System, device, and method for raman analysis of fluid samples

Abstract

Systems, devices, and methods for Raman analysis of a fluid sample are disclosed. The system can include a flow cell defining a sample flow channel configured to allow the sample to therethrough flow. The system can also include an excitation light source configured to emit Raman excitation light, and an objective lens configured to focus the Raman excitation light to irradiate the sample in a sample interrogation region intersecting the sample flow channel and to collect backward-scattered Raman light emerging from the sample. The system can further include a reflector positioned opposite from the objective lens across the sample flow channel and configured to reflect forward-directed light emerging from the sample back toward the sample interrogation region to enhance an intensity of the backward-scattered Raman light collected by the objective lens. The system can also include an optical spectrometer configured to detect the enhanced backward-scattered Raman light.

Description

SYSTEM, DEVICE, AND METHOD FOR RAMAN ANALYSIS OF FLUID SAMPLESCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority under applicable laws to U.S. Provisional Patent Application No. 63 / 594,179 filed on October 30, 2023, the content of which is incorporated herein by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The technical field generally relates to analytical spectroscopy and, more particularly to techniques for Raman analysis of fluid samples in various industrial, commercial, and scientific applications.BACKGROUND

[0003] Raman spectroscopy is an analytical technique used to obtain structure and chemical composition information about a sample by probing its molecular vibrational modes via inelastic light scattering of monochromatic excitation light. Raman spectroscopy measurements can be depicted as a spectrum of scattered light intensity plotted as a function of Raman shift, which represents the energy difference between the excitation light and the detected Raman scattered light. Raman spectra are composed of numerous peaks, whose parameters (e.g., peak position, intensity, and linewidth) contains qualitative and quantitative information about various species-specific physico-chemical parameters. Raman spectroscopy offers several advantages. It is a non-destructive and non-invasive technique that can be applied to various types of materials using a wide range of excitation wavelengths and small sample volumes requiring no or little sample preparation.

[0004] Raman spectroscopy has been primarily used with solid samples, but it is also applicable to aqueous and other liquid samples, although with additional challenges. Because Raman signals from analytes in liquid samples tend to be fairly weak, obtaining suitably high signal-to-noise ratios can be difficult, especially in the case of dilute or low-concentration samples. For example, detecting and identifying low-concentration analytes or minor components in complex aqueous matrices can be challenging. Furthermore, the composition of the sample container can affect the Raman spectrum, particularly for inline and online measurement systems. For example, certain sample containers can produce fluorescence or Raman emissions that can overlap or otherwise interfere with Raman signals from sample analytes, making it difficult to distinguish their respective contributions in the Raman spectrum measurements. Furthermore, limited options are available for real-time Raman analyses performed inline or online in large-scale manufacturingand / or processing operations, involving extensive and complex design features that are often less efficient and reliable than benchtop batch analyses. Despite advances in the field, challenges remain in the development of Raman spectroscopy techniques for fluid sample characterization.SUMMARY

[0005] The present disclosure generally relates to techniques, including systems, devices, and methods, for characterization and analysis of fluid samples using Raman spectroscopy. The disclosed techniques can find use in various applications, notably in mining extraction and processing applications, such as in direct lithium extraction (DLE) operations.

[0006] The disclosed embodiments generally use a flow cell, an objective lens, and a reflector. The flow cell is configured to allow a fluid sample to flow therethrough along a sample flow channel. The objective lens is configured to focus Raman excitation light into a sample interrogation region that intersects the sample flow channel and to collect backward-scattered Raman light emerging from the fluid sample for detection and Raman analysis. The reflector, which can be embodied by a concave mirror, is positioned opposite from the objective lens across the sample flow channel and is configured to reflect forward-directed light emerging from the fluid sample back toward the sample interrogation region. The reflected forward-directed light can include forward-scattered Raman light generated from the fluid sample and / or residual Raman excitation light transmitted or elastically scattered by the fluid sample. In some embodiments, the reflector is located outside the flow cell, and the flow cell includes an optical window (e.g., made of sapphire) through which at least part of the forward-directed light can pass to exit the flow cell and reach the reflector.

[0007] The provision of the reflector can enhance (e.g., by a factor of about two) the intensity of the backward-scattered Raman light that is collected by the objective lens and that is ultimately detected and processed to generate Raman spectral data. The higher Raman signal intensity can lower the detection and quantitation limits, thus facilitating the analysis of low-concentration species. In some embodiments, the objective lens is positioned in direct contact with the fluid sample flowing through the flow cell, which can provide various advantages, notably in field-deployed industrial or manufacturing settings where the fluid sample is drawn off a fluid reservoir or diverted from a process flow stream. Such advantages include the capability to conduct Raman spectroscopy measurements without having to use internal standards or perform focus adjustments. These advantages can lead to shorter data acquisition times, which is often desirable or required in real-time or continuous measurements of ongoing processes and operations.

[0008] The embodiments disclosed herein include the following aspects:1. A system for Raman analysis of a fluid sample, the system including: a flow cell including a sample inlet, a sample outlet, and a flow cell body defining a sample flow channel configured to allow the fluid sample to flow from the sample inlet to the sample outlet; an excitation light source configured to emit Raman excitation light; an objective lens configured to: (i) focus the Raman excitation light into a sample interrogation region intersecting the sample flow channel for irradiating the fluid sample, and (ii) collect backward- scattered Raman light emerging from the fluid sample; a reflector positioned opposite from the objective lens across the sample flow channel, the reflector being configured to reflect forward-directed light emerging from the fluid sample back toward the sample interrogation region to enhance an intensity of the backward-scattered Raman light collected by the objective lens, wherein the reflected forward-directed light includes either or both of forward- scattered Raman light generated from the fluid sample and residual Raman excitation light transmitted or elastically scattered by the fluid sample; and an optical spectrometer configured to detect the backward-scattered Raman light collected by the objective lens.2. The system of aspect 1, wherein the excitation light source includes a laser source.3. The system of aspect 1 or 2, wherein the Raman excitation light has an excitation wavelength ranging from about 400 nm to about 1200 nm.4. The system of any one of aspects 1 to 3, wherein the objective lens is a dipping objective lens configured to provide a portion of a boundary of the sample flow channel.5. The system of aspect 4, wherein the objective lens is mounted into an opening formed in the flow cell body.6. The system of any one of aspects 1 to 3, wherein the objective lens is a fluid-immersion objective lens.7. The system of any one of aspects 1 to 6, wherein the objective lens has a focal length ranging from about 4.0 mm to about 5.0 mm.8. The system of any one of aspects 1 to 7, wherein the objective lens has a working distance ranging from about 3.0 mm to about 4.0 mm.9. The system of any one of aspects 1 to 8, wherein the reflector is a concave mirror.10. The system of aspect 9, wherein the concave mirror is a spherical mirror.11. The system of aspect 9 or 10, wherein the concave mirror has a center of curvature positioned within the sample interrogation region.12. The system of aspect 11, wherein the center of curvature of the concave mirror is positioned at a focal point of the objective lens.13. The system of any one of aspects 1 to 12, wherein the reflector is configured for position adjustment relative to the objective lens.14. The system of any one of aspects 1 to 13, wherein the flow cell includes a reflector-viewing window configured to: allow the forward-directed light incident thereon to pass therethrough to exit the flow cell and reach the reflector; and allow the forward-directed light reflected by the reflector to pass therethrough to re-enter the flow cell and reach the sample interrogation region.15. The system of aspect 14, wherein the reflector-viewing window is made of a window material including sapphire.16. The system of any one of aspects 1 to 15, further including an optical cage assembly configured to mount the flow cell, the objective lens, and the reflector in a coaxial serial arrangement.17. The system of any one of aspects 1 to 13, wherein the reflector is configured to provide a portion of a boundary of the sample flow channel.18. The system of aspect 17, wherein the reflector is mounted into an opening formed in the flow cell body.19. The system of aspect 18, wherein the reflector is configured for position adjustment within the opening relative to the objective lens.20. The system of any one of aspects 1 to 19, wherein the sample flow channel extends along a fluid flow direction substantially perpendicular to an objective axis of the objective lens.21. The system of any one of aspects 1 to 20, further including a computer device operatively coupled to the optical spectrometer and including a processor and a non-transitory computer readable storage medium having stored thereon computer readable instructions that, when executed by the processor, cause the processor to analyze the backward-scattered Raman light detected by the optical spectrometer and derive therefrom analyte information associated with the fluid sample.22. The system of aspect 21, wherein the analyte information associated with the fluid sample includes at least one of: (i) a concentration of one or more analytes in the fluid sample, (ii) a presence or absence of one or more analytes in the fluid sample, or (iii) chemical composition information about one or more analytes in the fluid sample.23. The system of aspect 21 or 22, wherein the one or more analytes include borates, carbonates, nitrates, nitrites, phosphates, phosphites, sulfates, sulfites, boric acid, carbonic acid, nitric acid, nitrous acid, phosphoric acid, phosphorous acid, sulfuric acid, sulfurous acid, or any combination thereof.24. The system of any one of aspects 1 to 23, wherein the sample fluid is an aqueous sample.25. The system of any one of aspects 1 to 24, wherein the sample fluid is a lithium-containing brine.26. The system of any one of aspects 1 to 24, wherein the sample fluid is a plant nutrient solution.27 The system of any one of aspects 1 to 26, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid stream flowing within a conduit.28. The system of aspect 27, wherein the sample outlet is configured to reintroduce the fluid sample into the fluid stream.29. The system of any one of aspects 1 to 26, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid contained in a fluid reservoir.30. The system of aspect 29, wherein the sample outlet is configured to reintroduce the fluid sample back into the fluid reservoir.31. A Raman flow cell device for use in performing Raman analysis of a fluid sample, the Raman cell flow device including: a flow cell including a sample inlet, a sample outlet, and a flow cell body defining a sample flow channel configured to allow the fluid sample to flow from the sample inlet to the sample outlet; an objective lens configured to: (i) to focus Raman excitation light received from an excitation light source into a sample interrogation region intersecting the sample flow channel for irradiating the fluid sample, and (ii) collect backward-scattered Raman light emerging from the fluid sample for detection of the collected backward-scattered Raman light by an optical spectrometer; and a reflector positioned opposite from the objective lens across the sample flow channel, the reflector being configured to reflect forward-directed light emerging from the fluid sample back toward the sample interrogation region to enhance an intensity of the backward-scattered Raman light collected by the objective lens, wherein the reflected forward-directed light includes either or both of forward-scattered Raman light generated from the fluid sample and residual Raman excitation light transmitted or elastically scattered by the fluid sample.32. The Raman flow cell device of aspect 31, wherein the objective lens is a dipping objective lens configured to provide a portion of a boundary of the sample flow channel.33. The Raman flow cell device of aspect 31 or 32, wherein the objective lens is a fluid-immersion objective lens.34. The Raman flow cell device of any one of aspects 31 to 33, wherein the objective lens has a focal length ranging from about 4.0 mm to about 5.0 mm, and a working distance ranging from about 3.0 mm to about 4.0 mm.35. The Raman flow cell device of any one of aspects 31 to 34, wherein the reflector is a concave mirror.36. The Raman flow cell device of aspect 35, wherein the concave mirror is a spherical concave mirror.37. The Raman flow cell device of aspect 35 or 36, wherein the concave mirror has a center of curvature positioned within the sample interrogation region.38. The Raman flow cell device of aspect 37, wherein the center of curvature of the concave mirror is positioned at a focal point of the objective lens.39. The Raman flow cell device of any one of aspects 31 to 38, wherein the reflector is configured for position adjustment relative to the objective lens.40. The Raman flow cell device of any one of aspects 31 to 39, wherein the flow cell includes a reflectorviewing window configured to: allow the forward-directed light incident thereon to pass therethrough to exit the flow cell and reach the reflector; and allow the forward-directed light reflected by the reflector to pass therethrough to re-enter the flow cell and reach the sample interrogation region.41. The Raman flow cell device of aspect 40, wherein the reflector-viewing window is made of a window material including sapphire.42. The Raman flow cell device of any one of aspects 31 to 41, further including an optical cage assembly configured to mount the flow cell, the objective lens, and the reflector in a coaxial serial arrangement.43. The Raman flow cell device of any one of aspects 31 to 39, wherein the reflector is configured to provide a portion of a boundary of the sample flow channel.44. The Raman flow cell device of any one of aspects 31 to 43, wherein the sample flow channel extends along a fluid flow direction substantially perpendicular to an objective axis of the objective lens.45. The Raman flow cell device of any one of aspects 31 to 44, wherein the sample fluid is an aqueous sample.46. The Raman flow cell device of any one of aspects 31 to 45, wherein the sample fluid is a lithium-containing brine.47. The Raman flow cell device of any one of aspects 31 to 46, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid stream flowing within a conduit.48. The Raman flow cell device of aspect 47, wherein the sample outlet is configured to discharge the fluid sample back into the fluid stream.49. The Raman flow cell device of any one of aspects 31 to 46, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid contained in a fluid reservoir.50. The Raman flow cell device of aspect 49, wherein the sample outlet is configured to discharge the fluid sample back into the fluid reservoir.51. A method of performing Raman analysis of a fluid sample, the method including: allowing the fluid sample to flow along a sample flow channel extending inside a flow cell; focusing Raman excitation light into a sample interrogation region intersecting the sample flow channel for irradiating the fluid sample; collecting backward-scattered Raman light emerging from the fluid sample; reflecting forward-directed light emerging from the fluid sample back toward the sample interrogation region to enhance an intensity of the collected backward-scattered Raman light originating from the fluid sample, wherein the reflected forward-directed light includes either or both of forward- scattered Raman light generated from the fluid sample and residual Raman excitation light transmitted or elastically scattered by the fluid sample; and detecting the collected backward-scattered Raman light.52. The method of aspect 51, further including emitting the Raman excitation light.53. The method of aspect 52, wherein the step of emitting the Raman excitation light includes selecting an excitation wavelength of the Raman excitation light in a range from about 400 nm to about 1200 nm.54. The method of any one of aspects 51 to 53, wherein the steps of focusing the Raman excitation light and collecting backward-scattered Raman light are performed with an objective lens in direct contact with the fluid sample flowing along the sample flow channel.55. The method of aspect 54, wherein the objective lens has a focal length ranging from about 4.0 mm to about 5.0 mm, and a working distance ranging from about 3.0 mm to about 4.0 mm.56. The method of any one of aspects 51 to 55, wherein the step of reflecting the forward-directed light emerging from the fluid sample is performed with a concave mirror.57. The method aspect 56, wherein the concave mirror has a center of curvature positioned within the sample interrogation region.58. The method of any one of aspects 51 to 57, wherein the step of reflecting the forward-directed light occurs outside the flow cell, is preceded by a step of allowing the forward-directed light to exit the flow cell, and is followed by a step of allowing the forward-directed light reflected by the reflector to pass therethrough to re-enter the flow cell and reach the sample interrogation region.59. The method of any one of aspects 51 to 58, wherein the Raman excitation light is focused perpendicularly to a fluid flow direction of the fluid sample.60. The method of any one of aspects 51 to 59, further including analyzing the backward-scattered Raman light and deriving therefrom analyte information associated with the fluid sample.61. The method of aspect 60, wherein the analyte information associated with the fluid sample includes at least one of: (i) a concentration of one or more analytes in the fluid sample, (ii) a presence or absence of one or more analytes in the fluid sample, or (iii) chemical composition information about one or more analytes in the fluid sample.62. The method of any one of aspects 51 to 61, wherein the sample fluid is an aqueous sample.63. The method of any one of aspects 51 to 62, wherein the sample fluid is a lithium-containing brine.64. The method of any one of aspects 51 to 63, wherein the step of allowing the fluid sample to flow along the sample flow channel includes:drawing off the fluid sample from a fluid stream flowing within a conduit; and introducing the drawn-off fluid sample into the sample flow channel.65. The method of aspect 64, wherein the step of allowing the fluid sample to flow along the sample flow channel includes: discharging the fluid sample from the sample flow channel; and reintroducing the discharged fluid stream into the fluid stream.66. The method of any one of aspects 51 to 63, wherein the step of allowing the fluid sample to flow along the sample flow channel includes: drawing off the fluid sample from a fluid contained in a fluid reservoir; and introducing the drawn-off fluid sample into the sample flow channel.67. The method of aspect 66, wherein the step of allowing the fluid sample to flow along the sample flow channel includes: discharging the fluid sample from the sample flow channel; and reintroducing the discharged fluid stream into the fluid reservoir.68. The method of any one of aspects 51 to 67, wherein the Raman analysis is performed in concert with additional analytical methodology.69. The method of aspect 68, wherein the Raman analysis is performed (i) prior to a secondary analysis, (ii) after a secondary analysis, or (iii) concurrently with a secondary analysis.70. The method of aspect 69, wherein the Raman analysis and the secondary analysis are performed on the same fluid sample.71. The method of aspects 69 or 70, wherein the secondary analysis is performed using some or all of the spectrophotometric components of the Raman system.72. The method of aspect 68 or 69, wherein the Raman and the secondary analysis are performed on separate fluid samples.

[0009] Other method and process steps may be performed prior, during or after the steps described herein. The order of one or more steps may also differ, and some of the steps may be omitted, repeated, and / or combined, as the case may be. It is also to be noted that some steps may be performed using various analysisand processing techniques, which may be implemented in hardware, software, firmware, or any combination thereof.

[0010] Other objects, features, and advantages of the present disclosure will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given byway of example only with reference to the appended drawings. Although specific features described in the above summary and in the detailed description below may be described with respect to specific embodiments or aspects, it should be noted that these specific features may be combined with one another unless stated otherwise.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig. 1 is a schematic top view of a system for Raman analysis of a fluid sample, in accordance with an embodiment.

[0012] Fig. 2 is a schematic side view of the system of Fig. 1.

[0013] Fig. 3 is a schematic perspective view of a Raman flow cell device, in accordance with an embodiment.

[0014] Fig. 4 is a schematic top view of a system for Raman analysis of a fluid sample, in accordance with another embodiment.

[0015] Fig. 5 is a schematic side view of a system for Raman analysis of a fluid sample, in accordance with another embodiment.

[0016] Fig. 6 is a flow diagram of a method for Raman analysis of a fluid sample, in accordance with an embodiment.

[0017] Fig. 7 is a schematic representation of an example direct lithium extraction (DLE) operation in which the present techniques may be implemented, in accordance with an embodiment.

[0018] Fig. 8 shows four panels, each with a Raman spectrum obtained using a system, device, and method in accordance with an embodiment. The solutions analyzed comprised carbonate, sulfate, borate, or boric acid as indicated in the individual panels.

[0019] Fig. 9 shows Raman spectral overlays obtained using a system, device, and method in accordance with an embodiment to analyze borate and boric acid species in solution under various pH conditions.

[0020] Fig. 10 shows a Raman spectrum obtained using a system, device, and method in accordance with an embodiment to analyze a brine solution containing lithium.

[0021] Fig. 11 shows an overlaid pair of Raman spectra obtained using a system, device, and method in accordance with an embodiment to analyze a solution with and without use of the reflector.

[0022] Fig. 12 shows four panels, each with an overlay of Raman spectra obtained using a system, device, and method in accordance with an embodiment. The solutions analyzed comprised carbonate, sulfate, borate, or boric acid as indicated in the individual panels, and the overlays depict various analyte concentrations as indicated in the individual panels.DETAILED DESCRIPTION

[0023] The present disclosure generally relates to Raman spectroscopy techniques, which include systems, devices, and methods, for characterization and analysis of fluid samples. The disclosed techniques can find use in various applications, notably in field-deployed environments where a fluid sample of interest is drawn off a fluid reservoir or diverted from a process flow stream.

[0024] The embodiments disclosed herein generally include or use a flow cell, an objective lens (e.g., a dipping objective lens), and a reflector (e.g., a concave mirror). The flow cell defines a sample flow channel along which a fluid sample is circulated. The objective lens is configured to focus Raman excitation light into a sample interrogation region that crosses the sample flow channel to irradiate the fluid sample and generate Raman scattering. The objective lens is also configured to collect backward-scattered Raman light emerging from the fluid sample. In some embodiments, the objective lens is mounted into the flow cell so as to be in direct contact with the stream of fluid sample. Such a configuration can allow Raman spectroscopy measurements to be performed without having to perform focus adjustment operations. This can lead to shorter acquisition times, which is often desirable in real-time or continuous monitoring of online / inline processes and operations.

[0025] The reflector is positioned opposite from the objective lens across the sample flow channel. The reflector is configured to reflect forward-directed light emerging from the fluid sample back toward the sample interrogation region. The reflected forward-directed light can include forward-scattered Raman light generated from the fluid sample and / or residual Raman excitation light transmitted or elastically scattered by the fluid sample. In embodiments where the reflector is located outside the flow cell, the flow cell can include an optical window (e.g., made of sapphire) configured to allow at least part of the forward-directed light to exit the flow cell and reach the reflector. The reflector can enhance the intensity of the backward- scattered Raman light that is collected by the objective lens and ultimately detected, which in turn can improve detection and quantitation limits of low-concentration analytes.

[0026] The present techniques can find use in various fields of applications and industries that use or may benefit from Raman spectroscopy for characterization and monitoring of fluid samples. Non-limiting examples of possible fields of use include mining extraction and processing; petrochemical; environmental; industrial process control (e.g., bioprocessing, polymer synthesis, food and beverage processing); hazardous waste monitoring; soil remediation; medical; pharmaceutical; forensic; and toxicology. One more specific example is the field of lithium mining from brines, in particular for Raman analysis of brine streams produced or otherwise used at different stages of direct lithium extraction (DLE) operations. For example, real-time quantitative analysis of the analyte species can help in understanding mass balance and chemical equilibria conditions, and therefore achieve more effective and prompt control over chemical extraction processes. The present techniques can be implemented in various environments and settings, including on-site and field- deployed operations (e.g., in mining and other industrial applications), manufacturing facilities, research and development laboratories, and the like. Depending on the application, the present techniques can be used with portable or fixed test instruments.

[0027] The present techniques can be used to perform measurements in various field-deployed industrial or manufacturing settings. In some embodiments, Raman measurements can be carried out on a sample drawn off a fluid reservoir or diverted from a process flow stream. Such measurements can be fully automated and carried out without the need for human intervention or sample removal from the process, in contrast to offline analysis (e.g., in a laboratory setting). The present techniques may also allow for real-time or continuous process analysis, monitoring, and control. The term "real-time" is used herein as a practical term to refer to measurements that can be conducted without significant time delay.

[0028] The term "fluid sample" refers herein to any substance or medium having the ability to flow that can be characterized by Raman spectroscopy. The term "fluid" is meant to encompass substances and media of various viscosities, and it may in some instances be used interchangeably with the term "liquid". Fluid samples may be broadly classified as organic, inorganic, or biological. Depending on the circumstances, a fluid sample can refer to a pure substance (e.g., water), a homogeneous solution (e.g., brine) containing one or more solutes dissolved in a solvent, a heterogeneous mixture (e.g., suspension, dispersion, emulsion, slurry, colloid), a cream, a gel, a paste, or the like. Solutions can be aqueous or non-aqueous, and they can use any suitable type of organic or inorganic solvents, including polar protic, polar aprotic, and non-polar solvents. More specific examples of possible solvents include hexane, heptane, chloroform, dichloromethane, methanol, ethanol, isopropanol. As those skilled in the art will appreciate, non-aqueous applications will have signal-to-noise losses due to the inherent Raman activity of the solvent. In some embodiments, consideration should be given to the lens material to ensure proper compatibility with the selected solvent. Fluid samplescan contain one or more analytes of interest. The term "analyte" is intended to refer herein to any intended constituents or unintended constituents (e.g., impurities or contaminants) present in a fluid sample that can be probed by Raman spectroscopy. In some instances, terms such as "component", "compound", and "species" may be used interchangeably with the term "analyte". Non-limiting examples of analytes present in brines used in DLE processes include boric acid, sulfuric acid, carbonic acid, borates, sulfates, bi-sulfates, carbonates, and bi-carbonates. It is appreciated that various other types of Raman-active, soluble species may be contemplated in other applications. For example, pharmaceutical synthetic routes employing the use of Suzuki coupling reactions, or similar methodologies wherein a process intermediate may include a borate or boric acid, which may be detected in situ, in process streams, in the final product, or any combination thereof. For example, hydroponic may perform analysis of the prepared solutions to analyze nutrient content (e.g., nitrates, nitrites, phosphates, phosphites, and sulfates) prior to application within the hydroponic system, and / or in waste collection streams.

[0029] In the present techniques, Raman spectroscopy can be used to provide various types of quantitative and qualitative information about the structure and chemical composition of a fluid sample. Non-limiting examples of information that can be obtained from Raman spectra include information about the identification, quantitation (e.g., relative and absolute concentration), and structure of chemical species in a sample; information about chemical bonds and molecular structure and interactions; information about the impact of external parameters (e.g., temperature, pH, ionic strength) on sample properties (e.g., as a function of time); or any information that can affect species-specific vibrational states and modes. It is appreciated that the basic principles underlying Raman spectroscopy, including the theory of Raman scattering and the measurement and analysis of Raman spectra, are generally known in the art and need not be described in detail herein other than to facilitate an understanding of the present techniques.

[0030] Various aspects and implementations of the present techniques are described below with reference to the figures.

[0031] Referring to Figs. 1 and 2, there are illustrated schematic views of an embodiment of a system 100 for Raman analysis of a fluid sample 102. As noted above, the fluid sample 102 may include any fluid substance or medium known or expected to contain analytes that may be characterized or monitored using Raman spectroscopy. For example, in DLE applications, the fluid sample 102 may be a lithium-containing brine stream, a substantially purified lithium process stream, a lithium-depleted impurity stream, a process water recovery stream, or a lithium carbonate product stream.

[0032] Depending on the circumstances or requirements of a given application, the Raman system 100 can be deployed in various configurations for many purposes and applications relating to fluid sample analysis and monitoring of ongoing processes, conditions, and operations. For example, the Raman system 100 may be provided along a flow bypass or diversion structure connected to a process flow line (e.g., a flow-through pipe or conduit) through which a stream of the fluid sample 102 is flowing. In other embodiments, the Raman system 100 may be connected (e.g., along a sample circulation loop or extraction line) to a reservoir (e.g., a reactor or storage vessel) containing the fluid sample 102.

[0033] The Raman system 100 generally includes a flow cell 104, an excitation light source 106, an objective lens 108, a reflector 110, and an optical spectrometer 112. The flow cell 104 includes a sample inlet 114, a sample outlet 116, and a flow cell body 118. The flow cell body 118 defines a sample flow channel 120 therein configured to allow the fluid sample 102 to flow from the sample inlet 114 to the sample outlet 116. The flow cell 104 may be configured for continuous flow or intermittent flow. For example, the flow cell 104 may be configured to allow flow through the sample flow channel 120 to be started and stopped (at any cadence), and the Raman measurement may be taken while flow is stopped or occurring at any rate. The excitation light source 106 is configured to emit Raman excitation light 122 at an excitation wavelength along an excitation light path 124 leading to objective lens 108. The objective lens 108 is configured to focus the Raman excitation light 122 into a sample interrogation region 126 that intersects the sample flow channel 120 for irradiating the fluid sample 102. The objective lens 108 is also configured to collect backward-scattered Raman light 128 emerging from the fluid sample 102 upon irradiation by the Raman excitation light 122. The reflector 110 is positioned opposite from the objective lens 108 across the sample flow channel 120. The reflector 110 is configured to reflect forward-directed light 130 emerging from the fluid sample 102 back toward the sample interrogation region 126 to enhance an intensity of the backward-scattered Raman light 128 generated by the fluid sample 102 and collected by the objective lens 108. Depending on the circumstances, the forward- directed light 130 reflected into the fluid sample 102 can include either or both of forward-scattered Raman light 132 generated from the fluid sample 102 and residual Raman excitation light 134 transmitted or elastically scattered by the fluid sample 102. The backward-scattered Raman light 128 collected by the objective lens 108 is directed along a detection light path 136 leading to the optical spectrometer 112. The optical spectrometer 112 is configured to detect the backward-scattered Raman light 128 collected by the objective lens 108 and generate therefrom Raman detection signals. It is noted that the figures generally depict light at the excitation wavelength with solid lines and Raman scattered light with dashed lines.

[0034] In some embodiments, various components of the Raman system 100, including at least the flow cell 104, the excitation light source 106, the objective lens 108, the reflector 110, and the opticalspectrometer 112, may be packaged together in a substantially self-contained housing or container. In some embodiments, the Raman system 100 may be sold in such a packaged configuration. The packaging of the Raman system 100 can help prevent foreign matter such as rain, moisture, dust, dirt, debris, and the like, from reaching the system components during field deployments or on-site uses, for example, in industrial or environmental monitoring applications, particularly in open-air conditions. Packaging can also reduce the risks of damaging or causing optical misalignment among the system components as a result of accidental shock or inadvertent mishandling, and may also provide safety measures for nominal operation of laser equipment.

[0035] Referring briefly to Fig. 3, in some embodiments, the flow cell 104, the objective lens 108, and the reflector 110 can define a Raman flow cell device 138 configured for use in the Raman system 100 along with the excitation light source 106 and the optical spectrometer 112. In some embodiments, the Raman flow cell device 138 may be manufactured and sold as a single unit for use with the excitation light source 106 and the optical spectrometer 112 to form the Raman system 100.

[0036] The structure, configuration, and operation of these components and other possible components of, or coupled to, the Raman system 100 are described in greater detail below. It is appreciated that Figs. 1 and 2, and likewise for other figures described below, are meant to provide schematic representations that aim to illustrate a number of components and features of the Raman system 100, such that additional components and features that may be useful or necessary for practical operation may not be specifically depicted. Non-limiting examples of such additional features and components can include, to name a few, power supplies, electrical connections, optical links and connections (e.g., optical fibers, optical waveguides, free-space optics), optical components (e.g., lenses, mirrors, filters), fluid supply lines (e.g., conduits, such as pipes ortubes), pressure and flow control devices (e.g., pumps, valves, regulators, restrictors), processors and controllers, and other types of hardware and equipment.

[0037] The flow cell 104 can be embodied by any appropriate fluidic device capable of allowing the fluid sample 102 to flow therethrough along a flow path that crosses the focal spot volume of the objective lens 108 for irradiation of the fluid sample 102 by the Raman excitation light 122. The flow cell body 118 may be made of various materials including, but not limited to, polyetheretherketone (PEEK), polyoxymethylene (POM), polytetrafluoroethylene (PTFE, commonly known by its trade name, Teflon®). In some embodiments, the material may be selected primarily for chemical resistance properties, for the solvent, analyte, pH range, and temperature range of the operation. The flow cell body 118 encloses an interior volume that defines the sample flow channel 120. The sample flow channel 120 extends lengthwise along a fluid flow direction 140 along which the fluid sample 102 is allowed to flow. The region of the sample flow channel 120 intersectedby the focal volume of the objective lens defines the sample interrogation region 126. In the illustrated embodiment, the sample inlet 114 is located at a first end of the flow cell body 118, and the sample outlet 116 is located at a second end of the flow cell body 118 that is opposite to the first end along the fluid flow direction 140. In some embodiments, the sample flow channel 120 may have a length ranging from about 5 mm to about 10 mm, and a cross-sectional area ranging from about 40 mm2to about 100 mm2. However, the shape, size, and configuration of the sample flow channel 120 may be varied depending on the circumstances or requirements of a given application. In some embodiments, the length of the sample flow channel 120 may be selected based on the size of the focal spot volume provided by the objective lens 108.

[0038] The sample inlet and outlet 114, 116 may each be provided as an orifice or conduit defined in a wall of the flow cell body 118. The sample inlet and outlet 114, 116 may each be of any suitable size, shape, and configuration, which may be selected based on desired or required characteristics of the sample flow stream.

[0039] The sample inlet 114 may be in fluidic communication with a sample supply source 142 via a suitable inlet supply line 144. The inlet supply line 144 may be, or be part of, a flow diversion line configured to extract or draw out a portion of the fluid sample stream from the sample supply source 142 and into the sample flow channel 120 via the sample inlet 114. In some embodiments, the sample supply source 142 may be a process line (e.g., a conduit, such as a pipe or tube) through which the fluid sample 102 is flowing as part of an ongoing process or operation. For example, the ongoing process or operation may be implemented in mining or other industrial or field-deployed applications. In other embodiments, the sample supply source 142 may be a reservoir in which the fluid sample 102 is contained (e.g., for storage, treatment, or processing), also possibly as part of an ongoing process or operation.

[0040] In some embodiments, the fluid sample 102 may be conveyed a single time through the flow cell 104. Such embodiments can be referred to as single-pass or open-circuit implementations. In some of these implementations, the sample outlet 116 may be in fluidic communication with the sample supply source 142, via a suitable outlet supply line 146, as in the embodiment of Figs. 1 and 2. In such implementations, the Raman system 100 may be configured to return the fluid sample 102 back to the sample supply source 142 after passage of the fluid sample 102 through the flow cell 104 for Raman analysis. In other implementations, the suitable outlet supply line 146 may be in fluidic communication not with the sample supply source 142 but rather with a sample collector for further processing (e.g., treatment, reuse, recycling, discharge, or disposal). In yet other embodiments, the same stream of fluid sample 102 may be conveyed multiple times through the flow cell 104. Such embodiments can be referred to as multiple-pass or closed-circuit implementations. In such implementations, the fluid sample 102 exiting the flow cell 104 from the sampleoutlet 116 may be returned to the sample inlet 114 via a sample recirculation line to re-enter the flow cell 104 and go through another Raman acquisition cycle.

[0041] Referring still to Figs. 1 and 2, the Raman system 100 may further include a pump assembly 148 in fluidic communication with the flow cell 104 and configured to control a flow of the fluid sample 102 along the sample flow channel 120. The pump assembly 148 may include one or more pumps connected at the sample inlet 114 and / or the sample outlet 116. The one or more pumps may be any suitable type, such as peristaltic pumps, diaphragm pumps, syringe pumps, or piston pumps. The pump assembly 148 is configured to operate at a flow rate appropriate for conducting Raman spectroscopy measurements on the fluid sample 102 as the fluid sample 102 is passed through the flow cell 104. In some embodiments, the flow rate of the fluid sample 102 along the sample flow channel 120 may range from about 2 mL / min to about 10 mL / min. The flow rate may be selected based on various factors, for example the intensity of the Raman excitation light 122 or the concentration of analytes of interest present in the fluid sample 102.

[0042] The excitation light source 106 can be embodied by any appropriate device or combination of devices capable of generating the Raman excitation light 122 with beam characteristics suitable for use in Raman spectroscopy. In some embodiments, the excitation light source 106 is a laser source configured to emit Raman excitation light 122 as a laser beam with a sufficiently high intensity and a sufficiently narrow optical bandwidth (e.g., nearly monochromatic). Non-limiting examples of laser sources that can be used in Raman spectroscopy include solid-state lasers, including bulk crystal lasers and fiber lasers; semiconductor lasers, including laser diodes; gas lasers, including ion lasers; and dye lasers. Non-laser light sources, such as lightemitting diodes (LEDs), may also be used in some embodiments. Depending on the circumstances or requirements of a given application, the excitation light source 106 may be operated in a continuous-wave or pulsed regime. In some embodiments, the excitation light source 106 may be configured to emit the Raman excitation light 122 in the visible, ultraviolet, or near-infrared range of the electromagnetic spectrum. For example, in some embodiments, the Raman excitation light 122 may have an excitation wavelength lying within a waveband ranging from about 200 nm to about 2500 nm, and more particularly, from about 400 nm to about 1200 nm. Non-limiting examples of excitation wavelengths commonly used in Raman spectroscopy include 244 nm, 266 nm, 320 nm, 355 nm (ultraviolet); 405 nm, 458 nm, 473 nm, 515 nm, 532 nm, 594 nm, 633 nm, 660 nm, 671 nm (visible); and 785 nm, 830 nm, 980 nm, 1064 nm (near infrared).

[0043] The excitation light source 106 may be selected based on various factors. Non-limiting examples of such factors include, to name a few, the excitation wavelength; the spectral linewidth and purity; the frequency stability; the beam quality; the output power and power stability; the compactness, reliably, ruggedness, and cost; and, for pulsed light sources, pulse characteristics such as the peak power, repetitionrate, duration, and temporal shape. In particular, the choice of the excitation wavelength can be made based on factors such as the Raman scattering intensity, the detection sensitivity, the spatial resolution, and the fluorescence suppression. It is appreciated that the theory, instrumentation, and operation of excitation light sources commonly used in Raman spectroscopy applications are generally known in the art and need not be described in detail herein other than to facilitate an understanding of the present techniques.

[0044] The term "objective lens" is used herein to refer to a single lens or a compound lens (i.e., a collection of single lenses arranged along a common axis). The objective lens 108 has an objective axis 150 and a focal point 152. In some embodiments, the objective lens 108 may have the following parameters: a magnification ranging from about 10X to 100X, particularly from about 20Xto about 60X; a numerical aperture ranging from about 0.2 to about 1.2, particularly from about 0.6 to about 1.0; a focal length ranging from about 3.0 mm to about 7.0 mm particularly from about 4.0 mm to about 5.0 mm; and a working distance ranging from about 2.0 mm to about 6.0 mm, particularly from about 3.0 mm to about 4.0 mm. In the illustrated embodiment, the objective axis 150 is perpendicular to the fluid flow direction 140 and the focal point 152 is located along the center axis of the sample flow channel 120, but neither condition is a requirement. The sample interrogation region 126 encompasses a region around the focal point 152 whose size is defined by the focal spot volume of the Raman excitation light 112 produced by the objective lens 108.

[0045] In the illustrated embodiment, the objective lens 108 is a dipping objective lens configured to provide a portion of a boundary of the sample flow channel 120. In this configuration, the tip of the objective lens 108 is in direct contact with the fluid sample 102 flowing through the sample flow channel 120 during operation of the system 100. In the illustrated embodiment, the objective lens 108 is mounted in a leak-proof manner into an opening formed in the flow cell body 118, but other arrangements are possible in other embodiments. Positioning the tip of the objective lens 108 in contact with the fluid sample 102 may provide various advantages, such as improved numerical aperture and resolution; reduced refractive-index-mismatch- induced spherical aberrations; possibility of quantitative Raman measurements without internal standards; and shorter Raman measurement times by not requiring focus adjustment due to the fact that at least part of the analytes in the fluid sample 102 will always be in focus. In contrast, implementations in which the objective lens 108 is not in contact with the fluid sample 102 may be associated with an increased likelihood of having to perform focus adjustments between measurements due to lens-positioning variations.

[0046] Referring to Fig. 4, there is illustrated another embodiment of a system 100 for Raman analysis of a fluid sample 102. The embodiment of Fig. 4 shares many features with the embodiment of Figs. 1 and 2, which need not be described again, but differs in that the objective lens 108 is not in direct contact with the sample fluid 102 during operation of the system 100. In this embodiment, the flow cell 104 may include an objective-viewing window 154 facing the objective lens 108 to provide an optical interface between the objective lens 108 and the sample interrogation region 126. For example, the objective-viewing window 154 may be mounted in a leak-proof manner into an opening formed in a wall of the flow cell body 118. In such embodiments, the objective lens 108 may be a fluid-immersion objective lens (e.g., a water-immersion objective lens or an oil-immersion objective lens) or an air objective lens.

[0047] Returning to Figs. 1 and 2, in operation of the Raman system 100 the objective lens 108 is configured to receive the Raman excitation light 122 from the excitation light source 106 and focus the Raman excitation light 122 to the sample interrogation region 126 to irradiate the fluid sample 102 flowing along the sample flow channel 120. In general, most of the Raman excitation light 122 interacting with the fluid sample 102 passes through unscattered or is elastically scattered (i.e., Rayleigh scattered), and thus remains at the same wavelength as the excitation wavelength. A small fraction of the Raman excitation light 122 is inelastically scattered (i.e., Raman scattered) by interaction with vibrating chemical bonds in the fluid sample 102, with wavelengths different from the excitation wavelength. These wavelength differences are referred to as Raman shifts and are typically expressed in wavenumber units. Raman shifts are species-specific and can be used as fingerprints for deriving structure and chemical composition of a fluid sample 102. Depending on whether the Raman scattered wavelength is longer or shorter than the excitation wavelength, the Raman scattering will be referred to as Stokes or anti-Stokes Raman scattering. Since Stokes Raman scattering is generally much stronger than anti-Stokes Raman scattering, it is more commonly used in Raman spectroscopy. However, the present techniques can be implemented using both Stokes and anti-Stokes Raman scattering.

[0048] Since both Rayleigh scattering and Raman scattering occur in all directions, Raman spectroscopy measurements can be made from any position relative to the sample depending on the circumstances or requirements of a given application. In the present disclosure, terms such as "forward-scattered" and "forward-directed" refer to light scattered or directed along a direction oriented at an acute angle (i.e., an angle whose magnitude is less than 90°) to the incident direction of the Raman excitation light 122, whereas terms such as "backward-scattered" and "backward-directed" refer to light scattered or directed along a direction oriented at an obtuse angle (i.e., an angle whose magnitude lies 90° and 180°) to the incident direction of the Raman excitation light 122.

[0049] The objective lens 108 is configured to collect backward-scattered Raman light 128 generated in the fluid sample 102. Due to the low probability of occurrence of Raman scattering compared to Rayleigh scattering, the backward-scattered Raman intensities in conventional Raman spectroscopy tend to be relatively weak, despite the use of high-power light sources and high-throughput detectors. This is often thecase for fluid samples, particularly those with low analyte concentrations. The Raman signal-to-noise ratio can be enhanced by increasing the amount of Raman scattered light reaching the detector.

[0050] In the present techniques, the signal-to-noise ratio of measured Raman signals can be increased by providing a reflector 110 facing the objective lens 108 from across the sample flow channel 120. The reflector 110 is configured to reflect forward-directed light 130 emerging from the fluid sample 102 back toward the sample interrogation region 126. The forward-directed light 130 can include (i) forward-scattered Raman light 132 generated in the fluid sample 102 during the first pass of the Raman excitation light 122, and (ii) residual Raman excitation light 134 having passed through the fluid sample 102 without scattering or elastically scattered. The wavelength of the forward-scattered Raman light 132 and the wavelength of the residual Raman excitation light 134 are respectively different from and equal to the excitation wavelength.

[0051] As the reflected forward-directed light 130 propagates backward into the fluid sample 102, both its contributions can act to increase the intensity of the backward-scattered Raman light 128 generated within the fluid sample 102 that can be collected by the objective lens and ultimately detected by the optical spectrometer 112. Depending on the circumstances or requirements of a given application, the reflected forward-directed light 130 can include only reflected forward-scattered Raman light 132, only reflected residual Raman excitation light 134, or both reflected forward-scattered Raman light 132 and reflected residual Raman excitation light 134 (as in Fig. 2). The spectral content of the reflected forward-directed light 130 can be controlled in different ways, for example, by interposing a suitable spectral filter between the sample interrogation region 126 and the reflector 110, or by providing the reflector 110 with suitable dichroic properties. In this manner, either one, but not both, of the forward-scattered Raman light 132 and the residual Raman excitation light 134 can reach, or be reflected by, the reflector 110 to return into the fluid sample 220.

[0052] In the illustrated embodiment, the reflector 110 is embodied by a concave mirror, which can be either spherical or non-spherical. Various types of concave mirrors having a suitably high reflectance in the spectral range of the forward-directed light 130 exist and can be used in the disclosed embodiments, including metal- coated (e.g., silver coated, aluminum-coated or gold-coated) mirrors, dielectric-coated mirrors, and crystal coated mirrors. The reflector 110 may be suitably sized, shaped, and positioned to ensure that most or at least significant amount of the reflected forward-directed light 130 is directed within sample interrogation region 126 and toward the focal point of the objective lens 108. In the illustrated embodiment, this can be achieved by providing the reflector 110 as a concave mirror whose center of curvature coincides with the focal point of the objective lens 108. In other embodiments, the reflector 110 may be embodied by another type of reflecting element, for example, a plane mirror or a retroreflector (e.g., a corner cube).

[0053] In the illustrated embodiment, the reflector 110 is located outside the flow cell 104. The flow cell 104 includes a reflector-viewing window 156 configured to allow at least part of the forward-directed light 130 incident thereon to pass therethrough to exit the flow cell 104 and reach the reflector 110. The reflectorviewing window 156 is also configured to allow at least part of the forward-directed light 130 reflected by the reflector 110 to pass therethrough to re-enter the flow cell 104 and reach the sample interrogation region 126. In the illustrated embodiment, the reflector-viewing window 156 is mounted in a leak-proof manner into an opening formed in the flow cell body 118 and facing the objective lens 108 from across the sample flow from channel 120. Other arrangements for the reflector-viewing window 156 are possible in other embodiments.

[0054] Various types of optical windows having a suitably high transmittance in the spectral range of the forward-directed light 130 exist and can be used in the disclosed embodiments. In particular, various window materials and thicknesses can be used. In some embodiments, the reflector-viewing window 156 may be composed of sapphire (a-AI2O3) and have thickness ranging from about 1 mm to about 5 mm. Possible advantages of using sapphire as a window include its substantial chemical resistance, wide transmittance spectrum extending from the ultraviolet to the mid-infrared, high mechanical strength, and high thermal stability. Other examples of possible window materials include, to name a few, fused silica, borosilicate crown glass (N-BK7), calcium fluoride, magnesium fluoride, and potassium bromide. As those skilled in the art will appreciate, chemical resistance of the selected window material can be appropriately matched with the operating conditions (e.g., resistance to solvent, pH, temperature) for the intended application. The dimensions of the reflector-viewing window 156 can be selected in accordance with various factors, such as its spacing from the focal point of the objective lens 108, its spacing from the reflector 110, the size of the reflector 110, and the numerical aperture of the objective lens 108.

[0055] In some embodiments, the reflector-viewing window 156 may operate as a spectral filter (e.g., a long- pass or short-pass edge filter) configured control the spectral content of the reflected forward-directed light 130 by transmitting one of the forward-scattered Raman light 132 and the residual Raman excitation light 134 and absorbing the other. In other embodiments, a spectral filter may be positioned outside the flow cell 104, between the reflector-viewing window 146 and the reflector 130, to achieve further control over the spectral content of the reflected forward-directed light 130. Providing a spectral filter outside the outside the flow cell 104 may be required or desirable in some applications, as spectral filters often include sensitive or delicate components that could be damaged or otherwise negatively affected by direct contact with the fluid sample 102.

[0056] In some embodiments, providing the reflector 110 outside the flow cell 104 can be advantageous in that it can allow for the use of concave mirrors with a greater range of radii of curvature while keeping the center of curvature within the sample interrogation region 126 (e.g., at or near the focal point of the objective lens 108). Another possible advantage of having the reflector 110 outside the flow cell 104 is the ease of removing the reflector from the system 100 (e.g., for cleaning, replacement, or any other maintenance operation) and adjusting its position with respect to the objective lens 108 (e.g., its spacing from the objective lens 108 along a direction parallel to the objective axis 150). For this purpose, the Raman system 100 in Figs. 1 and 2 includes a movable reflector mount 158 configured to hold and move the reflector 110 relative to the objective lens 108. In the illustrated embodiment, the movable reflector mount 158 allows the reflector 110 to be moved closer to or farther from the objective lens 108 along a direction parallel to the objective axis 150. Other position or orientation adjustment capabilities are possible in other embodiments. Yet another possible advantage of providing the reflector 110 outside the flow cell 104 is to avoid direct contact with the fluid sample 102 during operation of the system 100. This is because certain reflector materials (e.g., silica-based) have low chemical resistance and may suffer from reduced reflection performance over time as result of direct contact with the fluid sample 102 (e.g., following corrosion or pitting).

[0057] Referring to Fig. 5, there are illustrated schematic views of another embodiment of a system 100 for Raman analysis of a fluid sample 102. The embodiment of Fig. 5 share many features with the embodiment of Figs. 1 and 2, which need not be described again, but differs in that the reflector 110 (embodied as a concave mirror) is configured to provide a portion of a boundary of the sample flow channel 120 and is therefore in direct contact with the sample fluid 102 during operation of the system 100. More specifically, the reflector 110 is mounted in a leak-proof manner into an opening formed in the flow cell body 118 and facing the objective lens 108 from across the sample flow channel 120. In some embodiments, the reflector 110 may be mounted in a movable manner within the opening to allow its position relative to the objective lens to be varied.

[0058] Returning to Figs. 1 and 2, the Raman system 100 includes relay optics 160 arranged along the excitation light path 124 and the detection light path 136. The relay optics 160 are configured to: (i) relay the Raman excitation light 122 from the excitation light source 106 to the objective lens 108, and (ii) relay the collected backward-scattered Raman light 128 from the objective lens 108 to the optical spectrometer 112. The relay optics 160 can include any number of optical components configured to direct, shape, filter, split, focus, collimate, expand, or otherwise condition or act on the Raman excitation light 122 and the collected backward-scattered Raman light 128. Non-limiting examples of optical components that can be used as part of the relay optics 160 include lenses, reflectors, spectral filters, beamsplitters, prisms, diffraction gratings,and optical fibers and waveguides. In the illustrated embodiment, the relay optics 160 include two mirrors 162i, 1622disposed along the excitation light path 124; a long-pass-short-reflect dichroic mirror 164 disposed where the excitation light path 124 and the detection light path 136 meet; and a long-pass Raman filter 166, a Raman focusing lens 168 and an optical fiber 170 disposed along the detection light path 136 downstream of the dichroic mirror 164. The long-pass Raman filter 166 is configured to remove or at least further attenuate any residual excitation Raman light 122 having passed through the long-pass-short-reflect dichroic mirror 164.

[0059] In operation, the Raman excitation light 122 is reflected successively by the first mirror 162i, the second mirror 1622, and the dichroic mirror 164, from which it emerges along a direction parallel to the objective axis 150 to reach the objective lens 108. The backward-scattered Raman light 128 collected by the objective lens 108 passes successively through the dichroic mirror 164 and the long-pass Raman filter 166, is focused by the Raman focusing lens 168, and enters the optical fiber 170 to be delivered to the optical spectrometer 112. It is noted that the relay optics depicted in Figs. 1 and 2 are for purposes of illustration only, and that various other configurations, including more, fewer, or different optical components, are contemplated. For example, in some embodiments, an optical fiber may be coupled between the excitation light source 106 and the first mirror 162i.

[0060] The Raman system 100 includes an optical cage assembly 172 (not depicted in Fig. 1 for clarity) configured to mount multiple system components (i.e., caged components) in a rigid, stable, and compact structure. The optical cage assembly 172 includes four rods 174 configured for insertion in apertures formed in cage mounts 158 into which the caged components are inserted in series along a common axis. It is noted that one of the cage mounts 158 is the movable reflector mount mentioned above. In the illustrated embodiment, the common axis parallel to the objective axis 150, and the caged components include the flow cell 104, the objective lens 108, the reflector 110, the dichroic mirror 164, the long-pass Raman filter 166, and the Raman focusing lens 168. It is noted that the optical cage assembly 172 depicted in Figs. 1 and 2 is for purposes of illustration only, and that other embodiments can include different optical cage assemblies or none at all.

[0061] In the illustrated embodiment, the optical spectrometer 112 receives the collected backward- scattered Raman light 128 via the optical fiber 170. Other embodiments may not use fiber optics, in which case the collected backward-scattered Raman light 128 may be delivered to the optical spectrometer 112 via free-space optics. The optical spectrometer 112 can be embodied by any optical detector or combination of optical detectors capable of measuring a spectrally dependent response of an optical signal over a specified spectral range. There are two main categories of optical spectrometers used in Raman spectroscopy,dispersive and non-dispersive, which differ in how they analyze Raman scattered light. In dispersive spectrometers, the Raman scattered light is spatially split and dispersed into its constituent spectral components by a wavelength selector (e.g., a prism or diffraction grating) before reaching a photodetector array (e.g., a charge-coupled device (CCD) detector). In non-dispersive spectrometers, the Raman scattered light passes through an interferometer to produce an interferogram, which is then Fourier-transformed into a Raman spectrum. Both types of Raman spectrometers can be used in the present techniques. In some embodiments, the optical spectrometer 112 may be configured to operate within a Raman shift wavenumber range extending from about 200 cm-1to about 2000 cm-1, with a resolution ranging from about 2 cm-1to about 20 cm-1, although values outside these ranges are possible in other embodiments. It is appreciated that the theory, instrumentation, and operation of optical spectrometers commonly used in Raman spectroscopy applications are generally known in the art and need not be described in detail herein other than to facilitate an understanding of the present techniques.

[0062] Referring still to Figs. 1 and 2, the Raman system 100 may further include a computer device 176. The computer device 176 is configured to control, monitor, and / or coordinate the functions and operations of various components of the Raman system 100, for example, the excitation light source 106 and the optical spectrometer 112. The computer device 176 may also be configured to analyze the Raman detection signals generated by the optical spectrometer 112 to derive therefrom analyte information about the structure or chemical composition of the fluid sample 102. In some embodiments, the analyte information can include at least one of an amount or concentration of one or more analytes present in the fluid sample, a presence or absence of one or more analytes in the fluid sample, or chemical composition information about the one or more analytes in the fluid sample. In some embodiments, the computer device 176 can process the Raman detection signals into a Raman spectrum, which is a plot of Raman scattering intensity versus Raman shift. The wavenumber of the Raman shift represents the change in photon energy from the energy of the Raman excitation light 122. A Raman spectrum contains a number of peaks or bands (a subset of partly overlapping peaks). Each peak represents a specific vibrational mode of a chemical bond present in the fluid sample 102. The position of each peak can be used for chemical species identification, while the peak intensity can be related to the corresponding chemical species concentration. Other peak parameters, such as the peak linewidth and shape, can also be considered in Raman spectrum analysis. Chemical species identification can be carried out by matching measured spectral signatures with reference spectral signatures stored in a Raman spectrum library or previously obtained experimentally. It is appreciated that the principles underlying Raman spectrum analysis to derive analyte information about a sample under test are generally known in the art and need not be described in detail herein other than to facilitate an understanding of the present techniques.

[0063] The computer device 176 can be implemented in hardware, software, firmware, or any combination thereof, and be connected to various components of the Raman system 100 via wired and / or wireless communication links to send and / or receive various types of signals, such as timing signals, control signals, measurement signals, and data signals. The computer device 176 may be controlled by direct user input and / or by programmed instructions, and may include an operating system for controlling and managing various functions of the Raman system 100. Depending on the application, the computer device 176 may be fully or partly integrated with, or physically separate from, the other hardware components of the system 100. For example, in some embodiments the functions of the computer device 176 relating to the analysis of Raman spectra data may be fully or partly integrated into the optical spectrometer 112. The computer device 176 may also be configured to analyze the Raman detection signals generated by the optical spectrometer 112 to derive therefrom information about the structure or chemical composition of the fluid sample 102. In some embodiments, the computer device 176 may include a distributed and / or cloud computing network. In Figs. 1 and 2, the computer device 176 generally includes a processor 178 and a memory 180.

[0064] The processor 178 may be able to execute computer programs, also generally known as commands, instructions, functions, processes, software codes, executables, applications, and the like. While the processor 178 is depicted in Fig. 1 as a single entity for illustrative purposes, the term "processor" should not be construed as being limited to a single processor, and accordingly, any known processor architecture may be used. In some implementations, the processor 178 may include a plurality of processing units. Such processing units may be physically located within the same device, or the processor 178 may represent processing functionality of a plurality of devices operating in coordination. For example, the processor 178 may include or be part of a computer; a microprocessor; a microcontroller; a coprocessor; a central processing unit (CPU); a special-purpose programmable logic device, such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC); and / or any other devices configured to electronically process information and to operate collectively as a processor.

[0065] The memory 180 is a non-transitory and tangible computer product capable of storing computer programs, executable instructions, and other data to be retrieved by the processor 178 for the implementation of various steps of the techniques disclosed herein. The memory 180 may be any computer data storage device or assembly of such devices, including a random-access memory (RAM); a dynamic RAM; a read-only memory (ROM); a magnetic storage device; an optical storage device; a flash drive memory; and / or any other non-transitory memory technologies. The memory 180 may be coupled to, or included in, the processor 178. While the memory 180 is depicted in Fig. 1 as a single entity for illustrative purposes, theterm "memory" should not be construed as being limited to a single memory unit, and accordingly, any known memory architecture may be used. In some embodiments, the memory 180 may include a plurality of memory units. Such memory units may be physically located within the same device, or the memory 180 can represent the functionalities of a plurality of devices operating in coordination.

[0066] Referring to Fig. 6, there is illustrated a flow diagram of a method 600 of performing Raman analysis of a fluid sample. The fluid sample can be any suitable sample that can be analyzed by Raman spectroscopy, for example, an aqueous sample such as lithium-containing brine. The method 600 of Fig. 6 may be implemented in a Raman system or Raman flow cell devices such as those described above, or other suitable systems and devices. It is noted that method 600 of Fig. 6 may share many features similar to those described with respect to structure, configuration, and operation of system implementations. Such similar features need not be described again below.

[0067] The method includes a step 602 of allowing the fluid sample to flow along a sample flow channel extending inside a flow cell. The flow cell may be of various constructions, such as described above. In some embodiments, the fluid sample may be taken from a process stream flowing within a conduit (e.g., a primary stream, a slip stream, a utility stream, a by-product stream, a waste stream). In such embodiments, the allowing step 602 can include an operation of drawing off the fluid sample from a fluid stream flowing within a conduit, and an operation of introducing the drawn-off fluid sample into the sample flow channel. The allowing step 602 can also include an operation of discharging the fluid sample from the sample flow channel, and an operation of reintroducing the discharged fluid stream into the fluid stream. In other variants, the discharged fluid sample is not reintroduced into the fluid stream.

[0068] In other embodiments, the fluid sample may be taken from a fluid contained in a reservoir (e.g., a reaction or storage vessel). The fluid in the reservoir may, but need not, be under stagnant or near stagnant conditions. In such embodiments, the allowing step 602 can include an operation of drawing off the fluid sample from the fluid contained in a fluid reservoir, and an operation of introducing the drawn-off fluid sample into the sample flow channel. The allowing step 602 can also include an operation of discharging the fluid sample from the sample flow channel, and an operation of reintroducing the discharged fluid stream into the fluid reservoir. In other variants, the discharged fluid sample is not reintroduced into the fluid reservoir.

[0069] The method 600 of Fig. 6 also includes a step 604 of focusing Raman excitation light into a sample interrogation region intersecting the sample flow channel for irradiating the fluid sample. The Raman excitation light may be emitted from a laser source and may have an excitation wavelength ranging fromabout 400 nm to about 1200 nm. In some embodiments, the Raman excitation light may be focused perpendicularly to a fluid flow direction of the fluid sample, although this is not a requirement. The method 600 of Fig. 6 further includes a step 606 of collecting backward-scattered Raman light emerging from the fluid sample. In some embodiments, the step 604 of focusing the Raman excitation light and the step 606 collecting backward-scattered Raman light are performed with an objective lens (e.g., a dipping objective lens) in direct contact with the fluid sample flowing along the sample flow channel. In some embodiments, the objective lens has a focal length ranging from about 4.0 mm to about 5.0 mm, and a working distance ranging from about 3.0 mm to about 4.0 mm, but values outside these ranges can be used in other embodiments.

[0070] The method 600 of Fig. 6 also includes a step 608 of reflecting forward-directed light emerging from the fluid sample back toward the sample interrogation region to enhance an intensity of the collected backward-scattered Raman light originating from the fluid sample. As mentioned above, the forward-directed light emerging from the fluid sample can include forward-scattered Raman light generated from the fluid sample and residual Raman excitation light transmitted or elastically scattered by the fluid sample. Depending on the application, either or both of these two contributions to the forward-directed light may be reflected back toward the sample interrogation region to enhance the amount of backward-scattered Raman light generated by the fluid sample and collected by the objective lens. In some embodiments, the reflecting step 608 can be performed with a concave mirror (e.g., a spherical concave mirror). In some embodiments, the concave mirror has a center of curvature positioned within the sample interrogation region, for example, at or near a focal point of the objective lens.

[0071] In some embodiments, the reflection of the forward-directed light occurs outside the flow cell. In such embodiments, the method 600 can include an operation of providing the flow cell with a reflectorviewing window configured to allow both (i) the forward-directed light incident to exit the flow cell, and (ii) the forward-directed light reflected by the reflector to pass therethrough to re-enter the flow cell and reach the sample interrogation region.

[0072] The method 600 of Fig. 6 further includes a step 610 of detecting the collected backward-scattered Raman light, for example, using a suitable optical spectrometer. The detected backward-scattered Raman light can be analyzed by Raman spectroscopy analysis techniques to derive therefrom analyte information associated with the fluid sample. In some embodiments, the analyte information can include composition or concentration information about analytes present in the fluid sample, or an indication of presence or absence of one or more analytes in the fluid sample.

[0073] In some embodiments, one or more secondary analyses may be performed on the fluid sample. The secondary analysis may include, but is not limited to, ultraviolet-visible spectroscopy, laser-induced breakdown spectroscopy, inductively coupled plasma optical emission spectrometry, and / or inductively coupled plasma mass spectrometry. Such a secondary analysis may be executed prior to the Raman analysis. For example, a specific secondary analysis may be executed ahead of a Raman analysis due to overall process constraints (e.g., analysis equipment limitations, installation piping, and flow design) and / or to generate data in support of the Raman analysis (e.g., to determine analyte and / or matrix information to complement Raman data processing). When necessary (e.g., due to the nature of the secondary analysis, wherein the secondary analysis is destructive and / or significantly modifies the analytes or fluid matrix), the Raman analysis may optionally be performed on a separate fluid sample, such as on an isolated fluid sample stream and / or a second fluid sample aliquot. The Raman analysis and secondary analysis may also be performed on the same fluid sample. For example, each analysis may be executed in either order on a single fluid sample stream (e.g., Raman analysis followed by secondary analysis, or secondary analysis followed by Raman analysis) and / or a single sample aliquot. Where both analyses employ similar components (e.g., optical lenses, emission source, detector array), it is possible for both analyses to use the same components and be performed in the same flow cell.

[0074] As noted above, some implementations of the techniques disclosed herein can be used for Raman characterization and analysis of various fluid samples produced or otherwise used at different stages of DLE operations. Fig. 7 shows a schematic example of a DLE operation 700 in which the present techniques may be used. It is appreciated that the DLE operation 700 depicted in Fig. 7 is for purposes of illustration only, and that various other DLE operation configurations, including more, fewer, or different components, are contemplated.

[0075] The DLE operation 700 includes a pretreatment technology 702, a sorbent technology 704, a boron removal technology 706, a water recovery technology 708, a polishing technology 710, a carbonation technology 712, and finishing technologies 714. In the DLE operation 700, brine flows into the pretreatment technology 702 via flow path 716 where it is converted into pre-treated brine, which flows into the sorbent technology 704 via flow path 718. The sorbent technology 704 provides lithium-depleted brine which may be stored, discarded, or recycled via flow path 719. The sorbent technology 704 also provides lithium eluate which flows to the boron removal technology 706 via flow path 720. The boron removal technology 706 provides boron-lean lithium eluate, which flows to the water recovery technology 708 via flow path 722. The water recovery technology 708 provides lithium concentrate, which flows to the polishing technology 710 via flow path 724. The polishing technology 710 provides polished lithium concentrate, which flows to thecarbonation technology 712 via flow path 726. The carbonation technology 712 provides lithium carbonate, which may be dried, filtered, rinsed, recrystallized, or otherwise purified by the finishing technologies 714. The DLE operation 700 also includes a recycle loop 728 from the water recovery technology 708 to the sorbent technology 704. In this recycle loop 728, recovered water is used as eluent, which may be supplemented with makeup water via flow path 730.

[0076] In DLE, pretreatment technologies are generally employed to remove gases, remove fine particle solids, reduce total dissolved solids, remove specific impurities (such as arsenic, iron, and / or silica), separate aqueous / non-aqueous phases, adjust inlet pH, and / or adjust inlet temperature. Pretreatment technologies, such as the pretreatment technology 702 depicted in Fig. 7, are generally known in the art and are not discussed in detail in the present disclosure. Those skilled in the art will appreciate that pretreatment technologies may be deployed in various positions within a DLE operation or may not be required at all. The systems, devices, and / or methods of the present disclosure may improve pretreatment processing by, for example, determining the concentration of contaminants (such as sulfate and boron species) in flow path 716 and 718. The results may be used to optimize the pretreatment technology 702 and / or to ensure the composition in the flow path 718 is within tolerance limits for the sorbent technology 704.

[0077] In DLE, sorbent technologies are generally employed to selectively extract lithium. Sorbent technologies, such as the sorbent technology 704 depicted in Fig. 7, are generally known in the art and are not discussed in detail in the present disclosure. Those skilled in the art will appreciate that pretreatment technologies may be deployed in various positions within a DLE operation or may not be required at all. The systems, devices, and / or methods of the present disclosure may improve sorbent technologies by, for example, determining the concentration of contaminants (such as sulfate and borate) in flow path 718, 719, and 729. The results may be used to optimize the sorbent technology 704 and / or to ensure the composition in the flow path 720 is within tolerance limits for the boron removal technology 706.

[0078] In DLE, boron removal technologies are generally employed to remove boron containing compounds, such as boric acid (B(OH)3), borate anion ( [B(OH)]4“), and polyborate ([B3O3(OH)4]“ and / or [B3O3(OH)5]2-), from lithium containing solutions, for example, by ion exchange. Boron removal technologies, such as the boron removal technology 706, are generally known in the art and are not discussed in detail in the present disclosure. Those skilled in the art will appreciate that boron removal technologies may be deployed in various positions within a DLE operation or may not be required at all. For example, the boron removal technology 706 depicted in Fig. 7 may be positioned upstream of the sorbent technology 704, downstream of the water recovery technology 708, or otherwise positioned within the DLE operation 700. The systems, devices, and / or methods of the present disclosure may improve boron removal processing by, for example,determining the concentration of various boron species in flow path 720 and / or 722. The results may be used to optimize the boron removal technology 706 and / or to ensure the composition in the flow path 722 is within tolerance limits for the water recovery technology 708.

[0079] In DLE, polishing technologies are generally employed to remove magnesium and calcium from lithium-containing solution, for example, by addition of caustic and oxalic acid. Polishing technologies, such as the polishing technology 710 depicted in Fig. 7, are generally known in the art and are not discussed in detail in the present disclosure. Those skilled in the art will appreciate that polishing technologies may be deployed in various positions within a DLE operation or may not be required at all.

[0080] In DLE, carbonation technologies are generally employed to precipitate lithium carbonate from solution, for example by addition of sodium carbonate. Carbonation technologies, such as the carbonation technology 712 depicted in Fig. 7, are generally known in the art and are not discussed in detail in the present disclosure. Those skilled in the art will appreciate that carbonation technologies may be deployed in various positions within a DLE operation or may not be required at all. The systems, devices, and / or methods of the present disclosure may improve carbonation technologies by, for example, detecting carbonate concentration before and / or after the carbonation technology 712. Detecting carbonate concentration after the carbonation technology 712 may facilitate quantification of the chemical equilibrium associated with carbonation and may aid in determining the amount of precipitating agent required.

[0081] In DLE, finishing technologies are generally employed to filter, rinse, recrystallize, and / or otherwise purify lithium carbonate, lithium chloride, or lithium hydroxide. Finishing technologies, such as the finishing technologies 714 depicted in Fig. 7, are generally known in the art and are not discussed in detail in the present disclosure. Those skilled in the art will appreciate that finishing technologies may be deployed in various positions within a DLE operation or may not be required at all. The systems, devices, and / or methods of the present disclosure may improve finishing technologies by, for example, detecting contaminant concentration before finishing technology 712.EXAMPLES & EXPERIMENTATION

[0082] The following description reports work conducted to study and investigate certain aspects of the present techniques. It is appreciated that the Raman systems, devices, and methods disclosed may have a number of features, variations, and applications. As such, the following description is provided to further illustrate some aspects and capabilities of the present techniques, but should not be construed as in any way limiting their scope.

[0083] In an archetypal system and device configuration used for the present experiments, a syringe pump and a laser were configured as follows. A syringe pump having an input port and an output port was used. The input port was connected to a reagent source (e.g., column, slip stream, sample bottle, etc.) via a capillary tube. The output was connected to the fluid cell by a capillary tube. A sample (about 1.0 mL) was injected into the flow cell by actuating the pump. A 532 nm laser (continuous wave, 300 mW) was used as the light source for excitation, and it was left to warm up for about 30 minutes before collection of any spectra.

[0084] Spectra acquisition and baseline correction were completed as follows for the present experiments. Spectra were collected by exposing the sample to the focused laser for hundreds of milliseconds to several seconds depending on the concentration of the analyte and the Raman sensitivity of the vibrational mode of that species. The number of scans was between about 5 and about 20 based on the desired signal to noise ratio. Baseline subtraction of the spectra was implemented in Python using the pybaselines package and the statistics-sensitive non-linear iterative peak-clipping (SNIP) method.

[0085] Fig. 8 shows four panels, each with a Raman spectra obtained using a system, device, and method in accordance with an embodiment. The solutions analyzed comprised carbonate, sulfate, borate, or boric acid as indicated in the individual panels. The upper left panel shows the Raman band typical of carbonate at about 1060 cm-1. The upper right panel shows the Raman band typical of sulfate at about 980 cm-1. The bottom left panel shows the Raman band associated with boric acid at about 875 cm-1. The bottom right panel shows the Raman band associated with borate at about 745 cm-1.

[0086] Fig. 9 shows Raman spectral overlays obtained using a system, device, and method in accordance with an embodiment to analyze borate and boric acid species in solution. The overlays show how the relative intensities of the peaks associated with borate and boric acid change with the pH. Boron speciation can be quantified from the relative peak intensities.

[0087] Fig. 10 shows a Raman spectrum obtained using a system, device, and method in accordance with an embodiment to analyze a brine solution containing lithium. The spectrum shows a strong band at 980 cm-1that is assigned to sulfate. The spectrum also shows bands at 875 cm-1and 745 cm-1that are assigned to boric acid and borate, respectively.

[0088] Fig. 11 shows an overlaid pair of Raman spectra obtained using a system, device, and method in accordance with an embodiment to analyze a solution with and without obstruction of the reflector. The spectrum depicted with a solid line was collected without obstructing the reflector. The spectrum depicted with the hashed line was collected while a beam blocker obstructed the reflector. The beam blocker waspositioned just in front of the reflector to prevent the laser and forward-scattered light from reaching the reflector. Comparison of the two spectra indicates that use of the reflector amplified the signal by a factor of about 3.4.

[0089] Fig. 12 shows four panels, each with an overlay of Raman spectra obtained using a system, device, and method in accordance with an embodiment. The solutions analyzed comprised carbonate, sulfate, borate, or boric acid as indicated in the individual panels, and the overlays depict various analyte concentrations as indicated in the individual panels. Each set of overlays shows the effect of concentration of the corresponding species on the peak intensity. Those skilled in the art can use such information to generate calibration curves by plotting peak intensity as a function of concentration. This calibration facilitates quantification of the species of interest and determination of lower detection limits (LOD).

[0090] In the present disclosure, similar features in the drawings have been given similar reference numerals. To avoid cluttering certain figures, some elements may not be indicated if they were already identified in a preceding figure. The elements of the drawings are not necessarily depicted to scale, since emphasis is placed on clearly illustrating the elements and structures of the present embodiments. Positional descriptors indicating the location and / or orientation of one element with respect to another element are used herein for ease and clarity of description. Unless otherwise indicated, these positional descriptors should be taken in the context of the figures and should not be considered limiting. In particular, positional descriptors are intended to encompass different orientations in the use or operation of the present embodiments, in addition to the orientations exemplified in the figures. Furthermore, when a first element is referred to as being "on", "above", "below", "over", or "under" a second element, the first element can be either directly or indirectly on, above, below, over, or under the second element, respectively, such that one or multiple intervening elements may be disposed between the first element and the second element.

[0091] The terms "a", "an", and "one" are defined herein to mean "at least one", that is, these terms do not exclude a plural number of elements, unless stated otherwise.

[0092] The term "or" is defined herein to mean "and / or", unless stated otherwise.

[0093] Terms such as "substantially", "generally", and "about", which modify a value, condition, or characteristic of a feature of an exemplary embodiment, should be understood to mean that the value, condition, or characteristic is defined within tolerances that are acceptable for the proper operation of this exemplary embodiment for its intended application and / or that fall within an acceptable range of experimental error. In particular, the term "about" generally refers to a range of numbers that one skilled inthe art would consider equivalent to the stated value (e.g., having the same or an equivalent function or result). In some instances, the term "about" means a variation of ±10% of the stated value. It is noted that all numeric values used herein are assumed to be modified by the term "about", unless stated otherwise. The term "between", when used herein to refer to a range of numbers or values defined by endpoints, is intended to include both endpoints, unless stated otherwise.

[0094] The term "based on" as used herein is intended to mean "based at least in part on", whether directly or indirectly, and to encompass both "based solely on" and "based partly on". In particular, the term "based on" may also be understood as meaning "from", "depending on", "representative of", "indicative of", "associated with", "relating to", and the like.

[0095] The terms "match", "matching", and "matched" refer herein to a condition in which two elements are either the same or within some predetermined tolerance of each other. That is, these terms are meant to encompass not only "exactly" or "identically" matching the two elements, but also "substantially", "approximately", or "sufficiently" matching the two elements, as well as providing a higher or best match among a plurality of matching possibilities.

[0096] The terms "connected" and "coupled", and derivatives and variants thereof, refer herein to any connection or coupling, either direct or indirect, between two or more elements, unless stated otherwise. For example, the connection or coupling between the elements may be mechanical, optical, electrical, magnetic, thermal, chemical, logical, fluidic, operational, or any combination thereof.

[0097] The term "concurrently" refers herein to two or more processes that occur during coincident or overlapping time periods. The term "concurrently" does not necessarily imply complete synchronicity and encompasses various scenarios including time-coincident or simultaneous occurrence of two processes; occurrence of a first process that both begins and ends during the duration of a second process; and occurrence of a first process that begins during the duration of a second process, but ends after completion of the second process.

[0098] In the present disclosure, the term "measured" when referring to a quantity or parameter is intended to mean that the quantity or parameter can be measured either directly or indirectly. In the case of indirect measurement, the quantity or parameter can be derived, retrieved, inferred or otherwise determined from directly measured data.

[0099] The terms "light" and "optical", and variants and derivatives thereof, refer herein to radiation in any appropriate region of the electromagnetic spectrum. These terms are not limited to visible light, but may alsoinclude invisible regions of the electromagnetic spectrum including, without limitation, the ultraviolet and infrared spectral bands. For example, in some embodiments the present techniques can be implemented with optical signals having an optical signal bandwidth lying within a wavelength band ranging from about 200 nm (in the ultraviolet) to about 2500 nm (in the near infrared). Those skilled in the art will understand, however, that this wavelength range is provided for illustrative purposes only and that the present techniques may operate beyond this range. It is noted that spectral variables such as wavelength, frequency, wavenumber, and energy may be used interchangeably herein, since converting between these different quantities is straightforward and well known in the art.

[0100] Numerous modifications could be made to the embodiments described above without departing from the scope of the appended claims.

Claims

CLAIMS1. A system for Raman analysis of a fluid sample, the system comprising: a flow cell comprising a sample inlet, a sample outlet, and a flow cell body defining a sample flow channel configured to allow the fluid sample to flow from the sample inlet to the sample outlet; an excitation light source configured to emit Raman excitation light; an objective lens configured to: (i) focus the Raman excitation light into a sample interrogation region intersecting the sample flow channel for irradiating the fluid sample and (ii) collect backward- scattered Raman light emerging from the fluid sample; a reflector positioned opposite from the objective lens across the sample flow channel, the reflector being configured to reflect forward-directed light emerging from the fluid sample back toward the sample interrogation region to enhance an intensity of the backward-scattered Raman light collected by the objective lens, wherein the reflected forward-directed light comprises either or both of forward- scattered Raman light generated from the fluid sample and residual Raman excitation light transmitted or elastically scattered by the fluid sample; and an optical spectrometer configured to detect the backward-scattered Raman light collected by the objective lens.

2. The system of claim 1, wherein the excitation light source comprises a laser source.

3. The system of claim 1 or 2, wherein the Raman excitation light has an excitation wavelength ranging from about 400 nm to about 1200 nm.

4. The system of any one of claims 1 to 3, wherein the objective lens is a dipping objective lens configured to provide a portion of a boundary of the sample flow channel.

5. The system of claim 4, wherein the objective lens is mounted into an opening formed in the flow cell body.

6. The system of any one of claims 1 to 3, wherein the objective lens is a fluid-immersion objective lens.

7. The system of any one of claims 1 to 6, wherein the objective lens has a focal length ranging from about 4.0 mm to about 5.0 mm.

8. The system of any one of claims 1 to 7, wherein the objective lens has a working distance ranging from about 3.0 mm to about 4.0 mm.

9. The system of any one of claims 1 to 8, wherein the reflector is a concave mirror.

10. The system of claim 9, wherein the concave mirror is a spherical mirror.

11. The system of claim 9 or 10, wherein the concave mirror has a center of curvature positioned within the sample interrogation region.

12. The system of claim 11, wherein the center of curvature of the concave mirror is positioned at a focal point of the objective lens.

13. The system of any one of claims 1 to 12, wherein the reflector is configured for position adjustment relative to the objective lens.

14. The system of any one of claims 1 to 13, wherein the flow cell comprises a reflector-viewing window configured to: allow the forward-directed light incident thereon to pass therethrough to exit the flow cell and reach the reflector; and allow the forward-directed light reflected by the reflector to pass therethrough to re-enter the flow cell and reach the sample interrogation region.

15. The system of claim 14, wherein the reflector-viewing window is made of a window material comprising sapphire.

16. The system of any one of claims 1 to 15, further comprising an optical cage assembly configured to mount the flow cell, the objective lens, and the reflector in a coaxial serial arrangement.

17. The system of any one of claims 1 to 13, wherein the reflector is configured to provide a portion of a boundary of the sample flow channel.

18. The system of claim 17, wherein the reflector is mounted into an opening formed in the flow cell body.

19. The system of claim 18, wherein the reflector is configured for position adjustment within the opening relative to the objective lens.

20. The system of any one of claims 1 to 19, wherein the sample flow channel extends along a fluid flow direction substantially perpendicular to an objective axis of the objective lens.

21. The system of any one of claims 1 to 20, further comprising a computer device operatively coupled to the optical spectrometer and comprising a processor and a non-transitory computer readable storage medium having stored thereon computer readable instructions that, when executed by the processor, cause theprocessor to analyze the backward-scattered Raman light detected by the optical spectrometer and derive therefrom analyte information associated with the fluid sample.

22. The system of claim 21, wherein the analyte information associated with the fluid sample comprises at least one of: (i) a concentration of one or more analytes in the fluid sample, (ii) a presence or absence of one or more analytes in the fluid sample, or (iii) chemical composition information about one or more analytes in the fluid sample.

23. The system of claim 21 or 22, wherein the one or more analytes comprise borates, carbonates, nitrates, nitrites, phosphates, phosphites, sulfates, sulfites, carbonic acid, nitric acid, nitrous acid, phosphoric acid, phosphorous acid, sulfuric acid, sulfurous acid, boric acid, or any combination thereof.

24. The system of any one of claims 1 to 23, wherein the sample fluid is an aqueous sample.

25. The system of any one of claims 1 to 24, wherein the sample fluid is a lithium-containing brine.

26. The system of any one of claims 1 to 24, wherein the sample fluid is a plant nutrient solution.

27. The system of any one of claims 1 to 26, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid stream flowing within a conduit.

28. The system of claim 27, wherein the sample outlet is configured to reintroduce the fluid sample into the fluid stream.

29. The system of any one of claims 1 to 26, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid contained in a fluid reservoir.

30. The system of claim 29, wherein the sample outlet is configured to reintroduce the fluid sample back into the fluid reservoir.

31. A Raman flow cell device for use in performing Raman analysis of a fluid sample, the Raman cell flow device comprising: a flow cell comprising a sample inlet, a sample outlet, and a flow cell body defining a sample flow channel configured to allow the fluid sample to flow from the sample inlet to the sample outlet; an objective lens configured to: (i) to focus Raman excitation light received from an excitation light source into a sample interrogation region intersecting the sample flow channel for irradiating the fluid sample, and (ii) collect backward-scattered Raman light emerging from the fluid sample for detection of the collected backward-scattered Raman light by an optical spectrometer; anda reflector positioned opposite from the objective lens across the sample flow channel, the reflector being configured to reflect forward-directed light emerging from the fluid sample back toward the sample interrogation region to enhance an intensity of the backward-scattered Raman light collected by the objective lens, wherein the reflected forward-directed light comprises either or both of forward- scattered Raman light generated from the fluid sample and residual Raman excitation light transmitted or elastically scattered by the fluid sample.

32. The Raman flow cell device of claim 31, wherein the objective lens is a dipping objective lens configured to provide a portion of a boundary of the sample flow channel.

33. The Raman flow cell device of claim 31 or 32, wherein the objective lens is a fluid-immersion objective lens.

34. The Raman flow cell device of any one of claims 31 to 33, wherein the objective lens has a focal length ranging from about 4.0 mm to about 5.0 mm, and a working distance ranging from about 3.0 mm to about 4.0 mm.

35. The Raman flow cell device of any one of claims 31 to 34, wherein the reflector is a concave mirror.

36. The Raman flow cell device of claim 35, wherein the concave mirror is a spherical concave mirror.

37. The Raman flow cell device of claim 35 or 36, wherein the concave mirror has a center of curvature positioned within the sample interrogation region.

38. The Raman flow cell device of claim 37, wherein the center of curvature of the concave mirror is positioned at a focal point of the objective lens.

39. The Raman flow cell device of any one of claims 31 to 38, wherein the reflector is configured for position adjustment relative to the objective lens.

40. The Raman flow cell device of any one of claims 31 to 39, wherein the flow cell comprises a reflectorviewing window configured to: allow the forward-directed light incident thereon to pass therethrough to exit the flow cell and reach the reflector; and allow the forward-directed light reflected by the reflector to pass therethrough to re-enter the flow cell and reach the sample interrogation region.

41. The Raman flow cell device of claim 40, wherein the reflector-viewing window is made of a window material comprising sapphire.

42. The Raman flow cell device of any one of claims 31 to 41, further comprising an optical cage assembly configured to mount the flow cell, the objective lens, and the reflector in a coaxial serial arrangement.

43. The Raman flow cell device of any one of claims 31 to 39, wherein the reflector is configured to provide a portion of a boundary of the sample flow channel.

44. The Raman flow cell device of any one of claims 31 to 43, wherein the sample flow channel extends along a fluid flow direction substantially perpendicular to an objective axis of the objective lens.

45. The Raman flow cell device of any one of claims 31 to 44, wherein the sample fluid is an aqueous sample.

46. The Raman flow cell device of any one of claims 31 to 45, wherein the sample fluid is a lithium-containing brine.

47. The Raman flow cell device of any one of claims 31 to 46, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid stream flowing within a conduit.

48. The Raman flow cell device of claim 47, wherein the sample outlet is configured to discharge the fluid sample back into the fluid stream.

49. The Raman flow cell device of any one of claims 31 to 46, wherein the sample inlet is configured to take in the fluid sample therethrough from a fluid contained in a fluid reservoir.

50. The Raman flow cell device of claim 49, wherein the sample outlet is configured to discharge the fluid sample back into the fluid reservoir.

51. A method of performing Raman analysis of a fluid sample, the method comprising: allowing the fluid sample to flow along a sample flow channel extending inside a flow cell; focusing Raman excitation light into a sample interrogation region intersecting the sample flow channel for irradiating the fluid sample; collecting backward-scattered Raman light emerging from the fluid sample; reflecting forward-directed light emerging from the fluid sample back toward the sample interrogation region to enhance an intensity of the collected backward-scattered Raman light originating from the fluid sample, wherein the reflected forward-directed light comprises either or both of forward-scattered Raman light generated from the fluid sample and residual Raman excitation light transmitted or elastically scattered by the fluid sample; and detecting the collected backward-scattered Raman light.

52. The method of claim 51, further comprising emitting the Raman excitation light.

53. The method of claim 52, wherein the step of emitting the Raman excitation light comprises selecting an excitation wavelength of the Raman excitation light in a range from about 400 nm to about 1200 nm.

54. The method of any one of claims 51 to 53, wherein the steps of focusing the Raman excitation light and collecting backward-scattered Raman light are performed with an objective lens in direct contact with the fluid sample flowing along the sample flow channel.

55. The method of claim 54, wherein the objective lens has a focal length ranging from about 4.0 mm to about 5.0 mm, and a working distance ranging from about 3.0 mm to about 4.0 mm.

56. The method of any one of claims 51 to 55, wherein the step of reflecting the forward-directed light emerging from the fluid sample is performed with a concave mirror.

57. The method claim 56, wherein the concave mirror has a center of curvature positioned within the sample interrogation region.

58. The method of any one of claims 51 to 57, wherein the step of reflecting the forward-directed light occurs outside the flow cell, is preceded by a step of allowing the forward-directed light to exit the flow cell, and is followed by a step of allowing the forward-directed light reflected by the reflector to pass therethrough to re-enter the flow cell and reach the sample interrogation region.

59. The method of any one of claims 51 to 58, wherein the Raman excitation light is focused perpendicularly to a fluid flow direction of the fluid sample.

60. The method of any one of claims 51 to 59, further comprising analyzing the backward-scattered Raman light and deriving therefrom analyte information associated with the fluid sample.

61. The method of claim 60, wherein the analyte information associated with the fluid sample comprises at least one of: (i) a concentration of one or more analytes in the fluid sample, (ii) a presence or absence of one or more analytes in the fluid sample, or (iii) chemical composition information about one or more analytes in the fluid sample.

62. The method of any one of claims 51 to 61, wherein the sample fluid is an aqueous sample.

63. The method of any one of claims 51 to 62, wherein the sample fluid is a lithium-containing brine.

64. The method of any one of claims 51 to 63, wherein the step of allowing the fluid sample to flow along the sample flow channel comprises: drawing off the fluid sample from a fluid stream flowing within a conduit; and introducing the drawn-off fluid sample into the sample flow channel.

65. The method of claim 64, wherein the step of allowing the fluid sample to flow along the sample flow channel comprises: discharging the fluid sample from the sample flow channel; and reintroducing the discharged fluid stream into the fluid stream.

66. The method of any one of claims 51 to 63, wherein the step of allowing the fluid sample to flow along the sample flow channel comprises: drawing off the fluid sample from a fluid contained in a fluid reservoir; and introducing the drawn-off fluid sample into the sample flow channel.

67. The method of claim 66, wherein the step of allowing the fluid sample to flow along the sample flow channel comprises: discharging the fluid sample from the sample flow channel; and reintroducing the discharged fluid stream into the fluid reservoir.

68. The method of any one of claims 51 to 67, wherein the Raman analysis is performed in concert with additional analytical methodology.

69. The method of claim 68, wherein the Raman analysis is performed (i) prior to a secondary analysis, (ii) after a secondary analysis, or (iii) concurrently with a secondary analysis.

70. The method of claim 69, wherein the Raman analysis and the secondary analysis are performed on the same fluid sample.

71. The method of claim 69 or 70, wherein the secondary analysis is performed using some or all of the spectrophotometric components of the Raman system.

72. The method of claim 69, wherein the Raman and secondary analysis are performed on separate fluid samples.

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