US3925663A

US3925663A - Extended monopole spectrometers and filters

Info

Publication number: US3925663A
Application number: US374369A
Authority: US
Inventors: John Barry Hiller; John Alan Richards; Richard Meredyth Huey
Original assignee: Unisearch Ltd
Current assignee: Unisearch Ltd
Priority date: 1972-06-28
Filing date: 1973-06-28
Publication date: 1975-12-09
Anticipated expiration: 1992-12-09
Also published as: DE2332960A1; CA976280A; GB1404386A; JPS49133086A; NL7309023A

Abstract

In a monopole mass spectrometer the conventional angle electrode and hyperbolic cylindrical electrode are replaced by an electrode consisting of a hollow or solid circular cylindrical electrode surrounded by a hollow square cylindrical electrode. This provides the possibility of dividing the circular cylindrical electrode into 2, 3 or 4 parts by an insulating structure which may or may not be vacuum sealed to the surrounding square cylindrical electrode, thereby enabling a number of ion beams to be mass filtered simultaneously by only two analysing electrodes. It also offers the possibility of utilising the hollow square cylindrical electrode as a portion of the vacuum containment vessel for the mass spectrometer.

Description

Unite States Patent [191 Hiller et al.

1 EXTENDED MONOPOLE SPECTROMETERS AND FILTERS [75] Inventors: John Barry Hiller, Thornleigh; John Alan Richards, Townsville; Richard Meredyth Huey, Sylvania, all of Australia [73] Assignee: Unisearch Limited, Kensington,

Australia [22] Filed: June 28, 1973 [21] Appl. No; 374,369

[30] Foreign Application Priority Data Dec. 9, 1975 Primary ExaminerJames W. Lawrence Assistant Examiner-B. C. Anderson Attorney, Agent, or Firm-Browdy and Neimark [571 I ABSTRACT In a monopole mass spectrometer the conventional angle electrode and hyperbolic cylindrical electrode are replaced by an electrode consisting of a hollow or solid circular cylindrical electrode surrounded by a hollow square cylindrical electrode. This provides the possibility of dividing the circular cylindrical electrode into 2, 3 or 4 parts by an insulating structure which may or may not be vacuum sealed to the surrounding square cylindrical electrode, thereby enabling a number of ion beams to be mass filtered simultaneously by only two analysing electrodes. It also offers the possibility of utilising the hollow square cylindrical electrode as a portion of the vacuum containment vessel for the mass spectrometer.

13 Claims, 10 Drawing Figures .5. Patent Dec. 9, 1975 Sheet 10f3 3,925,663

US. Patent Dec. 9, 1975 Sheet 2 of3 3,925,663

FIG Lb US. Patent Dec. 9, 1975 Sheet 3 of3 3,925,663

of a hollowor solid circular cylindrical electrode sur-' rounded by a hollow squarecylindrical electrode. The circular cylindrical electrode may' in certain forms of the invention be divided into 2, 3 or 4 segments or quadrants by an insulating structure which may or may not extend to the hollow square cylindrical electrode.

In order that the nature of the invention may. be better understood, preferred forms thereof are'hereinafter described by way of example with reference to the accompanying drawings in which: a

FIG. 1 is anend view of a conventional monopole spectrometer;

FIG. 2 is an exploded isometric sketch of a fourfold monopole mass spectrometer incorporatinganalyzing electrodes according to theinvention,

FIG. 3 is an end view of the basic form of analyzing electrodes according to the invention,

FIG. 4a is a similar view of a further form of the invention in which the circular cylindrical electrode is divided into four quadrants by an insulating structure which extends to and is vacuum sealed to the hollow square cylindrical electrode, a

FIG. 4b is a similar view of a further form of the invention similar to that of FIG. 4a in which the insulating structure does not extend to the square cylindrical electrode,

FIG. 5a is a similar view of a further formof the invention in which the circular cylindrical electrode is divided into two semi-circular segments by an insulating structure.

FIG. 5b is a similar view of a still further form of the invention in which the circular cylindrical electrode is divided into three segments by an insulating structure and,

FIGS. 6, 6a and 6b illustrate the manner in which spatial extensions and duplications of the structures shown in the figures referred to above may be arranged.

The monopole mass spectrometer, originally proposed by von Zahn (U. VONZAHN, Monopole Spec- FIG. 2 more than is necessary for an understanding of the present invention.

In-FIG. 2 a central circular section cylindrical electrode is indicated at 1 and this is supported in the center of a square cylindrical box electrode 2 the space between the electrodes being evacuated, At one end of the assembly is a'suitable means for ionizing and inject ing a gaseous sample into four channels of the fourfold monopole structure, which are constituted by the spaces defined between the cylindrical rod electrode and the four corners of the box electrode 2. A suitable trometer, A New Electric Field'Mass Spectrometer,

Rev. Sci. Inst., 34, (1963), 1-4) and the device which is termed conventional in this specification, has analyzing electrodes which consist of an angle electrode A and a hyperbolic cylindrical electrode B connected to a source C of potential of, for example, the form g(t) =-U -Vcos t as shown in FIG. 1 of the accompanying drawings. In the mode of operation commonly employed the angle electrode A is held at electrically zero, or earth, potential whilst the hyperbolic cylindrical electrode B is driven by a constant potential to which has been added a sinusoidal potential. Alternatively,

the hyperbolic cylindrical electrode can be supplied with any other suitably periodic high frequency waveform.

FIG. 2 shows a fourfold monopole mass spectrometer in a purely diagrammatic form illustrating the use of an electrode configuration similar to that shown in FIG. 3 and described below. As the present invention is concerned purely with the configuration of the analyzing electrodes and as the structure and functioning of mass it is not proposed to describe the arrangement shown in time varying voltage generator for exciting the cylindrical rod electrode 1 is indicated at 4 and 5 indicates a vacuum sealed electrical feed-through through which connection is made to the electrode 1. 6, 7, 8, and 9 represent the ion beams to be analyzed. Four Faraday

cup collectors

10, 11, 12 and 13 serve to detect the stable ion currents in each of the four monopole channels of the fourfold monopole structure which originate from the ionfbeams 6, 7, 8 and 9-. The output from this latter is led by means of a vacuum sealed electrical feed-through 16 to a suitable current measuring instrument 14 such as an electrometer amplifier. The portion trodes of the monopole mass spectrometer can be extended with resulting improvements in performance and/or increases in versatility and flexibility, thereby leading to a new class of monopole device..lnherent in the evolution of this new class is the approximation of the hyperbolic cylindrical electrode by a circular cylindrical electrode of a suitable diameter. This approximation is common place for the quadrupole mass spectrometer. Having made this approximation the angle .electrode A of FIG. 1 can be extended into a hollow square cylinder as shown, for example in FIG. 3,

, thereby causing the circular cylindrical, or rod, electrode 17 to be shared in common by the four angle electrodes l8, 19, 20 and 21 so formed. This creates, with only two analysing electrodes, a structure through which four ion beams can be mass filtered simultaneously as will be appreciated from a consideration of FIG. 2. When these four beams are fed from a common ion source such as 3 of FIG. 2 and are terminated by a common ion detector (Faraday cup collectors 10, ll, 12 and 13 of FIG. 2) a monopole-based mass spectrometer is produced which has a sensitivity of four times that of the conventional monopole mass spectrometer.

In addition to improved sensitivity a further feature of the structure just described, as with the following elaborations thereon, is the possibility of using the surrounding square cylindrical electrode as a portion of the vacuum containment vessel for the mass spectrometer, as is the case in the arrangement shown in FIG. 2, thus leading to an analyzing structure of physically small dimensions. An outcome of this is the ease with which the structure may be pumped.

Another simplifying feature is the possibility of making the rod electrode hollow thereby allowing electrical connections to the ion source to be carried within it. This would permit all wiring to the device to be made via a rear mounted plate as is usual for present day quadrupole devices.

Two elaborations of the above structure are shown in FIG. 4a and 4b in both of which the single rod electrode 22 is segmented into four quadrants separated by and mounted upon a cruciform electrically insulating arrangement 23 the extremities of which are vacuum sealed to the box electrode 24. In the first configuration the insulating structure is shown extended so that the four monopole structures formed by the rod and box electrodes 22 and 24 may filter beams originating in four ion sources which in turn may be sampling either four separate inlets or one common inlet. Since the four quadrants of the rod electrode are electrically isolated, each monopole structure may be tuned to filter different masses by suitably adjusting either the magnitude of the periodic high frequency potentials (and DC. potentials should they be used) applied to the quadrants, which is to be preferred, or alternatively the frequencies of the periodic potentials. Four separate sources of potential g1 (t) to g4 (t) are indicated in the drawing.

Inthe second configuration, shown in FIG. 4b the four quadrants of the single rod electrodeare again electrically insulated, however the insulation 26 does not extend to the walls of the hollow box electrode 27, thereby not requiring vacuum sealing at the intersections. Since the property of strong focussing will ensure that ions being transmitted by a quadrupole-based instrument will be constrained by electric forces largely to the dielectric region between the electrodes, each quadrant may be excited by suitably differing waveforms from sources gl(t) g4(t) thereby allowing the device to analyze one common sample for four differing mass numbers.

The configuration shown in FIGS. a and 5b are subject to the same comments as set out above and represent variations which may be found desirable in certain applications. In these figures the broken lines at the outer extremities of the

insulators

28 and 29 indicate that these may either be continued to the

hollow box electrodes

30 and 31 respectively and vacuum sealed to them or not as desired.

As is illustrated in FIGS. 6a and 6b all the single electrode configurations shown in FIG. 6 or any of those described above may be extended or duplicated to any desired extent.

We claim:

1. A monopole mass spectrometer comprising:

an analyzing configuration consisting of a circular cylindrical electrode extending coaxially within a surrounding hollow-square cylindrical electrode;

means for injecting ionized beams into said spec trometer between said circular cylindrical electrode and said square cylindrical electrode;

means for detecting said beams disposed opposite said injecting means; and

means for applying potential to both said circular cylindrical electrode and to said hollow square cylindrical electrode.

2. The combination claimed in claim 1 wherein said circular cylindrical electrode is hollow.

3. The combination claimed in claim 1 wherein said circular cylindrical electrode is divided into four quadrants by a cruciform insulating structure.

4. The combination claimed in claim 3 wherein the extremities of said insulating structure are vacuum sealed to the hollow square cylindrical electrode to form four vacuum separated monopole structures.

5. The combination claimed in claim 1 wherein said circular cylindrical electrode is divided into two segments by an insulating structure.

6. The combination claimed in claim 5 wherein the extremities of said insulating structure are vacuum sealed to the hollow square cylindrical electrode to form two vacuum separated monopole structures.

7. The combination claimed in claim 1 wherein said circular cylindrical electrode is divided into three segments by an insulating structure.

8. The combination claimed in claim 7 wherein the extremities of said insulating structure are vacuum sealed to the hollow square cylindrical electrode to form three vacuum separated monopole structures.

9. The combination claimed in claim 1 wherein said hollow square cylindrical electrode forms part of a vacuum containment vessel for the mass spectrometer.

10. The combination claimed in claim 3, wherein said means for applying potential is applied to each quad-' rant of the circular cylindrical electrode.

1 1. The combination claimed in claim 5, wherein said means for applying potential is applied to each segment of the circular cylindrical electrode.

12. The combination claimed in claim 7, wherein said means for applying potential is applied to each segment of the circular cylindrical electrode.

13. The combination claimed in claim 1, wherein said square cylindrical electrode is at a potential of zero.

Claims

1. A monopole mass spectrometer comprising: an analyzing configuration consisting of a circular cylindrical electrode extending coaxially within a surrounding hollow square cylindrical electrode; means for injecting ionized beams into said spectrometer between said circular cylindrical electrode and said square cylindrical electrode; means for detecting said beams disposed opposite said injecting means; and means for applying potential to both said circular cylindrical electrode and to said hollow square cylindrical electrode.

10. The combination claimed in claim 3, wherein said means for applying potential is applied to each quadrant of the circular cylindrical electrode.

11. The combination claimed in claim 5, wherein said means for applying potential is applied to each segment of the circular cylindrical electrode.