Multi-reflecting time-of-flight mass spectrometers

Abstract

A multi-reflecting time of flight mass analyser is disclosed in which the ion flight path is maintained relatively small and the duty cycle is made relatively high. Spatial focusing of the ions in the dimension (z-dimension) in which the mirrors (36) are elongated can be eliminated whilst maintaining a reasonably high sensitivity and resolution.

Claims

1. A multi-reflecting time of flight mass analyser comprising: an ion accelerator; two ion mirrors arranged for reflecting ions in a first dimension (x-dimension) and being elongated in a second dimension (z-dimension); and an ion detector; wherein the ion accelerator is arranged and configured for accelerating ions into a first of the ion mirrors at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension) and wherein the ions are reflected at least four times by the ion mirrors; wherein the ions are not spatially focussed in the second dimension (z-dimension) as they travel from the ion accelerator to the detector; and wherein the mass analyser has a duty cycle of ≥5%, a resolution of ≥20,000, wherein the distance in the first dimension (x-dimension) between points of reflection in the two ion mirrors is ≤1000 mm; and wherein the mass analyser is configured such that the ions travel a distance in the second dimension (z-dimension) from the ion accelerator to the detector of ≤700 mm.

2. The mass analyser of claim 1, wherein each mirror has at least four electrodes arranged and configured such that the first order time of flight focussing of ions is substantially independent of the position of the ions in the plane orthogonal to the first dimension (y-z plane).

3. The mass analyser of claim 1, coupled to an ion source for supplying said ions to the ion accelerator, wherein the ion source is arranged such that said ion accelerator receives ions from the ion source travelling in the second dimension (z-dimension).

4. The mass analyser of claim 1, wherein the distance in the second dimension (z-dimension) from the ion accelerator to the detector is one of: ≤650 mm; ≤600 mm; ≤550 mm; ≤500 mm; ≤480 mm; ≤460 mm; ≤440 mm; ≤420 mm; <400 mm; ≤380 mm; ≤360 mm; ≤340 mm; ≤320 mm; ≤300 mm; ≤280 mm; ≤260 mm; ≤240 mm; ≤220 mm; or ≤200 mm.

5. The mass analyser of claim 1, wherein the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors is: ≤800 mm; ≤750 mm; ≤700 mm; ≤650 mm; ≤600 mm; ≤550 mm; ≤500 mm; ≤450 mm; or ≤400 mm.

6. The mass analyser of claim 1, wherein the ion accelerator, ion mirrors and detector are arranged and configured so that the ions are reflected at least x times by the ion mirrors as the ions travel from the ion accelerator to the detector; wherein x is 5-6.

7. The mass analyser of claim 1, wherein the ions travel ≤650 mm in the second dimension (z-dimension) from the ion accelerator to the detector; wherein the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors is ≤750 mm; and wherein the ions are reflected only between 4 and 15 times by the ion mirrors as the travel from the ion accelerator to the detector.

8. The mass analyser of claim 1, wherein ions travel in the second dimension (z-dimension) with an energy of: ≤140 eV; ≤120 eV; ≤100 eV; ≤90 eV; ≤80 eV; ≤70 eV; ≤60 eV; ≤50 eV; ≤40 eV; ≤30 eV; ≤20 eV; or ≤10 eV.

9. The mass analyser of claim 1, wherein a region substantially free of electric fields is arranged between the ion mirrors such that when the ions are reflected between the ion mirrors they travel through said region; and wherein the ions have a kinetic energy E, when between the ion mirrors and/or in said region substantially free of electric fields; wherein E is: ≥1 keV; ≥2 keV; ≥3 keV; ≥4 keV; ≥5 keV; ≥6 keV; ≥7 keV; ≥8 keV; ≥9 keV; ≥10 keV; ≥11 keV; ≥12 keV; ≥13 keV; ≥14 keV; or ≥15 keV.

10. The mass analyser of claim 1, coupled to an ion guide for guiding ions into the ion accelerator and a heater for heating said ion guide.

11. The mass analyser of claim 1, comprising a heater for heating electrodes of the ion accelerator.

12. The mass analyser of claim 1, coupled to a collimator for collimating the ions passing towards the ion accelerator, the collimator configured to collimate ions in the first dimension (x-dimension) and/or a dimension (y-dimension) orthogonal to both the first and second dimensions.

13. The mass analyser of claim 1, coupled to ion optics arranged and configured to expand the ion beam passing towards the ion accelerator in the first dimension (x-dimension) and/or a dimension (y-dimension) orthogonal to both the first and second dimensions.

14. The mass analyser of claim 1, coupled to an ion separator for separating ion spatially, or according to mass to charge ratio or ion mobility, in the second dimension (z-dimension) prior to the ions entering the ion accelerator.

15. A method of time of flight mass analysis comprising: providing a mass analyser as claimed in claim 1; and controlling the ion accelerator so as to accelerate ions into the first ion mirror at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension), wherein the ions are reflected at least four times by the ion mirrors, wherein the distance in the first dimension (x-dimension) between points of reflection in the two ion mirrors is ≤1000 mm, wherein the ions travel a distance in the second dimension (z-dimension) from the ion accelerator to the detector of ≤700 mm, and wherein the ions are not spatially focussed in the second dimension (z-dimension) as they travel from the ion accelerator to the detector; wherein the ions are detected by the detector and time of flight mass analysed with a duty cycle of ≥5% and a resolution of ≥20,000.

16. The mass analyser of claim 1, wherein substantially all of the ions that reach the detector have undergone the same number of ion mirror reflections.

17. A multi-reflecting time of flight mass analyser comprising: an ion accelerator; two ion mirrors arranged for reflecting ions in a first dimension (x-dimension) and being elongated in a second dimension (z-dimension); an ion detector; wherein the ion accelerator is arranged and configured for accelerating ions into a first of the ion mirrors at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension) and such that the ions are reflected at least four times by the ion mirrors; and wherein the ions are reflected so as to pass from one of the ion mirrors to the other of the ion mirrors n times, and wherein the ions are not spatially focussed in the second dimension (z-dimension) by periodic lenses during ≥60% of these n times; and wherein the mass analyser has a duty cycle of ≥5%, and a resolution of ≥20,000, wherein the distance in the first dimension (x-dimension) between points of reflection in the two ion mirrors is ≤800 mm, and wherein the mass analyser is configured such that the ions travel a distance in the second dimension (z-dimension) from the ion accelerator to the detector of ≤700 mm.

18. A method of time of flight mass analysis comprising: providing a mass analyser as claimed claim 17; and controlling the ion accelerator so as to accelerate ions into the first ion mirror at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension), wherein the ions are reflected at least four times by the ion mirrors, wherein the ions are reflected so as to pass from one of the ion mirrors to the other of the ion mirrors n times, and wherein the ions are not spatially focused in the second dimension (z-dimension) during ≥60% of these n times.

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 an MR-TOF-MS instrument according to the prior art;

(3) FIG. 2 shows another MR-TOF-MS instrument according to the prior art;

(4) FIG. 3 shows a schematic of an embodiment of the invention;

(5) FIG. 4 show a schematic of another embodiment of the invention;

(6) FIGS. 5A-5B show the resolution and duty cycle modelled for different sized MR-TOF-MS instruments, for ions having an energy in the field-free region between the mirrors of 9.2 keV;

(7) FIG. 6A-6B show data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for ions having an energy in the field-free region between the mirrors of 6 keV;

(8) FIG. 7 shows data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for ions having an energy in the field-free region between the mirrors of 3 keV, 4 keV and 5 keV;

(9) FIG. 8 shows data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for ions being reflected in the mirrors five times and having an energy in the field-free region between the mirrors of between 4-10 keV;

(10) FIG. 9 shows data for corresponding parameters to those shown in FIG. 8, except that the data is modelled for ions being reflected in the mirrors six times;

(11) FIG. 10 shows data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for achieving a duty cycle of around 10%; and

(12) FIG. 11 shows data for corresponding parameters to those shown in FIGS. 5A-5B, for instruments having a medium size.

DETAILED DESCRIPTION

(13) FIG. 1 shows the MR-TOF-MS instrument of SU 1725289. The instrument comprises two ion mirrors 10 separated in the x-dimension by a field-free region 12. Each ion mirror 10 comprises three pairs of electrodes 3-8 that are elongated in the z-dimension. An ion source 1 is arranged in the field-free region 12 at one end of the instrument (in the z-dimension) and an ion detector 2 is arranged at the other end of the instrument (in the z-dimension).

(14) In use, the ion source 1 accelerates ions into a first of the ion mirrors 10 at an inclination angle to the x-axis. The ions therefore have a velocity in the x-dimension and also a drift velocity in the z-dimension. The ions enter into the first ion mirror 10 and are reflected back towards the second of the ion mirrors 10. The ions then enter the second mirror and are reflected back to the first ion mirror. The first ion mirror then reflects the ions back to the second ion mirror. This continues and the ions are continually reflected between the two ion mirrors as they drift along the device in the z-dimension until the ions impact upon ion detector 2. The ions therefore follow a substantially sinusoidal mean trajectory within the x-z plane between the ion source 1 and the ion detector 2.

(15) FIG. 2 shows an MR-TOF-MS instrument disclosed in WO 2005/001878. This instrument is similar to that of SU 1725289 in that ions from an ion source 24 are reflected multiple times between two ion mirrors 21 as they drift in the z-dimension towards an ion detector 26. However, the instrument of WO 2005/001878 also comprises a set of periodic lenses 23 within the field-free region 27 between the ion mirrors 21. These lenses 23 are arranged such that the ion packets pass through them as they are reflected between the ion mirrors 21. Voltages are applied to the electrodes of the lenses 23 so as to spatially focus the ion packets in the z-dimension. This prevents the ion packets from diverging excessively in the z-dimension and overlapping with each other, and from becoming longer than the detector 26 in the z-dimension by the time they reach the detector 26.

(16) Embodiments of the present invention relate to an MR-TOF-MS instrument not having a set of lenses 23 within the field-free region between the ion mirrors.

(17) According to a first aspect the present invention provides a multi-reflecting time of flight mass analyser comprising:

(18) an ion accelerator;

(19) two ion mirrors arranged for reflecting ions in a first dimension (x-dimension) and being elongated in a second dimension (z-dimension); and

(20) an ion detector;

(21) wherein the ion accelerator is arranged and configured for accelerating ions into a first of the ion mirrors at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension);

(22) wherein the ions are not spatially focussed in the second dimension (z-dimension) as they travel from the ion accelerator to the detector; and

(23) wherein the mass analyser has a duty cycle of ≥5%, a resolution of ≥20,000, wherein the distance in the first dimension (x-dimension) between points of reflection in the two ion mirrors is ≤1000 mm; and wherein the mass analyser is configured such that the ions travel a distance in the second dimension (z-dimension) from the ion accelerator to the detector of ≤700 mm.

(24) Although the term “duty cycle” is well understood to the person skilled in the art, for the avoidance of doubt, duty cycle is the proportion of time that ions from a continuous ion source are accepted into a mass analyser. For orthogonal acceleration ion accelerators, such as those according to the embodiments of the invention, the duty cycle is given by:

(25) $\mathrm{DutyCycle}=\frac{D}{L}\sqrt{\frac{m/z}{{\left(m/z\right)}_{\mathrm{ma}x}}}$
where D is the length in the second dimension (z-dimension) of the ion packet when it is orthogonally accelerated by the ion accelerator (i.e. the length in second dimension of the orthogonal acceleration region of the ion accelerator); L is the distance, in the second dimension, from the centre of the orthogonal acceleration region of the ion accelerator to the centre of the detection region of the ion detector; (m/z) is the mass to charge ratio of an ion being analysed; and (m/z).sub.max is the maximum mass to charge ratio of interest desired to be analysed.

(26) It is therefore apparent that the duty cycle of the mass analyser is mass dependent. This is because ions of higher mass to charge ratio take longer to pass through and fill the extraction region of the ion accelerator. However, when describing a mass analyser, the skilled person considers the duty cycle of the mass analyser to be the duty cycle for the maximum mass to charge ratio of interest, i.e. the duty cycle when (m/z)=(m/z).sub.max in the equation above. Accordingly, when duty cycle is referred to herein, it refers to the ratio of D/L (as a percentage), which is a value defined purely by the geometric parameters D and L of the mass analyser. This may also be known as the “sampling efficiency”.

(27) Also, for the avoidance of doubt, the term resolution used herein has its normal meaning in the art, i.e. m/(A m) at FWHM, where m is mass to charge ratio.

(28) The following features are disclosed in relation to the first aspect of the invention.

(29) Each mirror may have at least four electrodes arranged and configured such that the first order time of flight focussing of ions is substantially independent of the position of the ions in the plane orthogonal to the first dimension (y-z plane).

(30) Therefore, the first order time of flight focussing of ions may be substantially independent of the position of the ions in both the second dimension (z-dimension) and a third dimension (y-dimension) that is orthogonal to the first and second dimensions (x and z dimensions).

(31) The mass analyser may comprise voltage sources for applying at least four different voltages to the four different electrodes in each ion mirror for reflecting ions and achieving said time of flight focussing.

(32) The ions are not spatially focussed in the second dimension (z-dimension) as they travel from the ion accelerator to the detector. As such, ion lenses are not provided between the ion mirrors for spatially focussing ions in the second dimension (z-dimension). Similarly, the ion mirrors are not configured to spatially focus the ions in the second dimension (z-dimension).

(33) The ion detector may be spaced from the ion accelerator in the second dimension (z-dimension). Alternatively, the ions may travel from the ion accelerator in a first direction in the second dimension (z-dimension) and may then be reflected by a reflecting electrode so as to travel in a second, opposite direction in the second dimension (z-dimension) to the detector. One or more further reflection electrodes may be provided to cause one or more further z-dimension reflections, with the detector positioned appropriately to detect the ions after these z-dimension reflections.

(34) Embodiments of the invention provide a spectrometer comprising the mass analyser described herein.

(35) The spectrometer may comprise an ion source for supplying said ions to the ion accelerator, wherein the ion source is arranged such that said ion accelerator receives ions from the ion source travelling in the second dimension (z-dimension).

(36) This arrangement provides the mass analyser with a relatively high duty cycle. As described above, the duty cycle is the ratio of length in second dimension (z-dimension) of the ion packet, when it is accelerated by the ion accelerator, to the distance from the centre of the ion accelerator to the centre of the detector. The embodiments of the invention relate to a relatively small mass analyser and therefore it is desired for the ion accelerator to pulse out a relatively elongated ion packet (in the second, z-dimension) in order to achieve a relatively high duty cycle. The relatively elongated ion packet in the second dimension (z-dimension) is facilitated by providing the ions to the ion accelerator travelling in the second dimension (z-dimension). This is contrary to conventional multi-reflecting TOF spectrometers, in which the ion packet is desired to be maintained very small in the second dimension (z-dimension) so that a high number of ion mirror reflections can be performed before the ion packets diverge in the second dimension (z-dimension) to the extent that they overlap in the second dimension (z-dimension). In order to achieve this, such conventional instruments provide the ions to the ion accelerator in a direction corresponding to a third dimension that is perpendicular to the first and second dimensions described herein. Consequently, such conventional instruments suffer from a relatively low duty cycle.

(37) The ion source may be a continuous ion source for substantially continually generating ions, or may be a pulsed ion source.

(38) The mass analyser may have a duty cycle of ≥10%.

(39) As described above, the mass analyser has a duty cycle of ≥5%. It is contemplated that the mass analyser may have a duty cycle of: ≥6%, ≥7%, ≥8%, ≥9%, ≥10%, ≥11%, ≥12%, ≥13%, ≥14%, ≥15%, ≥16%, ≥17%, ≥18%, ≥19%, ≥20%, ≥25%, ≥30%. Additionally, or alternatively, it is contemplated that the mass analyser may have a duty cycle of: ≤30%, ≤25%, ≤20%, ≤19%, ≤18%, ≤17%, ≤16%, ≤15%, ≤14%, ≤13%, ≤12%, ≤11%, ≤10%, ≤9%, ≤8%, ≤7%, or ≤6%.

(40) Any one of these listed upper end points of the duty cycle may be combined with any one of the lower end points of the duty cycle listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the duty cycle may be combined with any one or any combination of ranges described in relation to: resolution; and/or distance in the second dimension (z-dimension) from the ion accelerator to the detector; and/or distance in the first direction (x-dimension) between points of reflection in the two ion mirrors; and/or number of reflections; and/or ion energy in the second dimension; and/or electric field strength; and/or kinetic energy.

(41) The mass analyser may be configured such that the ions travel a first distance in the second dimension (z-dimension) from the ion accelerator to the detector, wherein the ion accelerator is arranged and configured to pulse packets of ions having an initial length in the second dimension (z-dimension), and wherein the first distance and initial length are such that the spectrometer has a duty cycle of ≥5%.

(42) However, the first distance and initial length may be arranged such that the duty cycle is any of the other ranges of duty cycle disclosed herein.

(43) The mass analyser may have a resolution of ≥30,000.

(44) However, it is contemplated that the mass analyser may have a resolution of: ≥22000, ≥24000, ≥26000, ≥28000, ≥30000, ≥35000, ≥40000, ≥45000, ≥50000, ≥60000, ≥70000, ≥80000, ≥90000, or ≥100000. Additionally, or alternatively, it is contemplated that the mass analyser may have a resolution of: ≤100000, 5 90000, ≤80000, ≤70000, ≤60000, ≤50000, ≤45000, ≤40000, ≤35000, ≤30000, ≤28000, ≤26000, ≤24000, or ≤22000.

(45) Any one of these listed upper end points of the resolution may be combined with any one of the lower end points of the resolution listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the resolution may be combined with any one or any combination of ranges described in relation to: duty cycle; and/or distance in the second dimension (z-dimension) from the ion accelerator to the detector; and/or distance in the first direction (x-dimension) between points of reflection in the two ion mirrors; and/or number of reflections; and/or ion energy in the second dimension; and/or electric field strength; and/or kinetic energy.

(46) The distance in the second dimension (z-dimension) from the ion accelerator to the detector may be one of: ≤650 mm; ≤600 mm; ≤550 mm; ≤500 mm; ≤480 mm; ≤460 mm; ≤440 mm; ≤420 mm; ≤400 mm; ≤380 mm; ≤360 mm; ≤340 mm; ≤320 mm; ≤300 mm; ≤280 mm; ≤260 mm; ≤240 mm; ≤220 mm; or ≤200 mm; and/or the first distance in the second dimension (z-dimension) from the ion accelerator to the detector may be one of: ≥100 mm; ≥120 mm; ≥140 mm; ≥160 mm; ≥180 mm; ≥200 mm; ≥220 mm; ≥240 mm; ≥260 mm; ≥280 mm; ≥300 mm; ≥320 mm; ≥340 mm; ≥360 mm; ≥380 mm; or ≥400 mm. Any one of these listed upper end points of the first distance in the second dimension (z-dimension) may be combined with any one of the lower end points of the first distance in the second dimension (z-dimension) that are listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the distance from the ion accelerator to the detector may be combined with any one or any combination of ranges described in relation to: duty cycle; and/or resolution; and/or distance in the first direction (x-dimension) between points of reflection in the two ion mirrors; and/or number of reflections; and/or ion energy in the second dimension; and/or electric field strength; and/or kinetic energy.

(47) The distance in the first direction (x-dimension) between points of reflection in the two ion mirrors may be: ≤950 mm; ≤900 mm; ≤850 mm; ≤800 mm; ≤750 mm; ≤700 mm; ≤650 mm; ≤600 mm; ≤550 mm; ≤500 mm; ≤450 mm; or ≤400 mm; and/or the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors may be: ≥350 mm; ≥360 mm; ≥380 mm; ≥400 mm; ≥450 mm; ≥500 mm; ≥550 mm; ≥600 mm; ≥650 mm; ≥700 mm; ≥750 mm; ≥800 mm; ≥850 mm; or ≥900 mm.

(48) Any one of these listed upper end points of the distance between points of reflection in the two ion mirrors may be combined with any one of the lower end points of the distance between points of reflection in the two ion mirrors that are listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the distance between the points of reflection may be combined with any one or any combination of ranges described in relation to: duty cycle; and/or resolution; and/or distance in the second dimension (z-dimension) from the ion accelerator to the detector; and/or number of reflections; and/or ion energy in the second dimension; and/or electric field strength; and/or kinetic energy.

(49) The ion accelerator, ion mirrors and detector may be arranged and configured so that the ions are reflected at least x times by the ion mirrors as the travel from the ion accelerator to the detector; wherein x is: ≥2, ≥3, ≥4, ≥5, ≥6, ≥7, ≥8, ≥9, ≥10, ≥11, ≥12, ≥13, ≥14, or ≥15; and/or wherein x is: ≤15; ≤14; ≤13; ≤12; ≤11; ≤10; ≤9; ≤8; ≤7; ≤6; ≤5; ≤4; ≤3; or ≤2; and/or wherein x is 3-10; wherein x is 4-9; wherein x is 5-10; wherein x is 3-6; wherein x is 4-5; or; wherein x is 5-6.

(50) Any one of these listed upper end points of the number of reflections may be combined with any one of the lower end points of the number of reflections that are listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the number of reflections may be combined with any one or any combination of ranges described in relation to: duty cycle; and/or resolution; and/or distance in the second dimension (z-dimension) from the ion accelerator to the detector; and/or distance in the first direction (x-dimension) between points of reflection in the two ion mirrors; and/or ion energy in the second dimension; and/or electric field strength; and/or kinetic energy.

(51) The ions may travel between 100 mm and 450 mm in the second dimension (z-dimension) from the ion accelerator to the detector; wherein the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors may be between 350 and 950 mm; and wherein the ions may be reflected between 2 and 15 times by the ion mirrors as the travel from the ion accelerator to the detector.

(52) Alternatively, the ions may travel between 150 mm and 400 mm in the second dimension (z-dimension) from the ion accelerator to the detector; wherein the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors may be between 400 and 900 mm; and wherein the ions may be reflected between 3 and 10 times by the ion mirrors as the travel from the ion accelerator to the detector. Alternatively, the ions may travel between 150 mm and 350 mm in the second dimension (z-dimension). Alternatively, or additionally, the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors may be between 400 and 600 mm.

(53) It is contemplated that the ions may travel between 100 mm and 400 mm in the second dimension (z-dimension) from the ion accelerator to the detector; wherein the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors may be between 300 and 700 mm; and wherein the ions may be reflected between 3 and 6 times by the ion mirrors as the travel from the ion accelerator to the detector. Alternatively, the ions may travel between 150 mm and 350 mm in the second dimension (z-dimension) from the ion accelerator to the detector. Alternatively, or additionally, the distance in the first direction (x-dimension) between points of reflection in the two ion mirrors is between 400 and 600 mm. Additionally, or instead of either one of both of these parameters, the ions may be reflected between 4 and 5 times, or between 5 and 6 times, by the ion mirrors as the travel from the ion accelerator to the detector.

(54) The spectrometer may be configured to cause the ions to travel in the second dimension (z-dimension) with an energy of: ≤140 eV; ≤120 eV; ≤100 eV; ≤90 eV; ≤80 eV; ≤70 eV; ≤60 eV; ≤50 eV; ≤40 eV; ≤30 eV; ≤20 eV; or ≤10 eV; and/or the spectrometer may be configured to cause the ions to travel in the second dimension (z-dimension) with an energy of: ≥120 eV; ≥100 eV; ≥90 eV; ≥80 eV; ≥70 eV; ≥60 eV; ≥50 eV; ≥40 eV; ≥30 eV; ≥20 eV; or ≥10 eV. The spectrometer may be configured to cause the ions to travel in the second dimension (z-dimension) with an energy between: 15-70 eV; 10-65 eV; 10-60 eV; 20-100 eV; 25-100 eV; 20-90 eV; 40-60 eV; 30-50 eV; 20-30 eV; 20-45 eV; 25-40 eV; 15-40 eV; 10-45 eV; or 10-25 eV.

(55) Any one of these listed upper end points of the energy may be combined with any one of the lower end points of the energy that are listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the energy in the second dimension may be combined with any one or any combination of ranges described in relation to: duty cycle; and/or resolution; and/or distance in the second dimension (z-dimension) from the ion accelerator to the detector; and/or distance in the first direction (x-dimension) between points of reflection in the two ion mirrors; and/or number of reflections; and/or electric field strength; and/or kinetic energy.

(56) The ranges of resolution, duty cycle and size of the mass analyser (i.e. the distance in the first direction between points of reflection in the two ion mirrors, and the distance travelled between the ion accelerator and detector in the second dimension) described herein are for practical values of Time of Flight energies and mirror voltages.

(57) The ion accelerator may be configured to generate an electric field of y V/mm for accelerating the ions; wherein y is: ≥700; ≥650; ≥600; ≥580; ≥560; ≥540; ≥520; ≥500; ≥480; ≥460; ≥440; ≥420; ≥400; ≥380; ≥360; ≥340; ≥320; ≥300; ≥280; ≥260; ≥240; 220; or ≥200; and/or wherein y is: ≤700; ≤650; ≤600; ≤580; ≤560; ≤540; ≤520; ≤500; ≤480; ≤460; ≤440; ≤420; ≤400; ≤380; ≤360; ≤340; ≤320; ≤300; ≤280; ≤260; ≤240; ≤220; or ≤200.

(58) Any one of these listed upper end points of the electric field may be combined with any one of the lower end points of the electric field that are listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the electric field strength may be combined with any one or any combination of ranges described in relation to: duty cycle; and/or resolution; and/or distance in the second dimension (z-dimension) from the ion accelerator to the detector; and/or distance in the first direction (x-dimension) between points of reflection in the two ion mirrors; and/or number of reflections; and/or ion energy in the second dimension; and/or kinetic energy.

(59) A region substantially free of electric fields may be arranged between the ion mirrors such that when the ions are reflected between the ion mirrors they travel through said region.

(60) The ions may have a kinetic energy E, when between the ion mirrors and/or in said region substantially free of electric fields; wherein E is: ≥1 keV; ≥2 keV; ≥3 keV; ≥4 keV; ≥5 keV; ≥6 keV; ≥7 keV; ≥8 keV; ≥9 keV; ≥10 keV; ≥11 keV; ≥12 keV; ≥13 keV; ≥14 keV; or ≥15 keV; and/or wherein E is ≤15 keV; ≤14 keV; ≤13 keV; ≤12 keV; ≤11 keV; ≤10 keV; ≤9 keV; ≤8 keV; ≤7 keV; ≤6 keV; or ≤5 keV; and/or between 5 and 10 keV.

(61) Any one of these listed upper end points of the kinetic energy may be combined with any one of the lower end points of the kinetic energy that are listed above (where the upper end point is higher than the lower end point. Any one or combination of these end points may also be combined with any one of the ranges (or combination or ranges) described in relation to any one, or any combination, of the other parameters discussed herein. For example, any one or combination of the end points or ranges described in relation to the kinetic energy may be combined with any one or any combination of ranges described in relation to: duty cycle; and/or resolution; and/or distance in the second dimension (z-dimension) from the ion accelerator to the detector; and/or distance in the first direction (x-dimension) between points of reflection in the two ion mirrors; and/or number of reflections; and/or ion energy in the second dimension; and/or electric field strength.

(62) The spectrometer may comprise an ion guide for guiding ions into the ion accelerator and a heater 39 for heating said ion guide.

(63) The spectrometer may comprise a heater for heating electrodes of the ion accelerator.

(64) The spectrometer may comprise a heater arranged and configured to heat the ion guide and/or accelerator to a temperature of: ≥100° C., ≥110° C., ≥120° C., ≥130° C., ≥140° C., or ≥150° C. Heating the various components as described herein may assist in reducing interface charging.

(65) The ion accelerator disclosed herein may be a gridless ion accelerator. If the ion accelerator is heated, then a gridless ion accelerator does not suffer from sagging of the grid that would otherwise be caused by the heating.

(66) The spectrometer may comprise a collimator for collimating the ions passing towards the ion accelerator, the collimator configured to collimate ions in the first dimension (x-dimension) and/or a dimension (y-dimension) orthogonal to both the first and second dimensions.

(67) The spectrometer may comprise ion optics 33 arranged and configured to expand the ion beam passing towards the ion accelerator in the first dimension (x-dimension) and/or a dimension (y-dimension) orthogonal to both the first and second dimensions.

(68) The spectrometer may comprise an ion separator for separating ion spatially, or according to mass to chare ratio or ion mobility, in the second dimension (z-dimension) prior to the ions entering the ion accelerator.

(69) From a second aspect the present invention provides a multi-reflecting time of flight mass analyser comprising:

(70) an ion accelerator;

(71) two ion mirrors arranged for reflecting ions in a first dimension (x-dimension) and being elongated in a second dimension (z-dimension); and

(72) an ion detector;

(73) wherein the ion accelerator is arranged and configured for accelerating ions into a first of the ion mirrors at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension); and

(74) wherein the ions are reflected so as to pass from one of the ion mirrors to the other of the ion mirrors n times, and wherein the ions are not spatially focussed in the second dimension (z-dimension) during ≥60% of these n times.

(75) The mass analyser according to said second aspect may have any of the features disclosed herein in relation to said first aspect, except wherein the mass analyser may or may not be limited to the ions not being spatially focussed in the second dimension (z-dimension) as they travel from the ion accelerator to the detector (e.g. during the entire flight from the ion accelerator to the detector), as described in relation to the first aspect. It is contemplated that there may be some spatial focussed in the second dimension (z-dimension) between some of the mirror reflections. Therefore, according to the second aspect of the invention, the ions are not spatially focussed in the second dimension (z-dimension) during ≥60% of said n times. Optionally, the ions are not spatially focussed in the second dimension (z-dimension) during ≥65%, ≥70%, ≥75%, ≥80%, ≥85%, ≥90%, ≥ or 95% of said n times.

(76) The mass analyser according to said second aspect may have any of the features disclosed herein in relation to said first aspect, except wherein the mass analyser may or may not be limited to the duty cycle being ≥5%, as described in relation to the first aspect.

(77) The mass analyser according to said second aspect may have any of the features disclosed herein in relation to said first aspect, except wherein the mass analyser may or may not be limited to the resolution being ≥20,000, as described in relation to the first aspect.

(78) The mass analyser according to said second aspect may have any of the features disclosed herein in relation to said first aspect, except wherein the mass analyser may or may not be limited to said distance in the first dimension (x-dimension) between points of reflection in the two ion mirrors being ≤1000 mm, as described in relation to the first aspect

(79) The mass analyser according to said second aspect may have any of the features disclosed herein in relation to said first aspect, except wherein the mass analyser may or may not be limited to the distance the ions travel in the second dimension (z-dimension) from the ion accelerator to the detector being ≤700 mm, as described in relation to the first aspect.

(80) The first aspect of the invention also provides a method of time of flight mass analysis comprising:

(81) providing a mass analyser as described in relation to said first aspect of the invention; and

(82) controlling the ion accelerator so as to accelerate ions into the first ion mirror at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension), wherein the distance in the first dimension (x-dimension) between points of reflection in the two ion mirrors is ≤1000 mm, wherein the ions travel a distance in the second dimension (z-dimension) from the ion accelerator to the detector of ≤700 mm, and wherein the ions are not spatially focussed in the second dimension (z-dimension) as they travel from the ion accelerator to the detector;

(83) wherein the ions are detected by the detector and time of flight mass analysed with a duty cycle of ≥5% and a resolution of ≥20,000.

(84) The second aspect of the invention also provides a method of time of flight mass analysis comprising:

(85) providing a mass analyser as described in relation to said second aspect of the invention; and

(86) controlling the ion accelerator so as to accelerate ions into the first ion mirror at an angle to the first dimension such that the ions are repeatedly reflected between the ion mirrors in the first dimension (x-dimension) as they travel in the second dimension (z-dimension), wherein the ions are reflected so as to pass from one of the ion mirrors to the other of the ion mirrors n times, and wherein the ions are not spatially focussed in the second dimension (z-dimension) during ≥60% of these n times.

(87) Specific embodiments of the invention will now be described with reference to the drawings in order to assist in the understanding of the invention.

(88) FIG. 3 shows a schematic of an embodiment of the present invention. The spectrometer comprises an ion entrance 30 for receiving an ion beam 32 along an entrance axis, an ion accelerator 34 for orthogonally accelerating the received ions in a pulsed manner, a pair of ion mirrors 36 for reflecting the ions, and an ion detector 38 for detecting the ions. Each ion mirror 36 comprises a plurality of electrodes (arranged along the x-dimension) so that different voltages may be applied to the electrodes to cause the ions to be reflected. The electrodes are elongated in the Z-dimension, which allows the ions to be reflected multiple times by each mirror, as will be described in more detail below. Each ion mirror may form a two-dimensional electrostatic field in the X-Y plane. The drift space 40 arranged between the ion mirrors 36 may be substantially electric field-free such that when the ions are reflected and travel in the space between the ion mirrors they travel through a substantially field-free region.

(89) In use, ions are supplied to the ion entrance 30, either as a continuous ion beam or an intermittent or pulsed manner. The ions are desirably transmitted into the ion entrance along an axis aligned with the z-dimension. This allows the duty cycle of the instrument to remain high. However, it is contemplated that the ions could be introduced along an entrance axis that is aligned with the y-dimension. The ions pass from the ion entrance to the ion accelerator 34, which pulses the ions (e.g. periodically) in the x-dimension such that packets of ions 31 travel in the x-dimension towards and into a first of the ion mirrors 36. The ions retain a component of velocity in the z-dimension from that which they had when passing into the ion accelerator 34, or a provided with such a component of velocity in the z-dimension (e.g. if the ion entered the ion accelerator along the y-dimension). As such, ions are injected into the time of flight region 40 of the instrument at a small angle of inclination to the x-dimension, with a major velocity component in the x-dimension towards the ion mirror 36 and a minor velocity component in the z-dimension towards the detector 38.

(90) The ions pass into a first of the ion mirrors and are reflected back towards the second of the ion mirrors. The ions pass through the field-free region 40 between the mirrors 38 as they travel towards the second ion mirror and they separate according to their mass to charge ratios in the known manner that occurs in time of flight mass analysers. The ions then enter the second mirror and are reflected back to the first ion mirror, again passing through the field-free region between the mirrors as they travel towards the first ion mirror. The first ion mirror then reflects the ions back to the second ion mirror. This continues and the ions are continually reflected between the two ion mirrors as they drift along the device in the z-dimension until the ions impact upon ion detector. The ions therefore follow a substantially sinusoidal mean trajectory within the x-z plane between the ion source and the ion detector. Although four ion reflections are shown in FIG. 3, other numbers of ion reflections are contemplated, as described elsewhere herein.

(91) The time that has elapsed between a given ion being pulsed from the ion accelerator to the time that the ion is detected may be determined and used, along with the knowledge of the flight path length, to calculate the mass to charge ratio of that ion.

(92) As described above, when duty cycle is referred to herein it refers to the ratio of D/L (as a percentage), where D is the length in the z-dimension of the ion packet 31 when it is orthogonally accelerated by the ion accelerator 34 (i.e. the length in z-dimension of the orthogonal acceleration region of the ion accelerator 31), and L is the distance in the z-dimension from the centre of the orthogonal acceleration region of the ion accelerator 34 to the centre of the detection region of the ion detector 38.

(93) No focusing of the ions is provided in the z-dimension between the ion mirrors, e.g. there are no periodic lenses focussing the ions in the z-dimension. As such, each packet of ions expands in the z-dimension as it travels from the ion accelerator to the detector. MR-TOF-MS instruments have conventionally sought to obtain a very high resolution and hence require a high number of reflections between the ion mirrors. Therefore, conventionally it has been considered necessary to provide z-dimension focussing between the ion mirrors to prevent the width of the ion packet diverging to the extent that it becomes larger than the detector width by the time it has completed the high number of mirror reflections and reached the detector. This was considered necessary to maintain an acceptable sensitivity of the instrument. Also, if the ion packets diverge too much in the z-dimension, then some ions may reach the detector having only been reflected a first number of times, whereas other ions may reach the detector having been reflected a larger number of times. Ions may therefore have significantly different flight path lengths through the field-free region on the way to the detector, which is undesirable in time of flight mass analysers. However, the inventors of the present invention have realised that if the ion flight path within the instrument is maintained relatively small and the duty cycle (i.e. D/L) made relatively high, then the z-dimension focussing can be eliminated.

(94) Therefore, the distance S between the points of reflection in the two ion mirrors is maintained relatively small, and the distance W that the ions travel in the z-dimension from the ion accelerator to the detector is maintained relatively small.

(95) It is contemplated that collimators may be provided to collimate the ions packets in the z-dimension as they travel from the ion accelerator to the detector. This ensures that all ions perform the same number of reflections in the ion mirrors between the ion accelerator and detector (i.e. prevents aliasing at the detector).

(96) Optionally, each ion mirror may have at least four electrodes to which four different (non-grounded) voltages are applied. Each ion mirror may comprise additional electrodes, which may be grounded or maintained at the same voltages as other electrodes in the mirror. Each mirror optionally has at least four electrodes arranged and configured such that the first order time of flight focussing of ions is substantially independent of the position of the ions in the y-z plane, i.e. independent of the position of the ions in both the y-dimension and z-dimension (to the first order approximation). FIG. 3 shows exemplary voltages that may be applied to the electrodes of one of the ion mirrors. Although not illustrated, the same voltages may be applied to the other ion mirror in a symmetrical manner. For example, the entrance electrode of each ion mirror is maintained at a drift voltage (e.g. −5 kV), thereby maintaining a field-free region between the ion mirrors. An electrode further into the ion mirror may be maintained at a lower (or higher, depending on ion polarity) voltage (e.g. −10 kV). An electrode further into the ion mirror may be maintained at the drift voltage (e.g. −5 kV). An electrode further into the ion mirror may be maintained at a lower (or higher) voltage (e.g. −10 kV). One or more further electrodes into the ion mirror may be maintained at one or more higher, optionally progressively higher, voltages (e.g. 11 kV and +2 kV) so as to reflect the ions back out of the mirror.

(97) The ion entrance may receive ions from an ion guide 33 that may, for example, collimate the ions in the y-dimension and/or x-dimension, e.g. using a slit collimator. The ion guide may be heated, e.g. to ≥100° C., ≥110° C., ≥120° C., ≥130° C., ≥140° C., or ≥150° C.

(98) It is contemplated that the ion beam may be expanded in the y-dimension and/or x-dimension prior to entering the ion accelerator 34. Alternatively, or additionally, the ions may be separated in the z-dimension prior to entering the ion accelerator 34.

(99) The electrodes of the ion accelerator 34 may be heated, e.g. to ≥100° C., ≥110° C., ≥120° C., ≥130° C., ≥140° C., or ≥150° C. Alternatively, or additionally, a gridless ion accelerator be used. If the ion accelerator is heated, then a gridless ion accelerator does not suffer from sagging of the grid that would otherwise be caused by the heating.

(100) Heating the various components as described herein may assist in reducing interface charging.

(101) Although the ion accelerator 34 has been described as receiving a beam of ions, it is contemplated that the ion accelerator may alternatively comprise a pulsed ion source.

(102) FIG. 4 shows another embodiment of the present invention. This embodiment is substantially the same as that shown in FIG. 3, except that the detector 38 is located on the same side of the instrument (in the z-dimension) as the ion accelerator 34, and the instrument comprises a reflection electrode 42 for reflecting the ions back in the z-dimension towards the detector 38. In use, the ions pass through the instrument in the same way as in FIG. 3 and are reflected multiple times between the ion mirrors 36 as they pass in a first direction in the z-dimension. After a number of reflections, the ions pass to the reflection electrode 42, which may be arranged between the ion mirrors. The reflection electrode 42 reflects the ions back in the z-dimension such that they drift in a second direction opposite to the first direction. As the ions drift in the second direction they continue to be reflected between the ion mirrors 36 until they impact upon the ion detector 38. This embodiment allows more reflections to occur in a given physical space, as compared to the embodiment of FIG. 3. It is contemplated that the ions could be reflected in the z-dimension one or more further times and the detector located appropriately to receive ions after these one or more further z-reflections.

(103) FIGS. 5A-5B show the resolution and duty cycle modelled for different sized MR-TOF-MS instruments (i.e. having different W and S distances) and having no z-dimension focussing. The data is modelled for ions having an energy in the field-free region between the mirrors of 9.2 keV.

(104) FIG. 6A-6B show data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for ions having an energy in the field-free region between the mirrors of 6 keV.

(105) FIG. 7 shows data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for ions having an energy in the field-free region between the mirrors of 3 keV, 4 keV and 5 keV.

(106) FIG. 8 shows data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for ions being reflected in the mirrors five times and having an energy in the field-free region between the mirrors of between 4-10 keV.

(107) FIG. 9 shows data for corresponding parameters to those shown in FIG. 8, except that the data is modelled for ions being reflected in the mirrors six times.

(108) FIG. 10 shows data for corresponding parameters to those shown in FIGS. 5A-5B, except that the data is modelled for achieving a duty cycle of around 10%.

(109) FIG. 11 shows data for corresponding parameters to those shown in FIGS. 5A-5B, for instruments having a medium size.

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