US3654457A

US3654457A - Ion source device equipped with sample heating means for use in mass spectrometer

Info

Publication number: US3654457A
Application number: US798363A
Authority: US
Inventors: Masayoshi Yano; Tamotsu Noda
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1968-02-12
Filing date: 1969-02-11
Publication date: 1972-04-04
Anticipated expiration: 1989-04-04

Abstract

An ion source for a mass spectrometer having a sample cell containing a sample, a mesh filament surrounding the sample cell and a radiant heat shield surrounding the mesh filament, in which the sample cell is heated to a high temperature by being bombarded with thermoelectrons emitted from the filament so that the sample in the cell is vaporized and led toward the ion source to be ionized. In the device, the sample cell and the radiant heat shield are maintained at a high potential and a low potential, respectively, relative to the potential at the filament so that the thermoelectrons emitted from the filament can be accelerated toward the sample cell.

Description

United States Patent Yano et a1.

[54] ION SOURCE DEVICE EQUIPPED WITH SAMPLE HEATING MEANS FOR USE IN MASS SPECTROMETER [72] Inventors: Masayoshi Yano; Tamotsu Noda, both of Katsuta-shi, Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Feb. 11, 1969 [2]] Appl. No.: 798,363

is 3,654,457 [451 Apr. 4, 1972 2,733,342 l/l956 Wouters ..250/41.9 SR 2,942,098 6/1960 Smith ..13/31 X FOREIGN PATENTS OR APPLICATIONS 1,162,180 9/1958 France ..l3/3l Primary Examiner-James W. Lawrence Assistant Examiner-A. L. Birch Attorney-Craig, Antonelli, Stewart & Hill [5 7] ABSTRACT An ion source for a mass spectrometer having a sample cell containing a sample, a mesh filament surrounding the sample cell and a radiant heat shield surrounding the mesh filament, in which the sample cell is heated to a high temperature by being bombarded with thermoelectrons emitted from the filament so that the sample in the cell is vaporized and led toward the ion source to be ionized. In the device, the sample cell and the radiant heat shield are maintained at a high potential and a low potential, respectively, relative to the potential at the filament so that the thermoelectrons emitted from the filament can be accelerated toward the sample cell.

Claims, 5 Drawing Figures 3 r 22 1 e. 2 75% J v I 7/ 73; f 7' 5 Ma 48 l '50 44 47 165. 67

'PATENTEDAPR 41912 3.654457 SHEET 1 0F 2' INVENTORS mm, )mm Mo Tn/mrzu mam ATTORNI'TYS PATENTEDAPR 4:912 3,654,457

' sum 2 or 2 ION SOURCE DEVICE EQUIPPED WITH SAMPLE HEATING MEANS FOR USE IN MASS SPECTROMETER BACKGROUND OF THE INVENTION Field Of The Invention This invention relates to ion source devices equipped with sample heating means for use in mass spectrometers and more particularly to an ion source device of the kind described above in which a sample cell containing therein a sample is heated by means of electron bombardment so as to vaporize the sample in the sample cell and to ionize the vaporized sample.

Description Of The Prior Art In a mass spectrometer, analysis of a sample such as a solid, a mixture of a solid and a liquid, or a mixture of a solid and a gas which would not be vaporized unless heated to a high temperature is frequently required. The sample may be an inorganic material such as a metal, alloy, ceramic, graphite or the like. An ion source of the Knudsen cell type is well known in the art as a device which satisfies the above requirement. In view of the fact that a sample in a mass spectrometer must be ionized in a gaseous state and in order that a sample as described above which would not be vaporized unless heat is applied thereto can be satisfactorily vaporized by heating, the ion source of the Knudsen cell type comprises a sample cell containing a sample therein, a filament for heating the cell, and a plurality of radiant heat shielding plates for shielding heat radiated from the sample cell.

Further, in view of the fact that the sample must be heated to a high temperature, for example, of the order of 2500 C., a method of emitting thermoelectrons from the filament and bombarding the sample cell with the electrons is commonly employed in an ion source of the Knudsen cell type. On account of the necessity for heating the sample to a high temperature, it is very important in any ion source of the Knudsen cell type to effectively direct the thermoelectrons emitted from the filament toward the sample cell for heating the sample cell to a high temperature and to prevent the radiant heat shielding plates from being bombarded by the thermoelectrons during the analysis of the sample.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel and improved ion source device equipped with sample heating means for use in a mass spectrometer which satisfies reasonably such requirements.

In accordance with the present invention, there is provided an ion source device equipped with sample heating means for use in a mass spectrometer comprising a sample cell for containing therein a sample, said sample cell having an opening, heating means disposed to surround said sample cell for emitting thermoelectrons to heat said sample thereby to vaporize the same, radiant heat shielding means disposed to surround said heating means so as to serve as a shield against the radiant heat emanating from said heating means, first electrical power supply means for supplying the heating means with a quantity of electricity, electrical power supply means for applying a high potential to said sample cell and a low potential to said radiant heat shielding means relative to the potential at said heating means in order to accelerate the thermoelectrons emitted from said heating means toward said sample cell, and ion source means for ionizing the sample which is vaporized in said sample cell and passes through said opening in said sample cell.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of an embodiment of the ion source device equipped with sample heating means for use in a mass spectrometer according to the present invention.

FIG. 2 is a sectional view taken on the line II-ll' in FIG. 1.

FIG. 3 is a horizontal sectional view taken on the line Ill-III in FIG. I.

FIG. 4 is a developed view of part of a mesh filament shown in FIGS. 1 and 2.

FIG. 5 is an electrical circuit diagram of power supply means for the filament, thermoelectron accelerating means and degassing means preferably used in the device shown in FIGS. I and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1, 2 and 3, there is shown an embodiment of the ion source device equipped with sample heating means for use in a mass spectrometer according to the present invention. The device includes an ion source section 1, a sample heating section 4 partitioned from the ion source section I by means of a partition plate 2 which has an opening 3 of relatively small diameter bored in its central portion, a shutter mechanism 5 and sample cell observing sections 6 and 7. The ion source section 1 comprises an ion source chamber 8 and an ion source 9 disposed thereinside. The ion source 9 comprises an ionization chamber 13 having sample beam passages 10 and 10, an ion beam passage 11, and ionizing

electron passages

12 and 12 bored in the walls thereof, a repeller electrode 14 mounted within the ionization chamber 13, a lens 15 and a slit plate 16 disposed opposite to the ion beam passage 11, a filament 17 disposed opposite to the ionizing electron passage 2, a target 18 disposed opposite to the ionizing electron passage 12' so as to collect the electrons emitted from the filament 17, and a magnet 19 for establishing a magnetic field in the advancing direction of the electrons, which are emitted from the filament 17 toward the target 18 through the ionizing

electron passages

12 and 12, so as to collimate the electrons while imparting a gyrating movement to the electrons. The sample beam passing through the sample beam passages 10 and 10', the ion beam passing through the ion beam passage 11 and the ionizing electron beam passing through the ionizing

electron passages

12 and 12 stand at right angles with respect to one another. The ion source section 1 comprises further an exit slit plate 20 disposed in the ion source chamber 8 and a telefocusing lens 21 for focusing the beam of ions from the ion source 9 on the slit of the exit slit plate 20. The lens 21 is mechanically assembled as a unit with the ion source 9, and the unit is supported by an ion source supporting member 22 provided on a suitable portion of the wall of the ion source chamber 8. Although not shown, there is actually an evacuating pump which evacuates the interior of the ion source chamber 8 through an evacuating conduit 23 connected to a suitable portion of the wall of the ion source chamber 8.

The sample heating section 4 comprises a sample cell chamber 24, a sample cell assembly 25 disposed within the chamber 24, a filament assembly 26, and a group of radiant heat shielding cylinders having aligned openings 27 and 28 bored through an upper central portion and a suitable portion at the side thereof, respectively. The sample cell assembly 25 comprises a sample cell 31 receiving a sample thereinside, a sample cell support 32 for mounting the sample cell 31 thereon, a support base 34 for supporting the cell support 32 through three support rods 33 (only two of them are shown in FIG. 1), and a stack of electrical and thermal insulators 35 for supporting the support base 34 thereon. The lower end of the sample cell chamber 24 is provided with a removable flange 36 which has a central opening 37. Another flange 55 is detachably fixed to the flange 36 so as to close the opening 37 of the flange 36. A double tube 38 extends through the center of the flange 55 and a cooling medium such as water flows through the double tube 38. The stack of electrical and thermal insulators 35 is supported on the top of the double tube 38 through a support block 39. Therefore, it may be said that the flange 55 serves as a base for supporting the sample cell assembly 25. The sample cell 31 is constituted by a cell body 40 and a cap 42 covering the upper end of the cell body 40. The cap 42 has a central opening 41. The stack 35 comprises a plurality of electrically and thermally insulating members 43, 44 and 45 which are spaced a suitable distance from each other by

spacers

46 and 47 and are securely fixed together by screws 48 and 49. The uppermost electrically and thermally insulating member 43 is fixed to the support base 34 by screws 51 with spacers 50 interposed therebetween so as to maintain a suitable spacing between the member 43 and the support base 34. The lowermost electrically and thermally insulating member 45 is fixed to the support block 39 by screws 56 and is in intimate contact with the support block 39. Various materials may be employed to form the elements constituting the sample cell assembly 25. For example, tantalum which has a high melting point, can easily be machined and has a low vapor pressure may be employed to form the sample cell 31, and tungsten having a high resistance against heat may be employed to form the support rods 33, while boron nitride which is highly resistive to thermal shock, has a high melting point and can easily be machined may be employed to form the stack 35 of electrically and thermally insulating members. Further, tantalum which is resistive to heat may be employed to form the sample cell support 32 and the support base 34. The number of electrically and thermally insulating members 43, 44 and 45 may suitably be increased when required.

The filament assembly 26 comprises a cylindrical lower supporting member 60 of tantalum, a cylindrical upper supporting member 62 of tantalum having four large openings 61 bored in the wall thereof (although only two of them are shown in FIG. 1), a cylindrical mesh filament 63 whose upper and lower ends are secured to the respective

cylindrical members

62 and 60 by welding, and a plurality of supporting pillars 65 of stainless steel for supporting the two

cylindrical members

60 and 62 through

insulating blocks

70, 71, 72 and 73 of boron nitride which are electrical and thermal insulators. These supporting pillars 65 are secured on a supporting ring 67 of stainless steel which is supported on the flange 36 through a plurality of spacers 66 of alumina. As best shown in FIG. 4, the mesh filament 63 is in the form of a mesh of a multiplicity of tungsten wires 68 having a wire diameter of the order of 0.15 mm and a spacing between wires of the order of 7 mm. The wires 68 are spot-welded to each other at their intersections 69.

The radiant heat shielding cylinder group 30 comprises a plurality of spaced cylindrical shielding members of tantalum. These cylindrical members are welded at their lower end to a first base plate 75 of tantalum. The first base plate 75 is supported on a second base plate 77 through a plurality of supporting rods 76. The second base plate 77 is supported on a supporting ring 79 through a plurality of supporting pillars 150. The supporting ring 79 is supported on the flange 36 through a plurality of spacers 78 of alumina which are electrical and thermal insulators.

The shutter mechanism is mounted on a portion of the side wall of the ion source chamber 8. The shutter mechanism 5 comprises a stationary hollow cylindrical member 81 having a pin 80 extending into the hollow space thereof, a rotary member 83 which is internally threaded as at 82 and is received in the hollow space of the cylindrical member 81 so as to be rotatable about its axis but not movable in its axial direction, a reciprocating member 86 which is externally threaded as at 84 at one end thereof for threaded engagement with the internally threaded portion 82 of the rotary member 83 and has an axial groove 85 on a portion of its outer periphery adjacent to the other end thereof so that the pin 80 can engage the groove 85, a shutter plate 88 which is fixed to the other end of the reciprocating member 86, which is provided with a sample beam passage 87 having a small pumping conductance, and which is slidably positioned on the partition plate 2, a flange 89 to which the stationary hollow cylindrical member 81 is fixed, a vacuum sealing bellows 90 disposed between the flange 89 and the reciprocating member 86, and a knob 91 secured to the rotary member 83.

The sample cell observing section 6 is mounted on the upper end of the ion source section 1 and comprises an optical window plate 92, and a shutter 94 of magnetic material which is disposed within the ion source chamber 8 so as to be pivotal about a pivot shaft 93. The sample cell observing section 7 is mounted in the side wall of the sample cell chamber 24 and comprises an optical window plate 95, and a shutter 97 of magnetic material which is disposed within the sample cell chamber 24 so as to be pivotal about a pivot shaft 96. The

openings

27, 3 and the passages 10, 10'Jre designed to align on the same axis so that the interior of the sample cell 31 can be observed from the optical window plate 92 through the passages and

openings

10, 10, 87, 3, 27 and 41. One of the openings 61 and the openings 28 align on the same axis so that the outer surface of the sample cell 31 can be observed from the optical window plate through the openings 28, one of the openings 61 and the mesh of the mesh filament 63.

Although not shown, there is actually provided an evacuating pump which acts to evacuate the interior of the sample cell chamber 24 independently of the ion source chamber 8 through an exhaust conduit 100 suitably connected to a portion of the side wall of the sample cell chamber 24.

FIG. 5 is a schematic electrical circuit diagram of power supply means for the filament, thermoelectron accelerating means and degassing means in the embodiment of the present invention. The circuit includes three

power sources

101, 250 and 200 and one change-over switch 103. The negative terminal of the power source 101 is connected with the positive terminal of the power source 200, and an intermediate point 201 therebetween is connected with the filament 63. The positive terminal of the power source 101 is connected with the sample cell 31 and also with the change-over contact 105 of the change-over switch 103, while the negative terminal of the power source 200 is connected with the other change-over contact 106 of the change-over switch 103. The common contact 107 of the change-over switch 103. The common contact 107 of the change-over switch 103 is connected with the radiant heat shielding cylinder group 30.

The device according to the present invention having a structure as described above operates in a manner as described below.

At first, it is supposed that the sample cell 31 contains already a sample which is to be subjected to mass analysis. ln the above state, the evacuating pump means (not shown) is operated to evacuate the interior of the ion source chamber 8 and the interior of the sample cell chamber 24 through the exhaust conduits 23 and 100 independently of each other. The mesh filament 63 is heated by current supplied from the power supply means 250 so as to emit thermal electrons therefrom. The change-over switch 103 is so set that its common contact 107 is connected with the contact 105 in order to maintain the sample cell 31 and the radiant heat shielding cylinder group 30 at a high potential with respect to the potential at the filament 63. Practically, the potential at the sample cell 31 and the radiant heat shielding cylinder group 30 is kept by about 500 to 2000 volts higher than the potential at the filament 63. Therefore, the thermoelectrons emitted from the filament 63 are accelerated by the electric field to move toward and impinge against the sample cell 31 and the radiant heat shielding cylinder group 30. Thus, the sample cell 31 and the structure surrounding the sample cell 31, that is, the radiant heat shielding cylinder group 30 are heated by the electrons impinging thereagainst. As a result, undesirable gas particles deposited on or adsorbed in the surface of these members are effectively released. The released gas is discharged through the exhaust conduit 100.

Needless to say, the opening or sample beam passage 3 is closed by the shutter 88 which is urged to its passage closing position in a manner as described below. Turning of the knob 91 rotates the rotary member 83 which is associated with the knob 91. As the rotary member 83 is rotated, the reciprocating member 86 is moved in the direction as shown by arrow A due to the fact that the internal threads 82 provided on the rotary member 83 are in threaded engagement with the external threads 84 provided on the reciprocating member 86 and the pin 80 extending from the stationary hollow cylindrical member 81 engages the axial groove 85 provided on the reciprocating member 86. As the reciprocating member 86 is moved in the direction of arrow A, the shutter 88 associated with the reciprocating member 86 is moved in the same direction. Thus, by turning the knob 91 in one direction, it is possible to move the opening 87 of the shutter 88 away from the sample beam passage 3 thereby to close the sample beam passage 3 by the shutter 88. Therefore, the undesirable gas within the sample cell chamber 24 released by the degassing operation does not enter the ion source chamber 8 which is thereby continuously maintained at a predetermined pressure and objectionable fouling of the ion source 9 with the gas can rationally be avoided.

The shutter mechanism 5 is then manipulated to open the sample beam passage 3. In other words, the opening 87 of the shutter 88 is aligned with the sample beam passage 3. In the meantime, the change-over switch 103 is shifted to a position at which the common contact 107 is connected with the contact 106, whereby the potential at the radiant heat shielding cylinder group 30 becomes lower than the potential at the filament 63 although the potential at the sample cell 31 is left higher than the potential at the filament 63. For example, the potential applied to the radiant heat shielding cylinder group 30 is lower by about 50 volts than the potential applied to the filament 63. Further, the potential at the cylindrical member 62 is lower by about a few volts than the potential at the mesh filament 63 because the positive and negative sides of the power supply means 250 are connected with the mesh filament 63 and the cylindrical member 62, respectively. Accordingly, the thermoelectrons emitted from the filament 63 are accelerated toward the sample cell 31 to impinge against the sample cell 31, and at the same time, the thermoelectrons tending to move toward the cylindrical member 62 and the radiant heat shielding cylinder group 30 from the filament 63 are repelled back toward the filament 63 to impinge against the sample cell 31 by the action of the electric fields established between the filament 63 and the cylindrical member 62 and between the filament 63 and the radiant heat shielding cylinder group 30. Thus, the sample cell 31 can very effectively be heated with a small electric power. Further, by virtue of the fact that the radiant heat shielding cylinder group 30 is almost free from impingement thereagainst of the electrons emitted from the filament 63 and tending to move toward the radiant head shielding cylinder group 30, undesirable release of gas deposited on or adsorbed in the radiant heat shielding cylinder group 30 can effectively be avoided during the period other than the degassing operation, that is, the period when the analysis is being carried out. The filament 63 is in the form of a cylindrical mesh screen which comprises a multiplicity of tungsten wires 68 welded to one another at their intersections 69 as shown in FIG. 4 and is secured at its opposite ends to the cylindrical supporting

members

60 and 62, respectively. By virtue of the above structure, the sample cell 31 can uniformly be heated and heating can very stably be effected because the filament itself is free from any thermal deformation.

When the sample cell 31 is heated in the manner described above, the sample contained therein is vaporized. The vaporized sample enters in the form of a beam into the ionization chamber 13 through the aligned openings and

passage

41, 27, 3, 87 and 10. The electrons emitted from the ionizing electron emitting filament 17 and passed through the passages 12 and 12'40 be collected by the target 18 impinge against the vaporized sample, within the ionization chamber 13 to ionize the latter. The ionizing electrons are uniformly collimated while being imparted with a gyrating movement by the magnetic field established by the magnet 19 so that the sample entering the ionization chamber 13 can effectively be ionized. The sample which has not been ionized within the ionization chamber 13 passes out of the chamber 13 by way of the passage The ions ionized within the ionization chamber 13 pass through the passage 1 l to be focused on the slit of the slit plate 16 by the action of the lens 15. The ions passed through the slit of the slit plate 16 are focused on the slit of the slit plate 20 by the action of the telefocusing lens 21. Although not shown, the ions existing from the slit of the slit plate 20 are led toward an analysis tube for the sake of analysis.

The magnet 19 may be disposed outside of the ion source chamber 8. In such a case, however, the ion source section 1 is necessarily large-sized since the sample heating section 4 must inevitably be large-sized. Therefore, it is unable to obtain a sufficient magnetic field strength when the magnet 19 is disposed outside of the ion source chamber 8. It will be understood that the disposition of the magnet 19 within the ion source chamber 8 in the arrangement according to the present invention is so effective that the magnet 19 may have a relatively small size so as to simply obtain a predetermined magnetic field strength.

In order that the sample within the sample cell 31 can be heated to a high temperature of, for example, about 2,500 C. by the electron bombardment, it is quite important that the radiant heat from the sample cell 31 as well as the conduction of heat be shielded as much as possible. Further, in view of the fact that a high voltage is applied to the sample cell 31, it is quite important that the sample cell 31 be completely electrically insulated from the base or flange 55 or the like. To deal with such a requirement, the radiant heat shielding cylinder group 30 is especially provided in the present invention so as to prevent the radiated heat from the sample cell 31 and the filament 63 from escaping outwardly. Further, in accordance with the present invention, the stack of electrical and thermal insulators 35 is especially provided to provide a shield against heat which is radiated from the sample cell 31 and tends to escape past the sample cell assembly 25 toward the base or flange 55 or the like by conduction. Furthermore, the stack 35 consists of a plurality of electrically and thermally insulating members 43, 44 and 45 which are suitably spaced from each other. Thus, a perfect shield against the conducted heat can be provided. Moreover, these electrically and thermally insulating members 43, 44 and 45 serve also as an effective electrical insulation against the base or flange 55 supporting the sample cell 31 thereon. A cooling medium such as water is led into the double tube 38 for cooling the stack of electrical and thermal insulators 35 so as to rationally prevent any reduction in the electrically insulating function of the stack of electrical and thermal insulators 35 due to an undesirable increase in temperature.

A relatively large amount of vaporized sample gas emerging from the sample cell 31 flows through the opening 41 of the cell 31 toward the ion source 9 in a considerably dispersed state. Further, although the gas attach deposited on or adsorbed in the radiant heat shielding cylinder group 30 has been released prior to the analysis, some gas particles still deposited on or adsorbed in the radiant heat shielding cylinder group 30 may be led through the opening 3 toward the ion source chamber 8 during analysis. These gases may foul the ion source 9 and bring forth an objectionable reduction in the degree of vacuum within the ion source chamber 8. In order to restrict the flow of vaporized sample gas emerging from the sample cell 31 to a suitable area so that the unnecessary sample gas and the deposited or adsorbed gas may not be led toward the ion source chamber 8, the beam passage 87 of small diameter having a small pumping conductance is provided in the shutter 88, and the ion source chamber 8 and the sample cell chamber 24 are arranged to be evacuated independently of each other. In such an evacuating system, for example, the pressure within the ion source chamber 8 may be set at 5 X 10* to 10 X 10" 7 Torr and the pressure within the sample cell chamber 24 in the vicinity of the sample cell 31 may be set at 5 X 10 8 to 10 X 10 6 Torr.

In accordance with the present invention, the internal temperature of the sample cell 31 can directly be observed from the sample cell observing section 6 through the aligned passages and

openings

10', 10, 87, 3, 27 and 41 for the purpose of measuring the temperature of the sample. For the sake of measuring the temperature and uniformity of the sample cell 31, observation of a plurality of surface holes (need not be a through holes), not shown, of l to 2 mm. in diameter of the sample cell 31 is much more effective than observation of a single hole of the sample cell 31. To this end, another sample cell observing section 7 is provided according to the present invention so that the temperature at each surface hole of the sample cell 31 can be observed from the optical window plate 94 through the openings 28 and one of the openings 61.

The sample gas, adsorbed gas and the like may deposit to form a coating on the

optical window plates

92 and 95 in the sample cell observing sections 6 and 7. In order to avoid such trouble, the

shutters

94 and 97 are provided in accordance with the present invention. These shutters must be opened during the observation of the sample cell 31 and kept closed except for the observation. The mechanism for effecting the opening and closure of the shutters may be realized in a variety of forms. For example, a shutter shaft may be fitted to the shutter in vacuum and may have a portion thereof projected to the outside of the device, and this projecting portion may be manipulated to open or close the shutter. However, a vacuum seal is required to seal the outwardly projecting portion of the shutter shaft. When the vacuum seal consists of rubber, the seal may be damaged by the action of heat. Further, in any of the cases where the vacuum seal is made of rubber and a metal, a suitable thermal insulator must be fitted on the projecting portion of the shutter shaft so that such portion can be contacted manually.

In accordance with the present invention, a magnet is disposed outside of the ion source chamber 8 opposite to the shutter 94 so that the force of magnetic attraction can be utilized to close the shutter 94 by turning it about the pivot shaft 93. Of course, the shutter 97 is also closed by a mechanism similar to the above. It will be understood therefore that the above problem can rationally be solved by the present invention.

While a preferred embodiment of the present invention has been described in detail with reference to the drawings, it will be understood that the embodiment is merely exemplary of the present invention and many changes and modifications may be made therein without departing from the spirit of the present invention.

We claim:

1. An ion source device equipped with sample heating means for use in a mass spectrometer comprising a sample cell for containing therein a sample, said sample cell having an opening, heating means disposed to surround said sample cell for emitting thermoelectrons to heat said sample thereby to vaporize the same, radiant heat shielding means disposed to surround said heating means so as to serve as a shield against the radiant heat emanating from said heating means, first electrical power supply means for supplying a quantity of electricity to the heating means, second electrical power supply means for applying a high potential to said sample cell and a low potential to said radiant heat shielding means relative to the potential at said heating means in order to accelerate the thermoelectrons emitted from said heating means toward said sample cell, and ion source means for ionizing the sample which is vaporized in said sample cell and passes through said opening in said sample cell.

2. An ion source device as claimed in claim 1, in which said electrical power supply means includes potential selecting means for selectively maintaining said radiant heat shielding means at a high or a low potential relative to the potential at said heating means.

3. An ion source device as claimed in claim 1, further comprising means for supporting said sample cell on a base, and a plurality of electrically and thermally insulating members for intercepting the conduction of heat from either one of said sample cell and said base to the other through said sample cell supporting means and electrically insulating said base from said sample cell.

4. An ion source device as claimed in claim 1, in which there is provided means for supporting said sample cell on a base, and a plurality of electrically and thermally insulating members for intercepting the conduction of heat from either one of said sample cell and said base to the other through said sample cell supporting means and electrically insulating said base from said sample cell, and said electrical power supply means includes potential selecting means for selectively maintaining said radiant heat shielding means at a high or low potential relative to the potential at said heating means.

5. An ion source device as claimed in claim 3, in which cooling means is provided to cool at least one of said electrically and thermally insulating members.

6. An ion source device as claimed in claim 4, in which cooling means is provided to cool at least one of said electrically and thermally insulating members.

7. An ion source device as claimed in claim 1, in which there is provided means for supporting said heating means, and said heating means comprises a cylindrical filament made by disposing a multiplicity of metal wires in the form of a grid and welding the metal wires to each other at their intersections, said cylindrical filament being fixed at its opposite ends to said supporting means.

8. An ion source device as claimed in claim 2, in which there is provided means for supporting said heating means, and said heating means comprises a cylindrical filament made by disposing a multiplicity of metal wires in the form of a grid and welding the metal wires to each other at their intersections, said cylindrical filament being fixed at its opposite ends to said supporting means.

9. An ion source device as claimed in claim 1, further comprising a first chamber for accommodating therein said ion source means, a second chamber for accommodating therein at least said sample cell, said heating means and said radiant heat shielding means, a partition wall for partitioning said first chamber from said second chamber, said partition wall having an opening of relatively small diameter for allowing passage therethrough of sample gas flowing toward said ion source means, a shutter movable to and fro over said partition wall, said shutter having a sample gas passage having a small discharge conductance, means for causing the to-and-fro movement of said shutter over said partition wall, and means for evacuating said first and second chambers independently of each other.

10. An ion source device as claimed in claim 2, further comprising a first chamber for accommodating therein said ion source means, a second chamber for accommodating therein at least said sample cell, said heating means and said radiant heat shielding means, a partition wall for partitioning said first chamber from said second chamber, said partition wall having an opening of relatively small diameter for allowing passage therethrough of sample gas flowing toward said ion source means, a shutter movable to and fro over said partition wall, said shutter having a sample gas passage having a small discharge conductance, means for causing the to-and-fro movement of said shutter over said partition wall, and means for evacuating said first and second chambers independently of each other.

11. An ion source device as claimed in claim 9, further comprising an optical plate provided on said first chamber for observing said sample cell therethrough, and a shutter of magnetic material disposed within said first chamber adjacent to said optical plate so as to be pivotal toward an away from said optical plate, said shutter being urged to its open and closed position by a magnet disposed outside of said first chamber.

12. An ion source device as claimed in claim 10, further comprising an optical plate provided on said first chamber for observing said sample cell therethrough, and a shutter of magnetic material disposed within said first chamber adjacent to said optical plate so as to be pivotal toward and away from said optical plate, said shutter being urged to its open and closed position by a magnet disposed outside of said first chamber.

13. An ion source device as claimed in claim 1, in which there is provided a chamber for accommodating therein said ion source means, and said ion source means includes an electron generator for ionizing the sample gas led therein from said sample cell, and a collimator disposed within said chamber for collimating the electrons emitted from said electron generator.

14. An ion source device as claimed in claim 2, in which there is provided a chamber for accommodating therein said ion source means, and said ion source means includes an electron generator for ionizing the sample gas led therein from said sample cell, and a collimator disposed within said chamber for collimating the electrons emitted from said electron generator.

15. An ion source device as claimed in claim 6, further comprising means for supporting said heating means, a first chamber for accommodating therein said ion source means, a second chamber for accommodating therein said sample cell, said heating means, said radiant heat shielding means and said electrically and thermally insulating members, a partition wall for partitioning said first chamber from said second chamber, said partition wall having an opening of relatively small diameter for allowing passage therethrough of sample gas flowing toward said ion source means, a shutter movable to and fro over said partition wall, said shutter having a sample gas passage having a small discharge conductance, means for causing the to-and-fro movement of said shutter over said partition wall, means for evacuating said first and second chambers independently of each other, an optical plate provided on said first chamber for observing said sample cell therethrough, and a shutter of magnetic material disposed within said first chamber adjacent to said optical plate so as to be pivotal toward and away from said optical plate, said shutter being urged to its open and closed position by a magnet disposed outside of said first chamber, said heating means comprising a cylindrical filament made by disposing a multiplicity of metal wires in the form of a grid and welding the metal wires to each other at their intersections, said cylindrical filament being fixed at its opposite ends to said supporting means, said ion source means including an electron generator for ionizing the sample gas led therein from said sample cell, a target for collecting the ions emitted from said electron generator, and a collimator disposed within said first chamber for collimating the electrons emitted from said electron generator.