MEASUREMENT DEVICE AND METHOD FOR ANALYZING A SAMPLE GAS BY INFRARED ABSORPTION SPECTROSCOPY

• US 20110270113A1
• Filed: 12/21/2010
• Published: 11/03/2011
• Est. Priority Date: 12/24/2009
• Status: Active Grant

• Current Assignee: Humedics GmbH (Advanced Biological Laboratories SA)
• Original Assignee: Humedics GmbH (Advanced Biological Laboratories SA)
• Inventors: Rubin, Tom, Heyne, Karsten
• Granted Patent: US 9,541,497 B2
• Time in Patent Office: Days
• US Class Current: 600/531
• CPC Class Codes: A61B 5/082 Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath A61B5/083, A61B5/091 take precedence
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61M 16/12 by mixing different gases
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/39 using tunable lasers
• CPC Class Codes: G01N 2800/085 Liver diseases, e.g. portal hypertension, fibrosis, cirrhosis, bilirubin

Abstract

A measurement device and a method for analyzing a sample gas by infrared absorption spectroscopy are described. The measurement device comprises: a measurement chamber with the sample gas to be analyzed, a laser being arranged in relation to the measurement chamber such that light being emitted from the laser radiates through the measurement chamber, a detection device detecting the light being emitted from the laser and radiated through the measurement chamber, and an evaluation unit evaluating signals generated by the detection device regarding a light absorption occurred in the measurement chamber. Provision is made that the laser is a narrowband emitting laser, the line width of which is smaller or equal to the width of an infrared absorption line to be measured of the sample gas, the laser is designed and arranged such that the laser frequency is varied periodically within a defined spectral range, wherein the laser frequency and its variation are chosen such that at least one infrared absorption line to be measured of the sample gas lies in the defined spectral range, and the detection device is designed and arranged such that it detects the light being emitted from the laser and radiated through the measurement chamber in such a time-resolved manner that the light absorption can be determined frequency-resolved within the defined spectral range, wherein the detection device carries out a single absorption measurement within 10⁻⁵ s or faster. Furthermore, the measurement device is suited and can be arranged to measure the respiratory gas of a human or animal as sample gas, wherein the respiratory gas exchanges in the measurement chamber only by the respiration of the human or animal, and the respiratory resistance of the measurement device is less than 60 mbar.

Claims

1. A measurement device for analyzing a sample gas by infrared absorption spectroscopy, comprising:

a measurement chamber with the sample gas to be analyzed,

a laser being arranged in relation to the measurement chamber such that light being emitted from the laser radiates through the measurement chamber,

a detection device detecting the light being emitted from the laser and radiated through the measurement chamber, and

an evaluation unit evaluating signals generated by the detection device regarding a light absorption occurred in the measurement chamber, wherein

the laser is a narrowband emitting laser, the line width of which is smaller or equal to the width of an infrared absorption line to be measured of the sample gas, wherein

the laser is designed and arranged such that the laser frequency is varied periodically within a defined spectral range, wherein the laser frequency and its variation are chosen such that at least one infrared absorption line to be measured of the sample gas lies in the defined spectral range, and wherein

the detection device is designed and arranged such that it detects the light being emitted from the laser and radiated through the measurement chamber in such a time-resolved manner that the light absorption can be determined frequency-resolved within the defined spectral range, wherein

the detection device carries out a single absorption measurement within 10<sup>−

5</sup> s or faster and in that the measurement device is suited and can be arranged to measure the respiratory gas of a human or animal as sample gas, wherein the respiratory gas exchanges in the measurement chamber only by the respiration of the human or animal, and the respiratory resistance of the measurement device is less than 60 mbar.

2. The measurement device according to claim 1, wherein the laser frequency and its variation are chosen such that at least two infrared absorption lines of the sample gas lie in the defined spectral range.

3. The measurement device according to claim 2, wherein the evaluation unit is designed and arranged to determine the ratio of two isotopes, elements or molecules of the sample gas on the basis of the light absorptions occurring at the two absorption lines.

4. The measurement device according to claim 3, wherein the evaluation unit is designed and arranged to determine the ratio of the two isotopes, elements or molecules in real time.

6. The measurement device according to claim 1, wherein the measurement chamber is minor-less and light emitted from the laser passes through the measurement chamber exactly once.

7. The measurement device according to claim 6, wherein the measurement chamber has an inlet window through which the laser light enters the measurement chamber and an outlet window through which the transmitted light exits the measurement chamber.

8. The measurement device according to claim 1, wherein furthermore tempering means for tempering the measurement chamber onto a constant temperature are provided.

10. The measurement device according to claim 1, wherein the sample gas flows through the measurement chamber continuously or intermittently and wherein the measurement chamber has an open construction without valves or air flaps which would hinder the flow of the sample gas into and out of the measurement chamber.

11. The measurement device according to claim 10, wherein the measurement device has an essentially constant cross section between gas inlet into the measurement device and gas exit out of the measurement device for the sample gas flowing through.

13. The measurement device according to claim 10, wherein the measurement device is designed and arranged such that a time-resolved light detection by the detection device occurs during flowing-through of the sample gas through the measurement chamber.

14. The measurement device according to claim 1, having a spirometer detecting the volumetric flow rate of the sample gas flowing through the measurement chamber.

19. The measurement device according to claim 1, wherein means for tuning the laser are provided for varying the frequency of the laser, said means applying a voltage being periodically modulated by a modulation frequency to the laser head of the laser, wherein the applied voltage is attended by a short term temperature increase and therewith by a frequency shift.

23. The measurement device according to claim 1, wherein the laser signal is pulsed with a pulse duration of particularly less than 200 ns, in particular of less than 100 ns.

25. The measurement device according to claim 1, wherein the detection device is designed and arranged to be read out with a frequency that is twice as big as the frequency by which the laser emits light pulses.

26. The measurement device according to claim 1, wherein the measurement device is formed such that the light emitted from the laser is divided into to two partial beams, wherein the one partial beam passes through the measurement chamber and the other partial beam is detected by a reference detection device and wherein the evaluation unit evaluates the signals of the reference detection device for standardizing the signal intensity of the laser.

28. The measurement device according to claim 1, wherein the measurement device is designed and arranged to determine the ratio of the ¹³CO₂/¹²CO₂ isotope concentration in the respiratory gas of a human or animal in a time-resolved manner.

29. The measurement device according to claim 1, wherein the measurement device is designed and arranged to conduct a quantitative measurement of a metabolic parameter in the respiratory gas in real time.

30. The measurement device according to claim 1, wherein the measurement device is designed and arranged to determine the carbon dioxide concentration of the respiratory gas in the range between 0.08% and 8% in flow-through in real time.

32. A method for analyzing a sample gas by infrared absorption spectroscopy in a measurement device according to any of the preceding claims, having the steps of:

radiating a measurement chamber with light being emitted from a narrowband laser, the line width of which is smaller or equal to the width of an infrared absorption line to be measured of a sample gas being present in the measurement chamber, wherein the laser frequency is varied periodically within a defined spectral range, and the laser frequency and its variation are chosen such that at least one infrared absorption line to be measured of the sample gas lies in the defined spectral range,

time-resolved detecting the light emitted from the laser and radiated through the measurement chamber, wherein a single absorption measurement is carried out within 10<sup>−

5</sup> s or faster, and

evaluating the detected signals regarding a light absorption occurred in the measurement chamber, wherein the light absorption is determined frequency-resolved within the defined spectral range, wherein

the sample gas is the respiratory gas of a human or animal, wherein the respiratory gas is exchanged in the measurement chamber only by the respiration of the human or animal, and wherein the respiratory resistance of the measurement device is less than 60 mbar.

33. The method according to claim 32, wherein the ratio of two isotopes, elements or molecules of the sample gas is determined which have absorption lines lying within the defined spectral range.

5. (canceled)

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27. (canceled)

31. (canceled)