US2548859A - Mass spectrometer - Google Patents

Description

April 1951 c. E. BERRY 2,548,859

MASS SPECTROMETER Filed June 17, 1948 2 Sheets-Sheet l IN VEN TOR. CLIFFORD E. BERRY A T TORNE Y April 1951 c. E. BERRY 2,548,859

MASS SPECTROMETER Filed June 1'7, 1948 2 Sheets-Sheet 2 4A 5A 2A 3A 3A 4A 2A 35 INVENTOR. CL IFFORD E. BERRY A TTORNEY Patented Apr. 17, 1951 UNITED STATES PATENT OFFICE '2,548;859 MASS SPECTROMETER Clifiord E. Berry, Pasadena, Calif., assignor to Consolidated Engineering Corporation, Pasadena, Calif., a corporation of California Application June 17, 1948, Serial No. 33,596

are introduced. In the ionization chamber the During passage through the analyzer chamber the ions are subjected to a transverse electricj'or magnetic field or both, to separate them accordin to their mass-tocharge ratios into a plurality of diverging beams of ions. Each ion beam is composed of ions of the same specific mass and differing from the ions in the other beams. The diverging beams are successively focused on an ion collector'by varying the potential applied to the accelerating electrodes or by varying the intensity of the transverse field in the analyzer tube. The current produced by the discharge of each beam on the ion collector is a measure of the partial pressure of the molecules (from which the ions were derived) in the sample being analyzed. i

In accordance with the present invention, there is provided an ion source which possesses a number of advantages both with respect to application and function over the conventional ion source. to facilitate an .understanding of the objectives of the invention. I .1.: The number of separate parts required has been materially reduced.

2. The function of insulating and mounting the several parts is accomplished by one member instead of a plurality of members.

3. The parts-are attached in definite and stable position by brazin them to their supporting members. i

4:. Closely adjacent surfaces which can hold contaminating material and thus slow down evacuation have been eliminated.

Some of these advantages are listed.

accomplished in accordance with the invention by the construction of an ion source comprising an insulating plate having a plurality of conductive wires or rods sealed therethrough. A series of metal parts are mounted over all or a part of the plurality of rods and are held thereto and in appropriate relationship to each other by brazing to one or more of the rods. The series of metal members form successively from the insulating disk a sample inlet, an ionization chamber, pusher electrodes housed in the ionization chamber, a first ion slit, a second ion slit,

and a third ion slit. An electron emitting filament is mounted adjacent an outer wall of the ionization chamber. The filament emits an electron beam which is directed through a slit in the wall and transversely across the ionization chamber. v

A feature of my invention is the combined function of the plurality of conducting rods which serve (1) as supports to which the several parts are affiXed and (2) as electrical leads supplying appropriate potentials to the various parts of the ion source. Additionally, the rods permit spacing of the various parts to (1) facilitate cleaning, (2) eliminate closely adjacent difficultly evacuated surfaces, and (3) insulate the necessary parts from each other.

The invention will be more clearly understood with reference to the following detailed description taken in relation to the accompanying drawings wherein:

Fig. i is a. partial sectional view of a mass spectrometer showing the relationship of the ion source of the invention to the sample inlet means and analyzer'tube;

Fig. 2 is-a section view ofthe ion source;

Fig. 3 is a horizontal section taken on the line 3-3'of Fig. 2;

Fig. 4 is a-vertical sectiontaken on the line 44 of Fig. 3; V i

--Fig. 5 is an exploded view of the ion source showing each of the elements thereof in perspective; and L Fig. 6 is a bottom perspective view of the laterally aligned element of Fig. 5.

Referring to the drawing and particularly to Fig. 1 thereof, the ion source In is shown mounted within the'inlet end of a mass spectrometer I]. The mass spectrometer includes an analyzer tube [2 and an evacuating tube "I4; Generally, the

evacuating tube M is connected to apparatus capable of producing a high degree of vacuum such as a molecular pump, mercury diffusion pump or I The foregoing "and. other improvements are the like. The evacuating tube [4 opens through 3 a wall of a tubular member I3 which surrounds the ion source 10 and from which the analyzer tube l2 projects.

A tubular member H, projecting into tubular member I 3, is clamped between flange 24, attached to tube 13, and a flange l6, and serves to support the ion source inside tube l3. The ion source includes a plurality of conducting rods 2, 3, 4, 5 (see Fig. 5), shown in Fig. 1 projecting downwardly from the ion source. In the mounting as shown, a circular metal disk 22 is brazed to the several rods 5, and is in turn bolted to the top of the tube l1.

The tube i3 is provided at-its lower endwith a flange 24 which rests against a flange 25 formed on the lower end of the tube 11. The tube I! in turn rests against the flange I6. The flange 25 on tube I? is provided with electric inlet leads 26, 21 through which the several rods l, 2, 3 and 4 of the ion source I may beconnected to a voltage supply circuit to establish appropriate potentials at the various parts of the ion source. The rods 5 which are connected through the metal plate 22 in conductive relationship to the tube H are at; the same potential as the tube 11.

The ion source lfl-includes a nipple 28 extending through the disk 22 and the top of the tubular member H. The nipple 28 is connected to a sample source (not shown) by means of a flexible sample inlet tube 30 extending through the tubular member ll and the flange I6.

The construction of the ion source l9 can best be understood by reference to Figsp2, 3, 4, 5 and 6. Referring first to the exploded perspective View of Fig. 5-, the ion source'includesan insulating plate 3d, a first disk 35 through which the inlet nipple 28 is afiixed, split pusher electrodes 36, 31, a second'disk 38 having a recess 40. which forms an ionization chamber withthe adjoining face of the disk 35 and having a first ion slit '42 in the top thereof, a third disk M defining a second ion slit and a fourth disk 45defininga third ion slit.

The plate sd isiconveniently, fabricatedof glass and preferably; glass having. a co-efficient of expansion approximating that of the conductive rodssealed therethrough. Preferably the rods are tungsten. The construction of an insulating disk of this type with such rods sealed therethrough is described indetail in my co-pending application Serial-No. 760,196, filed July 11, 1947, and entitled Metallic-Glass Joints. Y

As shown in Fig. 5 the plate 34 contains 15 straight tungsten wiresor rods of-varying lengths arranged in two concentriccircles; 6 in the inner circle and 9 in the outer. Some of: the wires project through the back surface of the disk a short distance so that appropriate electrical connections can be made to them. Two spaces in the outer concentric circle are unfilled, leaving a blank section of glass which is ground off to form a flat face 34A. Ahole 48 is drilled in the middle of thepla-te throughwhich the gas inlet tube 28 projects (see Fig. 4). The various tungsten rods are denoted. by numerals from I to 5. These designations will be used to identify the rods when the mounting of thevarious parts is described. I

. The disk 35is made from asolid piece of metal, generally circular in plan with the exception of a fiat face 35A. When the ion source is assembled, the face 35A coincides with the surface 34A of the insulating plate 34. The disk 35is provided with a central hole-58 into-which the inlet nipple 28 Each of these holes is made larger than the rods so that no connection exists when the disk 35 is placed on the plate 34. The clearance between the rods and so called clearance holes in the successive disks is clearly apparent in Figs. 2 and 4.

u The several clearance holes in the disks and pusher electrodes are designated by numerals corresponding to the numbers of the support rods which extend through these holes. Thus the number 2 rods project through the clearance is brazed. There are 15 holesdrilledin the block to 'inatch'the' l5 rods projecting from the plate 34.

holes 2A in the disk 35.

Ferrules 553, El, 62, and 53 (Figs. 3 and 4) are brazed into the holes 3A in the disk 35. When this disk is mounted on the plate 34 as shown in Figs. 2, 3 and l, the rods 3 project through the ferrules 68, BI, 62', and 63 and are brazed thereto to hold the disk and the plate together in spaced relationship.

In attaching ,themetaldisk 35 to the glassplate 34, a spacing of a few thousandths of an inch is maintained between the. block and the disk by means of removable spacers. After completing; the assembly, the spacers are. removed. leaving. sufficient space so that the adjoining faces. of the block and the. disk may be readily cleaned. In the drawing the several members. are shown touching each other; itbeing impossible to illustrate a spacing in the order of magnitude of a few thousandths of aninch. Additionally, although highly desirable, such spacing is not absolutely essential to the. functioning. of theionsource.

As mentioned above, oneof the. objects of the invention is to provide an ion. source. wherein closely adjacent surfaces'are eliminated so as to reduce-the consequent interference with evacuation. The termplosely adjacent surfaces, as applied relative to an: ion source. operating at reduced pressures, refers to metal surfaces which are actually touching. In. suchcase, because of microscopic unevenness in the. adjoining faces, evacuation is impeded. Thev spacing of a few thousandths of an inch provided between the disk 35 and the plate 34 is considered. in. this application to be a-large space inthat it. isof such mag.- nitude as not to interfere. with the evacuating process. p

The disk 35. is provided with two oppositely located peripheral notches. and 65 which form thin lips 64A, 65A, inthe. top of the disk. These lips are usedas hereinafter described, for spot welding the disk 38.- to the :disk 35.

In my co-pending patent. application Serial No. 763,886, filed July. 26,-. 19.47,. and entitled Welding, and relating to the fabrication of ionization chambers for mass. spectrometers, it was pointed out that dimculties. are. encountered in brazingthe'various parts of. an ionization chamber orion'source to-tungsten leads such as the .rods extending, from: the plate 34. Since the brazing alloymeltsatabout 100.0963. it isimpossible to heat the Whole assembly'including the glass plate' 3'4 to this brazingpointwithout damage. Further, a difficulty normally encountered in the brazing operation is splattering of the molten alloy; even microscopic splatters of the material on the glass. plate'or on otherparts of the ion source will cause subsequent difficulties in operation.

In the last mentioned co-pending application I described theconstructionand use of. ferrules such as the ferrules 60, 61, 62 and 63.whereby the foregoing .difficulties were eliminated .As there described, the ferrule has a cup-shaped upper portion forming an annulus around the rod in ment, completely avoids spattering of. the solder or other welding material after it becomes fused and provides an intense localizedaheat :for the fusing operation without necessitating applica-z tion of intense heat to the whole apparatus.

The recess 46 in disk 38 forms, with the adjoining face of disk 35, anionization chamber inwhich ionization of the sample 'molecules. takes place. Disposed in the chamber and directly above the disk 35 arepusher electrodes 36 and 31. members conveniently constructed by splitting a disk into two parts. Each electrode is provided with a hole 23 (Fig. alignable 'with the rods 2 projecting from the glass plate 34. Ferrules B6, and 61 are brazed in the holes 2B and the rods 2 projecting from the glass plate are brazed to'the ferrules to hold the electrodes in spaced and fixed relationship to the other parts.

Proceeding with the description of the apparatus in the order of assembly, a'small rectangular gold member is brazed to the upper end of wire I which projects through a clearance hole l-A in the disk 35. The gold rectangle I0 forms an electron catcher as more fully described hereinafter.

The second disk 38 contains Bclearance holes through which all of the rods numbered 4 and 5 project without touching the disk. These several clearance holes are designated either 4B or 53, to indicate which of the rods 4-and 5 project therethrough and are in alignment with the holes 4A and 5A in the disk 35. I

As hereinbefore described, a; recess 40 is formed in one faceof the second disk leaving a thinface 12 on the other side of the disk. .A slit 42 is cut in the face 12 and serves as a first ion slit.

A fiat 38A is formed across one side of the disk in alignmentwiththe flat faces 35A and 34A of the members 35 and 34.respectively for the like purpose of providing: space for an electron emitting filament 14 (Fig. 2). A thin lip-15 is left above the fiat surface 38A'to act as a shield for thefilament 14. A slit '16 is cutin the fiat 38A' opening into the chamber formed by the recess 40. A somewhat larger slit 18 is'cut in the opposite side of the recess 40 giving access to a smaller recess 19 in which the electron catcher "I0 is placed. Electrons generated by the filament pass as a beam through the slits 1B and 18 and impinge on the electron collector 10. During traversal of the chamber 40, the electrons ioni'ze the sample molecules therein.

The disk 38 is provided with oppositely spaced peripheral notches 80 and BI in alignmentlvvith the notches B4 and 65 in the disk 35. The notches 80 and 8| form thin lips 80A and BIA in the lower edge of the disk 38. The first and second disks are joined by spot welding the lipsprovided by the several notches (see Fig. 4). A space of a few thousandths of an inch is provided between the parts during assembly to allow cleaning of the surfaces and to eliminate closelyadjacent' sur-' faces for the reasons given above. Y I

These electrodes comprise two D-shaped The member comprises a split disk forming two D-shaped parts 44A and B. These form a second ion slit 440. Each of parts 44A and 44B is provided with holes 40 and 50 through which the rods 4 and 5 project. Ferrules 82, 83, 84 and 85 are brazed into each of the holes 40 in-the members 44A and 44B, and the appropriate rods are brazed thereto. v

The member 45 comprises a disk having are cess 86 in one face thereof leaving a thin opposite face 81. The face 81 is provided with a slit-88 therein. The disk 45 is provided with holes 5D in which ferrules 90, 9|, 92, and 93 are brazed.

(Figs. 2 and 4.)

As illustrated in the drawing, all of the clearance holes as well as all of the holes in the ferrules are oversize in order to reduce the precision necessary in the location of the wires and. the fer-g In assembling the ion source, all of the rules. parts are held in correct position by an accurate fixture and are brazed together while so held.

Thus, in the final assembly the wires are not strained in any way and there is no distortion in the ion source when removed from the fixture.

As shown in Figs. 2 and 4 the plate 34 is provided on both its upper and lower surfaces with strengthening bosses around each of the wires with the exception hereinafter noted. There are no supporting bosses in the upper face of the plate around wires l and 2 (Fig. 2). poses of clarity in Fig. 5 all of the bosses are eliminated from the plate 34. Thereason for. eliminating the upper bosses around wires l and 2 is to reduce gas leakage from the ionization chamber throughthe holes IA, 2A and IB in the disks 35 and 38. Thus, as above described, these clearance holes are made larger than the wires for the double purpose of avoiding contact of the wires with the blocks 35 and 38 and also for the purpose of. facilitating assembly of the ion source. Gasle'akage through these holes will be directly proportional to their size and inversely proportional to their length. It follows that by elimination of the upper bosses from the disk 44 the length of the holes IA and 2A will be increased and gas leakage will be reduced. This is not a necessary feature of the invention but is illustrated as a preferred embodiment thereof.

Although onespecific means of mounting the ion source of the invention in amass spectrometer. is illustrated in detail in Fig. 1, it is to be understood that the ion source is designed for use in substantially any mass spectrometer. means of mounting the ion source within any given instrument will be determined by the design of the mass spectrometer. The present in vention is not intended to be limited tothe mounting of the ion source as shown in Fig. 1. v The feature of the invention which involves the mounting of the several parts of the ion source to diifer'ent ones of a plurality of semirigid rods projecting from an insulator plate 34 is not limited to the particular configuration of,

rods shown in the drawings. Thus, for convenience in manufacturing, the plurality of supports are arranged in two concentric circles as shown in Fig. 5. However, any arrangement may be employed and the relative positioning of the shorter and longer rods may be interchanged without interfering with the functioning of the ion source. Any rearrangement will, of course, necessitate relocation of. the clearance holesinthe several members. In short, the illustrated 7'5 arrangement of the 'ro'dswlth respect'toeach For purvs other iS nOtE essential i to the-: proper-wfunctionln or construction ofx'the iontsource;

Not; only have :I'provided :anion source which;

8? thirdsdislrxcn;;thelsidesopposite:the1 second disk a;

pluralltysofyconductive supports passing. through the-several":disks;.means:-afiixingthe first, third;

in the fixture the several parts are-brazed tothe appropriate wires. By such a practice-the ion source: is constructed as aunit and may be --inserted or withdrawn from the mass spectrometer as aunit: The advantages of thistype of construction -and'method"of-fabricationwithrespect to: manufacture and" with respect to periodic cleaning of-the ion source, are manifest;

I cla-im:

1. Irran ion source for amass spectrometer-"thecombination which comprises afirst" conductive disk having an inlet therein for-moleculesto be ionized, a second conductive disk aflixed against the-first disk and-having recess therein opening toward the first disk and defining an ionization chamber, the second diskhaving an ion" slit in it opposite the first disk, a third conductive disk havinga-n ion slitin alignment with the ion slit in the=second diskand-spaced from the second disk on the side oppositethefirst disk, a plurality of conductive supports passing throughthe several disks, and means afiixing-the first disk and thethirdj disk to separate ones of the saidsupp r 2; In an ion sourcejor a; mass spectrometer the combination whichcomprises-a first conductive disk having an inlet thereinfor molecules to be ionized, a second conductive disk, disposed against the first diskand affixed thereto, and, having a recess therein opening toward the first disk and defining an ionizationchamber, the second disk havingan ion slit'in it opposite the first disk, a

pair; of pusher electrodes uspended in the ionization chamber independent of, the first: and:

second disks; athird conductive disk having an ion-slit in alignment with the ion slitin the second diskand spaced from; the seconddisk on the side opposite; the first disk, a fourthconductive disk havingan ion slit in alignment with the ion slit in,

the third" disk and spaced from the third'disk on the'side: opposite the second; disk, and'plurality of' conductive supports passing through the several disks-and means affixing the first, third and fourth disks andthe pusherelectrodes to separate-ones of said supports.

3. In an ion source-for a mass spectrometer-the combination which comprises a first conductive diskhavingan inlet": therein for the molecules tobe ionized; a second conductive disk disposed against and affixed" to the first disk and having a recess therein opening towardthefirst disk and defining an ionization chamber; the second conductive disk having an ionslit in it oppositethe flrstdisk, a pair of pusher electrodessuspended in the ionization chamber independent of the first and-second disks, a third conductive disk having anion slit'in alignment'with the ionslit in the second disk and spacedfrom the seconddisk on the side' opposite thefirst disk, a fourth conduc-i tive diskhaving an ionslitzinalignmentwith the ion slit-in: the third disk and spaced, from the and: fourth disks and the pair; of. pusher;v elec--' trodes: to: separate. ones oi; said supports, and means rorea-nchoringthe plurality 01 supports in;

fixed relationship. toeach other.

4.: Apparatus accordin to claim 3 wherein the meansrforanchoring the. several: supports com prisesga glass plate through which .theconductive, supportsaresealed;

5. In-ian-aion source; for :a. mass spectrometer.

the. oombin ationwhichcomprises a first conduct tive=diskahaving.v an inlet therein for molecules, to

be ionized; a. second: conductive disk. disposed againsta-ndamxed, to; the first'disk, agfirst recess in the-second diskopening toward the first disk:

and defining an ionization chamber, a. second recessin the second 1 disk opening tOWflldithB. first;

disk; a fiIStTSlit. in the second disk. communicat ingbetween the firstzrecess and the second recess, a: second-1 slit in the; second disk communicatingbetween the first recess and the exterior of thedisk opposite the-firsttslit, third slit communicating with the first-recess opposite the firsttdisk,

a. third conductive disk having an ion slit in,

alignment with the third-slit inthesecond disk andrspacedfrom the second disk on-theside op posite the first disk, aplurality of conductivesupe ports; passing through the several disks, means afiixing the first and third disks to separate ones of saidsupports, one'of said supports extending into the second. recess. inzthe. second disk, an elec tron catchergmounted on. said one of said supports and amelectromemitting element disposed adjacent said second disk in alignment with said second slit therein.

6:. Inan. ion source for: a mass spectrometer,.

the improvement which comprises a sintered' glass disk; a plurality'of conductive rods sealedthrough V the idisk,,the ionization chamber, pusher-v electrodes; and; accelerating, electrodes being mounted top-separate onesofsaid pluralityof 'roclsv in spacedrelationship.toeach other.

8., In. anion source-, for -a mass, spectrometer having several component parts. including means, forionizing molecules-and means for discharging,

ions ,fltomkthen ion. source, the improvement which comprises a, plurality of conductive members sealed through an insulating member andispaced from each other, the several component partsof the ion source being mounted to. difierentones of said conductive members in spaced relation- Ship;

9. In an ion sourceforamass spectrometer, the combination which comprises a plurality-oi conductive: rods sealed through. an insulating member; and: means mountedto separate-ones of the plurality of rods to form an ionization necessitate; relocation of the clearance holes in the; several? members. In short, the illustrated :5 arrangement off thei rodswith: respect to each each other and from the means forming the ionization chamber.

CLIFFORD E. BERRY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,071,597 Viasselli Feb. 23, 1937 2,084,858 Metcalf June 22, 1937 10 Number Name Date 2,437,130 Scott et a1 Mar. 2 1948 2,444,968 Washburn July 13, 1948 OTHER REFERENCES Coggeshall et a1.: Review of Scientific Instruments, May 1943, vol. 14, pages 125-129.

Honig: Journal of Applied Physics, November 1945, vol. 16, pages 646-654.

Nier: Review of Scientific Instruments, June 1947, vol. 18, pages 398 and 399.

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