Multi-electrode harmonic Kingdon trap with electron and ion multi-port input

Abstract

The invention relates to the field of mass spectrometry, in particular to a mass spectrometer based on a multi-electrode harmonic Kingdon trap configured for electron and ion multi-port input, electrons are used for ionizing gas molecules in the trap, ions are ions generated in an ion source outside the trap, each port can be used autonomously and comprises two external electrodes and four internal electrodes, and each internal electrode is used for generating an ion source outside the trap. A detector configured to excite periodic motion of ions in the well along the axis of symmetry and to detect a signal caused by oscillation of the ions in a secondary potential within the well; wherein the mass spectrometer is provided with several electron sources outside the Kingdon trap, the electron sources being at a negative potential U sufficient to accelerate electrons and penetrate into the trap and configured to ionize analyte gas molecules within the trap with electrons having an energy value changing from U in the vicinity of the external electrode to zero at the electron turning point; wherein the mass spectrometer is equipped with a plurality of ion sources located outside the Kingdon trap, and if the ion sources are not merged, each type of ion source can use a separate port.

Description

Technical Field

[0001] The present invention relates to the field of mass spectrometry, and in particular, describes a mass spectrometer based on a multi-electrode harmonic Kingdon trap, the device being designed as a multi-port input for electrons and ions, the electrons being used to ionize gas molecules in the trap, and the ions being ions generated in an ion source outside the trap. The technical solution can be applied to a variety of technical fields. Background Art

[0002] Modern mass spectrometry is a sensitive, rapid, and informative method for atomic and molecular analysis of substances, and is widely used in many fields of science and technology. The identification of molecules using mass spectrometry requires high-resolution and high-precision mass measurements. For a long time, Fourier transform ion cyclotron resonance (ICR) mass spectrometry has met these requirements; however, a significant disadvantage of this method is the need to use superconducting cryogenic magnets with high (7 Tesla and above) magnetic induction, which leads to high operating costs and large size and weight of the equipment itself. Another mass spectrometer that is close to ICR-based instruments in terms of resolution and accuracy is an instrument using the Kingdon ion trap principle (hereafter referred to as Kingdon trap, Kingdon, KH: A method of neutralizing the space charge of electrons by positive ionization at extremely low gas pressure. Physical Review. 21, 408-418 (1923)). An example of such a mass spectrometer is the common orbital ion trap, in which ions with high kinetic energy (several thousand electron volts) are introduced into the ion trap and then captured and stored using an electric field, which was first proposed as a mass spectrometer in Knight's work (Knight, RD: Storage of ions in laser-generated plasmas. Appl. Phys. Letters. 38, 221-223 (1981)). Subsequently, Makarov created such a mass spectrometer and named it the Orbitrap (Eliuk, S., Makarov, A.: The evolution of the orbital trap mass spectrometer. Annals of Analytical Chemistry. 8, 61-80 (2015)). In the orbital ion trap of the orbital trap, electrodes of special shapes generate an axially symmetric electrostatic field. Ions with sufficient angular momentum introduced from the outside perpendicular to the trap axis and at a certain distance from the center of the trap enter the field for capture. After the potential of the central electrode changes by a pulse, the angular momentum of these ions changes, and they begin to move along a stable circular trajectory around the central electrode, while oscillating along the axis of the central electrode (z-axis) in the secondary potential generated by the trap electrode along the z-axis. The ions oscillate harmonic along the z-axis, and their frequency is inversely proportional to the square root of the mass-to-charge ratio of the ions. Considering that the potential is quadratically related to the z-coordinate, this frequency is independent of the ion oscillation amplitude. The measured quantity is the difference between the potentials caused by the moving ions on the external electrodes. Since the axial oscillation frequency of the ions does not depend on their energy, and the electric field is set with high precision and good stability, high resolution is achieved, and the mass can be measured with high precision by measuring the axial oscillation frequency. Another feature of the orbital trap is that it can capture and measure the mass of a relatively large number of ions at the same time. The work of Yu.K.Golikov's team showed that the Kingdon-Knight trap can contain multiple internal electrodes while having a quadratic dependence of the electrostatic field consistent with the direction of the internal electrodes.Similar patents for our proposed multi-electrode harmonic Kingdon trap with multi-port input for electrons and ions are as follows: a mass spectrometer disclosed in U.S. Patent US 7989758B2 (owned by Bruker Daltonik GMBH, issued on August 2, 2011, IPC B01D59 / 44; H01J49 / 00), which contains a so-called Cassini trap; and a mass spectrometer based on a multi-electrode harmonic Kingdon trap disclosed in patent RU 2693570C1 (autonomous non-profit higher education organization "Skolkovo Institute of Science and Technology", issued on July 3, 2019, IPC H01J 49 / 42).

[0003] The proposed technical solution aims to remedy the shortcomings of the current state of the art and differs from the prior art in that the proposed solution is configured as a multi-port input for electrons and ions. Summary of the invention

[0004] The technical problem addressed by the claimed solution is to create a mass spectrometer based on a multi-electrode harmonic Kingdon trap configured with multi-port inputs for electrons and ions, the electrons being used to ionize gas molecules within the trap and the ions being generated in an ion source outside the trap.

[0005] A technical result is that the trap design allows the use of two independent electron sources, which increases the reliability of the device and extends the operating time without replacing the cathode. Another technical result is that ions can be introduced into the trap from multiple directions.

[0006] The claimed technical result is obtained by implementing a mass spectrometer based on a multi-electrode harmonic Kingdon trap, the device being configured with multi-port inputs for electrons and ions, the electrons being used to ionize gas molecules in the trap, the ions being ions generated in an ion source outside the trap, wherein each port can be used autonomously, and comprising two outer electrodes and four inner electrodes, which are symmetrically placed, configured to excite the periodic motion of the ions in the trap along the axis of symmetry, and to detect signals caused by the oscillation of the ions in the quadratic potential in the trap, wherein a potential is applied to the inner electrodes, and an electric field is generated outside these electrodes, the potential value of which is quadratic with respect to the coordinates of the inner electrodes along the axis of the trap; wherein the geometry of the inner electrode surface is consistent with the geometry of the equipotential surface on the inner electrode corresponding to a voltage of -4 kV, and the outer electrode has the geometry of the equipotential surface at a distance of 20-90 mm from the center of the trap along the X-axis direction perpendicular to the axis of symmetry; wherein a pulsed potential of a special time distribution is provided to the inner electrode for capturing ions formed in the trap during ionization of analyte gas molecules with electrons, and a pulsed potential of another shape is used for capturing ions formed in the ion source outside the trap;

[0007] The mass spectrometer is provided with a plurality of electron sources outside the Kingdon trap, which are at a negative potential U sufficient to accelerate the electrons and penetrate the trap, and are configured to ionize the analyte gas molecules in the trap with electrons whose energy value changes from U in the area near the external electrode to zero at the electron turning point, wherein the negative potential of the trap field generated by the internal electrode is consistent with the potential applied to the electron source; wherein the mass spectrometer is equipped with a plurality of ion sources outside the Kingdon trap, and if the ion sources are not merged, a separate port can be used for each type of ion source. .

[0008] In one embodiment, an electron source may be implemented using automated electron emission.

[0009] In one embodiment, an ion source is implemented outside a Kingdon ion trap using electron impact ionization, and the ions are transported into the trap via ion optics.

[0010] In one embodiment, an ion source is implemented using field ionization and transported into the trap via an ion optical system.

[0011] In one embodiment, an ion source is implemented using field desorption, and the ions are transported into the trap by an ion optical system.

[0012] In one embodiment, an ion source is implemented by MALDI (Matrix Assisted Laser Desorption / Ionization), and ions are transported into the trap by ion optics.

[0013] In one embodiment, an ion source is achieved by electrospray, and ions are transported into the trap by ion optics.

[0014] In one embodiment, at least one ion source is achieved by an atmospheric ionization method, and the ions are transported to the trap by an ion optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following is a description of the embodiments of the present invention based on the accompanying drawings, which are used to explain the essence of the present invention and in no way limit the scope of the present invention. The accompanying drawings of this application are as follows:

[0016] Figure 1 The ion trapping efficiency in the z=0.75 plane or the photoionization efficiency of different regions in the trap is shown.

[0017] Figure 2 A simulation of the ion motion after ionization at z=0 is shown.

[0018] Figure 3Shows the ion trajectories generated in the regions of -0.1 mm < x < 0.1 mm, 77 mm < y < 90 mm and -0.1 mm < y < 0.1 mm, 77 mm < x < 90 mm.

[0019] Figure 4 Shows the oscillation of ions along the z-axis after excitation or injection when z ≠ 0 (exciting SWIFT 600 - 60 kHz 20 V, 13 ms). Detailed implementation

[0020] The following detailed disclosure of embodiments of the present invention provides many details of the embodiments to ensure a clear understanding of the present invention. However, for those skilled in the art, it is obvious how to use the present invention whether or not these details of its embodiments are available. In other cases, well-known methods, procedures, and components are not described in detail to avoid complicating the features for understanding the present invention.

[0021] Furthermore, the above statements will clearly show that the present invention is not limited to the proposed embodiments. For those skilled in the art, many potential modifications, changes, variations, and substitutions that retain the essence and form of the present invention will be obvious.

[0022] To better understand the present invention, the following are some terms used in the description of the present invention. In the description of the present invention, the terms "comprising" and "including" are construed as "including but not limited to". These terms should not be construed as "consisting only of". Unless otherwise defined, the technical and scientific terms in this application have the standard meanings commonly accepted in scientific and technical literature.

[0023] In a harmonic Kingdon trap, there are several ways to create ions for mass spectrometry. Gaseous substances can be ionized outside the trap, for example, in a standard NIRA ion source. When the ions pass through the trap, they are introduced into the trap from the ion source by capturing them in the field, just as done in an orbitrap. The advantage of this method is that a standard ionization energy of 70 volts can be used, so that an electron bombardment mass spectrometry database can be used to identify molecules and a magnetic field can be used to calibrate the ionization electrons. The disadvantage of this method is that an ion accumulation device is required before releasing the ions into the trap, otherwise the efficiency of selecting ions for mass spectrometry will be very low.

[0024] Another ionization method is ionization inside the trap. This can be achieved in two ways: grounding all the electrodes of the trap, which allows recording the electron energy; and applying a potential to the electrodes. In the first case, the duty cycle is small enough to be negligible, because the ions in the trap can be trapped only at the ionization moment (microseconds), in the second case, the ionization energy will have a large dispersion, because it depends on the birthplace of the ion, which is located on the path of the ionized electron. The electron trajectory does not coincide with the electric field lines inside the trap; the energy of the electrons diffused during ionization is as high as 400 electron volts (the electron energy in the trap ranges from 0-400eV). The mass spectrum produced by this ionization is usually inconsistent with the mass spectrum obtained with standard ionization energy and needs to be corrected. The ions formed by this ionization method will be trapped by the trap. Simulations of the ionization process show that the capture efficiency is in the range of 10%-60%. Experiments have shown that the lifetime of ions after formation and capture in the trap exceeds 1000 milliseconds.

[0025] In order to receive the signal, it is necessary to excite the ions in the direction of the quadratic power of one of the coordinates of the potential, in particular along the inner electrodes of the trap. In the case of the introduction of ions from a storage device, this can be achieved by introducing ions that are not in the center of the trap, as in an orbital trap. This causes the ions to enter a field of a quadratic potential, not in the center where the potential is minimum, but in a region of potential above the central potential, and to begin to oscillate harmonically in this quadratic potential. When the ions are introduced into the center, their motion in the quadratic potential must be excited by applying an alternating voltage with a frequency that coincides with the resonant frequency of the harmonic oscillations of the ions in the quadratic field to the outer or inner electrodes of the trap, for which the electrodes must be cut along the vertical symmetry plane. The voltage amplitude is experimentally adjusted to obtain the maximum ion signal amplitude and resolution. In order to selectively excite ions of a specific mass, the SWIFT method can be used, as in FT ICR mass spectrometry. This method involves the synthesis of a spectrum whose transformation produces a time signal of the desired frequency and amplitude to excite ions in a specific mass range or ions of a specific mass. The programmed SWIFT time signal is supplied from the DAC through an amplifier to the excitation electrode. For external input of ions into the Kingdon trap, any type of ion source can be used, which allows ionization of gaseous, liquid and solid substances. In the case of gas analysis, ions can be generated directly in the Kingdon trap using electron impact ionization and photoionization.

[0026] The four-electrode symmetric harmonic Kingdon trap has four extended planes between the single inner electrodes, in which ions and electrons can be introduced into the trap. These planes are equivalent. Therefore, this trap can be used with multiple types of ion sources in a mass spectrometer. These may include ion sources that ionize inside the trap, such as: electron bombardment ion sources and laser photoionization ion sources, field desorption and field ionization ion sources; there may also be ion sources of electrons outside the trap, such as MALDI sources, electrospray sources and any other ion sources that produce ionization at atmospheric pressure.

[0027] The mass spectrometer is implemented based on a multi-electrode harmonic Kingdon trap and is configured as an electron and ion multi-port input, where the electrons are used to ionize the gas molecules in the trap, and the ions are ions generated in an ion source outside the trap. In this technical solution, each port can be used independently. The present invention comprises two symmetrically placed external electrodes and four internal electrodes. The external electrodes are configured for excitation, for exciting the periodic motion of ions in the trap along the axis of symmetry, and for detecting signals caused by ions in the trap that oscillate at a secondary potential. A potential is applied to the internal electrodes, and an electric field is generated outside these electrodes, whose potential is quadratic to the coordinates of the internal electrodes of the trap axis. The quadratic nature of the potential is provided by the shape of the internal and external electrodes. The geometry of the surface of the internal electrode is consistent with the geometry of the equipotential surface corresponding to the -4kV voltage on the internal electrode (this voltage determines the oscillation frequency of the ions along the z-axis, which can vary between -500V and -10kV in the case of positive ions, and can vary within the same voltage range of positive polarity in the case of negative ions). The external electrode has an equipotential surface geometry about 20mm-90mm from the center of the trap along the X-axis direction perpendicular to the axis of symmetry. A pulsed potential of a particular time profile is applied to the inner electrode to capture ions formed within the trap during ionization of analyte gas molecules with electrons, and a pulsed potential of a different shape is applied to capture ions formed in an ion source outside the trap.

[0028] The mass spectrometer can be equipped with several electron sources outside the Kingdon trap, which are at a negative potential U, sufficient to accelerate and penetrate the electrons into the trap, and are configured to ionize the analyte gas molecules in the trap with electrons whose energy value changes from U in the area near the external electrode to zero at the electron turning point, wherein the negative potential of the trap field generated by the internal electrode is consistent with the potential applied to the electron source. The mass spectrometer can be equipped with several ion sources outside the Kingdon trap. It should be noted that if the ion sources are not combined (e.g., MALDI and an electrospray source using an ion funnel), each type of ion source uses a separate port.

[0029] Ionizing electrons in the electron source can be produced by field emission; ions can be produced by field ionization methods; field desorption; matrix-assisted laser desorption / ionization (MALDI); electrospray and by an atmospheric ionization method.

[0030] Well field and electrode shape.

[0031] In the proposed solution, the inner electrodes are spaced apart along the surface of the cube and are placed symmetrically. The inner electrodes are formed by equipotential surfaces corresponding to a voltage of -4 kV, and the outer electrodes are formed by equipotential surfaces extending from about 20 mm to 90 mm from the center of the well in the X direction.

[0032] The dimensions of the trap electrodes are defined by the need to achieve the highest possible precision during the manufacturing process. The axial oscillation frequency of the trap depends on the voltage on the internal electrode. The processed surface area should not exceed 200 mm x 200 mm x 200 mm, i.e. the working volume of the most precise milling machine. Other conditions being equal, the larger the size of the machine's working area, the greater the influence of thermal expansion and the lower the manufacturing precision.

[0033] The proposed technical solution allows the introduction of ions into the trap from multiple directions. In the case of electron bombardment ionization inside the trap, the trap design allows the use of two independent electron sources, which increases the reliability of the device and prolongs the working time without replacing the cathode.

[0034] Figure 1 The ion capture efficiency in the z=0.75 plane or the photoionization efficiency of different regions of the trap is shown, where 1, 2 and 3 are photo-offline.

[0035] Although the present invention has been described with reference to the disclosed embodiments, it will be appreciated by those skilled in the art that the specific experiments described in detail are only for illustrative purposes and should not be interpreted as limiting the scope of the present invention in any way. It should be understood that various modifications can be made without departing from the essence of the present invention.

Claims

1. A mass spectrometer based on a multi-electrode harmonic Kingdon trap, configured for multi-port input of electrons and ions, the electrons being used to ionize gas molecules in the trap, the ions being ions generated in an ion source outside the trap, wherein each port can be used autonomously, and comprising two external electrodes and four internal electrodes, which are symmetrically placed and configured to excite the periodic motion of the ions in the trap along an axis of symmetry and to detect signals caused by oscillations of the ions in a quadratic potential in the trap, wherein a potential is applied to the internal electrodes to generate an electric field outside these electrodes, the potential value of which is quadratic with respect to the coordinates of the internal electrodes along the trap axis; wherein, The geometry of the inner electrode surface is consistent with the geometry of the equipotential surface on the inner electrode corresponding to a voltage of -4 kV, and the outer electrode has the geometry of the equipotential surface at a distance of 20-90 mm from the center of the well along the X-axis direction perpendicular to the symmetry axis; wherein the mass spectrometer is provided with a number of electron sources outside the Kingdon trap, the electron sources being at a negative potential U sufficient to accelerate the electrons and penetrate into the trap, and being configured to ionize analyte gas molecules in the trap with electrons having energy values ​​varying from U in the region near the outer electrode to zero at the electron turning point, wherein the negative potential of the trap field generated by the inner electrode coincides with the potential applied to the electron source; Ionization occurs outside the trap, and ions enter the trap in sequence through one of four ports.

2. The mass spectrometer according to claim 1, characterized in that At least one electron source is achieved by field ionization.

3. The mass spectrometer according to claim 1, characterized in that At least one electron source is realized by field desorption.

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