Patent Publication Number: US-2022214307-A1

Title: Ion analyzer

Description:
TECHNICAL FIELD 
     The present invention relates to an ion analyzer. 
     BACKGROUND ART 
     One of methods for ionizing a sample that are used in a mass spectrometer is a matrix assisted laser desorption/ionization (MALDI) method (Patent Literatures 1 to 3). In the matrix assisted laser desorption/ionization method, a substance (matrix material) that easily absorbs laser light and is easily ionized is applied to a surface of a sample, so that the matrix material incorporates sample molecules. Then, the matrix material incorporating the sample molecules are microcrystallized, and laser light is irradiated on the matrix material to ionize the sample molecules. The ions generated from the sample molecules are provided to an ion analyzer for mass spectrometry, ion mobility analysis, or the like. An ion source that generates ions by the MALDI method is called a MALDI ion source, and a mass spectrometer including a MALDI ion source is called a matrix assisted laser desorption/ionization mass spectrometer (MALDI-MS). 
     As the MALDI ion source, in many cases, a vacuum MALDI ion source is used in which sample molecules are ionized in the vacuum atmosphere. Ions generated by the vacuum MALDI ion source in an ionization chamber are introduced into a mass spectrometry chamber, which is communicated with the ionization chamber through an ion introduction port. The mass spectrometry chamber is provided with an ion transport optical system constituted by an ion lens and the like, an ion trap, and an ion detection unit. The ions introduced through the ion introduction port are converged by the ion transport optical system and introduced into the ion trap. A radio-frequency voltage for trapping ions is applied to the ion trap. A cooling gas such as helium gas is introduced into the ion trap, and the ions are cooled by collision with the cooling gas and trapped in the vicinity of the center in the ion trap. After that, the ions are serially released from the ion trap and detected by the ion detection unit. 
     In the above MALDI-MS, the vacuum MALDI ion source needs to have a degree of vacuum of 10 −1  to 10 −2  Pa. On the other hand, the ion transport optical system and the ion detection unit need to have a pressure (high vacuum) of 10 −3  Pa or less. Therefore, in the MALDI-MS, the ionization chamber and the mass spectrometry chamber are independently evacuated by a turbo-molecular pump. When the cooling gas is introduced into the ion trap, the degree of vacuum in the ion trap becomes 10 −1  to 10 −2  Pa. Therefore, in the mass spectrometry chamber, a space in which the ion trap is located and a space containing the ion transport optical system and the ion detection unit are separated with a partition wall, and each of the spaces is evacuated by the turbo-molecular pump. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP H10-228881 A 
         Patent Literature 2: WO 2018/092271 A 
         Patent Literature 3: JP 2016-115565 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     As described above, in the conventional MALDI-MS, it is necessary to use a plurality of turbo-molecular pumps in order to evacuate a plurality of spaces required to have different degree of vacuums, and there is a problem that the device is accordingly large and expensive. 
     The MALDI-MS has been described here as an example, but the same problem as described above lies with a device using a vacuum ionization source other than the MALDI ion source and with a device that performs mobility analysis of ions trapped in an ion trap. 
     An object of the present invention is to achieve downsizing and cost reduction of an ion analyzer in which ions derived from a sample and generated in a vacuum ion source are trapped in an ion trapping unit and then analyzed. 
     Solution to Problem 
     An ion analyzer according to the present invention made to solve the above problem includes: 
     an ionization chamber: 
     an analysis chamber separated from the ionization chamber by a partition wall in which an opening is formed: 
     an ionization unit configured to generate ions from a sample in the ionization chamber; 
     an ion transport unit provided in the analysis chamber and configured to transport the ions generated in the ionization unit; 
     an ion trapping unit provided in the analysis chamber and configured to trap the ions transported by the ion transport unit; 
     an ion detection unit provided in the analysis chamber and configured to detect the ions released from the ion trapping unit; and 
     a single evacuation mechanism connected only to the analysis chamber and configured to evacuate the analysis chamber to a pressure of 10 3  Pa or less. 
     Advantageous Effects of Invention 
     In an ion analyzer, an ion transport unit and an ion detection unit are generally required to have a high degree of vacuum (to have a low pressure) with a pressure of 10 −3  Pa or less. On the other hand, the degree of vacuum required for an ion source disposed in an ionization chamber is about 10 −1  to 10 −2  Pa, which is lower than the degree of vacuum required for the ion transport unit and the ion detection unit. Therefore, in the ion analyzer according to the present invention, a single evacuation mechanism that evacuates the space to which the evacuation mechanism is connected to the pressure of 10 −3  Pa or less is connected only to the analysis chamber to directly evacuate the analysis chamber, and at the same time, to also evacuate the ionization chamber indirectly through the opening. After the analysis chamber and the ionization chamber are each evacuated to a predetermined degree of vacuum, the ionization unit is operated to generate ions from a sample. At the same time as or slightly later than the generation of ions from the sample, a predetermined gas (cooling gas) is introduced into the ion trapping unit. The ions introduced into the ion trapping unit are cooled by collision with the cooling gas, and are trapped near the center of the ion trapping unit. The cooling gas introduced into the ion trapping unit gradually flows out to the analysis chamber, so that the degree of vacuum in the analysis chamber decreases. Therefore, the ions are trapped in the ion trapping unit until the gas is evacuated by the evacuation mechanism and the degree of vacuum in the analysis chamber reaches a predetermined degree of vacuum. Then, after the degree of vacuum in the analysis chamber reaches the predetermined degree of vacuum, the ions are sequentially released from the ion trapping unit and are detected by the ion detection unit. 
     The single evacuation mechanism is composed of, for example, a main pump such as a turbo-molecular pump for high vacuum pumping and an auxiliary pump such as a diaphragm pump for rough pumping. The main pump that performs high vacuum pumping is generally large and expensive. Since the ion analyzer according to the present invention includes only a single evacuation mechanism connected only to the analysis chamber, it is possible to achieve downsizing and cost reduction compared with a conventional ion analyzer including a plurality of such evacuation mechanisms. Note that the expression “single evacuation mechanism” is a limitation related to the main pump (that is, the evacuation mechanism that evacuates the space to which the evacuation mechanism is connected to a pressure of 10 −3  Pa or less), and does not exclude a form in which, for example, a roughing pump is connected to the ionization chamber where a load lock operation is performed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram of a main part of a mass spectrometer as an embodiment of an ion analyzer according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A mass spectrometer that is an embodiment of an ion analyzer according to the present invention will be described below with reference to the drawings. The mass spectrometer of the present embodiment is a matrix laser desorption/ionization-ion trap (MALDI-IT) mass spectrometer that causes an ion trap (IT) to mass-separate ions generated by a matrix-assisted laser desorption/ionization (MALDI) ion source. 
       FIG. 1  shows a configuration of a main part of a mass spectrometer  1  of the present embodiment. The mass spectrometer  1  is roughly configured with an ionization chamber  10 , a mass spectrometry chamber  20 , a voltage applying unit  30 , and a control unit  40 . A partition wall  21  is provided between the ionization chamber  10  and the mass spectrometry chamber  20 . The partition wall  21  is provided with an opening  211  in a tapered shape that is gradually wider toward the mass spectrometry chamber  20  side. 
     The ionization chamber  10  is provided with a sample stage  12  on which there is placed a sample plate  111  having a plurality of wells for accommodating a sample  11 . There is also provided a stage moving mechanism  13  to move the sample stage  12  between a measurement position (position shown in  FIG. 1 ) and a replacement position and to move the sample stage  12  close to and away from the opening  211  at the measurement position. There are also provided a valve  14  and a valve moving mechanism  15  for moving the valve  14  between a closing position (position shown in  FIG. 1 ) at which the valve closes the opening  211  and a retraction position. The valve  14  and the valve moving mechanism  15  constitute a load lock mechanism. The ionization chamber  10  is further provided with a mechanism (not shown in the drawing) for an analyst to open and close the ionization chamber  10  to replace the sample plate  11 . Other than the above, the ionization chamber  10  is provided with a diaphragm pump (roughing pump, not shown in the drawing) that evacuates the ionization chamber  10  to a pressure of about 10 3  Pa when a load lock operation is performed. In the present embodiment, a diaphragm pump is connected to the ionization chamber  10 ; however, such a configuration including a roughing pump is a preferable aspect but is not essential to the present invention. 
     Outside the ionization chamber  10  and the mass spectrometry chamber  20 , there are disposed: a laser light source  3  that applies laser light to the sample  11  on the sample stage  12  at the measurement position; and a camera  5  that observes a surface of the sample via a half mirror  4 . 
     The mass spectrometry chamber  20  is provided with a first ion lens  22 , a deflection unit  23 , a second ion lens  24 , an ion trap  25 , and an ion detector  26  in this order from the side closer to the ionization chamber  10 . The first ion lens  22  and the second ion lens  24  are each configured with a plurality of annular electrodes arranged along a central axis (ion optical axis) of a flight path of ions. 
     The deflection unit  23  includes four rod electrodes  231  to  234 . Under control of the control unit  40 , the voltage applying unit  30  applies a voltage of the opposite polarity to the ions to the rod electrode  231  and a voltage of the same polarity as the ions to each of the other rod electrodes  232  to  234 . 
     The ion trap  25  is a three-dimensional ion trap including an annular ring electrode  251  in an annular shape and a pair of end cap electrodes (inlet-side end cap electrode  252  and outlet-side end cap electrode  253 ) disposed to be opposite to each other with the ring electrode  251  interposed between the pair of endcap electrodes. An ion introduction hole  254  is formed in the inlet-side end cap electrode  252 , and an ion ejection hole  255  is formed in the outlet-side end cap electrode  253 . Under control of the control unit  40 , the voltage applying unit  30  applies either a radio-frequency voltage or a direct-current voltage or a combined voltage of the both to each of the electrodes  251 ,  252 , and  253  at a predetermined timing. By appropriately changing these voltages, ions are trapped inside the ion trap  25 , and the trapped ions are released. The ions released from the ion trap  25  are detected by the ion detector  26 . 
     The inlet-side end cap electrode  252  and the ring electrode  251  are fixedly coupled to each other with an insulating member  251 , and the outlet-side end cap electrode  253  and the ring electrode  251  are fixedly coupled to each other with an annular insulating member  256 . The insulating members  256  are each provided with a plurality of (for example, four) openings at equal intervals in a circumferential direction, so that an internal space of the ion trap  25  and the mass spectrometry chamber  20  communicate with each other through the openings. The openings of the insulating members  256  are formed sufficiently larger than the ion introduction hole  254  of the inlet-side end cap electrode  252  and the ion ejection hole  255  of the outlet-side end cap electrode  253 . 
     To the ion trap  25  there is attached a gas supply unit  27  that supplies one or more inert gases (helium, nitrogen, argon, and the like) at a predetermined flow rate into the ion trap  25 . The gas supply unit  27  includes: a gas supply source  271  of a plurality of types gases that are selectively fed; a gas passage  272  connecting the gas supply source  271  and the ion trap  25 ; and a valve  273  provided on the gas passage  272 . 
     A vacuum evacuation mechanism  28  is connected to a chamber wall surface constituting the mass spectrometry chamber  20  at a position facing the ion trap  25  and the ion detector  26 . The vacuum evacuation mechanism  28  includes a turbo-molecular pump as a main pump, and a diaphragm pump as an auxiliary pump. In the vicinity of the ion detector  26  in the mass spectrometry chamber  20 , there is attached a vacuum gauge  29  for measuring a pressure in the mass spectrometry chamber  20 . 
     Next, a measurement flow using the mass spectrometer of the present embodiment will be described. 
     First, cause the valve moving mechanism  15  in the ionization chamber  10  to operate so as to close the opening  211  with the valve  14 . Next, open the ionization chamber  10 , cause the stage moving mechanism  13  to operate so as to move the sample stage  12  to the replacement position, and place sample plate  111  on the sample stage  12 . During the series of operations, an inside of the ionization chamber  10  is opened to the atmosphere. After that, close the ionization chamber  10 , cause the diaphragm pump to rough pump the ionization chamber  10 , and at the same time, cause the stage moving mechanism  13  to operate so as to move the sample stage  12  to the measurement position. 
     After the sample stage  12  is moved to the measurement position, when a user instructs to start measurement, the control unit  40  operates the above units as follows. 
     First, the valve moving mechanism  15  operates so as to cause the valve  14  to open the opening  211 . Subsequently, the diaphragm pump, which is the auxiliary pump of the vacuum evacuation mechanism  28 , operates to rough pump the inside of the mass spectrometry chamber  20 . In addition, the inside of the ionization chamber  10  is also rough pumped through the opening  211 . As a result, the mass spectrometry chamber  20  and the ionization chamber  10  are rough pumped to about 10 −1  to 10 −2  Pa. Then, the turbo-molecular pump, which is the main pump, operates to high vacuum pump the inside of the mass spectrometry chamber  20 . At this time, the inside of the ionization chamber  10  is also vacuum pumped through the opening  211 . Since the ionization chamber  10  is evacuated through the opening  211 , the degree of vacuum does not necessarily reach the same degree of vacuum as in the mass spectrometry chamber  20 . However, the degree of vacuum required to generate ions from the sample  11  in the ionization chamber  10  is about 10 −1  to 10 −2  Pa, and there is no particular problem even when the ionization chamber  10  is at about a degree of vacuum achieved by rough pumping. After that, the vacuum evacuation mechanism  28  continues vacuum pumping of the mass spectrometry chamber  20  until the measurement is completed. 
     After the pressure in the mass spectrometry chamber  20  becomes 10 −3  Pa or less, the laser light source  3  operate to apply laser light to a surface of the sample  11  on the sample stage  12  at the measurement position. The application of laser generates ions from the sample  11 . The ions generated from the sample  11  are drawn, through the opening  211 , into the mass spectrometry chamber  20  having a higher degree of vacuum than the ionization chamber  10 . The ions drawn into the mass spectrometry chamber  20  are converged by the first ion lens  22 , and a flight direction of the ions is deflected by the deflection unit  23 . The ions are further converged by the second ion lens  24 , and then enter the ion trap  25  through the ion introduction hole  254  of the inlet-side end cap electrode  252 . A previously determined radio-frequency voltage (or a voltage obtained by superposing a radio-frequency voltage and a direct-current voltage) is applied to each of the ring electrode  251 , the inlet-side end cap electrode  252 , and the outlet-side end cap electrode  253 , whereby ions having a predetermined mass-to-charge ratio (or mass-to-charge ratio range) are trapped in the ion trap  25 . 
     Helium gas is introduced into the ion trap  25  from the gas supply unit  27  simultaneously with the application of the laser light to the sample  11  or slightly later than) the application of the laser light to the sample  11 . The helium gas is used as a cooling gas. Due to collision between the ions and the helium gas, a kinetic energy of the ions trapped in the ion trap  25  decreases. Then, these ions are gradually cooled and converged in the vicinity of a center of the ion trap  25 . 
     The helium gas introduced into the ion trap  25  flows out from the openings of the insulating members  256  into the mass spectrometry chamber  20 . The degree of vacuum in the mass spectrometry chamber  20  therefore decreases temporarily. Therefore, the degree of vacuum in the mass spectrometry chamber  20  is waited to become more than or equal to that at the start of measurement (until the pressure becomes 10 −3  Pa or less). In the meantime, the ions cooled by the cooling gas are kept trapped inside the ion trap  25 . 
     After the pressure in the mass spectrometry chamber  20  become 10 −3  Pa or less, the applied voltages to the ring electrode  251 , the inlet-side end cap electrode  252 , and the outlet-side end cap electrode  253  are appropriately changed so as to change the mass-to-charge ratio (or mass-to-charge ratio range) of the ions trapped in the ion trap  25 , so that the ions having a specific mass-to-charge ratio (or mass-to-charge ratio range) are released from the ion trap  25  and are detected by the ion detector  26 . 
     The above description is about an example in which the ions generated from a sample are measured as they are, but it is possible to perform a tandem mass spectrometry (MS/MS) measurement or a multi stage mass spectrometry (MS n ) measurement in which the ions generated from a sample are cleaved and measured a plurality of times. In this case, after the ions are cooled with helium gas, precursor ions are selected by applying the radio-frequency voltages (or the voltage obtained by superposing a radio-frequency voltage and a direct-current voltage) that trap only the ions having a predetermined mass-to-charge ratio in the ion trap  25 , to the ring electrode  251 , the inlet-side end cap electrode  252 , and the outlet-side end cap electrode  253 . After that, a collision gas (for example, nitrogen gas or argon gas) is introduced into the ion trap  25  from the gas supply unit  27 . Further, the precursor ions trapped in the ion trap  25  are excited and cleaved by collision with the collision gas to generate product ions. 
     Then, it is waited that the cooling gas and the collision gas having flown out to the mass spectrometry chamber  20  through the openings of the insulating members  256  are evacuated by the vacuum evacuation mechanism  28  and that the degree of vacuum in the mass spectrometry chamber  20  becomes 10 −3  Pa or higher degree of vacuum, which is equivalent to the degree of vacuum at the start of measurement. In the meantime, the product ions are trapped inside the ion trap  25 . 
     After the pressure in the mass spectrometry chamber  20  has becomes 10 −3  Pa or less, the voltages applied to the ring electrode  251 , the inlet-side end cap electrode  252 , and the outlet-side end cap electrode  253  are appropriately changed, and the ions trapped in the ion trap  25  are released and detected by the ion detector  26 . 
     As described above, in the mass spectrometer  1  of the present embodiment, only a single vacuum evacuation mechanism  28  evacuates each of the ionization chamber  10  and the mass spectrometry chamber  20  to a required degree of vacuum. Therefore, it is possible to manufacture a mass spectrometer at a smaller size and at a lower cost as compared with a conventional mass spectrometer using a vacuum evacuation mechanism for each of spaces having different required degrees of vacuum. 
     As described above, a high degree of vacuum is required for the mass spectrometry chamber  20 , and once the mass spectrometry chamber  20  is opened to the atmosphere, it takes time to vacuum pump. Therefore, as described in the above embodiment, in the case where the configuration includes the load lock mechanism that opens the ionization chamber  10  to the atmosphere at the time of setting the sample, only the ionization chamber  20  is opened to the atmosphere to set the sample in a state where the opening  211  of the mass spectrometry chamber  20  is closed by the valve  14  and the inside of the mass spectrometry chamber  10  is maintained in vacuum. 
     When the ionization chamber  10  is opened to the atmosphere, water vapor contained in the atmosphere also enters the ionization chamber  10  and adheres to a wall surface and the like. Once water molecules adhere to the wall surface and the like in the ionization chamber  10 , the water molecules are not easily separated but gradually separated. Until the water molecules are completely separated from the wall surface and the like, it is difficult to make the degree of vacuum higher than a certain constant pressure even if the vacuum pumping is continued. Since the degree of vacuum required for the ionization chamber  10  is not so high, the water molecules are not a problem. However, when water molecules separated from the wall surface and the like of the ionization chamber  10  enter the inside of the mass spectrometry chamber  20  through the opening  211 , the degree of vacuum in the mass spectrometry chamber  20  becomes deteriorated. The pressure of the mass spectrometry chamber  20  is required to be 10 −3  Pa or less, and if the opening  211  has too large a diameter, the amount of water molecules entering the mass spectrometry chamber  20  from the ionization chamber  10  is larger than the amount of water molecules exhausted by the vacuum evacuation mechanism  28  (in particular, turbo-molecular pump), so that the required degree of vacuum cannot be obtained. Therefore, it is necessary to determine the diameter of the opening  211  so that the inflow speed (inflow amount) of water molecules from the ionization chamber  10  to the mass spectrometry chamber  20  becomes equal to or less than the evacuation speed (exhaust amount) by the turbo-molecular pump. An example of how to determine the diameter of the opening  211  will be described below. 
     Suppose that the pressure in the mass spectrometry chamber  20  is P 1  (Pa), the pressure in the ionization chamber  10  is P 2  (Pa), and the diameter of the opening  211  is D (m). Since a molecular velocity (flow velocity) at room temperature (20° C.) of water molecules (H 2 O) flying in a vacuum atmosphere like in the ionization chamber  10  and the mass spectrometry chamber  20  in the present embodiment is about 600 m/s, a model is constructed in which water molecules enter the mass spectrometry chamber  20  from the ionization chamber  10  through the opening  211  having an area of π/4×D 2  (m 2 ) at a velocity of 600 (m/s). 
     An intrusion volume (a volume, in the ionization chamber  10 , of water molecules entering the mass spectrometry chamber  20  per second) V 2  (m 3 /s) of water molecules into the mass spectrometry chamber  20  is π/4×D 2  (m 2 )×600 (m/s)=150πD 2  (m 3 /s). When ambient temperature of the mass spectrometer  1  is constant, the variables R and T in the gas state equation PV=nRT are constant. Since the number n of molecules of water molecules is unchanged between at the time of passing through the opening  211  and after entering the mass spectrometry chamber  20 , the value on the right side is constant, and therefore the PV on the left side is also constant. 
     The value of P 2 V 2  of water molecules moving from the ionization chamber  10  to the mass spectrometry chamber  20  is P 2 V 2 =P 2×150 πD 2 . In addition, since the evacuation speed V 1  of a general turbo-molecular pump is about 30 L/s=30×10 −3  (m 3 /s) or more, the value of P 1 V 1  of the water molecules exhausted from the mass spectrometry chamber  20  by the turbo-molecular pump is P 1 V 1 =P 1 ×30×10 −3  (m 3 /s)=30×10 −3 ×P 1 . 
     Here, in the case of P 2 V 2 &gt;P 1 V 1 , the amount of water molecules entering the mass spectrometry chamber  20  from the ionization chamber  10  is larger than the amount of water molecules exhausted from the mass spectrometry chamber  20 , so that the degree of vacuum in the mass spectrometry chamber  20  becomes deteriorated. Therefore, it is necessary to determine the diameter D of the opening so as to satisfy a relationship P 2 V 2 ≤P 1 V 1 . That is, from a conditional expression P 2 ×150πD 2 ≤30×10 −3 ×P 1 , following Mathematical Expression 1 is obtained. 
     
       
         
           
             
               
                 
                   D 
                   ≦ 
                   
                     
                       
                         
                           10 
                           
                             - 
                             3 
                           
                         
                         
                           5 
                           ⁢ 
                           π 
                         
                       
                       × 
                       
                         
                           P 
                           1 
                         
                         
                           P 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Therefore, by substituting, on the basis of the configuration of the mass spectrometer actually used for measurement, an assumed pressure of the ionization chamber  10  and a pressure required for the mass spectrometry chamber  20  into above Mathematical Expression 1, the diameter D of the opening suitable for the configuration of the mass spectrometer can be determined. 
     The inventors of the present invention set various diameters of the opening  211  and measured the pressure in the mass spectrometry chamber  20  with respect to the various diameters while exhausting the mass spectrometry chamber  20  with the turbo-molecular pump, and found that when the diameter of the opening  211  is 6.0 mm or less, the required degree of vacuum (pressure of 10 −3  Pa or less) can be obtained. 
     When the above model and the actual measurement results are summarized, it can be said that when the diameter of the opening  211  is 6.0 mm or less in the mass spectrometer having a general configuration, there is no problem in practical use (in other words, the degree of vacuum in the mass spectrometry chamber  20  does not become worse than 10 −3  Pa) and that the mass spectrometry chamber  20  can be maintained at ultra-high vacuum also by setting the diameter of the opening  211  to be less than or equal to the value obtained by substituting the pressure and the like assumed in the mass spectrometer to be actually used into above Mathematical Expression 1. 
     The above embodiment is merely an example and can be appropriately modified without departing from the spirit of the present invention. 
     The above embodiment is a MALDI-IT type mass spectrometer, but a mass spectrometer including an ionization source other than the MALDI or a mass separation unit other than the IT can have the same configuration as described above. In addition, not only the mass spectrometer but also an ion mobility analyzer and the like can adopt the same configuration as described above. 
     Various embodiments of the present invention have been described in detail with reference to the drawing, and lastly, various aspects of the present invention will be described. 
     An ion analyzer of a first aspect of the present invention includes: 
     an ionization chamber; 
     an analysis chamber separated from the ionization chamber by a partition wall in which an opening is formed; 
     an ionization unit configured to generate ions from a sample in the ionization chamber; 
     an ion transport unit provided in the analysis chamber and configured to transport the ions generated in the ionization unit; 
     an ion trapping unit provided in the analysis chamber and configured to trap the ions transported by the ion transport unit; 
     an ion detection unit provided in the analysis chamber and configured to detect the ions released from the ion trapping unit; and 
     a single evacuation mechanism connected only to the analysis chamber and configured to evacuate the analysis chamber to a pressure of 10 −3  Pa or less. 
     In the ion analyzer of the first aspect of the present invention, the analysis chamber is directly exhausted by a single evacuation mechanism that is connected only to the analysis chamber and is configured to evacuate the space to which the evacuation mechanism is connected to the pressure of 10 −3  Pa or less, and at the same time, to also evacuate the ionization chamber indirectly through the opening. After the analysis chamber and the ionization chamber are each evacuated to a predetermined degree of vacuum, the ionization unit is operated to generate ions from a sample. At the same time as or slightly later than the generation of ions from the sample, a predetermined gas (cooling gas) is introduced into the ion trapping unit. The ions introduced into the ion trapping unit are cooled by collision with the cooling gas, and are trapped near the center of the ion trapping unit. The cooling gas introduced into the ion trapping unit gradually flows out to the analysis chamber, so that the degree of vacuum in the analysis chamber decreases. Therefore, the ions are trapped in the ion trapping unit until the gas is exhausted by an evacuation mechanism and the degree of vacuum in the mass spectrometry chamber reaches a predetermined degree of vacuum. Then, after the degree of vacuum in the mass spectrometry chamber reaches the predetermined degree of vacuum, the ions are sequentially released from the ion trapping unit and are detected by the ion detection unit. 
     The above single evacuation mechanism includes, for example, a main pump such as a turbo-molecular pump for high vacuum pumping and an auxiliary pump such as a diaphragm pump for rough pumping. The main pump that performs high vacuum pumping is generally large and expensive. Since the ion analyzer according to the present invention includes only a single evacuation mechanism connected only to the analysis chamber, it is possible to achieve downsizing and cost reduction compared with a conventional ion analyzer including a plurality of such evacuation mechanisms. 
     An ion analyzer of a second aspect includes, in the ion analyzer of the first aspect, a load lock mechanism that is provided in the ionization chamber and has a valve configured to open and close the opening. 
     In the ion analyzer of the second aspect, it is possible to replace the sample without releasing the mass spectrometry chamber to the atmosphere, by causing the valve to close the opening. 
     Regarding an ion analyzer of a third aspect of the present invention, in the ion analyzer of the above first or second aspect, the opening has a diameter of 6.0 mm or less. 
     In the ion analyzer of the third aspect, since the diameter of the opening is 6.0 mm or less, the amount of water molecules that can enter the mass spectrometry chamber from the ionization chamber is suppressed, and the mass spectrometry chamber can therefore be reliably maintained at ultrahigh vacuum. Although the opening is assumed to be circular in this aspect, the shape of the opening is not limited to a circular shape, and it is possible to use an opening having an appropriate shape having an area equal to or less than the area of a circular shape having a diameter of 6.0 mm. 
     An ion analyzer of a fourth aspect of the present invention further includes, in the ion analyzer of any one of the first to third aspects: 
     a gas introduction unit configured to introduce a predetermined gas into the ion trapping unit; and 
     a control unit configured: to cause the ionization unit to operate and generate the ions from the sample, and in addition, to cause the gas introduction unit to operate; to trap the ions in the ion trapping unit until a degree of vacuum in the analysis chamber reaches a predetermined degree of vacuum; and then to release the ions from the ion trapping unit to detect the ions by the ion detection unit. 
     By using the ion analyzer of the fourth aspect, it is possible to analyze ions, without bothering an analyst, at an appropriate timing when the ion analysis chamber reaches a predetermined degree of vacuum. 
     Regarding an ion analyzer of a fifth aspect of the present invention, in the ion analyzer of any one of the first to fourth aspects, the ion trapping unit is an ion trap. 
     In the ion analyzer of the fifth aspect, since the ion trap can function as both the ion trapping unit and the mass separation unit, the device can be downsized. 
     REFERENCE SIGNS LIST 
     
         
           1  . . . Mass Spectrometer 
           3  . . . Laser Light Source 
           4  . . . Half Mirror 
           5  . . . Camera 
           10  . . . Ionization Chamber 
           11  . . . Sample 
           111  . . . Sample Plate 
           12  . . . Sample Stage 
           13  . . . Stage Moving Mechanism 
           14  . . . Valve 
           15  . . . Valve Moving Mechanism 
           20  . . . Mass Spectrometry Chamber 
           21  . . . Partition Wall 
           211  . . . Opening 
           22  . . . First Ion Lens 
           23  . . . Deflection Unit 
           231  to  234  . . . Rod Electrode 
           24  . . . Second Ion Lens 
           25  . . . Ion Trap 
           251  . . . Ring Electrode 
           252  . . . Inlet-side End Cap Electrode 
           253  . . . Outlet-side End Cap Electrode 
           254  . . . Ion Introduction Hole 
           255  . . . Ion Ejection Hole 
           256  . . . Insulating Member 
           26  . . . Ion Detector 
           27  . . . Gas Supply Unit 
           271  . . . Gas Supply Source 
           272  . . . Gas Passage 
           273  . . . Valve 
           28  . . . Vacuum Evacuation Mechanism 
           29  . . . Vacuum Gauge 
           30  . . . Voltage Applying Unit 
           40  . . . Control Unit