Mass spectrometry device

Abstract

The objective of the present invention is to increase the amount of ions introduced into a vacuum unit of a mass spectrometry device. To this end: a first deflecting electrode (5), an ionization probe (105), and a second deflecting electrode (6) are arranged sequentially along an ion introduction direction (X-axis direction); the ionization probe (105), the second deflecting electrode (6), and a pore (108) are arranged sequentially along an ion injection direction (-Z-axis direction); the absolute value of a first deflecting electrode voltage (V1) is equal to or greater than the absolute value of a second deflecting electrode voltage (V2); and the absolute value of an aperture electrode voltage (Va) is less than the absolute value of the second deflecting electrode voltage (V2).

Description

mass spectrometer

[0001] The present invention relates to a mass spectrometer.

[0002] A typical atmospheric pressure ionization mass spectrometer analyzes the mass of ions generated at atmospheric pressure by introducing them into a vacuum. There are various ion sources for generating ions at atmospheric pressure, including electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and matrix-assisted laser desorption ionization (MALDI). However, all of these methods produce noise components in addition to the desired ions. For example, ESI ion sources ionize a liquid sample by applying a high voltage while the liquid sample flows through a small-diameter metal capillary. This simultaneously generates noise components such as charged and neutral droplets in addition to ions. The ions and noise components thus generated are introduced into the vacuum chamber through a narrow aperture connecting the atmospheric pressure chamber and the vacuum chamber.

[0003] In particular, in ESI ion sources that ionize liquid samples by spraying them at high flow rates, the direction of spraying the liquid sample from the probe and the direction of ion introduction into the vacuum are orthogonal or oblique to prevent droplet components from being introduced into the vacuum. In this orientation, the heavy droplet components travel straight after spraying, preventing their introduction into the vacuum. On the other hand, charged vaporized ions are guided to the tip of the orifice by the potential difference between the probe tip and the orifice, and are preferentially introduced into the vacuum by the airflow generated by the pressure difference with the vacuum. However, because most of the generated ions are swept away by the spray flow, the amount of ions introduced into the vacuum is only a fraction of the amount actually ionized. Therefore, increasing the amount of ions introduced into the vacuum is important for improving sensitivity. Common approaches to increasing the amount of ions introduced into the vacuum are to enlarge the orifice diameter and improve the performance of the vacuum exhaust pump to increase the exhaust volume and thus the amount of ions drawn into the vacuum. While this method achieves improved sensitivity, it also increases the amount of droplet components that penetrate the vacuum, reducing robustness. It also requires a more powerful pump, which increases the size and manufacturing costs of the device.

[0004] As another method for improving the amount of ions introduced without increasing the exhaust volume, the abstract of the following Patent Document 1 states that "a flat focusing electrode (8) is arranged so that the inlet end (9a) of a heated capillary (9) that introduces ions into a subsequent vacuum chamber is inserted into the opening (8a), and a flat reflecting electrode (7) is arranged in a position opposite to the focusing electrode (8) across the spray flow ejected from the ionization probe (5). In addition, a grounded auxiliary electrode (6) is arranged between the ionization probe (5) and the reflecting electrode (7) and focusing electrode (8). The heated capillary (9) The capillary is grounded, and when measuring positive ions, voltages V1 and V2, where V1 > V2 > 0, are applied to the reflecting electrode (7) and focusing electrode (8). A reflective electric field is formed in the space between the reflecting electrode (7) and focusing electrode (8) to reflect and deflect ions originating from the sample components traveling on the spray stream, and a focusing electric field is formed near the inlet end (9a) to focus the ions at the inlet end (9a). Ions originating from the sample components are separated from the gas stream and efficiently collected at the inlet end (9a), where they are sucked into the heated capillary (9) and sent to the mass analysis section.

[0005] International Publication No. 2018 / 078693

[0006] However, in the above-mentioned technology, there is a demand for an even greater amount of ions to be introduced into the vacuum part. The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a mass spectrometer that introduces a large amount of ions into the vacuum part.

[0007] In order to solve the above problem, the mass spectrometer of the present invention comprises an ionization probe that injects a spray containing ions in an ion injection direction when a liquid sample is supplied thereto; an aperture electrode having an aperture for sending the generated ions to a vacuum chamber and arranged so that the ion injection direction and the direction of ion introduction into the aperture are perpendicular or oblique; first and second deflection electrodes that deflect ions; and a power supply unit that applies a first deflection electrode voltage to the first deflection electrode, a second deflection electrode voltage to the second deflection electrode, an ionization probe voltage to the ionization probe, and an aperture electrode voltage to the aperture electrode, respectively, wherein the first deflection electrode, the ionization probe, and the second deflection electrode are arranged sequentially along the ion introduction direction, and the ionization probe, the second deflection electrode, and the aperture are arranged sequentially along the ion injection direction, and the absolute value of the first deflection electrode voltage is equal to or greater than the absolute value of the second deflection electrode voltage, and the absolute value of the aperture electrode voltage is less than the absolute value of the second deflection electrode voltage.

[0008] According to the present invention, the amount of ions introduced into the vacuum section can be increased.

[0009] 1 is a schematic diagram of a mass spectrometer according to a first embodiment; FIG. 1 is a schematic diagram of essential parts of an ion source, etc.; FIG. 2 is a schematic diagram of a counter electrode, etc., viewed from the X-axis direction; FIG. 3 is a block diagram of a computer; FIG. 4 is a diagram showing simulation results of an electrostatic field inside an ion source; FIG. 5 is a diagram showing examples of measurement results of signal intensity in the first embodiment and comparative examples #1 and #2; FIG. 6 is a diagram showing examples of measurement results of signal intensity for various voltage values ​​in the first embodiment; FIG. 7 is a schematic diagram of a counter electrode, etc., viewed from the X-axis direction in the second embodiment; FIG. 8 is a schematic diagram of essential parts of an ion source in a third embodiment; FIG. 9 is a schematic diagram of a counter electrode, etc., viewed from the X-axis direction in the third embodiment; FIG. 10 is a schematic diagram of essential parts of an ion source in a fourth embodiment; FIG. 11 is a schematic diagram of a counter electrode, etc., in the fourth embodiment, viewed from the X-axis direction.

[0010] [Summary of the embodiment] According to the technology applying the contents of the above-mentioned Patent Document 1, it is believed that the amount of ions introduced can be increased by guiding ions using an electric field. However, in a configuration in which the liquid sample is sprayed perpendicular to the ion introduction direction, the distribution and movement speed of ions are asymmetric between the upstream and downstream sides of the spray from the orifice, and therefore the potential required to form an optimal electric field differs around the orifice. Therefore, in a configuration in which the orifice is surrounded by electrodes of the same potential, the ion focusing effect on the orifice is limited. Furthermore, in a configuration in which the orifice is surrounded by electrodes, removing the electrodes during maintenance is cumbersome, which makes maintenance difficult.

[0011] For the same reason, the auxiliary electrode surrounding the spray stream also presents maintenance problems. Furthermore, because the auxiliary electrode is installed close to the sample injection section, it is easily contaminated by the injected liquid sample, resulting in unstable electric field formation. For these reasons, the following embodiments provide an ion source and a mass spectrometer that operate more favorably for asymmetric ion distributions around the ion injection section in a mass spectrometer configured such that the liquid sample injection direction is perpendicular or oblique to the ion introduction direction. That is, the present invention provides an ion source and a mass spectrometer that are capable of effectively generating an ion-induced electric field, have a simple structure, are easy to maintain, and are less susceptible to contamination by the liquid sample.

[0012] First Embodiment Overall Configuration of Mass Spectrometer Figure 1 is a schematic diagram of a mass spectrometer 101 according to the first embodiment. The mass spectrometer 101 includes a housing 104, an ionization probe 105, a power supply unit 109, and vacuum pumps 121, 122, and 123. The housing 104 is formed in a generally cylindrical shape with both ends closed. The housing 104 in Figure 1 is shown in a schematic cross-sectional shape along its central axis. The axis along the central axis of the housing 104 is referred to as the X-axis, and the axis perpendicular to the X-axis and extending upward in Figure 1 is referred to as the Z-axis. The axis extending from the back to the front of the page is referred to as the Y-axis.

[0013] The housing 104 is divided by a plurality of partition walls (not numbered), each of which has a through hole 108, 119, or 120 formed therein in the axial direction. The spaces formed by these partition walls are referred to, from left to right, as the ion source chamber 106, and vacuum chambers 116, 117, and 118. The ion source chamber 106, the internal components of the ion source chamber 106 (details of which will be described later), and the ionization probe 105 are collectively referred to as the ion source 102.

[0014] The ionization probe 105 introduces a liquid sample into the ion source chamber 106, which generates ions (not shown) in the ion source 102. An aperture electrode 107 is formed at the right end of the ion source chamber 106 in the drawing, and an aperture 108 connects a partition wall (not numbered) to the aperture electrode 107. The ions generated in the ion source 102 are introduced into the vacuum chamber 116 through the aperture 108.

[0015] The ions that reach vacuum chamber 116 are further introduced into vacuum chamber 118 via vacuum chamber 117. The ions that reach vacuum chamber 118 are then analyzed in mass analysis unit 103. Various voltages are applied to mass analysis unit 103 by power supply unit 109. Control unit 110 controls the timing and voltage values ​​of voltage application by power supply unit 109.

[0016] In the ion source 102, in addition to ions, unnecessary noise components such as droplets that should not be introduced into the vacuum chamber 116 and vaporized components of the droplets are generated. To prevent these noise components from leaking into the vacuum chamber 116, the space between the ion source chamber 102 and the vacuum chamber 116 may be sealed (or nearly sealed). Furthermore, the ion source chamber 106 may be provided with an exhaust section 113 to exhaust these noise components.

[0017] Since a voltage is applied to the aperture electrode 107 (details will be described later), the housing 104 and the aperture electrode 107 are insulated via an insulator (not shown). The above-mentioned apertures 119 and 120 are also ion passages, similar to the aperture 108, and a voltage may be applied to the member having each aperture. In this case, it is preferable to insulate the housing 104 from the peripheral portions of the apertures 119 and 120 via an insulator (not shown). In the example of FIG. 1 , the mass spectrometer 101 includes three vacuum chambers 116, 117, and 118, but the number of vacuum chambers may be more or less than this.

[0018] The vacuum chambers 116, 117, and 118 are evacuated by vacuum pumps 121, 122, and 123, respectively, and their atmospheric pressures are generally maintained at approximately several hundred Pa, several Pa, and 0.1 Pa or less, respectively. The vacuum chamber 117 is provided with an ion transport unit 124 that focuses and transmits ions. A multipole electrode, an electrostatic lens, or the like can be used for the ion transport unit 124. The ion transport unit 124 may be disposed in another vacuum chamber, such as the vacuum chambers 116 and 118. A high-frequency voltage, a DC voltage, an AC voltage, or a combination of these voltages is applied to the ion transport unit 124 from the power supply unit 109.

[0019] In the illustrated example, the mass analysis unit 103 includes an ion analysis unit 125 and a detector 126. The ion analysis unit 125 separates and dissociates ions, and may be an ion trap, a quadrupole filter electrode, a collision cell, a time-of-flight mass analyzer (TOF), or a combination of these. Ions that pass through the ion analysis unit 125 are detected by the detector 126. The detector 126 may be an electron multiplier, a multichannel plate (MCP), or the like.

[0020] The ions detected by the detector 126 are converted into electrical signals, etc., and information such as the mass and intensity of the ions can be analyzed in detail by the control unit 110. The control unit 110 also includes an input / output unit and memory for receiving instructions from the user and controlling voltage, etc., and also includes software necessary for power supply operation, etc. The voltage supplied from the power supply unit 109 to the mass analysis unit 103 can be a radio frequency voltage, a direct current voltage, an alternating current voltage, or a combination of these.

[0021] 2 is a schematic diagram of the main components of the ion source 102. As described above, the ion source 102 includes the ionization probe 105 and the aperture electrode 107, and the aperture electrode 107 has an aperture 108 formed therein. The ion source 102 further includes a first deflection electrode 5, a second deflection electrode 6, and a counter electrode 7.

[0022] The aperture electrode 107 is formed in a substantially cylindrical shape, and its tip (the left end in the figure) is formed in a conical shape. The aperture 108 is formed so as to pass through the central axis of the aperture electrode 107. The counter electrode 7 is formed in a substantially funnel shape that covers the aperture electrode 107, and an opening 7a is formed at a location facing the aperture 108. This forms a gas passage (no reference numeral) between the aperture electrode 107 and the counter electrode 7 through which gas passes. The first deflecting electrode 5 and the second deflecting electrode 6 are formed in a substantially rectangular block shape.

[0023] The ionization probe 105 in this embodiment is an electrospray ion source (ESI) and includes a capillary 1 and cylindrical tubes 2 and 3. The capillary 1 is cylindrical, and a liquid sample is supplied to it. The cylindrical tubes 2 and 3 are arranged concentrically with the capillary 1, and the cylindrical tube 3 is arranged on the outer periphery of the cylindrical tube 2.

[0024] In the ion source 102, the −Z-axis direction, which is the direction of ion injection from the ionization probe 105, and the X-axis direction, which is the direction of ion introduction into the orifice 108, are orthogonal to each other. However, the ion injection direction and the ion introduction direction may be oblique to each other.

[0025] As shown in FIG. 2 , the tip 1a of the capillary 1, the second deflection electrode 6, and the opening 7a at the tip of the counter electrode 7 are sequentially arranged along the −Z-axis direction, which is the ion injection direction. The tip 1a of the capillary 1, one end (upper end) of the first deflection electrode 5, the aperture 108, and the other end (lower end) of the first deflection electrode 5 are sequentially arranged along the −Z-axis direction. The first deflection electrode 5, the tip 1a of the capillary 1, and the opening 7a are sequentially arranged along the X-axis direction, which is the ion introduction direction. In the figure, the left end of the aperture 108 is referred to as the aperture entrance 108a. The positions of the second deflection electrode 6 and the aperture entrance 108a in the X-axis direction are also close to the position of the aperture 7a of the counter electrode 7 in the X-axis direction.

[0026] Examples of dimensions of each part are described below. The distance between the tip 1a of the capillary 1 and the orifice entrance 108a is 25 mm in the Z-axis direction and 7 mm in the X-axis direction. The distance between the first deflection electrode 5 and the orifice entrance 108a is 17 mm in the X-axis direction. The distance between the second deflection electrode 6 and the orifice entrance 108a is 11 mm vertically in the Z-axis direction and 0.5 mm in the X-axis direction. The distance between the opening 7a of the counter electrode 7 and the orifice entrance 108a is 1 mm in the X-axis direction. In addition, the width D6 (see Figure 3) of the second deflection electrode 6 in the Y-axis direction is 15 mm. Note that the above-mentioned dimensions are merely examples, and the dimensions of each part are not limited to those described above.

[0027] 3 is a schematic diagram of the counter electrode 7 and other electrodes as viewed from the X-axis direction. In FIG. 3, the dimension of the first deflection electrode 5 is indicated by a dashed line. As shown in the figure, the widths of the first deflection electrode 5 and the counter electrode 7 in the Y-axis direction are approximately the same.

[0028] Returning to FIG. 2 , the power supply unit 109 includes an ionization probe power supply 12, a first deflection electrode power supply 13, a second deflection electrode power supply 14, a counter electrode power supply 15, and an aperture electrode power supply 16. The ionization probe power supply 12 applies an ionization probe voltage Vi to the capillary 1 of the ionization probe 105. The first deflection electrode power supply 13 applies a first deflection electrode voltage V1 to the first deflection electrode 5. The second deflection electrode power supply 14 applies a second deflection electrode voltage V2 to the second deflection electrode 6. The counter electrode power supply 15 applies a counter electrode voltage Vc to the counter electrode 7. The aperture electrode power supply 16 applies an aperture electrode voltage Va to the aperture electrode 107.

[0029] The control unit 110 sets each of the above-mentioned voltages depending on the type of ions to be introduced into the vacuum chamber 116 (see FIG. 1 ). However, the control unit 110 maintains the relationship "|V1|≧|V2|>|Vc|>|Va|" for each of the above-mentioned voltages.

[0030] <Operation of First Embodiment> Next, the operation of the first embodiment will be described. The ionization probe 105 generates ions of a liquid sample using a principle known as electrospray ionization (ESI). That is, the ionization probe power supply 12 applies an ionization probe voltage Vi to a metal capillary 1, and a pump (not shown) supplies the liquid sample to the capillary 1. As a result, a spray 18 containing ions of the liquid sample is ejected from the tip 1a of the capillary 1. In the process of ion generation using the ESI method, droplets of the liquid sample repeatedly split, eventually becoming very fine droplets that are then ionized.

[0031] Droplets that are not sufficiently atomized during the ionization process include neutral droplets and charged droplets. To reduce these droplets, a cylindrical tube 2 is provided on the outer periphery of the capillary 1. That is, when gas is supplied between the capillary 1 and the cylindrical tube 2, the gas is ejected at high speed from the outlet end 2a of the cylindrical tube 2. This promotes atomization of the droplets. Furthermore, a cylindrical tube 3 is provided outside the cylindrical tube 2, through which high-temperature gas heated by a heater flows and is ejected from the outlet end 3a. This heats and evaporates the ejected droplets, further promoting ionization.

[0032] The ions and droplets generated under atmospheric pressure become a spray 18 and move in the −Z-axis direction, which is the ion injection direction, i.e., downward in FIG. 2, until they reach the region between the first deflection electrode 5 and the second deflection electrode 6. As described above, the voltages of the various components set by the control unit 110 have the relationship "|V1|≧|V2|>|Vc|>|Va|". Here, when the charge of the ions to be generated is positive, these voltages have the relationship "V1≧V2>Vc>Va". On the other hand, when the charge of the ions is negative, the polarity of these voltages is reversed.

[0033] FIG. 4 is a block diagram of a computer 980. The control unit 110 shown in FIGS. 1 and 2 includes one or more computers 980 shown in FIG. 4. In FIG. 4, the computer 980 includes a CPU 981, a storage unit 982, a communication I / F (interface) 983, an input / output I / F 984, and a media I / F 985. The storage unit 982 includes a RAM 982a, a ROM 982b, and an SSD (Solid State Drive) 982c. The communication I / F 983 is connected to a communication circuit 986. The input / output I / F 984 is connected to an input / output device 987. The media I / F 985 reads and writes data from a recording medium 988. The ROM 982b stores an IPL (Initial Program Loader) executed by the CPU, etc. The SSD 982c stores control programs, various data, etc. The CPU 981 executes control programs and the like read from the SSD 982c to the RAM 982a to realize various functions.

[0034] Figure 5 shows the results of a simulation of the electrostatic field inside the ion source 102. In Figure 5, the direction of the arrow indicates the direction of the electric field. The simulation conditions for Figure 5, including the positional relationship of each part, are as follows: - The distance between the tip end 1a of the capillary 1 and the orifice entrance 108a is 25 mm vertically (Z-axis direction) and 7 mm horizontally (X-axis direction). - The distance between the first deflection electrode 5 and the orifice entrance 108a is 17 mm horizontally (X-axis direction). - The distance between the second deflection electrode 6 and the orifice entrance 108a is 11 mm vertically (Z-axis direction) and 0.5 mm horizontally (X-axis direction). - The distance between the opening 7a of the counter electrode 7 and the orifice entrance 108a is 1 mm horizontally (X-axis direction).

[0035] In addition, the voltages set by the control unit 110 are as follows: the ionization probe voltage Vi is 4500 [V], the first deflection electrode voltage V1 is 4000 [V], the second deflection electrode voltage V2 is 2000 [V], the counter electrode voltage Vc is 650 [V], and the aperture electrode voltage Va is 80 [V].

[0036] As a result, an electric field is formed between the first deflection electrode 5 and the second deflection electrode 6, which pushes positive ions toward the second deflection electrode 6. This electric field induces some of the ions toward the second deflection electrode 6. In addition, an electric field directed toward the counter electrode 7 is formed between the first deflection electrode 5 and the counter electrode 7.

[0037] The ions guided below the second deflection electrode 6 are further guided to the opening 7a of the counter electrode 7 by the electric field generated between the second deflection electrode 6 and the counter electrode 7. In this case, in order to form an electric field having a sufficiently wide range relative to the width of the ion distribution in the Y-axis direction, it is desirable that the width D6 (see FIG. 3) of the second deflection electrode 6 in the Y-axis direction be 10 mm or more.

[0038] Furthermore, ions that cannot be guided to the second deflection electrode 6 and continue to flow downstream of the spray flow 18 reach the gap between the first deflection electrode 5 and the opening 7a. The ions are then guided to the opening 7a by a stronger electric field generated by the potential difference "V1-V3" between the two. The ions guided to the opening 7a of the counter electrode 7 in this way are accelerated to the orifice entrance 108a by the electric field generated by the potential difference between the counter electrode 7 and the orifice electrode 107.

[0039] The ions guided to the aperture entrance 108a are then introduced into the vacuum chamber 116 by an air current generated by the pressure difference between the atmospheric pressure in the ion source chamber 106 and the vacuum chamber 116 (see FIG. 36).

[0040] Returning to FIG. 2 , the counter electrode 7 is provided to cover the outside of the aperture electrode 107. An inert gas 19 is passed through the gap between the counter electrode 7 and the aperture electrode 107, and a gas flow 20 is ejected from the opening 7 a of the counter electrode 7. In addition to normal ions, the nebulized flow 18 contains noise components such as neutral droplets with no charge and charged droplets with a low charge-to-mass ratio. These noise components are difficult to accelerate by an electric field. Therefore, in this embodiment, the gas flow 20 is ejected from the opening 7 a, thereby preventing the noise components from entering the aperture 108. At the same time, the gas flow 20 can promote evaporation of droplets that are not sufficiently vaporized. By providing the counter electrode 7 in this manner, the robustness of the mass spectrometer 101 can be improved.

[0041] The size, shape, etc. of the electrodes 5 and 6 shown in Figures 2 and 3 are not particularly limited, and various sizes and shapes can be used as long as the desired positional relationship is satisfied. An example is shown below. First, the first deflection electrode 5 is required to generate an electric field that is sufficiently wide for the ion distribution range in the spray flow 18. Therefore, the width of the first deflection electrode 5 in the Y-axis direction is desirably 15 mm or more. For example, the first deflection electrode 5 may be formed in a flat plate shape, with a vertical width in the Z-axis direction of 30 mm and a horizontal width in the Y-axis direction of 15 mm. In this example, the first deflection electrode 5 can generate an electric field that is sufficiently wide for the ion distribution range in the spray flow. Furthermore, to suppress discharge from the first deflection electrode 5, it is desirably chamfered to provide a gentle curve.

[0042] Furthermore, although the second deflection electrode 6 shown in FIGS. 2 and 3 has a rectangular parallelepiped block shape with the Y-axis direction as the longitudinal direction, the shape of the second deflection electrode 6 is not limited to this. For example, the second deflection electrode 6 may be formed in a cylindrical shape with the central axis in the Y-axis direction. Forming the electrode in a cylindrical shape eliminates corners, thereby suppressing discharge from the second deflection electrode 6. Furthermore, adopting a simple "cylindrical" shape can reduce manufacturing costs and facilitates attachment, removal, and cleaning during maintenance. Furthermore, in this embodiment, the second deflection electrode 6 has a simple structure in which it is disposed above the counter electrode 7, so the structure is not complicated and high maintainability can be achieved.

[0043] <Comparative Examples> (Comparative Example #1) Here, various comparative examples will be described to clarify the effects of the first embodiment. First, comparative example #1 is the same as the configuration of the first embodiment (see FIG. 2 ) except that the second deflection electrode 6 is removed. In comparative example #1, the ions contained in the nebulized flow 18 and serving as the measurement target are also blocked by the gas flow 20, making it difficult for them to reach the opening 7a of the counter electrode 7. This reduces the number of ions introduced into the vacuum chamber 116 (see FIG. 1 ), resulting in a problem of reduced sensitivity of the mass spectrometer 101. As described above, according to the first embodiment, the installation of the first deflection electrode 5 and the second deflection electrode 6 makes it possible to achieve both robustness and high sensitivity.

[0044] Furthermore, when an electrode is placed near the ionization probe 105 using the ESI method, a large amount of sprayed ions and droplets will collide with the electrode surface over a long period of use. This can cause material to accumulate on the electrode surface, forming a film and causing charging, which can destabilize the electric field formation. In particular, the second deflection electrode 6 is close to the pore entrance 108a, and is positioned toward which ions deflected by the first deflection electrode 5 are directed, which is thought to make it more susceptible to charging. However, in this embodiment, the second deflection electrode 6 is placed closer to the vacuum chamber 116 (see FIG. 1 ) than the opening 7a of the counter electrode 7, and a gas flow 20 is injected from the opening 7a. This gas flow 20 can prevent contamination of the second deflection electrode 6, enabling a stable electric field to be formed.

[0045] (Comparative Example #2) Next, Comparative Example #2 will be described. Comparative Example #2 is the same as the configuration of the first embodiment except that the first deflection electrode 5 and the second deflection electrode 6 are removed. In Comparative Example #2, ions are even less likely to reach the opening 7a of the counter electrode 7 than in Comparative Example #1.

[0046] FIG. 6 shows examples of signal intensity measurement results for the first embodiment and comparative examples #1 and #2. In FIG. 6, a solution of reserpine, a type of organic compound, was used as the liquid sample. Here, the "signal intensity" on the vertical axis represents the signal intensity detected by the detector 126 installed in the vacuum chamber 118 (see FIG. 1), and the unit is arbitrary units. The conditions for the positional relationship of each component, applied voltage, etc. in the first embodiment are the same as those in the simulation shown in FIG. 5. Furthermore, in comparative examples #1 and #2, the conditions for the highest sensitivity during reserpine measurement were selected.

[0047] 6, the amount of ions introduced in Comparative Example #1 is increased compared to Comparative Example #2, resulting in a signal strength that is approximately 1.6 times stronger. Furthermore, in the first embodiment, the amount of ions introduced is increased, and the signal strength is increased by approximately 2.1 times compared to Comparative Example #2. The simulation results and the experimental results using a real system show that by providing the second deflection electrode 6 in addition to the first deflection electrode 5, an effective ion-inducing electric field as described above is formed, thereby increasing the amount of ions introduced.

[0048] Fig. 7 is a diagram showing an example of measurement results of signal strength for various voltage values ​​in the first embodiment. The bar graph in Fig. 7 shows the signal strength when the first deflection electrode voltage V1 is changed to 0, 1, 2, 3, 4, and 5 [kV] and the second deflection electrode voltage V2 is changed to 0, 1, 2, 3, and 4 [kV] for each first deflection electrode voltage V1.

[0049] 7, it can be seen that the higher the first deflection electrode voltage V1, the higher the second deflection electrode voltage V2 at which the signal intensity is maximized. Furthermore, for any first deflection electrode voltage V1, the signal intensity is maximized at the second deflection electrode voltage V2 at which the magnitude relationship between the voltages V1 and V2 is "V1 ≥ V2." As described above, it is preferable to impose this magnitude relationship of "V1 ≥ V2" in order to form an electric field that guides ions toward the counter electrode 7 and the aperture electrode 107.

[0050] In the ion source 102 shown in FIG. 2, the signal intensity is maximized when V1 = 2 kV and V2 = 2 kV. However, the positions of the first deflection electrode 5 and the second deflection electrode 6 and the optimal voltage values ​​are interrelated, and the optimal voltage conditions vary depending on the device configuration and the liquid sample. For example, to prevent contamination by the sprayed liquid sample, it may be possible to further increase the distance between the spray flow 18, the first deflection electrode 5, and the second deflection electrode 6 from the experimental conditions. Even in this case, a large signal intensity can be obtained by maintaining the relationship "V1 ≧ V2."

[0051] Conversely, it is also possible to further reduce the distance between the spray 18, the first deflection electrode 5, and the second deflection electrode 6 compared to the experimental conditions. Even in this case, a large signal strength can be obtained by maintaining the relationship "V1 ≥ V2." When ensuring sufficient distance from the spray to each electrode to prevent contamination of the electrodes, it is desirable that the second deflection electrode voltage V2 be higher than the counter electrode voltage Vc in order to effectively form an electric field. Furthermore, it is desirable that the second deflection electrode voltage V2 be 2 kV or higher.

[0052] Furthermore, because the difficulty of ionization varies for each liquid sample, the optimal ionization probe voltage Vi and ion distribution in the spray flow differ for each liquid sample. Therefore, the optimal values ​​for the ionization probe voltage Vi of the ionization probe 105 and the distance between the tip 1 a of the capillary 1 and the orifice entrance 108 a also differ for each liquid sample. Therefore, it is preferable to adjust the positional relationship between each component or the applied voltage to each component depending on the type of liquid sample. Adjustments depending on the type of liquid sample can be made to either the positional relationship or the applied voltage, and can be freely adjusted within the range of feasible positional relationship or applied voltage.

[0053] 7, the optimal values ​​of voltages V1 and V2 are the same, 2 kV. Therefore, by adjusting the positions of electrodes 5 and 6, it is possible to keep voltages V1 and V2 at the same value, and a sufficiently large signal intensity can be obtained. In this case, the number of voltages that power supply unit 109 must generate is reduced, which simplifies power supply unit 109 and reduces the cost of mass spectrometer 101.

[0054] Second Embodiment Next, a mass spectrometer according to a second embodiment will be described. In the description of each embodiment, parts corresponding to those in the other embodiments described above will be designated by the same reference numerals, and their description may be omitted. The configuration of the mass spectrometer according to the second embodiment is similar to that of the mass spectrometer 101 according to the first embodiment (see FIGS. 1 to 4), except for the following points. In other words, in the second embodiment, a second deflection electrode 26 shown in FIG. 8 is used in place of the second deflection electrode 6 (see FIG. 2) in the first embodiment.

[0055] FIG. 8 is a schematic diagram of the counter electrode 7 and other components in the second embodiment, viewed from the X-axis direction. In FIG. 8 , the dimensions of the first deflection electrode 5 are indicated by a dashed-dotted line. The second deflection electrode 26 has a shape obtained by curving a rectangular plate into an arc. The center of this arc is located on the central axis of the opening 7a of the counter electrode 7 and the aperture 108. This creates an electric field that focuses on the central axis from the opposing surface 26a of the second deflection electrode 6 that faces the central axis. This allows ions pushed out by the first deflection electrode 5 (see FIG. 2 ) to be concentrated at the opening 7a, thereby increasing the amount of ions introduced into the aperture 108. It is also desirable to chamfer the corners of the second deflection electrode 26 to reduce the curve.

[0056] Third Embodiment A mass spectrometer according to a third embodiment will now be described. The configuration of the mass spectrometer according to the third embodiment is similar to that of the mass spectrometer 101 according to the first embodiment (see FIGS. 1 to 4), except for the following points. That is, in the third embodiment, the second deflection electrode 6 (see FIG. 2) in the first embodiment is replaced by a second deflection electrode 36 shown in FIGS. 9 and 10.

[0057] FIG. 9 is a schematic diagram of a main part of an ion source according to the third embodiment. FIG. 10 is a schematic diagram of the counter electrode 7 and other components according to the third embodiment, viewed from the X-axis direction. In FIG. 10, the dimensions of the first deflection electrode 5 are indicated by a dashed line. As shown in FIGS. 9 and 10, the second deflection electrode 36 has a shape in which the lower part of a rectangular parallelepiped block is cut out along a parabolic surface. In other words, the second deflection electrode 36 has a parabolic opposing surface 36a that faces the central axis (not shown) of the orifice 108. The opposing surface 36a faces the spray 18, and its focal point (not shown) is located near the opening 7a of the counter electrode 7 on the central axis of the orifice 108.

[0058] According to the third embodiment, the shape of the second deflection electrode 36 described above allows the generation of an electric field that focuses ions near the opening 7a over a wide area, thereby further improving the amount of ion introduction. In the above example, the opposing surface 36a may be changed to a spherical surface. Whether the opposing surface 36a is a parabolic surface or a spherical surface, the opposing surface 36a faces the central axis of the orifice 108, and has a shape that approaches the central axis of the orifice 108 as it approaches the orifice 108.

[0059] [Fourth Embodiment] Next, a mass spectrometer according to a fourth embodiment will be described. The configuration of the mass spectrometer according to the fourth embodiment is similar to that of the mass spectrometer 101 according to the first embodiment (see FIGS. 1 to 4), except for the following points. That is, in the mass spectrometer according to the fourth embodiment, an ion source 142 shown in FIG. 11 is used instead of the ion source 102 shown in FIG. 2.

[0060] 11 is a schematic diagram of a main part of an ion source 142 according to the fourth embodiment. The ion source 142 includes all of the components of the ion source 102 (see FIG. 2) according to the first embodiment, and further includes a third deflection electrode 21 below (in the −Z-axis direction) the opening 7a of the counter electrode 7. In the fourth embodiment, the tip end 1a of the capillary 1, the second deflection electrode 6, the opening 7a, and the third deflection electrode 21 are sequentially arranged along the −Z-axis direction, which is the ion injection direction.

[0061] The power supply unit 109 also includes a third deflection electrode power supply 22 that applies a third deflection electrode voltage V3 (not shown) to the third deflection electrode 21. The control unit 17 commands the third deflection electrode voltage V3 to the third deflection electrode 21. The control unit 17 then sets these voltages so that the magnitude relationship between the voltages applied to the electrodes, etc. satisfies "|V1|≧|V2|>|Vc|>|Va| and |V2|≧|V3|."

[0062] Fig. 12 is a schematic diagram of the counter electrode 7 and other components in the fourth embodiment as viewed from the X-axis direction. In Fig. 12, the dimensions of the first deflection electrode 5 are indicated by a dashed line. In the illustrated example, the second deflection electrode 6 and the third deflection electrode 21 have substantially the same shape and dimensions. However, the shapes and dimensions of the two electrodes may be different. In the fourth embodiment, the shapes, dimensions, and voltages of the components other than those described above are the same as those of the first embodiment.

[0063] Next, the operation of the fourth embodiment will be described. Some of the ions deflected by the first deflection electrode 5 also reach the downstream side in the −Z axis direction of the opening 7a of the counter electrode 7. The third deflection electrode 21 in the fourth embodiment is responsible for forming an electric field that focuses the ions that have reached the downstream side of the opening 7a toward the opening 7a.

[0064] Furthermore, since the second deflection electrode voltage V2 and the third deflection electrode voltage V3 have the relationship "|V2|≧|V3|", the effect of the second deflection electrode 6 in guiding ions to the opening 7a is not substantially impaired. In this way, by providing the third deflection electrode 21, it is possible to form an electric field that is more finely adjusted with respect to the ion distribution around the opening 7a. As a result, this embodiment can further increase the amount of ion introduction compared to the first embodiment.

[0065] The magnitude relationship between the counter electrode voltage Vc and the third deflection electrode voltage V3 varies depending on the ions to be measured. Therefore, it is preferable to control the ion distribution by adjusting the optimal voltage relationship between the voltages V3 and Vc depending on the deflection state of the first deflection electrode 5. The optimization of the configuration may be achieved by adjusting the electrode voltage values ​​or the electrode positions. Furthermore, the third deflection electrode 21 in this embodiment can effectively increase the amount of ion introduction even in a configuration without a counter electrode 7 (not shown). The second deflection electrode 6 and the third deflection electrode 21 may have various shapes, such as the shapes of the second deflection electrode 26 (see FIG. 8) and the second deflection electrode 36 (see FIG. 9) shown in the second and third embodiments.

[0066] [Modifications] The present invention is not limited to the above-described embodiment, and various modifications are possible. The above-described embodiment is provided as an example to facilitate understanding of the present invention, and is not necessarily limited to an embodiment including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to delete part of the configuration of each embodiment, or to add or replace other configurations. Furthermore, the control lines and information lines shown in the figures are those considered necessary for explanation, and do not necessarily represent all control lines and information lines necessary for the product. In reality, it is possible to consider that almost all components are interconnected. Possible modifications of the above-described embodiment include, for example, the following.

[0067] (1) The electrodes 5, 6, 7, 21, and 107 in each of the above-described embodiments may be equipped with heaters for heating these electrodes and temperature sensors for measuring the temperatures of each electrode. In this case, the control unit 110 may adjust the current flowing through the heaters so that the detection results of each temperature sensor approach their respective predetermined set values. If the nebulized flow 18 is cooled, ionization of the liquid sample is hindered. Therefore, by heating each electrode, ionization of the liquid sample can be promoted, further improving sensitivity and robustness.

[0068] (2) In the above embodiments, the first deflection electrode 5 has a rectangular parallelepiped block shape, but the shape of the first deflection electrode 5 is not limited to this. That is, the surface of the first deflection electrode 5 facing the aperture 108 (the right side surface in FIGS. 2, 11, etc.) may be a cylindrical surface or a concave surface that is a parabolic surface. When a cylindrical surface is used, it is preferable that its central axis intersects with the central axis of the aperture 108. Furthermore, when a parabolic surface is used, it is preferable that its focal point is located on the central axis of the aperture 108. This makes it possible to form an electric field that concentrates ions into the aperture.

[0069] [Effects of the Embodiments] As described above, according to the above-described embodiments, the first deflection electrode 5, the ionization probe 105, and the second deflection electrodes 6, 26, and 36 are sequentially arranged along the ion introduction direction (X-axis direction), the ionization probe 105, the second deflection electrodes 6, 26, and 36, and the orifice 108 are sequentially arranged along the ion injection direction (-Z-axis direction), the absolute value of the first deflection electrode voltage V1 is equal to or greater than the absolute value of the second deflection electrode voltage V2, and the absolute value of the orifice electrode voltage Va is less than the absolute value of the second deflection electrode voltage V2. This makes it possible to increase the amount of ions introduced into the vacuum chamber 116 while suppressing the intrusion of noise components into the vacuum chamber 116, and to achieve high sensitivity of the mass spectrometer 101.

[0070] The mass spectrometer 101 further includes a counter electrode 7 that covers the aperture electrode 107 while forming a gap between the aperture electrode 107 that allows air to pass through, and has an opening 7a at a location facing the aperture 108, and the power supply unit 109 further applies a counter electrode voltage Vc to the counter electrode 7, and it is more preferable that the absolute value of the counter electrode voltage Vc is greater than the absolute value of the aperture electrode voltage Va and smaller than the absolute value of the second deflection electrode voltage V2. This allows ions to be guided to the opening 7a by the electric field generated between the first deflection electrode 5 and the counter electrode 7, thereby making it possible to achieve even higher sensitivity for the mass spectrometer 101.

[0071] It is more preferable that the first deflection electrode 5, the ionization probe 105, the opening 7a, and the second deflection electrodes 6, 26, and 36 are arranged in this order along the ion introduction direction (X-axis direction), thereby making it possible to achieve even higher sensitivity for the mass spectrometer 101.

[0072] Furthermore, as in the fourth embodiment, the mass spectrometer 101 further includes a third deflection electrode 21 that deflects ions, and the power supply unit 109 further applies a third deflection electrode voltage V3 to the third deflection electrode 21. It is even more preferable that the positional relationship of the components is such that the first deflection electrode 5, the ionization probe 105, and the third deflection electrode 21 are sequentially arranged along the direction of ion introduction into the orifice 108 (X-axis direction), and the ionization probe 105, the second deflection electrodes 6, 26, 36, the orifice 108, and the third deflection electrode 21 are sequentially arranged along the ion injection direction (-Z-axis direction). This makes it possible to use the third deflection electrode 21 to form an electric field that is more finely adjusted with respect to the ion distribution around the opening 7a of the counter electrode 7.

[0073] Furthermore, it is more preferable that the width of the second deflection electrodes 6, 26, 36 in a plane perpendicular to the direction of ion introduction into the aperture 108 (X-axis direction) is 10 mm or more, and the absolute value of the second deflection electrode voltage V2 is 2000 V or more. This makes it possible to realize the formation of an electric field having a sufficiently wide range relative to the width of the ion distribution in the Y-axis direction.

[0074] Furthermore, as in the second and third embodiments, it is more preferable that the second deflection electrodes (26, 36) have surfaces curved in an arc shape so as to have the same central axis as the central axis of the orifice 108, and have opposing surfaces 26a, 36a that face the central axis of the orifice 108. This allows ions to be guided toward the central axis of the orifice 108, thereby making the mass spectrometer 101 even more sensitive.

[0075] Furthermore, as in the third embodiment, it is more preferable that the facing surface 36a is a parabolic surface having a focal point on the central axis of the aperture 108. This makes it possible to guide ions to the focal point on the central axis of the aperture 108.

[0076] Furthermore, as in the third embodiment, it is more preferable that the second deflection electrode 36 has an opposing surface 36a that faces the central axis of the orifice 108 and has a shape that approaches the central axis of the orifice 108 as it approaches the orifice 108. This makes it possible to guide ions toward the orifice entrance 108a.

[0077] As described in the modified example, it is more preferable that the first deflecting electrode 5 and the second deflecting electrodes 6, 26, 36 each include an internal heater and a temperature sensor, and further include a control unit 17 that adjusts the current supplied to the heater so that the detection results of the temperature sensors approach their respective predetermined set values. This makes it possible to prevent the nebulized flow 18 from being cooled, and to promote ionization of the liquid sample.

[0078] It is more preferable that the ionization probe 105, one end (upper end) of the first deflection electrode 5, the aperture 108, and the other end (lower end) of the first deflection electrode 5 are arranged in this order along the ion injection direction (-Z axis direction). This allows the first deflection electrode 5 to form an electric field that directs ions toward the aperture 108.

[0079] Furthermore, it is more preferable that the surface of the first deflection electrode 5 facing the aperture 108 be a concave cylindrical surface whose central axis intersects with the central axis of the aperture 108, or a concave parabolic surface whose focal point is located on the central axis of the aperture 108. This allows the first deflection electrode 5 to form an electric field that concentrates ions into the aperture 108.

[0080] 5 First deflection electrode 6, 26, 36 Second deflection electrode 7 Counter electrode 7a Opening 17 Control section 18 Spray flow 21 Third deflection electrode 26a, 36a Opposing surface 101 Mass spectrometer 105 Ionization probe 107 Pore electrode 108 Pore 109 Power supply section 116 Vacuum chamber V1 First deflection electrode voltage V2 Second deflection electrode voltage V3 Third deflection electrode voltage Va Pore electrode voltage Vc Counter electrode voltage Vi Ionization probe voltage

Claims

1. A mass spectrometer comprising: an ionization probe that injects a spray containing ions in an ion injection direction when a liquid sample is supplied; an aperture electrode having an aperture for sending generated ions into a vacuum chamber, the aperture electrode being arranged so that the ion injection direction and the direction of ion introduction into the aperture are perpendicular or oblique; first and second deflection electrodes that deflect ions; and a power supply unit that applies a first deflection electrode voltage to the first deflection electrode, a second deflection electrode voltage to the second deflection electrode, an ionization probe voltage to the ionization probe, and an aperture electrode voltage to the aperture electrode, respectively; wherein the first deflection electrode, the ionization probe, and the second deflection electrode are arranged sequentially along the ion introduction direction; and the ionization probe, the second deflection electrode, and the aperture are arranged sequentially along the ion injection direction; and the absolute value of the first deflection electrode voltage is equal to or greater than the absolute value of the second deflection electrode voltage, and the absolute value of the aperture electrode voltage is less than the absolute value of the second deflection electrode voltage.

2. The mass spectrometer according to claim 1, further comprising a counter electrode that covers the aperture electrode while forming a gap that allows air to pass between the aperture electrode and the counter electrode and has an opening at a location facing the aperture, wherein the power supply unit further applies a counter electrode voltage to the counter electrode, and the absolute value of the counter electrode voltage is greater than the absolute value of the aperture electrode voltage and less than the absolute value of the second deflection electrode voltage.

3. The mass spectrometer according to claim 1, further comprising a counter electrode that covers the aperture electrode while forming a gap that allows air to pass between the counter electrode and the aperture electrode, and has an opening facing the aperture, and wherein the first deflection electrode, the ionization probe, the opening, and the second deflection electrode are sequentially arranged along the ion introduction direction.

4. The mass spectrometer according to claim 1, further comprising a third deflection electrode that deflects ions, wherein the power supply unit further applies a third deflection electrode voltage to the third deflection electrode (21), and wherein the positional relationship of each component is such that the first deflection electrode, the ionization probe, and the third deflection electrode are sequentially arranged along the direction of ion introduction into the orifice, and the ionization probe, the second deflection electrode, the orifice, and the third deflection electrode are sequentially arranged along the direction of ion injection.

5. The mass spectrometer according to claim 1, wherein the width of the second deflection electrode in a plane perpendicular to the direction of ion introduction into the aperture is 10 mm or more, and the absolute value of the voltage applied to the second deflection electrode is 2000 V or more.

6. The mass spectrometer according to claim 5, wherein the second deflection electrode has a surface curved in an arc shape so as to have the same central axis as the central axis of the aperture, and has an opposing surface facing the central axis of the aperture.

7. The mass spectrometer according to claim 6, wherein the opposing surface is a parabolic surface having a focal point on the central axis of the aperture.

8. The mass spectrometer according to claim 1, wherein the second deflection electrode has a facing surface that faces the central axis of the aperture and has a shape that approaches the central axis of the aperture as it approaches the aperture.

9. The mass spectrometer according to claim 1, wherein the first deflection electrode and the second deflection electrode each have an internal heater and a temperature sensor, and further comprises a control unit that adjusts the current supplied to the heater so that the detection results of the temperature sensors approach their respective predetermined set values.

10. The mass spectrometer according to claim 1, wherein the ionization probe, one end of the first deflection electrode, the aperture, and the other end of the first deflection electrode are arranged in this order along the ion injection direction.

11. The mass spectrometer according to claim 1, wherein the surface of the first deflection electrode facing the pore is a concave cylindrical surface whose central axis intersects with the central axis of the pore, or a concave parabolic surface whose focal point is located on the central axis of the pore.

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