US3590243A

US3590243A - Sample insertion vacuum lock and probe assembly for mass spectrometers

Info

Publication number: US3590243A
Application number: US837549A
Authority: US
Inventors: Richard E Perrin; Billy A Hopper
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1969-06-30
Filing date: 1969-06-30
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29

Abstract

A sample insertion vacuum lock and probe assembly for use in mass spectrometers is disclosed in which an axially extending sample carrier is mounted for reciprocal movement into and out of an ion chamber. Electrical connection with the sample carrier probe is made through sliding engagement of the probe with an electrical contact support assembly mounted in the ion chamber. A vacuum lock and a vacuum system is provided to insure that the vacuum in the ion chamber is not disturbed. Mechanical locking means and positioning means are included to prevent accidental destruction of the vacuum and to precisely position the sample within the ion chamber.

Description

United States Patent [72] Inventors Richard E. Perrin;

Billy A. Hopper, both of Tulsa, Okla. [21] Appl. No. 837.549 [22] Filed June 30. 1969 [45] Patented June 29, 1971 [73] Assignee Avco Corp.

Tulsa. Okla.

[54] SAMPLE INSERTlON VACUUM'LOCK AND PROBE ASSEMBLY FOR MASS SPECTROMETERS 2 Claims, 3 Drawing Figs.

[52] U.S.Cl 250/419 S. 250/4l.9 SE [5 I] Int. Cl H0lj 39/34 {50] Field of Search 250/419 SE, 41.9 S

[56] References Cited UNITED STATES PATENTS 2,756,341 7/1956 White 250/419 Primary Examiner-William F. Lindquist Attorneys-Charles M. Hogan and Eugene C. Goodale ABSTRACT: A sample insertion vacuum lock and probe assembly for use in mass spectrometers is disclosed in which an axially extending sample carrier is mounted for reciprocal movement into and out of an ion chamber. Electrical connection with the sample carrier probe is made through sliding engagement of the probe with an electrical contact support assembly mounted in the ion chamber. A vacuum lock and a vacuum system is provided to insure that the vacuum in the ion chamber is not disturbed. Mechanical locking means and positioning means are included to prevent accidental destruction of the vacuum and to precisely position the sample within the ion chamber.

72 PUMP PUMP PATENTEUJUNZSISH 3.590243 SHEET 2 OF 3 INVENTORS. RICHARD E. PERRIN BY BILLY A. H

SAMPLE INSERTION VACUUM LOCK AND PROBE ASSEMBLY FOR MASS SPECTROMETERS BACKGROUND OF THE INVENTION The present invention relates to vacuum locks and more particularly to vacuum locks and specimen carrying probes used in mass spectrometers for changing specimens to be analyzed.

The analysis of samples by standard surface ionization mass spectrometry techniques requires that the sample undergoing analysis be inserted directly into the mass spectrometer ion source. The ion source of the mass spectrometer standardly operates at a pressure no greater than 1 l0 torr. It is therefore necessary, in operation, to provide either a rapid method of pumping out the ion source after changing a sample or a method of inserting the-sample without breaking the mass spectrometer vacuum.

Previous techniques; typically utilized in mass spectrometric analyses, provided a method of removing atmospheric pressures from the ion source region after insertion of the sample. Adsorbtion of atmospheric water increases the time required to achieve operational vacuum; typically a minimum of l5minutes is required to reach operational levels. Adsorbtion also reduces source life due to reactions between it and the sample materials resulting in rapid contamination of the ion source.

One common method of inserting samples into a thermal emission mass spectrometer consists of venting the ion source to atmosphere and inserting the filament hat carrying the sample through the back cover flange. This method requires that the entire ion sourcebe pumped out after each new saniple. In addition to severely limiting sample throughput, this procedure also increases contamination to the ion sou'fce and decreases filament life on the ion gauges.

Two approaches have been used by others to eliminate these problems. The first approach consists of mounting several filament hats on a rotatable wheel. This approach has two undesirable features. The chance of cross contamination between filaments is greater and the life of the electrical con tacts is extremely short. 7

The second approach has been to use a vacuum lock. A vacuum lock is a device which permits the interchange of some piece of equipment into or out of a vacuum chamber without loss of the vacuum. In the field of mass spectroscopy, the use of a vacuum lock assembly to interchange samplesfor ionization by the thermal emission method has proven to be helpful, particularly to those investigators whose needs require a high quantity of routine analyses to be performed. In such locks, the specimen carrier is moved by a thrust rod through a valve aperture from the locked chamber into the analyzer, or other vacuum chamber, and subsequently removed. The shaft of the sample probe is usually inserted through a series of differentially pumped chambers divided by Teflon or Viton seals. In this manner the pressure in the final chamber can be equalized with the pressure in the ion source chamber before the valve between the chambers is opened. These systems have been quite expensive to build. The principal cause for this expense is the practice of making electrical connections to the filaments through vacuum seals in the back of the sample probe. The high accelerating voltages needed for ionization require large feedthroughs which increase the sample probe diameter to at least three inches. Such large probes cannot be conveniently handled without elaborate and expensive mechanical or electrical drive mechanisms.

In accordance with the present invention, the drawbacks of presently existing sample insertion vacuum lock devices are overcome by providing a vacuum lock having greater utility and efficiency. The improved assembly of the present invention provides for the precise alignment of filaments and eliminates the need for the usual metal filament hat. All electrical connections are made as the-sample carrier slides into position, thus eliminating the need for insulated vacuum feedthroughs in the probe assembly. The diameter and size of the sample carrier and probe are significantly smaller than previous devices so that no special valves or drive mechanisms are required and the cost of the vacuum lock is significantly reduced.

SUMMARY OF THE INVENTION The present invention provides an improved sample insertion vacuum lock and probe assembly for use in mass spectrometers which eliminates or minimizes the disadvantages encountered in previous systems utilizing sample insertion techniques. The invention comprises a novel sample insertion probe assembly which permits axial insertion of thesample carrier and probe into the ion source. Axial insertion allows a more precise location of the filaments in relation to the source plates and eliminates the need for attaching the back source plates to the insertion probe; thus permitting the usage of sliding contacts which make direct electrical contact with the specimen carrier as the specimen is inserted.

The electrical contacts are located within the vacuum system or ion chamber and the usage of sliding and biased electrical contacts insures constant continuous electrical connection between the electrical system and filaments. Locating electrical contacts in this manner eliminates the usage of high voltage vacuum feedthroughs in the probe assembly. The sample carrier and driver probe are of a smaller diameter and thus reduces the volume of air to-be evacuated from a differential pumping chamber and also contributes to the usage efficiency of the mass spectrometer. A mechanical probe positioner or position limiting device provides a fail safe mechanical system to prevent destruction of the vacuum within the ion source region and also to prevent jamming of the sample into the gate valve on insertion.

Other details, uses, and advantages of this invention will become apparent as the following description of the exemplary embodiment thereof presented in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show a present exemplary embodiment of this invention in which:

FIG. 1 is a side view partially in cross section illustrating an exemplary embodiment of this invention showing the specimen carrier and probe in operational position within the ion chamber;

FIG. 2 is an end view' taken on the line 2-2 of FIG. 1, illustrating the electrical support assembly; and

FIG. 3 is a cross-sectional view of the electrical contact assembly taken on the line 3-3 of FIG. 2.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT Reference is now made to FIG. 1 which shows one exemplary embodiment of the improved sample insertion vacuum lock and probe assembly which is designated generally by the reference numeral 10 and is mounted to a vacuum chamber such as a mass spectrometer ion chamber 12. Conventionally mounted within the ion chamber 12 is an ion source, shown generally as 14, adjacent to which the specimen to be analyzed must be placed.

The specimen to be analyzed is placed on filament elements 16 and 18 (FIG. 2). Filaments l6 and 18, together with an ionization filament 17, are secured to a specimen or sample carrier 20. The carrier 20 is attached in axial alignment with a driver probe 22 in any convenient manner, such as by threadable engagement with a threaded end portion of probe 22. On the other end of probe 22 is a handle element 25 for ease in the insertion and removal of the probe assembly.

The electrical energy necessary to cause the vaporization and ionization of the specimen is supplied to the filaments through a novel electrical contactor ring and switch assembly 23 which is best seen in FIGS. 2 and 3.

The contact support assembly 23 includes a supporting ring or plate 24 which is mounted in the ion chamber by any suitable means. The plate 24 has an aperture 26 formed therethrough. A plurality of contact members, 2811-231, are mounted to the plate 24 with one end of each contact member extending into the aperture area. It is also seen that the axis of each contact member 28 is normal to the axis of the plate aperture.

Each respective contact member 28 includes an outer casing 30 having a central stepped passageway 32 formed therethrough. An inner contact element 34 is slidably mounted in the passage 32 and biased outwardly or into the aperture area 26 by any resilient means such as spring 36. It is seen that the spring 36 abuts against the stepped inner surface of passageway 32 at the one end and against the sliding member 34 at the other.

Apertures 33 and 40 are respectively formed though outer casing 30 and the sliding member 34. It is also noted that the aperture 38 is of greater diameter than the aperture 40. An electrical lead or connector wire 42 extends through aperture 40 and is secured to contact 34 by any suitable means such as a setscrew 43. Thus, with the lead 42 connected to member 34, the sliding movement of member 34 is limited to the amount of clearance between the lead 42 and the aperture 38 of casing 30. Lead 42 is connected to a source of energy which provides the electrical energy for the vaporization of the specimen.

The sample carrier 20 is mounted for reciprocal movement through the aperture 26 in a manner which will be described herebelow. The carrier 20 is made of an insulating material such as a low water adsorbtion ceramic and is mounted to be coaxial with the axis of the plate aperture 26. Stationary contact members 44 are secured to the outer surface of the sample carrier 20 by any suitable means such as screws 46. A like number of contact members, 44a-44f, as there are contact members 28 of the contact support assembly 23, are mounted on the sample carrier so that each stationary contact member cooperatively engages a slidable contact element. Sample carrier 20 has a groove or channel 48 formed thereon in which the contact members 44 are mounted. This facilitates for ease in construction of the contact elements 44 in that the sloping edge need not come to a point to insure ease in sliding engagement with the member 34.

Filaments

16, 17 and 18 each consist of two leg portions and an interconnecting element between the respective leg portions. Each filament leg is respectively secured to a conducting member or rod SOa-Stlf. Each of the conducting rods is connected to a corresponding stationary contact member by the screws 46. Hence, there is electrical continuity between each electrical lead 42 and each filament leg through the respective contacts 34 and 44, screws 46, and conducting rod 50. As an example, the filament l6 legs are attached to

rods

50c and 50f which are in turn in electrical contact with

stationary contacts

44c and 44f.

Referring again to FIG. 11, the assembly may be considered, when assembled, as a one-piece unit which is attached to the ion chamber 12 through an adapter plate which is secured to the ion chamber by any conventional means such as bolts. Thus, the entire assembly 10 may be removed as one piece when desired. However once the assembly 101 is mounted to the ion chamber 12, specimens may be inserted and removed from the chamber without destroying the vacuum therein as will be explained herebelow.

A standard commercially available, high-vacuum gate valve shown generally as 52 isolates the vacuum within chamber 12 from the atmosphere whenever the probe 22 is withdrawn. The gate valve 52 is attached by suitable means to the adapter plate. Extending axially outward from the valve 52 is an outer casing 54 which, when the probe 22 is inserted therethrough, defines chambers 56 and 58. An O-ring 60 is mounted within casing 54 to coact with the probe 22 and form a seal separating chambers 56 and 58. An O-ring 62 is mounted at the outward end of the casing 54 to coact with the probe 22 and form a seal between chamber 56 and atmosphere. A jam nut 64 threadably engages the end of casing 54 and is tightened thereon so as to compress the O-ring 62 to form a tight seal.

A conduit 66 is in communication between chamber 56 and fore pump 68. A valve 69 is placed in conduit 66 between the chamber 56 and fore pump 63. A conduit 70 is in communication between the chamber 58 and diffusion pump 72. A valve 71 is inserted in the conduit 70 between chamber 58 and pump 72. A conduit 74 and valve 76 are placed upstream of

valves

69 and 71.

The pumps and valving assemblies provide for two stages of differentiaL pumping across the surface of the probe 22 when the probe is inserted therethrough. In operation, the valves are initially in a closed position with the probe 22 and sample carrier 20 withdraw from the assembly. It is also noted that the gate valve 52 is closed whenever the probe 22 is withdrawn. To provide the differential pumping, the probe 22 with sample carrier 20 attached is inserted into the casing 54 to engage 0-

rings

60 and 62. At this time,

valves

69 and 76 are opened and fore pump 68 will reduce the pressure in chambers 56 and 58 to a pressure of about 50 microns in the first stage operation. Valve 76 is closed and valve 71 is opened to bring chamber 58 in communication with the diffusion pump 72 for second stage operation. Pumping during this stage is continued until the pressure in the chamber 58 is reduced to the instrument vacuum pressure approximately l l0 torr. When this pressure is reached, the high-vacuum gate valve 52 can be opened without fear of destroying the instrument vacuum within ion chamber 12 and the sample carrier 20 and probe 22 can be inserted into specimen vaporization position. The operational instrument vacuum in the second stage operation is rapidly achieved due to the extremely small Volume of chamber 58 to be evacuated.

A probe-positioning device and safety device is shown generally as 78. The positioning device 78 includes a shaft 30 which is pivotally mounted at 82 to a suitable clamp 84 which is secured about casing 54. Bolt 85 serves as a height-adjusting element so that shaft 80 may be positioned parallel with casing 54. A guide member 86 is adjustably secured to the shaft 80 by suitable means such as setscrews 88. An axial groove 90 is formed in guide 86 for receiving a dowel or pin 92 which is mounted in handle 25. Guide 86 is positioned along shaft 80 to prevent the overtravel of probe 22 and carrier 20 which, if overtravel occurred, would result in damage to the ion source 14 and the specimen carrying filaments. Groove 90 also serves as a positioning guide to properly align the filaments with the ion source. In other wordsf the probe 22 is inserted until the pin 92 engages the inner end of groove 90 and thus precisely positions and aligns the filaments relative to the ion source 14.

A stop member 94 is attached near the outer end of shaft 80 and serves to prevent the inadvertent destruction of the ion chamber vacuum during withdrawal of the probe 22 and also to prevent destruction of the gate vaLve 52 and filament elements upon insertion of the probe 22. With the shaft 80 in the parallel to casing 54 position, the shaft 22 can only be axially retracted until the pin 92 engages side 96 of stop member 94. This position is shown in the phantom line of FIG. 1. At this position, the sample carrier 20 is also shown in phantom lines. Hence, when this position is reached the gate valve 52 may be closed to isolate the ion chamber 12 vacuum from atmosphere. To complete the withdrawal of probe 22, such as to obtain a new specimen,

valves

69, 71 and 76 are closed, shaft 80 is raised about its pivot point 82 to clear pin 92 (as shown in phantom lines) and shaft 22 is withdrawn the remainder of the way out of casing 54.

Prior to insertion of the probe 22, the shaft 80 is once again returned to the parallel position. Probe 22 is inserted in casing 54 until pin 92 engages side 98 of the stop member 94. At this point, the differential pumping may be started as previously described.

In operation, a sample specimen is evaporated to dryness on the leg connecting portion of

filaments

16 and 18. The filaments are then inserted into the respective conducting rods 50 on the end of the ceramic sample carrier 20. The carrier 20, with the filaments attached thereto, is attached to the driver probe 22 and the loaded probe is inserted into the casing 54 until pin 92 engages side 98 of the stop member 94.

Valves

69 and 76 are opened to allow the first stage differential pumping to bring the chamber 56 and 58 down to the approximate 50- micron level. At this time, valve 76 is closed and valve 7] opened to allow the diffusion pump 72 to evacuate chamber 58 down to the instrument vacuum pressure. When chamber 58 has reached the ion chamber vacuum pressure, gate valve 52 is opened, shaft 80 is rotated about its pivot point and probe 22 inserted until pin 92 clears stop member 94. The shaft 80 is returned to its parallel position and probe 22 is inserted to maximum depth through the assembly 10 until pin 92 reaches the inner end of groove 90. At this point, the filament elements have been properly positioned relative to the ion source and the electrical contacts on the sample carrier have made contact with the spring-loaded contacts of the switch assembly 23. The filament power supplies are then activated and vaporization and ionization of the specimen takes place. After sample analysis, the filament power supplies are turned off and the ceramic sample carrier 20 is allowed to cool prior to withdrawal from the ion source. After cooling of the carrier 20, the probe 22 is withdrawn from the ion chamber until pin 92 engages side 96 of stop member 94. At this position, gate valve 52 is closed to isolate the ion chamber 12 from atmosphere.

Valves

69 and 71 are closed, shaft 80 rotated about its pivot point and probe 22 is completely withdrawn for the attachment ofa new sample specimen.

The invention in operation, has proven a capability of loading a sample of uranium into the instrument and returning the source pressure to the required operation vacuum range of 1 l0 torr in less than 3 minutes. Insertion of the same sample utilizing standard techniques; venting the source region and then pumping down after the sample insertion typically requires a minimum of 25 minutes to return the pressure to operational levels of 1x10 torr. Thus, this invention, at a minimum, doubles sample output and efficiency of the instrument to which it is attached. An additional benefit is the doubling of the source life of the mass spectrometer due to elimination of contaminant from the ion source. it is seen that by making use of the novel location of the electrical contacts within the vacuum system, the usage of sliding and springloaded electrical contacts insures constant continuous electrical flow. Locating electrical contacts in this manner eliminates the use of high-voltage vacuum feedthroughs in the probe. This feature enables the probe design to be ofa smaller diameter, thus reducing the volume of air to be evacuated from the differential chamber and contributing to the usage efficiency of the mass spectrometer.

The use of an axial movement of the probe is advantageous since previous devices utilized probes inserted at right angles to the direction of ion beam travel. This invention inserts the probe in axial alignment into the ion source, thus permitting first, a more precise location of the filaments in relation to the source plates and ion beam, and second, it eliminates the need for attaching the back source plates to the insertion probe permitting the usage of sliding contacts which make direct electrical contact as the sample is inserted.

A further advance to the art of this invention is the use of the probe positioner or position-limiting device which provides a fail-safe mechanical means to prevent the inadvertent destruction of the vacuum within the ion source region and also prevents jamming the specimen and filament elements into the gate valve on insertion of the probe.

While a present exemplary embodiment of this invention has been illustrated and described, it will be recognized that this invention may be otherwise variously embodied and prac ticed by those skilled in the art.

' What we claim is:

l. A sample insertion vacuum lock and probe assembly for mass spectrometers comprising in combination:

a contact-supporting plate having an aperture therethrough mounted within an ion chamber of a mass spectrometer, said plate being mounted in said ion chamber so that the aperture is in axial alignment with the ion source and ion beam;

a plurality of electrical contact members mounted to said plate normal to the axis of the aperture area, each contact member having one end extending into the aperture area,

each of said contact members comprising an outer casing having an axially stepped bore therethrough;

a slidable inner contact element mounted within each of the outer casings for slidable movement relative to the casing, one end of each of said inner contact elements extending beyond the end of the casing and into the aperture area;

resilient means mounted in each stepped bore for biasing each inner contact element into the aperture area;

means connecting each of said contact members to a source of electrical energy, said means limiting the relative movement ofeach ofsaid inner contact elements;

vacuum lock assembly mounted exteriorly of the ion chamber, said vacuum lock being in axial alignment with the ion source and ion beam of the ion chamber, said vacuum lock comprising a high-vacuum gate valve mounted exteriorly of the ion chamber;

a casing attached to said gate valve and extending axially outward from said valve, said gate valve and said casing defining a concurrent axially aligned passageway therethrough, said passageway being in axial alignment with an ion beam of the ion chamber;

a specimen-inserting probe sealingly mountable for reciprocal movement in said passageway for insertion and removal of specimens to be analyzed into the ion chamber, said probe comprising a driving shaft portion sealingly insertable through the vacuum lock;

a forwardly projecting specimen carrier portion mounted at one end of said driving shaft, said driving portion and carrier portion being axially aligned for direct axial alignment with the ion source and ion beam upon insertion of the probe through the vacuum lock and into the ion chamber, said carrier portion and said driving portion remaining attached during ion analysis;

a plurality of stationary contact elements secured to said carrying portion for slidable engagement with said slidable inner contact elements, each of said stationary contact elements being positioned about the outer surface of the carrying portion for cooperative engagement with a corresponding biased inner contact element wherein electrical contact is made when the carrying portion is inserted through said plate aperture area and electrical contact is broken when said carrying portion is removed from said plate aperture area;

a positioning member mounted adjacent the other end of said driving shaft member;

evacuation means for providing staged evacuation of said vacuum lock assembly upon partial insertion of said probe through said passageway wherein said vacuum lock assembly is evacuated to instrument vacuum pressure;

positioning means attached to the vacuum lock assembly for cooperative engagement with said driving shaft providing fail-safe stops to limiting axial movement of the insertion probe to prevent destruction of the ion chamber vacuum and providing proper alignment of said specimen carrier,

said positioning means comprising a clamp mounted on said casing;

a shaft pivotally mounted on said clamp;

means for adjusting said shaft position relative to said casguide means secured to said shaft for engagement with said position member to position said specimen carrier portion thereby; and

wherein said filament means are aligned relative to the ion beam upon full insertion of the specimen insertion probe into the ion chamber;

conducting means connecting said stationary contact elements with said filament means; and wherein said specimen carrier portion is formed of a low water adsorption ceramic.

(s/se) Patent: No.

Inventor(s) Dated June 29, 1971 Richard E. Perrin & Billy A. Hopper It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1,

Column 3,

Column 4,

Column Column Cokumn Column Column 6,

line

"withdraw" should be withdrawn "1 x 10 should be 1 x 10' "vaLve" should be valve "1 x 10 should be 1 x 10' "1 x 10 should be 1 X 10' "to" should be for Signed and sealed this 28th day of December 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

Attesting Officer ROBERT GOTTSCHALK Acting Commissioner of Patents

Claims

2. The combination as set forth in claim 1 further comprising filament means secured to the end of said carrying portion wherein said filament means are aligned relative to the ion beam upon full insertion of the specimen insertion probe into the ion chamber; conducting means connecting said stationary contact elements with said filament means; and wherein said specimen carrier portion is formed of a low water adsorption ceramic.