Axial ion source

Abstract

To provide an electron impact ion source.SOLUTION: An electron impact ion source includes a first ionization region including an opening configured to accept a first molecule within the first ionization region configured to accept an electron beam along a first axis to generate a first ion beam along the first axis from the first molecule, and a second separate ionization region including an entrance configured to accept a second molecule within a second ionization region configured to accept the electron beam along the first axis to generate a second ion beam along the first axis from the second molecule.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates generally to the generation of ions 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 technology]

[0002] In electron impact (EI) ion sources (also known as electron ionization ion sources), electrons are typically emitted from a heated filament and accelerated into an ionization chamber containing sample gas molecules. The sample gas molecules are ionized by the electron impact and extracted from the ionization chamber using an extraction electrode. Most EI sources employ one or more permanent magnets to focus and direct the ionizing electron beam through the ionization chamber.

[0003] A classic EI source is the cross-beam ion source (Nier-type ion source), an example of which is described in I. G. Brown, The Physics and Technology of Ion Sources, Wiley, 2004. A typical cross-beam ion source is illustrated in FIG. 1. In these EI sources, a positive voltage is typically applied between the pusher electrode P and the extraction electrode E to accelerate and focus the generated ions through a slit in the extraction electrode E. Ions generated near the aperture where the electrons enter the ionization chamber are drawn into the aperture, while ions generated at a greater distance from the ion beam axis do not pass through the slit in the extraction electrode E. As a result, only a small portion of the ions generated in region R in FIG. 1 are extracted from the ion source and made available to the mass spectrometer.

[0004] A more 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 Park et al, Effect of magnetic field in electron-impact ion sources and simulation of electron trajectories, Review of Scientific Instruments 77. A schematic of ion extraction from an axial ion source is shown in Figure 2. A positive voltage is applied between the two extraction electrodes E1 and E2, which simultaneously extracts ions from the ionization chamber and directs electrons back towards the heated filament. In this configuration, the ionization chamber is the region between the pusher electrode P and the extraction electrode E1. A small positive voltage can be applied between the pusher electrode P and the extraction electrode E1 to draw ions into the ion source exit. This can also prevent ions from being drawn into the hole in the pusher electrode where the electrons enter the ionization chamber.

[0005] The ion extraction efficiency can be improved by using an axial ion source compared to a Nier type ion source, since the generated ions travel along the ion source axis and can be prevented from being drawn into the hole. The high extraction efficiency of an axial ion source can correspond to high sensitivity, which can be useful, for example, in gas chromatography mass spectrometry (GC-MS). In GC-MS, an axial ion source can be used, for example, in a quadrupole mass spectrometer or a sector magnetic field mass spectrometer.

[0006] US Patent No. 9,117,617 describes an ion source having a body with an ionization chamber positioned along the ion source axis and a lens assembly also positioned along the ion source axis. The lens assembly includes an extractor positioned at the end of the ionization chamber and a first lens element located outside the ionization chamber and spaced apart from the extractor along the ion source axis. The extractor directs the ion beam out of the ionization chamber along the ion source axis, and the first lens element reflects the electron beam back towards the electron source. However, the electrodes of the ion source are prone to contamination by molecules introduced into the body. Furthermore, 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 gas inlet adapted to supply a sample gas to be ionized to an ionization region, a calibration unit adapted to supply a calibration gas to be ionized in the same ionization region, and an ionization unit adapted to ionize the sample gas and / or the calibration gas in the ionization region, the calibration unit comprising at least one evaporation source for generating the calibration gas by evaporating a source material. However, the ionization efficiency of the sample gas in this configuration is limited. Moreover, this configuration complicates or prevents the use of common calibration gases, such as perfluorokerosene or perfluorotributylamine.

[0008] US Patent No. 7,541,597 describes an in situ method for cleaning mass spectrometer ion source electrodes by plasma etching. A small amount of non-reactive ion etching ("sputtering") may also be used. However, this method does not work well for more complex ion source geometries, or for sources with small sized areas, since it relies on the plasma being able to reach the areas that need cleaning.

[0009] WO 2018 / 231631 relates to an ion source including a gas source, a nozzle, an electron source, and an electrode. The gas source delivers gas through a nozzle to an ionization chamber evacuated and is at a pressure higher than the pressure of the ionization chamber evacuated. The gas passing through the nozzle expands freely in an ionization region of the ionization chamber. The electron source emits electrons through the expanding gas in the ionization region to ionize at least a portion of the expanding gas. The electrode generates an electric field for ion flow from the ionization region to a mass filter, is located at a distance from the nozzle, and is oriented to limit the exposure of the electrode to the gas. However, the ionization efficiency of this configuration is not sufficient.

[0010] It would be desirable to overcome the problems set forth above. Summary of the Invention

[0011] It is against this background that a method and ion source for providing ions to a mass analyzer or another downstream element is provided. Additional aspects appear in the description and claims.

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

[0013] This EI source configuration may mean that the conditions in each ionization region may be allowed to be manipulated separately. This may allow for finer control of the EI source and may allow for benefits associated with different modes of operation to be achieved. For example, one ionization region may be operated to allow for high ionization efficiency while the other ionization region may be operated to allow for improved ion beam focusing. In another example, the pressure inside each ionization region may be individually controlled, which may allow for the ionization efficiency of molecules in each ionization region to be separately monitored and / or adjusted. This may improve the overall ionization efficiency of the EI source.

[0014] In a further example, providing two separate ionization regions may 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 may be kept away from the ion source electrode (e.g., by being introduced into an ionization region distal to the ion source electrode or by being introduced along a second axis). The ion source electrode may be one or more of 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] By reducing or limiting contamination, it may be possible to maintain long-term stability and high sensitivity of the ion source, since fewer ions may be lost on negatively charged areas. Thus, the regulation of the EI source (or analytical equipment including the EI source) may be made more robust. Furthermore, the lifetime and analytical robustness of high sensitivity settings may be improved, perhaps by about 5 times or more. Also, the risk of the electron beam being blocked by negative charge accumulation may be reduced. Furthermore, more complex geometries may be kept clean (or less contaminated) without the need for regular cleaning sessions, which may allow for higher sample throughput and ease of use. Thus, the cost of analysis may also be reduced.

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

[0017] This disclosure also relates to another consideration of axial EI ion sources (which may be combined with the previous discussion). A flow of molecules is provided in a first ionization volume of an EI source configured to receive an electron beam along a first axis and to operate at high or ultra-high vacuum. An ion beam is generated along the first axis from the molecules in the first ionization volume. The electron beam is reflected back toward a receiving portion of the first ionization volume, and the ions may be 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 may form a (substantially) directed molecular beam. Thus, contamination of the EI source electrode may be limited, reduced, or prevented, since the molecules may not be directed toward the electrode. Furthermore, due to the high vacuum conditions, ion production in the region near the EI source electrode may be suppressed. This may result in a narrower (more monoenergetic) distribution of ion kinetic energies, 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, a first ionization region including an opening configured to receive a first molecule within the first ionization region, the first ionization region configured to receive the electron beam along a first axis to generate a first ion beam from the first molecule along the first axis; An electron impact ion source is provided that includes a second separate ionization region including an entrance configured to accept a second molecule into the second ionization region, the second ionization region configured to accept the electron beam along a first axis to generate a second ion beam along the first axis to ionize the second molecule.

[0020] Thus, an electron impact ion source may be provided that may enable the advantages discussed above.

[0021] According to a second aspect, receiving an electron beam into a first ionization region along a first axis and generating a first ion beam from the first molecules in the first ionization region with the electron beam along the first axis; A method of electron ionization is provided that includes receiving an electron beam along a first axis into a second separate ionization region and generating a second ion beam from second molecules along the first axis with the electron beam.

[0022] According to a third aspect, An electron impact ion source is provided that includes an ionization region including an opening configured to accept molecules within the ionization region, the ionization region configured to operate at high vacuum and to accept an electron beam along a first axis to generate an ion beam along the first axis from the molecules.

[0023] Thus, an electron impact ion source may be provided that may enable the advantages discussed above.

[0024] According to a fourth aspect, receiving an electron beam into an ionization region along a first axis and generating an ion beam from a first molecule in the first ionization region with the electron beam along the first axis; and operating the first ionization region at a high vacuum.

[0025] The electron impact ion source described above can be implemented in an analytical instrument.

[0026] The above-described methods may be implemented as a computer program comprising instructions for operating a computer or computer system. The computer program may be stored on a non-transitory computer-readable medium.

[0027] The computer or computer system (or other hardware and / or software configured to implement the methods) may be embodied as a controller configured to operate an analytical instrument. The above methods may be implemented in a system comprising an analytical instrument and a controller.

[0028] It should be noted that any feature described herein may be used with any specific aspect or embodiment described herein. Further, any combination of features of any specific device, structure, or method is provided even if the combination is not explicitly disclosed.

[0029] The invention will now be described with reference to the accompanying drawings which depict different embodiments thereof, the drawings being provided purely by way of example and not by way of limitation.

[0030] The invention may be put into practice in many ways and a preferred embodiment may hereinafter be described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0031] [Figure 1] 1 illustrates a schematic of a cross-beam (Nier type) ion source. [Diagram 2] 1 shows a schematic of an axial ion source. [Diagram 3] 1 illustrates a graph of the decrease in signal intensity of a triple quadrupole GC-MS / MS system exposed to a constant flow of PFTBA into the ion source over a period of several hours. [Figure 4] 1 illustrates a schematic of an ion source including two ionization regions. [Figure 5A] FIG. 2 shows a diagram of an ion source with two beam crossing ionization regions and an additional ionization region. [Figure 5B] 1 illustrates a schematic of an ion source comprising two beam intersecting ionization regions where accepted molecules are directed away from an ion source electrode, and an additional ionization region. [Figure 6] 1 is a schematic depiction of an ion source with two beam crossing ionization regions. [Figure 7] 1 illustrates generally an ion source with two ionization chambers and corresponding exemplary electrical potentials within the ion source. [Figure 8] 1 illustrates an embodiment of an ion source comprising an ionization chamber and a beam crossing ionization region. [Figure 9] 1 illustrates an embodiment of an ion source comprising two cross-beam ionization regions and a further ionization region disposed between the two cross-beam ionization regions. [Figure 10] 1 shows a graph illustrating the difference in peak shape for a conventional axial ion source compared to an axial ion source in which minimum ionization occurs in the region around extraction electrodes E1 and E2. [Figure 11] 1 illustrates generally an analytical instrument, such as (for example) a mass spectrometer, in which an ion source according to the present disclosure can be utilized.

[0032] It should be noted that the figures are illustrated in schematic form for simplicity and are not necessarily drawn to scale, and similar features are provided with the same (or similar) reference numbers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] In a typical ion source, the sample and calibrant molecules (usually in gaseous form) are introduced into a single ionization chamber of the ion source. The sample and calibrant molecules mix in the single ionization chamber and are 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 either reflected back through the extraction electrode (axial source) or collected on an electrode opposite the electron entrance aperture (cross-beam source). The calibrant molecules are typically of known atomic mass or mass-to-charge (m / z) ratio that produce calibration peaks that correspond to known m / z values ​​in the measured mass spectrum. The calibration peaks can then be used to determine the mass-to-charge ratio of peaks that correspond to unknown molecules.

[0034] When the sample and calibrant molecules are mixed in a single ionization chamber, the same operating conditions of the ion source are used to ionize both the sample and calibrant molecules. However, while certain operating conditions may be more beneficial for the sample molecules than the calibrant molecules, in conventional ion sources it is not possible to individually adjust the operating conditions for each set of molecules in the ionization region.

[0035] The increased gas pressure in the ionization chamber can increase the ionization efficiency in addition to the high extraction efficiency that can be obtained with an axial ion source. However, the increased gas pressure in the ionization chamber can also accelerate the contamination of the ion source electrodes. In particular, an insulating layer of sample and calibrant molecules can form on the ion source electrodes and then be charged by the impinging electrons. Ions can then be lost on these negatively charged regions. As an example, the circular region around the opening can be particularly susceptible to charging. Axial ion sources are particularly prone to ion loss on negatively charged regions because there is typically no substantial electric field gradient in the ionization chamber. In extreme cases, the negative charge can build up enough to completely block the electron beam.

[0036] 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 measurements. For example, calibration compounds such as PFK and PFTBA tend to strongly contaminate the ion source electrodes, leading to a visible coating forming on the electrodes.

[0037] A lock mass is an ion of known mass-to-charge ratio that can allow real-time recalibration by correction of m / z shifts resulting from instrument drift. The lock mass can allow the analytical instrument to rapidly shift to the relevant portion of the mass spectrum. This can be used to more quickly and easily analyze small regions around the peak center. This can be particularly useful for dioxin measurements, which can be performed using, for example, magnetic sector GC-MS instruments.

[0038] Supply of lock mass may be required throughout the analysis. For example, the US Environmental Protection Agency (EPA) Method 1613B is considered the "gold standard" for dioxin analysis. Method 1613B requires the use of a high-resolution GC-MS and continuous measurement of the PFK lock mass simultaneously with the measurement of the dioxin sample. To obtain a valid measurement, the signal strength of the PFK lock mass is stable as specified in Method 1613B. However, a constant flow of PFK into the ion source over several hours poses challenges for axial ion sources with closed ionization chambers. For example, the contamination problems discussed above may typically result in a decrease in signal strength over a period of time, which may make it impractical to use the lock mass or may require additional time and effort to correct for the decrease in signal strength. Thus, achieving an absolute standard may be difficult, especially after many experiments.

[0039] FIG. 3 illustrates the decrease in signal intensity of a triple quadrupole GC-MS / MS system exposed to a constant flow of PFTBA into the ion source over several hours. As can be seen from the results, the decrease in abundance after about one hour is significant. It is clear that it is difficult to achieve absolute standards using an axial ion source in current equipment. Although it may be possible to obtain measurements that comply with the 1613B standard using a cross-beam ion source (as the cross-beam ion source may be less susceptible to contamination), using a cross-beam source means forgoing the increased sensitivity that can be achieved with an axial ion source. It is therefore preferable to provide an axial ion source with a lower contamination rate.

[0040] FIG. 4 shows a schematic of an exemplary implementation of an ion source. The ion source 400 comprises an electron source 403, an electron lens (pusher electrode) 404, a first ionization region 401, a second ionization region 402, and a reflecting and extracting electrode 406. The ion source 400 may be surrounded by a vacuum environment (which may be high vacuum). The electron lens 404 and the reflecting and extracting 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, meaning 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 RF electric 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.

[0041] Both (static) magnetic and RF electric fields can be used to focus positively and negatively charged particles. However, RF electric fields may not allow both ions and electrons (which typically have a mass-to-charge ratio that is four orders of magnitude smaller than that of ions) to be confined simultaneously in the ion source 400. In particular, 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 sharply as it deviates from the ion guide axis. Thus, ions (positively or negatively charged) moving away from the ion guide axis move into a region of high RF electric field and are pushed back towards the ion guide axis as a result of many cycles of the oscillating RF electric field acting on the ions. In contrast, electrons (which are much lighter than ions) can move fast enough through the ion guide such that the RF electric field (which has a frequency in the MHz range) appears static to the electrons. Thus, rather than being focused along the ion guide axis, the electrons are simply deflected away from the ion guide axis and attracted towards the ion guide electrode that is positive (as the electrons are moving through the ion guide).

[0042] In other words, an RF electric field with a typical frequency in the MHz range may be used to bind ions in the ion source, but that same RF electric field is seen as more of a static field by the much faster moving electrons. As a result, the electrons may be deflected away from the ion source axis and attracted towards the RF multipole electrodes, which are positive as they move through the ion source. In contrast, the focusing effect of the magnetic field is stronger for lighter particles than for heavier particles. For example, magnets in an axial ion source can strongly focus electrons (electron beams) along the ion source axis, while having negligible focusing effect on the (much heavier) ions. Thus, using one or more magnets in an axial ion source may allow both ion beams and electron beams to be focused in the ion source.

[0043] 4, an electron beam 411 is emitted along a first axis from an electron source 403, which may comprise a cathode (not shown) configured for thermionic emission. For example, the cathode may comprise one or more filaments, which may be comprised of, for example, tungsten or rhenium wire (or alloys thereof). The cathode is heated to an incandescent temperature to emit electrons, which may typically be accomplished by passing an electric current through the cathode.

[0044] The resulting electron beam 411 may be focused into the first ionization region via the electron lens 404 (which may be any suitable electrode or electrodes for focusing the electron beam). In other words, the electron lens 404 may be configured to receive one or more voltages to generate an electric field, thereby directing or focusing the electron beam into the first ionization region. The electron lens 404 may also be configured to push ions out of the electron entrance aperture. The electron beam 411 is preferably collimated into the first ionization region by a magnetic field generated by one or more magnets, which may be permanent magnets or non-permanent (e.g., semi-permanent) magnets. For example, a disk-shaped magnet may be placed behind the electron source 403 to generate the magnetic field. Additional magnets may be used as well.

[0045] The use of one or more magnets can be useful in the electron impact ionization region because the electron impact converts molecules into positive ions, thus resulting in the presence of positive ions and negative electrons in the electron impact ionization region. The use of an RF electric field can cause electrons (which typically have a mass-to-charge ratio that is four orders of magnitude smaller than that of the ions) to be ejected from the ion source (because the RF field appears stationary relative to the fast moving electrons). In contrast, a magnetic field can allow both the ion beam and the electron beam 411 to be confined within the ion source 400, thus allowing both to enter the second ionization region 402.

[0046] The magnetic field is preferably applied parallel to the direction of the electron beam 411. The electrons may therefore travel along a spiral path, which may increase the path length of the electrons and thereby increase the probability of electron collisions.

[0047] A first molecule 408 (which may include a sample molecule to be analyzed or a calibration molecule) is introduced into the first ionization region 401 through a first opening or inlet, where ions may be generated by collisions between the neutral molecule and electrons in the electron beam 411. The collisions may result in positive ions or negative ions. For example, the electrons in the electron beam may cause a neutral molecule to release an electron due to the transfer of kinetic energy, resulting in a positive ion. In another example, the electrons may be captured by a neutral molecule, resulting in a negative ion.

[0048] The first ionization region 401 includes a first opening or inlet. The opening can be in the first ionization region 401 itself (e.g., an opening in a wall of the first ionization region 401), or the first ionization region 401 can include a component (which may also be referred to as a molecule delivery element) having an opening through which the first molecule 408 is received. For example, the first ionization region 401 can include a nozzle or tube (e.g., a capillary tube, etc.), or another component having an opening.

[0049] The first molecules 408 may be received into the first ionization region 401 as a stream or beam of molecules, and may be received from an analytical instrument, such as a gas chromatograph. A molecular beam may be generated by expanding a high pressure gas through a small opening into a chamber at a lower pressure.

[0050] The molecules 408 may be received as a (substantially) continuous stream of molecules for use as a lock mass. The decrease in signal intensity of the continuous stream over a period of time may be less than 10%, 5%, 1%, or another value. This period of time may be on the order of a few hours, for example, 5-10 hours.

[0051] The electron beam 411 ionizes the first molecule 408 in the first ionization region 401, and a resulting ion beam 407 of first ions is generated along a first axis. That is, both the electron beam and the ion beam 407 travel along the first axis. Because the first ionization region 401 is configured for electron impact ionization, the first ionization region 401 may also be referred to as the "first electron impact ionization region 401." The ion beam 407 may be considered to include a "first ion beam" because a beam of ions is generated from the first molecule. The ion beam 407 or first ion beam is guided to the second ionization region 402. A second molecule 409 (which may be a sample molecule to be analyzed, a calibration molecule, or a lock mass) is introduced into the second ionization region 402. The second molecule 409 may also be received into the second ionization region 402 through a second opening or inlet, or as a beam of molecules. The second molecule 409 may be received from an analytical instrument, such as a gas chromatograph.

[0052] The second ionization region 402 includes a second opening or inlet. The second opening can be in the second ionization region 402 itself (e.g., an opening in a wall of the second ionization region 402), or the second ionization region 402 can include a component (which may also be referred to as a molecule delivery element) having an opening through which the second molecule 408 is received. For example, the second ionization region 402 can include a nozzle or tube (e.g., a capillary tube, etc.), or another component having an opening.

[0053] The electron beam 411 ionizes the second molecules 409 in the second ionization region 402. In other words, the ion beam 407 further includes the second ions. Because the second ionization region 402 is configured for electron impact ionization, the second ionization region 402 may also be referred to as the "second electron impact ionization region 402." Thus, the ion beam 407 may be considered to include the first ion beam and a "second ion beam" generated from the second molecules. The electrode 406 (which may be within the second ionization region 402 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 in the second ionization region 402 from the first ionization region 401) and a voltage to reflect the electron beam 411.

[0054] The first and second molecules 408, 409 are ionized in the respective first and second ionization regions 401, 402 to generate an ion beam 407 along a first axis. The ion beam 407 can be fed to a mass analyzer or downstream components. A (small) positive voltage can be applied between the electron lens 404 and the reflecting / extracting electrode 406 to move the positive ions towards the ion source outlet 412. In other words, an axial gradient can be applied between the electron lens 404 and the reflecting and extracting electrode 406. The positive voltage can also prevent the ions from being drawn into the hole of the electron lens 404 where the electrons enter the first ionization chamber 401. In the example where negative ions are generated, a (small) negative voltage can be applied between the electron lens 404 and the reflecting and / or extracting electrode 406.

[0055] 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) that intersects the first axis. In other words, the flow of the molecules 408 and / or 409 may overlap with the electron beam 411 received in at least one ionization region. The first molecule and / or the second molecule 408 and / or 409 may be efficiently ionized by the electron beam 411 as a result of the intersection of the second axis with 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 or in contact with the ion source electrodes 404 and / or 406. Thus, contamination of the ion source electrodes 404 and / or 406 may be prevented or reduced.

[0056] In other words, an electron impact ion source may be provided that includes a first ionization region including an opening configured to accept a first molecule within the first ionization region, the first ionization region configured to accept an electron beam along a first axis to generate an ion beam along the first axis from the first molecule, and a second separate ionization region configured to accept the electron beam along the first axis, the second ionization region including an inlet configured to accept a second molecule into the second ionization region along a second axis that intersects the first axis to ionize the second molecule.

[0057] A corresponding method of electron ionization may be provided, comprising receiving an electron beam into a first ionization region along a first axis and generating an ion beam along the first axis from a first molecule in the first ionization region with 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 and generating an ion beam along the first axis from the second molecule.

[0058] Preferably, the second axis may be perpendicular to the first axis. Thus, a simple configuration may be provided that may limit, prevent, or reduce contamination of the ion source electrodes 404 and / or 406. In another example, the crossing angle may be selected based on the location of the ion source electrodes 404 and / or 406 relative to the ionization region where the molecules 408 and / or 409 are received along the second axis. The crossing angle may be selected, for example, to direct the molecules away from the plane of the ion source electrodes 404 and / or 406.

[0059] Although 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 crossing angle may be selected such that the direction of travel of the molecular beam is at least partially reverse (opposite) to the electron beam direction of travel. At least partially reverse may mean that the vector components of the molecular beam direction of travel are antiparallel (opposite the direction of the vector components) to the vector components of the electron beam direction of travel. Preferably, the direction of travel may be at least partially reverse to the electron beam direction of travel when the ionization region 402 is adjacent to the extraction and reflection electrode 406. Thus, the molecular beam may be at least partially directed towards the electron lens 404, but contamination of the electron lens 404 may still be avoided, reduced, and / or limited. For example, the crossing angle may be such that the second molecule cannot or is unlikely to reach the ion source electrode. The angle may be, for example, 70 to 90 degrees. Additionally or alternatively, the length d of the ionization region 402 may be large enough such that the second molecule 409 does 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, such that the second molecule cannot or is unlikely to reach the ion source electrode as well. Other configurations are possible that may mean that contamination of the electron lens 404 can be reduced or limited.

[0060] In another example, the intersection angle may be selected such that the molecular beam direction of travel 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 may mean that a vector component of the molecular beam direction of travel is parallel to a vector component of the electron beam direction of travel (the vector components have the same direction). As discussed above with respect to the electron lens 404, the molecular beam may be at least partially directed towards the extraction and repeller electrode 406, but contamination of the extraction and repeller electrode 406 may still be avoided, reduced, and / or limited.

[0061] In addition to or instead of receiving molecules 408 or 409 along the second axis, one or both of the ionization regions 401, 402 may be configured to operate in a high vacuum. Stated another way, an axial ion source may be provided in which a portion of the electron beam is disposed in a high vacuum. The high vacuum may be achieved by use of a vacuum pump (or a vacuum pump in series) which may be connected (directly or indirectly) to at least one of the ionization regions. When the ionization regions are configured to operate in a high vacuum, there may be only one ionization region.

[0062] A high vacuum corresponds to a lower pressure in the ionization region (compared to the pressure range conventionally used in the ionization region), which may reduce the probability of generating ions from the electron beam 411. Thus, a high vacuum region may result in less ionization (although sufficient ionization efficiency may be maintained or improved, for example, by introducing molecules along the second axis). This in turn may allow for efficient 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 at high vacuum may also be configured to receive the molecules 408 and / or 409 along the second axis. This may allow for a particularly efficient prevention or reduction of contamination, since the molecules may not be directed towards the electrodes 404 and / or 406 and the probability of reaching the electrodes 404 and / or 406 may be reduced.

[0063] The vacuum may be a high or ultra-high vacuum, which may improve the reduction or prevention of contamination. The ion source 400 may be configured to operate in a high or ultra-high vacuum in one or more ways. In one example, the at least one ionization region 401 and / or 402 may be configured such that the length d of the at least one ionization region 401 and / or 402 along a dimension parallel to the first axis is less than twice the mean free path of the molecules 408 and / or 409. In other words, the mean free path of the molecules 408 and / or 409 may be greater than half (0.5 times) the length d of the at least one ionization region 401 and / or 402. Thus, the molecules 408 and / or 409 may travel in a straight line to form a substantially directed beam of molecules. Thus, the molecules 408 and / or 409 may not be deflected by collisions with other molecules and may therefore be less likely to contaminate the ion source electrodes. Preferably, the mean free path is greater than the length d, and most preferably, is at least ten times greater than the length d.

[0064] Optionally, at least one of the ionization regions has a pressure of 0.1 Pa (1×10 -3 mbar) or less, or -6 Pa(10 -8 As defined in ISO 3529-1:2019, high vacuum is defined as a pressure below 1×10 -6 Pa~0.1Pa (1×10 -8 mbar~1×10 -3 mbar), and ultra-high vacuum can be correlated to pressures in the range of 1×10 -9 Pa~1×10 -6 Pa(1×10 -11 mbar~1×10 -8The pressure range may correspond to a pressure in the range of 10 to 100 mbar. However, it will be appreciated that the pressure range corresponding to high or ultra-high vacuum may depend on various factors, such as, for example, the dimensions of the ionization chamber, the temperature within the ionization chamber, and the molecular species in the ionization region, and therefore other pressure ranges may be used. For molecules with larger collision cross sections, such as PFK or FC43, the pressure in the ionization region may be in the range of 10 to 100 mbar to avoid or sufficiently reduce collisions. -3 A larger volume of the ionization region may similarly need to be less than 10 mbar to sufficiently reduce collisions. -3 Pressures below mbar may be required. Preferably, the pressure range corresponds to operating at least one ionization region at high or ultra-high vacuum.

[0065] The presence of molecular flow (and therefore the high or ultra-high vacuum regime) can be determined in a straightforward and empirically verifiable manner by the Knudsen number, which is

number

[0066] 4, the first ionization region 401 is separate from the second ionization region 402. This may allow the conditions in the first ionization region 401 to be operated separately from the conditions in the second ionization region 402. The conditions may be set by one or more operating parameters of the EI source, which may include the pressure within each ionization region, one or more voltages applied to one or more ion source electrodes, the axis along which each molecule is received or introduced, or another operating parameter. In one example, the first ionization region 401 may be operated at high pressure and molecules may be introduced into the second ionization region 402 along a second axis that intersects the first axis.

[0067] In one example, the first ionization region and the second ionization region 401, 402 may be spatially separated (offset from each other). The offset may be along a dimension parallel to the first axis. When the first ionization region and the second ionization region 401, 402 are spatially separated, the first molecules 408 may be ionized primarily in the first region 401 and the second molecules 409 may be ionized primarily in the second region 402. However, some of the first molecules 408 may be ionized in the second ionization region 402, or vice versa. In other words, there may be some overlap between the two ionization regions.

[0068] In another example, the first ionization region and the second ionization region 401, 402 may be spatially separated such that there is no (or substantially no) spatial overlap between the spatial and / or angular extents of the first and second molecules 408, 409. In one example, the spatial separation may be achieved by providing a spacer region between the first and second ionization regions. The spacer region may be a further ionization region, as discussed with reference to Figures 5A, 5B, and 9. If a spacer region or a further ionization region is present during operation of the ion source 400, it is not necessary to introduce molecules into the spacer region or the further ionization region.

[0069] In another example, the length d of the first ionization region and / or the second ionization region 401, 402 along a dimension parallel to the first axis may be large enough that the spatial extent of the first and second molecules 408, 409 has a low overlap probability. For example, the overlap probability may be less than 50%, less than 10%, less than 5%, or less than 1%. The overlap probability may also be less than another value.

[0070] In yet another example, there may be a separation element or barrier between the first ionization region 401 and the second ionization region 402 that may be added to the spatial separation. By providing a barrier in addition to the spatial separation, contamination of the ion source electrodes may be further reduced or limited compared to spatial separation alone. The separation element may inhibit or reduce the number of molecules exchanged between the two ionization regions, which may mean that the molecules in the first region are primarily ionized in the first region and the molecules in the second region are primarily 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.

[0071] The separation wall may form part of a wall at least partially surrounding one or both of the first and second ionization regions 401, 402. For example, one or both of the ionization regions 401, 402 may be an ionization chamber. Higher or highest sensitivity may be achieved by providing an axial ion source with an at least partially closed ionization chamber. Preferably, one or both of the ionization regions 401, 402 may be mostly closed. An at least partially or mostly closed ionization chamber may result in an increase in gas pressure within the ionization chamber. This may be as much as 1×10 -4 ~1×10 -2 Pressures may be in the mbar range, although it will be understood that the pressure range may depend on various factors, such as, for example, the dimensions of the ionization chamber, the temperature within the ionization chamber, and the molecular species within the ionization region.

[0072] In a further example, instead of spatial separation, a separation element may be provided, i.e., the ionization regions may spatially overlap such that, except for the presence of the separation element, molecules would not be primarily ionized in each ionization region. The separation element may be sufficient to reduce or limit contamination of the ion source electrodes.

[0073] The length d shown in Figure 4 is merely exemplary and need not be the same value for both the first and second ionization regions. The first and second ionization regions 401, 402 (and spacer region, if present) may be of any suitable size and may be of different lengths or volumes. The spacer region, if present, may be the same length or volume as one of the first and second ionization regions 401, 402, or may be of a different length or volume.

[0074] Although the first and second molecules 408 and 409 are shown in FIG. 4 as being introduced at a common side of the ion source 400, it will be understood that the molecules may be provided from different (e.g., opposite) sides of the ion source 400. Similarly, the first and second molecules 408 and 409 need not be received along an axis orthogonal (perpendicular) to the first axis. Instead, the first and second molecules 408, 409 may be received at any suitable angle relative to the first axis. For example, in the region that extracts and transmits the ion beam 407 directly to the reflector electrode 406, the molecules may be received along another axis at an angle of 90 to 180 degrees relative to the first axis. Thus, the molecules may be oriented at least partially opposite to the direction of travel of the electron beam 411. In another example, in the region that receives the electron beam 411 directly from the electron lens 404, the molecules may be received along an axis at an angle of 90 degrees or less relative to the first axis. Thus, the molecules may be directed along the direction of travel of the electron beam 411. Either or both of these configurations may help to avoid electrode contamination, since either or both sets of molecules may not be directed towards the multiple electrodes 404 and / or 406.

[0075] The ion source 400 may be implemented in an analytical instrument. The ion source 400 and / or components of the analytical instrument may be controlled by a controller (not shown). The controller may include a computer acting as a data processor to receive data from the mass analyzer, the data representing the mass analysis or amount of ions detected from the mass analyzer. The computer may also function as a data processor to process the data to provide a mass spectrum and / or quantitative analysis of the ions. The controller may further include a display and a user input device to allow a user to view and input or select information. The user input device may be a keyboard and / or a mouse.

[0076] The ionization regions 401, 402 (and spacer regions, if present) may be arranged in one of several ways. Exemplary implementations are discussed with reference to Figures 5A, 5B, and 6-10. However, it will be understood that implementations other than those illustrated generally in Figures 5A, 5B, and 6-10 are possible.

[0077] Figure 5A illustrates an exemplary embodiment of the ion source illustrated diagrammatically in Figure 4. The ion source 500A comprises an electron source 403, an electron lens 404, a reflecting and extracting electrode 406, a two beam intersecting ionization region 520, and a spacer region 530. The two beam intersecting ionization region 520 is an ionization region in which molecules 525 are introduced along an axis that intersects with the first axis.

[0078] 5, the regions 520, 530 may be arranged in other manners. Additionally, 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 three or more beam intersection regions 520. Similarly, the ion source 500A may include two or more spacer regions 530, or no spacer regions 530.

[0079] A third molecule 535 (which may be a sample molecule to be analyzed or a calibration molecule) may be received within the spacer region 530. The spacer region may be a further ionization region, and the third molecule 535 may be ionized as discussed above in relation to the first and second ionization regions 401, 402 of Figure 4. For example, the further ionization region 535 may be configured to operate under high or ultra-high vacuum conditions, and / or the third molecule 535 may be received within the further ionization region 535 along an axis that intersects the first axis.

[0080] As discussed above with reference to FIG. 4, the ion source 500A may be configured to operate under high or ultra-high vacuum conditions by dimensioning the at least one ionization region such that the length d is less than the mean free path length. Additionally or alternatively, the at least one ionization region may be configured such that the extent 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 extent a (divergence of the molecular beam) of the molecules 525 and / or 535 may be less than the length d of the at least one ionization region. Additionally or alternatively, the at least one ionization region may be configured such that the extent 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 extent θ of the molecules 525 and / or 535 may not intersect the plane of the ion source electrodes 404 and / or 406. Any of these options may be achieved by a sufficiently large ionization region, an inlet that limits the extent of the molecules (e.g., spatial extent α and / or angular extent θ), an inlet that is positioned distal to the electrode, and / or a pressure within the ionization region that allows a majority of the molecules (e.g., 50% or more) to reach the opposite side of the ionization region from the inlet. The ionization region may be configured such that a different percentage of the molecules reach the opposite side of the respective opening and / or inlet. For example, 40%, 60%, 80% or 90% of each first molecule and / or second molecule may reach the opposite side of the respective opening and / or inlet. The spatial extent α and angular extent θ shown in FIG. 5A are merely exemplary and may be any suitable value.

[0081] 5B illustrates an exemplary embodiment of the ion source illustrated generally in FIGS. 4 and 5A. In FIG. 5B, the two beam intersection ionization region 520 is the calibrant ionization region and the ionization region 530 is the sample ionization region. The ionization region 530 is a high pressure ionization region (typically 1×10 -4 ~1×10 -25A, different numbers of each type of ionization region 520, 530 may be present in the ion source 500B, and the ionization regions 520, 530 may be arranged in one of several ways.

[0082] For example, the beam crossing ionization region 520 may be positioned before and / or after the ionization region 530. The calibration molecules 525 may be introduced along an axis at any suitable angle relative to the axis of the electron beam 411. However, preferably, the calibration 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 location of the ion source electrodes 404 and / or 406 relative to the ionization region 520. For example, if the beam crossing 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 repeller electrodes 406 (e.g., the region 520 transmits the ion beam 407 directly to the extraction and repeller electrodes 406), the axis may be at an angle of 90 to 180 degrees relative to the first axis. Although both examples are illustrated in FIG. 5B, 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 multiple electrodes 404, 406.

[0083] In another example, the at least two beam intersection ionization regions 520 may be positioned sequentially. Thus, the ionization region 530 may be located before or after the at least two beam intersection ionization regions 520. Alternatively, the ionization region 530 may not be present. Such an exemplary embodiment is discussed with reference to FIG.

[0084] When the ion source 500B includes two or more calibrant ionization regions (not necessarily each cross-beam ionization region), the calibrant molecules 525 may be different species of molecules. For example, one calibrant ionization region may be used to ionize PFK molecules and another calibrant ionization region may be used to ionize FC43 molecules. Thus, multiple calibrants may be introduced into the ion source in a straightforward manner without increasing the amount of source electrode contamination and allowing sufficient ionization of the various calibrant molecules.

[0085] 5B, the ionization region 530 may be surrounded by an enclosure wall 531 to separate the ionization region 530 from the beam crossing ionization region 520. The enclosure wall 531 may only partially surround the ionization region 530. Openings in the enclosure wall may allow for transmission or guidance of the electron beam 411 and the ion beam 407 through the ion source 500. Additional openings may allow for introduction of sample molecules 535 into the sample ionization region 530.

[0086] The ion source may comprise two or more (e.g., three) ionization regions 530. The two or more ionization regions 530 may be disposed on either side of one or more beam crossing ionization regions 520 and / or positioned consecutively. The sample molecules in some or all of the sample ionization regions 530 may be molecules of different species. Some or all of the sample ionization regions may be at least partially surrounded by a perimeter wall 531.

[0087] As discussed above in connection with Figures 4 and 5A, the cross-beam ionization region 520 and the ionization region 530 may be of any suitable dimensions and may be different sizes or have different volumes. Similarly, some or all of the same type of ionization region (cross-beam, high vacuum or high pressure) may have different dimensions or volumes. The calibration molecules 525 and the sample molecules 535 may be introduced along any suitable axis and need not be introduced on a common side of the ion source 500. Furthermore, the spatial spread α and angular spread θ shown in Figure 5B are merely exemplary.

[0088] Although beam intersection region 520 is described above as a calibration ionization region and ionization region 530 as a sample ionization region, it will be understood that calibration molecules may be introduced into ionization region 530 (in place of sample molecules) and / or sample molecules may be introduced into one or both of beam intersection regions 520 (in place of calibration molecules).

[0089] 6 illustrates a particular exemplary embodiment of an axial ion source. In this example, a first ionization region and a second ionization region 601, 602 of an ion source 600 are spatially separated by an optional dividing wall 640 (separation element) between the ionization regions. A first molecular species beam 642a is introduced into the first ionization region via a gas flow delivery element 641a. The gas flow delivery element can be a nozzle or a tube (e.g., a capillary) or another structure. A second molecular species beam 642b is received into the second ionization region via a gas flow delivery element 641b.

[0090] Both ionization regions may preferably operate under high vacuum conditions, which may allow the beams 642a and 642b to be substantially directed (the molecules in the beams may travel in a straight line). Thus, the divergence of the beams 642a and 642b may be less than the length d of the first and second ionization regions 601 and 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.

[0091] Although the first molecular species beam 642a and the second molecular species beam 642b are illustrated as being centered along an axis perpendicular to the axis of the electron beam 411, one or both of the axes may be at another angle relative to the electron beam axis.

[0092] A waste container (not shown) or dump may be located opposite one or both of the inlets 641a, 641b. Because the molecules in the molecular beams 642a, 642b may travel along a straight path (e.g., because the ionization region operates under high vacuum conditions), the molecules may generally be directed toward the waste container. Thus, the molecules may be less likely to contaminate other components of the ion source 600. The waste container may be removable. This may mean that the waste container can be cleaned by removing it from the ion source 600. Thus, the ion source 600 may be easier to clean, for example, it may be possible to clean areas of small dimensions that are not easily cleanable via known methods such as in-situ cleaning. The waste container may be realized by a cylindrical element closed at one end. The waste container may be present in any of the ion source implementations discussed herein.

[0093] 7 shows a further exemplary embodiment of an ion source, which may be surrounded by a vacuum, preferably a high vacuum. An electron beam 411 may be guided through a first ionization chamber 701, into which a first molecular species 708 may be introduced via an inlet 741a. The gas pressure in the first ionization chamber 701 may be (e.g., 1×10 -4 ~1×10 -2 In one embodiment, the first ionization chamber 701 may be at least partially closed (e.g., in the range of 100 to 200 mbar), which may increase the ionization efficiency of the first molecular species 708. In other words, the first ionization chamber 701 may not be operated under high vacuum conditions. The first ionization region 701 is preferably at least partially closed, and most preferably is a conductance-limited ionization chamber. A conductance-limited ionization chamber may, for example, be closed away from an opening through which particles (usually electrons), molecules (typically ions and neutrals), and / or atoms enter and exit the ionization chamber.

[0094] The first ionization chamber 701 may be followed by a separate ionization section 702 into which a second molecular species 709 is introduced via an inlet 741b. The separate ionization section 702 is then subjected to high pressure (e.g., 1×10 -4 ~1×10 -2 The second ionization region 702 may be operated at low pressures (in the mbar range) which may increase the ionization efficiency of the second molecular species 709. In other words, the second ionization chamber may not be operated under high vacuum conditions. The second ionization region 702 is preferably at least partially closed, and most preferably is a conductance limited ionization chamber.

[0095] An optional gap 750 may be present in the surrounding wall 731b facing the inlet 741b. Because the molecules 709 are uncharged (neutral) molecules, the molecules 709 that are not ionized by the electron beam 411 may typically reach the second ionization section 702 on the opposite side to the inlet 741b. Thus, if the gap 750 is present, the molecules 709 may be able to exit the second ionization section 702 (e.g., if the molecules 709 experience no or few collisions and thus may travel along a straight path), which may improve the contamination resistance of the ion source 700. This may be particularly useful if the molecules 709 are molecules with a high sticking probability, since the gap 750 may prevent the molecules 709 from contaminating the surface of the surrounding wall 731b facing the inlet 741b. The illustrated gap 750 is merely exemplary and may be larger or smaller than illustrated. Furthermore, although not shown, an optional gap may also or alternatively be present in the peripheral wall 731a opposite the inlet 741a.

[0096] A waste container (not shown) for molecules 709 may additionally or alternatively be placed opposite inlet 741b. Similarly, a waste container for molecules 708 may additionally or alternatively be placed opposite inlet 741a. The waste container or dump may be removable. This may mean that the waste container can be cleaned by removing it from the ion source 700. Thus, the ion source 700 may be easier to clean, for example, it may be possible to clean areas of small size that are not easily cleanable via known methods such as in-situ cleaning. The waste container may be realized by a cylindrical element closed at one end. The waste container may be present in any of the ion source implementations discussed herein.

[0097] Both ionization regions 701, 702 are subjected to high pressure (e.g., 1×10 -4 ~1×10 -2 By operating at higher pressures (mbar range), it may be possible to increase the local pressure of each molecular species 708, 709. For example, efficient ionization of different molecular species may require different local pressures. By providing two or more ionization regions within which the pressures can be separately controlled, the overall ionization efficiency may be improved.

[0098] The ionization regions 701, 702 may be configurable between high vacuum and high pressure modes of operation. For example, the ion source 700 may be configured such that one or more of the ionization chambers operate under high vacuum conditions. Thus, the first molecular species and / or the second molecular species may emerge from the inlets 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 within which the pressures can be separately controlled may allow improved control over ionization efficiency and / or ion source electrode contamination.

[0099] 7, in sector field mass spectrometry, ions typically enter a magnetic and / or electrostatic sector and are then accelerated before reaching one or more detectors. This can be accomplished by applying a potential to the ion source and maintaining one or more detectors at ground potential. Positive ions are accelerated by the drop in potential between the ion source and one or more detectors.

[0100] Exemplary potentials for the ion source 700 are illustrated in FIG. 7, where a potential U is shown along the ion source axis z. The potential may typically be 3000 V, but other potential values ​​may be used. The potential in the ionization regions 701, 702 may be constant or substantially constant with a small potential difference (e.g., 5 V or less) to promote the ions to subsequent regions. The potential may begin to decrease in the region of the extraction electrodes E1 and E2. Thus, positive ions may be accelerated out of the ion source by the decrease in potential, while negatively charged electrons may experience a change in potential as the potential increases and may be reflected back toward the ion source cathode.

[0101] As discussed above with reference to FIG. 4, negative ions may be generated instead of positive ions. In this case, the voltage applied to electrode E2 should be positive with respect to the voltage applied to electrode E1 to extract negative ions from the ionization chamber 702. In other words, the potential may begin to increase in the region of the extraction electrodes E1 and E2 to accelerate the negative ions out of the ion source. Also, to prevent electrons from being accelerated and extracted from the ionization chamber 702 (because electrons have the same polarity as negative ions), a magnetic field may be generated using one or more magnets to deflect the electrons away from a first axis (which may correspond to the ion source axis). In one example, the magnetic field may deflect the electrons away from the first axis before they reach the region between electrodes E1 and E2. For example, the magnetic field may deflect the electrons away from the first axis of the ionization chamber 702 in the region near the extraction and / or repeller electrodes E1 and E2.

[0102] Since an axial magnetic field is applied to the ion source to guide the electrons and ions along a common axis of the ion source (as discussed with respect to FIG. 4), the deflection magnetic field may include a correction to the axial magnetic field. In another example, the deflection magnetic field may be a separate magnetic field (e.g., generated by a different magnet).

[0103] In this implementation, the electrons may not be directed back towards the cathode, but instead may pass through the ionization chamber 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 repeller electrodes E1 and E2).

[0104] Thus, ions can be extracted from the ion source 700 while deflecting electrons away from the ion source exit 412. This is because while the magnetic field can 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 the ions' larger mass.

[0105] Different implementations of dedicated ionization regions may be combined. Various combinations may enable specific benefits such as reduced or limited ion source electrode contamination and high ionization efficiency.

[0106] For example, Figure 8 illustrates an exemplary ion source in which an ionization chamber and a directed molecular beam are implemented. 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 in the ionization chamber 701 via an inlet 741a. The at least partially closed ionization chamber 701 may allow for achieving a high ionization efficiency for the first molecular species 708.

[0107] The second molecular species may be received as a molecular beam 642b directed into the second ionization region 602, which may be accomplished by providing the second ionization region 602 as a high vacuum region. While the second ionization region 602 is illustrated as an open (non-enclosed) region, it will be understood that separating or surrounding elements (e.g., walls) may be present. Additionally, although not shown, a waste container, as discussed with respect to Figures 6 and 7, may be positioned opposite the inlet 641b.

[0108] A second molecular species, preferably comprising neutral calibration 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 stored in first ionization chamber 701 (because the pressure in second ionization chamber 602 may be lower), a sufficient number of calibrant ions may still be provided to a mass analyzer or another downstream element.

[0109] The directed beam 642b may allow to minimize contact of the second molecular species with the extraction electrodes E1, E2. This may be particularly useful when the second molecular species is a calibration molecule with a high sticking probability, such as, for example, PFK or PFTBA. The reflection of electrons and the extraction of ions between the electrodes E1 and E2 may preferably also be performed in a (high) vacuum. The mechanical dimensions of the electrodes E1 and E2 may be determined by optical considerations of the electrons and / or ions.

[0110] Additionally, providing the second ionization region 602 as a high vacuum region may allow for a more monoenergetic distribution of ion kinetic energy. Due to the change in potential in the region of the extraction electrodes E1 and E2 (as illustrated in FIG. 7), ions generated in this region may not receive the full acceleration voltage (e.g., 3000V) that ions generated in other regions (e.g., toward the first ionization region 701 or the portion of the second ionization region 702 from which the electron beam 411 is received) may receive. Thus, ions generated in the extraction electrode region may not pass or be focused to downstream elements of the analytical instrument. For example, ions may not be able to pass through one or more sector field instruments and / or may not reach one or more detectors. However, providing the second ionization region 602 as a high vacuum region may suppress the generation of ions in the extraction electrode region. Thus, the proportion of ions generated in the second ionization region 602 that receive the full acceleration voltage may be greater. This may result in a less broad distribution of ion kinetic energies, which may in turn improve the focusing of ions onto downstream elements of the analytical instrument.

[0111] In another example, the first and second ionization regions 701, 602 may be reversed such that the ionization region closer to or adjacent to the electron lens 404 may receive a directed molecular beam and the second ionization is the ionization chamber. In this case, the directed beam may minimize contact of the first molecular species with the electron lens electrode 404 and allow for increased ionization efficiency of the second molecular species.

[0112] As discussed above with reference to Figure 4, three or more separate ionization regions may be implemented. One exemplary embodiment including three ionization regions is illustrated in Figure 9, which shares similarities with the embodiments discussed in relation to Figures 5B, 6, and 8. In this exemplary embodiment, an ion source 900 comprises two beam intersecting ionization regions 901, 903 in which molecules are directed along an axis intersecting the electron beam axis. Thus, at least some of the molecules received from the respective inlets 941a, 941b may be ionized by the intersection of the molecular beams 942a, 942b with the electron beam 411.

[0113] In FIG. 9, the further ionization region 902 is included between the two ionization regions 901, 903. However, it will be understood that the further ionization region 902 can be included elsewhere in the ion source 900. The further ionization region 902 is an ionization chamber, which may be at least partially surrounded by a peripheral wall 931. The peripheral wall 931 may mean that molecules can be received in the further 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. Furthermore, the peripheral wall 931 may allow an increase or rise in the gas pressure in the ionization region 902, which may increase the ionization efficiency in the further ionization region 902. The ionization efficiency may be further improved if the further ionization region 902 includes a conductance-limited ionization chamber. A conductance-limited ionization chamber may, for example, be closed off from an opening through which particles (usually electrons) and molecules (typically ions and neutrals, but may include atoms) enter and exit the ionization chamber.

[0114] The configuration of the ionization regions 901, 902, 903 in Figure 9 may be particularly beneficial for achieving high ionization efficiency while avoiding or reducing electrode contamination. This configuration may also be particularly useful for experiments that require a lock mass during measurement.

[0115] In one example, the molecules introduced into each region 901, 902, 903 may be of the same species. Thus, the molecules may be efficiently ionized in the further ionization region 902 while being ionized in the two ionization regions 901, 903 with limited or reduced contamination of the electrodes 404, 406. Thus, it may be possible to ionize more molecules without a corresponding increase in electrode contamination.

[0116] In another example, some of the received molecules may be different species. The molecules received in one or both of the two ionization regions 901, 903 may be, for example, calibration molecules. The calibration molecules may also be different species. By providing the calibration molecules along an axis that intersects the electron beam axis, contamination of the electrodes 404, 406 may be reduced or prevented. This configuration may also result in other parts of the ion source 900 having to be cleaned less frequently (e.g., if a waste container is provided along an axis opposite one or both of the inlets 941a and / or 941b).

[0117] Referring to FIG. 10, a graph is shown illustrating the difference in peak shape obtained using a sector magnetic field mass analyzer for a conventional axial ion source compared to an axial ion source with extraction electrodes E1 and E2 located in high vacuum to minimize ionization in that region. One problem that can occur with an axial ion source is that the distribution of ion kinetic energies can be much broader than that of ions typically produced in a Nier ion source. For example, ions produced in the region adjacent to the extraction electrodes E1 and E2 can have a lower kinetic energy than the majority of ions produced in the ionization region. An ion beam with a wide distribution of ion kinetic energies can be only partially focused to the mass analyzer detector. Thus, a percentage of ions from the ion beam are excluded from the measurement, which can affect the accuracy of the measurement. For example, the measurement of isotope ratios can be inaccurate. The wide distribution of ion kinetic energies can be a particular problem with a single focusing sector magnetic field mass analyzer, where only a single magnetic sector can be used to separate ions according to their mass-to-charge ratio.

[0118] Incomplete focusing of the ion beam on the detector may result in an inaccurate peak shape, e.g., a peak without a flat peak plateau. Such a peak is illustrated by the solid line in FIG. 10. However, by providing a high vacuum region in the vicinity of the extraction electrodes E1 and E2, the generation of ions in the region near the extraction electrodes E1 and E2 may be suppressed. Thus, the distribution of ion kinetic energy may be more monoenergetic. The dashed line in FIG. 10 illustrates 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). As can be seen from FIG. 10, the peak shape is improved when the region near the extraction electrodes E1 and E2 is a high vacuum region compared to the high pressure ionization region. Thus, by using an ion source geometry, such as that shown in FIG. 8, which may prevent a large portion of the molecules from being ionized near the electrodes E1 and E2, a more monoenergetic ion source may be possible in addition to or instead of allowing neutral molecules to be kept far from the ion source electrodes 404 and / or 406. A less broad (more monoenergetic) distribution of ion kinetic energies may result in improved focusing of the ion beam onto a detector in a mass analyzer or another downstream element.

[0119] A mass spectrometer in which the ion source of the present disclosure may be utilized is shown generally in FIG. 11. The mass spectrometer 1000 may include an ion source 1010, at least one mass analyzer 1020, and a detector or detectors 1030. The at least one mass analyzer 1020 may include a multipole mass analyzer (e.g., a quadrupole mass analyzer, etc.), a magnetic sector mass analyzer, and / or another type of mass analyzer. The 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 interfacing between the ion source 1010, the at least one mass analyzer 1020, and the detector 1030. For example, components may be present to transmit, guide, and / or store ions and / or other components.

[0120] The present disclosure may further provide a use of an electron impact 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 calibration molecule, and optionally, the calibration molecule may include perfluorokerosene (PFK) or perfluorotributylamine (PFTBA).

[0121] Although examples of ion sources are described above primarily in the context of electron ionization, it will be understood that the ion sources disclosed herein may additionally or alternatively be configured for other forms of ionization. For example, chemical ionization is a technique that also employs the use of an electron beam. Similarly, while examples of ion sources are described above generally with respect to an electron beam generating positive ions, it will 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. Thus, as discussed above with reference to FIG. 7, an increasing electric potential may be used to extract negative ions from the ion source. If an electron beam is used (or other negatively charged particles such as a negative ion beam are used), a (modifying) magnetic field may be employed to prevent the electrons from being extracted.

[0122] 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. Embodiments may also be implemented in distributed computing environments in which tasks are performed by remote processing devices linked through a network.

[0123] 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 memory, including volatile and non-volatile storage media. Different parts of the system may be connected using networks (e.g., wireless and wired networks). The computer system may include one or more interfaces. The computer system may include a suitable operating system, such as, for example, UNIX (including Linux) or Windows (RTM).

[0124] Certain embodiments may also be embodied as computer readable code on a non-transitory computer readable medium. A computer readable medium is any data storage device that can store data and that can then be read by a computer system. Examples of computer readable media include hard drives, network attached storage (NAS), read only memory, random access memory, CD-ROM, CD-R, CD-RW, magnetic tape, and other optical or non-optical data storage devices. The computer readable medium may also be distributed over computer systems coupled to a network, resulting in distributed storage and execution of the computer readable code. Although embodiments according to the present disclosure are described with reference to certain types of devices and applications, particularly mass analyzers and mass spectrometers, and the embodiments have particular advantages in such cases, as discussed herein, the approach according to the present disclosure may be applied to other types of devices and / or applications. Each feature disclosed herein may be replaced by an alternative feature serving the same, equivalent, or similar purpose, unless otherwise specified. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

[0125] All aspects and / or features disclosed herein may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. In particular, 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 separately (not in combination).

[0126] The methods and apparatus of the present disclosure can be utilized with a variety of electrode configurations. Individual electrodes can be planar, hemispherical, rectangular, or other shapes. The electrodes can be PCB printed electrodes.

[0127] There is an implicit "about" in front of temperatures, concentrations, times, pressures, flow rates, cross-sectional areas, voltages, currents, etc. discussed in the present teachings, and thus it is understood that very small, minor deviations are within the scope of the present teachings. Furthermore, values ​​that are referred to as "equal" may actually differ by less than a threshold amount. The threshold amount may be, for example, 5%. The threshold may also be greater than 5% (e.g., 10%, 20%, or 50%) or less than 5% (e.g., 2% or 1%).

[0128] As used herein, including in the claims, the singular forms of the terms herein are to be construed as including the plural and vice versa unless the context indicates otherwise. For example, in the claims, references to the singular forms, including "a" or "an" (such as an electrode), mean "one or more" (e.g., one or more electrodes), unless the context indicates otherwise.

[0129] Throughout the specification and claims of this disclosure, words such as "comprise," "including," "having," and "contain," as well as variations of words such as "comprising" and "comprises" or the like, mean "including, but not limited to," and are not intended to exclude other components. Additionally, the use of "or" is inclusive, such that the phrase "A or B" is true when "A" is true, when "B" is true, or when both "A" and "B" are true. Additionally, the use of parenthetical terms is inclusive, such that the phrase "(C)D" is true when "D" is true, or when both "C" and "D" are true. For example, the term "(high) vacuum" can mean "high vacuum" or "vacuum."

[0130] The use of any and all examples or exemplary language provided herein (such as, for example, and similar language) is intended merely to better illustrate the invention and does not pose a limitation on the scope of the disclosure unless specifically claimed. No language in the specification should be construed as indicating any element not claimed as essential to the practice of the disclosure.

[0131] The terms "first" and "second" may be reversed or referred to with different numerical designations without changing the scope of the invention. That is, an element referred to as a "first" element (e.g., first ionization region 401) may instead 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 instead be considered a "first" element (e.g., first ionization region 401).

[0132] Any steps described herein may be performed in any order, or simultaneously, unless otherwise stated or otherwise required by context. Furthermore, if a step is described as being performed after another step, this does not exclude intervening steps from being performed.

[0133] Moreover, unless otherwise understood or stated, implicitly or explicitly, it is understood that for any given component or embodiment described herein, any of the possible candidates or alternatives listed for that component may be generally used, either individually or in combination with one another, and further, unless otherwise understood or stated, implicitly or explicitly, it is understood that the listing of any such candidates or alternatives is merely exemplary and not limiting.

[0134] In this detailed description of various embodiments, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. However, those skilled in the art will understand that these various embodiments may be practiced with or without these specific details. Moreover, those skilled in the art can readily understand that the specific order in which the method is presented and performed is illustrative, and it is contemplated that the order may be altered and still remain within the scope of the various embodiments disclosed herein.

[0135] All literature and similar materials cited in this application, including but not limited to patents, patent applications, articles, books, treaties, and Internet web pages, are expressly incorporated by reference in their entirety for any purpose. Unless otherwise stated, 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. 1. An electron impact ion source comprising: a first electron impact ionization region including an opening configured to accept a first molecule into the first ionization region, the first ionization region configured to accept an electron beam along a first axis to generate a first ion beam from the first molecule along the first axis; and a separate second electron impact ionization region including an entrance configured to accept a second molecule into the second ionization region, the second ionization region configured to accept the electron beam along the first axis to generate a second ion beam along the first axis from the second molecule.

2. 2. The electron impact ion source of claim 1, wherein the inlet is configured to receive the second molecule along a second axis that intersects the first axis to ionize the second molecule, and / or the opening is configured to receive the first molecule along an acceptance axis that intersects the first axis to ionize the first molecule.

3. 3. The electron impact ion source of claim 1, wherein the second ionization region is spatially separated from the first ionization region such that the first molecules are primarily ionized in the first ionization region and the second molecules are primarily ionized in the second ionization region.

4. 4. An electron impact ion source according to claim 1, further comprising a separation element between the first ionization region and the second ionization region, the separation element preferably at least partially surrounding one or both of the first ionization region and the second ionization region.

5. 5. The electron impact ion source according to claim 1, 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 in a vacuum.

6. 6. The electron impact ion source of claim 5, wherein the vacuum is a high vacuum or an ultra-high vacuum.

7. 7. The electron impact ion source of claim 6, wherein the electron impact ion source is configured such that a mean free path of the first molecule and / or the second molecule is greater than half a length of the first ionization region and / or the second ionization region, respectively, along a dimension parallel to the first axis.

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

9. The first ionization region and / or the second ionization region are the extent of each of the first and / or second molecules along the dimension parallel to the first axis is less than the length; and / or 9. An electron impact ion source according to claim 1, wherein the extent of each of the first molecules and / or the second molecules is configured so as not to intersect the plane of one or more ion source electrodes.

10. the second ionization region is configured such that the second axis does not intersect a plane of one or more ion source electrodes; and / or 10. An electron impact ion source according to any one of claims 2 to 9, wherein the first ionization region is configured such that the acceptance axis does not intersect a plane of one or more ion source electrodes.

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

12. 12. An electron impact ion source according to any one of claims 1 to 11, wherein the first molecule and / or the second molecule comprises a calibration molecule, the calibration molecule preferably comprising perfluorokerosene (PFK) or perfluorotributylamine (PFTBA).

13. 13. An electron impact ion source according to any one of claims 2 to 12, further comprising a waste container positioned along the second axis to receive non-ionized molecules and / or further comprising a waste container positioned along the reception axis to receive non-ionized molecules.

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

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

16. 1. A method for electron ionization comprising the steps of: receiving an electron beam into a first ionization region along a first axis, the electron beam generating a first ion beam from first molecules in the first ionization region along the first axis; receiving the electron beam along the first axis into a separate second ionization region, and generating a second ion beam along the first axis from second molecules in the second ionization region with the electron beam.

17. 17. The method of claim 16, further comprising: accepting a second molecule into the second ionization region along a second axis that intersects the first axis to generate the second ion beam; and / or accepting a first molecule into the first ionization region along an acceptance axis that intersects the first axis to generate the first ion beam.

18. the second ionization region is spatially separated from the first ionization region such that the first molecules are primarily ionized in the first ionization region and the second molecules are primarily ionized in the second ionization region; and / or a separation element is disposed between the first ionization region and the second ionization region; and / or 18. The method of claim 16 or 17, 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 in a vacuum.

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

21. 21. The method of claim 20, wherein the mean free path of the first molecule and / or the second molecule is greater than half 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 10 times greater than the length.

22. the extent of the first molecule and / or the second molecule along said dimension is smaller than said 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 one or more ion source electrodes; and / or 22. The method of any one of claims 17 to 21, wherein an acceptance axis along which the first molecule is accepted into the first ionization region does not intersect a plane of 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 calibration molecule.

24. A computer program comprising instructions which, when executed by a computer, cause the computer to control an analytical instrument equipped with an electron impact ion source to carry out the 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 an electron impact ion source according to any one of the preceding claims.

27. 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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