US3440417A

US3440417A - Vacuum lock sample insertion probe for a mass spectrometer

Info

Publication number: US3440417A
Application number: US460392A
Authority: US
Inventors: John Stewart Heath
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1964-06-03
Filing date: 1965-06-01
Publication date: 1969-04-22
Anticipated expiration: 1986-04-22
Also published as: GB1092803A; FR1436995A; DE1573970A1

Description

April 22, 1969 Y s H H 3,440,417

VACUUM LOCK SAMPLE INSER'IION PROBE FOR A MASS SPECTROME'IER Filed June 1, 1965' Sheet of 3 April 22, 1969 J. 5. HEATH 3,440,417

VACUUM LOCK SAMPLE INSERTION PROBE FOR A MASS SPECTROMETER Filed June 1, 1965 Sheet L of s April 22, 1969 J. S..HEATH 3,440,417

VACUUM LOCK SAMPLE INSERTION PROBE FOR A MASS SPECTROMETER Filed June 1, 1965 Sheet 3 us ZIO ill/'// 1 United States Patent US. Cl. 250-419 17 Claims ABSTRACT OF THE DISCLOSURE A vacuum lock shaft insertion arrangement for evacuable apparatus such as a mass spectrometer, which arrangement comprises a body part having a shaft passageway formed therethrough for reciprocal insertion and withdrawal of the shaft, a rotary valve member disposed athwart said passageway and rotatable about a transverse axis and having both a through-bore formed transversely of said axis and an axial bore extending laterally from the through-bore. The body part has an exhaust duct which remains in communication with the through bore of the valve member via the axial bore both in the passageway-opened and the passageway-closed positions of the valve. The body part also contains in the passageway, on opposite sides of the valve member, sealing members each having a sealing surface conforming to and sealingly engaging the facing surface of the valve member, and also having a radially resilient tubular part concentrically disposed with respect to the passageway for passing the shaft and sealingly engaging it with radial resilience.

This invention relates to evacuable apparatus such as mass spectrometers and relates more particularly to an improved vacuum lock shaft insertion arrangement for such equipment.

The interior of a mass spectrometer must be evacuated, during use, to a high degree of vacuum, and in order to avoid the need to evacuate the complete equipment each time a specimen to be examined is replaced, it is well known to provide some form of vacuum lock through which a solid specimen can be inserted into the ion source chamber, and through which the specimen can be removed. One possible form of vacuum lock is used in conjunction with a specimen carrier which itself is carried by a shaft pushed in towards the ion source chamber through different vacuum stages, so that the space surrounding the actual specimen is progressively evacuated. Insertion of the shaft causes sealing between the shaft and surrounding seals, while when the shaft is partly withdrawn, a valve can be closed so that communication between the ion source chamber and the atmosphere, when the shaft is fully withdrawn, is prevented.

An object of the present invention is the provision of an improved vacuum lock for a mass spectrometer, which is highly effective when the carrier shaft has been fully withdrawn.

The invention consists of a vacuum lock shaft insertion arrangement for evacuable apparatus such as a mass spectrometer, which arrangement comprises a body part having a shaft passageway formed therethrough for reciprocal insertion and withdrawal of the shaft, a rotary valve member disposed athwart said passageway and rotatable about a transverse axis and having both a throughbore formed transversely of said axis and an axial bore extending laterally from the through-bore. The body part has an exhaust duct which remains in communication with the through-bore of the valve member via the axial 3,440,417 Patented Apr. 22, 1969 bore both in the open position of the valve (in which the through-bore is in alignment with the shaft passageway for insertion of the shaft therethrough) and in the closed position (in which the through-bore is transverse to the passageway and the valve member therefore obturates the passageway). The body part also contains in the passageway, on opposite sides of the valve member, seal ing members each having a sealing surface conforming to and sealingly engaging the facing surface of the valve member, and also having a radially resilient tubular part concentrically disposed with respect to the passageway for passing the shaft and :sealingly engaging it with radial resilience.

The part of the passageway on the side of the valve remote from the high vacuum interior of the apparatus is preferably additionally provided with an outer sealing member adapted to engage the periphery of the shaft and provide a fluid-tight seal therewith, and a second exhaust duct in communication with the space between this outer sealing member and the adjacent sealing member of the two which engage the valve member, whereby when the shaft is fully inserted the transverse bore can be evacuated to a lower absolute pressure than the space between the two seals.

When the valve is open and the shaft extends through the valve, the two seals. which engage the valve member enable the part of the passageway lying between these two seals and including the transverse bore to be maintained at an absolute pressure which is greater than that in the high vacuum interior of the apparatus, but is less than that in the outer part of the passageway.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which:

FIGURE 1 is a schematic sectional side elevation of a mass spectrometer;

FIGURE 2 is a sectional side elevation of a vacuum lock associated with an ion source chamber shown in FIGURE 1;

FIGURE 3 is a sectional side elevation through an ionisation chamber insert shown in FIGURE 2, but drawn to a larger scale than that figure;

FIGURE 4 is a sectional side elevation through a specimen insertion shaft adapted for insertion into the vacuum lock of FIGURE 2; and

FIGURE 5 is a sectional side elevation of an alternative form of specimen insertion shaft.

The mass spectrometer shown in FIGURE 1 includes an ion source chamber 1 which can be pumped to a high vacuum by a pump 3 acting through a cold trap 5. The ion outlet 7 from the chamber 1 communicates with an electrostatic analyser chamber 9, arranged for evacuation to a high vacuum by a pump 11 acting through a cold trap 13. The outlet 15 from chamber 9 includes a monitor collector 17 and leads to a magnetic analyser chamber 19. The outlet 21 from chamber 19 leads to a chamber 23 in which are arranged an auxiliary collector 25, an adjustable slit member 27, and an electron multiplier 29, from which the output can be led to an amplifier providing the useful output from the mass spectrometer. The form of mass spectrometer described above is well known in the art, and detailed explanation herein is not necessary.

Referring now to FIGURES 2 to 4, the ion source chamber 1 includes a pedestal 35 arranged to accept an ionisation chamber insert 36.

There are a variety of ways in which the ionisation chamber of an electron bombardment ion source can be arranged, each having particular advantages for certain types of specimen material. Inorganic materials in general must be evaporated from a furnace or from the surface of a filament direct into the ionising electron beam. Organic materials of low molecular weight can be evaporated at relatively high pressure externally to the source and passed into the source via a leak or alternatively can be evaporated direct in the source region provided that the temperature can be kept sufficiently w. High molecular weight organic materials present the most difficult problem as they may commence to decompose at a lower temperature than that needed to provide a sufficient rate of varporisation. In this case it is usually necessary that the temperature of the ionisation chamber should be the same as the specimen temperature in order that the partial pressure of specimen vapor in the chamber should be as high as possible while minimising decomposition.

Using the vacuum lock of the present invention, the arrangement of the source can be quickly changed to suit dilfering specimens. This is achieved firstly by providing a variety of ionisation chambers which can be put into and removed from the source chamber, through the vacuum lock using a shaft having at its end a means for engaging and releasing the inserted chamber. Secondly different types of specimen insertion probes are provided by which specimens can be introduced into the source region in such position that specimen vapor passes into the ionisation chamber. These probes differ according to the method of controlling the specimen temperature and the form of the specimen (solid, liquid, or gaseous) catered for.

The insert shown in FIGURE 3 has a body 37 made of non-magnetic material incorporating a special lug 38 by which it can be grasped by an insert charging shaft. The insert includes a chamber 39 and a bore 41 entering the chamber 39 from one side. One end of chamber 39 is closed by a plate 43 formed with a slit 45 through which the ions leave the chamber 39 under the influence of an ion repellor plate 47. An ionising electron beam enters and exits through holes 49 in the sides of chamber 39. Exact location of the insert is not required as the position of the electron beam and the ion beam defining slits are independent of the insert position. Specimens are introduced by a specimen insertion probe either through bore 41 or through a bore' 51 into the actual electron beam. Gaseous specimens or specimens vaporised external to the source region enter the chamber through the hole 53 from a fixed inlet.

A specimen insertion probe is shown in FIGURE 4. A hollow pillar 57 made of alumina with one end closed is sealed into the insertion end of a tubular shaft 59 which is ground on its outer surface to a very fine cylindrical finish. The specimen is in a container 61 which is placed in a cavity in a solid rod 63 mounted on the alumina pillar. An electrical heater 65 is located within the pillar and is used to control the temperature of the specimen. This heater can be replaced with a cooling de vice if required. This arrangement has the advantage that as the specimen is in good thermal contact with the heater (or cooler) but is electrically insulated from it, the heater (or cooler) need not be operated at the source voltage of +8 kilovolts used in the ion chamber. A disc 67 fixed to the outer end of the shaft has a hole 69 near its periphery which coacts with a long dowel 71 and the disc itself cooperates with a stop 72, both of which are fitted on the body of a vacuum lock 73 fitted to the ion source chamber. This type of disc is fitted to all shafts for use with the ion source and ensures that the correct angular orientation is maintained when each shaft is inserted for the last two inches of its travel.

The vacuum lock 73 is shown in detail in FIGURE 2, and includes a cylindrical body part 73A at the outer end of which is fitted dowel 71. A passageway 75 extends through the body part and has arranged within it the various members of the vacuum lock. A rotary valve 77, in the form of a ball formed at one point with a radial boss 79 and at the diametrically opposite point with a radially operating shaft 81, is clamped between two sealing

members

83 and 85 formed with surfaces complementary to the ball. Member 83 is biased inwardly towards the valve 77 by a compression spring 87, and a tubular part 83A is biased radially inwardly by an encircling spring 89. The member 85 is similarly biased towards the ball valve 77 by a compression spring 97 and includes a tubular part 85A, which will be referred to as the inner seal, biased inwardly by an encircling spring 99. The boss 79 is formed with an axial bore 79A which communicates with a transverse bore 77A through the ball of the rotary valve and this bore 79A is always in communication with a duct 101 leading to a vacuum pump 105. The part 106 of the passageway outwardly of the valve 77 is connected by a duct 107 to a vacuum pump 111, while the part of the passageway 75 on the inner side of the valve 77 is evacuable by the pump 3. The outer end of the passageway 75 is provided with a sealing member 113, which will be referred to as the outer seal, having a thin tubular part 113A biased radially inwardly by an encircling spring 115. The various sealing members are made out of mineral filled polytetrafluorethylene.

When the specimen insertion probe is inserted into the passageway 75, its shaft portion first enters the thin tubular part 113A of the sealing member 113, and forms therewith a fluid-tight seal. This movement is checked by engagement of the disc 67 with the stop 72. The pump 111 is then used to evacuate this part of the passageway 75 to a vacuum, for example to an absolute pressure of 50 millitorr. The absolute pressure inside the bores of the rotary valve 77, which is in the closed position, is about 0.1 millitorr. The valve 77 is then opened and the shaft first rotated to free disc 67 for the stop 72, and the shaft then entered further until it engages first part A of the seal 85 and subsequently the part 83A of the seal 83. Further inward movement of the shaft enables the specimen to be inserted into the insert 37 for analysis.

When the used specimen is to be removed from the insert 37, the specimen insertion probe is first withdrawn until disc 67 engages stop 72, so that the valve 77 may be closed, and then, with valve closed, is fully turned to disengage the disc from the stop and is fully withdrawn. Since the bores within the rotary valve 77 are maintained by the pump at a high degree of vacuum, leakage of air through the valve 77 into the chamber 1 is substantially completely inhibited.

Referring now to FIGURE 5, the alternative form of specimen insertion probe shown therein is particularly suitable for use with specimen materials of very high molecular weight. The shaft includes a tube 201 made of non-magnetic material and which extends axially inside a tubular shaft 202 which is ground on its outer surface to a fine cylindrical finish. An electrical heater 203 surrounds the part of the tube 201 which is immediately within the shaft 202, and a coiled pipe 204 surrounds a part of the tube 201 which lies inwardly of the heater 203. The ends of pipe 204 are brought out through nozzles in the outer end of the shaft and in use a flow of cold air can, when desired, be maintained through the pipe 204. Positioned within the tube 201 is a soft-iron plunger 206 linked by a rod 207 to a short hollow cylinder 208 which is a free sliding fit within the tube 201. A specimen tube 209 has one end retained in the cylinder 208 by a spring 210, and extends beyond the end 202A of the shaft 202 inside an electrically insulating tube 211 which is coaxial with the tube 201 and is fitted within a bore in the end wall 202A. Mounted on the outside of the tube 201 is a permanent magnet 215 which is provided with an operating rod 216 by which the magnet can he slid along the tube 201 to effect movement of the plunger 206 and thus the specimen tube 209. The outer end 201A of the tube 201 is plugged so that in use the inside of the tube 201 can be subjected to a vacuum without increase of air through the specimen tube.

Also mounted on the end 202A of the shaft 202 is a rod 222 of electrically insulating material having one end fitted Within a recess 223 and held therein by a spring clip 224 also mounted on the shaft end. This rod is adapted near its outer end to constitute a specimen carrier 225. As in the case of the specimen insertion probe shown in FIGURE 4, a disc 267 is fixed to the outer end of the shaft 2&2 and is provided with a hole 269 near its periphery which coacts with the long dowel 71 fitted to the body of the vacuum lock, and ensures that the correct angular orientation is maintained, as the shaft is inserted into the vacuum lock, over the last two inches of its travel.

In use of the specimen insertion probe shown in FIGURE 5, the specimen is placed in the tube 209. By movement of the rod 216 the magnet 215 is moved to a position in which the cylinder 208 can have the end of the specimen tube inserted into it, and the specimen tube then withdrawn to the position shown by outward movement of the rod 216. The shaft is then inserted into the vacuum lock so that the tube 211 is opposite the bore 51 (see FIGURE 3). Current is now passed through the electrical heater 203 and a temperature gradient is established along the tube 201 between this heater and the part of the tube cooled by the cooling tube 204, and also between the heater and the source insert 36. The specimen tube used appropriately locates the actual specimen at a desired point in these temperature gradients, and by varying the position of the specimen its temperature and hence its rate of evaporation into the ion source insert 36 can be controlled by the operator. It is found in practice that the rate of evaporation responds very quickly to changes in the position of the specimen, thereby overcoming a disadvantage which exists where the specimen is in permanent contact with a relatively large mass of metal the temperature of which can be changed only slowly.

To obtain a precise mass determination of a molecule of high molecular weight, it is necessary to introduce together into the source insert 36 the specimen vapor and also the vapor of a known reference compound of comparable molecular weight. This is achieved by placing a specimen of the reference compound in the specimen carrier 225. When inserted into the source insert through the bore 41 (see FIGURE 3), this carrier locates the reference compound beneath a hole in the ion repeller 47, and its temperature will be that of the source insert 36, which can be controlled by a suitable electrical heater. The unknown specimen can then be introduced as described above. In this way, the rate of evaporation of the unknown and reference specimens can be controlled independently although both are carried by the insertion shaft. The rate of evaporation of the reference compound is slow to respond to changes in heat input to the electrical heater of the source insert 36, but in general this is of secondary importance.

What I claim is:

1. A vacuum lock shaft-insertion arrangement for evacuable apparatus such as a mass spectrometer, said arrangement comprising:

a body part having a shaft passageway therethrough,

an insertion shaft reciprocably movable in said passageway for insertion and withdrawal,

a rotary valve member disposed athwart said passageway and rotatable about an axis lying transversely of the passageway,

said value member having a through-bore formed trans versely of said axis and an axial bore extending laterally from said through-bore, and being rotatable in the absence of said shaft between an open position in which said through-bore is in alignment with said passageway for insertion of the shaft therethrough and a valve-closed position in which said throughbore is transverse to said passageway,

said body part having an exhaust duct which is in communication with said through-bore via said axial bore in each of said positions of the valve member,

and sealing members included in said passageway at opposite sides of the valve member therein, each said sealing member having a sealing surface conforming to and sealingly engaging the peripheral surface of the valve member and also having a radially resilient tubular part concentrically disposed with respect to the passageway for passing the shaft and sealingly engaging its periphery.

2. A vacuum lock arrangement according to claim 1 including in said passageway, on opposite sides of the valve member, respective springs acting on said sealing members to urge them into their sealing engagement with the valve member.

3. A vacuum lock arrangement according to claim 1 including around the tubular parts of said sealing members respective encircling spring imparting said radial resilience.

4. A vacuum lock arrangement according to claim 1 comprising in the outer part of said passageway as defined at one side of said valve member a tubular sealing member concentrically disposed with respect to the passageway for sealingly engaging the periphery of the shaft, said tubular sealing member being spaced from the sealing :member engaging the valve member at said one side thereof said body part having a further exhaust duct in com munication with the said passageway at a position between these two sealing members.

5. A vacuum lock shaft-insertion arrangement for evacuable apparatus such as a mass spectrometer, said arrangement comprising:

a body part having a shaft passageway therethrough,

said valve member having a through-bore formed transversely of said axis and an axial bore extending laterally from said through-bore, and being rotatable in the absence of said shaft between an open position in which said through-bore is in alignment with said pasageway for insertion of the shaft therethrough and a valve-closed position in which said throughbore is transverse to said passageway,

said body part having an exhaust duct which is in communication with said through-bore via said axial bore in each of said position-s of the valve member,

first and second sealing members included in said passageway at opposite sides of the valve member therein,

these sealing members each having a sealing surface conforming to and sealingly engaging the peripheral surface of the valve member and also having a radially resilient tubular part concentrically disposed with respect to said passageway for passing the shaft and sealingly engaging its periphery,

a third sealing member included in said passageway at a position spaced from said first sealing member on the same side of the valve member as is said first sealing member,

this third sealing member being of tubular form concentrically disposed with respect to the passageway for passing the shaft and sealingly engaging its periphery,

and said body part having a further exhaust duct in communication with the part of said passageway that lies between said first and third sealing members therein.

6. A vacuum lock arangement according to claim 5 including on said shaft and said body part respective cooperating locating members mutually engageable to define a partially inserted shaft position, in which the shaft extends through the third sealing member only into said part of said passageway between the first and third sealing members, and disengageable to permit withdrawal of the shaft and also to permit full insertion of the shaft through said valve member and said first and second sealing members.

7. A vacuum lock arrangement according to claim 6 wherein shaft is rotatable between two angular positions for engagement disengagement of said locating members, said arrangement including further cooperating means on said shaft and body part for ensuring a predetermined angular orientation of said shaft when fully inserted.

8. A vacuum lock arrrangement according to claim 6 wherein said locating members comprise on the shaft a disc and on the body part a stop member engageable with said disc to define said partially inserted shaft position, the shaft being rotatable between a first angular position thereof in which insertion of the shaft is stopped at the partially inserted position by engagement between said disc and stop member but the shaft is free to be withdrawn and a second angular position in which withdrawal of the shaft from its fully inserted position is stopped at the partially inserted position by engagement between said disc and stop member but the shaft is free to be moved from this partially inserted position to its fully inserted position.

9. A vacuum lock arrangement according to claim 6 including a specimen insertion probe for insertion of a specimen into said evacuable apparatus, said probe comprising:

said insertion shaft with its one of said locating means thereon,

a member at the insertion end of said shaft having means for carrying specimen material,

and an electrical heating or cooling means included as part of the probe for controlling the temperature of such specimen material.

10. A vacuum lock arrangement according to claim 9 including in said probe at the insertion end of its shaft a forwardly projecting alumina pillar containing said heating or cooling means, and specimen carrying member being of thermally conductive material and attached to said pillar.

11. A vacuum lock arrangement according to claim 6 including a specimen insertion probe for introducing specimen material into the evacuable apparatus, said probe comprising:

said insertion shaft with its one of said locating members, said shaft being hollow,

a non-magnetic tube within said shaft and radially spaced therefrom,

magnetically coupled members within said tube and said radial space respectively,

an external operating member,

the member within said space being mechanically connected to and axially movable by said operating memher,

the member within the tube being axially movable with the member within the tube by virtue of the magnetic coupling therebetween,

means for establishing a region of temperature gradient along the shaft,

a specimen carrier mechanically coupled to said axially movable member Within the tube for adjustment of the position of said carrier within said gradient regen,

and means at the insertion end of the shaft permitting egress of specimen vapor from said tube.

12. A vacuum lock arrangement according to claim 11 including electrical insulation means mounting said tube within said hollow shaft and a vapor egress tube of electrical insulation material containing the specimen carrier within said gradient region and projecting from the insertion end of the shaft.

13. A vacuum lock specimen insertion probe comprising an insertion shaft part sealingly insertable through the vacuum lock, a forwardly projecting alumina pillar mounted at the insertion end of said shaft part, heating or cooling means wholly within said pillar and a specimen carrying member of thermally conductive material attached to said pillar at a point separate from said means so that the pillar provides electrical insulation between said means and said member.

14. A vacuum lock specimen insertion probe comprising:

a hollow insertion shaft part sealingly insertable through the vacuum lock,

a non-magnetic tube within said shaft and radially spaced therefrom,

an external operating member,

the member within said space being mechanically connected to and axially movable by said operating member,

the member within the tube being axially movable with the member within said space by virtue of the magnetic coupling therein,

and a specimen carrier mechanically coupled to the axially movable member within said tube for axial adjustment of the position of said carrier.

15. A vacuum lock specimen insertion probe according to claim 14 further including means in said hollow shaft for establishing a region of temperature gradient along the shaft, said specimen carrier being axially movable within the region for adjustment of its axial position therein.

16.A vacuum lock specimen insertion probe according to claim 14 further comprising specimen heating means within said shaft, electrical insulation means mounting said tube within the shaft, and a vapor egress tube of electrical insulation material containing the specimen carrier and projecting from the insertion end of the shaft.

17. A vacuum lock specimen insertion probe according to claim 16 further comprising at the insertion end of the shaft a further specimen carrier projecting forwardly from said end.

References Cited UNITED STATES PATENTS 3,117,223 1/196-4 Brunnee. 3,158,740 11/1964 Craig et a1. 3,171,958 3/1965 Coleman.

RALPH G. NILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner.

US. Cl. X.R.