US3047717A

US3047717A - Focusing mass spectrometer

Info

Publication number: US3047717A
Application number: US645282A
Authority: US
Inventors: Iwata Giichi
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-03-31
Filing date: 1957-03-11
Publication date: 1962-07-31
Anticipated expiration: 1979-07-31

Description

July 31, 1962 Filed March 11, 1957 Fig.

GHCHI lWATA FOCUSING MASS SPECTROMETER- 5 Sheets-Sheet 1 AC. Pawer PP Y Genera/0r D. C Power 57 Supp y earf/z J Po/e pie ce Guch'z [warn July 31, 1962 GllCHl IWATA FOCUSING MASS SPECTROMETER 5 Sheets-Sheet 2 Filed March 11, '1957 Fig 3 INSUZAT/O/V v lllllll lNSULAT/0N 3 Sheets-Sheet 3 Filed March 11, 1957 INSULATION Vhy States ate'nt 3,047,717 Patented July 31, 1962 3,047,717 FOCUSING MASS SPECTROMETER Giichi Iwata, 1209 Sugano, Ichikawa City, Japan Filed Mar. 11, 1957, Ser. No. 645,282 Claims priority, application Japan Mar. 31, 1956 5 Claims. (Cl. 25041.9)

of any known mass spectrometers and ion separator invented up to present never attained the optimum value of 100% This applies also to the trochoidal mass spectrometer invented by Bleakney and Hippie, Phys. Rev, vol. 53, p. 521, 1938, since ions emitted substantially in one plane only reach the ion detector.

The combination of special electric and magnetic fields ofthe present invention will produce a perfect focusing effect for ions of like mass-to-charge ratio regardless of their initial velocity and position.

It is therefore an object of this invention to provide a method and apparatus having a perfect focusing effect for ions of like mass-to-charge ratio regardless of their initial velocity and position.

Electric and magnetic fields utilized are, with respect to a Cartesian coordinate system x, y and 2, as follows:

V fi e -yew) B, magnetic field strength. V, potential difference. I, defining the longitudinal dimension of electrode.

Equations of motion of an ion:

m, mass; a, charge; and 1, time.

Introducing a new variable One combines the first and the second equations into a single equation as follows:

for simplicity, equations of motion become Calculating Calculating =e"* one gets an equation for 5 Hence the solution of equations of motion-will be where A stands for where quantities marked by the suffix 0 denote their initial values at 2:0.

Returning to g, one gets If one puts )\=v, therefore one gets at t=1r/v i r rfi (Fug-1) to 21 20 because of sin vt=sin 1r=0, and cos vl=COS 1r=l.

The three quantities are defined as follows:

m a half value of Larmor frequency.

Q wil frequency of vertical oscillation of ion.

All ions starting from a point (t Z converge therefore to its image point regardless of their initial velocity (it); (it).

numbered 102 and 103 respectively. Because of the relation the angle which said

projections

102 and 103 form with the vertex 101 of the ion source and the ion current detector or collector on the xy-plane is 40.5

Generally speaking ions which do not have the desired mass-to-charge ratio travel along arouate paths similar to that of ions which have the desired mass-to-charge ratio, but. do not converge at any point, thus rotating around the z-axis.

Ions that start from the point (9,, Z and have special mass-to-charge ratios 3e/m and e/2m, e/m being the desired mass-to-charge ratio, will be equally focused to their image points respectively regardless of their initial velocities.

The relation of electric and magnetic fields follows from the relation The general principle of perfect focusing is as stated above.

Its essential task is to combine the uniform magnetic field with the hyperboloidal electric field.

Means for producing the above electric and magnetic fields are numerous.

An example of a mass spectrometer utilizing the above electric and magnetic fields is shown in the drawings, where:

FIGURE 1 is a diagram showing the contemplated mathematical configuration of the ion path in the device of the invention.

FIG. 2 is a perspective view of a simplified schematic representation of the mass spectrometer, with portions cut away and some elements removed;

FIG. 3 shows a side view of a portion of an electrode;

FIG. 4 shows a model of a hyperboloid of one sheet;

FIG. 5 shows a horizontal view of a portion of an electrode;

FIG. 5 (A) is a cross-sectional view of the element shown in FIG. 5.

FIG. 6 shows a sectional view of the ion source and the ion current detector or collector;

FIG. 7 shows a schematical diagram of required voltage supply and a potential distribution inside the electrode.

The same reference characters denote the same parts throughout the specification and the several views of the drawings.

Referring more specifically to the drawings, FIG. 2

in particular the apparatus proper is shown enclosed in a cylindrical tank 1 which is evacuated. The z-aXis is shown passing through point 101 in FIG. 1. Within the boundary of the tank 1 a uniform magnetic field is maintained in parallel with the symmetrical axis of an electrode which produces a hyperboloidal electric field. Said electrode consists of two parallel circular rings 2 and 3 supported by six bronze uprights 4, a net 5 of conducting copper wires connecting said rings 2 and 3 and a pair of parallel

insulating discs

6 and 7, facing each other, perpendicular to the direction of said magnetic field, and equipped with a plurality of concentric conducting rings 21 insulated from each other. The rings 2 and 3 are made of nonferromagnetic metal such as bronze or stainless steel and have a number of holes 8 equidistantly spaced on their inside edges. Conducting copper wires 5 are netted through these holes 8 in such a manner that the wires inclined by tan 0= 4 As explained throughout the specification, the function of the net of conducting copper wires is as follows:

The net of conducting copper wires forms the side surface of the hyperboloid of one sheet. If the potential of the hyper-boloidal electric field is the side surface should be maintained at the constant potential which is produced by the apparatus shown in FIG. 7. This potential equals the potential of the rings further-most from the centers mounted on the upper and lower discs. On each of the insulating discs (upper 7 and lower 6), shown in FIG. 5, a number of concentric circular copper rings 21 are mounted equidistantly and maintained at appropriate potentials.

The discs on which the concentric copper rings are mounted are insulating materials and the concentric copper rings are insulated from each other. The concentric copper rings are maintained at appropriate potential by the apparatus shown in FIG. 7.

If p is the potential at the center of the disc, go; the potential at the ring 2 or 3 and n the number of concentric rings 21 on each disc, the proper potentials to apply to the concentric rings 21 on each disc will be as the following: as

Where 2d denotes the vertical distance of said rings 2 and 3.

An ion source, that is, means for omitting ions, comprises pipe 9 having a Window 24 and inner pipe 25, shown in FIG. 6. Pipe 25 is insulated from pipe 9 by means of Pyrex glass. Pipe 9 passes through disc 6 by hole 23 perforated through disc 6, as shown in FIG. 5, and disc 7 by a hole perforated therethrough, inclining at an angle 35.25 for the disc plane. An ion starting from window 24 'in a plane parallel to the

discs

6 and 7 travels a path such as shown in FIGURE 1 in the same plane, but an ion starting from window 24 in an outward direction from the plane goes apart from the plane, and returns to the plane to collide upon detector 26. If there is no detector, the ion oscillates up and down about the plane, while the projection of the ion on the plane travels a path such as shown in FIGURE 1. Since the electric potential is constant on any hyperboloidal surface x +y 2z ==k, k const., the electric potential is also constant along any generator of the hyperboloidal surface, and any generator inclines at an angle 0=35.25,

determined by the relation tan Ii=I/ /2 for the disc plane. Window 24 is substantially on the median plane equidistant from the upper disc 7 and the lower disc 6. Inner pipe 25 has a gap inside window 24.

An ion detector or collector, that is, means for detecting or collecting ions, comprises pipe 10 having Window 26 and inner pipe 27 and is of the same shape as said ion source except that inner pipe 27 has no gap. Pipe It? is insulated from pipe 10 by means of Pyrex glass. Pipe 10 is positioned at a position, which is reached by pipe 9 after a rotation by an angle 40.5 around the symmetrical axis of said electrode and a reflection with respect to said median plane, as shown in FIG. 3. Pipe 10 passes through disc 6 by hole 22 perforated therethrough, and disc 7 by a hole perforated therethrough. Window 26 is substantially on said median plane. Projections of parts of pipe 9 and pipe 10 on the plane of disc 6 are shown as 32 and 33 respectively in FIG. 5.

The emission of ions is effected as follows. A low voltage is developed across said gap of inner pipe 25 and an electron beam is formed between said gap. Molecules of a sample to be analyzed are introduced within inner pipe 25, ionized at said gap, accelerated by a potential difference between pipe 9 and pipe 25, and drawn out through window 24. After traversing arcuate paths, ions having the desired mass-to-charge ratio converge to pipe 27 through window 26. Ions which have not the desired mass-tocharge ratio and are not collected by the ion collector travel around the symmetrical axis of said electrode to impinge finally upon a screen 41. I

The screen 41 shown in FIGURES 2, 3 and 5 is an insulating rectangular plate equipped with a plurality of rectilinear conducting wires 42, inclining at an inclination of 35.25 for the disc plane. Three sides of screen 41 are limited by said electrode, the other side of screen 41 passes the center of said electrode. The position of screen 41 is shown by the projection 51 in FIG. 5 of screen 41 on disc 6 and by an elevation of screen 41 in FIG. 3. Each of rectilinear conducting wires 42 shown in FIG. 5 of screen 41 connects one of concentric rings 21 on disc 6 to one of concentric rings of disc 7.

The ions that impinge upon the electrode and screen 41 will lose their energy and charge and are to be pumped out by a pumping system. On the bottom of the tank 1 are provided a positive terminal 11 and a negative terminal 12 for the electrode, a terminal 16 for the ion current detector or collector and terminals 13, 14 and 15 for the ion' source.

In order to measure ions of various mass-to-charge ratio, magnetic field strength B or potential difference V is to be varied so as to satisfy the relation All ions starting from any point (5 z at the time of 1:0 converge therefore to the starting point at the time of t='n'/)\ and perform a periodic motion with the period of rr/h.

In this case the relation of magnetic field strength B and potential difference V is as follows:

A D.C. power supply can be constructed according to a well-known model described in a :book by William C. Elmore and Matthew Sands, entitled: Electronics-Experimental Techniques, 1949 edition.

When a DC. power is supplied through a potential divided to the electrode, there results a hyperboloidal electric field in a space defined by said electrodes.

While the salient features of this invention have been described in detail with respect to one embodiment it will of course be apparent that numerous modifications may be made within the spirit andscope of this invention and it is therefore not intended to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

1. A mass spectrometer comprising means to produc a uniform magnetic field; means to produce a hyperboloidal electric field including an electrode; said electrode comprising a pair of parallel insulating discs, facing each other, perpendicular to the direction of said magnetic field; a plurality of concentric conducting rings insulated from each other mounted to said discs; a pair of circular rings, each of said circularrings being connected to the outermost ring of each of said parallel insulating discs; a net of a hyperboloidal surf-ace constructed with conducting wires connecting said pair of circular rings; means energizing said electrode to provide a hyperboloidal electric field within a space defined by said electrode, an ion source and an ion detector-collector positioned within said space.

2. A mass spectrometer as claimed in claim 1, comprising in addition a screen of an insulating plate including a plurality of conducting wires connecting separately a plurality of concentric conducting rings of one disc of said pair of discs to a plurality of concentric conducting rings of the other disc of said pair of discs, said screen being positioned within said space and limited by said electrode and by a plane perpendicular to said discs and passing the center of said electrode.

3. A mass spectrometer comprising in combination an evacuated tank, means to produce a hyperboloidal electric field within said tank including an electrode, means to produce a uniform magnetic field in parallel with the symmetrical axis of said electrode and an ion source and an ion current detector within said electric field.

4. A mass spectrometer comprising in combination an 1 evacuated tank means to produce a hyperboloidal electric field including an electrode, said electrode comprising a pair of concentric rings of conducting wires facing each other and a net of a hyperboloidal surface constructed with conducting wires connecting the outer rings of said pair of concentric rings, means to produce a uniform magnetic field in parallel with the symmetrical axis of said electrode and an ion source and an ion current detector within said electric field and said magnetic field.

5. A mass spectrometer comprising in combination means to produce a hyperboloidal electric field including an electrode, and means to produce a uniform magnetic field in parallel with the symmetrical axis of said electrode, in the relation of References Cited in the file of this patent UNITED STATES PATENTS 2,221,467 Bleakney Nov. 12, 1940 2,752,501 Robinson June 26, 1956 2,752,503 Slepian June 26, 1956 2,844,726 Robinson July 22, 1958 FOREIGN PATENTS 1,049,592 France Aug. 19, 1953