METHOD AND APPARATUS FOR SPATIAL COMPRESSION AND INCREASED MOBILITY RESOLUTION OF IONS

Abstract

Methods and apparatuses for ion peak compression and increasing resolution of ions are disclosed. Packets of ions are introduced into a device. A first electric field is applied for dispersing the ion packets temporally or spatially according to their mobilities. A second intermittent traveling wave is applied for regrouping or merging the dispersed ion packets into a lesser number of trapping regions with narrower peaks. The ions packets are compressed into the narrower peak regions by varying a duty cycle of the intermittent traveling wave.

Claims

1-4. (canceled)

5. An apparatus for ion peak compression comprising: a first region configured to receive ion packets and a first electric field for dispersing the ion packets temporally or spatially into a first number of trapping regions according to their mobilities; and second region configured to receive a second electric field forming an intermittent traveling wave, the intermittent traveling wave including a varying duty cycle therein for regrouping or merging the dispersed ion packets into a second number of trapping regions smaller than the first number.

6. The apparatus of claim 5, wherein the ion packets are regrouped or merged into narrower peak regions by variation of the duty cycle of the intermittent traveling wave.

7. The apparatus of claim 5, wherein the first electric field is a traveling wave.

8. (canceled)

9. The apparatus of claim 5, wherein the direction of ion motion in the first region is orthogonally aligned to the direction of ion motion in the second region.

10. The apparatus of claim 5, wherein the direction of ion motion in the first region is aligned in the same direction to the direction of ion motion in the second region.

11. The apparatus of claim 5, wherein the first region and the second region are aligned at any angle between 0°-359° relative to one another.

12. A method of ion peak compression comprising: introducing ion packets into a device having a first region and a second region; applying a first electric field to the first region for dispersing the ion packets temporally or spatially into a first number of trapping regions according to their mobilities; and applying a second electric field, different than the se to the second region to form an intermittent traveling wave including a varying duty cycle therein for regrouping or merging the dispersed ion packets into a second number of trapping regions smaller than the first number.

13. The method of claim 12, further comprising varying the duty cycle of the intermittent traveling wave to control the regrouping or merging of the ion packets.

14. The method of claim 12, wherein the first electric field is a traveling wave.

15. (canceled)

16. The method of claim 12, wherein the direction of ion motion in the first region is orthogonally aligned to the direction of ion motion in the second region.

17. The method of claim 12, wherein the direction of ion motion in the first region is aligned in the same direction as the direction of ion motion in the second region.

18. The method of claim 12, wherein the first region and the second region are aligned at any angle between 0°-359° relative to one another.

19. The method of claim 12, wherein the intermittent traveling wave merges ions from two or more trapping regions into one.

20. The method of claim 12, wherein the intermittent traveling wave merges ions from four or more trapping regions into one.

21. The method of claim 12, wherein the intermittent traveling wave is replaced with a non-intermittent traveling wave after a predetermined range of ion packets are regrouped or merged prior to detection.

22. A method of ion peak compression comprising: introducing ion packets into a device having a first region and a second region; applying a first electric field to the first region for dispersing the ion packets into a first number of trapping regions or bins; and applying a second electric field to the second region to form an intermittent traveling wave including a varying duty cycle therein for regrouping or merging the dispersed ion packets into a second number of trapping regions or bins; wherein the ion packets are temporally narrower than the dispersed ion packets.

23. The method of claim 22, further comprising varying the duty cycle of the intermittent traveling wave to control the regrouping or merging of the ion packets.

24. The method of claim 22, wherein the first electric field is a traveling wave field.

25. The method of claim 22, wherein the first region and the second region are aligned at any angle between 0°-359° relative to one another.

26. The method of claim 22, wherein the intermittent traveling wave merges ions from two or more trapping regions into one.

27. The method of claim 22, wherein the intermittent traveling wave merges ions from four or more trapping regions into one.

28. The method of claim 22, wherein the intermittent traveling wave is replaced with a non-intermittent traveling wave after a predetermined range of ion packets are regrouped or merged and prior to detection.

29. A method of increasing resolution of ions in ion mobility spectrometry (IMS) comprising: introducing ion packets into an IMS device having a first region, a second region, and a third region; separating the ions according to their mobilities by applying a traveling wave (TW) to the first region; compressing the ion packets by applying a second intermittent traveling wave including a varying duty cycle therein to the second region; and reversing the TW so that no separation occurs as the ion packets are moved back to a position prior to the separating step.

30. (canceled)

31. The method of claim 29, further comprising, after the step of reversing the TW, compressing the ion packets by applying a third intermittent traveling wave including a varying duty cycle therein to the third region.

32. The method of claim 29, wherein no ion separation occurs during the reversing step.

33. The method of claim 29, wherein the reversing step further comprises decreasing the speed or increasing the amplitude of the TW.

34. The method of claim 29, wherein the method effectively increases a path length for IMS separations without physically increasing the IMS device.

35. An apparatus for increasing resolution of ions in ion mobility spectrometry (IMS) comprising: a separation region configured to receive ion packets and a constant or variable electric field traveling in a first direction for separating the ions according to their mobilities; an ion compression region for narrowing or compressing the ion packets, the ion compression region configured to receive a second electric field including a varying duty cycle therein and travelling in a second direction, wherein the second electric field drives the ion packets in the second direction, and wherein the second direction is reverse of the first direction.

36. The apparatus of claim 35, wherein the IMS device is a SLIM IMS device.

37. An apparatus for increasing resolution of ions in ion mobility spectrometry (IMS) comprising: an IMS device in which packets of ions-or a continuous beam of ions is received, wherein the IMS device is configured to generate a constant or variable electric field for partially separating the received ions according to their mobilities; a first ion compressor configured to receive partially separated ions and to generate an electric field including a varying duty cycle therein for partially narrowing or compressing the ion packets after separation by the IMS device; a second ion compressor configured to receive partially separated ion packets after passage through the ion separator and the first ion compressor and to compress the partially separated ion packets so as to produce a final separation with much greater peak intensities and S/N.

38. The apparatus of claim 37 wherein the IMS device is a SLIM IMS device.

39. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a schematic diagram of an apparatus for ion peak compression including a normal traveling wave and a “stuttering” or intermittent traveling wave, in accordance with one embodiment of the present invention. Linear and other arrangements are also practical.

[0031] FIGS. 2A-2C shows the results of spatial peak compression using the apparatus of FIG. 1. FIG. 2A is the initial distribution of the ion peak spread, and FIGS. 2B and 2C involving application of the intermittent traveling wave having a narrowing effect on the distribution of the ions.

[0032] FIGS. 3A and 3B shows the spatial peak compression with no compression (FIG. 3A) and with 2× compression after imposition of the intermittent traveling wave (FIG. 3B).

[0033] FIG. 4A shows ion motion through a separation region orthogonally aligned to a compressor region of the apparatus, in accordance with one embodiment of the present invention.

[0034] FIG. 4B is a graph of frequency over time for a normal traveling wave applied to the separation region.

[0035] FIG. 4C is a graph of frequency over time for the intermittent traveling wave applied to the compressor region of the apparatus.

[0036] FIG. 5 is one variation of the separation and compressor regions, with the two regions aligned in the same or similar direction.

[0037] FIG. 6 is another variation of the separation and compressor regions, with the compressor region preceding the separation region.

[0038] FIG. 7 is another variation of the separation and compressor regions, which includes dynamically gating ions into either of the two regions.

[0039] FIGS. 8A, 8B, and 8C are variations of the separation and compressor regions, with any combination of relative size and relative position of the two regions.

[0040] FIGS. 9A and 9B show the arrival time distribution and intensities of a non-compressed ion packet (FIG. 9A) and a compressed ion packet (FIG. 9B).

[0041] FIGS. 10A and 10B show the arrival time distribution and intensities of a non-compressed continuous ion beam (FIG. 10A) and a compressed continuous ion beam (FIG. 10B).

[0042] FIG. 11 illustrates change in duty cycle when the voltage is applied to one of the compressor electrodes of FIG. 1 over time. Initially there is no compression, then the duty cycle changes to allow the compression, and then after a certain time the duty cycle is changed to a different duty cycle which may be similar or different to the initial duty cycle.

[0043] FIG. 12 is a simplified block diagram of an apparatus for increasing resolution in IMS, in accordance with one embodiment of the present invention.

[0044] FIGS. 13A-13E show the different stages, some optional, for increasing resolution in IMS, in accordance with one embodiment of the present invention, including ion separation (FIG. 13A), optional ion compression with reversing of the electric field direction (FIG. 13B), ions moving back to a position prior to the separation stage (FIG. 13C), optional ion compression (FIG. 13D), and repeating, if considered necessary, ion separation until a desired resolution is obtained (FIG. 13E).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The following description includes preferred embodiments of the present invention. It will be clear from this description of the invention that the invention is not limited to these illustrated embodiments but that the invention also includes a variety of modifications and embodiments thereto. Therefore the present description should be seen as illustrative and not limiting. While the invention is susceptible of various modifications and alternative constructions, it should be understood, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims.

[0046] Disclosed are methods, devices, and apparatuses for increasing signal-to-noise ratio in traveling wave ion mobility and other applications in which ions are separated based on their mobilities when an external force, e.g., a voltage field, is imposed on the ions, or separated by other means, including before ionization. The present invention includes the imposition of an intermittent or “stuttering” traveling wave that sorts, compresses, or regroups ions into fewer mobility ‘bins’, where bin is defined herein as one of the trapping regions between two waves. Signal intensity increases as a result of this binning of ions with the same or very similar mobilities. Any loss of resolution as a result of peak bunching can be regained by a short additional drift time after the sorting/regrouping/compressing step. This “rebinning” can simply be combining each two or more adjacent bins into one—i.e. giving a compression ratio of 2 or larger integer value, but other more complex rebinnings are feasible, and where the compression ratio varies or is programmed in a certain fashion, to e.g. apply greater compression as peaks get broader during a separation.

[0047] The present invention also discloses methods, devices, and apparatuses for increasing the resolution of traveling wave ion mobility separations by effectively increasing the path length for achieving IMS separations without physically increasing the IMS device or cell. Thus, the same path length may be utilized multiple times as desired to achieve high resolution.

[0048] FIG. 1 is a schematic diagram of an apparatus for ion mobility separations, in accordance with one embodiment of the present invention. As ions are introduced into the apparatus or device, a traveling wave electric field is applied for separating the ion packets temporally or spatially according to their mobilities. As such, the ions are dispersed or spread out over multiple traveling traps or bins. When this “normal” or continuously moving traveling wave is interfaced with a second region where a “stuttering” or intermittent traveling wave—where the moving traveling wave stops intermittently—the ions which are spread out over the multiple trapping bins of the normal traveling wave get repopulated into a lesser number of trapping regions with narrower peaks. Thus, the ions that were dispersed over a long path of many traveling traps are sorted into a different, narrower distribution involving a smaller number of bins.

[0049] The extent of such repopulation is dependent on the duty cycle of the intermittent traveling wave, i.e. the relative time for which the traveling wave stops and moves. After a chosen or predetermined range of ion mobility peaks are so re-populated, the intermittent traveling wave can be replaced with a normal traveling wave. This can occur prior to detection

[0050] A higher signal-to-noise ratio is achieved as a result of the regrouping of ions with similar mobilities into narrower mobility bins or traps. By interfacing the two electric fields—the normal traveling wave and the intermittent traveling wave—repeatedly, say, in a multiple pass type of separation, a larger number of cycles will be enabled. By appropriately choosing the frequency and order of such peak bunching, practically infinite peak resolution may be feasible.

[0051] FIGS. 2A-2C shows the results of spatial peak compression using the apparatus of FIG. 1. FIG. 2A is the initial distribution or peak of the ions spread over 48 electrodes in this example. The full width half maximum (FWHM) for the initial distribution was approximately 16 mm.

[0052] FIGS. 2B and 2C show the narrowing effect on the distribution of the ions when the intermittent traveling wave is applied. In FIG. 2B, ions in two bins are merged into one, and the FWHM is reduced to approximately 9 mm. FIG. 2C shows the effect of merging 4 bins of ions into one. The FWHM in FIG. 2C is decreased further to approximately 6.3 mm, leading to an increase in signal-to-noise ratio.

[0053] FIGS. 3A and 3B shows the spatial peak compression with no compression (FIG. 3A) and with 2× compression after imposition of the intermittent traveling wave (FIG. 3B), for two ions with different mobilities −K.sub.0=1.17 cm.sup.2/V.Math.s and K.sub.0=1.00 cm.sup.2/V.Math.s.

[0054] FIG. 4A shows ion motion through a separation region orthogonally aligned to a compressor region of the apparatus, in accordance with one embodiment of the present invention. The normal traveling wave region, referred to as the separation region, has a constant traveling wave frequency as shown in the graph of FIG. 4B and is, in this example, vertically oriented and orthogonal to the intermittent traveling wave region. The intermittent traveling wave region, referred to as the compressor region, has an intermittently non-zero traveling wave frequency as shown in the graph of FIG. 4C and is, in this example, horizontally oriented. The arrow indicates the ion trajectory path

[0055] FIG. 5 is one variation of the separation and compressor regions of FIG. 4A, with the two regions aligned in the same or similar direction. The effect on signal-to-noise and resolution when the regions are aligned in the same direction is similar to the orthogonal orientation of FIG. 4A.

[0056] FIG. 6 is another variation of the separation and compressor regions of FIG. 4A and FIG. 5, with the compressor region preceding the separation region. The configuration of FIG. 6 may be useful, for example, when ion trapping or separating prior to ion compression is not necessary; the compressor is used as an injection device for subsequent separation.

[0057] FIG. 7 is another variation of the separation and compressor regions for devices that include dynamically gating ions into either of the two regions, namely the separation and compressor regions.

[0058] FIGS. 8A, 8B, and 8C are variations of the separation and compressor regions, with any combination of relative size and relative position of the two regions. FIG. 8A shows a compressor region followed by a separation region, and then a repeat of the same pattern. FIGS. 8B and 8C show the regions configured with or in orbital motion.

[0059] FIGS. 9A and 9B show the arrival time distribution and intensities of a non-compressed ion packet (FIG. 9A) and a compressed ion packet (FIG. 9B).

[0060] FIGS. 10A and 10B show the arrival time distribution and intensities of a non-compressed continuous mode ion beam (FIG. 10A) and a compressed continuous mode ion beam (FIG. 10B).

[0061] FIG. 11 illustrates change in duty cycle when the voltage is applied to one of the compressor electrodes of FIG. 1 over time. Initially there is no compression, then the duty cycle changes to allow the compression, and then after a certain time the duty cycle is changed to a different duty cycle which may be similar or different to the initial duty cycle.

[0062] FIG. 12 is a simplified block diagram of an apparatus for increasing resolution in IMS, in accordance with one embodiment of the present invention. The apparatus includes an optional ion compressor coupled to an IMS separation device which is further coupled to another optional ion compressor.

[0063] FIGS. 13A-13E show the different stages, some optional, for increasing resolution in IMS, in accordance with one embodiment of the present invention. In FIG. 13A, pulsed ions are introduced into an IMS device where they are then separated according to their mobilities by applying a constant or variable electric field to the device. Next, in FIG. 13B, an optional ion compressor narrows or compresses the ions, and the electric field is reversed. Reversing the electric field causes the ions to move back to a position prior to the separation stage, as shown in FIG. 13C. Another optional ion compression stage is shown in FIG. 13D. No IMS separation occurs between FIGS. 13B-13D. The process may be repeated, as shown in FIG. 13E, until a desired resolution is obtained.

[0064] While a number of embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims, therefore, are intended to cover all such changes and modifications as they fall within the true spirit and scope of the invention.