Detection of Gases

Worrell C. and Gallen N., Trace-level detection of gases and vapours with mid-infra-red hollow waveguides,./. Phys. D Appl. Phys., 1997 30 1984-1995. 

Mohebati A., King TA., Remote detection of gases by diode laser spectroscopy, J. Modem Optics 1988 35 (3) 319-324. 

Fluorescence quenching resulting from the collision of the analyte with a fluorescent compound (see Chapter 4). This method is particularly well suited to the detection of gases such as oxygen (dissolved in water or blood), SO2, H2S, ammonia, HC1, Cl2, chlorocarbons, etc. 

Because chemical reactions on the catalytic metal surface are responsible for the detection of gases, the sensor response is highly temperature-dependent. In general, an increased temperature gives a faster gas response (see Section 2.5.1 and [2]). Thus, both the catalytic metal type and the temperature influence the gas response [23, 24]. 

There are numerous instruments available for the measurement of the compositions of (or simply for the detection of) gases. These sensors employ a wide variety of physical and chemical methods and many can also be used for analysing liquids by vaporising the liquid sample before it is passed through the instrument. A selection is described in Table 6.16. 

It has been suggested that adsorption of dipolar gas molecules at the surface of the insulator of a field-effect transistor can be used as a principle for detection of gases. It would work in only one type of FET discussed in this book. 

Thus the value of the dielectric constant at the sample/metal interface determines the shift of the resonance. When adsorption of molecules at the metal surface results in the change of the refractive index or of the local value of the dielectric constant, the change of reflectivity is observed. This phenomenon has been used as the mechanism for detection of gases (Fig. 9.18a) and of adsorbed biomolecules (Fig. 9.18b). The depth of penetration of the surface plasmon is comparable to that of the evanescent field, that is, 100-500 nm for the visible-near infrared range. 

Bariain C, Matias IR, Fernandez-Valdivielso C, Arregui FJ, Rodriguez-Mendez ML, de Saja JA. Optical fiber sensor based on luthetium bisphthalocyanine for the detection of gases using standard telecommunication wavelengths. Sens Actuators 2003 B93 153-8. 

Thin metal Hlms (Pt, Pd) have been used for the adsorption and detection of gases such as H2 and NH3 [138,139]. While the interaction mechanisms for these sensors were not specified, it is well known that H2 dissolves to a significant extent in Pd, with concomitant changes in the density, electrical conductivity, and mechanical properties of the fllm. The H2/Pt interaction as well as the interaction of NHa with both Pd and Pt undoubtedly involves chemisorption on surface sites. Metal thin films deposited by nearly all techniques are polycrystalline chemisorption along grain boundaries can often lead to a response that is considerably larger than predicted from the properties of metal single crystals. 

Fig. 12.1 Main approaches for selective detection of gases and possibilities for applications of combinatorial methods...

Figure 7. Photograph of spectrometer unit for detection of gases.

Using the spectrometer unit for the detection of gases, we measnred the absorbance of six different gases snlfur dioxide, arsine, bromomethane, chlorine, ethylene oxide, hydrogen chloride and ammonia. The absorbance and its first derivative spectra ate shown in Figures 8 and 9. 

Finally, Taguchi s group developed an integrated system for the detection of gases and volatile liquids [71]. The detection was based on changes in electrical resistance, which occurs when polymer-coated microelectrodes were exposed to the different samples. In this investigation, pH and sodium chloride were detected, and it is claimed that this approach may even be used to detect color for display device applications. This may lead to further development of an electronic eye. 

Abstract We review recent progress in wide bandgap thin-film and nanorod sensors made from GaN or ZnO and related materials for applications in the detection of gases such as oxygen, carbon dioxide and hydrogen. Practical aspects are covered, such as the use of differential sensor pairs to eliminate the effects of temperature variations and of the effect of humidity on the detection sensitivity. 

This technique is limited to detection of the evolved gases from a PEC experiment. After illumination, the electrode should be analyzed for signs of corrosion and the electrolyte should be separately analyzed to evaluate the presence of any corrosion products. For the separate detection of gases from the anode and cathode, the cell should ideally be divided into two compartments using a separator such as a fine pore glass frit or ion exchange membrane (Fig. 9.2b) to prevent product crossover which can be a major limitation in single compartment cells. 

Yajima et al. 1993) and sodium measurements in molten metals (Kumar and Fray 1989, 1993). In recent years there has been a considerable increase in research, development and applications of solid-electrolyte-based chemical sensors for the detection of gases such as CO2, SOx, H2O, NO c, HCl, CO and hydrocarbons (HCs). It is interesting to note that rare-earth elements are prominent components of many of the above sensors. 

Suitable probes should be installed in the soil at the property boundary surrounding the landfill to enable detection of gases migrating away from the facility. 

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