Reflectors for time-of-flight mass spectrometers having plates with symmetric shielding edges

Abstract

The invention relates to reflectors for time-of-flight mass spectrometers, and especially their design. A Mamyrin reflector is provided which consists of metal plates with cut-out internal apertures, and symmetric shielding edges which are set back from the inner edges. The dipole field formed by these shielding edges penetrates only slightly through the plates and into the interior of the reflector. With a good mechanical design, the resolving power of the time-of-flight mass spectrometer increases by around fifteen percent compared to the best prior art to date.

Claims

1. A reflector for a time-of-flight mass spectrometer in which approaching ions are decelerated and re-accelerated by electric fields, the reflector comprising a plurality of apertured potential plates having inward-protruding narrow plate lugs and being arranged substantially parallel to one another and separated by insulating spacers in a first direction, wherein an electric field in an interior of the reflector is formed substantially by the narrow plate lugs, and wherein each potential plate has a symmetric shielding edge that extends symmetrically in the first direction to both sides of the narrow plate lug of that potential plate at a predetermined distance from an interior of the reflector.

2. The reflector according to claim 1, wherein the potential plates are manufactured from planar metal plates.

3. The reflector according to claim 2, wherein the potential plates are laser cut from the metal plates.

4. A reflector for a time-of-flight mass spectrometer in which approaching ions are decelerated and re-accelerated by electric fields, the reflector comprising a plurality of apertured potential plates arranged substantially parallel to one another and separated by insulating spacers in a first direction, wherein each potential plate has a symmetric shielding edge that extends symmetrically in the first direction to both sides of the potential plate at a predetermined distance from an interior of the reflector, and wherein each potential plate comprises a metal base plate with tabs extending therefrom and two angle plates with openings through which the tabs pass such that the angle plates reside adjacent to an outer edge of the base plate and extend in a substantially perpendicular direction to form the shielding edge.

5. The reflector according to claim 4, wherein the tabs of a potential plate are integral with and parallel to the base plate and the openings in the angle plates comprise slits within which the tabs reside such that the potential plates are positioned and mechanically stabilized thereby.

6. The reflector according to claim 1, wherein the spacers which electrically insulate the potential plates from one another are located to a side of the shielding edges away from the apertures of the potential plates.

7. The reflector according to claim 1, wherein a single, continuously homogeneous field is generated by the potential plates.

8. The reflector according to claim 1, wherein the potential plates generate a first, relatively strong deceleration field region that reduces the speed of approaching ions, and a second, much weaker reflection field region that brings the ions to a standstill and reflects them.

9. The reflector according to claim 1, wherein an electric circuit of the potential plates comprises voltage dividers made of precision resistors in order to achieve a potential which increases as uniformly as possible from plate to plate.

10. A time-of-flight mass spectrometer having a reflector according to claim 1.

11. The mass spectrometer according to claim 10, wherein the potential plates are manufactured from planar metal plates.

12. The mass spectrometer according to claim 11, wherein the potential plates are laser cut from the metal plates.

13. The mass spectrometer according to claim 11, wherein each potential plate comprises a metal base plate with tabs extending therefrom and two angle plates with openings through which the tabs pass such that the angle plates reside adjacent to an outer edge of the base plate and extend in a substantially perpendicular direction to form the shielding edges.

14. The mass spectrometer according to claim 13, wherein the tabs of a potential plate are integral with and parallel to the base plate and the openings in the angle plates comprise slits within which the tabs reside such that the potential plates are positioned and mechanically stabilized thereby.

15. The mass spectrometer according to claim 10, wherein the spacers which electrically insulate the potential plates from one another are located to a side of the shielding edges away from the apertures of the potential plates.

16. The mass spectrometer according to claim 10, wherein a single, continuously homogeneous field is generated by the potential plates.

17. The mass spectrometer according to claim 10, wherein the potential plates generate a first, relatively strong deceleration field region that reduces the speed of the approaching ions, and a second, much weaker reflection field region that brings the ions to a standstill and reflects them.

18. The mass spectrometer according to claim 10, wherein an electric circuit of the potential plates comprises voltage dividers made of precision resistors in order to achieve a potential which increases as uniformly as possible from plate to plate.

19. A reflector for a time-of-flight mass spectrometer in which approaching ions are decelerated and re-accelerated by electric fields, the reflector comprising a plurality of apertured potential plates arranged substantially parallel to one another and separated by insulating spacers in a first direction, wherein each potential plate has a symmetric shielding edge that extends symmetrically in the first direction to both sides of the potential plate at a predetermined distance from an interior of the reflector, and wherein each potential plate comprises a metal base plate having insertion lugs extending therefrom and further comprises peripheral plates having apertures through which the insertion lugs pass and being aligned perpendicularly with the metal base plate, whereby the peripheral plates form the symmetric shielding edge around the metal base plate.

20. The reflector according to claim 19, wherein the insertion lugs of the metal base plate are fixed to the peripheral plates in the apertures by laser welding to produce a torsion-resistant structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematically simplified representation of an OTOF mass spectrometer which corresponds to the prior art, but in which a reflector according to the innovative design described here can be used.

(2) FIG. 2 shows part from a Mamyrin reflector according to the original prior art. The metal plates (21) are stacked closely (i.e., arranged in series one after the other) to largely prevent the ground potential of the surroundings from penetrating into the interior (24). The plates are kept apart by precisely formed spacers (22), made usually of ceramic, and held together by a post (23).

(3) FIG. 3 depicts part of a similar Mamyrin reflector. Here the plates (21) are not stacked so closely, but equipped with inner shielding edges to shield against the external potential. The resolving power is hardly better than that of the arrangement in FIG. 2, but significantly fewer plates (21) are required.

(4) FIG. 4 depicts an embodiment which provides a resolving power which is around 10 to 15 percent better than with the embodiments in FIGS. 2 and 3. Here, the shielding edges of the metal plates (26) are set further back so that the potential in the interior (24) is essentially determined by the metal lugs (27). The potential in the interior has a smooth characteristic.

(5) FIG. 5 depicts an embodiment according to principles of this invention. The set back shielding edges of the metal plates (28) are now arranged largely symmetrically to the plane of the plates and form dipoles between the plate lugs (29). The mass resolution can be increased by about a further 15 percent compared to the embodiment of FIG. 4.

(6) FIG. 6 depicts the simple way they are manufactured from a base plate (30) and two angle plates (31), of which only one is shown for the sake of clarity. In a preferred embodiment, all the plates are laser cut to avoid any warping or burring. After they have been assembled, the edges and insertion lugs can be laser welded; this produces a structure which is extremely torsion-resistant.

(7) FIG. 7 shows the structure of an embodiment of a plate (30) in plan view (with the two angle plates 31; thick black outline).

DETAILED DESCRIPTION

(8) The present invention provides a reflector which has a simple design and offers an improved mass resolution. It may be part of a mass spectrometer like that shown in FIG. 1, for which ions are generated at atmospheric pressure in an ion source (1) with a spray capillary (2), and these ions are introduced into the vacuum system through a capillary (3). A conventional RF ion funnel (4) guides the ions into a first RF quadrupole rod system (5), which can be operated both as a simple ion guide and also as a mass filter for selecting a species of parent ion to be fragmented. The unselected or selected ions are fed continuously through the ring diaphragm (6) and into the storage device (7); selected parent ions can be fragmented in this process by energetic collisions. The storage device (7) has an almost gastight casing and is charged with collision gas through the gas feeder (8) in order to focus the ions by means of collisions and to collect them in the axis. Ions are extracted from the storage device (7) through the switchable extraction lens (9). This lens, together with the einzel lens (10), shapes the ions into a fine primary beam (11) and sends them to the ion pulser (12). The ion pulser (12) periodically pulses out a section of the primary ion beam (11) orthogonally into the high-potential drift region (13), which is the mass-dispersive region of the time-of-flight mass spectrometer, thus generating the new ion beam (14) each time. The ion beam (14) is reflected in the reflector (15) with second-order energy focusing, and is measured in the detector (16). The mass spectrometer is evacuated by the pumps (17). The reflector (15) represents a two-stage Mamyrin reflector in the example shown, with two grids (18) and (19), which enclose a first strong deceleration field, followed by a weaker reflection field. The velocity spread means that the linear bunches of ions widen out all the way into the reflector, but the velocity focusing causes them to be very finely refocused again up to the detector. This produces the high mass resolution.

(9) Unlike prior art reflectors, the reflector of the present invention comprises metal plates whose symmetric shielding edges are set further back, as depicted in FIG. 5 for part of the reflector, by way of example. The dipole field formed by these shielding edges and the surrounding recipient, which is at ground potential, penetrates to a lesser extent through the plates into the interior of the reflector than is the case with previous embodiments. The improvement in the resolving power was optimized by field simulations on a computer, and it has been possible to confirm this experimentally. When the mechanical design is sturdy and precise, the resolving power of the time-of-flight mass spectrometer is increased by around a further 15 percent compared to the best prior art to date.

(10) FIG. 6 shows the structure and production of the reflector plates according to FIG. 5 in an example embodiment. The manufacture of a base plate (30) and two angle plates (31), of which only one is visible for reasons of clarity, is relatively simple and very low cost compared to machining them from solid material. In one embodiment, the base plates (30) and the angle plates (31) are laser cut very precisely with computer control from very flat sheet material around one millimeter thick in order to prevent any warping or the formation of burr at the edges. They are relatively easy to put together thanks to the locating tabs (32) and (33) and the insertion lugs (34), which fit through the precisely shaped apertures (35). After they have been put together, the angle plates and insertion lugs can be fixed to each other by laser welding, which results in a very torsion-resistant structure. In the example shown, the locating tabs have circular openings to hold spacers, which are made of ceramic, or other suitable insulating material. They position the reflector plates very precisely with respect to each other.

(11) The drawing in FIG. 6 does not show the example embodiment in fine detail. The potential plates (30) are relatively thick, at 1 mm, in order to give the necessary mechanical strength. Consequently, a large number of surfaces abutting one another are created between the narrow edges of these plates (30) and the angle plates (31), and these can be difficult to evacuate. One skilled in the art will recognize, however, that pumpable gaps can be formed between the narrow edges of the potential plates (30) and the angle plates (31) by specially forming the contour of the potential plates (30).

(12) The person skilled in the art will find it easy to develop further interesting embodiments based on the devices for the reflection of ions according to the invention. These shall also be covered by this patent application to the extent that they derive from this invention.