Abstract:
An electrode assembly for capillary electrophoresis (CE) comprises a manifold ( 310 ), a connector ( 305 ) a sheath ( 300 ), and a seal ( 325 ). A capillary tube ( 100 ) passes through the manifold, the connector, the sheath, and the seal, stopping just beyond the end of the sheath. The sheath is fillable with water ( 330 ) or another fluid that cools the capillary tube in the vicinity of the electrode, thereby preventing degradation of a sample due to heat. The sheath may be metal or plastic with a metal sleeve electrode on its exterior. The sheath is sufficiently strong to penetrate a rubber or other pierceable cap on a vial. The manifold and connector incorporate an air path ( 605, 312, 307 ) so that when the electrode is fully inserted into a vial, the contents ( 650 ) of the vial are at atmospheric pressure (or another applied pressure or vacuum).

Description:
BACKGROUND 
     Prior Art—Electrophoresis—FIGS.  1 - 4   
     Electrophoresis is a powerful and well-known method that is used in many fields of science to separate molecules having different sizes and different intrinsic electrical charges in order to analyze and synthesize chemical compounds. It is used in DNA sequencing, in the separation of mixtures of proteins, and the like. Two principal methods for performing electrophoretic separations are in routine use today, the planar gel matrix and capillary electrophoresis. These will now be discussed. 
     Planar Gel Matrix: 
     In this method a planar gel matrix (flat body of a gel), such as agarose (a complex carbohydrate polysaccharide obtained from agar), is provided and electrodes are located at opposite edges of the gel. A mixture of ionized, i.e., charged, molecules of a substance to be analyzed is applied or positioned in the gel near a first electrode at one edge of the gel, and an DC electrical potential is applied to the electrodes. Because of their intrinsic electrical charge the electrical potential across the gel urges the ionized molecules to move away from the first electrode and toward the second. The motion of the charged molecules is impeded by the structure of the molecules within the gel. The speed at which the charged molecules move depends upon their size, i.e., smaller molecules having a particular electrical charge move faster through the gel than larger ones with the same charge. Thus the difference in speeds results in separation of the previously mixed molecules. In most cases the various molecular species are not normally visible to the human eye. Prior to separation they are combined with dye molecules or tagged with radioactive atoms in well-known fashion, thus rendering them visible, either by direct visual inspection or through the exposure of the separation to a photographic film. This separation is analyzed to quantify the size and numbers of molecules contained in the original mixture. 
     Capillary Electrophoresis: 
     The second method, capillary electrophoresis (CE), is used by analytical chemists to separate, in a substance, ionic species from mixtures of chemical compounds. Instead of the planar-gel arrangement described above, CE employs a narrow tube (capillary) through which the molecules move. The different molecules in the substance separate while moving due to the fact that different molecules have different movement speeds within the capillary. 
     The present patent relates to the second method, CE.  FIGS. 1 and 2  are schematic drawings of a prior-art apparatus for performing a CE separation using an “on-capillary” detection. “On-capillary” means the point at which the separation is detected is in a section of the tube or capillary that is used in the actual separation, i.e., there is no separate detection cell. The apparatus comprises a capillary tube  100 , a source of DC electrical potential  105 , an anode  110 , and a cathode  115 . Cathode  115  and anode  110  are respectively connected to source  105  by electrical conductors  135  and  130 . A light source  120  and a detector  125  arranged so shine light through tube  100 . Tube  100  is filled with a matrix substance such as a buffer solution  140 , i.e., one that resists changes in pH when small quantities of a base or acid are added to it. The ends of capillary tube  100  are inserted into solutions contained in vials or other containers  116 ,  117 , and  118 . Capillary tube  100  is typically made of glass or quartz and has a narrow bore (internal diameter) ranging between 50 and 100 microns (2 to 4 mils), an outer diameter of 200-360 microns (8 to 14 mils), and length of 20 to 50 cm (8 to 20 in.), although other sizes are used. 
       FIG. 1  shows the apparatus being loaded with a sample mixture  145  of an ionic species, such as biological molecules, having an intrinsic electrical charge. In this case, the intrinsic electrical charge of the molecules is positive so that they will move away from anode  110  toward cathode  115  as they are separated. If the intrinsic molecular charge is known to be negative, the electrical source polarity would be reversed, or the sample can be introduced at the cathode. The right-hand end of capillary  100  and cathode  115  are immersed in a buffer solution  140  in vial  118 . 
     To load sample  145 , electrical source  105  and light source  120  are de-energized. Vial  116  containing a solution of sample  145  to be separated is positioned so that anode  110  and the left-hand end of capillary  100  are immersed in sample solution  145 . A small amount of the sample is urged into capillary  100 , using either hydrostatic pressure or a brief application of electrical potential from source  105 , in well-known fashion. After introduction of the sample, vial  116  is removed and replaced with vial  117  ( FIG. 2 ) so that, prior to separation, the sample forms a band in a uniform matrix. 
       FIG. 2  shows the prior-art apparatus of  FIG. 1  in use. Electrical source  105  and light source  120  are energized. Detector  125 , such as a photodiode or photomultiplier tube, is connected to a computer  200  or other data recorder. An DC electric field is established between anode  110  and cathode  115  within matrix  140  in capillary tube  100 . This field urges the molecular components comprising sample  145  ( FIG. 1 ) to move toward the cathode. As explained, the smaller molecules move faster within matrix  140  and are thus separated from the slower-moving larger molecules. Light source  120  and detector  125  are located near cathode  115  since separation of the molecular species will be greatest at that location. Light source  120  emits a predetermined wavelength or band or bands of wavelengths of light of known intensity. Light from source  120  is arranged to shine through matrix  140  in capillary tube  100  and then onto detector  125 . When illuminated, the molecules in sample  145  either absorb or absorb and re-emit light that is captured by detector  125 . The intensities of the incident light from source  120  and the light reaching detector  125  are compared and recorded in computer  200  for later analysis. Sample concentration is calculated using a well-known formula, the Beer-Lambert law, explained, e.g., at http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law, q.v. 
     Electrodes  110  and  115  are shown schematically in  FIGS. 1 and 2 . I have found that prior-art electrode designs did not perform optimally since contamination of the sample and overheating at the electrodes occurred. 
     The following is a list of some possibly relevant prior art that shows prior art CE electrodes. Following this list I provide a discussion of these references. 
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 U. S. patents 
               
             
          
           
               
                 patent or  
                 Kind  
                 Issue or  
                 Patentee or  
               
               
                 Pub. Nr. 
                 Code 
                 Pub. Date 
                 Applicant 
               
               
                   
               
               
                 5,037,523 
                 B1 
                 Aug. 6, 1991 
                 Weinberger et al. 
               
               
                 5,364,521 
                 B1 
                 Nov. 15, 1994 
                 Zimmermann 
               
               
                 7,662,269 
                 B2 
                 Feb. 16, 2010 
                 Maeshima et al. 
               
               
                   
               
             
          
         
       
     
     NON-PATENT LITERATURE 
     
         
         Musheev et al., Analytical Chemistry, Vol. 82, 2010, pp 8692-95 
       
    
     Weinberger shows a temperature controlled, air-cooled cartridge for CE. The ends of a capillary tube each pass through the center of an electrode that has an inside diameter slightly larger than that of the outside diameter of the capillary. They extend a short distance beyond the ends of their respective electrodes before entering a manifold. Although Weinberger discusses applying pressure and vacuum for the purposes of filling and flushing the capillary tube, he does not show details of how the electrode tube is sealed in order to accomplish this. 
     Zimmermann shows a CE apparatus comprising a pair of housings, each with a sealing and electrode arrangement, and a removable cassette that contains a capillary tube. The ends of the capillary tube extend outside the cassette at predetermined locations. Each housing contains a funnel, a silicone rubber seal with a central bore beneath the funnel, and a tubular electrode beneath the seal. The axes of the funnel, the bore of the seal, and the electrode are aligned so that a capillary tube can be inserted through all three parts, with the end of the capillary tube extending beyond the end of the electrode. The funnel is movable over a short distance within the housing. When a cassette is inserted into the CE apparatus the capillary tube is passed through the funnel and out beyond the end of the electrode a predetermined distance where it can be inserted into various solutions as desired. In use, the lower end of the cassette is urged against the upper end of the funnel pressing the lower end of the funnel downward against the seal, thereby compressing it. When the seal is compressed, it prevents passage of fluid or gas (either from pressure or vacuum) through the housing. Samples and solutions can then be urged into or out of the capillary by applying differential pressure or vacuum to the two ends of the capillary tube. There is a slight gap between the outside of the capillary tube and the inside of the electrode tube. This is necessary to permit slidable insertion of the capillary tube into the electrode tube. In this case, unwanted materials such as previously analyzed samples can lodge in the space between the capillary and electrode tubings and cause cross-contamination of samples. 
     Maeshima shows a simple arrangement for holding the ends of a capillary tube. In a first embodiment, the end of at least one capillary is secured in an insulating member adjacent a wire electrode. Capillary tubing is very fragile and easily damaged when unintended force is applied. This embodiment exposes the ends of the very fragile capillary to damage and, although inexpensive and simple, is vulnerable to breakage. In a second embodiment, the end of at least one capillary is passed through an electrode tube and the electrode tube is secured to the insulating member. As in Zimmerman, there is a slight gap between the outside of the capillary tube and the inside of the electrode tube. This is necessary to permit slidable insertion of the capillary tube into the electrode tube. In this case, unwanted materials such as previously analyzed samples can lodge in the space between the capillary and electrode tubings and cause cross-contamination of samples. 
     Musheev et al. discuss Joule heating as it affects CE. The migration of species within a CE capillary tube is caused by an electrical potential that is applied between the ends of the capillary. A current flows because of the applied potential. The power associated with the applied potential and resultant current results in Joule (i.e. electrical) heating of the CE capillary tube. Excess heating is known to adversely affect the quality of separation and detection in CE analyses. Although they take Joule heating into account elsewhere along the capillary tube, none of the above patent references minimize Joule heating in the vicinity of the CE electrodes. 
     Many liquid samples for CE analysis are stored in sealed vials that have a septum at the top. Rather than remove a cap or lid from the vial to reach the sample, a piercing means is urged through the septum and into the sample. 
     I have found that Joule heating in the vicinity of the electrodes, cross-contamination, and piercing septum are three significant issues in electrode design. None of the prior-art references addressed all three issues. Maeshima&#39;s first embodiment is good for heat dissipation but cannot pierce a septum. Weinberger&#39;s and Zimmermann&#39;s designs can pierce a septum but have poor heat dissipation and are subject to cross-contamination. Thus the above-described references are each useful for their intended purposes but each has one or more disadvantages as noted. 
     SUMMARY 
     I have discovered a new design that overcomes some limitations of the prior art. In one aspect, my design comprises a capillary tube, a sheath that is rigidly joined to a connector, and a seal between the inner wall of the sheath and the outer wall of the capillary. My design is strong enough to penetrate the septum of a sample vial, reduces or eliminates cross-contamination of samples, and provides for cooling the capillary tube in the vicinity of the electrode. 
    
    
     
       DRAWING FIGURES 
         FIGS. 1 and 2  show a prior-art CE system. 
         FIGS. 3 and 4  show aspects of a first embodiment. 
         FIG. 5  shows one aspect of an alternative embodiment. 
         FIGS. 6 and 7  show the embodiment of  FIGS. 3 and 4  in use. 
         FIG. 8  shows the embodiment of  FIG. 5  in use. 
         FIGS. 9 through 11  show aspects of a third embodiment. 
         FIGS. 12 and 13  show alternative aspects of the embodiment of  FIGS. 3 and 4 . 
     
    
    
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 DRAWING REFERENCE NUMERALS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  100 
                 Capillary tube 
                  105 
                 Electrical source 
               
               
                  110 
                 Anode 
                  115 
                 Cathode 
               
               
                  116 
                 Container 
                  117 
                 Container 
               
               
                  118 
                 Container 
                  120 
                 Light source 
               
               
                  125 
                 Detector 
                  130 
                 Conductor 
               
               
                  135 
                 Conductor 
                  140 
                 Matrix 
               
               
                  145 
                 Sample 
                  200 
                 Computer 
               
               
                  300 
                 Sheath 
                  305 
                 Connector 
               
               
                  306 
                 Bore 
                  307 
                 Bore 
               
               
                  310 
                 Manifold 
                  311 
                 Bore 
               
               
                  312 
                 Bore 
                  320 
                 Piercing point 
               
               
                  325 
                 Seal 
                  326 
                 Lumen 
               
               
                  330 
                 Liquid 
                  400 
                 Sleeve 
               
               
                  600 
                 Housing 
                  605 
                 Bore 
               
               
                  610 
                 Bore 
                  615 
                 Bore 
               
               
                  620 
                 Seal 
                  625 
                 Lumen 
               
               
                  630 
                 Plate 
                  635 
                 Hole 
               
               
                  640 
                 Fastener 
                  645 
                 Electric contact bar 
               
               
                  650 
                 Vial 
                  655 
                 Cap 
               
               
                  660 
                 Solution 
                  900 
                 Seat fitting 
               
               
                  905 
                 Bore 
                  910 
                 Bore 
               
               
                  915 
                 Spring 
                  920 
                 Conductor 
               
               
                  925 
                 Seal 
                  930 
                 Opening 
               
               
                  931 
                 Opening 
                  935 
                 Plate 
               
               
                  940 
                 Opening 
                  945 
                 Cartridge housing 
               
               
                  950 
                 Aperture 
                  955 
                 Seal 
               
               
                  960 
                 Nut 
                  965 
                 Bore 
               
               
                 1200 
                 Connector 
                 1205 
                 Bore 
               
               
                 1210 
                 Bore 
                 1300 
                 Connector 
               
               
                 1305 
                 Shoulder 
                 1310 
                 Fingers 
               
               
                   
               
             
          
         
       
     
     DESCRIPTION 
     First Embodiment—FIGS.  3  Through  5   
       FIGS. 3 through 5  show sectional side views of two aspects of a first embodiment. 
     In the prior-art apparatus of  FIGS. 1 and 2 , the end of capillary tube  100  is merely positioned below the surface of the contents of containers  116 ,  117 , and  118 . In many cases, such containers are sealed at the top by a thin membrane, usually rubber, as described below. The membrane must be pierced so that capillary tube  100  can be inserted into these contents. Capillary tube  100  doesn&#39;t have sufficient strength to pierce a membrane by itself and a strengthening element is required. When the prior-art apparatus is in use, Joule heating at the electrodes can cause decomposition of the sample being separated. 
     First Aspect. 
       FIGS. 3 and 4  show a first aspect of a first embodiment of a capillary electrophoresis electrode. Instead of an isolated metal wire electrodes  110  and  115  in  FIGS. 1 and 2 , a tubular electrode is designed to provide both thermal and mechanical protection for the end of capillary tube  100 . 
     In this aspect, a tubular metal sheath  300  ( FIG. 3 ) is rigidly joined to an electrically conductive connector  305 . The joint between sheath  300  and connector  305  is formed by a friction fit, swaging, gluing, welding, or threading. Connector  305  is secured in a manifold  310  by threading, although a friction fit or swaging, gluing, or welding can be used. The lower end of sheath  300  is beveled to form a piercing point  320  that is used to pierce a rubber membrane, as described below. The angle formed by piercing point  320  with respect to the axis of sheath  300  can be selected from 0 to nearly 90 degrees as shown in  FIG. 3 . The angle is determined by the thickness and hardness of the membrane to be pierced, the expected ease of piercing, and the strength and stiffness of sheath  300  so that sheath  300  is not bent as it enters the membrane. In some cases, there will be no requirement for piercing a membrane so piercing point  320  can have any angular shape. 
     Connector  305  has a central axial bore  306  and a radial bore  307 . Manifold  310  has a central axial bore  311  that is contiguous with bore  306  of connector  305 , and also a radial bore  312 . Bores  306 ,  307 ,  311 , and  312  form an air path for a purpose described below. 
       FIG. 3  shows a capillary tube  100  in position above manifold  310  in preparation for installation into sheath  300 . The lower end of sheath  300  contains an inner elastomeric seal  325 . Seal  325  has an inner lumen  326  with diameter slightly less than the outer diameter of capillary tube  100 . Seal  325  is a pliable elastomer such as silicone rubber, although other materials can be used. 
       FIG. 4  shows capillary tube  100  fully installed into sheath  300 . Capillary tube  100  is inserted into sheath  300  by passing it through bore  311  of manifold  310 , bore  306  of connector  305 , and lumen  326  of seal  325 . Capillary  100  extends a short distance, on the order of 0.5 to 1.0 mm, beyond the lower end of sheath  300 . 
       FIGS. 3 and 4  show a liquid  330  contained within sheath  300 . In a first option, capillary tube  100  is installed and then water  330  is added to sheath  300  via bores  311  and  306  or bore  307  and fills sheath  300  to a point about 1 mm below bore  307 . Alternatively, sheath  300  can be immersed in a vial of liquid to a depth about 1 mm below bore  307  and liquid  330  flows into sheath  300  via lumen  326  of seal  325 . Capillary tube  100  is then installed, sealing the liquid within sheath  300 . Liquid  330  cools capillary  100  within sheath  300 . Liquid  330  is water, although other fluids, such as ethylene glycol, or a mixture of water and ethylene glycol can be used. 
     Second Aspect. 
       FIG. 5  shows a second aspect of the first embodiment. A tubular plastic sheath  300 ′ is used instead of metal sheath  300  ( FIG. 3 ). Sheath  300 ′ is secured and sealed within a metal sleeve  400  that in turn is rigidly joined to a metal connector  305 ′. Both are secured by a friction fit, swaging, gluing, threading, or welding. As in the first aspect, a capillary  100  extends downward through an electrically conductive connector  305 ′ and sheath  300 ′, exiting and extending a predetermined distance below the bottom of sheath  300 ′. As it exits sheath  300 ′, capillary  100  passes through a lumen  326  in a rubber seal  325  that blocks the passage of liquids and gasses past the bottom of capillary  100 . As before, the bottom of sheath  300 ′ optionally includes a beveled region  320 ′ which may or may not have the same angle with respect to sheath  300 ′ as piercing point  320  has to sheath  300  ( FIG. 3 ). 
     Sheaths  300  and  300 ′ are typically 20-30 mm long, with inner diameter of 0.8-1.0 mm and outer diameter of 1.2-1.6 mm. Sheath  300  is made of stainless steel, aluminum, platinum, or a metal alloy. Sheath  300 ′ is made of polypropylene, PEEK (PolyEtherEtherKetone), or any other suitable plastic that does not bend or break when used and which is chemically inert with respect to the CE being performed. Seal  325  is about 3 mm long. Piercing points  320  and  320 ′ are typically angled at 30 degrees with respect to the axis of sheaths  300  and  300 ′. Other dimensions can be used. 
     OPERATION 
     First Embodiment—FIGS.  6  to  8   
       FIG. 6  shows an exploded cross-sectional view of one aspect of the present embodiment in preparation for use. Capillary  100  is installed in sheath  300  which in turn is installed in connector  305  and connector  305  is installed in manifold  310 . Manifold  310  is installed in a housing  600 . Housing  600  is normally rigidly mounted in a CE apparatus (not shown). Housing  600  is electrically insulative in this aspect, although it can be electrically conductive provided it is mounted safely in order to prevent electrical shocks and shorts. 
     Housing  600  includes a first bore  605  that communicates with bore  312  in manifold  310 , allowing the passage of air, and a second bore  610  that communicates with bore  311  in manifold  310 , allowing the passage of capillary  100 . Housing  600  also includes a third bore  615  contiguous with second bore  610 . An elastomeric seal  620  is installed in bore  615 . Seal  620  has a central lumen  625  through which capillary  100  is passed as capillary  100  is prepared for installation in the overall CE apparatus (not shown). A pressure plate  630  is installed above seal  620 . Plate  630  has a central hole  635 , slightly larger in diameter than capillary tube  100 , for the passage of capillary tube  100  into the remainder of the CE apparatus. A pair of fasteners  640  are used to secure plate  630  to housing  600 . When fasteners  640  are tightened, plate  630  compresses seal  615  around capillary tube  100 , securing it in place in housing  600 . 
     An electric contact bar  645  passes through a wall of housing  600  and makes firm mechanical and electrical contact with manifold  310 . Thus electric contact bar  645  is electrically connected to electrode  300  via manifold  310  and connector  305 . Electric contact bar  645  is connected to a CE power source during the CE process. It is made of a suitable metal such as copper, stainless steel, aluminum, or an alloy and is of sufficient diameter to pass the current required for CE with negligible voltage drop along its length. 
     A vial  650  containing either a sample or buffer solution  660  is shown at the bottom of  FIG. 6 . Vial  650  is sealed with a well-known puncturable membrane cap  655 . When the CE apparatus is in use, vial  650  is urged upward, as indicated by the vertical arrow. The pointed bottom  320  of sheath  300  pierces cap  655  and in inserted into vial  650  until the top of cap  655  rests firmly against the bottom of manifold  310 . 
       FIG. 7  shows the apparatus of  FIG. 6  ready for use. The full length of electrode  300  is within vial  650  and piercing point  320  is immersed in the fluid contained in vial  650 . In addition, the lower end of connector  305  has also punctured cap  655  so that bore  307  lies entirely beneath cap  655 . The bottom circumference of connector  305  is beveled to further facilitate the penetration of connector  305  through cap  655 . Fasteners  640  are tightened, urging plate  630  against the top of housing  600  and compressing seal  625  against capillary tube  100  and sealing against air leakage via the top of housing  600 . 
       FIG. 8  shows the assembly of  FIG. 5  installed and ready for use. In this case, fluid  660  in vial  650  must be in contact with metal sleeve electrode  400 . The depth of sleeve  400  in fluid  660  depends on the requirements for a specific CE application. 
     During CE analysis, bore  605  is connected to a pressurized air (or other gas) source (not shown). Air is urged into vial  650  through bores  605 ,  312 ,  306  and  307  and the local increase in pressure urges fluid  660  to enter capillary tube  100  in order to load a quantity of sample or buffer solution into capillary tube  100  for separation. The details of loading capillary tube  100  are discussed above. Electric current passes from a power supply (not shown) through contact bar  645 , manifold  310 , connector  305 , sleeve  400 , and solution  660  to enter matrix  140  ( FIG. 1 ). IT then passes through matrix  140  to the distal end of capillary tube  100 , another electrode at the distal end of capillary tube  100 , and finally returns to the power supply. 
     In both aspects of the present embodiment, water  330  (or other fluid) within sheath  300  has sufficient heat capacity to absorb heat and cool capillary tube  100  during a CE separation. In addition, water  330  has sufficient thermal conductivity to conduct heat from capillary tube  100  to sheath  300  and then on to fluid  660  in order to provide additional cooling. Therefore, my new electrode alleviates Joule heating in the vicinity of the CE electrodes. 
     DESCRIPTION AND OPERATION 
     Alternative Aspects—FIGS.  9  to  13   
     Prior art CE apparatuses frequently provide a CE capillary tube and various associated fittings in cartridge form so that an operator can easily change capillary tubes.  FIGS. 9 through 11  show the above embodiments incorporated into a cartridge format. 
       FIG. 9  is an exploded view of the present aspect showing an easily assembled and disassembled cartridge unit. An electrode assembly according to the first aspect described above is used as an example here, but the second aspect described above can also be used interchangeably. 
     The first structure is a seat fitting  900  which is fixed on instrument frame (not shown) and contains a first bore  905 . A second bore  910  provides an air conduit between bores  905  and outside source. An electrically conductive spring  915  extends upward from seat fitting  900 . An electrical conductor  920  is connected to spring  915  and is sealed where it passes through seat fitting  900 . Conductor  920  is connected to the CE power supply (not shown) during use. 
     Above seat fitting  900  is a removable elastomeric seal  925 . An opening  930  at left side of seal  925  is positioned above spring  915  and has diameter sufficient to allow spring  915  to freely pass therethrough. An opening  931  in middle of seal  925  has diameter sufficient to allow connector  305  and air to pass therethrough. 
     An electrically conductive plate  935  is shown above seal  925 . Plate  935  has a threaded aperture  940  with threads that match those on connector  305 . During assembly, connector  305  is threadably secured into plate  935 . 
     A cartridge housing  945  is shown above plate  935 . In preparation for use, plate  935  is affixed to housing  945  using fasteners, glue, etc. in order to simplify assembly of the various components shown in  FIGS. 9-11 . Seal  925  may also be fixed temporarily to housing  945  to facilitate assembly. 
       FIG. 10  is a bottom view of seal  925  and plate  935  showing their relative positions and sizes. 
     Housing  945  also includes a threaded aperture  950 . An elastomeric seal  955  is positioned above aperture  950  and sized to easily fit into aperture  950 . A threaded nut  960  is positioned above housing  945 . A central bore  965  in nut  960  is sized to pass a capillary  100  in preparation for use. 
     Sheath  300  with internal seal  325  is secured to connector  305  that has bore  306 , but bore  307  is omitted, as shown. Air can move up through bores  905 ,  931  and  306  to reach the content of sheath  300  and move down through bore  905  to vial  650 . Since the first aspect described above is used in this example, sheath  300  is electrically conductive and is secured and electrically connected to connector  305 . 
       FIG. 11  shows a cross-sectional view of the apparatus of  FIG. 9  assembled and ready for use. Capillary  100  has been inserted as described above. Nut  960  has been threadably secured within aperture  950  of cartridge housing  945 , compressing seal  955  around capillary  100 , thereby providing a pressure seal and mechanical clamping action to hold capillary  100  in place. Seat fitting  900  is fixed on a CE apparatus (not shown) by a clamp, screws, or other means (not shown). By urging cartridge housing  945  from the top and vial  650  from the bottom against the apparatus, an air-tight chamber is formed. At same time, spring  915  has passed through opening  930  in seal  925  and is in secure electrical contact with plate  935 . 
       FIG. 12  shows a cross-sectional view of another alternative aspect of the apparatus of  FIG. 7 . Capillary  100  is secured within a metal sheath  300 ′, as described above in connection with  FIG. 7 . Connector  305  is replaced by a modified connector  1200  which has a wider bore  1205  that allows sheath  300 ′ to pass through it. Sheath  300 ′ is secured within a hole  1202  at the bottom of connector  1200  by friction, swaging, gluing, threading, soldering, welding, or the like. Connector  1200  is secured within manifold  310  by one or more of the same means, i.e. friction, etc. Connector  1200  includes two bores: an axial bore  1205  and a radial bore  1210 . Air flow from the entrance of bore  605  to the inside of vial  650  is now communicated through bores  1205  and  1210 . This aspect of the embodiment provides a longer cooling bath than that described above. 
       FIG. 13  shows a perspective view of an alternative connector for creating an air passage and holding sheath  300 ′. Connector  1300  is an electrically conductive holder for a sheath  300 ′ into which a capillary  100  is inserted, as described above. Connector  1300  has a central bore that is larger in diameter than sheath  300 ′. Sheath  300 ′ is inserted into connector  1300  from either end and is secured by a pair of fingers  1310  by gluing, threading, soldering, welding, or the like. Sheath  300 ′ projects a predetermined distance below connector  1300 . Connector  1300  further includes a shoulder  1305 . In use, connector  1300  is secured within manifold  310 , by threading or other means described above. Air from bore  605  in manifold  310  ( FIG. 12 ) passes into connector  1300  at its top end and exits below shoulder  1305 , as shown by the lower arrow in  FIG. 13 . Connector  1300  has larger opening and straight passage for airflow than connector  305  and  1200 . 
     Compared to the previous designs, the cartridge embodiment ( FIGS. 9-11 ) makes changing capillary tubes easier and provides a longer cooling section for the capillary tube. Both alternative connectors  1200  ( FIG. 12) and 1300  have longer cooling section. 
     CONCLUSIONS, RAMIFICATIONS, AND SCOPE 
     I have provided an improved electrode assembly for use in CE. In the past, Joule heating concentrated at the electrode and could degrade samples locally and cause errors in CE analyses. I have alleviated this Joule heating by placing a thermally conductive water bath around the end of the capillary tube that is near or inside the electrode. Therefore CE analyses performed using my electrode assembly do not present as much uncertainty as with heating at that point. In addition, my electrode also reduces cross-contamination by the electrode while it has sufficient mechanical strength to pierce a septum. 
     While the above description contains many specificities, these should not be construed as limitations on the scope, but as exemplifications of some present embodiments. Many other ramifications and variations are possible within the teachings herein. For example, metal electrode  300  in  FIG. 3  can be divided into two sections: a beveled tip section and a simple tubing section. These two sections can be manufactured separately and then welded or otherwise bonded together. Similarly, sleeve  400  in  FIG. 5  can be long and the plastic tubing  300 ′ can be very short, making it a metal electrode with plastic beveled tip. In some cases, the beveled tip can be eliminated. Sleeve  400  and connector  305 ′ in  FIG. 5  can be machined as one piece. Sleeve  400  can be replaced by a metal coating or plating. Bore  307  on connector  305  can be eliminated and water can be filled up to bore  312 , while air pressure or vacuum will be applied through an additional channel or from the other end of the capillary. A plastic sheet or cap can be attached to the lower surface of manifold  310  in order to improve chemical resistance. 
     Thus the scope should be determined by the appended claims and their legal equivalents, rather than the examples and particulars given.