Abstract:
A reusable liquid chromatographic column consists of three parts, a column body with an integral outlet port molded on one end, a sealing insert with an inlet port, and a perforated cap providing downward force to compress the sealing insert into the column body. A wedge-like seal is employed to seal the connection between the sealing insert and the column body. Two filters on both ends of the column body are used to prevent escape of packing materials from the column chamber under pressure. Hand tightening is adequate to seal the connection by screwing the perforated cap onto the column body. The column is reusable due to its simple disassembling and reassembling processes. It is also disposable due to its inexpensive fabricating materials and manufacturing process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 11/307,312 filed on Jan. 31, 2006, now U.S. Pat. No. 7,704,388, which is hereby incorporated by reference in its entirety into this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to liquid chromatographic columns and methods of assembling and disassembling reusable, economic, and leak-free chromatographic columns. 
     Liquid chromatography is an analytical chromatographic technique that is based on differences in partitioning behaviors between a mobile phase and a stationary phase to separate the components in a mixture, more specifically, to separate ions or molecules dissolved in a solvent. A column is packed with the stationary phase and the mobile phase carries the mixture through it. Sample components having stronger affinity with the stationary phase spend longer time in the column and are separated from components that have weaker affinity with the stationary phase and pass through the column faster. 
     In pursuit of optimal separation, the chromatography system is usually operated under pressure to facilitate the flow of the mobile phase in the stationary phase. As a consequence, the columns demand effective seals to prevent the mobile phase from leaking out of the pressurized passage. An O-ring employed in some prior art methods (U.S. Pat. No. 5,601,708 and U.S. Pat. No. 6,436,284) can provide a good seal for the openings of the column, but some organic solvents used as a mobile phase in liquid chromatography can damage the O-ring after a lengthy soaking in the solvents. The methods for making commercially available disposable columns (U.S. Pat. Nos. 6,565,745 and 6,949,194) involve the use of a snap-on cap to form a sealing connection between the column body and the sealing head. This technique could lead to sealing failure under substantial pressure build-up. In addition, the use of snap-on cap with cantilever members and the ramped detents molded on the column body forms a tight interference fit, which practically makes the column solely for one-time use due to the inability in disassembling column for repeated uses. Columns made of glass (U.S. Pat. No. 6,811,688) cannot withstand a pressurized system and cost more than plastic columns. Other prior art technique (U.S. Pat. No. 6,797,174) requires a complicated process involving six separate pieces and one spacer ring. A low-pressure liquid chromatographic cartridge is provided with a resilient fluid tight seal (US Patent Application 2005/0247632), but the rotation resulted from threading the cap onto the cartridge container could cause seal failure and the cartridge is not reusable. 
     All these prior art techniques have the drawbacks of high cost for column assembly, seal failure, or one-time use. It is the object of this invention to provide reusable, economic, and leak-proof liquid chromatographic columns for the separation and purification of organic compounds. 
     SUMMARY OF THE INVENTION 
     The invention is aimed at providing reusable, economic and leak-proof liquid chromatographic columns. It is still aimed at providing a simple, but reliable process to assemble and disassemble the columns. In one aspect, the columns can be reusable since the assembly and disassembly processes are easy to fulfill without assistance from special devices or machines. Conventional tools, such as pliers, wrenches, and tweezers, are adequate to disassemble and assemble the columns. In another aspect, the columns are also disposable due to its inexpensive materials and simple assembly process. 
     The column includes three separate parts, a cylindrical body with one end having one port molded as a single piece to the body and the other end with an opening for loading the packing material and sealing, a sealing insert molded with another port directed toward the body chamber, and a perforated cap used to force the sealing insert into the column body by use of hand-tightening. At the both ends of the packing material loaded in the column chamber, two filters are employed to prevent the packing material from entering the ports. 
     In the preferred embodiment, a wedge-like seal is adopted to the connection between the column body with a tapered rim on the inner wall and the sealing insert with a conical circumference. The outer wall on the opening portion of the column body is molded with male threads for the perforated cap comprising female threads. The sealing insert, along with the perforated cap around it, is placed into the column body. By turning the cap onto the column base, the perforated cap provides straight downward force to push the sealing insert into the column body to form a compression type fining. The perforated cap has small ridges on the outer wall to aid in gripping and hand-tightening with ease. 
     One of the advantages and features of this invention is the column designed for repeated uses. Although the used column is disposable, it can afford multiple uses with appropriate disassembling and reassembling processes. The used column is readily disassembled by unscrewing the perforated cap, pulling out the sealing insert, and then removing filters and the packing material. After reloading with new packing material and filters into the used column body, the used sealing insert and perforated cap are reassembled onto the column body to form a new column with tight seal. A column in this embodiment can be reused up to ten times, preferably two to three times with replacement of new packing material and filters each time. The number of using times is subject to the integrity of the sealing interface between the sealing insert and the column body. A smooth surface free of cracks or niches is indispensable for the column reassembly. The invented liquid-chromatographic columns can sustain relatively high pressure up to 180 psi. 
     The column may also be disposable thanks to its inexpensive fabricating material, such as polyethylene, polypropylene, and its economic assembling process. Packing materials include silica, silica gel, alumina, regenerated silica, regenerated silica gel, regenerated alumina, and the like. Hand-tightening without or with slight assistance from wrenches or pliers is sufficient to provide reliable seal under substantial internal pressure. Other advantages of this invention will be described in the preferred embodiment thereof and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of easy understanding the advantages this invention brings, the following seven drawings are used to explicitly describe the column features and the assembling and disassembling processes. 
         FIG. 1  is a perspective view of the whole column based on this invention; 
         FIG. 2  is an exploded cross-sectional view of the column of  FIG. 1 ; 
         FIG. 3  is a fragmentary sectional view of the sealing part; 
         FIG. 4  is a perspective view of the sealing insert (Type I); 
         FIG. 5  is a cross-sectional view of the sealing insert of  FIG. 4 ; 
         FIG. 6  is a perspective view of the sealing insert (Type II); and 
         FIG. 7  is a perspective view of the perforated cap. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a perspective view of the whole column in this embodiment. The chromatographic column  10  with a cylindrical structure has a sealing insert  18  with a molded inlet port  14 , a perforated cap  20 , and a column body  12  with a molded outlet port  16 . The packing material is loaded inside the column chamber  13 . In the operation procedure, the inlet port  14  is connected to a source where the mobile phase flows into the column  10 . The mobile phase carries mixture from the inlet port  14  to outlet port  16  through the packing material in which components are separated due to different retention times caused by the difference in affinity of each component to the packing material. The outlet port delivers the separated components to a detecting device to identify or quantify each component, which is finally collected in containers. The size of the column  10  varies with the amount of separated samples. 
     Referring to  FIG. 2 , it is seen that the column  10  has five pieces in sequence: a perforated cap  20  with an opening  56 , a sealing insert  18  with an inlet port  14 , an inlet filter  22 , an outlet filter  24 , and a column body  12  molded with an outlet port  16 . The cylindrical chamber  13  is for filling the packing material, such as silica gel. Two filters  22  and  24 , porous frit, are placed on the two ends of the column chamber  13  to avoid the leaks of the packing material from the column body  12 . The inlet port  14  is integrally molded on the sealing insert  18 , which is placed into the open end of the column body in the assembling process. A perforated cap  20  with female threads  54  is used to fix the sealing insert  18  into the column body  12  with a sealing connection. 
     The sealing connection of the apparatus is shown in  FIG. 3 . The wedge-like seal is used to form a tight seal at the inlet end. The inlet opening of the column body  12  consists of a tapered end  26 , which receives a slope  36  on the sealing insert  18  to form the sealing surface. The perforated cap  20  is placed onto the sealing insert  18  to provide downward force to push the sealing insert  18  into the column body  12  by screwing down the perforated cap onto the column body. In this sealing connection, the perforated cap  20  with female threads  54  plays a role as a nut with female threads and the column body  12  is like a hollow bolt with male threads  28  on the outer wall. The sealing insert  18  is forced to move linearly downward into the column body  12  without tangential rotating movement. A compression-type fitting is formed between the slope  36  of the sealing insert  18  and the tapered rim  26 . The use of threads in the connection allows easy disconnection of the perforated cap  20 , the sealing insert  18 , and the column body  12  without damaging the sealing interface. The outer diameter of the step  44  of the sealing insert  20  is sized to fit within the perforation opening  56  of the perforated cap  20  with minimum radial clearance of 0.01 mm to 10 mm between the two. The clearance leads to easy operation and avoids tangential rotating movement between the sealing insert  18  and the tapered end  26  during the cyclic operation of assembly, disassembly, and reassembly. The design aimed at easy disassembly and reassembly of the column provides a base for reusing the column with multiple times. 
       FIG. 4  shows a conventional design (Type-I) for the insert  18 . The inlet port  14  has a female luer fitting with partial male threads  40  to connect to a source where the mobile phase flows through. Finger-tightening is adequate to connect the inlet port to the source of the mobile phase by turning the fitting on. Referring to  FIG. 5 , the radius of the circumferential stair  32  is extended to be a little larger than the inner radius of the opening of the column body  12  in avoidance of the whole sealing insert  18  entering the column body  12 . A side slope  36  with an angle from 5 to 75.degree., preferably from 10 to 50.degree., mating the surface of the tapered end  26  allows the sealing insert  18  to slide into the column body  12 . Three stairs  38 ,  42  and  44  are employed to reinforce the hardness and mechanical strength of the inlet port. Although the stairs with other numbers of more than three or less than one (no stair) can be used, two to three stairs are preferred in the invention for repeated uses. The height of the stair  38  is equal to the height of the circumferential stair  32  in order to receive even downward force in the center and on the edge of the sealing insert  18 . The use of the recess  46  between stair  38  and  32  is aimed at saving materials and avoiding the insert deformation caused by thick layer in the molding process. 
     As shown in  FIG. 5 , a conical shape  48 , which is open toward the inlet filter  22  at the end the inlet passage, is designed to allow even dispersion of fluid cross the filter  22  and the packing materials in the column body  12 . The sealing insert  18  has an additional circular protrusion  50  on the rim of the insert bottom  51 . The protrusion with a height of 1.5 mm (e.g. 0.5 to 5 mm, preferably 1 to 3 mm) has a 75.degree. angle (e.g. 30 to 150.degree., preferably 60 to 120.degree.) in section and protrudes downward from the surface  51 . After compressed downward, the protrusion  50  can dig into the filter  22 , which is tightly against the walls of the column body  12  to stop the movement of packing materials under pressure, to form a seal in case that any defect fitting between the filter  22  and the column wall cause the leaks of the packing material. Accordingly, another protrusion  25  with the size equal to the protrusion  50  is positioned against the filter  24  at the outlet end to prevent leaks of the packing material to the outlet port  16 . The disk-shaped filters  22  and  24  are made of porous polymer with elasticity for receiving pressing from the protrusions  50  and  25 , respectively. 
     An alternative design (Type-II) for the sealing insert is shown in  FIG. 6 . The sealing insert  19  has radial spokes  45 A- 45 F with a number of 6 (e.g. 2 to 16, preferably 4 to 12). The spokes  45 A- 45 F molded on the bottom  43  of the sealing insert  19  are used to increase the mechanical strength of the bottom  43  and enable the bottom to withstand substantial internal pressure. The spoke height is lower than that of the circumferential step  41 . The spokes  45 A- 45 F are extended from the stair  39  outwardly, but not reach to the wall of the circumferential step  41 . The space between the end of each spoke and the wall is intended to make the sealing slope receive the even force from the tapered rim  26 . Stairs  37  and  39  are used to reinforce the mechanical strength of insert port  14 . This spoke-molded insert is preferably designed for a big size column, which has a large contact surface between the sealing insert and filter  22 . Bottom surface  43  integrated with spokes of the sealing insert  19  can prevent deformation under high internal pressure. The radial spokes can also be employed to increase the mechanical strength of the bottom  58  at the outlet of the column body  12  for the sake of high internal pressure tolerance. 
     The compressive force applied to pushing sealing insert  18  downward is provided from perforated cap  20  by screwing it onto column body  12 .  FIG. 7  shows the perspective view of perforated cap  20 , which functions as a nut with female threads  54 . Knurls  52 , regular small ridges on the outer surface of perforated cap  20 , assist to prevent slipping while the connection is tightened by hands through gripping perforated cap  20 . Referring to the cross-sectional view of the column  10  in  FIG. 2 , female threads  54  along with male threads  28  on the outer wall of the column body  12  can be clockwise or counter-clockwise. A perforation  56  sized between the diameters of the stair  44  and the stair  38  is formed on the top of the cap  20  to ensure that the downward force is evenly scattered on the stairs  32  and  38  of the insert  18 . The connection with separate sealing insert  18  and perforated cap  20  provides only straight linear movement between the slope  36  and the tapered end  26  instead of tangential movement, which can cause abrasion and defects at the sealing interface and eventually give rise to a failed seal. 
     In the packing process of a chromatographic column, the filter  24  with the diameter equal to the bottom size of the column body  12  is firmly placed against the protrusion  25 . The packing materials are introduced to the column chamber  13  with the assistance of vacuum hooked to the outlet port, or just by vibrating the column body  12  to ensure the packing materials closely packed inside the column chamber. Any void volume in the packing materials should be prohibited since it can lead to poor separation efficiency. After the packing material nearly reaches to the tapered end  26 , the inlet filter  22  is placed on the top of the packing material layer. The sealing insert  18  is then inserted into the tapered end  26 . Once the perforated cap  20  is aligned onto the sealing insert  18 , the connection can be firmly formed by turning the perforated cap  20  onto the column body  12 . A wrench or a pair of pliers may be applicable to aiding tightening, but hand tightening is adequate to assemble the column with tight seal. 
     The column allows a number of repeated uses since it can be easily disassembled and reassembled with hands. After the packing material in the used column is dry, the perforated cap  20  is readily unscrewed from the column body  12 . The filters  22  and  24 , as well as the packing material, are then removed from the column chamber  13 . Three parts including the perforated cap  20 , the sealing insert  18 , and the column body  12 , can be cleaned with organic solvents for the next use. With replacement of the packing material and two filters, a new column can be easily reassembled according to the assembling process described above. During the assembling and disassembling process, the contact surfaces of the tapered end  26  and the slope  36  should be kept clean, smooth, and free of any cracks or niches. The column can be used up to ten times with care of three reusable parts, the perforated cap  20 , the sealing insert  18 , and the column body  12 . 
     In this design, the sealing connection consisting of the sealing insert  18  and the perforated cap  20  performs as an inlet end, as described above. However, in the preferred embodiment, the inlet port  14  and outlet port  16  can switch positions if the female luer fitting with partial male threads  40  is molded on the column end  16 . As a consequence, the sealing connection would be on the outlet end. The mobile phase flows into the column through the molded end and flows out of the column through the sealing connection end. Indeed, such an upside-down design would enhance the column resistance against leaks under a pressurized system since the outlet pressure is always lower than the inlet pressure. 
     In one embodiment, the device comprises a one-piece reusable plastic tubular body comprising a first open end having an inside diameter ID1. The body further comprises external threads disposed about the first open end. The body further comprises a tapered rim disposed at the first open end. 
     The device further comprises a sealing insert comprising a stem extending upward from the base. The stem comprises first and second annular stairs, and an inlet port. The first annular stair has an outside diameter OD1. The second annular stair has an outside diameter OD2. The outside diameter OD1 of the first annular stair is larger than the outside diameter OD2 of the second annular stair. The stem further comprises a third annular stair disposed above the second annular stair. The third annular stair has an outside diameter OD3. The outside diameter OD2 of the second annular stair is larger than the outside diameter OD3 of the third annular stair. The first annular stair has a height H1 relative to the top surface of the base. The annular wall surrounds the first annular stair of the stem. The annular wall is substantially spaced apart from the first annular stair to form an annular recessed portion with the top surface. The annular wall comprises an upper annular end, an annular sloped surface, and a lower annular protrusion. The upper annular end of the annular wall has a height H2 relative to the top surface of the base. The height H1 of the first annular stair is equal to the height H2 of the upper annular end of the annular wall. The sealing insert further comprises an annular wall disposed at the perimeter of the base. The upper annular end of the annular wall has an outside diameter OD4 that is larger than the inside diameter ID1 of the first open end of the tubular body. 
     The device further comprises a one-piece reusable plastic cap comprising a top wall, a central opening disposed in the top wall, and an annular sidewall having internal threads removably engaged with the external threads of the tubular body. The inlet port of the stem passes thru the central opening and extends outward of the top wall of the cap. The central opening has an inside diameter ID2. The inside diameter ID2 of central opening is less than the outside diameter OD1 of the first annular stair. 
     The preferred embodiments and illustrative details set forth should merely be regarded as descriptive disclosure. Various other changes and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.