Fiber optic probe for light scattering measurements

• US 5,404,218 A
• Filed: 11/18/1993
• Issued: 04/04/1995
• Est. Priority Date: 11/18/1993
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Department Of Energy
• Original Assignee: United States Department of Energy
• Inventors: Prather, William S., Livingston, Ronald R., Nave, Stanley E.
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US08/154,353
• Time in Patent Office: 502 Days
• Field of Search: 356/301, 356/307, 356/244, 356/246
• US Class Current: 356/301
• CPC Class Codes: G01N 21/65 Raman scattering
• CPC Class Codes: G01N 2201/08 Optical fibres; light guides

Abstract

A fiber optic probe and a method for using the probe for light scattering analyses of a sample. The probe includes a probe body with an inlet for admitting a sample into an interior sample chamber, a first optical fiber for transmitting light from a source into the chamber, and a second optical fiber for transmitting light to a detector such as a spectrophotometer. The interior surface of the probe carries a coating that substantially prevents non-scattered light from reaching the second fiber. The probe is placed in a region where the presence and concentration of an analyte of interest are to be detected, and a sample is admitted into the chamber. Exciting light is transmitted into the sample chamber by the first fiber, where the light interacts with the sample to produce Raman-scattered light. At least some of the Raman-scattered light is received by the second fiber and transmitted to the detector for analysis. Two Raman spectra are measured, at different pressures. The first spectrum is subtracted from the second to remove background effects, and the resulting sample Raman spectrum is compared to a set of stored library spectra to determine the presence and concentration of the analyte.

Claims

1. A probe for use in light scattering analyses of a sample, said probe for use with a source of light and a spectrophotometer, said probe comprising:

a probe body having an interior, an interior surface, and means formed in said probe body for admitting said sample into said interior, said sample in said interior having a pressure;

means for controlling said pressure;

first light-transmitting means for transmitting exciting light from said source into said interior, a first portion of said exciting light interacting with said sample to produce Raman-scattered light, a remaining portion of said exciting light producing non-Raman-scattered light in said interior;

second light-transmitting means for transmitting light from said interior to said spectrophotometer; and

means for preventing a substantial portion of said non-Raman-scattered light from reaching said second light-transmitting means.

2. The apparatus as recited in claim 1, wherein said preventing means further comprises a light-absorbing coating carried by said interior surface.

3. The apparatus as recited in claim 1, wherein said preventing means further comprises:

a light-absorbing coating carried by said interior surface, said coating comprising;

an adhesive; and

a quantity of carbon black particles mixed with said adhesive.

4. The apparatus as recited in claim 1, wherein said probe body further comprises a proximal end and a distal end, said distal end having an interior surface, said first and second light-transmitting means in optical communication with said proximal end, and wherein said preventing means further comprises a light-absorbing coating carried by said interior surface of said distal end.

5. The apparatus as recited in claim 1, wherein said first light-transmitting means further comprises at least one optical fiber having a proximal end and a distal end, said proximal end in optical communication with said source and said distal end in optical communication with said interior, and

wherein said second light-transmitting means further comprises at least one optical fiber having a proximal end and a distal end, said proximal end in optical communication with said spectrophotometer and said distal end in optical communication with said interior.

6. The apparatus as recited in claim 1, wherein said probe body further comprises a proximal end and a distal end, said distal end having an interior surface, said first light-transmitting means in optical communication with said proximal end, and wherein said probe body is dimensioned so that diverging light emitted by said first light-transmitting means reaches said interior surface of said distal end before striking said interior surface of said probe body.

7. A probe for use in light scattering measurements of a sample containing molecules, said probe for use with a source of light and a spectrophotometer, said probe comprising:

a probe body having an interior, an interior surface, and an inlet;

at least one light-transmitting fiber having a proximal end and a distal end, said proximal end in optical communication with said source and said distal end in optical communication with said interior,

said at least one light-transmitting fiber transmitting exciting light from said source into said interior, a portion of said exciting light interacting with said sample molecules to produce Raman-scattered light,

a remaining portion of said exciting light interacting with said sample molecules and said interior surface to produce non-Raman-scattered light;

at least one light-receiving fiber having a proximal end and a distal end, said proximal end in optical communication with a spectrophotometer and said distal end in optical communication with said interior,

said light-receiving fiber transmitting light from said interior to said spectrophotometer; and

a coating carried by said interior surface, Said coating including an adhesive and a quantity of carbon black particles carried by said adhesive, said coating preventing a substantial portion of said non-Raman-scattered light from reaching said at least one light-receiving fiber.

8. The apparatus as recited in claim 7, wherein said interior further comprises a proximal end and a distal end, said distal ends of said at least one light-transmitting fiber and said at least one light-receiving fiber in optical communication with said proximal end, said distal end of said interior having an interior surface, and wherein said coating is carried by said interior surface of said distal end.

9. The apparatus as recited in claim 7, wherein a sample in said interior has a pressure, further comprising means in fluid communication with said inlet for controlling said pressure.

10. The apparatus as recited in claim 7, wherein said source of light has a wavelength, further comprising a filter in optical communication with said at least one light-receiving fiber, said filter absorbing at least a portion of light having said wavelength.

11. The apparatus as recited in claim 7, wherein light passing through said at least one light-transmitting fiber interacts therewith to produce Raman-scattered light having at least one wavelength, further comprising a filter in optical communication with said light-transmitting fiber, said filter absorbing at least a portion of light having said at least one wavelength.

12. The apparatus as recited in claim 7, wherein said distal ends of said at least one light-transmitting fiber and said at least one light-receiving fiber are adjacent and parallel.

13. The apparatus as recited in claim 7, wherein said distal ends of said at least one light-transmitting fiber and said at least one light-receiving fiber are grouped in a bundle, said light-receiving fibers surrounding said light-transmitting fiber.

14. The apparatus as recited in claim 7, further comprising means in operative connection with said inlet for preventing particles from entering said interior.

15. The apparatus as recited in claim 7, further comprising a window positioned just beyond said distal ends of said light-transmitting and said light-receiving fibers, said window preventing contact of said fibers with a sample contained in said interior.

16. The apparatus as recited in claim 7, wherein said probe body further comprises a proximal end and a distal end, said distal end having an interior surface, said distal end of said at least one light-transmitting fiber in optical communication with said proximal end, and wherein said probe body is dimensioned so that diverging light emitted by said least one light-transmitting fiber reaches said interior surface of said distal end before striking said interior surface of said probe body.

17. A method for detecting the presence and concentration of an analyte in a sample, said sample having a pressure, said method comprising the steps of:

directing exciting light into said sample so that at least a portion of said exciting light interacts with said sample to produce Raman-scattered light, a remaining portion of said exciting light producing non-Raman-scattered light;

transmitting at least a portion of said Raman-scattered light to a spectrophotometer with an optical fiber, while preventing at least a portion of said non-Raman-scattered light from reaching said optical fiber;

measuring a first Raman spectrum from said transmitted light, said pressure having a first value;

changing said pressure of said sample to a second value;

measuring a second Raman spectrum from said transmitted light; and

comparing said first and said second Raman spectra to determine said presence and said concentration of said analyte.

18. The method as recited in claim 17, wherein said analyte has a reference Raman spectrum, and wherein said comparing step further comprises:

subtracting said first Raman spectrum from said second Raman spectrum to obtain a sample Raman spectrum; and

comparing said sample Raman spectrum to said reference Raman spectrum to determine if said spectra match.

19. The method as recited in claim 17, wherein said analyte has a reference Raman spectrum having at least one reference line with a delta wavelength and an intensity, and wherein said comparing step further comprises:

subtracting said first Raman spectrum frown said second Raman spectrum to obtain a sample Raman spectrum, said sample spectrum having at least one Raman line with a delta wavelength and an intensity;

comparing said delta wavelengths of said at least one Raman line and said at least one reference line to determine if said sample spectrum and said reference spectrum match; and

comparing said intensities of said at least one Raman line and said at least one reference line to determine said concentration of said analyte in said sample.

20. The method as recited in claim 17, wherein said light-directing step further comprises the step of passing said exciting light into a chamber containing said sample, said chamber having a light-absorbing interior surface, said surface absorbing at least a portion of light not reaching said optical fiber.