Ion beam filtering

Abstract

An ion beam filter for receiving, from an ion source, a beam of ions and for transmitting ions selected from the beam of ions, the ion beam filter extending along an ion optical axis. A pair of ion optical devices is spaced along the ion optical axis and comprising a first ion optical device configured to spread the ion beam and a second ion optical device configured arranged downstream of the first ion optical device and arranged to recombine constituents of the spread beam into a single narrowed beam. A mass defining filter aperture (e.g., slit) is located between first and second ion optical devices. An array of ion optical lenses is arranged between the first ion optical device and the mass defining filter aperture (e.g., slit) and arranged between the mass defining aperture (e.g., slit) and the second ion optical device. A first ion optical lens of the array of ion optical lenses is configured to cause the paths of the ions in the beam to become substantially parallel between the first ion optical lens and second ion optical lens at the location of the mass defining filter aperture (e.g., slit).

Description

[0001] ION BEAM FILTERING

[0002] This application claims priority from GB2410707.0 filed 22 July 2024, the contents and elements of which are herein incorporated by reference for all purposes.

[0003] Field of the Invention

[0004] The present invention relates to methods and apparatus for mass spectrometry. In some aspects, this invention relates to beam filter arrangements in mass spectrometers, particularly mass spectrometers which use an inductively coupled plasma as the source of ions which are then passed into a mass analyser arrangement to enable ions of different mass to be separated, their abundance measured or their relative abundance analysed. So-called inductively coupled plasma mass spectrometers are widely used in many fields.

[0005] Background

[0006] Various arrangements of such spectrometers are disclosed in the patent literature. In particular, attention is drawn to specifications GB2535826, GB2545670, EP3769334 and its divisional EP3901984. All of these disclose ways of filtering the beam of ions between an ion source and a mass analyser in order to improve the performance of the spectrometer itself.

[0007] In particular, EP3769334 and its divisional EP3901984 disclose the use of a static field mass filter arranged between an ion source and a mass analyser and it discloses a static field mass filter incorporating two Wien filters one of which spreads the ion beam out and the other recombining it, and which can include an inverting lens located between the two Wien filters. This arrangement is illustrated in Figures 10b and 10c of EP3910984, and operates in practice as follows:

[0008] The ion beam entering at the left of Figure 10b is focussed to form an image at the mass defining slit with an Einzel lens. Between a first Einzel lens and the mass defining slit is a first Wien filter which acts to separate the ions according to their m / z ratio which means ions of different masses leave the Wien filter with a range of mass dependent inclinations. Mass selection is carried out directly after the first Wien filter, prior to the point of maximum dispersion with the ions moving away from the optical axis.

[0009] After mass selection, the mass dependent inclination is reversed by using a second Einzel lens set to an appropriate voltage, which inverts the ions paths back towards to optical axis. The Einzel lens is split into four segments (opposite faces at same potential) which minimises the vertical defocussing that would occur otherwise. In Figure 10b the inverted beam enters a second Wien filter and second Einzel lens, and due to the symmetry of the system, recombines to form an image at the exit slit on the right of the Figure.

[0010] In a modification, shown in Figure 10c of EP3901984, an inverting lens is located just downstream of the mass defining slit. The arrangements disclosed in these two specifications suffer from a number of disadvantages, including having a fixed location electromagnet so a magnetic field is always present in some capacity which affects the ion path.

[0011] The optical acceptance of the second Einzel in the dispersive plane limits the maximum allowable B field for a given transmitted mass, and the arrangements shown give rise to a large image magnification at the mass defining slit due to the system geometry.

[0012] The present invention has been devised in light of the above considerations. Summary of the Invention

[0013] In a first aspect, the invention may provide an ion beam filter for receiving, from an ion source, a beam of ions and for transmitting ions selected from the beam of ions, the ion beam filter extending along an ion optical axis and comprising: a pair of ion optical devices spaced along the ion optical axis and comprising a first ion optical device configured to spread the ion beam and a second ion optical device configured arranged downstream of the first ion optical device and arranged to recombine constituents of the spread beam into a single narrowed beam, wherein each said ion optical device is configured to form a magnetic field extending in a direction across the ion optical axis and to form an electric field extending in a direction across the ion optical axis and across the direction of the magnetic field, therewith to deflect ions of the beam in directions transverse to the ion optical axis to an extent according to their respective velocity; a mass defining filter aperture (e.g., a slit) located between first and second ion optical devices; and, an array of ion optical lenses comprising a first ion optical lens arranged between the first ion optical device and the mass defining aperture (e.g., a slit) and a second ion optical lens arranged between the mass defining aperture (e.g., a slit) and the second ion optical device; wherein the first ion optical lens of the array of ion optical lenses is configured to cause the paths of the ions (e.g., trajectories) in the beam to become substantially parallel between the first ion optical lens and second ion optical lens, preferably at or adjacent to the location of the mass defining filter aperture (e.g., a slit).

[0014] In this way, improved resolution of the filtering of the ion beam may be achieved by implementing the filtering upon a spread-out beam that is collimated (i.e., parallel beam constituents). Unwanted constituents may be removed, and / or desired constituents of the beam may be more accurately selected.

[0015] Also, with the ion beam filter according to the first aspect, it is possible for the mass defining filter aperture to be positioned at a plane (e.g. equidistant from the pair of ion optical devices) at which ions having the same m / z converge spatially as they approach the plane and diverge spatially as they recede from the plane (see e.g. discussion below, and also Figure 2, and Figures 29 and 30).

[0016] The ion beam filter may be arranged for location between an ion source and a mass analyser in a mass spectrometer. The ion source may comprise an inductively coupled plasma (ICP) ion source.

[0017] A collision / reaction cell (CRC) may be positioned between the ion beam filter and the mass analyser in the mass spectrometer. The ion beam filter may be used to define a specific mass transmission window, which may allow for the use of reactive gases inside the collision / reaction cell, e.g. for interference removal that would otherwise cause additional interferences at the mass analyser or for analyte mass shifting to avoid interferences.

[0018] In the following disclosures, references are made, in some places, to “Wien filter”. The common usage of this term, in the art, typically refers to a device comprising at least the following two parts:

[0019] (1) a first part comprising an ion optical device configured to form a magnetic field extending in a direction across an ion optical axis and to form an electric field extending in a direction across the ion optical axis and across the direction of the magnetic field, therewith to deflect ions of an ion beam passing through it in directions transverse to the ion optical axis (e.g., the beam axis) to an extent according to their respective ion velocity;

[0020] (2) a second part comprising an aperture (e.g., a slit or hole) positioned downstream of the first part for transmitting only those ions deflected by the first part to pass through the aperture, and to prevent onward transmission of ions that deflected otherwise. Some less common usages of the term “Wien filter” are present in the prior art, and those usages intend to refer more broadly to at least the first part (1) identified above, and optionally to include the second feature (2) identified above, as the context permits. For the avoidance of doubt, explicit references herein to “Wien filter” may be understood to be consistent with the more broadly-defined usage of this term within the art, and to encompass at least the first part (1) identified above, and optionally to include the second feature (2) identified above, as the context permits.

[0021] In the following disclosures, references are made, in some places, to a “lens field array” and this term may be understood to include a reference to an ion optical lens comprising an array of electrodes operable to generate an electric field to act upon ions to achieve a lens functionality.

[0022] The first ion optical device may be configured to deflect received ions in directions so as to follow deflected respective ion paths (e.g., trajectories), and the first ion optical lens is configured to receive the deflected ions from the first ion optical device and to deflect the received ions according to their respective deflected ion paths (e.g., trajectories). Thus, the degree of deflection of an ion may be determined according to the trajectory upon which it enters the ion optical lens. This trajectory-dependent deflection may be achieved by creating an electrical potential within the ion optical device that comprises a spatial distribution (e.g., linear, quadratic or cubic etc.) in a direction across the ion optical axis of the ion optical lens. In this way, a synergy is formed between the trajectory-dispersing action of the ion optical device and the trajectory-dependent deflection of the ion optical lens to respond to different ion trajectories delivered to it by the ion optical device.

[0023] The mass defining aperture (e.g., slit) may be configured for selectively transmitting only ions received from the first ion optical lens upon respective ion paths (e.g., trajectories) that pass through the mass defining filter aperture (e.g., a slit), and for obstructing transmission of received ions upon other ion paths (e.g., trajectories). The mass defining filter aperture (e.g., slit) may be formed between two the edges of two ion barrier walls, each being independently movable in a direction perpendicular to the ion optical axis whereby the location and width of the mass defining filter aperture (e.g., a slit) may be independently adjusted.

[0024] The ion beam filter may comprise an ion blocking device located within or adjacent to (e.g. upstream or downstream of) the space of the mass defining filter aperture and configured to block ions from the ion beam received from the first ion optical lens upon at least one (e.g. respective) ion path (e.g., one or more trajectories) that intersects the ion blocking device for preventing the transmission of received ions upon the at least one intersecting ion path, whilst allowing transmission of other ions in the ion beam. The ion blocking device may be configured to block ions having one or more predetermined m / z values. The ion blocking device may provide the function of a notch filter to remove a small portion of ions from the beam that would otherwise have been transmitted by the mass defining filter aperture. This may be useful e.g. to remove unwanted components of the ion beam, e.g. Argon (which can cause damage to downstream components in a mass spectrometer).

[0025] The ion blocking device may be configured (e.g. suitably positioned) to block some but not all ions having the one or more predetermined m / z values, e.g. to allow some of the ions having the predetermined m / z values to be measured by a downstream mass analyser. This may be useful when ions having the predetermined m / z values might otherwise saturate the mass analyser, but it would be useful to measure some of the ions having the predetermined m / z value.

[0026] The ion blocking device may take the form of an ion collector. The ion collector may comprise an ion detector for generating an ion detection signal in response to the collection of ions. The ion detector may comprise a Faraday Cup, for example. The ion beam filter may include a translation assembly configured to move the ion blocking device (which may take the form of an ion collector) transversely relative to the ion optical axis thereby to selectively position the ion collector laterally relative to the mass defining filter aperture (e.g., a slit). When the ion blocking device takes the form of an ion collector comprising an ion detector, this may allow the provision of a mass spectrometry function in itself, as noted in an aspect of the invention below.

[0027] The ion beam filter may be arranged such that the first ion optical device is configured to receive said beam of ions, to deflect ions thereof and to output ions thereof upon respective ion paths (e.g., trajectories) that diverge, thereby to spread the beam of ions. The ion beam filter may be arranged such that the first ion optical lens is configured to receive ions from the first ion optical device upon said respective ion paths (e.g., trajectories) and to deflect the received ions so as to output ions upon respective ion paths (e.g., trajectories) that are substantially parallel, thereby substantially to collimate the beam of ions such that ion paths (e.g., trajectories) subsequently received by the mass defining aperture (e.g., slit) are substantially parallel. The ion beam filter may be arranged such that the second ion optical lens is configured to receive, via the mass defining filter aperture (e.g., a slit), ions from the first ion optical lens upon said substantially parallel paths (e.g., trajectories) and to deflect the received ions so as to output ions upon respective ion paths (e.g., trajectories) that converge, thereby to narrow the beam of ions. The ion beam filter may be arranged such that the second ion optical device is configured to receive ions from the second ion optical lens and to deflect the received ions so as to output ions upon respective trajectories that are substantially parallel, thereby substantially to collimate the narrowed beam of ions.

[0028] The ion beam filter may comprise a first transverse-focussing ion optical lens (which may also be referred to herein as a “vertical lens”) located upon the ion optical axis between the first ion optical device and the first ion optical lens and a second transverse-focussing ion optical lens located upon the ion optical axis between the second ion optical lens and the second ion optical device, wherein each transverse- focussing ion optical lens is configured to deflect ions of the beam in directions transverse to the ion optical axis and transverse to the deflection by the first and second ion optical devices.

[0029] One or more of the first ion optical device and the second ion optical device may comprise an ion entrance opening for receiving ions, an ion exit opening from which received ions are output, and an ion transmission channel for transmission of received ions in a direction along an ion optical axis from the ion entrance opening to the ion exit opening, the ion optical device further comprising: a magnetic yoke formed around the ion transmission channel; and, a first permanent magnet which is attached to the magnetic yoke within the ion transmission channel and a second permanent magnet which is attached to the yoke within the ion transmission channel in spaced opposition to the first permanent magnet across the ion transmission channel to form therebetween said magnetic field extending in a direction across the ion optical axis.

[0030] One or each of the permanent magnets may comprise a Neodymium Iron Boron (NdFeB) magnet. A magnet grade of between N24 up to N52, preferably N42, may be used. The grade N42 means a neodymium magnet has a maximum energy product of 42 MGOe (here the unt “MGOe” refers to MegaGauss Oersteds where 1 MGOe (cgs units) equals 7958kJ / m3 (SI units)). This refers to the maximum magnetic energy that the material can be stored, as would be readily appreciated by the person skilled in the art.

[0031] The magnetic yoke may provide a magnetic field flux-return path internally within the magnetic yoke for a magnetic field passing from the first permanent magnet to the second permanent magnet, and an external magnetic field flux-return path which spans across the ion transmission channel from the second permanent magnet to the opposing first permanent magnet to form therebetween a magnetic field extending in a direction across the ion optical axis. The ion beam filter may comprise (e.g. in an aforementioned ion optical device) a first array of electrodes extending in free space across the first permanent magnet within the ion transmission channel, and a second array of electrodes extending in free space across the second permanent magnet within the ion transmission channel in spaced opposition to the first array of electrodes across the ion transmission channel, wherein the first and second arrays of electrodes are configured to receive respective voltage signals therewith collectively to form said electric field extending in a direction across the ion optical axis and across the direction of the magnetic field. By providing the electrode array in free space one is able to avoid the need to use the magnets to support the electrodes, and thereby avoid the use of dielectric materials to bond electrodes to the surface of the permanent magnets. The removal of dielectric material from the beam path has the benefit that any injection current from the charged particle beam will not cause instability issues. By providing the electrode array in free space one is also able to allow the disassembly of the ion optical device to permit cleaning and / or optional removal and replacement of a permanent magnet to change its geometry or grade, as desired.

[0032] The ion beam filter (e.g. in an aforementioned ion optical device) may comprise a first electrode support plate adjacent to the ion entrance opening and a second electrode support plate adjacent to the ion exit opening, wherein the first array of electrodes is suspended in free space between the first electrode support plate and the second electrode support plate, and the first and second electrode support plates are each formed of a non-conducting material bearing: one or more electrical contact terminals configured to receive a voltage signal from amongst said respective voltage signals, and one or more conductive tracks electrically connecting one or more electrodes amongst the first array of electrodes to the one or more electrical contact terminals.

[0033] The ion beam filter (e.g. in an aforementioned ion optical device) may comprise a third electrode support plate adjacent to the ion entrance opening and a fourth electrode support plate adjacent to the ion exit opening, wherein the second array of electrodes is suspended in free space between the third electrode support plate and the fourth electrode support plate, and the third and fourth electrode support plates are each formed of a non-conducting material bearing: one or more electrical contact terminals configured to receive a voltage signal from amongst said respective voltage signals, and one or more conductive tracks electrically connecting one or more electrodes amongst the second array of electrodes to the one or more electrical contact terminals.

[0034] The first electrode support plate and the third electrode support plate may each comprise a respective part of one common electrode support plate. The second electrode support plate and the fourth electrode support plate may each comprise a respective part of one common electrode support plate.

[0035] The one or more electrical contact terminals may comprise a spring-loaded contact or a Pogo Pin permitting the one or more electrical contact terminals to be mechanically pressed into electrical contact with a source of said respective voltage signals (e.g., from a power source).

[0036] The magnetic yoke may comprise a two-piece yoke assembly comprising: a first yoke piece to which the first permanent magnet and second permanent magnet are attached; and, a separate second yoke piece attached to the first yoke piece to form a lateral side of the ion transmission channel; wherein the second yoke piece is detachable from the first yoke piece to reveal the ion transmission channel to permit a lateral access to the ion transmission channel, and re-attachable to the first yoke piece to complete said magnetic field flux-return path internally within the magnetic yoke. In some examples (not shown), the magnetic yoke may comprise a plurality of successive said two-piece yoke assemblies connected in mutual alignment in succession along the ion optical axis thereby forming a concatenated array.

[0037] The first array of electrodes and the second array of electrodes may each comprise a plurality of spatially separated electrodes each of which extends in a direction along the ion transmission channel wherein each electrode of the respective array of electrodes is spaced apart from each neighbouring electrode of the respective array in a direction extending across the ion transmission channel.

[0038] The first permanent magnet and / or the second permanent magnet may be removeable and replaceable to permit adjustment of a geometry and / or a grade of the permanent magnet according to a replacement permanent magnet.

[0039] The ion beam filter may comprise: a carriage to which the first ion optical device and / or the second ion optical device are mounted wherein the chassis is operable to move between: a deployed position in which the ion transmission channel of the first ion optical device and / or the ion transmission channel of the second ion optical device is aligned with the ion optical axis of the ion beam filter; and, a retracted position in which the ion transmission channel of the first ion optical device and / or the ion transmission channel of the second ion optical device is laterally displaced from the ion optical axis of the ion beam filter to an extent sufficient that ions or the ion beam are neither received into the ion transmission channel nor obstructed by the first ion optical device and / or by the second ion optical device.

[0040] The ion beam filter may comprise a magnetic shield assembly laterally offset from the ion transmission channel by a lateral offset corresponding to the lateral displacement between the deployed position and the retracted position, wherein the magnetic shield assembly is positionable, by positioning the carriage in the retracted position, to shield the flow of ions from a magnetic field flux extending along the magnetic field flux-return path external to the magnetic yoke of the first ion optical device and / or the second ion optical device.

[0041] The magnetic shield assembly may comprise a tubular conduit defining a longitudinal conduit axis configured to extend in a direction substantially parallel to the ion optical axis of the first ion optical device and / or the second ion optical device, and configured to receive the flow of ions therealong when the translation stage is in the retracted position.

[0042] The magnetic shield assembly may comprise a material having a relative permeability of at least 80,000. In other examples the magnetic shield assembly may comprise a material having a relative permeability of less than 80,000. The magnetic shield assembly may comprise a Mu Metal material. The magnetic shield assembly may be tubular to permit transmission of the ion beam along the tubular axis thereof.

[0043] One or more of the first ion optical lens and the second ion optical lens may comprise an ion entrance opening for receiving ions, an ion exit opening from which received ions are output, and an ion transmission channel for transmission of received ions in a direction along an ion optical axis from the ion entrance opening to the ion exit opening, the ion optical lens further comprising: one or more electrode plates configured to receive respective voltage signals therewith collectively to form an electric field to produce an ion optical effect within the ion transmission channel; a chassis to which the plurality of electrode plates are attached in spaced succession within the ion optical axis; wherein the one or more electrode plates each comprise at least one attachment through- opening formed therein, and the chassis comprises one or more mounting rods formed of an electrically non-conducting material which passes through the attachment through-opening of each of the one or more electrode plates thereby to attach the one or more electrode plates to the chassis along the one or more mounting rods without forming an electrical connection between the one or more electrode plates.

[0044] Each of the one or more electrode plates may be bonded to the at least one mounting rod by a nonconducting bonding material bonded to a surface of the at least one said mounting rod and bonded to a surface of the one or more electrode plates thereby connecting each respective electrode plate to the at least one mounting rod.

[0045] The non-conducting bonding material may form a continuous bond circumferentially around the mounting rod to which it is bonded and forms a continuous bond circumferentially around the attachment through- opening of the electrode plate to which it is bonded.

[0046] The non-conducting bonding material may comprise a resin, such as an epoxy resin of the like.

[0047] The one or more mounting rods may comprise a ceramic material.

[0048] The ion beam filter may comprise a first einzel lens located upon the ion optical axis upstream of the first ion optical device and a second einzel lens located upon the ion optical axis downstream of the second ion optical device, wherein the first einzel lens is configured to bring ions having the same m / z to a spatial focus at the mass defining filter aperture plane (defined below). The second einzel lens may be configured to focus the ion beam so that the ion beam profile matches that of the ion beam that entered the ion beam filter. Thus the second einzel lens may be identical to the first einzel lens, mirrored about the mass defining filter aperture plane.

[0049] The mass defining filter aperture may be located at a mass defining filter aperture plane perpendicular to the ion optical axis. The mass defining filter aperture plane may provide a mirror axis of symmetry for multiple pairs of ion optical components within the ion beam filter. Thus, the ion beam filter may include multiple pairs of ion optical components, wherein each pair of ion optical components includes (respectively) a first component located on a first side of the mass defining filter aperture and a second component located on a second side of the mass defining filter aperture, the first and second components being equidistant from the mass defining filter aperture plane (along the ion optical axis). One such pair of ion optical components may be the first and second ion optical devices. Another such pair of ion optical components may be the first and second ion optical lenses. Another such pair of ion optical components may include the first and second transverse-focussing ion optical lenses (as discussed below). Another such pair of ion optical components may include first and second einzel lenses.

[0050] The ion beam filter may include one or more ion optical components configured to bring ions having a same m / z (in the ion beam) to a focus at the mass defining filter aperture plane, i.e. so that ions having a same m / z converge spatially as they approach the mass defining filter aperture plane and diverge spatially as they recede from the mass defining filter aperture plane (see e.g. Figure 2, and Figures 29 and 30). The ion optical components configured to bring ions to a focus in this way may include e.g. any one or more of the first einzel lens, the first ion optical device, the first transverse focusing ion optical lens, and the first ion optical lens.

[0051] The ion beam filter may include one or more additional ion optical components (i.e. in addition to those mentioned above) for providing additional focusing.

[0052] In a second aspect, the invention may comprise a mass spectrometer comprising an ion beam filter according to the invention in its first aspect. The mass spectrometer may additionally comprise an ion source and a mass analyser. The ion beam filter may be in location between an ion source and a mass analyser of the mass spectrometer. The ion source may comprise an inductively coupled plasma (ICP) ion source. The mass spectrometer may additionally comprise a collision / reaction cell (CRC). The collision / reaction cell (CRC) of the mass spectrometer may be positioned between the ion beam filter and the mass analyser in the mass spectrometer.

[0053] In a third aspect, the invention may provide an ion beam filtering method for selected ions from the beam of ions for transmission along an ion optical axis, the method comprising: providing, on the ion optical axis, a pair of ion optical devices spaced along the ion optical axis and: by a first said ion optical device, spreading the ion beam; by a second said ion optical device arranged downstream of the first ion optical device, recombining constituents of the spread beam into a single narrowed beam; wherein, by each said ion optical device, forming a magnetic field extending in a direction across the ion optical axis and forming an electric field extending in a direction across the ion optical axis and across the direction of the magnetic field, and therewith deflect ions of the beam in directions transverse to the ion optical axis to an extent according to their respective velocity; providing, on the ion optical axis, a mass defining filter aperture (e.g., a slit) located between first and second ion optical devices; and, providing, on the ion optical axis, an array of ion optical lenses comprising a first ion optical lens arranged between the first ion optical device and the mass defining filter aperture (e.g., a slit) and a second ion optical lens arranged between the mass defining aperture (e.g., slit) and the second ion optical device; and, by the first ion optical lens of the array of ion optical lenses, causing the paths (e.g., trajectories) of the ions in the beam to become substantially parallel between the first ion optical lens and second ion optical lens at the location of the mass defining filter aperture (e.g., a slit).

[0054] In a fourth aspect, the invention may provide an ion beam filter for receiving, from an ion source, a beam of ions and for transmitting ions selected from the beam of ions, the ion beam filter extending along an ion optical axis and comprising: a first ion optical device and a second ion optical device, each being configured to form: a magnetic field extending in a direction across the ion optical axis; and, an electric field extending in a direction across the ion optical axis and across the direction of the magnetic field; such that ions received thereby are deflected in directions transverse to the ion optical axis to an extent according to their velocity so as to follow deflected respective ion paths (e.g., trajectories); a first ion optical lens and a second ion optical lens, each being configured to receive ions and to deflect ions received thereby according to their respective ion paths (e.g., trajectories); and, a mass defining aperture (e.g., slit) located between the first ion optical lens and a second ion optical lens and configured for selectively transmitting only ions received from the first ion optical lens upon respective ion paths (e.g., trajectories) that pass through the aperture (e.g., slit), and for preventing transmission of received ions upon other ion paths (e.g., trajectories); wherein: the first ion optical device is configured to receive said beam of ions, to deflect ions thereof and to output ions thereof upon respective ion paths (e.g., trajectories) that diverge, thereby to spread the beam of ions; the first ion optical lens is configured to receive ions from the first ion optical device upon said respective ion paths (e.g., trajectories) and to deflect the received ions so as to output ions upon respective ion trajectories (e.g., trajectories) that are substantially parallel, thereby substantially to collimate the beam of ions such that ion paths (e.g., trajectories) subsequently received by the aperture (e.g., slit) are substantially parallel; the second ion optical lens is configured to receive, via the aperture (e.g., slit), ions from the first ion optical lens upon said substantially parallel ion paths (e.g., trajectories) and to deflect the received ions so as to output ions upon respective ion paths (e.g., trajectories) that converge, thereby to narrow the beam of ions; and, the second ion optical device is configured to receive ions from the second ion optical lens and to deflect the received ions so as to output ions upon respective ion paths (e.g., trajectories) that are substantially parallel, thereby substantially to collimate the narrowed beam of ions.

[0055] An ion optical device disclosed above in relation to the invention in its first aspect may be made and sold as an independent entity, separately from the ion beam filter.

[0056] Accordingly, in a fifth aspect, the invention may provide an ion optical device comprising an ion entrance opening for receiving ions, an ion exit opening from which received ions are output, and an ion transmission channel for transmission of received ions in a direction along an ion optical axis from the ion entrance opening to the ion exit opening, the ion optical device further comprising: a magnetic yoke formed around the ion transmission channel; a first permanent magnet which is attached to the magnetic yoke within the ion transmission channel and a second permanent magnet which is attached to the yoke within the ion transmission channel in spaced opposition to the first permanent magnet across the ion transmission channel; wherein the magnetic yoke provides a magnetic field flux-return path internally within the magnetic yoke for a magnetic field passing from the first permanent magnet to the second permanent magnet, and an external magnetic field flux-return path which spans across the ion transmission channel from the second permanent magnet to the opposing first permanent magnet to form therebetween a magnetic field extending in a direction across the ion optical axis; a first array of electrodes extending in free space across the first permanent magnet within the ion transmission channel, and a second array of electrodes extending in free space across the second permanent magnet within the ion transmission channel in spaced opposition to the first array of electrodes across the ion transmission channel, wherein the first and second arrays of electrodes are configured to receive respective voltage signals therewith collectively to form an electric field extending in a direction across the ion optical axis and across the direction of the magnetic field such that received ions transmitted through the ion transmission channel are deflected in directions transverse to the ion optical axis to an extent according to their velocity thereby to output the ions upon dispersed trajectories.

[0057] Any one or more of the further optional features of an ion optical device disclose above in relation to the invention in its first aspect may be considered similarly as further optional features of the ion optical device in the fifth aspect of the invention.

[0058] In a sixth aspect, the invention may provide an ion beam filter for receiving, from an ion source, a beam of ions and for transmitting ions selected from the beam of ions, the ion beam filter extending along an ion optical axis and comprising: a carriage to which a first ion optical device according to the invention in its fifth aspect and / or a second ion optical device according to the invention in its fifth aspect, are mounted wherein the chassis is operable to move between: a deployed position in which the ion transmission channel of the first ion optical device and / or the ion transmission channel of the second ion optical device is aligned with the ion optical axis of the ion beam filter; and, a retracted position in which the ion transmission channel of the first ion optical device and / or the ion transmission channel of the second ion optical device is laterally displaced from the ion optical axis of the ion beam filter to an extent sufficient that ions or the ion beam are neither received into the ion transmission channel nor obstructed by the first ion optical device and / or by the second ion optical device. An ion beam filter disclosed above in relation to the invention in its sixth aspect may be according to the invention in its first aspect. An ion optical device disclosed above in relation to the invention in its sixth aspect first aspect may be according to the invention in its fifth aspect.

[0059] In a seventh aspect, the invention may provide a mass spectrometer comprising: an ion source for producing, from a sample, a plurality of ions each sharing substantially the same kinetic energy and each possessing a respective mass from a plurality of different masses present amongst the plurality of ions; the ion optical device according to the invention in its fifth aspect, arranged for receiving the plurality of ions such that received ions transmitted through the ion transmission channel are deflected in directions transverse to the ion optical axis to an extent according to their mass thereby to output the ions upon dispersed ion paths (e.g., trajectories); an ion optical lens arranged for receiving deflected ions upon the dispersed ion paths (e.g., trajectories) and for further deflecting the received ions in directions transverse to the optical axis to cause the paths (e.g., trajectories) of the ions output by the ion optical lens to be substantially parallel to the ion optical axis; and, an ion detector arranged to move in a direction transverse to the ion optical axis to different selected positions in a plane containing the dispersed ion paths (e.g., trajectories) thereby to detect ions of different masses present amongst the plurality of ions according to the different selected positions of the ion detector.

[0060] An ion optical device disclosed above in relation to the invention in its sixth aspect may be according to the invention in its fifth aspect.

[0061] In an eighth aspect, the invention may provide an ion optical lens or lens element (e.g., for use in a mass spectrometer apparatus) comprising an ion entrance opening for receiving ions, an ion exit opening from which received ions are output, and an ion transmission channel for transmission of received ions in a direction along an ion optical axis from the ion entrance opening to the ion exit opening, the ion optical lens (or lens element) further comprising: one or more electrode plates configured to receive respective voltage signals therewith collectively to form an electric field to produce an ion optical effect within the ion transmission channel; a chassis to which the plurality of electrode plates are attached in spaced succession within the ion optical axis; wherein the one or more electrode plates each comprise at least one attachment through-opening formed therein, and the chassis comprises one or more mounting rods formed of an electrically nonconducting material which passes through the attachment through-opening of each of the one or more electrode plates thereby to attach the one or more electrode plates to the chassis along the one or more mounting rods without forming an electrical connection between the one or more electrode plates.

[0062] An ion optical lens disclosed above in relation to the invention in its eighth aspect may be employed as an ion optical lens within the invention in its first aspect or its fourth aspect. The ion optical lens may form an Einsel lens, for example, or other ion optical lens or lens element.

[0063] According to a ninth aspect of the present invention there may be provided a beam filter arrangement for location between an ion source and a mass analyser in a mass spectrometer and including a pair of spaced Wien filters arranged to spread the ion beam and subsequently recombine constituents of the beam into a single narrow beam. For example the invention in this aspect may provide a beam filter arrangement for location between an ion source and a mass analyser in a mass spectrometer, and comprising a pair of spaced Wien filters, the first to spread the ion beam and the second arranged downstream of the first and arranged to recombine constituents of the beam into a single narrow beam, and a mass defining slit located between first and second Wien filters and lens field arrays between the first Wien filter and the mass defining slit and between the mass defining slit and the second Wien filter, the lens field arrays being arranged to cause the paths of the ions in the beam between the two lens field arrays to be substantially parallel.

[0064] The beam filter arrangement may comprise a first vertical lens between the first Wien filter and the upstream lens field array and a second vertical lens between the downstream lens field array and the downstream Wien filter.

[0065] The mass defining slit may be formed between two the edges of two ion barrier walls, each independently movable in a direction perpendicular to the main beam direction whereby the location and width of the mass defining slit may be independently adjusted. The beam filter arrangement according may comprise a notch filter positioned within the space of the mass defining slit.

[0066] A beam filter arrangement may comprise a mechanism of device means to move the notch filter transversely relative to the beam direction and between a position where it is located outside the ion beam, where it is centrally located relative to the ion beam, and one where it is positioned symmetrically non-adjacent to the initial position, and all points therein.

[0067] The beam filter arrangement may be mounted and grounded (e.g., electrically) to a carriage located in a vacuum chamber across which the ion beam traverses, the carriage being movable transverse to the beam direction from a position where the beam passes through the beam filter (mass filter) to one in which it travels to one side thereof.

[0068] The carriage may be electrically isolated from the ground potential, such that the carriage reference potential can be adjusted.

[0069] The permanent magnet geometry and grade may be adjusted to generate a range of available performance criteria.

[0070] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0071] Summary of the Figures

[0072] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0073] Figure 1 is a diagrammatic illustration of an ion source chamber forming part of a mass spectrometer.

[0074] Figure 2 is a diagrammatic view of the upstream portion of a beam filter arrangement in accordance with the present invention.

[0075] Figure 3 is a diagrammatic illustration of a complete ion beam filter arrangement.

[0076] Figure 4 is a diagrammatic illustration of the arrangement of Figure 3 mounted on a carriage movable transversely to the direction of the ion beam, and in a position where the ion beam filter is not in the path of the ion beam.

[0077] Figure 5 is a diagrammatic illustration of the ion beam filter arrangement when located in the path of the ion beam between the ion source and the mass analyser.

[0078] Figure 6 shows a cross-sectional view of an ion optical device.

[0079] Figures 7(A), 7(B) and 7(C) show views of an ion optical device consistent with the ion optical device of Figure 6: (A) an isometric view; (B) a cross-sectional view of the device of Figure 7(A), and; (C) another cross-sectional view of the device of Figure 7(A). Figures 8(A), 8(B) and 8(C) show views of electrode arrays in an ion optical device consistent with the ion optical device of Figure 6: (A) a plan view; (B) an isometric cross-sectional view of the electrode arrays of Figure 8(A), and; (C) a isometric view of the electrode arrays of Figure 8(A).

[0080] Figures 9(A), 9(B) and 9(C) show views of stages of assembly of an ion optical device consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C) and the electrode arrays of Figures 8(A), 8(B) and 8(C): (A) a plan view; (B) an isometric view of the device of Figure 8(A), and; (C) a isometric view of the electrode arrays of Figure 8(A).

[0081] Figure 10a shows a cross-sectional view of a hexapolar electric potential formed by a hexapolar electrode rod set.

[0082] Figure 11a shows a view of the cubic form of a hexapolar electric potential as measured along a line joining two opposing hexapolar electrodes of the electrode rod set of Figure 10.

[0083] Figure 12a shows a view of the cubic form of an electric potential formed at points between opposing electrodes of the electrode arrays of Figures 8(A), 8(B) and 8(C) in an ion optical device consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C) when a hexapolar electric potential is used.

[0084] Figure 10b shows a cross-sectional view of a quadrupolar electric potential formed by a quadrupolar electrode rod set.

[0085] Figure 11b shows a view of quadrupolar electric potential as measured along a line joining two opposing quadrupolar electrodes of the electrode rod set of Figure 10b.

[0086] Figure 12b shows a view of the electric potential formed at points between opposing electrodes of the electrode arrays of Figures 8(A), 8(B) and 8(C) in an ion optical device consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C) when a quadrupolar electric potential is used.

[0087] Figures 13, 14 and 15 show views of an ion optical lens: Figure 13 - an isometric view; Figure 14 - a transparent view of the lens of Figure 13, and; Figure 15 - a cross-sectional view of the lens of Figure 13.

[0088] Figures 16 shows a schematic view of an electrode structure amongst a set of electrodes within the ion optical lens of Figure 13, Figure 14 and Figure 15.

[0089] Figures 17, 18 and 19 show views of an ion optical lens: Figure 17 - an isometric view; Figure 18 - a cross-sectional isometric view of the lens of Figure 17, and; Figure 19 - a cross-sectional side view of the lens of Figure 17.

[0090] Figure 20 shows a views of the ion optical lens of Figure 17 mounted in electrical connection with a circuit board via a set of spring pin (Pogo Pin) connectors.

[0091] Figure 21 shows a views of the ion optical lens of Figures 13 to 15 mounted in connection with a mass defining filter aperture (e.g., a slit) and a notch filter useable as an ion detector.

[0092] Figure 22 shows an ion beam filter arrangement consistent with Figure 5 in which both ion optical devices of a pair of ion optical devices of the beam filter are mounted upon a retractable carriage. The carriage is shown in the deployed position.

[0093] Figure 23 shows an ion beam filter arrangement of Figure 22 in the carriage is shown in the retracted position.

[0094] Figures 24 and 25 show views an ion optical device consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C) and Figures 8(A), 8(B) and 8(C) and Figures 9(A), 9(B) and 9(C). Figure 24 - an isometric view of the ion optical device, and; Figure 25 - a plan view of the ion optical device. Figures 26, 27 and 28 show views of an ion optical lens.

[0095] Figures 29 and 30 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species: Figure 29 - a ‘top-down’ view of a horizontal plane within the assembly; Figure 30 - a ‘sideways’ view of a vertical plane within the assembly.

[0096] Figures 31 and 32 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species: Figure 31 - a ‘top-down’ view of a horizontal plane within the assembly in which the mass defining filter aperture (e.g., a slit) of the assembly is positioned in a first position to allow transmission of a selected atomic species and to prevent transmission of other atomic species; Figure 32 - a ‘top-down’ view of a horizontal plane within the assembly in which the mass defining filter aperture (e.g., a slit) of the assembly is positioned in a different second position to allow transmission of a different selected atomic species and to prevent transmission of other atomic species.

[0097] Figures 33 and 34 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species: Figure 33 - a ‘top-down’ view of a horizontal plane within the assembly in which the magnetic field magnitude within both ion optical devices has been selected (i.e. though change of magnet grade or geometry) such that a substantial proportion of the atomic ion species from the source (i.e. between an m / z of 5 and 300) is transmitted, defining a broad transmission window; Figure 34 - a ‘top-down’ view of a horizontal plane within the assembly in which an ion device has been positioned to intersect the trajectory of an atomic ion species of given m / z value within the broad transmission window, such that this atomic ion species is not transmitted downstream.

[0098] Figures 35, 36 and 37 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species where the magnetic fields magnitude of the ion optical devices match that of Figure 33,34: Figure 35 - a ‘top-down’ view of a horizontal plane within the assembly in which the relative lateral displacements of the atomic ion species are of a first magnitude, wherein the reference potential of the ion beam filter assembly is held at 0V; Figure 36 - a ‘top-down’ view of a horizontal plane within the assembly in which the relative lateral displacements of the atomic ion species are of a second magnitude, wherein the reference potential of the ion beam filter assembly is held at 3000V; Figure 37 - a ‘top-down’ view of a horizontal plane within the assembly in which the relative lateral displacements of the atomic ion species are of a third magnitude, wherein the reference potential of the ion beam filter assembly is held at 4000V.

[0099] Detailed Description of the Invention

[0100] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0101] Figure 1 shows the arrangements in an ion source chamber arranged upstream of the ion beam filter arrangement. The ion beam is extracted from an ion source 1 on the left of the diagram and focussed by appropriate known extraction optics 2 and a source Einzel lens 3 on to a source defining slit 4. Downstream of the source defining slit 4 is a beam profiling slit 5 which cuts off the more divergent parts of the beam so that the emergent beam, to the right of the beam profiling slit 5 as shown in Figure 1 , is relatively narrow and matches the upstream optics of the ion beam filter arrangement. This beam profiling causes no observable signal loss to the instrument as the mass analyser defines a narrower beam profile further downstream, meaning these parts of the beam are rejected in the mass analyser even if the source defining slit is removed. Additional to this, the source defining slit also works as an effective shield for the downstream optics from the ICP source itself, minimising particle deposition on all downstream optics. Figure 2 shows the path of the ion beam and more particularly the separated paths of ions in the beam between its entrance into the vacuum chamber in which the beam filter is installed and a mass defining slit, onto which the transmitted beam is focussed. Focussing takes place by way of passing the beam through a pre-filter lens arrangement 6 of known type, so that the focussed image is located in the region of a mass defining slit 7 shown at the right-hand end Figure 2.

[0102] The focus point at the mass defining slit 7 is preferably arranged to provide a spatial magnification of approximately one by using appropriate geometry. Between the mass defining slit 7 and the pre-filter lens 6 are located successively an ion optical device (e.g., also referred to herein as a “Wien filter” as noted above) 8, a vertical lens 9, a baffle 10 and an ion optical lens (e.g., also referred to herein as a “lens field array” as noted above) 11 . Ions in the beam experience negligible focusing but significant deflection as they pass through the Wien filter 8. The path length is short and the electric field in the Wien filter linear, so that the beam is spread out with ions of different masses following different trajectories within the Wien filter.

[0103] As indicated by the divergent paths in Figure 2, the ions of different masses spread out from the original beam but are focussed at slit 7. The vertical lens 9 acts to focus the beam vertically to compensate for the downstream defocussing caused by the lens field array. The separated spread out beam of ions then passes through the lens field array 11 with any outlier ions being prevented from passing through the lens field array 11 by means of baffle 10. This also minimises secondary scattered particle transmission.

[0104] In operation, a quadratic voltage on the lens field array 11 is adjusted so that the ions move in paths which are parallel to the optical axis of the spectrometer. The mass defining slit is formed by two plates 7. The separation between the edges of the plates 7 may be varied to adjust the width of the mass defining slit and the plates may also be moved transversely to the direction of the beam to adjust its position, so enabling only ions in part of the beam to pass through, dependent upon their mass. If desired, as shown in Figure 2, ions of a certain mass may be captured by means of a notch filter 12 which can be moved transversely to the direction of the beam to a position where ions of a certain mass are captured and thus removed from the beam.

[0105] The ions in the beam are then recombined into a single beam running along the optical path of the apparatus by passing through a “mirror image” arrangement of lens field array, upstream vertical lens and Wien filter. These are denoted respectively 14, 15 and 16 in the complete diagram of the beam filter arrangement shown in Figure 3. As seen in Figure 3, to the right of Wien filter 16 is a final beam focussing array 17 of known type. The ion optical device (Wien filter) 8, the vertical lens 9 and the ion optical lens 11 may be referred to, respectively, as the first ion optical device 8, the first vertical lens 9 and the first ion optical lens 11. The ion optical lens 14, the vertical lens 15 and the ion optical device (Wien filter) 16 may be referred to, respectively, as the second ion optical lens 14, the second vertical lens 15 and the second ion optical device (Wien filter) 16.

[0106] In this way, the ion beam filter is arranged for receiving, from an ion source (e.g., of Figure 1), a beam of ions and for transmitting ions selected from the beam of ions, the ion beam filter extending along an ion optical axis. The ion beam filter comprises a pair of ion optical devices (also referred to as “Wien filters” in a broad sense as noted above), 8 and 16, spaced along the ion optical axis and comprising a first ion optical device 8 configured to spread the ion beam and a second ion optical device 16 configured arranged downstream of the first ion optical device 11 to recombine constituents of the spread beam into a single narrowed beam. Each of the first and second ion optical devices is configured to form a magnetic field extending in a direction across the ion optical axis and to form an electric field extending in a direction across the ion optical axis and across the direction of the magnetic field, therewith to deflect ions of the beam in directions transverse to the ion optical axis to an extent according to their respective velocity. A mass defining filter aperture (e.g., a slit 7) is located between first and second ion optical devices. An array of ion optical lenses, 11 and 14, comprises a first ion optical lens 11 (also referred to as a “lens field array” in a sense as noted above) arranged between the first ion optical device 8 and the mass defining aperture (e.g., a slit 7) and a second ion optical lens 14 (also referred to as a “lens field array” in a sense as noted above) is arranged between the mass defining aperture (e.g., a slit 7) and the second ion optical device 16. The first ion optical lens 11 of the array of ion optical lenses is configured to cause the paths of the ions (e.g., trajectories) in the beam to become substantially parallel (i.e. the mass dependent inclination is zero) between the first ion optical lens 11 and second ion optical lens 14 at or adjacent to the location of the mass defining filter aperture (e.g., a slit 7). A pair of Einzel lenses, 6 and 17, are arranged equidistantly upstream and downstream of the ion optical devices, 8 and 16, with the first Einzel lens 6 configured to generate a spatial focus in the region of the mass defining slit 7. This spatial focus is maintained for laterally dispersed paths, such that all ion paths spatially converge as they approach the mass defining slit 7 and spatially diverge as they recede from the mass defining slit 7. The second Einzel lens 17 is configured to adjust the ion beam filter exit beam profile to match the ion beam filter entrance beam profile, which due to the symmetry of the system should match the configuration of the first Einzel lens 6.

[0107] Due to the system symmetry, defined about a mirror axis at the mass defining slit 7, it may be of use to consider that the ion beam filter could be thought of as a Tandem MS system. The first mass spectrometer, comprising of the first ion optical device 8, first transverse-focussing ion optical lens 9, and the first ion optical lens 11 , laterally disperse ions according to their velocity, with all trajectories upstream of the ion optical device and downstream of the ion optical lens travelling parallel to the ion optical axis. Each one of the constituent parts of the ion beam come to a spatial focus near to the mass defining slit as shown in Figure 2, and as such, it will be apparent to a skilled reader that symmetrically replicating this first mass spectrometer with a second mass spectrometer placed downstream of the mass defining slit 7, respectively comprising of the second ion optical lens 14, second transverse-focussing ion optical lens 15 and the second ion optical device 16, will effectively negate the lateral displacement seen at the mass defining slit.

[0108] The first ion optical device 8 is configured to deflect received ions in directions so as to follow deflected respective ion paths (e.g., trajectories), and the first ion optical lens 11 is configured to receive the deflected ions from the first ion optical device and to deflect the received ions according to their respective deflected ion paths (e.g., trajectories). In other words, an electric potential may be formed within the first ion optical lens 11 which varies in space within the ion optical lens such that ions upon differing trajectories are received by the ion optical lens at differing spatial locations and, therefore, are subject to differing electric forces which cause the paths (trajectories) of the received ions to become parallel and to be output by the first ion optical lens in parallel. The spatial variation of the electric potential formed within the first ion optical lens may be substantially quadratic in form in direction transverse to the ion optical axis of the ion optical lens. The quadratic form of the electrical potential may be such that a minimum value of the electric potential resides substantially at the centre of the ion optical lens upon its ion optical axis and increases in magnitude either side of the minimum value. The quadratic form of the electric potential may extend axially along the optical axis in the sense the general quadratic shape generally or approximately persists along most or all of the length of the optical axis of the ion optical lens where the electrical potential exists (excluding the effects of fringing fields near the ends of the ion optical lens).

[0109] The mass defining filter aperture 7 is formed between two the edges of two ion barrier walls, each being independently movable in a direction perpendicular to the ion optical axis whereby the location and width of the mass defining filter aperture 7 is independently adjustable to adjust the width and / or lateral location of the aperture. The mass defining aperture 7 is configured for selectively transmitting only ions received from the first ion optical lens 11 upon respective ion paths (e.g., trajectories) that pass through the mass defining filter aperture, and for obstructing transmission of received ions upon other ion paths that cause ions to impact upon one of the ion barrier walls.

[0110] The notch filter 12 of the ion beam filter is an ion blocking device which may take the form of an ion collector, such as a Faraday Cup, or the like, located within or adjacent to the space of the mass defining filter aperture. The ion collector may be configured to collect ions from the beam received from the first ion optical lens 11 upon respective ion paths that intersect the ion collector. The ion collector may include an ion detector. Thus, by being movable in a direction perpendicular to the ion optical axis, the ion collector not only prevents the transmission of received ions upon such intersecting ion paths, thereby serving the function of a notch filter, but also serves the function of producing ion flux information useable to generate a mass spectrum sampled in a direction lateral to the ion optical axis across the spread-out ion beam. Accordingly, the ion beam filter includes a translation assembly (not shown) configured to move the ion collector transversely relative to the ion optical axis thereby to selectively position the ion collector laterally relative to the mass defining filter aperture (e.g., a slit).

[0111] As can be seen from Figure 3, the ion beam filter is arranged such that the first ion optical device 8 is receives a beam of ions, it deflects ions of the beam and outputs ions upon respective ion paths (e.g., trajectories) that diverge, thereby to spread the beam of ions. This serves the function of ion optical beam divergence. The ion beam filter is further arranged such that the first ion optical lens 11 receives ions from the first ion optical device 8 upon their respective ion paths and deflects the received ions so as to output ions upon respective ion paths that are substantially parallel. This serves the function of ion optical collimation of the beam of ions such that ion paths subsequently received by the mass defining aperture 7 are substantially parallel. The ion beam filter is yet further arranged such that the second ion optical lens 14 receives, via the mass defining filter aperture 7, ions from the first ion optical lens 11 upon their substantially parallel paths and deflects the received ions so as to output ions upon respective ion paths that begin to converge, thereby to increasingly narrow the beam of ions. The second ion optical device 16 receives ions from the second ion optical lens 14 and deflects those ions so as to output ions upon respective trajectories that are once more substantially parallel. This serves the function of substantially collimating the narrowed beam of ions.

[0112] The “vertical” lenses 9 and 15 referred to herein each comprises transverse-focussing ion optical lens. A first transverse-focussing ion optical lens 9 is located upon the ion optical axis between the first ion optical device 8 and the first ion optical lens 11 . A second transverse-focussing ion optical lens 15 is located upon the ion optical axis between the second ion optical lens 14 and the second ion optical device 16. Each transverse-focussing ion optical lens is configured to deflect ions of the beam in directions transverse to the ion optical axis and transverse to the deflection by the first and second ion optical devices. If the plane in which the ion beam is dispersed by the first ion optical device 8 is assumed to be a horizontal plane, then the transverse-focussing ion optical lenses are configured to achieve their respective focussing effects by ion deflection within the “vertical” plane and so are referred to herein as “vertical” lenses only for this reason. Of course, if the plane in which the ion beam is dispersed by the first ion optical device 8 is assumed to be a vertical plane, then the transverse-focussing ion optical lenses are configured to achieve their respective focussing effects by ion deflection within the “horizontal” plane, and could then be referred to herein as “horizontal” lenses accordingly.

[0113] As shown diagrammatically in Figures 4 and 5, components 8 to 11 and 14 to 16 of the beam filter arrangements are mounted on a base plate or carriage 20 which can be moved relative to the floor of the vacuum chamber in which the arrangement is located and in a direction transverse to the direction of the ion beam, between a position which the ion beam filter is not deployed, shown in Figure 4, to one in which the ion beam does pass through the filter, as shown in Figure 5. Mounted on carriage 20 are two electric field shields 24 to shield the path of the beam from stray electric fields when the filter arrangement is not deployed, as shown in Figure 4. Contributing to this shielding of the direct path of the ion beam through the vacuum chamber from its inlet denoted 22 to its outlet denoted 23 (whence it passes into another vacuum chamber) are two mild steel shields 25 mounted on carriage 20 and two mild steel shields 26 mounted on the floor of the vacuum chamber, to shield the path of the beam from stray magnetic fields.

[0114] When the ion beam filter is in use as shown in Figure 5, the notch filter 12, shown in Figure 4 in a retracted position, is extended to the relevant position as shown in Figure 5 in order to remove ions of a certain mass from the beam. The position of carriage 20 is controlled by way of suitable mechanical control systems which enable it to be shifted in a direction perpendicular to the direction of the ion beam, its end of travel positions being defined by stops 28 fixed to the structure of the vacuum chamber itself.

[0115] Because the Wien filters can be controlled to (also) provide both quadratic and cubic magnetic fields, it is possible to control the precise effect of the Wien filters so as to allow fine tuning of the focus position and to rotate the focal plane. As can be seen from Figure 3, between the two lens field arrays 11 and 14 the width of the ion beam is increased which enables a greater mass range to be measured. The mass defining slit 11 is at the focus point where the ions in the beam are at maximum distances from one another.

[0116] An advantage of providing a notch filter in the embodiment illustrated is not simply to enable the removal from the beam of ions of a certain mass, which constitute undesirable complicating species, and which are preferably removed from the beam prior to its entry into the mass analyser, for example removal of argon from the beam, as noted in some of the prior art specifications referred to above. The notch filter 12 can be swept across the entire width of the mass defining slit which assists in calibrating the unit.

[0117] The entire filter assembly is normally operated at ground potential, with the ions in the beam travelling through it with kinetic energy defined by the acceleration potential applied to the beam. This makes the electrical arrangements needed very simple. It is possibly desired to arrange for the Wien filters, vertical lenses and lens field arrays to be biased to a reference potential in order to decrease the kinetic energy of the particles forming the ion beam. This is of particular value in improving the resolution of the filter itself without, however, having any adverse effect on the treatment of the beam downstream of the filter.

[0118] The arrangement of the filter on a carriage as explained above enables the entire spectrometer to be operated with or without filter, and without deflecting the straight path between ion source and mass analyser. This contrasts with the necessity of moving the beam along one or other of two paths as illustrated in specification GB2535826 referenced above, and the direction of the outlet beam being displaced from that of the inlet beam. With the addition of a second ‘path deflector’ to the system illustrated in GB2535826, to bring the beam back on axis prior to transmission into the mass analyser, this system can selectively use the mass filter and CRC in tandem, isolation or not at all, with no compromises to the standard path.

[0119] Reference numerals assigned to items within figures 1 to 5 are as follows:

[0120] 1 ICP source

[0121] 2 Extraction optics

[0122] 3 Source Einzel lens

[0123] 4 Source defining slit

[0124] 5 Beam profiling slit

[0125] 6 Pre-filter Einzel lens

[0126] 7 Mass defining slits

[0127] 8 First “Wien filter”

[0128] 9 First vertical lens 10 Lens field array entrance baffles

[0129] 11 First “lens field array”

[0130] 12 Notch assembly

[0131] 14 Second “lens field array”

[0132] 15 Second vertical lens

[0133] 16 Second “Wien filter”

[0134] 17 Post-filter Einzel lens

[0135] 20 Retracting optics plate

[0136] 22 Filter chamber vacuum inlet

[0137] 23 Filter chamber vacuum outlet

[0138] 24 Electric field shield

[0139] 25 Moving mild steel shield

[0140] 26 Fixed mild steel shield

[0141] 28 Retraction / Extension stops

[0142] 29 Precision linear guide.

[0143] Figure 6 shows a cross-sectional view of an ion optical device (also referred to herein as a “Wien filter” as noted above). The ion optical device, 8 or 16, comprises an ion transmission channel 37 for transmission of received ions in a direction along an ion optical axis extending (in a direction perpendicular to the page of Figure 6) from an ion entrance opening to an ion exit opening. A magnetic yoke 30 is formed around the ion transmission channel. A first permanent magnet 32 is attached to the magnetic yoke within the ion transmission channel 37 and a second permanent magnet 34 is also attached to the yoke within the ion transmission channel in spaced opposition to the first permanent magnet across the ion transmission channel 37. The two permanent magnets form between them a magnetic field, B, extending in a direction across the ion optical axis. In one example, each of the first and second permanent magnets may comprise a 5mm thick Neodymium Iron Boron (NdFeB) magnet. A magnet grade of N42 may be used. The grade N42 means a neodymium magnet has a maximum energy product of 42 MGOe (here the unt “MGOe” refers to Mega-Gauss Oersteds where 1 MGOe (cgs units) equals 7958kJ / m3 (SI units)). This refers to the maximum magnetic energy that the material can be stored, as would be readily appreciated by the person skilled in the art.

[0144] The magnetic yoke provides a magnetic field flux-return path internally within the magnetic yoke for those other parts of the magnetic field passing from the first permanent magnet 32 to the second permanent magnet 34 in looping paths. The yoke also provides an external magnetic field flux-return path which spans across the ion transmission channel 37 from the second permanent magnet 34 to the opposing first permanent magnet 32 to form between them the magnetic field extending in a direction across the ion optical axis.

[0145] The ion optical device comprises a first array of electrodes 40 extending in free space across the first permanent magnet 32 within the ion transmission channel 37, and a second array of electrodes 42 extending in free space across the second permanent magnet 34 within the ion transmission channel 37 in spaced opposition to the first array of electrodes across the ion transmission channel. Both the first array and the second array of electrodes comprise a plurality of elongated, separated electrode strips each of which extends longitudinally in a direction along the ion transmission channel substantially parallel to the ion optical axis. The array of such separate electrode strips extends in a substantially coplanar arrangement that extents both along and laterally across the ion transmission channel 37 in a direction transverse to the ion optical axis. A respective one of two end electrode plates, 36 and 38, are disposed at each one of two respective sides of the ion transmission channel so as to be aligned in register each other in spaced opposition across the ion transmission channel either side of the first and second arrays of electrodes, 40 and 42.

[0146] The first and second arrays of electrodes are configured to receive respective voltage signals from a power source (not shown) therewith collectively to form an electric potential, <t>, having a spatial distribution possessing a spatial gradient defining an electric field, E, extending in a direction across the ion optical axis and across the direction of the magnetic field. The two end electrode plates, 36 and 38, are arranged to receive respective voltage signals which are consistent with the spatial distribution of the electric potential, <t>, formed by the opposing electrode arrays, and consistent with the spatial gradient defining an electric field, E, such that the electric field passes from one end electrode plate to the other in a substantially uniform direction and magnitude.

[0147] Figures 7(A), 7(B) and 7(C) show views of a magnet assembly 30 which forms part of an ion optical device consistent with the ion optical device of Figure 6. In Figure 7(A) an isometric view is shown. The magnet assembly 30 includes a magnetic yoke 31 , first and second permanent magnets 32, 34 and first and second terminator plates 48, 50. The magnetic yoke 31 comprises a first yoke piece 44 and a second yoke piece 46. The first permanent magnet 32 and the second permanent magnet 34 are attached to the first yoke piece 44. The separate second yoke piece 46 is attached (e.g. by screws) to the first yoke piece 44 to form the ion transmission channel 37, which can be seen in Figure 7(A). In this example, the first yoke piece 44 is C-shaped and the second yoke piece 46 is planar. The first yoke piece 44 and the second yoke piece 46 thus meet at a junction 47 at a lateral end of the magnetic yoke 31. This junction 47 can be viewed in Figure 7(A) and also Figure 6. The first and second yoke pieces 44, 46 may be formed e.g. of mild steel.

[0148] The second yoke piece 46 is detachable from the first yoke piece 44 (e.g. by unscrewing one from the other). This permits a lateral access to the ion transmission channel 37. Attaching the first yoke piece 46 to the second yoke piece 46 completes the magnetic field flux-return path internally within the magnet assembly 30. Such access (provided by detaching the second yoke piece 46 from the first yoke piece 44) allows a given first permanent magnet 32 and / or second permanent magnet 34 to be initially attached to the first yoke piece 44 and to be subsequently removed and replaced with a different first permanent magnet 44 and / or second permanent magnet 46. This lateral access also permits the first and second arrays of electrodes (which also form part of the ion optical device, as discussed later) to be easily positioned in the ion transmission channel 34. Thus, the first permanent magnet 32 and / or the second permanent magnet 34 are removeable and replaceable to permit adjustment of a geometry and / or a grade of the permanent magnet according to application requirements.

[0149] First and second terminator plates 48 and 50, formed of mild steel or other suitable shielding material, and each possessing a respective through-slit for ion transmission, are placed over opposite longitudinal ends of the magnet assembly 30. The terminator plates 48, 50 act to minimise the extent of the fringe field along the ion optical axis. It may be beneficial for both the yoke and terminators to be made of a material that has a higher relative permeability than mild steel to further minimise the external fringing field that could impact the ion beam when the ion optical device is in the retracted position.

[0150] Figure 7(B) is a vertical cross-sectional view of the magnet assembly 30 of Figure 7(A), taken along the ion optical axis. Figure 7(C) is a horizontal cross-sectional view of the magnet assembly 30 of Figure 7(A) also taken along the ion optical axis. In Figure 7(B) the first permanent magnet 32 can be seen (this is obscured from view in Figures 7(A) and 7(C)).

[0151] We can see that the magnet assembly 30 is relatively simple to assemble, with the permanent magnets 32, 34 being mounted within the first yoke piece 44, that is then closed off by the second yoke piece 46 which provides a secondary field return path. This closed geometry minimises the magnitude of the stray magnetic fields that could impact nearby optics in the lateral direction and is an useful design feature when retracting the magnet assembly 30 away from the optical axis (see Figures 22 and 23 and supporting description). As discussed above, the terminator plates 48 and 50 act to minimise the extent of the fringe field along the ion optical axis.

[0152] Figures 8(A), 8(B) and 8(C) show views of electrode arrays in an ion optical device in isolation. Note that these electrode arrays correspond to the electrode arrays of the ion optical device of Figure 6, also note that the magnetic yoke assembly of figures 7(A) to 7(C) do not include the electrode assemblies (for clarity). However, the electrode arrangements shown in figures 8(A), 8(B) and 8(C) are the arrangements that these electrodes possess when assembled in the ion optical device.

[0153] Figures 9(A), 9(B) and 9(C) show views of stages of assembly of an ion optical device consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C) and the electrode arrays of Figures 8(A), 8(B) and 8(C). A first electrode support plate 64 of electrically non-conducting material (e.g., PCB substrate) is configured to be placed adjacent to the ion entrance opening of the ion optical device to access the ion transmission channel 37 and a second electrode support plate 68 of electrically nonconducting material (e.g., PCB substrate) parallel to the first electrode support plate is configured to be placed adjacent to the ion exit opening of the ion optical device at the exit end of the ion transmission channel.

[0154] The first array of electrodes 40 is suspended in free space between the first electrode support plate and the second electrode support plate, and the first and second electrode support plates bear one or more electrical contact terminals, 70, configured to receive a voltage signal from a power source (not shown) from amongst the respective voltage signals required to generate the electric field, E, within the ion transmission channel. One or more conductive tracks (not shown, but starting from track ends 65) are formed on the support places (e.g., as PCB circuit tracks) to electrically connect the electrodes of the first and second arrays of electrodes, 36, 38, 40 and 42, to the one or more electrical contact terminals, 70.

[0155] In the example shown, one common electrode support plate 64 is provided to electrically connect, and to physically support, the adjacent proximal ends of the first and second electrode arrays, 36, 38, 40 and 42, and one separate common electrode support plate 68 is provided to electrically connect, and to physically support, the adjacent distal ends of the first and second electrode arrays. In other arrangements (not shown) the one common electrode support plate 64 may be split into two separate plate parts each one of which supports a respective one of the adjacent proximal ends of the first and second electrode arrays, 36, 38, 40 and 42. Similarly, in other arrangements (not shown) the one common electrode support plate 68 may be split into two separate plate parts each one of which supports a respective one of the adjacent distal ends of the first and second electrode arrays, 36, 38, 40 and 42. The electrical contact terminals 70 each comprise a spring-loaded contact or a Pogo Pin permitting the electrical contact terminals to be mechanically pressed into electrical contact with a source of said respective voltage signals (e.g., from a power source). Figures 9(B) and 9(C) show views of the electrode arrays, as supported by the support plates, inserted in position within the magnetic yoke assembly, 44 and 46.

[0156] Thus, a series of vertically symmetrical electrodes form arrays 40 and 42, being spaced laterally between full height outer plates 36 and 38, are used to generate a specific electric field within the magnet gap of the ion optical device (velocity selector). If the plates are independently controlled, then any known electric potential spatial distributions can be generated within. The electrode optics as laid out in the ion optical device enable ease of fitting the optics within magnet assembly of the device. The electrodes of the ion optical device of Figure 9(C) are mounted on to two PCBs, positioned respectively at the front and rear of the magnet assembly. This mounting method has the benefit of removing all dielectric material from the beam path within the ion optical device, such that any injection current from the charged particle beam could not cause instability issues. The primary electric potential spatial distribution used within the ion optical device is the linear spatial distribution, as the main function of this assembly is to assist in dispersing ion trajectories according to their velocity to assist in selecting an ion mass of interest for the downstream optics.

[0157] This can be achieved through independent control of the voltage applied to each electrode within a given electrode array, or through using a chain of identical resistors between two outputs to function as a first voltage divider (i.e. a linear distribution), whereby divisions of the divided voltage are fed to appropriate electrodes within the electrode arrays, as desired. The linear voltage distribution described herein, when specifically implemented within the ion optical device shall be referred to as the “mass selection voltage”, as the magnitude of the linear voltage distribution defines the centrally transmitted mass of the ion optical device for a given magnetic field strength. A variation of this technique could use a symmetrical chain of varied value resistors (it may be beneficial for these resistors to be adjustable for fine tuning) to generate a second voltage divider (i.e. a quadratic or octupolar distribution, the former having been done previously with the technology disclosed within EP0857353B1), whereby divisions of the divided voltage are fed to appropriate electrodes within the electrode arrays, as desired. An additional variation of this technique could use a non-symmetrical chain of varied value resistors (it may also be beneficial for these resistors to be adjustable for fine tuning) to generate a third voltage divider (i.e. a cubic distribution, disclosed due to its importance in image plane rotation), whereby divisions of the divided voltage are fed to appropriate electrodes within the electrode arrays, as desired. This method of voltage division may be used to supply voltages to electrodes of an ion optical device disclosed herein and / or to an ion optical lens as disclosed herein. In some examples it may be beneficial to independently control the voltage applied to each electrode as this allows for the independent use and variational sum of any of the voltage distributions disclosed herein.

[0158] Figure 10a shows a cross-sectional view of a hexapolar electric potential 72 formed by a hexapolar electrode rod set 71 . Figure 11a shows a view of the cubic form of a hexapolar electric potential as measured along a line 74 joining two opposing hexapolar electrodes of the electrode rod set of Figure 10a. Figure 12a shows a view of the cubic spatial form and a linear spatial form of the variation of electric voltages applied equally to successive opposing pairs of electrodes within two opposing arrays of electrodes, 36, 38, 40 and 42, of Figures 8(A), 8(B) and 8(C) in an ion optical device consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C). Figure 12a can also be taken to show spatial form of the variation of electric voltages applied equally to successive opposing pairs of electrodes 84 within an ion lens of Figures 13, 14 and 15.

[0159] Schematically shown in Figure 12a is a first array of twelve separate electrodes, 40 or 84, and a second array of twelve separate electrodes, 42 or 84, that is laterally spaced apart from the first array and is aligned in register with the first array such that each electrode of the second array directly opposes one corresponding electrode of the second array. The x-axis of Figure 12a denotes the spatial distance from a zero-position corresponding to the middle of the first array and the middle of the second array. Six electrodes of the first array extent within the first array to the left of the zero-position, and six electrodes of the second array extent within the second array to the left of the zero-position in exactly the same way. Similarly, six electrodes of the first array extent within the first array to the right of the zero-position, and six electrodes of the second array extent within the second array to the right of the zero-position in exactly the same way. This produces twelve pairs of directly opposing electrodes, six pairs to the left and six pairs to the right. Now apply the same voltage to each given pair of electrodes, but apply different voltages to different electrode pairs selected from a pre-selected set of voltages. For example, in Figure 12a, two examples of pre-selected sets of voltages are shown. Each pre-selected voltage set is pre-set in the sense that voltages applied to the pairs of electrodes at corresponding opposite sides of the zeroposition are low, and the voltages applied to successive pairs of electrodes at successively greater lateral positions away from the zero-position successively increase in magnitude. This means that space between the electrodes of any given pair of electrodes can be considered to contain, to a good approximation, an electric potential having a value corresponding to the voltage applied to that pair of electrodes according to the pre-selected voltage set. If the applied voltages change linearly from one electrode pair to the next, as indicated by the voltage set 77, then so too does the electric potential between the opposing electrode arrays. If the applied voltages change in the manner of a cubic spatial shape from one electrode pair to the next, as indicated by the voltage set 78, then so too does the electric potential between the opposing electrode arrays.

[0160] In these two examples, the voltage sets have different polarities on the right of the zero-position (+ve polarity) as opposed to the left of the zero-position (-ve polarity). In other examples, such as a voltage set describing a quadratic spatial form, the voltage sets have the same polarities on the right of the zeroposition as on the left of the zero-position (-ve or +ve polarity).

[0161] A voltage set with a linear spatial form 77 may be used to produce a uniform electric field, E, such as in an ion optical device disclosed herein. A voltage set with a quadratic spatial form may be used in an ion optical lens such as disclosed herein. A voltage set with a cubic or octupolar spatial shape may be used to form a correspondingly-shaped electric potential.

[0162] Figure 12a shows an example of how to generate an electric potential having a linear spatial form or a cubic spatial form. Some of the different spatial forms that may be generated are shown in Table 1 together with the effect they will have on an ion beam passing through such an electric potential.

[0163] Table 1 :

[0164] One can see that ion optical lens comprises a series plates displaced laterally and mirrored vertically, with the outermost plates 89c differing in that each is one continuous plate. By independently controlling the potential on each plate, noting that the top array of plates are linked with the respective bottom plates, as discussed in more detail below, we can set up a lateral field distribution that can approximate the lateral component of any field distribution or sum of field distributions, most notably the linear, quadratic, hexapole and octupole fields. The effects of these field distributions have been briefly summarised in Table 1 , and it should be noted here that these distributions can easily be setup in a non-symmetrical manner.

[0165] By way of example, Figure 10b shows a cross-sectional view of a quadrupolar electric potential 72 formed by a quadrupolar electrode rod set 71 . Figure 11 b shows a view of the electric potential as measured along a line 74 joining two opposing quadrupolar electrodes of the electrode rod set of Figure 10b. Figure 12b shows the variation of electric voltages applied equally to successive opposing pairs of electrodes within two opposing arrays of electrodes, 36, 38, 40 and 42, of Figures 8(A), 8(B) and 8(C) in an ion optical device consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C) when a quadrupolar electric potential is used. Figure 12b can also be taken to show spatial form of the variation of electric voltages applied equally to successive opposing pairs of electrodes 84 within an ion lens of Figures 13, 14 and 15.

[0166] It may be of use to consider the technology described within EP0857353B1 , where a large pair of ion optical lenses are used to adjust the mass dependent inclination and mass dispersion of the beam paths found downstream of a MS analyser sector magnet, where each independent electrode potential can be adjusted, that is to say, a specific additional potential can be applied to one electrode, or a subset of electrodes therein, rather than just being limited to a potential distribution being applied along the entire ion optical lens. This may be of use in instances where the field distribution at the ion optical axis requires fine tuning, or specific field potentials are required that don’t fall within the definition of a ‘conventional’ field distribution.

[0167] Figures 13, 14 and 15 show views of an ion optical lens 80. Figure 13 shows an isometric view of the lens, Figure 14 shows a transparent view of the lens, and Figure 15 shows a cross-sectional view of the lens. Figures 16 shows a schematic view of an electrode structure amongst a set of electrodes within the ion optical lens of Figure 13, Figure 14 and Figure 15. This ion optical lens 80 is an example of the first ion optical lens 11 and second ion optical lens 14 of the ion beam filter disclosed herein. The ion optical lens 80 comprises an ion entrance opening 82 for receiving ions, an ion exit opening 83 from which received ions are output, and an ion transmission channel extending through the lens from the ion entrance opening to the ion exit opening for transmission of received ions in a direction along an ion optical axis, “OA”, from the ion entrance opening to the ion exit opening. The ion optical lens further comprises a plurality of electrode plates 84 configured to receive respective voltage signals, from a power source (not shown), such that collectively the electrode plates form an electric field to produce an ion optical effect within the ion transmission channel. Table 1 gives examples of the spatial form of an electrical potential that may be formed within the ion transmission channel of the ion optical lens in this way.

[0168] The ion optical lens 80 has a chassis 87 to which the plurality of electrode plates 84 are attached in spaced succession within (i.e., across, in the example) the ion optical axis. Each electrode plate comprises a planar sheet of conductive material (e.g., steel) which is positioned to extend in a plane generally parallel to the ion optical axis, OA, and to present a terminal plate edge to the ion transmission channel. The terminal plate edge is also generally parallel to the ion optical axis and extends in a direction along the ion transmission channel. The plurality of electrode plates comprises a first electrode plate array 89a extending in a direction transversely across the ion optical axis, OA, and a second electrode plate array 89b also extending in a direction transversely across the ion optical axis and in spaced opposition to the first electrode plate array across the ion optical axis. The first and second electrode plate arrays form separate pairs of electrode plates in which one electrode plate of the first electrode array is paired with one electrode plate of the second electrode plate array in such a way that the terminal plate edges of the two electrode plates of the pair are substantially parallel to each other and positioned in spaced opposition across the ion transmission channel.

[0169] The electrode plates of each electrode plate pair are integrally formed from the same one continuous piece of conductive material (e.g., steel) such that one plate of the pair is physically connected to the other plate of the pair by a conductive support bridging part 85. Each electrode pair may be formed, for example, by cutting a template electrode pair from a planar sheet of conductive material to form a planar template in which the two electrode plates of the pair, and the support bridge between them, lie in the same plane. Then, the support bridge may be bent a number of times as desired and as necessary to arrange the two electrode plates of the template electrode pair such that the two electrode plates are substantially coplanar, and such that terminal plate edges of the two electrode plates of the pair are substantially parallel to each other in spaced opposition from each other. Figure 16 shows a schematic example of such an arrangement. This has the possible benefit of permitting the orientations of, and spacings between, the two electrode plates of the array to be accurately determined and substantially fixed by the support bridge if required. It also has the benefit that only one voltage signal (e.g., one voltage from a voltage set discussed herein) needs to be supplied to either one of the two electrode plates of a given pair, or to the support bridge, to allow both electrode plates to acquire the same voltage to allow the two electrode plate arrays to generate a desired electric potential spatial form within the transmission channel of the ion optical lens (examples are listed in Table 1).

[0170] The electrode plates each comprise an attachment through-opening 86b formed therein, and the chassis comprises a plurality of mounting rods 86 formed of an electrically non-conducting material, such as a ceramic. Each mounting rod passes through the attachment through-opening 86b of a respective electrode plate of the ion lens 80 to attach the electrode plates to the chassis in an array extending along the mounting rod without forming an electrical connection between the one or more electrode plates of the mounted array.

[0171] Each of the one or more electrode plates is bonded to a respective mounting rod by a non-conducting bonding material 90 comprising a resin (e.g., epoxy resin) bonded simultaneously to a surface of the mounting rod 86 and to a surface of a respective electrode plate thereby connecting each respective electrode plate to the mounting rod 86. The bonding material may comprise a heat activated adhesive. The non-conducting bonding material is formed as a washer or ring of material so as to form a continuous bond circumferentially around the mounting rod to which it is bonded. It forms a continuous bond circumferentially around the attachment through-opening 86b of the electrode plate to which it is bonded. In assembling the ion optical lens, the first and second arrays, 89a and 89b, of the electrode plates 84 may be assembled (slotted) onto a pair of parallel mounting rods 86, with each electrode plate array being mounted upon a respective one of the two parallel mounting rods. A plurality of rings of bonding material are also slotted onto respective mounting rods at one or both sides of each of the attachments through openings 86b. The full assembly of successive pairs of electrode plates, and attendant rings of bonding material, collectively mounted upon the two mounting rods (see Figure 14) may then be heated to cause the rings of bonding material to adhere to, and bond with, both the mounting rod upon which it is mounted and the electrode plate with which it has been placed in contact. The assembled first and second electrode plate arrays may then be mounted, as one, into the chassis 87 of the ion optical lens It may be of use to build the disclosed assembly within the chassis prior to heating, such that the entire ion optical lens is bonded together in one process as disclosed herein.

[0172] Figures 17, 18 and 19 show views of an ion optical lens in the form of an Einzel lens 92 in which electrode plates forming an array 94 of electrode plates are mounted upon a pair of mounting rods 86 using bonding material 90 in this way. Figure 17 shows an isometric view of the Einsel lens, Figure 18 shows a cross-sectional isometric view of the Einzel lens, and Figure 19 shows a cross-sectional side view of the Einzel lens. Figure 20 shows a view of the Einzel lens of Figure 17 mounted in electrical connection with a circuit board 96 via a set of spring pin (Pogo Pin) connectors 98 forming electrical contact terminals arranged in electrical connection with electrode plates of the Einzel lens and permitting the electrical contact terminals to be mechanically pressed into electrical contact with a source of respective voltage signals (e.g., from a power source) for supplying voltages to respective electrode plates. As can be seen in Figure 20, the variable diaphragm assembly 99 comprising three diaphragm apertures of differing diameter, can be seen downstream of the Einzel (ion flow in the beam is from right to left here). The largest diaphragm aperture may be used to maximise transmission. When required, a smaller aperture may be selected by translating the variable diaphragm assembly 99 laterally across the beam axis, which will lead to an improvement in filter performance at the cost of overall transmission. Figure 21 shows a view of the second ion optical lens 80 of Figures 13 to 15 mounted in connection with a mass defining filter aperture (e.g., a slit 104) and an ion blocking device 108, taking the form of a faraday cup 108 which comprises an ion detector. This specific form of the ion blocking device may be analogous to the notch filter 12 described previously. The mass defining aperture 104 is formed between by the space between opposing parallel coplanar edges of a pair of barrier plates 100 and 102, denoted as “H” in Figure 21 . Each barrier plate is connected to a mounting arm, 112 and 114 respectively, which is independently slidingly moveable in directions transverse to the ion optical axis of the lens 80, as indicated. This allows the width and / or lateral position of the mass defining aperture to be selected as desired. Similarly, the ion collector 108 of the notch filter is connected to a mounting arm, 110, which is independently slidingly moveable in directions transverse to the ion optical axis of the lens 80, as indicated. This allows the lateral position of the notch filter (e.g., ion detector) to be selected as desired.

[0173] When the ion blocking device 108 comprises an ion detector, an arrangement such as is schematically shown in Figure 2 may define a mass spectrometer for use with an ion source for producing, from a sample, a plurality of ions each sharing substantially the same kinetic energy and each possessing a respective mass from a plurality of different masses present amongst the plurality of ions. The mass spectrometer may comprise the ion optical device 8 (e.g., item 55 of Figure 9(C)) arranged for receiving the plurality of ions such that received ions transmitted through the ion transmission channel are deflected in directions transverse to the ion optical axis of the ion optical device to an extent according to their mass thereby to output the ions upon dispersed ion paths (e.g., trajectories). An ion optical lens 11 (e.g., 80 of Figures 13 to 15) may be arranged for receiving deflected ions upon the dispersed ion paths (e.g., trajectories) and for further deflecting the received ions in directions transverse to the optical axis to cause the paths (e.g., trajectories) of the ions output by the ion optical lens to be substantially parallel to the ion optical axis. The ion blocking device (with ion detector) may be arranged to move in a direction transverse to the ion optical axis to different selected positions in a plane containing the dispersed ion paths (e.g., trajectories) thereby to detect ions of different masses present amongst the plurality of ions according to the different selected positions of the ion detector. In this way, mass spectral data may be obtained which describes an ion mass spectrum. In other examples, it may be of use to use a plurality of ion blocking devices or a bank of fixed position detectors for specific applications.

[0174] Figure 22 shows an ion beam filter arrangement 116 consistent with Figure 5 in which both ion optical devices 55 of a pair of ion optical devices of the beam filter are mounted upon a retractable carriage 120 (e.g., translation stage). The carriage 120 is arranged upon a support platform assembly, 124 and 126, in such a way as to be moveable linearly between a deployed position as shown in Figure 22 and a retracted position as shown in Figure 23. The ion beam filter 116 comprises a carriage to which the first and second ion optical devices 55 are mounted wherein the chassis is operable to move between a deployed position shown in Figure 22 in which the ion transmission channel of the first and second ion optical devices are both aligned with the ion optical axis OA of the ion beam filter, and a retracted position shown in Figure 23 in which the ion transmission channels of the first and second ion optical devices are laterally displaced from the ion optical axis OA of the ion beam filter to an extent sufficient that ions or the ion beam are neither received into the ion transmission channel nor obstructed by the first or second ion optical device 55.

[0175] Figures 24 and 25 show views of the retractably deployable ion optical devices 55 employed in the beam filter arrangement shown in Figures 22 and 23. The ion optical device is consistent with the ion optical device of Figure 6 and Figures 7(A), 7(B) and 7(C) and Figures 8(A), 8(B) and 8(C) and Figures 9(A), 9(B) and 9(C). Figure 24 shows an isometric view of the ion optical device, and Figure 25 shows a plan view of the ion optical device. The ion beam filter in this arrangement comprises, attached adjacent to each respective one of the two ion optical devices 55, a respective one or to magnetic shield assemblies 122 laterally offset from the ion transmission channel of a given ion optical device 55 by a lateral offset corresponding to the lateral displacement between the deployed position and the retracted position. The magnetic shield assembly 122 is positionable, by positioning the carriage 120 in the retracted position of Figure 23, to shield the flow of ions from a magnetic field flux, B, extending along the magnetic field fluxreturn path external to the magnetic yoke, 44 and 46 of Figure 6, of the respective optical devices 55.

[0176] The magnetic shield assemblies 122 each comprise a tubular conduit defining a longitudinal conduit axis configured to extend in a direction substantially parallel to the ion optical axis of the respective optical device 55 associated with it. Each magnetic shield assembly is configured to receive the flow of ions therealong when the chassis (e.g. translation stage) is in the retracted position. In some examples, the magnetic shield assembly may comprise a material having a relative permeability of at least 80,000 to allow good magnetic shielding. A so-called “Mu Metal” may be used.

[0177] Accordingly, as some of the magnetic field lines from the ion optical devices 55 encompass the entire assembly, a Mu Metal shield may be used to terminate the residual field when the carriage is in the retracted position. The most notable property of Mu Metal is its relative magnetic permeability of ~100,000, making it a very effective magnetic field terminator. For the current embodiment of the system, the “vertical” lenses, ion optical lenses and the mass defining aperture (e.g., slit) assembly are built on a stationary plate (denoted “K” in Figure 23) of the support platform assembly, 124 and 126, and are electrically grounded when the carriage is in the retracted position, while the ion optical devices (velocity selectors) are retracted on a retraction plate (denoted “I” in Figure 23) of the carriage, and the ion beam filter is not in use. The mass defining aperture and notch filter can also simply be retracted in this mode of operation.

[0178] Figures 26, 27 and 28 show views of an ion optical lens 130 assembled to provide a “vertical” lens 9 or 15 referred to herein with respect to Figures 2 to 5. This ion optical lens 130 provides a transverse-focussing ion optical lens noted above and is configured to deflect ions of the beam in directions transverse to the ion optical axis and transverse to the deflection by the first and second ion optical devices 55. The lens comprises a pair of separate and separated electrode pates, 132 and 134, suspended between inner and outer support plates 131. Each of the two electrode plates of the pair of electrode plates possesses a linear terminal plate edge arranged in opposed opposition to the terminal plate edge of the other plate of the pair across the ion optical axis of the ion beam filter. The lens is constructed according to the use of non-conducting support rods 86 and attendant non-conductive bonding material 90 to mount the pair of electrode plates between inner and outer support plates 131 , in a manner as referred to herein with respect to the ion optical lens 80 and Einzel lens 92 herein.

[0179] The “vertical” lenses are primarily used to mitigate a slight vertical defocussing that is introduced by the ion optical lenses, 11 , 14 or 80, of the ion beam filter, by ensuring there is a vertical and horizontal focus at the mass defining aperture, one may provide better recombination of the beam both vertically and horizontally downstream of the ion beam filter.

[0180] Figures 29 and 30 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species. Figure 29 shows a ‘top-down’ view of a horizontal plane within the assembly and Figure 30 shows a ‘sideways’ view of a vertical plane within the assembly. Items denoted “D”, “E”, “F”, “G” and “H” correspond to, respectively: an Einzel lens (6 or 92); an ion optical device (8, 30 or 55); a transverse-focussing ion optical lens (9 or 130); an ion optical lens (11 or 80); a mass-defining aperture (7 or 100 and 102). The same succession of components is arrayed along the ion optical axis of the ion beam filter in reverse order extending away from the mass defining aperture “H”, as discussed above. Simulated trajectories of a 6kV beam of ions comprising: Lithium 7, Magnesium 24, Argon 40, Strontium 88, Neodymium 142, Hafnium 180, Lead 208 and Uranium 238 are shown. These are the result of simulations using a well-known simulation software package known as: “SIMION”. This shows that the mass filter can successfully recombine the different particle bundles downstream of the second ion optical element, such that the beam can be manipulated without introducing any form of mass fractionation.

[0181] Figures 31 and 32 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species: Figure 31 shows a ‘top-down’ view of a horizontal plane within the assembly in which the mass defining filter aperture (e.g., a slit) of the assembly is positioned in a first position to allow transmission of a selected atomic species and to prevent transmission of other atomic species. Figure 32 shows a ‘top-down’ view of a horizontal plane within the assembly in which the mass defining filter aperture (e.g., a slit) of the assembly is positioned in a different second position to allow transmission of a different selected atomic species and to prevent transmission of other atomic species. To define a specific mass window, there are two methods one may follow. One may adjust the mass selection voltage to centre a mass of interest, with the mass defining aperture being narrowed about the centre of the system until a required window is achieved, as shown in the Figure 31 . Here the mass of interest, Strontium, is being transmitted along the optical axis.

[0182] One can also consider a scenario in which one leaves the mass selection voltage as it is, and by moving (and / or expanding or narrowing) the mass defining aperture one can choose a different mass range to transmit. By running off axis, as shown in the second view of Figure 32, the shield plates forming the mass defining aperture “H” block the line of site from the ion source to the downstream optics, such that all neutrals are blocked. The latter option would be of particular use for users who prioritise minimising instrumental tuning on a day-to-day basis, as the movement of the shield plates has no impact on the instrumental tuning with the exception of Argon removal which significantly impacts space charge effects.

[0183] It will be appreciated that the invention implements an ion beam filtering method for selected ions from the beam of ions for transmission along an ion optical axis, the method comprising: providing, on the ion optical axis, a pair of ion optical devices spaced along the ion optical axis and: by a first such ion optical device, spreading the ion beam; by a second such ion optical device arranged downstream of the first ion optical device, recombining constituents of the spread beam into a single narrowed beam; wherein, by each said ion optical device, a magnetic field is formed extending in a direction across the ion optical axis and an electric field is formed extending in a direction across the ion optical axis and across the direction of the magnetic field, therewith to deflect ions of the beam in directions transverse to the ion optical axis to an extent according to their respective velocity; providing, on the ion optical axis, a mass defining filter aperture located between first and second ion optical devices; and, providing, on the ion optical axis, an array of ion optical lenses comprising a first ion optical lens arranged between the first ion optical device and the mass defining filter aperture and a second ion optical lens arranged between the mass defining aperture and the second ion optical device; and, by the first ion optical lens of the array of ion optical lenses, causing the paths of the ions in the beam to become substantially parallel between the first ion optical lens and second ion optical lens at the location of the mass defining filter aperture.

[0184] Figures 33 and 34 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species: Figure 33 - a ‘top-down’ view of a horizontal plane within the assembly in which the magnetic field magnitude within both ion optical devices has been selected (i.e. though change of magnet grade or geometry) such that a substantial proportion of the atomic ion species from the source (i.e. between an m / z of 5 and 300) is transmitted, defining a broad transmission window; Figure 34 - a ‘top-down’ view of a horizontal plane within the assembly in which an ion blocking device (e.g. as described previously herein) has been positioned to intersect the trajectory of an atomic ion species of given m / z within the broad transmission window, such that this atomic ion species is not transmitted downstream.

[0185] The position of the ion blocking device can be adjusted to any lateral point within the width of the ion beam filter such that any trajectory of an atomic ion species that is transmitted from the first ion optical lens can be intercepted by appropriate positioning of said ion blocking device. One can consider a useful scenario wherein the ion blocking device intercepts the trajectory of the large Argon beam from the ICP source, as is shown in Figure 34 where only one specific m / z trajectory is blocked, while allowing transmission of all other m / z trajectories within this predetermined transmission window. As the ion beam is primarily constituted of Argon ions from the ICP source, rejection of this ion species leads to a reduction of downstream space charge effects, an improvement in overall analyte transmission, a reduction in abundance tailing within the MS analyser and a reduction in downstream ion optical component deterioration through collisions with the ion beam. While these benefits are attainable through the rejection of Argon by appropriate positioning of the mass defining slit apertures 100,102, as shown in Figure 31 , a user would have to choose to also reject all masses above or below this m / z, depending on the choice of slit (i.e. 100 may act as a low pass filter, 102 may act as a high pass filter). The use of an ion optical device as set out above allows a user to gain all of the benefits of Argon removal, through selective rejection of a small portion of the transmission window, without having to adjust the configuration of the ion beam filter when swapping between different atomic ion species within the MS analyser.

[0186] One can also consider a scenario wherein the ion blocking device takes the form of an ion collector (e.g. Faraday cup), the ion collector comprising an ion detector for generating an ion detection signal in response to the collection of ions, as the ion collector is swept across the width of the ion beam filter. This ion detection signal may be plotted against detector position to form a mass spectrum characterized by the ion beam filter setup. This mass spectrum could for instance be used to confirm the relative lateral displacements of specific atomic ion species for instrument calibration or to assist with specific transmission window setup without relying upon the MS analyser optics.

[0187] A further scenario can be considered wherein the ion blocking device is constructed out of a porous sheet metal, such that the obstructed trajectory is attenuated by an adjustable factor, through adjustment of the porosity of the sheet metal. This would allow for precise measurements of the attenuated atomic ion species with the MS analyser without having to directly measure the large unattenuated beam, which could otherwise cause considerable damage to the detectors in the detector array. The ion blocking device could still be of use as an ion collector for calibration purposes, as the unobstructed proportion of the beam could be accounted for.

[0188] Figures 35, 36 and 37 show cross-sectional views of an ion beam filter assembly with simulated ion paths (trajectories) shown for several different atomic ion species where the magnetic fields magnitude of the ion optical devices match that of Figures 33 and 34: Figure 35 - a ‘top-down’ view of a horizontal plane within the assembly in which the relative lateral displacements of the atomic ion species are of a first magnitude, wherein the reference potential of the ion beam filter assembly is held at 0V; Figure 36 - a ‘top-down’ view of a horizontal plane within the assembly in which the relative lateral displacements of the atomic ion species are of a second magnitude, wherein the reference potential of the ion beam filter assembly is held at 3000V; Figure 37 - a ‘top-down’ view of a horizontal plane within the assembly in which the relative lateral displacements of the atomic ion species are of a third magnitude, wherein the reference potential of the ion beam filter assembly is held at 4000V.

[0189] Due to the fundamental design of the mass spectrometer, wherein the ion source is held at a first potential (i.e. 6000V), an ion beam extracted from the source travelling downstream to a region held at a second potential (i.e. 0V) will gain kinetic energy equal to the difference in potential energy between these two points, in this instance approximately 6000eV. If the second potential were to be changed to a third potential (i.e. 4000V), the resultant ion beam kinetic energy would be 2000eV.

[0190] We can consider a scenario wherein the reference potential of the ion beam filter, namely the reference potential of the components built upon both the retractable carriage and stationary plate E through H (i.e. by building the stationary and retractable mounting plates on isolating supports and connecting this isolated assembly to a reference potential). The ion beam kinetic energy could be adjusted within the length of the ion beam filter to increase the relative lateral dispersion generated by the ion optical devices, due to the fact that the strength of the magnetic field within the ion optical devices will not be impacted by this reference potential change. This scenario would require an adjustment of electric potentials for all biased ion optical components to account for the change in the ion beam kinetic energy. The first Einzel lens D, would also be adjusted to account for the defocussing effect of the ion beam deceleration, such that a spatial focus would be maintained at the plane of the mass defining filter slit (i.e. the beam is spatially converging as it travels toward the plane of the mass defining filter slit and spatially diverging as it travels downstream of the mass defining filter slit.)

[0191] A halving of the ion beam kinetic energy would lead to a relative increase of lateral dispersion of / 2, leading to an improved mass resolution due to the increased mass separation, as shown by comparing Figures 35 and 36. Figure 37 shows an additional scenario wherein a further increase in lateral dispersion could be achieved through the use of a reference potential of 4000V. The flexibility of the system as highlighted in Figure 35,36 and 37 could be of use for users who require a range of lateral dispersion values dependent on their specific applications. This biasing method could not only be applied to the ion beam filter configuration generating a relatively low lateral dispersion as laid out in Figure 35, but also to that of the ion beam filter configuration generating a relatively high lateral dispersion as laid out in Figure 31 , to further increase the ion beam filter performance. It should be noted that the consistently rejected atomic ion species of Figures 35,36 and 37 is Argon, which was used as a point of reference by leaving the ion blocking device in the same position throughout and adjusting the electric field of the ion optical device to maintain Argon removal.

[0192] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0193] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0194] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0195] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0196] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

[0197] Examples

[0198] EXAMPLE 1

[0199] In a practical embodiment of a mass spectroscopy apparatus or unit comprising a beam filter (mass filter) arrangement according to an aspect of the invention, the apparatus may operate as follows:

[0200] 1 . An ion beam is extracted from the source and focussed onto to the source defining slit.

[0201] 2. A secondary beam profiling slit rejects the most divergent parts of the beam to minimise the aberrations at the mass filtering focal point of the beam filter (mass filter).

[0202] 3. The transmitted beam is focussed with the pre-filter lens to form an image in the region of the mass defining slit. a. The focus point is preferentially characterised with a spatial magnification of ~1 by using appropriate geometry.

[0203] 4. Due to the short magnetic path length and linear electric field of the Wien filter, the beam experiences negligible focussing and significant deflection by the Wien filter.

[0204] 5. Ions with different masses follow different trajectories within the Wien filter, leading to non-zero values of A / 6 and X / 6. a. A / 6 is the mass dependent inclination coefficient, used to determine the inclination difference between an ion of mass M+AM and a reference particle of mass M. b. X / 6 is the mass dependent position coefficient, used to determine the position difference between an ion of mass M+AM and a reference particle of mass M. c. The values of A / 6 and X / 6 are dependent on the ion energy and magnetic field strengths.

[0205] 6. Ions of different masses spatially diverge after leaving the Wien filter, increasing the dispersion achieved at the mass defining slit. a. This helps reduce the total length of the Wien filter to reduce the likelihood of ion rejection within the length of the Wien filter, thus improving the system reliability due to a reduction in particle deposition within the assembly itself.

[0206] 7. The beam is focussed vertically to account for the downstream defocussing from the lens field arrays.

[0207] 8. Some masses are rejected prior to or at the entrance of the lens field array, where baffles are fitted to eliminate the issues that arise from primary ions and secondary scattered particles. 9. By adjusting the quadratic voltage on the first lens field array, the A / 6 term can be reduced to ~0, such that all beam paths exit the lens field array parallel to the optical axis. a. Ion will travel downstream with a fixed value of X / 6 b. Some horizontal focussing and vertical defocussing occurs, accounted for by the upstream vertical lens and pre-filter lens.

[0208] 10. The mass defining slit is composed of a ‘high mass’ and ‘low mass’ slit, which can be moved independently. This allows for central and offset positioning of the slit, the latter minimising downstream transmission of neutral species from the source.

[0209] 11. A notch filter can be used reject a central mass window while allowing masses around this window to be transmitted.

[0210] 12. After the mass defining slit, the geometry, electric and magnet fields are mirrored exactly to recombine the transmitted beams back on to the optical axis, such that X / 6 and A / 6 are ~0. This condition allows for downstream beam manipulation, with no need to retune the beam filter (mass filter).

[0211] Further aspects of the spectrometer comprising a beam filter arrangement according to an aspect of the invention may include:

[0212] Filter retraction:

[0213] The entire beam filter (mass filter) assembly can be mounted on a moving optics plate so that the beam filter can be moved off-axis when mass filtering is not required.

[0214] A precision linear guide may be provided to define the allowable path the assembly can take when moved. This may be controlled by a linear controller which can take the form of a linear drive or a simple pneumatic actuator. The exact end point position of the plate may be defined by internal geometry constraints. This can be achieved in a multitude of ways, for example retraction and extension stops. A spring mechanism can be used between the linear controller and the optics plate such that the system can be over driven to ensure good alignment.

[0215] In such a system, the pre-filter and post-filter lenses preferably are not mounted on the retracting plate, but directly to the vacuum chamber instead. When the beam filter is retracted within the vacuum chamber, the pre-filter lens maintains a focus near the mass defining slit, while the post-filter lens maintains transmission through the downstream optics. This minimises instrument tuning between modes.

[0216] The standard path may be shielded from any stray magnetic fields with a mild steel shield fitted near to the permanent magnets. These could be mounted on the optics plate or to the chamber itself.

[0217] The standard path can be shielded from any stray electric fields with a grounded shield fitted on the optics plate, arranged so that as the beam filter is retracted, this shield moves into place over the standard path.

[0218] Wien filter:

[0219] Independent control of Wien filter tracks (i.e., field-generating electrodes) may be provided to allow for the use of higher order field corrections to be superimposed over the linear field, such as quadratic and cubic fields: a. The quadratic field allows for fine tuning of the focus position. b. The cubic field rotates the focal plane. c. Other higher order and non-symmetrical corrections could also be used. The Wien filter preferably comprises: a. A mild steel terminator at the entrance and exit, to terminate the B field. b. A 316 stainless steel terminator at the entrance and exit, to independently terminate the E field without impacting the B field termination. c. Two permanent magnets may be mounted within an encompassing yoke. i. The geometry and grade of the magnets may be adjusted such that the resultant B field can be tailored to specific filtering requirements. d. A series of 316 stainless steel folded tracks (i.e., field-generating electrodes) may be provided to apply the electric field along the length of the Wien filter where: i. The tracks may be isolated by a PCB, mounted vertically on the face and rear of the assembly (e.g., external to the Wien filter). ii. The tracks may run off the edge of the PCB (vertically) and may be folded through the centre of the assembly (along the beam path), with a small vacuum gap separating the tracks from the magnet surface(s) (which may be held at some reference potential, e.g. grounded).

[0220] Hi. This means that there is no dielectric material inside the Wien filter itself, which drastically improves the working lifetime of the assembly and minimises the risk of any dielectric charge injection within the assembly.

[0221] Vertical lens:

[0222] Preferably a pair of vertical lenses, placed between the Wien filters and lens field arrays, are provided to correct the vertical defocussing that may be introduced by the lens field arrays. The vertical defocussing may be a byproduct of horizontal focussing done to generate the parallel beam paths at the lens field array exit, analogous to quadrupole defocussing.

[0223] Lens field array:

[0224] The main advantages of a parallel set of beams defined by two lens field arrays are: a. lens field arrays have a large beam acceptance in the dispersion plane allowing for a wider range of masses for a given B field. b. The intermediate mass defining slit lies at the point of maximum dispersion. c. The intermediate space allows for simple slit and notch filter designs.

[0225] Mass-defining slit and notch filter:

[0226] The mass-defining slit(s) is (are) preferably arranged so that it (they) can be fully retracted out of the beam path and may be arranged to be driven past the axial point from both sides. This could be done to block the line of site between the mass analyser and the ICP source, thus improving the analyser performance.

[0227] This may be achieved by blocking the unwanted neutral beam from the source, to reduce collisional energy losses in the analyser.

[0228] The notch filter is preferably arranged so that it can be swept over the full width of the mass defining slit which would generate a mass spectrum, which is useful for calibration of the system.

[0229] The notch filter may be primarily designed or used to catch the large Argon beam from the ICP source but can be used for any problematic mass or even to minimise neutral species transmission. Filter biasing:

[0230] The entire beam filter (mass filter) assembly in the first instance sits at the ground potential so that the ion beam travels through with some kinetic energy defined by the acceleration potential, simplifying the electrical supplies needed. However, it is useful if the system is designed such that the elements between and including the Wien filters can be biased to some reference potential, thus decreasing the kinetic energy of the particles, and increasing the resolution of the beam filter (mass filter), without impacting the rest of the instrument.

[0231] This can simply involve isolating the retracting optics plate, mass defining slits and notch filter such that a reference potential can be set to define the ion energy through the beam filter (mass filter).

[0232] Constructing a beam filter (mass filter) arrangement in accordance with an aspect of the present invention provides a number of advantages compared with earlier known systems. One of these derives from the use of the notch filter, where removal of the Ar+ beam leads to the following improvements on the standard path: a. Increase in sensitivity for all transmitted masses due to the lack of space charge, primarily at the mass analyser defining slit. b. Increase lifetime of the mass analyser defining slit. c. Improved abundance sensitivity due to less ion-ion collisions in the mass analyser. d. Theoretical improvements in mass analyser performance (high resolution).

[0233] In the case of mass spectrometers using a collision / reaction cell (CRC) there are specific advantages:

[0234] It should be noted that the CRC path does not lie on the optical axis. The beam is deflected onto an offset but parallel beam axis by using electrostatic ‘path deflectors’, after which the beam is then brought back onto the original axis with a second path deflector. All these optics lie downstream of the beam filter (mass filter) in another vacuum chamber and as such can be treated separately. This layout means that there is no line of sight from the ICP source to the CRC, or from the CRC to the mass analyser. Thus, any neutral beam from the source will not impact the CRC chemistry, and any neutral beam from the CRC will not be transmitted into the mass analyser.

[0235] Removal of the Ar+ beam leads to the following additional benefits to the CRC path: a. Reduced mass fractionation at the entrance of the CRC. b. Ar+ removal by charge transfer with Hydrogen currently dominates the cell chemistry, which would not be necessary if removed prior to entering the cell.

[0236] Furthermore, defining a specific mass transmission window allows for the use of reactive gases inside the collision cell for interference removal that would otherwise cause additional interferences at the mass analyser.

[0237] References

[0238] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0239] [1] GB2535826

[0240] [2] EP3901984

[0241] [3] GB2545670 [4] EP3769334

[0242] The following clauses, which form part of the description, provide general expressions of the disclosure herein:

[0243] A1 . A beam filter arrangement for location between an ion source and a mass analyser in a mass spectrometer, and including a pair of spaced Wien filters, the first to spread the ion beam and the second arranged downstream of the first and arranged to recombine constituents of the beam into a single narrow beam, and a mass defining slit located between first and second Wien filters and characterised by lens field arrays between the first Wien filter and the mass defining slit and between the mass defining slit and the second Wien filter, the lens field arrays being arranged to cause the paths of the ions in the beam between the two lens field arrays to be substantially parallel.

[0244] A2. A beam filter arrangement according to clause A1 and including a first vertical lens between the first Wien filter and the upstream lens field array and a second vertical lens between the downstream lens field array and the downstream Wien filter.

[0245] A3. A beam filter arrangement according to clause A1 or A2 where the mass defining slit is formed between two the edges of two ion barrier walls, each independently movable in a direction perpendicular to the main beam direction whereby the location and width of the mass defining slit may be independently adjusted.

[0246] A4. A beam filter arrangement according to any one of clauses A1 to A3 wherein a notch filter is positioned within the space of the mass defining slit.

[0247] A5. A beam filter arrangement according to clause A4 and including means to move the notch filter transversely relative to the beam direction and between a position where it is located outside the ion beam, where it is centrally located relative to the ion beam, and one where it is positioned symmetrically non-adjacent to the initial position, and all points therein.

[0248] A6. A beam filter arrangement according to any one of clauses A1 to A5 wherein the arrangement is mounted and grounded to a carriage located in a vacuum chamber across which the ion beam traverses, the carriage being movable transverse to the beam direction from a position where the beam passes through the mass filter to one in which it travels to one side thereof.

[0249] A7. A beam filter arrangement according to clause A6 wherein the carriage is electrically isolated from the ground potential, such that the carriage reference potential can be adjusted.

[0250] A8. A beam filter arrangement according to any one of clauses A1 to A7 wherein the permanent magnet geometry and grade can be adjusted to generate a range of available performance criteria.

[0251] A9. A beam filter arrangement for location between an ion source and a mass analyser in a mass spectrometer, includes a pair of spaced Wien filters, 8, 16, the first to spread the ion beam and the second arranged downstream of the first and arranged to recombine constituents of the beam into a single narrow beam. A mass defining slit 7 is located between first and second Wien filters. Lens field arrays 11 ,14 are located between the first Wien filter 8 and the mass defining slit 7 and between the mass defining slit 7 and the second Wien filter 16. The lens field arrays are arranged to cause the paths of the ions in the beam between the two lens field arrays to be substantially parallel. A movable notch filter may be positioned in the mass defining slit to remove a particular species from the ion beam.

Claims

Claims:1 . An ion beam filter for receiving, from an ion source, a beam of ions and for transmitting ions selected from the beam of ions, the ion beam filter extending along an ion optical axis and comprising: a pair of ion optical devices spaced along the ion optical axis and comprising a first ion optical device configured to spread the ion beam and a second ion optical device configured arranged downstream of the first ion optical device and arranged to recombine constituents of the spread beam into a single narrowed beam, wherein each said ion optical device is configured to form a magnetic field extending in a direction across the ion optical axis and to form an electric field extending in a direction across the ion optical axis and across the direction of the magnetic field, therewith to deflect ions of the beam in directions transverse to the ion optical axis to an extent according to their respective velocity; a mass defining filter aperture located between first and second ion optical devices; and, an array of ion optical lenses comprising a first ion optical lens arranged between the first ion optical device and the mass defining filter aperture and a second ion optical lens arranged between the mass defining aperture and the second ion optical device; wherein the first ion optical lens of the array of ion optical lenses is configured to cause the paths of the ions in the beam to become substantially parallel between the first ion optical lens and second ion optical lens at or adjacent to the location of the mass defining filter aperture.

2. An ion beam filter according to claim 1 wherein the first ion optical device is configured to deflect received ions in directions so as to follow deflected respective ion paths, and the first ion optical lens is configured to receive said deflected ions from the first ion optical device and to deflect the received ions according to their respective deflected ion paths.

3. An ion beam filter according to any preceding claim wherein the mass defining aperture is configured for selectively transmitting only ions received from the first ion optical lens upon respective ion paths that pass through the mass defining filter aperture, and for obstructing transmission of received ions upon other ion paths.

4. An ion beam filter according to claim 3 where the mass defining filter aperture is formed between two the edges of two ion barrier walls, each being independently movable in a direction perpendicular to the ion optical axis whereby the location and width of the mass defining filter aperture may be independently adjusted.

5. An ion beam filter according to any preceding claim comprising an ion blocking device located within or adjacent to the space of the mass defining filter aperture and configured to block ions from the ion beam received from the first ion optical lens upon at least one ion path that intersects the ion blocking device for preventing the transmission of received ions upon the at least one intersecting ion path, whilst allowing transmission of other ions in the ion beam.

6. An ion beam filter according to claim 5, wherein the ion blocking device is configured to block ions having one or more predetermined m / z values7. An ion beam filter according to claim 6, wherein the ion blocking device is configured to block some but not all ions having the one or more predetermined m / z values.

8. An ion beam filter according to any of claims 5 to 7, wherein the ion blocking device takes the form of an ion collector, the ion collector comprising an ion detector for generating an ion detection signal in response to the collection of ions.

9. An ion beam filter according to any one of claims 5 to 8 including a translation assembly configured to move the ion blocking device transversely relative to the ion optical axis thereby to selectively position the ion blocking device laterally relative to the mass defining filter aperture.

10. An ion beam filter according to any preceding claim wherein: the first ion optical device is configured to receive said beam of ions, to deflect ions thereof and to output ions thereof upon respective ion paths that diverge, thereby to spread the beam of ions; the first ion optical lens is configured to receive ions from the first ion optical device upon said respective ion paths and to deflect the received ions so as to output ions upon respective ion paths that are substantially parallel, thereby substantially to collimate the beam of ions such that ion paths subsequently received by the mass defining aperture are substantially parallel; the second ion optical lens is configured to receive, via the mass defining filter aperture, ions from the first ion optical lens upon said substantially parallel paths and to deflect the received ions so as to output ions upon respective ion paths that converge, thereby to narrow the beam of ions; and, the second ion optical device is configured to receive ions from the second ion optical lens and to deflect the received ions so as to output ions upon respective trajectories that are substantially parallel, thereby substantially to collimate the narrowed beam of ions.

11. An ion beam filter according to any preceding claim comprising a first transverse-focussing ion optical lens located upon the ion optical axis between the first ion optical device and the first ion optical lens and a second transverse-focussing ion optical lens located upon the ion optical axis between the second ion optical lens and the second ion optical device, wherein each transverse-focussing ion optical lens is configured to deflect ions of the beam in directions transverse to the ion optical axis and transverse to the deflection by the first and second ion optical devices.

12. An ion beam filter according to any preceding claim wherein one or more of the first ion optical device and the second ion optical device comprises an ion entrance opening for receiving ions, an ion exit opening from which received ions are output, and an ion transmission channel for transmission of received ions in a direction along an ion optical axis from the ion entrance opening to the ion exit opening, the ion optical device further comprising: a magnetic yoke formed around the ion transmission channel; a first permanent magnet which is attached to the magnetic yoke within the ion transmission channel and a second permanent magnet which is attached to the yoke within the ion transmission channel in spaced opposition to the first permanent magnet across the ion transmission channel to form therebetween said magnetic field extending in a direction across the ion optical axis13. An ion beam filter according to claim 12 wherein the magnetic yoke provides a magnetic field flux-return path internally within the magnetic yoke for a magnetic field passing from the first permanent magnet to the second permanent magnet, and an external magnetic field flux-return path which spans across the ion transmission channel from the second permanent magnet to the opposing first permanent magnet to form therebetween a magnetic field extending in a direction across the ion optical axis.

14. An ion beam filter according to claim 12 or claim 13 comprising a first array of electrodes extending in free space across the first permanent magnet within the ion transmission channel, and a second array of electrodes extending in free space across the second permanent magnet within the ion transmission channel in spaced opposition to the first array of electrodes across the ion transmission channel, wherein the first and second arrays of electrodes are configured to receive respective voltage signals therewith collectively to form said electric field extending in a direction across the ion optical axis and across the direction of the magnetic field.

15. An ion beam filter according to any of claims 12 to 14 comprising a first electrode support plate adjacent to the ion entrance opening and a second electrode support plate adjacent to the ion exit opening, wherein the first array of electrodes is suspended in free space between the first electrode support plate and the second electrode support plate, and the first and second electrode support plates are each formed of a non-conducting material bearing:one or more electrical contact terminals configured to receive a voltage signal from amongst said respective voltage signals, and one or more conductive tracks electrically connecting one or more electrodes amongst the first array of electrodes to the one or more electrical contact terminals.

16. An ion beam filter according to claim 15 comprising a third electrode support plate adjacent to the ion entrance opening and a fourth electrode support plate adjacent to the ion exit opening, wherein the second array of electrodes is suspended in free space between the third electrode support plate and the fourth electrode support plate, and the third and fourth electrode support plates are each formed of a nonconducting material bearing: one or more electrical contact terminals configured to receive a voltage signal from amongst said respective voltage signals, and one or more conductive tracks electrically connecting one or more electrodes amongst the second array of electrodes to the one or more electrical contact terminals.

17. An ion beam filter according to claim 16 wherein the first electrode support plate and the third electrode support plate each comprise a respective part of one common electrode support plate.

18. An ion beam filter according to claim 16 or claim 17 wherein the second electrode support plate and the fourth electrode support plate each comprise a respective part of one common electrode support plate.

19. An ion beam filter according to any of claims 15 to 18 wherein said one or more electrical contact terminals comprises a spring-loaded contact or a Pogo Pin permitting the one or more electrical contact terminals to be mechanically pressed into electrical contact with a source of said respective voltage signals.

20. An ion beam filter according to any of claims 12 to 19 wherein the magnetic yoke comprises a two-piece yoke assembly comprising: a first yoke piece to which the first permanent magnet and second permanent magnet are attached; and, a separate second yoke piece attached to the first yoke piece to form a lateral side of the ion transmission channel; wherein the second yoke piece is detachable from the first yoke piece to reveal the ion transmission channel to permit a lateral access to the ion transmission channel, and re-attachable to the first yoke piece to complete said magnetic field flux-return path internally within the magnetic yoke.21 . An ion beam filter according to any of claims 12 to 20 wherein the first array of electrodes and the second array of electrodes each comprises a plurality of spatially separated electrodes each of which extends in a direction along the ion transmission channel wherein each electrode of the respective array of electrodes is spaced apart from each neighbouring electrode of the respective array in a direction extending across the ion transmission channel.

22. An ion beam filter arrangement according to any one of claims 12 to 21 wherein the first permanent magnet and / or the second permanent magnet are removeable and replaceable to permit adjustment of a geometry and / or a grade of the permanent magnet according to a replacement permanent magnet.

23. An ion beam filter according to any of claims 12 to 22 comprising: a carriage to which the first ion optical device and / or the second ion optical device are mounted wherein the chassis is operable to move between: a deployed position in which the ion transmission channel of the first ion optical deviceand / or the ion transmission channel of the second ion optical device is aligned with the ion optical axis of the ion beam filter; and, a retracted position in which the ion transmission channel of the first ion optical device and / or the ion transmission channel of the second ion optical device is laterally displaced from the ion optical axis of the ion beam filter to an extent sufficient that ions or the ion beam are neither received into the ion transmission channel nor obstructed by the first ion optical device and / or by the second ion optical device.

24. An ion beam filter according to claim 23 comprising a magnetic shield assembly laterally offset from the ion transmission channel by a lateral offset corresponding to the lateral displacement between the deployed position and the retracted position, wherein the magnetic shield assembly is positionable, by positioning the carriage in the retracted position, to shield the flow of ions from a magnetic field flux extending along the magnetic field flux-return path external to the magnetic yoke of the first ion optical device and / or the second ion optical device.

25. An ion beam filter according to claim 24 wherein the magnetic shield assembly comprises a tubular conduit defining a longitudinal conduit axis configured to extend in a direction substantially parallel to the ion optical axis of the first ion optical device and / or the second ion optical device, and configured to receive the flow of ions therealong when the translation stage is in the retracted position.

26. An ion beam filter according to claim 24 or 25 wherein the magnetic shield assembly comprises a material having a relative permeability of at least 80,000.

27. An ion beam filter according to any preceding claim wherein one or more of the first ion optical lens and the second ion optical lens comprises an ion entrance opening for receiving ions, an ion exit opening from which received ions are output, and an ion transmission channel for transmission of received ions in a direction along an ion optical axis from the ion entrance opening to the ion exit opening, the ion optical lens further comprising: one or more electrode plates configured to receive respective voltage signals therewith collectively to form an electric field to produce an ion optical effect within the ion transmission channel; a chassis to which the plurality of electrode plates are attached in spaced succession within the ion optical axis; wherein the one or more electrode plates each comprise at least one attachment through- opening formed therein, and the chassis comprises one or more mounting rods formed of an electrically non-conducting material which passes through the attachment through-opening of each of the one or more electrode plates thereby to attach the one or more electrode plates to the chassis along the one or more mounting rods without forming an electrical connection between the one or more electrode plates.

28. An ion beam filter according to claim 27 wherein each of the one or more electrode plates is bonded to the at least one mounting rod by a non-conducting bonding material bonded to a surface of the at least one said mounting rod and bonded to a surface of the one or more electrode plates thereby connecting each respective electrode plate to the at least one mounting rod.

29. An ion beam filter according to claim 28 wherein the non-conducting bonding material forms a continuous bond circumferentially around the mounting rod to which it is bonded and forms a continuous bond circumferentially around the attachment through-opening of the electrode plate to which it is bonded.

30. An ion beam filter according to any of claims 27 to 29 wherein the non-conducting bonding material comprises a resin.31 . An ion beam filter according to any of claims 27 to 30 wherein the one or more mounting rods comprise a ceramic material.

32. A mass spectrometer comprising an ion beam filter according to any preceding claim.

33. An ion beam filtering method for selected ions from the beam of ions for transmission along an ion optical axis, the method comprising: providing, on the ion optical axis, a pair of ion optical devices spaced along the ion optical axis and: by a first said ion optical device, spreading the ion beam; by a second said ion optical device arranged downstream of the first ion optical device, recombining constituents of the spread beam into a single narrowed beam; wherein, by each said ion optical device, a magnetic field is formed extending in a direction across the ion optical axis and an electric field is formed extending in a direction across the ion optical axis and across the direction of the magnetic field, therewith to deflect ions of the beam in directions transverse to the ion optical axis to an extent according to their respective velocity; providing, on the ion optical axis, a mass defining filter aperture located between first and second ion optical devices; and, providing, on the ion optical axis, an array of ion optical lenses comprising a first ion optical lens arranged between the first ion optical device and the mass defining filter aperture and a second ion optical lens arranged between the mass defining aperture and the second ion optical device; and, by the first ion optical lens of the array of ion optical lenses, causing the paths of the ions in the beam to become substantially parallel between the first ion optical lens and second ion optical lens at the location of the mass defining filter aperture.

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