# US 5,751,415 A · Raman spectroscopy apparatus and method for continuous chemical analysis of fluid streams > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,751,415 A - Document ID: US5751415A - Status: Granted - Kind: A - Application number: 08/647,586 - Filed: 1996-05-13 - Granted: 1998-05-12 - Earliest claimed: 1996-05-13 - Assignees: Process Instruments, Inc. - Inventors: Lee M. Smith; Robert E. Benner; Douglas A. Christensen; Joel M. Harris; Carl W. Johnson; Richard D. Rallison - Web page: https://patentgrep.com/patent/US5751415A ## CPC - G01J 3/02: Details - G01J 3/0218: {using optical fibers} - G01J 3/18: using diffraction elements, e.g. grating (gratings per se G02B) - G01J 3/44: Raman spectrometry; Scattering spectrometry {; Fluorescence spectrometry} - G01N 21/65: Raman scattering - G01N 21/658: {enhancement Raman, e.g. surface plasmons} - G01N 2021/651: {Cuvettes therefore} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract Apparatus and methods for analyzing the chemical composition of fluid streams using Raman spectroscopy are disclosed. The invention is particularly useful in continuously analyzing a fluid stream containing petroleum products, aqueous or biological fluids. The apparatus includes a laser source for producing light having an excitation wavelength. The light is introduced into a bundle of optical fibers connected to a tubular Raman enhancement cell. A transparent optical element (lens and/or window) acts as a barrier element to isolate the flowing sample stream from the optical components. The Raman enhancement cell is configured to allow continuous sample fluid flow therethrough, and it is preferably lined with a material having an index of refraction less than the index of refraction of the fluid stream. Scattered light from the enhancement cell preferably exits the optical fibers as a linear optical signal. A Raman spectrometer passes the optical signal through an excitation wavelength filter, an optical slit, and a volume holographic transmission grating with an aberration correction device before transmitting the optical signal to a charge coupled device array which converts the optical signal into a corresponding electronic signal. The electronic signal is analyzed and converted by computer into a representation of the chemical analysis of the fluid stream. ## Claims ### Claim 1 A method for continuously analyzing the composition of a fluid stream using Raman spectroscopy comprising the steps of: (a) introducing the fluid stream into a tubular Raman enhancement cell comprising: a fluid stream inlet and a fluid stream outlet located adjacent the ends of the enhancement cell for continuous fluid flow through the enhancement cell; an optical connector located at one end of the enhancement cell for connecting a bundle of optical fibers to the enhancement cell, wherein said bundle of optical fibers includes at least one excitation optical fiber and one or more collection optical fibers; and a transparent fluid barrier located between the bundle of optical fibers and the enhancement cell; (b) introducing light having an excitation wavelength into the Raman enhancement cell through the excitation optical fiber; (c) collecting backscattered Raman light from the enhancement cell with the one or more collection optical fibers; (d) measuring the backscattered light with a Raman spectrometer comprising: a linear array of the one or more collection optical fibers for generating an optical signal of the scattered light from the enhancement cell; a filter for rejecting portions of the optical signal having the excitation wavelength; a volume holographic transmission grating to disperse the light; a transmissive aberration correction element for correcting optical aberrations introduced into optical signal by the volume holographic transmission grating, said aberration correction element comprising at least one optically transparent wedge or prism; and a charge coupled device array for converting the optical signal into a corresponding electronic signal; and (e) converting the electronic signal into a representation of the chemical analysis of the fluid stream. ### Claim 2 (depends on 1) A method as defined in claim 1, wherein the backscattered light is measured with a Raman spectrometer comprising a plurality of optical lenses for receiving and conveying the optical signal from the linear array of the collection optical fibers to the charge coupled device array. ### Claim 3 (depends on 1) A method as defined in claim 1, wherein the fluid stream introduced into a tubular Raman enhancement cell contains petroleum products. ### Claim 4 (depends on 1) A method as defined in claim 1, further comprising the step of positioning the Raman enhancement cell at a remote location from the Raman spectrometer. ### Claim 5 (depends on 1) A method as defined in claim 1, wherein the tubular Raman enhancement cell is lined with a material having an index of refraction less than the index of refraction of the fluid stream. ### Claim 6 (depends on 5) A method as defined in claim 5, wherein the tubular Raman enhancement cell is lined with a fluorinated polymer. ### Claim 7 (depends on 6) A method as defined in claim 6, wherein the fluorinated polymer is selected from the group consisting of polytetrafluoroethylene (PTFE), FEP, PFA, AF and Tefzel. ### Claim 8 (depends on 5) A method as defined in claim 5, wherein the fluid stream introduced into a tubular Raman enhancement cell contains petroleum products and wherein the tubular Raman enhancement cell is lined with a polymer having an index of refraction less than 1.4. ### Claim 9 (depends on 5) A method as defined in claim 5, wherein the fluid stream introduced into a tubular Raman enhancement cell contains aqueous or biological solutions and wherein the tubular Raman enhancement cell is lined with a polymer having an index of refraction less than 1.33. ### Claim 10 (depends on 1) A method as defined in claim 1, wherein the tubular Raman enhancement cell has a length in the range from about 0.1 m to about 4 m. ### Claim 11 (depends on 1) A method as defined in claim 1, wherein the tubular Raman enhancement cell has a diameter in the range from about 0.005 to 0.2 inches. ### Claim 12 (depends on 1) A method as defined in claim 1, further comprising the step of aligning the tubular Raman enhancement cell in a linear orientation between the fluid stream inlet and the fluid stream outlet. ### Claim 13 (depends on 1) A method as defined in claim 1, further comprising the step of aligning the tubular Raman enhancement cell in a curved orientation between the fluid stream inlet and the fluid stream outlet. ### Claim 14 (depends on 1) A method as defined in claim 1, wherein the aberration correction element comprises two optically transparent wedges or prisms. ### Claim 15 (depends on 1) A method as defined in claim 1, wherein the bundle of optical fibers includes from 20 to 50 collection optical fibers. ### Claim 16 (depends on 1) A method as defined in claim 1, wherein the backscattered light is measured with a Raman spectrometer comprising an optical slit. ### Claim 17 (depends on 16) A method as defined in claim 16, wherein the optical slit has dimensions comparable to the linear array of collection optical fibers. ### Claim 18 (depends on 16) A method as defined in claim 16, wherein the optical slit has a width in the range from 10 microns to 150 microns. ### Claim 19 (depends on 1) A method as defined in claim 1, wherein the transparent fluid barrier includes a layer of index matching fluid to maintain optimum optical coupling between the bundle of optical fibers and the fluid barrier. ### Claim 20 An apparatus for analyzing the composition of a fluid stream using Raman spectroscopy comprising: a laser source for producing light having an excitation wavelength; a bundle of optical fibers comprising one or more excitation optical fibers and a plurality of collection optical fibers; a tubular Raman enhancement cell comprising: a fluid stream inlet and a fluid stream outlet located adjacent the ends of the enhancement cell for continuous fluid flow through the enhancement cell; an optical connector located at one end of the enhancement cell for connecting the bundle of optical fibers to the enhancement cell; and a transparent fluid barrier located between the bundle of optical fibers and the enhancement cell; a Raman spectrometer comprising: a linear array of the collection optical fibers for generating a linear optical signal of the scattered light from the enhancement cell; a filter for rejecting portions of the optical signal having the excitation wavelength; a volume holographic transmission grating to disperse the signal and a transmissive aberration correction element for correcting optical aberrations introduced into optical signal by the volume holographic transmission grating, said aberration correction element comprising at least one optically transparent wedge or prism; and a charge coupled device array for converting the optical signal into a corresponding electronic signal; and a computer for converting the electronic signal into a representation of the chemical analysis of the fluid stream. ### Claim 21 (depends on 20) An apparatus as defined in claim 20, wherein the Raman spectrometer further comprises a plurality of optical lenses for receiving and conveying the optical signal from the linear array of the collection optical fibers to the charge coupled device array. ### Claim 22 (depends on 20) An apparatus as defined in claim 20, wherein the tubular Raman enhancement cell is lined with a material having an index of refraction less than the index of refraction of the fluid stream. ### Claim 23 (depends on 20) An apparatus as defined in claim 20, wherein the tubular Raman enhancement cell is lined with a fluorinated polymer. ### Claim 24 (depends on 23) An apparatus as defined in claim 23, wherein the fluorinated polymer is selected from the group consisting of polytetrafluoroethylene (PTFE), FEP, PFA, AF and Tefzel. ### Claim 25 (depends on 20) An apparatus as defined in claim 20, wherein the fluid stream contains petroleum products and the tubular Raman enhancement cell is lined with a polymer having an index of refraction less than 1.4. ### Claim 26 (depends on 20) An apparatus as defined in claim 20, wherein the fluid stream contains aqueous or biological solutions and the tubular Raman enhancement cell is lined with a polymer having an index of refraction less than 1.33. ### Claim 27 (depends on 20) An apparatus as defined in claim 20, wherein the tubular Raman enhancement cell has a length in the range from about 0.1 m to about 4 m. ### Claim 28 (depends on 20) An apparatus as defined in claim 20, wherein the tubular Raman enhancement cell has a diameter in the range from about 0.005 to 0.2 inches. ### Claim 29 (depends on 20) An apparatus as defined in claim 20, wherein the tubular Raman enhancement cell is constructed of a flexible material. ### Claim 30 (depends on 20) An apparatus as defined in claim 20, wherein the tubular Raman enhancement cell is constructed of a rigid material. ### Claim 31 (depends on 20) An apparatus as defined in claim 20, wherein the aberration correction element comprises two optically transparent wedges or prisms. ### Claim 32 (depends on 31) An apparatus as defined in claim 31, wherein the volume holographic transmission grating is in physical contact with the aberration correction element. ### Claim 33 (depends on 20) An apparatus as defined in claim 20, wherein the aberration correction element and optical lenses are coated with anti-reflection coatings to minimize light losses. ### Claim 34 (depends on 20) An apparatus as defined in claim 20, wherein the bundle of optical fibers includes from 20 to 50 collection optical fibers. ### Claim 35 (depends on 20) An apparatus as defined in claim 20, wherein the Raman spectrometer further comprises an optical slit. ### Claim 36 (depends on 35) An apparatus as defined in claim 35, wherein the optical slit has dimensions comparable to the linear array of collection optical fibers. ### Claim 37 (depends on 35) An apparatus as defined in claim 35, wherein the optical slit has a width in the range from 10 microns to 150 microns. ### Claim 38 (depends on 20) An apparatus as defined in claim 20, wherein the transparent fluid barrier includes a lens. ### Claim 39 (depends on 20) An apparatus as defined in claim 20, wherein the transparent fluid barrier includes an optical window. ### Claim 40 (depends on 20) An apparatus as defined in claim 20, wherein the transparent fluid barrier includes a layer of index matching fluid to maintain optimum optical coupling between the bundle of optical fibers and the fluid barrier. ### Claim 41 An apparatus for analyzing the composition of a sample using Raman spectroscopy comprising: a laser source for producing light having an excitation wavelength, wherein the light is directed into a sample and wherein a Raman signal exits the sample as an optical signal; a Raman spectrometer configured to receive the optical signal comprising: a filter for rejecting portions of the optical signal having the excitation wavelength; an optical slit; a volume holographic transmission grating to disperse the optical signal and a transmissive aberration correction element for correcting optical aberrations introduced into optical signal by the volume holographic transmission grating, said aberration correction element comprising at least one optically transparent wedge or prism; and a charge coupled device array for converting the optical signal into a corresponding electronic signal; and a computer for converting the electronic signal into a representation of the chemical analysis of the sample. ### Claim 42 (depends on 41) An apparatus as defined in claim 41, wherein the Raman spectrometer further comprises a plurality of optical lenses for receiving and conveying the optical signal to the charge coupled device array. ### Claim 43 (depends on 41) An apparatus as defined in claim 41, wherein the aberration correction element comprises two optically transparent wedges or prisms. ### Claim 44 (depends on 43) An apparatus as defined in claim 43, wherein the volume holographic transmission grating is in physical contact with the aberration correction element. ### Claim 45 (depends on 41) An apparatus as defined in claim 41, wherein the aberration correction element and optical lenses are coated with anti-reflection coatings to minimize light losses.