Abstract:
An analytical instrument fitting assembly for coupling first and second analytical fluid conduits is provided. The fitting assembly includes a first fitting defining a central passage adapted to receive a first fluid conduit defining an internal diameter of no greater than 0.040 inch and a second fitting. The second fitting defines a central passage extending between first and second ends and is in fluid communication with the first fitting. A separation device is disposed within a central passages of the first and second fittings to selectively separate liquids passing therethrough. The fitting assembly further includes a retractable end fitting having a housing, a tube extending within the housing, and a biasing member. Selective positioning of the tube within the housing minimizes dead space between the tube and the second end.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/884,186, filed Jan. 9, 2007. 
    
    
     TECHNICAL FIELD 
     The disclosed subject matter relates generally to fittings used to connect miniature conduits, and particularly to connectors for fluid transfer in analytical instruments. 
     BACKGROUND 
     Numerous types of equipment used for the analysis or purification of chemical compounds utilize miniature fluid conduits, such as metallic tubing, through which liquid samples pass. An analytical technique, such as liquid chromatography, uses a column (conduit) packed with a packing material in order to analyze and identify chemical properties of certain fluids. For example, an analyte may be introduced into one end of the column, and a carrier fluid then run through the column. The length of time that the analyte is retained within the column can enable analysis and identification of the analyte. A popular form of liquid chromatography is High Performance Liquid Chromatography (HPLC) in which the sample is pumped through the column under an elevated pressure, typically at 300 to 6,000 psi. Another, relatively newer liquid chromatography form is Ultrahigh Pressure Liquid Chromatography (UHPLC) in which system pressure extends upward to 1400 bar or 20,000 psi. Both HPLC and UHPLC are examples of analytical instrumentation that utilize fluid transfer at elevated pressures. 
     Liquid chromatography systems, such as HPLC or UHPLC systems, typically include several components. For example, such a system may include a pump; an injection valve or autosampler for injecting the analyte; a precolumn filter to remove particulate matter in the analyte solution that might clog the column; a packed bed to retain irreversibly adsorbed chemical material; the HPLC column itself; and a detector that analyzes the carrier fluid as it leaves the column. These various components may typically be connected by a miniature fluid conduit, such as metallic or polymeric tubing, usually having an internal diameter of 0.003 to 0.040 inch. 
     All of these various components and lengths of tubing are typically interconnected by threaded fittings. Fittings for connecting various components and lengths of tubing are disclosed in prior patents, for example, U.S. Pat. Nos. 5,525,303; 5,730,943; and 6,095,572, the disclosures of which are herein all incorporated by reference herein. Often, a first internally threaded fitting seals to a first component with a ferrule or similar sealing device. The first fitting is threadedly connected through multiple turns by hand or by use of a wrench or wrenches to a second fitting having a corresponding external fitting, which is in turn sealed to a second component by a ferrule or other seal. Disconnecting these fittings for component replacement, maintenance, or reconfiguration often requires the use of a wrench or wrenches to unthread the fittings. While hand-tightened threaded fittings eliminate the need for wrenches or other tools these fittings typically could not stand up to the extreme pressures of HPLC or UHPLC. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that is further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     An analytical instrument fitting assembly for coupling first and second analytical fluid conduits is provided. The fitting assembly includes a first fitting defining a central passage adapted to receive a first fluid conduit defining an internal diameter of no greater than 0.040 inch and a second fitting. The second fitting defines a central passage extending between first and second ends and is in fluid communication with the first fitting. 
     In one embodiment, the fitting assembly also includes a packed bed disposed within the central passages of the first and second fittings. Such a packed bed includes a body at least partially filled with a separating media and a first seal disposed on a first end of the body to seal the filter material within the body. The fitting assembly also includes a retractable end fitting at least partially disposed within the second end of the second fitting. The retractable end fitting includes a housing, a tube extending within the housing, and a biasing member extending between the housing and a washer disposed on the tube to allow selective positioning of the tube within the housing relative to the second end of the second fitting to minimize dead space between the tube and the second end. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an isometric view of an exemplary embodiment of a high pressure connect fitting according to the present disclosure; 
         FIG. 2  is a cross-sectional view of the high pressure connect fitting shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a first fitting and a second fitting of the high pressure connect fitting shown in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of a retractable end fitting of the high pressure connect fitting shown in  FIG. 1 ; 
         FIG. 5  is an partial isometric exploded view of the high pressure connect fitting shown in  FIG. 1 ; 
         FIG. 6  is a cross-sectional view of a packed bed of the high pressure connect fitting shown in  FIG. 1 ; 
         FIG. 7  is an exploded cross-sectional view of the packed bed shown in  FIG. 6 ; 
         FIG. 8  is a partial exploded cross-sectional view of the packed bed and the second fitting of the high pressure connect fitting shown in  FIG. 1 ; 
         FIG. 9  is a partial cross-sectional view of the packed bed and the second fitting of the high pressure connect fitting shown in  FIG. 8 ; 
         FIG. 10  is a cross-sectional view of an alternate embodiment of a high pressure connect fitting according to the present disclosure; and 
         FIG. 11  is an exploded cross-sectional view of a filter cartridge of the high pressure connect fitting shown in  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     A first exemplary embodiment of a high pressure connect fitting assembly  20  is shown in  FIGS. 1 and 2 . The high pressure connect fitting  20  includes a first fitting  22  rotatably coupled to a second fitting  24  with a lock ring  26  or coupler. A retractable end fitting  28  is slidingly secured to the end of the second fitting  24  opposite the first fitting  22 . The fitting assembly  20  serves as a connector between various miniature fluid conduit terminals, such as, for example, a fluid line in  32  and a column inlet port  34 , both shown in phantom in  FIG. 2 . 
     As best shown in  FIG. 3 , the first fitting  22  is preferably of unitary construction and includes a tubular body  40  having a proximal end  42  and a distal end  44 . A central passage  46  extends from the proximal end  42  to the distal end  44  of body  40 . A portion of the central passage  46  includes a threaded portion  48  configured to engage an externally threaded mating coupling of a miniature fluid conduit. 
     The central passage  46  narrows in diameter at its distal terminus to form a tapered chamber  50  that extends from the internally threaded portion  48  toward the distal end  44  of the first fitting  22 . The tapered chamber  50  includes a frustoconical sealing surface  52  that seals against a conventional ferrule received coaxially from the coupling of the miniature fluid conduit. The central passage  46  further narrows to form a cylindrical chamber  54  that extends distally from the tapered chamber  50 . The cylindrical chamber  54  forms a “tube stop” that closely and fully receives the tip of a coupling of a miniature fluid conduit, as described in greater detail below. 
     The cylindrical chamber  54  further narrows to form a passage  56  extending from the cylindrical chamber  54  to a sealing recess  58  located on the proximal end of a larger annular recess  60  formed in the distal end  44  of the first fitting  22 . The passage  56  is sized to correspond to the internal diameter of the fluid conduit  32 , which is typically in the range of 0.005 to 0.040 inch. When the fluid conduit  32  is coupled to the first fitting  22 , the tip of the fluid conduit  32  contacts the end surface of the cylindrical chamber  54 . Thus, a “zero-dead volume” connection is created between the fluid conduit and the first fitting  22  so that fluid discharged from the fluid conduit  32  can only enter the small diameter passage  56  in the first fitting  22 . 
     As shown in  FIGS. 1 and 3 , the outer surface of the first fitting  22  includes diametrically opposed flat surfaces  62  to allow engagement a wrench or similar tool, if desired, to rotate the first fitting  22  or to prevent the first fitting from rotating as the fluid conduit  32  is coupled or decoupled to the first fitting  22 . In an alternate embodiment, the first fitting  22  has a knurled outer surface to facilitate gripping the first fitting  22  while coupling or decoupling the fluid conduit. 
     The outer surface of the first fitting  22  includes an annular groove  64  between the flat surfaces  62  and the distal end  44  of the first fitting  22 . On the distal side of the annular groove  64 , the outer diameter of the first fitting  22  increases to define a shoulder  66  that faces the proximal end  42  of the first fitting. 
     Still referring to  FIG. 3 , the second fitting  24  includes a tubular body  80  with a proximal end  82  and a distal end  84 . A central passage  86  extends from the proximal end  82  to the distal end  84  of the body  80 . The proximal end of central passage  86  terminates in an annular recess  88  adapted to receive a retractable end fitting  28  (described later). As best shown in  FIGS. 3 and 5 , diametrically opposed longitudinal grooves  90  extend along the surface of the annular recess  88 . The annular recess  88  also includes an annular groove  106  extending circumferentially around the recess  88  near the proximal end  82  of the second fitting  24 . The second fitting  24  further includes an external threaded surface  92  formed on the distal end  84  thereof. 
     The central passage  86  narrows in diameter at its distal terminus to form a tapered chamber  94 . The tapered chamber  94  is defined by a frustoconical sealing surface  96  that seals against a conventional ferrule included on the end of the retractable end fitting  28  shown in  FIG. 4 . Referring back to  FIG. 3 , a cylindrical chamber  98  extends from the tapered chamber  94  toward the distal end  84  of the second fitting  24 . The cylindrical chamber  98  forms a “tube stop” that closely and fully receives the distal tip of the retractable end fitting  28 . The cylindrical chamber  98  further narrows to form a passage  100  that extends from the cylindrical chamber  98  to a tapered sealing recess  102  located at the proximal end of an annular recess  104  formed in the distal end  44  of first fitting  22 . The passage  100  is sized to correspond to the internal diameter of the distal tip of the retractable end fitting  28  in order to form a zero-dead volume connection therewith. 
     As best shown in  FIGS. 1 and 5 , the outer surface of the second fitting  24  includes flat surfaces  162  to allow engagement a wrench or similar tool, if desired, to rotate the second fitting  24  as the high pressure connect fitting  20  is coupled or decoupled to a downstream system component  34 . In an alternate embodiment, the second fitting  24  has a knurled outer surface to facilitate gripping the second fitting  24  while coupling or decoupling the high pressure connect fitting  20  to the downstream system component  34 . 
     Still referring to  FIG. 3 , the lock ring  26  has a tubular body  120  with a proximal end  122  and a distal end  124 . An annular protrusion  126  extends radially inward from the inner surface of the lock ring  26  at the proximal end  122  thereof. The interior portion of the lock ring  26  also includes a threaded surface  128  at the distal end  124  of the lock ring  26 . The internal threaded surface  128  of the lock ring  26  is configured to threadedly engage the external threaded surface  92  of the second fitting  24 . Specifically, the lock ring  26  is adapted to connect the first and second fittings  22  and  24  by application of a torque, or coupling force, to the lock ring  26  preferably, but not necessarily, without the use of a mechanical hand tool, such as a wrench. In one embodiment, the range of the coupling force is substantially between 0.1-5.0 inch-pounds to rotate the lock ring  26  less than 90° from an unlocked position wherein the first and second fittings are detachable from the lock ring  26 . As an example, the lock ring  26  a coupling force of substantially between 0.5-2.0 inch-pounds to rotate the lock ring  26  substantially between 45°-60° from the unlocked position. 
     The lock ring  26  engages the first fitting  22  and the second fitting  24  in order to couple the first fitting  22  to the second fitting  24 . The distal end  44  of the first fitting  22  is positioned within the interior portion of the lock ring  26  so that the distal side of the annular protrusion  126  of the lock ring  26  abuts the proximal side of the internal shoulder  66  of the first fitting  22 . A snap ring  68  is positioned circumferentially around the body of the first fitting  22  and is retained in the annular groove  64  in the first fitting  22 . With the snap ring  68  so located, the annular protrusion  126  of the first fitting  22  is retained between the snap ring  68  and the internal shoulder  64  of the first fitting  22 , thereby restraining the first fitting  22  against translational movement relative to the lock ring  26 . At the same time, the first fitting  22  is unrestrained against rotation relative to the lock ring  26 . 
     The second fitting  24  is secured to the lock ring  26  by engaging the threads  92  on the distal end  44  of the second fitting  24  with the internal threaded surface  128  located at the distal end  124  of the lock ring  26 . Thus, with the first and second fittings  32  and  34  secured to the lock ring  26  in the illustrated manner, the first fitting  22  is coupled to the second fitting  24 . The described coupling restrains the first fitting  22  from translational movement relative to the second fitting  24 , but allows rotational movement to occur therebetween. 
     As may be seen best by referring to  FIG. 4 , the retractable end fitting  28  includes a tube  140  having a proximal end  142  and a distal end  144 . The tube  140  is disposed within a center portion of a threaded fitting  146 , or body, which has a proximal end  148  and a distal end  150 , so that the proximal and distal ends  142  and  144  of the tube  140  extend from the proximal and distal ends  148  and  150 , respectively, of the threaded fitting  146 . 
     The threaded fitting  146  has external threads  156  sized to threadedly engage the internal threads of a corresponding mating instrument inlet or outlet shown in  FIG. 2 . The threaded fitting  146  includes a shoulder  158  facing the proximal end  148  of the threaded fitting  146 . A generally cylindrical recess  152  is located on the distal end  150  of the threaded fitting  146 . As shown in  FIG. 4 , the recess defines an interior shoulder  154  within the fitting  146 . 
     Still referring to  FIG. 4 , a ferrule  170  is slidably mounted on the distal end  144  of the tube  140  so that the distal end  144  of the tube  140  extends from the tapered end of the ferrule  170 . A support washer  172  is slidably mounted to the distal end  144  of the tube opposite the tapered end of the ferrule  170 , i.e. between the ferrule  170  and the threaded fitting  146 . A helical spring  166 , or biasing member, is positioned coaxially around the tube  140  between the support washer  172  and the distal end  150  of the threaded fitting  146 . One end of the spring  166  engages the support washer  172  and the other end of the spring  166  engages the shoulder  154  located within the recess  152  at the distal end  150  of the threaded fitting  146  to provide a force that biases the support washer  172  and ferrule  170  away from the threaded fitting  146 . 
     A second ferrule  174  is slidingly mounted to the proximal end  142  of the tube  140  so that the proximal end  142  of the tube  140  extends from the tapered end of the ferrule  174 . The end of the ferrule  174  opposite the tapered end abuts the proximal end  148  of the threaded fitting  146 . 
     The retractable end fitting  28  is slidably coupled to the second fitting  24  so that the retractable end fitting  28  extends from the proximal end  82  of the second fitting  24 , but is capable of at least partially retracting within the second fitting  32 . Referring to  FIGS. 2-5 , the retractable end fitting  28  is disposed within the annular recess  88  in the second fitting  24  so that the distal end  144  of the end fitting tube  140  is positioned within the cylindrical chamber  98  of the second fitting  24 . The support washer  172  is located within and engages the passage  86  in the second fitting  24  to provide further support to the distal end  144  of the tube  140 . The helical spring  166  biases the support washer  172  toward the distal end  144  of the tube  140 , which in turn biases the tapered end of the ferrule  170  into the tapered chamber  94  of the second fitting  24 . The ferrule  170  engages the sealing surface  96  of the tapered chamber  94  to form a seal therebetween. Because the tube  140  is capable of sliding relative to the ferrule  170  and the support washer  172 , dead space between the distal end  144  of the tube  140  and the small diameter passage  100  at the end of the cylindrical chamber  98  is eliminated. 
     The retractable end fitting  28  is contained within the annular recess  88  of the second fitting  24  with a snap ring  164 . As best shown in  FIGS. 2 and 3 , the snap ring  164  is positioned within the groove  106  in the annular recess  88  of the second fitting  24  so that the snap ring  64  engages the shoulder  158  of the threaded fitting  146 , thereby keeping the threaded fitting  146  at least partially contained within the annular recess  88 . The helical spring  166  provides a force at the distal end  150  of the threaded fitting  146  to bias the distal end  150  of the threaded fitting  146  toward the proximal end  82  of the second fitting  24 . Thus, the shoulder  150  of the threaded fitting  146  maintains contact with the snap ring  164 , i.e. the retractable end fitting  28  remains fully extended, unless or until a force is applied to the threaded fitting  146  sufficient to overcome the biasing force of the helical spring  166 , which results in the threaded fitting  146  retracting into the annular recess  88  of the second fitting  24 . 
     As best shown in  FIGS. 2 and 5 , a pair of pins  180  are positioned between the second fitting  24  and the retractable end fitting  28 . Each pin  180  is partially disposed within one of the axial grooves  90  in the second fitting  24 , and also within one of the axial grooves  160  in the retractable end fitting  28 . The engagement of the pins  180  with the grooves  90  and  160  of the second fitting  24  and the retractable end fitting  28  prevent rotation of the retractable end fitting  28  relative to the second fitting  24 . Although the illustrated embodiment is shown with two pins  180 , it will be appreciated that any suitable number of pins can be used, including, for example, one pin or three or more pins. 
     As previously noted, the threaded fitting  146  and the ferrule  174  of the retractable end fitting  28  are capable of sliding relative to the tube  140 . As a result, the amount by which the proximal end  142  of the tube  140  extends from the tapered end of the ferrule  174  changes as necessary when the high pressure connect fitting  20  is coupled to a corresponding mating instrument inlet or outlet  34  in order to eliminate dead space between the proximal end of the tube  142  and the corresponding mating instrument inlet or outlet  34 . This creates a zero dead volume attachment. 
     Referring back to  FIGS. 2 and 3 , a packed bed  30  is disposed within the cavity formed by the annular recess  60  of the first fitting  22  and the annular recess  104  of the second fitting  24  when the first and second fittings  22  and  24  are coupled together with the lock ring  26 . As best shown in  FIGS. 6 and 7 , the packed bed  30  has a generally cylindrical body  200  with an input end  202 , an output end  204 , and a central passage  206  extending therethrough. The input end  202  and output end  204  of the body  200  each includes an annular recess  208  in which a seal  220  is disposed. The seals  220  at the input end  202  and the output end  204  of the body  200  are identical both in configuration and operation. 
     The seal  220  is preferably manufactured from a polymer, such as polyetheretherketone (“PEEK”). The seal  220  includes a body portion  222 , an integrally formed tip  224 , and a centrally extending passage  226 . The body  222  of the seal  220  is sized and configured to fit within the annular recess  208  at the input end  202  or the output end  204  of the packed bed body  200 . A porous plug  230  has an annular body sized to fit within the annular recess  228  in the seal  220 . The porous plug  230  is formed from a material that selectively allows certain materials to pass through the plug  230 , while restricting the passage of other materials. 
     A packing material (or separating media)  232  is disposed within the passage  206  of the packed bed  30 . The packing material  232  may be a particulate packing material, through which particles greater than a predetermined size are prevented from passing. Alternately, the packing material may be a chemical packing material, such as a selectively absorbent or adsorbent packing material that filters out substances having specific chemical properties. It should be appreciated that any known packing material suitable for selectively filtering fluids passing therethrough can be included without departing from the scope of the disclosure. 
     With a seal  220  positioned in the annular recess  208  at each end of the packed bed body, and a porous plug  230  disposed within the annular recess  228  of each seal  220 , the packing material  232  is contained within the packed bed  30 . A fluid to be filtered is introduced to the input end  202  of the packed bed  30  and passes through the seal  220  and the porous plug  230 . As the fluid passes through the packed bed  30 , undesired elements are adsorbed by the packing material  232 , and the filtered fluid exits the packed bed  30  through the porous plug  230  and the seal  220  at the output end  204  of the packed bed  30 . 
     As seated within the cavity formed by the annular recess  60  in the first fitting  22  and the annular recess  104  in the second fitting  24 , the seals  220  of the packed bed  30  engage the sealing recess  58  and  102  of the first fitting  22  and the second fitting  24 , respectively. The engagement of the seal  220  with the first fitting  22  is similar to the engagement of the seal  220  with the second fitting  34 . Accordingly, the engagement of one seal  220  with the second fitting  24  will be described with the understanding that the description is applicable to the engagement of the other seal  220  with the first fitting  22 . 
     Referring to  FIGS. 8 and 9 , as the seal  200  engages the second fitting  24 , the tip  224  of the seal  200  contacts the walls of the tapered sealing cavity  102  to form a primary seal  240 . The volume of space between the very end of the tip  224  and the end of the sealing cavity  102  defines a dead space  242 . As the seal  220  is axially compressed within the annular recess  104 , the tip  224  not only engages the walls of the tapered sealing cavity  102  to form the primary seal, but also deforms to occupy space otherwise associated with the dead space  242 . As, the tip  224  of the seal  200  engages the tapered sealing cavity  102 , the end face  210  of the seal  220  compresses against the end  108  of the annular recess  104  to form a secondary seal  244  extending radially around the tip  224  of the seal  200 . 
     In addition to providing a secondary seal  24 , contact between the end face  210  of the seal  220  and the end  108  of the annular recess  104  serves to limit the deformation of the seal tip  224 . As previously described, the second fitting  24  is coupled to the first fitting  22  by threadedly engaging the second fitting  24  to a lock ring  26  that is also coupled to the first fitting  22 . As the lock ring  26  is rotated relative to the second fitting  24  the distal end  84  of the second fitting  24  is drawn toward the distal end  44  of the first fitting  22 . As a result, the overall length of the cavity formed by the annular recess  60  in the first fitting  22  and the annular recess  104  in the second fitting  24  is reduced. Absent the contact between the end face  210  of the seal  220  and the end  108  of the annular recess  104 , over tightening the lock ring  26  would force the tip  224  of the seal  220  into the sealing recess  102  to the point where deformation of the tip would potentially block the passage  226  extending through the seal. However, engagement of the end face  210  of the seal  220  with the end  108  of the annular recess  104  limits the amount by which the length of the cavity can be reduced. As a result, the amount by which the tip  224  extends into the sealing recess  102 , and thus the deformation of the tip  244 , is limited. 
     An alternate embodiment of the disclosed high pressure connect fitting is illustrated in  FIGS. 10 and 11 . The high pressure connect fitting  250  shown in  FIG. 10  is similar to the high pressure connect fitting  20  shown in  FIG. 2 , except that the packed bed  30  of the previously described fitting  20  is replaced with a unidirectional filter cartridge  252 . The unidirectional filter cartridge  252  includes an inlet end  286 , which is positioned within the annular recess  60  of the first fitting  22 , and a discharge end  288 , which is positioned within the annular recess  104  of the second fitting  24 . 
     As best shown in  FIG. 11 , the unidirectional filter cartridge  252  includes a generally cylindrical body  254  with a first annular recess  256  at the inlet end  286  opposed by a second annular recess  258  at the discharge end  288 . The first and second annular recesses  256  and  258  are connected by a passage  256  extending through the body  254 . 
     The diameter of the filter cartridge  252  is greater at the inlet end  286  than at the discharge end  288 . As shown in  FIG. 12 , the diameter of the annular recess  104  in the second fitting  24  is larger than the diameter of the discharge end  288  of the filter cartridge  252 , but smaller than the diameter of the inlet end  286  of the filter cartridge  252 . As a result, the inlet end  286  of the filter cartridge  252  can not be inserted into the annular recess  104  of the second fitting  24 . Consequently, the unidirectional filter cartridge  252  can only be installed in the high pressure connect fitting  250  in one orientation, i.e. with the inlet end  286  disposed within the first fitting  22 , and the discharge end  288  disposed within the second fitting  24 . It should be appreciated that various other configurations can be employed to ensure proper orientation of the filter cartridge  252 , such as, for example, having the larger diameter at the outlet end of the cartridge or having different cross-sectional profiles at each end of the filter cartridge. 
     A first seal  262  is similar to the seal  220  of the previously described embodiment. The first seal  262  has generally cylindrical body  264 , with a tip  266  on one side and a central passage  268  extending therethrough. The first seal  262  is preferably manufactured from a polymer, such as PEEK. The first seal  262  is disposed within the first annular recess  256  of the body  254  of the filter cartridge  252 . 
     A second seal  270  is similar to the first seal  262 , having a generally cylindrical body  272 , a tip  274 , and a passage  276  extending therethrough. However, the second seal  270  further includes an annular recess  278  opposite the tip  274 . The annular recess  278  is sized and configured to receive one or more filter elements  280 . Each filter element may be formed from a particulate filter material, through which particles greater than a predetermined size are prevented from passing, or a chemical filter material, such as a selectively absorbent or adsorbent material that selectively filters out substances having particular chemical properties. It should be appreciated that any known filter element suitable for selectively filtering fluids passing therethrough can be included without departing from the scope of the disclosure. 
     With one or more filter elements  280  positioned in the annular recess  278  of the second seal  270 , the second seal  270  is received into the second annular recess  258  of the body  254  of the filter cartridge  252 . 
     When the filter cartridge  252  is installed in the high pressure connect fitting  250 , first seal  262  forms a primary seal  282  and a secondary seal  284  with the first fitting  22 . Similarly, the second seal  270  forms a primary seal  282  and a secondary seal  284  with the second fitting  24 . As a result, fluid passing through the high pressure connect fitting passes through the filter cartridge  252  and is filtered by the filter elements  280  contained therein. 
     While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.