CHROMATOGRAPHY DEVICES, POROUS MEDIUM MODULES USED IN CHROMATOGRAPHY DEVICES, AND METHODS FOR MAKING POROUS MEDIUM MODULES

Abstract: A separation device includes an inlet (12), an outlet (14), a porous medium module (20) and a porous medium module holder (40) holding the porous medium module. The porous medium module holder (40) and the porous medium module (20) define a flow path providing fluid communication between the inlet and the outlet.

Description: CHROMATOGRAPHY DEVICES, POROUS MEDIUM MODULES USED IN CHROMATOGRAPHY DEVICES, AND METHODS FOR MAKING POROUS MEDIUM MODULES The present application claims the benefit of priority of United States Patent Application No. 60/121,667 filed on February 25, 1999 and United States Patent Application No. 60/168,738 filed on December 6, 1999. United States Applications No. 60/121,667 and No. 60/168,738 and all other patent applications, patents, and publications listed in the present application are incorporated by reference. FIELD OF THE INVENTION This invention is related to chromatography devices, porous medium modules used in chromatography devices and methods for making porous medium modules, including a porous medium module having a stack of porous media, such as porous membranes or sheets. BACKGROUND OF THE INVENTION Chromatography is a term applied to a variety of separation techniques and can be classified in several ways, including gas chromatography and liquid chromatography, such as ion exchange chromatography, affinity chromatography, size exclusion chromatography, etc. The term "chromatography" as used herein includes any conventional chromatographic and/or adsorptive separation technique. A chromatography process may be illustrated using ion exchange chromatography. Ion exchange chromatography usually involves a two-step process for separating components from the fluid containing the components. First, a test sample including a fluid and the components contained therein is passed through a chromatography device such as a chromatography column. The chromatography device usually includes a stationary separation medium, such as a bed of porous beads or a stack of porous membranes or sheets, for separating or isolating the components from the fluid. As the test sample passes through the chromatography device the components become associated with the separation medium by any of a variety of chemical and/or physical processes. For example, the components may become chemically or physically attached to the separation medium. In the case of ion exchange chromatography, the components may be attached to the medium by electric charge. Second, after the test sample has passed through the separation medium and the components in the test sample are attached to the separation medium, a continuous stream of an eluent is passed through the separation medium, whereupon the components attached to the separation medium are released to the eluent. In ion exchange chromatography, the eluent may be a salt solution, ions of which replace the components on the separation medium. Typically, the salt concentration is varied with time either gradually using gradient elution or suddenly as in step or isochratic elution. Because different components have different affinities for the separation medium, the time at which each component is released into the eluent may vary. For example, in gradient elution where the salt concentration increases with time, the component having the least affinity for the separation medium will be released into the eluent first, and the component having the most affinity for the separation medium will be released into the eluent last. The presence of each component in the eluent is .generally detected by measuring changes in the physiochemical properties (for example, by measuring the adsorption of light at 280 nm) of the eluent as the eluent exits the separation medium. A plot of the changes of these properties versus time will exhibit response peaks corresponding to the presence of the components contained in the eluent. Whether a component is contained in the test sample may be determined by examining the existence of the corresponding peak. To obtain high purity, it is desirable that the peaks be well separated. To achieve high concentration, it is desirable that the peaks be narrow. To accurately determine whether a component is contained in the test sample, it is desirable that the response peaks in the plot are narrow and well separated. To obtain narrow or well-separated, well- defined response peaks, it is desirable that the flow of the fluid, such as the test sample and/or the eluent, through the separation medium is uniform. Uniform fluid flow through a separation medium may be characterized by such parameters as uniform flow rate per unit area across the entire flow area and uniform residence time for fluid traversing each streamline of the flow. Residence time is defined as the time during which a fluid particle is within the chromatography device as a whole or within one or more parts of the chromatography device, such as the separation medium. In many conventional chromatography devices, the flow of the test sample is non- uniform. For example, the test sample entering the separation medium may not be uniformly distributed across the entire flow area and "channeling" may occur as a result. "Channeling" is a phenomenon where certain areas of the fluid front of the test sample have a higher flow rate than other areas of the fluid front. The portions of the separation medium experiencing higher flow rates may encounter greater quantities of the components and may become saturated before other portions of the separation medium. This may cause the component to "break through" to the outlet of the device before the entire medium is saturated, thus reducing the total quantity of the component that may be captured before some is lost at the outlet. The non-uniform flow of an eluent may cause a component to appear sooner in a portion of the eluent having a higher flow rate and later in a portion of the eluent having a lower flow rate. Even if the eluent has uniform flow rates, non-uniform residence times may cause the component to appear sooner in a portion of the eluent having a shorter residence time and later in a portion of the eluent having a longer residence time. These phenomena may cause the component to appear in the different streamlines of the eluent at different times. Consequently, non-uniform flow may cause the component to appear in a longer segment of the eluent flow stream at a lower concentration, making the response peaks wider and less concentrated. Wider and less concentrated response peaks may lead to an overlapping of the response peaks, making the identification of the response peaks, and consequently the identification and separation of the corresponding components, more difficult. There are a number of factors that may affect the uniformity of fluid flow within a chromatography device. For example, leakage around a part of or the entire separation medium may cause a portion of the fluid to bypass the separation medium, resulting in both non-uniform flow rate and non-uniform residence time. Additionally, stagnant flow areas caused by irregularities in the flow path may produce non-uniformity of flow. Irregularities in the flow path may be created by seals, such as O-ring seals and/or gaskets, used to seal the separation medium in the flow path. Further, non-homogenous packing of the separation medium may also cause non-uniform flow. For example, the areas of the separation medium having higher packing density may have more flow resistance to fluid flow, reducing flow rate and increasing residence time. SUMMARY OF THE INVENTION This invention provides porous medium modules and methods for making porous medium modules, which overcome many of the drawbacks of the prior art, including the problems discussed above. In accordance with one aspect of the invention, a porous medium module for use in adsorptive and/or chromatographic separations includes a hollow housing member, a plurality of porous media stacked in the hollow housing member, and a sealant disposed between the stacked porous media and the hollow housing member and sealing an outer periphery of the stacked porous media. In accordance with another aspect of the invention, a porous medium module for use in adsorptive and/or chromatographic separations includes a plurality of stacked porous media having an outer periphery, and a sealant disposed around the outer periphery of the stacked porous media. The sealant penetrates into the outer periphery of the stacked porous media, and the depth of penetration of the sealant into the outer periphery of the stacked porous media is substantially uniform. In accordance with another aspect of the invention, a porous medium module for use in adsorptive and/or chromatographic separations includes a hollow housing member having an inner surface, a plurality of porous media stacked in the hollow housing member, and a sealant disposed between the stacked porous media and the hollow housing member, wherein the housing member includes a configuration that interlocks the housing member and the sealant. In accordance with another aspect of the invention, a porous medium module for use in adsorptive and/or chromatographic separations comprises a hollow housing member, a plurality of porous media stacked in the hollow housing member, and a mechanism operatively associated with the hollow housing member and the stack of porous media, wherein the mechanism centers the stack of porous media in the hollow housing member. In accordance with another aspect of the invention, a porous medium module for use in adsorptive and/or chromatographic separations comprises a plurality of stacked porous media having an outer periphery, at least one porous medium support having an outer peripheral region, the porous medium support being operatively associated with the stacked porous media, and a sealant disposed around the stacked porous media and the porous medium support. The sealant penetrates into the outer periphery of the stacked porous media and into the outer periphery of the porous medium support, and at least a portion of the outer peripheral region of the porous medium support is at least partially obstructed to reduce the penetration of the sealant into the porous medium support. In accordance with aspect of the invention, a porous medium module for use in adsorptive and/or chromatographic separations comprises first and second permeable porous medium supports, a plurality of porous media stacked and compressed between the first and second permeable porous medium supports, and a hollow peripheral arrangement disposed around the supports and the media and coupled to the edges of the supports and media to seal and support the supports and media. In accordance with another aspect of the invention, a porous medium module for use in adsorptive and/or chromatographic separations includes first and second porous medium supports, a plurality of porous media stacked between the first and second permeable porous medium supports, and a sealant coupled to the porous medium supports to secure the porous medium supports to the porous media. In accordance with another aspect of the invention, a porous medium module for use in separations comprises a plurality of stacked porous media having an outer periphery and a first end, and a sealant disposed around the outer periphery of the stacked porous media, the sealant forming at least a portion of a first seal gland near the first end of the stack. In accordance with another aspect of the invention, a porous medium module for use in separation comprises a plurality of stacked porous media having an outer periphery and a first end, and a sealant disposed around the outer periphery of the stacked porous media, the sealant forming a first seat arrangement near the first end of the stack. In accordance with another aspect of the invention, a method for making a porous medium module comprises stacking a plurality of porous media, disposing a liquid sealant around the outer periphery of the stack of porous media, allowing the sealant to penetrate into the outer periphery of the stack of porous media, and allowing the liquid sealant to solidify to form a seal around the stacked porous media. Porous medium modules embodying various aspects of the present invention have a number of advantages over the prior art. For example, the porous medium modules may provide a strong, effective seal for the stacked porous media. The sealant preferably contacts and/or penetrates the outer periphery of the porous media, forming a strong, effective seal around the porous media and preventing leakage around and laterally through the outer periphery of the stacked porous media. Additionally, the porous medium modules may minimize stagnant flow areas in the flow path. The sealant of the porous medium module may be arranged to penetrate evenly and uniformly into the stack of porous media, minimizing the formation of crannies and crevices. The porous medium modules preferably do not use any mechanical sealing devices, such as O-ring seals or gaskets, or any mechanical fastening means, such as bolts, to seal and secure the stacked porous media within the module, thus minimizing the formation of stagnant flow areas. Further, the porous medium modules may include porous media in a compressed state, which offers a number of advantages. For example, compressing the porous media reduces the possibility of non-homogenous packing. The porous media preferably are compressed uniformly before they are sealed within the porous medium module, ensuring homogenous packing. In conventional chromatography devices, the bonding and sealing process generally involves the use of O-ring seals or gaskets to seal the porous media and the use of bolts to secure the stack of porous media. The use of O-ring seals, gaskets or bolts generally involves the compression of only a portion of the porous media, causing non-homogenous packing. An additional advantage of compressing the porous media is that it reduces the gap between adjacent porous media, preventing the sealant from penetrating much further between adjacent porous media layers than it does edgewise into the outer periphery of each media layer. This minimizes the formation of crannies and crevices in the flow path and consequently the formation of stagnant flow areas. A further advantage of compressing the porous media is that the porous medium module may have a more consistent separation performance. An important parameter affecting the separation performance of a porous medium module is the height of the porous media. Compression of the porous media may allow a more precise control of the height of the porous media and consequently a more consistent separation performance for the porous medium module. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view of one embodiment of a chromatography device. Figure 2 is a sectional view of one embodiment of a porous medium module. Figure 3 is a sectional view of another embodiment of a porous medium module, illustrating the penetration of sealant into the porous media. Figure 4 is a sectional view of another embodiment of a porous medium module, illustrating the penetration of sealant into the porous media and the porous medium supports. Figure 5 is a sectional view of another embodiment of a chromatography device. Figure 6 is a sectional view of the porous medium module used in the embodiment shown in Figure 5. Figure 7 is a partial sectional view of the porous medium module used in the embodiment shown in Figures 5 and 6, showing sealant penetration into the porous membranes and porous medium supports. Figure 8 is a partial sectional view of the porous medium module used in the embodiment shown in Figures 5 and 6, showing a housing member with beveled ends. Figure 9 is a top view of the porous medium module used in the embodiment shown in Figure 5, showing spacers disposed between the housing member and the stack of porous membranes and porous medium supports. Figure 10 is a partial sectional view of the porous medium module used in the embodiment shown in Figures 5 and 6, showing a ring seal seated on the sealant. Figure 11 is a partial sectional view of another embodiment of a device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 illustrates one example of a chromatography device 10 embodying the invention. The chromatography device 10 may include an inlet 12, an outlet 14, a porous medium module 20 and a porous medium module holder 40 holding the porous medium module 20. The porous medium module holder 40 and/or the porous medium module 20 may define a flow path providing fluid communication between the inlet 12 and the outlet 14. The porous medium module 20 may be disposed in the flow path and may include a single porous medium or a plurality of porous media 22. A fluid, such as a test sample or an eluent, may enter the chromatography device 10 through the inlet 12, pass through the porous medium module 20 and exit the chromatography device 10 through the outlet 14. A chromatography device may include only one porous medium module 20, as shown in Figure 1, or it may include a plurality of porous medium modules disposed in one or more porous medium module holders. The plurality of porous medium modules may be arranged within a porous medium module holder in various parallel, series, or series/parallel arrangements. A chromatography device can include multiple inlets and multiple outlets, and each inlet or outlet may serve one or more porous medium modules. A wide variety of porous medium module holders may be used with the porous medium module. For example, in the embodiment shown in Figure 1, the porous medium module holder 40 preferably includes two holder sections such as opposed plates 42, 44 between which the porous medium module 20 may be disposed. Connectors, such as a plurality of bolts 46 or clamps, may secure the porous medium module 20 between the two plates 42, 44. The inlet 12 and outlet 14 may be respectively placed near the centers of the two plates 42, 44, and each of the inlet 12 and outlet 14 may include a female threaded socket intended to receive a male threaded fitting with substantially the same inner diameter as the passage 16, 18. A first flow distributor arrangement 52 may be disposed in the flow path between the inlet 12 and the porous medium module 20 and/or a second flow distributor arrangement 54 may be disposed in the flow path between the porous medium module 20 and the outlet 14. Each flow distributor arrangement 52, 54 may include a tapered space 60, 62 and one or more porous fluid distributors 30, 32, 56, 58 operatively associated with the tapered space 60, 62. For example, a flow distributor arrangement 52 may include a tapered space 60 and two flow distributors 30, 56. Alternatively, the flow distributor arrangement 52 may include only one of the two distributors 30, 56. Each of the tapered spaces may be substantially free of structures, e.g., completely free of structures. Alternatively, one or both of the tapered spaces may include structures, such as support structures and/or flow channels. The first flow distributor arrangement 52 may be disposed between the inlet fluid passage 16 and the porous medium module 20 facing the inlet fluid passage 16. The second flow distributor arrangement 54 may be disposed between the outlet fluid passage 18 and the end of the porous medium module 20 facing the outlet fluid passage 18. Some preferred flow distributor arrangements are described in detail in United States Patent Application No. 60/121,701 by Mark Hurwitz, Thomas Sorensen, John Strempel, and Thomas Fendya, titled "Chromatography Devices and Flow Distributor Arrangements Used in Chromatography Devices," filed on February 25, 1999; United States Patent Application No. 60/168,750 by Mark Hurwitz, Thomas Sorensen, John Strempel, and Thomas Fendya, titled "Chromatography Devices and Flow Distributor Arrangements Used in Chromatography Devices," filed on December 6, 1999; and an International Application by Mark Hurwitz, Thomas Sorensen, John Strempel, and Thomas Fendya, titled "Chromatography Devices and Flow Distributor Arrangements Used in Chromatography Devices, " filed February 25, 2000, which applications are incorporated in their entirety by reference. Alternatively, the porous medium module holder may have any suitable configuration. For example, the porous medium module holder may have a hollow, cylindrical configuration or a configuration similar to that of a container. The inlet and outlet may be placed at any suitable locations, as long as they allow a test sample or an eluent to enter and exit the chromatography device 10, respectively. In some embodiments, the porous medium module holder may include a key mechanism that ensures that the porous medium module holder and the porous medium module are properly aligned when the porous medium module is disposed in the porous medium module holder. Preferably, each of the plates 42, 44 of the module holder 40 is sealed to the end of the porous medium module 20 to prevent radially outward leakage through the gap between the plate 42, 44 and the end of the porous medium module 20. Preferably, the seal is arranged to prevent the creation of any stagnant flow areas. Fluid flowing into and out of any stagnant areas may create non-uniform flow rates and residence times. The seal can be provided in a variety of ways. In the embodiment shown in Figure 1, for example, seals, such as ring seals or annular gaskets, may be provided. Alternatively, the seals may be integral or unitary with the sealant 24 of the porous medium module 20. The plates 42, 44 or the porous medium module 20, or both, may have an annular groove to accommodate each seal 48, 49. To prevent the formation of stagnant flow areas, the inner diameter of each seal 48, 49 preferably is substantially the same as the diameter of the flow path through the porous medium module 20. Also, when each seal is compressed into an annular groove, the seal preferably seals the opening of the groove from the fluid so that the fluid does not flow into the groove, preventing the formation of stagnant flow areas in the groove. In the embodiment shown in Figure 1, each seal 48, 49 has a generally rectangular (or trapezoidal) cross-section, and the groove has a generally rectangular (or trapezoidal) cross-section. The seal 48, 49 and groove are so dimensioned that, when the seal is compressed into the groove, the opening of the groove is substantially sealed by the seal 48, 49. As illustrated in Figures 1 and 2, an exemplary embodiment of the porous medium module 20 of the present invention may include a plurality of stacked porous media 22 and a sealant 24 disposed around the periphery of the stacked porous media 22. In some preferred embodiments, the sealant 24 may penetrate into the outer periphery of the stacked porous media 22 to form a strong, effective seal. In other embodiments, the sealant 24 may penetrate far less, or may not significantly penetrate into the outer periphery of the stacked porous media 22 but may contact the outer periphery to form a strong, effective seal. In some embodiments, the porous medium module 20 may also include a hollow housing member 26, and the sealant 24 may be disposed between the stacked porous media 22 and the hollow housing member 26. The porous medium module 20 may also include first and/or second porous media supports 30, 32, which is operatively associated with the stack of porous media 22. For example, first and/or second porous media supports 30, 32 may be disposed respectively at the ends of the stack of porous media 22. The stacked porous media may have any suitable configuration, depending on the desired configuration of the chromatography device. In the embodiment shown in Figures 1 and 2, the stack of porous media 22 has a substantially cylindrical configuration having a generally circular cross section. Alternatively, the stack of porous media may have, for example, a square, rectangular or polygonal cross section. The stacked porous media 22 may include any desired number of layers of porous media 22, depending on the specific application. The number of layers of porous media may be selected according to any suitable criterion. For example, it may be desirable to select the number of layers by establishing a maximum pressure drop for a desired axial flow rate through the porous medium module. In the illustrated embodiment, the stack of porous media 22 may include from about 2 or fewer to about 125 or more layers, preferably from about 65 to about 100 layers, more preferably from about 70 to about 100 layers, e.g., about 95 layers, of axially stacked porous media. For some embodiments, such as sampling modules, the stack of porous media may include from about 5 to about 50 layers, preferably from about 10-30 layers, e.g., 16 layers, of axially stacked porous media. The number of layers of porous media 22 may also be selected to obtain a desired compression ratio for a given pre-compression height of the porous media 22. Compression ratio is defined as the ratio of the post-compression height of the porous media over the pre-compression height of the porous media. A variety of porous media, including any porous medium suitable for use in membrane chromatography, may be utilized in the porous medium module. The porous medium may have any suitable structure and may be formed from any suitable type of material. For example, the porous medium may include a porous substrate formed from an inorganic material, such as a metal or a ceramic, including glass, or the porous medium may include a natural or synthetic polymer, such as poly ether sulfone, polysulfone, polyvinylidene fluoride, polyester, nylon or cellulose. The substrate may be, for example, a porous sheet of sintered or resin-bonded inorganic particles or fibers, a woven or non- woven sheet of polymeric fibers, or a porous polymeric film or membrane. The substrate may be naturally useful as a chromatography medium or it may be modified physically and/or chemically to be more useful as a chromatography medium. For example, the substrate may be charge-modified to provide a positive or negative charge, or it may be coated or surface-modified to provide one or more interactive substances, such as affinity ligands, antibodies, and antigens. Alternatively or additionally, the porous substrate may be impregnated with various substances, such as porous resins, useful in chromatography. Some preferred porous separation media are described in detail in United States Patent Application No. 60/121,668 by Chung-Jen Hou, Peter Konstantin and Yujing Yang, entitled "Negatively Charged Membrane" and filed February 25, 1999; an International Application by Chung-Jen Hou, Peter Konstantin and Yujing Yang, entitled "Negatively Charged Membrane" and filed February 25, 2000; United States Patent Application No. 60/121,669 by Jayesh Dharia, Chung-Jen Hou, Peter Konstantin and Yujing Yang, entitled "Positively Charged Membrane" and filed February 25, 1999; United States Patent Application No. 60/121,670 by Xiaosong Wu, Jayesh Dharia, Peter Konstantin and Yujing Yang, entitled "Positively Charged Membrane" and filed February 25, 1999; an International Application by Xiaosong Wu, Jayesh Dharia, Chung-Jen Hou, Peter Konstantin, and Yujing Yang, entitled "Positively Charged Membrane" and filed February 25, 2000; and United States Patent Application No. 60/134,197 by Xiaosong Wu, Joe Kinsey, and Michael Ishee, entitled "Endotoxin Retentive Membranes" and filed May 14, 1999. These patent applications are incorporated by reference in their entirety. Each porous medium may include one or more layers and may be supported or unsupported. For example, the porous medium may comprise an externally or internally supported polymeric membrane. Further, suitable porous media may have a variety of pore structures, permeabilities, and dimensions. For example, the porous medium may have a uniform pore structure or a non-uniform pore structure, such as a graded pore structure or an asymmetrical pore structure. The porous medium may have a removal rating in the range from about 0.2μ or less to about 5.0μ or more, more preferably in the range from about 0.3μ to about 1.5μ. The thickness of each porous medium may be in the range from about 0.001 inch or less to about 0.5 inch or more. Preferably, the thickness is less than about 0.010 inch and more preferably in the range from about 0.002 inch to about 0.008 inch, for example, from about 0.003 inch to about 0.007 inch. Further, the membrane layers are preferably each of uniform thickness across their flow area, preferably within about +/-20% of the nominal thickness of the membranes, more preferably within about +/-10% of the nominal thickness. The lateral dimension(s), e.g., the diameter, may be as large as may be practically manufactured, for example, up to about 1 meter or more. In the embodiment shown in Figure 1, the diameter of the membrane is preferably about 40 cm or less, e.g., about 15 cm or less. The porous media 22 are preferably stacked one on another, as shown, for example, in Figure 3. The opposing surfaces of each porous medium may be identical or different. Where the opposing surfaces are different, adjacent media may be stacked on one another with similar surfaces facing one another or dissimilar surfaces facing one another. For example, a porous medium may have a "shiny" side (i.e. , a smooth side) and a "dull" side (i.e., a rougher side). Typically, the roughness of the "shiny" surface is on the order of the pore size of the porous medium. When two porous media are stacked together with their "shiny" sides facing each other, the gap between them tends to be smaller. On the other hand, the gap tends to be larger when two "dull" sides face each other. Accordingly, when porous media are stacked, the "shiny" side of one porous medium preferably faces the "dull" side of another porous medium. In this way, the gaps between two layers of porous media may be more consistent. To prevent a test sample or an eluent, which passes axially through the stack of porous media 22, from leaking radially through the side surface of the stacked porous media 22, a sealant 24 is preferably disposed around and preferably seals the outer periphery of the stack of porous media 22. The sealant 24 may have any configuration that effectively seals the porous media 22, depending on the configuration of the porous media 22. In the illustrated embodiment, the sealant 24 has a hollow cylindrical configuration and is disposed around the cylindrical side surface of the stack of porous media 22. The sealant 24 may also serve to support the stack of porous media 22 at the outer periphery. The sealant 24 may comprise any suitable material which will seal and/or bond to the outer periphery of the stack of porous media 22. One example of a suitable material is a thermoplastic material such as a polyethylene, polyolefin, or polypropylene. Thermoplastic materials may be particularly useful if the sealant is to be injection molded around the stack of porous media. Another example of a suitable material is material which may be applied around the stack of porous media as a liquid and then cured or hardened to form a seal and/ or bond. One example of a curable material is a thermosetting material such as an epoxy, silicone, or curable polyurethane. A preferred thermosetting material is a bi-component polyurethane. In a preferred embodiment of the porous medium module 20, as illustrated in Figure 3, the sealant 24 may penetrate (1) radially (i.e. , edgewise) into the outer periphery of each porous medium 22 of the stack and/or (2) radially between adjacent porous media 22 of the stack to form a strong, effective seal and to ensure that the sealant 24 is securely bonded to the porous media 22. This can be done, for example, by applying the sealant as a liquid around the stack of porous media 22. The liquid sealant is then allowed to penetrate a short distance radially into the outer peripheries of the porous media, filling the interstices in the porous media 22 at the outer periphery, and to penetrate a short distance radially into gaps between the layers of porous media 22. The liquid sealant then hardens to form the solid sealant 24. In the illustrated embodiment, for example, the sealant 24 may penetrate into and between the porous media 22 to define an inwardly facing side surface of the sealant 24 which is positioned radially inwardly from the outwardly facing side surface of the media stack 22. The sealant 24 thus prevents leakage radially through and circumferentially around the side surface of the media stack and ensures that the sealant 24 is securely bonded to the porous media 22. In preferred embodiments, the depth of the penetration of the sealant 24 into and between the porous media 22 may be controlled to achieve various desired results. For example, the sealant 24 preferably penetrates into the porous media 22 sufficiently deep to form a strong, effective seal and/or bond but not so deep as to unduly reduce the effective flow area axially through the stack of porous media 22. Additionally, the depth of penetration into and between the porous media preferably is substantially uniform along the stack of the porous media 22. For many embodiments of the invention, the sealant may penetrate between adjacent porous media layers further than it penetrates edgewise into the outer periphery of each media layer. For other embodiments, the sealant may penetrate edgewise into the outer periphery of each media layer further than it penetrates between adjacent layers. In either event, for porous media having a thickness of about 0.010 inch or less, the maximum variation (d) along the stack of porous media, as shown in Figure 4, may be less than or equal to about 0.010 inch, preferably less than or equal to about 0.005 inch. However, for all porous media regardless of their thickness, the maximum variation (d) is most preferably less than or about equal to the thickness of the porous medium. In addition, the pitch of the variation, i.e., the axial distance from one peak of penetration to the next adjacent peak of penetration, is most preferably greater than or about equal to d. Limiting the maximum variation in the depth of penetration thus provides a sealant which has an inwardly facing surface that is substantially uniform. Chromatography porous medium modules embodying this aspect of the invention are superior to many chromatography devices which have a non-uniform depth of penetration. Non-uniform penetration creates crannies, crevices and other areas where fluid flow stagnates. Test samples and eluents flowing through these devices move in and out of these stagnant areas with highly non-uniform flow rates and residence times, broadening response peaks and reducing resolution. By providing substantially uniform inwardly facing sealant surfaces, porous medium modules embodying this aspect of the invention may exhibit far more uniform flow velocities and residence times, sharper peaks, and enhanced resolution. The first and second permeable porous medium supports 30, 32 may perform a number of functions. For example, they may support and protect the axial ends of the stack of porous media 22. They may be used to provide a uniform axial compression to the stack of porous media 22 to prevent the porous media 22 from, for example, bulging at the center of the porous media 22, resulting in a uniformly packed porous media 22. The permeable porous medium supports 30, 32 may also serve as flow distributors, directing flow to or from the stack of porous media 22, to provide more uniform flow velocities and residence times. The porous medium supports may have any suitable configuration that allows the porous medium supports to perform one or more of the above functions. Each porous medium support may be a single layer structure which performs one or more of the above functions or it may comprise a multilayer structure, each layer performing one or more of the above functions. Each of the porous medium supports 30, 32 may be identical and may have a shape similar to the shape of a porous medium. The lateral dimension(s) of each support member may be similar to those of the porous medium or they may be larger or smaller. For example, the porous medium supports may extend beyond the outer periphery of the stack of porous media to the sealant or may extend over or within the sealant, e.g. , to the hollow housing member. The outer periphery of the porous medium supports may then be sealed by the sealant, enhancing the structural integrity of the porous medium module. In the embodiment illustrated in Figures 1 and 2, the porous medium supports 30, 32 may have the configuration of a circular disk with a diameter similar to that of the porous media 22. The thickness of each porous medium support may vary along one or both of the lateral dimensions, e.g., the diameter, of the porous medium support. In some embodiments, the porous medium support may have a configuration with a varying thickness, such as a conical configuration, which may be useful in distributing flow evenly to the stack of porous media. In the embodiment shown in Figure 1, the thickness is preferably substantially constant along the lateral dimensions of the porous medium support 30, 32. Further, the outer periphery of each porous medium support 30, 32 may be beveled, as shown in Figure 4. The beveled periphery of porous medium supports 30, 32 allows the sealant 34 to be positioned over a portion of each porous medium support 30, 32 to secure the porous medium supports 30, 32 to the stack of porous media 22. Each porous medium support may be permeable at least in a region overlying the stack of porous media and may be permeable over substantially the entire area. While the permeability of each porous medium support may vary along one or both lateral dimensions, the permeability is preferably uniform. Further, each porous medium support is preferably much more permeable than the stack of porous media. For example, the porosity of each porous medium support may be much greater than the porosity of each porous medium. In some preferred embodiments, the removal rating of the porous medium support may be in the range from about 10.0μ or less to about 50.0μ or more, preferably in the range from about 20.0μ to about 50.0μ, while the removal rating for the porous medium may be in the range from about 0.5μ or less to about 1.5μ or more. Further, the pressure drop through each porous medium support is preferably much less than the pressure drop through the stack of porous media. For example, the pressure drop through each porous medium support may be less than or equal to about 10% of the pressure drop through the stack of porous media, preferably less than or equal to about 1 % of the pressure drop through the stack of porous media. The porous medium supports may be fashioned from a wide variety of materials and in a wide variety of ways to support the stack of porous media and/or distribute flow to the porous media. For example, the porous medium supports preferably have sufficient structural integrity to evenly support the stack of porous media under compression and more preferably without any billowing of the porous media, thereby providing a media stack having a uniform height between the porous medium supports. Materials suitable for the porous medium supports include metals, ceramics, and polymers which are compatible with the test samples and eluents. Configurations suitable for the porous medium supports include perforated plates and rigid screens or meshes which may have openings from about 25 microns and or less to about 0.062 inch or more, preferably from about 0.010 to about 0.030 inch. Preferred configurations include a rigid porous sheet, supported or unsupported, of bonded or sintered metallic or polymeric particles or fibers. One example is a 0.08-inch thick unsupported porous sheet of sintered stainless steel particles. As shown in Figure 4, the sealant 24 may also penetrate radially (i.e. , edgewise) into the outer periphery of each porous medium support 30, 32 and/or may penetrate radially between each porous medium support 30, 32 and the adjacent porous medium 22. Preferably, the penetration of the sealant 24 into the porous medium supports 30, 32 and between each porous medium support 30, 32 and the adjacent porous medium 22 is similar to the penetration of sealant 24 into the stack of porous media 22, in terms of both the depth of penetration and the variation of penetration, resulting in a sealant which has an inwardly facing surface that may be substantially uniform. In some preferred embodiments, the depth of penetration into the porous medium supports 30, 32 and between each porous medium support 30, 32 and the adjacent porous medium 22 is substantially equal to or slightly greater than the depth of penetration into the porous media 22 and between the porous media 22. Preferably, the variation of penetration into the porous medium supports and the porous media is also similarly limited to maintain a smooth flow path from one porous medium support through the stack of porous media to the other porous medium support, resulting in a uniform fluid flow through the porous medium module 20. Because the porous medium supports 30, 32 may be far more permeable than the porous media 22, at least a portion of the outer periphery of each porous medium support 30, 32 may be treated or otherwise obstructed in any suitable manner to reduce permeability at the outer periphery. The reduced permeability limits the depth of penetration of the sealant into the porous medium support 30, 32 so that the penetration of sealant into the porous medium support 30, 32 is substantially the same as, or only somewhat greater than, the penetration of the sealant into the porous media 22. For example, at least a portion of the outer periphery of the porous medium supports may be coated or impregnated with any suitable material that limits permeability at the outer periphery. Additionally or alternatively, at least a portion of the outer periphery of each porous medium support may be machined in a manner which reduces its permeability. In the embodiment illustrated in Figure 4, a portion of each porous medium support 30, 32 is beveled in a manner which reduces the permeability at the outer periphery of the porous medium support. The bevels 35 may be formed, for example, by laser cutting, water-jet cutting, machine cutting or grinding. In this manner, the pores on the beveled portion 35 of the outer periphery may be completely, substantially or partially obstructed, limiting the depth of penetration of the sealant. The bevel 35, or other treatment, preferably does not encompass the full outer peripheral surface of a porous medium support, as shown in Figure 4. A portion 36 of the side surface of each porous medium support 30, 32 may remain unobstructed or only slightly obstructed, and the size of the unobstructed or only slightly obstructed portion 36 may be selected to control the depth of penetration of the sealant. For example, it may be 60% or less, preferably 35% or less, e.g., 25% , of the thickness of the porous medium support. The porous medium module shown in Figure 4 comprises a sealant bonding and sealing a plurality of porous media 22 between opposite porous medium supports 30, 32. In the illustrated embodiment, several layers of identical porous media 22 are the only layers disposed between the opposing porous medium supports 30, 32. However, the stack may be configured in any other suitable manner. For example, layers or regions of dissimilar porous media may be disposed in the stack. Further, additional structures may be disposed in the stack. For example, one or more structural supports, such as the porous medium supports, and/or one or more flow distributors or headers may be disposed at various locations, e.g. , axially spaced locations, within the stack. For all of these embodiments, the sealant is preferably disposed around the outer periphery of the stack bonding and sealing the various layers and defining an axial flow path through the porous medium module. The hollow housing member 26 principally functions to support the porous medium module 20 against the radially outwardly directed forces of a fluid flowing under pressure through the porous medium module 20. Additionally, the hollow housing member 26 may axially support the porous medium module 20 when the porous medium module 20 is sealed in the porous medium module holder 40. Further, the hollow housing member 26 may serve as a container for the sealant 24 when the sealant 24 is applied to the porous media 22 and the porous medium supports 30, 32. The hollow housing member 26 may be configured in a variety of ways. For example, it may have a shape similar, or dissimilar, to the shape of the stack of porous media. The interior surface of the hollow housing member may be smooth or it may have a configuration, e.g., protrusions or indentations, that mechanically interlocks with the sealant. In the illustrated embodiments, the hollow housing member comprises a hollow cylinder 26 concentrically arranged with the stack of porous media 22. The hollow cylinder has an inner diameter greater than the outer diameter of the stack of porous media 22, and the sealant 24 is disposed between them. The inner surface of the hollow cylinder 26 abuts the sealant 24 and may be smooth. The hollow housing member 26 may be fashioned from a variety of materials which provide sufficient strength to support the porous medium module 20. For example, the hollow housing member 26 may comprise a metal, such as stainless steel. Alternatively, the hollow housing member may comprise a plastic material such as an engineering plastic. For some applications, such as low-pressure chromatography, the plastic may comprise any suitable thermoplastic material, such as polypropylene, polysulfone, polyetheretherketone, or any other suitable engineering plastic. In some embodiments, it may be desirable to form the sealant and the hollow housing member as a single element, e.g., omitting a separate hollow housing member. For example, a thermoplastic material may be injection molded around the stack of porous media and porous medium supports, the thermoplastic material serving as both sealant and hollow housing member. As another example, a thermosetting material, such as a polyurethane, may serve as both sealant and hollow housing member. Porous medium modules embodying the invention may be made in a variety of ways. For example, layers of porous media may first be stacked and axially compressed between opposite porous medium supports. The layers of porous medium may be compressed axially against one another as they are being stacked, or they may be laid one on another without compression and then axially compressed by pressing the porous medium supports against the stack. The stack, including the porous medium supports, may be compressed for a variety of reasons. For example, compressing the stack may provide even more uniform interfaces between adjacent layers and it may provide a greater amount of chromatographically active media within a given volume. Compressing the stack, including the porous medium supports, also aids in limiting the depth of sealant penetration, and providing a more uniform depth of sealant penetration, into the stack of porous media and porous medium supports. The amount of compression may depend on parameters such as the nature and thickness of each porous medium layer and the desired pressure drop through the stack of porous media. For many embodiments, the stack preferably has a compression ratio in the range from about 70% or less to about 95% or more, preferably from about 75% to about 90% , more preferably from about 75% to about 85% , e.g., 80% . If desired, the hollow housing member 26, or any suitable device, may be used as a stop to more precisely control the height of the stack after compression and consequently the amount of compression. For example, the height of the hollow housing member 26 may be chosen to be about the same as the desired height of the stack after compression. The stack then may be compressed to the height of the hollow housing member 26, and the hollow housing member 26 may prevent the stack from being compressed further. Preferably, the compression of the stack is maintained when the stack is disposed in the hollow housing member. The stack may be maintained in compression in any suitable manner, including by applying a weight to the top of the stack or by applying a predetermined pressure to the opposing porous medium supports by a mechanical or hydraulic press. A liquid sealant may be applied around the outer periphery of the stacked porous media and porous medium supports, preferably with the stack under compression. The stack may be maintained in compression in any suitable manner, including by applying a weight to the top of the stack or by applying a predetermined pressure to the opposing porous medium supports by a mechanical or hydraulic press. The compressed stack may be placed in a mold and a heated, liquid thermoplastic sealant may be inserted, e.g. , via an injection-molding technique, into the mold around the outer periphery of the stack. The areas of the mold which may come in contact with the sealant may be lined with teflon to prevent the sealant from being stuck to the mold. Preferably, the temperature of the heated, liquid thermoplastic sealant is sufficiently low, or the heated liquid is cooled sufficiently quickly, that the porous media layers are not damaged by the heat. Alternatively, instead of liquid thermoplastic sealant, a thermosetting material or any other curable liquid sealant may be inserted into the mold around the outer periphery of the stack at room temperature. With the stack under compression, the liquid sealant, e.g. , the thermoplastic sealant or the thermosetting sealant, may penetrate to a more limited depth and more substantially uniformly radially into the stack as previously described. Pressure may be applied to the liquid sealant in the mold so that the liquid sealant may penetrate the side surface of the stack. The pressure at which the liquid sealant is applied to the stack may vary depending on such parameters as the type of sealant, the nature of the porous medium, and the desired depth and uniformity of penetration. For example, the pressure may be less than about 5 psi, more preferably less than about 1 psi. In some cases, pressure may not be applied to the liquid sealant because the sealant can penetrate the side surface of the stack without pressure. Alternatively, instead of inserting a liquid sealant into the mold, a solid sealant may be placed in the mold around the outer periphery of the stack and may then be melted or softened to fill the mold around the outer periphery of the stack and to penetrate radially into the stack. As stated above, preferably, the temperature of the melted or softened sealant is sufficiently low, or the melted or softened sealant is cooled sufficiently quickly, so that the porous media are not damaged by the heat. If desired, a pressure may be applied to the molten or softened sealant to assist it in filling the mold around the outer periphery of the stack and in penetrating into the stack. The solid sealant may include one or more pieces and may have any suitable configuration that allows it to be placed in the mold around the outer periphery of the stack. For example, the solid sealant may include a single piece with a hollow, annular configuration, such as a hollow, cylindrical configuration, so that it can be placed around a cylindrical stack. Preferably, the volume of the solid sealant is about the same as the volume of the sealant filling the mold around the outer periphery of the stack plus the volume of the sealant penetrating into the stack. In this way, the sealant, when solidified in the mold, may substantially fill the mold and may be flush with the end surfaces of the stack, ensuring that the sealant substantially surrounds and seals the entire outer periphery of the stack. The solid sealant may be formed from any suitable material, such as thermoplastic material, e.g. , poly olef ins. Once the sealant is applied to the outer periphery of the stack of porous media and porous medium supports, the sealant is allowed to solidify, for example, by cooling in case of a heated, liquid thermoplastic sealant and/or by curing in case of a thermosetting sealant or any other curable liquid sealant. The solidified sealant seals the side surface of the stack of porous media and porous medium supports. The sealant also preferably joins, e.g. , bonds to or mechanically interlocks with, the porous medium supports and the porous media and substantially maintains them in position relative to one another, thereby maintaining the stack of porous media in compression. The beveled edges of the porous medium supports allow the sealant to solidify over at least a portion of the opposing faces of the porous medium supports. This enhances the ability of the sealant to secure the porous medium supports to the porous media and maintain the porous media under compression. For those embodiments that include a hollow housing member, the sealed stack of porous media may be inserted inside the hollow housing member after the sealant solidifies. Preferably, however, the hollow housing member may be inserted into the mold before the introduction of the liquid or solid sealant, or the hollow housing member may comprise the outer wall of the mold. The hollow housing member may be placed concentrically with respect to the stack of porous media with an annular space between the outer peripheral surface of the stack and the inner peripheral surface of the hollow housing member. The sealant may then be introduced into the space. As the sealant solidifies, it may bond to the hollow housing member, interlock with any configuration on the inner surface of the hollow housing member, and/or expand against the hollow housing member, securing the sealant and stack within the hollow housing member. A preferred mode of operation of a chromatography device of the present invention may be illustrated while referring to the embodiment shown in Figure 1. See previous application. A fluid, such as a test sample or an eluent, may be introduced into the chromatography device 10 through the inlet passage 16. From the inlet passage 16, the fluid passes through the first flow distributor arrangement 52 into the porous media 22. For example, in the illustrated embodiment the fluid passes from the inlet passage 16 through the first porous flow distributor 56 and into the tapered space 60. The flow distributor 56 may reduce flow disturbances, such as flow recirculation, vortices, and eddies, and flow non-uniformities as the fluid flows into the tapered space 60 from the inlet passage 16. The tapered space 60 preferably distributes uniformly the fluid from the inlet passage 16 to the porous medium module 20, which has a larger flow area than the inlet passage 16. In the illustrated embodiment, the tapered space 60 enhances the distribution of the fluid from the inlet passage 16 to the second porous flow distributor, e.g., the porous medium support 30 of the porous medium module 20. From the tapered space 60, the fluid flows through the second flow distributor 30. The second flow distributor further reduces flow disturbances and enhances the uniformity of flow rates and residence times as the fluid flows from the tapered space 60 into the porous media 22. The fluid then passes through the porous medium module 20 and through the stack of porous media 22 with a substantially uniform flow front, which can be characterized by, for example, uniform flow velocity and/or uniform residence time for substantially all streamlines of the fluid. The porous medium module 20 includes a number of features, which allow the fluid to maintain a substantially uniform flow front. For example, as the fluid passes through the porous medium module 20, the substantially uniform inwardly facing surface which is defined by the sealant 24 penetrating into the side surface of the stack of porous media 22 and porous medium supports 30, 32, minimizes flow disturbances, such as flow recirculation, vortices, and eddies, and flow non-uniformities. As the fluid flows axially through the porous media supports 30, 32 and the stack of porous media 22, the fluid streamlines at the outer portions of the supports and media are not unduly retarded by an uneven inwardly facing sealant surface. Further, undesirable mixing of the sample or eluent within the porous media supports 30, 32 and the porous media stack 22 is inhibited by the substantially uniform inwardly facing surface of the sealant. The fluid flows substantially evenly along the sealant surface without being drawn into and held up by any large nooks, crannies, or crevices in the sealant surface. Further, the fluid flows substantially evenly along the outer portions of the porous media supports 30, 32 and the stack of porous media 22 because the sealant forms a highly effective seal against radial leakage of the fluid. The fluid also flows substantially uniformly through the inner regions of the porous media stack 22. The fluid experiences a resistance to axial flow which is substantially uniform radially from the center to the outer portions of the stack. The porous media preferably have a substantially uniform thickness and permeability and the stack of porous media is uniformly compressed by the porous medium supports, providing a uniformly packed module having a resistance to axial flow which is substantially uniform radially. Further, undesirable mixing of the fluid in gaps and pockets between the porous media is prevented. Compressing the stack of porous media substantially eliminates these gaps and pockets. Consequently, the fluid flows axially through the stack of porous media with a substantially uniform flow front including uniform flow velocities and residence times within the stack. After passing through the porous media 22, the fluid passes through the second flow distributor arrangement 54 to the outlet passage 18. For example, in the illustrated embodiment, the fluid passes through the second porous flow distributor, e.g., the porous medium support 32, through the tapered space 62 through the first porous flow distributor 58 to the outlet passage 18. Each of the components of the second flow distributor arrangement 54 functions in a manner analogous to the components of the first flow distributor arrangement 52 to provide more uniform flow characteristics for fluid flowing to the outlet passage 18. The first porous flow distributor 58 may reduce flow disturbances as the fluid flows from the tapered space 62 into the outlet passage 18. By providing uniform flow characteristics, especially uniform flow characteristics within the porous media module, the chromatography device 10 significantly enhances the chromatographic separations of the porous media 22. For example, the chromatographic peaks may be much more narrow, well-separated and well-defined than those resulting from conventional chromatographic separations. Once the chromatographic separation has been completed, the porous medium module 20 may be cleaned for use in another separation. For example, the porous medium module may be removed from the housing and placed in a separate cleaning fixture or, preferably, the porous medium module may remain in the housing. A cleaning solution may then be passed through the porous medium module, including the porous media supports and the stationary separation medium, e.g. , the stack of porous media. One advantage associated with cleaning the porous medium module while it is in the housing is that the housing, including the walls of the tapered space, any porous flow distributor in the housing, and the fluid passages in the housing, are all cleaned along with the porous medium module. The cleaning solution may comprise any suitable cleaning agent, e.g., sodium hydroxide or hydrochloric acid in an aqueous solution at, for example, a one normal concentration. The cleaning solution is preferably directed in the opposite direction through the chromatography device, i.e. , from the outlet through the porous medium module to the inlet, but may be passed in either direction through the device. Because the sealant presents a substantially uniform inwardly facing surface within the porous media stack, flushing the porous medium module with a cleaning solution very thoroughly removes residue from the porous media. Once the chromatography device has been cleaned (or once a new or previously cleaned porous medium module 20, has been substituted between the cleaned plates 42, 44 along with new or cleaned seals 48, 49), another chromatographic separation may proceed. Figure 5 illustrates another example of a chromatography device 110 embodying the invention. The chromatography device 110 may include an inlet 112, an outlet 114, a porous medium module 120, and a porous medium module holder 140 retaining the porous medium module 120. The chromatography device 110 may include first and/or second flow distributor arrangements 152, 154. The first flow distributor arrangement 152 may be disposed in the flow path between the inlet 112 and the porous medium module 120, and the second flow distributor arrangement 154 may be disposed in the flow path between the porous medium module 120 and the outlet 114. The exemplary embodiment 110 shown in Figure 5 is similar to the embodiment 10 shown in Figure 1 in many aspects. Thus, much of the discussion regarding the embodiment 10 shown in Figure 1 is applicable to this embodiment 110. This embodiment 110 will be described with the emphasis on the differences between the two embodiments 10, 110. Similar to the porous medium module 20 shown in Figure 1 , the porous medium module 120 shown in Figure 5 may include a stack of porous media 122 and a sealant 124 disposed around the porous media 122. The porous medium module 120 may also include a hollow housing member 126, and the sealant 124 may be disposed between the stack of porous media 122 and the hollow housing member 126. The porous medium module 120 may also include first and/or second porous medium supports 130, 132 disposed respectively at the ends 125, 127 of the stack of porous media 122. The sealant 124 may also be similar to the sealant 24 shown in Figure 1. The sealant 124 may penetrate (1) radially (i.e. , edgewise) into the outer periphery of each porous medium 122 and/or (2) radially between adjacent porous media 122 to form a strong, effective seal and to ensure that the sealant 124 is securely bonded to the porous media 122. The sealant 124, which has penetrated the side surface 123 of the porous media 122, defines an inwardly facing side surface that forms the inner surface of the flow path through the porous media 122. Preferably, this surface is substantially free from crannies, crevices and other areas where fluid flow may stagnate. The sealant 124 may be made from any of the materials from which the sealant 24 may be made. The first and second porous medium supports 130, 132 may also be similar to the porous medium supports 30, 32 shown in Figure 1. For example, the first and second porous medium supports 130, 132 may perform any of the functions that the porous medium supports 30, 32 perform, and may have any suitable configuration that allows them to perform one or more of the functions. The lateral dimension(s) of each medium support may be similar to those of the porous media or they may be larger or smaller. For example, as shown in Figure 5, the porous medium supports 130, 132 extend laterally beyond the outer periphery of the stack of porous media 122 over a portion of the sealant 124. The thickness of each porous medium support may vary along one or both of the lateral dimensions of the porous medium support. In the embodiment shown in Figure 5, the porous medium supports 130, 132 each have a substantially constant thickness, although they may have a thickness varied to provide uniform flow through the chromatography device. For example, the porous medium supports may have a conical configuration, which may be particularly suitable for chromatography devices of large sizes. Similar to the outer periphery of the porous medium supports 30, 32, the outer periphery of each porous medium support 130, 132 may be treated to reduce its permeability so that the depth of sealant penetration into the more permeable porous medium support 130, 132 is about the same as the depth of sealant penetration into the stack of less permeable porous media 22. There are many methods to reduce the permeability of a porous medium support at its outer periphery, in addition to the methods discussed above with respect to the porous medium supports 30, 32. For example, the outer peripheral region of a porous medium support may be compressed to reduce its permeability by reducing the size of the pores or closing the pores. The outer peripheral region of a porous medium support can be compressed in a number of ways. In some embodiments, the surfaces 168, 170, 172, 174 of the porous medium supports 130, 132 may be axially compressed near the outer periphery. Alternatively or additionally, the side surface 184, 186 of the porous medium supports 130, 132 may be compressed radially inwardly. Further, the outer periphery of a porous medium support may be compressed at an angle between the axial and radial positions, producing a compressed, beveled outer edge. There are still other ways to compress the outer peripheral region of a porous medium support. In the embodiment shown in Figures 5-7, for example, each porous medium support 130, 132 is axially compressed to form opposing circular grooves 131, 133 in the outer peripheral region inside the outer periphery. The opposed compressed grooves 131, 133 are particularly effective at reducing or preventing radially inward sealant penetration of the porous medium supports 130, 132 beyond the grooves 131, 133. By pressing opposing grooves in the porous medium support, the porosity of the compacted portion between the opposing grooves is limited and the density is increased, significantly reducing the permeability of the densified or compacted portion. Consequently, the sealant is unable to penetrate radially inwardly substantially past the densified portion. Alternatively, the compressed grooves and the densified portions in each surface of the porous medium support may be offset or only one surface of the porous medium support may have a compressed groove and a densified portion, e.g. , the surface facing the porous media. The grooves are preferably configured as a continuous circle and may have any suitable cross section, such as a triangular, rectangular, or dome- shaped configuration, as shown in Figure 5. Alternatively, the outer peripheral region of the porous medium support may initially have a protrusion, such as a circular ridge, formed in one or both of the surfaces of the porous medium support in the outer peripheral region. Preferably, the porous medium support initially has generally opposing circular protrusions in opposite surfaces of the support. These protrusions are then pressed to yield a generally flat surface on the porous medium support and a corresponding densified portion within the porous medium support. Additionally or alternatively, the outer periphery of the porous medium supports 130, 132 may be coated or impregnated with any suitable coating material to reduce its permeability. A suitable coating material may be applied to the area of a porous medium support 130, 132 which may come in contact with the sealant, such as the side surface 184, 186 and/or one or both of the end surfaces 168, 170, 172, 174 near the outer periphery. Preferably, the coating material is not applied to the area of the porous medium supports 130, 132 through which the test sample or the eluent is intended to flow, to ensure that the fluid can flow through the porous medium support in an unobstructed, uniform manner. In some embodiments, two or more layers of the same or different coating materials may be applied. Suitable coating materials may include a polymer, such as polyethylene, polyolefin, polypropylene, bicomponent polyurethane or teflon. A sealant may be used as a coating material. In a preferred embodiment, the coating may include one coat of teflon or one or two coats of bicomponent polyurethane. The coating material may be applied to the outer peripheral region in different ways to reduce sealant penetration. For example, if a porous medium support has a compressed groove on one or both of its flat surfaces, the grooves may be filled with a coating material or a sealant to reduce or prevent sealant penetration beyond the grooves . The grooves are preferably filled with the coating material to present a uniform, e.g., flat, face along the surface of the porous media support. Alternatively or additionally, the side surface and/or one or both of the flat surfaces between the compressed grooves and the outer edge may be coated or impregnated with a coating material. Another method of limiting sealant penetration of the porous medium supports involves applying a tape to the outer peripheral region of the porous medium supports to reduce sealant penetration. For example, the tape may be applied to the side surface 184, 186 at the edge and/or one or both of the end surfaces 168, 170, 172, 174 near the outer periphery and even inwardly of the compressed grooves. After the tape is applied, the sealant may be applied to the porous media supports and the stack of porous media. After the sealant has solidified, the portion of the tape covering the test sample/eluent flow area of the porous medium supports may be peeled off. In this way, the sealant is prevented from obstructing the flow areas of the porous medium supports. The hollow housing member 126 shown in Figure 5 may be similar to the hollow housing member 26 shown in Figure 1. Further, the hollow housing member 126 may include a mechanism which interlocks the housing member 126 and the sealant 124. In the embodiment shown in Figure 5, the mechanism includes a configuration on the housing member 126, which configuration may include, for example, one or more protrusions and/or indentations or any irregularities in the inner surface. The protrusions may include a circular ridge, an axial rib, or any other suitable projection. The indentation may include a recess, such as a circular or axial groove, or a hole. When a sealant is applied between the hollow housing member and the stack of porous media, the configuration on the inner surface of the housing member creates a mating configuration on the outer surface of the sealant. The two configurations, which are a mirror image of each other, interlock the housing member and the sealant and prevent relative movement between them. In the embodiment shown in Figure 5, the configuration on the inner surface of housing member 126 includes indentations in the form of bevels 178, 180 at the ends of the housing member 126. The sealant 124 may protrude over the bevels 178, 180, interlocking with the bevels 178, 180 to prevent relative movement, e.g. , relative axial movement, between the housing member 126 and the sealant 124. The mating configurations may also be arranged to prevent relative rotational movement. Forces are applied to compress the stack of porous media and porous medium supports when the sealant is applied to the outer periphery of the stack. Preferably, after the forces have been removed and the sealant has solidified, the porous medium supports remain securely attached to the stack of porous media, and the porous media remain under compression. Although various devices, including mechanical devices such as clamps and fasteners, may be used to secure the porous medium supports to the stack of porous media, it is preferred that the sealant serves this purpose. Preferably, the sealant is securely attached to the porous medium supports, as well as the porous media, so that when the forces are removed, the porous medium supports remain in place and continue to compress the porous media. The sealant may be securely attached to the porous medium supports in many different ways. For example, the sealant may be securely attached to the porous medium supports simply because it penetrates into the surfaces of the porous medium supports. Alternatively or additionally, the side surfaces of the porous medium supports may include protrusions and/or indentations so that the sealant may be more securely attached to the porous medium supports. Further, the porous medium supports may extend into the sealant. In the embodiment 110 shown in Figure 5, the sealant 124 extends beyond the ends of the stack in the axial direction, and, as shown in Figure 8, a portion 188 of the sealant 124 may then extend radially inwardly over the end surfaces 168, 172 of the porous medium supports 130, 132. In this way, the sealant 124 acts as a clamp to more securely hold together the stack of porous media 122 and porous medium supports 130, 132, as well as preventing lateral displacement of the porous media supports and the porous media. Preferably, the stack of the porous media and the porous medium supports is substantially concentrically arranged with the hollow housing member. Radial displacement of one or more of the porous media supports and the porous media may create a crevice or a nook at the edge of the test sample/eluent flow path, introducing flow nonuniformities. To this end, the porous medium module may include a mechanism which centers the stack of porous media and porous medium supports. For example, the mechanism may include a plurality of spacers disposed between the housing member and the stack. The spacers preferably are dimensioned so that they center at least the stack of the porous media in the housing member. In the illustrated embodiment, as shown in Figure 9, each spacer 182 has a cylindrical configuration, and the diameter of each spacer 182 is approximately equal to the difference between the inner radius of the housing member 126 and the outer radius of the stack. When the spacers 182 are disposed around the stack between the housing member 126 and the stack, they center the stack within the housing member 126. Further, the height of the spacers may be arranged to provide a stop for the porous media supports to facilitate adequate compression without over- compression as they are pressed against the porous media stack. The method of making the porous medium module 120 shown in Figure 5 may be similar to the method of making the porous medium module 20 shown in Figure 1. The method of making the porous medium module 120 is described below with the emphasis on the differences between the two methods. The outer peripheral regions of the porous media supports are preferably processed to reduce penetration of the sealant, as previously described. For example, opposing grooves may be pressed into the outer peripheral region and the grooves may be coated and/ or preferably filled with a coating material. The layers of porous media 122 may be compressed axially against one another as they are being stacked, or they may be laid one on another without compression and then axially compressed by pressing the porous medium supports 130, 132 against the stack. The hollow housing member 126 and the stack, including the porous media supports, may then be inserted into a mold (not shown). The hollow housing member 126 may comprise the outer sidewall of the mold, and the mold may close the open ends of the hollow housing member 126. Layers of porous media 122 and/or the porous medium supports 130, 132 preferably are centered in the hollow housing member 126. The stack of porous media 122 and porous medium supports 130, 132 is preferably stacked within the hollow housing member 126, and a plurality of spacers 182 may be placed between the housing member 126 and the stack of porous media 22 to center the stack in the housing member 126. The spacers 182 may be left in the hollow housing member 126, or they may be removed before the sealant is injected into the space between the hollow housing member 126 and the stack of porous media 122 and porous medium supports 130, 132. Alternatively, other suitable centering mechanisms may be used to center the stack within the hollow housing member 126. For example, a split-ring centering mechanism may be used, or a centering member, e.g. , a centering ring may be used for each of the porous medium supports 130, 132 and the stack of porous media 122. The centering ring for each porous medium support 130, 132 preferably has an inner diameter substantially equal to the diameter of the porous medium support 130, 132 and an outer diameter substantially equal to the inner diameter of the hollow housing member 126. The centering ring for the stack of porous media 122 preferably has an inner diameter substantially equal to the diameter of the stack and an outer diameter substantially equal to the inner diameter of the hollow housing member 126. Using the centering rings, the porous media 122 and the porous medium supports 130, 132 may be centered in the hollow housing member 126 either at the same time or sequentially. For example, one of the porous medium supports 130, 132 may be centered in the hollow housing member 126 with a centering ring. Then the centering ring may be removed, and a second centering ring may be used to center the porous media 122 in the hollow housing member 126. Next, the second centering ring may be removed, and a third centering may be used to center the second porous medium support 130, 132 in the hollow housing member 126. Then the third centering ring may be removed. If the two porous medium supports 130, 132 have the same diameter, the first centering ring may be used to center the second porous medium support 130, 132. A sealant, e.g., a liquid sealant, similar to the ones described above, may be applied around the outer periphery of the stacked porous media 122 and porous medium supports 130, 132, preferably after the stack has been compressed. The pressure at which the sealant is applied to the stack 122 may vary depending on the type of sealant, the nature of the porous media 122, and the desired depth and uniformity of penetration. Preferably, the pressure is low. For example, the pressure may be less than about 5 psig, more preferably less than about 1 psig, most preferably close to or at 0 psig. Preferably, the housing member 126 includes a protrusion or an indentation such as the bevels 178, 180 shown in Figure 5, and the sealant is allowed to flow into the beveled areas. Further, the sealant may flow over the outer edge of each porous medium support 130, 132 and radially inwardly onto the outer surface 172, 168 of the porous medium support 130, 132 but preferably not beyond the compressed groove 131, 133. Once the sealant is applied to the outer periphery of the stack of porous media 122 and porous medium supports 130, 132, the sealant is allowed to solidify, for example, by cooling and/ or curing, preferably under pressure. Cooling and/or curing under pressure may reduce the formation of gas bubbles in the sealant as the sealant solidifies. The curing temperatures and pressures may vary depending, for example, on the sealant used. For example, for a bicomponent polyurethane, the curing temperature may be on the order of about 90°F and the curing pressure may be on the order of about 90 psig. The solidified sealant seals the side surface of the stack of porous media 122, as well as the outer periphery of the porous medium supports 130, 132. The sealant is also be securely attached to the porous medium supports 130, 132 and the porous media 22 so that the porous medium supports 130, 132 remain in place and maintain the stack of porous media 122 in compression. The porous medium module holder 140 may be similar to the porous medium module holder 40 shown in Figure 1. The porous medium module holder 140 preferably includes two plates 142, 144 between which the porous medium module 120 may be disposed. Connectors, such as a plurality of bolts 146 or clamps, may secure the porous medium module 120 between the two plates 142, 144. In the illustrated embodiment, the inlet 112 and outlet 114 are preferably placed near the center of the two plates 142, 144, respectively. Seals 148, 149 may be provided to prevent radially outward leakage between the porous medium module 120 and the plates 142, 144 of the porous medium module holder 140. On one side, each seal 148, 149 may be pressed against a plate 142, 144, and on the other side, the seal 148, 149 may be pressed against the porous medium module 120, for example, against one or more of the housing member 126, the sealant 124 and the porous medium support 130, 132. Preferably, the seals 148, 149 are not pressed against only a permeable area of the porous medium supports, because there is a possibility that fluid may bypass the seal 148, 149 and leak radially outwards through the permeable area of the porous medium supports 130, 132. Thus, each seal 148, 149 is preferably pressed against the housing member 126, the sealant 124 or an impermeable area of the porous medium support 130, 132. Preferably, each seal 148, 149 is placed near the outer edge of the porous medium module 120 outside of the flow area of the porous medium module 120. Each plate 142, 144 or the porous medium module 120, or both, may have an annular groove which serves as a seal gland to accommodate a seal 148, 149. In the embodiment shown in Figure 5, each of the seals 148, 149 is placed in an annular groove in a plate 142, 144 of the module holder 140 and may be sealed against a porous medium support 130, 132 and/or the sealant 124. For example, the seal 148, 149 may be sealed against an impermeable portion of the porous medium support 130, 132, which portion is impregnated with the sealant 124 and/or a coating material. Alternatively, the seal 148, 149 may be sealed against the sealant 124, the sealant 124 forming a portion of the seal gland. For example, as shown in Figure 10, the sealant 124 may include a portion 135 extending radially inwardly over the outer surface 172 of the porous medium support 132 and a portion extending generally axially outwardly from the porous medium support 132. These two portions of the sealant form part of the seal gland. The seal 149 may be sealed against these portions of the sealant 124 in the seal gland to prevent radially outward leakage. Preferably, the portion 135 of sealant 124 is smooth and flat so it can form a secure seal with the seal 149. As yet another alternative, the sealant may include only the generally axially extending portion of the seal gland, as shown in Figure 8. The seal 149 is the sealed against the sealant and the impermeable portion of the porous medium support. The embodiment shown in Figure 5 preferably includes both first and second flow distributor arrangements 152, 154, although it may include only one of the flow distributor arrangements 152, 154. The first flow distributor arrangement 152 preferably is disposed in the flow path between the inlet passage 112 and the porous medium module 120, where the inlet passage 112 has a smaller flow area than the porous medium module 120. The second flow distributor arrangement 154 preferably is disposed in the flow path between the porous medium module 120 and the outlet passage 114, and the porous medium module 120 has a larger flow area than the outlet passage 114. Generally, a flow distributor arrangement may be disposed at any place in the flow path where there is a change in flow area. As shown in Figure 5, the first flow distributor arrangement 152 preferably includes a tapered space 160. The tapered space 160 comprises at least a portion of the transition in the flow path between the smaller flow area of the inlet passage 112 and the larger flow area of the porous media 122. The first flow distributor arrangement may also include a porous flow distributor that is operatively associated with the tapered space. The porous flow distributor may be disposed at any suitable location, such as a location between the inlet passage and the tapered space, in the tapered space, between the tapered space and the porous medium module, or in the porous medium module. In the embodiment shown in Figure 5, the porous flow distributor includes the first porous medium support 130 and is disposed in the porous medium module 120, although the porous flow distributor may be a part separate from the porous medium module 120 and the porous medium module holder 140. Alternative embodiments of the flow distributor arrangement are described in detail in previously referenced United States Patent Applications No. 60/121,701 and No. 60/1678,750 and the International Application titled "Chromatography Devices and Flow Distributor Arrangements Used in Chromatography Devices, " any of which embodiments may be used in the present example 110 of a chromatography device according to the present invention. The operation of the chromatography device 110 may be substantially the same as that of the chromatography device 10, which is described above. Figure 11 illustrates another example of a device 200 embodying the invention. The device may include an inlet 201, an outlet 202, a porous medium module 210, and a porous medium holder 220 retaining the porous medium module 210. The inlet 201 and the outlet 202 define a flow path through the device 200 and the porous medium module 210 is deposed in the flow path. In the illustrated embodiment the device 200 does not include any flow distributor arrangements. However, a flow distributor arrangement may be provided in the flow path between the inlet 201 and the porous medium module 210 and/or between the porous medium module 210 and the outlet 202. Similar to the porous media module holders shown in the previous embodiments, the porous media holder 220 preferably comprises holder sections such as two opposed plates 221, 222 which contain the porous medium module 210. The inlet 201 and the outlet 202 may be respectively disposed in the plates 221, 222. The porous medium module 210 may be used in a wide variety of separations. For example, the porous medium module 210 may be used as a sampling module. Similar to the porous medium modules shown in previous embodiments, the porous medium module 210 shown in Figure 11 may include a stack of porous media 211 and a sealant 212 disposed around the porous media 211. The porous media 211 may be similar to the porous media of any of the previous embodiments. The porous medium module may include a hollow housing member disposed around the sealant, a first porous medium support disposed at one end of the porous media stack, and/or a second porous medium support disposed at the other end of the porous media stack. However, the porous medium module 210 preferably does not include a hollow housing member or any porous medium supports, having as its principal structural components only the stack of porous media 211 and the sealant 212. The sealant 212 may be similar to the sealant in any of the previous embodiments. For example, the sealant 206 may penetrate (1) radially into the outer periphery of each porous medium 211 and/or (2) radially between adjacent porous media 211 to form a strong, effective seal and to ensure that the sealant 212 is securely bonded to the porous media 211. The sealant 212 may define an inwardly facing side surface that forms the inner surface of the flow path through the porous media 211. Preferably, this surface is substantially free of crannies, crevices and other areas where fluid flow may stagnate. However, the variation in sealant penetration may be larger than in previous embodiments. The porous media module 210 may be formed in a manner similar to any of the porous media modules of the previous embodiments. For example, the layers of porous media 211 may be compressed, e.g., between opposed plates, and confined within a mold. The sealant 212 may then be applied around the outer periphery of the compressed porous media stack. Again, the pressure at which the sealant is applied may vary depending on the type of sealant, the nature of the porous media, and the desired depth and uniformity of penetration. The sealant, after it solidifies, may extend axially beyond one or both ends of the stack of porous media, but in the illustrated embodiment the sealant 212 is substantially even with the ends of the porous medium stack. The sealant 212 of the porous media module 210 preferably includes a seat arrangement 213 on one or both ends of the module 210. The seat arrangement 213 is operatively associated with a sealing mechanism, such as a circular seal edge 223, on the porous media holder 220. The configuration of the seat arrangement 213 may generally correspond to the configuration of the seal edge 223. For a circular seal edge 223, the seat arrangement 213 may also be circular. Preferably, opposing seal edges 223 are disposed on the plates 221, 222 and contact the seat arrangements 213 on opposite ends of the porous media module 210 when the plates 221, 222 are mounted to one another, e.g. , by a threaded connector or a clamping mechanism. The seat arrangement 213 may be contoured but is preferably flat and may be located outside of the effective flow area of the stack of porous media 211, preferably outside the outer diameter of the porous media 211. Further the sealant 212 is preferably compliant, e.g. , elastic. For example, the sealant 212 may be formed from a compliant or resilient polyurethane. When the plates 221, 222 are mounted to one another and the seal edges 223 engage the seat arrangements 213, the seal edges 223 may compress the compliant sealant 212 and effect a reliable seal between the porous media module 210 and the module holder 220. The module holder 220 may include stops 224 to prevent over compression of the sealant 212. The operation, including the cleaning, of the device 200 shown in Figure 11 may be similar to the operation of any previous embodiment. While various aspects of the invention have been described with respect to several embodiments, many variations in these embodiments would be obvious to those of ordinary skill in the art in light of the teachings in this specification. For example, in accordance with the present invention, one or more or all of the features of any of the disclosed embodiments may be substituted and/or combined with one or more or all of the features of any of the other disclosed embodiments. For example, any and all of the methods for reducing the permeability of a porous medium support 130, 132 at its periphery, which are discussed with respect to the embodiment 110 shown in Figure 5, can be used to reduce the permeability of a porous medium support 30, 32 at its periphery shown in Figure 1. Further, in accordance with the present invention, fewer than all of the features of each of the disclosed embodiments may be included. For example, the hollow housing member 126 may not include any configuration on its inner surface for interlocking the housing member 126 and the sealant 124. Accordingly, all features, modifications and variations of the disclosed embodiments are encompassed within the spirit and scope of the invention as currently or hereafter claimed.

Claims: CLAIMS 1. A porous medium module for use in adsorptive and/or chromatographic separations, the porous medium module comprising: a hollow housing member; a plurality of porous media stacked in the hollow housing member; and a sealant disposed between the stacked porous media and the hollow housing member and sealing an outer periphery of the stacked porous media. 2. The porous medium module of claim 1 , wherein the sealant penetrates into the outer periphery of the stacked porous media. 3. The porous medium module of claim 2, wherein the depth of sealant penetration into the outer periphery of the stacked porous media is substantially uniform. 4. A porous medium module for use in adsorptive and/or chromatographic separations, the porous medium module comprising: a plurality of stacked porous media having an outer periphery; and a sealant disposed around the outer periphery of the stacked porous media and penetrating into the outer periphery of the stacked porous media, wherein the depth of penetration of the sealant into the outer periphery of the stacked porous media is substantially uniform. 5. The porous medium module of claim 2, 3 or 4, wherein the sealant penetrates into each porous medium and between adjacent porous media. 6. The porous medium module of any one of claims 2 to 5, wherein a maximum variation of sealant penetration is less than or equal to a thickness of each porous medium. 7. The porous medium module of any one of claims 2 to 6, wherein a maximum variation of sealant penetration is less than or equal to a pitch of variation of sealant penetration. 8. The porous medium module of any one of the preceding claims comprising at least a porous medium support operatively associated with the stacked porous media. 9. The porous medium module of any one of the preceding claims, wherein the porous media are axially compressed. 10. The porous medium module of claim 9 comprising two porous medium supports, wherein the porous media are axially compressed by the two porous medium supports. 11. The porous medium module of any one of the preceding claims, wherein the sealant comprises a thermoplastic material. 12. The porous medium module of any one of claims 1 to 10, wherein the sealant comprises a curable material. 13. The porous medium module of claim 12, wherein the sealant comprises a thermosetting material. 14. A porous medium module for use in adsorptive and/or chromatographic separations, the porous medium module comprising: a hollow housing member having an inner surface; a plurality of porous media stacked in the hollow housing member; and a sealant disposed between the stacked porous media and the hollow housing member, wherein the housing member includes a configuration that interlocks the housing member and the sealant. 15. The porous medium module of claim 14, wherein the configuration includes a recess on the inner surface of the housing member. 16. The porous medium module of claim 15, wherein the housing member includes first and second ends, and the recess includes a chamfer at each of the first and second ends. 17. The porous medium module of claim 15 or 16, wherein the recess includes a circular groove between the first end and the second end. 18. The porous medium module of claim 15, 16 or 17, wherein the sealant protrudes into the recess to interlock the housing member and the sealant. 19. The porous medium module of any one of claims 14 to 18, wherein the configuration includes a protrusion. 20. The porous medium module of claim 19, wherein the protrusion protrudes into the sealant to interlock the housing member and the sealant. 21. A porous medium module for use in adsorptive and/or chromatographic separations, the porous medium module comprising: a hollow housing member; a plurality of porous media stacked in the hollow housing member; and a mechanism operatively associated with the hollow housing member and the stack of porous media, wherein the mechanism centers the stack of porous media in the hollow housing member. 22. A porous medium module for use in adsorptive and/or chromatographic separations, the porous medium module comprising: a plurality of stacked porous media having an outer periphery; at least one porous medium support having an outer peripheral region, the porous medium support being operatively associated with the stacked porous media; and a sealant disposed around the stacked porous media and the porous medium support, the sealant penetrating into the outer periphery of the stacked porous media and into the outer periphery of the porous medium support, at least a portion of the outer peripheral region of the porous medium support being at least partially obstructed to reduce the penetration of the sealant into the porous medium support. 23. The porous medium module of claim 22, wherein the porous medium support has first and second surfaces and the stack of porous media has first and second end surfaces, and the second surface of the porous medium support contacts the first end surface of the stacked porous media. 24. The porous medium module of claim 22 or 23, wherein the obstructed portion of the porous medium support includes a first densified portion which reduces the radially penetration of the sealant. 25. The porous medium module of claim 24, wherein the first densified portion corresponds to a first compressed groove placed inwardly from the outer periphery of the porous medium support. 26. The porous medium module of claim 24 or 25, wherein the first compressed groove has a circular configuration. 27. The porous medium module of any one of claims 24 to 26, wherein the obstructed portion of the porous medium support includes a second densified portion corresponding to a second compressed groove on the second surface. 28. The porous medium module of claim 27, wherein the first and second compressed grooves oppose one another. 29. The porous medium module of claim 27 or 28, wherein at least one of the grooves is filled with a coating material. 30. The porous medium module of claim 27, 28 or 29, wherein both grooves are filled with a coating material. 31. The porous medium module of any of claims 22-30, wherein at least a portion of the outer peripheral region is coated with a coating material. 32. The porous medium module of any one of claims 22 or 31, wherein a tape is applied to the outer peripheral region of the porous medium supports to reduce the sealant penetration. 33. The porous medium module of any one of claims 22 to 32, wherein the porous medium support has a generally circular configuration and the stacked porous media has a generally cylindrical configuration, the diameter of the porous medium support being greater than the diameter of the stacked porous media. 34. A porous medium module for use in adsorptive and/or chromatographic separations, the porous medium module comprising: first and second permeable porous medium supports; a plurality of porous media stacked and compressed between the first and second permeable porous medium supports; and a hollow peripheral arrangement disposed around the supports and the media and coupled to the edges of the supports and media to seal and support the supports and media. 35. The porous medium module of claim 34, wherein the hollow peripheral arrangement includes a sealant. 36. A porous medium module for use in adsorptive and/or chromatographic separations, the porous medium module comprising: first and second porous medium supports; a plurality of porous media stacked between the first and second permeable porous medium supports; and a sealant coupled to the porous medium supports to secure the porous medium supports to the porous media. 37. The porous medium module of claim 36, wherein the sealant is disposed around the porous medium supports and porous media. 38. The porous medium module of claim 35, 36 or 37, wherein the sealant penetrates into and is attached to a side surface of each porous medium support. 39. The porous medium module of claim 35, 36, 37 or 38, wherein each porous medium support has first and second surfaces, and the second surface of each porous medium support contacts the stack of porous media, and wherein the sealant extends radially inwardly from the outer periphery of the porous medium support over the first surfaces of the porous medium supports. 40. A method for making a porous medium module, comprising: stacking a plurality of porous media; disposing a liquid sealant around the outer periphery of the stack of porous media; allowing the sealant to penetrate into the outer periphery of the stack of porous media; and allowing the liquid sealant to solidify to form a seal around the stacked porous media. 41. The method of claim 40 including compressing the stacked porous media while the liquid sealant is being disposed around the porous media. 42. The method of claim 40 or 41 , wherein the depth of penetration of the sealant into the outer periphery of the stacked porous media is substantially uniform. 43. The method of claim 42, wherein a maximum variation of sealant penetration is less than or equal to a thickness of each porous medium. 44. The method of claim 42 or 43, wherein a maximum variation of sealant penetration is less than or equal to a pitch of variation of sealant penetration. 45. The method of any one of claims 40 to 44, wherein allowing the liquid sealant to solidify includes allowing the sealant to solidify under pressure. 46. The method of any one of claims 40 to 45 including compressing a first porous medium support near an outer edge of the first porous medium support to form a groove on at least one of first and second surfaces of the first porous medium support. 47. The method of claim 46 including compressing a second porous medium support near an outer edge of the second porous medium support to form a groove on at least one of first and second surfaces of the second porous medium support. 48. The method of claim 46 or 47 including placing the first porous medium support at a first end of the stacked porous media. 49. The method of claim 47 or 48 including placing the second porous medium support at a second end of the stacked porous media. 50. The method of claim 47, 48 or 49 including compressing the stacked porous media between the first and second porous medium supports. 51. The method of any one of claims 46 to 50 including applying at least one coat of a polymer to an outer periphery of each porous medium support. 52. The method of claim 51 including applying at least one coat of the polymer to a side surface of each porous medium support. 53. The method of claim 51 or 52 including applying at least one coat of the polymer to at least one of the first and second surfaces of each porous medium support between the groove and the outer edge of the porous medium support. 54. The method of any one of claims 46 to 47 including applying a tape to at least one of the first and second surfaces of each porous medium support between the groove and the outer edge of the porous medium support before disposing the liquid sealant around the outer periphery of the stacked porous media. 55. The method of claim 54 including peeling off the tape from the porous medium supports after the liquid sealant has solidified. 56. The method of any one of claims 46 to 55 including filling the grooves of the porous medium supports with the polymer. 58. The method of any one of claims 51 to 56, wherein the polymer is bicomponent polyurethane. 59. The method of claim 58, wherein applying at least one coat of bicomponent polyurethane includes applying at least two coats of bicomponent polyurethane. 60. The method of any one of claims 46 to 59 including placing the first porous medium support at a first end of the stacked porous media. 61. The method of claim 60, wherein a first surface of the first porous medium support contacts the first end surface of the stacked porous media and a second surface of the first porous medium support faces away from the stacked porous media. 62. The method of claim 60 or 61 including placing the second porous medium support at a second end of the stacked porous media. 63. The method of claim 61, wherein a first surface of the second porous medium support contacts the second end surface of the stacked porous media and a second surface of the second porous medium support faces away from the stacked porous media. 64. The method of any one of claims 46 to 63 including placing the stacked porous media and each porous medium support in a hollow housing member. 65. The method of claim 64 including centering the stacked porous media and each porous medium support in the hollow housing member using a plurality of spacers. 66. The method of claim 64 or 65 including placing the stacked porous media, each porous medium support and the hollow housing member in a mold. 67. The method of claim 66, wherein the housing member includes two open ends, and the mold closes the two open ends of the housing member. 68. The method of any one of claims 64 to 67, wherein disposing a liquid sealant around the outer periphery of the stack of porous media includes injecting the sealant into the housing member slowly at a low pressure. 69. The method of any one of claims 46 to 68, wherein disposing a liquid sealant around the outer periphery of the stacked porous media includes allowing the sealant to flow over each porous medium support so that the sealant covers an area of the second surface of each porous medium support between the compressed groove and the outer edge of the porous medium support. 70. A porous medium module for use in separations, the porous medium module comprising: a plurality of stacked porous media having an outer periphery and a first end; and a sealant disposed around the outer periphery of the stacked porous media, the sealant forming at least a portion of a first seal gland near the first end of the stack. 71. The porous medium module of claim 70, wherein the stack has a second end, and the sealant forms at least a portion of a second seal gland near the second end of the stack. 72. A porous medium module for use in separations, the porous medium module comprising: a plurality of stacked porous media having an outer periphery and a first end; and a sealant disposed around the outer periphery of the stacked porous media, the sealant forming a first seat arrangement near the first end of the stack. 73. The porous media module of claim 72, wherein the stack has a second end and the sealant forms a second seat arrangement near the second end of the stack. 74. A chromatography device for use in adsorptive and/or chromatographic separations, the chromatography device comprising: an inlet; an outlet; the porous medium module of any one of the claims 1 to 39, 70 and 71; and a porous medium module holder, wherein the porous medium module is disposed in the porous medium module holder. 75. The chromatography device of claim 74, wherein the holder includes first and second plates between which the porous medium module is disposed. 76. The chromatography device of claim 74 comprising first and second seals, wherein the first seal seals a gap between the first plate and the porous medium module, and the second plate seals a gap between the second plate and the porous medium module. 77. The chromatography device of claim 76, wherein the first seal is the first seal gland, and the second seal is the second seal gland.

Inventors: BUSH GARY, FENDYA THOMAS J, HURWITZ MARK F, SORENSEN THOMAS, STREMPEL JOHN, BUSH, GARY, FENDYA, THOMAS, J., HURWITZ, MARK, F., SORENSEN, THOMAS, STREMPEL, JOHN
Applicants: BUSH GARY, FENDYA THOMAS J, HURWITZ MARK F, PALL CORP, SORENSEN THOMAS, STREMPEL JOHN, BUSH, GARY, FENDYA, THOMAS, J., HURWITZ, MARK, F., PALL CORPORATION, SORENSEN, THOMAS, STREMPEL, JOHN
Application year: 2000
Main classification: G01N30
IPC codes: B01D15, G01N30