Chemical sensors oxygen

Kerry J.P., Papkovsky D.B., Development and use of non-destructive, continuous assessment, chemical oxygen sensors in packs containing sensitive foodstuffs. Res. Adv. Food Sci. 2002 3 121-140. 

Electrochemical Microsensors. The most successful chemical microsensor in use as of the mid-1990s is the oxygen sensor found in the exhaust system of almost all modem automobiles (see Exhaust control, automotive). It is an electrochemical sensor that uses a soHd electrolyte, often doped Zr02, as an oxygen ion conductor. The sensor exemplifies many of the properties considered desirable for all chemical microsensors. It works in a process-control situation and has very fast (- 100 ms) response time for feedback control. It is relatively inexpensive because it is designed specifically for one task and is mass-produced. It is relatively immune to other chemical species found in exhaust that could act as interferants. It performs in a very hostile environment and is reHable over a long period of time (36). 

Electrochemistry plays an important role in the large domain of. sensors, especially for gas analysis, that turn the chemical concentration of a gas component into an electrical signal. The longest-established sensors of this kind depend on superionic conductors, notably stabilised zirconia. The most important is probably the oxygen sensor used for analysing automobile exhaust gases (Figure 11.10). The space on one side of a solid-oxide electrolyte is filled with the gas to be analysed, the other side... 

In recent years further concepts have been developed for the construction of polymer-based diodes, requiring either two conjugated polymers (PA and poly(A-methyl-pyrrole) 2 > or poly(A-methylpyrrole in a p-type silicon wafer solid-state field-effect transistor By modifying the transistor switching, these electronic devices can also be employed as pH-sensitive chemical sensors or as hydrogen or oxygen sensors 221) in aqueous solutions. Recently a PPy alcohol sensor has also been reported 222). 

A number of optical chemical sensor systems have been developed for food and packaging applications and proven their utility. Some sensors, such as phase-fluorimetric oxygen sensor, have already reached high degree of maturity and demonstrated their potential for use on a mass scale. While the others still require extensive research, development and search for new solutions, so as to match basic practical requirements for such sensors. The experience and lessons learned with current optical sensor systems must be... 

Izu, N. Murayama, N. Shin, W. Matsubara, I. Kanzaki, S. 2004. Resistive oxygen sensors using cerium oxide thin films prepared by metal organic chemical vapor deposition and sputtering. Jpn. J. Appl. Phys. 43 6920-6924. 

Uses. Jewelry oxygen sensor in internal combustion engines chemical and electrical industries dentistry windings of high-temperature furnaces electroplating photography cancer chemotherapeutic agents... 

Fiber optical sensors are popular devices for the design of optical chemosen-sors. They are based on the change of optical properties (such as adsorption or luminescence) of particular chemical indicators. For example, fiber optical oxygen sensors are produced by the immobilization of oxygen sensitive dyes on the tip of an optical fiber and in an appropriate matrix. 

CaO has been used to some degree as a stabilizer and is attractive due to its low cost. Its ionic conductivity, however, is approximately an order of magnitude less than an equivalent yttria stabilized body. There has also been some question about the chemical stability of a CaO stabilized body, although this may be more of a factor with a partially stabilized body than a fully stabilized body. Calcia fully stabilized ZrO has been and may still be used in commercial production of oxygen sensors. 

When rebreathing systems are used for the delivery of xenon, its concentration within the system needs to be closely monitored. Infrared gas analysers cannot detect xenon, since it is a single atom, and as it is chemically inert its physical properties must be utilised. Mass spectrometry is the most accurate method but it is expensive and it is impractical for clinical use. A calibrated katharometer combined with a galvanic oxygen sensor is a satisfactory alternative which provides a reasonably accurate measure ( 1%). 

Figure 3 shows a TWC system and a typical performance of the TWC. The three components are highly purified over the catalyst around the stoichiometric point. The oxidizing and reducing components have almost the same chemical equivalent in the narrow shadowed region, and CO, HC and NOx are converted into H20, C02 and N2 (Fig. 3b). The atmosphere of the TWC is automatically controlled around the stoichiometric point by the TWC system. The flow rate of air is monitored and the fuel injection is controlled by a computerized system to obtain a suitable A/F ratio (Fig. 3c). The signal from oxygen sensor is used as a feedback for the fuel and air injection control loop. Therefore, the exhaust gases are fluctuating streams between oxidizing and reducing periodically and alternatively.

Logothetis, E.M. (1987) In Turner, D.R. (Ed.) Oxygen Sensors for Automotive Applications, in Chemical Sensors. Electrochemical Society, p. 142. 

Figure 9. I-V characteristics of amperometric oxygen sensor (700 °C). Reproduced with permission from Ref. 6. Copyright 1984 Japan Association of Chemical Sensors.

Jeong, B.G., S.M. Yoon, C.H. Choi, et al. 2007. Performance of an electrochemical COD (chemical oxygen demand) sensor with an electrode-surface grinding unit. J. Environ. Monit. 9 1352-1357. 

Fig. 7 Vertical distribution versus density (agy kg m 3) of temperature (T), salinity (S), transmission (Xmiss), dissolved oxygen measured with YSI oxygen sensor (02SB), dissolved oxygen measured by Winkler titration (02), hydrogen sulfide (H2S), phosphate (PO4), silicate (Si), nitrite (N02), ammonia (NH4), dissolved manganese (Mn diss), bivalent iron (Fe(II)), and trivalent iron (Fe(III)) at a station near the Bosporus (Cast 16, RV Knorr 172-05 cruise, April 04,2003). Concentrations of chemical parameters are in xM...

O. S. Wolfbeis, Oxygen Sensors, in Fiber Optic Chemical Sensors and Biosensors, O. S. Wolfbeis, Ed., CRC Press, Boston 1991 pp. 19-54. 

Chemical methods can also be employed to assess the competition between the formation of 02 and O2. A specific chemical probe may react either with 02 or O2 and 5ueld a fluorescent product. For example, nonfluorescent 3 -(p-aminophenyl)fluorescein reacts with hydroxyl radicals, formed subsequently to the formation of O2, to give fluorescein as oxidation product (83), whereas Singlet Oxygen Sensor Green (Molecular Probes) specifically reacts with 02 to give another fluorescent product (84). Admittedly, this again is not a direct comparison between 02 and O2, and the conversion... 

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