Abstract:
A mass spectrometry device that can perform highly robust, highly sensitive, and low-noise analysis and addresses the problems of preventing reductions in ion transfer efficiency and of suppressing the introduction of noise components from droplets, etc. An ion source generates ions, a vacuum chamber is evacuated by an evacuation means and for analyzing the mass of ions, and an ion introduction electrode introduces ions into the vacuum chamber. The ion introduction electrode has an ion-source-side front-stage pore, a vacuum-chamber-side rear-stage pore, and an intermediate pressure chamber between the front-stage pore and the rear-stage pore, the cross-sectional area of an ion inlet of the intermediate pressure chamber is larger than the cross-sectional area of the front-stage pore, the position of the central axis of the front-stage pore and the position of the central axis of the rear-stage pore are eccentric, and the cross-sectional area of an ion outlet of the intermediate pressure chamber is smaller than the cross-sectional area of the ion inlet.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a mass spectrometry device that is highly robust and can perform highly sensitive and low-noise analyses. 
       BACKGROUND ART 
       [0002]    Ordinary atmospheric pressure ionization mass spectrometry devices are configured to introduce ions generated under atmospheric pressure into vacuum and analyze the mass of the ions. 
         [0003]    Ion sources for generating ions under atmospheric pressure are available in a variety of types, including electrospray ionization (ESI) type, atmospheric pressure chemical ionization (APCI) type, matrix-assisted laser desorption-ionization (MALDI) type, and the like. In any type, a substance that makes a noise component is produced in addition to desired ions. For example, ESI ion sources are configured to ionize a sample by applying high voltage while pouring a sample solution into a small-diameter metal capillary. For this reason, noise components, such as charged droplets and neutral droplets, are also produced at the same time as ions. 
         [0004]    An ordinary mass spectrometry device is composed of several spaces partitioned by a pore and each space is evacuated by a vacuum pump. The spaces are increased in degree of vacuum (reduced in pressure) as it goes rearward. A first space separated from atmospheric pressure by a first pore electrode (AP 1 ) is often evacuated by a rotary pump or the like and kept at a degree of vacuum of several hundreds of Pa or so. A second space partitioned from the first space by a second pore electrode (AP 2 ) is provided with an ion transport unit (quadrupole electrode, electrostatic lens electrode, or the like) that converges and transmits ions. The second space is often evacuated to several Pa or so by a turbo molecular pump or the like. A third space partitioned from the second space by a third pore electrode (AP 3 ) is provided with: an ion analysis unit (ion trap, quadrupole filter electrode, collision cell, time-of-flight mass spectrometer (TOF), or the like) for ion separation and dissociation; and a detection unit for detecting ions. The third space is often evacuated to 0.1 Pa or below by a turbo molecular pump or the like. There are also mass spectrometry devices with more than three partitioned spaces but devices including three spaces or so are in common use. 
         [0005]    Generated ions and the like (including noise components) pass through AP 1  and are introduced into a vacuum vessel. The ions thereafter pass through AP 2  and are converged on the central axis at the ion transport unit. The ions thereafter pass through AP 3  and are separated by mass or decomposed at the ion analysis unit. Thus, the structure of the ions can be analyzed in more detail. The ions are finally detected at the detection unit. 
         [0006]    In most typical mass spectrometers, AP 1 , AP 2 , and AP 3  are often coaxially disposed. The above-mentioned droplets other than ions are less susceptible to the electric field of the pore electrode, ion transport unit, and ion analysis unit and basically tend to travel in a straight line. For this reason, if droplets traveling in a straight line are excessively introduced, the droplets can arrive at a detector and this leads to a shortened life of the detector. 
         [0007]    To address this problem, in the technology described in Patent Literature 1, a member having multiple holes is placed between an ion source and AP 1 . This member does not have a hole positioned coaxially with AP 1  and the introduction of noise components from AP 1  can be reduced. However, the member having the multiple holes is disposed outside AP 1 , and the front face and back face of the member are both placed at atmospheric pressure. 
         [0008]    To remove droplets traveling in a straight line, the central axis of AP 1  and the central axis of AP 2  are made orthogonal to each other in the technology described in Patent Literature 2; and the central axis of AP 1  and the central axis of AP 2  are eccentrically disposed in the technology described in Patent Literature 3. However, in the equipment configurations in Patent Literature 2 and Patent Literature 3, a right-angled space between AP 1  and AP 2  is evacuated in a direction orthogonal to the central axis of AP 2  by a vacuum exhaust pump such as a rotary pump. FIG. 1 in Patent Literature 4 illustrates an equipment configuration in which the central axis of AP 1  is cranked. 
       CITATION LIST 
     Patent Literature 
       [0009]    PTL 1: U.S. Pat. No. 5,986,259 
         [0010]    PTL 2: U.S. Pat. No. 5,756,994 
         [0011]    PTL 3: U.S. Pat. No. 6,700,119 
         [0012]    PTL 4: Japanese Patent Application Laid-Open No. 2010-157499 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0013]    In the equipment configuration described in Patent Literature 1, the upstream side of AP 1  is under atmospheric pressure and a pressure difference between an inlet and an outlet of AP 1  is increased. For this reason, a flow is brought into a sound velocity state in proximity to an outlet of AP 1  and this can produce a Mach disk. Since a flow is disturbed by a Mach disk in proximity to an outlet of AP 1 , the efficiency of ion introduction to AP 2  is degraded. 
         [0014]    In the equipment configuration in Patent Literature 2 or Patent Literature 3, a right-angled space between AP 1  and AP 2  is evacuated in a direction orthogonal to the central axis of AP 2  by a vacuum exhaust pump such as a rotary pump. For this reason, even ions are exhausted together with noise components such as droplets and this causes an ion loss and incurs degradation in sensitivity. 
         [0015]    In the equipment configuration in Patent Literature 4, the central axes of AP 1  and AP 2  are in eccentric positional relation because of a cranked flow path but the flow path is substantially constant in inside diameter from an inlet toward an outlet of AP 1 . For this reason, a flow is made laminar and the flow is more intensified by pipe friction as it is brought closer to the center of the pipe. As a result, there is a possibility that a noise factor such as droplets flows out of an outlet of AP 1  as well together with the flow. As in Patent Literature 1, there is a large pressure difference between an inlet and an outlet of AP 1 ; therefore, a flow is brought into a sound velocity state in proximity to an outlet of AP 1  and this can cause a Mach disk. For this reason, a flow is disturbed in proximity to an outlet of AP 1  by a Mach disk and the efficiency of ion introduction to AP 2  is degraded. 
       Solution to Problem 
       [0016]    To address the above problems, a mass spectrometry device of the present invention is provided with: an ion source that generates ions; a vacuum chamber that is evacuated by an evacuation means and is for analyzing the mass of ions; and an ion introduction electrode that introduces ions into the vacuum chamber. The present invention is characterized in that: the ion introduction electrode has an ion source-side front-stage pore, a vacuum chamber-side rear-stage pore, and an intermediate pressure chamber located between the front-stage pore and the rear-stage pore; the cross-sectional area of an ion inlet of the intermediate pressure chamber is larger than the cross-sectional area of the front-stage pore; the central axis of the front-stage pore and the central axis of the rear-stage pore are eccentrically positioned; and the cross-sectional area of an ion outlet of the intermediate pressure chamber is smaller than the cross-sectional area of an ion inlet thereof. 
         [0017]    The present invention is further characterized in that the angle formed between the wall surface of the intermediate pressure chamber and the direction of the central axis of the front-stage pore is acute. In particular, it is desirable that the angle formed between the wall surface of the intermediate pressure chamber and the direction of the central axis of the front-stage pore should be 15° to 75°. 
         [0018]    Further, it is desirable that the pressure in the intermediate pressure chamber should be 2000 to 30000 Pa. When P o  is taken for the primary-side pressure of the front-stage pore and P M  is taken for the secondary-side pressure thereof, it is desirable that P M /P o ≦0.5. 
       Advantageous Effects of Invention 
       [0019]    The present invention enables implementing a mass spectrometry device of high robustness and sensitivity and low noise. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is an equipment configuration drawing of a first example. 
           [0021]      FIG. 2(A)  is an explanatory drawing of an ion introduction electrode in the first example as viewed from the direction of an ion source. 
           [0022]      FIG. 2(B)  is an explanatory drawing of a section of an ion introduction electrode in the first example taken along the central axis thereof. 
           [0023]      FIG. 3(A)  is an explanatory drawing of an ion introduction electrode used for performance comparison with an ion introduction electrode in the first example as viewed from the direction of an ion source. 
           [0024]      FIG. 3(B)  is an explanatory drawing of a section of an ion introduction electrode used for performance comparison with an ion introduction electrode in the first example taken along the central axis thereof. 
           [0025]      FIG. 4(A)  is an explanatory drawing of an ion introduction electrode used for performance comparison with an ion introduction electrode in the first example as viewed from the direction of an ion source. 
           [0026]      FIG. 4(B)  is an explanatory drawing of an ion introduction electrode used for performance comparison with an ion introduction electrode in the first example taken along the central axis thereof. 
           [0027]      FIG. 5  is an explanatory drawing indicating results with respect to droplet noise intensity and ion intensity depending on the angle of ion incidence to an intermediate pressure chamber in the first example. 
           [0028]      FIG. 6  is an explanatory drawing indicating results with respect to ion intensity depending on the pressure in an intermediate pressure chamber in the first example. 
           [0029]      FIG. 7  is an explanatory drawing illustrating an effect of an intermediate pressure chamber in the first example. 
           [0030]      FIG. 8  is an explanatory drawing indicating a result of performance comparison depending on the inside diameter and length of a rear-stage first pore in the first example. 
           [0031]      FIG. 9  is an explanatory drawing indicating a result of a fluid simulation with an ion introduction electrode used for performance comparison with an ion introduction electrode in the first example. 
           [0032]      FIG. 10  is an explanatory drawing illustrating relation between the inside diameter and the length of a rear-stage first pore in the first example. 
           [0033]      FIG. 11(A)  is an explanatory drawing of an ion introduction electrode in a second example as viewed from the direction of an ion source. 
           [0034]      FIG. 11(B)  is an explanatory drawing of a section of an ion introduction electrode in the second example taken along the central axis thereof. 
           [0035]      FIG. 12(A)  is an explanatory drawing of an ion introduction electrode in a third example as viewed from the direction of an ion source. 
           [0036]      FIG. 12(B)  is an explanatory drawing of a section of an ion introduction electrode in the third example taken along the central axis thereof. 
           [0037]      FIG. 13(A)  is an explanatory drawing of an ion introduction electrode in a fourth example as viewed from the direction of an ion source. 
           [0038]      FIG. 13(B)  is an explanatory drawing of a section of an ion introduction electrode in the fourth example taken along the central axis thereof. 
           [0039]      FIG. 14(A)  is an explanatory drawing of an ion introduction electrode in a fifth example as viewed from the direction of an ion source. 
           [0040]      FIG. 14(B)  is an explanatory drawing of a section of an ion introduction electrode in the fifth example taken along the central axis thereof. 
           [0041]      FIG. 15(A)  is an explanatory drawing of an ion introduction electrode in a sixth example as viewed from the direction of an ion source. 
           [0042]      FIG. 15(B)  is an explanatory drawing of a section of an ion introduction electrode in the sixth example taken along the central axis thereof. 
           [0043]      FIG. 16(A)  is an explanatory drawing of an ion introduction electrode in a seventh example as viewed from the direction of an ion source. 
           [0044]      FIG. 16(B)  is an explanatory drawing of a section of an ion introduction electrode in the seventh example taken along the central axis thereof. 
           [0045]      FIG. 17(A)  is an explanatory drawing of an ion introduction electrode in an eighth example as viewed from the direction of an ion source. 
           [0046]      FIG. 17(B)  is an explanatory drawing of a section of an ion introduction electrode in the eighth example taken along the central axis thereof. 
           [0047]      FIG. 18(A)  is an explanatory drawing of an ion introduction electrode in a ninth example as viewed from the direction of an ion source. 
           [0048]      FIG. 18(B)  is an explanatory drawing of a section of an ion introduction electrode in the ninth example taken along the central axis thereof. 
           [0049]      FIG. 19(A)  is an explanatory drawing of an ion introduction electrode in a 10th example as viewed from the direction of an ion source. 
           [0050]      FIG. 19(B)  is an explanatory drawing of a section of an ion introduction electrode in the 10th example taken along the central axis thereof. 
           [0051]      FIG. 20(A)  is an explanatory drawing of an ion introduction electrode in an 11th example as viewed from the direction of an ion source. 
           [0052]      FIG. 20(B)  is an explanatory drawing of a section of an ion introduction electrode in the 11th example taken along the central axis thereof. 
           [0053]      FIG. 21  is an equipment configuration drawing of a 12th example. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Example 1 
       [0054]    With respect to a first example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the first example is characterized in that: there is provided such a tapered intermediate pressure chamber that the internal cross-sectional area thereof is continuously reduced as it goes along the traveling direction of ions. 
         [0055]      FIG. 1  is an explanatory drawing illustrating a configuration of a mass spectrometry device using the above characteristic. The mass spectrometry device  1  is made up mainly of an ion source  2  placed under atmospheric pressure and a vacuum vessel  3 . The ion source  2  shown in  FIG. 1  generates the ions of a sample solution on a principle designated as electrospray ionization (ESI) scheme. According to the principle of ESI scheme, the ions  7  of a sample solution  6  are generated by supplying the sample solution  6  into a metal capillary  4  while applying high voltage thereto from a power supply  5 . In the process of the ion generation principle by the ESI scheme, the droplets  8  of the sample solution  6  are repeatedly fragmented and finally turned into very fine droplets and ionized. Droplets that cannot be sufficiently turned into fine droplets in the process of ionization include neutral droplets, charged droplets, and the like. To reduce these droplets  8 , a pipe  9  is provided outside the metal capillary  4  and gas  10  is let to flow therebetween. Then the gas  10  is sprayed form an outlet end  11  of the pipe  9  to facilitate vaporization of the droplets  8 . 
         [0056]    The ions  7  and droplets  8  generated under atmospheric pressure pass through an ion introduction electrode  12  and are introduced into a first vacuum chamber  13 . The ions  7  thereafter pass through a hole  15  formed in a second pore electrode  14  and are introduced into a second vacuum chamber  16 . The second vacuum chamber  16  is provided with an ion transport unit  17  that converges and transmits ions. For the ion transport unit  17 , a quadrupole electrode, an electrostatic lens electrode, or the like can be used. The ions  18  that passed through the ion transport unit  17  pass through a hole  20  formed in a third pore electrode  19  and are introduced into a third vacuum chamber  21 . The third vacuum chamber  21  is provided with an ion analysis unit  22  for ion separation and dissociation. For the ion analysis unit  22 , an ion trap, a quadrupole filter electrode, a collision cell, a time-of-flight mass spectrometer (TOF), or the like can be used. The ions  23  that passed through the ion analysis unit  22  are detected at a detector  24 . For the detector  24 , an electron multiplier, a multi-channel plate (MCP), or the like can be used. The ions  23  detected at the detector  24  are converted into electrical signals or the like and information such as the mass, strength, and the like of the ions can be analyzed in details at a control unit  25 . The control unit  25  has an input/output unit, a memory, and the like for accepting instruction input from a user and controlling voltage and the like and also includes software and the like required for power supply operation. 
         [0057]    The first vacuum chamber  13  is evacuated by a rotary pump (RP)  26  and held at several hundreds of Pa or so. The second vacuum chamber  16  is evacuated by a turbo molecular pump (TMP)  27  and held at several Pa or so. The third vacuum chamber  21  is evacuated by TMP  28  and held at 0.1 Pa or below. Further, such an electrode  29  as shown in  FIG. 1  is disposed outside the ion introduction electrode  12  and gas  30  is introduced into a gap therebetween. The gas is then sprayed from an outlet end  31  of the electrode  29  to reduce droplets  8  introduced into the vacuum vessel  3 . 
         [0058]    When the device is used, direct-current or alternating-current voltage is applied from a power supply  62  to the ion introduction electrode  12 , second pore electrode  14 , ion transport unit  17 , third pore electrode  19 , ion analysis unit  22 , detector  24 , electrode  29 , and the like. 
         [0059]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the first example with reference to  FIGS. 2(A) and 2(B) .  FIG. 2(A)  illustrates the introduction electrode  12  as viewed from the ion source  2  side; and  FIG. 2(B)  illustrates a section of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  is composed mainly of three elements: a front-stage first pore  35 , an intermediate pressure chamber  33 , and a rear-stage first pore  36 . The front-stage first pore  35  is Φd 1  in inside diameter and L 1  in length; and the rear-stage first pore  36  is Φd 2  in inside diameter and L 2  in length. The intermediate pressure chamber  33  located between the front-stage first pore  35  and the rear-stage first pore  36  has a conical tapered internal shape, which is α° in apical angle, OD in inlet diameter, and Φd 2  in outlet diameter. The central axis  37  of the front-stage first pore  35  and the central axis  38  of the rear-stage first pore  36  are eccentrically positioned with an axial offset=X. The axial offset cited herein refers to a distance between the axial center of the front-stage first pore  35  and the axial center of the rear-stage first pore  36 . 
         [0060]    Gas containing ions  7  and droplets  8  from under atmospheric pressure is first introduced along the central axis  37  of the front-stage first pore  35  as indicated by line  39 . The introduced gas containing ions  7  and droplets  8  collides with the internal surface of the intermediate pressure chamber  33  at a collision point  40 . β° is taken as an incident angle at the time of collision. When the central axis  37  of the front-stage first pore  35  and the taper center of the intermediate pressure chamber  33  are parallel to each other, a relation of β=α/2 holds. It assumed that ions travel along the axial direction of the front-stage first pore. At this time, the angle formed between the axial direction of the front-stage first pore and the wall surface of the intermediate pressure chamber is set as β. The central axis  37  of the front-stage first pore  35  and the taper center of the intermediate pressure chamber  33  need not necessarily be parallel to each other. After collision, an air flow changes the direction thereof and travels along the internal surface angle of the intermediate pressure chamber  33  as indicated by line  41 . The air flow thereafter changes the direction thereof again in proximity to an inlet of the rear-stage first pore  36  and travels along the central axis  38  of the rear-stage first pore  36  as indicated by line  42 , being then introduced into the first vacuum chamber  13 . 
         [0061]    At this time, an important thing is that when the air flow passes through the ion introduction electrode  12 , the cross-sectional area of the flow path discontinuously changes. Specifically, during proceeding from the front-stage first pore  35  to the intermediate pressure chamber  33 , the cross-sectional area is rapidly increased and thus the air flow can become turbulent. When the velocity of the air flow from the front-stage first pore  35  is brought into a sound velocity state, a turbulent flow is prone to occur in proximity to an outlet of the front-stage first pore  35 . When P o  (=atmospheric pressure) is taken as the primary-side pressure of the front-stage first pore  35  and P M  is taken for the secondary-side pressure, it is desirable that a condition of P M /P o ≦0.5, which is a sound velocity condition, should be established to obtain a turbulent flow. The primary-side pressure cited herein refers to a pressure in proximity to an inlet of the front-stage first pore  35  and the secondary-side pressure refers to a pressure at an outlet to the intermediate pressure chamber  33 . Since a turbulent flow occurs, small-diameter ions  7  and the like low in inertia travel along a flow going downstream while large-diameter droplets  8  and the like high in inertia cannot make a turn and collide with the collision point  40 . This enables prevention of inflow of droplets to the downstream area. Ordinary intra-pipe flow constant in inside diameter (≈laminar flow) is more accelerated with proximity to the pipe center because of the influence of pipe friction and is significantly decelerated in proximity to a pipe inner wall. For this reason, there is a possibility that a noise factor such as droplets also flows out of an outlet of the rear-stage first pore  36  along a strong flow in proximity to the pipe center. That is, even when an intra-pipe flow path is cranked, droplets and the like less possibly collide with the pipe interior. 
         [0062]    Another important thing is the intermediate pressure chamber  33  in such a taper shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. That the cross-sectional area of the interior is continuously reduced means that a flow velocity is gradually increased. An air flow becomes turbulent and uncontrollable once in proximity to an inlet of the intermediate pressure chamber  33 . However, by adopting such a shape of the intermediate pressure chamber  33  that there is a velocity distribution along a traveling direction like a taper shape, an air flow can be forcedly produced on the downstream side. 
         [0063]    A further another important thing is that there is not an outlet in the intermediate pressure chamber  33  other than the rear-stage first pore  36  and thus ions  7  introduced into the intermediate pressure chamber  33  can pass therethrough without a loss. 
         [0064]    In  FIG. 2(B) , a front-stage member  32  and a rear-stage member  34  are depicted as separate members but these members may be a single member. However, it is desirable that these members should be formed of two structures as shown in  FIG. 2(B)  in terms of manufacturing costs of parts and the like. Further, the intermediate pressure chamber  33  and the rear-stage first pore  36  may be formed of separate members. Further, the front-stage first pore  35  and the intermediate pressure chamber  33  may be formed of a single member and only the rear-stage first pore  36  may be formed of a separate member. 
         [0065]    A description will be given to results of performance comparisons conducted using ion introduction electrodes shown in  FIGS. 3(A) and 3(B)  and  FIGS. 4(A) and 4(B)  and an ion introduction electrode  12  in this example. The ion introduction electrode  12  in this example and the ion introduction electrodes shown in  FIGS. 3(A) and 3(B)  and  FIGS. 4(A) and 4(B)  are fundamentally differently configured; but in the following description, the same reference numerals and the like as in this example will be used for similar elements for simplification of comparison. The description of configuration elements and functions overlapped with those described with reference to  FIGS. 2(A) and 2(B)  will be omitted for the sake of simplification. 
         [0066]      FIGS. 3(A) and 3(B)  illustrate a configuration in which an incident angle β=90° at the time of collision, that is, collision occurs at a right angle. Meanwhile,  FIGS. 4(A) and 4(B)  illustrate a configuration in which an axial offset X=0 mm (central axis  37 =central axis  38 ), that is, there is not a collision point  40  or a line  41  indicating a changed direction (Though there is not collision, this will be hereafter expressed as incident angle β=0° configuration for the sake of convenience).  FIG. 5  indicates results of comparison of  FIG. 2(B)  (β=15°, 30°, 45°, 60°, 75°) with  FIG. 3(B)  (β=90° and  FIG. 4(B)  (β=0°. The upper part of  FIG. 5  indicates a droplet noise intensity result  43  and the lower part thereof indicates an ion intensity (reserpine ions: m/z609) result  44 . The configurations in  FIG. 2(A)  and  FIG. 3(A)  were all set to an axial offset X=3 mm. Other conditions were: d 1 =Φ0.65 mm, L 1 =20 mm, d 2 =Φ2 mm, L 2 =6 mm. It can be seen from the droplet noise intensity result  43  that with other configurations than the configuration shown in  FIG. 4(B) , in which the axial offset X=0 mm, droplet noise intensity can be reduced to 1/100 or less. This verifies the effectiveness of this example. Meanwhile, the ion intensity results  44  indicates that all the configurations including a taper shape shown in  FIG. 2(B)  obtain higher intensity than those shown in  FIG. 3(B)  and  FIG. 4(B) . The reason of this is an effect of the intermediate pressure chamber  33  having a velocity distribution specific to taper shapes as described up to this point. With such a right-angled structure in which β=90° as shown in  FIG. 3(B) , a rate vector toward the downstream area which is the traveling direction of air flows does not exist in the intermediate pressure chamber. As a result, the amount drawn in only by a flow velocity locally accelerated in proximity to an inlet of the rear-stage first pore is equivalent to an amount of introduction and this degrades sensitivity. With the configuration of X=0 mm shown in  FIG. 4(B) , the central axis  37  of the front-stage first pore  35  and the central axis  38  of the rear-stage first pore  36  are coaxial with each other and d 1 ≦d 2 . Therefore, a near-sound velocity jet stream in proximity to an outlet of the front-stage first pore  35  goes through the rear-stage first pore  36  and is introduced directly into the first vacuum chamber  13 . For this reason, ion transmission efficiency in a rear stage is degraded by turbulence of a flow. Therefore, it can be concluded that at least an incident angle β=15 to 75° is a favorable condition. 
         [0067]    A description will be given to a result of ion intensity comparison with the configuration of an incident angle β=30° depending on the internal pressure of the intermediate pressure chamber  33  with reference to  FIG. 6 .  FIG. 6  indicates an internal pressure (P M ) dependence result  61  with the intermediate pressure chamber  33  with respect to ion intensity (reserpine ions: m/z609). The values of P M  are obtained by converting conditions such as d 1 , L 1 , d 2 , L 2  and the pressure of the first vacuum chamber  13 =P 1  using Formula 1 below. Here, P 0 =atmospheric pressure (10 5  Pa). 
         [0000]        P   M =(( d   1   4   ×P   0   2   /L   1   +d   2   4   ×P   1   2   /L   2 )/( d   1   4   /L   1   +d   2   4   /L   2 )) 1/2   (Formula 1)
 
         [0068]    It can be concluded from  FIG. 6  that a range of 2000 to 30000 Pa or so is optimal. This optimal pressure condition is half or less of the inlet-side pressure (10 5  Pa) of the front-stage first pore  35 . Therefore, a sound velocity state is established in proximity to an outlet of the front-stage first pore  35  and a Mach disk can be formed there. The distance M L  from an outlet of the front-stage first pore  35  to the Mach disk can be expressed by Formula 2 below. 
         [0000]        M   L =0.67× P   O   /P   M ) 1/2   ×d   1   (Formula 2)
 
         [0069]    From Formula 2, M L  is 0.8 to 3 mm under the condition of d 1 =Φ0.65. From Formula 3, the diameter M D  of the Mach disk in the position of M L  can be 1.5 mm or so at the maximum. 
         [0000]        M   D =0.4 to 0.5× M   L   (Formula 3)
 
         [0070]    According to this result, spraying can occur within the maximum diameter 1.5 mm (radius: 0.75 mm) in proximity to the collision point  40  on the inner wall of the intermediate pressure chamber  33 . Therefore, unless an axial offset X is set to X≧M D /2+d 2 /2, there is a danger than an outlet jet of the front-stage first pore  35  is sprayed directly to the rear-stage first pore  36 . Specifically, it is required to adopt an arrangement of X≧1.75 mm under the conditions of d 1 =Φ0.65 mm and d 2 =Φ2 mm. Similarly, unless the taper inlet diameter ΦD of the intermediate pressure chamber  33  is set to ΦD≧2×(X+M D /2), an introduction loss occurs at the taper inlet. Specifically, it is required to adopt an arrangement of OD≧Φ4 mm (taper inlet area≧12 mm 2 ) under the conditions of d 1 =Φ0.65 mm and d 2 =Φ2 mm. It is desirable that these values should be set to X≧1.5 mm and a taper inlet area≧12 mm 2  or so depending on the dimensions of d 1  and d 2 . 
         [0071]    A jet stream that is in a sound velocity state at an outlet of the front-stage first pore  35  is advantageous to this example. In this example, as mentioned above, droplets are removed by utilizing turbulence of a flow at an inlet of the intermediate pressure chamber  33  and the effect of ion permeability enhancement is brought about by taper shape. The interior of the intermediate pressure chamber  33  is as low as 2000 to 30000 Pa as compared with atmospheric pressure. This reduces a pressure difference between an inlet and an outlet of the rear-stage first pore  36 ; as a result, turbulence of a flow is more mitigated than with ordinary configurations only with a first pore electrode and ion transmission efficiency in a rear stage is enhanced. 
         [0072]    A description will be given to a result of performance comparison of an ordinary equipment configuration without the intermediate pressure chamber  33  and the rear-stage first pore  36  with the configuration of this example ( FIG. 2(B) ) with reference to  FIG. 7 .  FIG. 7  indicates a comparison result  45  with respect to the presence or absence of the intermediate pressure chamber. It can be seen from  FIG. 7  that with the configuration without the intermediate pressure chamber  33 , ion intensity (reserpine ions: m/z609) is reduced to 70% or less of that with the configuration with the intermediate pressure chamber. This result indicates the following as described above: a pressure difference between an inlet and an outlet of the rear-stage first pore  36  is reduced by the intermediate pressure chamber  33  and the rear-stage first pore  36 ; for this reason, a flow velocity at an outlet of the rear-stage first pore  36  is made lower than with the ordinary equipment configuration and a loss in ion transmission due to turbulence of a flow is reduced. This evaluation was conducted with the configuration of: d 1 =Φ0.65 mm, L 1 =20 mm, d 2 =Φ2 mm, L 2 =6 mm, β=30°, and X=3 mm. 
         [0073]    A description will be given to a result of performance comparison depending on the diameter d 2  and length L 2  of the rear-stage first pore  36  with reference to  FIG. 8 .  FIG. 8  indicates a comparison result  46  with respect to the structure of the rear-stage first pore. It can be seen from  FIG. 8  that with the configuration of d 2 =Φ4 mm and length L 2 =0.5 mm, ion intensity (reserpine ions: m/z609) is reduced to ⅕ or below of that with the configuration of d 2 =Φ2 mm and length L 2 =6 mm. 
         [0074]      FIG. 9  indicates a fluid simulation result  47  with the configuration of d 2 =Φ4 mm and length L 2 =0.5 mm conducted to verify the above result. The many arrows in  FIG. 9  indicate the directions of fluid flows. It can be seen from  FIG. 9  that many arrows are plotted along an extension line  48  of a taper angle of the intermediate pressure chamber  33 . In particular, there are very many arrows in the direction of the extension line  48  within the range  49 , encircled with a dotted line, sprayed from the rear-stage first pore  36 . Also in an actual experimental system, like this flow, spraying was obliquely carried out with respect to the central axis  38  of the rear-stage first pore  36 . It is suspected that ion transmission efficiency in a rear stage is markedly degraded for this reason. 
         [0075]    Based on these results, a description will be given to an optimum configuration with reference to  FIG. 10 . To avoid the fluid simulation result in  FIG. 9 , it is required to take the measure illustrated in  FIG. 10 . That is, it is required that the extension line  48  of a taper angle of the intermediate pressure chamber  33  and the inner wall of the rear-stage first pore  36  intersect with each other (at a cross point  50 ). That is, an outlet end  51  of the rear-stage first pore  36  must be located on the downstream side with the extension line  48  in between. Specifically, the position L 3  of the cross point  50  is expressed by Formula 4. 
         [0000]        L   3   =d   2 ×tan(90−β)  (Formula 4)
 
         [0076]    When the condition of β=15 to 75° taken as optimum in  FIG. 5  is substituted, L 3 /d 2 =0.3 to 3.7. That is, it is required to establish a condition of L 3 /d 2 ≧0.3 depending on the taper angle. 
         [0077]    In the second to 11th examples described later, when the angle of the wall surface of the intermediate pressure chamber differs between the ion inlet side and the outlet side, an optimum angle only has to be selected for β. To do this, an average value may be taken as an optimum angle or an optimum angle may be calculated using an angle on the rear-stage pore  36 . 
       Example 2 
       [0078]    In relation to a second example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the second example is characterized in that the second example has: such a taper shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions; and an intermediate pressure chamber including a straight cylindrical portion. 
         [0079]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the second example with reference to  FIGS. 11(A) and 11(B) .  FIG. 11(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 11(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 11(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. In the ion introduction electrode  12  shown in  FIG. 11(B) , the intermediate pressure chamber  33  is composed of a front-stage portion  33 - 1  and a rear-stage portion  33 - 2 . Like the intermediate pressure chamber  33  described with reference to  FIG. 2(B) , the rear-stage portion  33 - 2  is in such a taper shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. In contrast with this, the front-stage portion  33 - 1  is in a straight cylindrical shape and the cross-sectional area thereof is unchanged. In the structure of the intermediate pressure chamber  33  shown in  FIG. 11(B) , at least a part thereof is provided with such a taper shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. As a result, the same functions as described with reference to  FIGS. 2(A) and 2(B)  can be basically obtained. Provision of the front-stage portion  33 - 1  enables the distance from an outlet of the front-stage first pore  35  to the collision point  40  to be lengthened. This is the case even when the taper center inlet diameter OD and the incident angle β are identical with those in the first example. This brings about an advantage that contamination due to a rebound from collision can be reduced in proximity to an outlet of the front-stage first pore  35 . 
         [0080]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 11(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . 
       Example 3 
       [0081]    In relation to a third example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the third example is characterized in that the intermediate pressure chamber has such a taper shape having two different angles that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. 
         [0082]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the third example with reference to  FIGS. 12(A) and 12(B) .  FIG. 12(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 12(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 12(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. In the ion introduction electrode  12  shown in  FIG. 12 , the intermediate pressure chamber  33  is composed of a front-stage portion  33 - 1  and a rear-stage portion  33 - 2 . Like the intermediate pressure chamber  33  described with reference to  FIG. 2(B) , the front-stage portion  33 - 1  and the rear-stage portion  33 - 2  are also in such a taper shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. However, the front-stage portion  33 - 1  and the rear-stage portion  33 - 2  are different from each other in taper angle. The taper of the front-stage portion  33 - 1  has an incident angle β. The taper of the rear-stage portion  33 - 2  is at an angle θ corresponding to β, where β&lt;θ. In this example, like the structure of the intermediate pressure chamber  33  shown in  FIG. 12(B) , each of the tapers having two different angles is in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. Even with these taper shapes, the same functions as described with reference to  FIG. 2(B)  can be obtained. Since the angle θ of the rear-stage portion  33 - 2  is larger than the angle β of the front-stage portion  33 - 1 , an advantage is brought about. After collision at the collision point  40  in the front-stage portion  33 - 1 , a quantity of droplets introduced into the rear-stage first pore  36  can be reduced. In the example shown in  FIG. 12(B) , the intermediate pressure chamber  33  has two different taper angles. Even in an intermediate pressure chamber  33  in a multi-staged taper shape having more than two taper angles, the same effects can be obtained. 
         [0083]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 12(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . 
       Example 4 
       [0084]    In relation to a fourth example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the fourth example is characterized in that the intermediate pressure chamber in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions is configured as follows: unlike tapers, the cross-sectional shape thereof is not linearly changed but is curvilinearly changed. Therefore, the intermediate pressure chamber in the fourth example has a bowl-like internal shape. This intermediate pressure chamber is similar in structure to what is obtained by infinitely increasing a number of stages of the intermediate pressure chamber in the third example having a multi-staged taper shape including multiple taper angles. 
         [0085]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the fourth example with reference to  FIGS. 13(A) and 13(B) .  FIG. 13(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 13(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 13(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. In the ion introduction electrode  12  shown in  FIG. 13(B) , the intermediate pressure chamber  33  is in such a shape (bowl shape) that the cross-sectional shape thereof is not linearly changed like tapers but is curvilinearly changed. In the case of this configuration, an incident angle β is formed by a curved tangential line  52  at a section at a collision point  40 . The intermediate pressure chamber  33  in  FIG. 13(B)  is also in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions; therefore, the same effects as described with reference to  FIG. 2(B)  can be basically obtained. Since the tangential angle of a section of the intermediate pressure chamber  33  is continuously and gently changed with traveling of ions, ions can be introduced into the rear-stage first pore  36  with a less loss. 
         [0086]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 13(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . 
       Example 5 
       [0087]    In relation to a fifth example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the fifth example is characterized in that the intermediate pressure chamber has such a taper shape having two different angles that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. 
         [0088]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the fifth example with reference to  FIGS. 14(A) and 14(B) .  FIG. 14(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 14(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 14(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. In the ion introduction electrode  12  shown in  FIG. 14(B) , the intermediate pressure chamber  33  is composed of a front-stage portion  33 - 1  and a rear-stage portion  33 - 2 . Like the intermediate pressure chamber  33  described with reference to  FIG. 2(B) , the front-stage portion  33 - 1  and the rear-stage portion  33 - 2  are also in such a taper shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. However, the front-stage portion  33 - 1  and the rear-stage portion  33 - 2  are different from each other in taper angle. The taper of the front-stage portion  33 - 1  has an incident angle β. The taper of the rear-stage portion  33 - 2  is at an angle θ corresponding to β, where β&gt;θ. In this example, like the structure of the intermediate pressure chamber  33  shown in  FIG. 14(B) , each of the tapers having two different angles is in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions. Even with these taper shapes, the same functions as described with reference to  FIG. 2(B)  can be basically obtained. Since the angle β of the front-stage portion  33 - 1  is larger than the angle θ of the rear-stage portion  33 - 2 , an advantage is brought about. After collision at the collision point  40  in the front-stage portion  33 - 1 , a loss in a quantity of ions introduced into the rear-stage first pore  36  can be prevented. In the example shown in  FIG. 14(B) , the intermediate pressure chamber  33  has two different taper angles. Even in an intermediate pressure chamber  33  in a multi-staged taper shape having more than two taper angles, the same effects can be obtained. 
         [0089]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 14(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . 
       Example 6 
       [0090]    In relation to a sixth example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the sixth example is characterized in that the intermediate pressure chamber in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions is configured as follows: unlike tapers, the cross-sectional shape thereof is not linearly changed but is curvilinearly changed. Therefore, the intermediate pressure chamber in the sixth example has a trumpet-like internal shape. This intermediate pressure chamber is similar in structure to what is obtained by infinitely increasing a number of stages of the intermediate pressure chamber in the fifth example having a multi-staged taper shape including multiple taper angles. 
         [0091]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the sixth example with reference to  FIGS. 15(A) and 15(B) .  FIG. 15(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 15(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 15(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. In the ion introduction electrode  12  shown in  FIG. 15(B) , the intermediate pressure chamber  33  is in such a shape (trumpet shape) that the cross-sectional shape thereof is not linearly changed like tapers but is curvilinearly changed. In the case of this configuration, an incident angle β is formed by a curved tangential line  52  at a section at a collision point  40 . The intermediate pressure chamber  33  in  FIG. 15(B)  is also in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions; therefore, the same effects as described with reference to  FIG. 2(B)  can be basically obtained. Since the tangential angle of a section of the intermediate pressure chamber  33  is continuously and gently changed with traveling of ions, ions can be introduced into the rear-stage first pore  36  with a less loss. 
         [0092]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 15(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . 
       Example 7 
       [0093]    In relation to a seventh example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the seventh example is characterized in that the intermediate pressure chamber has such a shape that the cross-sectional area of the interior thereof is stepwise reduced as it goes along the traveling direction of ions. 
         [0094]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the seventh example with reference to  FIGS. 16(A) and 16(B) .  FIG. 16(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 16(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 16(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. In the ion introduction electrode  12  shown in  FIG. 16(B) , the intermediate pressure chamber  53  is composed of multiple stair-like stepped portions  53 - 1  to  53 - n . The stepped portions  53 - 1  to  53 - n  are in such a shape that the cross-sectional area of the interior thereof is stepwise reduced as it goes along the traveling direction of ions. The structure of the intermediate pressure chamber  53  shown in  FIG. 16(B)  is in such a shape that the cross-sectional area of the interior thereof is stepwise reduced as it goes along the direction of ions. Even in this shape, the same functions as described with reference to  FIG. 2(B)  can be obtained. When a straight cylindrical portion partly exists as shown in  FIG. 16(B) , no problem arises. It is desirable that the collision point  40  should be located in a taper shape as shown in  FIG. 16(B) . However, if the collision point is located on a curved surface as in the fourth example or the sixth example, no problem arises. Further, if the collision point  40  is located in a position overlapped with a stair-like step, no problem arises. However, in cases where the collision point  40  is overlapped with a step, an axial offset X is of the order of millimeters and thus it is desirable that a step pitch should be set to as sufficiently smaller a value as 0.1 mm or so. 
         [0095]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 16(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . 
       Example 8 
       [0096]    In relation to an eighth example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the eighth example is characterized in that the intermediate pressure chamber in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions is configured as follows: there is a sloped portion only on the front-stage first pore side as viewed from the rear-stage first pore. 
         [0097]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the eighth example with reference to  FIGS. 17(A) and 17(B) .  FIG. 17(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 17(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 17(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. In the ion introduction electrode  12  shown in  FIG. 17(B) , the intermediate pressure chamber  33  is not symmetrical with respect to the central axis  38  of the rear-stage first pore  36  like tapers. The intermediate pressure chamber is in such a shape that there is a sloped portion only in the direction of the central axis  37  of the front-stage first pore  35  as viewed from the central axis  38  of the rear-stage first pore  36 . In this case, the inlet area A of the intermediate pressure chamber  33  only has to be approximately half of a taper inlet area mm 2  or so, which is a desirable condition described in relation to the first example and this enables sufficient size reduction. A condition of A 6 mm 2  or so is desirable for size. Since an inlet area is reduced, a pressure difference from the front-stage first pore  35  becomes smaller than in the case shown in  FIG. 2(B) ; however, an ion loss is accordingly made relatively small. The intermediate pressure chamber  33  in  FIG. 17(B)  is also in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions; therefore, the same effects as described with reference to  FIG. 2(B)  can be basically obtained. 
         [0098]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 17(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . 
       Example 9 
       [0099]    In relation to a ninth example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the ninth example is characterized in that: there is provided the intermediate pressure chamber in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions; and there are multiple front-stage first pores. 
         [0100]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the ninth example with reference to  FIGS. 18(A) and 18(B) .  FIG. 18(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 18(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 18(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. The ion introduction electrode  12  shown in  FIG. 18(B)  is characterized in that there are multiple front-stage first pores  35 . In the example in  FIG. 18(B) , a number of the front-stage first pores  35  is six but any number of front-stage first pores  35  is acceptable. Increasing a number of the front-stage first pores  35  increases the amount of flow introduced into the intermediate pressure chamber  33  by an amount equivalent to the number of the front-stage first pores  35 . However, since the intermediate pressure chamber  33  in  FIG. 18(B)  is also in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions, the same effects as described with reference to  FIG. 2(B)  can be basically obtained. 
         [0101]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 18(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . The front-stage first pores  35  in  FIG. 18(B)  can be combined with the configurations of the intermediate pressure chambers  33  shown in  FIG. 11(B)  to  FIG. 17(B) . 
       Example 10 
       [0102]    In relation to a 10th example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the 10th example is characterized in that: there is provided the intermediate pressure chamber in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions; and the front-stage first pore and the intermediate pressure chamber are so structured that they are electrically insulated from each other. 
         [0103]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the 10th example with reference to  FIGS. 19(A) and 19(B) .  FIG. 19(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 19(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 19(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. The ion introduction electrode  12  shown in  FIG. 19(B)  is characterized in that the front-stage member  32  and the rear-stage member  34  can be electrically insulated from each other by an insulator  54 . Since the front-stage member  32  and the rear-stage member  34  are electrically insulated from each other, independent different potentials can be applied thereto from power supplies  55 ,  56 . In  FIG. 19(B) , the intermediate pressure chamber  33  and the rear-stage first pore  36  are depicted as a single member. Instead, the intermediate pressure chamber  33  and the rear-stage first pore  36  may also be formed of separate members and be electrically insulated from each other by an insulator. Since the intermediate pressure chamber  33  in  FIG. 19(B)  is also in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions, the same effects as described with reference to  FIG. 2(B)  can be basically obtained. 
         [0104]    Like the ion introduction electrode  12  shown in  FIG. 2 , the ion introduction electrode  12  in  FIG. 19(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . The insulating structure in  FIG. 19(B)  can be combined with the configurations of the ion introduction electrodes  12  in  FIG. 11(B)  to  FIG. 18(B) . 
       Example 11 
       [0105]    In relation to an 11th example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the 11th example is characterized in that there are provided the intermediate pressure chamber in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions and a heating means for heating the ion introduction electrode. 
         [0106]    A detailed description will be given to a configuration of an ion introduction electrode  12  in the 11th example with reference to  FIGS. 20(A) and 20(B) .  FIG. 20(A)  illustrates the ion introduction electrode  12  as viewed from the direction of an ion source  2 ; and  FIG. 20(B)  is a cross-sectional view of the ion introduction electrode  12  taken along the central axis thereof. The ion introduction electrode  12  shown in  FIG. 20(B)  is basically substantially identical with the ion introduction electrode  12  described with reference to  FIG. 2(B)  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration shown in  FIG. 2(B)  will be described. The ion introduction electrode  12  shown in  FIG. 20(B)  is characterized in that there are provided heating means  57 ,  58  for heating the ion introduction electrode  12 . Heating the ion introduction electrode  12  makes it possible to evaporate and vaporize droplets  8  introduced into the ion introduction electrode  12  and suppress the inflow of droplets  8  to the subsequent area. In the example in  FIG. 20(B) , the front-stage member  32  and the rear-stage member  34  are independently heated with the separate heating means  57 ,  58  but both the members may be heated with a single heating means. Further, a part of the intermediate pressure chamber  33  and a part of the rear-stage first pore  36  may be independently heated with separate heating means.  FIG. 20(B)  depicts that the heating means  57 ,  58  are coiled heating wires but the heating means may be a heater or the like in any other form. 
         [0107]    Like the ion introduction electrode  12  shown in  FIG. 2(B) , the ion introduction electrode  12  in  FIG. 20(B)  can also be combined with the equipment configuration described with reference to  FIG. 1 . The ion introduction electrode  12  in  FIG. 20(B)  can be combined with the configurations of the ion introduction electrodes  12  in  FIG. 11(B)  to  FIG. 19(B) . 
       Example 12 
       [0108]    In relation to a 12th example, a description will be given to an equipment configuration in which an ion introduction electrode for introducing ions from under atmospheric pressure into vacuum is composed of three elements: a front-stage first pore, an intermediate pressure chamber, and a rear-stage first pore. The equipment configuration of the 12th example is characterized in that: there is provided the intermediate pressure chamber in such a shape that the cross-sectional area of the interior thereof is continuously reduced as it goes along the traveling direction of ions; and a first vacuum chamber is provided with an ion convergence unit. A detailed description will be given to a configuration of a mass spectrometry device  1  in the 12th example with reference to  FIG. 21 . The mass spectrometry device  1  shown in  FIG. 21  is basically substantially identical with the mass spectrometry device  1  described with reference to  FIG. 1  in configuration and function. Therefore, a redundant description will be omitted and only a difference from the configuration in  FIG. 1  will be described. The mass spectrometry device  1  shown in  FIG. 21  is characterized in that an ion convergence unit  59  is disposed in the first vacuum chamber  13 . The ion convergence unit  59  can be formed of multiple ring-shaped electrodes or multiple rod-shaped electrodes and applies direct-current voltage or alternating-current voltage (including high-frequency voltage) or simultaneously both of these voltages. Ions are thereby converged in proximity to the central axis thereof. Ions  7  that passed through the ion introduction electrode  12  and were introduced into the first vacuum chamber  13  are converged by the ion convergence unit  59  in proximity to the central axis  60  thereof. As a result, the efficiency of ion introduction into a hole  15  in a subsequent second pore electrode  14  is enhanced and thus sensitivity is enhanced. Other configuration elements and the like are the same as those described with reference to  FIG. 1 . When used, direct-current or alternating-current voltage is applied from a power supply  62  to the ion convergence unit  59 . 
         [0109]    It is also possible to combine the ion introduction electrodes  12  in  FIG. 2(B)  and  FIG. 11(B)  to  FIG. 20(B)  with the mass spectrometry device  1  in  FIG. 21 . 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  . . . Mass spectrometry device, 
               2  . . . Ion source, 
               3  . . . Vacuum vessel, 
               4  . . . Metal capillary, 
               5  . . . Power supply, 
               6  . . . Sample solution, 
               7  . . . Ion, 
               8  . . . Droplet, 
               9  . . . Pipe, 
               10  . . . Gas, 
               11  . . . Outlet end, 
               12  . . . Ion introduction electrode, 
               13  . . . First vacuum chamber, 
               14  . . . Second pore electrode, 
               15  . . . Hole, 
               16  . . . Second vacuum chamber, 
               17  . . . Ion transport unit, 
               18  . . . Ion, 
               19  . . . Third pore electrode, 
               20  . . . Hole, 
               21  . . . Third vacuum chamber, 
               22  . . . Ion analysis unit, 
               23  . . . Ion, 
               24  . . . Detector, 
               25  . . . Control unit, 
               26  . . . Rotary pump (RP), 
               27  . . . Turbo molecular pump (TMP), 
               28  . . . Turbo molecular pump (TMP), 
               29  . . . Electrode, 
               30  . . . Gas, 
               31  . . . Outlet end, 
               32  . . . Front-stage member, 
               33  . . . Intermediate pressure chamber, 
               33 - 1  . . . Front-stage portion, 
               33 - 2  . . . Rear-stage portion, 
               34  . . . Rear-stage member, 
               35  . . . Front-stage first pore, 
               36  . . . Rear-stage first pore, 
               37  . . . Central axis, 
               38  . . . Central axis, 
               39  . . . Line, 
               40  . . . Collision point, 
               41  . . . Line, 
               42  . . . Line, 
               43  . . . Droplet noise intensity, 
               44  . . . ion intensity, 
               45  . . . Comparison result depending on presence or absence of intermediate pressure chamber, 
               46  . . . Comparison result depending on structure of rear-stage first pore, 
               47  . . . Fluid simulation result, 
               48  . . . Extension line of taper angle, 
               49  . . . Range, 
               50  . . . Cross point, 
               51  . . . Outlet end, 
               52  . . . Tangential line, 
               53  . . . Intermediate pressure chamber, 
               53 - 1  to  53 - n  . . . Stepped portion, 
               54  . . . Insulator, 
               55  . . . Power supply, 
               56  . . . Power supply, 
               57  . . . Heating means, 
               58  . . . Heating means, 
               59  . . . Ion convergence unit, 
               60  . . . Central axis, 
               61  . . . Internal pressure (P M ) dependence result with intermediate pressure chamber, 
               62  . . . Power supply.