US3522428A

US3522428A - Mass spectrometer having a plurality of relatively movable collectors

Info

Publication number: US3522428A
Application number: US638827A
Authority: US
Inventors: Patrick Powers
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1966-05-17
Filing date: 1967-05-16
Publication date: 1970-08-04
Anticipated expiration: 1987-08-04
Also published as: GB1161395A; DE1598023A1

Description

Aug.14, 1970 RELATIVELY MOVABLE COLLECTORS 2 Sheets-Sheet 1 Filed May 16, 1967 1 5 M W OE H mm m w 8 W W mm Av Q Q Q H mm P Wfi m UHIIIIIJ I ll w IJII lluainfliifli mwp A 0Q Ql c 1 m Nm\ om\ United States Patent U.S. Cl. 250-41.9 14 Claims ABSTRACT OF THE DISCLOSURE A mass spectrometer is provided with a collector arrangement in which collectors are movable relative to one another. Each collector is adapted to receive a portion of the mass spectrum analyzed.

CROSS REFERENCE TO RELATED APPLICATION Mass Spectrometer Sample Movement and Ion Beam Deflector, Ser. No. 638,857, filed May 16, 1967, by Patrick Powers.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to collector structure for mass spectrometers and more particularly to a collector structure in which the collectors are movable relative to one another.

Description of the prior art The present invention is particularly useful with spark-source mass spectrometers. In a spark-source mass spectrometer, ions of a material to be studied are produced by applying a high voltage across two electrodes, one or both of which are composed of the sample material, to thereby produce a spark between them. During the period of the spark, ions emanate from the sample material and are accelerated, for example, by a high voltage accelerating electrode. The ions form an ion beam which is deflected by magnetic and, in so-called double focusing instruments, electrostatic means, and a particular portion of the mass spectrum represented by the ion beam is read as an output on a photographic or electric collector.

When analyzing materials with a spark-source mass spectrometer, it has been customary to use photographic detection so that the variations in the ion beam are averaged out by taking exposures of sufiicient duration on a photographic plate. The accuracy of measuring relative concentrations of impurities in some types of sample material is relatively poor. The range of error may be as much as 20% to 30% or more.

This inaccuracy results from a number of conditions, one of which is the non-linear response and uneveness of photographic emulsions. Specifically, the photographic material has an emulsion layer with silver halide deposited on the surface. It is difiicult to obtain a precisely uniform distribution of the silver halide and the silver halide tends to become embedded in the emulsion. Those portions of the silver halide embedded in the emulsion will not be properly exposed by the ions and an irregular distribution of the silver halide on the surface of the emulsion will result in uneven exposures. Photographic techniques present further problems attendant to the difficulties of insertion and removal of a photographic plate from the vacuum chamber of a mass spectrometer before and after exposure.

If electrical detection by known methods is used, then 3,522,428 Patented Aug. 4, 1970 only one peak in the mass spectrum can be viewed at a time, and because of the varying nature of the ions produced by the spark, the results of such analysis are usually worse and rarely better than with photographic detection.

SUMMARY OF THE INVENTION According to one form of the present invention, electrical detection means in or for a mass spectrometer comprises a series of ion collectors mounted or mountable at respective positions at which they can collect ions in respective different regions of a mass spectrum, the collectors being adjustable in position relative to one another so that selected ion beams in the mass spectrum may be intercepted by the respective individual collectors.

Each collector is capable of producing an electrical output indicative of the intensity of the ion beam intercepted by it. More specifically, it is contemplated that the collectors are movably mounted on a plate, each collector being insulated from the other collectors and from ground. The plate upon which the collectors are mounted may be permanently mountable in the analyzer portion of the mass spectrometer or may be insertable into the analyzer through a vacuum lock in the same manner as a photoplate. The mounting structure for each collector is preferably provided with a tongue or other contact means slidably engaging one of a plurality of stationary output conductors for conveying an electrical signal from the collector out of the evacuated portion of the mass spectrometer to suitable external amplifiers.

With a permanently-mounted plate within the mass spectrometer, the individual collectors or collector units could be made adjustable from outside the evacuated portion of the mass spectrometer by mechanical means such as the threaded rod arrangement described in the British patent specification No. 957,117, published May 6, 1964, entitled Improvements Relating to Mass Spectrometers. As described in the aforementioned specification, each collector unit may be mounted on a guide rod and a threaded rod, which is rotatable by a shaft extending through a vacuum-tight seal of the mass spectrometer. Rotation of the shaft moves the collector unit along the rods across the paths of the individual ion beams.

With an insertable and removable plate, it is preferred to adjust the respective positions of the collectors prior to insertion into the collecting region of the instrument. The respective positions of the collectors are determined by means of a template which, for example, may be a previously exposed and developed photoplate or a fluorescent plate with a long decay time.

Employing such arrangements, simultaneous detection of many or all of the interesting impurities in a sample may be achieved in a manner which avoids inherent disadvantages of a photographic plate. It is believed that the analytical accuracy obtainable with the novel arrangement may well approach that of instruments employing optical spectroscopy.

Accordingly, an object of the present invention is to provide a novel and improved mass spectrometer and method of operating a mass spectrometer for analyzing ions of a sample material with greater accuracy than by photographic means.

An additional object of the present invention is to provide a novel and improved mechanism for electrical ion beam detection enabling a mass spectrometer to simultaneously produce a number of electrical outputs indicative of the respective intensities of ion beams in different regions of the mass spectrum.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematic sectional view of a mass spectrometer equipped with the novel collector arrangement of this invention;

FIG. 2 is a side elevational view of the novel collector arrangement;

FIG. 3 is a bottom view of the arrangement shown in FIG. 2;

FIG. 4 is an enlarged view of one of the collector units as seen from the plane indicated by line 4-4 in FIG. 3; and

FIG. 5 is a side elevational view of an alternative form of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a single focusing mass spectrometer includes an ion source for producing ions of material to be analyzed, for example, by developing a high voltage spark between two electrodes, one or both of which is a sample. A suitable technique for producing ions is described in the referenced co-pending application of Patrick Powers. The ions are emitted from the ion source 10 and accelerated by known techniques and are established along respective paths as a plurality of ion beams 11. The ion beams 11 pass through and are deflected by a magnetic field in a magnetic analyzer 12, the amount of deflection of ions included in an individual ion beam depending upon the mass of ions included in it. The ion beams 11 are directed toward a collector arrangement 13 situated in the paths of the ion beams 11 within the evacuated portion of the mass spectrometer. The ion beams 11 impinge on respective individual collectors which are a part of the collector arrangement 13, to produce a plurality of outputs indicative of the composition of each respective ion beam.

Referring to FIGS. 2-4, the collector arrangement of one form of the present invention generally comprises a support plate 14 having two elongated entrance slots or tracks 15, 15' aligned end-to-end longitudinally along the support plate 14 near the top thereof. The right-hand portion of the collector structure shown in FIGS. 2 and 3 is fragmented, however, it has the same construction as the left-hand portion shown in detail. The support plate 14 should be aligned transversely to the path of travel of the ion beams and should be so oriented that the entrance slots 15, 15 will receive ions over a range of the mass spectrum to be analyzed.

The support plate 14 has closely spaced, longitudinally aligned, guide slots or

tracks

16, 16. The support plate 14 also has closely spaced, longitudinally aligned, guide slots or

tracks

18, 18 arranged parallel to the

guide slots

16, 16 respectively. The entrance slot 15 and the

guide slots

16, 18 are substantially the same length and are parallel to one another. Similarly, the entrance slot 15' and the guide slots or tracks 16, 18' are substantially the same length and are parallel to one another.

A support block 20 is fixed to and extends from the support plate 14 at the left hand end of the support plate as viewed in FIGS. 2 and 3. The support block 20 is spaced a short distance from the ends of the

guide slots

16, 18. Similarly, a support block 22 is fixed to and extends from the face of the support plate 14 near its opposite end and is spaced a short distance from the ends of the guide slots or tracks 16, 18'. The

support blocks

20, 22 are preferably composed of an insulating material such as polytetrafluoroethylene (referred to as PTFE), marketed by E. I. Du Pont under the trademark Teflon.

A group of spaced, parallel output conductors 24-29 are spaced from and arranged in a plane parallel to the support plate 14. The output conductors 24-29 abut the

support blocks

20, 22. Clamping

blocks

30, 32 secure the output conductors 24-29 against the

support blocks

20, 22. The

clamping blocks

30, 32 are also composed of PTFE and are secured against the

support blocks

20, 22 to firmly secure the output conductors 24-29 by means of

clamp screws

34, 36 respectively, located between alternate rows of the conductors 24-29.

The collector arrangement shown in FIGS. 2 and 3 includes three collector units designated generally by the

numerals

40, 41, 42 supported by the support plate 14. For convenience purposes, only three units are shown, however, it is contemplated that the embodiments shown in FIGS. 2 and 3 will include a total of six collector units three shown arranged along the left-hand portion of the support plate 14 and three more (not shown) arranged along the right-hand portion. It should be understood that the present invention is not limited to the use of six units, and more or less may be used as desired. All of the collector units are identically constructed except for the positioning of output connections to the respective output conductors 24-29.

For convenience, only the collector unit 40 shown in detail in FIG. 4 will be described in detail. since it is identical to the others. The collector unit 40 includes a U- shaped frame 44 which itself includes a body portion 46 aligned normal to the plane of the support plate 14, a base arm portion 47 slidably engaging and parallel to the support plate 14 and an upper arm portion 48, partially hidden, spaced from and parallel to the base arm portion 47. The base arm portion 47 includes two spaced portions 50, 51 which project in opposite directions from the base arm portion 47. The portions 50, 51, have threaded

bores

52, 53 for receiving screws 54, 55 respectively. The shaft portions of the screws 54, 55 pass through and are slidably disposed in the slots or

tracks

18, 16, respectively, to permit movement of the frame 44 along the support plate 14 in a path normal to the plane of the drawing shown in FIG. 4 and transverse to the path of the ion beam indicated by the arrow B through the entrance slot 15.

A collector mount 60 including a secured portion 61 and a mounting portion 62 is connected to the upper arm portion 48 at the secured portion 61 by means of screws 64. The mounting portion 62 is bent toward the arm portion 47 to form an obtuse angle with the secured portion 61. The mounting portion 62 includes a depending projection 68 aligned parallel to the body portion 46. A collector plate 70 is connected to the projection 68.

The mounting portion 62 has a plurality of equally spaced holes 65 arranged in a row. A connection in the form of a tongue is mounted on the mounting portion 62 and secured thereto by screws 91 disposed in the holes 65 at the end of the mounting portion 62 farthest from the body portion 46. The connection 90 lies in a plane somewhat parallel to the mounting portion 62 and has an indentation 92 at one end for receiving and engaging the output conductor 24 and thereby conducting an output signal to the output conductor 24. Additionally, it should be understood that the other five collector units will each have a similar connection for engaging a selected one of the output conductors 25-29.

A detection means upon which a respective ion beam impinges comprises an electron multiplier connected to the frame 44. The multiplier 100 may, for example, be a Mullard B Series tube. As shown in FIG. 4, the ion beam travels in the path of the arrow B and impinges on a detecting portion of the multiplier 100.

The inputs to the multiplier 100 are taken via conductors 110, 111 from

contacts

114, 115, respectively, spaced from one another at the outer face of the body portion 46. Electrical contact is made with a pair of

busbars

120, 121 by means of

suitable contacts

124, 125. The

busbars

120, 121 are spaced and parallel to one another and to the path of travel of the collector unit 40 so that electrical contact may be maintained with

terminals

114, 115 while the collector unit 40 is moved back and forth. The ends of the

busbars

120, 121 are connected to the support blocks 20, 22, respectively, and are connected to a suitable supply voltage for the multiplier 100 via conductors 128, 129. The output end of the multiplier 100 is electrically connected to the collector plate 70. Sir

nals from the multiplier are transmitted from the collector plate 70 via the output conductor 24.

As already mentioned, the collector units are similarly constructed and differ only in the. means for conducting an electrical signal to the output conductors 24-29. As shown, the collector unit 40 is adapted to transfer a signal to output conductor 24, collector unit 41 is adapted to transfer an output signal to output conductor 25, and collector unit 42 is adapted to transfer an output signal to the conductor 26. Also, all three

collector units

40, 41, 42 receive the appropriate input potential from the

busbars

120, 121.

In operation, if the collector arrangement is intended to be permanently mounted within a mass spectrometer, suitable adjustment means may be provided as described in the British specification No. 957,117. If the collector arrangement is intended to be inserted and removed from a mass spectrometer, a suitable template can be made on a previously exposed and developed photographic plate or on a fluorescent plate with a long decay time. The respective positions of the individual collector units may be chosen to correspond with the position of peaks appearing on the template and the collector arrangement may then be inserted into the mass spectrometer to electrically detect ions in a predetermined portion of the mass spectrum.

An alternative form of the present invention is shown in FIG. 5. This arrangement similarly has a support plate 130 having entrance slots 132, 133 aligned end-to-end olngitudinally near an edge of the support plate 130. The support plate 130 also includes adjustment slots 135, 136 to provide room for movement of clamps 138, 139 slidably connected to the support plate 130. The clamps 138, 139

hold ion collectors

142, 143, respectively, arranged adjacent the entrance slots 132, 133, respectively, each for receiving an oncoming ion beam in a predetermined range of the mass spectrum. The

ion collectors

142, 143 are ceramic tubes which are lined with a suitable conductive, collecting metal material. Upper portions of the

ion collectors

142, 143 are cut away to provide concave surfaces oriented toward the entrance slots 132, 133.

The output from the ion collector 142 is taken via a conductor 146 through a ceramic tube 147 connected to the support plate 130 by means of a clamp 148. An output conductor 149 from the ion collector 143 and the conductor 146 both pass through twin bores in a ceramic tube 150 indicated in dotted lines connected to the support plate 130 by means of a clamp 152 also indicated in dotted lines. The

conductors

146, 149 then proceed to

contacts

154, 155 respectively mounted on

slides

157, 158, respectively, slidably arranged on a ceramic support rod 159. The outputs from the

ion collectors

142, 143 are ultimately taken from the

contacts

154, 155.

As with the first form of the present invention, it may be preferable to provide means for moving

ion collectors

142, 143 to desired locations with the entire collector arrangement mounted within an evacuated portion of a mass spectrometer.

With both forms of the invention described in detail, it will be apparent to a person of ordinary skill in the art how many individual collectors should be used in the analysis of a particular substance and what portions of the mass spectrum should be studied. As described above, the individual collector positions may be selected either before exposure, or if external adjustment means is employed, adjustments may additionally be made during exposure.

Although the invention has been described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms 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 mass spectrometer for analysis of material comprising:

(a) an ion source for producing ions of a material to be analyzed, the ions established in a beam along a path;

(b) magnetic deflection means disposed near the path of the ion beam for deflecting the ions into a plurality of ion beams;

(c) a collector structure including:

a plurality of collector assemblies;

a base plate having at least one elongated ion beam opening therein and parallel track means for supporting said plurality of collector assemblies;

fastener means associated with each said collector assembly for securing said associated assembly to said track means;

each assembly including a generally U-shaped frame member having a base connected to said fastener means, a body portion, and an upper arm portion;

a plurality of output conductors each connected to a different assembly for transmitting signals from the assemblies;

each of the assemblies also includes a collector secured to the upper arm and a connection connecting the collector to its output conductor;

each assembly further includes a mechanism sensitive to ion bombardment connected to the collector for emitting signals when struck by ions that have passed through said opening;

4 said plurality of output conductors adapted to be coupled to an indicator means for providing an output indication representative of said emitted signals.

2. The apparatus of claim 1 wherein the collectors are multiplier tubes.

3. The apparatus of claim 1 wherein the collectors each include a non-conductive tube lined with a metal conductive material.

4. An electrical collector mechanism for a mass spectrometer comprising:

(a) a base plate having elongated slits and at least one parallel elongated ion beam transmitting opening;

(b) a plurality of collector assemblies each secured to the base plate by a plurality of fasteners passing through said slits;

(c) each assembly including a generally U-shaped frame member having a base connected to said fasteners, a body portion, and an upper arm portion;

(d) a plurality of output conductors each connected to a difierent assembly for transmitting signals from the assemblies;

(e) each of the assemblies also includes a collector secured .to the upper arm and a connection connecting the collector to its output conductor;

(f) each assembly further includes a mechanism sensitive to ion bombardment connected to the collector for emitting signals when struck by ions that have passed through said opening;

(g) said plurality of output conductors adapted to be coupled to an indicator means for providing an output indication representative of said emitted signals.

5. The structure of claim 4 wherein each collector assembly includes an electron multiplier for receiving an ion beam.

6. The collector mechanism of claim 4 wherein each of the assemblies includes a connector in sliding engagement with its associated output conductor whereby to maintain electrical contact in any adjusted position.

7. The collector mechanism of claim 4 wherein each of the assemblies includes a connection removably secured to the balance of the assembly at a selected location in alignment with its output conductor and the assemblies are identical except for the selected position of the connection.

8. The mechanism of claim 4 wherein each mechanism sensitive to ion bombardment includes a non-conductive tube lined with a metal conductive material.

9. An electrical collector for a mass spectrometer comprising:

a plurality of collector assemblies;

a base plate having at least one elongated ion beam opening therein and track means generally parallel to said beam opening for supporting said plurality of collector assemblies;

a plurality of output conductors each connected to a diflerent assembly for transmitting signals from the assemblies;

said plurality of output conductors adapted to be cou pled to an indicator means for providing an output indication representative of said emitted signals.

10. The apparatus of claim 9 wherein the collectors each include a non-conductive tube lined with a metal conductive material.

11. The mechanism of claim 9 wherein each mechanism sensitive to ion bombardment is an electron multiplier.

12. An electrical collector as defined in claim 9 wherein said track means is an elongated track means situated in parallel relationship with respect to said elongated ion beam opening.

13. An electrical collector as defined in claim 12 wherein said track means includes a pair of elongated track means situated in parallel relationship with respect to each other.

14. An electrical collector as defined in claim 12 wherein said track means is defined by at least one elongated slit extending through said base plate and being generally parallel to said ion beam opening, and each said collector assembly is secured to said base plate by said associated fastener means extending through said elongated slit.

References Cited UNITED STATES PATENTS 2,566,037 8/1951 Shewell 2504l.9 2,854,583 9/1958 Robinson 2504l.9 3,240,931 3/1966 Wiley et al 2504l.9

FOREIGN PATENTS 957,117 5/1964 Great Britain.

WILLIAM F. LINDQUIST, Primary Examiner