EP4248485A2

EP4248485A2 - Removable ion source capable of axial or cross beam ionization

Info

Publication number: EP4248485A2
Application number: EP21827311.8A
Authority: EP
Inventors: Edward B. Mccauley; Dustin D. HOLDEN
Original assignee: Thermo Finnigan LLC
Current assignee: Thermo Finnigan LLC
Priority date: 2020-11-19
Filing date: 2021-11-19
Publication date: 2023-09-27
Also published as: WO2022109252A3; CN116529848A; WO2022109252A2

Abstract

An ion source including an ionization assembly, first and second electron sources, and a magnet assembly. The ionization assembly includes an ionization chamber and at least one ion lens. The ionization assembly has a primary axis defined by the direction of an ion beam exiting the ionization assembly and the ionization chamber and the at least one ion lens are arranged along the primary axis. The first electron source is aligned along the primary axis of the ionization assembly and is configured to provide an electron beam parallel to the primary axis. The second electron source is adjacent to the ionization assembly and is configured to provide an electron beam orthogonal to the primary axis. The magnet assembly includes a magnet. The magnet assembly is movable between a first position in which the magnet is aligned with the first electron source and a second position in which the magnet is aligned with the second electron source.

Description

REMOVABLE ION SOURCE CAPABLE OF AXIAL OR CROSS BEAM IONIZATION

FIELD

[0001] The present disclosure generally relates to the field of mass spectrometry including a removable ion source capable of axial or cross beam ionization.

INTRODUCTION

[0002] Mass spectrometry can be used to perform detailed analyses on samples. Furthermore, mass spectrometry can provide both qualitative (is compound X present in the sample) and quantitative (how much of compound X is present in the sample) data for a large number of compounds in a sample. These capabilities have been used for a wide variety of analyses, such as to test for drug use, determine pesticide residues in food, monitor water quality, and the like.

[0003] There are several different techniques that can be used to ionize a sample, with some techniques working better for some compounds and other techniques working better for other compounds. For example, electron impact ionization (El) involves impacting the sample with electrons to produce ions. In another example, chemical ionization (CI) involves the ionization of a reagent gas by electron impact, and the ionized reagent gas reacts with the sample to ionize the sample. CI can be useful for identification of molecular weight when El results in excessive fragmentation.

[0004] Mass spectrometers with the ability to perform multiple ionization techniques can be used to analyze a wider variety of compounds. From the foregoing it will be appreciated that a need exists for improved ion sources.

SUMMARY

[0005] An ion source can include an ionization assembly, first and second electron sources, and a magnet assembly. The ionization assembly can include an ionization chamber and at least one ion lens. The ionization assembly can have a primary axis defined by the direction of an ion beam exiting the ionization assembly and the ionization chamber and the at least one ion lens can be arranged along the primary axis. The first electron source can be aligned along the primary axis of the ionization assembly and can be configured to provide an electron beam parallel to the primary axis. The second electron source can be adjacent to the ionization assembly and can be configured to provide an electron beam orthogonal to the primary axis. The magnet assembly can include a first magnet and a second magnet. The magnet assembly can be movable between a first position in which the first magnet is aligned with the first electron source and a second position in which the second magnet is aligned with the second electron source.

DRAWINGS

[0006] For a more complete understanding of the principles disclosed herein, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0007] Figure 1 is a block diagram of an exemplary mass spectrometry system, in accordance with various embodiments.

[0008] Figure 2 is a diagram of an ion source, in accordance with various embodiments.

[0009] Figures 3A and 3B illustrate the operation of an exemplary magnet assembly in conjunction with the ion source, in accordance with various embodiments.

[0010] Figures 4A and 4B illustrate the operation of another exemplary magnet assembly in conjunction with the ion source, in accordance with various embodiments.

[0011] Figures 5 illustrates an exemplary method of switching between modes of an ion source, in accordance with various embodiments.

[0012] Figures 6 illustrates an exemplary method of removing the ion source, in accordance with various embodiments.

[0013] It is to be understood that the figures are not necessarily drawn to scale, nor are the objects in the figures necessarily drawn to scale in relationship to one another. The figures are depictions that are intended to bring clarity and understanding to various embodiments of apparatuses, systems, and methods disclosed herein. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Moreover, it should be appreciated that the drawings are not intended to limit the scope of the present teachings in any way.

DESCRIPTION OF VARIOUS EMBODIMENTS

[0014] Embodiments of removable ion sources capable of axial or cross beam ionization are described herein.

[0015] The section headings used herein are for organizational purposes only and are not to be construed as limiting the described subject matter in any way.

[0016] In this detailed description of the various embodiments, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the embodiments disclosed. One skilled in the art will appreciate, however, that these various embodiments may be practiced with or without these specific details. In other instances, structures and devices are shown in block diagram form. Furthermore, one skilled in the art can readily appreciate that the specific sequences in which methods are presented and performed are illustrative and it is contemplated that the sequences can be varied and still remain within the spirit and scope of the various embodiments disclosed herein.

[0017] All literature and similar materials cited in this application, including but not limited to, patents, patent applications, articles, books, treatises, and internet web pages are expressly incorporated by reference in their entirety for any purpose. Unless described otherwise, all technical and scientific terms used herein have a meaning as is commonly understood by one of ordinary skill in the art to which the various embodiments described herein belongs.

[0018] It will be appreciated that there is an implied “about” prior to the temperatures, concentrations, times, pressures, flow rates, cross-sectional areas, etc. discussed in the present teachings, such that slight and insubstantial deviations are within the scope of the present teachings. In this application, the use of the singular includes the plural unless specifically stated otherwise. Also, the use of “comprise”, “comprises”, “comprising”, “contain”, “contains”, “containing”, “include”, “includes”, and “including” are not intended to be limiting. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings.

[0019] As used herein, "a" or "an" also may refer to "at least one" or "one or more." Also, the use of “or” is inclusive, such that the phrase “A or B” is true when “A” is true, “B” is true, or both “A” and “B” are true. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0020] A “system” sets forth a set of components, real or abstract, comprising a whole where each component interacts with or is related to at least one other component within the whole.

MASS SPECTROMETRY PLATFORMS

[0021] Various embodiments of mass spectrometry platform 100 can include components as displayed in the block diagram of Figure 1. In various embodiments, elements of Figure 1 can be incorporated into mass spectrometry platform 100. According to various embodiments, mass spectrometer 100 can include an ion source 102, , a mass analyzer 106, an ion detector 108, and a controller 110.

[0022] In various embodiments, the ion source 102 generates a plurality of ions from a sample. The ion source can include, but is not limited to, an electron ionization (El) source, a chemical ionization (CI) source, and the like.

[0023] In various embodiments, the mass analyzer 106 can separate ions based on a mass-to-charge ratio of the ions. For example, the mass analyzer 106 can include a quadrupole mass filter analyzer, a quadrupole ion trap analyzer, a time-of- flight (TOF) analyzer, an electrostatic trap (e.g., Orbitrap) mass analyzer, Fourier transform ion cyclotron resonance (FT-ICR) mass analyzer, and the like. In various embodiments, the mass analyzer 106 can also be configured to fragment the ions using collision induced dissociation (CID) electron transfer dissociation (ETD), electron capture dissociation (ECD), photo induced dissociation (PID), surface induced dissociation (SID), and the like, and further separate the fragmented ions based on the mass-to-charge ratio. In various embodiments, the mass analyzer 106 can be a hybrid system incorporating one or more mass analyzers and mass separators coupled by various combinations of ion optics and storage devices. For example, a hybrid system can a linear ion trap (LIT), a high energy collision dissociation device (HCD), an ion transport system, and a TOF.

[0024] In various embodiments, the ion detector 108 can detect ions. For example, the ion detector 108 can include an electron multiplier, a Faraday cup, and the like. Ions leaving the mass analyzer can be detected by the ion detector. In various embodiments, the ion detector can be quantitative, such that an accurate count of the ions can be determined. In various embodiments, such as with an electrostatic trap mass analyzer, the mass analyzer detects the ions, combining the properties of both the mass analyzer 106 and the ion detector 108 into one device.

[0025] In various embodiments, the controller 110 can communicate with the ion source 102, the mass analyzer 106, and the ion detector 108. For example, the controller 110 can configure the ion source 102 or enable/disable the ion source 102. Additionally, the controller 110 can configure the mass analyzer 106 to select a particular mass range to detect. Further, the controller 110 can adjust the sensitivity of the ion detector 108, such as by adjusting the gain. Additionally, the controller 110 can adjust the polarity of the ion detector 108 based on the polarity of the ions being detected. For example, the ion detector 108 can be configured to detect positive ions or be configured to detected negative ions.

ION SOURCE

[0026] Ion sources which utilize an on-axis electron beam (on axis with the ion beam) can present problems when utilized for Chemical Ionization. For Negative Chemical Ionization (NCI), problems with electron charging near the ion exit aperture can result in rapid loss of sensitivity due to repelling of analyte ions back into the ion volume. The exit aperture can be larger for NCI in order to mitigate charging, but then the electron beam passes far into the Q0 ion guide resulting in extended down time for cleaning the Q0 ion guide. Positive Chemical Ionization (PCI) is less problematic as charging near the exit aperture attracts analyte ions, but spectra contain Electron Ionization (El) fragments due to interaction of the electron beam with lower pressure neutrals outside of the ion volume. Switching to a Nier-type cross-beam CI source can require changing hardware to include a magnet yoke. This can require venting of the instrument and subsequent down time. Consequently, for PCI or NCI it is desirable to keep the electron beam confined in the higher-pressure ion volume.

[0027] Figures 2 is a diagram illustrating an ion source 200 capable of both axial mode operation and cross-beam (Nier) type operation, which can be used as ion source 102 of mass spectrometry platform 100. Ion source 200 can include a first electron source 202, a second electron source 204 an electron lens 206, an ionization chamber 208, lens elements 210, 212, and 214, and RF ion guide 216. Ion source 200 can include an axis 230 along which ions are directed out of the ionization chamber to other components of the mass spectrometer.

[0028] Electron source 202 can include a thermionic filament 218 and electron source 204 can include a thermionic filament 220 for the generation of electrons. In various embodiments, electron sources 202 and 204 can include additional thermionic filaments for redundancy or increased electron production. In alternate embodiments, electron sources 202 and 204 can include a field emitter. The electrons from electron source 202 can travel along axis 230 into ionization chamber 208 of ion source 200 to ionize gas molecules. Electron lens 206 can serve to prevent the ions from traveling back towards the electron source. The electrons from electron source 204 can travel orthogonally to the axis of the ion source 200 into the ionization chamber 208 to ionize gas molecules.

[0029] Ionization chamber 206 can include gas inlet 222 for directing a gas sample into an ionization volume 224 defined by the ionization chamber 208. In a first mode, gas molecules within the ionization volume 224 can be ionized by the electrons from the thermionic filament 218. Lenses 208 and 210 can define a post ionization volume 226. Post ionization volume 226 can be a region where ions can be formed which has a lower pressure for the sample. Post ionization volume 226 can include regions of the lenses where electrons are present. In various embodiments, it may also include areas outside of the ionization volume and the lenses. Wall 228 can restrict the flow of gas from ionization volume 224 to the post ionization volume 226, creating a substantial pressure difference between the ionization volume 224 and post ionization volume 226. While ionization can occur in post ionization volume 226, significantly more ions can be generated in ionization volume 224 due to the lower sample density in the post ionization volume 226. [0030] In a second cross-beam (Nier) mode, gas molecules within the ionization volume 224 can be ionized by the electrons from the thermionic filament 220. The electrons are directed along electron source axis 232 which is orthogonal to the ion source axis 230. As the electrons are directed orthogonally into the ionization volume 232, the electrons are substantially contained within the ionization volume 224 and do not ionize gas molecules in the post ionization volume 226.

[0031] Lens 212 and 214 and RF ion guide 216 can assist in the movement of ions along axis 230 from the ionization volume 224 to additional ion optical elements which direct the ions to mass analyzer 106 of mass spectrometry platform 100.

[0032] A single rotatable magnet assembly can house differing magnets optimized for El or CI operation. The position of the magnet can be altered mechanically or a magnet external to the vacuum chamber can cause the magnet to rotate in the opposite position if the assembly is well balanced. This allows crossbeam ionization for PCI and NCI, while also allowing axial mode operation for high sensitivity El. The ability to change the electron beam orientation without the need to vent can significantly reduce down time.

[0033] Figures 3A and 3B illustrate a magnet assembly 302 for use with electron ionization ion source 200 capable of both axial mode operation and crossbeam (Nier) type operation. The magnet assembly includes a first magnet 304 and a second magnet 306. Additionally, magnet assembly is mounted on hinge pin 308 so the magnet assembly can rotate on hinge pin 308 between a first position illustrated in Figure 3 A and a second position illustrated in Figure 3B.

[0034] In the first position in Figure 3 A, the first magnet 304 is adjacent to electron source 202 and the ion source can be operated in axial mode, such as for El. The electrons travel from thermionic filament 218 of source 202 along the axis 230 into ionization volume 224 of ion source 200. Magnetic fields from magnet 304 can provide magnetic containment reducing the spread of the electrons as they travel along the axis 230 into ionization volume 224.

[0035] In the second position in Figure 3B, the second magnet 306 is adjacent to the electron source 204 and the ion source can be operated cross-beam (Nier) mode, such as for PCI and NCI. The electrons travel from thermionic filament 220 of source 204 along the electron source axis 232 into ionization volume 224 of ion source 200. Magnetic fields from magnet 306 can provide magnetic containment reducing the spread of the electrons as they travel along the axis 230 into ionization volume 224. Additionally, the rotation of magnet assembly 302 into the second position can allow passage of ion source assembly 200 via a vacuum insertion/removal tool (IR Tool) without venting.

[0036] Figures 4A and 4B illustrate a single magnet assembly 402 which can rotate about 270 degrees around pivot point 408. The position of the magnet can be altered mechanically. This allows cross-beam ionization for PCI and NCI, while also allowing axial mode operation for high sensitivity El. The ability to change the electron beam orientation without the need to vent can significantly reduce down time.

[0037] Figures 4A and 4B illustrate a magnet assembly 402 for use with electron ionization ion source 200 capable of both axial mode operation and crossbeam (Nier) type operation. The magnet assembly includes a first magnet 404 and a second magnet 406. Additionally, magnet assembly is mounted on pivot point 408 so the magnet assembly can rotate 270 degrees between a first position illustrated in Figure 4 A and a second position illustrated in Figure 4B. As magnets 404 and 406 are adjacent to one another, magnets 404 and 406 can be oriented to reinforce one another and create a stronger magnetic field. Thus, the use of smaller magnets or even a single magnet are possible.

[0038] In the first position in Figure 4A, magnets 404 and 406 are aligned with electron source 202 and the ion source can be operated in axial mode, such as for El. The electrons travel from thermionic filament 218 of source 202 along the axis 230 into ionization volume 224 of ion source 200. Magnetic fields from magnets 404 and 406 can provide magnetic containment reducing the spread of the electrons as they travel along the axis 230 into ionization volume 224.

[0039] In the second position in Figure 4B, magnets 404 and 406 are aligned with the electron source 204 and the ion source can be operated cross-beam (Nier) mode, such as for PCI and NCI. The electrons travel from thermionic filament 220 of source 204 along the electron source axis 232 into ionization volume 224 of ion source 200. Magnetic fields from magnets 404 and 406 can provide magnetic containment reducing the spread of the electrons as they travel along the axis 230 into ionization volume 224. Additionally, the rotation of magnet assembly 402 into the second position can allow passage of ion source assembly 200 via a vacuum insertion/removal tool (IR Tool) without venting.

[0040] In various embodiments, the magnet assembly 402 can be moved by a mechanical linkage or an electric motor. In some embodiments, an external magnet can apply a force to magnets 404 and 406 to cause the rotation of the magnet assembly. In various embodiments, a counterweight can be used to balance the weight of the magnet to reduce the force needed to rotate the magnet assembly 402 around pivot point 408.

[0041] In various embodiments, it can be preferable for the magnets to avoid direct contact with high temperature source parts. The magnet assembly can be attached to a rotatable shaft made of heat conductive aluminum in contact with cooler portions of the vacuum chamber. The magnet may further comprise temperature compensated Samarium Cobalt magnets which have a low change in B as a function of temperature.

[0042] In various embodiments, the ion source can be used with direct insertion probes (DIP) and direct exposure probes (DEP) when the magnet assembly is in the second position and aligned for cross-beam (Nier) mode.

[0043] Figure 5 illustrates a method of switching modes of an ion source. At 502, the first electron source can be energized with a magnet assembly in a first position. The first position of the magnet assembly can align a magnet with the first electron source. The first electron source can produce electrons that cause the ionization a sample, as indicated at 504. Ionizing the sample can include direct ionization by the electrons, such as El, or indirect ionization where a reagent is ionized and reacts with the sample, such as CI. The ionized sample can be analyzed by mass spectrometry to identify and quantify compounds in the sample.

[0044] At 506, the first electron source can be turned off, and, at 508, the magnet assembly can be rotated to a second position. The second position of the magnet assembly can align a magnet with a second electron source. At 510, the second electron source can be energized, and, at 512, the electrons produced by the second electron source can cause the ionization of a sample. Ionizing the sample can include direct ionization by the electrons, such as El, or indirect ionization where a reagent is ionized and reacts with the sample, such as CI. The ionized sample can be analyzed by mass spectrometry to identify and quantify compounds in the sample.

[0045] At 514, the second electron source can be turned off, and at 516, the magnet assembly can be rotated back to the first position. Once in the first position, the method can return to 502 to use the first electron source.

[0046] Figure 6 illustrates a method of removing of an ion source. At 602, the first electron source can be energized with a magnet assembly in a first position. The first position of the magnet assembly can align a magnet with the first electron source. The first electron source can produce electrons that cause the ionization a sample, as indicated at 604. Ionizing the sample can include direct ionization by the electrons, such as El, or indirect ionization where a reagent is ionized and reacts with the sample, such as CI. The ionized sample can be analyzed by mass spectrometry to identify and quantify compounds in the sample.

[0047] At 606, the first electron source can be turned off, and, at 608, the magnet assembly can be rotated to a second position. In the second position of the magnet assembly, the magnet assembly may not block removal of the ion source. At 610, the first electron source and/or the ion source can be removed and/or replaced. In various embodiments, the ion source can be removed without venting the vacuum chamber, such as by isolating the ion source from the vacuum chamber. In various embodiments, the ion source can be cleaned and reinstalled. In various embodiments, the electron source can be replaced, such as when a thermionic filament fails.

[0048] At 612, the magnet assembly can be rotated back to the first position. Once in the first position, the method can return to 602 to use the first electron source.

[0049] While the present teachings are described in conjunction with various embodiments, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.

[0050] Further, in describing various embodiments, the specification may have presented a method and/or process as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the various embodiments.

Claims

WHAT IS CLAIMED IS:

1. An ion source comprising: an ionization assembly including an ionization chamber and at least one ion lens, the removable ionization assembly having a primary axis defined by the direction of an ion beam exiting the ionization assembly, the ionization chamber and the at least one ion lens arranged along the primary axis; and a first electron source aligned along the primary axis of the ionization assembly and configured to provide an electron beam parallel to the primary axis; a second electron source adjacent to the ionization assembly and configured to provide an electron beam orthogonal to the primary axis; a magnet assembly including a magnet; the magnet assembly movable between a first position in which the magnet is aligned with the first electron source and a second position in which the magnet is aligned with the second electron source.

2. The ion source of claim 1 , wherein the ion source operates in an electron ionization mode when the magnet assembly is in the first position.

3. The ion source of claim 1 or 2, wherein the ion source operates in a chemical ionization mode when the magnet assembly is in the second position.

4. The ion source of any of the preceding claims, wherein at least one of the first electron source and the second electron source includes a thermionic filament.

5. The ion source of any of the preceding claims, wherein at least one of the first electron source and the second electron source includes a field emitter.

6. The ion source of any of the preceding claims, wherein the ionization assembly is removable when the magnet assembly is in the second position.

7. The ion source of any of the preceding claims, wherein a direct insertion probe (DIP) and direct exposure probe (DEP) can be inserted into the ionization assembly when the magnet assembly is in the second position. The ion source of any of the preceding claims, wherein the magnet is a temperature compensated samarium cobalt magnet. The ion source of any of the preceding claims, wherein the magnet assembly includes a second magnet. The ion source of any of the preceding claims, wherein the magnet assembly is thermally coupled to a portion of the vacuum chamber, the portion of the vacuum chamber acting as a heat sink. An ion source comprising: an ionization assembly including an ionization chamber and at least one ion lens, the removable ionization assembly having a primary axis defined by the direction of an ion beam exiting the ionization assembly, the ionization chamber and the at least one ion lens arranged along the primary axis; and a first electron source aligned along the primary axis of the ionization assembly and configured to provide an electron beam parallel to the primary axis; a second electron source adjacent to the ionization assembly and configured to provide an electron beam orthogonal to the primary axis; a magnet assembly including a first magnet and a second magnet; the magnet assembly movable between a first position in which the first magnet is aligned with the first electron source and a second position in which the second magnet is aligned with the second electron source. The ion source of claim 11, wherein the ion source operates in an electron ionization mode when the magnet assembly is in the first position. The ion source of claim 11 or 12, wherein the ion source operates in a chemical ionization mode when the magnet assembly is in the second position. The ion source of any of claims 11-13, wherein at least one of the first electron source and the second electron source includes a thermionic filament. The ion source of any of claims 11-14, wherein at least one of the first electron source and the second electron source includes a field emitter. The ion source of any of claims 11-15, wherein the ionization assembly is removable when the magnet assembly is in the second position. The ion source of any of claims 11-16, wherein a direct insertion probe (DIP) and direct exposure probe (DEP) can be inserted into the ionization assembly when the magnet assembly is in the second position. The ion source of any of claims 11-17, wherein the first magnet or the second magnet is a temperature compensated samarium cobalt magnet. The ion source of any of claims 11-18, wherein the magnet assembly is thermally coupled to a portion of the vacuum chamber, the portion of the vacuum chamber acting as a heat sink. A method of operating an ion source in two modes, comprising: using a first electron source to ionize a first sample within an ionization assembly of the ion source, the ionization assembly having a primary axis defined by the direction of an ion beam exiting the ionization assembly, the ionization chamber and at least one ion lens arranged along the primary axis, a magnet assembly, including one or more magnets, positioned to align at least one of the one or more magnets with the first electron source, the first electron source aligned along the primary axis of the ionization assembly and configured to provide an electron beam parallel to the primary axis; moving the magnet assembly to a second position in which at least one of the one or more magnets is aligned with a second electron source adjacent to the ionization assembly, the second electron source configured to provide an electron beam orthogonal to the primary axis; using the second electron source to ionize a second sample within an ionization assembly.

14 The method of claim 20, wherein the ion source operates in an electron ionization mode when the at least one of the one or more magnets is aligned with the first electron source. The method of claim 20 or 21, wherein the ion source operates in a chemical ionization mode when the at least one of the one or more magnets is aligned with the second electron source. The method of claim 20, 21, or 22, further comprising inserting a direct insertion probe (DIP) and direct exposure probe (DEP) into the ionization assembly when the magnet assembly is in the second position. A method of removing an ionization assembly from an ion source, comprising: moving a magnet assembly including a magnet from a first position in which the magnet is aligned with an electron source to a second position in which the magnet does not obstruct removal of the ionization assembly, the ionization assembly having a primary axis defined by the direction of an ion beam exiting the ionization assembly, the ionization chamber and at least one ion lens arranged along the primary axis, the electron source aligned along the primary axis of the ionization assembly and configured to provide an electron beam parallel to the primary axis; and removing the ionization assembly from the ion source. The method of claim 24, further comprising inserting the ionization assembly or a replacement ionization assembly into the ion source; and moving the magnet assembly from the second position to the first position. The method of claim 24 or 25, further comprising using electron source to ionize a sample when the magnet is in the first position.

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