US 2005.0078308A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2005/0078308A1 Gilby (43) Pub. Date: Apr. 14, 2005

(54) OPAQUE ADDITIVE TO BLOCK STRAY (30) Foreign Application Priority Data LIGHT IN TEFLONOOab AF LIGHT GUIDING FLOWCELLS Feb. 25, 2003 (WO)...... PCT/US03/05811 (75) Inventor: Anthony C. Gilby, Foxborough, MA Publication Classification US (US) (51) Int. Cl...... G01N 21/05 Correspondence Address: (52) U.S. Cl...... 356/246 Anthony J. Janiuk Waters Technologies Corporation cio Waters Investments Limited (57) ABSTRACT 34 Maple Street Milford MA 01757 (US 9 (US) The present invention is directed to the use of a light (73) Assignee: WATERS INVESTMENTS LIMITED, absorbing wall material to eliminate Stray light paths in New Castle, DE light-guiding Structures, Such as those used for HPLC absor bance detection. More Specifically, the present invention (21) Appl. No.: 10/911,126 relates to the use of carbon-doped Teflon(R) AF, or “black Teflon(RAF, for all or part of the walls of a light-guiding (22) Filed: Aug. 4, 2004 flowcell adapted for use in HPLC absorbance detection.

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Patent Application Publication Apr. 14, 2005 Sheet 3 of 5 US 2005/0078308A1

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C S. 3 O s 3 cus Z O C 9 d Z Patent Application Publication Apr. 14, 2005 Sheet 4 of 5 US 2005/0078308A1

ent Application Publication Apr. 14, 2005 Sheet 5 of 5

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Y 'N Y ro FIG. 5 US 2005/0078308A1 Apr. 14, 2005

OPAQUE ADDITIVE TO BLOCK STRAY LIGHT IN TEFLONOOAB AF LIGHT-GUIDING FLOWCELLS AC AA (1c)1

CROSS REFERENCE TO RELATED APPLICATIONS 0007 Ac represents the smallest analyte concentration 0001. This application claims priority from a PCT Inter that can be detected and AA the corresponding Smallest national Patent Application No. PCT/US03/05811, filed Feb. change in absorbance that can be measured. This represents 25, 2003 and U.S. Provisional Patent Application No. the noise at the absorbance baseline, the output of the 60/359,354, filed Feb. 25, 2002. The contents of these absorbance detector. applications are incorporated herein by reference. 0008 As illustrated by equation (1b), low absorbance noise requires a high light signal 10 and low noise in the BACKGROUND OF THE INVENTION measurement of I, i.e. a high signal-to-noise (S/N) ratio in the raw transmittance measurement. In a well-designed 0002 The present invention relates generally to the use of detector, shot noise, which is proportional to the Square root a light absorbing wall material to eliminate Stray light paths of the light Signal, dominates, So high SIN requires highlight in light-guiding applications, Such as High Performance throughput. Liquid Chromatography (HPLC), and Capillary Zone Elec trophoresis (CZE) spectroscopic analysis. 0009 Light-guiding flowcells enable low volume cells to be constructed with high light throughput and long path 0003) Systems for light absorption detection generally length. The liquid Sample is contained in a tube of material comprise four basic components, a light Source, a means for having a lower refractive index (RI) than the mobile phase. Selecting wavelengths to be used, a light-guiding vessel, Light is introduced into one end of the tube and propagates typically in the form of a hollow tube or capillary through down the axis of the tube making multiple internal reflec which a sample to be analyzed and light are passed (a tions before emerging at the other end. The liquid is analo flowcell), and a light detector which measures the amount of gous to the core of an optical fiber and the material of the light transmitted through the flowcell. Large optical tube is analogous to the cladding. The condition for light throughput can be achieved when the light is guided along guiding is that the rays incident on the liquid/wall boundary the capillary Similar to the way light is guided along an do So at an angle of incidence greater than the critical angle optical fiber. 0004. A flowcell must be constructed from materials that are resistant to the Solutions encountered in liquid chroma 12 (2a) tography or CE. To achieve high Sensitivity to Small con centrations of analyte, the cell must have a high optical throughput and a long pathlength. If the quantity of analyte 0010 where n is the RI of the liquid, and n is the RI of is Small and capillary Separation techniques are used, the the wall of the flowcell. volume of the cell must also be Small, otherwise band Spreading and loSS of chromatographic resolution occurs. 0011 The numerical aperture (NA) of the guided beam is The transmittance, T, of light through Such a System filled given by: with a light absorbing Sample is determined in accordance with Beer's law: 0012. Where p is the largest angle, between a ray entering the cell from air and the cell axis, which meets the guiding (1a) condition. The guiding mechanism is termed total internal reflection (TIR) (1b) 0013 Recently, flowcells having an inner surface of an amorphous fluoropolymer material that has an index of refraction lower than that of common chromatography Sol vents, e.g. water, have enabled light-guiding flowcells to be 0005 where I is the light exiting the flowcell when constructed. it is filled with clear mobile phase and I is the light 0014 Light introduced along the axis of the tube is power exiting the flowcell when analyte is present. b guided in the fluid by total internal reflection at the fluid wall is the path length of the flowcell conventionally boundary. The amorphous fluoropolymer material Teflon(R) expressed in centimeters, c is the analyte concentra AF 1600 and 2400 are preferred tube materials because they tion in M or moles/liter and e is the molar absorp are transparent throughout the visible and ultraViolet Spec tivity expressed in units of cm (moles/liter). A is trum, they have an unusually low refractive index (1.31 and the absorbance, a dimensionless number expressed 1.29 respectively) and are chemically inert. As a compari in absorbance units (au). son, the RI of water at the same wavelength is 1.333. All common Solvents (as methanol/water mixtures and acetoni 0006 The requirement for highlight throughput and long trile) have a higher RI than water and therefore also Teflon(R) pathlength is illustrated by differentiating equation (1b). AF. Only pure methanol has an index slightly below water, US 2005/0078308A1 Apr. 14, 2005

but still above that of Teflon(E) AF. Even at different wave inlet and outlet ports, whereby the walls and fluid effect lengths, the fluoropolymerS retain the RI advantage. guiding of the light by attenuated total reflection, the walls having minimal absorptive effect on the guided light. The 0015. However, it is difficult to construct a cell with amorphous fluoropolymer walls without Some light entering walls have an absorption coefficient in the range of 0.1 to the end croSS-Section of the wall, or Some light 18 being 100 mm at a wavelength within the wavelength range of scattered into the wall from the liquid, or some light 18 UV, visible and near IR. A preferred material for the walls entering the fluid from the walls after bypassing part or all is Teflon(R) AF fluoropolymer doped with a black dopant of the Sample fluid. These aberrant light paths result in a Such as carbon black. A concentration of carbon black Stray light background and inaccuracy in the readings, between 0.01% and 1% by weight of the fluoropolymer is limiting the linearity and dynamic range of a detector that is sufficient to absorb stray light. Supposed to receive only light that has passed through the 0021 Another embodiment is an apparatus for housing a liquid. liquid Sample and for exposing the liquid Sample to light. 0016 One Strategy to control Stray light positions opaque The apparatus comprises a conduit having a wall formed of masks between the walls and the light, but the Small diam an amorphous fluoropolymer having a refractive indeX leSS eter tubes of HPLC and CZE equipment makes the align than the refractive index of water and having an absorption ment of Such masks difficult and time consuming. A Second coefficient of a magnitude Such that when the conduit is Strategy to control Stray light Supplies entering light through filled with water, visible and ultra-violet light can be trans mitted, Substantially without loss, along the axis of the an optical fiber having an OD that fits between the walls, but conduit by attenuated total reflection but visible and ultra the amount of light coupled into the liquid is reduced Violet light are Substantially completely absorbed in passage geometrically by the reduced area through the walls of the conduit. 0.017. The difficulty of controlling stray light becomes greater as fluid croSS-Sections are made Smaller. For capil 0022. A method of performing photometric analysis of a lary HPLC or CZE detection, a fluid channel ID of 100 um liquid Sample with improved linearity of detection com or leSS is needed to create a Small Volume flowcell, with prises introducing the liquid Sample into a conduit having a Sufficient pathlength to preserve analytical Sensitivity. A wall formed of an amorphous fluoropolymer having a refrac better way is needed to fabricate light guiding flowcells to tive indeX less than a refractive index of water and having an absorption coefficient Sufficient to Substantially attenuate avoid the difficulties of controlling stray light outlined above light propagation through the Wall, Shining light axially onto the conduit filled with Sample liquid, receiving light trans SUMMARY OF THE INVENTION ferred through the liquid Sample at a detector; and deter 0.018. The present invention provides an apparatus and mining the concentration of the Sample in the liquid by method for controlling Stray light in Vessels having Small measuring the light absorption of the Sample. When light is croSS Sections, used especially for light absorption measure axially shone onto the conduit filled with Sample liquid, light mentS. transferred through the liquid Sample is detected and the concentration of Sample in the liquid is determined. Alter 0019. In a preferred application, the vessel is a flowcell nately the Sample concentration can be determined used the receiving analyte from a HPLC apparatus. One embodiment emitted florescence or Raman Scattered light. is a device for receiving one or more Samples and measuring light emitted or refracted therefrom. This device comprises 0023. A set of light-guiding flowcells for a fluid com a vessel with a cavity for containing a Sample during a prises a set of channels formed in a Substrate of material measuring process, where the vessel comprises at least one having an index of refraction lower than the index of the wall in fluid contact with the Sample, the wall having a fluid and an absorption coefficient sufficient to substantially composition having an index of refraction lower than the attenuate light propagating through the material. A Set of index of refraction of a fluid in the sample. Further the wall channel covers formed in a Section of material having an has an absorption coefficient Sufficient to Substantially index of refraction and absorption coefficient identical to the attenuate light propagating through the wall and the vessel Substrate of material is fixed to the Set of channels forming has at least one means for passage of transmitting light, a set of covered channels. At least one covered channel, or wherein light within the cavity is guided by attenuated total interconnected Set of covered channels, has a fluid inlet and reflection into the sample. By judicious choice of the wall outlet port. At least one covered channel has a Source of light absorption coefficient, the light guided through the fluid by at a light entrance end and has a light exit end. The at least internal reflection is only minimally attenuated. The means one covered channel and fluid therefore effect guiding of the for means for passage of transmitting light may be an light by attenuated total reflection and the at least one opening, a window, a lens or an optical fiber. A preferred covered channel has minimal absorptive effect on the light material for the wall is Teflon(R) AF fluoropolymer doped guided by internal reflection. A covered channel may be with a black dopant Such as carbon black. configured as a separation column. The interconnected chan nels for perform analysis on a fluid passing therethrough 0020. Another embodiment is a light-guiding apparatus when the output of the Separation column is connected to the comprising a fluid channel bounded by at least one wall, the light-guiding channel, where the light exit end is connected composition of the wall having an index of refraction lower to a detector external to the set of flowcells. than the index of refraction of a fluid in the fluid channel and having an absorption coefficient Sufficient to Substantially 0024. A typical use for the invention is in a flowcell for attenuate light propagating through the walls. The apparatus HPLC or CE absorbance detection where the flowcell is further comprises an entrance and exit for light, the entrance constructed from a hollow tube of low index material Such and exit perpendicular to an axis of the channel and fluid as Teflon(E) AF 2400, darkened wherein the wall material is US 2005/0078308A1 Apr. 14, 2005

Sufficiently absorbing to block light transmission through the 0034 Adequate light blocking can be achieved if the light wall. At the same time, the absorption by the wall is low transmitted through the tube wall, parallel to the lumen, is enough that light guiding is Substantially unaffected. Car reduced to one part in 1,000 of the incident intensity, within bon-doped Teflon(RAF, or “black Teflon(RAF," is a material a distance of 5 mm. This essentially eliminates Stray light well adapted for all or part of the walls of such a light through the bulk material. With these parameters, Equation guiding flowcell for use in HPLC absorbance detection (3) yields an absorption coefficient of C=1.4 mm. The effect of this change in the material on the light-guiding BRIEF DESCRIPTION OF THE DRAWINGS properties is considered below. 0.025 These and other features and advantages of the 0035. When light rays are guided by total internal reflec present invention will become more apparent from the tion at the boundary between core material and a lower index following detailed description taken in conjunction with the cladding, there is a Small penetration of light into the low accompanying drawings wherein like reference characters index medium. If the low index medium is transparent, the denote corresponding parts throughout the Several views, internal reflection is 100%. But, if the low index medium and wherein: absorbs light, Some energy is trapped in the penetrating 0.026 FIG. 1. is a simplified diagram of a light guiding evanescent light wave and the proceSS is referred to as attenuated total reflection (ATR). When absorption is low, as vessel according to the invention; in the present design, relatively simple expressions can be 0.027 FIG. 2. is a simplified diagram of the light-guiding used to calculate the effective thickness of Teflon(E) AF, vessel in the form of a flowcell according to the invention; penetrated by the light at each internal reflection (see 0028 FIG. 3. is a graph illustrating the depth of penetra Harrick N.J., Internal Reflection Spectroscopy, Harrick Sci entific Corp., Ossining, N.Y., 1987, p. 43). The effective tion of a light wave into a wall according to the invention; thickness depends on the wavelength, angle of incidence, 0029 FIG. 4. is a diagram of a flowcell constructed refractive index of the two media, and on the plane of incorporating the invention; and polarization. The physical orientations of the components 0030 FIG. 5 is a simplified diagram of a “lab-on-a chip” are illustrated in FIG. 4. implemented utilizing the invention. 0036 For light polarized perpendicular to the plane of incidence effective thickness is: DETAILED DESCRIPTION 0.031) A light-guiding structure that has Superior signal to noise characteristics can be constructed if the absorption deep) = - 1n2 cosé - (4a) coefficient of the walls of the liquid containing vessel are PP1 (sino-1,2, judiciously chosen to only minimally attenuate the light guided through the liquid by internal reflection. The vessel may be formed to contain a single Sample, as an array of 0037 For light polarized parallel to the plane of inci Single Sample vessels or as flowcell capable of analyzing a dence effective thickness is: Sequence of Samples. The basis of the invention is discussed utilizing as an example a light guiding flowcell which is Simple and easy to construct, minimizes Stray light and Anacosé(2sine- ni) (4b) exhibits maximum light throughput for a chosen Volume and deparallet) = pathlength. The low RI wall material is made sufficiently absorbing to block Stray light paths that bypass part of or all of the liquid Sample, a cause of nonlinearity between absor 0038 where: n is the refractive index of medium 1, the bance and concentration. The absence of masks or optical fluid Sample fibers inserted into the flowcell lumen allows optical throughput to be maximized. 0039) n is the refractive index of medium 2, the Teflon(RAF in contact with the fluid 0 is the angle of 0.032 The following discussion justifies the assertion that incidence of a ray internally reflected at the boundary a bulk absorption coefficient for the low index wall material between the two can be chosen Such that undesired rays that enter the wall are absorbed, and yet desired rays, which are guided along the 0040 n=n/n flowcell channel, are transmitted without loss. Absorption of 0041 vs-W/n is the wavelength in medium 1. ) is light through a material is described by the Bouguer/Lam the wavelength in air. bert law: 0042. One possible application utilizes a 5 mm long light-guiding flowcell having an ID of 100 um, a numerical | -ab (3) aperture (NA) of the tube of 0.27 and a beam of light having a wavelength of 250 nm. The rays that make the largest angle with the axis (arcsin(NA)), and reflect from the boundary closest to the critical angle, make about ten 0.033 where C. is the material absorption coefficient in reflections and penetrate the deepest into the wall. The units of reciprocal length, b is the distance traveled in the effective thickness of Teflon(RAF traversed by these rays is, material and, ignoring end reflection losses, Io and I are the assuming unpolarized light, the average of equations (4a) light intensity, or power, entering and leaving the material and (4b) above. For the worst case ray, the effective thick respectively. neSS is 1.4 um per reflection or 14 um for the full length of US 2005/0078308A1 Apr. 14, 2005

the flowcell. Using this value for b, and the value of a guide. This is the guided ray which experiences the largest calculated above, equation (3) gives the transmittance of the attenuation from wall absorption and is the one whose data guided light as 0.98. Rays making a Smaller angle with the are plotted in FIG. 3. axis have an even higher transmittance. These calculations 0046) If ten times the concentration of black dopant were indicate that with this absorption coefficient, which is suf used, giving a wall absorption coefficient of C=14 mm', ficiently large to block light transmitted through the dark transmittance of the worst case ray would drop to 82%, a ened Teflon(R) AF wall, attenuation of the guided beam is significant but tolerable loss. This allows reasonable latitude negligible. in Selecting the concentration of the opaque dopant, or alternatively, allows the dopant absorption coefficient to 0.043 FIG. 1 illustrates a single sample vessel 2 con vary by a factor often over the desired wavelength range and Structed using the invention for measuring light after it Still meet the necessary criteria. traverses the Sample. The Sample to be tested is placed in the cavity 6 of the vessel 2. An means for passage of light 10 is 0047 A preferred opaque dopant is chemically resistant provided in the walls 4 of vessel 2 to allow light to enter 16 to HPLC Solvents and pH range, and has as flat a spectrum and exit 16'. The means for passage of light may be an as possible over the wavelength region of interest, 200 to 800 nm. Carbon black has been incorporated into fused opening, a window, a lens or an optic fiber. Since the walls Silica to make “black quartz used to block Stray light paths 4 are formed of darkened Teflon(RAF, light having an angle in flowcells and cuvettes, particularly those used to analyze of incidence leSS than the critical angle, is guided down the fluorescence (See Hulme, U.S. Pat. No. 5,493.405; Fujita et cavity and some of the light is reflected off the end of the al., U.S. Pat. No. 6,106,777). In these cells, no light guiding cavity to be measured as it exits the cavity. Light that is involved because the wall material has a higher indeX than impinges on the end surfaces 11 of the walls 4 is absorbed the analytical fluid. However, as a material which blocks and does not interfere with the measurement. This vessel can transmitted light over a wide range of wavelengths, carbon be adapted for other configurations. An array of vessels 2 is a good choice for the present application to light guided can be constructed to test multiple Samples. If a window cells. Other materials could be used, such as finely divided replaces reflecting Surface 8, the measurement Sensor can be metal particles. Many different dopants could be used over placed opposite the light Source. This adaptation may prove more restricted wavelength ranges. advantageous for high Volume Screening of discrete 0048 FIG. 4 illustrates how a flowcell incorporating the samples. When the vessel 2 is further modified to allow invention may be constructed. The flowcell body 42 is through passage of a Sample fluid, a flowcell Such as constructed from a sealable material Such as PEEK in illustrated in FIG. 2 is formed. multiple parts. The tube of darkened Teflon(R) AF 44 is 0044 FIG. 2 illustrates the simplified design of a flow supported in part of the cell body 42. Fluid 38 enters the cell made possible using this invention. Tube 17 has dark body via capillary 40 and is brought to the tube cavity 43 by ened Teflon(EAF walls. Fluid under test enters at one end 18 channels 45 etched in metal gaskets 32 between the body of tube 17 and exits at the other end 19. Incident light 16, 24 parts 42. After passing through the tube 44, fluid is further is oriented at an angle within the NA of tube 17. The source directed through the metal gaskets 32 and out a fluid port 34. of light 19 is wider than the ID of the tube 17 and is aligned Light 36 enters the flowcell via an optic fiber 35 so as to with the axis. Light 16 that is oriented to enter the liquid traverse the fluid-filled tube cavity 43. At the exit side of the medium having an RI of n is guided down the cavity 15 tube 44, a window 30 allows light 46 to exit the flowcell because the angle of incidence, 0, is less than the critical toward the Sensor. It is evident that light passes along the angle. Light 24 that falls outside the cavity enters the cell length of the light guiding tube 44. In this flowcell, the parts walls 4, travels a small distance, and is absorbed. FIG. 2 of the metal gaskets 32 that cover the ends of the tube walls shows a simple window 26 at the exit of the light-guiding 44 are not critical for light blocking because the opacity of flowcell. This avoids matching and aligning an optical fiber the walls of tube 44 prevents stray light from entering the to the flow cell exit and leads to better optical efficiency. The fluid path. entrance to the flowcell can also be a window, with the light 0049. In one embodiment, finely-divided carbon black is focussed on the entrance. Rays hitting the walls 4 if the tube mixed with Teflon(R) AF 2400 resin in powder form. The 17 are absorbed as above. The design is simplified because carbon black concentration is on the order of 0.01%-1%. In masks are no longer needed at the end of the cell. Optical a preferred embodiment the carbon black concentration is efficiency is maximized because the whole of the fluid path approximately 0.1%. The resultant mixture is used to make croSS-Section can be flooded with light. “black' Teflon(E) AF tubing by extrusion or drawing using 004.5 FIG.3 shows the number of reflections (diamonds) well-established methods. The low level of carbon black made by a light wave undergoing total internal reflection does not materially affect the ability to fabricate tubing. from the inside wall of a Teflon(E) AF tube filled with water When the “black' Teflon(R) AF tubing is used in a light in the case calculated above to determine the effect on guiding flowcell, it blocks the transmission of light through transmittance. Also plotted is the “effective thickness” the cell walls So none of that Stray light can reach the (squares) of Teflon(R) AF material traversed by the light detector and cause errors in the measurement. during its passage through the light guide. This enables the 0050 “Lab-on-a-chip” structures, where certain channels attenuation of a beam of light to be calculated as it makes are fluidic connections, Separation columns and reaction multiple reflections down the tube. The data in FIG. 3 are chambers have been produced on planar Substrates. AS a plotted against numerical aperture, NA. NA defines the cone Second embodiment of the present invention, Strips of of rays entering the light guide. The most inclined ray makes “black' Teflon(E) AF are extruded in ribbon form, several an angle sin(NA) with the axis in air external to the light mm wide by about 1 mm thick. Sections of this are used as US 2005/0078308A1 Apr. 14, 2005 the Substrate to form patterns of channels by, for example, Said Sample and having an absorption coefficient hot embossing. Two Such Substrates bonded together, or one Sufficient to Substantially attenuate light propagating with an unstructured lid, are used to create "lab-on-a-chip' through Said at least one wall; and Structures with unique properties. Some channels in the chip are used as fluidic connections to other channels formed as at least one means for passage of transmitting light; Separation columns or the like. These can be connected to wherein light within Said cavity is guided by attenuated fluid containing light-guides created for detection. Windows total reflection into Said Sample. into light-guiding Sections are created and lengths of optical 2. The device of claim 1 wherein said vessel has at least fiber bonded into the sandwich to bring the needed light onto one fluid inlet for receiving Said Sample. the chip for attachment to the appropriate channel. Using 3. The device of claim 1 wherein said vessel has at least opaque “black” Teflon(RAF material as the Substrate blocks one fluid outlet for discharging Said Sample. Stray light and allows light-guiding detection channels to be 4. The device of claim 1 wherein Said means for passage constructed. In addition, the “black' Teflon(E) AF bulk mate of transmitted light is Selected from the group comprising an rial prevents any Stray light from the other Sections of the opening, a window, a lens and an optic fiber. chip from leaking light to the detection System. This 5. The device of claim 1 further comprising a reflective improves detector linearity, as previously discussed. Use of Surface opposite Said means for passage of transmitted light the light-blocking Substrate allows multiple light-guiding for returning Said light that has passed through Said Sample flowcells to be constructed on the Same chip, without back to Said means through said Sample. cross-talk. 6. The device of claim 1 further comprising means for 0051 FIG. 5 illustrates a simplified representation of a transmitting light to Said Sample and a window, opposite Said “lab-on-a-chip” made possible by the invention. Substrate means, for receiving light that has passed through Said 50 is formed from “black Teflon(E) AF. Channel 51 forms a Sample. fluidic connection from an entrance 52 to a channel 54 7. The device of claim 1 wherein a length of said cavity formed as a separation column. Light fibers 56 and 58 are is between 10 and 50 times an inner diameter of said cavity. bonded So as to form part of the end walls of light guiding 8. The device of claim 1 wherein said walls are formed of channel 60 used to measure the absorbance of a Sample Teflon(RAF fluoropolymer. passing through channel 60. The fluid exits the structure 9. The device of claim 8 wherein said Teflon(E) AF through channel 62. On the same Substrate, a Separate fluoropolymer is doped with black dopant. light-guiding flowcell allows measurement the absorbance 10. The device of claim 9 wherein said black dopant is of a fluid passing through channel 53 to channel 67 which is carbon black or finely divided metal particles. the measurement channel. Separate light fibers 68, 70 are 11. The device of claim 8 wherein a concentration of Said bonded to channel 67 to form the light entrance and exit. dopant is between 0.01 and 0.1% of said fluoropolymer. Because of the opacity of Substrate 50, light is confined to 12. The device of claim 8 wherein a concentration of Said the two light-guiding measurement channels 60, 67. dopant is approximately 0.1% of the fluoropolymer. 0.052 While the application of light-blocking low RI 13. A light-guiding apparatus comprising: material has been discussed in the context of absorption a fluid channel bounded by at least one wall, the compo measurement, the material is also applicable to light guiding Sition of Said at least one wall having an index of applications used for fluorescence and Raman detection. The refraction lower than an index of refraction of a fluid in opaque cell walls absorb unwanted excitation light which Said fluid channel and having an absorption coefficient enters or is Scattered into the cell walls. Sufficient to Substantially attenuate light propagating 0053. The material has been discussed in the context of a through Said walls, cuvette formed of an optically transparent material drawn into the form of a cylindrical thin-walled capillary as used in an entrance for light, Said entrance perpendicular to an absorbance measurement. However, further applications of axis of Said channel; the “black' Teflon(E) AF form the cuvette into a container an exit for light, Said exit perpendicular to Said axis, and with a reflective Surface opposite a light entering window/ opening or a vessel with transparent windows opposite each fluid inlet and outlet ports, whereby said walls and fluid other. effect guiding of Said light by attenuated total reflec tion, Said walls having minimal absorptive effect on the 0054. It is understood that various modifications may be guided light. made to the embodiments disclosed herein. Therefore, the 14. The light-guiding apparatus of claim 13 wherein Said above descriptions should not be considered limiting, but walls are formed in a hollow tube. merely as exemplifications of the various embodiments. 15. The light-guiding apparatus of claim 13 wherein Said Those skilled in the art will envision other modifications walls have an absorption coefficient in the range of 0.1 to within the Scope and Spirit of the claims appended hereto. 100 mm at a wavelength within a wavelength range of UV, 1. A device for receiving one or more Samples and visible and near IR. measuring light emitted or refracted therefrom comprising: 16. The light-guiding apparatus of claim 13 wherein Said walls are formed of Teflon(E) AF fluoropolymer. a vessel with a cavity for containing a Sample during a 17. The light-guiding apparatus of claim 16 wherein Said measuring process, Said vessel comprising: Teflon(RAF is doped with black dopant. at least one wall in fluid contact with Said Sample, Said 18. The light-guiding apparatus of claim 17 wherein Said wall having a composition having an index of refrac black dopant is carbon black or finely divided metal par tion lower than an index of refraction of a fluid in ticles. US 2005/0078308A1 Apr. 14, 2005

19. The light-guiding apparatus of claim 18 wherein a to determine a Sample concentration and a Sample identity, concentration of said black dopant is between 0.01%-1% by Such that unwanted Scattered excitation light entering Said weight of the fluoropolymer. conduit wall is Suppressed and does not reach a detector. 20. The light-guiding apparatus of claim 19 wherein Said 26. A Set of light-guiding flowcells for a fluid comprising: dopant concentration is approximately 0.1% of the fluo ropolymer. a Set of channels formed in a Substrate of material having 21. The light-guiding apparatus of claim 13 wherein the an index of refraction lower than an index of said fluid apparatus is a flowcell. and an absorption coefficient Sufficient to Substantially 22. The light-guiding apparatus of claim 13 wherein Said attenuate light propagating through Said material; fluid inlet and outlet ports are configured off Said axis. a set of channel covers formed in a Section of material 23. An apparatus for housing a liquid Sample and for having an index of refraction identical to Said Substrate exposing Said liquid Sample to light, Said apparatus com material and an absorption coefficient Sufficient to prising: Substantially attenuate light propagating through Said a conduit having a wall formed of an amorphous fluo material, Said Set of channel covers fixed to Said Set of ropolymer having a refractive indeX leSS than the channels forming a set of covered channels, refractive index of water and having an absorption at least one covered channel having a fluid inlet and outlet coefficient of a magnitude Such that when Said conduit port configured off an axis of Said covered channel; is filled with water, visible light and ultra-violet light can be transmitted, Substantially without loss, along an at least one covered channel having a Source of light at a axis of Said conduit by attenuated total reflection and light entrance end and having a light exit end; visible light and ultra-violet light are substantially whereby said at least one covered channel and fluid effect completely absorbed in passage through the wall of guiding of Said light by attenuated total reflection and Said conduit. Said at least one covered channel has minimal absorp 24. A method of performing photometric analysis of a tive effect on Said light guided by internal reflection. liquid Sample comprising: 27. The set of light-guiding flowcells of claim 26 further comprising an optical fiber bonded to at least one covered introducing Said liquid Sample into a conduit having a channel providing Said light Source. wall formed of an amorphous fluoropolymer having a 28. The set of light-guiding flowcells of claim 26 whereby refractive indeX less than a refractive index of water the material forming said closed channels prevents light and having an absorption coefficient Sufficient to Sub crosstalk between flowcells. Stantially attenuate light propagation through Said wall; 28. The set of light-guiding flowcells of claim 26 wherein Shining light axially onto Said conduit filled with Sample at least one covered channel is configured as a separation liquid; column. 29. The set of light-guiding flowcells of claim 26 wherein receiving light transferred through said liquid Sample at a at least one covered channel is configured as a fluidic detector; and connection. determining a concentration of Said Sample in Said liquid 30. The set of light-guiding flowcells of claim 25 wherein by light absorption by the sample, whereby linearity of said Substrate and said section are formed of Teflon(E) AF detection is improved. fluoropolymer doped with a black dopant at a concentration 25. The method of claim 24 whereby said light shining of between 0.01-0.1% of the fluoropolymer. axially is at an excitation wavelength and Said light trans ferred is emitted fluorescence or Raman Scattered light used k k k k k