US3849656A

US3849656A - Plural sample ion source

Info

Publication number: US3849656A
Application number: US00876078A
Authority: US
Inventors: M Wallington
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1968-12-17
Filing date: 1969-11-12
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19
Also published as: FR2026374A1; GB1252569A; SE356396B; NL6918712A; DE1962617A1

Abstract

An ion source for separately ionizing a plurality of vaporized samples and focusing the ions produced by the ionization into an ion beam containing ions from each of the vaporized samples. The ion source comprises an ionization chamber having an aperture through which ions are emitted, means for emitting an electron beam into the ionization chamber, at least one ion control electrode for establishing an ion control field, and partition means for dividing the ionization chamber into a first and second electron bombardment chamber. The ion source also includes a first and second gas storage vessel for respectively introducing at least a first and second vaporized sample into the first and second electron bombardment chambers, respectively, so that the first and second vaporized samples are independently ionized.

Description

PLURAL SAMPLE ION SOURCE Inventor: Michael J. Wallington, Manchester,

England Assignee: Associated Electrical Industries Limited, London, England Filed: Nov. 12, 1969 Appl. N0.: 876,078

Foreign Application Priority Data Dec. 17, 1968 Great Britain 59940/68 us. c1 250/424, 250/285, 250/423, 250/427, 313/63 1111. C1. H0lj 39/34 Field of Search. 250/41.9 G, 41.9 SB, 41.9 SE

References Cited UNITED STATES PATENTS 11/1956 Dietz 250/41.9

11/1967 Jenckel 250/41.9 10/1968 Wanless et a1 250/41.9

57021465 VE55EL.

[ Nov. 19, 1974 Primary Examiner-William F. Lindquist Attorney, Agent, or Firm-Watts, Hoffmann, Fisher & Heinke Co.

[57] ABSTRACT An ion source for separately ionizing a plurality of vaporized samples and focusing the ions produced by the ionization into an ion beam containing ions from each of the vaporized samples. The ion source comprises an ionization chamber having an aperture through which ions are emitted, means for emitting an electron beam into the ionization chamber, at least one ion control electrode for establishing an ion control field, and partition means for dividing the ionization chamber into a first and second electron bombardment chamber. The ion source also includes a first and second gas storage vessel for respectively introducing at least a first and second vaporized sample into the first and second electron bombardment chambers, respectively, so that the first and second vaporized samples are independently ionized.

14 Claims, 2 Drawing Figures STORAGE V5555!- 5UPPLY HOUSE DE TEC T02 PLURAL SAMPLE ION SOURCE BACKGROUND OF THE INVENTION This invention pertains to the art of ion sources and, more particularly, to improved ion sources for independently ionizing a plurality of gas samples.

Known ion sources have included an ionization chamber into which two different gas samples are introduced in order to ionize the samples by electron bombardment. Generally, one of the gas samples is a reference sample of which the spectral peaks are of a known mass, and the other sample is an unknown sample in which the spectral peaks thereof are to be compared with those of the reference sample. The molecules of the gas samples are ionized by an electron beam which passes through the chamber, and the ions produced by this ionization process are then focused and accelerated by a series of electrodes so that the ions are projected through an ion exit slit in the ion source. When such ion sources are employed in a mass spectrometer system, the projected ions are directed into a magnetic analyzer of the spectrometer.

In these mass spectrometer systems, it is desirable to maintain the ion current of each of the gas samples at a relatively high value. In order to obtain an ion current of a relatively high level, it is necessary to increase the value of the ionizing electron beam current, or altematively, it is necessary to increase the total pressure of the two samples in the ionization region. It has been found, however, that when the ionizing electron beam current is sufficiently high and the total pressure of the two samples in the ionization region exceeds a certain critical value, an increase in the partial pressure of one of the gas samples causes a decrease in the number of ions produced from the other sample. Thus, when the reference sample is introduced into the ionization chamber, i.e., an increase in the partial pressure of the reference sample, the number of ions of the unknown sample present in the ion beam decreases. This decrease in the number of ions developed by the unknown sample whenever the reference sample is introduced into the ionization chamber results in a decrease in the intensity of the spectral peaks of the unknown sample, thereby resulting in measurement errors.

More particularly, it has been found that if nitrogen is present in an ionization chamber at a pressure exceeding a certain critical value, the nitrogen ion current in the ion beam decreases approximately exponentially as the pressure of another sample, such as heptacosa fluoro tributylamine, is linearly increased.

SUMMARY OF THE INVENTION The present invention is directed toward an ion source in which a plurality of vaporized samples may be independently ionized, thereby overcoming the noted disadvantages, and others, of such previous ion sources.

In accordance with one aspect of the present invention, the ion source for separately ionizing a plurality of gas samples comprises an ionization chamber having an aperture for the passage of ions, means for emitting an electron beam into the ionization chamber for developing ions by electron bombardment, at least one ion control electrode for establishing an ion control field, and partition means for dividing the ionization chamber into a first and second electron bombardment chamber, so that a first and second gas sample may be independently ionized. A pair of gas storage vessels are respectively associated with the first and second electron bombardment chambers so that the first and second gas samples may be separately introduced into the electron bombardment chambers.

In accordance with another aspect of the present invention, there is provided, in a mass spectrometer, an ion source having an ionization chamber for separately .ionizing a plurality of vaporized samples. The ionization chamber includes an evacuatable chamber having an aperture for the passage of ions, means for dividing the evacuatable chamber into at least a first and second electron bombardment chamber, means for emitting an electron beam into the ionization chamber for developing ions by electron bombardment, and means for establishing an ion transporting field for propelling the ions through the aperture so that the ions are directed into an ion beam. A pair of passage means are provided for introducing a first and a second gas sample into the first and second electron bombardment chambers, respectively, so that the first and second gas samples are independently ionized.

In accordance with still another aspect of the present invention, the electron beam emitting means includes a pair of electron emitting elements for respectively emitting a first electron beam into the first electron bombardment chamber and a second electron beam into the second electron bombardment chamber so that the first and second vaporized samples are separately ionized by the pair of electron beams.

In accordance with a still further aspect of the present invention, the ion source includes means for evacuating air from the first and second electron bombardment chamber.

In accordance with another aspect of the present invention there is provided a method of generating an ion beam containing ions from a plurality of vaporized samples. The steps in accordance with this method include, introducing a first and second vaporized sample into a first and second electron bombardment chamber, separately ionizing the first and second vaporized sample in the first and second electron bombardment chambers respectively to thereby generate ions from the vaporized samples, and, accelerating the ions produced from both of the vaporized samples through an aperture means to thereby form a single ion beam.

The primary object of the present invention is to provide an ion source having an ionization chamber for separately ionizing a plurality of vaporized samples.

Another object of the present invention is to provide an ion source wherein the ionization chamber includes partition means for dividing the ionization chamber into a plurality of separate electron bombardment chambers so that a plurality of gas samples may be independently ionized.

A further object of the present invention is to provide an ion source wherein at least two gas samples are separately ionized. and the ions developed upon ionization of the two gas samples are then focused into an ion beam.

A still further object of the present invention is to provide an ionization chamber wherein at least two vaporized samples may be ionized in a manner such that an increase in the partial pressure of one of the samples has substantially no effect on the number of ions developed by the other vaporized sample.

Another object of the present invention is to provide an ion source wherein at least two gas samples may be ionized in such a manner such that an increase in the partial pressure of one gas sample has substantially no effect on the ionization of the other sample.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the invention will become apparent from the following description of the preferred embodiment of the invention as read in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram, sectional view of an ion source illustrating a preferred embodiment of the present invention; and,

FIG. 2 is a sectional view of the ion source illustrated in FIG. 1, taken along line 2--2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 illustrates a mass spectrometer 10, which generally comprises an evacuatable chamber 14 which encloses an ionization chamber 12 and a collector assembly 13. The ionization chamber 12 includes an aperture 16 for the passage of ions, and a partition wall 18 which divides the ionization chamber 12 into a pair of electron bombardment chambers 20, 22. The aperture 16 is defined by a pair of chamber walls 23, 25, each of which has a leading edge 27, 29, which slopes away from the aperture 16. The walls 23, 25 are electrically insulated from the remainder of electron bombardment chamber 20, 22, and each of the wall 23, 25 is electrically connected to voltage supply source 8-]. The edge 31 of partition wall 18 tapers to a point so as to direct the ions through the generally funnel shaped aperture 16. Ionization chamber 12 is electrically connected to a voltage sup ply S-l. Positioned within electron bombardment chamber 20 is a generally arcuate shaped ion repeller electrode 24, which is electrically connected to a voltage supply source S-l. Similarly, positioned within electron bombardment chamber 22 is a generally arcuate shaped ion repeller electrode 26 which is electrically connected to voltage supply source 8-1.

The electron bombardment chambers 20, 22 are respectively coupled to a pair of gas storage vessels 28, 30, electrically insulated from ionization chambers 20 and 22, so that a first and second gas sample may be introduced into the electron bombardment chambers 20, 22. Also, an electron beam 32 is emitted into electron bombardment chamber 20 by the flow of the electrons between a cathode 34 and an anode 36 through a pair of apertures 38, 40 in electron bombardment chamber 20. The cathode 34 and anode 36 are connected to voltage supply source -1 in a known manner for providing the flow of an electron current between these elements. In a similar manner, an electron beam 42 is emitted into electron bombardment chamber 22 by another anode-cathode arrangement positioned across bombardment chamber 22.

Mass spectrometer also includes a vacuum pump 44 for maintaining a relatively high vacuum in evacuatable chamber 14. The ions generated upon ionization of the two gas samples in electron bombardment chambers 20, 22 are respectively accelerated by

repeller electrodes

24, 26, and are emitted through aperture 16 to form a single beam of ions containing ions from both samples. This beam of ions is then focused by a pair of

beam centering electrodes

48, 50 and a pair of

ground electrodes

52, 54, so that the beam passes through a ground slit 56 and is projected to collector assembly 13.

The collector assembly 13 includes an outlet aperture 58 and a collector electrode 60, which are respectively connected to voltage supply source S-1 and a detector D1 of known design. Each of the

electrodes

48, 50, 52, 54, as well as evacuatable chamber 14, is electrically connected to voltage supply source S-] in a known manner.

Thus, upon introduction of

electron beams

32, 42, into electron bombardment chambers 20, 22, the two gas samples present in bombardment chambers 20, 22 are ionized and accelerated by the

arcuate repeller electrodes

24, 26 thereby propelling the ions through the funnel-shaped aperture 16 in ionization chamber 12. It has been found that by separately controlling the voltage signal applied to the chamber walls 23, 25, optimum performance of each bombardment chamber 20, 22 may be obtained even though there is a slight variation in the geometrical dimensions of the bombardment chamber 20, 22. The ions from the gas samples are accelerated and focused into a single beam containing ions generated from both samples. Accordingly, an increase in the partial pressure applied to the gas sample in electron bombardment chamber 20 has substantially no effect on the number of ions generated by the gas sample in electron bombardment chamber 22, and similarly, an increase in the partial pressure applied to the gas sample in bombardment chamber 22 has substantially no effect on the number of ions generated by the gas sample in chamber 20. As is apparent, the energy level of electron beam 32 may be set equal to the energy level of the electron beam 42, or these energy levels may be set at different values, depending on the nature of the spectrometric analysis to be conducted.

Although the invention has been shown in connection with a preferred embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Having now described my invention, I claim:

1. An ion source for a mass spectrometer comprising:

a. an evacuable ionization chamber;

b. inlet means for introducing a plurality of vaporized samples into separate regions of said chamber;

c. common aperture means defining at least one opening in communication with said ionization chamber through which ions formed in each of said regions exit to form an ion beam;

= d. partition means within said chamber for restricting the movement of the vaporized samples between said regions;

e. means for developing ions of the samples in their respective regions of said chamber;

f. electrode means for accelerating the ions through said common aperture means thereby producing an ion beam containing ions from each of the samples; and,

g. said partition means extending to a position adjacent said common aperture means to define flow paths whereby ions from each of said regions may exit said ionization chamber through said opening without passing through any other regions.

2. The apparatus of claim 1 wherein said common aperture means comprises a single centrally located opening communicating with said ionization chamber, and said partition means divides said ionization chamber into substantially symmetrical regions of substantially equal size.

3. The apparatus of claim 1 wherein said opening has edges shaped to facilitate the flow of ions from said ionization chamber and the formation of a single ion beam.

4. The apparatus of claim 1 wherein the portion of said partition means which extends in the region of said opening is shaped to facilitate the flow of ions from said ionization chamber and the formation of a single ion beam.

5. The apparatus of claim 4 wherein said portion comprises edges tapered toward the region of said opening to provide said portion with a substantially pointed configuration.

6. The apparatus of claim 1 wherein:

said partition means divides said chamber into first and second electron bombardment chambers; and

said inlet means comprises first and second inlet passage means for respectively introducing first and second vaporized samples into said first and second electron bombardment chambers.

7. The apparatus of claim 6 wherein said partition means extends adjacent said opening in a plane which is substantially perpendicular to the plane of said openmg.

8. The apparatus of claim 7 wherein the portion of said partition means which extends in the region of said opening, and the edges of said opening are shaped to facilitate the flow of ions from said ionization chamber and the formation of a single ion beam.

9. The apparatus of claim 1 wherein said aperture means comprises an ion exit slit, the edges of which are tapered to facilitate the flow of ions from said ionization chamber and the formation of a single ion beam.

10. The apparatus of claim 1 wherein said electrode means comprises a separate repeller plate disposed in each of said regions for accelerating the ions produced in that region into the ion beam.

11. An ion source for separately ionizing a plurality of gas samples, comprising:

a. an ionization chamber having a single aperture through which ions are emitted;

b. inlet means for introducing a plurality of gas samples into separate regions of said chamber;

c. means for developing ions of the samples in their respective regions of said chamber;

d. partition means within said chamber for restricting the movement of the samples between said regions;

e. ion control electrode means in each of said regions for establishing an ion control field for propelling ions through said aperture to form a single ion beam including ions of each of the samples; and,

f. said partition means extending to a position adjacent said aperture to define flow paths whereby ions from each of said regions may exit said ionization chamber through said aperture without passing into any of the other regions.

12. The apparatus of claim 11 wherein said ion control means in each of said regions comprises a separate ion control electrode positioned in each of said regions.

13. A method of generating an ion beam containing ions from a plurality of vaporized samples with an ion source including an ionization chamber partitioned into separate ionization regions and having a common aperture means through which ions exit the ionization chamber, comprising the steps of:

introducing a first vaporized sample into a first one of said regions;

introducing a second vaporized sample into a second one of said regions; separately ionizing each of said samples in its respective region by electron bombardment; and,

accelerating ions produced in each of said regions through said common aperture means to produce an ion beam containing ions of each of said samples.

14. A method of generating an ion beam as defined in claim 13 comprising the steps of:

emitting a first electron beam through said first electron bombardment region for ionizing the first vaporized sample; and, emitting a second electron beam through said second electron bombardment region for ionizing the second vaporized sample so that the samples are ionized by separate electron beams.

Claims

1. An ion source for a mass spectrometer comprising: a. an evacuable ionization chamber; b. inlet means for introducing a plurality of vaporized samples into separate regions of said chamber; c. common aperture means defining at least one opening in communication with said ionization chamber through which ions formed in each of said regions exit to form an ion beam; d. partition means within said chamber for restricting the movement of the vaporized samples between said regions; e. means for developing ions of the samples in their respective regions of said chamber; f. electrode means for accelerating the ions through said common aperture means thereby producing an ion beam containing ions from each of the samples; and, g. said partition means extending to a position adjacent said common aperture means to define flow paths whereby ions from each of said regions may exit said ionization chamber through said opening without passing through any other regions.

6. The apparatus of claim 1 wherein: said partition means divides said chamber into first and second electron bombardment chambers; and said inlet means comprises first and second inlet passage means for respectively introducing first and second vaporized samples into said first and second electron bombardment chambers.

7. The apparatus of claim 6 wherein said partition means extends adjacent said opening in a plane which is substantially perpendicular to the plane of said opening.

11. An ion source for separately ionizing a plurality of gas samples, comprising: a. an ionization chamber having a single aperture through which ions are emitted; b. inlet means for introducing a plurality of gas samples into separate regions of said chamber; c. means for developing ions of the samples in their respective regions of said chamber; d. partition means within said chamber for restricting the movement of the samples between said regions; e. ion control electrode means in each of said regions for establishing an ion control field for propelling ions through said aperture to form a single ion beam including ions of each of the samples; and, f. said partition means extending to a position adjacent said aperture to define flow paths whereby ions from each of said regions may exit said ionization chamber through said aperture without passing into any of the other regions.

13. A method of generating an ion beam containing ions from a plurality of vaporized samples with an ion source including an ionization chamber partitioned into separate ionization regions and having a common aperture means through which ions exit the ionization chamber, comprising the steps of: introducing a first vaporized sample into a first one of said regions; introducing a second vaporized sample into a second one of said regions; separately ionizing each of said samples in its respective region by electron bombardment; and, accelerating ions produced in each of said regions through said common aperture means to produce an ion beam containing ions of each of said samples.

14. A method of generating an ion beam as defined in claim 13 comprising the steps of: emitting a first electron beam through said first electron bombardment region for ionizing the first vaporized sample; and, emitting a second electron beam through said second electron bombardment region for ionizing the second vaporized sample so that the samples are ionized by separate electron beams.