DYNAMIC ION FILTER FOR REDUCING HIGHLY ABUNDANT IONS

Abstract

The present disclosure relates to a device for filtering at least one selected ion from an ion beam includes a unit for creating an electric field for accelerating the ions of the ion beam along a flight path of predefinable length, and a controllable ion optical system, which delimits the flight path in one direction, and which is used to deflect the selected ion from a flight path of the ion beam. The device is further designed to control the ion optical system subject to a flight time of the selected ion along the flight path. The present disclosure also relates to a mass spectrometer having a device according to the present disclosure, and to a method for filtering at least one selected ion from an ion beam.

Claims

1-15. (canceled)

16. A device for filtering at least one selected ion from an ion beam, the device comprising: a unit configured to create an electric field capable of accelerating ions of the ion beam along a flight path of predefinable length; and a controllable ion optical system configured to delimit the flight path in one direction and to deflect the at least one selected ion from a flight path of the ion beam, wherein the device is configured to control the ion optical system based on a flight time of the at least one selected ion along the flight path.

17. The device of claim 16, further comprising a detector unit configured to detect and/or determine the masses, charges, mass-to-charge ratios and/or intensities of the ions comprising the ion beam.

18. The device of claim 16, further comprising a computing unit configured to determine the flight times, masses, charges, mass-to-charge ratios and/or intensities of the ions comprising the ion beam.

19. The device of claim 16, further comprising a control unit configured to control the ion optical system based on a flight time of the at least one selected ion along the flight path.

20. The device of claim 16, wherein the ion optical system comprises at least one Bradbury-Nielson gate.

21. The device of claim 16, comprising an ion trap configured to accumulate or deplete at least one predefinable ion or a plurality of predefinable ions within at least one predefinable range.

22. The device of claim 21, wherein the ion trap is an orbitrap or a C-trap.

23. The device of claim 16, further comprising a second ion optical system configured to direct the ion beam at least at a predefinable point in time such that the ion beam passes through the device.

24. A mass spectrometer comprising the device of claim 16.

25. A method for filtering at least one selected ion from an ion beam, the method comprising: accelerating ions comprising the ion beam along a flight path of predefinable length; and deflecting the at least one selected ion from the flight path of the ion beam based on a flight time of the at least one selected ion along the flight path.

26. The method of claim 25, wherein the at least one selected ion is determined based on at least one mass spectrum of the ion beam and/or based on the masses, charges, mass-to-charge ratios and/or intensities of the ions comprising the ion beam.

27. The method of claim 25, wherein at least one ion whose intensity exceeds a predefinable limit value is selected.

28. The method of claim 25, wherein at least one predefinable ion or predefinable ions within a predefinable range is/are accumulated or depleted.

29. The method of claim 28, wherein an accumulation factor or a depletion factor is determined.

30. The method of claim 28, wherein the at least one predefinable ion or the predefinable ions within the predefinable range is/are accumulated or depleted with a predefinable accumulation factor or a predefinable depletion factor.

Description

[0050] The present invention is now explained in greater detail with reference to the following figures. Identical elements in the figures are provided with the same reference signs. The following are shown:

[0051] FIG. 1 a first schematic embodiment of a device according to the invention;

[0052] FIG. 2 a second embodiment of a device according to the invention with an ion trap;

[0053] FIG. 3 a third embodiment of a device according to the invention with an ion optical system;

[0054] FIG. 4 a first embodiment of a mass spectrometer according to the invention with a device according to the invention;

[0055] FIG. 5 an embodiment of a mass spectrometer according to the invention with a device according to the invention, wherein the device is an integral component of the mass spectrometer;

[0056] FIG. 6 a mass spectrum over the entire mass range of the mass spectrometer (a) before and (b-d) after filtering selected ions from the respective ion beam.

[0057] FIG. 1 shows a schematic representation of a device 1 according to the invention for filtering selected ions (here on the basis of selected masses: m.sub.1 and m.sub.3) from an ion beam 2. The ion beam can be generated using any ionization method known from the prior art. The unit 3 is based on the principle of time-of-flight (TOF) measurement. The ions of the ion beam 2 are separated along their flight path F on the flight path of predefinable length d with regard to their masses m.sub.1-m.sub.3 or mass-to-charge ratios. Accordingly, the different ions m.sub.1-m.sub.3 impinge at different points in time on the ion optical system 4, which is arranged at the end of the flight path d. In order to travel the flight path d, the ions m.sub.1-m.sub.3 thus need different flight times t.sub.1-t.sub.3.

[0058] The ion optical system 4 serves to deflect the selected ions m.sub.1 and m.sub.3 from the flight path F of the ion beam 2. For this purpose, the device 1 is designed to control the ion optical system 4 subject to a flight time ti and t3 of the selected ions mi and m3 along the flight path d.

[0059] The non-deflected ions m.sub.2 of the ion beam 2 (for the simplified example shown here, it is only the ion m.sub.2; usually, a multiplicity of different ions m.sub.x-m.sub.y is not deflected from the flight path F) ultimately impinge on the detector 5, which is also any detector known from the prior art. For the embodiment according to FIG. 5, the detector unit 5 is part of the device 1. However, a separate detector unit 5 is by no means absolutely necessary for the device 1 according to the invention. Rather, an existing detector unit of a mass spectrometer can also be used.

[0060] In the example shown here, the device 1 furthermore comprises a in a computing unit 6 and a control unit 7, which are arranged together here by way of example. Within the scope of the present inventions, a wide variety of possibilities are also conceivable in this respect, and the invention is by no means limited to the variant shown here. Rather, numerous other variants are conceivable, all of which fall within the present invention. For example, the computing unit 6 may also be part of the detector unit 5.

[0061] By means of the computing unit 6, the flight times t.sub.1-t.sub.3, masses m.sub.1-m.sub.3, charges, mass-to-charge ratios and/or intensities of the ions contained in the ion beam 2 can be determined. The control unit 7 then serves to control the ion optical system 4 subject to a flight time t.sub.1 and t.sub.3 of the selected ions m.sub.1 and m.sub.3 along the flight path d. In the present case, the ion optical system 4 is, for example, switched on at times t.sub.1 and t.sub.3 respectively, in order to deflect the selected ions m.sub.1 and m.sub.3 from the flight path F. For example, for the purpose of deflecting the selected ions m.sub.1 and m.sub.3, the ion optical system comprises a Bradbury-Nielson gate.

[0062] According to the invention, at least one ion m.sub.1 or m.sub.3 is filtered in each case; apart from individual selected ions m.sub.1 and m.sub.3, it is also possible to deflect selected ranges with selected ions as a whole from the flight path F. The ranges are, for example, selected ranges for the masses, charges, mass-to-charge ratios and/or intensities for the respectively selected ions. All ions whose masses, charges, mass-to-charge ratios and/or intensities are in the respective selected range are then filtered.

[0063] The present invention is also not limited to determining the selected ions m.sub.1 and m.sub.3 on the basis of a spectrum recorded by the detector 5. The selected ions m.sub.1 and m.sub.3 can also be selected, for example, on the basis of specified lists. In this respect, numerous other possibilities are also conceivable, all of which fall within the present invention.

[0064] FIG. 2 shows another embodiment of a device 1 according to the invention. In addition to the embodiment according to FIG. 1, the device 1 according to FIG. 2 comprises an ion trap 8, which is arranged between the ion optical system 4 and the detector unit 5. The elements explained in conjunction with FIG. 1 are therefore not discussed again here.

[0065] In the ion trap 8, the predefinable ion m.sub.2 is accumulated or depleted before it impinges on the detector 5. Instead of the individual ion m.sub.2 shown here, a plurality of predefinable ions or ions of at least one predefinable range can also be accumulated or depleted.

[0066] FIG. 3 shows a third embodiment of a device 1 according to the invention. In contrast to the embodiment according to FIG. 1, the device 1 according to FIG. 3 comprises an ion optical system 9. In connection with FIG. 3, elements already explained are also not discussed again.

[0067] Like the ion optical system 4, the ion optical system 9 is controllable. In the present case, by suitable adjustment of at least individual components, here by way of example 9a and 9c, it can be achieved that the entire ion beam 2 runs along the flight path F1 and is detected in its entirety by the detector unit 5. At at least one point in time, by another suitable adjustment of at least individual components, here by way of example also 9a and 9c, it can be achieved that the ion beam 2 runs along the flight path F2, wherein the selected ions m1 and m3 are deflected from their flight path F2 before the remaining ion beam 2 reaches the detector unit 5.

[0068] The ion optical system 9 outlined here comprises a so-called ion pusher 9a, a reflector 9b and an ion mirror 9c. In addition to the embodiment shown here, numerous further embodiments of the ion optical system 9 are possible, which have other components, a different number of components and/or other arrangements of the components, and which all likewise fall within the present invention.

[0069] For the embodiment shown, the ion optical system 9 is also controlled by means of the control unit 7. However, it goes without saying that the ion optical system 9 in other embodiments can also be suitably controlled in a different manner.

[0070] By using an ion optical system 9, it is advantageously possible by means of the device 1 to carry out both scans over the entire available mass range and scans over predefinable subranges or over the entire available range minus the selected ions mi and m3.

[0071] FIG. 4 shows a mass spectrometer 10 according to the invention with a device 1 similar to the embodiment of the device 1 according to FIG. 3. The mass spectrometer 10 can be any mass spectrometer according to the prior art. The mass spectrometer comprises an ionization unit 11, by means of which the ion beam 2 is generated, an analyzer and a detector, both of which are combined with further components of the mass spectrometer 10 by reference sign 12. A device 1 according to the invention is arranged between the ionization unit 11 and the remaining components of the mass spectrometer 10 combined by reference sign 12. In the embodiment shown, the device 1 does not have its own detector unit 5, but uses an existing detector unit of the mass spectrometer 10. The same applies to the computing unit 6 and the control unit 7. The latter are also components of the mass spectrometer 10 and are combined by reference sign 12. The control of the ion optical system 4 and of the remaining components of the device 1 takes place analogously to the embodiments shown in the preceding figures. It should be noted that naturally, in other embodiments, a separate detector unit 5, computing unit 6 and/or control unit 7 for the device 1 may also be present.

[0072] In the case of a mass spectrometer 10 according to the invention, the device 1 can be formed on the one hand as a self-contained unit, which can be integrated into the existing mass spectrometer 10 as in the case of FIG. 4. However, it may also be an integral component of the mass spectrometer 10 as in the case of the exemplary embodiment shown in FIG. 5. The embodiment shown in FIG. 5 is a TOF mass spectrometer. In the case of such a mass spectrometer 10, a device 1 according to the invention can be integrated in a particularly simple manner.

[0073] As in the case of FIG. 4, the mass spectrometer comprises an ionization unit 11. Furthermore, an optical focusing unit 13 is optionally present. The mass spectrometer 10 shown furthermore has an ion optical system 9a′, 9b′, and a unit 3′ for creating an electric field for accelerating the ions along a flight path of predefinable length d. Such components essentially correspond to the components of the preceding figures provided with the same reference signs without apostrophes. In the present case, however, such components are part of the existing mass spectrometer 10. In contrast, the device 1 does not have corresponding separate components. The detector unit 5 and the ion optical system 4 are in contrast components of the device 1 according to the invention. For the sake of simplicity, the drawing of a computing unit 6 and a control unit 7 has been dispensed with for this figure. They can be implemented, for example, in accordance with one of the previously described embodiments. Optionally, the device 1 or the mass spectrometer 10 can have further components already discussed in connection with previous figures. For example, the ion optical system 9 may comprise an ion mirror 9c or else further units for directing and/or focusing the ion beam, or an ion trap 8 may additionally be present.

[0074] A schematic illustration of the method according to the invention is lastly shown in FIGS. 6. FIG. 6a shows a complete mass spectrum over the available range of mass-to-charge ratios I(m/z). The ion beam 2 contains various ions m.sub.1-m.sub.6, of which only the ions m.sub.1-m.sub.4 can be seen in the spectrum due to the low concentrations of some of the ions. The concentrations, and thus the intensities of the ions m.sub.5 and m.sub.6, are so low that they are below the sensitivity limit d.sub.L of the mass spectrometer 10. However, the ion m.sub.4 is also difficult to detect since it is only slightly above the sensitivity limit d.sub.L of the mass spectrometer 10.

[0075] In order to be able to also detect the low-concentration substances, the ions m.sub.1 and m.sub.3 are selectively filtered in a first step or filtering process according to the method according to the invention in accordance with one of the described embodiments. For this purpose, the ions m.sub.1 and m.sub.3 are selectively deflected by the ion optical system 4 at times t.sub.1 and t.sub.3, at which they respectively impinge on the ion optical system 4. The filter pattern used thus comprises two filter windows F.sub.1 and F.sub.2.

[0076] The result of this filtering is shown in FIG. 6b. The concentrations of the ions m.sub.1 and m.sub.3 are significantly reduced and are now ideally below the original sensitivity limit d.sub.L. On the other hand, the ions m.sub.2 and m.sub.4 are now both clearly detectable as a result of the shift of the dynamic sensitivity range downward.

[0077] In order to be able to detect the detectability of even less concentrated ions, such as the ions m.sub.5 and m.sub.6, which are shown as dashed lines in FIG. 6c, a further filtering process with respect to the second ion m.sub.2 can be carried out by means of the additional filter window F.sub.3, as FIG. 6c illustrates. In addition to the ions m.sub.1 and m.sub.3, the ion m.sub.2 is thus selectively filtered. The result of such further filtering is the subject matter of FIG. 6d. The previously undetectable ions m.sub.5, m.sub.2 and m.sub.6 can now be clearly detected. Depending on the application, suitable filter patterns can be designed by means of the method according to the invention, which selectively filter predefinable ions m.sub.x or predefinable ranges, for example mass ranges Δm, from the ion beam 2 in one or more subsequent filtering processes.

REFERENCE SIGNS

[0078] 1 Device according to the invention [0079] 2 Ion beam [0080] 3 Unit for creating an electric field [0081] 4 Ion optical system [0082] 5 Detector unit [0083] 6 Computing unit [0084] 7 Control unit [0085] 8 Ion trap [0086] 9, 9a-9c Ion optical system [0087] 10 Mass spectrometer [0088] 11 Ionization unit [0089] 12 Analyzer, detector and further components of the mass spectrometer [0090] F, F.sub.1, F.sub.2 Flight path [0091] m.sub.1-m.sub.6, m.sub.x Ion masses [0092] Δm Predefinable mass range [0093] t.sub.1-t.sub.3 Flight times [0094] d Flight path [0095] m.sub.1, m.sub.3 Selected ion masses [0096] m.sub.2 Predefinable ion mass [0097] F.sub.1-F.sub.3 Predefinable filter window of a filter pattern