MASS SPECTROMETER AND METHOD

Abstract

A charge detection mass spectrometer, CDMS, is described. The CDMS comprises: an electrostatic sector field ion trap and an inductive charge detector, wherein the electrostatic sector field ion trap is configured to define, at least in part, an ion path via the inductive charge detector; and a fragmentation device. A method is also described.

Claims

1. A charge detection mass spectrometer, CDMS, comprising: an electrostatic sector field ion trap and an inductive charge detector, wherein the electrostatic sector field ion trap is configured to define, at least in part, an ion path via the inductive charge detector; and a fragmentation device.

2. The CDMS according to claim 1, wherein the electrostatic sector field ion trap is configured to move an ion around the ion path defined, wherein moving the ion induces signals in the inductive charge detector, wherein the CDMS is configured to determine a mass to charge ratio and a charge of the ion using the induced signals, and determine the mass of the ion based on the determined mass to charge ratio and charge.

3. The CDMS according to claim 2, wherein the CDMS is configured to determine a mass of a precursor ion and the fragmentation device is configured to fragment the same precursor ion.

4. The CDMS according to any preceding claim, wherein the electrostatic sector field ion trap is configured to define, at least in part, the ion path via the fragmentation device.

5. The CDMS according to any of claims 1 to 3, comprising means for ejecting ions from the ion path into the fragmentation device, wherein the fragmentation device is external to the electrostatic sector field ion trap.

6. The CDMS according to claim 5, wherein the electrostatic sector field ion trap comprises an ion outlet for exit of ejected ions therethrough from the ion path.

7. The CDMS according to any previous claim, wherein the fragmentation device is configured to trap the precursor ion and/or a product ion thereof.

8. The CDMS according to any previous claim, wherein the fragmentation device is configured to increase an ion energy of the product ion to be introduced into the ion path.

9. The CDMS according to claim 7, wherein the fragmentation device is configured to introduce the product ion into the ion path by pulsing the product ion into the ion path.

10. The CDMS according to any previous claim, comprising an ion isolating optical element configured to isolate a precursor ion for fragmentation by the fragmentation device.

11. The CDMS according to claim 10, wherein the ion isolating optical element is configured to isolate a plurality of precursor ions for fragmentation, wherein the isolated plurality of precursor ions each have a mass between predetermined upper and lower mass thresholds.

12. The CDMS according to claim 10 or claim 11, wherein the ion isolating optical element comprises and/or is a quadrupole lens, an einzel lens, a deflection plate; and/or is provided by the electrostatic sector field ion trap; or a combination thereof.

13. The CDMS according to any of claims 10 to 12, wherein the ion isolating optical element is configured to isolate the one or more precursor ions by applying an electrical field according to an oscillation frequency, for example a harmonic thereof, of the one or more precursor ions in the electrostatic sector field ion trap.

14. The CDMS according to any previous claim, wherein the electrostatic sector field ion trap comprises a set of electrostatic sectors, including a first electrostatic sector and a second electrostatic sector.

15. The CDMS according to claim 14, wherein the first electrostatic sector comprises and/or is a cylindrical, a toroidal or a spherical electrostatic sector.

16. The CDMS according to any of claims 14 to 15, wherein the first electrostatic sector and the second electrostatic sector are mutually opposed, optionally wherein the set of electrostatic sectors includes only the first electrostatic sector and the second electrostatic sector.

17. The CDMS according to any of claims 4 to 7, wherein the first electrostatic sector comprises a set of shunts, including a first shunt, arranged to delimit a field due to the first electrostatic sector.

18. The CDMS according to any previous claim, wherein the electrostatic sector field ion trap is isochronous.

19. The CDMS according to any previous claim, wherein the electrostatic sector field ion trap is configured to define, at least in part, the ion path in two or three mutually-orthogonal dimensions.

20. The CDMS according to any previous claim, wherein the ion path defined by the electrostatic sector field ion trap includes a crossover.

21. The CDMS according to any previous claim, wherein the electrostatic sector field ion trap comprises an ion inlet for introduction of ions therethrough into the ion path.

22. The CDMS according to any previous claim, wherein the inductive charge detector comprises a first set of charge detector tubes, including a first charge detector tube, optionally wherein the first charge detector tube, having a length L and a width W, has a ratio of the length L to the width W in a range from 3:2 to 5:2, for example 2:1.

23. The CDMS according to any previous claim, wherein a portion of the ion path via the inductive charge detector is in a range from 30% to 70%, preferably in a range from 40% to 60%, for example 50%, of the ion path defined by the electrostatic sector field ion trap.

24. The CDMS according to any previous claim, comprising a set of electrostatic focus lenses, including a first focus lens, arranged to constrain, at least in part, the ion path in a first dimension, preferably wherein the first dimension is orthogonal to a direction of the ion path via the inductive charge detector.

25. The CDMS according to claim 17, wherein a cross-section of the ion path via the inductive charge detector is arcuate, having a central angle in a range from ?3? to +3?, preferably in a range from ?2? to +2?, more preferably in a range from ?1? to +1?.

26. The CDMS according to any previous claim, wherein the inductive charge detector is configured to operate at ground potential.

27. The CDMS according to any previous claim, comprising a lift device configured to increase an ion energy of ions to be introduced into the ion path, for example by pulsing the ions into the ion path, and optionally, wherein the lift device is configured to trap the ions to be introduced into the ion path.

28. A method of determining masses of ions, the method comprising: moving, by an electrostatic sector field ion trap, a precursor ion around an ion path defined, at least in part, thereby, via an inductive charge detector; inducing, by the moving precursor ion, a signal in the inductive charge detector; determining a mass of the precursor ion using the induced signal; fragmenting the precursor ion and providing a product ion therefrom; and determining a mass of the product ion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0160] For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

[0161] FIG. 1A schematically depicts a conventional CDMS; and FIG. 1B schematically depicts a conventional CDMS, based on the conventional CDMS of FIG. 1A;

[0162] FIGS. 2A and 2B schematically depict a conventional electrostatic sector field employing toroidal sector fields;

[0163] FIG. 3 schematically depicts an electrostatic sector field ion trap for an exemplary embodiment, additionally comprising shunts to control fringe fields;

[0164] FIG. 4A schematically depicts a CDMS according to an exemplary embodiment; and FIG. 4B schematically depicts elevation views, from above, the side and the end, of the locus of ion trajectories for the CDMS;

[0165] FIG. 5A schematically depicts a CDMS according to an exemplary embodiment, including a lens at the origin to confine ions in the axial (z) dimension; FIG. 5B schematically depicts elevation views, from above, the side and the end, of the locus of ion trajectories for the CDMS;

[0166] FIG. 5C is a perspective view of a SIMION simulation of ions for the CDMS; FIG. 5D is an axial cross-sectional view of the CDMS, in more detail; FIG. 5E is a cutaway perspective CAD image of part of the CDMS, in more detail; FIG. 5F is an exploded perspective CAD image of part of the CDMS, in more detail; and FIG. 5G is an axial cross-sectional view of the CDMS, in more detail;

[0167] FIG. 6 is a graph of change in frequency (%) as a function of ion energy deviation from ideal (%) for the CDMS of FIGS. 5A to 5C compared with a conventional CDMS;

[0168] FIGS. 7A and 7B schematically depict the advantage of a relatively narrow charge detection tube, to boost intensity of higher harmonics in the Fourier transform, for a CDMS according to an exemplary embodiment;

[0169] FIG. 8 schematically depicts a segmented charge detection tube, to give an increased number of transients per analyser pass, for a CDMS according to an exemplary embodiment;

[0170] FIG. 9 schematically depicts a CDMS according to an exemplary embodiment, comprising a lift device;

[0171] FIG. 10 schematically depicts a CDMS according to an exemplary embodiment;

[0172] FIG. 11 schematically depicts a CDMS according to an exemplary embodiment;

[0173] FIG. 12 schematically depicts a CDMS according to an exemplary embodiment;

[0174] FIG. 13 schematically depicts a CDMS according to an exemplary embodiment;

[0175] FIG. 14 schematically depicts a CDMS according to an exemplary embodiment;

[0176] FIG. 15 schematically depicts a method according to an exemplary embodiment;

[0177] FIG. 16 schematically depicts a conventional resonance mass separator;

[0178] FIG. 17A schematically depicts elevation views, from the side and the end, of the locus of ion trajectories of a CDMS according to an exemplary embodiment, including an ion isolating optical element at the origin, upon applying a voltage on a lens thereof to confine ions in the axial (z) dimension; FIG. 17B schematically depicts elevation views, from the side and the end, of the locus of ion trajectories upon applying an isolation voltage on the lens; and FIG. 17C schematically depicts elevation views, from the side and the end, of the locus of ion trajectories upon subsequently applying a voltage on the lens to further confine ions in the axial (z) dimension;

[0179] FIG. 18 schematically depicts a CDMS 18 according to an exemplary embodiment; and

[0180] FIG. 19 schematically depicts a CDMS 18 according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

[0181] FIG. 1A schematically depicts a conventional CDMS 10; and FIG. 1B schematically depicts a conventional CDMS 20, based on the conventional CDMS 10 of FIG. 1A.

[0182] FIG. 1A, in more detail, schematically depicts the CDMS 10 due to Contino and Jarrold [1]. The CDMS 10 includes an electrospray source 1 and is divided into four differentially pumped regions (I to IV). The first region I includes an ion funnel 2, the second and third regions II, III each include a hexapole ion guide 3 and the fourth region IV provides two alternative paths for ions via a focusing lens 4: an orthogonal reflectron time-of-flight mass spectrometer (TOF-MS) 5 or a dual hemispherical deflection analyser (HDA) 6 followed by a cone trap 7 incorporating an image charge detector tube. The oscillation frequency of an ion in the cone trap 7 is related to the m/z of the ion, but also depends on the ion's kinetic energy. To reduce the uncertainty in the m/z determination, the dual HDA 6 was employed to select a narrow window of ion kinetic energies to introduce into the cone trap 7. The HDA 6 consists of two concentric hemispherical electrodes, each having a deflection angle ?.sub.0 of 180?, held at different potentials, which produce an electric field proportional to 1/r.sup.2. As shown in FIG. 1A, the two hemispherical electrodes are placed in an S-shaped tandem arrangement, thus defining an open (c.f. a closed) ion path and allowing the ion beam to maintain its original direction upon exit. The electrode potentials applied to the two hemispherical electrodes determine which kinetic energies are passed and hence which ions are filtered. Carefully choosing these electrode potentials, as well the location and diameter of the entrance and exit apertures, improves the energy resolution of the dual HDA 6. The cone trap 7 consists of two conical end caps located 95.25 mm apart with a 6.35 mm diameter aperture, thereby providing an electrostatic linear ion trap. The number of ions entering the cone trap 7 was kept low enough such that the probability of trapping more than one ion was small. A charge detector tube (25.4 mm long, 6.35 mm ID) was held along the central axis by an insulator mounted within a shielded cylinder. When an ion passes through the detector tube, an image charge of equal magnitude but opposite sign is induced.

[0183] FIG. 1B, in more detail, schematically depicts the prior art geometry of the cylindrical ELIT trap (i.e. the CDMS 20) of reference [3]. This ELIT comprises two mutually-opposed equispaced three-electrode mirrors (E1, E2, E3 ) having grounded shield ring electrodes (GS) at respective entrances thereof to create field free regions between the end caps where the charge detector tube (C) is located. Potentials V1, V2, V3 respectively applied to the ring electrodes V1, V2, V3 were optimised to produce the smallest breadth in oscillation frequency for 100 axial ions having a Gaussian energy distribution of mean 130 eV/z and FWHM of 1 eV/z. This ELIT has a substantially improved energy dependence when compared to the cone trap 7 of the CDMS 10 and replaces the cone trap 7 of the CDMS 10. That is, the CDMS 20 also requires the upstream energy filtering device consisting of a dual hemisphere electrostatic energy selector (i.e. the dual HDA 6) so that the variation in oscillation frequency due to ion energy spread is kept to a minimum. The selection of a lower energy spread of ions reduces the overall transmission of the CDMS 20. As with the CDMS 10, the number of ions entering the ELIT was kept low enough such that the probability of trapping more than one ion was small.

[0184] It is an object of the present invention to improve ion transmission by allowing a larger portion of ions into the CDMS trap.

[0185] FIGS. 2A and 2B schematically depict a conventional electrostatic sector field employing toroidal sector fields.

[0186] The inventor of the present invention recognised that a better energy focussing characteristic may be achieved by employing a geometry first proposed by Poschenrieder [4], who considered time-of-flight energy focusing by electrostatic fields. Particularly, Poschenrieder considered configurations of linear drift spaces and fields in which the time-of-flight is no longer a function of the initial energy to first order but of the mass to charge ratio m/z only. Such configurations are also known as isochronous. For ions of about equal energy, electrostatic fields should be used since trajectories should be identical for all masses. While Poschenrieder limited treatment to toroidal sector fields, other configurations are possible, as described below.

[0187] Poschenrieder's work proposed the use of toroidal sector fields in special arrangements to compensate for initial ion conditions for time-of-flight mass spectrometry. FIGS. 2A and 2B shows the general form of such an arrangement. The device is considered from both radial (FIG. 2A) and axial (FIG. 2B) perspectives, each with a different radius of curvature for the electric field, hence they are known as toroidal sector field analysers. A DC potential V1 is applied to the inner electrode, having radius R1 in the radial plane and a DC potential V2 is applied to the outer electrode, having radius R2 in the radial plane. The ion optical axis has a radius R0 in the radial plane. The device has a deflection angle of ?.sub.0 and acceptance angles of 2?.sub.0 radially and 2? axially, effectively delimited by slits having widths u.sub.0 radially and w.sub.0 axially, respectively. Isochronous planes are disposed a distance g.sub.r from the entrance and the exit of the device, at angles ? to the ion optical axis, providing point focusing of ions thereat. The paper presents a number of geometries intended to be operated as time-of-flight (TOF) analysers whereby packets (also known as clouds) of ions are injected through an entrance aperture and detected at an exit plane using an electron multiplier or similar destructive detector. Electric sector TOF analysers have found application in imaging applications such as TOF-SIMS instruments due to their stigmatic properties [5]. However, they are less suited to the mainstream application of orthogonal acceleration (oa) TOF analysers due to their energy focussing characteristic being limited to first order. This is because orthogonal acceleration leads to very large energy spreads in the ion beam which are better compensated by reflectron-based TOF analysers [6]. The particular case of a CDMS instrument has no requirement for orthogonal acceleration and so the variation in ion energy is given only by the longitudinal variation in beam energy as determined by the upstream beam conditioning. Typical energy variations of a few percent can easily be accommodated by the first order energy focussing characteristic of the electrostatic sector field ion traps, which is superior to that demonstrated in [3]. The electrostatic sector field ion traps has a further advantage in that the ions travel at a substantially constant speed as determined by the acceleration energy. This improves the space charge capacity of sectors when compared to reflecting based devices in which ions must slow to a low speed as they turn around in the mirror section.

[0188] A particular geometry proposed by Poschenrieder for a TOF MS (but still problematic for TOF MS injection and detection) and improvements to it provide, as appreciated for the first time by the inventor, an electrostatic sector field ion trap for CDMS according an exemplary embodiment. Ion velocity v of an ideal ion, having a mass m, after entering an electrostatic sector field, with ion energy (1+?)mv.sub.0.sup.2/2, is given to first order by Equation (7) of Poschenrieder [4]:

[00003] $v = v_{0} [1 + \frac{1}{2} ? - u_{0} \cos ?_{0} h + \frac{?_{0}}{h} \sin ?_{0} h + \frac{?}{h^{2}} (1 - \cos ?_{0} h)]$ [0189] where: [0190] ? is the fractional ion energy spread for ions having been accelerated to an ion energy E.sub.a and where ?E<<E.sub.a:

?=?E/E.sub.a [0191] u is the deviation of the ion from the central path u.sub.0; [0192] h and k are auxiliary parameters given by:

[00004] $h = \sqrt{(2 - c)} k = \sqrt{cx} c = \frac{r_{0}}{?_{0}}$ [0193] where r.sub.0 is the radial radius and ?.sub.0 is the axial radius of the central equipotential plane; [0194] ?.sub.0 is the deflection angle of the sector field between the limits 180???.sub.0h?360?; and [0195] ?.sub.0 is the entrance angle.

[0196] The time-of-flight t.sub.e through the electrostatic sector field is then obtained by integration of

dt.sub.e=r.sub.0(1+u)ds/v [0197] which to first order gives Equation (8) of Poschenrieder [4]:

[00005] $t_{e} = r_{0} \sqrt{\frac{2 m}{E_{a}}} {\frac{?_{0}}{2} + ? [(\frac{1}{h^{2}} - \frac{1}{4}) ?_{0} - \frac{\sin ?_{0} h}{h^{3}}] + \frac{?_{0}}{h} (\frac{u_{0}}{?_{0}} h \sin ?_{0} h - \cos ?_{0} h + 1)}$

[0198] Elimination of the dependence of t.sub.e on the entrance angle ?.sub.0 requires Equation (9) of

[0199] Poschenrieder [4]:

[00006] $g_{r} = \frac{u_{0} r_{0}}{?_{0}} = \frac{r_{0}}{h} \tan (180 ? - \frac{?_{0} h}{2})$ [0200] which defines the distance g.sub.r of the source point form the field edge. With g.sub.r being positive, Equation (9) of Poschenrieder [4] describes an electrostatic sector field with a deflection angle (also known as sector angle) ?.sub.0 between the limits 180???.sub.0h?360?. This electrostatic sector field configuration has an intermediary image at ?.sub.i=?.sub.0/2 and a second image symmetric to the source point at a distance g.sub.r=g.sub.r from the field edge on the exit side.

[0201] An electrostatic sector field obeying Equation (9) of Poschenrieder [4] is simultaneously free of first-order chromatic aberrations at the second image. However, large lateral energy dispersion may be found at the intermediary image, though the transmitted energy spread may be limited here by a suitable stop.

[0202] The dispersion in time-of-flight ?t.sub.e due to the fractional ion energy spread ?=?E/E.sub.a within the electrostatic sector field is given by Equation (10) of Poschenrieder [4]:

[00007] $? t_{e} = r_{0} \sqrt{\frac{2 m}{E_{a}}} ? [(\frac{1}{h^{2}} - \frac{1}{4}) ?_{0} - \frac{\sin ?_{0} h}{h^{2}}]$

[0203] The dispersion ?t.sub.D along a linear drift tube of length D is given simply by Equation (11) of Poschenrieder [4]:

[00008] $? t_{D} = - \sqrt{\frac{2 m}{E_{a}}} ? \frac{D}{4}$

[0204] For an electrostatic sector field to be free of this person requires that ?t.sub.e+?t.sub.D=0, which leads to the focusing condition given by Equation 12 of Poschenrieder [4]:

[00009] $\frac{D}{4} = r_{0} [(\frac{1}{h^{2}} - \frac{1}{4}) ?_{0} - \frac{\sin ?_{0} h}{h^{3}}]$

[0205] The actual linear drift length D can comprise g.sub.r on the entrance side, g.sub.r on the exit side and some additional drift range d.

[0206] Hence, an electrostatic sector field obeying Equation 12 of Poschenrieder [4] will be free of any energy-dependent dispersion in time-of-flight (isochronous) for any two points comprising a linear drift range of total length D. In addition, this electrostatic sector field will provide achromatic radial imaging for a point G at a distance g.sub.r from the field edge.

[0207] Consider an electrostatic sector field with stigmatic imaging in which a radial and an axial intermediary image coincide at ?.sub.i=?.sub.0/2. If g.sub.a represents the distance of the entrance from the field slit for axial focusing, from the directional focusing properties of toroidal sector field, the distance g.sub.r of the source point form the field edge is given by Equation 20 of Poschenrieder [4]:

[00010] $g_{r} = g_{a} = \frac{r_{0}}{h} \tan (180 ? - \frac{?_{0} h}{2}) = \frac{r_{0}}{k} \tan (180 ? - \frac{?_{0} k}{2})$

[0208] Hence, it follows that h=k and c=1, which corresponds to a spherical condenser field. From Equation 12 of Poschenrieder [4] and setting D=2g.sub.r=2g.sub.a, Equation 21 of Poschenrieder [4] is obtained:

[00011] $\tan \frac{?_{0}}{2} = 2 \sin ?_{0} - \frac{3}{2} ?_{0}$

[0209] A graphical solution yields the values:

?.sub.0=199.2?

g.sub.r=5.9r

[0210] For this electrostatic sector field, the source and its image exactly coincide, as schematically depicted in FIG. 3, such that time and space focussing coincide. While Poschenrieder [4] noted that this electrostatic sector field is not well suited to a TOF mass spectrometer, the inventor has conversely appreciated that this electrostatic field is instead well-suited to an electrostatic field ion trap. Particularly, this electrostatic sector field is completely isochronous with respect to energy, in which resolution no longer depends on slit width. Note that these values for the deflection angle ?.sub.0=199.2? and the distance g.sub.r=5.9r were obtained graphically and thus computational methods of calculation may provide refined solutions. Furthermore, constructed geometries may allow for interplay between these values to some extent and/or to compensate for other electric fields, including residual or fringe fields. However, the distance g.sub.r may be critical for achieving true stigmatic performance.

[0211] Poschenrieder paper [4] concentrates on isochronicity (time aberrations) with respect to beam initial conditions (all zero to first order) but its treatment of stigmatic (spatial) aberrations was much less expansive. Poschenrieder [4] does not seem to consider the spatial aberrations of angle with respect to position or angle with respect to energy. However, the stigmatic (imaging) requirements of the CDMS are secondary compared with the isochronicity requirements of the CDMS: the stigmatic requirements being sufficiently stable ion trajectories for inductive charge detection, preferably to permit use of relatively narrow charge tubes as described herein, and to avoid ion loss arising from ions wandering away from the ion path.

[0212] FIG. 3 schematically depicts an electrostatic sector field ion trap 30 for an exemplary embodiment, additionally comprising shunts to control fringe fields. A Cartesian coordinate system (x, y, z) is employed for FIGS. 3 to 14, appropriately.

[0213] In this example, the electrostatic sector field ion trap 30 comprises a set of electrostatic sectors 31, including a first electrostatic sector 31A and a second electrostatic sector 31B. In this example, the first electrostatic sector 31A is a spherical electrostatic sector. In this example, the first electrostatic sector 31A and the second electrostatic sector 31B are mutually opposed. In this example, the set of electrostatic sectors 31 includes only the first electrostatic sector 31A and the second electrostatic 31B. In this example, the first electrostatic sector 31A comprises a set of shunts 32, including a first shunt 32A, arranged to delimit a field due to the first electrostatic sector 31A. In this example, the electrostatic sector field ion trap 30 is isochronous. In this example, the electrostatic sector field ion trap 30 is configured to define the ion path IP in three mutually-orthogonal dimensions. In this example, the ion path defined by the electrostatic sector field ion trap 30 includes a crossover. In this example, the electrostatic sector field ion trap 30 comprises an ion inlet 33 for introduction of ions therethrough into the ion path, particularly provided in the outer electrode of the first electrostatic sector 31A. In this example, the first electrostatic sector 31A has a deflection angle of ?.sub.0=199.2?. In this example, the field-free region has a length of g.sub.r=5.9r to the central cross over point (i.e. the origin, at which point focus is achieved). In this example, the electrostatic sector field ion trap 30 has rotational symmetry about the x axis through the origin. In this example, the electrostatic sector field ion trap 30 is symmetric in the y-z plane through the origin. In this example, the basic unit comprises two drift spaces (i.e. two field-free regions each having a length of g.sub.r=5.9r) and a spherical electrostatic sector 31A, 31B. In this example, the outer electrode of the first electrostatic sector 31A has an internal radius of 23 mm and the inner electrode of the first electrostatic sector 31A has an external radius of 17 mm such that there is a spherically radial gap of 6 mm therebetween. The first shunt 32A has a toroidal aperture of width 4 mm, thereby presenting a relatively large entrance aperture into the first electrostatic sector 31A. The second electrostatic sector 31B is generally as described with respect to the first electrostatic sector 31A, while not including the ion inlet 33.

[0214] FIG. 3, in more detail, shows the special case of two opposing spherical sectors 31A, 31B (same curvature for radial and axial fields) each with a deflection angle ?.sub.0=199.2?, and a field free region of 5.9R.sub.0(i.e. g.sub.r=5.9r) distance to the central cross over point (i.e. point focus). Poschenrieder understood that the closed path of this arrangement could prove problematic for injection and detection for traditional TOF analysis and went on to propose open geometric solutions more suitable for injection and detection means. That is, Poschenrieder did not propose the ion inlet 33 for introduction of ions therethrough. Furthermore, Poschenrieder did not propose the use of such an analyser for inductive detection, as employed in Fourier Transform mass spectrometers. To the best of the inventor's knowledge, the use of toroidal fields for inductive detection of a small cloud of ions in a Fourier transform trap was first proposed by Wollnik [7] in an arrangement using eight 45? toroidal sectors, but of otherwise unknown geometry, arranged in a ring formation for a TOF MS analyser. Also, latterly Verenchikov proposed the use of toroidal field with Fourier transform detection [8]. However, neither of these two proposals considered using such geometries for a CDMS.

[0215] In the arrangement of FIG. 3, ions are injected through a hole (i.e. ion inlet 33) in the outer electrode of the first electrostatic sector 31A while the potentials of the electrodes of the first electrostatic sector 31A are held at ground level. Once the trap is filled, these potentials are raised to their operating levels and the trapping process begins. Note the addition of shunts 32A, 32B to terminate the electric fields of the electrodes of the first electrostatic sector 31A, which would otherwise leak into the field-free region and destroy the operation of the electrostatic sector field ion trap. This particular shunt geometry is known in the art and was proposed by Herzog in 1935, see Yavor pp 230 [9].

[0216] FIG. 4A schematically depicts a CDMS 4 according to an exemplary embodiment; and FIG. 4B schematically depicts elevation views, from above, the side and the end, of the locus of ion trajectories for the CDMS 4.

[0217] In this example, the CDMS 4, comprises: an electrostatic sector field ion trap 40 and an inductive charge detector 400; wherein the electrostatic sector field ion trap 40 is configured to define, at least in part, an ion path via the inductive charge detector 400. The electrostatic sector field trap 40 is as described with respect to the electrostatic field ion trap 30, as described with respect to FIG. 3, description of which is omitted for brevity. Like reference signs denote like integers.

[0218] In this example, the electrostatic sector field ion trap 40 comprises a set of electrostatic sectors 41, including a first electrostatic sector 41A and a second electrostatic sector 41B. In this example, the first electrostatic sector 41A is a spherical electrostatic sector. In this example, the basic unit comprises two drift spaces and a spherical electrostatic sector. In this example, the first electrostatic sector 41A and the second electrostatic sector 41B are mutually opposed. In this example, the set of electrostatic sectors 41 includes only the first electrostatic sector 41A and the second electrostatic 41B. In this example, the first electrostatic sector 41A comprises a set of shunts 42, including a first shunt 42A, arranged to delimit a field due to the first electrostatic sector 41A. In this example, the electrostatic sector field ion trap 40 is isochronous to first order with respect to energy. In this example, the electrostatic sector field ion trap 40 is configured to define the ion path in three mutually-orthogonal dimensions. In this example, the ion path defined by the electrostatic sector field ion trap 40 includes a crossover. In this example, the electrostatic sector field ion trap 40 comprises an ion inlet 43 for introduction of ions therethrough into the ion path. In this example, the first electrostatic sector 41A has a deflection angle of ?.sub.0=199.2?. In this example, the field-free region has a length of g.sub.r=5.9r to the central cross over point (i.e. the origin). In this example, the second electrostatic sector 41B is as described with respect to the first electrostatic sector 41A. In this example, the electrostatic sector field ion trap 40 has rotational symmetry about the x axis through the origin. In this example, the electrostatic sector field ion trap 40 is symmetric in the y-z plane through the origin. In this example, the inductive charge detector 400 comprises a first set of charge detector tubes 410, including a first charge detector tube 410A and a second charge detector tube 410B. In this example, the first charge detector tube, having a length L and a width W, has a ratio of the length L to the width W in a range from 3:2 to 5:2, for example 2:1. In this example, a portion of the ion path via the inductive charge detector 400 is about 50% of the ion path defined by the electrostatic sector field ion trap 40.

[0219] SIMION [10] simulations were performed with the geometry shown in FIG. 4A and ions could be trapped for an indefinite period dependent on their initial conditions, as schematically depicted in FIG. 4B. If ions are restricted to a narrow axial range (small ??), then the resulting trajectories fill a finite arc in the y-z plane. Referring again to FIG. 4A and noting that the input ion conditions take the form of a beam of ions along the trajectory, T, it can be understood that the restoring force in the radial direction is stronger than that of the axial direction. The device is rotational symmetric about the x axis through the origin and so ions with a large angular component ? or axial spread ?? cause the ion trajectories to fill the whole electrostatic sector after many passes around the ion path making a hollow cone shape in the field free regions and spherical surface inside the sectors. In other words, the ions are trapped in a thin wall (ideally of infinitesimal thickness) that may be described as a pair of intersecting and mutually opposed cones or lobes, having approximately hemispherical end caps (corresponding with the gaps between the spherical electrodes of the electrostatic sectors having a deflection angle ?.sub.0 of nominally) 199.2?. The geometrical projections of the ion beam IP (shown in grey) adopted after many passes of the analyser (as required by CDMS) is shown in FIG. 4B.

[0220] FIG. 5A schematically depicts a CDMS 5 according to an exemplary embodiment, including a lens at the origin to confine ions in the axial z dimension; FIG. 5B schematically depicts elevation views, from above, the side and the end, of the locus of ion trajectories for the CDMS 5; and FIG. 5C is a perspective view of a SIMION simulation of ions for the CDMS 5; FIG. 5D is an axial cross-sectional view of the CDMS 5, in more detail; FIG. 5E is a cutaway perspective CAD image of part of the CDMS 5, in more detail; FIG. 5F is an exploded perspective CAD image of part of the CDMS 5, in more detail; and FIG. 5G is an axial cross-sectional view of the CDMS 5, in more detail.

[0221] The CDMS 5 is generally as described with respect to the CDMS 4, as described with respect to FIGS. 4A and 4B, description of which is omitted for brevity. Like reference signs denote like integers.

[0222] In this example, the electrostatic sector field ion trap 50 comprises a set of electrostatic sectors 51, including a first electrostatic sector 51A and a second electrostatic sector 51B. In this example, the first electrostatic sector 51A is a spherical electrostatic sector. In this example, the first electrostatic sector 51A and the second electrostatic sector 51B are mutually opposed. In this example, the set of electrostatic sectors 51 includes only the first electrostatic sector 51A and the second electrostatic 51B. In this example, the first electrostatic sector 51A comprises a set of shunts 52, including a first shunt 52A, arranged to delimit a field due to the first electrostatic sector 51A. In this example, the electrostatic sector field ion trap 50 is isochronous with respect to energy, to first order. In this example, the electrostatic sector field ion trap 50 is configured to define the ion path in three mutually-orthogonal dimensions. In this example, the ion path defined by the electrostatic sector field ion trap 50 includes a crossover. In this example, the electrostatic sector field ion trap 50 comprises an ion inlet 53 for introduction of ions therethrough into the ion path. In this example, the first electrostatic sector 51A has a deflection angle of ?.sub.0=199.2?. In this example, the field-free region has a length of g.sub.r=5.9r to the central cross over point (i.e. the origin). In this example, the second electrostatic sector 51B is as described with respect to the first electrostatic sector 51A. In this example, the electrostatic sector field ion trap 50 has rotational symmetry about the x axis through the origin. In this example, the electrostatic sector field ion trap 50 is symmetric in the y-z plane through the origin. In this example, the inductive charge detector 500 comprises a first set of charge detector tubes 510, including a first charge detector tube 510A and a second charge detector tube 510B. In this example, the first set of charge detector tubes 510 comprises an axially segmented charge detector tube, including 10 segments. In this example, the first charge detector tube, having a length L and a width W, has a ratio of the length L to the width W in a range from 3:2 to 5:2, for example 2:1. In this example, a portion of the ion path via the inductive charge detector 500 is about 50% of the ion path defined by the electrostatic sector field ion trap 50.

[0223] Referring again to FIG. 4B, the surfaces of revolution create a potential topological problem when concerned with the construction of some CDMS. If ions were allowed to rotate around the whole of the central axis (i.e. the x axis), support of the central or inner electrodes of the inductive charge detector 500 and/or the inner electrodes of the first electrostatic sector 51A and/or the second electrostatic sector 51B may be problematic since the ion trajectories entirely surround these inner electrodes in three dimensions. Generally, addition of a support would cause ions to collide therewith which would reduce the number of oscillations possible in the analyser. One or more supports, such as supports 52AS between, may bridge between the inner and the outer electrodes, for example, and by reducing cross-sectional areas thereof in the ion path, loss of ions through collisions therewith may be reduced. Additionally and/or alternatively, the ion path may be constrained so as to avoid the supports. Hence, a solution to this problem of collisions with the support is to include a set of electrostatic focus lenses, including a first focus lens, arranged to constrain, at least in part, the ion path in a first dimension. In this example, a planar einzel lens 54, comprising three electrodes, is shown in FIG. 5A in the center of the device at the crossover point, providing additional focussing in the z direction (Cartesian coordinates). The geometric projections of the ions after this first focus lens is added are shown in FIG. 5B(A) to (C). A cross section through the spherical electrodes is shown in FIG. 5B(D) with supports 52AS. The result is that ions are now confined to a finite angle and the supports 52AS may be placed away from the ion beam, thereby facilitating construction of the CDMS.

[0224] FIG. 5A schematically depicts a preferred embodiment with some typical values for device construction. An ion energy of 130 eV/z has been chosen to allow direct comparison of the state of the art ELIT trap of reference [3]. It should be understood that increasing the operating voltage (ion energy) for these devices may give higher frequencies and consequential improvements in signal to noise and resolution. Such a method has not yet been employed due the need to operate the field free region at a high potential, meaning the possibility of noise injection from the power supply. In the embodiment shown in FIG. 5A, the two charge tubes 510A, 510B are employed either side of the central z lens 54. Referring again to FIG. 3, we can see that g.sub.r=5.9r gives relatively long field free regions either side of the central lens allowing for charge tubes 510A, 510B of around 100 mm in length to be employed. Cross sections of the charge tubes 510A, 510B are shown. These charge tubes 510A, 510B present no topological problems for construction and may be easily made using the technique known as wire erosion or Electrical Discharge Machining (EDM), for example. Suitable segmented charge tubes are described with respect to FIG. 8.

[0225] FIGS. 5D to 5G depict the CDMS 5 in more detail. In this example, the first electrostatic sector 51A has a deflection angle of ?.sub.0=199.2?. In this example, the first electrostatic sector 51A comprises an outer spherical electrode 51AO, having an internal radius of 23 mm and an external radius of 28 mm, and an inner spherical electrode 51AI, having an external radius of 17 mm, concentric therewith, such that there is a spherically radial gap of 6 mm therebetween. In this example, the outer spherical electrode 51AO and the inner spherical electrode 51AI are respectively provided centrally in similarly square substantially planar frames, machined from UHV compatible electrical conductors such as 304 L or 316 L stainless steel (alternatively gold-coated glass, for example) and optionally electropolished. In this example, the shunt 52A is similarly provided in such a frame. Each frame includes four circular apertures formed proximal corners thereof for mounting on four corresponding insulator (e.g. ceramic such as alumina or Macor (RTM) or polymeric such as PTFE) rods 55A to 55D (55C and 55D not shown), for transversely aligning the outer spherical electrode 51AO, the inner spherical electrode 51AI and the shunt 52A. Insulator spacers 56A mutually space apart axially the outer spherical electrode 51AO and the inner spherical electrode 51AI. The outer spherical electrode 51AO, having a wall thickness of 5 mm, bulges quasi-hemispherically from the respective frame. The solid inner spherical electrode 51AI protrudes quasi-hemispherically from the respective frame, supported by two diametrically opposite supports 51AS, disposed so as to not present an obstruction in the figure of eight ion path IP, as flattened by the einzel lens 54. The dished shunt 52A inner electrode protrudes from the respective frame, supported by two diametrically opposite supports 52AS, generally as described with respect to the supports 51AS for the inner spherical electrode 51AI, thereby providing two quasi-semicircular apertures 521A, 521B (i.e. entrance and exit respectively) of radial width 4 mm.

[0226] The performance advantages of the present invention over the state of the art ELIT of reference [3] is shown in Table 1. The CDMS 5 has equivalent angular and spatial acceptance when compared to the ELIT of reference [3] but offers more transients per unit time and superior energy acceptance. This larger energy acceptance can lead to a better resolution/sensitivity characteristic. With prudent upstream beam collimation and an energy spread of 0.5 eV/z, single pass mass resolutions of several thousand are expected for this embodiment.

TABLE-US-00001 Parameter ELIT of reference [3] CDMS 5 Half TOF 50,000 m/z (s) 1.25E?04 4.30E?04 Transients/ms 8.00 23.26 Charge tube length (mm) 50 2 ? 100 Charge tube (mm) 6.35 5 KE 130 130 Energy acceptance (%) 0.40 4 Radial acceptance (mm) 1 1 (Y), 1.5 (Z) Angular acceptance (?) 2 2

[0227] Table 1: Performance advantages of the CDMS 5 according to an exemplary embodiment compared with the state of the art ELIT of reference [3]. The 23.26 transients per ms is based upon 10 segments of each charge tube. Without segmentation, the number of transients per ms is reduced to 2.326. Even without segmentation, the CDMS 5 is competitive and simpler, for example not requiring an upstream dual HAD to select a narrow window of ion kinetic energies to introduce into the electrostatic sector field ion trap 50. Conversely, even higher numbers of transients may be achieved using a lift device, as described with respect to of FIG. 9. FIG. 5C is a SIMION simulation of ions for the CDMS 5, after hundreds of turns, without loss of ions. The einzel lens constrains the ion trajectories compared with the SIMION simulation of ions for the CDMS 4, as shown in FIG. 4B.

[0228] FIG. 6 is a graph of change in frequency (%) as a function of ion energy deviation from ideal (%) for the CDMS 5 of FIGS. 5A to 5C compared with a conventional CDMS, particularly the CDMS of FIG. 1B. In more detail, SIMION simulations were performed and the energy focussing characteristic of the CDMS 5 was calculated. It was found that the addition of the z lens 54 gave no noticeable deterioration in device resolution. The first order focussing of this geometry is expected to yield a residual aberration that is parabolic in nature and this characteristic shown in FIG. 6. In other words, the electrostatic sector field ion trap 50 of the CDMS 5 is isochronous to first order with a parabolic residual at second order, giving a change in frequency of about 0.05%for an ion energy deviation of ?3%. In comparison, the ELIT trap of reference [3] is not isochronous to first order, instead having a linear residual at first order, giving a change in frequency of about 0.275% for an ion energy deviation of +3% and a change in frequency of about ?0.275% for an ion energy deviation of ?3%. Hence, the electrostatic sector field ion trap 50 of the CDMS 5 shows a superior tolerance to energy spread compared with the ELIT trap of reference [3], which is one of the main advantages of the present invention.

[0229] FIGS. 7A and 7B schematically depict the advantage of a relatively narrow charge detection tube, to boost intensity of higher harmonics in the Fourier transform, for a CDMS according to an exemplary embodiment.

[0230] In more detail, a further advantage of the present invention is afforded by the stigmatic or quasi-stigmatic focussing properties of the electrostatic sector field ion trap. These properties mean that the ion beam is confined to a narrow arc as it traverses the analyser. A narrow ion beam means that it is possible to use a similarly narrow charge tube for detection of ions. FIGS. 7A and 7B show how a narrower charge tube gives rise to a sharper transient signal. This signal has increased harmonic content at higher frequencies as a consequence of Fourier theory. Signal to noise ratio of processed waveforms increases with frequency and it is well known that using higher harmonics in Fourier transform mass spectrometry gives improved resolution.

[0231] FIG. 8 schematically depicts an inductive charge detector 800, generally as described with respect to the inductive charge detectors 400 and 500, comprising a first set of segmented charge detector tubes 810, including a first segmented charge detector tube 810A and a second segmented charge detector tube 810B to give an increased number of transients per analyser pass, for a CDMS according to an exemplary embodiment, such as the CDMS 4 and/or the CDMS 5. In this example, the first segmented charge detector tube 810A and the second segmented charge detector tube 810B are axially segmented, each including 10 segments.

[0232] The relatively long charge tubes afforded by the geometry of the CDMS 4 and the CDMS 5, for example, allow axial charge tube segmentation. As a general rule, the induced signal by the moving ion is negligible after it has passed a length of twice the tube width into said tube making an overly long tube wasteful of useful signal. FIG. 8 shows how segmentation may be employed to give a greater number of transient signals per pass. Such segmentation has been proposed before [11] with the use of multiple amplifiers. It is known that such segmentation will still provide an advantage with the use of a single amplifier as connected in FIG. 8. This principle was demonstrated in Fourier Transform Ion Cyclotron Resonance instruments, see for example, the work of Nikolaev [12].

[0233] Furthermore, the three-dimensional figure of eight path of the electrostatic sector field ion trap 40 and even the constrained three-dimensional figure of eight path of the electrostatic sector field ion trap 40 additionally and/or alternatively allow radial charge tube segmentation, as described previously.

[0234] FIG. 9 schematically depicts a CDMS 9 according to an exemplary embodiment, comprising a lift device 99. The CDMS 9 this generally is described with respect to the CDMS 5. The electrostatic sector field ion trap 90 and the inductive charge detector 900 are schematically depicted as a box, which may represent the electrostatic sector field ion trap 50 and the inductive charge detector 500 of the CDMS 5, for example. In order to increase throughput of an electrostatic sector field ion trap of a CDMS according to an exemplary embodiment, it is desirous to operate at relatively high ion beam kinetic energies, for example in a range from 100 eV to 1,000 eV. The advantages of operating at high energies are faster acquisitions and lower aberrations in respect of energy and angle. A first way to increase kinetic energy is to float the inductive charge detector 900 at a high accelerating potential (negative voltage for positive ions), as is commonly done for TOF analysers. However, in the case of CDMS, any noise present on the power supply will mask the very low induced signals of the CDMS analyser. Therefore, inductive charge detectors operated at ground potential are much preferred, as they can be effectively shielded from noise by adjacent grounded plates and coupled directly into the amplifier stage (which is a virtual earth). A second way to increase the kinetic energy is to float the upstream ion optical components by an elevated potential. This is known to be technically problematic and can cause electrical discharge of the components due to field breakdown arising from Paschen's Law. This effect is particularly problematic in the few mBar region, where RF ion guides are often employed, thereby limiting applied voltages to about 200 V and in turn, kinetic energy of the ions. A solution to the problem is to pulse a tube (such as a collimator) (i.e. the lift device 99) to a high potential during the fill up part of the CDMS cycle. In this way, problematic electrical discharges can be avoided as the collimator (or other ion optical elements) are operated at a high vacuum where voltage breakdown does not occur. FIG. 9 shows how such an upstream collimator 99 may be operated in a pulsed manner to increase the kinetic energy of the ions in the electrostatic sector field ion trap 90. Ions fill up a collimator tube 99 at some predetermined energy qV.sub.e. At a time t1, when the collimator tube 99 is full of ions, it is pulsed to an increased potential, V.sub.lift. This increases the energy of the ions as they enter the trap 90 as a pencil of spatially-separated ions, which is still operated with ground potential charge tubes 900 and shields (i.e. shunts). It should be understood that the electrostatic sector, through which the ions are introduced, is transiently also at ground potential while the ions are being introduced. The trap 90 is closed at a time t2, and the trapping cycle begins. Note that the sector electrodes, during the trapping cycle, must have increased voltages V.sub.i related to the ion energy by the following equation:

[00012] $V_{i} = 2 (\frac{R_{0}}{R_{i}} - 1) T_{o}$ [0235] where i=1, 2 and the kinetic energy is T.sub.o in electron volts which equals (V.sub.e+V.sub.lift).

[0236] FIG. 10 schematically depicts a CDMS 10 according to an exemplary embodiment. In this example, the CDMS 10 comprises: an electrostatic sector field ion trap 100 and an inductive charge detector 1000; wherein the electrostatic sector field ion trap 100 is configured to define, at least in part, an ion path via the inductive charge detector 1000.

[0237] In this example, the electrostatic sector field ion trap 100 is as described with respect to the MULTUM of reference [15]. In this example, the electrostatic sector field ion trap 100 comprises a set of electrostatic sectors 101, including a four similar cylindrical electrostatic sectors 101A to 101D, each having a deflection angle of ?.sub.0=156.87? and a deflection radius of 50 mm. In this example, the electrostatic sector field ion trap 100 comprises a set of electric quadrupole lenses 102, including eight electric quadrupole lenses 102A to 102H. In this example, the basic unit comprises four drift spaces, two electric quadrupole lenses and a cylindrical electrostatic sector. In this example, the electrostatic sector field ion trap 100 is isochronous to first order with respect to energy. In this example, the ion path defined by the electrostatic sector field ion trap 100 includes a crossover and has three fold planar symmetry therethrough. Ion injection may be by deflection, as described with respect to reference [14], or via an ion inlet.

[0238] In this example, the inductive charge detector 1000, generally as described with respect to the inductive charge detectors 400, 500 and 800, comprises a first set of segmented charge detector tubes 1010, including four segmented charge detector tubes 1010A, 1010B, 1010C, 1010D.

[0239] FIG. 11 schematically depicts a CDMS 11 according to an exemplary embodiment. In this example, the CDMS 11 comprises: an electrostatic sector field ion trap 110 and an inductive charge detector 1100; wherein the electrostatic sector field ion trap 110 is configured to define, at least in part, an ion path via the inductive charge detector 1100.

[0240] In this example, the electrostatic sector field ion trap 110 is as described with respect to the MULTUM Linear plus of reference [15] and is generally as described with respect to the electrostatic sector field ion trap 100, having additional electric quadrupole lenses to enable ion injection (and ejection).

[0241] In this example, the inductive charge detector 1100, generally as described with respect to the inductive charge detector 1000, comprises a first set of segmented charge detector tubes 1110, including four segmented charge detector tubes 1110A, 1110B, 1110C, 1110D.

[0242] FIG. 12 schematically depicts a CDMS 12 according to an exemplary embodiment. In this example, the CDMS 12 comprises: an electrostatic sector field ion trap 120 and an inductive charge detector 1200; wherein the electrostatic sector field ion trap 120 is configured to define, at least in part, an ion path via the inductive charge detector 1200.

[0243] In this example, the electrostatic sector field ion trap 120 is as described with respect to the MULTUM of reference [15]. In this example, the electrostatic sector field ion trap 120 comprises a set of electrostatic sectors 121, including four similar toroidal electrostatic sectors 121A to 121D, each having a deflection angle of ?.sub.0=157.10?, a deflection radius of 50 mm and a C1 value of 0.0337. In this example, the electrostatic sector field ion trap 120 does not comprise electric quadrupole lenses. In this example, the basic unit comprises two drift spaces and a toroidal electrostatic sector. In this example, the electrostatic sector field ion trap 120 is isochronous to first order with respect to energy. In this example, the ion path defined by the electrostatic sector field ion trap 120 includes a crossover and has three fold planar symmetry therethrough. Ion injection may be by deflection, as described with respect to reference [14], or via an ion inlet.

[0244] In this example, the inductive charge detector 1200, generally as described with respect to the inductive charge detector 1000, comprises a first set of segmented charge detector tubes 1210, including four segmented charge detector tubes 1210A, 1210B, 1210C, 1210D.

[0245] FIG. 13 schematically depicts a CDMS 13 according to an exemplary embodiment. In this example, the CDMS 13 comprises: an electrostatic sector field ion trap 130 and an inductive charge detector 1300; wherein the electrostatic sector field ion trap 130 is configured to define, at least in part, an ion path via the inductive charge detector 1300.

[0246] In this example, the electrostatic sector field ion trap 130 is as described with respect to the planar figure of eight of reference [15]. In this example, the electrostatic sector field ion trap 130 comprises a set of electrostatic sectors 131, including two similar cylindrical electrostatic sectors 131A to 131B, each having a deflection angle ?.sub.0=227.95? and a deflection radius of 50 mm. In this example, the electrostatic sector field ion trap 130 comprises a set of electric quadrupole lenses 132, including eight electric quadrupole lenses 132A to 132H. In this example, the basic unit comprises six drift spaces, four electric quadrupole lenses and a cylindrical electrostatic sector. In this example, the electrostatic sector field ion trap 130 is isochronous to first order with respect to energy. In this example, the ion path defined by the electrostatic sector field ion trap 130 includes a crossover and has three fold planar symmetry therethrough. Ion injection may be

[0247] by deflection, as described with respect to reference [14], or via an ion inlet. Since the electrostatic sector field ion trap 130 already has a planar figure of eight geometry, in contrast with the three dimensional figure of eight geometry of the electrostatic sector field ion traps 30, 40 and 50, the topological problem as described previously does not arise.

[0248] In this example, the inductive charge detector 1300, generally as described with respect to the inductive charge detector 1000, comprises a first set of segmented charge detector tubes 1310, including four segmented charge detector tubes 1310A, 1310B, 1310C, 1310D.

[0249] FIG. 14 schematically depicts a CDMS 14 according to an exemplary embodiment. In this example, the CDMS 14 comprises: an electrostatic sector field ion trap 140 and an inductive charge detector 1400; wherein the electrostatic sector field ion trap 140 is configured to define, at least in part, an ion path via the inductive charge detector 1400.

[0250] In this example, the electrostatic sector field ion trap 140 is as described with respect to the rhomboid of reference [16]. In this example, the electrostatic sector field ion trap 140 comprises a set of electrostatic sectors 141, including two double toroidal electrostatic sectors 142A, 142B, each including a first toroidal electrostatic sector 141A having a deflection angle of ?.sub.0=156.2? and a second toroidal electrostatic sector 141A having a deflection angle of ?.sub.0=23.8?. In this example, the electrostatic sector field ion trap 120 does not comprise electric quadrupole lenses. In this example, the basic unit comprises three drift spaces and two toroidal electrostatic sectors. In this example, the electrostatic sector field ion trap 140 is isochronous to first order with respect to energy. In this example, the ion path defined by the electrostatic sector field ion trap 140 does not include a crossover and has one plane of symmetry. Ion injection may be by deflection, as described with respect to reference [14], or via an ion inlet.

[0251] In this example, the inductive charge detector 1400, generally as described with respect to the inductive charge detector 1000, comprises a first set of segmented charge detector tubes 1410, including four segmented charge detector tubes 1410A, 1410B, 1410C, 1410D.

[0252] It should be understood that any of the CDMS 4 to 9 interface with the hexapole 3 of region III of the CDMS 10, thereby replacing region IV of CDMS 10, or interface with focusing lens 4 of region IV, thereby replacing the HAD 6 and modified cone trap with image charge detector 7 of region IV, wherein the orthogonal TOF-MS 5 is optionally removed.

[0253] FIG. 15 schematically depicts a method according to an exemplary embodiment. Particularly, the method is of determining masses of ions. The method comprises moving, by an electrostatic sector field ion trap, an ion around an ion path defined, at least in part, thereby, via an inductive charge detector (S1501). The method comprises inducing, by the moving ion, a signal in the inductive charge detector (S1502). The method comprises determining a mass of the ion using the induced signal (S1503). The method may comprise any of the steps described herein.

[0254] FIG. 16 schematically depicts a conventional resonance mass separator (RMS), as described in reference [19]. In more detail, FIG. 16 shows a SIMION model and spiral ion trajectories in a resonance mass separator, constructed of cylindrical sectors and sets of periodic einzel and quadrupolar lens. The model RMS 130 is constructed of cylindrical sectors 131 and 132 with different radii, similar to Sakurai et al (Nucl. Instrum. Meth. A427, 1999, 182-186). Cylindrical sectors generate substantially two-dimensional electrostatic field in the X-Y-plane. Ion path 133 is arranged spiral by injecting ion beam (or gently bunched ion packets) at small angle to the X-Y-plane and by confining ions with a set of periodic einzel lens 134 and with periodic quadrupolar lens 135. Ions follow a spiral ion path 133 which is composed of the curved oval mean ion path projection in the X-Y-plane and of relatively slow ion drift in the drift Z-direction. Periodic lens 134 and 135 do confine ion beam along the spiral ion path in spite of moderate ion packet divergence. Parameters of the modeled RMS are: ion trajectory is inscribed into 170?250 mm cell, ion path per revolution is 700 mm, Z-length is 200 mm to fit in 40 revolutions, forming overall L=28 m total flight path. Sectors are energized to pass 6 keV ion beams, so that target mass at m/z=1000 pass single revolution in T.sub.0=20 ?s and through the RMS in 800 us. Ion beam parameters are: 1 mm beam diameter, 4 mrad angular divergence, and FWHM=20 eV energy spread (Gauss distribution), which is excessive compared to ion beam emittance which could be obtained past gaseous RF guides. If no AC excitation is applied, ions of 1000 amu do pass through the RMS without losses. The AC excitation V=V.sub.0* sin[2?(N+0.5)/T.sub.0+?.sub.0] is then applied to quadrupolar lens 135, having 4 mm aperture and 4 mm effective length, accounting fringing fields. When AC signal is applied, the separator does filter multiple m/z bands, whose shape depends on the AC amplitude V.sub.0 and frequency F=(N+0.5)/T.sub.0.

[0255] FIGS. 17A to 17C schematically depict a CDMS 17 according to an exemplary embodiment. The CDMS 17 is generally as described with respect to the CDMS 4 and further comprises a fragmentation device (not shown) and an ion isolating optical element at the origin. The central element of the focussing lens is modified, compared with the corresponding focussing element of the CDMS 4, to allow introduction of the high frequency deflection field. The Z focussing capability of the lens required for efficient trapping in this geometry is still retained, but an additional deflection/focussing field is introduced in the orthogonal Y direction. In order to perform tandem mass spectrometry, it is necessary to first identify the target species of interest to isolate, this is the normal voltage configuration for CDMS as shown in FIG. 17A. This is performed on a fill by fill basis. In order to achieve the highest possible mass measurement precision for CDMS, the are allowed ions to perform many round trips of the analyser in order to ascertain the frequency (a function of m/z) and intensity (a function of signal intensity). Once the desired precursor mass is identified, an appropriate oscillating voltage of the form:

V=V.sub.0 cos[2?Ft] [0256] is applied to the central lens plate as shown in FIG. 17B. The time taken to perform the isolating step will depend on the resolution of separation required. This resolution may be determined by the closest distance in terms of m/z dependent oscillation frequencies for the different species contained in the trap. Once the chosen mass species has been isolated, knowledge of its frequency and phase of oscillation allows switching of the trap electrodes to direct ions out of the trap along the optic axis of the ions. The DC voltage on the central lens may be increased to confine ions more tightly to the Z axis (FIG. 17C.) in order that they may be accurately directed out of the trap when the sector electrodes are switched. Ions may be sent back upstream or downstream to the external fragmentation device. Fragmentation devices may be provided for the CDMS 5, 10, 11, 12, 13, 14 and 16, mutatis mutandis.

[0257] FIG. 18 schematically depicts a CDMS 18 according to an exemplary embodiment. The CDMS 18 is generally as described with respect to the CDMS 12 and further comprises a fragmentation device 185. In this example, the electrostatic sector field ion trap 180 is configured to define, at least in part, the ion path via the fragmentation device 185. Fragmentation devices may be provided for the CDMS 4, 5, 10, 11, 13, 14 and 16, mutatis mutandis.

[0258] FIG. 19 schematically depicts a CDMS 19 according to an exemplary embodiment. The CDMS 19 is generally as described with respect to the CDMS 17, wherein the fragmentation device 195 further comprises a lift device as described with the lift device 99 of the CDMS 9. Hence, isolated ions are thus sent back upstream to the external fragmentation device 195, fragmented therein and the product ions introduced into the ion path analogously to the product ions.

[0259] Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above.

[0260] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0261] All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.

[0262] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0263] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

REFERENCES

[0264] [1] Charge detection mass spectrometry for single ions with a limit of detection of 30 chargesInternational Journal of Mass Spectrometry 345-347 (2013) 153-159 [0265] [2] Charge Detection Mass Spectrometry with Almost Perfect Charge AccuracyAnal. Chem. 2015, 87, 10330-10337 [0266] [3] Optimized Electrostatic Linear Ion Trap for Charge Detection Mass SpectrometryJ. Am. Soc. Mass Spectrom. (2018) Oct; 29(10):2086-2095 [0267] [4] Multiple-Focusing Time-of-Flight Mass Spectrometers Part II. TOFMS with Equal Energy AccelerationInternational Journal of Mass Spectrometry and Ion Physics, 9 (1972): 357-373 [0268] [5] TOF-SIMS: Materials Analysis by Mass Spectrometry ISBN: 978-1-906715-17-5 [0269] [6] Orthogonal acceleration time-of-flight mass spectrometryMass Spectrom Rev. 2000 Mar-Apr; 19(2):65-107 [0270] [7] Energy-Isochronous Time-of-Flight Mass SpectrometersProceedings of the NATO Advanced Study Institute on Mass Spectrometry in Biomolecular Sciences Laceo Ameno, Ischia, Italy June 2?July 5, 1993, P111-146 [0271] [8] U.S. Pat. No. 9,082,604 [0272] [9] Advances in IMAGING and ELECTRON PHYSICSMikhail YavorOptics of Charged Particle Analysers Volume 157 p230 [0273] [10] SIMION? 2003-2019 Scientific Instrument Services Inc [0274] [11] WO 2012/083031 A1 [0275] [12] Analysis of harmonics for an elongated FTMS cell with multiple electrode detectionInternational Journal of Mass Spectrometry and Ion Processes, 157/158 (1996): 215-232 [0276] [13] U.S. Pat. No. 6,300,625 [0277] [14] Sakurai T, Nakabishi H, Hiasa T, Okanishi K. Nucl. Instrum. Methods A 1999; 427: 182. [0278] [15] Multi-turn time-of-flight mass spectrometers with electrostatic sectors, Michisato Toyoda, Daisuke Okumura, Morio Ishihara, ltsuo Katakuse, J. Mass Spectrom. 2003; 38: 1125-1142, https://doi.org/10.1002/jms.546 [0279] [16] M. Nishiguchi, et al., Journal of the Mass Spectrometry Society of Japan 44 (2009) 594. [0280] [17] Benner, W.H.: A gated electrostatic ion trap to repetitiously measure the charge and M/Z of large electrospray ions. Anal. Chem. 69, 4162-4168 (1997) [0281] [18] Infrared multiphoton dissociation tandem charge detection-mass spectrometry of single megadalton electrosprayed ions. Review of Scientific Instruments 82, 084104 (2011) [0282] [19] WO2017042665

MASS SPECTROMETER AND METHOD

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Abstract

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Description