Abstract:
The present invention relates to apparatus and devices ( 11 ) for placing light with samples for analysis and method of making and using such apparatus and device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 60/602,535, filed Aug. 18, 2004. The contents of these applications are incorporated herein by reference. 
     STATEMENT REGARDING FEDERALLY FUNDED RESEARCH AND DEVELOPMENT 
     Not Applicable 
     FIELD OF THE INVENTION 
     Embodiments of the present invention relate to apparatus and devices that produce a signal corresponding with an interaction of light with a sample. 
     BACKGROUND OF THE INVENTION 
     Embodiments of the present invention relate to devices that use light for the purpose of analysis. These devices and apparatus are used as detectors. It is convenient to refer to light as comprised of photons and this application will use the terms light and photons interchangeably. In such devices light is introduced into a vessel containing a sample; light leaving the vessel is measured. The absence or dimunition of light of a particular wavelength, present upon entry into the vessel suggests absorption of light by the sample or a constituent within the sample. The presence of light at an intensity or at a wavelength not present upon entry into the vessel suggests a shift in wavelength. These changes in the light entering and leaving a vessel are characteristic of the compounds in the sample. 
     The term “sample” is used in the broadest sense to indicate something that one wishes to evaluate. Samples can originate with industrial materials, chemical synthesis, or may have originated from biological sources. 
     Vessels which receive a flow of sample over time and subject such sample flow to light for analysis purposes are called optical flow cells. These vessels can comprise a length of conduit of similar dimensions or may represent a broadening or narrowing of the conduit. Such vessels typically will have inlets and outlets for sample and inlets and outlets for light. 
     Chromatography is the science of separations based on differences in affinity that different compositions have to an stationary phase. High performance liquid chromatography (HPLC) is performed in columns or cartridges. Solutions in which samples are dissolved are pumped through the columns or cartridges. The columns and cartridges conduits have an inert stationary phase. The components of the sample separate as they move through the stationary phase. It desirable to detect the separated components with a detector. 
     This application will use the term HPLC as referring to separations at pressures up to approximately 3,000 pounds per square inch (psi). At higher pressures, it is possible to perform sharper better defined separations with greater speed. However, higher pressures, referring now to the ultra high pressure range, approximately 4,000 psi to 15,000 psi, places extreme demands on equipment. 
     Mechanical stresses brought on by high sample pressures and the need for sample-wetted materials that resist the wide variety of HPLC solvents and samples can result in optical-fiber based flow cell designs that are difficult to manufacture. The end of a optical fiber placing light in or taking light out may need to be subjected to the ultra high pressure. The optical fiber, in these situations, is difficult to secure. The optical fiber must also be shielded from extraneous light. The flow cell vessel must also create a flow of sample in which all the sample is exposed to an equal amount of light; that is, there are no dead volumes. These difficulties are compounded by the small scale of the devices. It is desirable to have optical sensors which have small volumes. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to devices, apparatus and methods of making and using such devices and apparatus that employ light detection or sensing methods for analysis. The devices and apparatus of the present invention are well suited for applications at high and ultra-high liquid chromatography pressures. 
     One embodiment of the present invention features a device for connecting an optical fiber to a high pressure containment vessel. The device comprises a housing having an exterior surface and an optical fiber bore. The optical fiber bore has a first opening and a second opening. The first opening is for receiving and substantially engaging in sealing relationship one end of a optical fiber to form a fiber optic coupling surface on the exterior surface of said housing. The second opening is for receiving the optical fiber extending from the first opening and for receiving a potting material to secure the optical fiber in the optical fiber bore. 
     As used herein, the phrase “substantially engaging in sealing relationship” means the opening with the optical fiber does not leak excessively when the potting material is placed in the optical fiber bore. 
     Preferably, the device further comprises an optical fiber substantially engaged in sealing relationship in said first opening. And, more preferably, the device comprises a potting material within said optical fiber bore to secure said fiber. 
     Preferably, the device further comprises an optical fiber sleeve. The optical fiber sleeve is a cylindrical form that extends into the optical fiber bore to align, position and protect the optical fiber. The sleeve also complements the potting material in effecting a bonding of the optical fiber to the fiber bore. 
     Particularly for flow cell applications, a preferred device has a housing having a least one capillary bore. The capillary bore has a first capillary opening and a second capillary opening. The first capillary opening is for receiving and substantially engaging in sealing relationship one end of a capillary to form a capillary coupling surface on the exterior surface of said housing. The second capillary opening is for receiving the capillary extending from the first capillary opening and for receiving a potting material to secure the capillary in the capillary bore. 
     As used herein, the term capillary is used in a broad sense to refer to any pipe or tube or conduit unless the context of the sentence requires otherwise. Embodiments of the present invention are ideally suited for capillary scale conduits. That is, conduits having extremely small diameters. 
     Preferably, the device further comprises a capillary engaged in sealing relationship in said first capillary opening. And, preferably, the device comprises a potting material within said capillary bore to secure said capillary. One preferred embodiment is a device further comprising a capillary sleeve. The capillary sleeve extending into the capillary bore to align, position and protect the capillary. 
     Embodiments of the present invention are directed to flow cells and optical connectors to flow cells. Preferably, the housing has a flow cell receiving surface about the capillary opening and the optical fiber opening for affixing to a flow cell. The optical fiber has a light path, defined by light passing through its length. The flow cell has a chamber for receiving or discharging fluid into the capillary opening and the chamber is constructed and arranged with respect to the light path to receive or pass light from the optical fiber. 
     Preferably, the device further comprises a gasket. The gasket is affixed to the flow cell receiving surface to convey fluids and seal gaps between the housing and the flow cell. Preferably, gasket has a channel between the capillary opening and the optical fiber opening to direct fluid into or receive fluid from the chamber. This feature is particularly useful where the chamber has a wall comprised of a material having a lower refractive index than aqueous solutions. Sample fluids in the life sciences are often aqueous solutions. In this case, the light is efficiently guided down the chamber due to total internal reflection. That is, the wall is comprised of a material with a refractive index less than 1.333 at 589 nm. The gasket has a gasket opening to allow the passage of light into the chamber. The gasket opening is aligned with the light path of the optical fiber. The gasket is comprised of an opaque or reflective material positioned in the flow cell along the light path in one or more of the of the following positions: a.) to block light leaving the optical fiber and entering the wall material and b.) to block light that may enter the wall material from subsequently entering the optical fiber. 
     Materials which exhibit a low refractive index include amorphous fluorocarbon polymers. 
     A further embodiment of the present invention is a device for placing light into a sample in the nature of a flow cell. The device comprises a sample containment vessel having a chamber for containing sample and receiving light traveling a light path. The chamber has at least one wall parallel to the light path having a layer of a material having a refractive index less than the sample fluid, to form a light guide. The chamber has a light entrance for receiving light. The light entrance has a rim of the material with the low refractive index. The device further comprises a gasket covering the rim. The gasket has a gasket opening to allow light to enter or leave the chamber via the optical fiber. The gasket is opaque or reflective and the opening sized to light to prevent light from entering the material from the optical fiber or the optical fiber from receiving light from the material. Light that has passed through the wall material and is subsequently detected by the light sensing means is known to alter the signal from the sample. Such effect diminishes detection sensitivity. 
     Preferably, the device has a chamber with single entrance for receiving sample and light. And, preferably, the gasket has a channel for transporting sample to or away from said entrance. Such gasket has a connector surface for receiving a optical fiber connector with means for introducing sample into the channel. Thus, the device, in the form of a flow cell is affixed to a optical fiber connector with the gasket interposed there between. 
     A further embodiment of the present invention is directed to a gasket. The gasket has a composition of a opaque or reflective material. The gasket is for sealing a connection between a connector and a containment vessel. The connector is for placing light and a sample in the containment vessel. The containment vessel is for holding sample while the sample is subjected to light. The connector has a first opening for receiving or discharging sample, and a light emitting or receiving end of a optical fiber. The containment vessel has a single entrance for receiving or discharging light and sample. The entrance has a rim of a material having a refractive index less than water. The gasket has a first planar surface and a second planar surface, a opening and channel means. The opening is for allowing the passage of light and sample into the chamber. The gasket opening is in communication with the channel means. The channel means is in at least one of the first planar surface and second planar surface. The channel is for placement in communication with the first opening and the end of said optical fiber. The gasket covers and shields the rim from light from the optical fiber or shields the optical fiber from light from the rim. 
     Preferably, the gasket further comprises keying means to align said gasket with one or more features of the connector and the containment vessel. 
     Preferably, the channel is a groove extending between the first opening and the end of the optical fiber. The end of the optical fiber also corresponds to the gasket opening. 
     Embodiments of the present invention also feature a method of making a connector for an optical fiber. The method comprises the steps of providing a housing having an exterior surface and an optical fiber bore. The optical fiber bore has a first opening and a second opening. The first opening is for receiving and substantially engaging in sealing relationship, one end of a optical fiber to form a fiber optic coupling surface on the exterior surface of the housing. The second opening is for receiving the optical fiber extending from the first opening and for receiving a potting material to secure the optical fiber in the optical fiber bore. The method further comprises the step of placing a optical fiber in the first opening and extending through the second opening. And, the method comprises the step of placing a potting material in the second opening and allowing said potting material to substantially fill the optical fiber bore to secure the optical fiber. 
     A preferred potting material is a polyarylketone and ethylenes, such as polyetheretherketone (PEEK). Other potting materials comprise polytrifluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy (PFA), and fluoronated ethylenepropylene (FEP). 
     Preferably, the method further comprises the step of fitting an optical fiber sleeve into the optical fiber bore to align, position and protect said optical fiber prior to placing the potting material in the second opening. 
     Preferably, the method further comprises steps to secure capillaries and conduits. For example, without limitation, wherein the housing has a least one capillary bore, and the capillary bore has a first capillary opening and a second capillary opening, the first capillary opening receives and substantially engages in sealing relationship one end of a capillary to form a capillary coupling surface on the exterior surface of said housing. The second capillary opening receives the capillary extending from the first capillary opening. And, the method comprises the step of placing a potting material to secure the capillary in the capillary bore. 
     Preferably, the method further comprising the step of affixing a gasket to the housing or to the flow cell to which the housing will be attached. Preferably, the gasket has a channel, between the capillary opening and the optical fiber opening, to direct fluid or receive fluid from a chamber of a flow cell. 
     And, preferably, the chamber has a wall comprised of a material having a lower refractive index than aqueous solutions. The gasket is preferably comprised of an opaque or reflective material positioned along the light path. The gasket preferably blocks the light from traveling from the optical fiber from entering the material or blocks light traveling through the material from entering the optical fiber. Materials with low refractive indexes material include several amorphous fluorocarbon polymers. 
     Thus, embodiments of the present invention include methods of preventing stray light from entering a flow cell or from being discharged from a flow cell. Such method comprises the steps of providing a flow cell having a sample containment vessel. The vessel has a chamber for containing sample and receiving light traveling a light path. The chamber has at least one wall parallel to the light path having a layer of a material having a refractive index less than water to form a light guide. The chamber has a light entrance for receiving light with the entrance having a rim of the material. The method further comprises the step of fitting a gasket to cover the rim. The gasket is opaque or reflective to the light to prevent light from entering the material or from leaving the material. 
     These and other features and advantages of the present invention will be understood by individuals skilled in the art upon viewing the drawings and reading the detailed description of the invention that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts, in cross section, an apparatus for placing light in a sample embodying features of the present invention. 
         FIG. 2  depicts, in cross section, a connector embodying features of the present invention. 
         FIG. 3  depicts a top view of a gasket embodying features of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment of the present invention will be described in detail as methods, devices and apparatus for transmitting light into or receiving light exiting a vessel. Embodiments have particular application in situations in which the vessel contains fluid under high pressure. Optical fibers are difficult to secure and maintain optical transparency. Individuals skilled in the art will readily appreciate that the present invention has broad applications to situations where it is desirable to secure optical fibers for other purposes as well. 
     Turning first to  FIG. 1 , an apparatus, in the form of a flow cell, that embodies features of the present invention, is depicted generally designated by the numeral  11 . The apparatus  11  has the following major elements: a vessel  13 , vessel wall  17 , first gasket  19   a , second gasket  19   b , and a first connector device  21   a  and a second connector device  21   b.    
     The vessel wall  17  defines a chamber  25  for containing fluid, such as sample, under pressure. Embodiments of the present invention can withstand pressures greater than 4,000 psi and up to 15,000 psi. Light and sample are introduced into and taken out of the chamber  25  through at least one of the first connector device  21   a  and second connector device  21   b.    
     First connector device  21   a  and second connector device  21   b  are identical to facilitate the manufacture of the flow cell  11 . First connector device  21   a  and second connector device  21   b  are for connecting optical fibers  29   a  and  29   b  respectively to vessel  13 . Each first connector device  21   a  and second connector device  21   b  has a connector housing  31  having an exterior surface  33  and an optical fiber bore  35 . 
     This discussion will describe first connector  29   a  in detail for the purpose of clarity with the understanding the discussion applies to second connector  29   b  as well. Turning now to  FIG. 2 , first connector device  21   a  has a housing  31  shown in cross section. Housing  31  has a optical fiber bore  35  having a first opening  37  and a second opening  39 . The first opening  35  is for receiving and substantially engaging in sealing relationship one end of optical fiber  29   a . A fiber optic coupling surface  41  is formed on the exterior surface  33  of said housing  31 . There are well-known techniques such as optical polishing for producing a high quality optical finishes on the fiber coupling surface  41 . 
     Preferably, the housing  31  is made of metal or rigid plastics. A preferred material is stainless steel. The dimensions will be influenced by the size of the vessel  15 . A typical size is approximately 0.3 to 0.6 inches in diameter and similar dimensions in depth. The housing  31  fits to a vessel  13  appropriately sized in diameter and approximately 10 mm in length. 
     Returning now to  FIG. 1 , the second opening  39  is for receiving the optical fiber  29   a  extending from said first opening  37 . A potting material  45  in optical fiber bore  35  secures the optical fiber  29   a . Receiving and substantially engaging in sealing relationship, with respect to the optical fiber  29   a  in first opening  37  means that the potting material  45  does not leak excessively during the potting operation. 
     Preferably, during the potting operation, the potting material  45  is placed around the optical fiber  29   a . The optical fiber  29   a  is in place or is placed in the first opening  37  with the potting material  45  and the housing heated to a temperature that allows the potting material  45  to flow and occupy optical fiber bore  35 . 
     Preferably, the connector device  21   a  has a optical fiber sleeve  47  as best seen in  FIG. 2 . Optical fiber sleeve  47  has a cylindrical shape with an exterior diameter less than the optical fiber bore  35  and greater than the diameter of the optical fiber  29   a . Optical fiber sleeve  47  is placed into said optical fiber bore  35  and receives optical fiber  29   a  and potting material  45  to align, position and protect the optical fiber  29   a.    
     The connector device  21   a  has a least one capillary bore  51 . Capillary bore  51  has a first capillary opening  53  and a second capillary opening  55 . First capillary opening  53  is for receiving and substantially engaging in sealing relationship one end of a capillary  57  to form a capillary coupling surface  59  on the exterior surface  33  of housing  31 . The second capillary opening  55  is for receiving capillary  57  extending from said first capillary opening  53 . Capillary  57  can be sized to tightly fit the capillary bore  51  and be able to withstand pressures of greater than 4,000 psi and up to 15,000 psi. 
     For some applications it may be useful to increase the size of capillary bore  51  and second capillary opening  55  for receiving a potting material [not shown] in the manner described with respect to the optical fiber bore  35 , to secure the capillary  55  in the capillary bore  51 . And, for some applications, it is useful to use a capillary sleeve [not shown] in the manner of the optical fiber sleeve  47 . The capillary sleeve is a cylindrical form sized with an exterior diameter less than the capillary bore  51  and an interior diameter greater than the diameter of the capillary  57 , the capillary sleeve extending into the capillary bore to align, position and protect the capillary. 
     Housing  31  has a flow cell receiving surface  61  about the capillary first opening  53  and said optical fiber first opening  37  for affixing to a flow cell vessel  15 . Turning now to  FIG. 1 , flow cell  15  has a corresponding housing receiving surface  63   a  and  63   b  for connector device  21   a  and  21   b  respectively. The optical fiber  29   a  has a light path on axis (illustrated with arrows) and optical fiber  29   b  receives light along a light path after such light has traversed chamber  25 . Sample in the chamber  25  will alter the nature of the light received by optical fiber  29   b.    
     Chamber  25  is in fluid communication with capillaries  57   a  and  57   b  of the first connector device  21   a  and second connector device  21   b  to receive and discharge sample fluid. First gasket  19   a  is interposed between the vessel  15  at housing receiving surface  63   a  and flow cell receiving surface  61   a . Similarly second gasket  19   b  is interposed between the vessel  15  at housing receiving surface  63   b  and flow cell receiving surface  61   b . First gasket  19   a  and second gasket  19   b  convey fluids and seal gaps between the housings  31  of connector devices  21   a  and  21   b  and the flow cell. 
     At least one of the first gasket  19   a , second gasket  19   b , flow cell receiving surface  61  and housing receiving surface  63  have channel means to convey fluid between the respective capillary  57   a  or  57   b  and chamber  25 . A preferred channel means is a channel  67   a  and  67   b  in first gasket  19   a  and second gasket  19   b  respectively. 
     Turning now to  FIG. 3 , gasket  19   a  has a light opening  71  and a channel  67   a . The groove  67   a  extends to a position in communication with capillary opening. Gasket  19   a  is intended to be positioned with the channel  67   a  against the flow cell receiving surface  61  of the connector housing  31 . However, in the event it is desired to place channel  67   a  against the housing receiving surface  63  or the vessel  15 , a sample opening [not shown] is provided in gasket  19   a . In order to align the channel  67   a  and opening  71 , gasket  19   a  has keying means in the nature of holes  73 . Holes  73  cooperate with pins  79  as best seen in  FIG. 1 . 
     In the alternative, channel means in the form of a groove [not shown] can be provided in the flow cell receiving surface  61 , or the housing receiving surface  63  in which case the gasket  19   a  can omit the channel  67   a . Thus, the vessel  15  receives light and sample through a single entrance, and discharges light and sample through a single exit. 
     The chamber  25  of vessel  15  has a wall  17  of cylindrical form in which the cylinder axis is aligned with the light path. The wall  17  has a composition having a lower refractive index than aqueous solutions. One such material is an amorphous fluorocarbon polymer. One such material is sold under the trademark Teflon AF (Dupont). The wall having a low refractive index reflects light impinging on the wall  17  back into the chamber  25 . The wall  17  extends the length of the vessel  15  and forms a first rim  75   a  and a second rim  75   b  at the edges. Light entering the first rim  75   a  can interfere with the signal generated by the flow cell  11 . Light exiting the second rim  75   b  also interferes with the signal. 
     First gasket  19   a  and second gasket  19   b  are comprised of an opaque material. A preferred material is a metal capable of being readily etched to provide a channel. First gasket  19   a  is positioned along the light path to block the light from traveling from said optical fiber  29   a  from entering material of which wall  17  is made. Second gasket  19   b  is positioned along the light path to block light traveling through the material from entering the optical fiber  29   b . Optical fiber  29   b  would normally in communication with a photon detector [not shown]. 
     The flow cell  11  further comprises a pressure assembly  81 . Pressure assembly  81  has base  83  having a hollow  85  having an abutment ridge  87  for receiving second connector  21 . Second gasket  19   b , vessel  17 , first gasket  19   a , and first connector  19   a  are stacked within the hollow  85 . Affixing means in the form of a nut  89  compresses the elements held in hollow  85  to effect sealing. The flow cell  11  can receive sample at pressures of 4,000 psi and up to 15,000 psi. 
     Thus, we have described an apparatus for placing light into a sample. The apparatus has a vessel  15  having a chamber  25  for containing sample and receiving light traveling a light path. The chamber  25  has at least one wall  17  parallel to said light path having a layer of a material having a refractive index less than water to form a light guide. The chamber  25  has a light entrance in the form of optical fiber  29   a  for receiving light at the entrance having a rim  75  of the material. A first gasket  19   a , opaque or reflective to the light, covers the rim  75   a  to prevent light from entering said material. A second gasket  19   b , opaque or reflective to light, covers the rim  75   b  to prevent light from entering second optical fiber  29   b.    
     The flow cell  11  has a chamber  25  in which sample and light have a common entrance through first gasket  19   a  having a channel  67   a  for transporting sample to the chamber  25 . Similarly the flow cell  11  has a chamber  25  in which sample and light have a common exit through a second gasket  19   b  having a channel  67   b  for transporting sample from the chamber  25 . 
     Thus, we have disclosed a method of making a first connector  21   a  and second connector  21   b  for optical fiber  29   a  and  29   b  respectively. The method comprises the steps of providing a housing  31  having an exterior surface  33  and an optical fiber bore  35 . The optical fiber bore  35  has a first opening  37  and a second opening  39 . The first opening  37  is for receiving and substantially engaging in sealing relationship one end of a optical fiber  29   a  to form a fiber optic coupling surface  41  on the exterior surface  33  of the housing  31 . The second opening  39  is for receiving the optical fiber extending from said first opening  37  and for receiving a potting material  45  to secure said optical fiber  29  in the optical fiber bore  35 . The method further comprises the step of placing a optical fiber  29  in the first opening  37  and extending through said second opening  39  and placing a potting material  45  in the second opening  39  and allowing the potting material  45  to substantially fill the optical fiber bore  35  to secure the optical fiber  29 . 
     The method may be extended to capillaries wherein said housing  31  has a least one capillary bore  51 . The capillary bore  51  has a first capillary opening  53  and a second capillary opening  55 . The method further comprising the steps of placing a capillary  57  in the first capillary opening  53  and extending through the second opening  55  and placing a potting material  45  in the second capillary opening  55  to secure the capillary  57 . 
     Thus, we have disclosed a method of preventing stray light from entering a chamber  25  of a flow cell  11  or from being discharged from a chamber  25  of a flow cell  11 . The method comprises the steps of fitting a first gasket  19   a  or a second gasket  19   b  to cover a rim  75   a  or  75   b  respectively. 
     We have disclosed preferred embodiment of the present invention which embodiments are capable of modification and alteration without departing from the teaching and spirit of the invention. Thus, the present invention should not be limited to the precise detail herein but should encompass the subject matter of the following claims and their equivalents.