric response is highly linear over the 1–60 μM methyl parathion range examined (2-min adsorption), with a detection limit of 0.05 μmol/L (10-min adsorption) and good precision (RSD = 3.2%, n = 10). These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.

Evaluation of gas emissions from coal stockpile

Gas emissions of carbon dioxide, methane, dimethylsulfide, carbon monoxide and oxygen from a coal stockpile in Velenje were determined. Gases from the coal stockpile were collected in Alltech Standard sampling bags and then analysed using a capillary gas chromatograph and electrochemical sensors. A flame ionisation detector equipped with a Zr/Ni catalytic reactor was used for the determination of methane and carbon dioxide. Dimethylsulfide was detected with a flame photometric detector, and the concentrations of carbon monoxide and oxygen were determined by use of electrochemical sensors. The results showed that the main influence on gas emissions is related to the ambient temperature. Emissions of carbon dioxide during summer 2001 (average temperature during sampling period was 24 °C) were approximately 30-times higher than during winter 2002 (average temperature during sampling period was −2 °C) and were also influenced by the oxygen concentration. Carbon dioxide is mainly formed by oxidation of coal. Methane and dimethylsulfide are desorbed from coal, and are present in higher concentrations in stockpile emissions when stockpiles are renewed. The dimethylsulfide concentration, in contrast to laboratory experiments in stockpile emissions, falls immediately due to photo-degradation.

Characterisation of porous ceramic plugs for use in electrochemical sensors

In electrochemical sensors like pH-, reference- or ion-selective electrodes a porous ceramic plug (or diaphragm) maintains the conducting junction with the test solution. These liquid junctions should have a resistance as low as possible meanwhile avoiding leakage through the junction. Five porous magnesium stabilised zirconium oxide plugs with different porosity's and pore size (distribution) were investigated as liquid junctions. The physical properties of these porous plugs were investigated with SEM and Mercury Intrusion Porosimetry. Important working conditions of these porous plugs are the resistance of the porous plug filled with an electrolyte and the contamination speed through these porous plugs, both for the test solution as the reference solution. The first property was measured by a 4-wire resistance measurement. The second property was measured by measuring the flow through rate of the reference electrolyte through the plug. It was shown that an optimal plug i.e., low leakage and high conductivity through the membrane, had a high porosity and relative small pores (0.25 μm). A simple mathematical model based on the Hagen-Poiseuille equation was developed to describe the porous plug characteristics. It was shown that mathematical calculation of the porous plug resistance was in good agreement with experimental results.

Design and Use of Electrochemical Sensors in Enantioselective High Throughput Screening of Drugs. A Minireview

The importance of reliable detection systems for enantiomeric assays increases with the necessity of high throughput screening analysis of raw materials for the pharmaceutical industry. The utilization of electrochemical sensors in enantioselective analysis is an accurate and precise alternative to chromatographic techniques. The reliability of the response characteristics as well as of the analytical information obtained by using electrochemical sensors is strictly correlated with the design of the sensors. The designs evaluated for sensors have been based on PVC, imprinting polymers and carbon paste matrices. Among these, carbon paste sensors have been the most reliable and have been utilized for the construction of potentiometric, enantioselective membrane electrodes as well as for amperometric biosensors, and immunosensors. There are two ways to use the electrochemical sensors in enantioselective screening analysis: selective binding and catalyst selectivity. A molecule with a special chemical architecture is required for selective binding: a lock for a key. The high reliability of analytical information obtained using these sensors has made possible the automation of potentiometric and amperometric techniques by integration of enantioselective sensors as detectors in flow injection analysis and sequential injection analysis techniques.

Use of electrochemical sensors for the determination of wall turbulence characteristics in annular swirling decaying flows

The wall shear stress and turbulence features in swirling decaying flow were analyzed near the inner cylinder of a cylindrical annulus fitted with a tangential inlet. The experimental method was based on the determination of the limiting diffusional current on electrochemical sensors mounted flush to the surface of the inner cylinder. The mean value of the diffusional current leads to the mean wall velocity gradient, and the power spectral density of the current fluctuations is linked to that of the velocity gradient fluctuations through a transfer function. The analysis of the mean wall velocity gradient allowed the three-dimensionality of the swirl flow and the swirl decay along the flow path to be studied. Just downstream of the tangential inlet, a recirculation zone is set up near the inner cylinder, followed by a nonmonotonic decay of the swirl motion. These two zones define the three-dimensional flow region. The wall turbulence was characterized by both the turbulence intensity and the cutoff frequency, defined by the transition between the low-frequency plateau and the inertial subrange of the power spectral density. The turbulence intensity, which is quasi-independent of the Reynolds number, decreases with axial distance from the inlet section and has a more complex evolution with the circumferential position with respect to the axis of the tangential inlet.

Some recent studies on the use of electrochemical sensors in nonaqueous solution chemistry

AbstractFour recent studies in the authors' laboratory on the use of electrochemical sensors in nonaqueous solutions are reported. (1) Si3N4‐ and Ta2O5‐type ISFETs proved to be useful in nonaqueous solutions as sensors for pH and for proton solvation, because of their more rapid response than a conventional glass electrode. They were used to study the acid–base equilibria in γ‐butyrolactone and to determine the proton transfer activity coefficients between different solvents. (2) A univalent cation‐sensitive glass electrode was used to study the solvation of lithium ions in mixed solvents applicable to lithium batteries. (3) A membrane of polyacrylamide coupled to a cobalt phthalocyanine complex and coated onto a platinum electrode functioned as a sensor for fluoride and cyanide ions in aprotic solvents. It was used to determine the solubility products of alkali and alkaline earth metal fluorides and cyanides in acetonitrile and propylene carbonate. (4) A new method is proposed for the estimation of the liquid junction potential between different solvents, and a comparative study has been made between the new method and some conventional methods.

On the use of electrochemical sensors for local velocity measurement of viscoelastic fluids

Some problems connected with the application of the electrochemical method of measuring local velocity of viscoelastic polymer solutions have been presented and discussed. On the basis of the analysis of changes in the fluid flow structure due to viscoelastic properties, a modified Eq. (8) which describes the local mass transfer coefficients for wedge shape electrochemical probes has been obtained. On the basis of Eq. (8), own modification of the construction of electrochemical measuring probes has been proposed. The reliability of the proposed method has been successfully experimentally verified by the comparison of the obtained free jet velocity profiles with the literature data referring to results obtained by the laser-Doppler technique.

A new method for enzyme membrane preparation based on polyurethane technology: Electrode modification for sensor development

The new method developed for enzyme membrane preparation is based on cross-linking poly (vinyl alcohol) (PVAL) with triisocyanate (TIC) in the presence of enzyme. Dimethylsulfoxide (DMSO) was the only solvent found to dissolve PVAL, TIC and enzyme at room temperature, without completely denaturing the latter. The rate of gelation to form the desired network membrane can be controlled by the amount of solvent used. All the enzymes tested (alkaline phosphatase and alcohol, cholesterol and glucose oxidases) dissolved in DMSO and retained sufficient activity for use in electrochemical sensors. Membranes were formed on both graphite and platinized graphite electrodes. The resulting prototype sensors were examined with regard to feasibility of preparation, adhesion of the gels to the electrode surfaces, swelling properties of the gels in DMSO and aqueous buffers, and their electrochemical properties.

Enzyme-based electrochemical biosensors

There has been an increased interest in the use of electrochemical sensors in clinical diagnostics because of the recent trend toward testing in satellite laboratories and the physician's office. The coupling of enzymes with electrochemical sensors permits the simple determination of metabolites, therapeutic drugs, antigens, and antibodies.

Implanted electroenzymatic glucose sensors.

The advent of electrochemical sensors for intermittent sampling of blood gases and hydrogen ions in the clinic, intensive care, and surgical units has revolutionized diagnostic and critical care medical technics. The use of electrochemical sensors for continuous transcutaneous monitoring of blood gases is further enhancing the medical surveillance of patients. The more recent introduction of glucose and other electroenzymatic sensors has stimulated broad research in the development of metabolic monitoring. For the present research, the glucose sensor widely used for the rapid specific micro-analysis of whole blood and plasma is explored for possible use as an in vivo intravascular or tissue-implanted sensor. This sensor is based on the polarographic measurement of hydrogen peroxide generated by glucose oxidase (EC 1.1.3.4) held between two membranes. The first membrane allows the diffusion of glucose, ions, and many other small molecules, while the second membrane allows the diffusion of the glucose-generated hydrogen peroxide to the platinum surface, but excludes ascorbic acid, bilirubin, and uric acid. Such sensors respond rapidly and specifically when acutely implanted subcutaneously in cats and dogs. They function well as glucose-sensor-tipped venous catheters. One sensor was repeatedly used for in vitro polarograms, subcutaneous and blood glucose monitoring, over a period of ten months, with storage in the cold between uses, with the complete retention of its response characteristics.

Some developments in electromechanical sensors

The use of electrochemical sensors has largely superseded the laborious methods of chemical analysis previously used. This article looks at the past development and future possibilities of this type of transducer

On-line sensors in industrial water analysis

The advantage of electrochemical sensors and the problems inherent in their use in industrial environments are highlighted by a description of some current on-line analytical systems employing potentiometric and galvanic sensors and their performance in specific applications. A wide variety of aqueous samples is encountered, ranging from extremely dilute, relatively clean solutions to mixtures containing high levels of both dissolved and undissolved species. Sensor design is discussed in the light of these factors and of some of the other constraints within which the manufacture of sensors occurs. Some present trends in the design and use of electrochemical sensors are reviewed to indicate the prospects for the future in this field.

Use of electrochemical sensors for on-line monitoring of ionized calcium, potassium, and glucose in whole blood of living dogs.

We report the development and evaluation of electrochemical sensors for continuous on-line measurement of whole-blood ionized calcium, potassium, and glucose in living animals. Ionized calcium and potassium are measured with ion-selective electrodes, by using a unique differential approach. A polarographic sensor coupled with a membrane with bound glucose oxidase is used in the glucose analyzer. The modular concept of instrument design permits one mainframe, computer, and pump system to house any analyzer module or a combination of modules. A small volume of venous blood (about 2 mL/h) is continuously withdrawn from the subject through a double-lumen catheter and pumped through the analyzer(s). Results of in vitro correlation studies and studies in normal dogs (including responses of ionized calcium, potassium, and glucose to various stresses) support the validity of the measurements.