Systems and methods for monitoring relative concentrations of different isotopic forms of a chemical species

• US 5,957,858 A
• Filed: 12/10/1996
• Issued: 09/28/1999
• Est. Priority Date: 07/26/1996
• Status: Expired due to Fees

• Current Assignee: Polestar Technologies Inc.
• Original Assignee: Polestar Technologies Inc.
• Inventors: Kaunitz, Jonathan D., Micheels, Ronald H.
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): MANTIS MERCADER, ELENI M
• Application Number:
  US08/763,243
• Time in Patent Office: 1,022 Days
• Field of Search: 600/532, 600/529, 356/311, 250/339.03, 250/345
• US Class Current: 600/529
• CPC Class Codes: G01N 2021/3595 using FTIR
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

Method and system for measuring the relative concentrations of first and second isotopic forms of a chemical species within a sample. The present invention need not use a laser or high resolution spectrometer. The system typically includes a waveguide cell with good transmission of particular wavelengths of IR radiation, such as a hollow glass fiber waveguide cell. A source emits electromagnetic radiation, which is modulated at first and second wavelength bands that correspond to absorption bands of the first and second isotopic forms of the chemical species, respectively. In certain embodiments, the source is a filtered broad band source, such as a plurality of LEDs. In some embodiments, an FTIR spectrometer may serve as a filtered source and signal detector.

Claims

1. A system for monitoring relative concentrations of a chemical species, the system comprising:

a sample including first and second isotopic forms of the chemical species;

a source for simultaneously emitting electromagnetic radiation at first and second wavelength bands, the first wavelength band corresponding to an absorption band of the first isotopic form, the second wavelength band corresponding to an absorption band of the second isotopic form;

a device for modulating the electromagnetic radiation emitted by the source at the first and second wavelength bands;

a waveguide cell defining a sample cell having a pathlength of from about 30 centimeters to about 100 centimeters and an inner diameter of from about 0.3 millimeters to about 2.0 millimeters; and

a detector for detecting the first and second wavelength bands,

wherein the system is arranged such that at least a portion of the electromagnetic radiation emitted by the source is modulated by the device, enters the waveguide, impinges upon the sample contained within the sample cell defined by said waveguide cell, and at least 10% of the first and second wavelength bands of the portion of the electromagnetic radiation that enters the waveguide cell passes through the waveguide cell and impinges upon the detector.

2. The system according to claim 1, wherein the waveguide cell is a hollow waveguide cell.

3. The system according to claim 2, wherein the hollow waveguide cell includes a substrate material formed from metal or plastic.

4. The system according to claim 2, wherein the hollow waveguide cell includes a substrate material formed from silica.

5. The system according to claim 1 wherein the system is arranged such that at least about 30% of the first and second wavelength bands of electromagnetic radiation that enters the waveguide cell is transmitted through the waveguide cell to the detector.

6. The system according to claim 1, wherein the source is a broad band source, and wherein the system further comprises filters to define the first and second wavelength bands.

7. The system according to claim 1, wherein the source and detector include a Fourier transform infrared spectrometer.

8. The system according to claim 1, wherein the source is formed from first and second light emitting diodes, the first light emitting diode emitting electromagnetic radiation at the first wavelength band, and the second light emitting diode emitting electromagnetic radiation at the second wavelength band.

9. The system according to claim 8, wherein the source further includes a third light emitting diode, the third light emitting diode emitting electromagnetic radiation at a third wavelength band located between the first and second wavelength bands, and wherein the system further comprises a source monitor detector disposed between the source and the waveguide cell, and wherein a portion of the electromagnetic radiation at the first, second and third wavelength bands emitted by the source impinge upon the source monitor detector to correct for variations in an intensity of the electromagnetic radiation emitted by the source at the first, second and third wavelength bands.

10. The system according to claim 1, wherein the sample is a sample of human breath, the first isotopic form is ¹² CO₂ and the second isotopic form is ¹³ CO₂.

11. The system according to claim 1, wherein the source emits a third wavelength band of electromagnetic radiation, the third wavelength band being between the first and second wavelength bands, and not absorbed by said sample such that transmission of the third wavelength band changes with variations in an optical throughput efficiency of the system, wherein the third wavelength band is emitted by the source, modulated by the device, impinges on the waveguide sample cell and the sample and is detected by the detector.

12. The system according to claim 11, further comprising a source monitor detector disposed between the source and the waveguide cell,

wherein a portion of the electromagnetic radiation at the first, second and third wavelength bands emitted by the source impinge upon the source monitor detector to correct for variations in an intensity of the electromagnetic radiation emitted by the source at the first, second and third wavelength bands.

13. The system according to claim 11, wherein the source emits a fourth wavelength band, a distance between the third wavelength band and the first wavelength band being less than a distance between the fourth wavelength band and the first wavelength band, a distance between the fourth wavelength band and the second wavelength band being less than a distance the third wavelength band and the second wavelength band, and not absorbed by said sample such that transmission of the fourth wavelength band changes with variations in the optical throughout efficiency of the system,

wherein the fourth wavelength band is emitted by the source, modulated by the device, impinges upon the waveguide sample cell and the sample us detected by the detector.

14. The system according to claim 1, further comprising a source monitor detector disposed between the source and the waveguide cell,

wherein a portion of the electromagnetic radiation at the first and second wavelength bands emitted by the source impinge upon the source monitor detector to correct for variations in an intensity of the electromagnetic radiation emitted by the source at the first and second wavelength bands.

15. The system according to claim 1, further comprising:

at least one infrared transparent window;

an inlet valve formed from plastic;

inlet tubing formed from plastic;

an outlet valve formed from plastic; and

outlet tubing formed from plastic,

wherein the window is arranged such that the first and second wavelength bands of electromagnetic radiation emitted by the source impinge upon the window prior to entering the waveguide sample cell, and

wherein the inlet valve, inlet tubing, outlet valve and outlet tubing are arranged such that the sample can be input to the waveguide cell and output from the waveguide cell connecting tubing and inlet and outlet fittings, the system being constructed and arranged such that the waveguide cell can be used as a disposable item.

16. A system for monitoring relative concentrations of a chemical species, the system comprising:

a sample including first and second isotopic forms of the chemical species;

a source emitting a broad band of electromagnetic radiation including first and second wavelength bands, the first wavelength band corresponding to an absorption band of the first isotope, the second wavelength band corresponding to an absorption band of the second isotope;

first and second filters for filtering the broad band of radiation emitted by the source to define the first and second wavelength bands;

a device for modulating the first and second wavelength bands of radiation emitted by the source;

a waveguide cell defining a sample cell and having a pathlength of from about 30 centimeters to about 100 centimeters and an inner diameter of from about 0.3 millimeters to about 2.0 millimeters; and

a detector for detecting electromagnetic radiation at the first and second wavelengths,

wherein the system is arranged such that electromagnetic radiation emitted by the source is modulated by the device and filtered by the filters, impinges upon the sample, and at least 10% of the first and second wavelengths of electromagnetic radiation that enters the waveguide cell passes through the waveguide cell and impinges upon the detector.

17. The system according to claim 16, wherein the waveguide cell transmits at least about 20% of the first and second wavelength bands of electromagnetic radiation incident upon the waveguide cell.

18. The system according to claim 16, wherein the source is formed from first and second light emitting diodes, the first light emitting diode being emits electromagnetic radiation at the first wavelength band, the second light emitting diode being emits electromagnetic radiation at the second wavelength band.

19. The system according to claim 16, wherein the sample is a sample of human breath the first isotopic form is ¹² CO₂ and the second isotopic form is ¹³ CO₂.

20. The system according to claim 19, wherein the waveguide cell is a hollow glass fiber waveguide cell.

21. A method of measuring relative concentrations of a sample including first and second isotopic forms, the method comprising the steps of:

simultaneously emitting electromagnetic radiation at first and second wavelength bands;

modulating the first and second wavelength bands of electromagnetic radiation;

impinging at least a portion of the modulated first and second wavelengths of electromagnetic radiation upon the sample, the first wavelength band corresponding to an absorption band of the first isotopic form, the second wavelength band corresponding to an absorption band of the second isotopic form, the sample being contained within a waveguide cell having a pathlength of from about 30 centimeters to about 100 centimeters and an inner diameter of from about 0.3 millimeters to about 2.0 millimeters and transmitting at least about 10% of the first wavelength band and the second wavelength band of the portion of the electromagnetic radiation that entered the waveguide; and

measuring absorption of the modulated electromagnetic radiation at the first and second wavelength bands by the first and second isotopic forms of the chemical species, respectively.

22. The method according to claim 21, wherein the impinging step includes impinging the radiation upon a sample of human breath, and wherein the first isotopic form is ¹² CO₂ and the second isotopic form is ¹³ CO₂.

23. The method according to claim 22, wherein the impinging step includes impinging the radiation upon a sample contained within a hollow glass fiber waveguide cell.

24. The method according to claim 21, wherein the impinging step includes impinging the radiation upon a sample contained within a hollow glass fiber waveguide cell.

25. The method according to claim 21, wherein the emitting step includes simultaneously emitting a third wavelength band of electromagnetic radiation, the third wavelength band being between the first and second wavelength bands, the first and second isotopic forms being incapable of absorbing the third wavelength band such that the third wavelength band can be used to monitor variations in an optical throughput efficiency of the system.

26. The method according to claim 25, further comprising the step of modulating the first, second and third wavelengths.

27. A system for monitoring relative concentrations of a chemical species, the system comprising:

a sample including first and second isotopic forms of the chemical species;

an electromagnetic radiation source emitting first and second wavelength bands, the first wavelength band corresponding to an absorption band of the first isotopic form, the second wavelength band corresponding to an absorption band of the second isotopic form;

a device for modulating the electromagnetic radiation emitted by the source at the first and second wavelength bands;

a waveguide defining a sample cell,

said waveguide having a first window at one end and a second window at the opposite end and a pathlength from about 30 cm to about 100 cm; and

a detector,

wherein the system is arranged such that at least a portion of the electromagnetic radiation emitted by the source is modulated by the device, enters the waveguide through said first window, impinges upon the sample contained within the waveguide cell, at at least 10% of the first and second wavelength bands of electromagnetic radiation that enters the waveguide is transmitted through the waveguide sample cell and said second window and impinges upon the detector.

28. The system according to claim 27, wherein the system is arranged such that at least about 30% of the first and second wavelength bands of electromagnetic radiation that enters the wave guide is transmitted through the waveguide.

29. The system according to claim 27, wherein the waveguide cell has an inner diameter of from about 0.3 millimeters to about 2.0 millimeters.

30. The system according to claim 27, wherein the source is a broad band source, and wherein the system further comprises filters to define the first and second wavelength bands.

31. The system according to claim 27, wherein the detector includes a Fourier transform infrared spectrometer.

32. The system according to claim 27, wherein the source is formed from first and second light emitting diodes, the first light emitting diode emitting electromagnetic radiation at the first wavelength band, and the second light emitting diode emitting electromagnetic radiation at the second wavelength band.

33. The system according to claim 32, wherein the source further includes a third light emitting diode, the third light emitting diode emitting electromagnetic radiation at a third wavelength band located between the first and second wavelength bands, and wherein the system further comprises a source monitor detector disposed between the source and the waveguide cell, and wherein a portion of the electromagnetic radiation at the first, second and third wavelength bands emitted by the source impinge upon the source monitor detector to correct for variations in an intensity of the electromagnetic radiation emitted by the source at the first, second and third wavelength bands.

34. The system according to claim 27, wherein the sample is a sample of human breath, the first isotopic form is ¹² CO₂ and the second isotopic form is ¹³ CO₂.

35. The system according to claim 27, wherein the source emits a third wavelength band of electromagnetic radiation, the third wavelength band being between the first and second wavelength bands, and not absorbed by said first and second isotopic forms such that transmission of the third wavelength band changes with variations in an optical throughput efficiency of the system,

wherein the third wavelength band is emitted by the source, modulated by the device, impinges upon the waveguide sample cell and the sample and is detected by the detector.

36. The system according to claim 35, further comprising a source monitor detector disposed between the source and the waveguide cell,

wherein a portion of the electromagnetic radiation at the first, second and third wavelength bands emitted by the source impinge upon the source monitor detector to correct for variations in an intensity of the electromagnetic radiation emitted by the source at the first, second and third wavelength bands.

37. The system according to claim 35, wherein the source emits a fourth wavelength band, a distance between the third wavelength band and the first wavelength band being less than a distance between the fourth wavelength band and the first wavelength band, a distance between the fourth wavelength band and the second wavelength band being less than a distance the third wavelength band and the second wavelength band, and not absorbed by said first and second isotopic forms such that the fourth wavelength band changes with variations in the optical throughput efficiency of the system,

wherein the fourth wavelength band is emitted by the source, modulated by the device, impinges upon the waveguide sample cell and the sample and is detected by the detector.

38. The system according to claim 27, further comprising a source monitor detector disposed between the source and the waveguide cell,

wherein a portion of the electromagnetic radiation at the first and second wavelength bands emitted by the source impinge upon the source monitor detector to correct for variations in an intensity of the electromagnetic radiation emitted by the source at the first and second wavelength bands.

39. The system according to claim 27, further comprising:

at least one infrared transparent window;

an inlet valve formed from plastic;

inlet tubing formed from plastic;

an outlet valve formed from plastic; and

outlet tubing formed from plastic,

wherein the window is arranged such that the first and second wavelength bands of electromagnetic radiation emitted by the source impinge upon the window prior to entering the waveguide sample cell, and

wherein the inlet valve, inlet tubing, outlet valve and outlet tubing are arranged such that the sample can be input to the waveguide cell and output from the waveguide cell connecting tubing and inlet and outlet fittings, the system being constructed and arranged such that the waveguide cell can be used as a disposable item.

40. A system for monitoring relative concentrations of a chemical species, the system comprising:

a sample including first and second isotopic forms of the chemical species;

an electromagnetic radiation source, said source emitting broad band electromagnetic radiation including first and second wavelength bands, the first wavelength band corresponding to an absorption band of the first isotope, the second wavelength band corresponding to an absorption band of the second isotope;

a first bandpass filter, passing a wavelength band corresponding to said first wavelength band;

a second bandpass filter, passing a wavelength band corresponding to said second wavelength band;

a device for modulating the first and second wavelength bands of radiation emitted by the source;

a waveguide, said waveguide having a path length of about 30 cm to about 100 cm; and

a detector;

wherein the system is arranged such that at least a portion of electromagnetic radiation emitted by the source is modulated by the device and filtered by the filters, then enters the waveguide and impinges upon the sample, and at least 10% of the first wavelength and second wavelength of the portion of the electromagnetic radiation entering the waveguide are transmitted through the waveguide cell and impinges upon the detector.

41. A method of measuring relative concentrations of a sample including first and second isotopic forms, the method comprising the steps of:

introducing said sample into a waveguide sample cell having a pathlength of about 30 cm to about 100 cm;

simultaneously emitting electromagnetic radiation at first and second wavelength bands;

modulating the first and second wavelength bands of electromagnetic radiation;

impinging at least a portion of the modulated first and second wavelengths of electromagnetic radiation upon the sample in said waveguide sample cell, the first wavelength band corresponding to an absorption band of the first isotopic form, the second wavelength band corresponding to an absorption band of the second isotopic form; and

measuring absorption of the modulated electromagnetic radiation at the first and second wavelength bands by the first and second isotopic forms of the chemical species, respectively.