Patent Publication Number: US-11387090-B2

Title: Mass spectrometry device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2020-007265 filed Jan. 21, 2020, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a mass spectrometry device, and more particularly to a structure of a time-of-flight mass spectrometry device. 
     Description of Related Art 
     A time-of-flight mass spectrometry device comprises, for example, a pulse generator unit (typically an orthogonal acceleration unit) that generates ion pulses from an ion flow, a reflector unit that reverses the flight direction of the ion pulses, and a detector unit that detects the ion pulses from the reflector unit. In the course of the flight, the ion pulses elongate in the trajectory direction in accordance with the mass-to-charge ratios (m/z) of the individual ions constituting the ion pulses, and form a band-like shape. By detecting such ion pulses, mass spectrum information can be obtained. 
     In order to correctly introduce the ion flow to a reference plane of the pulse generator unit, an incidence regulator unit is provided upstream of the pulse generator unit. The incidence regulator unit comprises, for example, a vertically-arranged pair of blades. A gap between a pair of edges that form parts of the pair of blades functions as a slit through which the ion flow is passed. 
     JP 2004-362903 A discloses a time-of-flight mass spectrometry device comprising an incidence regulator unit. However, in JP 2004-362903 A, respective components constituting the mass spectrometry device are described schematically or abstractly, and no concrete structure can be identified from those descriptions. 
     In order to generate suitable ion pulses in a time-of-flight mass spectrometry device, it is necessary to position the incidence regulator unit relative to the pulse generator unit with high positioning accuracy. In other words, the spatial relationship between the incidence regulator unit and the pulse generator unit must be highly optimized. 
     Meanwhile, in the incidence regulator unit, in order to prevent or reduce soiling of the pair of blades with ions, the pair of blades are heated. It is desired to maintain an appropriately heated state of the incidence regulator unit while suppressing escape of heat therefrom. 
     One object of the present disclosure is to position, in a mass spectrometry device, an incidence regulator unit relative to a pulse generator unit with high positioning accuracy. An alternative object of the present disclosure is to maintain an appropriately heated state of an incidence regulator unit in a mass spectrometry device. 
     SUMMARY OF THE INVENTION 
     A mass spectrometry device according to the present disclosure comprises a base, a constructed unit including a pulse generator unit that generates ion pulses from an ion flow, a first support member that fixes the constructed unit with respect to the base while isolating the constructed unit from the base, an incidence regulator unit provided upstream of the pulse generator unit and having a slit through which the ion flow passes, and a second support member that fixes the incidence regulator unit with respect to the base while isolating the incidence regulator unit from the base and the constructed unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiment(s) of the present disclosure will be described based on the following figures, wherein: 
         FIG. 1  is a cross-sectional view showing a configuration of a mass spectrometry device according to an embodiment; 
         FIG. 2  is a cross-sectional view showing a detailed configuration of an incidence regulator unit and its surroundings; 
         FIG. 3  is a front view of the incidence regulator unit; 
         FIG. 4  is a cross-sectional view of the incidence regulator unit; and 
         FIG. 5  is a diagram for explaining positioning of the incidence regulator unit. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Embodiments will be described below based on the drawings. 
     (1) Overview of Embodiments 
     A mass spectrometry device according to an embodiment includes a base, a constructed unit, a first support member, an incidence regulator unit, and a second support member. The constructed unit comprises a pulse generator unit that generates ion pulses from an ion flow. The first support member is a member that fixes the constructed unit with respect to the base while isolating the constructed unit from the base. The incidence regulator unit is a unit provided upstream of the pulse generator unit, and has a slit through which the ion flow passes. The second support member is a member that fixes the incidence regulator unit with respect to the base while isolating the incidence regulator unit from the base and the constructed unit. 
     If the constructed unit, which comprises a pulse generator unit, and the incidence regulator unit are coupled to each other via a number of components, machining errors and assembly errors of the respective intervening components would accumulate, making it difficult to attain an appropriate spatial relationship between the pulse generator unit and the incidence regulator unit. In contrast, according to the above-described configuration, the constructed unit and the incidence regulator unit are both fixed with respect to a common base, so that the spatial relationship between the pulse generator unit and the incidence regulator unit can be easily optimized. Further, according to the above-described configuration, since the constructed unit is fixed with respect to the base via the first support member while the incidence regulator unit is fixed with respect to the base via the second support member, it is easy to heat the constructed unit and the incidence regulator unit independently of each other. That is, direct heat conduction to the base from the constructed unit and from the incidence regulator unit can be prevented, and escape of heat via the base can thereby be suppressed. In addition, since the constructed unit and the incidence regulator unit are not directly coupled, direct heat transfer between these units can be prevented. For this reason, the pulse generator unit (which may also be heated to prevent or reduce soiling with ions) and the incidence regulator unit can be easily maintained at their respective temperatures. 
     In an embodiment, the incidence regulator unit includes a main body, a pair of blades, and a heat source. The pair of blades are provided on the main body. The heat source is provided on the main body and serves to heat the pair of blades. By heating the pair of blades, soiling of the pair of blades with ions can be reduced. Soiling with ions leads to electrostatic charging, and due to this charging, the trajectory of the ion flow becomes unstable. When soiling with ions can be reduced, the trajectory of the ion flow can be stabilized, and workload for maintenance can be reduced. The potential of the pair of blades may be set to ground potential. 
     In an embodiment, when assuming that a direction parallel to a direction of travel of the ion flow is defined as a first direction, that a direction orthogonal to the first direction and parallel to the slit is defined as a second direction, and that a direction orthogonal to the first direction and the second direction is defined as a third direction, the main body extends in the second direction and the third direction. A pair of mounts is provided projecting toward both sides in the second direction from an end portion of the main body, which end portion is located toward the base. The second support member is a pair of support posts provided between the base and the pair of mounts. Each of the support posts extends in the third direction. 
     Since the mounts project from the two lateral faces of the main body, work for attaching the support posts to the mounts is facilitated. Further, heat escape can be suppressed as compared to a case in which the pair of support posts is directly attached to the main body. In an embodiment, the first direction is a first horizontal direction, the second direction is a second horizontal direction, and the third direction is a vertical direction. A portion (i.e., one end portion) of each support post may extend past the corresponding mount to the opposite side (i.e., a side located away from the base), and a portion (i.e., the other end portion) of each support post may extend into the base. 
     In an embodiment, each support post comprises a bolt. The bolt is placed through a through hole formed in the mount and a through hole formed in the support post, and is coupled to the base. The head of the bolt is exposed at the mount. According to this arrangement, access to the head of each bolt with a tool is facilitated. In other words, assembly work efficiency can be increased. 
     In an embodiment, the heat source includes a first heater embedded in the main body on one side of the pair of blades, and a second heater embedded in the main body on the other side of the pair of blades. According to this arrangement, since the pair of blades is located between the two heaters, the pair of blades can be uniformly heated in a stable manner. If the pair of support posts were directly attached to a lower part of the main body, heat generated by the two heaters would easily escape. In an embodiment, the pair of support posts are attached to the pair of mounts projecting from the main body instead of being attached to the main body, so that the heat conduction path is longer, and heat escape can be suppressed to some extent. Here, although it is possible to form the second support member with a single support post, in that case, the orientation of the incidence regulator unit tends to be unstable. According to the above-described arrangement, the incidence regulator unit can be fixed stably with respect to the base. 
     In an embodiment, on one side of the base, there are provided the constructed unit, the first support member, the incidence regulator unit, and the second support member, and further, a reflector unit that reflects ions from the pulse generator unit. On the other side of the base, a detector that detects ions from the reflector unit is provided. A member that holds the detector is fixed with respect to the base. 
     According to the above-described configuration, since the main structures are fixed with respect to the base, positioning accuracy of the respective components can be enhanced. Further, both of one side and the other side of the base can be used as the ion flight space, so that resolution can be increased. 
     (2) Details of Embodiments 
       FIG. 1  illustrates an example configuration of a time-of-flight mass spectrometry device  10  according to an embodiment. The illustrated mass spectrometry device  10  is, for example, a device that obtains mass spectrum information by ionizing a compound gas fed from a gas chromatograph (not shown) and analyzing masses of the individual ions produced as a result of the ionization. The time of flight (flight velocity) of each ion depends on mass-to-charge ratio (m/z) of that ion. Using this relationship, the mass-to-charge ratios (m/z) of the individual ions are determined. In  FIG. 1 , an x-direction denotes the first horizontal direction, and a z-direction denotes the vertical direction (upright direction). Although a y-direction is not shown in  FIG. 1 , the y-direction denotes the second horizontal direction. The respective directions are orthogonal to each other. 
     In  FIG. 1 , the mass spectrometry device  10  comprises a base  12 , which is a horizontal plate extending in the x-direction and the y-direction. The base  12  is installed on a floor via a plurality of legs  14 . The height of the base  12  is an intermediate height in the mass spectrometry device  10 . The base  12  is composed of a metal such as aluminum, for example. 
     On an upper side of the base  12 , a housing  16  is provided. On one side of the housing  16 , a housing  18  is provided. On a lower side of the base  12 , a housing  48  is provided. The housing  16 , the housing  18 , and the housing  48  are composed of a metal such as aluminum, for example, and the interiors of these housings are in a vacuum state. In  FIG. 1 , illustration of vacuum pumps is omitted. 
     On the inside of the housing  18 , an ion source  20  is provided. A gas from the gas chromatograph is introduced into the ion source  20  as a specimen. As the ion source  20 , ion sources operating according to various ionization methods can be employed. According to an embodiment, in the ion source  20 , ions are generated continuously, and the ions are ejected in a horizontal direction. As a result, an ion flow  24  is produced continuously. In the ion source or in the downstream region thereof, a pulse-like ion flow may be formed. Reference numeral  22  indicates an ion flow shaping unit including a lens system. This ion flow shaping unit can be referred to as an ion introducing unit from the perspective of an orthogonal acceleration unit  32  described further below. In the illustrated example configuration, the flow direction of the ion flow  24  is parallel to the x-direction. 
     On the housing  18 , an annular flange  26  is provided. The ion flow  24  passes through an opening  26 A formed in the flange  26 . The housing  16  has an opening  16 A for attaching the housing  18 . In the illustrated example configuration, a part of the flange  26  extends into the opening  16 A. It is possible to also provide a flange on the housing  16  side and to couple this flange with the flange  26 . In any case, the two housings  16 ,  18  are coupled to each other in such a manner that the vacuum inside the housings  16 ,  18  is maintained. 
     A constructed unit  28 , which is a structure or an assembly composed of a plurality of components, is arranged inside the housing  16 . The constructed unit  28  comprises the orthogonal acceleration unit  32  that functions as the pulse generator unit. The orthogonal acceleration unit  32  serves to periodically extract ion pulses from the ion flow. The ion pulses are emitted in the z-direction (upward in  FIG. 1 ). In  FIG. 1 , the trajectory of the ion pulses is indicated by reference numeral  44 . 
     A reflector unit  46  is referred to as a reflector or a reflectron, and serves to reverse the direction of travel of the individual ions. The reflector unit  46  comprises a plurality of electrodes that form an electric field for reflecting ions. The trajectory of the ion pulses before reversal is indicated by reference numeral  44 A, while the trajectory of the ion pulses after reversal is indicated by reference numeral  44 B. Because the ions constituting the ion pulses have various mass-to-charge ratios, the ion pulses elongate in the trajectory direction in the course of the flight. The entire flight path of the ion pulses corresponds to a mass analyzing section. 
     The orthogonal acceleration unit  32  comprises a plurality of electrodes. Among those electrodes,  FIG. 1  shows two electrodes  34 ,  36  that define a reference plane A. The electrode  34  is a pusher electrode, while the electrode  36  is a puller electrode. Each of these electrodes has a shape of a flat plate, and the two electrodes are arranged in parallel with each other. In the gap between the two electrodes, a plane corresponding to an intermediate position in the z-direction is the reference plane A. Although a plurality of additional electrodes are arranged alongside each other above the electrode  36 , illustration of those electrodes is omitted. 
     The constructed unit  28  is fixed to the base  12  by means of four support posts  30  while being spaced from the base  12  (and the housing  16 ). The support posts  30  constitute the first support member. The orthogonal acceleration unit  32  is heated by a heat source (not shown). For example, the temperature of the electrode  34  is maintained at 100° C. With this arrangement, soiling of the electrode  34  with ions can be reduced. Electrodes other than the electrode  34  may be heated. The heat source for the heating may be arranged inside or outside the constructed unit  28 . The heat source may be embedded in the electrode  34 . The heat source may be configured with, for example, one or more heaters. 
     Since the constructed unit  28  is fixed to the base  12  via the plurality of support posts  30 , heat conduction from the constructed unit  28  to the base  12  can be reduced as compared to a case in which the constructed unit  28  is directly fixed to the base  12 . The individual support posts  30  may be composed of a material having relatively low thermal conductivity. For example, the individual support posts  30  may be composed of stainless steel. When designing the mass spectrometry device  10 , thermal expansion of the respective components is taken into consideration. 
     Upstream of the orthogonal acceleration unit  32 , an incidence regulator unit  38 , which can be referred to as a regulator, is provided. The incidence regulator unit  38  includes a slit  40  through which the ion flow is passed. By means of the incidence regulator unit  38 , incidence of the ion flow is regulated in such a manner that the ion flow having a planar shape is located in the reference plane A. As described below, the incidence regulator unit  38  comprises components such as a pair of blades that define the slit, and a pair of heaters serving as a heat source for heating the pair of blades. 
     The incidence regulator unit  38  is fixed with respect to the base  12  by means of a pair of support posts  42  while being spaced from the base  12  (and the housing  16 ). The pair of support posts  42  function as the second support member. The support posts may be composed of stainless steel. The pair of blades are heated by the pair of heaters. The temperature of the pair of blades is maintained at 200° C., for example. Since the incidence regulator unit  38  is spaced from components other than the pair of support posts  42 , heat escape from the incidence regulator unit  38  is suppressed. When mounting the incidence regulator unit  38  in place, thermal expansion of the support posts  42  is taken into consideration. 
     If the incidence regulator unit  38  were directly fixed to the constructed unit  28 , heat transfer from the incidence regulator unit  38  to the constructed unit  28  would be generated, which would cause the temperature of the constructed unit  28  to be unstable or non-uniform, or as a result of which more electric energy would be required for maintaining the temperature of the pair of blades to a predetermined temperature. According to the configuration of the embodiment, generation of these problems can be avoided. Although attaching the incidence regulator unit  38  to the flange  26  might be considered, in that case, the amount of heat escape would be increased, and further, positioning error of the incidence regulator unit  38  would undesirably be increased. According to the configuration of the embodiment, occurrence of these problems can also be avoided. 
     Inside the housing  48 , a detector  50  is provided. By means of the detector  50 , the temporally-extended ion pulses are detected. Based on detection signals generated as a result of the detection, a mass spectrum is produced. An opening  12 A through which the ion pulses pass is formed in the base  12 . In an embodiment, the constructed unit  28 , the incidence regulator unit  38 , and the reflector unit  46  are provided on one side (more specifically, on the upper side) of the base  12 , while the detector  50  is provided on the other side (more specifically, on the lower side) of the base  12 . With this arrangement, the flight distance of the ion pulses is increased, and accuracy of mass spectrometry can thereby be enhanced. The detector  50  may be installed at a further lower position. By employing spaces on both sides of the base  12 , it becomes possible to configure such that the flight distance is 3 to 4 meters, for example. Since the housing  48  that holds the detector  50  is fixed to the base  12 , positioning accuracy of the detector  50  can be increased. 
     In the above-described configuration, a linear acceleration unit may be provided instead of the orthogonal acceleration unit. Further, the respective components may be arranged so as to invert the trajectory  44 . In  FIG. 1 , illustration of a data processor unit and a control unit is omitted. 
       FIG. 2  shows details of the incidence regulator unit  38  and its surroundings in an enlarged view. Meanwhile, the structure of the orthogonal acceleration unit  32  is expressed schematically. In  FIG. 2 , elements shown in  FIG. 1  are labeled with the same reference numerals, and their explanation will not be repeated below. 
     The housing  18  is attached to the housing  16 . These housings are composed of, for example, a metal such as aluminum. A round end portion  18 A of the housing  18  projects in the x-direction, and fits into the round opening  16 A formed on the housing  16 . The end portion  18 A has a round opening  18 B, and the annular flange  26  is arranged in the opening  18 B. At each point of joining between the above-noted plurality of components, a sealing member such as an O-ring is provided. 
     Inside the housing  16 , the constructed body  28  including the orthogonal acceleration unit  32  is arranged. The constructed body  28  is fixed to the base  12  by the support posts  30 . Inside the housing  16 , the incidence regulator unit  38  is provided, and is fixed to the base  12  by the pair of support posts  42 . The height of the incidence regulator unit  38 , or more specifically, the height of the slit, is adjusted to correspond, with high accuracy, to the above-described reference plane. Although a component that captures or blocks the ion flow that has passed in a horizontal direction through the orthogonal acceleration unit  32  is actually provided, its illustration is omitted. 
       FIG. 3  shows a front view of the incidence regulator unit  38 . The incidence regulator unit  38  comprises a main body  54 , the pair of blades  58 ,  60 , and heater units  64 ,  66 . The pair of blades  58 ,  60  are arranged alongside each other in the z-direction, and are detachably fastened to the main body  54  with a plurality of screws  62 . The pair of blades  58 ,  60  have a pair of edges  58 A,  60 A, and a width of the slit  80  in the z-direction is defined between these edges  58 A,  60 A. The main body  54  has an opening  56 , and the opening  56  defines a length of the slit  80  in the y-direction. This length is typically greater than the width of the ion flow. It is of course alternatively possible to use the opening  56  to limit the width, in the y-direction, of the ion flow. 
     For example, the blades  58 ,  60  are made of molybdenum, which is a non-magnetic metal. When the blades  58 ,  60  become soiled with ions to a degree exceeding a predetermined level, the pair of blades  58 ,  60  are removed from the main body  54  and are subjected to cleaning (more specifically, sanding). 
     At each of two ends of the main body  54  in the y-direction, a U-shaped groove is formed. A pair of heaters  68 ,  70  are arranged inside this pair of U-shaped grooves, and then the pair of U-shaped grooves are covered with a pair of covers  72 ,  74 . The pair of covers  72 ,  74  are fastened to the main body  54  with a plurality of screws  76 . The pair of U-shaped grooves, the pair of heaters  68 ,  70 , and the pair of covers  72 ,  74  constitute the pair of heater units  64 ,  66 . Upon heating, the pair of heaters  68 ,  70  expand, and their outer faces come in close contact with the inner faces of the respective U-shaped grooves, resulting in good heat conduction. For achieving better heat conduction, a heat conduction sheet such as a flexible copper foil may be arranged between the outer face of each heater  68 ,  70  and the inner face of the corresponding U-shaped groove. 
     The main body  54  has a plate-shaped form as a whole, and specifically has a rectangular shape when viewed in the x-direction. In other words, the main body  54  has a shape that extends in the y-direction and the z-direction. The width of main body  54  in the y-direction is indicated by reference numeral  100 . 
     A pair of mounts  79  are provided at lower portions of the main body  54 . The pair of mounts  79  project outward from the lower end portions, located on both sides in the y-direction, of the main body  54 . The extent of projection is indicated by reference numeral  102 . 
     The pair of mounts  79  are fixed to the base  12  by the pair of support posts  42 . The support posts  42  are of identical structure. Here, reference is made to the support post depicted in cutaway view on the right in  FIG. 3 . The mount  79  has a through hole formed therein along the z-direction. An outer sleeve  81  that forms a part of the post is provided underneath the mount  79 . The outer sleeve  81  has a through hole along the z-direction. A long bolt  82  is provided penetrating through the above-noted two through holes, which are aligned in the z-direction. A lower end portion  82 B of the bolt  82  constitutes a screw portion. Further, a threaded hole  84  is formed in the base  12 . The lower end portion  82 B is inserted into the threaded hole  84 , and these two elements are screwed together. A lower end portion of the outer sleeve  81  is also inserted into an upper part of the threaded hole  84 . 
     A head  82 A of the bolt  82  is exposed upward from the mount  79 . The head  82 A has a hexagonal recess to be engaged by a tip of a tool. By introducing a long tool from above as indicated by reference numeral  85 , the tip of the tool can be easily introduced into the recess. By rotating the tool in that state, fastening or removal of the bolt can be carried out. On the left side of the main body  54  also, bolt attachment and removal can be performed conveniently by introducing the tool in the same manner as described above. A structure similar to the above may be employed for each of the support posts that support the constructed unit. 
     The base  12  comprises a main part  51 , and a peripheral part  52  surrounding the main part  51 . The thickness of the main part  51  is greater than the thickness of the peripheral part  52 . The pair of support posts for fixing the incidence regulator unit  38  and the plurality of posts for fixing the constructed unit are secured to the main part  51 . The housings located on the upper side are fixed to the peripheral part  52 . 
       FIG. 4  shows a cross-section indicated by IV in  FIG. 3 . The main body  54  comprises, in the y-direction, a thin part and thick parts located on both sides thereof, and the pair of blades  58 ,  60  are attached to the thin part by the plurality of screws  62 . The edges  58 A,  60 A that form parts of the blades  58 ,  60  define the size of the slit  80  in the z-direction. The thin part has the opening  56 . On a far side of the thin part in the depth direction, a thick part is present, and this part constitutes the heater unit  64 . That is, a U-shaped groove is formed in the thick part, and a heater is arranged therein. The U-shaped groove is covered with the cover  72 , which is fastened with the plurality of screws  76 . A structure similar to that described above is also located on the near side of the thin part. Each of the support posts is composed of electrically conductive members. The base and the respective housings are set to ground potential, and the pair of blades  58 ,  60  are also set to ground potential. 
       FIG. 5  illustrates, in a schematic diagram, an instance of positioning of the slit  80 . For example, positioning of the slit  80  can be performed using a jig  92 . As already explained above, the slit  80  is defined by the pair of blades  58 ,  60 . The size of the slit  80  in the z-direction is indicated by t 1 . The central height of the slit  80  is at z 1 . In the example shown, the height z 0  of an upper face  90 A of a pusher electrode  90  serves as a reference. 
     The jig  92  comprises a block-shaped main body  94 , and a piece  96  that extends from the main body  94  in the horizontal direction. The size of the piece  96  in the z-direction is t 2 . From a substantial point of view, t 2  is equal to t 1 . In a state in which a lower face  94 A of the main body  94  is in close contact with the upper face  90 A, the intermediate level of the piece  96  is at height z 2 . When the height z 2  is equal to the height z 1 ; that is, when the piece  96  can be smoothly inserted into the slit  80  in that state, it can be determined that the height of the slit  80  is appropriate. When the piece  96  cannot be inserted into the slit  80 , the height of the slit  80  is to be adjusted. 
     By performing confirmation or adjustment of the height of the slit  80 , the incident ion flow can be appropriately arranged in place with respect to the reference plane of the orthogonal acceleration unit. The position and size of the slit may be confirmed or adjusted using a jig other than the jig shown. For example, the size of the slit  80  in the z-direction is 1 mm. For example, the length of the piece  96  is a few or several millimeters. For example, the jig is made of a metal. For example, the size of the main body of the jig in the horizontal directions is 10 mm by 10 mm. All numerical values mentioned in this specification are examples only. 
     The above-described embodiment includes a plurality of characteristic features. The individual characteristic features can also be used alone.