Ion injection into multi-pass mass spectrometers

Abstract

An improved multi-pass time-of-flight or electrostatic trap mass spectrometer (70) with an orthogonal accelerator, applicable to mirror based multi-reflecting (MR) or multi-turn (MT) analyzers. The orthogonal accelerator (64) is tilted and after first ion reflection or turn the ion packets are back deflected with a compensated deflector (40) by the same angle α to compensate for the time-front steering and for the chromatic angular spreads. The focal distance of deflector (40) is control by Matsuda plates or other means for producing quadrupolar field in the deflector. Interference with the detector rim is improved with dual deflector (68). The proposed improvements allow substantial extension of flight path and number of ion turns or reflections. The problems of analyzer angular misalignments by tilting of ion mirror (71) is compensated by electrical adjustments of ion beam (63) energy and deflection angles in deflectors (40) and (68).

Claims

1. A mass spectrometer comprising: a multi-pass time-of-flight mass analyzer or electrostatic ion trap having an orthogonal accelerator and electrodes arranged and configured so as to provide an ion drift region that is elongated in a drift direction (z-dimension) and to reflect or tum ions multiple times in an oscillating dimension (x-dimension) that is orthogonal to the drift direction; and an ion deflector located downstream of said orthogonal accelerator, and that is configured to back-steer an average ion trajectory of the ions passing through the ion deflector, in the drift direction, and to generate a quadrupolar field for controlling the spatial focusing of the ions in the drift direction.

2. The spectrometer of claim 1, wherein: (i) the multi-pass time-of-flight mass analyser is a multi-reflecting time of flight mass analyser having two ion mirrors that are elongated in the drift direction (z-dimension) and configured to reflect ions multiple times in the oscillation dimension (x-dimension), wherein the orthogonal accelerator is arranged to receive ions and accelerate them into one of the ion mirrors; or (ii) the multi-pass time-of-flight mass analyser is a multi-tum time of flight mass analyser having at least two electric sectors configured to tum ions multiple times in the oscillation dimension (x-dimension), wherein the orthogonal accelerator is arranged to receive ions and accelerate them into one of the sectors.

3. The spectrometer of claim 1, wherein the ion deflector is configured to generate a substantially quadratic potential profile in the drift direction.

4. The spectrometer of claim 1, wherein the ion deflector back steers all ions passing therethrough by the same angle; and/or wherein the ion deflector controls the spatial focusing of the ion packet in the drift direction such that the ion packet has substantially the same size in the drift dimension when it reaches an ion detector in the spectrometer as it did when it enters the ion deflector.

5. The spectrometer of claim 1, wherein the ion deflector controls the spatial focusing of the ion packet in the drift direction such that the ion packet has a smaller size in the drift dimension when it reaches a detector in the spectrometer than it did when it entered the ion deflector.

6. The spectrometer of claim 1, comprising at least one voltage supply configured to apply one or more first voltage to one or more electrode of the ion deflector for performing said back-steer and one or more second voltage to one or more electrode of the ion deflector for generating said quadrupolar field for said spatial focusing, wherein the one or more first voltage is decoupled from the one or more second voltage.

7. The spectrometer of any preceding claim 1, wherein the ion deflector comprises at least one plate electrode arranged substantially in the plane defined by the oscillation dimension and the dimension orthogonal to both the oscillation dimension and the drift direction (X-Y plane), wherein the plate electrode is configured back-steer the ions; and wherein the ion deflector comprises side plate electrodes arranged substantially orthogonal to the opposing electrodes and that are maintained at a different potential to the opposing electrodes for controlling the spatial focusing of the ions in the drift direction.

8. The spectrometer of claim 1, wherein said ion deflector is configured to provide said quadrupolar field by comprising one or more of: (i) a trans-axial lens/wedge; (iii) a deflector with aspect ratio between deflecting plates and side walls of less than 2; (iv) a gate shaped deflector; or (v) a torroidal deflector.

9. The spectrometer of claim 1, wherein the ion deflector focusses the ions in a y-dimension that is orthogonal to the drift direction and the oscillation dimension, and wherein the orthogonal accelerator and/or mass analyser or electrostatic ion trap is configured to compensate for this focusing.

10. The spectrometer of any preceding claim 1, wherein the ion deflector is arranged such that it receives ions that have already been reflected or turned in the oscillation dimension by the multi-pass time-of-flight mass analyser or electrostatic ion trap; optionally after the ions have been reflected or turned only a single time in the oscillation dimension by the multi-pass time-of-flight mass analyzer or electrostatic ion trap.

11. The spectrometer of claim 1, wherein said orthogonal accelerator is arranged and configured to receive ions along an ion receiving axis that is tilted at an angle to the drift direction, in a plane defined by the drift direction and the oscillation dimension (XZ-plane), and to pulse the ions orthogonally to the ion receiving axis such that the time front of the ions exiting the orthogonal accelerator is parallel to the ion receiving axis; and wherein the ion deflector is configured to back-steer the ions, in the drift direction, such that the time front of the ions becomes parallel, or more parallel, to the drift dimension and/or an impact surf ace of an ion detector after the ions exit the ion deflector.

12. The spectrometer of claim 11, wherein the ion receiving axis is tilted at an acute tilt angle β to the drift direction; wherein the ion deflector back steers ions passing therethrough by a back-steer angle ljl′, and wherein the tilt angle and back-steer angle are the same.

13. The spectrometer of claim 1, comprising an ion optical lens for spatially focusing or compressing the ion packet in the drift direction, wherein the ion deflector is configured to defocus the ion packet in the drift direction, and wherein the combination of the ion optical lens and ion deflector are configured to provide telescopic compression of the ion beam.

14. The spectrometer of claim 1, comprising an ion optical lens for compressing the ion packet in the drift direction by a factor C; wherein said orthogonal accelerator is arranged and configured to receive ions along an ion receiving axis that is tilted at an angle β to the drift direction, in a plane defined by the drift direction and the oscillation dimension (XZ-plane); wherein the ion deflector is configured to back-steer the ions, in the drift direction, by angle ψ, and wherein β=ψ/C.

15. The spectrometer of claim 1, comprising a further ion deflector proximate an ion detector in the spectrometer for deflecting an average ion trajectory passing through the ion deflector such that ions are guided onto a detecting surface of the ion detector.

16. A method of mass spectrometry comprising: providing the spectrometer of any preceding claim 1; transmitting ions into the orthogonal accelerator along an ion receiving axis; accelerating the ions orthogonally to the ion receiving axis in the orthogonal accelerator; and deflecting the ions downstream of said orthogonal accelerator so as to back-steer the average ion trajectory of the ions, in the drift direction, and controlling the spatial focusing of the ions in the drift direction with the quadrupolar field; wherein the ions are oscillated multiple times in the oscillation dimension by the multipass time-of-flight mass analyser or electrostatic ion trap as the ions drift through the drift region in the drift direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 shows prior art according to U.S. Pat. No. 6,717,132 having planar multi-reflecting TOF analyser and a gridless orthogonal pulsed accelerator;

(3) FIG. 2 shows prior art according to U.S. Pat. No. 7,504,620 having a planar multi-turn TOF mass analyser and an OA;

(4) FIG. 3 illustrates problems of the prior art MRTOF instrument of FIG. 1, i.e. low ion beam energy, limited number of reflections, ions hitting rims of OA and detector, and most important, loss of isochronicity at minor instrumental misalignments;

(5) FIG. 4 illustrates the difference between conventional deflectors of the prior art and balanced deflectors of the present invention;

(6) FIG. 5 shows an OA-MRTOF embodiment of the present invention with improved ion injection;

(7) FIG. 6 illustrates improvements of embodiments of the present invention for yet denser ion trajectory folding in MRTOF instruments;

(8) FIG. 7 illustrates a method of global compensation of instrumental misalignments and presents results of ion optical simulations, confirming recovery of the MRTOF isochronicity;

(9) FIG. 8 shows a mechanism and method of an embodiment of the present invention for compensated reversal of ion drift motion, in a sector MTTOF instrument; and

(10) FIG. 9 shows an electrostatic ion guide for ion beam transverse confinement within elongated and optionally curved orthogonal accelerators.

DETAILED DESCRIPTION

(11) Referring to FIG. 1, a prior art multi-reflecting TOF instrument 10 according to U.S. Pat. No. 6,717,132 is shown having an orthogonal accelerator (i.e. an OA-MRTOF instrument). The MRTOF instrument 10 comprises: an ion source 11 with a lens system 12 to form a parallel ion beam 13; an orthogonal accelerator (OA) 14 with a storage gap to admit the beam 13; a pair of gridless ion mirrors 16, separated by field-free drift region, and a detector 17. Both OA 14 and mirrors 16 are formed with plate electrodes having slit openings, oriented in the Z-direction, thus forming a two dimensional electrostatic field, symmetric about the XZ symmetry plane (also denoted as s-plane). Accelerator 14, ion mirrors 16 and detector 17 are parallel to the Z-axis.

(12) In operation, ion source 11 generates continuous ion beam. Commonly, ion sources 11 comprise gas-filled radio-frequency (RF) ion guides (not shown) for gaseous dampening of ion beams. Lens 12 forms a substantially parallel continuous ion beam 13, entering OA 14 along the Z-direction. Electrical pulse in OA 14 ejects ion packets 15. Packets 15 travel in the MRTOF analyser at a small inclination angle α to the x-axis, which is controlled by the ion source bias U.sub.Z. After multiple mirror reflections, ion packets hit detector 17. Specific energy of continuous ion beam 13 controls the inclination angle α and number of mirror reflections.

(13) Referring to FIG. 2, a prior art multi-turn TOF analyzer 20 according to U.S. Pat. No. 7,504,620 is shown having an orthogonal accelerator (i.e. an OA-MRTOF instrument). The instrument comprises: an ion source 11 with a lens system 12 to form a substantially parallel ion beam 13; an orthogonal accelerator (OA) 14 to admit the beam 13; four electrostatic sectors 26 with spiral laminations 27, separated by field-free drift regions, and a TOF detector 17.

(14) Similarly to the arrangement in FIG. 1, the OA 14 admits a slow (say, 10 eV) ion beam 13 and periodically ejects ion packets 25 along a spiral ion trajectory. Electrostatic sectors 26 are arranged isochronous for a spiral ion trajectory 27 with a figure-of-eight shaped ion trajectory 24 in the XY-plane and with a slow advancing in the drift Z-direction corresponding to a fixed inclination angle α. The energy U.sub.Z of ion beam 13 is arranged to inject ions at the inclination angle α.sub.0, matching a of laminated sectors.

(15) The laminated sectors 27 provide three dimensional electrostatic fields for ion packet 25 confinement in the drift Z-direction along the mean spiral trajectory 24. The fields of the four electrostatic sectors 27 also provide for isochronous ion oscillation along the—figure-of-eight shaped central curved ion trajectory 24 in the XY-plane (also denoted as s). If departing from technically complex lamination, the spiral trajectory may be arranged within two dimensional sectors. However, some means of controlling ion Z-motion are then required, very similar to MRTOF instruments.

(16) The improvements of the embodiments of the present invention are equally applicable to both MRTOF and MTTOF instruments.

(17) Referring to FIG. 3, simulation examples 30 and 31 are shown that illustrate problems of prior art MRTOF instruments 10, if pushing for higher resolutions and denser ion trajectory folding. Exemplary MRTOF parameters were used, including: D.sub.X=500 mm mirror cap-cap distance; D.sub.Z=250 mm wide portion of non-distorted XY-field; acceleration potential is U.sub.X=8 kV, OA rim=10 mm and detector rim=5 mm.

(18) In example 30, to fit 14 ion reflections (i.e. L=7 m ion flight path) the source bias is set to U.sub.Z=9V. Parallel ion rays with an initial ion packet length in the z-dimension of Z.sub.0=10 mm and no angular spread (Δα=0) start hitting rims of OA 14 and of detector 17. In example 31, the top ion mirror is tilted by λ=1 mrad, representing a realistic overall effective angle of mirror tilt considering built up faults of stack assemblies, standard accuracy of machining and moderate electrode bend by internal stress at machining. Every “hard” ion reflection in the top ion mirror then changes the inclination angle α by 2 mrad. The inclination angle α grows from α.sub.1=27 mrad to α.sub.2=41 mard, gradually expanding central trajectory. To hit the detector after N=14 reflections, the source bias has to be reduced to U.sub.Z=6V. The angular divergence is amplified by the mirror tilt and increases the ion packets width to ΔZ=18 mm, inducing ion losses on the rims. Obviously, slits in the drift space may be used to avoid trajectory overlaps, however, at a cost of additional ionic losses.

(19) In example 31, the inclination of ion mirror introduces yet another and much more serious problem. The time-front 15 of the ion packet becomes tilted by angle γ=14 mrad in-front of the detector. The total ion packet spreading in the time-of-flight X-direction ΔX=ΔZ*γ=0.3 mm does limit mass resolution to R<L/2ΔX=11,000 at L=7 m flight path, being low even for a regular TOF instrument and too low for MRTOF instruments. To avoid the limitation, the electrode precision has to be brought to a non-realistic level: λ<0.1 mrad, translated to better than 10 um accuracy and straightness of individual electrodes.

(20) Thus, attempts of increasing flight path length enforce much lower specific energies U.sub.Z of continuous ion beam and larger angular divergences Δα of ion packets, which induce ion losses and may produce spectral overlaps. Small mechanical imperfections also affect MRTOF resolution and require unreasonably high precision.

(21) Various embodiments of the present invention will now be described.

(22) It is desirable to keep instrument size relatively small, e.g. at about 0.5 m, or under. Using larger analyzers raises manufacturing cost close to the cubic power of the instrument size.

(23) Preferably, data system and detector time spreading (at peak base) shall not be pushed under DET=1.5-2 ns. This will avoid expensive ultra-fast detectors with strong signal ringing. It will also avoid artificial sharpening of resolution by “centroid detection” algorithms, ruining mass accuracy and merging mass isobars.

(24) To resolve practically important isobars at mass resolution RTOF/2DET, the peak width shall be less than isobaric mass difference, hence requiring longer flight time TOF and longer flight path L (calculated for 5 kV acceleration), all shown in the Table 1.

(25) TABLE-US-00001 TABLE 1 Mass Replacing difference, Resolution > TOF>, Flight elements mDa (M = 1000 amu) us Path L>, m C for H.sub.12 94 10,600 42 1.33 O for CH.sub.4 38.4 26,000 104 3.3 ClH for C.sub.3 24 41,600 167 5.3 N for CH.sub.2 12.4 80,600 320 10.1

(26) The table presents the most relevant and most frequent isobaric interferences of first isotopes. In case of LC-MS, the required resolution may be over 80,000. In case of GC-MS, where most of ions are under 500 amu, the required resolution may be over 40K.

(27) Thus, various embodiments of the present invention provide an ion flight path over 10 m in length. The mass analyser may also have a size of ≤0.5 m in any one (e.g. horizontal) dimension. The mass analyser may provide N passes (e.g. reflections or turns), where N>20. The analyser may be minimise the effect of aberrations of the ion optical scheme on resolution. Embodiments are able to operate at reasonably high ion beam energy (>30-50 eV) for improved ion beam admission into the orthogonal accelerator.

(28) Embodiments of the invention provide the instrument with sufficient resolution (e.g. R>80,000) and a flight path over 10 m for separating major isobaric interferences, achieved in compact and low cost instrument (e.g. having a size of about 0.5 m or under), without stressing the requirements of the detection system and not affecting peak fidelity.

(29) The below described embodiments are described in relation to particularly compact MRTOF analysers having a size (e.g. in the horizontal dimensions) of 450×250 mm, and operating at 8 kV acceleration voltage. However, other sized instruments and other acceleration voltages are contemplated.

(30) The below described embodiments of the present invention may employ ion deflectors, and optionally, improved deflectors with compensated over-focusing.

(31) Referring to FIG. 4, there are compared properties of a conventional deflector 41, and of a compensated deflector 40 of an embodiment of the present invention. Such a deflector 40 may be used to deflect ions in the z-dimension (drift dimension) of the mass analyser, e.g. as shown in FIG. 5.

(32) Referring back to FIG. 4, the conventional deflector 41 is composed of pair of parallel deflection plates, spaced by distance H. Potential difference U generates a deflecting field E.sub.ZU/H. Accounting for fringing fields, the field acts within distance D in the x-dimension. Ions of mean specific energy K at the lower part of the deflector (as seen in FIG. 4), are deflected by an angle ψ=D/2H*U/K. The deflector is known to steer the time front of the ion packet by the opposite angle γ=−ψ, which becomes evident when accounting that the upper ion rays (shown in FIG. 4) are slowed down within the deflector. The slow down of upper ion rays to U-K specific energy also causes a difference ε (where ε=ψ*U/K*z/H) in the deflection angle and introduces an inevitable angular dispersion and inevitable focusing properties of the deflector with focal distance F=2D/ψ.sup.2, where the strength of the focusing effect rapidly increases with the deflection angle amplitude such that:
γ(z)=−ψ(z)=U/K*D/2H+ε(z),
ε(z)=ψ*U/K*z/H; F=2D/ψ.sup.2

(33) The inevitable focusing of such conventional deflectors makes them a poor choice for controlling ion drift motion in MPTOF instruments. However, the inventor has recognised that an ion deflector may be used in an advantageous manner.

(34) Again referring to FIG. 4, the deflector 40 according to an embodiment of the present invention may comprise a built-in quadrupolar field (e.g. E.sub.Z=−2U.sub.Q*z/H.sup.2) designed for controlled spatial focusing of the ions, and being decoupled from the amplitude of ion steering. The exemplary compensated deflector 40 comprises a pair of opposing deflection plates 42 and also side plates 43 that are maintained at a different potential. Similar side plates for sectors are known as Matsuda plates. The additional quadrupolar field in deflector 40 provides the first order compensation for angular dispersion of conventional deflectors. The compensated deflector 40 steers all the ions by the same angle ψ, tilts the time front of the ion packet by angle γ=−ψ, and may be capable of compensating the over-focusing (i.e. F.fwdarw.∞) while avoiding the bending of the time front. Alternatively, the deflector 40 may be capable of controlling the focal distance F independent of the steering angle ψ. The parameters of the deflector 40 may therefore be given by:
E.sub.ZU/H−2U.sub.Q*z/H.sup.2,
γ=−ψ=−D/2H*U/K
F=D/(ψ.sup.2/2−K/U.sub.Q)

(35) The quadrupolar fields allows controlling spatial focusing (at negative U.sub.Q) and defocusing (at negative U.sub.Q) of the ions by the deflector 40.

(36) The quadrupolar field in the Z direction inevitably generates an opposite focusing or defocusing field in the transverse Y-direction. However, it has been recognised that the focal properties of MPTOF mass analyser (e.g. MRTOF mirrors) are sufficient to compensate for the Y-focusing of the quadrupolar deflectors 40, even without adjustments of ion mirror potentials and without any significant time-of-flight aberrations.

(37) Similar compensated deflectors are proposed to be constructed out of trans-axial (TA) deflectors, formed by wedge electrodes. Similarly to embodiment 40, an embodiment of the invention proposes using a first order correction, produced by an additional curvature of TA-wedge. Third, yet simpler compensated deflector can be arranged with a single potential while selecting the size of Matsuda plates, suitable for a narrower range of deflection angles. The asymmetric deflector is then formed with a deflecting electrode having gate shape, surrounded by shield, set at the drift potential. Forth, similarly (though more complex), the compensated deflector can be arranged with torroidal sector.

(38) As described above, various embodiments provide improved compensated ion deflectors to overcome the over-focusing problem of conventional ion deflectors, so as to control the focal distance of the deflectors, including defocusing by quadrupolar fields. Transverse effects of the quadrupolar field may be well compensated by the spatial and isochronous properties of MPTOF mass analyser.

(39) FIG. 5 shows an embodiment 50 of an MRTOF mass analyser having an orthogonal accelerator. The mass analyser comprises: two parallel gridless ion mirrors 16, elongated in the Z-direction and, separated by a floated drift space; an ion source 11 with a lens system 12 to form a parallel ion beam 13 substantially along or at small angle to the Z-direction; an orthogonal accelerator (OA) 54 tilted to the Z-axis by angle β; a compensated ion deflector 40, located downstream of OA 54, and preferably located after the first ion reflection; and a detector 17, also aligned with the Z-axis.

(40) In operation, ion source 11 generates continuous ion beam at specific energy U.sub.Z (e.g. defined by source 11 bias). Preferably, ion source 11 comprise gas-filled radio-frequency (RF) ion guide (not shown) for gaseous dampening of ion beam 13. Lens 12 forms a substantially parallel continuous ion beam 13. Ion beam 13 may enter OA 54 directly, while tilting at least the exit part of ion optics 12. It is more convenient and preferred to arrange the source along the Z-axis while steering the beam 13 by a deflector 51, followed by collimation of steered beam 53 with a slit 52 and yet preferably by a pair of heated slits for limiting both—the width and the divergence of beam 53.

(41) Beam 53 enters tilted OA 54. An electrical pulse in OA 54 ejects ion packets 55 along a mean ion ray inclined by angle α.sub.1=α.sub.0−β, where β is the OA tilt angle and α.sub.0 is natural inclination angle past OA, which is defined by the ion source bias and the ion energy in the z-dimension Ux: α.sub.0 (U.sub.Z/U.sub.X).sup.0.5. The time front of ion packets 55 stay parallel to the OA 54 and at an angle to the z-dimension of γ=β. In order to increase the number N of mirror reflections (and hence ion path length and resolution), the ion ray inclination angle α.sub.2 may be reduced by back steering ion packets in the deflector 40 by angle ψ. This is preferably performed after a single ion mirror reflection (which allows yet denser ray folding). The ion energy U.sub.Z, the OA tilt angle β and the back steering angle ψ of deflector 40 may be chosen and tuned so that the back steering angle ψ equals the time-front tilt angle γ: ψ=γ. As a result, the time-fronts of ion packets 56 becomes aligned and parallel with the Z-axis. After multiple mirror reflections, ion packets 59 hit detector 17 with time-fronts being parallel to the detector face. Mutual compensation of tilt and steering may occur at the following compensation conditions:
β=ψ=(α.sub.0−α.sub.1)/2 where α.sub.0=(U.sub.Z/U.sub.X).sup.0.5 and α.sub.1=D.sub.Z/D.sub.XN
where D.sub.Z is the distance in the z-dimension from the midpoint of the OA 54 to the midpoint of the detector 17, and D.sub.X is the cap-to-cap distance between the ion mirrors.

(42) It is believed that it had not previously been recognised that the combination of OA tilt and deflector steering does in fact compensate for the chromatic angular spread by the deflector at exactly the same condition:
α|K=0 and T|Z=0 at β=ψ

(43) A numerical example of an embodiment will now be described, again referring to FIG. 5. The method of compensated injection is illustrated with numbers for the exemplary compact MRTOF mass analyser having D.sub.X=450 mm and D.sub.Z=250 mm sizes. Note that the exemplary MRTOF mass analyser is shown geometrically distorted. The exemplary MRTOF mass analyser is chosen with positive (retarding) mirror lens electrodes for increasing the acceleration voltage to U.sub.X=8 kV at maximal mirror voltage amplitude under 10 kV.

(44) To enhance the ion beam admission into the OA and to reduce the angular divergence of ion packets Δα=ΔU.sub.Z/2(U.sub.Z*U.sub.X).sup.0.5, the ion beam specific energy is chosen U.sub.Z=80V, which corresponds to α.sub.0=100 mrad at U.sub.X=8 kV. The ray inclination angle is chosen to be α.sub.1=22 mrad to fit N=20 reflections into the compact MRTOF mass analyser, where the ion advance per reflection is L.sub.Z=10 mm, i.e. slightly smaller than the ion packets initial width Z.sub.0=10 mm. Note that such a small advance L.sub.Z becomes possible because of the optimal location of deflector 40, and because of the improved design of the deflector 40 arranged without the right deflection plate. Then the OA tilt and back steering angles are: β=ψ=(α.sub.0−α.sub.1)/2=39 mrad to provide for compensated steering while bringing the tilt angle of ion packets 56 to zero.

(45) Choosing higher energy U.sub.Z helps reducing ion packets angular divergence to as low as Δα=0.6 mrad. After N=20 reflections and L=10 m flight path, ion packets expand by 6 mm only. The potentials of the Matsuda plates in the deflector 40 may be chosen to focus initially parallel and Z.sub.0=10 mm wide ion packets into a point. Since chromatic angular spread by the deflector is compensated (α|K=0), the final width ΔZ of the ion packet 56 in-front of the detector is expected to be as low as 6 mm, i.e. allows the shown dense folding of ion trajectory.

(46) Increased the flight path to L=9 m corresponds to a flight time T=225 us for 1000 amu ions at U.sub.X=8 kV, thus setting a resolution limit of R=T/2ΔT>50,000 when using non stressed detectors with ΔT=2 ns time spread with smaller detector ringing.

(47) As described in relation to FIG. 5, the ion injection mechanism may be strongly improved by tilting the orthogonal accelerators and using a continuous ion beam, which are conventionally oriented in the drift Z-direction. To increase the ion beam energies at the OA entrance, the orthogonal accelerator may be slightly tilted to the drift z-axis by several degrees. At least one compensated deflector of TA-deflector/lens may be used for local steering of ion rays. The combination of tilt and steering may mutually compensate for the time-front tilt (T|Z=0 i.e. γ0). Increased ion energies improve the ion beam admission into the OA, help bypassing OA rims, and reduce the ion packet angular divergence. Back steering by the deflector allows reducing the ion ray inclination angle, and enables a larger number of ion reflections, thus increasing resolution. The location of the deflector directly after the first ion mirror reflection allows yet denser ray folding. The compensated tilt and steering simultaneously compensates for a chromatic angular spread of ion packets.

(48) If pushing the compact MRTOF mass analyser for higher resolutions, yet denser folding of the ion trajectory may become limited in the embodiment 50 by the ion packet interference with the deflector right wall and with the detector rim.

(49) Referring to FIG. 6, another embodiment 60 of an MRTOF mass analyser having an orthogonal accelerator is shown. The mass analyser comprises a number of components similar to those in embodiment 50: two parallel gridless ion mirrors 16; an ion source 11 with a lens system 12; an orthogonal accelerator (OA) 64 tilted by angle β; a compensated deflector 40 located after first ion reflection; and a detector 17 aligned with the Z-axis. Embodiment 60 further comprises improving elements, which may be used in combination or separately: a trans-axial (TA) wedge/lens 66; a lens (Einzel or trans-axial) 67 surrounding two adjacent ion trajectories; and a dual deflector 68 for ion packets displacement.

(50) Similar to mass analyser 50 of FIG. 5, in the embodiment of FIG. 6, ion source 11 generates a continuous ion beam at specific energy U.sub.Z. Lens 12 forms a substantially parallel continuous ion beam 13. The beam is corrected by dual deflector 61, so that the aligned beam 63 matches the common axis of OA 64 and of heated collimator 62, both tilted to the Z-axis by angle β. Similar to embodiment 50, the combination of tilted OA 64 and deflector 40 allows injecting ion beam at elevated energies, reducing the inclination angle from α.sub.0 to α.sub.1 in order to fit a larger number of reflections (e.g. N=30), while achieving zero tilt of ion packet 69 (γ=0), i.e. parallel to the detector 17 face.

(51) The combination of TA-lens/wedge 66 with the compensated deflector 40 allow arranging telescopic compression of the ion packet width, here from 10 mm to 5 mm. While TA lens 66 focuses ion packets to achieve two-fold compression, the potential of the Matsuda plate in the deflector 40 may be adjusted for moderate packet defocusing, so that initially parallel rays with ion packet width Z.sub.0=10 mm were spatially focused onto the detector. It is a new finding that with the ion packet spatial compression by factor C between OA 64 and deflector 40 (in this example C=2) there appears newly formulated condition for compensating of the time front tilt γ=0 (i.e. overall T|Z=0), occurring at β=ψ/C. Thus, the OA tilt angle becomes:
β=ψ/C=(α.sub.0−α.sub.1)/(1+C)

(52) where α.sub.0=(U.sub.Z/U.sub.X).sup.0.5 is defined by ion source bias U.sub.Z, and α.sub.1 is chosen from trajectory folding in MRTOF.

(53) When TA-wedge 67 is used for steering, still γ=0 may be recovered and relations for angles can be figured out with regular geometric considerations.

(54) To bypass the detector 17 rim, ion packets are preferably displaced by dual deflector 68, preferably also equipped with Matsuda plates. The dual symmetric deflector may compensate for time-front tilt. Slight asymmetry between deflector legs may be used for adjusting the scheme imperfections and misalignments.

(55) Optionally, an intermediate lens 67 (either Einzel or TA) may be arranged to surround two adjacent ion trajectories. The arrangement allows minor additional focusing and/or steering of ion rays, preferably set at long focal distance (say above 5-10 m).

(56) The tuning steps of the mass analyser will now be described.

(57) (1) At start, OA tilt angle β may be preliminary chosen from optimal ion beam energy and for the desired number of ion reflections N. The dual deflector 68 and TA-lens 67 may be set up at simulated voltages, while lens 67 may be either omitted or not energized;

(58) (2) The pair of tilted OA 64 and deflector 40 may be tuned for reaching both time-front recovery for γ=0, and adjusting angle α.sub.1 (for N reflections) by adjusting source bias U.sub.Z and steering angle ψ, Such tuning also compensates for some instrumental misalignments;

(59) (3) Spatial focusing of ion packets onto the detector 17 may be achieved by independent tuning of Matsuda plate potential in deflector 40 at negligible shifts of step (2) tuning;

(60) (4) Further optimizing tuning of the optional lens 69, or of the slight imbalance of the dual deflector 68 may be figured out experimentally.

(61) A numerical example will now be described again referring to FIG. 6. Embodiment 60 has been simulated for D.sub.X=450 mm, D.sub.Z=250 mm, U.sub.X=8 kV, and U.sub.Z=80V corresponding to α.sub.0=100 mrad. Ion rays are folded at α.sub.1=16 mrad corresponding to L.sub.Z=6 mm ion packet advance per reflections. Spatial compression of TA-lens C=2. Then the OA tilt angle β=(α.sub.0−α.sub.1)/(1+C)=26 mrad and the deflector steering angle ψ=C*β=52 mard. Lens 69 is not energized. With N=30 reflections, flight path becomes L=13.5 m and flight time T=360 us for 1000 amu ions, thus setting R=T/2ΔT=90,000 resolution limit when using non stressed detectors with ΔT=2 ns time spread. The resolution exceeds the target R=80,000 for LC-MS, i.e. sufficient for resolving most of isobaric interferences at m/z<1000.

(62) Various embodiments of the present invention therefore include a novel injection mechanism that has a built-in and not before fully appreciated virtue—an ability to compensate for mechanical imperfections of MPTOF mass analysers by electrical tuning of the instrument by adjusting of ion beam energies U.sub.Z, and deflector 40 steering angle.

(63) As described in relation to FIG. 6, a dual set of deflectors is proposed to cause ions to bypass detector rims and to provide for an additional mean for instrument tuning and adjustments.

(64) Telescopic spatial focusing is also arranged by a pair of compensated deflectors, where at least one deflector may be a transaxial (TA) lens/wedge, mutually optimized with the exit lens of gridless OA. A new method is discovered for mutual compensation of the time front tilt in pair of deflectors at spatial focusing/defocusing between them.

(65) Referring to FIG. 7, there are shown results of optical simulations for an exemplary MRTOF mass analyser 70, employing the MRTOF mass analyser of FIG. 6 with D.sub.X=450 mm, D.sub.Z=250 mm, and U=8 kV. The mass analyser 70 is different from mass analyser 60 by introducing a Φ=1 mrad tilt of the entire top mirror 71, representing a typical non intentional mechanical fault at manufacturing. If using the tuning settings of FIG. 6, resolution drops to 25,000 as shown in the graph 73. The resolution may be recovered to approximately R=50,000 as shown in icon 74 by increasing specific energy of continuous ion beam from U.sub.Z=57V to U.sub.Z=77V, and by retuning deflectors 40 and 68. Mass analyser 70 shows ion rays after the compensation when accounting for all realistic ion beam and ion packet spreads. Thus, simulations have confirmed that the novel method of compensating instrumental misalignments is valid.

(66) An important improvement is provided with the novel method of global compensation of parasitic time-front tilts, produced by unintentional instrumental misalignments. Additional compensating tilt is produced by first deflector (in pair with adjustments of ion beam energy) and by tuning the imbalance of the exit dual deflector.

(67) Referring back to FIG. 3, tilting of ion mirrors produces an additional parasitic tilt of time front 15, producing the major negative effect of instrumental misalignments. Referring back to FIG. 5, ion steering in deflector 40 allows varying the time front tilt γ by changing the 40 deflection angle ψ, thus compensating overall parasitic tilts for initially wide and parallel ion packets. To recover the desired inclination angle α.sub.1 of ion rays, one shall adjust ion beam specific energy U.sub.Z. Shifting energy may affect the ion admission from OA 64 to deflector 40. To solve this problem, one may either use a longer OA (preferably combined with entrance slit in deflector 40) or apply an additional ray steering with TA lens/wedge 66. The first part of the method, however, does not compensate the time-front tilt for point-sized and initially diverging ion packets, since they have negligible width in the deflector 40. This problem is solved by misbalance in deflector 68 legs. Thus, the novel method of FIG. 7 provide for the overall compensation of parasitic time-front tilts by any type of instrumental misalignments, while solving the problem for both components of ion packet phase space volume—initial width and initial divergence.

(68) Yet another improvement in compact trajectory folding is arranged with the novel mechanism and method of rear-edge Z-reflection, illustrated on the example of a sector MTTOF mass analyser, though being equally applicable to MRTOF mass analysers.

(69) FIG. 8 shows an embodiment 70 of an MPTOF mass analyser of the present invention comprising: a sector multi-turn analyzer 81 (also shown in X-Y plane) with two-dimensional fields, i.e. without laminations of embodiment 20; a tilted OA 64; a compensated deflector 40, a pair of telescopic compensated deflectors 82 and 83; and a compensated deflector 78 in-front of a detector 17.

(70) Similar to FIG. 5-7, ion injection employs tilted OA 64 and compensated deflector 40 for using elevated energies U.sub.Z of ion beam, reducing inclination angle to α.sub.2 while keeping the time front parallel to the Z-axis γ.sub.2=0. The analyzer 81 has zero field E.sub.Z in the Z-direction, thus, packets 85 arrive to deflector 82 at angle α.sub.2 and with γ.sub.2=0.

(71) Deflectors 82 and 83 are arranged for spatial focusing by 82 and defocusing by 83 with quadrupolar fields. The pair produces a telescopic packet compression and then expansion of ion packets Z-width by factor C: Z.sub.2/Z.sub.3C. Deflector 83 produces forward steering for angle ψ.sub.2 and deflector 84—reverse steering for angle ψ.sub.3. To return ion packet's 87 alignment with the Z-axis, i.e. T|Z=0 and γ.sub.2=0, the compression factor and the steering angles are chosen as: ψ.sub.2=−ψ.sub.3*C. Thus, here is introduced yet another novel method of compensated reversal of ion drift motion in MRTOF and MTTOF.

(72) After reverse drift in the analyzer 81, ions arrive to deflector 40 (assumed set static), change inclination angle from α.sub.2 to α.sub.1 and packets 89 have time front tilted for angle γ.sub.1. Deflector 88 steers ion packets for ψ=γ.sub.1 to bring time front parallel to the detector face. Matsuda plates in the deflector 88 may be adjusted to compensate for residual T|ZZ aberrations, accumulated due to analyzer imperfections or slight shift in the overall tuning.

(73) Back end reflection nearly doubles ion path and allow yet higher resolutions and/or yet more compact analyzers.

(74) As described in relation to FIG. 8, an improvement is provided by using telescopic focusing-defocusing deflectors for compensated rear-end reflection of ion packets in the drift direction for doubling the ion path. Optionally, similar deflection may be used for trapping ion packets for larger number of passes in so-called zoom mode.

(75) FIG. 9 shows an embodiment 90 comprising a novel ion guide 91 as described in a co-pending PCT application filed the same day as this application and entitled “ION GUIDE WITHIN PULSED CONVERTERS” (claiming priority from GB 1712618.6 filed 6 Aug. 2017), the entire contents of which are incorporated herein. Guide 91 comprises four rows of spatially alternated electrodes 93 and 94, each connected to own static potential DC1 and DC2, which are switched to different DC voltages U1 and U2 at ion pulsed ejection stage out of OA. Guide 91 forms a quadrupolar field 92 in XY-planes at each Z-section, where the field is spatially alternated at Z-step equal H. The overall field 92 distribution may be approximated by:
E=E.sub.0(x−y)*sin(2πz/H)

(76) Ion source 11, floated to bias U.sub.Z forms an ion beam 11 with about the same specific energy. Ion optics 12 forms a nearly parallel ion beam 13 with the beam diameter and divergence being optimized for ion transmission and spread within the guide 91, where the portion of beam 13 within the guide 91 is annotated as 63. Ions moving along the Z-axis, do sense time periodic quadrupolar field, and experience radial confinement. Contrary to RF fields, the effective well D(r) of the novel electrostatic confinement is mass independent:
D(r)=[E.sub.0.sup.2H.sup.2/2π.sup.2U.sub.Z]*(r.sup.2/R.sup.2)

(77) Electrostatic quadrupolar ion guide 91 may be used for improvement of the OA elongation at higher OA duty cycles, for a more accurate positioning of ion beam 63 within the OA, and for preventing the ion beam contact with OA surfaces.

(78) FIG. 9 shows an embodiment 96 of the present invention comprises two coaxial ion mirrors 97 with a two dimensional field being curved around a circular Z-axis; orthogonal accelerator 98 tilted by angle β to the Z-axis; within OA 98, an electrostatic quadrupolar ion guide 92; and at least one deflector 99 and/or 100. OA 98, guide 92, deflectors 99 and 100 may be either moderately elongated, straight, and tangentially aligned with the circular Z-axis, or they may be curved along the circular Z-axis. The ion guide 92 retains ion beam (13 at entrance) regardless of the OA and guide 92 curvature. The energy of ion beam 13 into tilted (by angle β to the Z-axis) OA is adjusted in combination steering angles of deflectors 99 and/or 100 to provide for mutual compensation of the time front tilt angle (T|Z=0) and for compensating the chromatic angular spread (α/K=0), as in FIG. 5. Coaxial mirrors may be forming either a time-of-flight mass spectrometer MRTOF MS or an electrostatic trap mass spectrometer E-Trap MS. Within E-Trap MS, the OA 98 may be displaced from the ion oscillation surface in the Y-direction and ion packets are then returned to the 2D symmetry plane of the analyzer field. Alternatively, OA may 98 be transparent for ions oscillating within the electrostatic tarp.

(79) Thus, improvements proposed for MPTOF MS with straight Z-axis are equally applicable to other isochronous electrostatic ion analyzers, such electrostatic traps and open traps and to other electrostatic analyzers with generally curved drift axis, such as cylindrical trap, exampled in WO2011086430, and or so-called elliptical TOF MS, exampled in US2011180702, as long as the analyzer field remains two-dimensional and the analyzer field has zero field component in the drift Z-direction.

(80) Annotations

(81) Coordinates and Times: x,y,z Cartesian coordinates; X, Y, Z—directions, denoted as: X for time-of-flight, Z for drift, Y for transverse; Z.sub.0—initial width of ion packets in the drift direction; ΔZ—full width of ion packet on the detector; D.sub.X and D.sub.Z—used height (e.g. cap-cap) and usable width of ion mirrors L—overall flight path N—number of ion reflections in mirror MRTOF or ion turns in sector MTTOF u-x—component of ion velocity; w-z—component of ion velocity; T—ion flight time through TOF MS from accelerator to the detector; ΔT—time spread of ion packet at the detector;

(82) Potentials and Fields: U—potentials or specific energy per charge; U.sub.Z and ΔU.sub.Z—specific energy of continuous ion beam and its spread; U.sub.X acceleration potential for ion packets in TOF direction; K and ΔK—ion energy in ion packets and its spread; δ=ΔK/K—relative energy spread of ion packets; E—x-component of accelerating field in the OA or in ion mirror around “turning” point; μ=m/z—ions specific mass or mass-to-charge ratio;

(83) Angles: α—inclination angle of ion trajectory relative to X-axis; Δα—angular divergence of ion packets; γ—tilt angle of time front in ion packets relative to Z-axis λ—tilt angle of “starting” equipotential to axis Z, where ions either start accelerating or are reflected within wedge fields of ion mirror θ—tilt angle of the entire ion mirror (usually, unintentional); φ—steering angle of ion trajectories or rays in various devices; ψ—steering angle in deflectors ε—spread in steering angle in conventional deflectors;

(84) Aberration Coefficients T|Z, T|ZZ, T|δ, T|δδ, etc;

(85) indexes are defined within the text

(86) Although the present invention has been describing with reference to preferred embodiments, it will be apparent to those skilled in the art that various modifications in form and detail may be made without departing from the scope of the present invention as set forth in the accompanying claims.