Process for spectrophotometric analysis

• US 5,223,715 A
• Filed: 09/20/1991
• Issued: 06/29/1993
• Est. Priority Date: 09/20/1991
• Status: Expired due to Term

• Current Assignee: Amoco Corporation (BP PLC)
• Original Assignee: Amoco Corporation (BP PLC)
• Inventors: Taylor, James L.
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Glick, Edward J.
• Application Number:
  US07/763,927
• Time in Patent Office: 648 Days
• Field of Search: 250/339, 250/340, 250/343, 250/344, 356/319, 356/323, 356/325, 356/328
• US Class Current: 250/343
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems
• CPC Class Codes: G01N 21/276 with alternation of sample and standard in optical path
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 2201/0618 Halogene sources
• CPC Class Codes: G01N 2201/067 Electro-optic, magneto-optic, acousto-optic elements
• CPC Class Codes: G01N 2201/129 Using chemometrical methods

Abstract

A process is provided for obtaining spectral information and quantifying the physical properties of a sample. The process comprises launching polychromatic light having a wavelength ranging from about 100 nanometers to about 2500 nanometers alternately through at least one sample channel and at least one reference channel, through at least one high-efficiency fiber optic switch. The sample and the polychromatic light along the sample channel are directed to a sample cell wherein the polychromatic light is passed through the sample, producing sample spectral information. The polychromatic light directed along the reference channel produces reference spectral information. The sample and reference spectral information is reproducibly and uniformly imaged by passing or conveying said sample and reference spectral information through a mode scrambler and the uniformly imaged sample and reference spectral information is then processed in a wavelength discrimination device wherein the uniformly imaged spectral information is separated into component wavelengths and the light intensity at each wavelength determined and recorded. A chemometric model and the separated and recorded uniformly imaged sample and reference spectral information are then utilized to predict the physical properties of the sample. The process of the present invention provides improved prediction accuracy, increased reliability, lower operating costs, and is easier to use and calibrate.

Claims

1. A process for obtaining spectral information and quantifying the physical properties of a sample comprising:

launching polychromatic light having a wavelength ranging from about 100 nanometers to about 2500 nanometers alternately through at least one sample channel and at least one reference channel, through a single fiber optic strand and at least one high-efficiency fiber optic switch having a coupling efficiency of not less than 50 percent;

passing said polychromatic light along said sample channel to said sample cell containing said sample wherein said polychromatic light is passed through said sample and sample spectral information produced;

routing said polychromatic light along said reference channel and producing reference spectral information;

reproducibly and uniformly imaging said sample and reference spectral information from said sample and reference channels by passing said spectral information through a mode scrambler;

processing said uniformly imaged sample and reference spectral information from said mode scrambler in a spectrograph wherein said uniformly imaged spectral information is separated into component wavelengths and the light intensity at each wavelength determined and recorded utilizing a photodiode array detector; and

utilizing said separated and recorded uniformly imaged sample and reference spectral information to predict said physical properties of said sample.

2. The process of claim 1 wherein said polychromatic light is in the wavelength ranges of from about 800 nanometers to about 2500 nanometers.

3. The process of claim 1 wherein said polychromatic light is generated from a tungsten-halogen lamp.

4. The process of claim 1 wherein said polychromatic light is alternately launched through said sample channel and said reference channel using a high-efficiency fiber optic switch cycling at a frequency ranging from about 10 cycles per second to about 0.01 cycles per second.

5. The process of claim 4 wherein said utilizing step comprises generation of filtered absorbance spectra and said mode scrambler reduces noise irreproducibilities in said filtered absorbance spectra, produced from said high-efficiency fiber optic switch, by a factor of at least 3 in the filtered absorbance spectra derived from said separated and recorded uniformly imaged sample and reference spectral information, over said process without a mode scrambler.

6. The process of claim 1 wherein said reproducibly and uniformly imaging step comprises directing sample and reference spectral information along from about 60 meters to about 600 meters of fiber optic cable.

7. The process of claim 1 wherein wavelength drift in said wavelength discrimination device is maintained at less than 0.30 nanometers.

8. A process for obtaining near infrared spectral information and quantifying the physical properties of a sample comprising:

launching polychromatic light having a wavelength ranging from about 800 nanometers to about 2500 nanometers alternately through a single fiber optic strand and at least one sample channel and at least one reference channel, through at least two high-efficiency mechanical motion mechanism fiber optic switches;

directing said sample to a sample cell;

passing said polychromatic light along said sample channel to said sample cell wherein said polychromatic light is passed through said sample and sample spectral information produced;

attenuating said polychromatic light along said reference channel and producing attenuated reference spectral information for balancing polychromatic light transmission between said reference and sample channels;

reproducibly and uniformly imaging said sample spectral information from said sample channel and said attenuated reference spectral information alternately by passing said spectral information through a mode scrambler;

processing said uniformly imaged sample and attenuated reference spectral information from said mode scrambler in a spectrograph wherein said uniformly imaged spectral information is diffracted into component wavelengths and the light intensity at each wavelength determined and recorded utilizing a photodiode array detector; and

utilizing a chemometric model and said diffracted and recorded uniformly imaged spectral information to predict said physical properties of said sample.

9. The process of claim 8 wherein said polychromatic light is in the wavelength range of from about 800 nanometers to about 1100 nanometers.

10. The process of claim 8 wherein said sample is crude petroleum and said polychromatic light wavelength spans at least one range selected from the group consisting of from about 1300 nanometers to about 1500 nanometers and from about 1600 nanometers to about 1800 nanometers.

11. The process of claim 8 wherein said polychromatic light is alternately launched through said sample channel and said reference channel from a high-efficiency fiber optic switch cycling at a frequency of from about 10 cycles per second to about 0.01 cycles per second.

12. The process of claim 8 wherein said utilizing step comprises generation of filtered absorbance spectra and said mode scrambler reduces noise irreproducibilities in said filtered absorbance spectra, produced from said high-efficiency fiber optic switches, by a factor of 3 in the filtered absorbance spectra derived from said diffracted and recorded uniformly imaged sample and reference spectral information, over said process without a mode scrambler.

13. The process of claim 8 wherein said photodiode array detector operates in a range not exceeding 85% of full scale light intensity required to saturate said detector.

14. The process of claim 8 wherein the photometric response of said spectrograph is substantially linear to better than 0.9% of full scale light intensity.

15. The process of claim 8 wherein said spectrograph temperature is maintained within 5.6°

C. of a constant operating temperature target.

16. The process of claim 8 wherein wavelength drift in said spectrograph is maintained at least than 0.30 nanometers.

17. The process of claim 8 wherein wavelength drift in said spectrograph is maintained at less than 0.03 nanometers.

18. The process of claim 8 wherein the resolution of said spectrograph is better than 4 nanometers.

19. A process for obtaining near infrared spectral information and quantifying the physical properties of a sample comprising:

launching polychromatic light having a wavelength ranging from about 800 nanometers to about 1100 nanometers alternately through at least one sample channel and one reference channel, through a single fiber optic strand and at least two high-efficiency latching type mechanical motion fiber optic switches;

directing said sample to a sample cell;

passing said polychromatic light along said sample channel to said sample cell wherein said polychromatic light is passed through said sample at least twice utilizing a light reflection device, wherein said polychromatic light contacting said light reflection device is reflected at least twice, and sample spectral information produced;

attenuating said polychromatic light along said reference channel and producing attenuated reference spectral information for balancing polychromatic light transmission between said reference and sample channels;

reproducibly and uniformly imaging said sample spectral information from said sample channel and said attenuated reference spectral information alternately by passing said spectral information through a mode scrambler;

processing said uniformly imaged sample and attenuated reference spectral information from said mode scrambler in a spectrograph wherein said uniformly imaged spectral information is diffracted into component wavelengths and the light intensity at each wavelength determined and recorded utilizing a photodiode array detector; and

utilizing a chemometric model and said diffracted and recorded uniformly imaged spectral information to predict said physical properties of said sample.

20. The process of claim 19 wherein said polychromatic light wavelength ranges from about 850 nanometers to about 1000 nanometers and said sample is a hydrocarbon liquid which is transparent or partially transparent over said wavelength range.

21. The process of claim 19 wherein said polychromatic light is alternately launched through said sample channel and said reference channel at a high-efficiency fiber optic switch cycling frequency of from about 1 cycle per second to about 0.1 cycles per second.

22. The process of claim 19 wherein said sample is conditioned and maintained within 11.1°

C. of a constant operating temperature target.

23. The process of claim 19 wherein said passing step for producing sample spectral information comprises passing said polychromatic light through said sample twice utilizing a light reflection device wherein said said polychromatic light contacting said light reflection device is reflected three times.

24. The process of claim 19 wherein said sample passes through said sample cell at a velocity of less than about 0.3 meters.

25. The process of claim 19 wherein wavelength drift in said spectrograph is maintained at less than 0.03 nanometers.

26. The process of claim 19 wherein the resolution of said spectrograph is better than 2 nanometers.