U.S. patent number 3,590,243 [Application Number 04/837,549] was granted by the patent office on 1971-06-29 for sample insertion vacuum lock and probe assembly for mass spectrometers.
This patent grant is currently assigned to Avco Corp.. Invention is credited to Billy A. Hopper, Richard E. Perrin.
United States Patent |
3,590,243 |
Perrin , et al. |
June 29, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
SAMPLE INSERTION VACUUM LOCK AND PROBE ASSEMBLY FOR MASS
SPECTROMETERS
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.
Inventors: |
Perrin; Richard E. (Tulsa,
OK), Hopper; Billy A. (Tulsa, OK) |
Assignee: |
Avco Corp. (Tulsa, OK)
|
Family
ID: |
25274778 |
Appl.
No.: |
04/837,549 |
Filed: |
June 30, 1969 |
Current U.S.
Class: |
250/430;
250/425 |
Current CPC
Class: |
H01J
49/0495 (20130101) |
Current International
Class: |
H01J
49/02 (20060101); H01J 49/04 (20060101); H01j
039/34 () |
Field of
Search: |
;250/41.9SE,41.9S |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lindquist; William F.
Claims
What we claim is:
1. 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 of
each of said inner contact elements;
a 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
casing;
guide means secured to said shaft for engagement with said position
member to position said specimen carrier portion thereby; and
a stop member secured adjacent the end of said shaft for engagement
with said positioning member for initially limiting the axial
insertion or withdrawal of the probe relative to the casing,
wherein upon moving said shaft about its pivot point the probe will
be allowed to pass the initial limiting position.
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.
Description
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.times.10 .sup.-.sup.6 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 15minutes 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 source be
pumped out after each new sample. In addition to severely limiting
sample throughput, this procedure also increases contamination to
the ion source 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 contacts is extremely
short.
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 samples for 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 the sample 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 16 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, 28a--28f, 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 38 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
50a--50f. 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 16 legs are
attached to rods 50e and 50f which are in turn in electrical
contact with stationary contacts 44e and 44f.
Referring again to FIG. 1, the assembly 10 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
10 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 68. 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 O-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 1.times.10 .sup.-.sup.6
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 80 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 words, 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 71 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 20 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 of a 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 .times.10
.sup.-.sup.6 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 1 .times.10 .sup.-.sup.6 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 spring-loaded 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 of a 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 practiced by
those skilled in the art.
* * * * *