Abstract:
A method and apparatus for creating a fluid tight seal between a capillary column and a connector. The method and apparatus are easy to employ and do not require the use of screws, ferrules, or additional tools. The method can be used for any capillary tubing as well as for megabore and microbore columns and tubing. In the method, a length of auxiliary tubing is placed over the outside of tubing requiring a fluid tight seal, such as a capillary column. After the capillary column is inserted into the connector, the length of auxiliary tubing is press-fit into the connector creating a secondary fluid tight seal. The auxiliary tubing provides additional mechanical stability during mechanical vibration and dramatically increases the tensile force required to compromise the fluid seal. This method can be used for many types of chromatography including gas chromatography and liquid chromatography. A connector assembly and fluid tight seal assembly are also disclosed.

Description:
TECHNICAL FIELD 
     The invention relates to capillary columns used to analyze chemical substances. More specifically, the invention is directed to a new method for creating a fluid tight seal between a capillary column and a connector. 
     BACKGROUND ART 
     Chromatographic apparatus used for both gas and liquid chromatography typically employ capillary columns to provide control passageways for substances to be analyzed. Areas of analytical application for capillary columns include gas chromatography, liquid microbore chromatography, capillary electrophoresis, and supercritical fluid chromatography. In most analytical applications today, glass, metal or flexible fused silica capillary columns are used. Occasionally, polymeric capillaries are also used. Frequently, it is necessary to join two pieces of capillary columns together in order to repair a broken column, to optimize a chemical separation by joining dissimilar columns, to extend the column length, or to add retention gaps or guard columns. In most analytical applications the column ends must also be connected to a sample injector and a detector. 
     Connectors are known in the art for receiving a fluid stream in a first fluid-bearing conduit and then delivering the received fluid stream to a second fluid-bearing conduit. In many cases, the fluid connection is obtained by manual manipulation of separate components that comprise the connector, such as by alignment and compression of a ferrule onto a column that is fitted to a receiving device. 
     The requirements placed upon a practical capillary connector for general use in chromatography applications are demanding. The connector must be able to withstand regular contact with chemically reactive substances and organic solvents. It must remain leak-free when operated at internal pressures ranging from zero (absolute) to several thousand pounds per square inch and over temperature cycles from sub-ambient to several hundred degrees Celsius. The thermal mass must be small and the thermal conductivity high to maintain thermal equilibrium between the column and its immediate surroundings. The dead volume in the joint must be as close to zero as possible 
     Many connectors have been devised to address the need for providing a fluid tight coupling between column ends and connectors. Some connectors employ a ferrule with a conical frustrum exterior and a longitudinal bore. The column end is inserted through the bore of the ferrule and then the column-ferrule assembly is inserted into the interior of the connector. The interior of the connector is shaped to receive the ferrule. Pressure is then applied to the ferrule via a threaded fastener creating a fluid tight seal. Other connectors known as press-fit connectors consist of a hollow glass elongated tube having a conical configuration. Press-fit connectors have a tapered internal bore narrowing from the end to the central portion. In use a column end is inserted into the open end of the connector and moved into the press-fit position. Press-fit glass tubes have also been used with a ferrule and compression fitting at each end to seal against the capillary column. These methods are also used to connect the ends of two columns together with a fluid tight seal. 
     Known connectors provide low dead volume and chemically inert connections but suffer from several disadvantages. The ferrule and compression style connectors require several moving parts and require careful assembly. Many require separate elastomeric seals to ensure fluid-tight connection. The components used to make the seal must be chemically inert to the substances used in the analytical chromatographic process, and must exhibit good temperature stability. These components increase the cost and the complexity of the fluid seal and the connector. All of these connections show increased leakage at high temperatures, increased leakage after thermal cycling, and a sensitivity to tensions/torques applied to the fluid sealing location. The drawn conical connector of the press-fit variety has been reported to suffer from inconsistent fluid seal, particularly with modern high temperature fused silica capillary columns. At elevated temperature the fluid seal has been reported to leak and come apart. 
     SUMMARY OF THE INVENTION 
     Method and apparatus for establishing a fluid seal between capillary columns and connectors with a tapered conical internal bore is described. These methods and apparatus can be used when attaching the end of a column to an injectorport or a detector. The methods and apparatus can also be used when joining two capillary columns together end to end utilizing a union connector. In addition to establishing fluid tight seals for capillary tubing, these methods and apparatus can be used on a variety of tubular objects such as on larger bore tubing such as microbore columns, and megabore columns. 
     The improved fluid tight seal is generally accomplished by the following steps: 1) an auxiliary length of tubing is closely fit over the outside diameter of the capillary column so that a short length of the capillary column remains exposed; 2) the capillary column is press-fit into a connector with an internal conical taper shaped bore creating a fluid seal, and; 3) the auxiliary tubing is then moved into the connector and press-fit into the conical taper section of the connector creating a second fluid seal. 
     One of the advantages of these methods and apparatus is that it simplifies the installation of a column into a connector. The assembly of the auxiliary length of tubing is very simple and no additional screws, ferrules or tools are required to create a fluid tight seal. The outside diameter of the auxiliary tubing need not be bonded or glued into the internal bore of the connector nor does the outside diameter of the capillary column need to be glued or bonded to the inside of the auxiliary tubing. The capillary column and auxiliary tubing are press-fit into place to create a reliable fluid seal. 
     When assembled, the auxiliary tubing provides an extra seal that provides several operational benefits. The increase in the fluid sealing surface area increases the stability of the fluid seal during mechanical vibration. This in turn increases the tensile force required to compromise the fluid seal which dramatically reduces the leak rate of the fluid seal. Additionally, the auxiliary tubing adds essentially no physical and thermal mass, is reliable, and is inexpensive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B each illustrate a single connector. 
     FIG. 2 depicts a press-fit glass union. 
     FIG. 3 depicts a three-way glass union. 
     FIG. 4 depicts a single connector illustrating primary and secondary fluid seals. 
     FIG. 5 depicts a single connector illustrating the addition of a bonding agent. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A simple method and apparatus for establishing a fluid seal between tubing and a connecting device that has an internal conical tapered bore is described. The method and apparatus applies to, for example, capillary columns and capillary tubing, and other tubing including microbore and megabore columns and tubing. Throughout the specification, any reference to capillary columns applies to capillary tubing, microbore and megabore columns and tubing unless otherwise noted. 
     The method utilizes an auxiliary length of tubing to reinforce the fluid tight seal a capillary column and a connector. Initially, the auxiliary length of tubing is “closely fit” over a capillary column. Throughout this application the phrase “closely fit” indicates that the inner diameter of the auxiliary tubing has a length or is “dimensioned” so that the capillary column can be inserted through the auxiliary tubing yet there is contact between the outer surface of the capillary column and the inner surface of the auxiliary tubing. The closeness of the fit is such that the auxiliary tubing will remain in place over the outside of the capillary column when subjected to mechanical vibration. 
     The end of the capillary column is inserted through the auxiliary length of tubing leaving a length of capillary column exposed. The exposed length of capillary column is long enough so that the capillary column can be inserted and press-fit into the connector without the leading edge of auxiliary tubing making contact with the internal bore of the connector. The capillary column is press-fit into a connector which has an internal conical tapered bore creating a first fluid tight seal. Subsequently, the auxiliary length of tubing is press-fit into the connector creating a second fluid tight seal. 
     The force during assembly deforms the auxiliary tubing such that a fluid seal is made between the leading edge of the auxiliary tubing and the taper bore of the connector. The force also presses the auxiliary tubing tight to the capillary column, creating a fluid seal between the auxiliary tubing and the capillary column. Both the first fluid seal made with the capillary tubing and the second fluid seal made with the auxiliary length of tubing are established in the internal conical tapered bore section of the connector or fitting. 
     FIG. 1A illustrates a sectional view of one embodiment for capillary columns. FIG. 1A shows an improved fluid tight seal consistent with this invention and accomplished by the following steps: 1) an auxiliary length of tubing  30  is closely fit over the outside diameter of a capillary column  20  so that a length of the capillary column  20  remains exposed; 2) the capillary column  20  is press-fit into a connector  40  having an internal conical taper shaped bore  55 ; and 3) the auxiliary tubing  30  is then moved into the connector  40  and press-fit into the conical taper shaped bore  55 . 
     The connector  40  includes a body  45  that has a flared entry  50  at one end. The flared entry  50  narrows into a tapered conical internal bore  55 . The internal bore  55  tapers to a portion  60  that has an essentially consistent diameter, which terminates at the end  65  of the body  45  of the connector  40 . The body  45  is preferably fabricated of ceramic, glass, metal such as stainless steel, or polymeric materials such as PEEK. Other materials may be used so long as they are able to withstand the conditions the connector will be exposed to. The flared entry  50  has a diameter that is wide enough to facilitate insertion of the capillary column  20  and the auxiliary length of tubing  30 . The tapered conical internal bore  55  is dimensioned so that a friction fit is created between the wall of the tapered conical internal bore  55  and the outer diameter of the inserted end of both the capillary column  20  and auxiliary tubing  30 . The internal bore  55  extends the length of the body  45  of the connector  40  and subtends at an angle that is approximately  2  degrees. However, this is only illustrative; the length, angle, and diameter of the tapered conical bore may vary according to the type of connector being used. Examples include connectors used for microbore and megabore tubing. The diameter of the portion  60  that has an essentially consistent diameter may also vary according to the type of connector used, but it is smaller than the diameter of the capillary column  20 . 
     The capillary column  20  is any capillary tubing including those used as columns for gas and liquid chromatography. Additionally the method of this invention encompasses tubing of larger diameter than capillary tubing. Examples of larger diameter tubing include microbore and megabore tubing. 
     The auxiliary length of tubing  30  is preferably formed from polyimide, but could be formed of other material and is limited only by chemical and mechanical compatibility, and intended temperature range of the seal. The internal diameter of the auxiliary length of tubing  30  and the outer diameter of the capillary column  20  have a ratio from 1/1 to 2/1. Preferably, the auxiliary tubing  30  has an internal diameter such that the capillary column  20  can be inserted into the auxiliary tubing yet the inside surface of the auxiliary tubing  30  is in contact with the outside surface of the capillary column  20 . The auxiliary tubing  30  has an outer diameter such that it can be press fit into the internal bore  55 . 
     The outside surface of the auxiliary length of tubing  30  does not require any glue or bonding agents to create the second or secondary fluid tight seal. However, in one embodiment of the invention, the addition of a suitable bonding agent is utilized. As illustrated in FIG. 5, the bonding agent  25  is applied to the outer surface  22  of the capillary column  20  before the auxiliary length of tubing  30  is closely fit over the capillary column  20 . Alternatively, the bonding agent  25  may be applied over the outer surface  32  of the auxiliary tubing  30  prior to being press fit into the connector  40 . The addition of a bonding agent  25  will increase the strength of the fluid seal and mechanical integrity of the connection. The choice of bonding agents is limited by chemical compatibility with the tubing material, the intended temperature range, and the thermal cycling of the application. A preferred bonding agent is a polyimide resin. In yet another embodiment, the auxiliary length of tubing is constructed of partially cured material that is the same material as the capillary column  20  coating material. This method of attachment will cause the auxiliary length of tubing  30  and the capillary column  20  to cure and bond together without the addition of a bonding agent when subjected to elevated temperatures. This method also can further increase the mechanical integrity of the connection between the capillary column  20  and the auxiliary tubing  30 . 
     FIGS. 1B,  2 , and  3  illustrate other embodiments. In general, the discussion of the components in FIG. 1A applies to FIGS. 1B,  2 , and  3 . 
     FIG. 1B illustrates a sectional view of another embodiment. The components are essentially the same as in FIG. 1A except that the capillary column  20  of FIG. 1A is substituted with a megabore column  70 . The megabore connector  90  is designed essentially the same as the connector  40  in FIG. 1A except that it is sized to receive a megabore column. 
     The auxiliary length of tubing  80  is closely fit over the outside diameter of the megabore column  70 . The megabore column  70  is inserted into the megabore connector  90  and press-fit into internal conical bore  105 . The auxiliary length of tubing  80  is then press-fit into the internal bore  105 . 
     FIG. 2 illustrates the sectional view of another embodiment. FIG. 2 shows two individual capillary columns  110   a  and  110   b  each with an auxiliary length of tubing  120   a  and  120   b  closely fit over the outside diameter of the capillary columns  110   a  and  110   b . The capillary columns  110   a  and  110   b  and the auxiliary lengths of tubing  120   a  and  120   b  are press-fit into a union connector  130 . 
     The union connector  130 , a press-fit union design, includes a body  135  that has flared entries  140   a  and  140   b  at both ends. Flared entries  140   a  and  140   b  narrow into tapered conical internal bores  145   a  and  145   b . The internal bores  145   a  and  145   b  taper to a portion  150  of internal bore that has an essentially consistent diameter. The portion  150  of internal bore has a diameter that is smaller than the diameter of either capillary column  110   a  or  110   b . The connector is a press fit glass union but other union designs can be used. The only required feature of a union used in this invention is that the internal bores  145   a  and  145   b  are dimensioned so that both the capillary tubes  110   a  and  110   b  and the auxiliary lengths of tubing  120   a  and  120   b  can be inserted and press-fit into the internal bores  145   a  and  145   b.    
     The capillary columns  110   a  and  110   b  can be any capillary tubing; they can be identical capillary columns or different ones depending on the intended use. The capillary columns  110   a  and  110   b  can also be tubing of a larger diameter such as microbore or megabore. 
     The auxiliary lengths of tubing  120   a  and  120   b  operate as they do in FIGS. 1A and 1B. The internal bore of the auxiliary lengths of tubing  120   a  and  120   b  and the outside diameter of the capillary columns  110   a  and  110   b  are dimensioned so that a close fit is created between the capillary columns  110   a  and  110   b  and the auxiliary lengths of tubing  120   a  and  120   b . The outside diameter of the auxiliary lengths of tubing  120   a  and  120   b  are dimensioned so that the auxiliary lengths of tubing  120   a  and  120   b  can be press-fit into internal bores  145   a  and  145   b.    
     FIG. 3 illustrates the sectional view of another embodiment. FIG. 3 shows three individual capillary columns  150   a ,  150   b , and  150   c  each with an auxiliary length of tubing  160   a ,  160   b , and  160   c  closely fit over the outside diameter of the capillary columns  150   a ,  150   b , and  150   c . The capillary columns  150   a ,  150   b , and  150   c , and the auxiliary lengths of tubing  160   a ,  160   b , and  160   c , are press-fit into a 3-way press-fit union connector  170 . The installation of the capillary columns  150   a ,  150   b , and  150   c  are performed in the same way as in FIG. 2 
     FIG. 4 illustrates an enlarged sectional view of a single connector incorporating the invention. FIG. 4 illustrates the primary and secondary fluid seal of the invention. The components are the same as in FIG.  1 A. The capillary column  20  is press-fit into the connector  40  creating the first or primary fluid tight seal  180 . The auxiliary length of tubing  30  is subsequently press fit into the connector  40  creating the second or secondary fluid tight seal  190 . Both seals are typically present in each of the embodiments shown in FIGS. 1A,  1 B,  2 , and  3 . 
     Usually, the force during assembly deforms the capillary column  20  so that a fluid seal is made between the leading edge  21  of the capillary column  20  and the tapered conical internal bore  55  section of the connector  40 . Additionally the force during assembly usually deforms the auxiliary length of tubing  30  so that a fluid seal is made between the leading edge  31  of the auxiliary length of tubing  30  and the tapered conical internal bore  55  section of the connector  40 . The force also presses the auxiliary length of tubing  30  tight to the outside surface of the capillary column  20  creating a fluid seal between the inside surface of the auxiliary length of tubing  30  eliminating a fluid flow path between the capillary column  20  and the auxiliary length of tubing  30 . Alternatively, any of the aforementioned seals may be made by a friction fit. The resulting connection has improved mechanical stability with minimal dead volume that is simple to install.