RU2831990C1 - Multi-electrode harmonized kingdon trap with multi-port input of ions through slot - Google Patents

Abstract

FIELD: mass spectrometry.

SUBSTANCE: mass spectrometer based on a multi-electrode harmonized Kingdon trap is implemented with the possibility of multi-port input of electrons for ionization of gas molecules inside the trap and ions created in ion sources outside the trap, where each port can be used independently of each other, and consists of two external and four internal electrodes, which are arranged symmetrically, configured to excite periodic movement of ions in the trap along the axis of symmetry and detect a signal induced by ions oscillating in a quadratic potential inside the trap. To input ions from an external source into the trap, a slot is used, which is located between external electrodes of the trap in the central plane of the trap, and to obtain a signal, movement of ions is excited in the direction in which the potential has a quadratic dependence on the coordinate.

EFFECT: high efficiency of transporting and capturing ions generated in ion sources outside the trap and accumulated in a linear quadrupole trap into a Kingdon trap for measuring their masses.

8 cl, 4 dwg

Description

AREA OF TECHNOLOGY

The invention relates to the field of mass spectrometry, namely, it describes a mass spectrometer based on various ion sources, an ion-optical ion transport system, an accumulative linear quadrupole trap and a multi-electrode harmonized Kingdon trap, implemented with the possibility of introducing ions created in ion sources outside the trap. The present technical solution can find application in many areas of technology.

LEVEL OF TECHNOLOGY

Modern mass spectrometry is a sensitive, fast and informative method of atomic and molecular analysis of substances, which has the widest applications in many areas of science and technology. The use of mass spectrometry for the identification of molecules requires high resolution for the separation and identification of ions of similar masses and high accuracy of mass measurement. For a long time, such requirements were met by ion cyclotron resonance (ICR) mass spectrometry with Fourier transform, however, a significant disadvantage of this method is the need to use superconducting cryo-magnets with high (7 Tesla and higher) magnetic induction, which leads to high operating costs and a large size, as well as the weight of the device itself. Another type of mass spectrometer, approaching the resolution and accuracy of ICR-based instruments, are instruments using the Kingdon ion trap principle (hereinafter referred to as the Kingdon trap; Kingdon, K.H.: A method for the neutralization of electron space charge by positive ionization at very low gas pressures. Phys. Rev. 21, 408-418 (1923)). An example of such a mass spectrometer is the widespread orbital ion trap, in which ions with high kinetic energy (several kiloelectron volts) introduced into the ion trap are captured and held using electric fields, first proposed in the work of Knight (Knight, R.D.: Storage of ions from laser produced plasmas. Appl. Phys. Lett. 38, 221-223 (1981)) as a mass spectrometer. Later, Makarov created such a mass spectrometer, which he called Orbitrap (Eliuk, S., Makarov, A.: Evolution of Orbitrap mass spectrometry instrumentation. Annu. Rev. Anal. Chem. 8, 61-80 (2015)). In the Orbitrap orbital ion trap, an axisymmetric static electric field is created by specially shaped electrodes. Ions entering the field with a momentum sufficient for capture, introduced from the outside perpendicular to the trap axis at some distance from the trap center, after a pulsed change in the potential of the central electrode, causing a change in their momentum, begin to move along stable cyclic trajectories around the central electrode and simultaneously oscillate along the axis (z axis) of the central electrode in a quadratic potential created by the trap electrodes along the z axis. Along the z-axis, the ions perform harmonic oscillations with a frequency inversely proportional to the square root of the ion mass-to-charge ratio. Since the electric potential depends quadratically on the z-coordinate, this frequency is independent of the ion oscillation amplitude. The measured value is the potential difference induced by moving ions on the external electrodes. Due to the fact that the ion axial oscillation frequency does not depend on their energy and that the electric field is established with high accuracy and stability, high resolution can be achieved and the mass can be determined with high accuracy from the measured axial oscillation frequency. The orbital trap is also characterized by the ability to simultaneously capture and measure the masses of a relatively large number of ions. In the works of the group of Yu.K. Golikova (Golikov, Y.K., et al., Integrable electrostatic ion traps. Appl. Phys. (Russian). 5, 50-57 (2006)), (Nikitina, D.V.: Ion trap Mass spectrometry in a dynamic mass spectrometry. Thesis for PhD degree, St. Petersburg, (2006), [https://search.rsl.ru/ru/record/01003303052]) showed that the Kingdon-Knight trap can contain more than one internal electrode and still have a quadratic dependence of the electrostatic field in the direction coinciding with the direction of the internal electrodes. Close analogues of the proposed by us MULTI-ELECTRODE HARMONIZED KINGDON TRAP WITH MULTI-PORT INPUT OF ELECTRONS AND IONS are: the mass spectrometer disclosed in US Patent No. US 7989758 B2 (owned by BRUKER DALTONIK GMBH and published on 02.08.2011 IPC B01D59/44; H01J49/00), containing the so-called Cassini trap; as well as the mass spectrometer based on the multi-electrode harmonized Kingdon trap, disclosed in patent RU 2693570 C1 (AUTONOMOUS NON-COMMERCIAL EDUCATIONAL ORGANIZATION OF HIGHER EDUCATION "SKOLKOVO INSTITUTE OF SCIENCE AND TECHNOLOGY") and published. 07/03/2019, IPC H01J49/42.

The proposed technical solution is aimed at eliminating the shortcomings of the current level of technology and differs from previously known ones in that the proposed solution is designed with the possibility of introducing ions through a gap between the external electrodes of the trap, used to excite the axial movement of ions and detect the signal induced on them by ions participating in the axial movement.

ESSENCE OF THE INVENTION

The technical problem that the claimed solution is aimed at solving is the creation of a mass spectrometer based on a multi-electrode harmonized Kingdon trap, implemented with the ability to transport and capture ions created in ion sources outside the trap and, in particular, accumulated in an accumulative linear quadrupole trap thrown into the Kingdon trap to measure their masses.

The technical result consists in the fact that the proposed solution, namely the design of a pair of a linear quadrupole trap and a Kingdon trap, allows for more efficient transportation and capture of ions created in ion sources outside the trap and accumulated in an accumulative linear quadrupole trap into the Kingdon trap for measuring their masses than in similar devices (orbitrap).

The claimed technical result is achieved by implementing a mass spectrometer based on a multi-electrode harmonized Kingdon trap, implemented with the possibility of multi-port input of electrons for ionization of gas molecules inside the trap and ions created in ion sources outside the trap, where each port can be used independently of each other, and consisting of two external and four internal electrodes, which are arranged symmetrically, made with the possibility of exciting periodic movement of ions in the trap along the axis of symmetry and detecting a signal induced by ions oscillating in a quadratic potential inside the trap, wherein a slit is used to introduce ions from an external source into the trap, which is located between the external electrodes of the trap in the central plane of the trap, and to obtain a signal, ion movement is excited in the direction in which the potential has a quadratic dependence on the coordinate, namely along the internal electrodes of the trap by applying an alternating voltage to the external electrodes forming the slit, containing the oscillation frequency of the ions along this direction; or

to introduce ions from an external source into the trap, a slit is used, located in one of the external electrodes, which does not lie in the central plane of the trap, and the ions enter the field with a quadratic potential not at its center, where the potential is minimal, but in the region above the potential in the center and begin to perform harmonic oscillations in this quadratic potential;

wherein a potential is applied to the internal electrodes that creates an electric field outside these electrodes, the potential value of which is quadratically dependent on the coordinate directed along the internal electrodes of the trap, wherein the quadratic nature of the potential is ensured by the shape of the internal and external electrodes, wherein the geometry of the surfaces of the internal electrodes coincides with the geometry of the equipotential surfaces corresponding to a voltage of -0.5-4 kV on the internal electrodes, and the external electrode has the geometry of an equipotential surface passing at a maximum distance of approximately 20 mm to 90 mm from the center of the trap along the direction of the X-axis perpendicular to the axis of symmetry; wherein pulsed potentials of a time profile are applied to the internal electrodes for capturing ions formed inside the trap during ionization of the analyte gas molecules by electrons, and pulsed potentials of a time profile of a different shape for capturing ions formed in ion sources external to the trap;

In this case, the mass spectrometer can be equipped with several ion sources located outside the Kingdon trap, which are under a potential U sufficient to accelerate the ions and their penetration into the trap; moreover, a separate port can be used for each type of ion source if the ion sources are not combined.

In one embodiment, the ion sources are located in close proximity to the trap in a single vacuum chamber.

In one embodiment, at least one ion source is implemented using electron impact ionization outside the Kingdon ion trap and the ions are transported into the trap by an ion-optical system, wherein the ion source can be located in close proximity to the trap in one vacuum chamber.

In one embodiment, at least one ion source is implemented using field ionization and is transported into the trap by an ion-optical system, wherein the ion source is located in close proximity to the trap in one vacuum chamber.

In one embodiment, at least one ion source is implemented using field desorption and the ions are transported into the trap by an ion-optical system, wherein the ion source is located in close proximity to the trap in one vacuum chamber.

In one embodiment, at least one ion source is implemented by means of MALDI (matrix-assisted laser desorption/ionization) and the ions are transported into the trap by an ion-optical system, wherein the ion source is located in close proximity to the trap in one vacuum chamber.

In one embodiment, at least one ion source is implemented by means of an electrospray, and the ions are transported into the trap by an ion-optical system.

In one embodiment, at least one ion source is implemented using one of the atmospheric ionization methods and the ions are transported into the trap by an ion-optical system.

DESCRIPTION OF DRAWINGS

The implementation of the invention will be described further in accordance with the attached drawings, which are presented to explain the essence of the invention and in no way limit the scope of the invention. The following drawings are attached to the application:

Fig. 1 illustrates a diagram of a Kingdon multielectrode trap with 4 external ion sources located directly on the outer body of the ion trap.

Fig. 2 illustrates a Kingdon multielectrode trap with a slit input of ions from external ion sources with field desorption (in two projections) and with field ionization.

Fig. 3 illustrates a Kingdon multielectrode trap with a slit input of ions from the outer quadrupole through a system of intermediate pumped chambers.

Fig. 4 illustrates in 3D image format a Kingdon multielectrode trap with a slit input of ions from an external quadrupole.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the embodiment of the invention, numerous implementation details are set forth in order to provide a clear understanding of the present invention. However, it will be apparent to one skilled in the art how the present invention may be used with or without these implementation details. In other instances, well-known methods, procedures, and components have not been described in detail in order not to unnecessarily obscure the features of the present invention.

In addition, it will be clear from the above description that the invention is not limited to the embodiment shown. Numerous possible modifications, changes, variations and substitutions, preserving the essence and form of the present invention, will be obvious to those skilled in the art.

For a better understanding of the present invention, some terms used in the present specification are provided below. In the description of the present invention, the terms "includes" and "including" are interpreted to mean "includes, but are not limited to." These terms are not intended to be construed as "consists only of." Unless otherwise defined, technical and scientific terms in this application have the standard meanings generally accepted in the scientific and technical literature.

The multielectrode harmonized Kindon trap, like the orbitrep, is a pulse device for measuring ion masses. Before introducing ions into the multielectrode harmonized Kindon trap in the case of ionization at atmospheric pressure and intermediate vacuum (electrospray, MALDI and other methods), it is necessary to accumulate ions in a separate accumulation trap for analysis, and then pulse them into the measuring trap. For this purpose, radiofrequency ion traps can be used, such as a three-dimensional Paul trap or linear quadrupole traps. In the orbitrep, a so-called C-trap is used for this purpose, which is a curved quadrupole that allows focusing the ions ejected from it into a round hole connecting the vacuum chambers of the C-trap and the analytical trap, with further transport of ions into the analytical trap using a transport ion-optical system. Since ions can be introduced into the multi-electrode Kingdon trap through a slit, and not only through a round hole, there is no need to focus ions to a point using a Field trap or a curved quadrupole (C-trap), but it is possible to use a linear short quadrupole and focus the ion ensemble accelerated in it into the slit between the external electrodes of the Kingdon trap, which simplifies the design of the focusing system and the transport of ions from the storage trap to the analytical one (Figs. 3 and 4).

Modeling of the process of ion transport from the storage trap to the analytical trap shows that the capture efficiency is from 10 to 60%. As experiments show, the lifetime of ions in the trap after their formation and capture is more than 1000 milliseconds.

It is possible to introduce ions from the storage trap into the analytical trap not at the center, but as it is done in the orbitrep. To do this, it is necessary to make an additional slit in the external electrodes of the analytical trap. When introducing ions through a slit in the central plane of the analytical trap, to obtain a signal it is necessary to excite the movement of ions in the direction in which the potential has a quadratic dependence on the coordinate, namely along the internal electrodes of the trap. When introducing through a slit lying not in the central plane of the analytical trap, the ions enter the field with a quadratic potential not at its center, where the potential is minimal, but in the area of the potential above the potential in the center and begin to perform harmonic oscillations in this quadratic potential. In the case of introducing ions at the center, their movement in a quadratic potential must be excited either by applying an alternating voltage with a frequency coinciding with the resonant frequencies of the harmonic oscillations of ions in a quadratic field to the external electrodes of the trap or to the internal ones, for which the electrodes must be cut along the vertical plane of symmetry. The voltage amplitude is adjusted experimentally to obtain the maximum amplitude of the signal from the ions and the resolving power. For selective excitation of ions of certain masses, the SWIFT method can be used, as in FT ICR mass spectrometry, but with a different way of forming the excitation signal, since the ion oscillation frequency in the Kingdon trap is inversely proportional to the square root of the mass, and in FT ICR it is inversely proportional to the mass. In this method, a frequency spectrum is synthesized, the transformation of which gives a time signal of the required frequency and amplitude for excitation of ions in a certain mass range or ions of certain masses. The programmed SWIFT time signal is fed from the DAC through an amplifier to the excitation electrodes. With external input of ions into the Kingdon trap, any types of ion sources can be used, which allows ionization of gaseous, liquid and solid substances.

The Kingdon four-electrode symmetric harmonized trap has four planes between the individual internal electrodes in which ions and electrons can be introduced into the trap (Figs. 1 and 2). These planes are equivalent. Due to this fact, it is possible to use such a trap with several types of ion sources in one mass spectrometer. Among them there can be ion sources with ionization inside the trap such as: an electron impact source and a laser photoionization source. There can also be sources with ionization outside the trap such as: sources with field desorption and field ionization, MALDI source, electrospray sources, and any other sources with ionization at atmospheric pressure.

The present mass spectrometer is implemented on the basis of a multi-electrode harmonized Kingdon trap, and is made with the possibility of multi-port input of electrons for ionization of gas molecules inside the trap and ions created in ion sources outside the trap. In the present technical solution, each port can be used independently of each other. The invention contains two external and four internal electrodes, which are located symmetrically. The external electrodes are made with the possibility of excitation, and with their help the excitation of periodic motion of ions in the trap along the axis of symmetry and detection of the signal induced by ions oscillating in a quadratic potential inside the trap are carried out. A potential is applied to the internal electrodes, creating an electric field outside these electrodes, the potential value of which quadratically depends on the coordinate along the internal electrodes of the trap axis. The squareness of the potential is ensured by the shape of the internal and external electrodes. The geometry of the surfaces of the internal electrodes coincides with the geometry of the equipotential surfaces corresponding to a voltage of -4 kV (or close to this value) on the internal electrodes (this voltage determines the frequency of ion oscillations along the z axis and can vary within the range from -500 V to -10 kV in the case of positive ions and the same range of positive polarity voltage in the case of negative ions). The external electrode has the geometry of an equipotential surface passing at a distance of from approximately 20 mm to 90 mm from the center of the trap along the direction of the X axis perpendicular to the symmetry axis. Pulsed potentials of a special time profile are applied to the internal electrodes to capture ions formed inside the trap during ionization of the analyte gas molecules by electrons and pulsed potentials of a different time profile are applied to capture ions formed in ion sources external to the trap.

The mass spectrometer can be equipped with several ion sources located outside the Kingdon trap, which are under a positive potential U sufficient to accelerate the ions and their penetration into the trap. It should be noted that a separate port is used for each type of ion source unless the ion sources are combined (such as MALDI and electrospray sources when using an ion funnel).

Ions can be created by field ionization; field desorption; matrix-assisted laser desorption/ionization (MALDI); electrospray, and by one of the atmospheric ionization methods. Ion sources that do not require low vacuum can be located in the immediate vicinity of the trap in the same vacuum chamber.

Trap field and electrode shape. In the proposed technical solution, the internal electrodes are spaced along the cube faces and are arranged symmetrically. The internal electrodes are formed by equipotential surfaces corresponding to a voltage of approximately -4 kV, and the external electrode is formed by an equipotential surface extending at a distance of approximately 20 mm to 90 mm from the trap center along the X direction.

The dimensions of the trap electrodes are determined by the requirements for achieving the highest possible accuracy in their manufacture. The frequency of axial oscillations of the trap depends on the voltage on the internal electrodes. In this case, the area of the processed surface should not exceed 200 mm × 200 mm × 100 mm, i.e., not more than the volume of the working area of the most precise milling machines. The larger the size of the working area of the machine, the greater the influence of thermal expansion and the worse the manufacturing accuracy, all other things being equal. The proposed technical solution allows introducing ions into the trap in several directions.

Fig. 1 shows a diagram of a multielectrode Kingdon trap with 4 external ion sources located directly on the outer body of the ion trap, where a slit input of ions into the trap is provided. The left half of the figure illustrates the Kingdon trap in the X, Y projection (section Z=0), and the right half of the figure illustrates the Kingdon trap in the Y, Z projection (section x=0). Ion source #1 - field desorption ionization complete with gateway 1. Ion source #2 - field ionization. Ion source #3 - Matrix-assisted laser desorption/ionization (MALDI) complete with gateway 2. Ion source #4 - Thermal ionization complete with gateway 3.

Fig. 2 illustrates the diagram of the Kingdon multielectrode trap with 2 external ion sources located directly on the outer body of the ion trap, where a slit input of ions into the trap is provided. The first source is with field desorption, and the second with field ionization. The left half of the figure illustrates the Kingdon trap in the X, Y projection (section Z=0), and the right half of the figure illustrates the Kingdon trap in the Y, Z projection (section x=0) with a source with field desorption. Ion source No. 1 - field desorption ionization complete with gateway 1. Ion source No. 2 - field ionization.

Fig. 3 and 4 illustrate the scheme of the multielectrode Kingdon trap with a slit input of ions from the external quadrupole through a system of intermediate pumped chambers. The input of ions into the trap is carried out through a slit between the external electrodes, the system of intermediate chambers is connected to each other using a slit interface. In the figures, the left half illustrates the Kingdon trap in the X, Y projection (section Z=0), and the right half illustrates the Kingdon trap in the Y, Z projection (section x=0).

Although the invention has been described with reference to the disclosed embodiments, it will be apparent to those skilled in the art that the specific experiments described in detail are provided merely for the purpose of illustrating the present invention and should not be considered as limiting the scope of the invention in any way. It will be understood that various modifications can be made without departing from the spirit of the present invention.

Claims (11)

1. A mass spectrometer based on a multi-electrode harmonized Kingdon trap, implemented with the possibility of multi-port input of electrons for ionization of gas molecules inside the trap and ions created in ion sources outside the trap, where each port can be used independently of each other, and consisting of two external and four internal electrodes that are arranged symmetrically, configured to excite periodic motion of ions in the trap along the axis of symmetry and detect a signal induced by ions oscillating in a quadratic potential inside the trap, wherein a slit is used to introduce ions from an external source into the trap, which is located between the external electrodes of the trap in the central plane of the trap, and to obtain a signal, ion motion is excited in a direction in which the potential has a quadratic dependence on the coordinate, namely along the internal electrodes of the trap by applying an alternating voltage to the external electrodes forming the slit, containing the frequency of ion oscillations along this direction; or to introduce ions from an external source into the trap, a slit is used, located in one of the external electrodes, which does not lie in the central plane of the trap, and the ions enter the field with a quadratic potential not at its center, where the potential is minimal, but in the region above the potential in the center and begin to perform harmonic oscillations in this quadratic potential; wherein a potential is applied to the internal electrodes, creating an electric field outside these electrodes, the value of the potential of which depends quadratically on the coordinate directed along the internal electrodes of the trap, wherein the quadratic nature of the potential is ensured by the shape of the internal and external electrodes, wherein the geometry of the surfaces of the internal electrodes coincides with the geometry of the equipotential surfaces corresponding to a voltage of -0.5-4 kV on the internal electrodes, and the external electrode has the geometry of an equipotential surface passing at a maximum distance of approximately 20 mm to 90 mm from the center of the trap along the direction of the X axis, perpendicular to the axis of symmetry; In this case, the mass spectrometer can be equipped with several ion sources located outside the Kingdon trap, which are under a potential U sufficient to accelerate the ions and their penetration into the trap; moreover, a separate port can be used for each type of ion source, if the ion sources are not combined. 2. A mass spectrometer according to item 1, characterized in that the ion sources are located in close proximity to the trap in one vacuum chamber. 3. A mass spectrometer according to claim 1, characterized in that at least one ion source is implemented using electron impact ionization outside the Kingdon ion trap and the ions are transported into the trap by an ion-optical system, wherein the ion source is located in the immediate vicinity of the trap in one vacuum chamber. 4. A mass spectrometer according to claim 1, characterized in that at least one ion source is implemented using field ionization and is transported into the trap by an ion-optical system, wherein the ion source is located in close proximity to the trap in one vacuum chamber. 5. A mass spectrometer according to claim 1, characterized in that at least one ion source is implemented using field desorption and the ions are transported into the trap by an ion-optical system, wherein the ion source is located in close proximity to the trap in one vacuum chamber. 6. A mass spectrometer according to claim 1, characterized in that at least one ion source is realized by means of MALDI (matrix-assisted laser desorption/ionization) and the ions are transported into the trap by an ion-optical system, wherein the ion source is located in the immediate vicinity of the trap in one vacuum chamber. 7. A mass spectrometer according to claim 1, characterized in that at least one ion source is realized by means of an electrospray and the ions are transported into the trap by an ion-optical system. 8. A mass spectrometer according to claim 1, characterized in that at least one ion source is realized by means of an atmospheric ionization method and the ions are transported into the trap by an ion-optical system.