Abstract:
Chromatography apparatus including an enclosure having a pressurizable chamber sized to removably receive a chromatography cartridge therein and an opening to the chamber, and a cap that closes the opening and has a flow passage for directing a sample to be analyzed to the cartridge, the cap having a sharp protruding member that surrounds the flow opening and makes sealable engagement with the cartridge by digging into the cartridge.

Description:
This is a continuation of application Ser. No. 08/224,264, filed Apr. 7, 1994, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to apparatus used to pressurize a removable chromatography cartridge. 
     In chromatographic procedures, a stationary phase such as a surface active powder is contained in a chromatography column. A mobile phase consisting of a carrier fluid and a sample of chemical to be identified, analyzed, or purified is passed through the column. Different components of the sample pass through the column at different rates and are thereby separated from each other, leaving the column at different times. 
     Voids in the stationary phase that may have resulted during shipping and other nonuniform packing conditions can deleteriously affect the operation of a chromatography column and the accuracy of the results. It is known to compress flexible-walled columns in order to close voids and provide uniform packing of the stationary phase. E.g., in U.S. Pat. No. 4,250,035, a chromatography column is made of polytetrafluoroethylene (PTFE) tubing sealed at the ends with porous frits. In one embodiment, the column is placed within a chamber that is pressurized to compress the deformable walls of the column and the stationary phase therein. This provides a uniform packing of the stationary phase and promotes the accuracy of the chromatography column. 
     It is also known to make a chromatography cartridge from polyethylene, or like material, and to mount the cartridge in a pressurizable compression module assembly having an outer cylindrical body and an end cap that has an O-ring around its outer surface for providing a seal with the end of the cartridge. The O-ring is made of resilient, flexible material, so as to provide a good seal, and is chemically-resistant, to reduce interaction with the mobile phase chemicals. Nevertheless, this O-ring may shrink or swell, leach compounds into the column or absorb the sample. 
     SUMMARY OF THE INVENTION 
     The invention features, in general, chromatography apparatus that includes an enclosure having a pressurizable chamber for receiving a chromatography cartridge therein and a cap for closing an opening to the enclosure. The cap has a sealing structure for mating with the enclosure and providing a seal to the enclosure around the opening. The cap also has a flow passage for directing a sample to be analyzed to the cartridge therein. The cap also has a sharp protruding member that surrounds the flow passage, is inside of the cap sealing structure, and is directed toward the chamber for making sealable engagement with the cartridge by digging into the cartridge. The sharp protruding member provides a reliable, long-lasting sealing structure that can be repeatedly used to make seals with removable chromatography cartridges without employing an O-ring, which can wear in use and will need to be replaced at significant expense. 
     In preferred embodiments, the apparatus has a mechanism to force the sharp protruding member into the wall of the cartridge. This mechanism can be provided by camming surfaces on the enclosure and the cap and a V-band that engages both camming surfaces and brings the enclosure and cap together as the band is tightened. The chromatography cartridge has a porous frit in a recess therein, and the cap has a plug portion sized to contact the frit. The sharp protruding member is preferably angular in section with two converging lines meeting at a point, the lines making an angle of between 20° and 120° (most preferably, between 50° and 90°). The protruding member preferably extends between 0.03&#34; and 0.15&#34; (most preferably between 0.05&#34; and 0.10&#34;). The enclosure preferably is cylindrical and has a pressure inlet for connecting to a source of pressurized liquid and a pressure relief valve. 
     Other advantages and features of the invention will be apparent from the description of the preferred embodiment thereof and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of chromatography apparatus according to the invention. 
     FIG. 2 is an enlarged view of a portion of FIG. 1 showing the sealing engagement between an end cap and an enclosure and between the end cap and a removable chromatography cartridge of the FIG. 1 apparatus. 
     FIG. 3 is a sectional view of a portion of the FIG. 1 end cap providing a knife edge sealing member. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the figures, chromatography apparatus 10 includes outer barrel 12, end caps 14, 16, and removable chromatography cartridge 18 within barrel 12 and between end caps 14, 16. Barrel 12 has pressure relief valve 20 in an opening to inner chamber 22. Barrel 12 acts as an enclosure for receiving and pressurizing cartridge 18 therein. 
     At both ends of barrel 12 are outer, annular recesses 24 and flanged ends 26 having inclined camming surfaces 28. End caps 14, 16 have mating flanges 30 with oppositely inclined camming surfaces 32. Flanged ends 26 also have an axially-directed annular recesses 34 containing sealing rings 36 therein. V-band 38 has inclined surfaces 40, 42 engaging camming surfaces 28, 32, respectively. V-band clamping knob 44 increases the tension in V-band 38, and, in so doing, biases end cap 16 axially toward barrel 12. 
     Chromatography cartridge 18 includes cylinder 46 made of food-grade, medium-density polyethylene and has a nominal inner diameter of three inches. Stationary phase media 48 is contained within cylinder 46 between thin porous frits 50, 52 and thick frits 54, 56, respectively. Frits 50 and 54 are received within inwardly directed annular recess 58, and frits 52 and 56 are received within inwardly directed annular recess 60. Cylinder 46 extends beyond frits 54, 56 and has diverging, inner conical surfaces 62, 64. End caps 14, 16 each have plug portions 66 with outer conical surfaces that mate with surfaces 62, 64 of cartridge 18. 
     Just outside of plug 66, each flange 30 has sharp protruding member 68 having a radius equal to the radius at the midsection at the end of the wall of cylinder 46. End caps 14, 16 are made of metal, and the ends of protruding member 68 are sharp so that they dig into the ends of the polyethylene cylinder 46 when force is applied to bring caps 14, 16 toward barrel 12 by V-bands 38. Referring to FIG. 3, it is seen that protruding member 68 makes a 60° angle in section and protrudes downward from surface 70 by 0.060&#34;-0.065&#34;. Other angles (e.g., 20° to 120°, preferably 50° to 90°) and distances (e.g. 0.03&#34; to 0.15&#34;, preferably 0.05&#34; to 0.10&#34;) could work. End caps 14, 16 also have flow passages 72, 74 through them. Passage 72 communicates with process inlet 76, and flow passage 74 communicates with process outlet 78. 
     In use, chromatography cartridge 18 can be installed in barrel 12 and easily removed and replaced with another cartridge when it is necessary to change to a different or new chromatographic media. A variety of stationary phase media may be used in the cartridges. The most commonly used are reverse phase, normal phase, ion-exchange, and size-exclusion packings. 
     When a new cartridge 18 is installed, it is inserted into barrel 12, and end caps 14 and 16 are moved into position. V-bands 38 are placed around flanged ends 28 and flanges 30 and are tightened with V-band clamping knobs 44. As V-bands 38 are tightened, flanged ends 28 and flanges 30 come closer together, compressing O-rings 36, and causing protruding members 68 to dig into the ends of cylinder 46. Because protruding members 68 are made of metal, they dig into the softer polyethylene cylinder 46. Protruding member 68 and side surface 70 is spaced with respect to the bottom of plug portions 66 so that the inner surfaces of plug portions 66 contact thick frits 54, 56 when flanged ends 28 and flanges 30 have been brought together. Protruding sealing member 68 provides a good seal between end caps 14, 16 and cylinder 46 without the need for O-rings with chemically resistant properties at these locations. 
     After cartridge 18 has been installed, chamber 22 is pressurized, via an opening not shown on the drawings, and the increased pressure compresses the walls of flexible polyethylene cylinder 46, providing uniform packing for the stationary phase media therein. A source of sample in a carrier liquid is connected to process inlet 76, and liquid leaves enclosure 12 via process outlet 78. 
     Other embodiments of the invention are within the scope of the appended claims. E.g., in place of V-band 38, other mechanisms could be used to hold end caps 14, 16 in place and bring them together. Also, other geometries could be used for protruding member 68.