Abstract:
A sample vaporization unit that attains enhancing of reproducibility through fixing of the sample vaporization unit. Sample vaporization unit ( 4 ) at its one end is connected to the distal end of glass insert ( 2 ) and at its other end is connected via glass tube ( 5 ) to one end of capillary column ( 6 ). The other end of the capillary column ( 6 ) is led to detector ( 8 ). The sample vaporization unit ( 4 ) is comprised of base frame ( 22 ), flow channel ( 24 ) provided in the base frame ( 22 ), and rugged portion ( 26 ) for sample vaporization provided by microfabrication within the flow channel ( 24 ). Any liquid sample flowing through the flow channel ( 24 ) is vaporized by feeding of energy to the rugged portion ( 26 ), and the vapor is subjected to separation by means of the column ( 6 ) and detection by means of the detector ( 8 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a gas chromatograph in which a liquid sample is vaporized by a sample vaporization unit and is then separated into its components to detect the sample components. 
     BACKGROUND ART 
       FIG. 7  is a schematic view of a conventional gas chromatograph. Reference numeral  2  denotes a glass insert of a sample introduction unit, and the distal end of the glass insert  2  is connected to one end of a capillary column  6 . The other end of the capillary column  6  is connected to a detector  8 . A carrier gas introduction tube  10  is connected to the proximal end portion of the sample introduction unit to supply a carrier gas whose pressure has been regulated. 
     A septum purge flow channel  12  for discharging part of a carrier gas is also provided at the proximal end portion of the sample introduction unit. The proximal end portion of the sample introduction unit is sealed with a septum  14 . A needle extending from a sample injector is allowed to penetrate the septum  14  in such a manner that the distal end of the needle is inserted into the inside of the glass insert  2 , and then a liquid sample is injected into the glass insert  2 . 
     The outer circumferential portion of the glass insert  2  is covered with a heating block  51 , and glass wool  53  held by a graphite ferrule  55  is placed inside the glass insert  2 . A liquid sample is injected from the upper side of the glass insert  2  into the glass insert  2  through a needle. The liquid sample is allowed to flow downward together with a carrier gas, and is then brought into contact with the glass wool  53 . The glass wool  53  is previously heated to about 250° C. by the heating block  51 , and therefore the liquid sample flowing through the glass wool is heated as well as mixed and is then vaporized. The vaporized sample is split into two and introduced into both the capillary column  6  and a split flow channel  11 . The sample flowing through the capillary column  6  is separated into its components, and the sample components are detected by the detector  8 . 
     Non-Patent Document 1: Anal. Chem. 73, 3639-3645 (2001) 
     Non-Patent Document 2: V. Lehmann, The 9th Annual International Workshop on Micro Electro Mechanical Systems, 1-6 (1996) 
     Non-Patent Document 3: Sensors and Actuators 74, 13-17, (1999) 
     Non-Patent Document 4: Silicon Micromachining (by M. Elwenspoek and H. V. Jansen), p. 323-326, 2001 
     Non-Patent Document 5: Henri Jansen et al., J. Micromech. Microeng. 5, 115 (1995) 
     Non-Patent Document 6: “Recent Trends in Microfabrication Studies” vol. 6, p. 14-20, 2000 
     DISCLOSURE OF THE INVENTION 
     Problem(s) to be Solved by the Invention 
     In the case of such a conventional gas chromatograph, the glass wool  55  placed in a vaporization chamber cannot be directly heated. Therefore, there is a case where a sample is not instantly vaporized in the vaporization chamber, thereby affecting the reproducibility of analysis. 
     Further, since the glass wool cannot be washed, it is necessary to exchange it, but there is a case where the size of the glass wool is changed before and after exchanging. In such a case, it is difficult to keep the glass wool at the same position in the glass insert  2  even when the ferrule is used, thereby affecting measurement reproducibility. In addition, the position of the glass wool in the glass insert is changed when the pressure of a carrier gas is changed. This also affects reproducibility of measurements. 
     It is therefore an object of the present invention to provide a gas chromatograph in which a sample vaporization unit is fixed to be capable of improving reproducibility. 
     The present invention is directed to a gas chromatograph including: a sample vaporization unit having a base frame, a flow channel provided in the base frame, and a rugged portion provided by microfabrication in the flow channel to vaporize a sample; an energy supply unit for supplying energy for heating the rugged portion; a column connected to the sample vaporization unit to separate the sample carried by a carrier gas from the sample vaporization unit into its components; and a detector connected to the discharge side of the column to detect the components of the sample discharged from the column. 
     The material of the rugged portion is not particularly limited as long as it can absorb energy. For example, the rugged portion is made of a material selected from the group consisting of silicon, an inorganic silicon compound, metal, carbon, ceramic, and a complex of two or more of them. 
     A preferred example of the rugged portion is one made of porous silicon. The porous silicon can be formed by, for example, anodizing silicon in hydrofluoric acid. 
     Another preferred example of the rugged portion is a pattern formed on the surface of a substrate so as to have a rectangular cross section. Such a pattern having a rectangular cross section can be formed by, for example, deep ion etching of silicon. 
     Yet another preferred example of the rugged portion is one constituted from needle-shaped projections. The needle-shaped projections can be formed by, for example, anisotropic dry etching of silicon. One example of such a rugged portion constituted from needle-shaped projections is black silicon. 
     Yet another preferred example of the rugged portion is one formed by molding. The rugged portion formed by molding may have a rectangular cross section or a circular cross section or may be constituted from needle-shaped projections. Such a rugged portion having a rectangular cross section or a circular cross section or constituted from needle-shaped projections may be formed by injection molding. 
     One example of the energy supply unit is one having an electrode connected to the rugged portion and a power supply device for supplying an electric current to the rugged portion through the electrode. In this case, the electrode for connecting the rugged portion to the power supply device may be formed by sputtering or vapor deposition. 
     Another example of the energy supply unit is an energy source for supplying radiant energy to the rugged portion. An example of the energy source includes an induction heater (IH). In this case, it is possible to irradiate the rugged portion with energy emitted from a position far from the rugged portion. 
     Between the energy source and the rugged portion, a lens for converging energy emitted from the energy source may be provided to efficiently irradiate the rugged portion with the energy. The lens is preferably one capable of converging energy. In a case where the energy is light, a converging lens may be used. 
     The base frame constituting the sample vaporization unit may be formed by bonding together at least two substrates. In this case, the flow channel is formed on at least one of the substrates. 
     Further, in this case, it is preferred that one of the substrates is a silicon substrate and the other substrate is a glass substrate. 
     Effect of the Invention 
     As described above, since the gas chromatograph according to the present invention includes a sample vaporization unit having a base frame, a flow channel provided in the base frame, and a rugged portion provided by microfabrication in the flow channel to vaporize a sample and an energy supply unit for supplying energy for heating the rugged portion, it is not necessary to provide glass wool, a glass insert, and a ferrule for holding the glass wool. This saves users from having to replace glass wool, a glass insert, and a ferrule, thereby making it possible to attain reproducibility of measurements and to reduce the size of the gas chromatograph. 
     When the energy supply unit has a power supply device, an electric current can be applied to porous silicon to increase the temperature of the porous silicon. This makes it possible to instantly vaporize a sample. 
     When the energy supply unit is a heat source for irradiating the rugged portion with radiant heat, the rugged portion can be irradiated with energy emitted from a position far from the rugged portion to increase the temperature of porous silicon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a gas chromatograph according to a first embodiment of the present invention. 
         FIG. 2  is an exploded perspective view of a sample vaporization unit of the gas chromatograph according to the first embodiment of the present invention. 
         FIG. 3  is a schematic perspective view of a gas chromatograph according to a second embodiment of the present invention. 
         FIG. 4(A)  to  FIG. 4(J)  show a flow chart for explaining one example of the process of forming porous silicon in the sample vaporization unit. 
         FIG. 5(A)  to  FIG. 5(G)  show a flowchart for explaining another example of the process of forming porous silicon in the sample vaporization unit. 
         FIG. 6  is a schematic view for explaining a rugged portion formed by machining a stainless steel plate. 
         FIG. 7  is a schematic view of a conventional gas chromatograph. 
     
    
    
     DESCRIPTION OF THE REFERENCE NUMERALS 
       2 . glass insert 
       4 . sample vaporization unit 
       5 . glass tube 
       6 . capillary column 
       7 . oven 
       8 . detector 
       10 .  11 . carrier gas flow channel 
       12 . septum purge flow channel 
       13 . split flow channel 
       14 . septum 
       16 . sample injector 
       18 . needle 
       22 . substrate 
       24 . flow channel 
       26 . rugged portion 
       27 . power supply device 
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinbelow, a first embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a schematic perspective view of a gas chromatograph according to the first embodiment of the present invention. Reference numeral  2  denotes a glass insert of a sample introduction unit, and the distal end of the glass insert  2  is connected to one end of a sample vaporization unit  4 . The other end of the sample vaporization unit  4  is connected to one end of a capillary column  6  through a glass tube  5 , and the other end of the capillary column  6  is connected to a detector  8 . The capillary column  6  is placed in an oven  7  for maintaining the capillary column  6  at a constant temperature. 
     A carrier gas introduction tube  10  is connected to the proximal end portion of the sample introduction unit to supply a carrier gas whose pressure has been regulated by a pressure-regulating system (not shown) to the proximal end portion of the sample introduction unit. 
     A septum purge flow channel  12  for discharging part of a carrier gas is also provided at the proximal end portion of the sample introduction unit. The septum purge flow channel  12  has a certain flow resistance. Further, the septum purge flow channel  12  has a pressure sensor  20  for detecting the pressure at the proximal end portion of the sample introduction unit. The pressure-regulating system of the carrier gas introduction tube  10  receives a detection output from the pressure sensor  20  to regulate the flow rate of a carrier gas. 
     The proximal end portion of the sample introduction unit is sealed with a septum  14 . A liquid sample is injected into the glass insert  2  by allowing a needle  18  of a syringe of a sample injector  16  to penetrate the septum  14  in such a manner that the distal end of the needle  18  is inserted into the inside of the glass insert  2 . The syringe for injecting a sample into the glass insert  2  through the needle  18  is controlled by the sample injector  16  so that a sample can be automatically injected into the glass insert  2 . 
     The sample vaporization unit  4  is, for example, a chip, and has a base frame  22 , a flow channel  24  provided in the base frame  22 , and a rugged portion  26  provided by microfabrication in the flow channel  24  to vaporize a sample. In order to electrically heat the rugged portion  26 , an electrode for connecting the rugged portion  26  to a power supply device  27  is provided. 
     A through hole  28  is provided on the sample introduction unit side of the flow channel  24  and a through hole  29  is provided on the sample discharge side of the flow channel  24 . The through hole  29  is connected to the glass tube  5 , and the glass tube  5  has a carrier gas introduction tube  11  and a split flow channel  13  for discharging part of a carrier gas. 
     The rugged portion  26  is made of at least one material selected from the group consisting of silicon, an inorganic silicon compound, metal, carbon, and ceramic or a complex of two or more of these materials. A method for forming the rugged portion  26 , which varies depending on the type of material used, and the shape of the rugged portion  26  will be described later. 
       FIG. 2  is an exploded perspective view of the sample vaporization unit of the gas chromatograph according to the first embodiment of the present invention. 
     Reference numeral  21  denotes a glass substrate, and  23  denotes a silicon substrate. The flow channel  24  is provided on one surface of the silicon substrate  23 . The through hole  29 , which serves as a sample outlet for discharging a sample from the flow channel  24 , is also provided in the silicon substrate  23 . The through hole  28 , which serves as a sample inlet for introducing a sample into the flow channel  24 , is provided in the glass substrate  21 . 
     The through hole  28  is located at a position corresponding to the rugged portion  26  provided in the flow channel  24 . A gold or platinum electrode formed by, for example, sputtering is provided on the upper surface of the rugged portion  26  and at a position at which the rugged portion  26  is connected to the external power supply device  27 . 
     The substrate  21  and the substrate  23  are bonded together in such a manner that the surface of the substrate  23  having the flow channel  24  is bonded to the substrate  21 . The sample vaporization unit  4  obtained by bonding together the substrates  21  and  23  is interposed between a jig  34  and a jig  36  in such a manner that a gasket  30  is provided between the upper surface of the sample vaporization unit  4  and the jig  34  and a gasket  32  is provided between the lower surface of the sample vaporization unit  4  and the jig  36 . Alternatively, O-rings may be used as the gaskets  30  and  32 . 
     The size of the sample vaporization unit  4  is not particularly limited, but each of the substrates  21  and  23  preferably has a size of about 20 mm×50 mm, and the flow channel  24  preferably has a width of about 2 mm, a depth of about 0.5 mm, and a length of about 30 mm. The rugged portion  26  preferably has a diameter of about 3 mm. 
     Hereinbelow, the operation of the gas chromatograph according to the first embodiment of the present invention will be described with reference to  FIG. 1 . 
     The temperature of the oven  7  is set to 150° C. to maintain the capillary column  6  at a constant temperature. The power supply device  27  applies an electric current to the rugged portion  26  so that the rugged portion  26  is heated to 250° C. 
     A carrier gas whose pressure has been regulated to be constant is supplied to the proximal end portion of the sample introduction unit. In this state, a liquid sample of about 1 μL is injected from the sample injector  16  into the glass insert  2  through the needle  18 . An excess of the carrier gas to be introduced into the glass insert  2  is discharged to the outside through the septum purge flow channel  12 . 
     The liquid sample is instantly vaporized by heat generated by the rugged portion  26 , and is carried by the carrier gas, which flows through the flow channel  24 , to the sample discharge side of the flow channel  24 , and is then split into two at a split ratio of 200:1 and introduced into both the split flow channel  13  and the capillary column  6 . The sample introduced into the column  6 , which is maintained at a constant temperature by the oven  7 , is separated in the column  6  into its components, and the sample components are detected by the detector  8 . 
     In the case of the gas chromatograph according to the first embodiment of the present invention, a liquid sample is injected from the sample injector  16  into the glass insert  2  through the needle  18 . However, sample injection may be carried out by dropping a sample of about 1 μL onto the surface of the rugged portion  26  through a sample injection port with the use of an automatic sampler, an automatic injector, or a microsyringe. 
     Hereinbelow, a second embodiment of the present invention will be described with reference to  FIG. 3 . 
     A gas chromatograph according to the second embodiment of the present invention has the same device configuration as the gas chromatograph shown in  FIG. 1 . More specifically, the distal end of the glass insert  2  is connected to one end of the sample vaporization unit  4 , the other end of the sample vaporization unit  4  is connected to one end of the capillary column  6  through the glass tube  5 , and the other end of the capillary column  6  is led to the detector  8 . The glass tube  5  has the carrier gas introduction tube  11  and the split flow channel  13  for discharging part of a carrier gas. 
     The sample vaporization unit  4  has the base frame  22 , the flow channel  24  provided in the base frame  22 , and the rugged portion  26  provided by microfabrication in the flow channel  24  to vaporize a sample. The through hole  28  is provided on the sample introduction unit side of the flow channel  24  and the through hole  29  is provided on the sample discharge side of the flow channel  24 . 
     In order to heat the rugged portion  26  by external radiant heat, an energy source  31  and a converging lens  30  for converging energy emitted from the energy source  31  are provided near the sample vaporization unit  4 . 
     Hereinbelow, the operation of the gas chromatograph according to the second embodiment of the present invention will be described. 
     A liquid sample is injected from the sample injector  16  into the glass insert  2  through the needle  18 , and is then introduced into the sample vaporization unit  4  together with a carrier gas introduced through the carrier gas introduction tube  10 . The rugged portion  26  provided in the sample vaporization unit  4  is previously heated to 250° C. by radiant heat emitted from the energy source  31 , and therefore the liquid sample is vaporized by heat generated by the rugged portion  26 . 
     The vaporized sample is carried by the carrier gas, which flows through the flow channel  24 , to the sample discharge side of the flow channel  24 , and is then split into two at a split ratio of 200:1 and introduced into both the split flow channel  13  and the capillary column  6 . The sample introduced into the column  6 , which is maintained at a constant temperature (150° C.) by the oven  7 , is separated in the column  6  into its components, and the sample components are detected by the detector  8 . 
     In the case of the gas chromatograph according to the second embodiment of the present invention, laser light such as N 2  laser light can be used as energy emitted from the energy source  31  (see Non-Patent Document 1). Particularly, in a case where the rugged portion  26  is made of silicon, YAG laser light or N 2  laser light is preferably used. 
     Further, in the case of the gas chromatograph according to the second embodiment of the present invention, the rugged portion  26  may be heated by electromagnetic induction. In this case, the rugged portion  26  is made of metal and magnetic lines of force are used as an energy source instead of the energy source  31  and the converging lens  30  for converging energy emitted from the energy source  31 . The rugged portion  26  is preferably made of iron, stainless steel, or an alloy of them. 
     Hereinbelow, a method for forming the sample vaporization unit and the rugged portion thereof will be described. 
     &lt;Method for Forming Rugged Portion  1  (Porous Silicon)&gt; 
       FIG. 4  is a flow chart for explaining the process of forming porous silicon in the sample vaporization unit. 
     (A) The silicon substrate  23  is prepared. 
     (B) The upper surface of the silicon substrate  23  is thermally oxidized to form a silicon oxide film  41  on the surface of the silicon substrate  23 . 
     (C) The silicon oxide film  41  is covered with a mask except for an area corresponding to the flow channel  24 , and an oxide film pattern  41   a  is formed on the silicon substrate  23  by photolithography process and etching. 
     (D) The flow channel  24  is formed on the silicon substrate  23  by ion etching the upper surface of the silicon substrate  23  using the oxide film pattern  41   a  as a mask. 
     (E) A photoresist is applied onto the silicon substrate  23  except for an area where the sample vaporization unit  26  should be formed, and a photoresist pattern  43  having an opening corresponding to the area where the sample vaporization unit should be formed is formed by photolithography process. 
     (F) The silicon substrate  23  is anodized in 20% hydrofluoric acid using the photoresist pattern  43  as a mask to form porous silicon in the area where the sample vaporization unit  26  should be formed (see Non-Patent Document 2). 
     (G) The photoresist pattern  43  is removed from both surfaces of the substrate  23 . 
     (H) The through hole  29  is formed by ultrasound machining at a position corresponding to a sample outlet for discharging a sample from the flow channel  24 . Alternatively, the through hole  29  may be formed by sandblasting. 
     (I) The silicon oxide film is removed using hydrofluoric acid. It is to be noted that the through hole  28  is previously formed by a process method such as sandblasting in the glass substrate  21  at a position corresponding to the rugged portion  26 . 
     (J) Finally, the glass substrate  21  and the silicon substrate  23  are bonded together by anodic bonding in such a manner that the upper surface of the silicon substrate  23  having the flow channel  24  is bonded to the glass substrate  21 . Alternatively, the glass substrate  21  and the silicon substrate  23  having a silicon oxide film formed thereon may be bonded together using hydrofluoric acid. 
     &lt;Method for Forming Rugged Portion  2  (Porous Silicon)&gt; 
       FIG. 5  is another flow chart for explaining the process of forming porous silicon in a chip serving as the sample vaporization unit. It is to be noted that in  FIG. 5 , views on the left side are sectional views and views on the right side are plan views. 
     (A) The silicon substrate  23  is prepared. 
     (B) The upper surface of the silicon substrate  23  is thermally oxidized to form a silicon oxide film  41  on the surface of the silicon substrate  23 . 
     (C) A resist (not shown) is applied onto the silicon oxide film  41  to form a resist pattern by photolithography process using a mask  42  shown in  FIG. 5  (C 2 ). The mask  42  has a pattern for forming the sample vaporization unit in the substrate  23 , and each black dot in the mask  42  represents a portion where a Cr film is present and an area except for the black dots in the mask  42  allows light to pass through it. Further, the silicon oxide film  41  is etched using the resist pattern as a mask to form a silicon oxide film pattern  44  on the silicon substrate  23 . 
     (D) The silicon substrate  23  is etched by deep ion etching using the silicon oxide film pattern  44  as a mask to form the rugged portion  26  (see Non-Patent Document 3). 
     (E) The flow channel  24  is formed on the surface of the silicon substrate  23  having the rugged portion  26  by photolithography process and ion etching. 
     (F) A Ti film and a Pt film are formed on the rugged portion  26  and on the surface of the silicon substrate  23  by sputtering using a mask to provide a 30 nm-thick conductive electrode  45  having the Ti film as a lower layer and the Pt film as an upper layer. 
     (G) The through hole  29  is formed by sandblasting in the silicone substrate  23  on the sample discharge side of the flow channel  24 . The upper surface of the silicon substrate  23  is bonded to the glass substrate  21  having the through hole  28  formed on the sample introduction side of the flow channel  24 . 
     The bonding of the upper surface of the silicone substrate  23  to the glass substrate  21  is carried out using hydrofluoric acid, and therefore a silicon oxide film is formed on the upper surface of the silicon substrate  23  by sputtering before bonding. 
     The step (G) has been described with reference to a case where bonding between the substrates  21  and  23  is carried out using hydrofluoric acid, but bonding between the substrates  21  and  23  may be carried out by anodic bonding. 
     &lt;Method for Forming Rugged Portion  3  (Dry Etching)&gt; 
     The rugged portion  26  may be formed by anisotropic dry etching. For example, needle-shaped projections (black silicon (see Non-Patent Document 5)) can be formed in a silicon substrate by using Black surface methodology (see Non-Patent Document 4). 
     For example, in a case where a RIE (reactive ion etching) machine is used, black silicon is formed by machining a silicon substrate under conditions where the applied power is 50 W, the etching pressure is 2.7 Pa, the flow rate of SF 6  gas is 20 sccm, and the flow rate of O 2  gas is 15 ccm. As described in Non-Patent Document 4 or 5, conditions for forming black silicon vary depending on the type of machine used. 
     &lt;Method for Forming Rugged Portion  4  (Metallic Rugged Portion)&gt; 
     The rugged portion may be formed by metallic powder injection molding. In this case, the rugged portion made of metal is formed by injection-molding a mixture of metallic powder (e.g., stainless steel, ceramic, iron, titanium, titanium alloy, iron-nickel alloy, tungsten alloy, or a mixture of two or more of them) and a plastic binder and degreasing and sintering an injection-molded product (see Non-Patent Document 6). 
     The material of the rugged portion  26  is not limited to silicon as long as it can absorb laser light used. For example, in a case where an N 2  laser is used as a laser source, Si, an inorganic silicon compound, metal, carbon, ceramic, or a complex of two or more of them can be used as the material of the rugged portion  26 , and in a case where a YAG laser is used as a laser source, metal, ceramic, or a complex of two or more of them can be used as the material of the rugged portion  26 . 
     As described above, the sample vaporization unit  4  can be easily formed by bonding together the silicon substrate  23  and the glass substrate  21 , but a substrate made of another material, such as a stainless steel substrate, may be used. 
     For example, in a case where a stainless steel plate is used, a structure serving as the rugged portion (e.g., porous silicon) is installed in the flow channel previously formed in the stainless steel plate. 
       FIG. 6  is a schematic view for explaining a rugged portion formed by machining a stainless steel plate. 
     A stainless steel jig  34  having a through hole  35  and a stainless steel jig  36  having a through hole  37  and the flow channel  24  are bonded together in such a manner that the flow channel  24  is interposed between the jig  34  and the jig  36 . Part of the flow channel  24  is designed as the rugged portion  26 , and the rugged portion  26  is connected to the power supply device  27 . 
     The rugged portion  26 , the flow channel  24 , and the through holes  35  and  37 , which are microstructures, can be formed by electro-discharge machining. The jigs  34  and  36  can be bonded together by any one of welding, pressure bonding, brazing and soldering, and bonding using an adhesive. 
     Alternatively, the rugged portion  26  and the flow channel  24  may be formed by directly machining one stainless steel substrate. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a gas chromatograph in which a liquid sample is vaporized by a sample vaporization unit and then separated into its components to detect the sample components.