The subject technology relates to fluid analysis assemblies using flow cells in analytical fluid chemistry applications such as spectrophotometry. More specifically, the subject technology relates to improved devices and methods for fabricating and sealing flow cells.
One type of conventional flow cell is described in U.S. Pat. No. 6,526,188 (the '188 patent). The major components of the '188 patent cell include: a module containing at least one optical fiber that transports light from a remote light source; a second similar module incorporating a conduit made of TEFLON® AF 2400 amorphous fluoropolymer (Dupont); and a third module that contains an optical fiber that collects light that has been transmitted through the conduit.
Alternatively, in the case of a window terminating the flow cell, the fluid path is incorporated into the module containing the fluoropolymer conduit. These approaches use PEEK™ polyetheretherketone (Victrex PLC, Lancashire, UK) as the injection moldable adhesive to form the various modules. PEEK™ polyetheretherketone is a suitable material because it has some compliancy so that the modules can, after suitable registration, form a flow cell capable of withstanding substantial pressures. Other known variations include a metal body containing the conduit and a metal housing for the module containing the fiber optic and capillary lines. The optical throughput efficiency of this cell is dependent upon the spatial registration of the modules. The tradeoff is low optical losses at the expense of demanding manufacturing specifications for the molded parts. Minimum separation between the optical fiber and light guiding fluid conduit is important when considering the efficient transfer of radiation from one light-bearing conduit to another.
One significant disadvantage of prior art flow-cell design is the potential for introducing light into the walls of the light guiding conduit. It is well known that such light can result in reduced dynamic range in quantifying analyte levels. That is, not all the light, which is received by the detector has passed through the fluid sample. This unwanted radiation is known as stray light.
Another conventional flow cell is disclosed in U.S. Pat. No. 7,298,472 (the '472 patent). The '472 patent discloses a flow cell assembly consisting of the known modules described above, however, in certain instances, metal is substituted for PEEK™ polyetheretherketone as the material of construction. The fluidic and optical conduits of the '472 patent are secured within the metal modules by different techniques. With regard to the fluidic conduits, PEEK™ tubing critically sized to corresponding undersized metal holes in the metal modules are used. As the PEEK™ tubing is pulled through these holes, it is necked down and remains under compression by the resulting interference fit.
Alternatively, the amorphous-fluoropolymer optical conduit is encased within another compliant TEFLON® tube, which as an assembly is pulled through another central hole of critical size within the flow cell module. This approach, in which a succession of interference fits are used to secure tubing members within the flow cell module, was earlier employed in U.S. Pat. No. 6,526,188 which discloses that the TEFLON® AF tube is accurately located within a PEEK™ body (or PEEK™ tube which itself is secured by an interference fit within a metal body) by locating it within an intermediate tube of complementary dimensions. This intermediate tube material can be PEEK™ material or other chemically inert materials such as a known fluorinated hydrocarbon (e.g., TEFLON® PFA perfluoroalkoxy polymer or TEFZEL® ethylene tetrafluoroethylene (ETFE) fluoropolymer (DuPont)).
In the '472 patent, a compliant intermediate gasket has etched features establishing the fluidic connection between the fluid conduits and the central amorphous-fluoropolymer light guiding tube. Whereas in the '188 patent, the means for establishing the fluidic connection between the fluid conduits and the central light guiding tube is accomplished by creating a connecting channel at the end surface of the cell body module. In the '472 patent, an etched trench in the intermediate gasket is created that extends from an off-center hole to a centrally located hole whose aperture matches that of the lumen of the amorphous-fluoropolymer conduit.
Fluid-connecting etched trenches are well-known for example in the field of planar fluidic circuits. The aperture-matching requirement is again needed to prevent stray light from entering the wall of the amorphous fluoropolymer tubing. A compliant gasket is needed to form the hydraulic seal between the otherwise hard, non-resilient surface of the metal modules or the hard exit window terminating the flow cell. The compliant gasket is formed either from a single material having the requisite compliancy, such as KAPTON® polyimide film (available from DuPont Electrical Technologies of Circleville, Ohio) or another suitably coated metal substrate. In the case of the known naturally compliant gasket, the required features (e.g., holes, passageways) are etched into the material itself, whereas for the overcoated metal gasket only the metal is etched. The compliant material is later deposited.
As discussed above, the addition of a compliant material to an etched metal gasket is also well-known in the art. Although a compliant gasket offers advantages in certain cases, there are inherent problems with this approach. First, the naturally compliant gasket affords limited material choices when consideration is given to methods for fabricating the actual features or fluid passageways into this form of gasket. For example, although native KAPTON® polyimide film can be configured with such features, its optical transmission properties are such as to render it useless for preventing light of wavelengths longer than about 300 nm from entering the walls of the light guiding conduit, thereby leading to stray light. This amount of stray light would be unacceptable for applications requiring analyte detection within the 190-800 nm range of wavelengths and longer.
A metal gasket overcoated with a compliant material largely overcomes the stray light problem. However new design issues are introduced. The first of these is the fill-in factor associated with any overcoating process. In other words, the cross-section profile of the added layer cannot be expected to match that of the compliant metal substrate. As a result, the dimensional characteristics of fine features such as holes or etched channels are modified. Specifically, such dimensions become smaller in some proportion to the thickness of the coated layer. In cases where fill-in is objectionable, the overcoated material within and adjacent the central thru-hole has to be removed, for example, by subsequent laser ablation techniques, which adds cost in terms of production time and yield. Although a thinner coating would appear to solve this problem, there is a practical limitation on how thin this added resilient layer can be made and still effect the necessary hydraulic seal.
A second problem with known overcoated gaskets is the finite thickness of the compliant gasket. The efficient transfer of light radiation from the input fiber to the lumen in the amorphous fluoropolymer and again, from the lumen to the exit module, depends upon the thickness of the gasket. It can be appreciated that as gasket thickness increases less light is transferred into and out of the lumen, thereby compromising analyte detection.
The subject technology relates to devices and methods for constructing flow cells for the analysis of small samples in solution. The subject technology includes sealing means for containing a high-pressure fluid and facilitating the efficient transfer of radiant energy through the flow cell. Flow cells of high optical throughput and low internal volume are contemplated by the subject technology, with particular application to flow cells, which employ light guiding means.
One advantage of the subject technology is the modular flow cell having high optical throughput with efficient transfer of radiant energy between flow cell modules while minimizing stray light. Hydraulic seals are provided herein, such as O-ring seals, eliminating the need for resiliently coated metal gaskets.
Another advantage of the subject technology is the use of precision etched metal discs whose accurately etched apertures and channel dimensions are preserved and whose thickness is minimized for optimum transmission of radiant energy between flow cell components, without the need for additional processing steps. It is an object of the subject technology to utilize cost effective assembly and fabrication processes for simplifying flow cell construction.
An additional advantage of the subject technology is an alternative means for sealing of flow cell modules or components constructed from rigid materials not involving resiliently-coated metal gaskets suitable for use with a broader range of lumen diameters, particularly to those having diameters less than about 0.1 mm (such lumens preferably being defined by an amorphous fluoropolymer, such as TEFLON® AF 2400 amorphous fluoropolymer, whose refractive index is less than that of a sample fluid in the lumen.)
It is another object of the subject technology to provide an alternative means for securing an optical fiber conduit within a flow cell module.
The subject technology is directed to a flow cell for a photometric device including a first module having a first body with a distal face defining a first annular channel. The first body also defines an axial central passage and at least one axial flow channel. A second module has a second body with a proximal face defining a second annular channel. The second body also defines at least one axial flow channel in fluid communication with the at least one axial flow channel of the first module. A first light guiding member is disposed within the axial central passage for exposing a fluid passing between the flow channels of the first and second modules to a desired wavelength range of light. To analyze the fluid, a second light guiding member e.g. TEFLON® AF, is disposed within the second module, and provides the remaining light from the first light guiding member to a detector outside of the flow cell. An assembly seals an interface between the distal and proximal faces such that the fluid does not leak from the flow channels. The assembly has a metal gasket between the distal and proximal faces, the metal gasket defining a flow path between the flow channels, a first compliant sealing member in the first annular channel as well as a second compliant sealing member in the second annular channel.
The flow cell of the subject invention further provides a first body that defines first and second axial flow channels and the second body having a second distal face defining an annular channel. The second body also defines first and second axial flow channels in fluid communication with the first and second axial flow channels of the first body, respectively. The flow cell may further include a third module having a distal face and a third proximal face defining an annular channel and a second assembly for sealing an interface between the distal and proximal faces of the second and third modules, respectively. The second assembly having a second metal gasket between the distal and proximal faces, the second metal gasket defining a second flow path between the first and second axial flow channels of the second body, a third compliant sealing member in the annular channel of the second distal face, and a fourth compliant sealing member in the annular channel of the third module. The third module may be a window or lens module.
The subject technology provides a method for securing the fiber whereby a collar is overmolded onto the optical fiber. The collared assembly is then pressed into a receiving bore of the corresponding flow cell module without imparting any direct stresses into the fiber. In this way, known low-cost manufacturing methods (e.g., molding, pressing) can be utilized.
One embodiment of the subject technology comprises a flow cell for a photometric device including a first module having a distal face defining a first annular channel. A second module has a proximal face defining a second annular channel and a light guiding member disposed within a central passage for exposing a fluid to a desired wavelength range of light. An assembly for sealing at least one flow channel is defined between the distal and proximal faces. The assembly comprises a metal gasket defining holes in fluid communication with the at least one flow channel. A first compliant sealing member is in the first annular channel for sealing a proximal face of the metal gasket and a second compliant sealing member is in the second annular channel for sealing a distal face of the metal gasket. The metal gasket may be etched to form the at least one flow channel. The first and second compliant sealing members may be selected from oval rings, circular rings, oval rings with flats, and square rings having rounded edges, or fabricated from so-called form-in-place resilient materials.
In another embodiment of the subject technology, a flow cell for a photometric device includes a first module having a distal face with a compliant coating selectively applied around a central passage. A second module has a proximal face with a compliant coating selectively applied thereto and a first light guiding member is disposed within the central passage for exposing a fluid to a desired wavelength of light. The flow cell further comprises a metal gasket assembly for sealing at least one flow channel defined between the distal and proximal faces. The metal gasket defines holes in fluid communication with the at least one flow channel.
In still another embodiment of the subject technology, a light guiding member for a flow cell includes an optical fiber shaft defining a cavity having a cladding layer for confining light within the shaft. A buffer layer is overmolded onto the cladding layer for providing structural integrity to the shaft and a plug portion is overmolded on the buffer layer at a top portion of the shaft for providing increased friction between the shaft when seated in a receiving bore of a flow cell. The optical fiber shaft defines a lumen, and the overmolded plug portion may be fabricated in a tapered dowel pin shape or a substantially conical shape.
In another embodiment of the subject technology, a flow cell for a photometric device includes a first module having a distal face defining a first annular channel. A second module has a proximal face defining a second annular channel, wherein the distal and proximal faces are sealed by a sealing member between the first and second annular channels. A first light guiding member is disposed with the first and second annular channels for exposing a fluid to a desired wavelength of light. The compliant sealing member may be an oval ring, a circular ring, an oval ring with flat sides or a square ring having rounded edges, or fabricated from so-called form-in-place resilient materials.
These and other features and advantages of the present invention will become more apparent from the following detailed descriptions taken in conjunction with the accompanying drawings wherein like reference characters denote corresponding parts throughout the several views, and wherein:
The present invention overcomes many of the prior art problems associated with flow cells. The advantages, and other features of the technology disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain preferred embodiments taken in conjunction with the drawings which set forth representative embodiments of the present invention and wherein like reference numerals identify similar structural elements.
Referring now to
The use of O-ring seals 32a-32d in the subject technology is driven by a fundamental need to minimize the separation between the main modules 12, 14 and 16 in order to optimize the transfer of radiant energy thru the flow cell sub-assembly 10, simultaneously preventing light from entering the wall of a light guiding member 30. The optical fiber 26 delivers the light to the waveguide 30 which has transparent walls. The central hole in the gasket 20 prevents light that leaves the optical fiber 26 from getting into the walls of the waveguide 30. The core diameter of the optical fiber can be made larger than the gasket's central hole to ease alignment requirements. At the other end of light guiding member 30, the central hole in the gasket 18 is employed to prevent any light which may have unintentionally entered the walls of the light guiding member 30 from reaching an optical collection system or detector outside of the flow cell.
The top module 12 is comprised of a body 56 having a shoulder 13 and defining two channels 57 and 58 having fluid transmitting members 22 and 24, respectively. The shouldered body 56 also defines a third channel 59 containing the optical conduit or fiber 26 sealed into the top module 12 by means of an overmolded feature 27. O-ring 32a is used to provide a fluidic seal. Fluid line 24 passes through the top module 12 while fluid line 22 is sealed within the top module 12 via an interference fit at the distal end or face 54a. The channels 57, 58 and 59 terminate flush with the distal face 54a of the shouldered body 56.
The middle module 14 consists of a tubular body 61 having a central axial passage 63 with a light guiding tubular member 30 disposed therein. The tubular member 30 is surrounded by an intermediate tube 28 which has an outer surface in intimate contact with the central passage 63 and an inner surface in intimate contact with the tubular light guiding member 30. The tubular member 28 is chosen from chemically inert materials such as perfluoroalkoxy polymer or other suitable thermoplastics such as PEEK™ polyetheretherketone or TEFZEL® fluoropolymer, while tubular light-guiding member 30 is preferably formed from a material that supports light guiding, such TEFLON® AF amorphous fluoropolymer or any other suitable material consistent with the requirement that for efficient light guiding the refractive index of light guiding member 30 must be less than that of the fluid medium passing through this member.
Fluidic line 24 is also fluidically sealed within an off-axis passage 65 in the middle module 14 by an interference fit similar to that employed for securing the fluid line 22 within the top module 12. Middle module 14 is shown configured with O-rings 32b and 32c set in respective annular grooves 52b and 52c in upper (e.g., proximal) and lower (e.g., distal) faces 54b and 54c.
The lower module 16 has a disc shaped body 71 of transparent material to form a simple window. The disc shaped body 71 also has an annular groove 52d in an upper face 54d equipped with an O-ring 32d. The disc shaped body 71 may be formed of fused silica or other materials that are transparent to the wavelengths of light passing through the flow cell. The disc-shaped body 71 is optionally shaped to function as an optical lens; for example, the lower face of the body 71 is optionally curved, such as spherical. O-ring materials are chosen to be compatible with the broad range of fluids employed in high pressure liquid chromatography (HPLC), ultra-high pressure liquid chromatography (UPLC), capillary electrophoresis (CE) or even other non-chromatographic environments. These materials include, for example, materials such as polytetraflouroethylene (PTFE) and KALREZ® elastomer (available from Dupont), or any other suitable material.
Light guiding member 30 is secured within tubular member 28, which has an outer diameter slightly larger than the corresponding central passage 63 in the middle module 14. The member 30 with tubular sleeve 28 form an assembly, which is secured within module 14 by virtue of an interference fit between tubular member 28 and central passage 63. The fluidic sample can enter the flow cell sub-assembly 10 via either conduit 22 or 24. Likewise, probe radiation from an external light source (not shown), such as a deuterium lamp may be launched into either the optical fiber 26 or focused through the lower module 16 onto the lumen of the light guiding member 30. As noted above, etched gaskets 20 and 18 establish fluidic connections between the three modules 12, 14 and 16 while also serving to mask light from entering the annular sidewall of the tubular member 30.
Some alternative embodiments of a flow-cell subassembly include a window or lens module at both ends of a subassembly. For example, the subassembly 10 is optionally modified to include an upper module having a body of transparent material to form a window or shaped to provide a mirror.
Referring now to
Referring now to
The etched features such as the channel 75 are designed to minimize unswept volume, which can cause dispersion (or broadening) of chromatographic peaks. This is particularly troublesome when the total tubular volume of the tubular member 30 is much below 0.3 microliters. Accordingly, for such low volume cells, only a partially etched channel 75 is desirable.
Referring now to
Referring again to
Light is delivered to the lumen of tubular member 30 via optical conduit 26. The light carrying capacity or etendue, Eo, of the flow cell sub-assembly 10 is given by:
E
o
=A
f·πNA2
where Af is the cross-sectional area of the light guide's lumen and NA is the numerical aperture of the light beam within the lumen which equals the sine of the maximum half-angle of light sustainable by the fluid-filled lumen of light guiding member 30, which in turn depends upon the refractive index of light guiding member 30 and that of the fluid contained therein.
The optical fiber 26 delivers radiation of an angular extent to match the etendue of the liquid core light guide but not an excess in terms of NA as this can lead to undesirable RI effects. Accordingly, it is preferable to use an optical fiber whose diameter is larger than the AF lumen but whose NA, set by opto-mechanical elements external to the flow cell 10, matches that of the AF guide. The larger diameter of the optical fiber 26 in cooperation with the restricting central aperture of the gasket 20 has the benefit of relaxed alignment requirements between the fiber and AF conduits.
The excess light emerging from the optical fiber 26 is blocked by the central thru-hole 76 of the gasket 20. However, as the gasket thickness increases, the angular extent of the light passing into the AF lumen 30 is reduced, thereby leading to an optical underfilling of light guiding member 30. The effect of this underfilling or reduction in etendue can be estimated by noting that the conventional ray model of optics gives a satisfactory description of light transmission through a multimode light guide wherein the fluid core diameter is typically greater than 50 microns, e.g., 100 microns.
In this case, the efficiency of the transfer of radiant energy from the optical fiber 26 to the tubular member 30 with interposed gasket 20 may be treated by the following expression:
E′=∫∫(cos θ1δA1 cos θ2δA2/R212)
The subscript ‘1’ refers to the area within the exit (emitting) face of the optical fiber 26 and ‘2’ refers to the receiving area within the lumen diameter of AF lumen 30. R12 represents the distance of a line connecting the center of each differential area and the cosine terms reflect the orientation of δA1 or δA2 relative to this line.
For an infinitely thin gasket, the above expression reduces to Eo. For a gasket of finite thickness, the above integration is carried out with results appearing in
Physically, each elemental area within the lumen of 30 is capable of accepting a cone of light whose NA is in accordance with Eo. As gasket thickness increases, some portion of these cones are occulted by the edge of the central hole 76 of gasket 20 closest to the optical fiber. Eventually the maximum angle of acceptance by the light guide is controlled by the gasket itself. This situation is shown as the dashed line in
Because gaskets 20 and 18 are employed at each end of the AF lumen 30, the overall loss, assuming that light which successfully passes into the entrance face of the tubular member 30 completely fills its exit lumen, is multiplied. For example, for Q=100, the loss L≈17%. The level transmitted into the lumen is 83% but undergoes a further loss of 17% upon exiting the lumen for an overall exit transmission, Tx, of 0.832 or 69%.
This situation is further illustrated by the data in Table 1 below which compares total transmission levels for four different lumen sizes—all at constant gasket thickness—where total transmission level corresponds to that emerging from the exit end of the flow cell sub-assembly 10, exclusive of Fresnel losses which are common to all listed configurations. High overall transmission levels are desirable for good analytical sensitivity.
Clearly low volume light guiding flow cells having lumen diameters on the order of 100 microns will experience unacceptable losses in light throughput using gaskets, which are otherwise suitable for larger lumen diameters. The addition of a compliant or resilient material to each side of a normally incompressible etched gasket will only exacerbate this loss. Therefore, a combination of an uncoated, precisely etched gasket and alternative sealing means imparted to the modules 12, 14 and 16 provides a path to the efficient transfer of light in small diameter fluid core light guides and fully useable for larger lumen diameters.
Referring now to
The coatings 142a-d may be chosen from a variety of materials such as PTFE, PVDF, FEP, TEFLON® AF 2400 amorphous fluoropolymer, AF1600 Cytop, or other chemically inert materials. The coatings 142a-d may be applied through spin coating, vapor deposition or other well known techniques. Depending upon the optical properties of the coating, critical areas such as the emitting face of optical fiber 126 or window of lower module 116 may be masked-off. The coatings 142a-d may also be applied to the gaskets 118 and 120 as opposed to the modules 112, 114 and 116.
Referring now to
The fluidic connection between modules 214 and 216 is a channel 246 formed in the corresponding face 254c of the middle module 214. An opaque coating may be applied to the window module 216 except in the central region which permits the unobstructed passage of radiant energy. Such coatings are well-known such as gold-over-chrome which is chemically inert. The fluid path is sealed against leakage with an O-ring 232c.
Referring now to
Referring now to
Molding permits accurate centration of the fiber along with consistent outside feature dimensions which permits for greater manufacturing yields. The relatively thin feature wall thickness means more uniform composition of molded material, thereby avoiding common molding defects such as internal voids. Although the receiving bore 59 in module 12 is shown as a single cross-section in
The optical fiber 26 has an outer buffer layer 31 surrounding a cladding layer 33, which surrounds the fiber core 35. The buffer layer 31 may be a KAPTON® film, which is bonded in place to prevent damage to the fiber core 35. The overmolded feature 27 may be PEEK™ material. The overmolded feature 27 may also have a different shape such as including a series of concentric ridges, be relatively thinner or thicker than shown, have a shallower draft and the like.
Referring now to
The flow cell sub-assembly 10 is sealed within the housing 468 through the use of a Belleville spring arrangement or stack 464 loaded onto the upper shoulder 413 of top module 12. The Belleville stack 464 is followed by a washer 466 with a shape as shown in
The anti-rotation washer maintains opto-mechanical alignment between the various modules and gaskets during tightening. As a result, the tightening process does not significantly impact overall light transmission which may occur due to relative rotations between the top module 12, gasket 20 and middle module 14. The Belleville stack 464 and anti-rotation feature of the washer 466 results in the tightening load being directed in a more fully axial direction with no or trivial change in overall cell energy.
Although the subject invention has been described with respect to preferred embodiments, those skilled in the art will readily appreciate that changes or modifications thereto may be made without departing from the scope of the subject invention as defined by the appended claims.
The entire contents of all patents, published patent applications, and other references cited herein are hereby expressly incorporated herein in their entireties by reference.
This application claims priority to U.S. Provisional Patent Application No. 61/055,241, filed May 22, 2008, the entire contents of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/US2009/044633 | 5/20/2009 | WO | 00 | 3/3/2011 |
Number | Date | Country | |
---|---|---|---|
61055241 | May 2008 | US |