Carbon dioxide sensor

Carbon dioxide devices were originally developed by Severinghaus and Bradley (102) to measure the partial pressure of carbon dioxide in blood. This electrode, still in use today (in various automated systems for blood gas analysis), consists of an ordinary glass pH electrode covered by a carbon dioxide membrane, usually silicone, with an electrolyte (sodium bicarbonate-sodium chloride) solution entrapped between (Fig. 6.21). When carbon dioxide from the outer sample diffuses through the semipermeable membrane, it lowers the pH of the inner solution  

Such changes in pH are sensed by the inner glass electrode. The overall cell potential is thus determined by the carbon dioxide concentration in the sample  

Such a Nernstian response of 59-mV/decade changes in concentration is commonly observed (at 25°C). Relation to the partial pressure carbon dioxide is accomplished by the use of Henry s law. A catheter sensor configuration has been developed for in vivo monitoring of blood carbon dioxide (104). 

By using different membranes, it is possible to obtain potentiometric sensors for gases such as sulfur dioxide or nitrogen dioxide. Such sensors employ similar (acid-base) or other equilibrium processes. These devices, along with their equilibrium processes and internal electrodes, are summarized in Table 6.2. Membrane coverage of other ion-selective electrodes (e.g., chloride) can be used for the sensing of other gases (e.g., chlorine). 

FIGURE 6-17 Schematic of the potentiometric sensor for carbon dioxide. (Reproduced with permission from reference 60.) 

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Vaisaia. The new C.ARBOCAP carbon dioxide sensor. Helsinki Vai.sala Oyj. http //www.vais-ala.com/. 

Zhang Z., Seitz W.R., A carbon dioxide sensor based on fluorescence, Anal. Chim. Acta 1984 160 305. 

Segawa H., Ohnishi E., Arai Y., Yoshida K., Sensitivity of fiber-optic carbon dioxide sensors utilizing indicator dye, Sens. ActuatB 2003 94 276-281. 

Weigl B.H., Wolfbeis O.S., Sensitivity studies on optical carbon dioxide sensors based on ion-pairing, Sens. Actuators B 1995 28 151-156. 

Neurauter G, Klimant I, Wolfbeis OS (1999) Microsecond lifetime-based optical carbon dioxide sensor using luminescence resonance energy transfer. Anal Chim Acta 382 67-75... 

The measurement of temperature is necessary for the calibration of most probes like blood oxygen, pH, ions, voltage, and carbon dioxide sensors. The use of optical methods to invasively measure physiological temperature has the advantage of electrical isolation, when compared to traditional approaches like the use of thermocouplers. 

GSSs are purposefully designed electrochemical cells, a galvanic cell in the case of carbon dioxide sensors, and an electrolytic cell in the case of the oxygen sensors. 

Carbon dioxide sensor — An electrochemical device for measuring the -+ partial pressure of carbon dioxide, originally developed for measurements with blood by Sever-inghaus and Bradley [i]. It consists of a glass electrode as used for pH measurements covered with a membrane selectively permeable for CO2, e.g., silicone. Between membrane and glass electrode an electrolyte solution containing NaCl and Na2C03 is entrapped. 

Carbon dioxide sensor — Figure. Schematic cross section of a carbon dioxide sensor... 

Another urea electrode uses a carbon dioxide sensor covered with urease to measure the second product of the urea-urease reaction, HCOs. Na " and K" " had no influence on this electrode and the linear range was 0.1-10 mM (64). 

Miura, N., Yao, S., Shimizu, Y. and Yamazoe, N. (1992) Carbon dioxide sensor using sodium ion conductor and binary carbonate auxiliary phase. J. Electrochem. Soc., 139 (5), 1384—8. 

Ikeda, S., Kondo, T. Kato, S., Ito, K., Nomura, K. and Fujita, Y. (1995) Carbon dioxide sensor using solid electrolytes with zirconium phosphate framework (2). Properties of the CO, gas sensor using Mgi.i5Zr4P5 7810.30,4 as electrolyte. Solid-State Ionics, 79, 354—7. 

As early as 1975, Ahn et al. developed an enzyme electrode for glutamate composed of L-glutamate decarboxylase (EC 4.1.1.15) and a carbon dioxide sensor. 

Potentiometric gas sensors for the reaction products, NH3 and CO2, have also been employed. Since these measurements are based on gas diffusion through a hydrophobic membrane, no direct disturbances by sample constituents occur. As early as 1969, Guilbault et al. coupled immobilized urease with a carbon dioxide sensor. Anfalt et al. (1973) applied an ammonia gas sensitive electrode to urea assay. A major drawback of these sensors is their long response time which is due to the slow diffusion of the gases. Since it takes several additional minutes to reach a new baseline after each measurement, only a few samples can be processed per hour. Guilbault et al. (1985) therefore tried an NH3 electrode, the interned buffer of which was exchanged after each measurement (double injection electrode). This approach led to a substantial decrease of the washing time. 

Fabrication of a microbial carbon dioxide sensor using semiconductor fabrication techniques Electroanalysis 1 305-9... 

The Severinghaus-type carbon dioxide sensor measures CO2 concentration by monitoring the resultant pH change when ambient CO2 dissolves into an internal electrolyte to form bicarbonate ions ... 

In addition to slow diffusion of the CO2 gas through the gas-permeable membrane, conventional Severinghaus-type carbon dioxide sensors suffer from an additional rate limitation, namely slow reaction kinetics. The hydration reaction of CO2... 

Constantine H P, Crow M R and Forster R E 1965 Rate of the reaction of carbon dioxide with human red blood cells Am. J. Physiol 208 801-11 Lutmann A, Miickenhoff K and Loeschcke H H 1978 Fast measurement of the CO2 partial pressure in gases and fluids Pfluegers Arch. Ges. Physiol 375 279-88 Wu X-Q, Shimizu Y and Egashira M 1989 Carbon dioxide sensor consisting of K2C03-polyethylene glycol solution supported on porous ceramics J. Electrochem. Soc. 136 2892-5... 

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