Abstract:
A column installation assembly for a Micro Gas Chromatograph that includes a coiled column is described. The assembly also includes a mechanism within the Micro Gas Chromatograph for removably securing the coiled column in place. A method for preparing a column for installment in a Micro Gas Chromatograph is also described

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to chromatography equipment and column assembly.  
       BACKGROUND OF THE INVENTION  
       [0002]     In gas chromatography (“GC”), the apparatus incorporated within the instrument that houses the column, is sometimes referred to as the column basket. As the columns are typically arranged in some form of coil, the size of the column basket is described in terms of its diameter. The diameter of the column basket generally dictates the size of the oven, which in turn dictates the overall size of the entire instrument size. Additionally, oven size and temperature needs dictate the power requirements of the instrument. In some markets there is a need for significantly smaller and faster gas chromatographs than the commonly available gas chromatograph. To those skilled in the art, this type of instrument is known as Micro GC.  
         [0003]     Currently, Micro-GCs include columns wound down to small diameter (˜2″) inside a copper can. The column is manually positioned inside the can by a process of winding the column into the can where it expands inside the copper can. In some instances, multiple columns are wound down and expand inside the copper can. The copper can with the column or columns is then installed into the Micro GC where it serves as the oven. This arrangement and process for installation has several drawbacks.  
         [0004]     First, Columns would by hand into cans is time-consuming and expensive. The entire installation process is typically performed by a skilled technician where the Micro GC is assembled for commercial use. As a result the end user cannot simply change columns or make repairs in the field. The entire unit must be shipped back to the manufacturer in order to change a column.  
         [0005]     Second, manual winding, in a small fixed can, limits the length of column that can be used in the assembly. As the column fills the can from the outside diameter inwards, the volume of the can and the column minimum bending radius limits how much material can fit in the oven, and therefore the maximum column length provided. Longer length columns are especially problematic and can only be handled through special hand wound processing. Column integrity and lifetime are a function of bending radius. Damage to column material is cumulative, such that material drawn over a small radius even for short periods may experience significant reductions in expected lifetime. The process of overbending the column material to fit it inside the current can configuration necessarily reduces its lifetime. Currently, column lengths are limited to about 14 meters before problems arise with the installation.  
         [0006]     Third, manual winding can be detrimental to the integrity of the column itself. The column packing or stationary phase can be disrupted by the process of winding it inside the can. Winding PLOT (Porous Layer Open Tubular) columns in particular degrades the internal coating by over bending the column during assembly, creating fractures in the brittle internal coating, producing shards or dust of stationary phase, which can degrade chromatography or adjacent devices such as micro injector valves.  
         [0007]     What is needed is a method of installing columns in a Micro GC that avoids manual winding of the column into the copper can. Further, an apparatus that allows easy installation and removal of the columns in a Micro GC is needed. It would be particularly advantageous to be able to easily and reliably install longer columns.  
       SUMMARY OF THE INVENTION  
       [0008]     A column installation assembly for a Micro Gas Chromatograph that includes a coiled column is described. The assembly also includes a mechanism within the Micro Gas Chromatograph for removably securing the coiled column in place. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, explain the advantages and principles of the invention. In the drawings,  
         [0010]      FIG. 1  is a perspective view of an air wound column around the winding template;  
         [0011]      FIG. 2  is a perspective view of an air wound column with a portion of the column fastened in position using ties with the winding template removed;  
         [0012]      FIG. 3  is plan view of a Micro GC configured to receive an air wound column;  
         [0013]      FIG. 4  is a plan view of a Micro GC with an air wound column placed in position;  
         [0014]      FIG. 5  is a plan view of a Micro GC with an air wound column installed in the Micro GC. 
     
    
     DETAILED DESCRIPTION  
       [0015]     Turning now to the drawings,  FIG. 1  illustrates an embodiment of an air wound column of the invention. The majority of the column  10  is wound in a coil  15  around a winding template  20 . A length of each end  25   a  and  25   b  of the column  10  remains unwound from the coil  15 .  
         [0016]     Preferably, the column  10  is wound around the winding template  20  using an automated respooling apparatus. While some column material is available in bulk spools, most analytic column material must be purchased in 30 meter or shorter lengths, already wound onto a conventional basket. In this instance, to the column is unwound from the basket onto a temporary spool without introducing any scratches, foreign material, twists or other stresses to the material. In particular, it is important not to bend the material to the extent that it would introduce large lifetime reducing stresses. From the temporary or bulk spool, the column material is metered through a tensioning device to the winding template  20 . A uniform small tension is important to feeding the material onto the template and ensuring it coils uniformly rather than stack up and collapse, leaving crossing tubing and internal voids in the bundle. Additionally, the tension also reduces the tendency of the relatively stiff tubing to spring out of the template before the assembly operation is complete. The metering of column length onto the template is preferably a non-contact operation. When the final length (typically 2-12 meters, but occasionally up to 30 meters) is counted onto the coil, a length of column at each end  25   a  and  25   b  is left un-looped and unsecured from the coil  15  of the assembled column and are fastened to the template with fastening devices  27   a  and  27   b . Then, the column is severed, and the template is removed from the winding machine.  
         [0017]     The internal diameter of the winding template is larger than the typical internal diameter of manually wound columns that are used inside of the copper can of conventional Micro GCs. As a result, this method of preparing the coil  15  places minimal stress on the integrity of the column packing and tubing. The preferred winding template  20  is a Teflon coated bobbin or spool. A Teflon coated bobbin or spool is easily removed from the coil  15  once the coil  15  is secured in shape, as discussed below. Although not required, it is preferred that the winding template  20  be removed from the coil  15  prior to use in a Micro GC as it may affect the heat distribution and overall performance once in place.  
         [0018]     Once the column  10  is coiled around the winding template  20 , at least a portion of the coil  15  must be secured or fasted in coil shape so that it does not uncoil or unravel when being handled.  FIG. 2  illustrates the preferred method of securing the coil  15  using physical fastening devices. Twist ties  30   a ,  30   b , and  30   c  of high temperature tape or string are fastened around the coil  15  positioned at approximately equidistant points around the circumference of the coil  15 . Twist ties  30   a    30   b , and  30   c  are twisted tightly enough so that the coil  15  does not unravel but not so tightly that it damages the column  10 .  FIG. 2  shows the use of three twist ties to fasten the coil  15 , however, less or more could be used to obtain the level of fastening needed. Additionally, other devises can be used in place of twist ties  30 . Non-limiting examples such as wire or clips can also be used.  
         [0019]     Additional methods for securing or fastening the coil  15  can also be used. In one embodiment, an adhesive (not shown) is applied while the coil is still positioned on the winding template  20 . The adhesive is cured prior to the subsequent removal of the coil  15  from the winding template  20 . The preferred adhesive is EPO-TEK 353ND, however other adhesives may be used. One advantage of epoxy adhesive, and to some extent high temperature tape, is that the regular cross section of the coiled column is retained, making precision fitting into the oven assembly of the Micro-GC easier, providing more uniform temperature for good chromatography. The effect of temperature on the adhesive is an important factor to consider when choosing a suitable adhesive. Also, its potential reactivity with the coating of the column  10  is another important factor.  
         [0020]     A length of column at each end  25   a  and  25   b  is left un-looped and unsecured from the coil  15 . The precise length left unsecured and un-looped at each end  25   a  and  25   b  is not critically important and can vary from application to application. The length must be long enough so that it may be properly installed in a Micro GC (discussed below). In the preferred embodiment, the final loop of each end  25   a  and  25   b  of the column  10  within the coil  15  is left unsecured as well. These unsecured loops are sometimes referred to service loops. The presence of service loops assists in the installation and service of the column  10 .  
         [0021]      FIG. 3  illustrates an inside view of a Micro GC  100  configured for installation of a pre-wound column. A circular groove  110  is positioned inside the Micro GC  100  and dimensioned to receive the coil  15  of a pre-wound column (not shown). The cylindrical groove  110  is formed from a circular outer wall  117 . The back  112  of the cylindrical oven groove  110  is preferably lined with copper for its heat conducting properties and preferably includes a heater  121 , bonded to the copper lining. The width of the groove  110  is preferably large enough to house multiple columns at once. The outer wall  117  is constructed from the same material as the housing of the Micro GC, which is typically high temperature plastic. Optionally, the groove may also be bordered on inner side of the groove with an inner wall  115 , which is concentric to with the outer wall  117 . Preferably, the inner and outer walls  115  and  117  are integral with the back wall of the housing, however, they need not be. The inner wall  115  is generally unbroken, while the outer wall  117  has a number of breaks  119  to allow for the ingress and egress of the column ends  25   a  and  25   b  (not shown). The remainder of the Micro GC is generally configured as a conventional Micro GC. One end has an injector  122  and the other end has a detector  124 . The specific type and position of the injector  122  and detector  124  can vary and will depend on the specific requirements of the user.  
         [0022]      FIG. 4  illustrates an inside view of the Micro GC  100  with a column  10  installed in position. The coil  15  of the pre-wound column  10  is placed in the groove  110 . The ends  25   a  and  25   b  are positioned out of the groove  110  through one of the breaks  119  in the outer wall  117  of the groove  110 . In order to provide some length adjustment, the free ends  25   a  and  25   b  of the column are preferably looped around inside the wall  117  to create a service loop. This provides enough axial travel for each column end for dressing or assembling it into the next device without requiring precision trimming and location. Typically, one end  25   a  will exit the groove  110  in the direction of the detector  124  and the other end  25   b  will exit the groove  110  in the position of the injector  122 .  
         [0023]     Once the column  10  is installed, a lid  130  is placed over top of the column  10  to complete the installation.  FIG. 5  illustrates the installation of the column  10  with the lid  130  in place. The lid  130  is also preferably constructed from copper. Other materials may be used, however the thermal properties of the material are a consideration. The lid  130  is dimensioned to fit firmly inside the outer wall  117  of the groove  110 . Clamping devises may also be used to hold the lid in place. Once the lid  130  is secured, the column ends may be coupled to the upstream and downstream devices.