WO1999057584A1 - Liquid core waveguide - Google Patents

Liquid core waveguide Download PDF

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Publication number
WO1999057584A1
WO1999057584A1 PCT/US1999/009395 US9909395W WO9957584A1 WO 1999057584 A1 WO1999057584 A1 WO 1999057584A1 US 9909395 W US9909395 W US 9909395W WO 9957584 A1 WO9957584 A1 WO 9957584A1
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WIPO (PCT)
Prior art keywords
length
tubing
liquid core
electromagnetic radiation
liquid
Prior art date
Application number
PCT/US1999/009395
Other languages
French (fr)
Inventor
Rob Waterbury
Bob Byrne
Original Assignee
University Of South Florida
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Filing date
Publication date
Application filed by University Of South Florida filed Critical University Of South Florida
Priority to AU38735/99A priority Critical patent/AU3873599A/en
Priority to EP99921551A priority patent/EP1116057A4/en
Publication of WO1999057584A1 publication Critical patent/WO1999057584A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/032—Optical fibres with cladding with or without a coating with non solid core or cladding
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions

Definitions

  • the present invention relates to a liquid core optical waveguide, and particularly to a liquid core optical waveguide for long pathlength absorbance spectroscopy.
  • Liquid core waveguides provide for long optical pathlengths by constraining light propagation within a liquid medium which has a higher refractive index (R.I.) than the surrounding solid tubing [15].
  • R.I. refractive index
  • What applicants believe to be the first Liquid Core Waveguide [16, 17] employed glass tubing (R.I. ⁇ 1.5) and a high refractive index liquid, bromobenzene (R.I 1.56).
  • Subsequent applications [18, 19] have also been confined to liquids with higher refractive indices than that of water (R.I ⁇ 1.33). There are very few materials which have an index of refraction less than that of water and even fewer which are chemically stable and inert.
  • the present invention provides a new and useful liquid core optical waveguide, particularly for long pathlength absorbance spectroscopy. Moreover, a long pathlength liquid core waveguide according to the present invention can be configured to fit within a relatively small space.
  • a liquid core waveguide is configured for long pathlength absorbance spectroscopy, and comprises a length of tubing having a liquid core with a substantially cylindrical configuration and a substantially constant cross section over the length of tubing.
  • the liquid core extends between the ends of the length of tubing.
  • Each of the ends of the length of tubing is configured to receive or discharge liquid from the liquid core.
  • each end is further configured such that electromagnetic radiation from a broadband light source can be introduced through one end into said liquid core and attenuated light can be directed (i.e. transmitted) through the liquid core and to an attenuated light receiver.
  • the length of tubing has an index of refraction less than the index of refraction of water, and is made from a material such that a cylindrical tube made from such material and having a liquid core diameter of about 560 ⁇ m, an outer diameter of about 800 ⁇ m, and a length of about 5 meters (“5 m") can be coiled within a volume space of about 1.57 cubic inches and support a body of aqueous medium over its length without crimping.
  • a liquid core waveguide of significant length can be supported in a relatively small volume space.
  • the length of tubing has a length of at least 20 cm between it's ends, and can extend from 5-10 meters, or more, between its ends. Moreover, the length of tubing has a substantially circular cross section over its length and has a wall thickness of at least 100 ⁇ m.
  • the length of tubing preferably has a ratio of length to liquid core volume that is ideally greater than 400 cm/cm 3 and, given manufacturing tolerances, as a practical matter has a ratio of length to liquid core volume that is greater than 300 cm/cm 3
  • the length of tubing is cylindrical and is formed of Teflon® AF-2400, has an inner diameter of about 560 ⁇ m, an outer diameter of about 800 ⁇ m, and is entwined in a housing which blocks ambient light from impinging on the length of tubing.
  • the term "entwined” is used to mean bent around multiple times in any manner, such as by way of example tightly coiled (little or no space between adjacent lengths), loosely coiled (more space between adjacent lengths), wound (as in thread wound around a spool or a length of rope wound), entwined in the ordinary sense (as in yarn entwined to form a ball of yarn), and haphazardly gathered into a "rats' nest.”
  • the interior of the housing can be adapted to prevent the coupling of scattered light between coils.
  • an entwined waveguide could be embedded in a material such as a metallic powder which is essentially opaque to light but thermally conductive, so that in the unlikely event that a particle in the waveguide caused light scattering, the risk of scattered light coupling between adjacent coils would be minimized.
  • the use of conductive powder can facilitate a thermostating capability to the waveguide.
  • a liquid core waveguide constructed according to the invention, with tubing formed of Teflon® AF-2400, and a water core provides substantially total internal reflection for light rays intersecting the water/tubing interface at 19° or less, or a Numerical Aperture (NA) of 0.32.
  • Teflon® AF-2400 liquid core waveguide is demonstrated for analysis of iron in aqueous solutions.
  • the invention as described below can also be used to extend the spectrophotometric detection limits of many other chemical species.
  • Figure 1 is a schematic illustration of a spectrophotometric system with a liquid core optical waveguide constructed according to the present invention.
  • Figure 2 is a cross sectional view of the liquid core waveguide, taken e.g. at 2-2 in figure 1.
  • the present invention relates to a liquid core optical waveguide which is particularly useful in long pathlength absorbance sprectroscopy.
  • the following description relates to an absorbance spectroscopy system using a relatively long pathlength optical waveguide according to the present invention.
  • FIG. 1 A system for quantitation of dissolved iron by long pathlength absorbance spectroscopy is shown in Figure 1.
  • the system includes a liquid core optical waveguide 10 including tubing 12 made of Teflon® AF-2400 (e.g from Biogeneral), with an inner diameter equal to 560 ⁇ m and an outer diameter equal to ⁇ OO ⁇ m.
  • a length of liquid core waveguide 10, e.g. about 5 meters in length, is coiled and placed in a 10 cm diameter chamber 14 which is configured to prevent ambient light coupling into the liquid core waveguide.
  • a "T" shaped connector 16 is designed to interface the liquid core waveguide 10 to an optical fiber 1 ⁇ A (e.g. Polymicro Technologies 150 ⁇ m core diameter), and standard 5 mm ID silicon tubing 20.
  • an optical fiber 1 ⁇ A e.g. Polymicro Technologies 150 ⁇ m core diameter
  • standard 5 mm ID silicon tubing 20 standard 5 mm ID silicon tubing 20.
  • This "T” shaped connector 16 allows insertion of the optical fiber 1 ⁇ A into a first end of the Teflon® AF-2400 tubing 12.
  • the end of the "T" shaped connector through which the optical fiber 1 ⁇ A is inserted is suitably sealed against fluid leakage.
  • the first end of the tubing 12 has a relatively tight fit with the "T” shaped connector 16, but additional sealant may be provided to make the connection substantially water tight.
  • a second "T" shaped connector 26 is disposed at the other end of the tubing 12. The connector 26 similarly supports the other end of the tubing 12, and allows insertion of an optical fiber 1 ⁇ B for transmitting attenuated light from the waveguide to a spectrometer 22.
  • the length of tubing has a substantially cylindrical configuration over its length.
  • the liquid core has a substantially circular cross section with a diameter "d" which, in the preferred embodiment is preferably about 560 ⁇ m and an outer diameter "D" which, in the preferred embodiment is about ⁇ OO ⁇ m.
  • the preferred wall thickness "t" of the tube is about 120 ⁇ m, leading applicants to conclude that given manufacturing tolerances, the wall thickness of a length of tubing according to the preferred embodiment would be at least about 10O ⁇ m.
  • a fiber-coupled Tungsten Halogen lamp 24 (Ocean Optics LS-1) and a CCD array spectrometer 22 (Ocean Optics S1000-TR-1) provide a broadband light source and spectral absorbance measurements, respectively.
  • Continuous sampling can be achieved with a peristaltic pump 2 ⁇ (e.g. Ismatec, model 7 ⁇ 016-30) at a flow rate of at least about 0.5 c ⁇ rVmin. Bubbles inadvertently introduced to the system are, however, easily flushed out by continuous pumping of sample.
  • regent(s) and sample(s) are combined to produce colored species which are introduced into the liquid core waveguide.
  • Reagents are generally analytical-reagent grade.
  • ferrozine (Sigma) reagent can be used as a colorimetric reagent.
  • Absorbance measurements of each sample can be made relative to a reference solution containing no ferrozine reagent but identical to the sample solution in all other respects.
  • reference solutions can be constituted from solutions which have had all iron or other trace metals removed using ion exchange resins.
  • the absorbance peak of the Fe(ll)-ferrozine complex (Fe(FZ) 3 ) at 562 nm (nanometers) can be used for the determination of Fe(ll) concentration.
  • the Fe(FZ) 3 absorbance maximum coincides with water's transmission window (4 ⁇ 0 - 700 nm), thus minimizing the extent of light absorption by water.
  • Absorbances are referenced to a non- absorbing wavelength (700 nm) in order to compensate for instrumental drift.
  • Analysis of aqueous solutions for total dissolved iron (Fe(lll) + Fe(ll)), rather than Fe(ll) alone, can be accomplished by including a reductant (such as hydroxylamine hydrochloride) in the mixed buffer solution [3].
  • the sample size requirement for liquid core waveguide analysis is very low.
  • analysis with a 4 meter liquid core waveguide having a liquid core diameter of about 560 ⁇ m requires less than 1.0 cm 3 .
  • the practical upper limit pathlength for liquid core waveguide analysis appears to be substantially larger than 4 meters (i.e. 10 - 20 meters).
  • Light throughput is not a limiting analytical parameter for pathlengths of this magnitude.
  • Flow throughput with a 4 meter liquid core waveguide with a diameter of about 560 ⁇ m is complete within about 2 minutes.
  • a cylindrical Teflon® AF 2400 tube with a 560 ⁇ m inner diameter and ⁇ OO ⁇ m outer diameter, and a length of at least 5 m can be entwined within a volume space of 1.57 cubic inches and support an aqueous core over it's length without crimping.
  • Entwined is used to mean bent around multiple times in any manner, such as by way of example tightly coiled (little or no space between adjacent lengths), loosely coiled (more space between adjacent lengths), wound (as in thread wound around a spool or a length of rope wound), entwined in the ordinary sense (as in yarn entwined to form a ball of yarn), and haphazardly gathered into a "rats' nest.”
  • a long pathlength waveguide having the foregoing construction can be housed in a relatively small volume space.
  • a liquid core waveguide having a length of about 4 meters, and an inner diameter of about 560 ⁇ m has an internal volume of less than 1 cm 3 and a length to volume ratio of at least 300cm/cm 3
  • the length of tubing preferably has a ratio of length to liquid core volume that is ideally greater than 400cm/cm 3 but applicants believe that, given manufacturing tolerances, as a practical matter a ratio of length to liquid core volume that is greater than 300 cm/cm 3 would be useful for practicing the principles of the present invention. In any event, it should be clear that relatively small sample sizes are required for conducting long pathlength absorbance spectroscopy according to the principles of the present invention. 2.
  • the principles of the present invention can be used to markedly extend the detection capabilities of many existing solution-based measurements obtained via absorbance spectroscopy.
  • the analytical apparatus required for this analysis is very simple and robust.
  • the overall analysis is quite amenable to miniaturization and autonomous in-situ analysis.
  • the length of tubing is made from a material such that a cylindrical tube of such material which has a length of about 5 meters, a liquid core cross section diameter of about 560 ⁇ m, and an outer diameter of about ⁇ OO ⁇ m could be entwined in a volume space of about 1.57 cu. in. and support an aqueous medium over its length without crimping.
  • the length of tubing in accordance with the invention is preferably at least 20 cm, more preferably at least about 1 meter, or even 4 meters, or even 5 to 10 meters in length or longer and is made from a material and is configured in terms of cross-sectional shape, internal diameter and wall thickness such that the tubing will exhibit substantially the same flexibility, structural integrity and ability to be wound or otherwise confined to a small volume in space without crimping as a cylindrical tube made from Teflon (preferably Teflon AF-2400) has a length of about 5 meters, a liquid core cross section diameter of about 560 ⁇ m, and an outer diameter of about ⁇ OO ⁇ m.).
  • T-shaped connectors are used in the preferred embodiment, it is contemplated that other configurations for 3 legged connectors (e.g. "Y" configurations) would work equally well in the present invention.

Abstract

A liquid core optical wave guide, particularly for long pathlengh absorbance spectroscopy. The liquid core waveguide has a relatively long pathlength and can be configured to fit within a relatively small space. The waveguide comprises a length of tubing (12) and a liquid core confined within the length of tubing (12), the tubing (12) having an index of refraction no less than the index of refraction of water, and the tubing (12) having a good flexibility. Preferably, the length of tubing (12) is several meters and a flexibility and structural integrity such that a cylindrical length of the tubing (12) having a liquid core diameter (d) of about 560 νm, an outer diameter (D) of about 800 νm, and a length of about 5 m can be coiled within a volume space of about 1.57 cubic inches, can support a body of aqueous medium over its length without crimping.

Description

Title: LIQUID CORE WAVEGUIDE
Government Support
This work was supported by the Office of Naval Research under contract # N00014-96-1-5011.
Technical Field The present invention relates to a liquid core optical waveguide, and particularly to a liquid core optical waveguide for long pathlength absorbance spectroscopy.
Introduction The importance of iron in biological and geochemical systems [1 , 2] has sustained an intense interest in the development of sensitive and robust techniques for analysis of iron in natural waters. In spite of the abundance of iron in the earth's crust, the low solubility and high reactivity of ferric iron, in addition to the obligate role of iron in metabolic processes, limits dissolved concentrations in most natural aqueous systems to nanomolar levels. Analytical methods developed for the determination of iron include colorimetry [3, 4], controlled-potential coulometry [5], and chemiluminescence analysis [6- 11]. Among the reagents which have been used for colorimetric analysis, ferrozine (FZ) has gained wide acceptance due to its high solubility and the high selectivity of FZ for ferrous iron [3]. In spite of the simplicity of colorimetric analysis with ferrozine and the relatively high molar absorptivity of the ferrous- ferrozine complex (2.79 x 104 dm3 mol"1 cm"1) [3], colorimetric analysis with conventional spectrometers and 10 cm pathlength absorbance cells have a detection limit larger than 10 nmol dm"3. Preconcentration techniques have been developed to improve detection limits [12-14]. However, this has resulted in greater analytical complexity and large sample volume requirements. It is believed known that the sensitivity of absorbance spectroscopy can be improved by extending optical pathlength. Liquid core waveguides provide for long optical pathlengths by constraining light propagation within a liquid medium which has a higher refractive index (R.I.) than the surrounding solid tubing [15]. What applicants believe to be the first Liquid Core Waveguide [16, 17] employed glass tubing (R.I. ~ 1.5) and a high refractive index liquid, bromobenzene (R.I = 1.56). Subsequent applications [18, 19] have also been confined to liquids with higher refractive indices than that of water (R.I ~ 1.33). There are very few materials which have an index of refraction less than that of water and even fewer which are chemically stable and inert.
Invention Summary The present invention provides a new and useful liquid core optical waveguide, particularly for long pathlength absorbance spectroscopy. Moreover, a long pathlength liquid core waveguide according to the present invention can be configured to fit within a relatively small space.
A liquid core waveguide, according to the present invention, is configured for long pathlength absorbance spectroscopy, and comprises a length of tubing having a liquid core with a substantially cylindrical configuration and a substantially constant cross section over the length of tubing. The liquid core extends between the ends of the length of tubing. Each of the ends of the length of tubing is configured to receive or discharge liquid from the liquid core. Moreover, each end is further configured such that electromagnetic radiation from a broadband light source can be introduced through one end into said liquid core and attenuated light can be directed (i.e. transmitted) through the liquid core and to an attenuated light receiver. The length of tubing has an index of refraction less than the index of refraction of water, and is made from a material such that a cylindrical tube made from such material and having a liquid core diameter of about 560μm, an outer diameter of about 800μm, and a length of about 5 meters ("5 m") can be coiled within a volume space of about 1.57 cubic inches and support a body of aqueous medium over its length without crimping. Thus, a liquid core waveguide of significant length can be supported in a relatively small volume space. As explained in more detail below, while the foregoing parametric description of the tubing is believed to be useful in describing the type of tubing, in terms of flexibility and integrity with which the present invention can be implemented, it is not intended to limit the invention to tubing of those exact dimensions.
In a liquid core waveguide according to the present invention, the length of tubing has a length of at least 20 cm between it's ends, and can extend from 5-10 meters, or more, between its ends. Moreover, the length of tubing has a substantially circular cross section over its length and has a wall thickness of at least 100μm.
Still further, the length of tubing preferably has a ratio of length to liquid core volume that is ideally greater than 400 cm/cm3 and, given manufacturing tolerances, as a practical matter has a ratio of length to liquid core volume that is greater than 300 cm/cm3
According to a preferred embodiment, the length of tubing is cylindrical and is formed of Teflon® AF-2400, has an inner diameter of about 560μm, an outer diameter of about 800μm, and is entwined in a housing which blocks ambient light from impinging on the length of tubing. In this application, the term "entwined" is used to mean bent around multiple times in any manner, such as by way of example tightly coiled (little or no space between adjacent lengths), loosely coiled (more space between adjacent lengths), wound (as in thread wound around a spool or a length of rope wound), entwined in the ordinary sense (as in yarn entwined to form a ball of yarn), and haphazardly gathered into a "rats' nest."
In addition, the interior of the housing can be adapted to prevent the coupling of scattered light between coils. For example, an entwined waveguide could be embedded in a material such as a metallic powder which is essentially opaque to light but thermally conductive, so that in the unlikely event that a particle in the waveguide caused light scattering, the risk of scattered light coupling between adjacent coils would be minimized. Further, the use of conductive powder (or alternatively a conductive fluid) can facilitate a thermostating capability to the waveguide.
A liquid core waveguide constructed according to the invention, with tubing formed of Teflon® AF-2400, and a water core provides substantially total internal reflection for light rays intersecting the water/tubing interface at 19° or less, or a Numerical Aperture (NA) of 0.32.
In the following detailed discussion, use of a Teflon® AF-2400 liquid core waveguide is demonstrated for analysis of iron in aqueous solutions. The invention as described below can also be used to extend the spectrophotometric detection limits of many other chemical species.
Further features of the present invention will become apparent from the following detailed description and the accompanying drawings.
Brief Description of the Drawings Figure 1 is a schematic illustration of a spectrophotometric system with a liquid core optical waveguide constructed according to the present invention; and
Figure 2 is a cross sectional view of the liquid core waveguide, taken e.g. at 2-2 in figure 1.
Detailed Description As described above, the present invention relates to a liquid core optical waveguide which is particularly useful in long pathlength absorbance sprectroscopy. The following description relates to an absorbance spectroscopy system using a relatively long pathlength optical waveguide according to the present invention. 1. System Setup
A system for quantitation of dissolved iron by long pathlength absorbance spectroscopy is shown in Figure 1. The system includes a liquid core optical waveguide 10 including tubing 12 made of Teflon® AF-2400 (e.g from Biogeneral), with an inner diameter equal to 560 μm and an outer diameter equal to δOO μm. A length of liquid core waveguide 10, e.g. about 5 meters in length, is coiled and placed in a 10 cm diameter chamber 14 which is configured to prevent ambient light coupling into the liquid core waveguide. A "T" shaped connector 16 is designed to interface the liquid core waveguide 10 to an optical fiber 1δA (e.g. Polymicro Technologies 150 μm core diameter), and standard 5 mm ID silicon tubing 20. This "T" shaped connector 16 allows insertion of the optical fiber 1δA into a first end of the Teflon® AF-2400 tubing 12. The end of the "T" shaped connector through which the optical fiber 1δA is inserted is suitably sealed against fluid leakage. Preferably, the first end of the tubing 12 has a relatively tight fit with the "T" shaped connector 16, but additional sealant may be provided to make the connection substantially water tight. A second "T" shaped connector 26 is disposed at the other end of the tubing 12. The connector 26 similarly supports the other end of the tubing 12, and allows insertion of an optical fiber 1δB for transmitting attenuated light from the waveguide to a spectrometer 22. (It should be noted that in Figure 1 , while the end of the tubing 12 within the "T" shaped connectors 16, 26 appear to have larger diameters than the than the remainder of the tubing, this is only for convenience of illustrating the relationship of the optical fibers 1δA, 18B to the ends of the length of tubing. In fact, the length of tubing has a substantially constant cross section over its entire length).
Also, as seen from Figure, the length of tubing has a substantially cylindrical configuration over its length. The liquid core has a substantially circular cross section with a diameter "d" which, in the preferred embodiment is preferably about 560μm and an outer diameter "D" which, in the preferred embodiment is about δOOμm. Thus, the preferred wall thickness "t" of the tube is about 120μm, leading applicants to conclude that given manufacturing tolerances, the wall thickness of a length of tubing according to the preferred embodiment would be at least about 10Oμm.
Sample solutions enter and exit the liquid core waveguide 10 through annular gaps between the optical fibers 1δA, 1δB and the ends of the length of tubing 12. A fiber-coupled Tungsten Halogen lamp 24 (Ocean Optics LS-1) and a CCD array spectrometer 22 (Ocean Optics S1000-TR-1) provide a broadband light source and spectral absorbance measurements, respectively. Continuous sampling can be achieved with a peristaltic pump 2δ(e.g. Ismatec, model 7δ016-30) at a flow rate of at least about 0.5 cπrVmin. Bubbles inadvertently introduced to the system are, however, easily flushed out by continuous pumping of sample. In order to perform absorbance spectroscopy, regent(s) and sample(s) are combined to produce colored species which are introduced into the liquid core waveguide. Reagents are generally analytical-reagent grade. As an example, for analysis of Ferrous iron, ferrozine (Sigma) reagent can be used as a colorimetric reagent. Moreover, buffer solutions, (pH = 5.5) can be used to optimize color development. Absorbance measurements of each sample can be made relative to a reference solution containing no ferrozine reagent but identical to the sample solution in all other respects. Alternatively, reference solutions can be constituted from solutions which have had all iron or other trace metals removed using ion exchange resins. The absorbance peak of the Fe(ll)-ferrozine complex (Fe(FZ)3) at 562 nm (nanometers) can be used for the determination of Fe(ll) concentration. The Fe(FZ)3 absorbance maximum coincides with water's transmission window (4δ0 - 700 nm), thus minimizing the extent of light absorption by water. Absorbances are referenced to a non- absorbing wavelength (700 nm) in order to compensate for instrumental drift. Analysis of aqueous solutions for total dissolved iron (Fe(lll) + Fe(ll)), rather than Fe(ll) alone, can be accomplished by including a reductant (such as hydroxylamine hydrochloride) in the mixed buffer solution [3].
The sample size requirement for liquid core waveguide analysis is very low. For example, analysis with a 4 meter liquid core waveguide having a liquid core diameter of about 560μm requires less than 1.0 cm3. The practical upper limit pathlength for liquid core waveguide analysis appears to be substantially larger than 4 meters (i.e. 10 - 20 meters). Light throughput is not a limiting analytical parameter for pathlengths of this magnitude. Flow throughput with a 4 meter liquid core waveguide with a diameter of about 560μm is complete within about 2 minutes.
Moreover, a cylindrical Teflon® AF 2400 tube with a 560μm inner diameter and δOOμm outer diameter, and a length of at least 5 m can be entwined within a volume space of 1.57 cubic inches and support an aqueous core over it's length without crimping. "Entwined" is used to mean bent around multiple times in any manner, such as by way of example tightly coiled (little or no space between adjacent lengths), loosely coiled (more space between adjacent lengths), wound (as in thread wound around a spool or a length of rope wound), entwined in the ordinary sense (as in yarn entwined to form a ball of yarn), and haphazardly gathered into a "rats' nest." Thus, a long pathlength waveguide having the foregoing construction, can be housed in a relatively small volume space.
One of the most significant advantages of liquid core waveguide absorbance spectroscopic iron analysis, using a waveguide according to the present invention, is its substantial simplicity. Only one step, addition of combined reagent to a sample, is prerequisite to absorbance measurement. The absence of preconcentration steps considerably lessens the potential for sample contamination. Thus, very low (sub nanomolar) iron concentrations can be measured with this technique. Moreover, a liquid core waveguide having a length of about 4 meters, and an inner diameter of about 560μm, has an internal volume of less than 1 cm3 and a length to volume ratio of at least 300cm/cm3 The length of tubing preferably has a ratio of length to liquid core volume that is ideally greater than 400cm/cm3 but applicants believe that, given manufacturing tolerances, as a practical matter a ratio of length to liquid core volume that is greater than 300 cm/cm3 would be useful for practicing the principles of the present invention. In any event, it should be clear that relatively small sample sizes are required for conducting long pathlength absorbance spectroscopy according to the principles of the present invention. 2. Conclusions
The principles of the present invention can be used to markedly extend the detection capabilities of many existing solution-based measurements obtained via absorbance spectroscopy. The analytical apparatus required for this analysis is very simple and robust. The overall analysis is quite amenable to miniaturization and autonomous in-situ analysis.
Also, it should be noted that it is useful to describe the flexibility and structural integrity of the length of tubing forming the liquid core waveguide according to the invention by certain parameters of the preferred embodiment (e.g. that the length of tubing is made from a material such that a cylindrical tube of such material which has a length of about 5 meters, a liquid core cross section diameter of about 560μm, and an outer diameter of about δOOμm could be entwined in a volume space of about 1.57 cu. in. and support an aqueous medium over its length without crimping. Putting it differently, the length of tubing in accordance with the invention is preferably at least 20 cm, more preferably at least about 1 meter, or even 4 meters, or even 5 to 10 meters in length or longer and is made from a material and is configured in terms of cross-sectional shape, internal diameter and wall thickness such that the tubing will exhibit substantially the same flexibility, structural integrity and ability to be wound or otherwise confined to a small volume in space without crimping as a cylindrical tube made from Teflon (preferably Teflon AF-2400) has a length of about 5 meters, a liquid core cross section diameter of about 560μm, and an outer diameter of about δOOμm.). However, such a parametric description of the tubing is believed to be useful in describing the type of tubing, in terms of flexibility and integrity with which the present invention can be implemented, but is not intended to limit the invention to tubing of those exact dimensions, other than may be recited in specific claims of this application. In addition, while the invention has been described above in terms of lengths of tubing in the range of 4 meters, 5-10 meters and longer, it is also contemplated that long pathlength absorbance spectroscopy can be practiced effectively with liquid core waveguides as short as 20 cm, and 1 meter in length, and also with liquid core waveguides on the order of several meters, 5- 10 meters, and longer, using the principles of the present invention. It is also believed advantageous that the length of tubing used in accordance with the present invention be unclad, i.e. not formed from a coated or laminated tube, but rather be composed of a single material, e.g. monolithic.
Still further, while T-shaped connectors are used in the preferred embodiment, it is contemplated that other configurations for 3 legged connectors (e.g. "Y" configurations) would work equally well in the present invention.
It is believed that with the foregoing description in mind, still other variations of long pathlength liquid core waveguides will become apparent to those skilled in the art. References
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211.
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[10] H. Obata, H. Karatani and E. Nakayama, Anal. Chem., 65 (1993)1524. [11] D.W. O'Sullivan, A.K. Hanson and D. R. Kester, Mar. Chem., 49 (1995) 65.
[12] H. Hong and D.R. Kester, Limnol. Oceanogr., 31 (19δ6) 512.
[13] D.W. King, J. Lin and D.R. Kester, Anal. Chim. Acta, 247 (1991) 125.
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[17] J. Stone, App. Phys. Lett., 20 (1972) 239.
[1δ] F. Tsunoda, A. Nomura, J. Yamada and S. Nishi, Appl. Spectra., 44 (1990)
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Claims

Claims
1. A liquid core waveguide configured for long pathlength spectroscopy, comprising a length of tubing having first and second ends and a liquid core having a substantially circular cross section and a substantially constant diameter defined within the length of tubing and extending between said first and second ends, each of said first and second ends being configured to receive or discharge liquid from the liquid core and each being further configured such that electromagnetic radiation from a broadband light source can be introduced through one of said first and second ends into said liquid core and attenuated light can be directed from said liquid core through the other of said first and second ends to an attenuated light receiver, said length of tubing having an index of refraction less than the index of refraction of water, and said length of tubing being made from a material such that a cylindrical tube made from such material and having a liquid core diameter of about 560μ, an outer diameter of about δOOμ and a length of about 5 m can be coiled within a volume space of about 1.57 cubic inches and support a body of aqueous medium over its length without crimping.
2. A liquid core waveguide as set forth in claim 1 , wherein said tubing has a length of at least 1 meter between said first and second ends.
3. A liquid core waveguide as set forth in claim 2, wherein said tubing has a wall thickness of at least 10Oμm.
4. A liquid core waveguide as set forth in any of claims 2, wherein said tubing has a ratio of length to liquid core volume that is greater than 300cm/cm3
5. A liquid core waveguide as set forth in claim 4, wherein said length of tubing is formed of Teflon® AF-2400. 6. A liquid core optical waveguide assembly for long pathlength absorbance spectroscopy, comprising: a) length of tubing having a first end and a second end; b) means, connected near said first end of said length of tubing, for optically coupling electromagnetic radiation from a source of electromagnetic radiation into said length of tubing;
10 c) means, connected near said first end of said length of tubing, for placing a source of sample fluid into fluid communication with said length of tubing; d) means, connected near said second end of said length of tubing, for optically coupling electromagnetic radiation from said length of tubing to a detector of electromagnetic radiation; e) means connected near said second end of said length of tubing for allowing fluid to exit said length of tubing.
7. A liquid core optical waveguide assembly for long pathlength absorbance spectroscopy according to claim 6, wherein said means for optically coupling electromagnetic radiation from a source of electromagnetic radiation into said length of tubing comprises a first adapter connected to said length of tubing and having an opening that accepts and holds an optical fiber from the source of electromagnetic radiation. δ. Liquid core optical waveguide assembly for long pathlength absorbance spectroscopy according to claim 7: wherein (i) said means for optically coupling electromagnetic radiation from a source of electromagnetic radiation into said length of tubing and (ii) said means for placing a source of sample fluid into fluid communication with said length of tubing comprise a fiber optic T element having at least first, second, and third openings; wherein said first opening accepts said first end of said length of tubing; wherein said second opening accepts an optical fiber from an optical fiber from the source of electromagnetic radiation and holds the optical fiber in an opening at said first end of said length of tubing; wherein said third opening accepts a source length of tubing extending from the source of sample fluid; and wherein said fiber optic T element includes a fluid path between said first and third openings being arranged so that fluid flows into said third opening, around the optical fiber, and into said length of tubing. 9. A liquid core optical waveguide assembly for long pathlength absorbance spectroscopy according to claim 6:
11 wherein said length of tubing has a pathlength associated therewith, said pathlength being the length from (i) said means for optically coupling electromagnetic radiation from a source of electromagnetic radiation into said length of tubing to (ii) said means for optically coupling electromagnetic radiation from said length of tubing to a detector of electromagnetic radiation; said length of tubing further has a sample volume associated therewith, said sample volume being a volume of the sample fluid contained in said length of tubing along said pathlength; and wherein said length of tubing has a flexibility and structural integrity such that a length of the tubing having a liquid core diameter of about 560μm and a length of about 5 m can be coiled within a volume space of about 1.57 cubic inches and support a body of aqueous medium over its length without crimping and a ratio of pathlength to sample volume that is greater than 300cm/cm3.
10. A liquid core optical waveguide assembly for long pathlength absorbance spectroscopy according to claim 9 wherein said length of tubing has a pathlength that is at least 5 meters.
11. A liquid core optical waveguide assembly for long pathlength absorbance spectroscopy according to any of claims 6, wherein said tubing is formed from Teflon® AF 2400. 12. A liquid core optical waveguide assembly for long pathlength absorbance spectroscopy according to claim 11 , where said length of tubing has a substantially cylindrical configuration over its length and a wall thickness of at least about 100μm over its length. 13. A system for analyzing a liquid sample, comprising: (a) a source of broadband electromagnetic radiation;
(b) a liquid core waveguide configured for long pathlength absorbance spectroscopy, and comprising a length of flexible tubing having a first end and a second end, said length of flexible tubing having a pathlength of at least 20 cm; (c) a spectrometer for providing spectrophotometric analysis of attenuated light from said liquid core waveguide;
12 (d) optical transmission means for optically transmitting electromagnetic radiation from said source of electromagnetic radiation into said length of tubing;
(e) liquid inlet means, located near said first end of said length of flexible tubing, for directing the liquid sample into said length of flexible tubing;
(f) optical receiving means for optically receiving attenuated electromagnetic radiation from said length of tubing and directing the attenuated electromagnetic radiation to said spectrometer; and
(g) liquid outlet means located near said second end of said length of tubing for allowing said liquid sample to flow out of said length of tubing. 14. A system as set forth in claim 13, wherein said liquid core waveguide is entwined and is disposed in a housing configured to block ambient light from impinging on said liquid core waveguide. 15. A system as set forth in claim 14, wherein said length of tubing has a flexibility and structural integrity such that a cylindrical length of the tubing having a liquid core diameter of about 560μm, an outer diameter of about δOOμm, and a length of about 5 m can be coiled within a volume space of about 1.57 cubic inches, can support a body of aqueous medium over its length without crimping, and has a ratio of pathlength to sample volume that is greater than 400 cm/cm3.
16. A system as set forth in claim 19, wherein said liquid core waveguide has a pathlength of several meters.
17. A system as set forth in claim 16, wherein said length of tubing is formed from Teflon® AF 2400.
1δ. A liquid core waveguide configured for use in spectrographic analysis comprising a length of flexible tubing (i) having a substantially circular cross section and a substantially constant diameter, (ii) having an index of refraction less than the index of refraction of a liquid disposed in the flexible tube, and (iii) being formed from a material such that a cylindrical tube made from such
13 material and having a liquid core diameter of about 560μm an outer diameter of about δOOμm and a length of about 5 meters can be coiled within a volume space of about 1.57 cubic inches and support a body of aqueous medium over its length without crimping, and a light coupling for at least one end of the flexible tubing. 19. The liquid core waveguide of claim 1δ, wherein the light coupling comprises a housing with a fluid port, a light port and a tube connector formed therein.
20. The liquid core waveguide of claim 19, wherein the fluid port is configured for attachment to a fluid conduit for directing liquid into or out of the tubing.
21. The liquid core waveguide of claim 19, wherein the light port is configured for connection to a light fiber for directing light to an analytical device.
22. A system for analyzing a liquid sample, comprising: a liquid core waveguide configured for absorbance spectroscopy, and comprising a length of flexible tubing having a first end and a second end, said length of flexible tubing having a pathlength of at least 1 meter; a source of electromagnetic radiation configured to transmit such radiation into said flexible tubing; a spectrometer for providing spectrophotometric analysis of attenuated light from said liquid core waveguide; liquid inlet means, located near said first end of said length of flexible tubing, for directing the liquid sample into said length of flexible tubing; optical receiving means for optically receiving attenuated electromagnetic radiation from said length of tubing and directing the attenuated electromagnetic radiation to said spectrometer; and liquid outlet means located near said second end of said length of tubing for allowing said liquid sample to flow out of said length of tubing.
14
PCT/US1999/009395 1998-05-01 1999-04-30 Liquid core waveguide WO1999057584A1 (en)

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WO2001095000A2 (en) * 2000-06-08 2001-12-13 Schleifring Und Apparatebau Gmbh Optical data transfer system
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EP3175921A1 (en) * 2015-12-04 2017-06-07 Consejo Superior De Investigaciones Científicas Biophotonic devices and methods of their use
CN106645092A (en) * 2017-02-24 2017-05-10 北京本立科技有限公司 Liquid-core waveguide Raman spectrum detection device based on centrifuging
CN106645092B (en) * 2017-02-24 2023-09-19 北京本立科技有限公司 Liquid core waveguide Raman spectrum detection device based on centrifugation
WO2021198030A1 (en) * 2020-03-30 2021-10-07 Volkswagen Ag Optical sensor for detecting a gas, use thereof, and means of transportation comprising such a sensor
WO2021198032A1 (en) * 2020-03-30 2021-10-07 Volkswagen Ag Dual measuring device for determining the quality of a gas, use thereof, and means of transportation comprising such a measuring device
WO2022091278A1 (en) * 2020-10-29 2022-05-05 日本電信電話株式会社 Optical waveguide device

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