Patent Publication Number: US-2012043211-A1

Title: Capillary electrophoresis apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a capillary electrophoresis apparatus, which separates and analyzes a sample such as nucleic acid and protein by electrophoresis. 
     BACKGROUND ART 
     In the capillary electrophoresis apparatus, a high voltage is applied to a capillary for performing the electrophoresis. Recently, the voltage to be applied becomes higher in order to speed up the electrophoresis. When a conductive component having potential difference is present near a cathode end of the capillary, there is possibility of occurrence of electric discharge. 
     Then, the conventional capillary electrophoresis apparatus is designed so as not to arrange the conductive component near the cathode end of the capillary in order to avoid the electric discharge. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent Application Laid-Open No. 2000-346828 
       
    
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     Recently, it is desired to further miniaturize the capillary electrophoresis apparatus. When the apparatus is miniaturized, the cathode end of the capillary and the conductive component are inevitably arranged so as to be close to each other. Therefore, the possibility of the occurrence of the electric discharge increases. 
     The inventor of the present application focuses on the fact that the possibility of the occurrence of the electric discharge depends on a spatial distance and a creeping distance between an exposed portion of an electrode attached to the cathode end of the capillary and the conductive component. Then, the inventor of the present application considers that it is possible to prevent the electric discharge when the spatial distance and the creeping distance are large even when the conductive component is arranged near the cathode end of the capillary. 
     An object of the present invention is to provide the capillary electrophoresis apparatus capable of avoiding the electric discharge even when the conductive component having the potential difference is arranged near the cathode end of the capillary. 
     Means to Solve the Problem 
     The present invention relates to a capillary electrophoresis apparatus, including: one or a plurality of capillaries; a load header including a capillary electrode through which the capillary penetrates; a power source, which applies a voltage to the capillary electrode; a constant temperature reservoir, which maintains an ambient temperature of the capillary constant; an optical system, which irradiates a sample separated by electrophoresis in the capillary with excitation light to detect fluorescence from the sample; a solution storage unit including a container in which the sample or electrolytic solution is contained and an anti-evaporation film to cover the container; and an auto sampler, which conveys the solution storage unit. 
     For example, the capillary electrode, which protrudes from a lower surface of the load header, penetrates through a space between the load header and the anti-evaporation film and further penetrates through a capillary hole formed on the anti-evaporation film to extend into the container. At least a portion exposed to the space between the load header and the anti-evaporation film of the capillary electrode is covered with an insulating member. Even when the conductive component is arranged near the cathode end of the capillary, the spatial distance and the creeping distance from the electrode attached to the cathode end of the capillary to the conductive component are large. 
     Effects of the Invention 
     The present invention is capable of avoiding the electric discharge even when the conductive component is arranged near the cathode end of the capillary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of an outline of an example of a capillary electrophoresis apparatus. 
         FIG. 2A  is a view of a capillary, a load header, and a solution storage unit in the example of the capillary electrophoresis apparatus. 
         FIG. 2B  is a view of a state in which the capillary, the load header, and the solution storage unit are assembled in the example of the capillary electrophoresis apparatus. 
         FIG. 3A  is a cross-sectional view of the capillary, the load header, and the solution storage unit in the capillary electrophoresis apparatus. 
         FIG. 3B  is an enlarged cross-sectional view of a part of the load header and the solution storage unit in the capillary electrophoresis apparatus. 
         FIG. 4A  is a cross-sectional view of a first example of an electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
         FIG. 4B  is an enlarged cross-sectional view of a part of the first example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
         FIG. 5A  is a view of an example of an anti-evaporation film in the capillary electrophoresis apparatus. 
         FIG. 5B  is a perspective view of the example of the anti-evaporation film in the capillary electrophoresis apparatus. 
         FIG. 6A  is a view of an example of the anti-evaporation film in the capillary electrophoresis apparatus. 
         FIG. 6B  is a perspective view of the example of the anti-evaporation film in the capillary electrophoresis apparatus. 
         FIG. 7A  is a cross-sectional view of a second example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
         FIG. 7B  is an enlarged cross-sectional view of a part of the second example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
         FIG. 8A  is a cross-sectional view of a third example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
         FIG. 8B  is an enlarged cross-sectional view of a part of the third example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
         FIG. 9A  is a cross-sectional view of a fourth example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
         FIG. 9B  is an enlarged cross-sectional view of a part of the fourth example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERAL 
     
         
           101  . . . capillary 
           102  . . . capillary array 
           103  . . . pump mechanism 
           104  . . . optical system 
           105  . . . high-voltage power source 
           106  . . . constant temperature reservoir 
           107  . . . auto sampler 
           108  . . . syringe 
           109  . . . block 
           110  . . . check valve 
           111  . . . polymer container 
           112  . . . anode buffer container 
           113  . . . anode electrode 
           114  . . . cathode electrode 
           115  . . . load header 
           116  . . . reference base 
           117  . . . capillary head 
           118  . . . capillary cathode end 
           119  . . . cooling fan 
           120  . . . capillary electrode 
           200  . . . anti-evaporation film 
           201  . . . main body 
           202  . . . capillary hole 
           203  . . . lower-side projection 
           204  . . . sealing unit 
           205 ,  207  . . . projection 
           210  . . . solution storage unit (solution tray) 
           301  . . . conductive material around capillary 
           401  . . . concave portion 
           402  . . . cover portion 
           403  . . . concave portion 
           404  . . . cover member 
           405  . . . welding or bonding 
           406  . . . coating 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
       FIG. 1  illustrates an outline of one example of a capillary electrophoresis apparatus. The capillary electrophoresis apparatus of this example has a capillary array  102  including one or a plurality of capillaries  101 , a pump mechanism  103  for injecting a polymer into the capillary  101 , an optical system  104  for irradiating a sample in the capillary  101  with light to detect fluorescence of the sample, a high-voltage power source  105  for applying a high voltage to the capillary  101 , a constant temperature reservoir  106  for maintaining a temperature of the capillary  101  constant, and an auto sampler  107  for conveying a container in which the sample, solution and the like are contained. 
     The capillary  101  is a replaceable member, which is replaced when a method of measurement is changed or when the capillary  101  is broken or deteriorated in quality. The capillary  101  is composed of a glass tube, of which inner diameter is from tens of microns to hundreds of microns and of which outer diameter is hundreds of microns, and a surface thereof is coated with polyimide. The capillary  101  is filled with a separation medium for giving difference in electrophoretic velocity at the time of electrophoresis. Although there are both of a liquid separation medium and a nonliquid separation medium as the separation medium, a liquid polymer is used in this embodiment. 
     A capillary head  117  is provided on one end of the capillary  101  and a capillary cathode end  118  is formed on the other end thereof. The capillary head  117  is obtained by binding the ends of the capillaries  101  and has a function to connect the pump mechanism  103  and the capillary  101  to each other. The capillary cathode end  118  is brought into contact with the sample, the solution and the like. The capillary  101  is fixed by a load header  115  on a side of the capillary cathode end. A cathode electrode  114  and a metallic hollow capillary electrode  120  are attached to the load header  115 . There is an electrical connection between the cathode electrode  114  and the capillary electrode  120 . The capillary cathode end  118  penetrates through the capillary electrode  120  to protrude from a tip thereof. 
     The optical system  104  is composed of an irradiation system and a detection system. The optical system  104  has a function to irradiate a part of the capillary  101  of which polyimide coating is removed, that is to say, a detection part with excitation light. The detection system has a function to detect the fluorescence from the sample in the detection part of the capillary  101 . The sample is analyzed by light detected by the detection system. 
     The pump mechanism  103  has a syringe  108 , a block  109 , a check valve  110 , a polymer container  111 , and an anode buffer container  112 . The capillary head  117  is connected to the block  109 , and according to this, the capillary  101  and a flow path in the block  109  are connected to each other. The capillary  101  is filled or refilled with the polymer in the polymer container  111  through the flow path in the block  109  by operation of the syringe  108 . The capillary  101  is refilled with the polymer for each measurement in order to improve performance of the measurement. 
     An anode electrode  113  is arranged in the anode buffer container  112 . The high-voltage power source  105  applies the high voltage between the anode electrode  113  and the cathode electrode  114 . 
     The constant temperature reservoir  106  of this example is a sandwich type by a rubber heater. That is to say, the capillary array  102  is hold in a planar manner between temperature controlling plates to which a heat insulating material and a heater are attached to maintain a temperature of the capillary to be constant. A temperature sensor for feedback is attached to the temperature controlling plate. Meanwhile, an air constant temperature reservoir may be used in place of the constant temperature reservoir  106  of this example. Also, it is possible to fix the capillary array  102  to a desired position of the optical system  104  by a reference base  116  provided on the capillary array  102 . Also, it is possible to arrange the capillary cathode end  118  and the capillary electrode  120  on a desired position by fixing the load header  115  of the capillary array to the constant temperature reservoir. 
     The auto sampler  107  is provided with three electric motors and a linear guide for moving a moving stage and is capable of moving the moving state in triaxial directions, that is to say, a vertical direction, a horizontal direction, and a depth direction. The moving stage may convey a buffer container, a cleaning container, a waste solution container, and a sample plate to the capillary cathode end  118  as needed. 
     The capillary electrophoresis apparatus is provided with a cooling fan  119 . A heating element such as the high-voltage power source  105  is provided in the apparatus. Then, the cooling fan  119  may generate circulation of air in the apparatus, thereby inhibiting local increase in temperature. 
     An example of a solution storage unit used by the capillary electrophoresis apparatus is described with reference to  FIGS. 2A and 2B . As illustrated in  FIG. 2A , the solution storage unit of this example has a container (solution tray)  210  and an anti-evaporation film  200 . The capillary electrode  120  being a tube-shaped member is attached to the load header  115 . The capillary  101  penetrates through the capillary electrode  120  and a tip end of the capillary, that is to say, the capillary cathode end  118  is exposed from a lower end of the capillary electrode  120 . In this manner, it is possible to apply the voltage to the polymer in the capillary  101  through the capillary electrode  120 . 
     The anti-evaporation film  200  has a main body  201 , a capillary hole  202 , and a lower-side projection  203 . A sealing unit  204  integrally formed with the main body  201  is provided in an opening of the capillary hole  202 . The sealing unit  204  is composed of a thin film of which center is cut in a cross-shape. The capillary electrode  120  penetrates through the capillary hole  202 . The sealing unit  204  adheres around the capillary electrode  120 , and according to this, evaporation of the solution stored in the container  210  from a gap between the capillary electrode  120  and the capillary hole  202  is prevented. 
     The load header  115  is composed of a resin material with a high electric insulation property and the container  210  and the anti-evaporation film  200  also are composed of the resin material with the high electric insulation property. 
       FIG. 2B  illustrates a state in which the capillary  101 , the load header  115 , the container  210 , and the anti-evaporation film  200  are assembled. The anti-evaporation film  200  is attached on the container  210 . The capillary  101  is inserted into the capillary hole  202  of the anti-evaporation film  200 . When conveying the solution storage unit by the auto sampler  107 , relative misalignment in a perpendicular direction may occur between the load header  115  and the anti-evaporation film  200 . Then, in this example, a clearance is generated between the load header  115  and the anti-evaporation film  200  as illustrated. Therefore, even when the relative misalignment occurs between the load header  115  and the anti-evaporation film  200 , it is possible to absorb the same by the clearance therebetween. When the clearance is not generated between the load header  115  and the anti-evaporation film  200 , if the relative misalignment in the perpendicular direction occurs between the load header  115  and the anti-evaporation film  200 , the container  210  and the auto sampler  107  are subjected to an excessive load. This does not occur in this example. 
     An electric discharge phenomenon in the capillary electrophoresis apparatus is described with reference to  FIGS. 3A and 3B . Suppose that there is a conductive material  301  around an assembly of the load header  115  and the solution storage unit as illustrated in  FIG. 3A . The conductive material  301  may be a shielding component for shielding an electromagnetic wave or a metallic frame of the constant temperature reservoir  106 . Suppose that, in a space between the capillary electrode  120  and the conductive material  301 , there is no obstacle between them. The electric discharge occurring in the space between the capillary electrode  120  and the conductive material  301  depends on a spatial distance and a creeping distance therebetween. 
     The spatial distance and the creeping distance are described with reference to  FIG. 3B . The spatial distance indicated by a solid arrow is the shortest distance between an exposed portion of the capillary electrode  120  and the conductive material  301  in the space. On the other hand, the creeping distance indicated by a broken arrow is the shortest distance along a surface of an insulator between the exposed portion of the capillary electrode  120  and the conductive material  301  in the space. However, the spatial distance and the creeping distance are measured along the same route in the space in which the insulator is not present. In order to avoid occurrence of the electric discharge between the capillary electrode  120  and the conductive material  301 , the spatial distance and the creeping distance should be larger than a predetermined value. That is to say, even when the conductive material  301  is arranged near the exposed portion of the capillary electrode  120 , the occurrence of the electric discharge may be avoided if the spatial distance and the creeping distance are larger than a predetermined threshold. The predetermined threshold differs for each applied voltage and further differs for each environment in which the capillary electrophoresis apparatus is installed. Therefore, the predetermined threshold may be obtained only by individual actual measurement. In the capillary electrophoresis apparatus, the voltage to be applied to the capillary electrode  120  is several kV in preliminary electrophoresis and tens of kV in main electrophoresis, for example. Therefore, the voltage may be actually applied to allow the electric discharge to occur. 
     A first example of an electric discharge preventing mechanism in the capillary electrophoresis apparatus is described with reference to  FIGS. 4A and 4B . Suppose that there is the conductive material  301  around the assembly of the load header  115  and the solution storage unit as illustrated in  FIG. 4A . Suppose that, in the space between the capillary electrode  120  and the conductive material  301 , there is no obstacle between them. 
     As illustrated in  FIG. 4B , the load header  115  of this example has a plurality of concave portions  401  on a lower surface thereof and a projection-shaped cover portion  402  is formed in the concave portion  401 . The capillary electrode  120  penetrates through a hole of the cover portion  402 . On the other hand, the capillary hole  202  through which the capillary electrode  120  penetrates is provided on the anti-evaporation film  200 . A cylindrical projection  205  is provided on an upper end of the capillary hole  202 . An outer diameter of the cylindrical projection  205  of the anti-evaporation film  200  is smaller than an inner diameter of the concave portion  401  of the load header  115 . At least a part of the cylindrical projection  205  is arranged in the concave portion  401  of the load header  115 . 
     The solid arrow indicates the route along which the spatial distance between the exposed portion of the capillary electrode  120  and the conductive material  301  is measured and the broken arrow indicates the route along which the creeping distance between the exposed portion of the capillary electrode  120  and the conductive material  301  is measured. First, the spatial distance is described. The capillary electrode  120  protrudes from a lower end of the cover portion  402  of the load header  115 . Therefore, a position A on an upper end of the exposed portion of the capillary electrode  120  is the closest to the conductive material  301 . Then, a linear distance measured along the route from the position A on the upper end of the exposed portion of the capillary electrode  120  through an inner edge B and an outer edge C of the cylindrical projection  205  of the anti-evaporation film  200 , an edge D of the concave portion  401  of the load header  115 , and the lower surface of the load header  115  is the spatial distance. The spatial distance in the capillary electrophoresis apparatus of this example is sufficiently longer than the spatial distance in the capillary electrophoresis apparatus illustrated in  FIG. 3B . 
     Next, the creeping distance is described. The linear distance measured along the route from the position A on the upper end of the exposed portion of the capillary electrode  120  through an edge E on an inner side of a bottom of the concave portion  401  of the load header  115 , an edge F on an outer side of the bottom of the concave portion  401 , the edge D of the concave portion  401  of the load header  115 , and the lower surface of the load header  115  is the creeping distance. The creeping distance in the capillary electrophoresis apparatus of this example is sufficiently longer than the creeping distance in the capillary electrophoresis apparatus illustrated in  FIG. 3B . 
     In this manner, the spatial distance and the creeping distance in the capillary electrophoresis apparatus of this example are longer than the spatial distance and the creeping distance in the capillary electrophoresis apparatus illustrated in  FIG. 3B , so that the electric discharge between the exposed portion of the capillary electrode  120  and the conductive material  301  does not easily occur. Therefore, in the capillary electrophoresis apparatus of this example, a position of the assembly of the load header and the solution storage unit may be set so as to be closer to the conductive material  301 . Therefore, miniaturization of the capillary electrophoresis apparatus may be realized. 
       FIGS. 5A and 5B  illustrate a first example of the anti-evaporation film. The anti-evaporation film  200  of this example has a plate-shaped main body  201 , the capillary holes  202 , the lower-side projection  203 , and the cylindrical projection  205 . Each of the capillary holes  202  is enclosed by one cylindrical projection  205 . Therefore, the number of the cylindrical projections  205  is the same as that of the capillary holes  202 . 
     Although the anti-evaporation film of this example is used in the first example of the electric discharge preventing mechanism illustrated in  FIGS. 4A and 4B  and a third example of the electric discharge preventing mechanism illustrated in  FIGS. 8A and 8B , this may also be used in a second example of the electric discharge preventing mechanism illustrated in  FIGS. 7A and 7B . Further, the anti-evaporation film of this example may also be used in a fourth example of the electric discharge preventing mechanism illustrated in  FIGS. 9A and 9B . 
       FIGS. 6A and 6B  illustrate still another example of the anti-evaporation film. The anti-evaporation film  200  of this example has the plate-shaped main body  201 , the capillary hole  202 , the lower-side projection  203 , and a cylindrical projection  207 . The sealing unit  204  integrally formed with the main body  201  is provided in the opening of the capillary hole  202 . The sealing unit  204  is composed of the thin film of which center is cut in the cross-shape. The projection  207  may be integrally formed with the main body  201 . All the capillary holes  202  are enclosed by one cylindrical projection  207 . Therefore, one cylindrical projection  207  is provided in this example. 
     Although the anti-evaporation film of this example is used in the second example of the electric discharge preventing mechanism illustrated in  FIGS. 7A and 7B , this may also be used in the first example of the electric discharge preventing mechanism illustrated in  FIGS. 4A and 4B  and the third example of the electric discharge preventing mechanism illustrated in  FIGS. 8A and 8B . Further, the anti-evaporation film of this example may also be used in the fourth example of the electric discharge preventing mechanism illustrated in  FIGS. 9A and 9B . 
     The second example of the electric discharge preventing mechanism in the capillary electrophoresis apparatus of this example is described with reference to  FIGS. 7A and 7B . As illustrated in  FIG. 7A , the load header  115  of this example has one concave portion  403  on the lower surface thereof and a plurality of projection-shaped cover portions  402  are formed in the concave portion  403 . The capillary electrode  120  penetrates through the hole of the cover portion  402 . On the other hand, a plurality of capillary holes  202  through each of which the capillary electrode  120  penetrates are provided on the anti-evaporation film  200 . One cylindrical projection  207  formed so as to enclose all the capillary holes  202  is provided on the upper surface of the anti-evaporation film  200 . At least a part of the cylindrical projection  207  of the anti-evaporation film  200  is arranged within the concave portion  403  of the load header  115 . 
     An example of dimensions of the spatial distance and the creeping distance is described with reference to  FIG. 7B . A thickness of the lower end of the projection-shaped cover portion  402  of the load header  115  is set to 0.1 mm, the dimension of a tapered portion of the cover portion  402 , that is to say, the distance from a lower end A to an upper end B of the tapered portion is set to 3 mm, the distance from the upper end B of the tapered portion to an edge C of the capillary hole  202  of the anti-evaporation film  200  is set to 4.1 mm, the distance from the edge C of the capillary hole  202  of the anti-evaporation film  200  to an inner edge D of the cylindrical projection  207  is set to 12.2 mm, the thickness of the cylindrical projection  207 , that is to say, the distance from the inner edge D to an outer edge E is set to 1 mm, and the distance from the outer edge E of the cylindrical projection  207  to an edge F of the concave portion  403  of the load header  115  is set to 6.8 mm. The spatial distance is 0.1+3+4.1+12.2+1+6.8=27.2 mm. 
     The distance from the upper end B of the tapered portion of the projection-shaped cover portion  402  of the load header  115  to a bottom of the concave portion  403  of the load header  115  is set to 16 mm, the dimension of the bottom of the concave portion  403  of the load header  115  is set to 8 mm, and a depth of the concave portion  403  of the load header  115  is set to 7 mm. The creeping distance is 0.1+3+16+8+7=34.1 mm. The distance from an inner wall of the concave portion  403  of the load header  115  to the capillary electrode  120  is set to 8.7 mm. In the capillary electrophoresis apparatus of this example, the spatial distance increases by 27.2−8.7=18.5 mm and the creeping distance increases by 34.1−8.7=25.4 mm as compared to the capillary electrophoresis apparatus in  FIG. 3B . 
     The third example of the electric discharge preventing mechanism is described with reference to  FIGS. 8A and 8B . The load header  115  of this example has a plurality of concave portions  401  on the lower surface thereof. A cover member  404  made of an insulating material is attached to each of the concave portions  401 . The cover member  404  is formed as a member different from the load header  115  to be fixed to the concave portion  401  of the load header  115  by welding or bonding  405 . 
     The capillary electrode  120  protrudes from a bottom surface of the concave portion  401  to penetrate through the hole of the cover member  404 . The cover member  404  of this example corresponds to the projection-shaped cover portion  402  in the first example of the electric discharge preventing mechanism in  FIG. 4B . In this manner, the spatial distance and the creeping distance are large in this example as in the example of the electric discharge preventing mechanism in  FIG. 4B . 
     Meanwhile, although the concave portion  401  is formed for each capillary electrode  120  in the load header  115  of this example as illustrated in  FIG. 8A , it is also possible to form one concave portion  403  on the load header  115  and provide one cylindrical projection  207  on the anti-evaporation film  200  so as to enclose all the capillary electrodes  120  as in the example illustrated in  FIG. 7A . 
     The fourth example of the electric discharge preventing mechanism is described with reference to  FIGS. 9A and 9B . The capillary electrophoresis apparatus of this example differs from the example in  FIGS. 3A and 3B  in that a coating  406  of the insulating material is attached to the capillary electrode  120 . That is to say, the coating  406  of the insulating material is formed on a portion of the capillary electrode  120  protruding from the lower surface of the load header  115 . The insulating material may be polyimide, for example. In this manner, the spatial distance and the creeping distance are large in this example as in the example in  FIG. 4B . 
     Although the anti-evaporation film illustrated in  FIG. 3A  may be used as the anti-evaporation film  200 , it is also possible to use the anti-evaporation film illustrated in  FIGS. 4A and 4B ,  FIGS. 5A and 5B , and  FIGS. 6A and 6B . 
     Although the examples of the present invention are described above, the present invention is not limited to the above-described examples and one skilled in the art will comprehend that various modifications may be made within the scope of the invention recited in claims.