Method and apparatus for measuring oxygen concentration
First Claim
1. A method of measuring oxygen concentration in a container comprising:
- providing a container having a luminescent compound disposed in an interior space of the container, the luminescent compound having a luminescent emission that is sensitive to quenching by oxygen;
irradiating the luminescent compound with light having a wavelength that is absorbed by the luminescent compound so that the luminescent compound is promoted into an excited state;
terminating the irradiation of the luminescent compound when the luminescent compound achieves a steady state between excitation and luminescence;
measuring luminescent intensity over a period of time to produce an exponential decay curve;
calculating the exponential coefficient of the curve to determine tau;
measuring a temperature that is indicative of the temperature of the luminescent compound during the time that the luminescent intensity is measured; and
calculating the oxygen concentration within the container using the following equation;
[O2]=(ATa(T)2+BTa(T)+CTa)(tau)2+(ATb(T)2+BTb(T)+CTb)(tau)+(ATc(T)2+BTc(T)+CTc)wherein;
T is the measured temperature;
tau is the exponential coefficient of the decay curve; and
ATa, BTa, CTa, ATb, BTb, CTb, ATc, BTc, and CTc are previously determined coefficients for the luminescent compound that describe the luminescent intensity of the luminescent compound as a function of oxygen concentration and temperature.
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Abstract
An apparatus and non-invasive method of measuring oxygen by exciting a luminescent compound disposed in a container and then measuring the intensity of the light emitted by the excited luminescent compound as it relaxes to the ground state. A plot of emission intensity as a function of time results in an exponential decay curve the area of which is inversely proportional to the oxygen concentration. The oxygen concentration can be determined over a wide temperature range by measuring the temperature of the container and the emission intensity and then applying the following equation:
[O2]=(ATa(T)2+BTa(T)+CTa)(tau)2+(ATb(T)2+BTb(T)+CTb)(tau)+(ATc(T)2+BTc(T)+CTc)
- T is the measured temperature;
- tau is the area of the exponential decay curve; and
- ATa, BTa, CTa, ATb, BTb, CTb, ATc, BTc, and CTc are coefficients that are specific to the luminescent compound being examined.
64 Citations
17 Claims
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1. A method of measuring oxygen concentration in a container comprising:
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providing a container having a luminescent compound disposed in an interior space of the container, the luminescent compound having a luminescent emission that is sensitive to quenching by oxygen; irradiating the luminescent compound with light having a wavelength that is absorbed by the luminescent compound so that the luminescent compound is promoted into an excited state; terminating the irradiation of the luminescent compound when the luminescent compound achieves a steady state between excitation and luminescence; measuring luminescent intensity over a period of time to produce an exponential decay curve; calculating the exponential coefficient of the curve to determine tau; measuring a temperature that is indicative of the temperature of the luminescent compound during the time that the luminescent intensity is measured; and calculating the oxygen concentration within the container using the following equation;
[O2]=(ATa(T)2+BTa(T)+CTa)(tau)2+(ATb(T)2+BTb(T)+CTb)(tau)+(ATc(T)2+BTc(T)+CTc)wherein; T is the measured temperature; tau is the exponential coefficient of the decay curve; and ATa, BTa, CTa, ATb, BTb, CTb, ATc, BTc, and CTc are previously determined coefficients for the luminescent compound that describe the luminescent intensity of the luminescent compound as a function of oxygen concentration and temperature. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
subtracting the baseline area from the area under the curve, and normalizing the curve.
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3. A method according to claim 1, wherein step of calculating the area of the exponential decay curve further includes integrating the area under the exponential decay curve.
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4. A method according to claim 2, wherein the step of determining a baseline area comprises determining a baseline area at a point on the curve having a value of at least 4 tau or greater.
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5. A method according to claim 2, wherein the step of determining a baseline area comprises determining a baseline area at a point on the curve having a value of at least 8 tau or greater.
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6. A method according to claim 1, wherein the luminescent compound comprises a metal porphyrin.
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7. A method according to claim 6, wherein the metal comprises palladium or platinum.
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8. A method according to claim 1, wherein the step of measuring the temperature of the container includes the step of contacting an outer surface of the container with a resistance temperature detector.
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9. A method according to claim 8, further comprising the step of thermally isolating the resistance temperature detector.
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10. A method according to claim 1, wherein the steps of irradiating the luminescent compound, terminating the irradiation of the luminescent compound, and measuring luminescent intensity are repeated n number of times and wherein n is from about 10 to 2500.
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11. A method according to claim 1, wherein the step of measuring luminescent intensity over a period of time further comprises:
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taking an intensity measurement every 1 to 100 microseconds to create a plurality of discrete time segments; repeating the steps of irradiating the luminescent compound, terminating the irradiation of the luminescent compound, and measuring luminescent intensity n number of times, wherein n is from about 10 to 2500 to create n number of discrete time segments; summing the n number of discrete time segments.
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12. A method according to claim 11, further comprising the steps of
determining a baseline area for the exponential decay curve at a value of 8 tau or greater; -
subtracting the baseline area from all summed time segments; normalizing the summed time segments; and integrating the summed time segments to determine tau.
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13. A method according to claim 1, further comprising the step of recalling the coefficients from a storage device.
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14. A method according to claim 13, further comprising selecting the luminescent compound from a plurality of luminescent compounds, wherein the luminescent compound is associated with coefficients in the storage device.
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15. A method according to claim 1, further comprising the step of positioning an apparatus having an excitation source, a detector, a temperature sensor, and a control unit in an oxygen measuring relationship with the container.
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16. A method according to claim 1, wherein in the container comprise a sealed package having a modified atmosphere.
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17. A method according to claim 1, wherein the step of measuring a temperature further comprises measuring the temperature of the container.
Specification