US3796872A

US3796872A - Mass spectrometry

Info

Publication number: US3796872A
Application number: US00207234A
Authority: US
Inventors: T Merren
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1970-12-18
Filing date: 1971-12-13
Publication date: 1974-03-12
Anticipated expiration: 1991-03-12
Also published as: GB1348495A

Abstract

A mass spectrometer in which plural beams of ions are generated from a common substance for simultaneous passage through an analyzer region. An auxiliary electrostatic analysis is performed on one of the analyzed beams which are received by separate collectors. Metastable ions are observed at one collector while their parents are observed at another collector.

Description

nited States Patent 1 Merren Mar. 12, 1974 MASS SPECTROMETRY 3,649,827 3/1972 Bell 250/419 ME 7 I t T l 1 Hale FOREIGN PATENTS OR APPLICATIONS 1,134,448 11/1968 Great Britain 250/41.9 ME [73] Ass1gnee: Associated ElectrIcal Industries Limited, London, England Filed: Dec. 13,1971 Przmary Exammer-Walter Stolwem Assistant Examiner-C. E. Church Foreign Application Priority Data [57] ABSTRACT Dec. 18, 1970 Great Britain 60229/70 A mass spectrometer in which plural beams of ions are generated from a common substance for simultaneous [52] US. Cl 250/285, 250/285, 250/296 passage through an analyzer region An auxiliary elec [51] Int. Cl. H01 39/34, BOld 59/44 trostatic analysis is performed on one of the analyzed [58] Field Of Search ME, G beams are received y Separate collectors. Metastable ions are observed at one collector while [56] References C'ted their parents are observed at another collector.

UNITED STATES PATENTS 3,573,453 4/1971 Powers 250/419 ME 8 Claims, 5 Drawing Figures .27. ON 17 I? J souRcE' j 51 1 ELECTRO ;7 AXIS 1 STAT/C I j ""I, 387 .ANALYS'ER 1, .I:;

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A TTORNEYS MASS SPECTROMETRY CROSS REFERENCE TO RELATED APPLICATIONS AND PATENTS Plural Beam Mass Spectrometer," Ser. No. 73,072, filed Sept. 17, 1970, by Brian Green.

Plural Beam Mass Spectrometer for Conducting High and Low Resolution Studies, US. Pat. No. 3,573,453, filed May 12, 1967 by Patrick Powers.

Beam Correcting Device for Mass Spectrometers and Method of Operation, Ser. No. 39,240, filed May 15, 1970 by Sidney Evans and Reginald Graham.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mass spectrometers and more particularly to a plural beam mass spectrometer in which a plurality of beams can be generated simultaneously and passed concurrently through a common analyzer region.

2. Prior Art In the analysis of substances with a mass spectrometer, ions of a substance being analyzed are generated in an ion source and then emitted from the source as an ion beam. The beam passes through, in the case of a single-focusing mass spectrometer, a magnetic analyzer; and in the case of a double-focusing mass spectrometer, an electrostatic analyzer and then a magnetic analyzer.

During a given analytical study, the accelerating voltage of the source or the voltage applied to the magnetic analyzer may be varied to scan the instrument. As the instrument is scanned, ions of different mass/charge ratios are deflected onto the collectors successively and the sample is thus analyzed.

In the referenced Powers patent, there is a disclosure of, among other things, the use of two ion sources which are capable of simultaneously producing two ion beams. The two beams are passed, in a common ion tube, through a single analyzer system and then collected respectively on each of two collectors. The two beams may be passed through the ion tube either simultaneously, or selectively, one at a time.

SUMMARY OF THE PRESENT INVENTION With the present invention one or more sources are positioned for emitting plural ion beams simultaneously. Each emitted beam passes through in the preferred embodiment, electrostatic and magnetic analyzers of relatively conventional construction. With the present invention there is provision of a divergentdeflector which may be referred toas the analyzed beam deflector. The divergent deflector deflects one of the beams away from the other after their passage through the analyzers.

The divergent deflector is an electrostatic deflector. Since it is an electrostatic deflector, it functions in a manner comparable to the electrostatic analyzer. This means that, ions undergoing metastable transitions in the analyzer are not deflected to the collector, but rather only parent ions, or fragments produced in the source, or those ions very close to the mass/charge ratios of the parent ions reach the collector; Thus, a metastable study may be conducted witha beam which is not deflected after it transverses the collector slit, while the parent ions in the other beam are analyzed.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying, drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a schematic view of a mass spectrometer partially in section in a plane of deflection of the analyzers of a preferred embodiment;

FIG. 2 is a fragmentary, partially schematic, plan view of a mass spectrometer showing the deflectors of the preferred embodiment;

FIG. 3 is an electrical schematic drawing showing the deflectors of the preferred embodiment and the circuitry for supplying power to them;

FIG. 4 is a plan view of the converging deflectors of the preferred embodiment; and,

FIG. 5 is a plan view of the auxiliary electrostatic analyzer of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and to FIG. l in particular, ion sources are in a source section shown generally at 110. The sources generate plural ion beams which are accelerated by electrodes within the sources through exit slits indicated schematically at 1111. After the beams have passed through the exit slits Ill, they pass through a source convergent deflector section 13 which will be described in greater detail presently. The convergent deflector brings the beams relatively close together. The beams then pass through an electrostatic analyzer 14 of relatively conventional construction.

After a beam has passed through the electrostatic analyzer 14, it may pass through an ion current collector or monitor 15. Ion collectors are known in the art and the collector 15 may be of known and conventional construction other than for modification to accommodate plural beams. The beam next passes through a magnetic analyzer 16 where it is further deflected. After the beam passes through the magnetic analyzer 16, it passes through a collector slit structure shown schematically at 117.

After the beams have passed through the slit structure 17, they pass through an auxiliary electrostatic analyzer section 18. Where there are two beams in the preferred construction, one beam passes through the divergent deflection section without further deflection and the other is deflected. After traversing the divergent deflection section, the beams enter a collector section 19. In the disclosed embodiment, one collector in the form of an electron multiplier tube 20 is shown in FIG. 11.

Referring now to FIG. 2, a somewhat diagrammatic plan view of a two-source double-beam mass spectrometer is shown. The source section 10 is composed of a pair of ion sources in

source housing

25, 26. The source housings 25, 26 define separated

chambers

27, 28 respectively. The separated

chambers

27, 28 are respectively and individually pumped through

exhaust passages

29, 30 to maintain conventional vacuum conditions in the

source chambers

27, 28.

Within each

source chamber

27, 28 an ion generating source of conventional construction is positioned. Each source may be, for example, a conventional electron bombardment source. On the other hand, one of the features of a plural beam mass spectrometer is that the sources need not be identical. One may provide two types of sources such as electron bombardment and field ionization to provide greater flexibility in conducting studies.

As is clearly indicated by the schematic showing of FIG. 2, ion beams indicated by pairs of dashed

lines

32, 33 are emitted from the sources. These beams, as emitted through the exit structure 11, are relatively widely spaced. If a study were conducted with the beams so spaced, it will be appreciated that very large electrostatic and

magnetic analyzers

14, 16 would be required and particularly the magnetic analyzer would be of large mass and expensive.

One of the optional features of this invention is pro vided in the source convergent deflection section 13. In this section, each of the two

beams

32, 33 is first deflected to a convergent path so that the beams approach one another and thereafter are deflected in the opposite direction to bring the beams back into parallel, but now much more closely spaced, relationship.

The convergent deflecting section is positioned within an evacuated mass spectrometer housing 35. The housing 35 thus envelopes not only, as is known in the art, the electrostatic and magnetic analyzers and collectors but also the convergent and divergent deflector sections.

The convergent deflector section has two pairs of oppositely charged convergent sectors or

deflector plates

36, 37 and 38, 39. The

convergent sectors

36, 37 de flect the beam 32 toward the beam 33; and, conversely, the

sectors

38, 39, deflect the beam 33 toward the beam 32. It will be seen that faces 36A-39A of the sectors of each pair are arcuately curved, defining segments of cylinders of common curvature. The curvature of these faces is equivalent to the curvature of the

beams

32, 33 as thev pass through their respective and associated convergent sectors.

The beams next pass through spaces delineated by a central common sector 40 and parallel path-producing

sectors

41, 42, respectively. The

sectors

41, 42 are charged so that the beams are oppositely deflected, through an angle corresponding to the angle produced in the convergent sectors, to bring the beams back into parallel but closer relationship.

The sectors 40-42 also have arcuately curved faces that are segments of cylinders. Thus, the common segment has a face 40A which is concentric to a face 41A and a face 408 which is concentric to a face 42A. These faces have curvatures corresponding to the desired curvature of the beam in the plane of FIG. 2 and equal and opposite to the curvature of the convergent sectors.

In mass spectrometry, since the molecules from which the ions are formed have random thermal velocity in the ion source, ions commonly have a small component of velocity in a direction that is in the plane of the drawing of FIG. 2. Therefore, to prevent any intermixing of the

beams

32, 33, a collimating slit structure 45 is provided. Collimating slit structure 45 respectively has collimating slit

apertures

46, 47 for the

beams

32, 33.

The deflected and

collimated beams

32, 33 traverse through a common ion tube, a portion of which is shown at 50. While in the tube, they pass through the electrostatic and

magnetic analyzers

14, 16 and thence through the collector slit structure 17. As has been indicated previously, the magnetic analyzer causes ion beam curvature. Accordingly, the slit structure 17 has slit

openings

51, 52 which are canted with respect to the plane of analyzer deflection, i.e., the plane of FIG. 1, and are in non-parallel relationship with one another. After the beam 32 has passed through the slit 5], it proceeds, without further deflection, to the electron multiplier 20. Since the beams are too close together to permit another electron multiplier 53 to be positioned in the path of the beam 33, the beam 33 is deflected outwardly in the auxiliary electrostatic analyzer section 18.

The auxiliary electrostatic analyzer section 18 performs an auxiliary electrostatic analysis on the beam 33, after it has been analyzed by the

analyzers

14, 16 in common with the beam 32. The auxiliary analyzer is composed of electrically charged

sectors

54, 55. These sectors, like the sectors in the convergence region 13, have arcuately

curved surfaces

54A, 55A each of which defines a segment of a cylinder. The curvature of the

surface

54A, 55A is, again, a curvature corresponding to the desired beam deflection curvature.

It will be appreciated that both beams can be analyzed, but for simplicity of manufacture and to facilitate the metastable studies described above, auxiliary analysis of only one of the two beams is preferred.

The instrument is constructed such that the total lengths of the path of travel of the two

beams

32, 33 are identical from their respective sources to their respective collectors. This permits precise comparative analysis of the two beams which have been analyzed in identical conditions.

In FIG. 3, a suitable method of deriving appropriate voltages for the various deflection sectors is shown. An array of fixed and variable resistors Rl-Rl4 is connected across an accelerated beam voltage supply 60. Suitable voltages are tapped from the array of resistors to give appropriate relative potentials between the

ion sources

25, 26 and the sectors of the

regions

13, 18.

The resistors R1 and R2 are preferably such that a major portion of the voltage from the accelerating voltage supply appears across R1, for example a positive voltage of 4,000 volts, and a minor portion appears across resistor R2, for example a negative voltage of 200 volts. The potentials for the sectors of the deflection regions are preferably arranged to be substantially equal and positive and negative with respect to ground. Suitable potentials for the sectors of the convergent regions 13 are plus and minus 170 volts and for the sectors of the divergent deflector plus and minus 60 volts. The potentials of at least one sector of each pair are preferably adjustable as shown in FIG. 3 by means of variable resistors R6, R7, R12, R13, R14. Apart from enabling the metastable analysis of the invention, the

variable resistors allow for setting up the mass spectrometer for operation and compensate for any errors in the manufacture of a spectrometer.

While FIGS. 2 and 3 are schematically illustrative of the arrangement and operation of the deflectors of the present invention, the construction of the deflectors is shown in more detail in FIGS. 4 and 5. At the outset it should be noted that FIGS. 4 and 5 are mirror reversals of the arrangements shown in FIGS. 2 and 3. Hence the ion beams travel right to left in FIGS. 4 and 5 rather than left to right as in FIGS. 2 and 3.

Referring to FIG. 4, the convergent deflector section 13 has annular mounting plates 100. A pair of

housings

101, 102 are secured to the mounting plate and are aligned by means of dowel pins 103. The

housings

101, 102 have cup-shaped tubular

side wall portions

104, 105 respectively defining upper and lower cylindrical chambers 106, 107. The housings also have mounting flanges 108, 109 which receive the dowel pins 103 and which connect with an inwardly extending annular flange 110 of the spectrometer housing 35. By this arrangement, the mounting plate 100 and the

housings

101, 102 are supported within the vacuum evacuated environment of the mass spectrometer housing 35.

A pair of

elongate supports

111, 112 extend respectively into the

housings

101, 102. The elongate supports 111, 112 are each of substantially semi-circular cross-section, having end wall portions of increased thickness to receive threaded

fasteners

113, 114. The fasteners 113 extend through the mounting plate 100 to secure the supports 11], 112 in place. The fasteners 114

mount end plates

115, 116 on the

supports

111, 112.

The

convergent deflectors

36, 37 and 38, 39 are spaced from the

end plates

115, 116 by glass balls 117. Threaded fasteners 118 of electrically insulative material extend through openings in the

end plates

115, 116 and into threaded apertures in the

deflectors

36, 39. The

deflectors

36, 39 are thus carried by and insulated from the

end plates

115, 116. A pair of fringe field correction plates 119, 120 are spaced from the opposite ends of the deflectors36, 37 and 38, 39 by glass balls 121. Electrically insulated threaded fasteners 122 extend through openings in the plates 119, 120 and into threaded apertures in the

deflectors

36, 39 to support the plates 119, 120 from the deflectors. A pair of

cross deflection plates

123, 124 and a pair of shield assemblies designated generally by the

numerals

125, 126 may also be supported from the fasteners 122. The

shield assemblies

125, 126 respectively include

shields

127, 128 which are maintained at ground potential and which are positioned parallel to the

beams

32, 33 within the region intermediate the

deflectors

36, 37, 38, 39 and 40, 41, 42.

A tubular support 130 extends leftwardly of the mounting plate 100. The tubular support has ends of enlarged thickness to receive threaded

fasteners

131, 132. The fasteners 131 extend through the mounting plate 100 and secure the support 130 in place. The fasteners 132 mount a plate 133 from the tubular support 130.

The plate 133 has openings 134 formed therethrough. An annular plate 135 is positioned to the left of the plate 133 and is spaced in parallel relationship therefrom by glass balls 137. Threaded fasteners 138 extend through openings in the plates 135, 136 and through the openings 134 and into threaded apertures in the

deflector sectors

41, 42. The

deflector sectors

41, 42 are spaced from the plate 133 by glass balls 139. A clamping arrangement is thereby provided for supporting the

sectors

41, 42 from the plate 133, while the

glass balls

137, 139 simultaneously serve to insulate the

sectors

41, 42 from the plate 133. Moreover, the plate 135 is also seen to be insulated from the plate 133. A tube 140 is secured to the plate 135. The ion beams 32, 33 enter the analyzer region 14 through the tube 140.

A pair of

plates

141, 142 are spaced from

deflector sectors

41, 42 by glass balls 143. Electrically insulated fasteners 144 extend through openings in the plates 14], 142 and into threaded apertures in the sectors 41,

42. The

plates

141, 142 are thereby insulated from and carried by the

sectors

41, 42. The

plates

141, 142 may be maintained at ground potential while the

deflector sectors

41, 42 may be electrically charged as previously explained. The central deflector sector 40 is supported intermediate the

sectors

41, 42 by fasteners, not shown.

It will be understood that the

plates

115, 116, 119, 120 and 141, 142,133 which are positioned adjacent the ends of the

deflectors

36, 37, 38, 39 and 40, 41, 42 respectively each have openings therethrough for the passage of the ion beams, and serve as field correction plates to correct for the field end effects which are present adjacent the deflector ends.

Referring to FIG. 6 the auxiliary analyzer section 18 is seen to include a main block 150. The main block connects with a tubular body 151. The tubular body 151 has a centrally located opening 152 through which the

beams

32, 33 pass as they emerge from the region of the magnetic analyzer 16. From the tubular body 151, the beams 32,- 33 pass into a chamber 153 formed within the main block 150. The beam 32 passes without further deflection to the electron multiplier 20. The beam 33 is deflected downwardly to the electron multiplier 21 by means of the electrically charged

deflector sectors

54, 55, whereby an auxiliary electrostatic analysis is performed on the beam 33. The

sectors

54, 55 are supported inside the chamber 153 by fasteners, not shown.

The electron multipliers 20, 21 are of a construction well known in the art and need not be described in detail. The

multipliers

20, 21 are positioned within

housings

154, 155 which are secured to the main block 150 in such fashion as will assure the preservation of a vacuum environment within the chamber 153. A pair of

amplifiers

156, 157 amplify the signals from the

multipliers

20, 21 in the usual fashion. A cover plate 158 is secured to the main block 150 so as to provide a vacuum seal.

Two mass spectrometric methods are possible with the above described apparatus. (In both methods, the ion beams are formed from the same substance or mixture of substances, in order that the metastable analysis may be meaningful, but this does not preclude an additional substance, such as a reference substance, being added to one ion source only).

In the first method, the voltages applied to the

sectors

54 and 55 are (by suitable adjustment of the variable resistors R8 and R12) such that metastable ions formed during and after passage of the ion beams 32 and 33 through the

main analyzers

14 and 16 are substantially excluded from the ion collector (53) in the path of ions passing through the auxiliary electrostatic analyzer formed by the

sectors

54 and 55, and also such that ions which have been formed in the ion source 28 and which have not undergone subsequent transitions pass through the auxiliary electrostatic analyzer to the ion collector 53.

In the second method, the auxiliary electrostatic analyzer can be used to investigate metastable ions fonned after the

main analyzers

14 and 16. The auxiliary analyzer is situated after the resolution slit.52 in the path of the ion beam 32, and therefore any metastable ions formed in the region between the

main analyzers

14 and 16 and the auxiliary electrostatic analyser will be rejected if the potential between the

sectors

54 and 55 is set (by means of R12) so that the parent ions are collected by the collector 53 associated with the auxiliary analyzer. (This may be contrasted with a single beam mass spectrometer in which an ion which passes through the exit face of the main analyzers and through the resolution slit is collected by the ion collector even if it dissociates and forms a metastable ion in this part of its path.)

The voltage between the

sectors

54 and 55 may be scanned so that the spectrum of the metastable ions formed in the region between the magnetic analyzer l6 and the auxiliary electrostatic analyzer can be obtained. Scanning can be undertaken by suitable manual variation of the resistor R12 or alternatively by connecting the

sectors

53 and 54 to a suitable source of scanning voltage.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A method of mass spectrometry performed with a plural beam mass spectrometer wherein a plurality of ion beams formed from a common substance are passed through a common analyser means including magnetic and electrostatic analysers and collected by individual ion collectors, comprising the steps of further electrostatically analysing one of the beams between the common analyser means and the respective ion collector, and directly collecting at least one other ion beam on a respective other ion collector without electrostatic analysis of said other ion beam between the common analyser means and said other ion collector.

2. The method of claim 1, wherein metastable ions are collected by said respective ion collector and parent ions of said metastable ions are collected by said other ion collector.

3. The method of claim 1, wherein parent ions are collected by said respective ion collector and metastable ions are collected by said other ion collector.

4. The method of claim 1 wherein the further electrostatic analysis of said one of the beams is performed by making a scanning variation of an electrostatic field.

5. The method of claim 1 wherein the further electrostatic analysis of said one of the beams is performed with a fixed electric field.

6. A method of mass spectrometry performed with a double-beam mass spectrometer having ion source means, a common analyser means including magnetic and electrostatic analysers, an auxiliary electrostatic analyser, and two ion collectors, comprising the steps of:

a. introducing a substance into said ion source means and forming two ion beams therefrom;

b. passing the two ion beams through the common analyser means;

c. thereafter collecting one of said ion beams directly on one of said ion collectors; and,

d. passing the other of said ion beams through said auxiliary electrostatic analyser, performing an auxiliary electrostatic analysis on said other ion beam and subsequently collecting ions passing through said auxiliary electrostatic analyser on the other of said ion collectors.

7. The method of claim 6 wherein the auxiliary electrostatic analysis is performed by a fixed electric field within said auxiliary electrostatic analyzer.

8. The method of claim 6 wherein the auxiliary electrostatic analysis is performed by making a scanning variation of an electric field within said auxiliary electrostatic analyzer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION h 1.2 1974 Patent No. 3 796 872 Dated Marc I Inventor(s) Thomas Ollver Merren It is certified that error appears in the shove -identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6', line 15, delete "6" and substitute (SEAL) Attest:

McCOY M. GIBSON, JR. Attesting Officer C. MARSHALL DANN Commissioner of Patents FORM PO-105OH0-69)

Claims

6. A method of mass spectrometry performed with a double-beam mass spectrometer having ion source means, a common analyser means including magnetic and electrostatic analysers, an auxiliary electrostatic analyser, and two ion collectors, comprising the steps of: a. introducing a substance into said ion source means and forming two ion beams therefrom; b. passing the two ion beams through the common analyser means; c. thereafter collecting one of said ion beams directly on one of said ion collectors; aNd, d. passing the other of said ion beams through said auxiliary electrostatic analyser, performing an auxiliary electrostatic analysis on said other ion beam and subsequently collecting ions passing through said auxiliary electrostatic analyser on the other of said ion collectors.