Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Calorimeter
Patent
1994-09-28
1996-01-02
Redding, David A.
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Calorimeter
422 56, 422 57, 422 8207, 422 8208, 422 83, 422 85, 422 86, 422 87, 436133, 128719, 128720, 12820523, G01N 2200
Patent
active
054806119
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with devices which provide a detectable indication that a volume of gas has an increased proportion of carbon dioxide compared to that present in normal ambient air. Such devices have a number of uses, one major use being to provide an indication of whether a tube has been correctly located in the airway (trachea) of a patient.
There are many clinical situations where it is necessary to place a tube in the trachea of a patient. This is done in order to supply air or a mixture of oxygen and other gases to the lungs of the patient. The correct placement of the tube in the trachea is very important. Accidents have been reported where the tube has been inadvertently placed in the oesophagus. It has been observed that the air in the trachea contains about 6% carbon dioxide, whereas the oesophagus contains air in which the concentration of carbon dioxide is normal (about 0.03%).
Several indicator devices which can detect the presence of an elevated proportion of carbon dioxide compared to that in air are known. Our prior PCT application WO91/05252 discloses a carbon dioxide monitor comprising a substrate provided with a colorimetric indicating member. The indicating member is an intimate mixture of a transparent polymer vehicle and a salt of an indicator anion and a lipophilic cation.
We have now devised a carbon dioxide detector provided with a fluorimetric sensing medium which is responsive to a carbon dioxide concentration in the proximal atmosphere. The inclusion of such fluorimetric media in a detector according to the present invention substantially enhances the sensitivity of such media in the detection of carbon dioxide.
According to the present invention therefore there is provided a carbon dioxide detector which comprises an indicating member comprising an intimate mixture of a polymer vehicle and a carbon dioxide sensing medium comprising an anionic fluorimetric dye and a lipophilic organic quaternary cation.
The response of the sensing medium to the level of carbon dioxide in the atmosphere involves the variation in the intensity of fluorescence emitted by the fluorimetric dye. The intensity of the fluorescence relies upon the fraction of the fluorimetric dye which is protonated which is in turn directly proportional to the carbon dioxide pressure. Protonation of the dye occurs via a reaction which involves both the lipophilic cation and the carbon dioxide as follows: ##STR1## where Q.sup.- is the lipophilic cation, and
As can be seen from the above reaction an increase in carbon dioxide pressure will result in a decrease in fluorescence. Where a qualitative indication of carbon dioxide concentration is required the change in fluorescence can be observed visually. However, where a quantative indication of carbon dioxide concentration is required the change in fluorescence can be monitored fluorimetrically.
The above reaction illustrates how the cation/fluorimetric dye complex generates the protonated form of the dye on reaction with carbon dioxide. The fluorimetric dye, being in anionic form in the complex, readily abstracts a proton form the water molecule in the presence of carbon dioxide. Such a phase transfer mechanism is advantageous as it promotes the sensitivity of the dye in the detection of carbon dioxide.
Preferred fluorimetric dyes include 1-hydroxypyrene-3,6,8-trisulphonate, 1,3-dihydroxypyrene-6,8-disulphonate, fluorescein, umbelliferone, 4methylumbelliferone, 3-benzothiazoylbelliferone, 7-hydroxycoumarin-3-carboxylic acid, 1-naphthol-2-sulphonate, 1-naphthol-4-sulphonate, 2-naphthol-6-sulphonate, 7-hydroxyflavone, 7-hydroxyisoflavone, 3-hydroxyxanthone, 3,6-dihydroxyxanthone, 7-hydroxy-4-methylchromon, 7-hydroxylepidone, 3-hydroxyxacridone, harmol methoiodide, salicylaldehyde semicarbazone and 2-hydroxycinnamic acid.
A particularly preferred dye comprises 1-hydroxypyrene-3,6,8-trisulphonate. The preference for 1-hydroxypyrene-3,6,8-trisulphonate is because of its low toxicity, a pk.sub.3 value in the range of 7.3-8.1 which is advantageous for making ph
REFERENCES:
patent: 5005572 (1991-04-01), Raenner et al.
patent: 5387525 (1995-02-01), Munkholm
Munkholm, C., et al. "Polymer Modification of Fiber Optic Chemical Sensors as a Method of Enhancing Fluorescence Signal for pH Measurement.", Anal. Chem. vol. 58, 1986, 1427-1430.
Weis, L., et al. "Fiber-Optic Fluorosensor for Oxygen and Carbon Dioxide", Anal. Chem. vol. 60, 1988, 2028-2030.
Chang Qing
Mills Andrew
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