6~7~7 BACKGROUND OF ~ IMV~:NTION
This invention relates generally to oxygen determinations and more particularly has reference to methods and apparatus for determining the con-centration of oxygen in a gaseous or liguld en-vironment based on luminescence quenching.
The two most common methods currently used for determining oxygen concentrations are the Winkler titration method and the oxygen electrode method.
The Winkler method is slow, intrusive, destroys the sample and does not lend itself to automation. The oxygen electrode method consumes oxygen, is sensitive to interferants such as Halothane anesthetic, is in-trusive, and is not readily applicable to the gas phase or vacuum systems. Hence, neither of these methods is particularly desirable.
It is known that many platinum group metal complexes luminesce intensely in the red region (600-650 nm) when excited with visible light or UV light (~ 550 nm).
Both the intensity and the lifetime of the luminescence is decreased when the complex is exposed to deactivators (quenchers). Oxygen, iron(III), copper(II), and mercury~II) are among the common guenchers. When a single quencher is present in an environment, the degree of intensity or lifetime quenching is directly related to the quencher concentration and can be used as an analytical method for determining that concentration.
~6~L7~L7 However, the inability of the method to discriminate among different quenchers in an envirollment has heretofore prevented the method from being universally applicable.
The discrimination problem is particularly acute when dealing with a liquid environment. If the luminescent complexe$ are dissolved directly in the solution, a variet~ of dissolved organic and inorganic, contaminants and interferents would contribute to the ~uenching-and would produce an erroneous indication of the oxygen concentration.
Because the luminescence quenching method presents the possibility of making oxygen determinations without the limitations inherent in the Winkler titration method and the oxygen electrode method, it is desirable to improve upon known methods and apparatus in the luminescence quenching art in order to make that method universally applicable.
Pertinent United States and foreign patents are found in Class 23, subclasses 26, 52, 83, 230, 259, 906 and 927; Class 73, subclass 19; Class 204, subclasses 1, lY, 192P and 195; Class 250, subclasses 71 and 361C;
Class 252, subclasses 188.3CL and 301.2; and Class 422, subclasses 52, 55-58, 83, 85-88 and 91 of the Official Classifications of Patents in the U. S. Patent and Trademark Offi~e.
Examples of pertinen-t patents are V. S. Patent Nos.
998,091; 1,456,964; 2,351,644; 2,929,687i 3,112,99~9;
3,697,226; 3,725,658; 3,764,269; 3,768, 976i 3,881,869;
- ` ~L2~;~7~
3,897,214; 3,976,451; 4,05~,490; ~,073,623; 4,089,797;
4,181,501; 4,231,754; 4,260,392; 4,272,249; 4,272,484 and 4,272,485.
U. S. Patent 3,725,658 shows a method and apparatus for detecting oxygen in a gas stream. The apparatus em-ploys a sensor film comprising afluorescent material dissolved in a carrier or solvent and supported on a substrate. Oxygen contained in the gas stream is dissolved into the Eilm and quenches the ~luorescent emission, the e~tent of quenching being proportional to the oxygen content of the gas stream.
U. S. Patent 3,764,269 shows the use of a gas permeable membrane which permits diffusion of a particular gas while providing protection against the adverse effects of the environment. An electrochemical device detects the concentration of gas which passes through the porous layer and activates the electrode~
U. S. Patent 3,881,869 discloses the chemiluminescent detection of ozone concentration in a gas sample. The gas sample conta`cts an organic polymer having a backbone chain consisting of carbon atoms to produce a chemiluminescent reaction. The concentration of ozone is proportional to the intensity of light emitted by the reaction.
U. S. Patent 4,089,79~ discloses chemiluminescent warning capsules having an air-reactive chemiluminescent formulation encapsulated with a catalyst. Crushing the capsule mixes the air-reactive formulation and the catalyst ~ 26~L7~7 in the external environment to produce chemi-luminescence if air is present.
U. S. Patent 4,272,484 uses fluorescence methods to measure oxygen content a~ter first separating blood protein fractions and other components b~ use o~ a gas permeable membrance. U. S Patent 4 r 272,485 is a related disclosure which includes a carrier which transports particles through the membrane.
U. S. Patent 3,112,999 discloses a gas, particularly carbon monoxide, which permeates a porous layer to make an indication.
U. S. Patent 2,929,687 discloses a dissolved oxygen test.
U. S. Patent 3,768,976 shows a polymeric ~ilm through which oxygen migrates to cause an indication.
U. S. Patent 3,976,451 describes selectively permeable membranes for passing oxygen.
- U. S. Patent 4,260,392 shows a selective-ly permeable plastic tape.
U. S. Patent 3,897,214 discloses reagents impregnated in plastic fibers.
U. S. Patent 3,697,266 discloses a system using a graded scale for visual comparison. The comparison scale is not placed in a solution. It is merely a screen.
U. S. Patent 998,091 discloses a color comparing scheme in which thickness is varied in a graded standard.
~61~7~7 U. S. Patents 4,181,501 and 4,054,490 disclose wedge shaped concentration sensors.
U. S. Patent 2,351,644 discloses a stepped sensor.
U. S. Patent 4,073,623 discloses a non-immersed sensor and standard used for visual comparisons.
U. S. Patent 1,456,964 discloses light intensity comparison.
The remaining patents are of lesser interest.
The following publications are also of interest:
Energy Transfer in Chemiluminescence, Roswell, Paul and White, Journal of the American Chemical Society, 92:16, August 12, 1970, pp. 4855-60; Oxygen Quenching of Charge-Transfer Excited States of Ruthenium tII) Complexes.
Evidence for Singlet Oxygen Production, Demas, Diemente and Harris, Journal of the American Chemical Society, 95:20, October 3, 1973, pp. 6864-65; Enerqy Transfer from Luminescent Transition Metal ComPlexes to Oxygen, Demas, Harris and McBride, Journal o~ the American Chemical Society, 99vll, May 25, 1977, pp. 3547-3551; Britton, Hydrogen Ions Their Determination and Importance in Pure and Industrial Chemistry, D. Van Nostrand Company, Inc. (1943) pp. 338-43; and Fiberoptics Simplify Remote Analyses, C~EN, September 27, 1982, pp. 28-30. Porphyrins XVIII.
Luminescencè of (Co), (Ni), Pd, Pt Complexes, East~ood and Gouterman, Journal of Melecular Spectroscopy, 35:3, September 1970, pp. 359-375; Porphrins. XIX. Tripdoublet and Quartet Luminescence in Cu and VO complexes, Gouterman, Mothies, 6~7~7 , Smith, and Caughey, Journal of Cehmical Physics, 5~:7, April 1, 1970, pp. 3795-3802; Electron-Transfer Quenching of the Luminescent Excited State of OctachlorodirhenatetIII), Nocera and Gray, Journal of the American Chemieal Society 103, 1971, pp. 7349-7350; Spectroscopic Properties and Redox Chemistry of the Phosphorescent State of Pt tP2_5)~H8~ , Che, Butler, and Gray, ~ournal of the Ameriean Chemical Soeiety 103, 1981, pp. 7796-7797; lectronie Speetroseop~
of Diphosphine- and Diarsine-Bridget R~odium (I) Dimers, Fordyce and Crosby, Journal of the American Chemical Soeiety 104, 1982, pp. 985-988.
The Demas, et al artieles diselose oxygen quenehing of ~-diimine eomplexes of Ru(II), Os~II), and Ir(III).
2, 2'-bipyridine, 1, 10-phenanthroline and substituted derivatives are used as ligands to form the metal-ligand eomplexes. A kine-tie meehanism for the eomplex oxyyen interaetion is proposed.
The Roswell artiele diseusses intermolecular energy transfer in ehemilumineseenee.
The Britton publication discloses a wedge method for the determination of indieator eonstants oE two-eolor indica-tors.
The C&EN artiele deals with PTFE control membranes in the eontext of laser optrodes and optical fibers.
The Eastwood artiele deseribes the room temperature lumineseenee and oxygen quenching of Pd and Pt porphyrin complexes in fluid solutions.
The Gouterman et al, article describes low temperature lumineseence of Cu and VO porphyrins. Extrapolation of their data to room temperature indicates oxygen quenchable lifetimes.
2~;~7~'7 The Nocera paper reports quenching of dinuclear Re~
species. Mononuclear and dinuclear ~e complexes also have quenchable excited states.
The Che paper reports long excited state lifetimes and solution oxygen quenching of a dimeric Pt complex in solution and long-lived quenchable excited states of Rh dimers.
The Fordyce reference reports long-lived low tempera-ture emissions of Rh(I) with bridging ligands. Rh~I) and Ir(I) data are referenced. Extrapolation of their data to room temperature suggests oxygen quenchable lifetimes.
SUMMARY OF THE INVENTION
The present invention overcomes the problems which exist in the prior art.
The present invention provides a method for measuring oxygen concentrations either in solutions or in the yas phase. The method is based on the shortening of the life-time or decrease in the emission intensity, i.e., quenching, of particular metal complexes, preferable ruthenium(II) complexes wlth c~ -diimine ligands in the presence of oxygen.
The oxygen concentrations can be directly related to the degree of quenching. To prevent the complexes from responding to con-taminants and interferents, the complex is protected by being immobilized in a gas permeable, solvent impermeable polymer, such as silicon rubber.
The invention provides an oxygen concentration sensor and a graded calibration standard which can be visually compared to determine oxygen concentration.
The sensor is a fluorophor immobilized in oxygen-permeable .
~2~7~q polymer~ The graded.calibration s-tandard is either tapered with thicker (brighter~ portions corresponding to lower oxygen concentrations on the sensor or with higher (brighter) concentrations of a fluorophor at one end of the standard. The sensor and standard are exposed to the environment being sampled and are excited by a light source. Intensity of the light emitted by the sensor is decreased by the oxygen. The eye, or an elec-tronic detector, is used to determine the part of the standard that has the same brightness as the sensor.
An object of the invention is to provide an improved method and apparatus for oxygen determinations.
A further object of the invention is to provide a method and apparatus for oxygen determination based on luminescence quenching.
Still another object of the invention is to provide an oxygen sensor having a platinum group metal complex with c~-diimine ligands immobilized in an oxygen permeable polymer which tends to prevent interfering quenchers from interacting with the complexes.
A further object of the invention is to provide a method for measuring oxygen concentrations which is usable in both liq.uid environments and gaseous environments.
A further object of the invention is to provide an oxygen determination method which is non-destructive and relatively non-intrusive and which readily lends itself to miniaturization and automation.
g Still another object of the invention is to provide a method for oxygen determination which is based on a quencher-related decrease in lifetime of the luminescence of a luminescent material and requires no reference.
Still another object of the invention is to provide a method of oxygen determination which is based on a quanti-tative quencher related decrease in the luminescence inten-sity of a luminescent material.
Yet another object of the invention is to provide an inexpensive method and apparatus for visually determining the extent of quenching.
Yet another object of the invention is to provide a method for determining oxygen concentration which involves comparing the emission intensity of a sensor to the emission intensity of a series of reference emitters.
In accordance with the present invention, a method for determining the presence of oxygen in an environment com-prises providing luminescent material whose intensity and llfetime of luminescence is quenchable by oxygen. The material is then incorporated in a carrier material which is relatively permeable to oxygen and relatively impermeable to interfering quenchers, thus forming a sensor. The sensor is exposed to an environment to be sampled. This allows oxygen in the environment to permeate the carrier material and quench the luminescent material. The quenching-related decrease in intensity or lifetime of luminescence is then measured. Then, the presence of oxygen can be determined based on the measured quenching.
Also in accordance with the present invention, a method for determining the amount of oxygen in an environment com-prises providing a sensor having luminescent material whose luminescence is quenchable in oxygen. A reference device is .~ _ ~ ~$
~12~L7~7 -9a-provided having -the luminescent material distributed therein in areas having differing amoun-ts of the material. The sen-sor and the reference are arranged in a proximate relation-ship and are exposed to an environment to be sampled. This allows the oxygen in the environment to quench the luminescent material in the sensor. The oxygen access to the luminescent material in the reference is restricted. The luminescence of the sensor is compared with the luminescence of the reference to determine a similarity of luminescence between the sensor and an area of the reference. The amount of oxygen in the environment ls determined based on the amount of luminescent material present in the area of the reference.
Still in accordance with the present invention, a sen-sor for determining the presence of oxygen in an environment comprises a luminescent material whose intensity and lifetime of luminescence is quenchable by oxygen. The luminescent material is incorporated in a carrier material which is rela-tively permeable to oxygen and relatively impermeable to interfering quenchers.
Still in accordance with the present invention, a moni-tor for determining oxygen concentration in an environment comprises a support which contains a mixture of luminescent materials quenchable by oxygen. The materials have differing sensitivities to oxygen quenching and have differing colors of emission.
Still in accordance with the present invention, an apparatus uses the phase shift of the luminescence of material relative to a modulated excitation source in order to measure the lifetime and relate it to the oxygen concen-tration.
-9b-The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram, in side view, of a visual oxygen monitoring system embodying features of the present invention.
Figure 2 is a top plan view of the sensor and reference shown in Figure 1.
Figure 3 is a detailed schematic diagram of a reference used with the system shown in Figures 1 and 2.
7~7 Figure 4 is a detailed schematic diagram of an al-terna-tive reference used with the system shown in Figures 1 and 2.
DETAILED DESCRIPTION OF Tl-IE INVENTION
The present invention provides a method and apparatus for measuring oxygen concentrations in liquid environments and gaseous environments. The method is based on the shortening of the lifetime or decrease in the emission intensity (quenching) of certain luminescent materials in the presence of oxygen.
The oxygen concentrations can be directly related to the degree of quenching in a manner well known in the art.
The luminescent materials are luminescent inorganic materials which luminesce when excited with visible or ultra-violet light and whose luminescence is quenchable by oxygen and other quenchers.
rrhe preferred luminescent materials are principally platinum group metal complexes, specifically, ruthenium, osmium, iridium, rhodium, palladium, platinium, rhenium and chromium complexes with C~-diimine ligands. In most instances, the tris complexes are used, but it is recognized that mixed ligand complexes can also be used to provide a degree of design flexi-bility not otherwise availabe. Suitable ligand metal complexes include complexes of ruthenium(II), osmium(II), iridium(III), rhodium(III), and chromium(III) ions with 2,2'-bipyridine, 1,10-phenanthroline, 4,7-diphenyl-(1,10-phenanthroline), 4,7-dimethyl-1,10-phenanthroline, 4,7-disulfonated-diphenyl-1,10-phenanthroline, 5-bromo-1,10-phenanthroline, 5-chloro-1,10 ~Z6~7~
phenanthroline, 2,2'-bi-2-thiazoline, 2,2'-bithiazole, and other c~ -diimine ligands.
Other suitable systems could include porphyrin or phthalocyanine complexes of Vo2 , Cu2 , Zn2~, Pt2 and Pd2+
or dimeric Rh, Pt/ or Ir complexes. 5uitable ligands would be etioporphyrin, octaethylporphin,-porphin and phtalocyanine.
To prevent the complexes from responding to contaminants and interferents, the complex is protected by being immobilized in a gas permeable, solvent impermeable polymer. Preferred polymers include Plexiglas*, polyvinyl chloride (PVC), polystyrene, polycarbonate, latex, fluorinated polymers such as Teflon* and silicon rubbers, such as GE RTV SILASTIC*118, which is very temperature resistant.- A sensor using SILASTIC*118 exhibits a substantial change in lifetime or intensity of luminescence on going from an oxygen saturated environment to a deoxygenated environment. The precision and accuracy of oxy-gen determinations is about 2 per cent arid the same responses are obtained for both lifetime and intensity ~uenching measure-ments. It responds rapidly to changes in both gas phase and solution dissolved oxygen concentrations. The plexiglass and PVC systems have lower oxygen sensitivities and are, thus, suitable for determinations at high (above atmospheric) oxygen pressures. Commercially available silicon rubber has a high permeability of oxygen and excludes highly polar compounds and hydrated ions which is why its use in the present invention is desirable.
The preferred oxygen sensor used tris(4,7-diphenyl-1,10-*: Trademarks .~ .
26~17 phenanthroline)ruthenium(II) dissolved in the SOLASTIC 188 material.
The luminescent complexes can be uniformly diffused into the polymer from dichloromethane and/or alcohol solutions.
Alternatively, the complexes can be mixed with the polymer be-fore final polymerization.
il`he metal complexes can be mechanically or chemically incorporated into the polymer matrix. In one embodiment, the complex molecules are chemically attached to the backbone of the matrix. Either a covalent or an ionic attachment o-f the complex to the polymer can be used. For example, cation exchange bound ~U~ complexes exhlbit high sensitivity to glS phase oxygen quenchlng.
The completed sensor is an integral device having the luminescent material incorporated directly into the self-sup-porting polymer barrier system. It can be ln the ~orm of a strip, a block, a sheet, a microsphere, a film or a laminate and it can be either solid or hollow. If desired, the sensor can be a thin sensing layer diffused onto a thick plate. An overcoat of a less reactive polyrner can be used to further reduce interactions with the solvent or quenahers.
In one embodiment, a thin film sensor is formed by leaching sodium from glass to ~or a porous matrix, dipping the glass into a solution o~ luminescent material and then covering the surface of the glass with a layer lmpermeable to water.
Sultable agents are silicon water probfing which reacts with the surface or polymer overcoats.
To reduce expenses, it is desirable that the sensor be in the form o~ reusable polymer coated cuvettes which are highly durable.
-13- '~ ~6 ~q ~
In use, the sensor is exposed to the liquid or gaseous environment being sampled. Because the polymer material has a relatively high permeability to oxygen, the oxygen will per-meate through the material and interact with -the luminescent material to act as a quencher. Howeve~, the polymer will ex-clude most common ionic and organic interferents and contami-nants.
The quenching-related decrease in the intensity or life-time of luminescence is measured and that measurement is used to determine the concentration of oxygen in the environment.
By measuring the luminescence lifetime or intensity using a back scattering technique, interferences caused by strong scat-tering or absorbing solutions are eliminated.
In an alternative embodiment, the sensor is excited by a modulated light source and a phase shift measurement is made of the luminescence to yield the lifetimes.
The present invention provides a particularly desirable means for oxygen determiatnion because it is non-invasive and does not consume oxygen. It is usable over an extremely wide range of oxygen concentrations or partial pressures and readily lends itself to miniaturized and automated analyses.
Test results have demonstra-ted that the present invention is sensitive, selective and readily implemented. With the preferred combination of metal complex and polymer matrix, a material has been prepared that shows a 3000~ increase in lumi-nescence lifetime on going from an oxygen saturated aqueous environment to a nitrogen saturated environment. Response time is subsecond to minutes depending on film thickness~ The same 7~7 complex-polymer sensor respond equally well to gas phase oxygen concentrations. Filrns of 0 .001"~ thickness have been shown to respond in <1/6 sec. and follow faithfully the oxygen con-centration in the breath of a human.
The ability of the polymer to protect the complex from interferents was shown by introducing a film into a concen-trated solution of iron(III). Normally iron(III) is an excel-lent quencher of unprotected complexes. Yet, even at the high iron(III) concentrations used, there was no detectable quenching~
Strong acid strong base, complexing agents (EDTA), and deter-gents (NaLS) were likewise without effect. ~he sensor is also immune to any deactivation by common anesthetic gases s~ch as Halothane and nitrous oxide at concentrations well above those used medically.
Applications for the present invention iclude: (i) measuring dissolved oxygen in aqueous samples and in oryanic solvents; (2) de-term1ning the oxygen for biochemical oxygen demand (BOD) measurements; ~3) measuring levels of oxygen in blood both in vi-tro and in vivo using a fiber-optic probe;
(4) measuring oxygen levels in air samples (e.g., mines, indus-trial hazard areas, oxygen tents, high pressure oxygen burn treatment and decompression chambers, industrial reactors space capsules, etc.); (5) measuring low oxygen levels in vacuum systems (i.e., a low-cost vacuum gauge); and (6) monitoring low oxygen levels in various chemical reaction vessels, e.g., glove boxes and other sytems purged with inert gas.
~26~7~L7 An application in Category 1 would inclucle pollution moni-toring of waste water.
The application in Category 2 is especially interesting in view of the above described test using iron~III). Iron(III) is added as a nutrient in BOD determinations. However, the test showed that iron(III) concentrations hundreds of tlmes larger than would be encountered in BOD analyses have no de-tectable quenching effect. BOD determinations using quantita-tive intenslty monitoring have been implemented.
The Category 3 applications could involve, for example, the placing of a sensor at the end of a fiber optic catheter for use in following oxygen concentrations in blood vessels and tissue the heart is beating. Such a system has great safety as there is no electrical connection to the patient.
Advantages of the present invention are that it is a~non-destructive and relatively non-intrusive method and that a common system can be used to measure oxygen in polluted, murky water, air samples, vacuum sys-tems and other diverse types of systems. The invention is operable over a temperature range of about -300F to about 400F.
In addition, the system lends i-tself readily -to measure-ments on very small sample size ( ~5~L), instrumental miniatu-rization, and automation. By encapsulating the complex probe in microscopic beads, oxygen concentrations can be measured under a microscope in growing cellular samples.
Quantitative intensity and lifetime methods for measuring oxygen concentrations are accurate and precise. There are many times, however, when a semiquantitative or qualitative method 31 ~6~717 ~ -16-of even lower cost is desirable.
To avoid the cost of a more elaborate instrument the present invention further provides a low cost visual detection system with an internal reference for semiquantitative or qualitative oxygen monitoring.
In the present invention, the human eye is used as the detector. The scheme is similar in application to pH paper except that one monitors oxygen concentrations by comparing the emission intensity of the sensor in the gas or liquid environ-ment to a series of reference emitters in that environment.
Although suitable for semi-quantitation of oxygen concentrations, the system is also usable as a go - no go system where instanta-neous visual discrimination between pure oxygen, air, or an oxy-gen-free system is required.
A schematic diagram of this system is shown in Figures 1 through 4.
A luminescent oxygen sensor 10 and a reference emitter 12 are placed side-by-side in the sample fluid or gas environment 14. The sensor 10 includes a fluorophor immobilized in an oxygen-permeable support, ~ , a polymer. The sensor 10 luminesces when the fluorophor is excited by a light source 16.
The intensity of the emitted light is decreased by oxygen in the environment 14 which serves as a ~uencher.
The human eye càn easily judge the differences in intensity of the emitted light when the sensor film is exposed to pure N2, air and 2 environments.
The estimation of the oxygen concentration beyond air, 2 or N2 is improved by using a reference emitter 12 which is a ~6~L7~7 concentration or optical density graded calibration standard.
In the standard, the same fluorophor as used in the sensor 10 would be immobilized in a riyid polymer, e.g., plexiglass, which shows limited permeability to 2 The fluorophor is distributed in the polymer in areas having different luminescence levels.
The reference emitter 12 next to the sensor 10 provides reference concentration information by emitting reference luminescence levels. The differences in 1uminescence between the sensor 10 and the reference 12 are visually determined by the human eye 18. ~n optional blocking filter 20 can be positioned between the eye 18 and the sensor 10 and reference 12 to improve viewing contrast by removing scattered excitation light. In addition, a filter (not shown) over the light source may be used to improve viewing by limiting excitation wavelengths.
In one embodiment, the standard 12' has a tapered wedge shape as shown in Figure 3. The luminescenceintensity at each point is determined by the thickness of the standard 12'.
The thicker (brighter) portions correspond to lower oxygen concentrations on the sensor 10. A non-uniform slope on the wedge improves the linearity of calibration.
In an alternative embodiment, the standard 12" is a concentration graded reference with the concentration of fluorophor contained therein increasing from one end to the other. The higner (brighter) concentrations correspond to lower o~ygen concentrations on the sensor. In the graded standard 1~" shown in FiguTe 4, the relative concentration of the fluorophor is indicated by the dot density. The sensor 12" is of uniform thickness.
7gl7 The graded concentration standard 12'' can be Eormed by withdrawing a polymer film from a solution containing the fluorophor material. The areas of the film which remain longer in the solution contain greater concentrations of the fluorophor.
In the preferred embodiment, the sensor 10 and the reference 12 are formed of identical luminescent materials.
This ensures that the emission colors are the same and that the observer wiil only be comparing intensities.
Fluorophors suitable for use in the present invention include, but are not limited to, the metal complexes discussed above. The preferred material is tris(4,7-diphenyl-1, 10-phenanthroline)ruthenium(II) immobilized in a silicon rubber polymer matrix. Other fluorophors and polymer matrices will give greater or lesser sensitivity.
The system shown in the figures is used by allowing the oxygen in the environment 14 to impinge upon the sensor 10 and reference 12. The support matrix in the sensor 10 is permeable to oxygen, and thus allows the oxygen to quench the luminscent material. The matrix in the reference 12 restricts oxygen access to the fluorophor material therein.
The luminescence of the quenched sensor 10 is then compared to theluminescence of the reference 12. The area of the reference 12 having the same luminescence as the sensor l0 is then visually selected. Krowledge of the amount of luminesc~nt material present in the selected area is used to determine
the amount of oxygen present in the environmen-t 1~. Wi~h proper calibration, a visual match of emission intensity can allow oxygen estimations to within a ew per cent.
For sensor 10, films of 0.001" thickness, the response time is subsecond. Thicker sensor films respond more slowly and provide indications of average oxygen concentrations.
In an alternative embodiment, the present invention contemplates the use of a self-referencing sensor. Such a sensor includes a mixture of fluorophors which have differing sensitivities to oxygen quenching and differing colors of emission. By suitably adjusting the characteristics, the sensor is made to change colors at different oxygen concentrations.
It is thus possible to completely dispense with the reference emitter 12 used with the system described above. The self-referencing sensor is especially useful in go-on cJo applications.
The referencing systems described above are inexpensive and provide stable, long-lasting, rapid monitors for gaseous or liquid oxygen levels. They can be incorporated into operating room gas lines, breathing masks, and other hospital devices where the shut-off or improper connection of oxygen could be fatal. They can also be used in mines and industrial areas where oxygen levels vary. Applications as far-reaching as space capsules and as ordinary as welding machines (He-arc purges) are also contemplated.
While the invention has been described with reference to specific embodiments, the exact nature and scope of the invention is defined in the following claims.