Charge reduction method and ion optical system

Abstract

To provide a method for reducing charge on a contaminated surface of an ion optical system.SOLUTION: In accordance with a first aspect, there is provided a method for reducing charge on a contaminated surface of an ion optical system, the contaminated surface having a layer of charged contaminant thereon, and the method comprising: generating charged particles by exciting a radiation source that is distinct from the contaminated surface of the ion optical system; and neutralizing at least a portion of the layer of charged contaminant by causing the charged particles to interact with the layer of charged contaminant; where (i) the radiation source comprises an electromagnetic radiation source, where exciting the radiation source comprises causing the electromagnetic radiation source to emit electromagnetic radiation, and generating the charged particles comprises causing the electromagnetic radiation to interact with the layer of charged contaminant and / or the ion optical system to generate the charged particles, and / or (ii) the radiation source comprises an electron source, where exciting the radiation source comprises causing the electron source to emit free electrons. In a second aspect, there is provided an ion optical system configured to reduce charge on a contaminated surface of the ion optical system.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to ion optics and methods for reducing charge on contaminated surfaces of the ion optics. [Background technology]

[0002] Ion optics are used in various analytical instruments to manipulate and transport ions. For example, ion optics are widely used in mass spectrometers to focus, transport, and eject ions from different regions. Examples of ion optical elements found in typical ion optics include ion guides, lenses, carpets, and funnels. In these elements, appropriate fields are applied by electrodes to manipulate ions. Ion optics typically apply electric and / or magnetic fields within the ion optics to manipulate charged ions, which experience electric and / or magnetic forces as they move through such fields. Some ion optics perform the sole function of transporting ions from one region to another, while some ion optics can capture, transport, and / or eject ions at different times.

[0003] Ion optics in various systems, including mass spectrometers (e.g., vacuum systems), can suffer from contamination caused by the deposition of ions on surfaces. These contaminations can become highly charged as the ions are deposited. Such contamination can adversely affect the performance of the ion optics by affecting the fields established within the ion optics. For example, charge build-up on electrodes within the ion optics can reduce the transmitted ion current or cause a broadening of the separation profile (e.g., in a quadrupole).

[0004] Attempts to solve these problems often involve venting the system and mechanically cleaning contaminated areas. Other methods of keeping the ion optics relatively free of contamination shorten the exposure time (e.g., as described in U.S. Pat. No. 9,543,131) or deflect ions to areas where charge build-up is less of a problem. For example, slits can be provided in the quadrupole rods to keep the relevant rod surfaces largely clean, as described in British Patent No. 2,555,032. A drawback of this technique, however, is that geometric changes to the quadrupole surface can affect (e.g., reduce to some extent) the mass resolution of the quadrupole.

[0005] Another approach is to add additional mass filters or electrodes to the quadrupole, which will filter out unwanted species and reduce contamination of the main quadrupole rods. Examples of this approach can be found in U.S. Patent Nos. 7,211,788 and 9,929,003. These solutions are known to work, but still require cleaning of the additional rods, albeit at longer time intervals.

[0006] It is an objective of the present disclosure to address these and other problems with existing ion-optical systems. Summary of the Invention

[0007] Against this background and according to a first aspect there is provided a method as set forth in claim 1. An ion-optical system as set forth in claim 18 is also provided.

[0008] The present disclosure seeks to improve the performance of ion-optical systems by partially or completely neutralizing regions of charged contamination. By reducing the charge on the surfaces of the ion-optical system, the perturbation potential caused by the charged contamination can be reduced. Since the perturbation potential degrades the performance of the ion-optical system, neutralizing the charge can be very advantageous.

[0009] Embodiments of the present disclosure use charged particles (e.g., protons, electrons, ions, and / or anions) to perform such neutralization. When electrons are used, they may be photoelectrons (i.e., electrons emitted from a material by the photoelectric effect) or other types of electrons, such as thermionic electrons (i.e., electrons emitted by thermionic emission from a material).

[0010] Embodiments of the present disclosure may be particularly useful in ion optics of high throughput mass spectrometry systems. Embodiments of the present disclosure are also useful in vacuum conditions and during operation of the ion optics. For example, the present disclosure provides methods and systems that may enable periodic removal (or at least reduction) of charged contaminants in the ion optics.

[0011] According to a first aspect, the present disclosure provides a method for reducing charge on a contaminated surface of an ion-optical system, the contaminated surface having a layer of charged contaminants thereon. The method includes generating charged particles by exciting a radiation source separate from the contaminated surface of the ion-optical system, and neutralizing at least a portion of the layer of charged contaminants by interacting the charged particles with the layer of charged contaminants, where (i) the radiation source includes an electromagnetic radiation source, and exciting the radiation source includes causing the electromagnetic radiation source to emit electromagnetic radiation, and generating the charged particles includes causing the electromagnetic radiation to interact with the layer of charged contaminants and / or the ion-optical system to generate the charged particles, and / or (ii) the radiation source includes an electron source, and exciting the radiation source includes causing the electron source to emit free electrons. "Exciting the radiation source" means that the radiation source (i.e., the electromagnetic radiation source and / or the electron source) is activated (i.e., turned on) to emit electromagnetic radiation (in the case of an electromagnetic radiation source) and / or free electrons (in the case of an electron source).

[0012] According to a first aspect, electromagnetic radiation may interact with a contaminated surface of an ion-optics system to generate charged particles.

[0013] In a second aspect, the present disclosure provides an ion-optics system configured to reduce charge on a contaminated surface of the ion-optics system. The ion-optics system comprises a surface and a radiation source configured to generate charged particles, the radiation source being separate from the contaminated surface. The ion-optics system is configured to neutralize at least a portion of a layer of charged contaminants on the surface by interacting the charged particles with the layer of charged contaminants. The radiation source includes (i) an electromagnetic radiation source configured to emit electromagnetic radiation that interacts with the layer of charged contaminants and / or the ion-optics to generate the charged particles, and / or (ii) an electron source configured to emit free electrons.

[0014] According to a second aspect, electromagnetic radiation can interact with a surface of the ion-optics system to generate charged particles.

[0015] In a third aspect, there is provided an analytical instrument comprising an ion-optical system as described above, the ion-optical system comprising an ion source configured to provide ions to the ion-optical system. The radiation source may be separate from the contaminated surface and the ion source.

[0016] These systems and methods advantageously allow charged contaminants (e.g., accumulated ions) on critical surfaces of the ion optics (e.g., electrodes) to be at least partially neutralized by charged particles. Neutralizing such charge can inhibit performance degradation of the ion optics resulting from normal use. These methods can be repeated frequently, thereby increasing throughput (as longer intervals between manual maintenance events are required). These methods and systems provide a relatively low-cost method of reducing charge that can be easily retrofitted to existing systems by adding one or more radiation sources.

[0017] The present disclosure also provides a method of reducing contamination of an ion-optical system having a contaminated surface having a layer of charged contaminants thereon, the method including exciting a charged particle source to generate charged particles having a kinetic energy greater than 0 eV, and neutralizing at least a portion of the layer of charged contaminants by directing the charged particles into the layer of charged contaminants, similar to the methods described above, to provide charged particles for at least partially neutralizing the contaminants.

[0018] The above-mentioned advantages and various other advantages will be apparent from this disclosure. The present disclosure will now be described, by way of example only, with reference to the accompanying figures. [Brief description of the drawings]

[0019] [Figure 1] 1 shows an ion optical system in a first embodiment. [Diagram 2] 3 shows an ion optical system in a second embodiment. [Diagram 3] 1 shows a quadrupole ion optical system in a third embodiment. [Figure 4] 4 shows a quadrupole ion optical system according to a fourth embodiment. [Diagram 5] 1 shows the effect of contamination on the separation profile. [Figure 6] 1 illustrates the effect of embodiments of the present disclosure on separation profiles. [Figure 7] 1 illustrates the continuous transmission of ions while an embodiment of the present disclosure is being implemented. [Figure 8] 13 shows an arrangement of a radiation source and quadrupole electrodes in the fifth embodiment. [Figure 9] The advantages of the fourth embodiment are shown. [Figure 10] 1 illustrates an analytical instrument according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A schematic diagram of a first embodiment of ion-optics 100 is shown in Figure 1. The ion-optics 100 comprises a contaminated surface 101 having a layer of charged contaminants 102 thereon. The layer of charged contaminants 102 is shown as having a positive charge (+) along the contaminated surface 101. The ion-optics 100 also comprises a radiation source 103 configured to generate charged particles. In this embodiment, the charged particles are electrons (shown as e-), although other types of charged particles can be used. The radiation source 103 is separate from the contaminated surface 101.

[0021] In the embodiment of Figure 1, the radiation source 103 emits electromagnetic radiation, as indicated by the dashed arrows. The electromagnetic radiation causes the emission of electrons, which is another form of radiation, namely beta radiation. The paths of these electrons are indicated by the solid arrows.

[0022] In use, the ion-optics 100 performs a method for reducing charge on the contaminated surface 101 of the ion-optics 100. Electrons are generated through the photoelectric effect following excitation of electrons by the radiation source 103. The ion-optics 100 neutralizes at least a portion of the layer of charged contaminants 102 by causing the electrons to interact with the layer of charged contaminants 102. This allows the electrons to neutralize the charge of the layer of charged contaminants 102, thereby partially neutralizing the layer of charged contaminants 102.

[0023] The radiation source 103 in Figure 1 generates electrons by the photoelectric effect, the radiation source 103 being an electromagnetic radiation source. Exciting the radiation source 103 includes causing the electromagnetic radiation source 103 to emit electromagnetic radiation to generate electrons (i.e., to indirectly generate free electrons by causing photons to generate photoelectrons). The ion-optical system 100 includes a luminescent material, and generating electrons (or other charged particles, if other charged particles are used) includes interacting the electromagnetic radiation with the luminescent material to generate electrons. The electromagnetic radiation source may be directed at the luminescent material and / or suitable optics may direct the electromagnetic radiation towards the luminescent material.

[0024] 1, the luminescent material is present in two separate elements of the ion-optics 100. A first portion of the luminescent material 104 is separate from the contaminated surface 101. Furthermore, the contaminated surface 101 itself serves as a second portion of the luminescent material.

[0025] In use, the radiation source 103 generates electrons for discharging and cleaning the contaminated surface 101 by emitting electromagnetic radiation (e.g., UV light radiation) that travels toward and interacts with the portion of the luminescent material. This radiation causes the contaminated surface 101 itself to emit electrons (herein described as the "internal photoelectric effect") and causes the first portion 104 of the luminescent material to emit free electrons (herein described as the "external photoelectric effect"). Thus, in the first embodiment of FIG. 1, the radiation source 103 is configured to generate photoelectrons in two different ways. These photoelectrons then at least partially neutralize the charged contaminants 102, thereby reducing the charge on the contaminated surface 101.

[0026] In the case of the external photoelectric effect, electrons typically leave a metal surface (or other light-emitting surface) surrounding a contaminated area with relatively low energy and fly toward the charged contaminated area, attracted only by charge, as shown in Figure 1. The curved path of the electrons in Figure 1 illustrates the way in which free electrons may be directed toward the charged contaminant 102.

[0027] In some cases, a relatively high voltage may be present on the electrodes, and the photoelectrons may be accelerated to generate secondary electrons, detached neutral particles, vacuum ultraviolet (VUV), and X-ray bremsstrahlung as well. Thus, the present disclosure also provides a method for cleaning a contaminated surface 101 using bombardment with high-speed electrons. Thus, in general terms, the ion-optics of the present disclosure may comprise one or more electrodes, and the methods described herein may include applying a voltage to at least one electrode of the ion-optics to accelerate charged particles (e.g., free electrons) and thereby generate additional radiation to neutralize at least a portion of the layer of charged contaminants. This may enhance the neutralization of the charged contaminants. In some cases, the methods may involve applying a magnetic field within the ion-optics to direct electrons or other charged particles toward the layer of charged contaminants. This may also improve charge neutralization.

[0028] In the case of the internal photoelectric effect, mobile electrons from a luminescent material (e.g., metal) below the layer of contaminant 102 travel to the contaminated surface 101. Some photons may reach the contaminated area after being reflected from surrounding surfaces (e.g., surrounding metal surfaces). The thickness of the layer is preferably thin enough to be transparent to electromagnetic radiation (e.g., UV photons). Typical thicknesses can be from more than 5 nm to several micrometers (e.g., 1-2 μm). Such layers can be fully or at least partially neutralized using the present disclosure. In some cases, when a layer of contaminant has a thickness of 1-2 μm, the layer can be nearly fully neutralized.

[0029] In a preferred embodiment, the luminescent material is a metallic material. Metallic materials can have an appropriate work function that allows the generation of a large enough number of electrons to perform neutralization. Thus, metals can be good electron sources. However, other materials can be used.

[0030] In some embodiments, the luminescent material comprises a contaminated surface of the ion-optics. The contaminated surface may be, for example, a surface of an electrode of the ion-optics. Electrodes in the ion-optics may become contaminated during normal operation. Some embodiments of the present disclosure take advantage of the fact that electrodes may also act as a good source of electrons or other charged particles that may be used to neutralize charged contaminants.

[0031] In FIG. 1, the first portion of the luminescent material 104 is shown as a generic luminescent material. It will be understood that the first portion of the luminescent material 104 may be an electrode of the ion-optics, or the first portion of the luminescent material 104 may be another luminescent surface near the contaminated surface 101. In some cases, the ion-optics may comprise a plurality of electrodes, the contaminated surface may be one of the plurality of electrodes, and the luminescent material may be another of the plurality of electrodes (or some other luminescent surface in the ion-optics). Each electrode of the plurality of electrodes may be contaminated, and each electrode of the plurality of electrodes may be configured to provide electrons for cleaning another electrode of the plurality of electrodes. Thus, the ion-optics may comprise one or more electrodes separate from at least a portion of the luminescent material and / or one or more electrodes that are at least a portion of the luminescent material.

[0032] The electromagnetic radiation sources described herein may include ultraviolet (UV) radiation sources. UV light can provide photons with the appropriate energy to cause the emission of electrons from common luminescent materials. The wavelength of light used can vary depending on the work function of the luminescent material. The electromagnetic radiation sources described herein may include one or more light emitting diodes (LEDs). LEDs are widely available and can provide photons with the appropriate energy to generate electrons. However, other photon sources may be provided.

[0033] 1, the radiation source 103 is configured to generate photoelectrons in two different ways, however, other ways of providing electrons are also possible.

[0034] Figure 2 shows a schematic diagram of a second embodiment of ion-optics 200. This embodiment is similar to the ion-optics 100 of Figure 1 in that the contaminated surface 101 has a layer of charged contaminants 102 thereon. The contaminated surface 101 and charged contaminants 102 are as described above in relation to Figure 1.

[0035] The radiation source 203 of the ion-optical system 200 of FIG. 2 is different from the radiation source of the ion-optical system 100 of FIG. 1. In this second embodiment, the radiation source 203 emits free electrons (i.e., generates free electrons directly) and is therefore a beta radiation source rather than an electromagnetic radiation source as in FIG. 1. When the radiation source 203 of the ion-optical system 200 is excited, the ion-optical system 200 neutralizes at least a part of the layer of the charged contaminant 102 by making the free electrons emitted by the radiation source 203 interact with the layer of the charged contaminant 102. Thus, the charge on the contaminated surface 101 is reduced. The accelerated free electrons can also evaporate the contaminant 102, which can be beneficial if the evaporated material does not cover other things important for a proper operating surface.

[0036] The radiation source 203 can be various types of radiation sources. For example, free electrons can be generated by thermal emission of electrons from a hot filament. Various materials can be used, such as tungsten and rhenium. In some embodiments, a field emission source can be used.

[0037] The systems of Figures 1 and 2 may be combined. For example, at least one electromagnetic radiation source (e.g., 103) and at least one beta radiation source (e.g., 203) may be provided in a single system. Other radiation sources may also be present.

[0038] Returning to the generality used above, in some embodiments the radiation source comprises an electron source (i.e. the charged particles may be electrons) and exciting the radiation source comprises causing the electron source to emit free electrons. In such cases the radiation source is therefore a beta radiation source. The electron source is preferably separate from the contaminated surface of the ion optics and may comprise a filament. Exciting the radiation source may comprise heating the filament to emit free electrons. Depending on the nature of the contaminant and the required energy of the electrons, different materials for the filament may be selected.

[0039] Although the embodiments described above use electrons as the charged particles to reduce the charge, other charged particles may be used. For example, although certain embodiments are described with respect to free electrons providing the discharge, the discharge may in fact be provided by any type of charge carrier, such as protons, electrons, ions, and / or anions. Thus, some embodiments may include using a proton source, an ion source, and / or anion source to generate the charged particles and interact with the layer of contaminants.

[0040] In some embodiments, the charged particles may be activated by electromagnetic radiation. This activation may mobilize the charged particles, which may be attracted to charged molecules, thereby neutralizing those molecules. For example, mobile protons may effect charging, or mobile electrons or ions / anions within the deposit itself may effect discharging. These mechanisms may be implemented in addition to, or instead of, the mechanisms described above in connection with Figures 1 and 2.

[0041] 3 and 4, a third and fourth embodiment of the present disclosure is implemented in a Thermo Scientific™ Orbitrap Exploris™ 480 mass spectrometer, which may be described as a quadrupole ion optics. Six UV LEDs with 265 nm emission wavelength (4.68 eV) are placed on either side of the quadrupole, so that the emitted UV light penetrates the openings (slits) in the quadrupole housing and falls partially on the inner surface of the quadrupole rods. The slits in the quadrupole housing are a structural feature of many known quadrupoles, and therefore the slits are already present in existing ion optics without any modifications being required. This may allow for easy retrofitting of the embodiments of the present disclosure.

[0042] In a general sense, the ion-optical system described herein may comprise a housing having one or more apertures (e.g., slits, which are elongated openings longer than they are wide). The methods described herein may further include passing radiation (e.g., electromagnetic radiation in Figures 1 and 3 and 4, or free electrons in Figure 2) through one or more apertures. If the radiation is electromagnetic radiation, it may interact with a luminescent material to generate electrons. Electrons or other charged particles may also be passed through such apertures (slits) in the housing.

[0043] In Figures 3 and 4, the UV LED is slightly displaced up or down relative to the ion axis plane to increase the efficiency of the irradiation of the rods. This is explained in more detail in relation to Figures 8 and 9. The quadrupole rods are previously contaminated with ubiquitin. Without the use of the embodiments of the present disclosure, further deposition of ubiquitin leads to rapid charging of the contaminated areas, which causes a broadening of the separation profile. The broadening can be observed with the FlexMix calibration solution at low m / z 69, as shown in Figure 5. The different curves correspond to different exposure times of the quadrupole to ubiquitin ions. Direct injection of concentrated ubiquitin solution corresponding to a ubiquitin flow of 10 μl / min or 250 ng / min is used for these data sets. In Figure 5, the broadening of the m / z 69 separation profile can be seen after the first 2 hours of operation.

[0044] When the UV LED is turned on and the deposition of ubiquitin is repeated, no broadening of the separation profile is observed even after 57 hours, as shown in FIG. 6. In particular, the quadrupole continues to operate normally and transmits ions despite the presence of photoelectrons, as shown in FIG. 7. Ions and electrons do not interfere, as their extremely low concentration makes the probability of interaction infinitesimal over the residence time of the ions in the quadrupole (which is typically on the order of microseconds). Quadrupole neutralization and operation periods can be modified as needed. It can thus be seen that the embodiments of the present disclosure can significantly increase the interval between maintenance or cleaning.

[0045] Referring now to FIG. 8, an arrangement of radiation sources and quadrupole electrodes is shown in a fifth embodiment. The arrangement of FIG. 8 can be implemented in any of the previous embodiments, including those using internal and / or external photoelectric effects. FIG. 8(a) is a side view and FIG. 8(b) is a front view. In FIG. 8, multiple radiation sources 1 are shown facing the quadrupole rods 2 and positioned proximate to the quadrupole rods 2. In FIG. 8, it can be seen that the radiation sources are spaced apart along the length of the rods, i.e., each radiation source is at a different distance along the length of the rod. Furthermore, the LEDs are offset from the axis of the rods. The radiation sources 1 are preferably LEDs, such as UV LEDs, although other radiation sources can be provided in a similar arrangement.

[0046] Figure 9 shows the advantage of the arrangement of Figure 8. Figure 9(a) shows a horizontal arrangement of the radiation source and Figure 9(b) shows a displaced arrangement of the radiation source. Schematic diagram of light transmission in a quadrupole. In Figures 9(a) and 9(b), the radiation source 1 faces a quadrupole rod 2, which has contaminant 3 (shown as a small rectangle) on it. As can be seen from Figure 9(b), a larger surface area of ​​the contaminated region is irradiated using the displaced arrangement of Figure 9(b).

[0047] When the ion-optics comprises a pair of electrodes (or any other pair of contaminated surfaces), there is a plane that bisects the pair of electrodes. As shown in FIG. 9, it may be advantageous for one or more (i.e., multiple) radiation sources to be displaced from (i.e., not located on) the plane that bisects the pair of electrodes. This may increase the area of ​​the electrodes that is irradiated and therefore neutralized. In some embodiments, the ion-optics may comprise multiple pairs of electrodes and multiple radiation sources, each of which is displaced from the plane that bisects the respective electrode pair. It may be advantageous for no radiation source to be on the plane that bisects any of the electrode pairs.

[0048] The embodiments described herein may be applied to components within an analytical instrument. Indeed, the ion-optics described herein may be part of an analytical instrument that includes an ion source configured to provide ions to the ion-optics. The methods described herein for reducing charge contamination of a contaminating surface may be applied to any component of an analytical instrument (except the ion source).

[0049] A schematic diagram of an exemplary analytical instrument 1 is shown in FIG. 10. As shown generally in FIG. 10, the exemplary analytical instrument 1 includes an ion source 10, a mass filter 20, a fragmentation device 30, and a mass analyzer 40. It should be noted that FIG. 10 is merely schematic, and the instrument may include any number of one or more additional components, and in embodiments may of course include any number of one or more additional components, such as ion optical devices. For example, the analytical instrument 1 may include one or more ion transmission stages disposed between any of the illustrated components, including, for example, an atmospheric pressure interface configured such that some or all of the ions may be suitably transmitted through the instrument 1. The ion transmission stages may optionally include any suitable number and configuration of ion optical devices, such as one or more ion guides, lenses, and / or other ion optical devices.

[0050] The ion optics described herein may comprise any of the described components of the analytical instrument 1 (except the ion source 10), and similarly the contaminated surface may be a surface of any of the described components of the analytical instrument 1 (except the ion source 10). Similarly, the methods of reducing charge on contaminated surfaces of the optics described herein may be applied to the surface of any component of the analytical instrument 1 (except the ion source 10). In particular, the ion optics may comprise at least a portion of the mass filter 20 and / or the fragmentation device 30 and / or the mass analyzer 40 and / or other optical devices of the analytical instrument 1. The surface of the ion optics that is contaminated may be a surface of the mass filter 20 and / or a surface of the fragmentation device 30 and / or a surface of the mass analyzer 40 and / or a surface of other optical devices of the analytical instrument 1. By way of example, the contaminated surface may be a surface of an electrode of a component of the analytical instrument 1. As the mass filter 20 is particularly susceptible to contamination, the methods of reducing charge on contaminated surfaces described herein may be most usefully applied to the mass filter 20 of the analytical instrument 1. Similarly, in a preferred embodiment, the ion optics comprises a mass filter 20 of the analytical instrument 1 and the contaminated surface is a surface of the mass filter 20 .

[0051] The ion source 10 is configured to generate ions from a sample. The ion source 10 may be coupled to a separation device (not shown), such as a liquid chromatography (LC) separation device, a gas chromatography (GC) separation device, or a capillary electrophoresis separation device, whereby the sample to be ionized in the ion source 10 comes from the separation device. The ion source 10 may be any suitable ion source, such as an electrospray ionisation (ESI) ion source, an atmospheric pressure ionisation (API) ion source, a chemical ionisation ion source, an electron impact (EI) ion source, or the like. Many other types of ionisation are possible.

[0052] As mentioned above, the disclosed method and the disclosed ion-optical system use a radiation source (not shown in FIG. 10). The radiation source may include an electromagnetic radiation source as illustrated by FIGS. 1, 3 and 4 and / or a free electron source as illustrated by FIG. 2. The radiation source is separate from the ion source 10 of the analytical instrument 1. The radiation source is separate from the contaminated surfaces of the components forming part of the ion-optical system. Because the radiation source of the ion-optical system is separate from the ion source 10 of the analytical instrument 1, neutralizing at least a part of the layer of charged contaminants does not require interruption of the ion flow from the ion source 10. In fact, the ion source 10 can be operated during excitation of the radiation source and neutralization of a part of the layer of charged contaminants by interaction with the charged particles generated by the excitation. In other words, neutralizing at least a part of the layer of charged contaminants can be performed while ions are flowing from the ion source 10.

[0053] As discussed in the context of the embodiments of Figures 3 and 4, the radiation source may optionally be located outside a housing surrounding the analytical instrument components, with radiation, free electrons or other charged particles passing through openings in the housing to neutralize contaminated surfaces of the components within the housing. Alternatively, as described in the context of the embodiments of Figures 8 and 9, the radiation source may be positioned proximate to the analytical instrument components. Optionally, multiple radiation sources may be used, as illustrated by Figures 8 and 9.

[0054] The analytical instrument 1 may additionally or alternatively include an ion separator (not shown) located downstream of the ion source and configured to separate sample ions according to their physicochemical properties. For example, the instrument 1 may include an ion mobility (IM) separator, a differential ion mobility separator, or a device configured to separate ions according to their mass-to-charge ratio (m / z). The ion-optical system described herein may comprise such an ion separator, and the contaminated surface may be a surface of the ion separator.

[0055] The mass filter 20 is positioned downstream of the ion source 10 and is configured to receive ions from the ion source 10 (optionally via an ion separator). The mass filter 20 is configured to filter the received ions according to their mass to charge ratio (m / z). The mass filter 20 may be configured such that received ions having an m / z within the m / z transmission window (or "isolation window") of the mass filter are transmitted onward by the mass filter, while received ions having an m / z outside the m / z transmission window are attenuated by the mass filter, i.e. are not transmitted onward by the mass filter. The m / z width and / or central m / z of the transmission window may be controllable (variable), for example by suitable control of RF and / or DC voltages applied to the electrodes of the mass filter 20. Thus, for example, the mass filter 20 may be operable in a transmission mode of operation in which most or all ions within a relatively wide m / z window are transmitted onward by the mass filter 20, and a filtering mode of operation in which only ions within a relatively narrow m / z window (centered on a desired m / z) are transmitted onward by the mass filter 20. The mass filter 20 may be any suitable type of mass filter, such as a quadrupole mass filter. Figures 3 and 4 are examples of embodiments of the claimed invention applied to a quadrupole mass filter.

[0056] The fragmentation device 30 is disposed downstream of the mass filter 20 and is configured to receive most or all of the ions transmitted by the mass filter 20. The fragmentation device 30 may be configured to selectively fragment some or all of the received ions, i.e., to generate fragment ions. The fragmentation device 30 may be operable in a fragmentation mode of operation in which most or all of the received ions are fragmented to generate fragment ions (which may then be transmitted onward from the fragmentation device 30), and a non-fragmentation mode of operation in which most or all of the received ions are transmitted onward without (intentionally) being fragmented. It is also possible to implement a non-fragmentation mode of operation by having ions bypass the fragmentation device 30. The fragmentation device 30 may also be operable in one or more intermediate modes of operation, e.g., in which the degree of fragmentation is controllable (variable). The fragmentation device 30 may also be operable in higher order (MS) modes, e.g., in which the fragment ions are further fragmented one or more times by the fragmentation device 30. N ) fragmented mode of operation.

[0057] The fragmentation device 30 may be any suitable type of fragmentation device, such as, for example, a collision induced dissociation (CID) fragmentation device, an electron induced dissociation (EID) fragmentation device, a photodissociation fragmentation device, etc. Many other types of fragmentation are possible.

[0058] The mass analyzer 40 is disposed downstream of the fragmentation device 30 and is configured to receive ions from the fragmentation device 30. Thus, the mass analyzer 40 may receive unfragmented precursor ions and / or fragment ions depending on the operation mode of the fragmentation device 30. The mass analyzer 40 is configured to analyze the received ions to determine the mass-to-charge ratio (m / z) and / or mass of the ions, i.e. to generate a mass spectrum of the ions. The mass analyzer 40 may be any suitable type of mass analyzer, for example an ion trap mass analyzer, an electrostatic orbital trap mass analyzer (such as an Orbitrap™ FT mass analyzer manufactured by Thermo Fisher Scientific), a time-of-flight (ToF) mass analyzer such as a multi-reflecting time-of-flight (MR-ToF) mass analyzer, or a quadrupole mass analyzer. Many other types of mass analyzers are possible.

[0059] In some embodiments, instrument 1 may include one or more mass analyzers. For example, instrument 1 may be a dual mass analyzer hybrid mass spectrometer of the type described in European Patent No. 3,410,463, the contents of which are incorporated herein by reference.

[0060] 10, the instrument 1 is under the control of a control unit 50, such as a suitably programmed computer, which controls the operation of the various components of the instrument, for example setting the voltages applied to the various components of the instrument. The control unit 50 may also receive and process data from the various components, including the analyzer. The control unit 50 may be configured to independently control the operation of the ion source 10 and the operation of the radiation source.

[0061] The instrument may be capable of operating in various modes of operation, in particular the instrument may be a tandem mass spectrometer capable of operating in MS1 ​​and MS2 modes of operation.

[0062] In the MS1 (or "full mass scan") mode of operation, for example, the mass filter 20 operates in its transmission mode of operation and the fragmentation device 30 operates in its non-fragmentation mode of operation such that unfragmented ("precursor" or "parent") ions over a wide m / z range (e.g., full mass range) are analyzed by the analyzer 40 to generate an MS1 ​​spectrum.

[0063] In the MS2 mode of operation, for example, the mass filter 20 operates in its filtering mode of operation and the fragmentation device 30 operates in its fragmentation mode of operation such that precursor ions in a selected narrow m / z range are fragmented and the resulting fragment ("product" or "daughter") ions are analyzed by the analyzer 40 to generate an MS2 spectrum.

[0064] The instrument may also be capable of operating in one or more higher order fragmentation modes of operation, such as, for example, an MS3 mode of operation, whereby precursor ions are fragmented, at least some of the resulting fragment ions are themselves fragmented, and second generation fragment ions ("granddaughter ions") are analyzed by the analyzer 40 to produce an MS3 spectrum. In general, the instrument can be operated in any order fragmentation mode of operation, i.e., an MS3 mode where N>2. N It may be operable in an operational mode.

[0065] It will be appreciated that many modifications may be made to the above-described systems and methods while retaining the advantages set forth above. For example, where particular components have been described, alternative components may be provided which provide the same or similar functionality.

[0066] Although this disclosure primarily discusses positively charged contamination, negatively charged contamination can be neutralized directly by electron bombardment and / or by electromagnetic radiation (e.g., UV light). Thus, in the methods and systems described herein, the layer of charged contaminant can be a layer of positively charged contaminant or a layer of negatively charged contaminant.

[0067] The embodiments of the present disclosure can be used in a variety of ion optics without changing the geometry of the ion optics, simply by adding a radiation source (e.g., an electromagnetic radiation source such as a UV source, or a filament) at an appropriate location. Thus, the present disclosure provides a universal solution compared to existing solutions. Furthermore, the embodiments of the present disclosure are relatively low cost, and the LEDs can be operated at much lower power than their nominal power to extend their lifetime.

[0068] The embodiments of the present disclosure can be used in various ion-optical systems, such as ion guides and ion traps (e.g., quadrupoles). In some cases, a magnetic field can be used to guide the electrons. A different source of electromagnetic radiation (e.g., UV light) may be placed outside the vacuum region, with the radiation entering through an optical fiber or a window.

[0069] Embodiments of the present disclosure can use various numbers of radiation sources, and while some embodiments use six LEDs, it will be appreciated that the number, type, and arrangement of radiation sources can be varied.

[0070] Any contaminated surface of RF and / or DC ion optics, such as a quadrupole, can be treated with embodiments of the present disclosure, including when such systems are filled with gas. In some embodiments, the gas pressure can reach (e.g., be adjusted to reach) a level where the mean free path of electrons is significantly smaller than the smallest gap between the nearest electrodes of different potentials. Thus, generalizing, embodiments of the present disclosure may include controlling the gas pressure in the ion optics (e.g., in the housing of a trap, such as a quadrupole) such that the mean free path of electrons is smaller than the spacing between electrodes in the ion optics (e.g., the nearest distance between adjacent electrodes). The gas pressure used is more relevant for the external photoelectric effect, since gas pressure does not play a significant role for the internal photoelectric effect. Even at higher gas pressures, electrons with certain energies can reach the contaminant after multiple scattering from the charged region.

[0071] As mentioned above, the energy of the electrons may vary depending on the particular contaminant and the particular contaminated surface. If the photoelectric effect is used, the energy of the electromagnetic radiation may be selected so that the electrons have at least the minimum energy (e.g., work function) required to leave the luminescent material (e.g., solid metal). The electrons may be accelerated by RF and / or DC voltages on the electrodes and / or may also be affected by potentials due to impurities. The electron energy may vary from 0 eV to 3 keV (or up to 2 keV, or 1 keV, etc.). Other values ​​may also be used depending on the situation. The photon energy may be set as the work function of the luminescent material ± up to 2 eV, or up to 1 eV, to take into account the possible effects of the electron distribution and adsorbates on the Fermi energy.

[0072] The work function is 4.4-4.5 eV for stainless steel and 4.5-5 eV for Invar (Fe-36Ni), depending on the cleanliness of the surface and the measurement technique. Photoelectrons from gold-coated Invar can also be used, with various work functions reported ranging from 4.8-5.4 eV. Thus, in some embodiments, the electrons can have energy greater than the work function of the material from which the light-emitting surface is formed.

[0073] In some embodiments, the electrodes (e.g., rods) may be coated with a metal having a lower work function to facilitate the generation of photoelectrons. For example, in general terms, at least one electrode of the ion optics (and optionally the contaminated surface) may be a coated electrode that is at least partially (or completely) coated with a material having a lower work function than the material of the coated electrode. Although tunneling currents may play a role in proteins for distances less than 5 nm, since the work function of Invar (a common material) is about 4.5-5 eV, substantial neutralization by tunneling is unlikely for contamination thicknesses >5 nm. In any case, at least some electrons may be transferred from the contaminated surface to the layer of contaminant without being strictly free electrons. These electrons are mobile electrons.

[0074] It will be appreciated that the methods and systems described herein may be used repeatedly. For example, the ion optics may be at least partially neutralized repeatedly. Thus, the present disclosure also provides, in general, a method of operating an ion optics system, the method including introducing a sample into the ion optics system, manipulating and ejecting the sample using the ion optics system, and performing any of the methods for reducing charge described herein on the ion optics system. These steps may be repeated one or more times. For example, the steps may be repeated at regular intervals or between each loading of a sample. In some cases, the method may be performed continuously while a sample is being captured, transported, or otherwise manipulated. Using these methods can ensure that the performance of the ion optics system is maintained.

[0075] Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

[0076] As used herein, including in the claims, unless the context indicates otherwise, the singular form of a term herein is to be construed as including the plural, and vice versa, where the context permits. For example, unless the context indicates otherwise, in the claims, singular references such as "a" or "an" (such as an electrode or a surface) mean "one or more" (e.g., one or more electrodes, or one or more surfaces). Throughout the description and claims of this disclosure, the words "comprise", "including", "having", and "contain", as well as variations of words such as "comprising" and "comprises" or the like, mean that the features being described include additional features that follow and are not intended to (and do not) exclude the presence of other components.

[0077] 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 disclosure 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 non-claimed element as essential to the practice of the disclosure.

[0078] 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.

[0079] 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).

[0080] Additionally, the present disclosure also provides methods of making and using the systems described herein, e.g., methods of making any of the systems described herein are provided, as are methods of using the systems described herein.

Claims

1. 1. A method for reducing charge on a contaminated surface of an ion-optical system, the contaminated surface having a layer of charged contaminants thereon, the method comprising: generating charged particles by exciting a radiation source separate from the contaminated surface of the ion-optics; and neutralizing at least a portion of the layer of charged contaminants by causing the charged particles to interact with the layer of charged contaminants; (i) the radiation source comprises an electromagnetic radiation source, and exciting the radiation source comprises causing the electromagnetic radiation source to emit electromagnetic radiation, and generating the charged particles comprises interacting the electromagnetic radiation with the layer of charged contaminant and / or the ion-optics to generate the charged particles; and / or (ii) The method, wherein the radiation source comprises an electron source, and exciting the radiation source comprises causing the electron source to emit free electrons.

2. 10. The method of claim 1 , wherein the ion-optics comprises a luminescent material, and generating the charged particles comprises interacting the electromagnetic radiation with the luminescent material to generate the charged particles, and optionally the luminescent material is a metallic material.

3. The method of claim 2 , wherein the luminescent material comprises the contaminated surface of the ion-optics, preferably the contaminated surface being a surface of an electrode of the ion-optics.

4. The method of claim 2 , wherein at least a portion of the luminescent material is separate from the contaminated surface.

5. The method of claim 2 , wherein the luminescent material generates electrons and / or photons when photons from the electromagnetic radiation source interact with the luminescent material.

6. 3. The method of claim 2, wherein the ion-optics comprises a housing having one or more apertures, the method further comprising passing the electromagnetic radiation through the one or more apertures to interact with the luminescent material to produce the charged particles.

7. The method of claim 2 , wherein the electromagnetic radiation source comprises an ultraviolet (UV) radiation source and / or the electromagnetic radiation source comprises one or more light emitting diodes (LEDs).

8. 2. The method of claim 1 , wherein the electron source is separate from the contaminated surface of the ion-optics and / or the electron source comprises a filament, and exciting the radiation source comprises heating the filament to emit the free electrons.

9. 2. The method of claim 1 , wherein the ion-optics comprises one or more electrodes, and the contaminated surface is a surface of the one or more electrodes, and optionally the method further comprises controlling a gas pressure in the ion-optics such that a mean free path of electrons is smaller than a spacing between electrodes in the ion-optics.

10. 2. The method of claim 1 , wherein the ion-optics comprises a pair of electrodes and the radiation source is displaced from a plane bisecting the pair of electrodes, and optionally the ion-optics comprises multiple pairs of electrodes and multiple radiation sources, each radiation source being displaced from a plane bisecting a respective pair of electrodes.

11. 10. The method of claim 1 , wherein the ion-optics comprises one or more electrodes, and further comprising applying a voltage to at least one electrode of the ion-optics to accelerate the charged particles and thereby generate additional radiation for neutralizing the at least a portion of the layer of charged contaminants.

12. The method of claim 1 , further comprising applying a magnetic field within the ion-optics system to direct the charged particles toward the layer of charged contaminants.

13. The method of claim 1 , wherein the ion optics is a quadrupole electrode system and / or the charged particles include any one or more of protons, electrons, ions and / or anions.

14. The method of claim 1 , wherein the layer of charged contaminant is a layer of positively charged contaminant.

15. 10. The method of claim 1, wherein the ion-optics is part of an analytical instrument that includes an ion source configured to provide ions to the ion-optics, and the radiation source is separate from the contaminated surface and the ion source.

16. 2. The method of claim 1 , wherein the ion-optical system is part of an analytical instrument that includes an ion source configured to provide ions to the ion-optical system, and wherein neutralizing at least a portion of the layer of charged contaminants by interacting the charged particles with the layer of charged contaminants is performed without requiring interruption of the flow of ions from the ion source.

17. 1. A method of operating an ion-optics system, comprising the steps of: (i) introducing a sample into the ion optics; (ii) manipulating and ejecting the sample using the ion optics; (iii) performing a method for reducing charge according to any one of the preceding claims on the ion optics; and optionally repeating steps (i), (ii) and (iii) one or more times.

18. an ion optics configured to reduce charge on a contaminant surface of the ion optics, the ion optics comprising: Surface and a radiation source configured to generate charged particles, the radiation source being separate from the surface; the ion-optics is configured to neutralize at least a portion of the layer of charged contaminants on the surface by causing the charged particles to interact with the layer of charged contaminants; (i) the radiation source comprises an electromagnetic radiation source configured to emit electromagnetic radiation that interacts with the layer of charged contaminant and / or the ion-optics to generate the charged particles; and / or (ii) ion-optics, wherein the radiation source includes an electron source configured to emit free electrons.

19. The ion-optics system of claim 18 , wherein the ion-optics system includes a luminescent material, and the electromagnetic radiation source is configured to emit electromagnetic radiation that interacts with the luminescent material to generate the charged particles.

20. Ion optics according to claim 18 configured to carry out the method of claim 1.

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