CN113066713A

CN113066713A - Ion optical device, mass spectrometer, and ion manipulation method

Info

Publication number: CN113066713A
Application number: CN202010003155.6A
Authority: CN
Inventors: 孙文剑; 张小强
Original assignee: Shimadzu Corp
Current assignee: Shimadzu Corp
Priority date: 2020-01-02
Filing date: 2020-01-02
Publication date: 2021-07-02
Also published as: WO2021137293A1

Abstract

The invention provides an ion optical device and a mass spectrometer, the ion optical device includes: a power supply device; an ion manipulation part configured by a plurality of electrodes electrically connected to a power supply device, the power supply device applying a voltage to the plurality of electrodes to form a radio frequency electric field and a direct current electric field, the ion manipulation part being capable of performing a periodic manipulation on ions, wherein each manipulation cycle includes a first time period and a second time period, the ion manipulation part further comprising: the first ion storage unit is used for storing ions by utilizing the potential balance between the radio frequency electric field and the direct current electric field in a first time period and releasing the ions according to a specific mass-to-charge ratio sequence by adjusting the potential balance in a second time period; and the second ion storage unit is used for receiving the ions from the first ion storage unit in a second time period and dividing the received ions into a plurality of pulses to be released to the target area in the second time period.

Description

Ion optical device, mass spectrometer, and ion manipulation method

Technical Field

The invention relates to the technical field of mass analysis, in particular to an ion optical device, a mass spectrometer and an ion operation method thereof.

Background

Some existing mass spectrometers, such as quadrupole-orthogonal time-of-flight mass spectrometers, typically operate in the following modes: ions generated by an ion source enter a quadrupole rod for mass selection through a series of vacuum interfaces and ion guide devices, selected parent ions enter a collision cavity for dissociation to generate a plurality of daughter ions, the daughter ions enter an ion extraction area in front of a flight cavity and are accelerated in an orthogonal mode, and high-resolution and high-precision mass spectra are generated due to different flight times of the ions. Therein, quadrupole rods are usually operated continuously in a scanning mode, while time-of-flight mass spectrometers are operated in a pulsed mode. If no modulation is done on the ions in front of the time-of-flight mass spectrometer, it is necessary to wait for the highest m/z ions to reach the detector for the pulse voltage in the acceleration region in front of the flight chamber before the next pulse can be generated. Ions enter the acceleration region continuously, so that the utilization efficiency, or duty cycle, of the ions by the time-of-flight mass spectrometer is low, resulting in ion loss. If the electrodes of the acceleration region are at a distance D from the detector and the effective width of the acceleration region is Δ l (the effective width can be considered to be the width of the ion beam that is accelerated before the acceleration region to eventually form a mass spectrum on the detector, which is typically smaller than the actual width of the acceleration electrodes), then the highest duty cycle of the instrument is related to the ion mass-to-charge ratio m/z:

here, (m/z)_maxRefers to the upper mass range limit. In most orthogonal time-of-flight instruments, the duty cycle is approximately between 5% and 30%. If an ion gate or ion trap is adopted, although ions can enter an ion extraction region in front of the time-of-flight mass spectrometer in a pulse mode, ions with different m/z are widened because the ions enter the ion extraction region in one flight process, and only ions within a certain m/z range reach the ion extraction region at the same time, so the mass range is greatly limited.

There are numerous prior art attempts to solve this problem. In US6770872 or US7208728, a three-dimensional ion trap is placed in front of the time-of-flight acceleration region, and the ion trap is made to work in conjunction with a time-of-flight mass spectrometer; alternatively, in US7714279, an rf guide device is used to store and release ions, ions with a small mass to charge ratio are released first, and the pulsed acceleration voltage is synchronized with the released ions by adjusting the parameters of the subsequent stage.

In patents US6504148, US7208728 and US7329862, ions are excited by axial resonance using linear ion traps to select a particular m/z of ion expulsion, synchronized in some way with the later stage time of flight mass spectrum to improve the duty cycle. However, this solution has the problem that the ions tend to have a high kinetic energy dispersion when being ejected in an excited manner. The special electrode arrangement of US7208728 can partially reduce the energy dispersion, but it is still difficult to fully meet the requirements of orthogonal time-of-flight mass spectrometry, and the speed of this approach is low, making it difficult to achieve fast tandem analysis.

In patent WO2007/125354, a radio frequency potential barrier is formed in an annular electrode array arranged along the axial direction, and the sequential release of ions in m/z can be realized by changing the balance between the traveling wave voltage or the direct current voltage along the axial direction and the radio frequency potential barrier; or Zeno trap as described in the patent US 745688, by changing the balance between the radio frequency potential barrier and the direct current potential barrier at the axial end of the device, ions are sequentially emitted from large to small in m/z sequence, the ions are accelerated to lower energy (20-50 eV) along the axial direction after being released, and the ions with large m/z have smaller speed and are gradually caught by the ions with small m/z. Adjusting the speed of releasing ions can make ions of different m/z reach the accelerating region of the flight chamber at the same time, so that the duty ratio close to 100% can be obtained. However, the above schemes have two problems, one is that the ion capacity is low, and the speed is limited by adopting a single ion storage unit. For example, Zeno trap, as is well known in the art, after the ions are released along the axial barrier, it takes a longer time to re-cool the radial direction, otherwise it is difficult to achieve a higher time-of-flight mass spectral resolution, and therefore the scan frequency of the Zeno trap is usually around 1kHz, which is much slower than the usual acceleration pulse frequency (5kHz to 10 kHz).

As another example, for the dual ion trap schemes described in patents US7208728 and US7329862, the first ion trap requires a longer cooling time due to resonant emission, so that the limited capacity of the first ion trap will limit the dynamic range of the mass spectrometer. Further, although the ion energy is high at the time of resonance emission and the second ion trap can be introduced to cool the ion to a certain extent, if the ion introduction frequency (usually, in the order of kHz) of the high flight time is kept up with, the cooling time in the order of milliseconds is too short to achieve sufficient cooling effect, and the resolution of the flight time is lowered.

Therefore, there is a need for an improved solution to the above problems of existing ion optical devices.

Disclosure of Invention

In view of the above problems in the prior art, the present invention provides an ion optical device, which can operate only for ions in a narrow mass-to-charge ratio distribution range at a time, improve the accuracy of ion operation, and synchronize with other devices at a higher operating frequency.

The ion optical device provided by the technical scheme of the invention comprises: a power supply device; an ion manipulation part configured by a plurality of electrodes electrically connected to a power supply device, the power supply device applying a voltage to the plurality of electrodes to form a radio frequency electric field and a direct current electric field, the ion manipulation part being capable of performing a periodic manipulation on ions, wherein each manipulation cycle includes a first time period and a second time period, the ion manipulation part further comprising: the first ion storage unit is used for storing ions by utilizing the potential balance between the radio frequency electric field and the direct current electric field in a first time period and releasing the ions according to a specific mass-to-charge ratio sequence by adjusting the potential balance in a second time period; and the second ion storage unit is used for receiving the ions from the first ion storage unit in a second time period and dividing the received ions into a plurality of pulses to be released to the target area in the second time period.

The ion optical device utilizes cooperation between two ion storage units to implement ion operation. The first ion storage unit is used for storing ions and releasing the stored ions to the second ion storage unit according to a specific mass-to-charge ratio sequence; the second ion storage unit is configured to divide the ions received from the first ion storage unit into a plurality of pulses to be released to the target region.

Because the ions received by the second ion storage unit are from the first ion storage unit, and the first ion storage unit releases ions sequentially according to a particular mass to charge ratio, the ions received by the second ion storage unit have been sequenced in order of mass to charge ratio. Therefore, the mass-to-charge ratio or range of mass-to-charge ratios of the ions received by the second ion storage unit is also determined during a particular time period.

Since the second ion storage unit is used for operating the ions, when the ions are not released, the received ions can be stored, and the second ion storage unit releases the ions in a pulse form, the operation process of the second ion storage unit for the ions in each operation period is composed of a plurality of 'storage-release' processes. The utilization of a plurality of 'storage-release' processes instead of the sustained release process can ensure that the ions aimed at in each release process have a specific mass-to-charge ratio or a narrow mass-to-charge ratio distribution range, thereby facilitating the precise implementation of ion operation.

Since the mass-to-charge ratio or mass-to-charge ratio range of the ions received by the second ion storage unit is also determined during a certain time period, the appropriate time interval between pulses can be calculated by combining the flight data (such as flight distance, flight speed, etc.) of the ions from the release position to the target region based on the mass-to-charge ratio or mass-to-charge ratio range of the ions corresponding to each pulse. By accurately setting the release timing of each pulse, ions of different mass-to-charge ratios or mass-to-charge ratio ranges can be controlled to arrive at a target region substantially simultaneously or at a specific timing sequence, and the duty ratio of the device is improved.

Moreover, because the first ion storage unit of the ion optical device provided in the technical solution of the present invention operates the ions by using the potential balance between the radio frequency electric field and the dc electric field, the kinetic energy of the ions does not need to be accelerated to the kinetic energy required by the resonance excitation mode in the process of expelling the ions, thereby reducing the cooling time required by the ions and increasing the speed of the cascade analysis.

In a preferred embodiment of the present invention, the plurality of electrodes includes a first electrode array and a second electrode array which are disposed parallel to and coaxially with each other. With the electrode array of the above form, the first ion storage unit and the second ion storage unit can be integrated, and the functions of the first ion storage unit and the second ion storage unit can be realized with a simple device.

Further, in a preferred embodiment of the present invention, the first ion storage unit is disposed in a peripheral region between the first electrode array and the second electrode array, and the second ion storage unit is disposed in a central region between the first electrode array and the second electrode array. The first ion storage unit is arranged in the peripheral area, the second ion storage unit is arranged in the central area, ions enter the optical device and then move to the peripheral area for storage, and the electrode array has larger ion storage capacity in the peripheral area extending along the radial direction, so that the dynamic range of the instrument can be effectively improved.

Further, in a preferred embodiment of the present invention, the first electrode array and the second electrode array are both composed of a plurality of ring electrodes, and the plurality of ring electrodes of the first electrode array and the plurality of ring electrodes of the second electrode array are disposed in a one-to-one correspondence.

In a preferred embodiment of the present invention, the adjusting the potential balance includes: the ions are pushed by the direct current electric field, and the amplitude of the radio frequency electric field is scanned from high to low or the frequency of the radio frequency electric field is scanned from low to high; alternatively, the strength of the dc electric field is swept from low to high.

In a preferred embodiment of the present invention, the second ion storage unit releases the received ions by changing a dc potential of at least a part of the plurality of electrodes.

In a preferred embodiment of the present invention, the specific mass-to-charge ratio sequence is a sequence of mass-to-charge ratios from large to small. Ions with a large mass-to-charge ratio (mass number) have the same kinetic energy and are relatively small in velocity compared to ions with a small mass-to-charge ratio (mass number). Releasing ions of large mass to charge ratio before ions of small mass to charge ratio enables ions of large mass to charge ratio to be gradually caught up by ions of small mass to charge ratio, thereby enabling the ions to reach the target region with the same kinetic energy substantially simultaneously or at a prescribed timing.

Further, in a preferred embodiment of the present invention, the time interval between adjacent pulses of the plurality of pulses gradually increases along the time axis.

Furthermore, the plurality of pulses respectively carry ions with different mass-to-charge ratio ranges, and the time interval is set according to the mass-to-charge ratio corresponding to each pulse.

In the preferred technical scheme of the invention, the potential balance is the balance between a pseudo-potential barrier generated by ions in a radio-frequency electric field and an electric potential barrier generated by the ions in a direct-current electric field.

The invention also provides a mass spectrometer with an ion optical device.

In a preferred embodiment of the invention, the target region is an ion extraction region of a pulsed mass analyzer, which is arranged downstream of the ion optics.

Further, in a preferred embodiment of the invention, the mass analyser is an orthogonal time-of-flight mass analyser.

Further, in a preferred aspect of the invention, the mass analyser is a quadrupole mass analyser, the ions released in pulses are split into a plurality of ions entering in the axial direction of the quadrupole mass analyser, and the scan voltages of the quadrupole mass analyser are synchronised according to the mass to charge ratio of the ions.

Further, in a preferred embodiment of the invention, the ion release of the second ion storage unit is synchronized with the pulse analysis of a pulsed mass analyzer.

In a preferred embodiment of the present invention, the pressure in the ion optical device is 0.002Pa to 0.05Pa, or 0.02Pa to 0.5Pa, or 0.2Pa to 5Pa, or 2Pa to 50Pa, or 20Pa to 500 Pa.

The invention also provides an ion operation method of an ion optical device, the ion optical device comprises a power supply device and an ion operation part, the ion operation part is composed of a plurality of electrodes which are electrically connected with the power supply device, the power supply device applies voltages on the plurality of electrodes to form a radio frequency electric field and a direct current electric field, the ion operation part comprises a first ion storage unit and a second ion storage unit, the ion operation method comprises a plurality of repeatedly executed periodic operations, wherein at least one operation cycle comprises a first time period and a second time period, and the ion operation method comprises the following steps in at least one operation cycle: in a first time period, the first ion storage unit stores ions by utilizing the potential balance of the ions in the radio frequency electric field and the direct current electric field; in a second time period, the first ion storage unit releases ions according to a specific mass-to-charge ratio sequence by adjusting potential balance; the second ion storage unit receives ions from the first ion storage unit during a second time period and discharges the received ions to the target region in a plurality of pulses.

In a preferred embodiment of the present invention, the specific mass-to-charge ratio sequence is from large to small.

Further, in a preferred embodiment of the present invention, the time interval between adjacent pulses of the plurality of pulses is non-uniform, and preferably, the time interval gradually increases along the time axis during the second period.

Further, in a preferred embodiment of the present invention, the plurality of pulses respectively carry ions of different mass-to-charge ratio ranges, and the time interval is set according to the mass-to-charge ratio corresponding to each pulse, so that the ions with different mass-to-charge ratios substantially simultaneously reach the target region with substantially the same kinetic energy.

Drawings

FIG. 1 is a schematic diagram of the structure of a mass spectrometer according to an embodiment;

FIG. 2 is a schematic flow chart of one cycle of operation of a method of ion manipulation according to one embodiment;

FIG. 3 is a schematic diagram illustrating a relationship between a first ion storage unit and a second ion storage unit in a time dimension according to an embodiment;

FIG. 4 is a schematic diagram showing the structure of a mass spectrometer according to a second embodiment;

fig. 5 is an ion spectrum diagram formed by ejecting ions from the first ion storage unit using computer simulation;

fig. 6 is an ion spectrum diagram formed by ejecting ions from the second ion storage unit, which is obtained by computer simulation.

Reference numerals: 1. 2, mass spectrometry; 11, a front stage device; 111, a collision chamber; 12, ion optics; 12M, ion manipulation section; 12E, a power supply device; 12a, 12b, a ring electrode array; 12c, 12d, a dc electrode; 121, a first ion storage unit; 1210, a ring electrode; 121a, 121b, area; 122, a second ion storage unit; 13, a post-stage device; 131, an optical lens; 132, an ion extraction region; 133, flight chamber.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in general with reference to the accompanying drawings. The embodiments of the present invention are not limited to the following embodiments, and various embodiments within the scope of the technical idea of the present invention can be adopted.

Term(s) for

Unless otherwise specified, the term "axial" refers to the direction of transport of ions along a preceding stage arrangement to a succeeding stage arrangement; the term "radial" refers to a direction through an axis in a plane perpendicular to the axial direction. The term "coupled" is intended to indicate a transmission relationship with ions between the two. The terms "front" and "rear" are used in reference to the upstream and downstream directions of ion transport, with "front" corresponding to the upstream direction of ion transport and "rear" corresponding to the downstream direction of ion transport.

Implementation mode one

The present embodiment provides a mass spectrometer 1 having a structure as shown in fig. 1, the mass spectrometer 1 including a front stage 11, an ion optical device 12 located at a rear stage of the front stage 11 to receive ions emitted from the front stage 11, and a rear stage 13 located at a rear stage of the ion optical device 12 to receive ions released from the ion optical device 12.

The ion optical device 12 includes an ion manipulation unit 12M and a power supply device 12E electrically connected to the ion manipulation unit 12M, the ion manipulation unit 12M is composed of a plurality of electrodes, and includes a first ion storage unit 121 and a second ion storage unit 122, the first ion storage unit 121 is coupled to the front stage device 11, receives ions from the front stage device 11, stores the ions, and then releases the ions to the second ion storage unit 122; the second ion storage unit 122 is disposed at a later stage of the first ion storage unit 121, receives ions from the first ion storage unit 121, stores and discharges the ions to the later stage device 13.

The first ion storage unit 121 includes a plurality of ring electrodes 1210 coaxially arranged, equally spaced, and of the same diameter. The first ion storage unit 121 adjusts the electric field shape inside the first ion storage unit 121 by changing the voltage applied to the ring electrode 1210, thereby operating the ions inside. The second ion storage unit 122 is an ion trap device having a smaller size relative to the first ion storage unit 121.

Referring to fig. 2, the following describes the operation process of the ion optical device 12 for ions in this embodiment, taking positive ions as an example. The ion optics 12 performs ion manipulation using a periodically repeating manipulation method, each manipulation cycle including a first time period T1 followed by a second time period T2.

During a first time period T1, performing:

s1. ions are introduced from the front stage apparatus 11 into the first ion storage unit 121.

S2. the first ion storage unit 121 stores ions by using the potential balance of the ions in the radio frequency electric field and the direct current electric field.

In this embodiment, one mode of introducing ions from the preceding device 11 is to set the entire voltage applied to the first ion storage unit 121 at a low dc potential and apply an rf voltage.

The ions are temporarily stored in the first ion storage unit 121 after being introduced, and in a subsequent process, the stored ions are released in a prescribed manner at a prescribed time by changing an electric field inside the first ion storage unit 121.

In this embodiment, by lowering the dc potential in the central region of the first ion storage unit 121 in the axial direction and raising the dc potentials at both ends during the pull-in process, a dc potential well is formed in the central region of the first ion storage unit 121 in the axial direction to store ions. Meanwhile, when radio frequency voltages with equal amplitude and opposite phases are applied to two adjacent ring electrodes 1210, the radio frequency electric field may form a "bounce force" (RF repelling force) on the surface of the ring electrodes 1210, and prevent ions from approaching the electrode surface. Therefore, the dc potential well can confine ions in the axial direction, the rf voltage can confine ions in the radial direction, and the ions are stably confined in the first ion storage unit 121 under the combined action of the dc potential well and the rf electric field.

At higher pressures, the maximum average effective bounce force generated by the rf electric field can be approximated as:

wherein m is the mass number of the ion, K is the mobility, V_RFIs the amplitude of the rf voltage and d is the spacing between adjacent ring electrodes 1210. In this embodiment, the first ion storage unit 121 has a plurality of pairs of ring electrodes 1210 having the same diameter, coaxially disposed, and uniformly spaced in the axial direction, and the ion storage capacity of the first ion storage unit 121 is improved by increasing the number of the ring electrodes 1210. In other embodiments of the invention, the ion capacity may also be expanded by decreasing the electrode spacing or increasing the rf voltage.

During the second period T2, the first ion storage unit 121 performs:

and S3, the first ion storage unit 121 releases ions according to a specific mass-to-charge ratio sequence by adjusting the potential balance of the radio frequency electric field and the direct current electric field.

In the region 121a, the phases of the rf voltages applied to the two adjacent ring electrodes 1210 are opposite, while in the region 121b, the phases of the rf voltages applied to the two adjacent ring electrodes are the same, and the amplitude of the rf voltage applied to the ring electrode in the region 121b is higher than that in the region 121 a.

Because of the above manner of applying the rf voltage, when the ions move to the region 121b under the driving action of the dc electric field, the ions are blocked by the pseudobarrier generated by the rf electric field in the region 121b, and thus ions having partial mass-to-charge ratios that do not satisfy the condition cannot cross the pseudobarrier of the rf electric field and are retained in the first ion storage unit 121. The ion release of the first ion storage unit 121 depends on the potential balance between the pseudobarrier of the radio frequency electric field and the potential barrier of the direct current electric field of the ions at the region 121 b.

The manner of adjusting the potential balance includes: a. the dc voltage of each ring electrode 1210 of the first ion storage unit 121 is changed to transfer the stored ions to the second ion storage unit 122 in the axial direction. b. The first ion storage unit 121 reduces the height of the barrier that the ions need to cross during the process of being ejected by adjusting the pseudobarrier of the rf electric field in the region 121b near the exit. c. Combination of the modes a and b. For example, the potential balance can be adjusted by pushing ions with a dc electric field and scanning the amplitude of the rf electric field from high to low or the frequency of the rf electric field from low to high; alternatively, the strength of the dc electric field is swept from low to high.

In this embodiment, the binding action to the ions having a large mass-to-charge ratio is preferentially reduced by scanning the pseudo potential barrier, and the ions are released in the order of the large mass-to-charge ratio. In particular, the magnitude of the binding effect that can be created by a pseudobarrier is related to the mass-to-charge ratio of the ions. For ions with large mass-to-charge ratio, the binding effect generated by the pseudopotential barrier is relatively weak, so that the ions are more easily pushed away from the first ion storage unit 121 by the direct current electric field; for ions with a small mass-to-charge ratio, the binding effect of the pseudobarrier is relatively strong, and the ions are retained in the first ion storage unit 121 due to the strong binding effect of the pseudobarrier until the pseudobarrier is gradually lowered to provide no sufficient binding effect.

By scanning (linearly decreasing with time) the amplitude of the radio frequency voltage (in other words, scanning the height of the pseudobarrier) based on the potential balance of the pseudobarrier and the direct current electric field, ions can be released in order of the mass-to-charge ratio from large to small. By scanning the amplitude of the rf voltage, the mass-to-charge ratio of ions that cross the pseudobarrier and enter the second ion storage unit 122 decreases linearly with time, and the mass-to-charge ratio of ions that correspond to ions that enter the second ion storage unit 122 can be easily calculated from the time parameter.

In the above manner, the first ion storage unit 121 can not only introduce ions of different mass/charge ratios from the front stage apparatus 11 and store them, but also discharge the stored ions to the second ion storage unit 122 in the order of the mass/charge ratios from large to small.

During the second time period T2, the second ion storage unit 122 performs:

and S4, the second ion storage unit 122 receives the ions from the first ion storage unit 122, divides the received ions into a plurality of pulses and releases the pulses to a target area.

In the ion optical device 12 of the present embodiment, the duty ratio of the ion optical device 12 and the resolution and dynamic range of the mass spectrometer 1 are improved by using the cooperation of the first ion storage unit 121 and the second ion storage unit 122 in the time dimension and the space dimension.

[ space dimension ]

In this embodiment, the ion storage capacity of the first ion storage unit 121 is increased by increasing the number of the ring electrodes 1210. Because the first ion storage unit 121 has a larger ion storage capacity, a larger proportion of, or even all, the ions generated by the preceding stage arrangement can still be processed at the slower scan rate.

While increasing the ion storage capacity, the ion packet will expand in the first ion storage unit 121 due to the coulomb repulsion between the ions and each other. Ions having the same mass to charge ratio will be distributed over a larger volume. This results in that during ejection of the ion packet from the first ion storage unit 121, ions near the exit (at the right end of the first ion storage unit 121 in fig. 1) and ions far from the exit will have a larger separation in the ejection time, and thus a wider distribution in the axial direction, which widens the collected mass spectrum peak and affects the resolution and duty ratio of the instrument.

In order to effectively alleviate or even avoid the negative effects caused by the space charge effect, in the present embodiment, by using the multiple "storage-release" pulse working processes of the second ion storage unit 122 in one operation cycle, the originally broadened ions can be compressed in the axial direction, and the ions with a specific mass-to-charge ratio or mass-to-charge ratio range are packed into a "compressed packet" (corresponding to one ion pulse) with a smaller volume and are transmitted to the subsequent device 13.

Specifically, since in the ion optical apparatus provided in the present embodiment, the function of receiving and storing ions released from the pre-stage apparatus 11 in a larger proportion, even completely, is mainly performed by the first ion storage unit 121, while the second ion storage unit 122 does not take on the above-described role, the ion storage capacity of the second ion storage unit 122 can be relatively small as long as it is sufficient to confine a small number of ions in a specific mass-to-charge ratio or mass-to-charge ratio range. Therefore, the second ion storage unit 122 requires only a small volume of equipment to achieve the above function.

Because the second ion storage unit 122 (relative to the first ion storage unit 121) has a smaller volume, ions originally distributed widely in the axial direction during the releasing process of the first ion storage unit 121 will be compressed during the storing process of the second ion storage unit 122, so that the space charge effect is effectively alleviated or even avoided, and the resolution and duty ratio of the mass spectrometer 1 are improved.

[ time dimension ]

In the time dimension, the cooperation between the first ion storage unit 121 and the second ion storage unit 122 is implemented by using the cooperation manner shown in fig. 3. Fig. 3 illustrates the matching relationship between the amplitude of the rf voltage at the region 121b of the first ion storage unit 121 and the dc voltage for driving out ions, such as the voltage at the exit (ion gate), of the second ion storage unit 122 in the time dimension, with reference to the same time axis as an example of one operation cycle of the ion optical device 12. The abscissa of fig. 3 is time, the upper half of the ordinate corresponding to the amplitude of the rf voltage at the region 121b of the first ion storage element 121 and the lower half of the ordinate corresponding to the value of the voltage of the ion gate at the exit of the second ion storage element 122.

Referring to fig. 3, during a first period T1 of one operation cycle, step S1 is performed; within the second period T2, steps S2 and S3 are performed. During the first time period T1, the execution manner of step S1 refers to the description of step S1, and is not repeated here.

During the second period T2, the first ion storage unit 121 causes the pseudobarrier to gradually decrease by linearly decreasing the radio frequency amplitude at the region 121b with time to release ions in order of the mass-to-charge ratio from large to small. Correspondingly, ions received from the first ion storage unit 121 will be further sliced into a plurality of pulses by the second ion storage unit 122 for release.

Specifically, the ion gate at the exit of the second ion storage unit 122 will operate in an intermittent on and off fashion. The second ion storage unit 122 will continuously receive and store ions received from the first ion storage unit 121 with the ion gate closed, and when the ion gate is opened, will release the currently stored ions to the back stage device 13, forming an ion pulse.

In particular, in this embodiment, the latter stage device 13 comprises an orthogonal time-of-flight mass analyser, the target region for ion release is an ion extraction region 132 located in the front stage of the orthogonal time-of-flight mass analyser, and the acceleration pulses of the ion extraction region 132 operate at a frequency in the order of kHZ (e.g. 8kHZ in this embodiment). In order to synchronize with the acceleration pulse of the ion extraction region 132, the second ion storage unit 122 needs to perform a door opening operation every approximately 125 μ s (corresponding to 8 kHz).

Since the first ion storage unit 121 releases ions in the order in which the mass-to-charge ratio linearly decreases with time, the mass-to-charge ratio or the mass-to-charge ratio range of ions packed in each ion pulse can be estimated from the release time of the ion pulse. According to the mass-to-charge ratio information corresponding to the ion pulses one to one, the electric field condition in the second ion storage unit 122, and the distance between the ion gate and the target region of the post-stage device 13, the time required for each ion pulse to move to the target region can be calculated, and further according to the calculation result, the release time of each ion pulse, that is, the time and duration of opening of each ion gate, can be set.

With continued reference to fig. 3, to enable different ion pulses to reach the target region at substantially the same kinetic energy, substantially simultaneously, increasing the duty cycle, the separation of the release time between adjacent ion pulses is non-uniform, and the lag in the release time of each ion pulse over the corresponding period (125 μ s in this embodiment) is increasing with time, i.e., t1< t2< t3 … < t 24. By accurately setting the release time of each ion pulse, it is ensured that ions with a smaller mass-to-charge ratio released later can just catch up with ions with a larger mass-to-charge ratio released earlier at the ion extraction region 132, and the duty ratio can be increased to 100% within a relatively wide mass range.

In this embodiment, each operation cycle lasts 5000 μ s, wherein the first time period T1 lasts 2000 μ s, the second time period T2 lasts 3000 μ s (including 24 ion pulses), and the duration of each opening of the ion gate is 10 μ s.

In a state where the ion gate is closed, ions released from the first ion storage unit 121 can be temporarily stored in the second ion storage unit 122, and in this process, ions are not lost (in some conventional ion optical devices, ions are continuously released without being blocked by the ion gate, and ions not blocked by the ion gate may be lost due to not being able to reach the target region at the same time). Furthermore, the second ion storage unit 122 does not change the mass-to-charge ratio release order of the ions, i.e., the mass-to-charge ratio order in which the ions are released is determined by the first ion storage unit 121. Furthermore, the pulsed release mode has a higher working frequency, can be conveniently synchronized with the working frequency of the post-stage device 13, and can divide the ion beam into a plurality of pulses for release, so that the mass-to-charge ratio range of ions in each ion pulse can be compressed, that is, each release of ions is only specific mass-to-charge ratio or a narrower mass-to-charge ratio range, thereby effectively improving the accuracy of control on each ion pulse, conveniently sending each pulse to a target area at the same time, and further improving the duty ratio.

In the above manner, the ion optical device 12 provided in the present embodiment has the following advantages: (1) the device can provide higher duty ratio in the tandem mass spectrum within a wide mass range, even can reach 100 percent, thereby improving the sensitivity of the device; (2) by utilizing the cooperation between the first ion storage unit 121 and the second ion storage unit 122, the expansion of the ion storage capacity of the ion optical device 12 is no longer limited or less limited by the space charge effect, which is beneficial to ensuring the wide dynamic range of the instrument. (3) The second ion storage unit 122 can be synchronized with the post-stage device 13 at a higher operating frequency, which effectively increases the speed of the cascade analysis.

Second embodiment

In the present embodiment, a mass spectrometer 1 is provided, in which a structure as shown in fig. 4 is adopted, a front stage device 11 can send ions generated from an ion source into a quadrupole for mass selection through a vacuum interface and other ion guide devices, the selected parent ions enter a collision cavity 111 for fragmentation and dissociation to generate a plurality of daughter ions, and the daughter ions are introduced into an ion optical device 12. The latter device 13 comprises an optical lens 131 for collimating plasma conditioning of ions, a pulsed ion extraction region 132 and an orthogonal time-of-flight mass spectrometer arranged in sequence along the ion transport direction. The orthogonal time-of-flight mass spectrometer includes a flight chamber 133, mirrors (not shown), a detector (not shown), and the like.

The ion manipulation unit 12M of the ion optical device 12 of the mass spectrometer 1 includes two sets of

annular electrode arrays

12a and 12b that are disposed parallel to and coaxially with each other, and each set of

annular electrode arrays

12a and 12b is composed of a plurality of concentrically disposed annular electrodes (preferably, but not limited to, illustrated circular rings).

Furthermore, the ion optical device 12 further includes a dc electrode 12c disposed on the front side of the ring electrode array 12a and a dc electrode 12d disposed on the rear side of the ring electrode array 12b, and a power supply device (not shown) applies a dc voltage to the dc electrode 12c and the dc electrode 12d to generate a dc electric field capable of driving ions to move in the axial direction, thereby introducing ions from the front stage device 11 or ejecting ions to the rear stage device 13.

In the ion optical device 12 of the present embodiment, the first ion storage unit 121 and the second ion storage unit 122 are formed in the peripheral and central structures, respectively, by applying a voltage to each electrode by the power supply device.

Referring to FIG. 4, the ion optics 12 adjust the DC potentials at the peripheral regions of the

annular electrode arrays

12a, 12b to form DC potential wells and apply RF voltages of the same magnitude and opposite phase to adjacent annular electrodes at the peripheral regions to form "bounce forces". In the above manner, ions can be efficiently stored between the ring electrode array 12a and the ring electrode array 12b in the peripheral region to serve as an ion storage space of the first ion storage unit 121. Since the first ion storage unit 121 is extended in the radial direction, the stored ions are distributed in a ring shape in the peripheral region, and the axial length of the apparatus can be shortened while the ion storage capacity is increased. In the central region of the

ring electrode arrays

12a and 12b, the rf electric field binds ions along the radial direction, and the dc electric field binds ions along the axial direction, so that ions can be effectively stored between the ring electrode array 12a and the ring electrode array 12b in the central region, so as to serve as an ion storage space of the second ion storage unit 122.

The hardware structure of the device, a modification (for example, using a quadrupole field type electrode), and the basic voltage application method thereof can be referred to the contents described in chinese patent CN 201610602789.7. In this embodiment, the first ion storage unit 121 and the second ion storage unit 122 are integrated in the ion optical device 12 having a centrosymmetric structure, so that the device is simpler and the voltage application is more flexible.

The first ion storage unit 121 and the second ion storage unit 122 can still be matched in the time dimension in the matching manner shown in fig. 3 of the first embodiment, so as to effectively improve the duty ratio and the analysis speed of the instrument.

Fig. 5 is an ion spectrum obtained by ejecting ions from the first ion storage unit 121 using computer simulation, where the abscissa is time and the ordinate is the ion number. The main ion peaks are distributed in the positions with mass-to-charge ratios of 1500Th, 1000Th, 500Th and 250 Th. As can be seen from fig. 5, the ions are sequentially ejected in order of the mass-to-charge ratio from large to small within an operation period of 3000 μ s, and the peak width of the ion of each mass-to-charge ratio is about 50-80 μ s.

Fig. 6 is an ion spectrum diagram formed by ejecting ions from the second ion storage unit 122, which is obtained by computer simulation. As can be seen from fig. 5, the ions are divided into a plurality of pulses for ejection by using the multiple "storage-release" processes of the second ion storage unit 122 in one operation cycle. Also, since ions are accumulated in the second ion storage unit 122 when not ejected, the slicing process does not cause loss of ions.

In particular, by reasonably setting the opening and closing time of the ion gate and controlling the time of the segmentation, ions with basically the same or completely the same mass-to-charge ratio can be packed into one ion pulse. The targeted implementation of the operation on each ion pulse will also result in a higher degree of accuracy of ion operation, since the mass-to-charge ratio distribution of the ions contained in each ion pulse is more concentrated. With the release pattern shown in fig. 6, ions will be ejected in a pulse-by-pulse manner, and the pulsed ejection process will facilitate the synchronization of the ion optics 12 with the higher operating frequency time-of-flight mass analyzer at the subsequent stage, facilitating a 100% duty cycle.

In some embodiments of the present invention, the post-stage device 13 may also employ other pulsed mass analyzers, such as a quadrupole mass analyzer. The ion optics provided in embodiments of the present invention can pack ions with a narrower mass to charge ratio distribution into one ion pulse and can adjust the release time of each ion pulse so that the ion pulses arrive at the ion extraction region of the mass analyser in a prescribed order. Thus, by configuring the quadrupole mass analyser to scan only a narrow mass to charge ratio distribution range corresponding to each ion pulse in synchronism, it is possible to ensure that fewer ions are lost per scan, improving the duty cycle. Furthermore, the same kinetic energy of the ions when they reach the ion extraction region is beneficial to improving the resolution of the quadrupole mass analyzer.

The ion optics 12 is preferably filled with a gas under pressure so that the dislodged ions can be rapidly cooled within the ion optics 12 by collisions with the background gas, which can be done under the combined action of the rf electric field, but cooling can also occur outside the ion optics 12. Accordingly, the ion optical device 12 can be adapted to different air pressures, ranging from 0.002Pa to 0.05Pa, or from 0.02Pa to 0.5Pa, or from 0.2Pa to 5Pa, or from 2Pa to 50Pa, or from 20Pa to 500 Pa.

So far, the technical solutions of the present invention have been described with reference to the accompanying drawings, but it is obvious to those skilled in the art that the scope of the present invention is not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.

Claims

1. An ion optical device, comprising:

a power supply device;

an ion manipulation part composed of a plurality of electrodes electrically connected to the power supply device, the power supply device applying a voltage to the plurality of electrodes to form a radio frequency electric field and a direct current electric field,

the ion manipulation part is capable of performing a periodic manipulation of ions, wherein each cycle of manipulation comprises a first time period and a second time period,

characterized in that the ion manipulation part comprises,

the first ion storage unit is used for storing ions by utilizing the potential balance of the ions between the radio frequency electric field and the direct current electric field in the first time period and releasing the ions in sequence according to a specific mass-to-charge ratio by adjusting the potential balance in the second time period;

and the second ion storage unit is used for receiving the ions from the first ion storage unit in the second time period and dividing the received ions into a plurality of pulses to be released to a target area in the second time period.

2. The ion optical apparatus of claim 1, wherein the plurality of electrodes comprises a first electrode array and a second electrode array disposed parallel and coaxial to each other.

3. The ion optical device according to claim 2, wherein the first ion storage unit is disposed in a peripheral region between the first electrode array and the second electrode array, and the second ion storage unit is disposed in a central region of the first electrode array and the second electrode array.

4. The ion optical device of claim 2, wherein the first electrode array and the second electrode array are each comprised of a plurality of ring electrodes, and the plurality of ring electrodes of the first electrode array are arranged in one-to-one correspondence with the plurality of ring electrodes of the second electrode array.

5. The ion optical device of claim 1, wherein the means for adjusting the potential balance comprises: the direct current electric field is used for pushing ions, and the amplitude of the radio frequency electric field is scanned from high to low or the frequency of the radio frequency electric field is scanned from low to high; alternatively, the strength of the dc electric field is scanned from low to high.

6. The ion optical apparatus of claim 1, wherein the second ion storage unit releases the received ions by changing a dc potential of at least a portion of the plurality of electrodes.

7. The ion optical device according to claim 1, wherein the specific mass to charge ratio order is a large to small mass to charge ratio order.

8. The ion optical apparatus of claim 7, wherein a time interval between adjacent pulses of the plurality of pulses gradually increases along a time axis.

9. The ion optical device of claim 8, wherein the plurality of pulses respectively carry ions of different mass-to-charge ratio ranges, and the time interval is set according to the mass-to-charge ratio range corresponding to each pulse.

10. A mass spectrometer having an ion optical device according to any one of claims 1 to 9.

11. The mass spectrometer of claim 10, wherein the target region is an ion extraction region of a pulsed mass analyzer disposed downstream of the ion optics.

12. The mass spectrometer of claim 11, wherein the mass analyzer is an orthogonal time-of-flight mass analyzer.

13. The mass spectrometer of claim 11, wherein the mass analyzer is a quadrupole mass analyzer, ions released in pulses are split into a plurality of ions entering along an axis of the quadrupole mass analyzer, and a scan voltage of the quadrupole mass analyzer is synchronized according to a mass-to-charge ratio of the ions.

14. The mass spectrometer of claim 11, wherein ion release from the second ion storage unit is synchronized with pulse analysis of the pulsed mass analyzer.

15. The mass spectrometer of claim 10, wherein the pressure of the gas within the ion optical device is between 0.002Pa and 0.05Pa, or between 0.02Pa and 0.5Pa, or between 0.2Pa and 5Pa, or between 2Pa and 50Pa, or between 20Pa and 500 Pa.

16. An ion operation method of an ion optical device, the ion optical device comprises a power supply device and an ion operation part, the ion operation part is composed of a plurality of electrodes which are electrically connected with the power supply device, the power supply device applies voltage on the plurality of electrodes to form a radio frequency electric field and a direct current electric field, the ion operation part comprises a first ion storage unit and a second ion storage unit,

the method of ion manipulation comprising a plurality of repeatedly performed periodic manipulations, wherein at least one cycle of manipulation comprises a first time period and a second time period, the method of ion manipulation comprising the steps of, during at least one cycle of manipulation:

during the first time period, the first ion storage unit stores ions by utilizing the potential balance of the ions in the radio frequency electric field and the direct current electric field;

during the second time period, the first ion storage unit releases ions according to a specific mass-to-charge ratio sequence by adjusting the potential balance;

and in the second time period, the second ion storage unit receives the ions from the first ion storage unit and divides the received ions into a plurality of pulses to be released to a target area.

17. The method of ion manipulation according to claim 16, wherein the specific mass-to-charge ratio order is from large to small.

18. The method of ion manipulation of an ion optical device of claim 17, wherein the time intervals between adjacent pulses of said plurality of pulses are non-uniform.

19. The method of claim 18, wherein the plurality of pulses each carry ions of a different range of mass-to-charge ratios, and the time interval is set according to the mass-to-charge ratio corresponding to each pulse.