Method and apparatus for measuring oxygen concentration

• US 20070212792A1
• Filed: 03/13/2006
• Published: 09/13/2007
• Est. Priority Date: 03/13/2006
• Status: Active Grant

• Current Assignee: Cryovac Incorporated (Sealed Air)
• Original Assignee: Cryovac Incorporated (Sealed Air)
• Inventors: Paul, Douglas, Austin, Darrell, Havens, Marvin
• Granted Patent: US 7,569,395 B2
• Time in Patent Office: Days
• US Class Current: 436/172
• CPC Class Codes: G01M 3/226 for containers, e.g. radiators
• CPC Class Codes: G01M 3/38 by using light G01M3/02 takes precedence
• CPC Class Codes: G01N 2021/6432 Quenching
• CPC Class Codes: G01N 2021/6478 Special lenses
• CPC Class Codes: G01N 21/6408 with measurement of decay time, time resolved fluorescence
• CPC Class Codes: G01N 21/643 non-biological material
• CPC Class Codes: G01N 2201/0221 Portable; cableless; compact; hand-held
• CPC Class Codes: G01N 2201/1211 for temperature
• CPC Class Codes: G01N 31/225 for oxygen, e.g. including dissolved oxygen
• CPC Class Codes: G01N 31/229 for investigating time/temperature history
• CPC Class Codes: Y10T 436/20 Oxygen containing

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]=(A_Ta(T)²+B_Ta(T)+C_Ta)(tau)²+(A_Tb(T)²+B_Tb(T)+C_Tb)(tau)+(A_Tc(T)²+B_Tc(T)+C_Tc) T is the measured temperature; tau is the area of the exponential decay curve; and

• • A_Ta, B_Ta, C_Ta, A_Tb, B_Tb, C_Tb, A_Tc, B_Tc, and C_Tc are coefficients that are specific to the luminescent compound being examined.

Claims

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]=(A_Ta(T)²+B_Ta(T)+C_Ta)(tau)²+(A_Tb(T)²+B_Tb(T)+C_Tb)(tau)+(A_Tc(T)²+B_Tc(T)+C_Tc)

wherein;

T is the measured temperature;

tau is the exponential coefficient of the decay curve; and

A_Ta, B_Ta, C_Ta, A_Tb, B_Tb, C_Tb, A_Tc, B_Tc, and C_Tc 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.

2. A method according to claim 1, wherein the step of calculating tau further includes

determining a baseline area for the exponential decay curve;

subtracting the baseline area from the area under the curve, and

normalizing the curve.

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.

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.

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.

6. A method according to claim 1, wherein the luminescent compound comprises a metal porphyrin.

7. A method according to claim 6, wherein metal porphyrin comprises palladium, platinum, or a combination thereof.

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.

9. A method according to claim 8, further comprising the step of thermally isolating the resistance temperature detector.

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.

11. A method according to claim 1, wherein the step of measuring luminescent intensity over a period of time further comprises:

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.

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.

13. A method according to claim 1, further comprising the step of recalling the coefficients from a storage device.

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.

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.

16. A method according to claim 1, wherein in the container comprise a sealed package having a modified atmosphere.

17. A method according to claim 1, wherein the step of measuring a temperature further comprises measuring the temperature of the container.

18. An apparatus for measuring the oxygen concentration within a container, the apparatus comprising:

an excitation source that is configured to generate excitation light having at least one wavelength that causes a luminescent compound to be promoted into an excited energy state;

a detector disposed in a position to receive luminescent light emitted by the excited luminescent compound, the detector being capable of converting the luminescent light into an electronic signal;

at least one temperature sensor configured for measuring a temperature that is indicative of the temperature of the luminescent compound; and

a control unit that is in communication with the detector and that is configured to calculate the oxygen concentration within the container using the following equation;

[O₂]=(A_Ta(T)²+B_Ta(T)+C_Ta)(tau)²+(A_Tb(T)²+B_Tb(T)+C_Tb)(tau)+(A_Tc(T)²+B_Tc(T)+C_Tc)

wherein;

T is the measured temperature;

tau is an area of an exponential decay curve that is produced by measuring luminescent intensity of an excited luminescent compound over a period of time; and

A_Ta, B_Ta, C_Ta, A_Tb, B_Tb, C_Tb, A_Tc, B_Tc, and C_Tc are previously determined coefficients that are specific to the luminescent compound.

19. A apparatus according to claim 18, wherein the control unit comprises an external computer that is operatively connected to the apparatus.

20. A apparatus according to claim 18, wherein the excitation source generates a range of wavelengths from about 200 to 600 nm.

21. A apparatus according to claim 18, wherein the control unit includes one or more algorithms for calculating tau.

22. A apparatus according to claim 18, wherein the one or more temperature sensors comprise a resistance temperature detector.

23. A apparatus according to claim 18, wherein the excitation source, focusing optics, and detector are disposed in a housing member, the housing member having a generally tubular shape and including an opening through which excitation light and luminescent light each exit and enter the housing member, respectively.

24. A apparatus according to claim 23, further comprising an insulating member disposed adjacent to the opening, the insulating member capable of thermally isolating the container from the housing member when the apparatus is positioned in a temperature measuring relationship with the container.

25. The apparatus according to claim 18, further comprising an associated memory component from which information is recallable, the recallable information including luminescent compound specific operational parameters, the luminescent compound specific coefficients, and combinations thereof.

26. The apparatus according to claim 25, wherein the operational parameters include intensity of the excitation light.

27. The apparatus according to claim 25, further comprising a data entry device that is in communication with the control unit, the data entry device being configured to input a representation of an identification code into the control unit.

28. A handheld apparatus for measuring the oxygen concentration within a sealed container comprising:

a housing member having an excitation source and a detector disposed therein and defining an opening through which excitation light generated by the excitation source exits the housing member and through which luminescent light emitted by an excited luminescent compound enters into the housing and is converted into an electronic signal by the detector;

one or more temperature sensors supported by the housing member so that when the handheld apparatus is moved into an oxygen-measuring relationship with a container, the one or more temperature sensors are in contact with the container and are thermally isolated from the housing member; and

a control unit that is operatively connected to the detector and the temperature sensor, wherein the control unit applies an algorithm to calculate the oxygen concentration within the container using the electronic signal from the detector and temperature data from the one or more temperature sensors.

29. A handheld apparatus according to claim 28, wherein the control unit includes a microprocessor and one or more algorithms for calculating the oxygen concentration within a container.

30. A handheld apparatus according to claim 29, wherein the one or more algorithms includes:

[O₂]=(A_Ta(T)²+B_Ta(T)+C_Ta)(tau)²+(A_Tb(T)²+B_Tb(T)+C_Tb)(tau)+(A_Tc(T)²+B_Tc(T)+C_Tc)

wherein;

T is the measured temperature;

tau is the measured decay of the excited luminescent compound; and

A_Ta, B_Ta, C_Ta, A_Tb, B_Tb, C_Tb, A_Tc, B_Tc, and C_Tc are previously determined coefficients for the luminescent compound.

31. A handheld apparatus according to claim 30, wherein the control unit comprises a memory component and A_Ta, B_Ta, C_Ta, A_Tb, B_Tb, C_Tb, A_Tc, B_Tc, and C_Tc are stored therein.

32. A handheld apparatus according to claim 31, further comprising a user interface that is in communication with the control unit, the user interface includes one or menus from which A_Ta, B_Ta, C_Ta, A_Tb, B_Tb, C_Tb, A_Tc, B_Tc, and C_Tc are recallable from the memory component.

33. A handheld apparatus according to claim 28, wherein the excitation source comprises a light emitting diode having a peak wavelength between 300 and 450 nm.

34. A handheld apparatus according to claim 28, wherein the one or more temperature sensors are disposed adjacent to an insulating member.

35. A handheld apparatus according to claim 34, wherein the insulating member has an annular-like shape and comprises a thermoplastic or thermoset material.

36. A handheld apparatus according to claim 28, wherein a Fresnel lens is disposed between the opening and the detector, the Fresnel lens comprising at least one mirror and a plurality of prisms that are configured to collect the luminescent light and intensify against the detector.