Infrared emission detection

• US 5,246,868 A
• Filed: 09/29/1989
• Issued: 09/21/1993
• Est. Priority Date: 10/26/1987
• Status: Expired due to Fees

• Current Assignee: Baylor University
• Original Assignee: Research Corporation Technologies
• Inventors: Srinivasan, Ravishankar, Kubala, Sidney W. Jr., Lam, Christopher K. Y., Tilotta, David C., Busch, Kenneth W., Busch, Marianna A., Hudson, M. Keith
• Primary Examiner(s): Housel, James C.
• Assistant Examiner(s): Snay, Jeffrey R.
• Application Number:
  US07/415,141
• Time in Patent Office: 1,453 Days
• Field of Search: 250/339, 250/338.4, 250/338.1, 356/311, 356/315, 356/316, 356/317, 436/155, 436/143, 436/171, 436/146, 436/133, 436/101, 436/124, 436/160, 422/82.05, 422/94, 422/78, 422/80, 422/54
• US Class Current: 436/101
• CPC Class Codes: G01N 2021/3125 Measuring the absorption by excited molecules
• CPC Class Codes: G01N 21/71 thermally excited
• CPC Class Codes: G01N 21/72 using flame burners
• CPC Class Codes: G01N 30/74 Optical detectors measurement of intensity, velocity, spectral content, polarisation, or phase of infrared, visible or ultraviolet light G01J
• CPC Class Codes: Y10T 436/153333 Halogen containing
• CPC Class Codes: Y10T 436/19 Halogen containing
• CPC Class Codes: Y10T 436/204998 Inorganic carbon compounds
• CPC Class Codes: Y10T 436/218 Total hydrocarbon, flammability, combustibility [e.g., air-fuel mixture, etc.]
• CPC Class Codes: Y10T 436/235 In an aqueous solution [e.g., TOC, etc.]

Abstract

Apparatus and method for qualitatively and quantitatively analyzing infrared emission from excited molecules in samples of interest is disclosed. Over the wavelength interval from 1 to 5 um, two strong emission bands are observed with a PbSe detector when organic compounds are introduced into an hydrogen/air flame. The band at 4.3 um (2326 cm^-1 is due to the asymmetric stretch of carbon dioxide while the band at 2.7 um is due to both water and carbon dioxide emission. The carbon dioxide emission at 4.3 um is most intense at the tip of the flame, and increases with the amount of organic compound introduced into the flame. For chromatographic application, an optical filter can be used to isolate the 4.3 um emission band. The infrared emission detection system finds application in the determination of total inorganic carbon, chloride and available chlorine in aqueous samples. The detector is optimized by use of a dual beam system with background subtraction capabilities thereby eliminating background noise and the fluctuations therein.

Claims

1. A method for detecting and making quantitative measurements of at least one selected component in a sample, in which at least one selected component of the sample, or at least one selected substance present in the sample and characteristic of the at least one selected component, is introduced into an exciting means, and when the at least one selected component is present in the sample, gas-phase, infrared-active molecules emit infrared radiation at at least one characteristic wavelength in proportion to the quantity of the at least one selected component in the sample, comprising the steps of:

a. exciting the gas-phase, infrared-active molecules with a flame to emit radiation, wherein when the at least one selected component is present in the sample, the gas-phase, infrared-active molecules emit radiation at at least one characteristic wavelength with an intensity proportional to the quantity of the at least one selected component in the sample, and wherein fluctuating background radiation is simultaneously emitted at the at least one characteristic wavelength of the gas-phase, infrared-active molecules and at other wavelengths,

b. splitting the emitted radiation into first and second beams;

c. first detecting radiation in the first beam at the at least one characteristic wavelength, and generating a first electrical signal representative of the emitted radiation at at least one characteristic wavelength, and secondly detecting radiation in the second beam having the emitted background radiation and generating a second electrical signal representative of the simultaneously emitted background radiation; and

d. combining the first and second electrical signals to cancel fluctuations in intensity at the at least one characteristic wavelength caused by fluctuations in the background radiation.

2. A method according to claim 1, wherein said first detecting step includes discriminating the at least one characteristic wavelength by allowing passage of radiation at the at least one characteristic wavelength and inhibiting the passage of other wavelengths, and said second detecting step includes discriminating against the at least one characteristic wavelength by allowing passage of the emitted background radiation and inhibiting the passage of radiation at the at least one characteristic wavelength.

3. A method according to claim 1, wherein said combining step includes subtracting the second electrical signal from the first electrical signal.

4. A method according to claim 1, further including attenuating the second beam to adjust the level of the second output signal.

5. A method for detecting and making quantitative measurements of at least one selected component in a sample, in which at least one selected component of the sample, or at least one selected substance produced from the at least one selected component in the sample and characteristic of the at least one selected component, is introduced into an exciting means, and when the at least one selected component is present in the sample, gas-phase infrared-active molecules emit infrared radiation at at least one characteristic wavelength in proportion to the quantity of the at least one selected component in the sample, comprising the steps of:

a. exciting the gas-phase, infrared-active molecules with a flame to emit radiation, wherein when the at least one selected component is present in the sample, the gas-phase infrared-active molecules emit radiation at at least one characteristic wavelength with an intensity proportional to the quantity of the at least one selected component in the sample; and

b. selectively detecting infrared radiation emitted at the at least one characteristic wavelength and generating an output signal representative thereof, and thereby determining the quantity of the at least one selected component in the sample.

6. A method according to claim 5, including the step of discriminating the at least one characteristic wavelength by allowing only the at least one characteristic wavelength to be detected in the detecting step while inhibiting the detection of other wavelengths.

7. A method according to claim 6, wherein said discriminating step includes separating the wavelengths of the emitted radiation into an infrared spectrum.

8. A method according to claim 6, wherein said discriminating step includes utilizing a monochromator.

9. A method according to claim 6, wherein said discriminating step includes utilizing an interferometer.

10. A method according to claim 9, wherein said discriminating step includes utilizing a computer coupled to the interferometer for performing a Fourier transform analysis on an output signal from the interferometer to thereby obtain a spectral analysis characteristic of the sample.

11. A method according to claim 5, further including utilizing a computer for performing signal processing on the output signal produced by said detecting step to provide an output indicative of the quantity of the at least one selected component present in the sample.

12. A method according to claim 5, including vaporizing a liquid sample and utilizing the resultant vapors in said exciting step.

13. A method according to claim 5, wherein said exciting step includes generating said flame fueled by hydrogen/air or hydrogen/oxygen.

14. A method according to claim 5, wherein the at least one selected component or the at least one selected substance contains carbonates or calcinates, further including acidifying the at least one selected component or the at least one selected substance to generate CO₂ therefrom, and utilizing the CO₂ so generated in the exciting step.

15. A method according to claim 5, wherein the at least one selected component or the at least one selected substance contains carbon-containing compounds, further including oxidizing the at least one selected component or the at least one selected substance to generate CO₂ therefrom, and utilizing the CO₂ so generated in the exciting step.

16. A method according to claim 5, wherein the at least one selected component or the at least one selected substance contains hypochlorous acid or hypochlorite ions, further including acidifying the at least one selected component or the at least one selected substance with HCl to generate Cl₂ therefrom, and utilizing the Cl₂ so generated in the exciting step, wherein said flame is a hydrogen/air or hydrogen/oxygen flame.

17. A method according to claim 5, wherein the at least one selected component or the at least one selected substance contains chloride ions, further including oxidizing and acidifying the at least one selected component or the at least one selected substance to generate chlorine Cl₂ therefrom, and utilizing the Cl₂ so generated in the exciting step, wherein said flame is a hydrogen/air or hydrogen/oxygen flame.

18. A method according to claim 5, wherein the at least one selected component of the sample or the at least one selected substance includes carbon-containing compounds, and said exciting step includes generating said flame, and oxidizing the at least one selected component of the sample or the at least one selected substance in the flame to generate CO₂ therefrom, and utilizing the CO₂ so generated in the exciting step.

19. A method according to claim 5, wherein the at least one selected component or the at least one selected substance includes chlorine-containing organic compounds, and said exciting step includes generating said flame, and combusting the at least one selected component or the at least one selected substance in the flame to thereby generate HCl therefrom, and utilizing the HCl so generated in the exciting step.

20. A method according to claim 5, wherein the at least one selected component or the at least one selected substance includes fluorine-containing organic compounds, and said exciting step includes generating said flame, and combusting the at least one selected component or the at least one selected substance in the flame to thereby generate HF therefrom, and utilizing the HF so generated in the exciting step.

21. Apparatus for detecting and making quantitative measurements of at least one selected component in a sample, in which at least one selected component of the sample, or at least one selected substance produced from the at least one selected component in the sample and characteristic of the at least one selected component, is introduced into an exciting means, and when the at least one selected component is present in the sample, gas-phase, infrared-active molecules emit infrared radiation at at least one characteristic wavelength in proportion to the quantity of the at least one selected component in the sample, comprising:

a. flame means for exciting the gas-phase, infrared-active molecules with a flame to emit radiation along a first path, wherein when the at least one selected component is present in the sample, the gas-phase, infrared-active molecules emit radiation at at least one characteristic wavelength with an intensity proportional to the quantity of the at least one selected component in the sample, and wherein the exciting means simultaneously emits fluctuating background radiation along said first path at the at least one characteristic wavelength of the gas-phase, infrared-active molecules and at other wavelengths,

b. beam splitting means disposed on said first path for directing a portion of the emitted radiation over a second path;

c. first and second infrared detector means located on said first and second paths respectively, wherein said first detector means generates a first electrical signal responsive to emitted radiation at the at least one characteristic wavelength, and said second detector means generates a second electrical signal responsive to the simultaneously emitted background radiation;

d. first wavelength discriminating means located on said first path between said beam splitting means and said first detector means, and second wavelength discriminating means located on said second path between said beam splitting means and said second detector means, wherein said first wavelength discriminating means allows passage of radiation at the at least one characteristic wavelength and inhibits the passage of other wavelengths, and said second wavelength discriminating means allows passage of the emitted background radiation and inhibits the passage of radiation at the at least one characteristic wavelength; and

e. means connected to said first and second detector means for combining the first and second electrical signals to thereby cause a cancellation of fluctuations in intensity at the at least one characteristic wavelength caused by fluctuations in the background radiation.

22. Apparatus according to claim 21, wherein said means for combining includes means for subtracting the second electrical signal from the first electrical signal.

23. Apparatus according to claim 21, further including optical attenuating means, located on said second path between said beam splitting means and said second detector means, for adjusting the level of the second output signal.

24. Apparatus according to claim 21, wherein said first and second detector means are coupled to a biasing circuit means for achieving equalization of the first and second output signals.

25. Apparatus for detecting and making quantitative measurements of at least one selected component in a sample, in which at least one selected component of the sample, or at least one selected substance produced from the at least one selected component in the sample and characteristic of the at least one selected component, is introduced into an exciting means, and when the at least one selected component is present in the sample, gas-phase infrared-active molecules emit infrared radiation at at least one characteristic wavelength in proportion to the quantity of the at least one selected component in the sample, comprising:

a. flame means for exciting the gas-phase, infrared-active molecules with a flame to emit radiation over a first path, wherein when the at least one selected component is present in the sample, the gas-phase, infrared-active molecules emit radiation at at least one characteristic wavelength with an intensity proportional to the quantity of the at least one selected component in the sample; and

b. infrared discriminating and detector means located on said given path for detecting infrared radiation at the at least one characteristic wavelength and for generating an output signal representative thereof, and thereby determining the quantity of the at least one selected component in the sample.

26. Apparatus according to claim 25, wherein said infrared discriminating and detector means includes wavelength discriminating means located on said path, between the exciting means and the infrared detector means, for allowing the at least one characteristic wavelength to pass from the exciting means to the detector means while inhibiting the passage of other wavelengths.

27. Apparatus according to claim 25, wherein said infrared discriminating and detector means includes means for separating the wavelength of the emitted radiation into an infrared spectrum.

28. Apparatus according to claim 25, wherein said infrared discriminating and detector means includes a monochromator.

29. Apparatus according to claim 25, further including a computer means, responsive to an output signal from the infrared detector means, for performing signal processing thereon to provide an output indicative of the quantity of the at least one selected component present in the sample.

30. Apparatus according to claim 25, wherein said infrared discriminating and detector means includes an interferometer.

31. Apparatus according to claim 30, further comprising a computer means, coupled to the interferometer, for performing a Fourier transform analysis on an output signal from the interferometer to thereby obtain a spectral analysis characteristic of the sample.

32. Apparatus according to claim 25, further including vaporizing means for vaporizing a liquid sample and for conducting the resultant vapors into said exciting means.

33. Apparatus according to claim 25, wherein said exciting means includes means for generating said flame fueled by hydrogen/air or hydrogen/oxygen.

34. Apparatus according to claim 25, wherein said infrared detector means includes a thermal infrared detector.

35. Apparatus according to claim 25, wherein said infrared detector means includes a quantum detector.

36. Apparatus according to claim 25, wherein the at least one selected component or the at least one selected substance contains carbonates or calcinates, further including means for acidifying the at least one selected component or the at least one selected substance to generate CO₂ therefrom, wherein the CO₂ so generated is introduced into the exciting means.

37. Apparatus according to claim 25, wherein the at least one selected component or the at least one selected substance contains carbon-containing compounds, further including means for oxidizing the at least one selected component or the at least one selected substance to generate CO₂ therefrom, wherein the CO₂ so generated is introduced into the exciting means.

38. Apparatus according to claim 25, wherein the at least one selected component or the at least one selected substance contains hypochlorous acid or hypochlorite ions, further including means for acidifying the at least one selected component or the at least one selected substance with HCl to generate Cl₂ therefrom, wherein the Cl₂ so generated is introduced into the exciting means, said exciting means including a hydrogen/air or hydrogen/oxygen flame.

39. Apparatus according to claim 25, wherein the at least one selected component or the at least one selected substance contains chloride ions, further including means for oxidizing and acidifying the at least one selected component or the at least one selected substance to generate chlorine Cl₂ therefrom, wherein the Cl₂ so generated is introduced into the exciting means, said exciting means including a hydrogen/air or hydrogen/oxygen flame.

40. Apparatus according to claim 25, wherein the at least one selected component of the sample or the at least one selected substance includes carbon-containing compounds, and said exciting means includes a flame generating means for oxidizing the at least one selected component of the sample or the at least one selected substance to generate CO₂ therefrom, wherein the CO₂ so generated is introduced into the exciting means.

41. Apparatus according to claim 25, wherein the at least one selected component or the at least one selected substance includes chlorine-containing organic compounds, and said exciting means includes a flame generating means for combusting the at least one selected component or the at least one selected substance to thereby generate HCl therefrom, wherein the HCl so generated is introduced into the exciting means.

42. Apparatus according to claim 25, wherein the at least one selected component or the at least one selected substance includes fluorine-containing organic compounds, and said exciting means includes a flame generating means for combusting the at least one selected component or the at least one selected substance to thereby generate HF therefrom, wherein the HF so generated is introduced into the exciting means.