Patent Publication Number: US-2023136178-A1

Title: Mass Spectrometer

Description:
TECHNICAL FIELD 
     The present invention relates to a mass spectrometer. 
     BACKGROUND ART 
     A mass spectrometer is a device ionizing a sample and analyzing ions according to a mass-to-charge ratio. In general, a mass spectrometer includes an ion source ionizing a sample, a mass spectrometry unit separating the ions according to a mass-to-charge ratio, and a detection unit detecting a quantity of the ions having passed through the mass spectrometry unit. 
     As a technology on an ion guide separating ions and an air flow, there is the description of U.S. Pat. No. 8,581,182 (Patent Literature 1). In this gazette, there is described an ion guide separating ions and an air flow by that the ions are transferred from the first ion guide to the second ion guide by overriding a pseudopotential barrier between the first ion guide and the second ion guide by DC potential. 
     Also, there is the pamphlet of WO 2016/135810 (Patent Literature 2). In this gazette, there is described an ion guide in which two rod electrode sets forms a single multipole ion guide in a region where the two rod electrode sets overlap with each other in the longitudinal direction, ions are transferred to the first rod electrode set to the second rod electrode set by a DC potential difference between the first rod electrode set and the second rod electrode set in the overlapping region, and thereby ions and an air flow are separated from each other. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Description of U.S. Pat. No. 8,581,182 
     [Patent Literature 2] Pamphlet of WO 2016/135810 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, according to the prior arts, there was a problem that there was a limit in ion permeation efficiency. 
     As one of concrete configuration examples in prior arts, in Patent Literature 1, there is described an example of an aspect where an exhaust port is disposed on the center axis of the first ion guide, and an air flow having passed through the first ion guide is discharged. However, since the position of the exhaust port is limited, the diameter of the exhaust port is limited. When the diameter of the exhaust port is small, the discharge efficiency lowers, and the degree of vacuum of a space where the ion guide is disposed lowers. When the degree of vacuum is low, the mean free path of ions becomes small, and the ion permeation efficiency lowers. 
     Further, although another concrete configuration example in prior arts is described in Patent Literature 2, there is no description on control of an air flow after ions and the air flow are separated from each other in Patent Literature 2. According to the configuration of Patent Literature 2, there is a problem that a turbulent flow occurs by collision of an air flow on a wall surface of the vacuum chamber where the ion guide is disposed, ions and the sir flow are mixed, and thereby the ion permeation efficiency lowers. 
     The present invention has been achieved to solve such problem, and there is provided a mass spectrometer for higher ion permeation efficiency. 
     Solution to Problem 
     In an example of a mass spectrometer according to the present invention, an air flow including ions is separated into an air flow and an ion flow by an ion guide in the first vacuum chamber, and the first vacuum chamber includes a straightening member reducing mixing of the air flow and the ion flow having been separated from each other. 
     The present specification includes the content of disclosure of Japanese Patent Application No. 2020-038168 that becomes a basis of priority of the present application. 
     Advantageous Effects of Invention 
     According to a mass spectrometer according to the present invention, the ion permeation efficiency is improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a configuration example of a mass spectrometer according to Example 1 of the present invention. 
         FIG.  2    is a configuration example of an ion guide to separate an ion flow and an air flow. 
         FIG.  3    is a view showing pseudopotential of an ion guide. 
         FIG.  4    is a view showing DC potential in a region  2  of an ion guide. 
         FIG.  5    is a view showing synthetic potential of pseudopotential and DC potential in a region  2  of an ion guide. 
         FIG.  6    is a view showing a situation of an ion flow and an air flow passing through an ion guide not having a current plate as a comparative example. 
         FIG.  7    is a view showing a situation of an ion flow and an air flow incident on a first vacuum chamber. 
         FIG.  8    is a view showing a situation of an ion flow and an air flow passing through an ion guide having a current plate. 
         FIG.  9    is a configuration example of a current plate according to Example 2 of the present invention. 
         FIG.  10    is a configuration example of a current plate according to Example 3 of the present invention. 
         FIG.  11    is a configuration example of a current plate according to Example 4 of the present invention. 
         FIG.  12    is a configuration example of an ion guide to separate an ion flow and an air flow according to Example 5 of the present invention. 
         FIG.  13    is a configuration example of an ion guide to separate an ion flow and an air flow according to Example 6 of the present invention. 
         FIG.  14    is a configuration example of an ion guide to separate an ion flow and an air flow according to Example 7 of the present invention. 
         FIG.  15    is a configuration example of an ion guide to separate an ion flow and an air flow according to Example 8 of the present invention. 
         FIG.  16    is a configuration example of an ion guide to separate an ion flow and an air flow according to Example 9 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be hereinafter explained using the drawings. 
     Example 1 
     In the present example, a comparatively simple embodiment will be explained. 
       FIG.  1    is a view showing a configuration example of a mass spectrometer according to the present example. The mass spectrometer includes following configurations.
         An ion source  101  ionizing a measurement sample   A pore  102  where ions generated in the ion source  101  pass through   An ion guide  103  where the ions having passed through the pore  102  pass through   A pore  104  where the ions having passed through the ion guide  103  pass through   A mass spectrometry unit  105  where the ions having passed through the pore  104  are analyzed   A detector  106  (detection unit) where the ions having been analyzed by the mass spectrometry unit  105  are detected   A first vacuum chamber  107  where the ion guide  103  is disposed, and the pore  102  and the pore  104  are provided   A second vacuum chamber  108  where the mass spectrometry unit  105  is disposed, and the pore  104  is provided   A vacuum pump  109  discharging the air in the first vacuum chamber  107     An exhaust port  111  connecting the first vacuum chamber  107  and the vacuum pump  109  to each other   A vacuum pump  110  discharging the air in the second vacuum chamber  108     An exhaust port  112  connecting the second vacuum chamber  108  and the vacuum pump  110  to each other   A current plate  113  (straightening member) disposed in the first vacuum chamber  107         

     In the ion source  101 , a measurement sample is ionized by a method such as an electrospray ionization method, an atmospheric pressure chemical ionization method, an atmospheric pressure photoionization method, and a matrix-assisted laser desorption ionization method. 
     The ions generated in the ion source  101  enter the first vacuum chamber  107  through the pore  102 . However, the concrete construction of the pore  102  can be designed optionally, may be one where a small hole is bored in a thin wall surface, and may be one like a fine tube where a small hole is bored in a thick wall surface for example. 
     It is also possible that an electrode and a vacuum chamber where ions pass though are provided before the first vacuum chamber  107 . 
     Neutral molecules, the air, minute water drops and the like also enter the first vacuum chamber  107  the first vacuum chamber  107  through the pore  102  along with the ions. For the purpose of discrimination. A flow of ions reaching the pore  104  is defined to be an ion flow  703 , and a flow of other than that is defined to be an air flow  704 . In the air flow  704 , not only the neutral molecules, the air, and the minute water drops described above but also a part of ions which cannot reach the pore  104  are included. 
     In the first vacuum chamber  107 , there is disposed the ion guide  103  having a function of separating the ion flow  703  and the air flow  704  from each other. Also, the first vacuum chamber  107  includes the current plate  113 . Actions of a mechanism and the current plate  113  will be described below, the mechanism being for separating the ion flow  703  and the air flow  704  from each other. The ion flow  703  separated from the air flow  704  by the ion guide  103  reaches the pore  104 , and enters the second vacuum chamber  108 . 
     The ion flow  703  having reached the pore  104  enters the second vacuum chamber  108 . The second vacuum chamber  108  includes the mass spectrometry unit  105 . In the mass spectrometry unit  105 , the ions are separated according to the mass-to-charge ratio by an electrical and/or magnetic action. For example, there are a magnetic field type where the trajectory of the ion is bent by a magnetic field, a quadrupole type where ions are separated by applying a radio frequency voltage (RF voltage) or a direct current voltage (DC voltage) to an electrode whose section is a bipolar plane, a flying time type where ions are detected by difference of the flying time, and so on. 
     The ions having been analyzed by the mass spectrometry unit  105  are detected by the detector  106 . In the detector  106 , the ions are detected by converting an ion signal into an electric signal utilizing a photoelectron multiplier tube and an electron multiplier tube for example. 
     Thus, the mass spectrometer causes the ions generated by the ion source  101  to pass through the first vacuum chamber  107  and the second vacuum chamber  108 , and transfers the same toward the detector  106 . 
     The air in the first vacuum chamber  107  is discharged by the vacuum pump  109 , and the air in the second vacuum chamber  108  is discharged by the vacuum pump  110 . Although the first vacuum chamber  107  and the second vacuum chamber  108  communicate with each other by the pore  104 , since the diameter of the pore  104  is limited, the first vacuum chamber  107  and the second vacuum chamber  108  are different from each other in terms of the pressure inside the chamber. 
     The first vacuum chamber  107  is close to the ion source  101  which is under the atmospheric pressure, and the pressure within the first vacuum chamber  107  is higher than the pressure within the second vacuum chamber  108 . The vacuum pump  109  and the vacuum pump  110  may be of the same type. Also, the vacuum pump  109  and the vacuum pump  110  may be a single pump respectively, and may be a system obtained by combining plural kinds of pumps such as combined usage of a turbo-molecular pump and a dry pump for example. 
     The first vacuum chamber  107  and the vacuum pump  109  are connected to each other by the exhaust port  111 , and the second vacuum chamber  108  and the vacuum pump  110  are connected to each other by the exhaust port  112 . With respect to the exhaust port  111  and the exhaust port  112 , as the diameter is larger, as there are less number of curves, and as the length to the vacuum pump  109  or the vacuum pump  110  is shorter, the exhaust efficiency is higher, and the pressure of the first vacuum chamber  107  and the second vacuum chamber  108  becomes lower. When the pressure of the first vacuum chamber  107  and the second vacuum chamber  108  is low, since the mean free path of ions becomes large, the permeation efficiency of the ion flow  703  becomes high. 
     A schematic drawing of the ion guide  103  is shown in  FIG.  2   . The ion guide  103  includes at least two electrode sets, and has a function of separating an air flow including ions introduced into the first vacuum chamber  107  from the ion source  101  into the ion flow  703  and the air flow  704 . 
     Although a configuration example of the ion guide  103  will be hereinafter explained, the configuration of the ion guide  103  is not limited to it and can be designed or changed optionally based on a known technology. For example, a part of the configurations described in Patent Literature 1 or 2 may be applied. Also, with respect to a portion where description is omitted on the detail of the ion guide  103 , description on Patent Literature 1 or 2 or other known technologies can be incorporated herein. 
     As the two electrode sets, in the X-axis direction, a first electrode set  201  is disposed on a side the ion flow  703  and the air flow  704  enter, and a second electrode set  202  is disposed on a side the ion flow  703  exits. 
     In  FIG.  2    and other drawings, explanation will be made using an orthogonal 3-dimensional coordinate system including the X-coordinate, the Y-coordinate, and the Z-coordinate. The X-axis direction is the longitudinal direction of the first electrode set  201  and the second electrode set  202 . Also, the X-axis direction corresponds to a direction along which the ions are transferred generally in each electrode set of the ion guide. The Z-axis direction corresponds to a direction along which the ion flow  703  is transferred from the first electrode set  201  to the second electrode set  202 . 
     In  FIG.  2   , with respect to the ion guide  103 , three regions divided in the X-axis direction are illustrated. The ion guide  103  includes a region  1 , a region  2 , and a region  3 . The region  2  is a region where the first electrode set  201  and the second electrode set  202  overlap with each other in the X-axis direction. The regions  1  and  3  are regions where the first electrode set  201  and the second electrode set  202  do not overlap with each other in the X-axis direction. 
       FIG.  2    is a configuration example of the ion guide  103  that can separate the ion flow  703  and the air flow  704  from each other.  FIG.  2 A  is an X-Z plan view.  FIG.  2 B  is a cross-sectional view by a plane perpendicular to the X-axis at positions X1, X2, and X3 in the X-axis direction in  FIG.  2 A .  FIG.  2 C  is a cross-sectional view by a plane perpendicular to the Z-axis at positions Z1 and Z2 in the Z-axis direction in  FIG.  2 A . 
     The ion guide  103  shown in  FIG.  2    includes the first electrode set  201  and the second electrode set  202 , and is configured of a multipole including rod electrodes. The first electrode set  201  forms a quadrupole configured of rod electrodes in the region  1 , and the second electrode set  202  forms a quadrupole configured of rod electrodes in the region  3 . These rod electrodes are disposed at positions in the vicinity of apexes of a generally square in a Y-Z plane for example. 
     In an example of  FIG.  2   , in the region  2 , a single octopole ion guide is formed so that four pieces in total of rods  201   a  and  201   d  adjacent to the second electrode set  202  in the first electrode set  201  and rods  202   b  and  202   c  adjacent to the first electrode set  201  in the second electrode set  202  are bent in the Y-axis direction so as to spread generally symmetrically with respect to the position Y1 in the Y-axis direction. Rod electrodes of the octopole are disposed at positions in the vicinity of apexes of a generally octagon in a Y-Z plane for example. Rods other than them namely rods  201   b ,  201   c ,  202   a , and  202   d  are formed into a linear shape for example. 
     Also, the configuration of the rod electrode in the ion guide is not limited to it but can be designed optionally, and can be formed of even number of piece of the rod electrodes in each of the regions  1  to  3 . 
     To the first electrode set  201  and the second electrode set  202 , an RF voltage and an offset DC voltage are applied, and thereby the ion flow  703  and the air flow  704  are separated from each other. 
     Signs “+” and “−” shown in  FIG.  2 B  show the phase of the RF voltage applied to each rod electrode. To a rod having the same sign, an RF voltage of the same frequency, the same amplitude, and the same phase is applied. To a rod having a different sign, an RF voltage of the same frequency, the same amplitude, and an opposite phase is applied. 
     In an example of  FIG.  2 B , since the rod  201   d  and the rod  202   c  become rod electrodes adjacent to each other in the region  2 , an RF voltage having a phase opposite to each other is applied. In a similar manner, since the rod  201   a  and the rod  202   b  become rod electrodes adjacent to each other in the region  2 , an RF voltage having a phase opposite to each other is applied. 
       FIG.  3    is a view showing pseudopotential formed by application of an optional RF voltage. The pseudopotential means potential imparting a force to ions on hourly average basis when an electric field fluctuating at a speed with which motion of the ions cannot follow sufficiently is applied. 
       FIG.  3 A  shows the height of the pseudopotential at a position (X1, Y1).  FIG.  3 B  shows the height of the pseudopotential at a position (X2, Y1) (also, in the present example, the electrode configuration is as per  FIG.  2   , and the height of the pseudopotential is shown by a solid line).  FIG.  3 C  shows the height of the pseudopotential at a position (X3, Y1). 
     In the ion guide  103  having the configuration of  FIG.  2   , a local minimum point of the pseudopotential exists on the Y-Z plane, and ions are basically converged onto this local minimum point, and proceed within the electrode. The local minimum point of the pseudopotential is hereinafter defined to be the center of the electrode. The center of the electrode is defined as a straight line extending in the X-axis direction for example, and configures the axis (the center axis). 
     In the region  1 , when ions within a specific mass-to-charge ratio range enter a portion where the first electrode set  201  is disposed, the ions are converged and proceed toward the center of the first electrode set  201 . The mass-to-charge ratio range where convergence takes place is determined depending on the frequency and the amplitude of the RF voltage to be applied. Therefore, it is required to adjust the frequency and the amplitude of the RF voltage by the mass-to-charge ratio of the ions which are intended to reach the pore  104 . 
     In the region  2 , there is no barrier of the pseudopotential between the first electrode set  201  and the second electrode set  202 . That is to say, the ion guide  103  forms a single ion guide in the region  2 . Therefore, the ions can go back and forth freely between the first electrode set  201  and the second electrode set  202 . Also, since it is not required to impart the ions with strong energy to override a potential barrier, the quantity of ions passing through the center axis of the second electrode set  202  and flying out to the opposite side can be reduced. 
     In the region  3 , similarly to the region  1 , when ions within a specific mass-to-charge ratio range enter a portion where the second electrode set  202  is disposed, the ions proceed while being converged toward the center of the second electrode set  202 . 
     Also, to the first electrode set  201  and the second electrode set  202 , an offset DC voltage of electric potential different from each other is applied. At this time, when the positive ions are intended to pass to the pore  104 , a voltage lower than that of the second electrode set  202  is applied to the second electrode set  202 , whereas when the negative ions are intended to pass to the pore  104 , a voltage higher than that of the second electrode set  202  is applied to the second electrode set  202 . 
     Further, from now on, although there is a case of giving explanation where the magnitude relation ship of the electric potential is limited to a case of separating the positive ions, the explanation is applicable to a case of separating the negative ions if the magnitude relation ship of the electric potential is reversed. 
       FIG.  4    shows the height of DC potential at a position (X2, Y1) formed by application of the offset DC voltage. The potential becomes low as the Z-coordinate is larger, namely the potential becomes low toward the side of the second electrode set  202 . The off set DC voltage applied to each rod can be designed optionally with a provision that the DC potential curve becomes monotonic decreasing. 
     When the off set DC voltage applied to each electrode is changed and the DC potential gradient is changed, the permeation efficiency of the ion flow  703  changes. This occurs by a cause that, for example, when the DC potential gradient is large, the kinetic energy of the ions becomes large, and the convergence efficiency of the ion flow  703  drops in the second electrode set  202 . Therefore, in a similar manner to the RF voltage, it is required to adjust the DC potential gradient according to the mass-to-charge ratio of the ions which are intended to permeate through to the pore  104 . 
       FIG.  5    shows the height of the potential (synthetic potential) obtained by synthesizing the pseudopotential and the DC potential at a position (X2, Y1). By combination of the RF voltage and the off set DC voltage, the ions move irreversibly from the center of the first electrode set  201  toward the center of the second electrode set  202 . Thus, the ion guide  103  forms electric potential that causes the ions having entered the first electrode set  201  to move from the first electrode set  201  to the second electrode set  202  in the region  2 . 
     When an ion incidence point of the first electrode set  201  is located within a range of several millimeters from the pore  102 , the convergence efficiency of the ion becomes high which is preferable. Here, “ion incidence point” means for example the center of the first electrode set  201  at the incident side end in the X-axis direction of the first electrode set  201 . The distance (distance in the three-dimensional space) of the ion incidence point from the pore  102  can be made 5 mm, 1 cm, 2 cm, and the like for example. 
     Also, it is preferable when the center of the second electrode set  202  is disposed at a position getting into alignment (so as to be generally coaxial for example) with the pore  104  at least at an exit side end in the X-axis direction of the second electrode set  202 . Also, when an ion exit point of the second electrode set  202  is located within a range of several millimeters from the pore  104 , the convergence efficiency of the ion becomes high which is preferable. Here, “ion exit point” means for example the center of the second electrode set  202  at the exit side end in the X-axis direction of the second electrode set  202 . The distance (distance in the three-dimensional space) of the ion exit point from the pore  104  can be made 5 mm, 1 cm, 2 cm, and the like for example. 
     Here, as a comparative example for explaining an action of the present invention, movement of the ion flow  703  and the air flow  704  within the first vacuum chamber  107  when the ion guide  103  of  FIG.  2    is used is shown in  FIG.  6   . Also, a detailed situation of the vicinity of the pore  102  is shown in  FIG.  7    (this drawing is applicable to the example 1 of the present invention and to a comparative example in a similar manner). 
     Since there is a pressure difference before and after the pore  102 , a barrel shock  701  and a Mach disk  702  are formed. By this impact, immediately after passing through the pore  102 , the ion flow  703  and the air flow  704  proceed within the first vacuum chamber  107  with a diameter generally the same as that of the Mach disk  702 . The diameter of the Mach disk  702  is determined depending on the diameter of the pore  102  and the pressure before and after the pore  102 . 
     The ion flow  703  having diffused at the time of entering the pore  102  is converged to the center of the first electrode set  201  by the action of the RF voltage described above, and proceeds within the first electrode set  201 . When the ion flow  703  reaches the region  2 , the ion flow  703  moves from the vicinity of the center of the first electrode set  201  to the center of the second electrode set  202  by the action of the offset DC voltage described above, and proceeds straight toward the pore  104  near the center of the second electrode set  202 . 
     On the other hand, since a substance such as the neutral molecule hardly receiving an electrical action gets mixed much into the air flow  704 , the air flow  704  passes the vicinity of the first electrode set  201  with a diameter generally the same as that of the Mach disk  702 . However, different from the ion flow  703 , the air flow  704  hardly moves toward the second electrode set  202 . By such mechanism, the ion flow  703  and the air flow  704  are separated from each other in the ion guide  103 . 
     In the comparative example of  FIG.  6   , since there does not exist the current plate  113  according to the example 1, the air flow  704  collides on a wall surface partitioning the first vacuum chamber  107  and the second vacuum chamber  108 , and a turbulent flow of the air flow  704  is generated. Since this turbulent flow is mixed with the ion flow  703  and the mean free path of the ion becomes small, the permeation efficiency of the pore  104  of the ion flow  703  drops, and the ion signal becomes unstable. 
     An example of an aspect of the current plate  113  according to the example 1 of the present invention and the situation of the movement of the ion flow  703  and the air flow  704  when the current plate  113  is utilized are shown in  FIG.  8   .  FIG.  8 A  is an X-Z plan view, and  FIG.  8 B  is a Y-Z plan view when the ion guide  103  is viewed from the pore  104 . 
     Although the shape of the current plate  113  is optional, it is a rectangular parallelepiped according to the present example, and is of a plate-like shape where the length in the X-axis direction (thickness) is small and the area of the X-Y plane is large. With such shape, manufacturing is easy. The thickness of the current plate  113  can be made 3 mm for example. The length in the X-axis direction of the current plate  113  can be made for example a length from a point where the ion flow  703  and the air flow  704  are separated from each other in the region  2  to the pore  104 . The point where the ion flow  703  and the air flow  704  are separated from each other in the region  2  can be decided for example by a person with an ordinary skill in the art by an experiment and the like. 
     As another example, the length in the X-axis direction of the current plate  113  can be made such length that the current plate  113  does not cover the region  2  but covers only the region  3 . Also, the entirety of the current plate  113  does not have to be of a flat surface shape, and a part or the entirety of the current plate  113  may be curved. 
     Also, in an example of  FIG.  8   , the current plate  113  is in contact with a wall surface of the exit side end of the first vacuum chamber  107 . Although such configuration is preferable in terms that the separation efficiency of the ion flow  703  and the air flow  704  becomes high, a configuration where the current plate  113  is not in contact with a wall surface is also possible. 
     Although the length in the Y-axis direction of the current plate  113  can be designed appropriately by a person with an ordinary skill in the art, it is the same or generally the same as the diameter of the quadrupole of the second electrode set  202  in the example of  FIG.  8   . As a modification, the length in the Y-axis direction of the current plate  113  may be made to be the same length as the diameter of the octopole formed in the region  2 , and may be made a length longer than that. 
     In order to prevent electric discharge from each electrode of the ion guide  103 , it is preferable that the current plate  113  is configured of an insulating material. For example, a resin material such as PEEK and a ceramic material such as alumina can be used. 
     At least a part of the current plate  113  is disposed between the center axis of the first electrode set  201  and the center axis of the second electrode set  202  in the Z-coordinate (so as to become parallel to each center axis for example). Thus, the ion flow  703  and the air flow  704  can be separated from each other efficiently. 
     In the current plate  113 , a plane having the largest area may be disposed to become parallel to the X-Y plane. The position of the current plate  113  in the Z-axis direction is preferable to be close to the second electrode set  202  in terms that the separation efficiency of the ion flow  703  and the air flow  704  becomes higher, and the current plate  113  may be configured to be in contact with the second electrode set  202  as shown in  FIG.  8    for example. 
     In the X-axis direction, the current plate  113  can be disposed at various positions according to the length of the current plate  113 . For example, in the example of  FIG.  8   , in a region after the ion flow  703  and the air flow  704  are separated from each other, the current plate  113  is disposed to be along the second electrode set  202 . Alternatively, for example, in a region after the ion flow  703  and the air flow  704  are separated from each other, the current plate  113  may be disposed to cover a range up to the pore  104 . In this case, the current plate  113  may be in contact with a wall surface where the pore  104  is formed (namely a wall surface partitioning the first vacuum chamber  107  and the second vacuum chamber  108  (shown in  FIG.  8   ), and may not. 
     In the Y-axis direction, the current plate  113  is disposed to become symmetric with respect to a position Y1 in the Y-axis direction in an example of  FIG.  8 B . 
     The current plate  113  reduces mixing of the air flow  704  and the ion flow  703  having been separated. For example, when the current plate  113  is disposed as  FIG.  8   , even when the air flow  704  may collide on a wall surface partitioning the first vacuum chamber  107  and the second vacuum chamber  108 , mixing with the ion flow  703  can be reduced. Therefore, the mean free path of the ion flow  703  becomes large, and efficiency of permeation of the ion flow  703  through the pore  104  becomes high. Also, the ion signal becomes more stable. 
     Further, when the exhaust port  111  is disposed to be on the first electrode set  201  side with respect to the second electrode set  202  in a position in the Z-axis direction, the air flow  704  can be removed more efficiently, and an effect secured becomes large. However, the position of the exhaust port  111  is not required to be disposed strictly, and therefore can be designed freely. 
     As described above, according to the present example, the configuration of each rod and the current plate  113  is comparatively simple, therefore manufacturing for example is easy, however, modifications as respective examples described below are also possible. 
     Example 2 
     In the present example, an example of the current plate  113  with an aspect different from Example 1 will be explained. 
       FIG.  9    shows a configuration example of the current plate  113  according to Example 2. This is an example where the current plate  113  having a shape similar to that of Example 1 is used in a layout different from that of Example 1. 
     The shape and the raw material of the current plate  113  can be made to be similar to those of Example 1. In the example of  FIG.  9   , the position of the current plate  113  in the X-axis direction and the Y-axis direction is similar to that of  FIG.  8   . 
     The position in the Z-axis direction of the incident side end (namely an end becoming the region  1  side in the X-axis direction) of the current plate  113  is located between the center axis of the first electrode set  201  and the center axis of the second electrode set  202 , and the position in the Z-axis direction of the exit side end (namely an end becoming the pore  104  side in the X-axis direction) of the current plate  113  is located on the Z-axis minus side, namely the exhaust port  111  side of the incident side end. Therefore, in the example of  FIG.  9   , a surface of the current plate  113  having the largest area has an inclination with respect to the X-Y plane. 
     With such inclined layout, the air flow  704  collides on the current plate  113 . Since the air flow  704  after collision proceeds toward the exhaust port  111  in  FIG.  9   , the air flow  704  can be discharged more efficiently. 
     Example 3 
     In the present example, an example of the current plate  113  with an aspect different from Example 1 and Example 2 will be explained. 
       FIG.  10    shows a configuration example of the current plate  113  according to Example 3. In the example of  FIG.  10   , the current plate  113  has a tubular shape extending in the X-axis direction, and both ends thereof open. The raw material of the current plate  113  is similar to that of Examples described above. The position in the X-axis direction of this current plate  113  having the tubular shape can be made similar to that of  FIG.  8    and  FIG.  9   . 
     The cross-sectional shape of the current plate  113  can be designed optionally as long as it is a closed figure and is for example a circle (in this case, the current plate  113  is of a cylindrical shape), an ellipse, or a polygon, and at least the diameter of a hollow portion of the tube only has to be larger than the diameter of the second electrode set  202 . 
     This current plate  113  having the tubular shape can be disposed to cover the second electrode set  202  in a region after the ion flow  703  and the air flow  704  have been separated from each other. This current plate  113  having the tubular shape may be in contact with the pore  104 , and may be in contact with the second electrode set  202 . 
     Thus, when the current plate  113  having a tubular shape is used, since the region  3  of the second electrode set  202  is protected by 360 degrees in the Y-Z plane, mixing of the turbulent flow generated by the air flow  704  and the ion flow  703  can be reduced further. 
     Example 4 
     In the present example, an example of the current plate  113  with an aspect different from Example 1, Example 2, and Example 3 will be explained. 
       FIG.  11    shows a configuration example of the current plate  113  according to Example 4.  FIG.  11    shows an example of the current plate  113  having a curved surface. This shape is a shape obtained by removing a part of the tube from the current plate  113  of  FIG.  10   , and the raw material can be made similar to that of Examples described above. The shape of the current plate  113  may be a shape where a part of a surface of a polyhedron is lacking. 
     Although the disposal position is similar to that of the current plate  113  of  FIG.  10   , the current plate  113  is disposed so that there exists a surface between the center axis of the first electrode set  201  and the center axis of the second electrode set  202 . 
     In Example 4, it is possible that both ends of the current plate  113  extend to the side of the ion flow  703  instead of the air flow  704  in a cross section (for example a cross section shown in  FIG.  1 B ) cut by a plane perpendicular to the center axis of the second electrode set  202 . Also, in an example of  FIG.  11 B , a part of the current plate  113  forms a flat surface namely a part of the cross section has a linear shape, however, the entirety of the current plate  113  may be curved, namely the entirety of the cross section may have a curved shape. 
     According to the present example, the degree of mixing of the ion flow  703  and the air flow  704  is lower compared to Example 1 and Example 2, and is higher compared to Example 3. Further, although the degree of mixing becomes higher compared to Example 3, the consumption amount of the raw material for manufacturing the current plate  113  is less. Therefore, a balance of the manufacturing cost of the apparatus and the effect secured can be selected. 
     Example 5 
     In the present example, an example of using the ion guide  103  with an aspect different from Example 1 will be explained. 
       FIG.  12    shows a configuration example of the ion guide  103  according to Example 5. The ion guide  103  includes the first electrode set  201  and the second electrode set  202 . In a similar manner to Example 1, each of the first electrode set  201  and the second electrode set  202  forms a quadrupole by rod electrodes. 
     The present example is different from Example 1 in terms that the cross section of a part of these rod electrodes is a semicircle. The electrode of the semicircle is the two rods  201   a  and  201   d  close to the second electrode set  202  with respect to the first electrode set  201 , and the two rods  202   b  and  202   c  close to the first electrode set  201  with respect to the second electrode set  202 . The cross section of the rod other than them has a circular shape. 
     In the region  2 , the rods  201   d  and  202   c  are adjacent to each other, and are arranged to configure a cross-sectional view approximating a semicircle. In a similar manner, the rods  201   a  and  202   b  are adjacent to each other, and are arranged to configure a cross-sectional view approximating a semicircle. The distance between the rods  201   d  and  202   c  can be made within a range of 0.1 mm to 2 mm, or approximately 0.1 mm to 2 mm. The same is applicable also to the distance between the rods  201   a  and  202   b.    
     With such disposal, a rod set including the rods  201   d  and  202   c  can be regarded to be one rod electrode in the region  2 . The same is applicable also to a rod set including the rods  201   a  and  202   b.    
     Therefore, in the region  2 , the ion guide  103  is configured of a hexapole by six electrodes in total of the rod  201   b , the rod  201   c , the rod  202   a , the rod  202   b , a rod set including the rods  201   d  and  202   c , and a rod set including the rods  201   a  and  202   b.    
     In the example of  FIG.  12   , in the region  2 , so that the hexapole is disposed on the apexes of a generally regular hexagon, four in total of the rods  201   d  and  202   c  and the rods  201   a  and  202   b  are bent in the Y-axis direction so as to spread generally symmetrically with respect to a position Y1 in the Y-axis direction. The rods other than them namely the rods  201   b ,  201   c ,  202   a , and  202   d  are formed into a linear shape for example. 
     In a similar manner to Example 1, with respect to the number of piece of the rod electrode in the first electrode set  201 , the number of piece of the rod electrode in the second electrode set  202 , and the number of piece of the rod electrode in an electrode formed by combination of the first electrode set  201  and the second electrode set  202  in the region  2 , the number of piece is no object as long as it is a multipole formed of only the rod electrodes of even number of piece. 
     Although the RF voltage and the DC voltage applied to the electrode are similar to those of Example 1, since each of the rods  201   d  and  202   c  is regarded to be one pole in the region  2 , the RF voltage with the same phase, the same frequency, and the same amplitude is applied to these rods. However, with respect to the DC voltage, it is not required to be equalized in these rods. The same is applicable also to the rods  201   a  and  202   b.    
     The principle in separating the ion flow  703  and the air flow  704  from each other by the ion guide  103  is similar to that of Example 1. 
     Example 6 
     In the present example, an example of using the ion guide  103  with an aspect different from Example 1 and Example 5 will be explained. 
       FIG.  13    shows a configuration example of the ion guide  103  according to Example 6. The ion guide  103  includes the first electrode set  201  and the second electrode set  202 . In an example of  FIG.  13   , each of the first electrode set  201  and the second electrode set  202  forms an octopole by the rod electrodes. 
     In the region  2 , four pieces in total of the rods  201   a ,  201   h ,  202   d , and  202   e  are bent in the Y-axis direction so as to spread generally symmetrically with respect to a position Y1 in the Y-axis direction. The cross-sectional view of the region  2  in the present example has a shape like an ellipse generally having a “constriction”. The rods other than them namely the rods  201   b  to  201   g ,  202   a  to  202   c , and  202   f  to  202   h  are formed into a linear shape for example. 
     With respect to all of the number of piece of the rod electrode in the first electrode set  201 , the number of piece of the rod electrode in the second electrode set  202 , and the number of piece of the rod electrode in a portion where there exists a “constriction” formed by combination of the first electrode set  201  and the second electrode set  202  in the region  2 , the number of piece is no object as long as it is a multipole formed of the rod electrodes of even number of piece. 
     The voltage applied to each rod can be made similar to that of Example 1 or Example 5. However, in the region  2 , since there exists a “constriction” described above, the situation of the pseudopotential is different from that of Example 1 and Example 5. An example of the pseudopotential in the present example is shown in  FIG.  3   . 
     A portion shown by a broken line in  FIG.  3 B  is a portion corresponding to the present example, and is different from Example 1 and Example 5. According to the present example (the disposal of  FIG.  13   ), in the region  2 , the ion guide  103  includes a potential barrier of the pseudopotential between the first electrode set  201  and the second electrode set  202 . 
     Ions can override this pseudopotential barrier by enlarging the DC potential difference between the first electrode set  201  and the second electrode set  202 . Due to presence of the pseudopotential barrier, the ion flow  703  is converged into the second electrode set  202  more strongly after moving to the second electrode set  202 , and therefore efficiency of permeation of the ion flow  703  through the pore  104  becomes high. 
     Example 7 
     In the present example, an example of using the ion guide  103  with an aspect different from Example 1, Example 5, and Example 6 will be explained. 
       FIG.  14    shows a configuration example of the ion guide  103  according to Example 7. The ion guide  103  includes the first electrode set  201  and the second electrode set  202 . According to the present example, the ion guide  103  is configured of a ring stack electrode. For example, the first electrode set  201  and the second electrode set  202  are ring stack electrodes formed by stacking ring-shape electrodes in the region  1  or the region  3 . 
     An RF voltage of an opposite phase is applied to electrodes adjacent to each other in the X-axis direction, and an RF voltage of the same phase is applied to rings of the same position in the X-axis direction. The off set DC voltage is similar to that of Examples described above. 
     The diameter of the ring electrode of the first electrode set  201  and the diameter of the ring electrode of the second electrode set  202  may be same with and different from each other. However, when the diameter of the second electrode set  202  is made smaller than the diameter of the ring electrode of the first electrode set  201 , the ion flow  703  is converged more strongly in the region  3 , and the efficiency of permeation through the pore  104  becomes high which is preferable. 
     The shape of the ion guide  103  in the region  2  may be a shape where there exists a constriction between the first electrode set  201  and the second electrode set  202  and a barrier of the pseudopotential is formed as  FIG.  14 B , and may be a shape where a barrier of the pseudopotential is not formed as  FIG.  14 C . 
     Example 8 
     In the present example, an example of using the ion guide  103  with an aspect different from Example 1, Example 5, Example 6, and Example 7 will be explained. 
       FIG.  15    shows a configuration example of the ion guide  103  according to Example 8. The ion guide  103  is different from Examples described above in terms that the region  1  or the region  3  is not included. 
       FIG.  15 A  is a configuration example of the ion guide  103  not including the region  1 . Such modification is applicable to the ion guide  103  of all aspects having been explained in Examples described above. The principle in separating the ion flow  703  and the air flow  704  from each other by the ion guide  103  is also similar to that of Examples described above. Since there is not the region  1 , the length in the X-axis direction of the ion guide  103  can be shortened. 
       FIG.  15 B  is a configuration example of the ion guide  103  not including the region  3 . Such modification is applicable to the ion guide  103  including a pseudopotential barrier between the first electrode set  201  and the second electrode set  202  in the region  2 . 
     Also, not only the region  3  but also the region  1  can be omitted further. With such modification, the ion guide  103  can be shortened further compared to the configuration of  FIG.  15 A . 
     By combination of the ion guide  103  of  FIG.  15    and the current plate  113 , a mass spectrometer that is compact, excellent in permeation efficiency of the ion flow  703 , and stable in an ion signal can be provided. 
     Example 9 
     In the present example, an example of using the ion guide  103  with an aspect different from Example 1, Example 5, Example 6, Example 7, and Example 8 will be explained. 
       FIG.  16    shows a configuration example of the ion guide  103  according to Example 9. In the ion guide  103 , the first electrode set  201  or the second electrode set  202  is divided into plural segments in the X-axis direction. Particularly, in an example of  FIG.  16   , the first electrode set  201  and the second electrode set  202  are divided into three segments respectively. 
     Respective segments are electrically insulated from each other. Respective segments may be insulated by leaving a gap, and may be insulated by filling the gaps between respective segments with an insulating material and connecting the segments with reach other. 
     Within the same electrode set, the frequency, the amplitude, and the phase of the RF voltage to be applied between the segments are same, but the offset DC voltage to be applied is changed. The offset DC voltage is applied to each rod so as to monotonically change in the X-axis direction and to monotonically change in the Z-axis direction also for example. 
     For example, by changing the gradient of the DC potential according to the position in the X-axis direction, the DC potential being generated between the first electrode set  201  and the second electrode set  202  in the region  2 , the ion flow  703  and the air flow  704  can be separated from each other more efficiently. 
     Also, in the second electrode set  202 , by arranging the DC potential gradient where the DC potential of the segment  1  is made high and the DC potential of the segment  3  is made low, the ion flow  703  can be transferred to the pore  104  more efficiently. 
     Other Examples 
     The present invention is not limited to examples described above, and various modifications are included. For example, examples described above were explained in detail for easy understanding of the present invention, and is not to be necessarily limited to one including all configurations having been explained. Also, a part of a configuration of an example can be substituted by a configuration of other examples, and a configuration of an example can be added with a configuration of other examples. Further, with respect to a part of the configuration of each example, it is possible to add other configurations, to be deleted, and to be substituted. 
     Also, each configuration, function, processing unit, processing means, and the like described above may be achieved by hardware by designing a part or all thereof by an integrated circuit for example. Also, each configuration, function, and the like described above may be achieved by software by that a processor interprets and executes a program achieving each function. Information of a program, a table, a file, and the like achieving each function can be placed in a recording device such as a memory, a hard disk, and an SSD (Solid State Drive) or a recording medium such as an IC card, an SD card, and a DVD. 
     Also, with respect to a control line and an information line, those considered to be required for explanation are shown, and all control lines and information lines of a product have not necessarily been shown. It is possible to consider that almost all configurations are actually connected with each other. 
     LIST OF REFERENCE SIGNS 
     
         
           101  ion source 
           102  pore 
           103  ion guide 
           104  pore 
           105  mass spectrometry unit 
           106  detector (detection unit) 
           107  first vacuum chamber 
           108  second vacuum chamber 
           109 ,  110  vacuum pump 
           111 ,  112  exhaust port 
           113  current plate (straightening member) 
           201  first electrode set 
           202  second electrode set 
           201   a  to  201   h ,  202   a  to  202   h  rod 
           701  barrel shock 
           702  mach disk 
           703  ion flow 
           704  air flow
 
All references, including publications, patents, and patent applications, cited herein are incorporated herein by reference.