Measuring trace components of complex gases using gas chromatography/absorption spectrometry

• US 20070273882A1
• Filed: 03/19/2007
• Published: 11/29/2007
• Est. Priority Date: 05/26/2006
• Status: Active Grant

• Current Assignee: Endress+Hauser Optical Analysis Incorporated
• Original Assignee: Spectrasensors, Inc. (Endress+Hauser AG)
• Inventors: Smith, Stevie Horton
• Granted Patent: US 7,511,802 B2
• Time in Patent Office: Days
• US Class Current: 356/437
• CPC Class Codes: G01N 21/031 Multipass arrangements
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• 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 2201/0691 Modulated (not pulsed supply)
• CPC Class Codes: G01N 30/74 Optical detectors measurement of intensity, velocity, spectral content, polarisation, or phase of infrared, visible or ultraviolet light G01J

Abstract

Low concentrations of complex gas mixture components may be detected and quantified using a gas-chromatograph to separate a gas mixture prior to analysis of one or more eluting components using an absorption spectrometer. Substantial reductions in analytical system complexity and improvements in reliability are achieved compared with other commonly used methods for analyzing such complex mixtures.

Claims

1. A method comprising:

injecting a first sample of a gas mixture containing a component into a first gas chromatography column through which a carrier gas flows, the component being transported by the carrier gas through the first gas chromatography column and eluting from the first gas chromatography column at a known elution time;

supplying the carrier gas and the component eluting from the first gas chromatography column into a sample cell of an absorption spectrometer at the elution time;

passing a light beam through the sample cell;

measuring an absorption of the light beam in the sample cell; and

converting the absorption to a concentration of the component in the sample cell.

2. A method as in claim 1, further comprising converting the concentration of the component in the sample cell to a concentration of the component in the gas mixture.

3. A method as in claim 1, further comprising:

operating the first gas chromatography column within a temperature-controlled enclosure; and

executing a programmed temperature ramp program to vary the temperature within the temperature-controlled enclosure after injecting the first sample.

4. A method as in claim 1, further comprising:

simultaneously injecting a second sample of the gas mixture into a second gas chromatography column through which the carrier gas flows, the component being transported by the carrier gas through the second column and eluting from the second column at the known elution time;

supplying the carrier gas and the component from the second column into the sample cell of the absorption spectrometer at the elution time with the carrier gas and the component from the first column.

5. A method as in claim 1, further comprising generating the light beam from a tunable diode laser.

6. A method as in claim 1, further comprising generating the light beam from a laser source selected from a vertical cavity surface emitting laser, a horizontal cavity surface emitting laser, a quantum cascade laser, a distributed feedback laser, and a color center laser.

7. A method as in claim 1, wherein the light beam is generated by a modulated laser source and the absorption spectrum is a harmonic absorption spectrum.

8. A method as in claim 1, wherein the light beam is generated by a modulated laser source and the absorption spectrum is a direct absorption spectrum.

9. A method as in claim 1 wherein the absorption spectrometer is a differential absorption spectrometer.

10. A method as in claim 1, further comprising:

monitoring a temperature within the temperature-controlled enclosure, and automatically injecting the first sample when the temperature is at a predetermined starting temperature.

11. An apparatus comprising:

a first gas chromatography column;

a first injector to deliver a first sample of a gas mixture into the first gas chromatography column;

an absorption spectrometer comprising a sample cell, a laser source that generates a beam of light passing through the sample cell, and a photodetector that quantifies absorption of the light beam in the sample cell;

a gas chromatograph outlet valve to divert gases exiting the gas chromatography column to the sample cell; and

a process controller that controls the injector port to deliver the first sample to the first gas chromatography column at a first time and the gas chromatograph outlet valve to divert the outflow from the first gas chromatography column to the sample cell at a second time that is selected to coincide with a retention time of a component of the first gas mixture.

12. An apparatus as in claim 11, wherein the process controller receives output data from the photodetector, records an absorption spectrum, and calculates a concentration of the component in the gas mixture.

13. An apparatus as in claim 11, wherein the absorption spectrometer further comprises a microprocessor that receives output data from the photodetector, records an absorption spectrum, and calculates a concentration of the component in the gas mixture.

14. An apparatus as in claim 11, further comprising:

a temperature-controlled enclosure comprising an oven heater, the gas chromatography column being positioned within the temperature-controlled enclosure,

and wherein the process controller commands the oven heater to vary the temperature within the temperature-controlled enclosure as a function of time after the first time according to a pre-determined program.

15. An apparatus as in claim 14, further comprising a temperature sensor positioned within the temperature-controlled enclosure, the temperature sensor communicating with the process controller.

16. An apparatus as in claim 15, wherein the process controller monitors an output signal from the temperature sensor and uses the output signal to determine when the temperature-controlled enclosure is at an appropriate temperature to begin an analysis run.

17. An apparatus as in claim 11, wherein the laser source is a tunable diode laser.

18. An apparatus as in claim 11, wherein the laser source is selected from a vertical cavity surface emitting laser, a horizontal cavity surface emitting laser, a quantum cascade laser, a distributed feedback laser, and a color center laser.

19. An apparatus as in claim 11, wherein the laser source is modulated and the absorption spectrum is a harmonic absorption spectrum.

20. An apparatus as in claim 11, wherein the laser source is modulated and the absorption spectrum is a direct absorption spectrum.

21. An apparatus as in claim 11, further comprising:

a scrubber that reduces the concentration of the component; and

one or more scrubber valves that may be operated to direct the gases exiting the first gas chromatography column through the scrubber prior to the sample cell or to bypass the scrubber.

22. An apparatus as in claim 11, further comprising:

one or more second gas chromatography columns; and

one or more second injectors to deliver one or more second samples of a gas mixture into the one or more second gas chromatography columns at the first time.

23. An apparatus comprising:

a first gas chromatography column;

a first injector to deliver a first sample of a gas mixture into the first gas chromatography column;

a gas chromatograph outlet valve to divert gases exiting the gas chromatography column to a sample cell of an absorption spectrometer; and

a process controller that controls the injector port to deliver the first sample to the first gas chromatography column at a first time and the gas chromatograph outlet valve to divert the outflow from the first gas chromatography column at a second time that is selected to coincide with a retention time of a component of the first gas mixture.

24. An apparatus comprising:

means for separating a first component in a gas mixture from one or more other components in the gas mixture;

means for injecting a sample of the gas mixture into the separation means;

means for containing the separated component as it leaves the separation means;

means for producing and directing a beam of light through the contained separated component;

means for recording an absorption spectrum for the separated component; and

processing means for processing the recorded spectrum and calculating a concentration of the component in the gas mixture.