Note: Descriptions are shown in the official language in which they were submitted.
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-
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
-4-
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
-5-
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
-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.
7~
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.
D
~6~7~
-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.
1~ .
7~7
-10-
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
-14-
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
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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
-17-
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
-18-
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
3~ L7~
--1 9--
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.
