Fast-response carbon dioxide

Gal-Or and Hoelscher (G5) have recently developed a fast and simple transient-response method for the measurement of concentration and volumetric mass-transfer coefficients in gas-liquid dispersions. The method involves the use of a transient response to a step change in the composition of the feed gas. The resulting change in the composition of the liquid phase of the dispersion is measured by means of a Clark electrode, which permits the rapid and accurate analysis of oxygen or carbon dioxide concentrations in a gas, in blood, or in any liquid mixture. 

The sensor for the measurement of high levels of CO2 in gas phase was developed, as well90. It was based on fluorescence resonance energy transfer between 0 long-lifetime ruthenium polypyridyl complex and the pH-active disazo dye Sudan III. The donor luminophore and the acceptor dye were both immobilized in a hydrophobic silica sol-gel/ethyl cellulose hybrid matrix. The sensor exhibited a fast and reversible response to carbon dioxide over a wide range of concentrations. 

The effect was used to detect traces of oxygen [103, 104) produced in the photosynthetic process. TTypaflavine, benzoflavine, Euchrysine 3R, Rheonine 3 A, Rhoduline Yellow, safranine, chlorophyll, and hematoporphyrin adsorbed on silica gel or aluminium oxide were the dyes that were most efficiently quenched. Unfortunately, most dyes are photolabile, and traces of water or ammonia strongly interfere. Hydrogen, nitrogen, methane, ethylene, and carbon dioxide are without influence. The method is suitable for the extremely sensitive determination of oxygen at partial pressures between O.S and 0.006 kPa and is characterized by a fast response tim but requires several seconds for regeneration. 

Expired air contains 2 to 5% carbon dioxide Although most carbon dioxide optodes are known to be particularly slow in response, the response time of this kind of sensor is less than 0 3 s (I) for 90% of the total signal change to occur. This is obviously due to the very thin coating. Such a fast response makes it possible to instrumentally monitor the concentration of carbon dioxide in respiratory air, but also to visually observe the continuous color change (from blue to yellow and back) while breathing through the capillary... 

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