Abstract:
A liner for mixing the sample gas and a carrier gas and delivering the gas mixture to the inlet end of a capillary tube of a gas chromatograph for analysis, comprises
   (a) a transparent tube having an inlet and an outlet and a bore with an inside surface, and   (b) at least one glass subcomponent permanently affixed to the liner tube wherein the subcomponent is at least one color.

Description:
FIELD OF THE INVENTION 
     This invention relates to injection ports for capillary gas chromatographs, and more particularly concerns liner units for inlets wherein a liquid sample is vaporized into a sample gas and mixed with a carrier gas, and a portion of the gas mixture is delivered to the inlet end of a capillary tube of a gas chromatograph, and even more particularly concerns marking such liners to identify the type and source of the liners and to provide proper orientation of the liner in the gas chromatography instrument. 
     DESCRIPTION OF THE PRIOR ART 
     Gas chromatography (GC) is a well known analytical technique where gas phase mixtures are separated into their individual components and subsequently identified. The technique may be employed to obtain both qualitative and quantitative information about the components of the mixture [1]. 
     Samples for GC are usually liquid and must be vaporized prior to introduction to the mobile phase gas stream. GC analysis is typically divided into four stages: 
     
         
         
           
             1. sample introduction, where liquid samples are introduced into the inlet, heated, and vaporized, 
             2. sample transfer, where the sample vapor is transferred all or in part onto the analytical column, 
             3. separation, where the sample is separated into its individual components as it passes through the analytical column, and 
             4. detection, where the separated components are identified as they exit the analytical column. 
           
         
       
    
     In conventional GC instrumentation the first two steps are achieved in the sample inlet hardware. Inlet hardware often includes a replaceable liner. Liners are normally operated at elevated temperatures, e.g., over 200° C. This enhances the rate of sample vaporization and reduces adsorption on the inner surface of the liner [1]. Many internal configurations are available for liners, as well as coatings for them [2-12]. 
     In most cases the configuration serves to enhance the degree of sample vaporization from the point of exit from the syringe needle to the column entrance, and provide gas phase sample homogeneity of components within the liquid mixture having different boiling points. A simple configuration for an inlet liner is a straight cylindrical tube of glass having a consistent inner diameter along the longitudinal path. Other configurations include more complex inner paths intended to increase turbulence, affect the comparatively short residence time the liquid sample is in the liner, or interrupt the liquid stream leaving the syringe needle. These internal configurations include tapers or goosenecks, baffles, funnels, inverted cup elements, spiral regions, and other points of flow constriction along the longitudinal path of the liner. 
     Other optional elements of liners include small quantities of packing materials such as glass wool [1] or Carbofrit™ (Trademark of Restek Corporation) packing material, which serve as additional surface area sources for heat transfer into the sample and as a physical filter for any solid/nonvolatile contaminants present in the liquid sample. 
     Liners are manufactured from glass, primarily borosilicate, but also fused quartz, and less commonly from metal, mainly stainless steel [13]. Various chemical coatings are applied to liners in order to reduce the degree of interaction between the sample and the surface of the liner. Sample-surface interactions may result in sample adsorption in the coatings, decomposition of the coatings, and formation of new reaction products; in each case resulting in undesirable peaks (or loss of desirable ones) in detection measurements of the components contained in the sample being analyzed in the separation analysis. In addition to low sample-surface interactions, it is also desirable for the liner coating to be thermally stable in order to minimize background signal contributions originating from the liner coating itself detected by the analytical equipment. For glass substrate liners, common deactivation techniques include chemically treating the exposed silanol groups with organosilane reagents such as hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMCS), and trimethylchlorosilane (TMCS) [13]. Prior to the deactivation process it is common for the liner substrate to undergo an aqueous acid leach process [13] whereby metal and metalloid impurities are removed from the surface. 
     It is often desirable for the liner to be optically transparent. It is particularly important to be able to see through the walls of these liners which contain packing material in order to ensure its proper plug position within the internal bore of the liner. It is also advantageous to be able to observe wool placement, and to be able to check for the presence of debris or other visual contaminants. For the purpose of this disclosure we will reference to liners that are manufactured from glass or other optically transparent materials. 
     Given the large number of GC instrument manufacturers, different instrument models, and considerable variety of liner designs, it is desirable to include markings on the liners that provide information relating to the variables listed above. It is further desirable to provide information relating to proper orientation of the liner in the GC instrument. 
     Information specific to liners is often provided by directly marking the liners with text, symbols, or logos. Methods for marking include silk screening or direct stamp printing on the outer surface of the liners. Marks are made on the surface using paint or ink, as well as mechanical and chemical etching techniques. These techniques, while widely used in the industry are often limited in their long term thermostability as well as their overall ease of visibility given the narrow dimensions of standard liners (e.g., on the order of 2-6 mm O.D.). Further, these techniques require additional steps in the liner manufacture, and may impact the subsequent chemical deactivation process following the mechanical forming of the glass substrate. 
     With the exception of the straight liner, which is essentially a straight glass tube having a uniform I.D and O.D. along the entire length, liners having more complex internal configurations are commonly manufactured by (1) heat fusing subcomponents to the inner surface of the straight tubing, or (2) thermoforming the outer wall of the straight tubing to create complex shapes on the inner wall. In the first case, glass subcomponents whose chemical compositions are compatible to the straight tubing are employed in order to ensure thorough fusing of the parts. In most cases the chemical composition of the subcomponents is essentially the same as the straight tube. 
     In some cases, more than one subcomponent is employed in the same straight tube. In still other cases, more than one subcomponent is employed where the first subcomponent resides inside the second subcomponent in a coaxial configuration. 
     SUMMARY OF THE INVENTION 
     We present an alternative to directly printing or otherwise marking the liner by taking advantage of the multicomponent nature of the liner assembly. We present replacing one or more of the liner subcomponents with dimensionally equivalent subcomponents made from pigment doped glass, the pigment for such glass preferably comprising inorganic pigments. In this fashion the liners whole or in part include a discreet colored region that is highly visible and can be employed to identify one liner from another or identify proper orientation in the GC instrument. 
     The liner unit at least comprises a tube having a bore extending between an inlet and outlet of the tube, but may also comprise an inlet expansion chamber in the bore for changing a liquid sample into a sample gas, a mixing chamber in the bore next to the inlet chamber, and an outlet chamber for delivering the thoroughly mixed sample and carrier gases to an inlet end of a capillary tube of a gas chromatograph. Employing one or more colored glass subassemblies of the liner during its manufacture enables easier identification of the liner type, proper orientation, or identification of the source of the liner. 
     Because of the techniques used in liner manufacture, any pigment employed in the glass subcomponents must be resistant to temperatures greater than the softening point of borosilicate glass (ca. 650° C.), and more preferably greater than the softening point of quartz (ca. 1650° C.). Inorganic ionic pigments such as cobalt (Co +2 ; blue color), nickel (Ni +2 ; green color) and iron (Fe +2 ; yellow to red color) are commonly employed as thermostable pigments in glass substrates [14] and are suitable examples for this application. 
     Employing a color doped subcomponent in the liner assembly provides a striking device to identify the liner without adding any steps beyond those essential to the liner manufacture. Preferably, the pigment concentrations in the glass liner subcomponents are sufficient to provide a noticeable color while maintaining optical transparency of the liner. 
     Employing pigment-doped glass for liner subcomponents allows for close melt compatibility between the doped and non-doped subcomponents. In the final assembly of the liner some of the glass surface of the subcomponent may be exposed to the sample path. Because the liner substrate undergoes an aqueous acid leach process prior to the deactivation process, inorganic pigment ions resident at or close to the surface of the colored glass would be removed and a higher purity silica surface would be presented to the deactivation chemistry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a view in cross-section of a liner found in the prior art. 
         FIG. 1B  is a view in cross-section of another liner found in the prior art. 
         FIG. 1C  is a view in cross-section of another liner found in the prior art. 
         FIG. 1D  is a view in cross-section of another liner found in the prior art. 
         FIG. 2A  is a view in cross-section of a sample inlet liner having a gooseneck taper and a dimple, constructed in accordance with the invention. 
         FIGS. 2B and 2C  are views in cross-section illustrating the fabrication of the gooseneck liner of  FIG. 2A . 
         FIG. 3A-1  is a view in cross-section of a cylindrical gooseneck subassembly of the invention. 
         FIG. 3A-2  is an end view of the cylindrical gooseneck subassembly shown in  FIG. 3A-1 . 
         FIG. 3B-1  is a view in cross-section of an alternative embodiment of a cylindrical gooseneck subassembly of the invention. 
         FIG. 3B-2  is an end view of the cylindrical gooseneck subassembly shown in  FIG. 3B-1 . 
         FIG. 3C-1  is a view in cross-section of another alternative embodiment of a cylindrical gooseneck subassembly of the invention. 
         FIG. 3C-2  is an end view of the cylindrical gooseneck subassembly shown in  FIG. 3C-1 . 
         FIG. 4A  is a view in cross-section of a Cyclosplitter™ liner constructed in accordance with the invention. 
         FIGS. 4B ,  4 C, and  4 D are views in cross-section illustrating the fabrication of the liner of  FIG. 4A . 
         FIG. 5A  is a view in cross-section of an alternative embodiment of a liner constructed in accordance with the invention. 
         FIG. 5B  is an end view of the liner shown in  FIG. 5A . 
         FIG. 5C  is a view in cross-section of another alternative embodiment of a liner constructed in accordance with the invention. 
         FIG. 5D  is a view in cross-section of another alternative embodiment of a liner constructed in accordance with the invention. 
         FIG. 5E  is a view in cross-section of a further alternative embodiment of a liner constructed in accordance with the invention. 
         FIG. 5F  is a view in cross-section of another alternative embodiment of a liner constructed in accordance with the invention. 
         FIG. 5G  is an end view of the liner shown in  FIG. 5F . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows some liner configurations commonly found in the industry. 
     In  FIGS. 1A-1D , sectional views of various sample inlet liner configurations are illustrated as known in the prior art. FIG. lA is an example of a straight through sample inlet liner  10  having a straight tube wall  11 .  FIG. 1B  shows a liner  20  which is an example of the liner  10  incorporating a gooseneck taper  21  where the taper region has a reduced inner diameter and the same outer diameter of the straight liner tube wall  11 . The liner  20  also has a dimple  22  which is a region of the liner  20  having both a reduced inner diameter and outer diameter.  FIG. 1C  shows a liner  30  which is an example of the liner  20  incorporating a matrix  31 , which may be comprised of wool, particles, wire bundles, or other materials know in the art.  FIG. 1D  shows a liner  40  which is an example of a Cyclosplitter.TM. liner [ 5 ] which includes the physical features of liner  20  and also includes a glass spiral core baffle  41  permanently affixed to the inner surface of the liner  40 . 
       FIG. 2A  is a sectional view of an inventive sample inlet liner  200  incorporating a gooseneck taper  202  where the taper region has a reduced inner diameter and the same outer diameter of the straight liner tube wall  201  and a dimple  203  which is a region of the liner  200  having both a reduced inner diameter and outer diameter. In  FIGS. 2B to 2C  the fabrication of the gooseneck liner  202  is illustrated. As shown in  FIG. 2B , a glass subassembly  205  is inserted into the straight tube  204  and permanently heat fused into place. In this particular case the glass subassembly  205  is made of colored glass. With the exception of the glass pigment, the chemical composition of the subassembly  205  is preferably the same material as the liner tube  204 . This improves the physical and chemical compatibility between the two components and ensures successful fusing of the components together. In  FIG. 2C  the dimple  203  is shown to be added after heat fusing the gooseneck taper into place. Common manufacturing practices to create the dimple include thermoforming, whereby the straight tube  204  is heated in a localized region to at least the softening point of the glass and then pinched into place. Often the straight tube  204  is rotated along the longitudinal axis in order to ensure a symmetrical dimple around the radial axis of the tube  204 . In commercial manufacture of liners the order of the steps illustrated here may be changed. 
       FIG. 3A-1  is a detail illustration of a cylindrical gooseneck subassembly  300  having a through channel  302 . The subassembly is made of colored glass, preferably colored borosilicate glass.  FIG. 3A-2  shows an end view of the subassembly  300  of  FIG. 3A-1 . Both ends of the gooseneck are chamfered giving the cross section profile  301 .  FIG. 3B-1  is a detail illustration of a cylindrical gooseneck subassembly  310  having a through channel  312 .  FIG. 3B-2  shows an end view of the subassembly  310  of  FIG. 3B-1  where the subassembly is made of one cylindrical layer of glass  313  surrounded by a second cylindrical layer of glass  311 , assembled in a coaxial configuration where the cumulative shape is equivalent to the single component gooseneck subassembly  300 . In this example either layer  313  or layer  311  or both contain color pigment. In the case where both layer  313  and  311  contain color pigment, they may be the same or different color. At some point during the manufacture of the liner, subassemblies  313  and  311  are fused together.  FIG. 3C-1  is a detail illustration of a cylindrical gooseneck subassembly  320  having a through channel  322 .  FIG. 3C-2  shows an end view of the subassembly  320  where the subassembly is made of one cylindrical layer of glass  324  surrounded by a second cylindrical layer of glass  323 , which is in turn surrounded by another cylindrical layer of glass  321  assembled in a coaxial configuration where the cumulative shape is equivalent to the single component gooseneck subassembly  300 . In this example any of the three layers  324 ,  323  or  321  may contain color pigment. In the case where any of the three layers  324 ,  323  or  321  contain color pigment, they may be the same or different color. At some point during the manufacture of the liner, the three layers  324 ,  323  and  321  are fused together. 
       FIG. 4A  shows a Cyclosplitter™ liner  400 , which is constructed in accordance with the invention, and which incorporates a gooseneck taper  402  where the taper region has a reduced inner diameter and the same outer diameter of the straight liner tube wall  404 , and a dimple  403  which is a region of the liner  400  having both a reduced inner diameter and outer diameter. The Cyclosplitter™ liner  400  also incorporates a glass spiral core baffle  406  permanently affixed to the inner surface of the liner. 
     In  FIGS. 4B to 4D , the fabrication of the Cyclosplitter™ liner  400  is illustrated. In  FIG. 4B , a glass spiral core baffle subassembly  406  is inserted into the straight tube  405  and permanently heat fused into place. In this particular case the core baffle subassembly  406  is made of colored glass. With the exception of the glass pigment, the chemical composition of the subassembly  406  is preferably the same material as the liner tube  405 . This improves the physical and chemical compatibility between the two components and ensures successful fusing of the components together. In  FIG. 4C  the gooseneck taper subassembly  407  is inserted into the straight tube  405  and permanently heat fused into place. In this particular case the glass subassembly  407  is made of colored glass. With the exception of the glass pigment, the chemical composition of the subassembly  407  is preferably the same material as the liner tube  405 . The color of spiral core baffle subassembly  406  may be the same as or different to the gooseneck taper subassembly  407 . In  FIG. 4D  the dimple  403  is applied to liner tube  405  in the same fashion as described previously. In commercial manufacture of liners the order of the steps illustrated here may be changed. 
       FIGS. 5A to 5G  show straight liners having colored regions along the longitudinal path of the straight tube. Liners in  FIGS. 5A to 5G  are made of glass, preferably borosilicate glass. The glass subassemblies are heat fused together. In  FIG. 5A  a straight tube liner  500  having a through hole or pathway  503  includes a clear glass sheath  501  and a colored glass sheath  502  which are assembled in a coaxial fashion.  FIG. 5B  shows an end view of the final assembly of liner  500 . 
     In  FIG. 5C  the liner  510 , having a through hold or pathway  513 , is assembled with the colored glass sheath  511  on the outside of the clear glass sheath  512 . This configuration is preferable when the chemical composition of the colored sheath  511  is sufficiently different from the clear glass  512  as to be potentially less compatible with either the deactivation chemistry or the gas sample. 
     In  FIG. 5D  the straight tube liner  520  having a through hole or pathway  523  includes two separate colored sheaths  522  and  524  inserted coaxially into the straight tube  521  where the total length of the two colored sheaths  522  and  524  matches the length of the straight tube  521 . In this case the colored sheaths  522  and  524  may be the same color or different colors. 
     In  FIG. 5E  the straight tube liner  530  having a through hole or pathway  533  includes a clear sheath  531  and a colored sheath  532  where the length of colored sheath  532  is less than the length of clear sheath  531 . In order to ensure an even inner diameter along the entire length of the liner  530 , the glass tube  531  may be thicker in the region without the colored sheath  532 . 
     In  FIG. 5F  the straight tube liner  540  having a through hole or pathway  543  includes three glass sheaths  541 ,  542 , and  544  which are assembled in a coaxial fashion.  FIG. 5G  shows an end view of the final assembly of liner  540 . Any or all of the glass sheaths  541 ,  542 , and  544  may be colored and more than three sheaths may be included in the liner assembly. As was illustrated in  FIG. 5C , any of the glass sheaths  541 ,  542 , and  544  may be composed of more than one shorter glass sheath assembled end to end where the total length of the sheaths matches the length of the straight tube. 
     The glass sheaths in each of  FIGS. 5A to 5G  are fused together, preferably by heat fusing. 
     Pigment may be added to any or all of the glass components (e.g., glass subassemblies  205 ,  300 , and  407 , glass layers  311 ,  313 ,  321 ,  323 , and  324 , glass spiral core baffles  406 , and glass sheaths  502 ,  511 ,  522 ,  524 ,  531 ,  541 ,  542 , and  544 ) of the inventive liners, as desired, using conventional methods known to those of ordinary skill in the art, such as by mixing pigment into the glass melt from which the glass components are formed. 
     The references referred to in this specification and listed below are hereby incorporated herein by reference. 
     REFERENCES 
     
         
         1. Konrad Grob in “Split and Splitless Injection for Quantitative Gas Chromatography, 4 th  Ed., Wiley-VCH, 2001. 
         2.  Anal. Chem.  2002, 74, 10-16 “The Two Options for Sample Evaporation in Hot GC Injectors: Thermospray and Band Formation. Optimization of Conditions and Injector Design” Koni Grob and Maurus Biedermann. 
         3. U.S. Pat. No. 5,954,862 “Sample Inlet Liner” William H. Wilson. 
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         10. U.S. Pat. No. 5,997,615 “Large-Sample Accessory for a Gas Chromatograph” Huan V. Luong, Hsing Kuang Lin, Howard Fruwirth, George S. Mueller. 
         11. U.S. Pat. No. 6,203,597 “Method and Apparatus for Mass Injection of Sample” Ryoichi Sasano, Kazuhiko Yamazaki, Masahiro Furuno. 
         12. U.S. Pat. No. 6,494,939 “Zero-Dilution Split Injector Liner Gas Chromatography” Andrew Tipler. 
         13. “A Guide To Gas Chromatography”, W. Rodel and G. Wolm, Huthig Verlag, GmbH, Heidelberg, Germany. 
         14. “Coloured Glasses” by W. A. Weyl, 1959, Society of Glass Technology, Sheffield.