Axial ion source

Abstract

An electron impact ion source includes: a first ionization region including an aperture configured to receive a first molecule into the first ionization region, the first ionization region configured to receive an electron beam along a first axis to generate a first ion beam from the first molecule along the first axis; and a second separate ionization region including an inlet configured to receive a second molecule into the second ionization region, the second ionization region configured to receive the electron beam along the first axis to generate a second ion beam from the second molecule along the first axis.

Description

Technical Field

[0001] The present disclosure relates generally to ion generation as used in analytical techniques including, for example, mass spectrometry, and in particular to electron impact ion sources, methods of electron impact ionization, and analytical instruments including electron impact ion sources. Background Art

[0002] In an electron impact (EI) ion source (also called an electron ionization ion source), electrons are typically emitted from a heated filament and accelerated into an ionization volume containing sample gas molecules. The sample gas molecules are ionized by electron bombardment and extracted from the ionization volume using extraction electrodes. In most EI sources, one or more permanent magnets are used to focus and direct the ionizing electron beam through the ionization volume.

[0003] A conventional EI source is a cross-beam ion source (Nier-type ion source), an example of which is described in IG Brown, The Physics and Technology of Ion Sources, Wiley, 2004. Figure 1 A typical cross-beam ion source is illustrated in FIG. In these EI sources, a positive voltage is usually applied between the thruster electrode P and the extraction electrode E, which accelerates the generated ions through the slit in the extraction electrode E and focuses the generated ions. Ions generated near the hole where the electrons enter the ionization volume are attracted to the hole, while ions generated at a greater distance from the beamline axis do not pass through the slit in the extraction electrode E. Therefore, only a small portion of the ions generated in the ionization volume are attracted to the slit in the extraction electrode E. Figure 1 The ions generated in region R are extracted from the ion source and provided to the mass spectrometer.

[0004] A recent development is the axial EI ion source. In an axial ion source, the electron beam axis is parallel to the ion beam axis. An example of this type of EI source is described in "Effect of magnetic field in electron-impact ion sources and simulation of electron trajectories, Review of Scientific Instruments 77" by Park et al. Figure 2A schematic diagram of ion extraction from an axial source is shown in FIG. A positive voltage is applied between the two extraction electrodes E1 and E2, which transfers electrons back to the heated filament while also extracting ions from the ionization volume. In this configuration, the ionization volume is the region between the thruster electrode P and the extraction electrode E1. A small positive voltage can be applied between the thruster electrode P and the extraction electrode E1 to drag ions to the source exit. This also prevents ions from being attracted to holes in the thruster electrodes where electrons enter the ionization volume.

[0005] The use of an axial ion source can improve ion extraction efficiency compared to a Nier-type ion source because the generated ions travel along the axis of the ion source and can prevent the ions from being attracted to the cavity. The high extraction efficiency of the axial ion source can correspond to high sensitivity, which can be useful, for example, in gas chromatography mass spectrometry (GC-MS). In GC-MS, the axial ion source can be used, for example, in a quadrupole or sector field mass spectrometer.

[0006] US 9,117,617 describes an ion source having a body including an ionization chamber positioned along a source axis and a lens assembly also positioned along the source axis. The lens assembly includes an extractor positioned at the end of the ionization chamber and a first lens element outside the ionization chamber and spaced from the extractor along the source axis. The extractor directs the ion beam out of the ionization chamber along the source axis, and the first lens element reflects the electron beam back to the electron source. However, the electrodes of the ion source are likely to be contaminated by molecules introduced into the body. In addition, these electrodes are difficult to clean in situ, and removing the body for periodic cleaning reduces sample throughput.

[0007] WO 2021 / 078368 relates to a mass spectrometer comprising a gas inlet adapted to supply a sample gas to be ionized into an ionization region, a calibration unit adapted to supply a calibration gas to be ionized into the same ionization region, and an ionization unit adapted to ionize the sample gas and / or the calibration gas in the ionization region, wherein the calibration unit comprises at least one evaporation source for generating the calibration gas by evaporating a source material. However, in this arrangement the ionization efficiency of the sample gas is limited. Furthermore, this arrangement complicates or prevents the use of commonly used calibration gases (such as perfluorokerosene or perfluorotributylamine).

[0008] US 7,541,597 describes an in-situ method for cleaning ion source electrodes in a mass spectrometer by plasma etching. A small amount of non-reactive ion etching ("sputtering") may also be present. However, this method does not work well for more complex ion source geometries or ion sources with small size areas because the method relies on the plasma being able to reach the area that needs to be cleaned.

[0009] WO 2018 / 231631 relates to an ion source comprising a gas source, a nozzle, an electron source and electrodes. The gas source delivers gas to an evacuated ionization volume via a nozzle, and the gas source is at a pressure higher than the pressure of the evacuated ionization volume. The gas passing through the nozzle is free to expand in the ionization region of the ionization volume. The electron source emits electrons through the expanded gas in the ionization region to ionize at least a portion of the expanded gas. The electrodes generate an electric field for the ion flow from the ionization region to the mass filter, and these electrodes are located at a certain distance from the nozzle and oriented to limit their exposure to the gas. However, the ionization efficiency of this arrangement is limited.

[0010] There is a need to overcome the above problems. Summary of the invention

[0011] Against this background, a method and an ion source for providing ions to a mass analyser or another downstream element are provided.Additional aspects emerge from the description and claims.

[0012] The present disclosure relates to an axial EI ion source. A first molecular stream is provided in a first ionization region of the EI source, which is configured to receive an electron beam along a first axis. A first ion beam is generated from a first molecule along the first axis. The electron beam is also provided in a second ionization region of the EI source, which is separated from the first ionization region along the first axis. A second molecular stream is further provided in the second ionization region to generate a second ion beam from a second molecule along the first axis. In other words, during operation of the EI source, an electron beam is available along the length of the first ionization region and the second ionization region to generate a first ion beam and a second ion beam. That is, ions are generated in at least two separate ionization regions using a single electron beam.

[0013] This EI source configuration may mean that the conditions of each ionization region can be allowed to be operated separately. This can enable more precise control of the EI source and can allow the advantages associated with different operating modes to be achieved. For example, one ionization region can be operated to achieve high ionization efficiency, while another ionization region can be operated to achieve improved ion beam focusing. In another example, the pressure inside each ionization region can be independently controlled, which can allow the ionization efficiency of the molecules in each ionization region to be monitored and / or adjusted separately. This can improve the overall ionization efficiency of the EI source.

[0014] In another example, providing two separate ionization regions can allow for limiting, reducing or minimizing contamination of the ion source electrode. For example, molecules that are more likely to contaminate the ion source electrode can be kept away from the ion source electrode (e.g., by introducing these molecules into the ionization region far from the ion source electrode or by introducing these molecules along the second axis). The ion source electrode can be one or more of the following: a lens or electrode for focusing an electron beam, a lens or electrode for extracting ions, a lens or electrode for reflecting electrons or an electron beam, or another electrode.

[0015] Reducing or limiting contamination can enable the long-term stability and high sensitivity of the ion source to be maintained, because fewer ions may be lost in the negatively charged region. Therefore, the tuning of the EI source (or an analytical instrument including an EI source) can be more robust. In addition, the life span and analytical robustness of the highly sensitive device can be improved, and can be improved by about five times or more. The risk of the electron beam being blocked by negative charge accumulation can also be reduced. In addition, more complex geometries can be kept clean (or less contaminated) without the need for regular cleaning, which can achieve higher sample throughput and ease of use. Therefore, the cost of analysis can also be reduced.

[0016] Preferably, a second molecular stream is provided along a second axis intersecting the first axis to ionize the second molecule. The second ionization region may be configured to receive an ion beam from the first ionization region along the first axis. In other words, the second ionization region may be arranged after (or downstream of) the first ionization region. The electron beam may be reflected back from the second ionization region, and ions are extracted for transmission to a mass analyzer or another downstream element.

[0017] The present disclosure also relates to another consideration of an axial EI ion source (which can be combined with the previous discussion). A molecular stream is provided into a first ionization region of the EI source, which is configured to receive an electron beam along a first axis and operates under high vacuum or ultra-high vacuum. An ion beam is generated from the molecules in the first ionization region along the first axis. The electron beam can be reflected back to a receiving portion of the first ionization region, and ions are extracted for transmission to a mass analyzer or another downstream element.

[0018] Operating the first ionization region under high vacuum conditions may mean that molecules may not have a high probability of colliding with other molecules, and thus a (substantially) directional molecular beam may be formed. Contamination of the EI source electrode may therefore be limited, reduced or prevented, as the molecules may not be drawn toward the electrode. In addition, due to the high vacuum conditions, the generation of ions in the region near the EI source electrode may be suppressed. This may result in a less extensive distribution of kinetic energy of the ions (more monoenergetic), which in turn may result in better focusing of the ion beam into the detector of the mass analyzer.

[0019] According to a first aspect, an electron bombardment ion source is provided, the electron bombardment ion source comprising:

[0020] a first ionization region including an aperture configured to receive a first molecule into the first ionization region, the first ionization region configured to receive an electron beam along a first axis to

[0021] generating a first ion beam from the first molecule along the first axis; and

[0022] A second separate ionization region includes an inlet configured to receive a second molecule into the second ionization region, the second ionization region being configured to receive the electron beam along the first axis to generate a second ion beam along the first axis to ionize the second molecule.

[0023] Therefore, an electron bombardment ion source capable of achieving the advantages discussed above can be provided.

[0024] According to a second aspect, there is provided a method for electron ionization, the method comprising:

[0025] receiving an electron beam into a first ionization region along a first axis and generating a first ion beam from the electron beam along the first axis from first molecules in the first ionization region; and

[0026] The electron beam is received along the first axis into a second separate ionization region and a second ion beam is generated from the electron beam along the first axis from the second molecules.

[0027] According to a third aspect, there is provided an electron bombardment ion source, the electron bombardment ion source comprising:

[0028] An ionization region includes an aperture configured to receive molecules into the ionization region, the ionization region being configured to operate under a high vacuum and to receive an electron beam along a first axis to generate an ion beam from the molecules along the first axis.

[0029] Therefore, an electron bombardment ion source capable of achieving the advantages discussed above can be provided.

[0030] According to a fourth aspect, there is provided a method for electron ionization, the method comprising:

[0031] receiving an electron beam into an ionization region along a first axis and generating an ion beam from the electron beam along the first axis from first molecules in the first ionization region; and

[0032] The first ionization region is operated under high vacuum.

[0033] The above-mentioned electron bombardment ion source can be realized in an analytical instrument.

[0034] The above method may be implemented as a computer program, which includes instructions for operating a computer or a computer system. The computer program may be stored on a non-transitory computer readable medium.

[0035] The computer or computer system (or other hardware and / or software configured to implement the method) may be embodied as a controller configured to operate an analytical instrument.The above method may be implemented in a system comprising an analytical instrument and a controller.

[0036] It should be noted that any feature described herein can be used with any specific aspect or embodiment described herein. In addition, any combination of specific device, structural or method features is also provided, even if the combination is not explicitly disclosed.

[0037] The invention will now be described with reference to the accompanying drawings which depict various embodiments of the invention, provided purely by way of example and not limitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention may be implemented in many ways and a preferred embodiment will now be described by way of example only and with reference to the accompanying drawings, in which:

[0039] Figure 1 A crossed beam (Nier type) ion source is schematically illustrated;

[0040] Figure 2 An axial ion source is schematically shown;

[0041] Figure 3 Graph illustrating the reduction in signal intensity of a triple quadrupole GC-MS / MS system exposed to a constant flow of PFTBA into the ion source for several hours;

[0042] Figure 4 An ion source including two ionization regions is schematically illustrated;

[0043] Figure 5A A diagram showing an ion source including two beam intersection ionization regions and an additional ionization region;

[0044] Figure 5B Schematically illustrates an ion source including two beam intersection ionization regions and an additional ionization region, in which the received molecules are directed away from the ion source electrodes;

[0045] Figure 6 An ion source including two beam intersection ionization regions is schematically depicted;

[0046] Figure 7 schematically illustrates an ion source including two ionization chambers and corresponding exemplary potentials within the ion source;

[0047] Figure 8 One embodiment of an ion source including an ionization chamber and a beam intersection ionization region is shown;

[0048] Fig. 9 An embodiment of an ion source including two beam intersection ionization regions and another ionization region disposed between the two beam intersection ionization regions is illustrated; and

[0049] Fig.10 Shown is a graph illustrating the difference in peak shape for a conventional axial ion source compared to an axial ion source in which minimal ionization occurs in the region around extraction electrodes El and E2.

[0050] Fig.11 An analytical instrument, such as a mass spectrometer (for example), in which an ion source according to the present disclosure may be utilized is schematically illustrated.

[0051] It should be noted that the figures are shown for simplicity and are not necessarily drawn to scale. Similar features are provided using the same (or similar) reference numerals. DETAILED DESCRIPTION

[0052] In a typical ion source, sample and calibrant molecules (usually in gaseous form) are introduced into a single ionization volume of the ion source. The sample and calibrant molecules are mixed in a single ionization volume and ionized by an electron beam. The ionized sample and calibrant molecules are then transmitted to a mass analyzer via an extraction electrode, while the electron beam is reflected back via the extraction electrode (axial source) or collected on an electrode (cross beam source) opposite to the electron entrance hole. The calibrant molecules are usually known atomic masses or mass-to-charge (m / z) ratios, which produce calibration peaks corresponding to known m / z values ​​in the measured mass spectrum. Therefore, the calibration peaks can be used to determine the mass-to-charge ratios of peaks corresponding to unknown molecules.

[0053] Since the sample and calibrant molecules are mixed in a single ionization volume, the same operating conditions of the ion source are used to ionize both the sample and calibrant molecules. However, although certain operating conditions may be more beneficial to sample molecules than to calibrant molecules, it is not possible in conventional ion sources to individually tailor operating conditions for each group of molecules in the ionization region.

[0054] In addition to the high extraction efficiency that can be obtained using an axial ion source, the increased gas pressure in the ionization volume can also increase the ionization efficiency. However, the increased gas pressure in the ionization volume may also accelerate the contamination of the ion source electrodes. Specifically, an insulating layer of sample and calibrant molecules can be formed on the ion source electrodes, which can then be charged by impacting electrons. Ions may then be lost in these negatively charged areas. As an example, the circular area around the hole may be particularly susceptible to charging. The axial ion source is particularly prone to losing ions in negatively charged areas because there is generally no significant electric field gradient in the ionization volume. In extreme cases, negative charge may accumulate to be sufficient to completely block the electron beam.

[0055] Contamination of the ion source can become an even more serious problem when using calibrants such as perfluorokerosene (PFK) or perfluorotributylamine (PFTBA, also known as FC43). These calibrants can be used, for example, to adjust the ion source or to provide a lock mass during a measurement. For example, calibrant compounds such as PFK and PFTBA tend to severely contaminate the ion source electrodes, often resulting in a visible coating on the electrodes.

[0056] The lock mass is an ion with a known mass-to-charge ratio that allows real-time recalibration by correcting for m / z shifts caused by instrument drift. The lock mass allows the analytical instrument to quickly shift to the relevant part of the mass spectrum. This can be used to more quickly and easily analyze small areas around the center of the peak. This may be particularly useful for dioxin measurements, for example, which can be performed using a magnetic sector GC-MS instrument.

[0057] The lock mass may need to be provided throughout the analysis. For example, the U.S. Environmental Protection Agency (EPA) Method 1613B is considered the "gold standard" for dioxin analysis. Method 1613B requires the use of high-resolution GC-MS and requires continuous measurement of the PFK lock mass while measuring the dioxin sample. In order to obtain valid measurements, the signal intensity of the PFK lock mass is stable, as specified in Method 1613B. However, the constant influx of PFK into the ion source over several hours presents challenges for axial ion sources with closed ionization volumes. For example, the contamination issues discussed above may often cause the signal intensity to decrease over a period of time, which may make the use of the lock mass difficult to achieve or require further time and labor to correct for the decrease in signal intensity. Therefore, achieving the gold standard may be difficult, especially after multiple experiments.

[0058] Figure 3 The reduction in signal intensity of a triple quadrupole GC-MS / MS system exposed to a constant PFTBA flow into the ion source for several hours is illustrated. As can be seen from the results, the abundance reduction is significant after about an hour. Obviously, it is difficult to achieve the gold standard using an axial ion source in current instruments. Although measurements that meet the 1613B standard can be obtained using a cross-beam ion source (because a cross-beam ion source may be less susceptible to contamination), using a cross-beam source means giving up the higher sensitivity that can be achieved using an axial ion source. Therefore, it is preferred to provide an axial ion source with a lower contamination rate.

[0059] Figure 4An exemplary implementation of an ion source is schematically shown. The ion source 400 includes an electron source 403, an electron lens (thruster electrode) 404, a first ionization region 401, a second ionization region 402, and a reflection and extraction electrode 406. The ion source 400 may be surrounded by a vacuum environment (which may be a high vacuum). The electron lens 404 and the reflection and extraction electrode 406 may be collectively referred to as a plurality of lenses 404, 406 or a plurality of electrodes 404, 406. The ion source may be an axial ion source, which means that both electrons and ions move along a common axis of the ion source. This may be achieved by an axial magnetic field. The axial magnetic field may also focus the ion beam. In other words, the use of a magnetic field rather than, for example, an electric RF field may allow the ion beam (which may be composed of positive ions) and the electron beam 411 to travel or pass along a common axis.

[0060] Both (static) magnetic fields and electric RF fields can be used to focus positively and negatively charged particles. However, the electric RF field may not allow both ions and electrons (whose mass-to-charge ratio is typically four orders of magnitude smaller than that of ions) to be confined within the ion source 400 at the same time. Specifically, in an electric RF ion guide, the electric field is zero (or close to zero) along the ion guide axis, but becomes non-zero and increases rapidly when deviating from the ion guide axis. Therefore, ions (positively or negatively charged) moving away from the ion guide axis move into a region of high electric RF field and are pushed back to the ion guide axis due to many cycles of the oscillating electric RF field acting on the ions. In contrast, electrons (much lighter than ions) can move through the ion guide quickly enough that the electric RF field (frequency in the MHz range) appears static to the electrons. Therefore, instead of being focused along the ion guide axis, the electrons are simply deflected away from the ion guide axis and attracted toward the positive ion guide electrode (as the electrons move through the ion guide).

[0061] In other words, although the electric RF field with typical frequency in the MHz range can be used to confine ions in the ion source, the same electric RF field is regarded as a static field by electrons moving much faster. Therefore, electrons can be deflected away from the source axis and attracted to those RF multipole electrodes, which are positive when the electrons move in the ion source. In contrast, the focusing effect of the magnetic field is stronger for lighter particles than for heavier particles. For example, the magnet in the axial ion source can focus electrons (electron beams) strongly along the source axis while having a negligible focusing effect on (much heavier) ions. Therefore, using one or more magnets in the axial ion source can allow both the ion beam and the electron beam to be focused in the ion source.

[0062] Still refer to Figure 4, the electron beam 411 is emitted along a first axis from an electron source 403, which may include a cathode (not shown) configured for thermionic emission. For example, the cathode may include one or more filaments, which may be composed of, for example, tungsten or rhenium filaments (or alloys thereof). The cathode is heated to an incandescent temperature to emit electrons, which can generally be achieved by passing an electric current through the cathode.

[0063] The resulting electron beam 411 can be focused into the first ionization region via an electron lens 404 (which can be any suitable electrode or electrodes for focusing the electron beam). In other words, the electron lens 404 can be configured to receive one or more voltages to generate an electric field, thereby guiding or focusing the electron beam into the first ionization region. The electron lens 404 can also be configured to push ions away from the electron entrance hole. The electron beam 411 is preferably collimated into the first ionization region by a magnetic field generated by one or more magnets, which can be permanent magnets or non-permanent magnets (e.g., semi-permanent magnets). For example, a disk magnet can be placed behind the electron source 403 to generate a magnetic field. Additional magnets can also be used.

[0064] The use of one or more magnets in the electron bombardment ionization region may be useful. This is because electron bombardment converts molecules into positive ions, resulting in the presence of positive ions and negative electrons in the electron bombardment ionization region. The use of an electric RF field may cause electrons (whose mass-to-charge ratio is typically four orders of magnitude smaller than that of ions) to be ejected from the ion source (because the electric RF field appears to be relatively static to fast-moving electrons). In contrast, a magnetic field may allow both the ion beam and the electron beam 411 to be confined within the ion source 400, and thus allow both to enter the second ionization region 402.

[0065] The magnetic field is preferably applied parallel to the direction of the electron beam 411. Thus, the electrons may follow a spiral path, which may increase their path length and thereby increase the probability of electron collisions.

[0066] The first molecule 408 (which may include a sample molecule to be analyzed or a calibrant molecule) is introduced into the first ionization region 401 via a first hole or inlet, where ions can be generated by collision of neutral molecules with electrons in the electron beam 411. The collision may produce positive ions or negative ions. For example, the electrons in the electron beam may cause the neutral molecules to eject electrons due to the transfer of kinetic energy, thereby producing positive ions. In another example, the electrons may be captured by the neutral molecules, thereby producing negative ions.

[0067] The first ionization region 401 includes a first hole or inlet. The hole can be in the first ionization region 401 itself (e.g., a hole in the wall of the first ionization region 401), or the first ionization region 401 can include a component (which can also be referred to as a molecule delivery element) having a hole through which the first molecule 408 is received. For example, the first ionization region 401 can include a nozzle or a tube (such as, for example, a capillary tube) or another component having an opening.

[0068] The first molecules 408 may be received into the first ionization region 401 as a molecular stream or beam, and may be received from an analytical instrument such as, for example, a gas chromatograph. The molecular beam may be produced by allowing a gas at a higher pressure to expand through a small orifice into a chamber at a lower pressure.

[0069] The molecules 408 may be received as a (substantially) continuous stream of molecules to serve as a lock mass. The signal intensity of the continuous stream may decrease by less than 10%, 5%, 1% or another value over a period of time. The period of time may be of the order of several hours and may be, for example, between 5 and 10 hours.

[0070] The electron beam 411 ionizes the first molecule 408 in the first ionization region 401, and generates an ion beam 407 of the resulting first ion along the first axis. That is, both the electron beam and the ion beam 407 travel along the first axis. Since the first ionization region 401 is configured for electron bombardment ionization, the first ionization region 401 may also be referred to as the "first electron bombardment ionization region 401". The ion beam 407 may be considered to include the "first ion beam" because the ion beam is generated from the first molecule. The ion beam 407 or the first ion beam is guided into the second ionization region 402. The second molecule 409 (which may be a sample molecule to be analyzed, a calibrant molecule, or a lock mass) is introduced into the second ionization region 402. The second molecule 409 may also be received in the second ionization region 402 via a second hole or inlet, and may be received as a molecular beam. The second molecule 409 may be received from an analytical instrument (such as, for example, a gas chromatograph).

[0071] The second ionization region 402 includes a second hole or inlet. The second hole can be in the second ionization region 402 itself (e.g., a hole in the wall of the second ionization region 402), or the second ionization region 402 can include a component (which can also be referred to as a molecule delivery element) having a hole through which the second molecule 408 is received. For example, the second ionization region 402 can include a nozzle or a tube (such as, for example, a capillary tube) or another component having an opening.

[0072] The electron beam 411 ionizes the second molecule 409 in the second ionization region 402. In other words, the ion beam 407 also includes the second ions. Since the second ionization region 402 is configured for electron impact ionization, the second ionization region 402 may also be referred to as a "second electron impact ionization region 402". Therefore, the ion beam 407 may be considered to include the first ion beam and a "second ion beam" generated by the second molecule. The electrode 406 (which may be within or adjacent to the second ionization region 402) is configured to receive a voltage to extract ions from the second ionization region 402 (including ions received from the first ionization region 401 into the second ionization region 402) and reflect the electron beam 411.

[0073] The first molecule 408 and the second molecule 409 are ionized in the respective first ionization region 401 and the second ionization region 402 to generate an ion beam 407 along a first axis. The ion beam 407 can be supplied to a mass analyzer or a downstream element. A (small) positive voltage can be applied between the electron lens 404 and the reflection / extraction electrode 406 to move the positive ions toward the ion source outlet 412. In other words, an axial gradient can be applied between the electron lens 404 and the reflection and extraction electrode 406. The positive voltage can also prevent the ions from being attracted to the holes in the electron lens 404, from which the electrons enter the first ionization volume 401. In an example in which negative ions are generated, a (small) negative voltage can be applied between the electron lens 404 and the reflection and / or extraction electrode 406.

[0074] At least one of the first ionization region 401 and the second ionization region 402 may be configured to receive the first molecule 408 or the second molecule 409, respectively, along a second axis (not shown) intersecting the first axis. In other words, the flow of molecules 408 and / or 409 may overlap with the electron beam 411 received into at least one ionization region. Since the second axis intersects the electron beam 411, the first molecule 408 and / or the second molecule 409 may be effectively ionized by the electron beam 411. When the molecules 408 and / or 409 are provided along the second axis, the molecules 408 and / or 409 may not be directed toward the ion source electrodes 404 and / or 406 or contact these ion source electrodes. Therefore, contamination of the ion source electrodes 404 and / or 406 may be prevented or reduced.

[0075] In other words, an electron bombardment ion source can be provided, which includes: a first electron bombardment ionization region, the first electron bombardment ionization region including a hole configured to receive a first molecule into the first ionization region, the first ionization region is configured to receive an electron beam along a first axis to generate an ion beam from the first molecule along the first axis; and a second separate ionization region, the second separate ionization region is configured to receive the electron beam along the first axis, the second ionization region includes an inlet, the inlet is configured to receive a second molecule into the second ionization region along a second axis intersecting the first axis to ionize the second molecule.

[0076] A corresponding electron ionization method can be provided, the method comprising: receiving an electron beam into a first ionization region along a first axis and generating an ion beam from a first molecule in the first ionization region along the first axis by the electron beam; and receiving the electron beam into a second separate ionization region along the first axis, and receiving a second molecule into the second ionization region along a second axis intersecting the first axis to generate an ion beam from the second molecule along the first axis.

[0077] Preferably, the second axis may be perpendicular to the first axis. Thus, a simple arrangement may be provided in which contamination of the ion source electrodes 404 and / or 406 may be limited, prevented or reduced. In another example, the intersection angle may be selected based on the position of the ion source electrodes 404 and / or 406 relative to the ionization region in which the molecules 408 and / or 409 are received along the second axis. For example, the intersection angle may be selected to direct the molecules away from the plane of the ion source electrodes 404 and / or 406.

[0078] Although the individual molecules in the molecular beam may travel along different paths, the molecular beam may have an overall direction of travel. In one example, the intersection angle may be selected so that the direction of travel of the molecular beam is at least partially opposite (opposite) to the direction of travel of the electron beam. At least partially opposite may mean that the vector component of the direction of travel of the molecular beam is antiparallel to the vector component in the direction of travel of the electron beam (the vector components are opposite in direction). Preferably, when the ionization region 402 is adjacent to the extraction and reflection electrode 406, the direction of travel may be at least partially opposite to the direction of travel of the electron beam. Although the molecular beam may thus be at least partially directed to the electron lens 404, contamination of the electron lens 404 may still be avoided, reduced and / or limited. For example, the intersection angle may be an angle that makes it impossible or unlikely for the second molecule to reach the ion source electrode. For example, the angle may be between 70 and 90 degrees. Additionally or alternatively, the length d of the ionization region 402 may be large enough so that the second molecule 409 will not or is unlikely to reach the electron lens 404. Additionally or alternatively, there may be a separation element between the ionization region 402 and the electron lens 404 so that the second molecule is similarly unable or unlikely to reach the ion source electrode. Other arrangements are also possible, which may mean that contamination of the electron lens 404 may be reduced or limited.

[0079] In another example, the intersection angle can be selected so that the direction of travel of the molecular beam is at least partially parallel to the electron beam (e.g., when the ionization region 401 is adjacent to the electrode lens 404). At least partially parallel can mean that the vector component of the direction of travel of the molecular beam is parallel to the vector component of the direction of travel of the electron beam (the vector components have the same direction). As discussed above with respect to the electron lens 404, although the molecular beam can be at least partially directed toward the extraction and reflection electrode 406, contamination of the extraction and reflection electrode 406 can still be avoided, reduced and / or limited.

[0080] In addition or alternatively to receiving molecules 408 or 409 along the second axis, one or both of the ionization regions 401, 402 may be configured to operate under high vacuum. In other words, an axial ion source may be provided in which a portion of the electron beam is placed in a high vacuum. The high vacuum may be achieved by using a vacuum pump (or a series of vacuum pumps) that may be connected (directly or indirectly) to at least one ionization region. In the case where the ionization regions are configured to operate under high vacuum, there may be only one ionization region.

[0081] A high vacuum corresponds to a lower pressure within the ionization region (compared to the pressure range conventionally used in the ionization region), which can reduce the probability of generating ions from the electron beam 411. Therefore, the high vacuum region can result in less ionization (although sufficient ionization efficiency can be maintained or improved by, for example, introducing molecules along the second axis). This in turn can enable effective prevention or reduction of contamination of the ion source electrodes 404 and / or 406. Preferably, one or both of the ionization regions 401, 402 configured to operate under a high vacuum can also be configured to receive molecules 408 and / or 409 along the second axis. This can allow particularly effective prevention or reduction of contamination because the molecules may not be directed toward the electrodes 404 and / or 406 and may have a reduced probability of reaching the electrodes 404 and / or 406.

[0082] The vacuum can be a high vacuum or an ultra-high vacuum, which can improve the reduction or prevention of contamination. The ion source 400 can be configured to operate in one or more ways under a high vacuum or an ultra-high vacuum. In one example, at least one ionization region 401 and / or 402 can be configured to make at least one ionization region 401 and / or 402 along the length d of the dimension parallel to the first axis less than twice the mean free path of molecules 408 and / or 409. In other words, the mean free path of molecules 408 and / or 409 can be more than half (0.5 times) of the length d of at least one ionization region 401 and / or 402. Therefore, molecules 408 and / or 409 can travel in a straight line to form a substantially oriented molecular beam. Therefore, molecules 408 and / or 409 may not be deflected due to collisions with other molecules, and therefore are unlikely to contaminate the ion source electrode. Preferably, the mean free path is greater than the length d, and most preferably at least ten times the length d.

[0083] Optionally, at least one ionization region may be configured to be at or below 0.1 Pa (1×10 -3 mbar) or less than or equal to 10 -6 Pa(10 -8 mbar). High vacuum can be operated with 1×10 -6 Pa to 0.1Pa (1×10 -8 mbar to 1×10 -3 mbar), and ultra-high vacuum can correspond to 1×10 -9 Pa to 1×10 -6 Pa(1×10 - 11 mbar to 1×10 -8mbar) range, as defined in ISO 3529-1:2019. However, it should be understood that another pressure range may be used, as the pressure range corresponding to a high vacuum or ultra-high vacuum may depend on various factors, such as the size of the ionization volume, the temperature within the ionization volume, and the molecular species within the ionization region. For molecules with larger collision cross sections, such as, for example, PFK or FC43, the pressure in the ionization region may need to be lower than 10 -3 mbar to avoid or substantially reduce collisions. Larger volumes of ionization may also require a pressure below 10 -3 Preferably, the pressure range corresponds to operating at least one ionization region under high vacuum or ultra-high vacuum.

[0084] The presence of molecular flow (and therefore high or ultra-high vacuum conditions) can be determined in a direct and empirically verifiable manner by the Knudsen number. The Knudsen number is a dimensionless number defined as Wherein λ is the mean free path, and L corresponds to a physical length, which may be the length of the ionization region in one dimension (e.g., a dimension parallel to the first axis). When the Knudsen number is greater than 0.5, the probability of molecular collisions may be low or substantially zero, such that the molecular flow may correspond to high vacuum conditions. Preferably, the Knudsen number is greater than or equal to 1. Most preferably, the Knudsen number is greater than or equal to 10 to further reduce the likelihood of molecular collisions. Thus, the molecules may be in a free molecular flow.

[0085] Still refer to Figure 4 , the first ionization region 401 is separated from the second ionization region 402. This allows the conditions of the first ionization region 401 to be operated separately from the conditions of the second ionization region 402. These conditions can be set by one or more operating parameters of the EI source, which can include the pressure in the corresponding ionization region, one or more voltages to be applied to one or more ion source electrodes, the axis along which the corresponding molecules are received or introduced, or another operating parameter. In one example, the first ionization region 401 can be operated at an elevated pressure, and the molecules can be introduced into the second ionization region 402 along a second axis that intersects the first axis.

[0086] In one example, the first ionization region 401 and the second ionization region 402 may be separated in space (offset from each other). The offset may be along a dimension parallel to the first axis. In the case where the first ionization region 401 and the second ionization region 402 are separated in space, the first molecule 408 may be mainly ionized in the first region 401 and the second molecule 409 may be mainly ionized in the second region 402. However, some of the first molecules 408 may be ionized in the second ionization region 402, and vice versa. In other words, there may be some overlap between the two ionization regions.

[0087] In another example, the first ionization region 401 and the second ionization region 402 can be separated in space such that there is no (or substantially no) spatial overlap between the spatial and / or angular spread of the first molecule 408 and the second molecule 409. In one example, the spatial separation can be achieved by providing a spacer between the first ionization region and the second ionization region. The spacer can be another ionization region, such as the reference Figure 5A , Figure 5B and Fig. 9 When molecules are present during operation of the ion source 400, there is no need to introduce the molecules into the spacer region or another ionization region.

[0088] In another example, the length d of the first ionization region 401 and / or the second ionization region 402 along the dimension parallel to the first axis can be large enough so that the spatial extents of the first molecule 408 and the second molecule 409 have a low probability of overlap. For example, the probability of overlap can be less than 50%, less than 10%, less than 5%, or less than 1%. The probability of overlap can also be less than another value.

[0089] In yet another example, there may also be a separation element or barrier between the first ionization region 401 and the second ionization region 402, which may be in addition to the spatial separation. Providing a barrier in addition to the spatial separation may further reduce or limit the contamination of the ion source electrodes compared to the spatial separation alone. The separation element may prevent or reduce the number of molecules exchanged between the two ionization regions, which may mean that the molecules in the first region are mainly ionized in the first region and the molecules in the second region are mainly ionized in the second region. The separation element may be, for example, a separation wall between the first ionization region 401 and the second ionization region 402.

[0090] The separation wall may form a portion of a wall that at least partially surrounds one or both of the first ionization region 401 and the second ionization region 402. For example, one or both of the ionization regions 401, 402 may be an ionization chamber. By providing an axial ion source with an at least partially enclosed ionization volume, a higher or highest sensitivity may be achieved. Preferably, one or both of the ionization regions 401, 402 may be mostly enclosed. An at least partially or mostly enclosed ionization volume may result in an increase in the gas pressure within the ionization volume. This may be in the range of 1×10 -4 and 1×10 -2 mbar, but it will be appreciated that the pressure range may depend on various factors such as the size of the ionization volume, the temperature within the ionization volume, and the molecular species within the ionization region.

[0091] In another example, a separation element may be provided instead of spatial separation. That is, the ionization regions may overlap spatially so that molecules are not primarily ionized in the respective ionization regions except for the presence of the separation element. The separation element may be sufficient to reduce or limit contamination of the ion source electrodes.

[0092] Figure 4 The length d shown in is merely illustrative and need not be the same value for both the first ionization region and the second ionization region. The first ionization region 401 and the second ionization region 402 (and the spacer, if present) may have any suitable size and may have different lengths or volumes. The spacer, if present, may have the same length or volume as one of the first ionization region 401 and the second ionization region 402, or may have a different length or volume.

[0093] Although the first molecule 408 and the second molecule 409 Figure 4 408 and 409. In the example of FIG. 409, the first molecule 408 and the second molecule 409 are illustrated as being introduced on a common side of the ion source 400, but it should be understood that these molecules can be provided from different (e.g., opposite) sides of the ion source 400. Similarly, it is not necessary to receive the first molecule 408 and the second molecule 409 along an axis that is orthogonal (perpendicular) to the first axis. Instead, the first molecule 408 and the second molecule 409 can be received at any suitable angle relative to the first axis. For example, in a region where the ion beam 407 is transmitted directly to the extraction and reflection electrode 406, the molecules can be received along another axis at an angle between 90 and 180 degrees relative to the first axis. Thus, the molecules can be guided at least partially in the opposite direction of the travel of the electron beam 411. In another example, in a region where the electron beam 411 is received directly from the electron lens 404, the molecules can be received along an axis that is 90 degrees or less relative to the first axis. Thus, the molecules can be guided along the travel direction of the electron beam 411. Either or both of these configurations may help avoid electrode contamination because either or both sets of molecules may not be drawn toward the plurality of electrodes 404 and / or 406 .

[0094] Ion source 400 can be implemented in an analytical instrument. Ion source 400 and / or components of the analytical instrument can be controlled by a controller (not shown). The controller may include a computer used as a data processor, and the data processor is used to receive data from a mass analyzer, and the data represents the mass analysis from the mass analyzer or the amount of the detected ions. The computer can also be used as a data processor to process data to provide a mass spectrum and / or quantitative analysis of the ions. The controller may also include a display and a user input device so that the user can view and input or select information. The user input device can be a keyboard and / or a mouse.

[0095] The ionization regions 401, 402 (and the spacer, if present) may be arranged in one of a number of ways. Figure 5A , Figure 5B and Figures 6 to 10 However, it should be understood that, except for Figure 5A , Figure 5B and Figures 6 to 10 Implementations other than those schematically illustrated in are also possible.

[0096] Figure 5A Illustrated Figure 4 00A includes an electron source 403, an electron lens 404, a reflection and extraction electrode 406, a two beam intersection ionization region 520, and a spacer region 530. The two beam intersection ionization region 520 is an ionization region in which molecules 525 are introduced along an axis that intersects the first axis.

[0097] In FIG. 5 , a spacer 530 is positioned between two beam intersection ionization regions 520, but the regions 520, 530 may be arranged in another manner. In addition, the ion source 500A may include a different number of each type of region. For example, there may be only one beam intersection ionization region 520 or more than two beam intersection regions 520. Similarly, more than one spacer 530 or no spacer 530 may be included in the ion source 500A.

[0098] A third molecule 535 (which may be a sample molecule to be analyzed or a calibrant molecule) may be received in the spacer 530. The spacer may be another ionization region, and the third molecule 535 may be as described above with respect to Figure 4 The first ionization region 401 and the second ionization region 402 are ionized as discussed above. For example, the other ionization region 535 can be configured to operate under high vacuum conditions or ultra-high vacuum conditions and / or the third molecule 535 can be received into the other ionization region 535 along an axis intersecting the first axis.

[0099] As mentioned above Figure 4As discussed, the ion source 500A can be configured to operate under high vacuum conditions or ultra-high vacuum conditions by sizing at least one ionization region such that the length d is less than the mean free path length. Additionally or alternatively, at least one ionization region can be configured such that the spread of the molecules 525 and / or 535 along a dimension parallel to the first axis is less than the length d of the at least one ionization region. For example, the spatial spread α (divergence of the molecular beam) of the molecules 525 and / or 535 can be less than the length d of the at least one ionization region. Additionally or alternatively, at least one ionization region can be configured such that the spread of the molecules 525 and / or 535 does not intersect the plane of the ion source electrodes 404 and / or 406. For example, the angular spread θ of the molecules 525 and / or 535 can not intersect the plane of the ion source electrodes 404 and / or 406. Any of these options can be achieved by a sufficiently large ionization region, an inlet that limits the spread (e.g., spatial spread α and / or angular spread θ) of the molecules, an inlet positioned distal to an electrode, and / or a pressure within the ionization region that allows most molecules (e.g., 50% or more) to reach the side of the ionization region opposite the inlet. The ionization region can be configured so that different percentages of molecules reach the side opposite the corresponding aperture and / or inlet. For example, 40%, 60%, 80%, or 90% of the corresponding first molecules and / or second molecules can reach the side opposite the corresponding aperture and / or inlet. Figure 5A The spatial spread α and angular spread θ shown in are merely exemplary and may be any suitable values.

[0100] Figure 5B Illustrated Figure 4 and Figure 5A An exemplary embodiment of an ion source is schematically illustrated in FIG. Figure 5B In the example, the two beams intersect. Ionization region 520 is the calibrant ionization region and ionization region 530 is the sample ionization region. Ionization region 530 can be a high pressure ionization region (usually at 1×10 -4 and 1×10 -2 mbar), which may be achieved by at least partially enclosing the ionization chamber 531, or may be an ionization zone operating under high vacuum or ultra-high vacuum. Figure 5A As noted, different numbers of each type of ionization regions 520, 530 may be present in the ion source 500B, and the ionization regions 520, 530 may be arranged in one of a variety of ways.

[0101] For example, the beam intersection ionization region 520 may be positioned before and / or after the ionization region 530. The calibrant molecules 525 may be introduced along an axis at any suitable angle relative to the axis of the electron beam 411. Preferably, however, the calibrant molecules 525 may be received along an axis that does not intersect the plane of the ion source electrodes 404 and / or 406. In other words, the axis may be selected based on the position of the ion source electrodes 404 and / or 406 relative to the ionization region 520. For example, in the case where the beam intersection ionization region 520 is adjacent to the electron lens 404 (e.g., the region 520 receives the electron beam 411 directly from the electron lens 404), the axis may be at an angle of 90 degrees or less relative to the first axis. In another example where the beam intersection ionization region 520 is adjacent to the extraction and reflection electrode 406 (e.g., the region 520 transmits the ion beam 407 directly to the extraction and reflection electrode 406), the axis may be at an angle of between 90 degrees and 180 degrees relative to the first axis. These two examples are similar in concept to those of FIG. Figure 5B , although there may be only one beam intersection region 520. Sample molecules 535 may be received along another axis at any suitable angle relative to the first axis. Thus, the calibrant and sample molecules may travel along paths that do not intersect the plurality of electrodes 404, 406.

[0102] In another example, at least two beam intersection ionization regions 520 may be positioned sequentially. Thus, the ionization region 530 may be disposed before or after the at least two beam intersection ionization regions 520. Alternatively, the ionization region 530 may not exist. Figure 6 Such exemplary embodiments are discussed.

[0103] In the case where the ion source 500B includes two or more calibrant ionization regions (not necessarily each being a beam intersection ionization region), the calibrant molecules 525 can be different types of molecules. For example, one calibrant ionization region can be used to ionize PFK molecules, while another calibrant ionization region can be used to ionize FC43 molecules. Thus, multiple calibrants can be introduced into the ion source in a straightforward manner without increasing the amount of ion source electrode contamination and enabling each calibrant molecule to be fully ionized.

[0104] Still refer to Figure 5B , the ionization region 530 can be surrounded by a wall 531 to separate the ionization region 530 from the beam intersection ionization region 520. The wall 531 can only partially surround the ionization region 530. The holes in the wall can allow the electron beam 411 and the ion beam 407 to be transmitted or directed through the ion source 500. Additional holes can allow sample molecules 535 to be introduced into the sample ionization region 530.

[0105] The ion source may include two or more (e.g., three) ionization regions 530. The two or more ionization regions 530 may be placed on either side of one or more beam intersection ionization regions 520 and / or positioned sequentially. The sample molecules in some or all of the sample ionization regions 530 may be different types of molecules. Some or all of the sample ionization regions may be at least partially surrounded by a surrounding wall 531.

[0106] As mentioned above about Figure 4 and Figure 5A As discussed, beam intersection ionization region 520 and ionization region 530 may be of any suitable dimensions and may be of different sizes or have different volumes. Similarly, some or all of the same type of ionization regions (beam intersection, high vacuum, or high pressure) may have different sizes or volumes. Calibrant molecules 525 and sample molecules 535 may be introduced along any suitable axis and need not be introduced on a common side of ion source 500. In addition, Figure 5B The spatial spread α and angular spread θ shown in are merely illustrative.

[0107] Although beam intersection region 520 has been described above as a calibrant ionization region and ionization region 530 has been described as a sample ionization region, it should be understood that calibration molecules can be introduced into ionization region 530 (instead of sample molecules) and / or sample molecules can be introduced into one or both of beam intersection regions 520 (instead of calibrant molecules).

[0108] Figure 6 A specific exemplary embodiment of an axial ion source is illustrated. In this example, a first ionization region 601 and a second ionization region 602 of an ion source 600 are spatially separated by an optional partition wall 640 (separation element) between the ionization regions. A first molecular species beam 642a is introduced into the first ionization region via a gas stream delivery element 641a. The gas stream delivery element can be a nozzle or a tube (e.g., a capillary) or another structure. A second molecular species beam 642b is received in the second ionization region via a gas stream delivery element 641b.

[0109] Both ionization regions may preferably be operated under high vacuum conditions, which may enable the beams 642a and 642b to be substantially directed (molecules in the beams may travel in straight lines). Thus, the divergence of the beams 642a and 642b may be less than the length d of the first ionization region 601 and the second ionization region 602, and / or the angular spread θ of the beams 642a and 642b may not intersect the plane of the ion source electrodes 404 and 406.

[0110] The first molecular species beam 642a and the second molecular species beam 642b are illustrated as being centered along axes that are orthogonal to the axis of the electron beam 411, but one or both of these axes may be at another angle relative to the electron beam axis.

[0111] A waste receiver (not shown) or a dumping device may be placed relative to one or both of the inlets 641a, 641b. When the molecules in the molecular beams 642a, 642b may travel along a straight path (e.g., because the ionization zone operates under high vacuum conditions), the molecules may be directed to the waste receiver generally. Therefore, these molecules may be less likely to contaminate other components of the ion source 600. The waste receiver may be removable. This may mean that the waste receiver may be cleaned by removing the waste receiver from the ion source 600. Therefore, the ion source 600 may be easier to clean and may clean small-sized areas that are not easy to clean via known methods (such as, for example, in-situ cleaning). The waste receiver may be realized by a cylindrical element closed at one end. The waste receiver may be present in any ion source implementation discussed herein.

[0112] Figure 7 701. Another exemplary embodiment of an ion source is shown, which may be surrounded by a vacuum, preferably a high vacuum. The electron beam 411 may be directed through a first ionization volume 701, into which a first molecular species 708 may be introduced via an inlet 741a. The gas pressure within the first ionization volume 701 may be increased (e.g., at 1×10 -4 and 1×10 -2 mbar), which can increase the ionization efficiency of the first molecular species 708. In other words, the first ionization volume 701 may not operate under high vacuum conditions. The first ionization region 701 is preferably at least partially closed, and most preferably a conductivity limited ionization chamber. For example, the conductivity limited ionization chamber can be closed except for the holes through which particles (generally electrons), molecules (usually ions and neutral molecules) and / or atoms enter and leave the ionization volume.

[0113] The first ionization volume 701 may be followed by a separate ionization section 702 into which the second molecular species 709 is introduced via inlet 741b. The separate ionization section 702 may be operated at an elevated pressure (e.g., at 1×10 -4 and 1×10 -2 mbar), which can increase the ionization efficiency of the second molecular species 709. In other words, the second ionization volume may not operate under high vacuum conditions. The second ionization region 702 is preferably at least partially enclosed, and most preferably is a conductivity-limited ionization chamber.

[0114] An optional gap 750 may be present in the surrounding wall 731b opposite to the inlet 741b. Since the molecule 709 is an uncharged (neutral) molecule, the molecule 709 that is not ionized by the electron beam 411 can usually reach the side of the second ionization part 702 opposite to the inlet 741b. When there is a gap 750, the molecule 709 can therefore be able to leave the second ionization part 702 (for example, if the molecule 709 does not experience a collision or experiences very little collision and can therefore move along a straight path), which can improve the contamination resistance of the ion source 700. When the molecule 709 is a molecule with a high probability of adhesion, this may be particularly useful because the gap 750 can prevent the molecule 709 from contaminating the surface of the surrounding wall 731b opposite to the inlet 741b. The illustrated gap 750 is only exemplary and may be larger or smaller than illustrated. In addition, although not shown, an optional gap may also or alternatively be present in the surrounding wall 731a opposite to the inlet 741a.

[0115] A waste receiver (not shown) for molecule 709 may additionally or alternatively be placed relative to inlet 741b. Similarly, a waste receiver for molecule 708 may also or alternatively be placed relative to inlet 741a. The waste receiver or dumping device may be removable. This may mean that the waste receiver can be cleaned by removing the waste receiver from the ion source 700. Therefore, the ion source 700 can be more easily cleaned and can clean small areas that are not easy to clean via known methods (such as, for example, in-situ cleaning). The waste receiver can be implemented by a cylindrical element with one end closed. The waste receiver may be present in any ion source implementation discussed herein.

[0116] At elevated pressure (e.g., at 1×10 -4 and 1×10 -2 Operating the two ionization regions 701, 702 in a range between 100 and 100 mbar may enable the local pressure of each molecular species 708, 709 to be enhanced. For example, different local pressures may be required for efficient ionization of different molecular species. Providing two or more ionization regions, the pressures within which may be individually controlled, may improve the overall ionization efficiency.

[0117] The ionization regions 701, 702 can be configured between high vacuum and high pressure operating modes. For example, the ion source 700 can be configured so that one or more ionization volumes operate under high vacuum conditions. Therefore, the first molecular species and / or the second molecular species can emerge from the inlet 741a and / or 741b to form a beam along an axis that crosses or intersects the axis of the electron beam 411. Providing two or more ionization regions (the pressures within which can be controlled separately) can allow for improved control of ionization efficiency and / or ion source electrode contamination.

[0118] Still refer to Figure 7In sector field mass spectrometry, ions are typically accelerated before entering the magnetic and / or electrostatic sectors and then reaching one or more detectors. This can be achieved by applying a potential to the ion source and maintaining the one or more detectors at ground potential. Positive ions will be accelerated by the potential drop between the ion source and the one or more detectors.

[0119] Figure 7 , wherein the potential U is indicated along the ion source axis z. The potential may typically be 3000 V, but other potential values ​​may also be used. The potential within the ionization regions 701, 702 may be constant, or substantially constant, with a small potential difference (e.g., 5 V or less) to facilitate ion entry into subsequent regions. The potential may begin to decrease in the region of the extraction electrodes E1 and E2. Thus, positive ions may be accelerated to leave the ion source by the decrease in potential, while negatively charged electrons experience a change in potential as the potential increases and may be reflected back in the direction of the source cathode.

[0120] As mentioned above Figure 4 As discussed, negative ions may be produced instead of positive ions. In this case, the voltage applied to electrode E2 should be positive relative to the voltage applied to electrode E1 to extract negative ions from the ionization volume 702. In other words, the potential may begin to increase in the region of extraction electrodes E1 and E2 to accelerate negative ions to leave the ion source. In order to prevent electrons from also being accelerated and attracted out of the ionization volume 702 (because they have the same polarity as negative ions), one or more magnets may be used to generate a magnetic field to deflect the electrons away from the first axis (the first axis may correspond to the ion source axis). In one example, the magnetic field may deflect the electrons away from the first axis before the electrons reach the region between electrodes E1 and E2. For example, the magnetic field may deflect the electrons away from the first axis in the ionization volume 702 in the region near extraction and / or reflection electrodes E1 and E2.

[0121] Since an axial magnetic field can be applied to the ion source to guide electrons and ions along a common axis of the ion source (e.g., Figure 4 As discussed above, the deflection magnetic field may include a modification of the axial magnetic field. In another example, the deflection magnetic field may be a separate magnetic field (eg, generated by a different magnet).

[0122] In this implementation, the electrons may not be transferred back to the cathode, but may pass through the ionization volume only once. Note that this implementation still corresponds to an axial ion source, since the electron beam axis is still parallel to the ion beam axis (even though the electrons may be deflected away from the first axis before reaching the extraction and / or reflection electrodes E1 and E2).

[0123] Ions may thus be extracted from the ion source 700 while electrons are deflected away from the ion source outlet 412. This is because, although the magnetic field may deflect electrons away from the first axis, (negative) ions may not be deflected (or may not be significantly deflected) away from the first axis due to their greater mass.

[0124] Different implementations of the dedicated ionization regions may be combined. Various combinations may achieve specific benefits, such as reduced or limited ion source electrode contamination and high ionization efficiency.

[0125] For example, Figure 8 An exemplary ion source is illustrated in which an ionization volume and a directed molecular beam are achieved. The ion source 800 may have an ambient vacuum, which may be a high vacuum. In the ion source 800, a first molecular species 708 may be received into the ionization volume 701 via an inlet 741a. The at least partially enclosed ionization volume 701 may enable the first molecular species 708 to achieve a high ionization efficiency.

[0126] The second molecular species can be received into the second ionization region 602 as a directed molecular beam 642b, which can be achieved by setting the second ionization region 602 as a high vacuum region. Although the second ionization region 602 is illustrated as an open (non-enclosed) region, it should be understood that there may be separation or surrounding elements (e.g., walls). In addition, although not shown, as with respect to Figure 6 and Figure 7 The waste receptacle in question may be positioned opposite the inlet 641b.

[0127] A second molecular species, which preferably comprises neutral calibrant gas molecules, may emerge from inlet 641b to form beam 642b along an axis that crosses or intersects the axis of electron beam 411. Although the ionization efficiency of the second molecular species may be lower than the ionization efficiency of the first molecular species accumulated within first ionization volume 701 (because the pressure in second ionization volume 602 may be lower), a sufficient number of calibrant ions may still be supplied to a mass analyzer or another downstream element.

[0128] The directional beam 642b can allow the second molecular species to minimize contact with the extraction electrodes E1, E2. This can be particularly useful when the second molecular species is a calibrant molecule with a high probability of adhesion (such as PFK or PFTBA). Electron reflection and ion extraction between electrodes E1 and E2 can also preferably be performed in a (high) vacuum. The mechanical dimensions of electrodes E1 and E2 can be determined by electronic and / or ion optical considerations.

[0129] Additionally, setting the second ionization region 602 to a high vacuum region can achieve a more monoenergetic distribution of ion kinetic energy. Figure 7), ions generated in this region may not receive the full acceleration voltage (e.g., 3000V) that ions generated in other regions (e.g., the first ionization region 701 or the portion of the receiving electron beam 411 toward the second ionization region 702) may receive. Therefore, ions generated in the extraction electrode region may not pass through or be focused into downstream elements of the analytical instrument. For example, the ions may not pass through one or more sector field instruments and / or may not reach one or more detectors. However, by setting the second ionization region 602 as a high vacuum region, the generation of ions in the extraction electrode region can be suppressed. Therefore, the proportion of ions generated in the second ionization region 602 that receive the full acceleration voltage can be greater. This may result in a less extensive distribution of kinetic energy of the ions, which in turn can improve the focusing of the ions to the downstream elements of the analytical instrument.

[0130] In another example, the first ionization region 701 and the second ionization region 602 can be reversed so that the ionization region closer to or adjacent to the electron lens 404 can receive the directed molecular beam and the second ionization is the ionization volume. In this case, the directed beam can allow the contact of the first molecular species with the electron lens electrode 404 to be minimized and the ionization efficiency of the second molecular species to be increased.

[0131] As mentioned above Figure 4 As discussed, more than two separate ionization regions may be implemented. Fig. 9 An exemplary embodiment including three ionization zones is illustrated in Figure 5B , Figure 6 and Figure 8 The embodiments discussed have similarities. In this exemplary embodiment, the ion source 900 includes two beam intersection ionization regions 901, 903, wherein molecules are directed along an axis that intersects the electron beam axis. Thus, at least some of the molecules received from the respective inlets 941a, 941b can be ionized by the intersection of the molecular beams 942a, 942b with the electron beam 411.

[0132] exist Fig. 9, another ionization region 902 is included between the two ionization regions 901, 903. However, it should be understood that the another ionization region 902 may be included elsewhere in the ion source 900. The another ionization region 902 is an ionization volume at least partially surrounded by a surrounding wall 931, and may be an ionization chamber. The surrounding wall 931 may mean that molecules may be received into the another ionization region 902 along any axis and still be ionized by the electron beam 411 without the risk of contaminating the ion source electrodes 404 and / or 406. In addition, the surrounding wall 931 may allow an increase or increase in the gas pressure within the ionization region 902, which may increase the ionization efficiency within the another ionization region 902. When the another ionization region 902 includes a conductivity-limited ionization chamber, the ionization efficiency may be further improved. For example, the conductivity-limited ionization chamber may be closed except for the holes from which particles (generally electrons) and molecules (usually ions and neutral molecules, but may include atoms) enter and leave the ionization volume.

[0133] Fig. 9 The arrangement of the ionization regions 901, 902, 903 in may be particularly beneficial for achieving high ionization efficiency while avoiding or reducing electrode contamination. The arrangement may also be particularly useful for experiments that require locking mass during measurement.

[0134] In one example, the molecules introduced into each zone 901, 902, 903 may be of the same species. Thus, the molecules may be efficiently ionized in the other ionization zone 902, as well as ionized in both ionization zones 901, 903, with limited or reduced contamination of the electrodes 404, 406. Thus, a greater number of molecules may be ionized without a corresponding increase in electrode contamination.

[0135] In another example, some of the molecules received may be of different species. For example, the molecules received into one or both of the two ionization regions 901, 903 may be calibrant molecules. The calibrant molecules may also be of different species. Providing the calibrant molecules along an axis that intersects the electron beam axis may reduce or prevent contamination of the electrodes 404, 406. This arrangement may also result in less frequent cleaning of other portions of the ion source 900 (e.g., if the waste receiver is disposed along the axis relative to one or both of the inlets 941a and / or 941b).

[0136] refer to Fig.10, shows a graph illustrating the difference in peak shape obtained using a sector field mass analyzer for a conventional axial ion source compared to an axial ion source having extraction electrodes E1 and E2 placed in a high vacuum to minimize ionization in the region. One problem that may occur with an axial ion source is that the distribution of ion kinetic energy may generally be much wider than the distribution of ions generated in a Nier-type ion source. For example, ions generated in a region adjacent to extraction electrodes E1 and E2 may have lower kinetic energy than most ions generated in the ionization region. An ion beam with a wide distribution of ion kinetic energy may be only partially focused into a detector of a mass analyzer. Therefore, a certain percentage of ions from the ion beam are ignored from the measurement, which may affect the accuracy of the measurement. For example, the measurement of isotope ratios may be inaccurate. The wide distribution of ion kinetic energy may be a particular problem with a single focusing sector field mass analyzer, in which only a single magnetic sector can be used to separate ions based on their mass-to-charge ratio.

[0137] Incomplete focusing of the ion beam into the detector may result in inaccurate peak shapes, for example, peaks without a flat peak plateau. Fig.10 However, by providing a high vacuum region near the extraction electrodes E1, E2, the generation of ions in the region around the extraction electrodes E1, E2 can be suppressed. Therefore, the distribution of ion kinetic energy can be more monoenergetic. Fig.10 The dashed line in exemplifies the peak shape after reducing the pressure in the region near the extraction electrodes E1 and E2 (in other words, providing a higher vacuum region). Fig.10 As can be seen in FIG. 1 , when the region near the extraction electrodes E1 and E2 is a high vacuum region, the peak shape is improved compared to the high pressure ionization region. Therefore, an ion source geometry that can prevent most molecules from being ionized near the electrodes E1 and E2 (such as, for example, Figure 8 ) can enable a more monoenergetic ion source, in addition to or instead of enabling neutral molecules to be kept away from ion source electrodes 404 and / or 406. A less broad distribution of ion kinetic energy (more monoenergetic) can result in improved focusing of the ion beam into a detector or another downstream element of a mass analyzer.

[0138] Fig.11Schematically illustrated is a mass spectrometer in which the ion source of the present disclosure can be utilized. The mass spectrometer 1000 may include an ion source 1010, at least one mass analyzer 1020, and one or more detectors 1030. At least one mass analyzer 1020 may include a multipole mass analyzer (such as, for example, a quadrupole mass analyzer), a sector field mass analyzer, and / or another type of mass analyzer. At least one detector 1030 may include a Faraday cup, at least one secondary electron multiplier (SEM) detector, and / or other detectors. The ion source 1010 may include an ion source 400, 500A, 500B, 600, 700, 800, or 900 as described above. Although not shown, there may be interface components for docking between the ion source 1010, at least one mass analyzer 1020, and the detector 1030. For example, there may be components and / or other components for transmitting, guiding, and / or storing ions.

[0139] The present disclosure may also provide for the use of an electron bombardment ion source. The use may include any one or more of the features discussed herein. For example, the first molecule and / or the second molecule may include a calibrant molecule, and optionally, the calibrant molecule may include perfluorokerosene (PFK) or perfluorotributylamine (PFTBA).

[0140] It should be understood that although examples of ion sources have been described above primarily in the context of electron ionization, the ion sources disclosed herein may additionally or alternatively be configured for another form of ionization. For example, chemical ionization is a technique that also employs an electron beam. Similarly, it should be understood that although examples of ion sources have been described above generally with reference to an electron beam generating positive ions, it should be understood that the polarity of the ions and / or beam may be reversed. For example, negative chemical ionization may be used to generate negative ions, or an electron beam may be used to generate negative ions. As described above with reference to Figure 7 As discussed, an increased potential can therefore be used to extract negative ions from an ion source. In the case of using an electron beam (or using other negatively charged particles, such as in a negative ion beam), a (modified) magnetic field can be employed to prevent electrons from being extracted.

[0141] The methods described herein may be implemented using computer system configurations including handheld devices, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, etc. The embodiments may also be practiced in distributed computing environments where tasks are performed by remote processing devices linked through a network.

[0142] The computer system may include a processor, such as a central processing unit (CPU). The processor may execute logic in the form of a software program. The computer system may include a memory including volatile and non-volatile storage media. The different parts of the system may be connected using a network (e.g., a wireless network and a wired network). The computer system may include one or more interfaces. For example, the computer system may contain a suitable operating system, such as UNIX (including Linux) or Windows (RTM).

[0143] Certain embodiments may also be implemented as computer-readable codes on non-transient computer-readable media. Computer-readable media is any data storage device that can store data that can be read by a computer system thereafter. Examples of computer-readable media include hard disk drives, network attached storage (NAS), read-only memory, random access memory, CD-ROM, CD-R, CD-RW, magnetic tapes, and other optical and non-optical data storage devices. Computer-readable media may also be distributed on network-coupled computer systems so that the computer-readable code is stored and executed in a distributed manner. Although embodiments according to the present disclosure have been described with reference to specific types of devices and applications (particularly mass analyzers and spectrometers) and the embodiments have specific advantages in this case, as discussed herein, methods according to the present disclosure may be applied to other types of devices and / or applications. Unless otherwise specified, each feature disclosed in this specification may be replaced with an alternative feature for the same, equivalent, or similar purpose. Therefore, unless otherwise specified, each feature disclosed is only an example of a series of equivalent or similar attribute features.

[0144] All aspects and / or features disclosed in this specification may be combined in any combination, except for at least some mutually exclusive combinations of such features and / or steps. Specifically, the preferred features of the present disclosure are applicable to all aspects and embodiments of the present disclosure and may be used in any combination. Similarly, features described in non-essential combinations may be used alone (not in combination).

[0145] The methods and apparatus of the present disclosure may be utilized with various electrode structures. Individual electrodes may be planar, hemispherical, rectangular, or other shapes. The electrodes may be PCB printed electrodes.

[0146] It should be understood that there is an implicit "about" before the temperature, concentration, time, pressure, flow rate, cross-sectional area, voltage, current, etc. discussed in the present teachings, so that there are slight and insubstantial deviations within the scope of the present teachings. In addition, the values ​​referred to as "equal" may actually differ by less than a threshold amount. For example, the threshold amount may be 5%. The threshold may also be greater than 5% (e.g., 10%, 20%, or 50%) or less than 5% (e.g., 2% or 1%).

[0147] As used herein, including in the claims, unless the context indicates otherwise, the singular form of the terms herein should be interpreted as including the plural form, and vice versa. For example, unless the context indicates otherwise, a singular reference herein, such as "an" (such as, an electrode) included in the claims means "one or more" (e.g., one or more electrodes).

[0148] In the specification and claims of the present disclosure, the words "comprise", "include", "have" and "contain" and variations of these words, for example, "include" and "includes" or similar words mean "including but not limited to", and are not intended to (and do not) exclude other components. In addition, 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. In addition, the use of terms in brackets is inclusive, such that the phrase "(C)D" is true when "D" is true, or both "C" and "D" are true. For example, the term "(high) vacuum" may refer to "high vacuum" or "vacuum".

[0149] The use of any and all examples or exemplary language ("such as", "for example", "for example" and similar language) provided herein is intended to better illustrate the present disclosure only and does not indicate a limitation on the scope of the present disclosure unless otherwise required. No language in this specification should be construed as indicating any non-required element necessary to practice the present disclosure.

[0150] The terms "first" and "second" may be reversed, or referred to by different numerical designators, without changing the scope of the invention. That is, an element referred to as a "first" element (e.g., first ionization region 401) may alternatively be referred to as a second element (e.g., second ionization region 401), and an element referred to as a "second" element (e.g., second ionization region 401) may alternatively be considered a "first" element (e.g., first ionization region 401).

[0151] Unless otherwise specified or the context otherwise requires, any steps described in this specification may be performed in any order or simultaneously. In addition, where a step is described as being performed after a step, this does not exclude intermediate steps being performed.

[0152] It should also be understood that, unless otherwise implicitly or explicitly understood or stated, for any given component or embodiment described herein, any possible candidates or alternatives listed for that component may generally be used alone or in combination with each other. It should be understood that any list of such candidates or alternatives is merely illustrative and not restrictive, unless otherwise implicitly or explicitly understood or stated.

[0153] In the detailed description of various embodiments, for the purpose of explanation, many specific details are set forth to provide a thorough understanding of the disclosed embodiments. However, those skilled in the art will appreciate that these various embodiments may be practiced with or without these specific details. In addition, those skilled in the art can readily appreciate that the specific order in which the methods are presented and executed is illustrative, and it is contemplated that the order may be changed and still remain within the scope of the various embodiments disclosed herein.

[0154] All literature and similar materials cited in this application, including but not limited to patents, patent applications, papers, books, monographs, and internet web pages, are expressly incorporated by reference in their entirety for any purpose. Unless otherwise defined, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which the various embodiments described herein belong.

Claims

1. An electron bombardment ion source, the electron bombardment ion source include: a first electron bombardment ionization region, the first electron bombardment ionization region comprising an aperture configured to receive a first molecule into the first ionization region, the first ionization region being configured to receive an electron beam along a first axis to generate a first ion beam from the first molecule along the first axis; and A second separate electron impact ionization region including an inlet configured to receive a second molecule into the second ionization region, the second ionization region being configured to receive the electron beam along the first axis to generate a second ion beam from the second molecule along the first axis.

2. The electron bombardment ion source according to claim 1, wherein the inlet is configured to receive the second molecule along a second axis intersecting the first axis to ionize the second molecule, and / or the hole is configured to receive the first molecule along a receiving axis intersecting the first axis to ionize the first molecule.

3. The electron bombardment ion source according to claim 1 or claim 2, wherein the second ionization region is spatially separated from the first ionization region so that the first molecules are mainly ionized in the first ionization region and the second molecules are mainly ionized in the second ionization region.

4. An electron bombardment ion source according to any preceding claim, wherein the ion source further comprises a separation element between the first ionization region and the second ionization region, wherein the separation element preferably at least partially surrounds one or both of the first ionization region and the second ionization region.

5. An electron bombardment ion source according to any preceding claim, wherein at least one of the first ionization region and the second ionization region is an ionization chamber, and / or at least one of the first ionization region and the second ionization region is configured to operate under vacuum. The electron bombardment ion source according to claim 5 , wherein the vacuum is a high vacuum or an ultra-high vacuum.

7. The electron bombardment ion source according to claim 6, wherein the electron bombardment ion source is configured so that the mean free path of the first molecule and / or the second molecule is more than half of the length of the corresponding first ionization region and / or second ionization region along the dimension parallel to the first axis.

8. The electron bombardment ion source according to claim 7, wherein the mean free path is greater than the length or at least ten times the length.

9. An electron bombardment ion source according to any preceding claim, wherein The first ionization region and / or the second ionization region are configured such that: The extent of the respective first and / or second molecules along the dimension parallel to the first axis is less than the length; and / or The extent of the respective first molecule and / or second molecule does not intersect the plane of the one or more ion source electrodes.

10. The electron bombardment ion source according to any one of claims 2 to 9, in: The second ionization region is configured such that the second axis does not intersect the plane of the one or more ion source electrodes; and / or The first ionization region is configured such that the receiving axis does not intersect the plane of the one or more ion source electrodes.

11. The electron bombardment ion source according to any one of claims 2 to 10, wherein the second axis is perpendicular to the first axis.

12. An electron impact ion source according to any preceding claim, wherein the first molecule and / or the second molecule comprises a calibrant molecule, wherein the calibrant molecule preferably comprises perfluorokerosene (PFK) or perfluorotributylamine (PFTBA).

13. The electron bombardment ion source according to any one of claims 2 to 12, further comprising a waste receiver positioned along the second axis to receive unionized molecules, and / or further comprising a waste receiver positioned along the receiving axis to receive unionized molecules.

14. The electron bombardment ion source of claim 13, wherein at least one of the waste receptacles positioned along the second axis and the receiving axis is removable.

15. An electron impact ion source according to any preceding claim, further comprising one or more magnets configured to generate an axial magnetic field to guide electrons and ions along a common axis.

16. A method for electron ionization, the method comprising: include: receiving an electron beam into a first ionization region along a first axis and generating a first ion beam from the electron beam along the first axis from first molecules in the first ionization region; The electron beam is received along the first axis into a second separate ionization region and a second ion beam is generated from the electron beam along the first axis from second molecules in the second ionization region.

17. The method according to claim 16 further includes receiving a second molecule into the second ionization region along a second axis intersecting the first axis to generate the second ion beam and / or receiving a first molecule into the first ionization region along a receiving axis intersecting the first axis to generate the first ion beam.

18. A method according to claim 16 or claim 17, in: The second ionization region is spatially separated from the first ionization region such that the first molecule is primarily ionized in the first ionization region and the second molecule is primarily ionized in the second ionization region; and / or A separation element is arranged between the first ionization region and the second ionization region; and / or Wherein at least one of the first ionization region and the second ionization region is an ionization chamber.

19. The method of any one of claims 16 to 18, further comprising operating the first ionization region and / or the second ionization region under vacuum.

20. The method of claim 19, wherein the vacuum is a high vacuum or an ultra-high vacuum.

21. The method of claim 20, wherein the mean free path of the first molecule and / or the second molecule is more than half of the length of the first ionization region and / or the second ionization region along a dimension parallel to the first axis, greater than the length or at least ten times the length.

22. The method according to any one of claims 17 to 21, in: The first molecule and / or the second molecule has an extent along the dimension that is smaller than the length; and / or The extent of the first molecule and / or the second molecule does not intersect the plane of one or more ion source electrodes; and / or The second axis does not intersect the plane of the one or more ion source electrodes; and / or The reception axis along which the first molecule is received into the first ionization region does not intersect the plane of the one or more ion source electrodes.

23. The method of any one of claims 16 to 22, wherein the first molecule and / or the second molecule comprises a calibrant molecule.

24. A computer program comprising instructions which, when executed by a computer, cause the computer to control an analytical instrument comprising an electron impact ion source to perform a method according to any one of claims 16 to 23.

25. A controller configured to operate an analytical instrument comprising an electron impact ion source according to the method of any one of claims 16 to 23.

26. An analytical instrument comprising the electron bombardment ion source according to any one of claims 1 to 15.

27. The analytical instrument of claim 26, wherein the analytical instrument comprises a mass spectrometer.

28. A system comprising an analytical instrument according to claim 26 or 27 and a controller according to claim 25.

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