Patent Publication Number: US-2006011532-A1

Title: Chromatography cartridge

Description:
TECHNICAL FIELD  
      This invention relates to a cartridge used in purification processes including liquid chromatography.  
     BACKGROUND  
      Liquid chromatography is a technique for separating the individual compounds that exist in a subject sample. In employing the technique, the subject sample is carried in a liquid, called a mobile phase. The mobile phase carrying the subject sample is caused to migrate through a media, called a stationary phase. Different components have differing rates of migration through the media, which effects the separation of the components in the subject sample. Liquid chromatography is commonly performed with reusable columns or with disposable cartridges, both of which are usually cylindrical, in which the media bed is bounded axially by porous members, or plates containing defined flow paths, through which the mobile phase flows.  
       FIGS. 1A and 1B  illustrate a conventional compression module  10  and chromatography cartridge  12 . The compression module  10  has a top head assembly  14  and a barrel assembly  16 . The cartridge  12  is configured to fit within the barrel assembly  16 , and the bed  19  is axially bounded by porous plates  18 ,  20 . Optionally, a sample module (not shown) carrying a sample to be purified can be placed within the cartridge  12  above the porous plate  18 . For example, a sample module as described in U.S. Pat. No. 6,139,733, issued Oct. 31, 2000 to Hargro et al., entitled “Module and Method for Introducing a Sample into a Chromatography Column”. The barrel assembly  16  includes a lower head  22  and a compressible seal  24 , such as an O-ring. The top head assembly  14  includes at least one compressible seal  26 , such as an O-ring, and may optionally include more than one, particularly if a sample module is used within the cartridge  12 . The cartridge  12  is loaded with a stationary phase forming the bed  19 , e.g., silica, which is bounded by the porous plates  18 ,  20 , and placed into the barrel assembly  16 . The porous plate  20  abuts the lower head  22 . The barrel assembly  16  is attached to the top head assembly  14 , and a top head  28  abuts the porous plate  18  in the cartridge  12 , or the upper surface of a sample module if a sample module is used. A knob  30  can be rotated by a user to lower the internal components of the top head assembly  14 , thereby asserting a downward force through the compression ring  34  and the top head  28  onto the upper porous plate  18 , compressing the seals  26 . The force is transferred through the cartridge to the lower head  22 , and compresses the seal  24 . The seals  26  and  24  prevent fluid from escaping either the top or bottom of the cartridge  12 . Fluid can drain from the cartridge  12  via a passage  32 , for example, to be collected in a collection vessel. Typically, the compression module  10  is reusable and the cartridge  12  is disposable.  
      Other conventional chromatography cartridges include using a glue dispenser tube filled with silica contained by a top and bottom plate. Outlet tubing is connected to the bottom of the tube. A cartridge module is used to position and hold a head inside the top of the glue tube to seal the tube and allow connection of inlet tubing. Syringe bodies are also used as chromatography columns and are filled with silica contained by a top and bottom plate. A syringe body without caps uses inlet and outlet connections similar to what are used with a glue tube cartridge. Syringe bodies with caps typically have a luer fitting molded into the cap as well as the bottom of the syringe body. Inlet and outlet tubes are connected to the luer fittings.  
       FIG. 2A  shows an exemplary chromatography system  50  including a solvent reservoir  52 , a pump  54 , a chromatography column  58  and a sample collection vessel  60 . A sample module  56  is shown inserted into the chromatography column  58 . The chromatography column  58  may include a compression module housing a chromatography cartridge. A sample to be purified can be pre-absorbed onto media in the sample module  56  and inserted into the cartridge of the chromatography column  58 . Solvent is then pumped from the solvent reservoir  52  through the sample module  56  and into the chromatography column  58  to perform a purification process. Alternatively, the sample can be injected or placed onto the top of the chromatography column  58  without using a sample module.  
      In yet another alternative, shown in  FIG. 2B , another exemplary chromatography system  70  includes a solvent reservoir  72 , a pump  74  and sample module  76  inserted into a remote holder  86 . The remote holder  86  is connected to an inlet of a chromatography column  78 . The chromatography column  78  can include a compression module and a cartridge. A sample collection vessel  84  is connected to an outlet  80  of the chromatography column  78 . A sample to be purified is pre-absorbed onto media in the sample module  76 , and then the module  76  is inserted into the remote holder  86 . Solvent is pumped from the solvent reservoir  72  through the sample module  76 , from where the solvent is directed into the chromatography column  78 .  
     SUMMARY  
      This invention relates to a cartridge used in purification processes including liquid chromatography. In general, in one aspect, the invention features an apparatus including a tubular member and at least one porous member fitted within the interior region of the tubular member. The tubular member has an interior surface forming an interior region and an exterior surface. The exterior surface includes one or more longitudinal ribs protruding from the exterior surface along at least a portion of the length of the exterior surface.  
      In general, in another aspect, the invention features an apparatus including a tubular member and at least one porous member fitted within the interior region of the tubular member. The tubular member can have an interior surface forming an interior region and an exterior surface. The porous member can include a frame having an annular outer member, and a porous inner member comprising a screen.  
      In general, in another aspect, the invention features an apparatus including a tubular member and at least one porous member fitted within the interior region of the tubular member. The tubular member includes an exterior surface, an interior surface forming an interior region, an inlet region, and an outlet region. The outlet region comprises an outlet plate that is positioned substantially perpendicular to a longitudinal axis of the tubular member and has an upper surface and a lower surface. The outlet plate includes an outlet opening extending through the outlet plate from the upper surface to the lower surface. An outlet member is attached to the lower surface of the outlet plate, the outlet member including an interior region forming an outlet passage. The outlet passage is axially aligned with the outlet opening formed in the outlet plate, and has a substantially cylindrical exterior region with a tapered end.  
      In general, in another aspect, the invention features an apparatus including a tubular member. The tubular member includes an exterior surface, an interior surface forming an interior region, an inlet region, and an outlet region. The outlet region includes an outlet plate that is positioned substantially perpendicular to a longitudinal axis of the tubular member and has an upper surface and a lower surface. The outlet plate includes an outlet opening extending through the outlet plate from the upper surface to the lower surface. An outlet member is attached to the lower surface of the outlet plate and includes an interior region forming an outlet passage, where the outlet passage is axially aligned with the outlet opening formed in the outlet plate. A guard member is attached to the lower surface of the outlet plate, the guard member having an interior region, where the outlet member is positioned within the interior region of the guard member.  
      In general, in another aspect, the invention features an apparatus including a tubular member. The tubular member has an interior surface forming an interior region and an exterior surface, where the exterior surface includes one or more ribs protruding from the exterior surface around all or a portion of the circumference of the exterior surface along at least a portion of the length of the exterior surface.  
      In general, in another aspect, the invention features an apparatus including a tubular member and at least one porous member fitted within an interior region of the tubular member. The tubular member has an interior surface forming an interior region and an exterior surface, where the interior surface of the tubular member has a substantially circular cross-section and includes at least one region of reduced interior diameter. The exterior circumferential surface of a porous member is positioned against the region of reduced interior diameter of the tubular member.  
      In general, in another aspect, the invention features an apparatus including a tubular member. The tubular member includes an exterior surface, an interior surface forming an interior region, an inlet region, and an outlet region. The outlet region includes an outlet plate that is positioned substantially perpendicular to a longitudinal axis of the tubular member and has an upper surface and a lower surface. The outlet plate includes an outlet opening extending through the outlet plate from the upper surface to the lower surface, and a plurality of ribs extending along at least a portion of the lower surface of the outlet plate. An outlet member is attached to the lower surface of the outlet plate and includes an interior region forming an outlet passage, where the outlet passage is axially aligned with the outlet opening formed in the outlet plate.  
      Implementations can include one or more of the following. At least one porous member can be orientated substantially perpendicular to a longitudinal axis of the tubular member and in contact with the interior surface of the tubular member. The exterior surface of the tubular member can include an upper portion having one or more projections protruding from the exterior surface. The one or more projections can be one or more ribs protruding from the exterior surface around all or a portion of the circumference of the exterior surface. The exterior surface of the tubular member can include a lower portion, wherein the one or more longitudinal ribs extend the length or a portion of the length of the lower portion.  
      The porous member can include a frame having an annular outer member, and a porous inner member. The porous member can further include one or more support members, where the porous inner member extends between the annular outer member and the one or more support members. The one or more support members can be radial support members. The porous inner member can be a screen. The frame of the porous member can be injection molded from plastic and the porous inner member can be a screen. The frame can further include a center support hub configured to deflect a jet of fluid.  
      The interior surface of the tubular member can have a substantially circular cross-section and include at least one region of reduced interior diameter. An exterior circumferential surface of a porous member can be positioned against a region of reduced interior diameter of the tubular member. The interior surface can include two regions of reduced interior diameter, including a first region of a first reduced interior diameter and a second region of a second reduced interior diameter, where the second reduced interior diameter is less than the first reduced interior diameter. The interior surface of the tubular member can have a substantially circular cross-section and the interior diameter can decrease from an inlet region toward an outlet region.  
      The tubular member can further include an inlet region and an outlet region. The outlet region can include an outlet plate that is positioned substantially perpendicular to a longitudinal axis of the tubular member and has an upper surface and a lower surface. The outlet plate can include an outlet opening extending through the outlet plate from the upper surface to the lower surface. An outlet member can be attached to the lower surface of the outlet plate and include an interior region forming an outlet passage, where the outlet passage is axially aligned with the outlet opening formed in the outlet plate. A first porous member can be positioned within the inlet region of the interior of the tubular member and a second porous member positioned within the outlet region of the interior of the tubular member.  
      The upper surface of the outlet plate can include a plurality of ribs extending from the interior surface of the tubular member toward the outlet opening, wherein the ribs are configured to support the second porous member. The lower surface of the outlet plate can include a plurality of ribs. Each of the plurality of ribs formed on the lower surface of the outlet plate can include a rib extending along at least a portion of a radius of the lower surface of the outlet plate. Alternatively, each of the plurality of ribs can include a rib extending across a width of at least a portion of the lower surface of the outlet plate.  
      A guard member can be attached to the lower surface of the outlet plate, the guard member including an interior region. The outlet member can be positioned within the interior region of the guard member. The lower surface of the outlet plate can include a plurality of ribs extending from an interior surface of the tubular member toward an exterior surface of the guard member attached thereto. The tubular member can be injection molded.  
      Implementations of the invention can realize one or more of the following advantages. The cartridge includes a collection area and an outlet member to direct fluid out of the cartridge, for example, into a collection vessel. Cartridges of varying length and diameter can have a uniformly sized and configured outlet member, which can be mated with a cartridge module or fluid connection. Having a uniform outlet member allows different sizes of cartridges to be used with a single cartridge module or fluid connection system. The outlet member is configured to provide a low connection force seal with exit fluid path, i.e., a user does not have to exert significant force to mate the outlet member to the exit fluid connection and create the seal. Twisting the cartridge to create a seal is not required, as is recommended if a luer fitting is used, thereby further facilitating connecting the cartridge to a fluid connection. Design tolerances can be relaxed due to the configuration of the sealing mechanism. Because an O-ring seal can be used against the substantially cylindrical outlet member, the location of the seal along the outlet member is not critical, allowing for some relaxation in axial design tolerances. By comparison, a luer fitting, for example, requires male and female luer parts be pressed tightly together, requiring more stringent axial design tolerances or compensation systems.  
      A guard member surrounding the outlet member protects the outlet member from damage, for example, if the cartridge is bumped or dropped. Ribs positioned on the upper surface of the outlet plate that support the lower porous member can keep the lower porous member from bowing under force into the collection area. Ribs formed along the lower surface of the outlet plate of the tubular member can create a strong bottom to resist internal pressures during a purification process, without excess stress on the outlet plate and limiting deflection to avoid disturbing the stationary phase within the cartridge. A conical outlet opening facilitates directing the flow of fluid from the cartridge into the outlet passage.  
      A textured surface, such as a knurled or stippled surface, or one or more circumferential ribs along the upper portion of the exterior surface of the cartridge provide a non-slip surface for a user to grip. The textured surface, projections or circumferential ribs can be configured to mate with corresponding features, e.g., grooves, formed on the interior of an outer annular member of a top head assembly of a cartridge module. When an axial force is exerted on the O-ring within the top head, the O-ring expands laterally causing a small increase in the outer diameter of the upper portion of the cartridge, which can cause the ribs on the cartridge to engage with the grooves in the top section. Engaging the ribs and grooves can increase the resistance of the assembly to separating due to the force of the internal pressure of the cartridge during a purification process.  
      Longitudinal ribs along the lower portion of the exterior surface of the cartridge can keep the cartridge from rolling. The ribs also add rigidity to the cartridge and can reduce or prevent bowing of the cartridge, for example, by increasing the bending moment of inertia of the cartridge. If the cartridge is formed from an injection molding process, the ribs can help plastic flow during the molding and can provide a surface to use when detaching the tubular member from a mandrel.  
      The tubular member and at least a portion, of the porous members can be formed from injection molding. Injection molding can provide a greater consistency of the interior diameter of the tubular member and a smoother internal surface, for example, as compared to an extruded tubular member. Spider lines, which are typical with a member formed by extrusion, can be avoided by injection molding. Injection molding the annular outer member and supports of the porous members can provide a better tolerance control on the exterior diameter of the porous members. Using a screen to create a porous member, as compared to, for example, a sentered porous plastic disk, can improve the quality of the porous members, e.g., due to there being fewer extractables. The porous member can have an overall smaller depth and therefore the total length of the cartridge can be smaller. Injection molding the annular outer member can provide a smoother surface that contacts the internal surface of the tubular member.  
      The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     DESCRIPTION OF DRAWINGS  
       FIG. 1A  shows a compression module.  
       FIG. 1B  shows a chromatography cartridge.  
       FIGS. 2A and 2B  show schematic representations of chromatography systems.  
       FIG. 3  shows a perspective view of a chromatography cartridge.  
       FIG. 4  shows a perspective, longitudinal cross-sectional view of a chromatography cartridge.  
       FIG. 5  shows a perspective view of a porous member.  
      FIGS.  6 A-C show longitudinal cross-sectional views of three alternative tubular members of a chromatography cartridge.  
       FIG. 7  shows an exploded view of a porous member and a portion of a tubular member of a chromatography cartridge.  
       FIG. 8A  shows a perspective, longitudinal cross-sectional view of a tubular member of a chromatography cartridge.  
       FIG. 8B  shows a longitudinal cross-sectional view of an enlarged portion of a tubular member of a chromatography cartridge.  
       FIG. 9A  shows a perspective view of the bottom of a chromatography cartridge.  
       FIG. 9B  shows a bottom view of a chromatography cartridge with an alternative ribbing configuration.  
       FIG. 10  shows a chromatography cartridge attached to a cartridge module.  
       FIG. 11  is a flowchart showing a process for using a chromatography cartridge to purify a sample.  
       FIG. 12  shows a side view of a chromatography cartridge.  
       FIG. 13A  shows a tubular member with an upper portion including protruding, angled ridges.  
       FIG. 13B  shows a schematic representation of a plan view of an upper portion of a tubular member included angled ridges.  
      FIGS.  14 A-C show a top head assembly configured to mate with the tubular member of  FIG. 13A . 
    
    
      Like reference symbols in the various drawings indicate like elements.  
     DETAILED DESCRIPTION  
       FIG. 3  shows a chromatography cartridge  100  that can be used in a purification process including, for example, a liquid chromatography operation, a scavenging operation or a reaction process. The cartridge  100  can be used in one of the exemplary chromatography systems described above or another purification system. The cartridge  100  includes a substantially tubular member  101  having an exterior surface  102  and an interior surface  104  that forms an interior region  106 . The exterior surface  102  can have an upper portion  108  and a lower portion  110 , where the upper portion includes ribs  112  arranged circumferentially about at least a portion of the exterior surface and the lower portion includes ribs  114  arranged longitudinally along at least a portion of the length of the lower portion  110  of the exterior surface  102 .  
      The circumferential ribs  112  can provide a non-slip surface for a user to grip when handling the cartridge  100 . Alternatively, the upper portion can include a textured surface, such as a knurled surface, stippled surface or surface with projections of some sort, to provide a non-slip gripping surface. The longitudinal ribs  114  can provide rigidity to the cartridge  100 , for example, to prevent bowing of the tubular member  101 . The longitudinal ribs  114  can also keep the cartridge  100  from rolling, for example, when placed horizontally on a surface such as a lab workbench.  
       FIG. 4  shows a perspective, cross-sectional view of the cartridge  100 , including upper and lower porous members  116 ,  118  positioned within the tubular member  101 . The upper porous member  116  is positioned within an inlet region  120  of the tubular member  101 , and the lower porous member  118  is positioned within an outlet region  122 . In the embodiment shown, the upper porous member  116  is positioned to provide space for a sample module (not shown) to be inserted into the inlet region  120  above the upper porous member  116 . In an alternative embodiment, the upper porous member  116  can be positioned closer to the inlet end  124  of the tubular member  101 , for example, if a sample module will not be used. Other configurations of the porous members can be used, e.g., a porous member can be approximately as thick as the member is wide.  
       FIG. 5  shows one embodiment of a porous member, which for illustrative purposes is shown as the upper porous member  116 . The porous member  116  includes a frame having a substantially annular outer member  128  and one or more radial support members  130 . A porous material  132  extends between the annular outer member  128  and the radial support members  130 . In one embodiment, the porous material  132  is a screen. For example, a screen can be formed from woven threads of 316 stainless steel screen. In one embodiment, the screen includes 325 threads per inch in one direction and 2300 threads per inch in a perpendicular direction, creating openings approximately 2 microns wide. The porous member  116  shown includes 6 radial support members  130 . More or fewer radial support members  130  can be included. Alternatively, support members of a different configuration can be used, for example, lateral supports of differing length extending across the width of the porous member. Other embodiments of porous members can be used, for example, a disk-shaped polyethylene porous plate. The center support hub  133  can deflect a jet of fluid, eliminating a “jetting effect” and spreading out the flow of fluid more evenly through the porous member and cartridge  100 .  
      The upper and lower porous members  116 ,  118  can be mounted to the interior surface  104  of the tubular member  101  by a friction fit, an adhesive, one or more mounting screws, ultrasonic or heat welding, or a combination of the above or using another convenient technique. In one embodiment, the interior diameter of the tubular member  101  includes regions of reduced diameter, so as to provide a friction fit surface against which to mount the upper and lower porous members  116 ,  118 , permitting the porous members  116 ,  118  to be positioned in the tubular member  101  without having to force them through the full length of the interior region  106 .  
       FIG. 6A  shows a cross-sectional view of the tubular member  101 . The interior surface  104  includes an upper region of reduced diameter  134  having interior diameter ID u  and a lower region of reduced diameter  136  having interior diameter ID 1 . The diameter can be reduced by a relatively small amount. For example, for a tubular member  101  having an interior diameter of approximately 1.57 inches, the interior diameter can be reduced approximately 0.005 to 0.010 of an inch. The exterior diameter of the upper and lower porous members  116 ,  118  is configured so as to friction fit within the corresponding region of reduced diameter  134 ,  136 . An angled lead-in region  135 ,  137  at each region of reduced diameter  134 ,  136  can facilitate insertion of the porous members  116 ,  118 .  
      In one embodiment, the lower region of reduced diameter  136  can have a smaller diameter than the upper region of reduced diameter  134 . That is, ID 1  is less than ID u . The exterior diameter of the lower porous member  118  is less than the exterior diameter of the upper porous member  116  by an amount approximately corresponding to the difference between ID u  and ID 1 . The lower porous member  118  can therefore pass through the upper region of reduced diameter  134  without interference as the lower porous member  118  is moved into position in the lower region of reduced diameter  136 .  
      Referring to  FIG. 6B , in another embodiment of a tubular member  101 ′, the diameter of the interior surface  104 ′ can be stepped to provide upper and lower regions of reduced diameter  134 ′ and  136 ′. For example, the interior diameter can be substantially constant in an upper section  109  of the interior. A short taper  111  can then be provided that leads into the upper region of reduced diameter  134 ′. Continuing down the interior, the reduced diameter can be maintained until a second short taper  113  is provided that leads into the lower region of reduced diameter  136 ′. The reduced diameter can continue until the end of the interior region of the tubular member  101 ′.  
      Referring to  FIGS. 4 and 6 C, in another embodiment of a tubular member  101 ″, the diameter of the interior surface  104 ″ can be slightly tapered, so as to gradually reduce from the inlet end  124 ″ toward the outlet region  122 ″. An upper region of reduced diameter  134 ″ has interior diameter ID u ″ and a lower region of reduced diameter 136″ has interior diameter ID 1 ″. The exterior diameter of the upper and lower porous members  116 ,  118  can be configured such that the upper porous member  116  can friction fit against the interior surface at the upper region of reduced diameter  134 ″, and the lower porous member  118  can be passed through the interior region  106 ″ until friction fitting against the interior surface at the lower region of reduced diameter  136 ″.  
      Referring to  FIG. 7 , to provide a better seal between the interior surface  104 ″ of the tubular member  101 ″ and the exterior surface of the porous members  116 ,  118 , the annular outer member  128 ′ can be tapered so as to substantially correspond to the taper of the interior surface at the desired location in the inlet and outlet regions respectively. For example, a cross-sectional view of a porous member  116 ′ is shown. The annular outer member  128 ′ has a tapered profile as shown at  117 . The tapered profile corresponds to the tapered profile of the interior surface  104 ″ of the tubular member  101 ″, so as to provide a friction fit at the upper region of reduced diameter  134 ″.  
       FIG. 8A  shows a perspective, cross-sectional view of the tubular member  101 .  FIG. 8B  shows an enlarged cross-sectional view of the outlet region  122  of the tubular member  101 . The outlet region  122  includes an outlet plate  138  that is positioned substantially perpendicular to the longitudinal axis  103  of the tubular member  101 . The outlet plate  138  has an upper surface  140  and a lower surface  142 . An outlet opening  144  extends through the outlet plate  138  from the upper surface  140  to the lower surface  142 . The outlet opening  144  can be conical to promote fluid flow through the opening  144 . One or more ribs  146  can be included on the upper surface  140 . The ribs  146  can provide support for the lower porous member  118 , which can be positioned directly above the outlet plate  138 . The outlet plate  138  can be formed integrally with the tubular member  101 , or alternatively, can be formed separately and attached to the tubular member  101 , for example, using ultrasonic welding, heat welding, hot air or hot plates joining techniques.  
      An outlet member  148  can be attached to or formed integrally with the lower surface  142 . The outlet member  148  includes an interior region forming an outlet passage  150  that is axially aligned with the outlet opening  144 . In one implementation the interior region is substantially cylindrical. The outlet member  148  includes a substantially cylindrical exterior surface and can have a tapered end. Solvent that is introduced into the chromatography cartridge  100  can thereby pass through the interior region  106 , i. e., through the upper porous member  116 , the stationary phase and the lower porous member  118 , into a collection area  152  formed between the lower porous member  118  and the outlet plate  138 . The solvent flows from the collection area  152  through the outlet opening  144  and passes into the outlet passage  150 . The outlet passage  150  can be connected to a collection vessel, e.g., via a bottom head of a cartridge module (discussed below).  
      A guard member  154  can also be attached to or formed integrally with the lower surface  142  of the outlet plate  138 . The guard member  154  is configured to protect the outlet member  148 , for example, from damage when handling the cartridge  100 . In one embodiment, the guard member  154  is substantially cylindrical with a hollow interior region that surrounds the outlet member  148  and is slightly longer than the outlet member  148 .  
       FIG. 9A  shows a perspective view of the bottom of the cartridge  100 . The guard member  154  and outlet member  148  are shown extending from the lower surface  142  of the outlet plate  138 . Optionally, support ribs, such as the radial support ribs  156  shown, can be included on the lower surface  142  of the outlet plate  138  to provide increased rigidity to the outlet region  122  of the cartridge  100 . Other configurations of support ribs can be used, for example, lateral support ribs  155  extending the width of the lower surface  142  of the outlet plate  138 , as shown in an alternate bottom view in  FIG. 9B . The exterior end of the substantially cylindrical outlet member  148  can be tapered to provide a snug fit into a connector, such as a flexible tube, to connect the cartridge to a collection vessel. The tapered end of the outlet member  148  can also allow necessary compression of seals, such as O-rings, used to create a seal about the outlet member  148 .  
      The cartridge  100  can be used with a cartridge module, for example, the cartridge module  160  shown in  FIG. 10  including a top head assembly  162 , a bottom head assembly  164  and one or more axial restraints  166  between the two assemblies  162 ,  164 . In the embodiment of the cartridge module  160  shown, the top head assembly  162  and bottom head assembly  164  are attached to an axial restraint  166 , which can be, in one embodiment, part of a piece of equipment. For example, the one or more axial restraints  166  may be one or more structural components of the equipment, and the top and bottom head assemblies  162 ,  164  may be cantilevered off of the equipment. In other embodiments, the cartridge module  160  can be a standalone assembly, and the one or more axial restraints can be formed from a solid tube extending between the top head assembly  162  and the bottom head assembly  164 , or alternatively, one or more lateral members can extend between the top head assembly  162  and the bottom head assembly  164 , leaving the cartridge substantially exposed. Whatever the configuration of the one or more axial restraints  166  may be, relative axial movement can be permitted between the top head assembly  162  and the bottom head assembly  164 .  
      The bottom head assembly  164  includes a base  170  attached to the axial restraint  166 . A contact member  182  is attached to the base  170 , which contact member  182  supports a compressible seal  168 , such as an O-ring. The contact member  182  is configured to mate with the outlet member  148  of the cartridge  100  and can fit between the outlet member  148  and the guard member  154 . The contact member  182  can have a substantially cylindrical interior region to receive the outlet member  148  of the cartridge  100 . The base  170  can be spring loaded (spring not shown), such that a spring urges the base  170  in a direction toward the top head assembly  162 . The spring force should be greater than the force exerted against the bottom head assembly  164  by the internal pressure of the chromatography column  100  during a chromatography operation, otherwise the internal pressure may force the bottom head assembly  164  to separate from the chromatography column  100 .  
      Although the bottom head assembly  164  is attached to the axial restraint  166 , because the bottom head assembly  164  may still move axially, different lengths of chromatography columns  100  can be accommodated by the cartridge module  160 . As long as the chromatography column  100  has an outlet member  148  configured to mate with the contact member  182 , the chromatography column  100  can be sealed to the bottom head assembly  164 .  
      The top head assembly  162  includes an upper head  172  supporting a compressible seal  174 , such as an O-ring. A lower surface of the upper head  172  abuts an upper surface of the sample module  105 , or can directly abut the upper surface of the upper porous member  116 , in the absence of a sample module  105 . The upper head  172  includes a passage  175  formed through the upper head  172 , including through a shaft  173  forming an upper portion of the upper head  172 . Fluid can be introduced into the chromatography column  100  through the passage  175 .  
      The top head assembly  162  further includes a knob assembly  184  that can be rotated to seal the top head assembly  162  to the cartridge  100 . The knob assembly  184  includes an annular component  185  having a threaded inner surface. The threaded inner surface of the annular component  185  mates with a threaded outer surface of a sleeve  186  positioned about the exterior of the shaft  173  of the upper head  172 . When the knob assembly  184  is rotated, the threading action between the annular component  185  and the sleeve  186  causes the knob assembly  184  to move upwardly and exert an upwardly force against a collar  187  affixed to the shaft  173  of the upper head  172 . The force causes the shaft  173  and the balance of the upper head  172  to move upwardly, thereby compressing the seal  174 . Other configurations can be used to compress the seal  174 .  
      In one embodiment, the circumferential ribs  112  formed on the exterior surface  102  of the upper portion  108  of the tubular member  101  can be configured to engage corresponding grooves formed in the inner surface  177  of an outer annular member  178  connected to the sleeve  186 . When the compressible seal  174  is compressed, the seal  174  expands laterally causing a small increase in the outer diameter of the upper portion  108  of the cartridge  100 , which can cause the circumferential ribs  112  on the cartridge  100  to engage with the grooves in the outer annular member  178 . Engaging the circumferential ribs  112  and grooves can increase the resistance of the assembly to separating due to the force of the internal pressure of the cartridge  100  during a purification process.  
      In another embodiment, the circumferential ribs  112  formed on the exterior surface  102  of the tubular member  101  can extend only partially around the circumference of the tubular member  101  at intervals. For example, the ribs can extend approximately 80-90° around the circumference on opposite sides of the tubular member  101  (i.e., at 0-90° and at 180-270° about the circumference). The partial circumferential ribs  112  can be used to create a lock between the tubular member  101  and the top head assembly  162  when the cartridge  100  is rotated approximately 90°.  
      The top head assembly  162  is affixed to the axial restraint  166 . The top head assembly  162  can be used with the chromatography column  100  without the sample module  105 . The configuration of the top head assembly  162  includes a space  188  between the outer annular member  178  and the interior components, such that in the absence of the sample module  105  the chromatography column  100  can be positioned with the upper surface of the porous member  116  abutting the lower surface of the upper head  172 .  
      The embodiment of the cartridge module  160  shown includes a bottom head assembly  164  that is spring-loaded in an upwardly direction (the slide and spring mechanism are not shown). Alternatively, the top head assembly  162  can be spring loaded downwardly, or both top and bottom head assemblies  162 ,  164  can be axially movable. The top and bottom head assemblies  162 ,  164  can also be lockable in any given position.  
      Referring to  FIGS. 3, 4 ,  6 A and  11 , an exemplary process  200  for purifying a sample using the cartridge  100  and the cartridge module  160  is shown. The lower porous member  118  is inserted into the interior region  106  of the tubular member  101  and friction fit against the interior surface  104  in the lower region of reduced diameter  136  (step  202 ). The interior region  106  is partially filled with a stationary phase  107 , such as a silica, leaving room for the upper porous member  116  and sample module  105  (step  204 ). The upper porous member  116  is inserted into the interior region  106  and friction fit against the interior surface  104  in the upper region of reduced interior diameter  134  (step  206 ). The sample module  105  is inserted into the interior region  106  to abut the upper surface of the upper porous member  116  (step  208 ). The cartridge  100  is inserted into the bottom head assembly  164  (step  210 ). The cartridge  100  is attached to the top head assembly  162  (step  212 ). Inserting the cartridge  100  into the bottom head assembly  164  can be as simple as a user positioning the outlet member  148  of the cartridge  100  over the contact member  182  of the bottom head assembly  164  and pushing the contact member  182  onto the outlet member  148 . The spring loaded action of the bottom head assembly  164  can be used as follows: push the bottom head assembly  164  downward using the cartridge  100 , relax the downward force on the cartridge  100 , allow the bottom head assembly to move upwardly, and thereby insert the cartridge  100  into the top head assembly  162 .  
      The sealing mechanism is activated to create a seal between the cartridge and the top head assembly  162  (step  214 ). For example, in the embodiment shown, a user can rotate the knob assembly  184  on the top head assembly  162  to compress the compressible seal  174 . Once a seal is created, the purification process is initiated (step  216 ), for example, by pumping a solvent through a passage  175  in the top head assembly  162  and into the cartridge  100 .  
      In one implementation, steps  202 - 206  may be performed at a facility manufacturing the cartridge  100 , and steps  208 - 216  may be performed by a user of the cartridge  100 , for example, in a laboratory.  
      Referring to  FIG. 12 , in one embodiment, the chromatography column  100  can include a ridge  190  formed along all or a portion of the circumference of exterior surface  102  of the column  100 . The ridge  190  provides a feature that the bottom head assembly  164  can be configured to connect to, in order to maintain a seal and connection between the bottom head assembly  164  and the column  100  during a chromatography operation. The ridge  190  is shown near the bottom of the column  100 , however, alternative configurations can be used. For example, the ridge  190  can be on the inside of the tubular member  101 , or on the outside of the guard member  154 . Configurations other than a ridge can also be used, such as grooves or holes, so long as the configuration provides a feature that can connect to the bottom head assembly  164 .  
       FIGS. 13A and 13B  show another embodiment of an upper portion  1302  of an exterior surface of a tubular member  1301 . The upper portion  1302  includes projections protruding from the exterior surface. For illustrative purposes,  FIG. 13B  shows a plan view of the projections if the exterior surface of the upper portion  1302  were laid flat (although  FIG. 13B  shows a slightly different embodiment, as described below). The projections include angled ridges  1304  that extend a portion (e.g., a quarter) of the circumference of the tubular member  1301  at an angle of inclination  1308 . In one embodiment the angle of inclination  1308  is approximately 19°, although a lesser or greater angle can be used. The projections also include vertical ridges  1306 , each vertical ridge forming a “backbone” for a set of the angled ridges  1304 . Additionally, a horizontal ridge  1310  can be included at the upper end of each set of angled ridges  1304 .  
      Vertical passages  1312  are formed between the sets of angled ridges  1304 , with one edge of the vertical passage  1312  formed by a vertical ridge  1306 . In the embodiment shown, there are four sets of angled ridges  1304 , however, in other embodiments there can be more or fewer sets of angled ridges  1304 . In the embodiment shown in  FIG. 13A , each set of angled ridges  1304  includes 8 angled ridges  1304 , whereas in the embodiment shown in  FIG. 13B , each set of angled ridges includes 4 angled ridges  1304 . More or fewer angled ridges  1304  can be included per set.  
      Referring to FIGS.  14 A-C, a top head assembly  1402  of one implementation of a cartridge module that can mate with the tubular member  1301  during a purification process is shown. An interior surface  1404  of the top head assembly  1402  includes protruding pins  1406 . There are four sets of pins  1406  (only three are shown) that are arranged at equidistant intervals about the circumference of the interior of the top head assembly  1402 . The pins  1406  are configured to fit within the vertical passages  1312  formed on the exterior surface of the tubular member  1301  when the tubular member  1301  is inserted into the top head assembly  1402 . A user can then rotate the top head assembly  1402  relative to the tubular member  1301 , forcing the pins  1406  into a space formed between two of the angled ridges  1304 . The angle of inclination  1308  of the angled ridges  1304  forms a lead-in angle, facilitating insertion of the pins  1406  into the spaces formed between the angled ridges  1304 . Nubs  1312  formed on the ends of the angled ridges  1304  can keep the pins  1406  within the space formed between two of the angled ridges  1304 , thereby locking the tubular member  1301  to the top head assembly  1402 .  
       FIG. 14B  shows a cut-away view of the top head assembly  1402  mated with the tubular member  1301 .  FIG. 14C  shows a top cross-sectional view of the top head assembly  1402  connected to the tubular member  1301  including an upper porous member  1314 . Pins  1406  protruding from the interior surface of the top head assembly  1402  are shown aligned with vertical passages  1312  formed on the exterior surface of the tubular member  1301 , before the top head assembly  1402  and tubular member  1301  have been rotated relative to one another to position the pins  1406  within spaces formed between the angled ridges  1304 .  
      In the embodiment shown in FIGS.  14 A-C, there is one set of pins  1406  for each vertical passage  1312  formed on the exterior of the cartridge  100 . However, in other embodiments, there can be fewer sets of pins  1406  than vertical passages  1312 . Additionally, in the embodiment shown in FIGS.  14 A-C, there is one pin in each set of pins  1406  corresponding to the number of spaces formed between the angled ridges  1304  in each set of angled ridges  1304  formed on the exterior of the cartridge  100 . More or fewer pins  1406  per set can be used, however, by increasing the number of pins  1406 , the force on the pins  1406  can be spread out over a larger contact area, minimizing the force exerted on any one pin  1406 . The horizontal and vertical ridges  1310 ,  1306  formed on the exterior of the cartridge  100  can assist an operator in guiding the pins  1406  into position when connecting the cartridge  100  to the top head assembly  162 .  
      The tubular member, including the various embodiments described above, as well as the annular outer member  128  and radial support members  130  of the porous members, can be manufactured from materials including plastics and metals. Injection molding can be used to fabricate the tubular member  101 , annular outer member  128  and radial support members  130  using materials such as polypropylene, polyethylene, Ultem, Valox, or Teflon. Although other fabrication techniques can be used, injection molding can provide a greater consistency of the interior diameter of the tubular member  101  and a smoother interior surface  104 , for example, as compared to an extruded tubular member. Spider lines, which are typical with a member formed by extrusion, can be avoided by injection molding. Injection molding the annular outer member  128  and the radial support members  130  of the porous members can provide a better tolerance control on the exterior diameter of the porous members. Using a screen in the porous members, as compared to, for example, a porous plastic disk, can improve the quality of the-porous members, e.g., due to there being fewer extractables. The screen can be molded into place during the injection molding process. The screen used in the porous members can be, in one embodiment, formed from threads of 316 stainless steel.  
      In one embodiment, the tubular member can have approximately the following dimensions:  
      interior diameter=1.57 inches;  
      exterior diameter=1.84 inches;  
      distance between lower surface of upper porous member and upper surface of lower porous member (bed length)=5.9 inches; and  
      total length=9 inches.  
      In one embodiment, a porous member can have approximately the following dimensions:  
      exterior diameter=1.58 inches;  
      thickness=0.25 inches  
      The use of terminology such as “upper” and “lower” throughout the specification and claims is for illustrative purposes only, to distinguish between various components of the cartridge. The use of “upper” and “lower” does not imply a particular orientation of the cartridge. For example, the upper surface of the outlet plate can be orientated above, below or beside the lower surface of the outlet plate, and visa versa, depending on whether the cartridge is positioned vertically upwards, vertically downwards or horizontally.  
      A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. The logic flow depicted in  FIG. 11  does not have to be performed in the order shown, or in a sequential order, and the steps of the invention can be performed in another order and still achieve desirous results. Accordingly, other embodiments are within the scope of the following claims.