WO2013002683A1

WO2013002683A1 - Static ion mass analyzer

Info

Publication number: WO2013002683A1
Application number: PCT/RU2012/000550
Authority: WO
Inventors: Вячеслав Данилович САЧЕНКО
Original assignee: Sachenko Viacheslav Danilovich
Priority date: 2011-06-30
Filing date: 2012-06-29
Publication date: 2013-01-03
Also published as: RU2456700C1

Abstract

The static ion mass analyzer comprises an ion source (1), a focusing system, an object slot (2), an aperture diaphragm (3), an energy-dispersive electrostatic sector (5), and an energy-dispersive magnetic sector (7). The electrostatic sector (5) is arranged relative to the magnetic sector (7) so that the directions of rotation of the optical axes (4, 6) in the electrostatic sector (5) and the magnetic sector (7) coincide. The electrostatic sector (5) is arranged relative to the ion source (1) so that the plane of the optical image of the object slot (2) is situated between the electrostatic sector (5) and the magnetic sector (7). An energy-filtering diaphragm (10) is disposed in the plane of the optical image of the object slot (2). A collimating lens (11) is disposed between the electrostatic sector (5) and the magnetic sector (7). The static ion mass analyzer has an elevated resolution in a simultaneous ion mass spectrum registration mode in cases where the energy of the ion beam is not uniform.

Description

STATIC ION MASS ANALYZER

The invention relates to analytical instrumentation, and in particular to static instruments and devices for analyzing the mass spectral composition of substances.

Static ion mass analyzers (SMAs) are based on the principle of spatial separation of ions by momenta in the static magnetic sector (MS), where each monopulse ion group has its own optical axis. In the uniform magnetic field, which is most often used in SMA, the optical axes of monopulse groups are arcs of circles, the radii of which, in the case of an insignificant spread of ion energies, depend on their mass, which makes it possible to carry out a precision mass analysis of ions . However, with ionic heterogeneity in energy, the resolving power of SMA deteriorates due to 1st order chromatic aberration (MS energy dispersion). Therefore, in modern SMA, conditions are provided for compensating the energy dispersion of MS by including the electrostatic sector (ES) in the composition of the SMA. Such ion-optical systems are called dual focus CMAs. Under conditions of a significant dispersion of ion energies, the resolution limit of a double focusing SMA is limited by the level of chromatic aberrations of the second and higher orders proportional to the powers of the ratio of the energy spread to the accelerating voltage. An effective way to reduce these chromatic aberrations in such cases is the energy filtration of ions.

Known single-focus mass spectrometer with dual focusing (see patent US 4766314, IPC H01J 49/32, publ. 08.23.1988), including an ion source (AI), a focusing system (FS), an exit slit (VSC), which object slit (OS) of the mass analyzer, aperture diaphragm (HELL), sequentially arranged static magnetic sector (MS), an intermediate electrostatic lens (EL) for electrical adjustment of the spectrometer, electrostatic sector (ES) and a single-collector mass spectrum detector . The ES is set relative to the MS in such a way that the direction of rotation of its optical axis in the ES is preserved in the MS. This option has historically been called the C-scheme, in contrast to the S-scheme, in which the directions of rotation of the optical axes in the ES and MS are opposite. EL It is installed in the plane of the intermediate optical image of the OSH, which allows one to simplify the setup of double focusing of ions.

The well-known mass spectrometer does not allow simultaneously recording the entire mass spectrum or its part, which is due to both the order of the MS and the ES (the ES is installed behind the MS) and the fact that double focusing takes place only for one monomass ion group, which is deduced by the parameter sweeps to a fixed axial orbit a priori. In this case, the detection of the lines of the mass spectrum is carried out by varying the sweep parameter with the consequent orbiting of all monomass ion groups into the orbit and registration of the mass spectrum by a single-collector detector, which is associated with a low mass spectrometer performance.

Known mass spectrometer with energy filtration of ions after their separation by mass in a magnetic field (see patent US 5166518, IPC H01J49 / 32, published 11.24.1992), including AI, FS, OSh, AD, sequentially installed MS, mass filtering gap , the first transporting lens, ES, the second transporting lens, ED and single-collector detector. MS and ES are installed according to the S-scheme.

The disadvantages of the known mass spectrometer are its low resolution and low productivity due to the single-collector method for detecting the mass spectrum.

Known tandem mass spectrometer type MS / MS, the second stage of which is made in the form of a two-stage dual focusing SMA (see patent US 4866267, IPC H0U 49/32, published 08.23.1988), including a source of "daughter" ions from the selected at the first stage of the mass spectrometer of monomass “parent” ions, and sequentially arranged Wien filter, MS and a spatially extended detector (PPD) of daughter ions.

A disadvantage of the known mass spectrometer is that double focusing over the range of orbits of the detected ions takes place only in a narrow range of approximately equal initial velocities, which accounts for the relatively narrow scope of this analogue.

The disadvantages of single-focus dual-focus mass spectrometers have led to the development of multi-collector mass spectrometers in which dual focusing occurs for all orbits of monomass ion groups. Such devices have advantages over single-collector mass spectrometers. An increase in the number of collectors and their optimal placement makes it possible to reduce the range of variation of the magnetic field induction or ion accelerating potential, and hence the time of recording the mass spectrum, which increases Expression and analysis performance are reduced. However, the implementation of the multi-collector mode of mass analysis imposes a number of fundamental optical and design conditions on the SMA, namely: a multi-collector mass spectrometer must a) provide double focusing for all registered monomass groups of ions simultaneously, b) ensure equality of rotation angles optical axes of monomass ion groups in the MS, c) have a straight line of the focus lines of the MS. The specified conditions are satisfied by the Mattauch-Herzog type MCA, in which the ES and MS are located in the S-scheme, the object gap (OS) is located in the front focal plane of the ES, and the geometric place of the optical foci of the MS forms a straight line. An essential feature of the Mattau-Herzog (MG) type SMA is the design of the MC made by a two-pole with a constant gap between the pole pieces, the output boundary of which is flat, made in such a way that the effective boundaries of the magnetic field and the input optical axis intersect at one point . This special construction, first described by Mattauch and Herzog (CMJ. Mattauch and RJ, Herzog. - Phys., 89, p. 789.1934, J. Mattauch and RJ, Herzog), ensures that the ion rotation angle in the MS field is independent of their mass . The indicated construction will be called below the “MG construction”. Practically all SMAs made according to the Mattauch-Herzog type include MC structures of the MG in their composition. Along with the above-mentioned advantages of the MTA of the Mattauch-Herzog type, their common drawback is known: the lack of intermediate focusing of ions by their angular spread, which does not make it possible to establish ED to reduce the energy spread of the analyzed ion beams.

A multi-collector magnetic mass spectrometer with double focusing is known, the MCA of which is made according to the Mattauch-Herzog type (see High-performance mass spectrometer with double focus. Instruments for scientific research, N? 2, pp. 37-44, 1985, A. O. Nir et al.), Including AI, FS, OSh, ES in the form of a sector of a cylindrical capacitor, MS of the MG design and a multi-collector detector, the receiving slits of which are installed along the focal line of the MS.

A disadvantage of the known mass spectrometer is its low resolution under conditions of significant energy dispersion of ions.

A multi-collector magnetic mass spectrometer with double focusing is known, the MCA of which is made according to the Mattauh-Herzog geometry (see Development of a miniaturized gas chromatograph-mass spectrometer with a microbore capillary columns and array detector. Analytical Chemistry, vol. 63, No. 18, p.2012-2016,1991, MP Sinha et al.), Including AI, FS, OSh, ES in the form of a sector of a cylindrical capacitor, MS design MG, electro-optical detector with a microchannel plate, installed along the focal line of the MS, and an automated mass spectrometer control system.

The disadvantage of this mass spectrometer, as well as the previous analogue, is the absence of an ion energy filtration system, which limits the resolution of the device under conditions of significant energy dispersion of the analyzed ions.

Known static mass analyzer of ions with double focusing (see patent RU 2231165, IPC N (49/26, published June 20, 2004), which coincides with the claimed solution for the largest number of essential features and adopted for the prototype. SMA is made according to the geometry of Mattauch -Herzog and includes AI, FS, OSh, aperture diaphragm, energy dispersive electrostatic sector (ES) and magnetic sector (MS) in the form of a bipolar magnet with a constant gap between the poles. The ES is made in the form of a sector of a cylindrical capacitor. MS output boundary flat and hollow Thus, the effective boundaries of the magnetic field and the input optical axis intersect at the same point.The SMA also includes a system for simultaneously recording mass spectral lines in the form of a multi-collector detector, the receiving slits of which are installed along the line of the MS foci, a mass spectrometer control system and an automated computer-based data collection system for cyclically recording and storing mass spectra.

The disadvantage of the prototype is the lack of an ion-beam energy filtration system and the fundamental impossibility of its installation, which significantly limits the level of resolution of the prototype in conditions where the ion beam to be mass spectrally analyzed is not uniform in energy.

An object of the present invention is to increase the resolving power of SMA in the mode of simultaneous recording of the ion mass spectrum under conditions of an ion beam that is not uniform in energy.

The problem is solved in that the static mass analyzer of ions includes an ion source (AI), a focusing system, an object slit, an aperture diaphragm, an energy dispersive electrostatic sector (ES), and a magnetic sector (MS) in the form of a bipolar magnet with a constant gap between the poles, and a system for the simultaneous registration of mass spectral lines. The output boundary of the MS is flat and made in such a way that the effective boundaries of the magnetic field and the input optical axis intersect at one point. The ES is set relative to the MS so that the directions of rotation of the optical axes in the ES and the MS coincide, and relative to the AI so that the plane of the optical image OS is located between ES and MS. An energy-filtering diaphragm (ED) is installed in the plane of the optical image of the OS. A collimating lens (CR) is installed between the ED and the MS, the front focal plane of which is located in the ED plane at the CL optical power _; satisfying the ratio:

where P _L is the optical power of the CL, mm ^"1 ;

D _e is the dispersion coefficient for ES energy in the ED plane, mm;

C _m is the dimensionless coefficient determined by the design of the magnetic sector, numerically equal to the product of the mass dispersion coefficient and the optical power of the MS, the same for all axial orbits of monomass ion groups in the MS field.

A system for simultaneously recording mass spectral lines can be implemented as a multi-collector ion detector with electrical registration of ion currents, receiving slits of which are installed in the focal planes of the MS corresponding to the axial orbits of the recorded monomass components of the ion beam.

Alternatively, the system for simultaneously recording mass spectral lines can be made in the form of a spatially extended detector, the receiving surface of which is mounted on the focal line of the static mass analyzer.

At least one lens can be installed between the object gap and the ES for the electrical adjustment of the SMA.

ES can be made in the form of a sector of an electrostatic capacitor with an equipotential optical axis, angle φ _β and radius r _{e of} rotation of the optical axis, axial radius a _{e of} curvature of its equipotential, and set at a distance L 'from OS to ES and at a distance L " from ES 5 to ED 10, the values of which are related to the coefficient D _{e of the} energy dispersion of ES 5, as it is easy to show, with a parametric dependence:

L '= r _e (Ce + l / t) / (ro s _e ) q', mm;

L "= r _e (c _e + t) / (co s _e ) q", mm;

D _e = r _e (l + t) / ro ² q, mm;

co = V (2- r _{e /} a _e ) - parameter of the "toroidality" of the capacitor,

q, q ', q "- correction factors due to small corrections related to the influence of ES edge fields whose values lie in the range between 0.9 and 1.1; parameter t> 0. In the most famous versions of ES in the form of a cylindrical and spherical capacitors o = 2 and ω = 1, respectively.

Unlike the SMA prototype, in the proposed mass analyzer, the ES and MS are installed according to the C-scheme, which allows focusing of ions according to the angular spread between the ES and MS and installing the ED in front of the MS. In this case, the ES is installed relative to the AI in such a way that an optical image of the SMA object slit is formed between the ES and the MS (in the prototype, the ES is installed relative to the AI so that the exit slit of the AI is located in the front focal plane of the ES); in the plane of the intermediate image of the OS is installed ED; a CR was installed in front of the MS, the design and position of which with respect to the ED was calculated so that its front focal plane is located in the ED plane at the optical power of the CR depending on the dispersion coefficient of the ES in the ED plane according to the equality

where P _L is the optical power of CL;

D _e is the dispersion coefficient for ES energy in the ED plane, mm;

The non-obviousness and novelty of the present invention are defined as follows. Two-stage SMA-focused double focusing MMAs were first described by Mattauch and Herzog in 1934. Around the same time, two-stage C-focusing dual-stage MMAs were known. From then until now, many variants of dual focusing SMA have been proposed, with the arrangement of ES and MS mainly according to the C-scheme (see Hintenberger, Koenig. In the book, Advances in Mass Spectrometry. Publishing House of Inl., 1963, pp. 26-45), since such a scheme allows focusing of ions in front of the MS and establishing the ED. However, a common drawback of all known CMA dual focus CMA variants is the curved focus line and the double focus condition for only one axial orbit, which does not allow the use of multi-collector detectors and requires the use of sequential scanning of the mass spectrum that displays monomass ions into the receiving gap of a single-collector detector. To date, only one group of double-focusing two-stage SMA variants is known, which allow the possibility of achieving double focusing simultaneously over the entire mass spectrum. These are options like Mattau- Duke with the arrangement of ES and MS according to the S-scheme and performing MS according to the MG design (see A.A.Sysoev, M.S. Chupakhin. Introduction to mass spectrometry, Atomizdat, 1977, p. 74). However, a common drawback of this group of SMA is the lack of the possibility of energy filtration of ions due to the fundamental absence of intermediate focusing between the ES and MS, since the output slit of the AI in such variants of the SMA should be located in the focal plane of the ES. Thus, the presence of intermediate focusing of ions and the ability to provide conditions for their energy filtration in known double focusing C-schemes are associated with the inevitable curvature of the focus line and the inability to provide double focusing at more than one point, while the known Dual focusing SMA circuits that allow double focusing over the entire spectrum of the axial orbits of monomass groups do not allow the possibility of ion energy filtration. From the foregoing, the non-obviousness and novelty of the proposed technical solution follows: over the 80-year history of the development of double focusing SMA, no solutions have been proposed that would violate this conflict. The solution proposed by the author first resolved it.

In the present invention, the problem is solved within the framework of C-schemes, since they create conditions for double focusing of ions while ensuring their intermediate focusing (due to opposite signs of the dispersion coefficients of ES and MS), and it is possible to set the ED.

The author found that in order to ensure double focusing simultaneously over the entire range of axial orbits of monomass ion groups, it is necessary to establish a collimating lens (CR) between the ED and the MS so that its front focal plane, with the value of the optical power determined by according to equality (1), the ES dispersion coefficient in the ED plane was located in the plane of the optical image of the OS where the ED was installed. In this case, when choosing the MS geometry according to the MG construction, the focus line turns out to be straight, a mass spectrometric mode receiving slot mnogokollektor- Nogo detector should be installed at the focal planes of the MS, The corresponding axial orbits monomassovyh groups of ions; in the mass spectrographic mode of the MCA using a spatially extended detector (PDD), the receiving surface of the PDA should be located on the focus line. The author found that with this solution in the plane of the optical image of the OS, double focusing of an arbitrary monomass group of ions is ensured. Moreover, the values of the dispersion coefficient of the MS and its optical power, therefore, and the coefficient C _t in the right-hand side of (1) are uniquely determined MC structure (see G. Volnik. Optics of charged particles, Energoizdat, 1987). The analysis shows that, in the case of the MG of the MG design, the specified coefficient is dimensionless, i.e. its value does not depend on the radius of the axial orbit of any monomass group. Thus, to ensure double focusing over the entire spectrum of the mass spectrum, it is necessary: to select the ES design and its location relative to the AI, calculate the dispersion coefficient of the ES in the plane of the optical image of the OSH, choose a convenient CR design, calculate the position of its front focal the plane upon excitation of the lens, corresponding to the optical power determined by the right-hand side of (1), and then set the CR between the ED and the MS in such a way that the calculated front focal plane of the CR coincides with plane ED.

The present invention is illustrated in the drawing, where

in Fig. 1 shows the optical part of the SMA prototype;

in Fig. 2 shows the CMA of the present invention.

In Fig. 1 are indicated: ion source 1, exit slit 2, aperture diaphragm 3, optical axis 4 in the energy dispersive electrostatic sector (ES) 5, optical axis b in the energy dispersive magnetic sector (MS) 7, having an input boundary of 8 and output boundary 9 (effective boundaries of the magnetic field MS 7 are indicated).

In Fig. 2 are indicated: ion source 1, exit slit 2, aperture diaphragm 3, optical axis 4 in the energy dispersive electrostatic sector (ES) 5, energy-filtering diaphragm (ED) 10 and collimating lens (CL) I, optical axis b in the dispersive energy magnetic sector (MS) 7 having an input boundary of 8 and an output boundary of 9 (the effective boundaries of the magnetic field of MS 7 are indicated)

The SMA prototype (see Fig. 1) is made according to the Mattauch-Herzog geometry. The exit slit 2, in the plane of which the focusing system (not shown) of the ion source 1 focuses the ion beam, is located in the front focal plane of ES 5. The directions of rotation of the optical axis 4 in ES 5 and optical axis b in MS 7 are opposite (S diagram). MS 7 is made according to the MG design, according to which the output boundary 9 intersects the optical axis b and the input boundary 8 at point 12. The ion beam formed in the source 1 is focused on the plane of the output slit 2 by a focusing system (not shown), is limited according to the size of the exit slit 2 and the divergence angle of the aperture diaphragm 3, then near the axis 4 ions follow in the direction of the electrostatic sector 5, where they are spatially separated by energy. After exiting ES 5, ions move in the direction of MS 7, enter it through border 8, exit from it through rectilinear border 9, being separated by mass and assembled into monomass groups moving near the corresponding axial orbits 13. In Fig.l, axial orbits 13 are shown, corresponding to three lines of the mass spectrum . After exiting MS 7, each monomassic group of ions is focused at points designated, respectively, Di, D ₂ , D ₃ , which form a focus line 14, on which, for example, a microchannel plate of a spatially extended detector (PPD) can be mounted or receiving slots of a multi-collector detector (not shown in the drawing).

In the depicted in Fig. 2 variant of the MCA of the claimed design, between the energy dispersive ES 5 and MS 7, an energy-filtering diaphragm (ED) 10 and a collimating lens (CL) 11 are installed. ED 10 is installed in the plane of the optical image of slit 2, CL 11 is installed so that the plane its front focus with optical power CR, corresponding to equation (1), is located in the plane of ED 10. ES 5 and MS 7 are installed according to the C-scheme. MS 7 is made by the design of MG similarly to Fig. 1. The input boundary 8 is non-orthogonal to the optical axis and is located at an angle ε to the normal to the boundary, which ensures that the focus line is removed from the output boundary 9. The ion beam formed in AI 1 focuses on the plane of the exit slit 2 by the focusing system (in Fig. .2), is limited by the size of the exit slit 2 and by the divergence angle of the aperture diaphragm 3, then near the axis 4 the ions follow in the direction of ES 5, where they are spatially separated into monoenergetic groups, each of which focuses in angular scatter in the plane ED 10. Ions passing through ED 10 are focused near point 15. Next, they follow the axis b in the direction of CR 11 and further, to MS 7, exit it, being formed into spatially separated monomass groups, move near the corresponding axial orbits 13. In Fig.2, the axial orbits 13 corresponding to the three lines of the mass spectrum are indicated. At the exit from MS 7, each monomassic group of ions is focused at the corresponding points, denoted by Di, D _{2 /} D ₃ , which form the focus line 14, on which, for example, a microchannel plate PPD (mass spectrograph mode) or receiving slots of a multi-collector detector (multi-collector mass spectrometer).

An electrostatic lens or a lens system (not shown in Fig. 2) can be installed between AI 1 and ES 5 to enable the electrical adjustment of the mass spectral resolution of the SMA.

ES 5 can be made in the form of a sector of an electrostatic capacitor with an equipotential optical axis, angle φ _θ and radius r _{e of} rotation of the optical axis, the axial radius a _{e of} curvature of its equipotential, and is set to the distance L 'from OSH to ES and at a distance L "from ES 5 to ED 10, the values of which are associated with the coefficient D _{e of the} energy dispersion of ES 5 with a parametric dependence:

L '= r _e (c _e + l / t) / (co s _e ) q', mm;

L "= r _e (c _e + t) / (co s _e ) q", mm;

D _e = r _e (l + t) / co ² q, mm;

where Се = ω5 (фο _e ), s _e = sin (co- (p _e ),

co = V (2-Ge / Ee) - parameter "toroidal ™" of the capacitor,

q, q ', q "- correction factors due to small corrections related to the influence of ES edge fields whose values lie in the range between 0.9 and 1.1; parameter t> 0.

In the most famous versions of ES in the form of a cylindrical and spherical capacitors co = V2 and ω = 1, respectively.

Claims

CLAIM.

1. A static mass analyzer of ions, including a source of ions (AI), a focusing system, an object slit, an aperture diaphragm, energy dispersive electrostatic sector (ES) and magnetic sector (MS) in the form of a bipolar magnet with a constant the gap between the poles, and a system for simultaneously recording mass spectral lines, while the output boundary of the MS is flat and made in such a way that the effective boundaries of the magnetic field and the input optical axis intersect at one point. The ES is set relative to the MS so that the directions of rotation of the optical axes in the ES and MS coincide, and is set relative to the AI in such a way that the plane of the optical image of the object slit is located between the ES and the MS, and an energy-filtering filter is installed in the plane of the optical image of the object slit aperture (ED), a collimating lens (CR) was installed between the ED and the MS, the front focal plane of which is located in the ED plane with the CR optical power satisfying the relation: where P _L is the CR optical power, mm ^"1 ;

D _e is the dispersion coefficient for ES energy in the ED plane, mm;

2. The static mass analyzer according to claim 1, characterized in that the system for simultaneous registration of mass spectral lines is made in the form of a multi-collector ion receiver with electrical registration of ion currents, the receiving slots of which are installed in the focal planes of the MS corresponding to the axial orbits registered monomass components of the ion beam.

3. The static mass analyzer according to claim 1, characterized in that the system for simultaneously recording mass spectral lines is made in the form of a spatially extended detector, the receiving surface of which is mounted on the focal line of the static mass analyzer.

4. The static mass analyzer according to claim 1, characterized in that at least one lens is installed between the object slit and the ES for the electrical adjustment of the SMA.

5. The static mass analyzer according to claim 1, characterized in that the ES is made in the form of a sector of an electrostatic capacitor with an equipotential optical axis, the angle q> _e and the radius r _{e of} rotation of the optical axis, the axial radius a _{e of} curvature of its equipotential, and is installed at a distance L 'from OSH to ES and at a distance L "from ES 5 to ED 10, which are associated with the coefficient D _{e of the} energy dispersion of ES 5 parametric dependence:

L '= r _e - (c _e + l / t) / (co-Se) -q', m;

L "= r _e (Ce + t) / (co S _e ) q", mm;

D _e = r _e (l + t) / co ² q, m;

Where Ce = COS (cO (p _e ), s _e = sin (co (p _e ), a> = V (2-r _e a _e ),

q, q ', q "- correction factors due to small corrections related to the influence of edge fields of ES, whose values are in the range between 0.9 and 1.1; parameter t> 0.