Electrochemical types

Little work has been carried out using electrochemical cells to analyze for impurities. Thermodynamic data have been measured for the interaction of nuclear fuels with liquid potassium using cells based on ThOj-YjOj electrolytes, so such cells could be used to monitor oxygen. Both the diffusion and electrochemical types of hydrogen and carbon meters should function satisfactorily in liquid potassium. 

Carbon monoxide sensor. Carbon monoxide is a toxic air pollutant originating from incomplete combustion of fuels in burners or engines. Despite a strong demand for a very reliable carbon monoxide sensor, the only available sensor was based on an electrochemical type until recently. In this type sensor, selectivity and sensitivity for CO can often be enhanced by selecting elecrode materials and electrode potential appropriately, but several disadvantages are encountered, such as, short life, difficult maintenance and a rather expensive price. 

The most widely used pH electrode in cell culture is the silver/silver chloride electrochemical type with internal gel (that can be sterilized when the whole bioreactor is autoclaved), or the combined type (which can be pressurized during sterilization, to compensate the medium pressurization and to avoid contamination of the sensor with culture medium) (Schiigerl, 1991). 

In general, single-point detectors, such as the catalytic, infrared, solid-state, and electrochemical types, can be put in locations up to 3,000 feet from the control room.14 Sampling systems are more limited because of the length of the tubing needed to bring the sample to the detector. 

The eluate should pass through the detector with the smallest cell volume first, except for detectors such as the electrochemical type in which sample substances are altered, in which case this detector must be arranged last of all. 

Electrochemical type-III sensors have been constructed for measuring NOx, C02, S02, and many other environmentally harmful gases in very low concentration ranges [5]. In these multilayer type-III gas sensors, no direct relation between a solid electrolyte and the target gas exists without the mediation of an attached auxiliary phase. 

In addition to the enzyme activity, charge transfer rate in electrochemical types is another key issue in enzymatic biosensors. Charge transfer rate from the active site to the electrode is closely related to the overpotential that is apphed. Lower overpotential reduces the probabihty of interference by redox active species. Facilitated charge transfer may also help maintaining the condition of diffusion limiting even when significant loss of enzyme activity deteriorates sensitivity. 

Mainly three types of oxygen sensors are used in clinical applications. Whereas the two electrochemical types have the largest market shares [12], paramagnetic sensors as the third type are important in combination with IR sensors for sidestream multi-gas analysis in anesthesia monitoring. Real multi-gas sensors such as mass spectrometers or Raman spectrometers are of minor importance. 

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However, another view can be taken, and that is that the electrochemical type of reaction— in which there is no collision between the... 

The improved commercial availability of solid-phase reaction systems, immobilized enzyme reactors and photochemical derivatization instruments is one such direction for a brief outline of some of these see [34]. There will undoubtedly be new developments in the application of analytical methods, particularly in liquid chromatography, that will exploit the practical advantages of these devices when they are linked to the most sensitive detection modes, particularly the fluorescence and electrochemical types of detector. 

In field applications, the monitoring of the type and level of pollutants is also of great importance, and information is often required in real time rather than the several days of delay needed for sending samples to the laboratory. In response to this need, major advances have been made in the development and application of small-scale, portable sensors for in situ monitoring of pollutants [153-158]. Sensors can be of the solid-state, optical, bio-, and electrochemical types, examples of the latter being pH- and ion-selective... 

Lanthanum fluoride has been examined for use as a solid electrolyte for an oxygen sensor operating at room temperature. Most of the oxygen sensors in commercial use work at elevated temperature the only exception is the electrochemical type which operates at room temperature. The sensor uses aqueous electrolytes and it is crucial to maintain the sensor in an appropriate condition at all times. Leakage and corrosion shorten the lifetime considerably. 

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