Classifications

• • 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.

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• Physics & Mathematics (AREA)
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• Investigating Or Analysing Materials By Optical Means (AREA)

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• 1999
  • 1999-04-30 AU AU38735/99A patent/AU3873599A/en not_active Abandoned
  • 1999-04-30 EP EP99921551A patent/EP1116057A4/de not_active Withdrawn
  • 1999-04-30 WO PCT/US1999/009395 patent/WO1999057584A1/en not_active Application Discontinuation

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