Abstract:
A mass spectrometer includes: a plasma generation device for generating plasma for ionizing an introduced sample; an interface device for drawing the plasma into vacuum; an ion lens device for extracting and inducing ions as an ion beam from the plasma; a collision/reaction cell for removing an interference ion from the ion beam; a mass analyzer or filter for allowing a predetermined ion in the ion beam from the collision/reaction cell to pass along a first axis based on a mass-to-charge ratio; an ion detector for detecting the ion; an ion deflection device before the mass analyzer, and also an ion deflection device between the mass analyzer and the ion detector. The mass spectrometer reduces background noises in a mass analyzer by removing neutral particles from the ion beam without reducing the measurement sensitivity on ions to be analyzed as much as possible.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. 119 of Japanese Patent Application No. 2013-273544, filed Dec. 27, 2013, titled “ION OPTICAL SYSTEM FOR PLASMA MASS SPECTROMETER,” the content of which is incorporated by reference herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a mass spectrometer using plasma as an ion source, particularly to a mass spectrometer with an ion deflector. 
       BACKGROUND 
       [0003]    As an analyzer for analyzing inorganic elements with high precision, a plasma mass spectrometer is known. This instrument introduces an atomized sample to be analyzed into plasma formed over a plasma torch; ionizes elements contained in the sample; extracts ions present in the plasma in the form of an ion beam; and conducts mass spectrum analysis on ions forming the ion beam. As plasma to which a sample is introduced, used are inductively-coupled plasma (ICP) generated using as an energy source a high frequency electromagnetic field provided from a coil adjacent to a plasma torch; or microwave plasma generated by a microwave introduced to a tip of a plasma torch. In general, the former is known as an inductively-coupled plasma mass spectrometer (ICP-MS) and the latter is known as a microwave plasma mass spectrometer (MPI-MS). 
         [0004]      FIG. 7  is a schematic view showing a basic concept of an exemplary inductively-coupled plasma mass spectrometer (hereinafter, also referred to simply as instrument)  11  according to the conventional art. The instrument  11  has a plasma torch  20  for generating plasma  22 , an interface section  30  placed at a position facing the plasma  22 , an ion lens section  50  placed behind the interface section  30 , an ion guide section  70  placed behind the ion lens section  50 , and a mass analysis section  80  placed behind the ion guide section  70 . The instrument  11  can generally measure positive ions, but it can also measure negative ions. This specification is described under the assumption that the device  11  measures positive ions. It is evident to those skilled in the art that when the instrument  11  measures negative ions, the polarity of a voltage to be applied to an electrode or the like is inverted. 
         [0005]    The plasma torch  20  has a coil  21  for generating a high frequency electromagnetic field near its tip, and is placed under atmospheric pressure. The coil  21  is connected to an RF power source not illustrated. In the plasma torch  20 , the high frequency electromagnetic field generated by the coil  21  produces high frequency inductively-coupled plasma  22 . In the plasma torch  20 , an atomized sample not illustrated is introduced into the plasma  22  from the front of the plasma torch  20 . The introduced sample not illustrated is vaporized and decomposed by the action of the plasma  22 ; and in cases of large majority of elements, they are finally converted into ions. The ionized sample not illustrated is contained in the plasma  22 . Further, within the plasma torch  20 , a gas flow occurs from the back end to the front end, so the plasma  22  extends towards a sampling cone  31 . 
         [0006]    The interface section  30  is provided with two cone members, that is the sampling cone  31  and a skimmer cone  33 . A part of plasma  32  having passed through an aperture  37  of the sampling cone  31  directly facing the plasma  22  reaches the skimmer cone  33  positioned further behind. Thereafter, a part of plasma  32  passes through an aperture  38  formed in the skimmer cone  33  and reaches the rear thereof. Gas molecules (including neutralized ions) not having passed through the skimmer cone  33  are discharged from the interface section  30  via an exhaust port  39  by a rotary pump RP. 
         [0007]    The ion lens section  50  is provided with a first electrode  53  and a second electrode  54  forming an extraction electrode section. The first electrode  53  or the second electrode  54  forming the extraction electrode section is at negative potential, and thus, only positive ions are extracted from the plasma  52  in the form of an ion beam. The ion beam is guided from the second electrode  54  into a collision/reaction cell  71  of the ion guide section  70 . However, an ion deflection lens is arranged subsequent to the second electrode  54  and the ion beam may be guided into the collision/reaction cell  71  via the ion deflection lens. 
         [0008]    The ion beam guided into the collision/reaction cell  71  is induced to a subsequent stage along a track determined by an electric field generated by a multipole electrode  73 . The multipole electrode  73  has, for example, an octapole structure. Further, a collision/reaction gas may be introduced from a feeding port  72  into the collision/reaction cell  71 . Molecules of the introduced gas cause reaction associated with collision or charge transfer with various ions contained in the ion beam, thereby removing, from the ion beam, polyatomic ions or interference ions that are composed of elements contained in carrier gas and the sample and cause interferences in mass spectra. 
         [0009]    During operation of the instrument  11 , the ion guide section  70  is exhausted together with the ion lens section  50  by using a turbo molecular pump (TMP 1 ). Therefore, molecules that have been contained in the plasma but neutralized within the ion lens section  50  or the ion guide section  70 , or molecules of collision/reaction gas that are introduced into the collision/reaction cell are exhausted through an exhaust port  79 . 
         [0010]    An ion beam  75  out of the collision/reaction cell  71  is introduced into the mass analysis section  80 . In the mass analysis section  80 , there is provided a multipole structure  81  of quadrupole, which is known as a quadrupole mass analyzer or a quadrupole mass filter (hereinafter, the multipole structure  81  is referred to as a mass analyzer). An electric field generated by the mass analyzer allows ions in the ion beam to pass through the mass analyzer  81  along an X-axis in  FIG. 7  and to be separated based on a mass-to-charge ratio. Subsequently, separated ions  85  (indicated by a broken line) are guided to a subsequent ion detector  82 . The mass analysis section  80  is also exhausted by using a turbo molecular pump (TMP 2 ) in the same manner as the ion guide section  70 , and unnecessary ions separated by the mass analyzer  81  and other molecules are exhausted through an exhaust port  84 . 
         [0011]    The ion detector  82  receives and detects ions separated at the mass analyzer  81  to convert into electric signals. For example, an inductively-coupled plasma mass spectrometer (ICP-MS) is an instrument having a large dynamic range to detect from signals for trace quantities (e.g., 0.1 cps) to signals for main components (e.g., 10 10  cps). In general, when detected signals are low, ion counting is used for measurement; and when detected signals are high, analog measurement is used. For example, in the case of ion counting, ions are introduced into a secondary electron multiplier thereby to be converted to 10 5  to 10 6 -times amplified electrons. Such electrons are converted into a voltage pulse and counted for a certain period of time and thereby, an ion count is obtained. 
         [0012]    In such a mass spectrometer, when ions are extracted from plasma at the first electrode  53  or the second electrode  54 , neutral particles with high energy are produced. Such neutral particles are generally known as a cause for background noises, and separation of these neutral particles from ions is required. Mechanisms for conducting such separation are disclosed, for example, in Patent Document 1 (Japanese Patent Laid-Open Publication No. H7-78,590); Patent Document 2 (National Publication of International Patent Application No. 2002-525,821); and Patent Document 3 (National Publication of International Patent Application No. 2004-515,882). 
         [0013]    Patent Document 1, for example, discloses that an ion lens has a 90° deflector, whereby neutral particles contained in an ion beam having passed through an interface are prevented from reaching a mass filter. Further, Patent Document 2 discloses that a beam composed of ions and neutral particles coming through an opening of a skimmer cone is reflected at 90° by an ion mirror and sent to a mass analyzer, whereby neutral particles are prevented from reaching the mass analyzer. 
         [0014]    Patent Document 3 discloses an ion mirror  42  similar to that of Patent Document 2. In order to increase the transmission of an ion injection port of a mass analysis section, Patent Document 3 also discloses that quadruple fringe electrodes  56  are provided between the ion mirror  42  and a linear quadruple mass analyzer  54 . Four rod-shaped electrodes of this quadruple fringe electrode  56  are curved while being kept parallel to each other, and prevent neutral particles from reaching the linear quadruple mass analyzer  54 . 
         [0015]    However, when ions are introduced into a mass analyzer (e.g., quadruple mass analyzer); and these ions are accelerated by an RF voltage of quadruple electrodes and collided with molecules of residual gas, the ions may be changed to neutral particles having energy before the collision. These neutral particles collide with a wall near within an ion detector thereby to generate secondary ions, which may be detected as background noises by the ion detector. In particular, a plasma mass spectrometer has a larger amount of ions derived from carrier gas than GC-MS or LC-MS. Thus, it is likely to have a drawback on background noises caused by the generation of neutral particles. 
         [0016]    Further, when a deflector or an ion mirror is arranged prior to a mass analyzer as disclosed in Patent Documents 1 to 3, a certain amount of ions to be measured is lost and the measurement sensitivity may be deteriorated. This is because a difference of deflection angle occurs due to the energy difference depending on the mass number of an ion; or a difference in the output position of an ion due to the incident position or the incident angle of the ion to a deflector. In addition, curved quadruple fringe electrodes disclosed in Patent Document 3 may have a reduced ion transmission in comparison with a simple straight fringe electrode. Curving four rod-shaped electrode while keeping them parallel to each other would result in a complicated structure and increase the cost and labor for processing. 
       SUMMARY 
       [0017]    To address the foregoing problems, in whole or in part, and/or other problems that may have been observed by persons skilled in the art, the present disclosure provides methods, processes, systems, apparatus, instruments, and/or devices, as described by way of example in implementations set forth below. 
         [0018]    Accordingly, an object of the present invention is to provide: a plasma mass spectrometer, which reduces background noises by removing neutral particles from an ion beam without deteriorating the measurement sensitivity for ions to be measured as much as possible; and an ion deflector, which has a simple an inexpensive structure as means for removing neutral particles from an ion beam. 
         [0019]    In order to achieve the above object, the present invention has a first ion deflector for removing neutral particles provided between a plasma ion source and a mass analyzer, and a second ion deflector provided between the mass analyzer and an ion detector, thereby deflecting an ion having passed through the mass analyzer by an electric field and enabling the ion to enter the ion detector. This prevents neutral particles and the like generated before introduction into the mass analyzer from being introduced into the mass analyzer; and removes neutral particles and the like contained in ions that have been generated mainly by the mass analyzer and have passed through the mass analyzer, consequently reducing background noises. 
         [0020]    According to one embodiment of the present invention, disclosed is a mass spectrometer having plasma generation device for generating plasma for ionizing an introduced sample; an interface device for drawing the plasma into vacuum; an ion lens device for extracting and inducing ions as an ion beam from the plasma; a collision/reaction cell for removing an interference ion from the ion beam; a mass analyzer for allowing a predetermined ion in the ion beam from the collision/reaction cell to pass along a first axis based on a mass-to-charge ratio; and an ion detector for detecting the ion. The mass spectrometer includes: at least one first ion deflection device disposed between the ion lens device and the mass analyzer to deflect ions and remove neutral particles or the like from the ion beam; and at least one second ion deflection device disposed between the mass analyzer and the ion detector to deflect ions, wherein the second ion deflection device has an electrode for generating an electric field, which enables a predetermined ion having passed through the mass analyzer along a first axis to be deflected and induced to the ion detector along a second axis. 
         [0021]    Further, the second ion deflection device may include, for example, a first shield with a first aperture allowing ions from the mass analyzer to pass and a second shield with a second aperture through the ion detector. The electrode may be arranged so as not to intersect with the first axis; and this signifies that, assuming that a neutral particle passes through the first aperture along the first axis and travels straight, the electrode is arranged so that the neutral particle does not collide with the electrode. In addition, a plurality of electrodes may be arranged so as to deflect ions passing through the first aperture while focusing the ions to the second aperture. 
         [0022]    Further, in such a case, the number of electrodes may be two, three, four or the like. However, when three electrodes are used, first and second electrodes are arranged so as to face each other across the first axis and the third electrode is arranged so as to face the first electrode across the second axis. The electrodes may be in the form of a rod. Further, the first and second axes may be at right angles to each other, and the angles may be other than the right angle. The first shield may be coupled to the second shield. 
       ADVANTAGES OF THE INVENTION 
       [0023]    The present invention has: at least one first ion deflection device arranged between the ion lens device and the mass analyzer, and at least one second ion deflection device arranged between the mass analyzer and the ion detector. This can prevent neutral particles and the like generated before mass separation of ions from being introduced into the mass analyzer and remove neutral particles and the like having passed through the mass analyzer generated mainly at the mass analyzer. Neutral particles having enough energy to generate secondary ions, which are detectable by the ion detector and background noises can be reduced. Further, the second ion deflection device can be formed with single or a plurality of rod-shaped electrodes as a main constituent element, and thus the structure thereof is simple and inexpensive. 
         [0024]    Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
           [0026]      FIG. 1  is a schematic view showing an embodiment of an inductively-coupled plasma mass spectrometer according to the present invention; 
           [0027]      FIG. 2  is a perspective view of a second ion deflector according to the present invention; 
           [0028]      FIG. 3  is a top view of the second ion deflector according to the present invention; 
           [0029]      FIG. 4  is a view showing a simulation result of the second ion deflector according to the present invention; 
           [0030]      FIG. 5  is a top view of an alternative second ion deflector according to the present invention; 
           [0031]      FIG. 6  is a top view of another alternative second ion deflector according to the present invention; and 
           [0032]      FIG. 7  is a schematic view showing a basic concept of a conventional inductively-coupled plasma mass spectrometer. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Embodiments of the present invention are hereinafter explained by referring to the accompanying drawings.  FIG. 1  is a schematic view showing a basic concept of an exemplary inductively-coupled plasma mass spectrometer (hereinafter, referred to simply as “instrument”)  10  of the present invention. The same constituent elements as in above-mentioned  FIG. 7  are denoted by the same reference numerals to omit explanations on the same constituent elements as in  FIG. 7 . The instrument  10  of the present invention differs from the conventional instrument  11  explained by the basic concept drawing in that the instrument  10  of the present invention has first and second ion deflection devices. As examples of the first ion deflection device, the instrument  10  of the present invention has an ion deflector  56  located at an ion lens section  50  and an ion deflector  76  located between a collision/reaction cell  71  and a quadrupole mass analysis section  80 . Further, the instrument  10  of the present application also has, as an example of the second ion deflection device, an ion deflector  100  between a mass analyzer  81  and an ion detector  82 . 
         [0034]    The ion deflector  56  is located at a latter part of the ion lens section  50  to deflect an ion beam  55  extracted by an extraction electrode section so that a traveling axis is shifted parallel, thereby introducing ions into a collision/reaction cell  71  while removing neutral particles and the like flown from plasma or generated at the extraction electrode section. For example, the ion deflector is composed of, as shown in  FIG. 1 , a cylindrical electrode  58  and a shield  57  with an aperture for allowing ions to pass through it. About −150 V of negative voltage, about +10 V of voltage, and about −100 V of negative voltage are applied to a second electrode  54 , the cylindrical electrode  58  and the shield  57 , respectively. The cylindrical electrode  58  is arranged so as to have its center axis displaced from an entry axis of the ion beam, so the ion beam is deflected by the potential of the inner face of the cylindrical electrode  58  to be close to an opposite side of the cylindrical electrode  58 . The ion beam is again deflected to pass through the aperture of the shield  57 . 
         [0035]    The ion deflector  76  is located between the collision/reaction cell  71  and the mass analyzer  81  to deflect an ion beam  75  having passed through the collision/reaction cell  71  so that a traveling axis is shifted parallel, thereby introducing ions into the mass analyzer  81  while removing neutral particles and the like generated at the ion lens section  50  or the collision/reaction cell  71 . For example, the ion deflector  76  is composed of, as shown in  FIG. 1 , a cylindrical electrode  77  having a part of cylinder cut out, and shields  78 ,  79  arranged before and after the cylindrical electrode  77  and each having an aperture for allowing ions to pass through it. About −50 V of negative voltage is applied to both of the shields  78 ,  79  and about +10 V of voltage is applied to the cylindrical electrode  77 . A part of the cylindrical electrode  77  at an ion entry side is cut out, so the ion beam is deflected by the potential of the inner face of the cylindrical electrode  77  to be close to an opposite side. The ion beam is again deflected to pass through the aperture of the shield  79 . 
         [0036]    The ion deflector  100  is located between the mass analyzer  81  and the ion detector  82 . The ion deflector  100  is configured to receive ions passing through the mass analyzer  81  (e.g., quadrupole mass analyzer) along the X-axis and deflect ions along the Y-axis to the ion detector  82 . That is, ions pass through the mass analyzer  81  along the X axis; are subjected to 90°-deflection by the ion deflector  100 ; and travel along the Y-axis to the ion detector  82 . The X- and Y-axes signify Cartesian coordinate system. Details of such ion deflector  100  are illustrated in  FIG. 2 . 
         [0037]      FIG. 2  is a perspective view of the ion deflector  100 , and  FIG. 3  is a top view of the ion deflector  100 . In  FIGS. 2 and 3 , the ion deflector  100  includes a first shield  140 , a second shield  150 , a first rod-shaped electrode  110 , a second rod-shaped electrode  120  and a third rod-shaped electrode  130 . The first shield  140  is arranged adjacent to the mass analyzer  81  and is orthogonal to the X-axis. Further, the first shield  140  includes an aperture  141  for allowing ions having passed through the mass analyzer  81  along the X-axis. The aperture  141  has a diameter of, for example, about 5 mm. The first rod-shaped electrode  110  and the second rod-shaped electrode  120  are arranged opposite to the mass analyzer  81  across the first shield  140  and are spaced from the first shield  140 . Then, the first and second rod-shaped electrodes  110  and  120  are arranged to face each other across the X-axis passing through the aperture  141 . Therefore, ions passing through the aperture  141  along the X-axis pass between the first and second rod-shaped electrodes  110  and  120 . The distance between the first shield  140  and the first or second rod-shaped electrode  110  or  120  is, for example, about 10 mm; and the distance between the first and second rod-shaped electrodes  110  and  120  is, for example, about 20 mm. 
         [0038]    The second shield  150  is orthogonal to the first shield  140  and is arranged adjacent to the ion detector  82 . The second shield  150  includes an aperture  151  leading to the ion detector  82 . This aperture  151  has a diameter of, for example, about 10 mm. The second shield  150  may be connected or disconnected to the first shield  140 . The first rod-shaped electrode  110  and the third rod-shaped electrode  130  are arranged opposite to the ion detector  82  across the second shield  150 , and are spaced from the second shield  150 . The first rod-shaped electrode  110  and the third rod-shaped electrode  130  are arranged to face each other across the axis parallel to the Y-axis passing through the aperture  151 . The distance between the second shield  150  and the first rod-shaped electrode  110  or the third rod-shaped electrode  130  is, for example, about 10 mm, and the distance between the first and third rod-shaped electrodes  110  and  130  is, for example, about 20 mm. 
         [0039]    About −300 V of voltage, for example, is applied to the first rod-shaped electrode  110 , and about 0 V of voltage, for example, is applied to each of the second and third rod-shaped electrodes  120  and  130 . Voltages applied to the second and third rod-shaped electrodes  120  and  130  may be the same. Further, about 0 V of voltage, for example, is applied to the first and second shields  140  and  150 . Application of a voltage to each electrode or each shield generates an electric field within the ion deflector  100 . This electric field deflects ions having passed through the aperture  141  at 90° so that the ions enter into the aperture  151  and also works to focus the ions to the aperture  151 . Therefore, ions having passed through the mass analyzer  81  along the X-axis are deflected at 90° by the ion deflector  100  and led to the ion detector  82  along the Y-axis. Such flow of ions is shown schematically by lines in  FIGS. 2 and 3 . 
         [0040]    Each of the first, second and third rod-shaped electrodes  110 ,  120  and  130  preferably has a circular cross-sectional shape, but may have other shapes such as oval shape, semicircular shape, triangular shape or rectangular shape. In the case that a rod-shaped electrode has a circular cross-sectional shape, the diameter is about 1 mm to 30 mm. The first, second and third rod-shaped electrodes  110 ,  120  and  130  can be made of, for example, stainless steel. Further, the first and second shields  140  and  150  can be made of, for example, stainless steel. 
         [0041]      FIG. 4  shows an exemplary simulation result of the ion deflector  100  of the present invention. Conditions for this simulation are that −400 V was applied to the first rod-shaped electrode  110 ; +20 V was applied to the second and third rod-shaped electrodes  120  and  130 ; −30 V was applied to the first and second shields  140  and  150 ; and the energy of ions was +5 eV. As is evident from  FIG. 4 , ions having passed through the aperture  141  are deflected at 90° to enter the aperture  151  and also are focused to the aperture  151 . 
         [0042]    The mass analyzer  81  emits a mass-separated ion beam together with neutral particles, which are a cause for background noises. However, when the neutral particles enter the ion deflector  100  of the present invention, they are not subjected to an electrostatic force and thus, they travel straight without 90°-deflection. That is, neutral particles or at least neutral particles having enough energy to generate secondary ions detectable by the detector are not allowed to go to the ion detector  82 . Consequently, background noises are reduced. Further, neutral particles having passed through the aperture  141  along the X-axis travel straight as described above, but collision of these neutral particles with, for example, a rod-shaped electrode or the like generates secondary ions, which are a cause for background noises. Therefore, a rod-shaped electrode has to be arranged at such a position that such straight-traveling neutral particles do not collide. 
         [0043]    TABLE 1 described below shows measured data on background noises obtained by using an ICP mass spectrometer  7700   x  manufactured by Agilent Technologies, Inc. as an experiment apparatus for cases: where the ion deflector  100  of the present invention was not used after mass separation (the instrument having a construction where the ion detector  82  was placed at the position for the ion deflector  100  in  FIG. 1 ) and the ion deflector  100  was incorporated and used after mass separation (the instrument of  FIG. 1 ). This measurement used plasma with a Low Matrix condition, and was conducted in a state where collision/reaction gas was not introduced in the collision/reaction cell. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Mass number (u) 
                 7 
                 89 
                 205 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Background noise when 
                 0.25 
                 0.8 
                 3.45 
               
               
                   
                 not used (CPS) 
               
               
                   
                 Background noise when 
                 0.1 
                 0.1 
                 1.2 
               
               
                   
                 used (CPS) 
               
               
                   
                 Ratio of background 
                 0.4 
                 0.13 
                 0.35 
               
               
                   
                 noises 
               
               
                   
                   
               
             
          
         
       
     
         [0044]    As is evident from TABLE 1, use of the ion deflector  100  of the present invention after mass separation reduces respective background noises for mass numbers  7   u ,  89   u  and  205   u  compared to the case where the ion deflector  100  is not used. Background noises for mass numbers  7   u ,  89   u  and  205   u  were reduced by 40%, 13% and 35%, respectively, and a significant improvement was observed. 
         [0045]    Hitherto, the ion deflector  100  of the present invention is explained so as to deflect incoming ions at 90° and output them (that is, the first shield  140  is orthogonal to the second shield  150 ). However, the angle for ion deflection, in other words the angle between the first and second shields  140  and  150 , is not necessarily 90°, and the angle between the first and second shields  140  and  150  may be, for example in the range of about 30° to about 180°. Further, the ion deflector  100  is explained so as to have three rod-shaped electrodes for ion deflection, but the number of electrodes is not necessarily three and it may be one, two, or four or more. For example,  FIG. 5  shows an ion deflector having two rod-shaped electrodes  110  and  111 , and  FIG. 6  shows an ion deflector having four rod-shaped electrodes  110 ,  111 ,  120  and  130 . In  FIGS. 5 and 6 , flow of ions is shown schematically by lines. The position of the rod-shaped electrode  111 , for example, may be an intersection of: a line extended from the third rod-shaped electrode  130  in parallel with the first shield  140 ; and a line extended from the rod-shaped electrode  120  in parallel with the second shield  150 . In the ion deflector of  FIG. 5 , for example, −300 V may be applied to the first rod-shaped electrode  110  and 0 V may be applied to the rod-shaped electrode  111 . In the ion deflector of  FIG. 6 , −300 V may be applied to the first rod-shaped electrode  110 , and 0 V may be applied to the second and third rod-shaped electrodes  120 ,  130  and the rod-shaped electrode  111 . However, when two or four rod-shaped electrodes are used, it is significant to arrange rod-shaped electrodes at such positions that neutral particles traveling straight after passed through the aperture  141  along the X-axis do not collide with the rod-shaped electrodes. In the case that the ion deflector  100  has only one rod-shaped electrode (e.g.,  110 ), the energy of ions is changed when the mass spectrometer  10  is operated in a collision gas mode (a mode for introducing collision gas into a collision/reaction cell), and therefore, it has been found that the function of the ion deflector  100  is not sufficient. 
       DESCRIPTION OF REFERENCE NUMERALS 
       [0000]    
       
         
           
               10  Mass spectrometer 
               20  Plasma torch 
               22  Plasma 
               30  Interface section 
               50  Ion lens section 
               56 ,  76  Ion deflector 
               71  Collision/reaction cell 
               81  Mass analyzer 
               82  Ion detector 
               100  Ion deflector 
               110 ,  111 ,  120 ,  130  Electrode 
               140 ,  150  Shield 
               141 ,  151  Aperture 
           
         
       
     
         [0059]    It will be understood that various aspects or details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.