JP2015198014A - Ion transport device and mass spectrometer using the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high ion transport efficiency while simplifying an electrode structure and voltage conditions of an axis-shifted ion transport optical system arranged in a first intermediate vacuum chamber 2. An off-axis ion transport optical system 20 includes an ion deflection element 20A including a cylindrical outer electrode 21 and a plate-shaped inner electrode 22 installed in an internal space thereof, and a plurality of concentric ring electrodes. The high frequency carpet 20B including the group 23 is provided. The ions introduced together with the gas flow through the heating capillary 6 are deflected by the DC electric field formed between the outer electrode 21 and the inner electrode 22 to be separated from the gas flow, and converge in the central axis direction of the outer electrode 21. Will be done. Further, the ions are pushed in the direction of the ring-shaped electrode group 23 by a DC electric field formed between the outer electrode 21 and the ring-shaped electrode group 23. As a result, the polarized and traveling ions are efficiently collected by the high-frequency carpet 20B and transported to the subsequent stage. [Selection diagram] Fig. 1

Description

  The present invention relates to an ion transport device that transports ions to the subsequent stage, and in particular, an ion transport device suitable for an atmospheric pressure ionization mass spectrometer such as an electrospray ionization mass spectrometer or an inductively coupled plasma mass spectrometer, and the apparatus. The present invention relates to a mass spectrometer.

  In a mass spectrometer using an atmospheric pressure ion source such as electrospray ionization method (ESI), atmospheric pressure chemical ionization method (APCI), atmospheric pressure photoionization method (APPI), the ionization chamber has a substantially atmospheric pressure atmosphere. The inside of the analysis chamber in which a mass separator such as a quadrupole mass filter and an ion detector are arranged needs to be kept in a high vacuum atmosphere. Therefore, in general, such an atmospheric pressure ionization mass spectrometer employs a configuration of a multistage differential exhaust system in which one or a plurality of intermediate vacuum chambers are provided between the ionization chamber and the analysis chamber, and the degree of vacuum is increased step by step. Has been. In a mass spectrometer having such a multistage differential evacuation system, an ion transport optical system, also called an ion lens or an ion guide, is arranged inside the intermediate vacuum chamber. The ion transport optical system is an element that transports ions to the subsequent stage while converging, accelerating or decelerating, and further deflecting ions by the action of a DC electric field, a high-frequency electric field, or both.

  In order to transport ions while efficiently collecting them, conventional mass spectrometers use ion transport optical systems having various structures and configurations. As one aspect of a widely used ion transport optical system, a large number of electrodes are provided around or along the ion optical axis, and the phases of adjacent electrodes among the many electrodes are 180 ° to each other. There are those that collect and transport ions while keeping them away from each electrode by applying a reversed high frequency voltage and applying a different DC voltage to each electrode in a superimposed manner.

  As a representative example of the ion transport optical system of this aspect, a multipole high-frequency ion guide having four or more even number of rod electrodes arranged around the ion optical axis, or arranged in the ion optical axis direction instead of the rod electrode. There is a multipole high-frequency ion guide using a virtual rod electrode composed of a plurality of electrode plates. Patent Document 1 discloses an ion transport optical system called an ion funnel having a structure in which a large number of aperture electrodes having circular openings are arranged along an ion optical axis. Furthermore, Patent Document 2 discloses an ion transport optical system called a high-frequency carpet in which a large number of ring-shaped electrodes are formed on a printed circuit board in a substantially concentric shape.

  In particular, in liquid chromatograph mass spectrometers and inductively coupled plasma mass spectrometers, noise caused by neutral particles introduced in a mixture with ions often becomes a problem. Therefore, in order to separate ions and neutral particles, the off-axis ion transport optics shifts the central axis of the ion entrance from the low vacuum region and the central axis of the ion exit to the high vacuum region. Systems are often used. In such an off-axis ion transport optical system, in particular, an ion funnel or a high-frequency carpet having a high ion trapping action is often used.

  The ion transport optical system as described above is designed based on simulation calculations of ion behavior, experiments with actual machines, and the like. However, it is not always easy to design an off-axis ion transport optical system arranged in a low vacuum region such as an intermediate vacuum chamber of an atmospheric pressure ionization mass spectrometer, particularly an intermediate vacuum chamber subsequent to the ionization chamber. This structure tends to be complicated, and the tolerance of the condition of the voltage applied to these electrodes tends to be narrow. The main reason is that in such a low vacuum region, the difference in the degree of vacuum from the previous region is large, so the gas flow flowing in from the previous region is strong, and the behavior of ions is influenced by not only the electric field but also the gas flow. It is because it receives greatly.

US Pat. No. 6,107,628 JP 2010-527095 A

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to efficiently remove ions that are the object of analysis while removing neutral particles while having a simple electrode structure and voltage conditions. An object of the present invention is to provide an ion transport device that can be collected and transported to a subsequent stage, such as a mass separator or another ion transport device, and a mass spectrometer using the device.

An ion transport device according to the present invention, which has been made to solve the above-described problems, is a method of using ions introduced through an ion introduction hole from a first region having a relatively high gas pressure to a second region having a relatively low gas pressure. An ion transport device disposed in the second region for sending to the subsequent stage through an ion emission hole having a central axis that is not collinear with the central axis of the ion introduction hole,
a) an ion deflector that deflects the orbit of ions introduced through the ion incident hole by the action of an electric field;
b) It is arranged between the ion deflector and the ion emission hole, has an ion optical axis on the same straight line as the central axis of the ion emission hole, and focuses ions near the ion optical axis by a high frequency electric field. While the ion collector that sends it to the latter stage,
The ion deflection unit comprises:
a1) A cylindrical outer electrode and a flat or rod-shaped inner electrode disposed in the inner space of the outer electrode so as to face a part of the inner peripheral surface of the outer electrode, and the outer electrode An electrode part in which the outer electrode and the inner electrode are respectively arranged so that an ion flow from the ion introduction hole is introduced between the inner peripheral surface of the electrode and the inner electrode;
a2) A DC electric field having a potential gradient toward which the ions are directed toward the inner electrode is formed between the inner peripheral surface of the outer electrode and the inner electrode, and ions are interposed between the outer electrode and the ion collector. A voltage generator that applies a predetermined DC voltage to each of the outer electrode, the inner electrode, and the ion collector so that a DC electric field having a potential gradient toward the ion collector is formed;
It is characterized by having.

  In the ion transport device according to the present invention, a strong gas flow is generated from the first region to the second region through the ion introduction hole due to the pressure difference between the first region and the second region across the ion introduction hole. Ions are introduced into the second region along this gas flow. In the second region, the gas flow and the ions are introduced into the space between the cylindrical outer electrode and the inner electrode that is flat or rod-shaped, but the gas flow is not affected by the electric field and is almost expanded. Go straight. Neutral particles such as non-ionized component molecules also go straight with the gas flow.

  On the other hand, due to the voltage applied to the outer electrode and the inner electrode from the voltage generator, the ions bend the trajectory in the direction of the inner electrode under the action of a DC electric field formed between the two electrodes. Further, since the outer electrode is cylindrical, a force for converging ions acts in the vicinity of the central axis of the cylinder of the outer electrode. Therefore, diffusion of ions is suppressed even when a strong gas flow strikes ions that travel while bending the orbit. Furthermore, since the electric field formed between the ion deflecting unit and the ion collecting unit exerts a pushing force from behind on the ions going to the ion collecting unit, the diffusion of ions is also reduced thereby. As a result, the ions introduced into the second region together with the gas flow are separated from the gas flow, reach a certain amount of the ion collector, and are efficiently captured by the high-frequency electric field formed by the ion collector and go to the subsequent stage. Sent.

  In order to form an appropriate DC electric field having the above-described potential gradient between the outer electrode and the inner electrode of the ion deflector and between the outer electrode and the ion collector, the inner electrode is an outer electrode. It may be arranged on the central axis of the cylinder. In addition, the inner electrode is inserted into the inner space of the outer electrode (the space surrounded by the circumferential surface of the cylindrical outer electrode and both open end faces), but the insertion length of the inner electrode into the inner space of the outer electrode is The distance between the inner electrode and the outer electrode in the inner space may be about ½ to the length of the outer electrode. This is because if the insertion length is too large, the potential gradient of the DC electric field formed between the outer electrode and the ion collector is not affected by the inner electrode, resulting in an appropriate shape. This is because the DC electric field formed between the outer electrode and the inner electrode does not produce a sufficient ion deflection action if too large.

  Further, in the ion transport device according to the present invention, the ions are converged near the central axis of the outer electrode cylinder by the action of the electric field formed in the ion deflector, but the ions are not confined by the high-frequency electric field. It is difficult to focus on. Therefore, in order to increase the ion transport efficiency, it is preferable to use an ion optical element having a characteristic that the acceptability of ions is good as the ion collector. Specifically, the above-described high-frequency carpet or ion funnel may be used as the ion collector.

That is, in a preferred embodiment of the ion transport device according to the present invention, the ion collector is
An electrode group consisting of a plurality of ring-shaped electrodes arranged substantially concentrically around the ion emission hole;
A voltage is applied to each of the plurality of ring-shaped electrodes, and a high-frequency voltage whose phases are reversed by 180 ° is applied to the ring-shaped electrodes adjacent in the radial direction, and ions are A second voltage generator for applying a different DC voltage to each ring electrode so that a potential gradient from the side toward the inner periphery is formed;
It is good to be the composition containing.

  Here, the plurality of ring electrodes included in the electrode group may be arranged on the same plane, but the ring electrodes are arranged slightly shifted in the central axis direction of the concentric circles of the plurality of ring electrodes. It may be a configured. In the latter configuration, the ring-shaped electrode having the largest opening diameter is positioned on the foremost side on the side where ions arrive, and the diameter of the opening is gradually reduced as it proceeds in the direction of the central axis of the concentric circle. A ring electrode may be disposed.

In the above aspect, when a high frequency voltage whose phases are inverted by 180 ° is applied to adjacent ring electrodes among the plurality of ring electrodes, ions are thereby moved away from the electrodes in the vicinity of the ring electrodes. A high frequency electric field having an action is formed. On the other hand, ions are pushed toward the ion collector, that is, the ring-shaped electrode, by a DC electric field formed between the ion deflector and the ion collector. By the action of these two electric fields, ions are collected in the vicinity of the electrode without contacting the ring electrode. Further, ions are caused to ring from the ring electrode located on the outer peripheral side of the electrode group to the inner ring side by the action of the DC electric field formed by the DC voltage applied to each ring electrode from the second voltage generator. It is transferred in the direction of the electrode. The ions collected in the opening located on the inner peripheral side are, for example, an action of a direct current electric field formed between the electrode group and a subsequent device, or an action of a gas flow using a gas pressure difference. For example, it is transported to the subsequent stage through the opening.
Thereby, even when the ions whose trajectories are bent by the ion deflection unit spread to some extent and reach the ion collection unit, the ions can be efficiently collected and sent to the next stage.

  Moreover, in the said aspect, it is more preferable to use the novel high frequency carpet as described in PCT / JP2013 / 066564 which the applicant of this application applied previously. That is, as a plurality of ring-shaped electrodes, when a ring-shaped electrode whose radial cross-sectional shape is a curved shape or a pseudo-curved shape in which a plurality of straight lines are combined is used, Good. When the cross-sectional shape of the ring electrode is curved or pseudo-curved, the intensity gradient of the high-frequency electric field generated in the vicinity of the ring electrode increases. As a result, the pseudo-potential gradient becomes steep and the potential well formed thereby becomes deep. Since the pseudopotential gradient becomes a pseudo repulsive force against ions, it can be avoided that the pseudopotential gradient becomes steep, so that ions are not too close to the ring electrode, and the loss of ions due to collision with the ring electrode is reduced. Can do.

The ion transport device according to the present invention has a large gas pressure difference between the first region and the second region, and the gas pressure in the second region is relatively high (the degree of vacuum is poor). This is highly effective in the situation where ions can be effectively converged by using.
Therefore, the mass spectrometer according to the present invention is a mass spectrometer having a multistage differential exhaust configuration, such as an atmospheric pressure ionization mass spectrometer such as an electrospray ionization mass spectrometer or an inductively coupled plasma mass spectrometer. The ion transport device according to the present invention is arranged inside the first intermediate vacuum chamber next to the ionization chamber or ion source.

  According to the mass spectrometer according to the present invention, the ion transport device disposed inside the first intermediate vacuum chamber efficiently collects the ions to be analyzed while accurately removing neutral particles that cause noise. Thus, it can be transported to an analysis chamber in which a mass separator such as a quadrupole mass filter is disposed. Thereby, measurement with high sensitivity and high accuracy can be performed.

  Further, even if the mass-to-charge ratio is the same, the degree of influence of ions from the gas flow varies depending on the valence, the three-dimensional structure, the size, and the like. In general, ions having high ion mobility such as a large valence and a small size are more susceptible to an electric field than a gas flow. For this reason, when the difference between the voltages applied to the inner electrode and the outer electrode is increased, ions having high ion mobility are deflected outside the trapping range by the ion collector or collide with the ion deflector itself. Thus, the ion transport apparatus according to the present invention has a function of separating ions according to ion mobility.

  Therefore, in the mass spectrometer according to the present invention, ions having a specific ion mobility or ion mobility range are selected by the ion transport device and subjected to mass analysis, so that the ion mobility or ion mobility of ions to be analyzed is selected. It is preferable to further include a control unit that controls the voltage generation unit so as to adjust a DC voltage applied to the outer electrode and the inner electrode according to a degree range.

  According to this configuration, it is possible to selectively measure only ions having a small ion mobility among ions that cannot be separated by a mass separator such as a quadrupole mass filter because they have the same mass-to-charge ratio. . Thereby, for example, multivalent ions can be excluded from ions having the same mass-to-charge ratio, and only ions having a monovalent or low valence can be detected.

  According to the ion transport device according to the present invention, an electrode having a relatively simple structure is used and the voltage applied to the electrode is reduced even in a situation where the gas flow flowing into the second region through the ion introduction hole is strong. While relaxing the conditions, the intermediate particles introduced into the second region together with the ions can be removed, and the ions to be analyzed can be collected with high efficiency and transported to the subsequent stage. Thereby, in the mass spectrometer using the ion transport device according to the present invention, the amount of ions provided for mass analysis can be increased and the analysis sensitivity can be improved. In addition, since the electrode structure and voltage conditions in the ion transport device can be simplified, it is possible to suppress an increase in cost while improving the performance of the device.

The schematic block diagram of one Example of the mass spectrometer using the ion transport apparatus which concerns on this invention. The schematic perspective view of the ion deflection | deviation element which is a part of off-axis ion transport optical system in the mass spectrometer of a present Example. The schematic perspective view of the high frequency carpet which is a part of the off-axis ion transport optical system in the mass spectrometer of a present Example. The schematic diagram which shows the general | schematic potential distribution of the electric field formed in the space between an ion deflection | deviation element and a high frequency carpet in the mass spectrometer of a present Example. The figure which shows the simulation result of the pseudo potential contour in the electric field formed of the off-axis ion transport optical system in the mass spectrometer of a present Example. The figure which shows the actual measurement result of the mass spectrum obtained by the case where the ion deflection element in the mass spectrometer of a present Example is used, and the case where it is not used. The figure which shows the actual measurement result of the mass spectrum obtained when the voltage applied to an ion deflection | deviation element is changed in the mass spectrometer of a present Example. The schematic block diagram of the off-axis ion optical system which is the other Example of the ion transport apparatus which concerns on this invention.

Hereinafter, an electrospray ionization mass spectrometer which is an embodiment of a mass spectrometer using an ion transport device according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of the mass spectrometer of the present embodiment.

As shown in FIG. 1, between the ionization chamber 1 which is a substantially atmospheric pressure atmosphere and the analysis chamber 4 which is maintained in a high vacuum atmosphere, a first intermediate vacuum chamber 2 which is a low vacuum atmosphere and the first intermediate chamber A second intermediate vacuum chamber 3 maintained at a vacuum level intermediate between the vacuum chamber 2 and the analysis chamber 4, and a configuration of a multistage differential evacuation system in which the vacuum level is increased stepwise in the direction of ion travel; It has become. For example, the gas pressure in the ionization chamber 1 is about 10 ⁵ Pa, the gas pressure in the first intermediate vacuum chamber 2 is about 100 Pa, the gas pressure in the second intermediate vacuum chamber 3 is about 1 to 10 ⁻² Pa, and the analysis chamber. The gas pressure in ⁴ is about 10 ⁻³ to 10 ⁻⁴ Pa.

  In the ionization chamber 1, a sample solution containing sample components is sprayed while being charged from the electrospray nozzle 5. The sprayed charged droplets are brought into contact with the surrounding atmosphere and are refined, and the sample components are ionized in the process of evaporating the solvent. Instead of the electrospray ionization method, other atmospheric pressure ionization methods such as an atmospheric pressure chemical ionization method and an atmospheric pressure photoionization method may be employed. Further, an inductively coupled plasma ionization method may be used.

  The ionization chamber 1 and the first intermediate vacuum chamber 2 communicate with each other by a small-sized heating capillary (corresponding to an ion introduction hole in the present invention) 6, and ions generated in the ionization chamber 1 are mainly heated capillary 6 is sucked into the heating capillary 6 by the pressure difference between both open ends. The ions are discharged into the first intermediate vacuum chamber 2 together with the gas flow flowing from the ionization chamber 1 into the first intermediate vacuum chamber 2. A partition wall that separates the first intermediate vacuum chamber 2 and the second intermediate vacuum chamber 3 is provided with a skimmer 7 having a small-diameter ion passage hole (corresponding to an ion emission hole in the present invention) 7 a at the top. The central axis C1 of the outlet end 6a of the heating capillary 6 that opens into the first intermediate vacuum chamber 2 and the central axis C2 of the ion passage hole 7a of the skimmer 7 are parallel and offset by a predetermined distance. ing. In the first intermediate vacuum chamber 2, a characteristic off-axis ion transport optical system 20 to be described later is disposed, and neutral particles are removed by the off-axis ion transport optical system 20, while ions are It is collected and sent to the second intermediate vacuum chamber 3.

  A quadrupole type or multipole type ion guide 8 is disposed in the second intermediate vacuum chamber 3, and ions are converged by the action of a high-frequency electric field formed by the ion guide 8 and sent into the analysis chamber 4. It is. In the analysis chamber 4, ions are introduced into the space in the long axis direction of the quadrupole mass filter 9 and specified by the action of the electric field formed by the high-frequency voltage and the DC voltage applied to the quadrupole mass filter 9. Only ions having a mass-to-charge ratio of m / z pass through the quadrupole mass filter 9 and reach the ion detector 10. The ion detector 10 generates a detection signal corresponding to the amount of incident ions and sends it to the data processing unit 11. Of the ions derived from the sample components generated in the ionization chamber 1, highly sensitive mass spectrometry can be realized by making the ions incident on the ion detector 10 while minimizing the loss of ions to be analyzed.

  The off-axis ion transport optical system 20 disposed in the first intermediate vacuum chamber 2 includes an ion deflection element 20A and a high-frequency carpet 20B. These detailed configurations will be described later. The DC voltage generator 14 applies predetermined DC voltages to the heating capillary 6, the ion deflection element 20 </ b> A, and the skimmer 7, and applies a DC bias voltage to the voltage superimposing unit 18 included in the high-frequency carpet driving unit 15. In the high-frequency carpet driving unit 15, the voltage superimposing unit 18 adds the high-frequency voltage (AC voltage) generated by the high-frequency power source 16, the DC voltage generated by the DC power source 17, and the DC bias voltage. A voltage is applied to each ring electrode included in the high frequency carpet 20B. The voltage values (amplitude values) of these voltages are controlled by the analysis control unit 13 based on instructions from the central control unit 12. A predetermined voltage is also applied to the electrospray nozzle 5, the ion guide 8, the quadrupole mass filter 9, etc., but these are not shown in FIG.

  2 is a schematic perspective view of the ion deflection element 20A, FIG. 3 is a schematic perspective view of the high-frequency carpet 20B, and FIG. 4 is an electric field formed in a space between the electrode portion of the ion deflection element 20A and the electrode portion of the high-frequency carpet 20B. It is a schematic diagram which shows a rough potential distribution.

  As shown in FIG. 2A, the ion deflection element 20A constituting the off-axis ion transport optical system 20 is electrically connected to the cylindrical outer electrode 21 and the inner space of the outer electrode 21. And a flat plate-like inner electrode 22 arranged in an insulated state (for example, in a non-contact state). The inner electrode 22 is disposed on the central axis of the outer electrode 21 so as to extend parallel to the central axis. In addition, the insertion length of the inner electrode 22 into the inner space of the outer electrode 21 (a cylindrical space surrounded by the peripheral surface of the outer electrode 21 and both open end faces) is between the inner electrode 22 and the outer electrode 21 in the inner space. It is sufficient that the distance is about ½ of the distance (d in FIG. 2A) to the length L of the outer electrode.

  In the outer electrode 21 and the inner electrode 22, the peripheral surface of the outer electrode 21 is parallel to the central axis C 1 of the outlet end 6 a of the heating capillary 6, and the central axis C 1 is between the inner peripheral surface of the outer electrode 21 and the inner electrode 22. (Ie, the distance from the central axis C to the inner peripheral surface of the outer electrode 21 and the distance from the central axis C to the inner electrode 22 are the same d as shown in FIG. 2). Is done. Instead of the plate-shaped inner electrode 22, a rod-shaped inner electrode 22B may be used as shown in FIG.

  Neutral particles such as gas flow, ions, and non-ionized component molecules that have passed through the heating capillary 6 are blown into the first intermediate vacuum chamber 2 from the outlet end 6a mainly in the direction along the central axis C1. Therefore, they are introduced into the space between the outer electrode 21 and the inner electrode 22. In the space between the outer electrode 21 and the inner electrode 22, a predetermined electric field is generated from the DC voltage generator 14 to each of the outer electrode 21 and the inner electrode 22 so that a DC electric field that deflects ions in the direction of the inner electrode 22 is formed. A DC voltage is applied. For example, when the analysis target is positive ions, a voltage higher than the voltage applied to the inner electrode 22 is applied to the outer electrode 21. Thereby, the trajectory of ions blown out from the outlet end 6a of the heating capillary 6 together with the strong gas flow bends in a direction approaching the inner electrode 22 as shown by a dotted line in FIG. On the other hand, the gas flow containing neutral particles having no electric charge travels straight without being influenced by the electric field. Thus, the ion stream is separated from the gas stream.

  Further, since the outer electrode 21 is cylindrical, the electric field formed between the inner peripheral surface of the outer electrode 21 and the inner electrode 22 causes ions in the inner space of the outer electrode 21 to be centered on the outer electrode 21. Has the effect of pushing in the direction. For this reason, the spread of ions while being deflected is suppressed and converges around the central axis of the outer electrode 21.

  As shown in FIG. 3, the high-frequency carpet 20 </ b> B includes a ring-shaped electrode group 23 including a plurality of ring-shaped electrodes 231, 232,... Arranged concentrically on a substantially plane. The ring-shaped electrode group 23 is disposed in front of the partition wall on which the skimmer 7 is formed so that the central axis thereof coincides with the central axis C2 (that is, the ion optical axis C) of the ion passage hole 7a of the skimmer 7. . Each of the ring-shaped electrodes 231, 232,... Has a circular shape with the same radius as a cross section cut along a plane including the central axis, that is, a radial cross section.

  The high-frequency carpet driving unit 15 causes the ring-shaped electrodes adjacent to the concentric radial direction in the ring-shaped electrode group 23, for example, the ring-shaped electrode 231 and the ring-shaped electrode 232 to have the same amplitude and have a phase of 180 degrees. Different high-frequency voltages + Vcosωt and −Vcosωt are applied, respectively. That is, + V cos ωt is applied to one of the ring electrodes alternately positioned in the radial direction of the ring electrode group 23 (ring electrodes 232 and 234 in the example of FIG. 3), and the other (ring electrode in the example of FIG. 3). -Vcosωt is applied to 231, 233, 235). The high frequency power supply 16 generates these high frequency voltages ± Vcosωt.

Further, the DC voltages U ₁ , U ₂ ,... Having different voltage values are applied to the ring-shaped electrodes 231, 232,. The DC voltages U ₁ , U ₂ ,... Applied to the ring electrodes 231, 232,... Have a downward slope from the outer peripheral side to the inner peripheral side of the ring electrode group 23, as shown in FIG. It is set to form a potential. Ascending / descending of this gradient varies depending on the polarity of ions, and the polarities of the DC voltages U ₁ , U ₂ ,... Vary depending on the polarity of ions to be analyzed. Since a DC electric field indicating such a downward gradient potential acts on ions located within a certain distance from the ring electrode group 23, the ions move according to the potential gradient. That is, the ions move from the outer peripheral side to the inner peripheral side of the ring-shaped electrode group 23, that is, move toward the central axis C2, and gather near the central axis C2.

  As described above, the high-frequency electric field formed in the vicinity of the ring-shaped electrodes 231, 232,... By the high-frequency voltage ± Vcos ωt has a pseudo-potential with a downward gradient that keeps ions away from the ring-shaped electrodes 231, 232,. On the other hand, in the space between the outer electrode 21 of the ion deflection element 20A and the ring-shaped electrode group 23 of the high-frequency carpet 20B, a downward gradient potential is formed from the outer electrode 21 toward the ring-shaped electrode group 23. The relationship between the DC voltage applied to the outer electrode 21 and the DC bias voltage applied to the ring electrode group 23 is determined. For example, when the analysis target is positive ions, a voltage higher than the voltage applied to the ring electrode group 23 is applied to the outer electrode 21. Therefore, as shown in FIG. 4, in the potential distribution along the ion optical axis C, a steep downward gradient potential is formed from the end surface on the outlet side of the outer electrode 21 toward the ring electrode group 23, and the ring electrode group A potential well is formed at a position a predetermined distance away from 23 in front of it. Therefore, the ions that are deflected and converged by the ion deflecting element 20A are pushed toward the ring-shaped electrode group 23, that is, their progress is promoted and captured by the potential well. The ring-shaped electrode group 23 is collected at the center portion by the potential indicating a downward gradient from the outer peripheral side to the inner peripheral side, sucked into the ion passage hole 7 a of the skimmer 7, and sent to the second intermediate vacuum chamber 3.

  FIG. 5 is a diagram showing simulation results of pseudopotential contour lines in an electric field formed by the off-axis ion transport optical system 20. In this example, 25 [V] is applied to the outer electrode 21, 15 [V] is applied to the inner electrode 22, and 20 [V] is applied to the outermost ring electrode in the ring electrode group 23. . From FIG. 5, a potential gradient that pushes positive ions in the direction of the inner electrode 22 is formed between the outer electrode 21 and the inner electrode 22, and the inside of the outer electrode 21 on the rear side of the rear end portion of the inner electrode 22. In the space, a potential gradient is formed so that positive ions converge near the central axis of the outer electrode 21, and in the space between the outer electrode 21 and the ring electrode group 23, positive ions are ring-shaped. It can be seen that a potential gradient that pushes in the direction of the electrode group 23 is formed. Thereby, the ions introduced into the first intermediate vacuum chamber 2 are separated from the gas flow by the ion deflection element 20A, and are efficiently collected by the high-frequency carpet 20B. From the results shown in FIG. 5, it can be seen that the degree of ion convergence in the ion deflection element 20 </ b> A can be controlled by the diameter of the outer electrode 21 and the voltage applied to the electrode 21.

6A is obtained when an ion deflecting element is used in the mass spectrometer of the present embodiment, and FIG. 6B is obtained when an ion deflecting element is not used (there is a high-frequency carpet, the shaft is offset, and there is no deflection). It is a figure which shows the result of having actually measured the obtained mass spectrum.
As shown in FIG. 6, the signal intensity is increased by about 50% by using the off-axis ion transport optical system having the above-described configuration. This is considered to be a result of improving the efficiency of collecting ions by an electric field by keeping ions away from a strong gas flow and making them less susceptible to the influence.

  In the off-axis ion transport optical system 20 described above, the ion trajectory is bent by the action of a DC electric field to separate the ions from the gas flow. The degree of influence of the gas flow and the electric field on the bending of the ion trajectory is as follows. It depends on the ion mobility related to the valence, three-dimensional structure, or size of ions. That is, ions having a high ion mobility, such as a high ion valence, are more susceptible to an electric field than a gas flow. Therefore, if the difference between the voltages applied to the outer electrode 21 and the inner electrode 22 is increased (the electric field strength is increased), the bending of the ion trajectory with high ion mobility increases, and the ions are collected by the high-frequency carpet 20B. It disappears when it falls outside the possible range or contacts the inner electrode 22 itself. That is, since the off-axis ion transport optical system 20 has a function of separating ions according to ion mobility, the ions having high ion mobility are excluded by using this, and only ions having low ion mobility are massed. A function to analyze can be added.

FIG. 7 is a diagram showing an actual measurement result of the mass spectrum obtained when the voltage difference Vsp applied to the outer electrode 21 and the inner electrode 22 of the ion deflection element 20A is changed in the mass spectrometer of the present embodiment. The sample is the same as the actual measurement example shown in FIG.
As shown in FIG. 7, it can be seen that when the voltage difference Vsp is increased, ions having a particularly small mass-to-charge ratio are not observed. This is because ions having a small mass-to-charge ratio (multivalent ions) are eliminated because the valence is large even if the molecular weight is the same.

  In order to perform ion selection using such a difference in ion mobility, for example, a voltage difference Vsp at which ions having an ion mobility or an ion mobility range are efficiently transported is examined in advance and stored in the analysis control unit 13. deep. When the mass-to-charge ratio or mass-to-charge ratio range of the ion to be analyzed is designated, the analysis control unit 13 selects the ion mobility or ion to be selected corresponding to the mass-to-charge ratio or mass-to-charge ratio range. The mobility range is obtained, and the DC voltage generator 14 is controlled so as to apply a voltage corresponding to the ion mobility or the ion mobility range. Thereby, even ions having the same mass-to-charge ratio have high ion mobility, that is, ions with high valence are eliminated by the off-axis ion transport optical system 20. At this time, since the off-axis ion transport optical system 20 does not select ions according to the mass-to-charge ratio, ions having close ion mobility and various mass-to-charge ratios are introduced into the quadrupole mass filter 9. Since ions having a specific mass-to-charge ratio are selected in the quadrupole mass filter 9, only ions having a specific mass-to-charge ratio and a small valence (or a close valence) are incident on the ion detector 10. To do. This makes it possible to selectively analyze only ions having a small valence with respect to molecules that easily generate multivalent ions upon ionization.

  Next, an off-axis ion transport optical system which is another embodiment of the ion transport device according to the present invention will be described with reference to a schematic configuration diagram shown in FIG. In FIG. 8, the same components as those in the off-axis ion transport optical system 20 in the above-described embodiment are denoted by the same reference numerals. That is, the off-axis ion transport optical system in this embodiment includes the same ion deflection element 20A as in the above embodiment and an ion funnel 20C instead of the high-frequency carpet 20B.

The ion funnel 20C includes a plurality of annular electrode groups 25 arranged along the ion optical axis C and having an inner diameter that gradually decreases in the ion traveling direction (rightward in FIG. 8).
A high frequency voltage whose phases are inverted from each other is applied to an annular electrode adjacent in the ion optical axis C direction from an ion funnel driving unit (not shown), and ions are moved to the respective annular electrodes in the ion optical axis C direction. Apply a different DC voltage. As a result, as in the case of the above-described high-frequency carpet 20B, the ions that are deflected and converged by the ion deflecting element 20A are collected efficiently and transported to the second intermediate vacuum chamber 3 through the ion passage hole 7a having a small diameter. be able to.

  The above-described embodiments are merely examples of the present invention, and it is obvious that changes, modifications, and additions are appropriately included in the scope of the claims of the present application within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Ionization chamber 2 ... 1st intermediate | middle vacuum chamber 3 ... 2nd intermediate | middle vacuum chamber 4 ... Analysis chamber 5 ... Electrospray nozzle 6 ... Heating capillary 7 ... Skimmer 7a ... Ion passage hole 8 ... Ion guide 9 ... Quadrupole mass filter DESCRIPTION OF SYMBOLS 10 ... Ion detector 11 ... Data processing part 12 ... Central control part 13 ... Analysis control part 14 ... DC voltage generation part 15 ... High frequency carpet drive part 16 ... High frequency power supply 17 ... DC power supply 18 ... Voltage superposition part 20 ... Off-axis ion Transport optical system 20A ... Ion deflection element 21 ... Outer electrode 22 ... Inner electrode 20B ... High frequency carpet 23 ... Ring electrode group 231-235 ... Ring electrode 20C ... Ion funnel 25 ... Annular electrode group

Claims (5)

Ions introduced through the ion introduction hole from the first region having a relatively high gas pressure to the second region having a relatively low gas pressure have a central axis that is not collinear with the central axis of the ion introduction hole. An ion transport device disposed in the second region for sending to the subsequent stage through the ion emission hole,
a) an ion deflector that deflects the orbit of ions introduced through the ion incident hole by the action of an electric field;
b) It is arranged between the ion deflector and the ion emission hole, has an ion optical axis on the same straight line as the central axis of the ion emission hole, and focuses ions near the ion optical axis by a high frequency electric field. While the ion collector that sends it to the latter stage,
The ion deflection unit comprises:
a1) A cylindrical outer electrode and a flat or rod-shaped inner electrode disposed in the inner space of the outer electrode so as to face a part of the inner peripheral surface of the outer electrode, and the outer electrode An electrode part in which the outer electrode and the inner electrode are respectively arranged so that an ion flow from the ion introduction hole is introduced between the inner peripheral surface of the electrode and the inner electrode;
a2) A DC electric field having a potential gradient toward which the ions are directed toward the inner electrode is formed between the inner peripheral surface of the outer electrode and the inner electrode, and ions are interposed between the outer electrode and the ion collector. A first voltage generator for applying a predetermined DC voltage to each of the outer electrode, the inner electrode, and the ion collector so that a DC electric field having a potential gradient toward the ion collector is formed;
An ion transport device comprising: The ion transport device according to claim 1,
The ion collector is
A ring-shaped electrode group comprising a plurality of ring-shaped electrodes arranged substantially concentrically around the ion emission hole;
A voltage is applied to each of the plurality of ring-shaped electrodes, and a high-frequency voltage whose phases are reversed by 180 ° is applied to the ring-shaped electrodes adjacent in the radial direction, and ions are added to the ring-shaped electrode group. A second voltage generator for applying a different DC voltage to each ring electrode so that a potential gradient from the outer periphery side to the inner periphery side is formed,
An ion transport device comprising: The ion transport device according to claim 1 or 2,
The outer electrode and the inner electrode are respectively arranged so that an ion flow from the ion introduction hole is introduced at a substantially intermediate position between the inner peripheral surface of the outer electrode and the inner electrode. Ion transport device. A mass spectrometer using the ion transport device according to claim 1,
The vacuum between an ion source that ionizes sample components under a substantially atmospheric pressure and an analysis chamber that is maintained in a high vacuum atmosphere in which a mass separation unit that separates ions according to the mass-to-charge ratio is disposed. It is provided that n (where n is an integer of 1 or more) intermediate vacuum chambers having higher degrees in order, and the ion transport device is disposed inside the first intermediate vacuum chamber next to the ion source. Characteristic mass spectrometer. The mass spectrometer according to claim 4,
In order to perform mass analysis by selecting ions having a specific ion mobility or ion mobility range by the ion transport device, the outer electrode and the inner side are selected according to the ion mobility or ion mobility range of the ion to be analyzed. A mass spectrometer further comprising: a control unit that controls the voltage generation unit so as to adjust a DC voltage applied to the electrode.

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