Linear electrostatic trap and method of operating the same

Abstract

The application provides a linear electrostatic trap and a working method thereof, the linear electrostatic trap comprising a power supply, the power supply applying radio frequency voltage and direct current voltage to electrodes; a plurality of groups of electrodes comprising a center group of electrodes and a peripheral group of electrodes, the center group of electrodes having an ion exit hole, the peripheral group of electrodes being symmetrically arranged about the center group of electrodes; each group of electrodes surrounding an ion channel, a plurality of groups of electrodes arranged in sequence forming a linear ion channel, the power supply applying radio frequency voltage and direct current voltage to each group of electrodes; the radio frequency voltage Vn of the nth group of electrodes being greater than the radio frequency voltage Vn-1 of the (n-1)th group of electrodes from the center group of electrodes to the peripheral group of electrodes. n The application has the advantages of simple structure and the like.

Description

TECHNICAL FIELD

[0001] The present invention relates to mass spectrometry, and in particular to a linear electrostatic trap and a method of operating the same. BACKGROUND

[0002] Ion traps, including RF ion traps, are known devices that allow for the storage of ions and ejection of stored ions into a mass analyzer such as an ion cyclotron resonance (ICR) analyzer.

[0003] S. Michael, M. Chien, D. Lubman in Rev. Sci. Instrum., 1992, 63, 4277-4284, patent US5569917, patent US5763878 describe the use of a 3D quadrupole ion trap as accumulator and injector into a TOF mass analyzer. However, in this prior art trap the volume of the ion cloud is limited, leading to severe Coulombic interactions between stored ions, thus greatly affecting the parameters of the resulting ion beam.

[0004] Linear ion traps and curved ion traps allow for an increase in the volume of the ion cloud, thus reducing the level at which space charge effects start to affect performance (typically, the number of ions allowed increases by an order of magnitude or more). Linear ion traps and curved ion traps have therefore proven more suitable for mass spectrometry measurements and for the injection of ions into a mass analyzer. Senko M.W. et al. in J. Am. Soc. Mass Spectrom. 1997, 8, 970-976 summarize a range of different traps for FT-ICR mass spectrometers and describe the use of an octapole ion guide as accumulator, followed by a second octapole as injector, with ions being transferred out of the trap in the direction of the trap axis, rather than in a direction perpendicular to the trap axis.

[0005] A curved multipole rod trap with perpendicular ejection is disclosed in patent US6872938, in particular a curved ion trap that focuses ions through a small entrance slit of an orbitrap mass analyzer. The focusing is provided by the shape of the curved ion trap itself and by the use of curved focusing and deflection optics between the trap and the orbitrap mass analyzer. Although the resulting configuration provides high performance, it has a number of drawbacks, such as:

[0006] 1. The configuration is complex to manufacture.

[0007] 2. The wide slit required by the configuration (width decreases close to the focus point) leads to an increased requirement for differential pumping.

[0008] 3. The trap has the disadvantage that its space charge capacity is lower than that of the orbitrap itself.

[0009] 4. The lens between the trap and the mass analyzer is curved, which is complex to manufacture and calibrate.

[0010] 5. The mass range of the ions accumulated and injected into the mass analyzer is limited.

[0011] Makarov et al. in patent US8017909B2 provided a curved linear trap, i.e. C-trap, which is a storage trap based on the principle of ion trap and can quickly inject ions into the Orbitrap detector. The ions enter the curved linear trap (C-trap) filled with gas through the gate electrode of the C-trap. The C-trap quadrupole applies an RF potential (500-1500Vpp, 3Mhz) to capture the ions radially. The entering ions are reflected by the trap electrode at the other end of the C-trap and begin to lose energy in the collision with nitrogen gas (~1mTorr) to cool in the C-trap. The ions form a long arc along the curved axis of the C-trap, and the ions are axially confined by simultaneously applying potentials on the gate electrode and the trap electrode of the C-trap (lifted to 200V and the lift rate is increased) (Makarov et al., 2006a). The ions are focused into a tight ion cloud by applying 1200, 1000 and 1100 volt DC pulses to the push electrode (the electrode farthest from the center of curvature of the C-trap), the pull electrode (the electrode closest to the center of curvature of the C-trap) and the upper and lower electrodes, respectively. The disadvantages of this scheme are:

[0012] 1. There is only one set of ejection voltages, and the voltages cannot be optimized, resulting in low focusing efficiency.

[0013] 2. The electrode structure is complex to design and difficult to process.

[0014] 3. The ions are compressed by the end cap electrode, and the ion storage efficiency is low. SUMMARY

[0015] To solve the above-mentioned deficiencies in the prior art, the present application provides a linear electrostatic trap.

[0016] The purpose of the present application is achieved by the following technical solutions:

[0017] A linear electrostatic trap, comprising a power supply for applying RF voltage and DC voltage to the electrodes; the linear electrostatic trap further comprises:

[0018] A plurality of groups of electrodes, including a central group of electrodes and a peripheral group of electrodes, the central group of electrodes having an ion exit hole, and the peripheral group of electrodes being symmetrically arranged about the central group of electrodes; each group of electrodes surrounds an ion channel, and the plurality of groups of electrodes arranged in sequence form a linear ion channel, and the power supply applies RF voltage and DC voltage to each group of electrodes;

[0019] RF voltage Vn on the nth electrode from the center electrode to the peripheral electrode n satisfies:

[0020] ,

[0021] (m / z) max is the highest mass-to-charge ratio of the ion packet, (m / z) min is the minimum mass-to-charge ratio of the ion packet, and K is a reference voltage.

[0022] The application also provides a working method of the linear ion trap.

[0023] The working method of the linear ion trap comprises the following steps:

[0024] (S1) A power supply applies RF voltage to a plurality of electrodes, and ions are stored in ion channels formed by the plurality of electrodes;

[0025] The plurality of electrodes comprises a center electrode and a peripheral electrode, the center electrode has an ion exit hole, and the peripheral electrode is symmetrically arranged about the center electrode; each electrode encloses an ion channel, and the plurality of electrodes arranged in sequence form a linear ion channel, and the power supply applies RF voltage and DC voltage to each electrode;

[0026] RF voltage Vn on the nth electrode from the center electrode to the peripheral electrode n satisfies:

[0027] , (m / z) max is the highest mass-to-charge ratio of the ion packet, (m / z) min is the minimum mass-to-charge ratio of the ion packet, and K is a reference voltage.

[0028] (S2) Adjusting the DC voltage on the plurality of electrodes so that the ions in the ion channel of the peripheral electrode enter the ion channel of the center electrode along the linear ion channel;

[0029] (S3) Changing the voltage of the center electrode to eject the ions in the ion channel of the center electrode, and the ions are ejected from the ion exit hole.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] 1. Simple structure;

[0032] By setting the radio frequency voltage on the multiple sets of electrodes (or adding the gap setting of the multiple sets of electrodes), the same radio frequency field effect of a complex structure can be realized by a simple straight electrode, ion cooling and confinement (i.e. storage) are realized; without the gate electrodes on both sides in the prior art, the axial field compression is realized;

[0033] 2. Without complex ion collection and compression devices;

[0034] 3. The program-controlled voltage can be applied to the electrodes, the voltage program can be better tuned and modulated according to the instrument state, so that the trap has better transmission efficiency, better compression focusing, and better ejection effect;

[0035] 4. By low machining precision and simpler structure, combined with more controllable voltage parameters, a better focusing effect than the complex curved arc trap is realized. BRIEF DESCRIPTION OF DRAWINGS

[0036] The disclosure of the present application will become more apparent with reference to the drawings. It is easy for those skilled in the art to understand that these drawings are only used to illustrate the technical solutions of the present application, and are not intended to limit the protection scope of the present application. In the drawings:

[0037] Figure 1 is a structural schematic diagram of a straight electrostatic trap according to an embodiment of the present application. DETAILED DESCRIPTION

[0038] Figure 1 The following description describes alternative specific embodiments of the present application to teach those skilled in the art how to implement and reproduce the present application. In order to teach the technical solutions of the present application, some conventional aspects have been simplified or omitted. Those skilled in the art should understand that variations or substitutions derived from these specific embodiments will be within the scope of the present application. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the present application. Therefore, the present application is not limited to the following alternative specific embodiments, but is only limited by the claims and their equivalents. Example 1

[0039] A straight electrostatic trap according to an embodiment of the present application, as shown in Figure 1 The straight electrostatic trap comprises:

[0040] a power supply, the power supply applies radio frequency voltage and direct current voltage to the electrodes;

[0041] a plurality of sets of electrodes, the plurality of sets of electrodes comprises a center set of electrodes and a peripheral set of electrodes, the center set of electrodes has an ion exit hole, the peripheral set of electrodes is symmetrically arranged about the center set of electrodes; each set of electrodes encloses an ion channel, and the plurality of sets of electrodes arranged in sequence form a straight ion channel, the power supply applies radio frequency voltage and direct current voltage to each set of electrodes;

[0042] RF voltage Vn on the nth electrode from the center electrode to the peripheral electrode direction n satisfies:

[0043] , (m / z) max is the highest mass-to-charge ratio of the ion packet, (m / z) min is the minimum mass-to-charge ratio of the ion packet, and K is a reference voltage, which is generally set to 2000 V according to the structure of the trap.

[0044] In order to reduce the structural complexity, further, each electrode is composed of two pairs of oppositely arranged electrodes, and the inner surface of the electrode is a plane.

[0045] In order to reduce the structural complexity, further, from the center electrode to the peripheral electrode direction, the length of each electrode in the direction parallel to the central axis of the ion channel is equal or increases.

[0046] The working method of the electrostatic trap according to the embodiment of the application comprises the steps of:

[0047] (S1) a power supply applies RF voltage to a plurality of electrodes, and ions are stored in an ion channel formed by the plurality of electrodes;

[0048] The plurality of electrodes comprises a center electrode and a peripheral electrode, the center electrode has an ion exit hole, and the peripheral electrode is symmetrically arranged about the center electrode; each electrode encloses an ion channel, and the plurality of electrodes arranged in sequence form a linear ion channel, and the power supply applies RF voltage and DC voltage to each electrode;

[0049] RF voltage Vn on the nth electrode from the center electrode to the peripheral electrode direction n satisfies:

[0050] , (m / z) max is the highest mass-to-charge ratio of the ion packet, (m / z) min is the minimum mass-to-charge ratio of the ion packet; and K is a reference voltage, which is generally set to 2000 V according to the structure of the trap.

[0051] (S2) adjusting the DC voltage on the plurality of electrodes so that the ions in the ion channel of the peripheral electrode enter the ion channel of the center electrode along the linear ion channel;

[0052] (S3) changing the voltage of the center electrode to eject the ions in the ion channel of the center electrode, and the ions are ejected from the ion exit hole.

[0053] For ion storage effect, further, in step (S1), the RF voltage amplitude applied on each electrode becomes larger from the central electrode to the peripheral electrode.

[0054] For reducing structural complexity, further, each electrode is composed of two pairs of oppositely arranged electrodes, and the inner surface of the electrode is a plane or a curved surface.

[0055] For reducing structural complexity, further, the length of each electrode in the direction parallel to the central axis of the ion channel is equal or becomes larger from the central electrode to the peripheral electrode. Embodiment 2

[0056] Application example of a linear electrostatic trap and a working method thereof according to embodiment 1 of the present application.

[0057] In this application example, as shown in Figure 1 , the device comprises five groups of electrodes arranged in sequence, i.e. two peripheral electrodes (from the second electrode P2 to the third electrode P3) arranged on both sides of the central electrode (i.e. the first electrode P1), and the four peripheral electrodes are symmetrically arranged about the central electrode; each electrode comprises two pairs of oppositely arranged (and perpendicular to each other) flat plate electrodes, forming a prismatic ion channel; the electrode of the central electrode has an ion exit hole, and the central axis of the exit hole is perpendicular to the central axis of the ion channel.

[0058] In each group of electrodes, the distance between the oppositely arranged flat plate electrodes is a=113mm, the total length of the electrostatic trap is b=40mm, and the gap between adjacent groups of electrodes becomes smaller in the direction from the peripheral electrode to the central electrode, with a gap range of 0.8-1.5mm;

[0059] The power supply applies RF voltages with different amplitudes to each group of electrodes to achieve ion trapping and transmission, wherein ,

[0060] The ion packet (m / z) max =500, (m / z) min =200, according to the structure of the trap, the reference voltage K=2000V. It can be seen that the RF voltage V1=1665V on the first electrode (P1), the RF voltage V2=1685V on the second electrode (P2), and the RF voltage V3=1720V on the third electrode (P3), and the RF voltage frequency is 3MHz

[0061] The working method of a linear electrostatic trap according to an embodiment of the present application, the working method of the linear electrostatic trap comprises the steps of:

[0062] (S1) the power supply applies RF voltages to a plurality of electrodes, the first

[0063] The radio frequency voltage V1 = 1665V on one set of electrodes (P1), the radio frequency voltage V2 = 1685V and V3 = 1720V on the second set of electrodes (P2), the radio frequency voltage frequency is 3MHz, and the ions are stored in a linear ion channel formed by multiple sets of electrodes.

[0064] (S2) Apply DC voltage to each group of electrodes gradually from the outside to the inside (i.e. from the third group of electrodes to the first group of electrodes), so that ions in the ion channels of the outer group of electrodes enter the ion channels of the central group of electrodes along the linear ion channels.

[0065] (S3) Change the voltage of the central electrode group to eject ions in the ion channel of the central electrode group, and the ions are ejected from the ion emission hole. Example 3

[0066] An application example of a linear electrostatic trap and its working method according to Embodiment 1 of the present invention.

[0067] In this application example, such as Figure 1 As shown, the device includes 15 sets of electrodes arranged sequentially, namely, 7 peripheral electrodes (from the second set of electrodes P2 to the eighth set of electrodes P8) are arranged on both sides of the central set of electrodes (i.e., the first set of electrodes P1), and 14 sets of peripheral electrodes are symmetrically arranged about the central set of electrodes; each set of electrodes includes two pairs of relatively parallel (and mutually perpendicular) flat plates forming a prism-shaped ion channel; the central set of electrodes has ion emission holes, and the central axis of the emission holes is perpendicular to the central axis of the ion channel.

[0068] The length of the plate electrodes along the direction parallel to the central axis of the ion channel is c=4mm, the distance between the relatively arranged plate electrodes is a=12mm, and the total length of the electrostatic trap is b=60mm.

[0069] use It can be seen that the gap J1 between the first group of electrodes (P1) and the second group of electrodes (P2) is 1.160 mm, and the gap J2 between the second group of electrodes (P2) and the third group of electrodes (P3) is 1.877 mm.

[0070] The power supply applies radio frequency voltages of different amplitudes to each group of electrodes to achieve ion trapping and transport. Among these methods, the use of… In the ion package (m / z) max =500, (m / z) min =200, reference voltage K=2000V.

[0071] It can be seen that the radio frequency voltage V1 on the first set of electrodes (P1) is 1665V, the radio frequency voltage V2 on the second set of electrodes (P2) is 1685V, V3 is 1720V, and so on, and the radio frequency voltage frequency is 3MHz.

[0072] An embodiment of the present invention provides a method for operating a linear electrostatic trap, the method comprising the following steps:

[0073] (S1) The power supply applies radio frequency voltage to multiple sets of electrodes. The radio frequency voltage V1 = 1665V on the first set of electrodes (P1), the radio frequency voltage V2 = 1685V on the second set of electrodes (P2), V3 = 1720V, and so on. Ions are stored in the linear ion channel formed by the multiple sets of electrodes.

[0074] (S2) Apply DC voltage to each group of electrodes gradually from the outside to the inside (i.e. from the eighth group of electrodes to the first group of electrodes), so that ions in the ion channels of the outer group of electrodes enter the ion channels of the central group of electrodes along the linear ion channels.

[0075] (S3) Change the voltage of the central electrode group to eject ions from the ion channel of the central electrode group, and the ions are ejected from the ion emission port. Example 4

[0076] An application example of a linear electrostatic trap and its working method according to Embodiment 1 of the present invention.

[0077] In this application example, such as Figure 1 As shown, the linear electrostatic trap includes nine sets of electrodes arranged sequentially, namely, four sets of peripheral electrodes (from the second set of electrodes P2 to the fifth set of electrodes P5) are arranged on both sides of the central set of electrodes (i.e., the first set of electrodes P1), and the eight sets of peripheral electrodes are symmetrically arranged about the central set of electrodes; each set of electrodes includes two pairs of oppositely arranged (and mutually perpendicular) electrodes, the inner surface of the electrodes is curved, forming a linear ion channel; the electrodes of the central set of electrodes have ion emission holes, and the central axis of the emission holes is perpendicular to the central axis of the ion channel.

[0078] The planar electrodes have different lengths along the direction parallel to the central axis of the ion channel. The lengths of the first group of electrodes are c1=2.5mm, the second group of electrodes are c2=2.8mm, the third group of electrodes are c3=3.15mm, the fourth group of electrodes are c4=3.5mm, and the fifth group of electrodes are c5=4.0mm. The minimum distance between the inner surfaces of the electrodes is a=10mm, and the total length of the electrostatic trap is b=29.4mm.

[0079] use The results show that the gap between the first group of electrodes (P1) and the second group of electrodes (P2) is J1=0.977mm, the gap between the second group of electrodes (P2) and the third group of electrodes (P3) is J2=1.392mm, the gap between the third group of electrodes (P3) and the fourth group of electrodes (P4) is J3=1.676mm, and the gap between the fourth group of electrodes (P4) and the fifth group of electrodes (P5) is J4=1.900mm.

[0080] The power supplies apply radio frequency voltages with different amplitudes to each group of electrodes to realize ion trapping and transmission, wherein , the ion packet (m / z) min =150, (m / z) max =1000. It can be seen that the radio frequency voltage V1=1691V on the first group of electrodes (P1), the radio frequency voltage V2=1828V on the second group of electrodes (P2), V3=2072V, V4=2423V…, and the radio frequency voltage frequency is 3MHz.

[0081] The working method of the linear electrostatic trap of the embodiment of the application comprises the steps of:

[0082] (S1) The power supplies apply radio frequency voltages to the nine groups of electrodes, wherein the radio frequency voltage V1=1691V on the first group of electrodes (P1), the radio frequency voltage V2=1828V on the second group of electrodes (P2), V3=2072V, V4=2423V…, the radio frequency voltage frequency is 3MHz, and ions are stored in the linear ion channels formed by the multiple groups of electrodes;

[0083] (S2) The direct current voltages are gradually applied to each group of electrodes from outside to inside (i.e. from the fifth group of electrodes to the first group of electrodes), so that the ions in the ion channels of the peripheral groups of electrodes enter the ion channel of the central group of electrodes along the linear ion channel;

[0084] (S3) The voltage of the central group of electrodes is changed, the ions in the ion channel of the central group of electrodes are ejected, and the ions are ejected from the ion ejection hole.

Claims

1. A linear electrostatic trap comprising a power supply applying a radio frequency voltage and a direct current voltage to electrodes; characterized in that, The linear electrostatic trap further comprises: a plurality of electrode groups, the plurality of electrode groups comprising a center electrode group and a plurality of peripheral electrode groups, the center electrode group having an ion exit hole, the plurality of peripheral electrode groups being symmetrically arranged with respect to the center electrode group; each electrode group encloses an ion channel, and the plurality of electrode groups arranged in sequence form a linear ion channel; and the power supply applies a radio frequency voltage and a direct current voltage to each electrode group. RF voltage Vn on the nth set of electrodes, as a function of the radial position r, is given by: n satisfies: ， (m / z) max is the highest mass-to-charge ratio of the ion packet, (m / z) min is the lowest mass-to-charge ratio of the ion packet, K is the reference voltage.

2. A linear electrostatic trap according to claim 1, wherein, Each electrode group is composed of two pairs of oppositely arranged electrodes, and the inner surface of the electrodes is a plane or a curved surface.

3. The linear electrostatic trap of claim 1, wherein, The length of each electrode group in the direction parallel to the central axis of the ion channel increases from the center electrode group to the peripheral electrode groups.

4. A method for operating a linear ion trap, the method comprising the steps of: (S1) applying a radio frequency voltage to a plurality of electrode groups by a power supply, and storing ions in ion channels formed by the plurality of electrode groups; the plurality of electrode groups comprising a center electrode group and a plurality of peripheral electrode groups, the center electrode group having an ion exit hole, the plurality of peripheral electrode groups being symmetrically arranged with respect to the center electrode group; each electrode group encloses an ion channel, and the plurality of electrode groups arranged in sequence form a linear ion channel; and the power supply applies a radio frequency voltage and a direct current voltage to each electrode group. RF voltage Vn on the nth set of electrodes, as a function of the radial position r, is given by: n satisfies: , (m / z) max is the highest mass-to-charge ratio of the ion packet, (m / z) min is the lowest mass-to-charge ratio of the ion packet, K is the reference voltage; (S2) adjusting the direct current voltage on the plurality of electrode groups so that ions in the ion channels of the peripheral electrode groups enter the ion channel of the center electrode group along the linear ion channel; (S3) changing the voltage of the center electrode group to eject ions in the ion channel of the center electrode group, and the ions are ejected from the ion exit hole.

5. The method of operating a linear ion trap of claim 4, wherein, In step (S1), the amplitude of the radio frequency voltage applied to each electrode group increases from the center electrode group to the peripheral electrode groups.

6. The method of operating a linear ion trap of claim 4, wherein, Each electrode group is composed of two pairs of oppositely arranged electrodes, and the inner surface of the electrodes is a plane or a curved surface.

7. The method of operating a linear ion trap of claim 4, wherein, The length of each electrode group in the direction parallel to the central axis of the ion channel increases from the center electrode group to the peripheral electrode groups.

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