Mass spectrometer

Abstract

An electrically conductive heat-blocking plate 11 with an opening 12 for allowing thermions to pass through is provided between a filament 3, whose temperature can be as high as 2000° to 3000° C., and an ionization chamber 2 . The heat-blocking plate 11 is thermally connected via an aluminum block 10 to a heater for maintaining the ionization chamber 2 within a range temperature from 200° to 300° C., and also electrically set at a ground potential, which is approximately equal to the potential of the ionization chamber 2. The heat-blocking plate 11 blocks the radiation heat that the filament 3 emits when energized. Thus, the wall of the ionization chamber 2 is prevented from being locally heated to an abnormally high temperature. As a result, the inner space of the ionization chamber 2 is maintained at an approximately uniform temperature, and the noise due to the decomposition of a metallic material by abnormal heating is prevented. The heat-blocking plate 11 also prevents a thermion-accelerating electric field from penetrating through an electron injection port 5 into the ionization chamber 2 and impeding the extraction of ions produced within the ionization chamber 2 . Thus, the ion extraction efficiency is also improved.

The invention claimed is: 
     
       1. A mass spectrometer including an ion source having a filament for generating thermions by being heated and an ionization chamber in which sample molecules are ionized by using the thermions, the ionization chamber having an electron injection port through which the thermions are introduced into an inner space thereof, wherein:
 a heat-blocking plate member, in which an opening for allowing electrons to pass through is formed on an axis connecting the filament and a center of the electron injection port, is provided in a space between the filament and the ionization chamber. 
 
     
     
       2. The mass spectrometer according to  claim 1 , wherein the heat-blocking plate member is thermally connected to a heating unit for heating the ionization chamber 
     
     
       3. The mass spectrometer according to  claim 1 , wherein the heat-blocking plate member is made of an electrically conductive material. 
     
     
       4. The mass spectrometer according to  claim 3 , wherein the electrically conductive heat-blocking plate member is identical in potential to the ionization chamber. 
     
     
       5. The mass spectrometer according to  claim 1 , wherein the heat-blocking plate member is located closer to the filament from a middle point between an outer wall surface of the ionization chamber and the filament. 
     
     
       6. The mass spectrometer according to  claim 2 , wherein the heat-blocking plate member is made of an electrically conductive material. 
     
     
       7. The mass spectrometer according to  claim 6 , wherein the electrically conductive heat-blocking plate member is identical in potential to the ionization chamber. 
     
     
       8. The mass spectrometer according to  claim 2 , wherein the heat-blocking plate member is located closer to the filament from a middle point between an outer wall surface of the ionization chamber and the filament. 
     
     
       9. The mass spectrometer according to  claim 3 , wherein the heat-blocking plate member is located closer to the filament from a middle point between an outer wall surface of the ionization chamber and the filament. 
     
     
       10. The mass spectrometer according to  claim 4 , wherein the heat-blocking plate member is located closer to the filament from a middle point between an outer wall surface of the ionization chamber and the filament. 
     
     
       11. The mass spectrometer according to  claim 6 , wherein the heat-blocking plate member is located closer to the filament from a middle point between an outer wall surface of the ionization chamber and the filament. 
     
     
       12. The mass spectrometer according to  claim 7 , wherein the heat-blocking plate member is located closer to the filament from a middle point between an outer wall surface of the ionization chamber and the filament. 
     
     
       13. The mass spectrometer according to  claim 7 , wherein the heating unit includes a conductive member attached to the ionization chamber, and the conductive member thermally connects the heat-blocking plate member to a heater of the heating unit and also electrically connects the heat-blocking plate member to the ionization chamber. 
     
     
       14. The mass spectrometer according to  claim 12 , wherein the heating unit includes a conductive member attached to the ionization chamber, and the conductive member thermally connects the heat-blocking plate member to a heater of the heating unit and also electrically connects the heat-blocking plate member to the ionization chamber. 
     
     
       15. A method of using a mass spectrometer, comprising:
 generating thermions using a heated filament;   passing the thermions through an opening in a heat blocking member; and   ionizing sample molecules in an ionization chamber using the thermions, the ionization chamber having an electron injection port through which the thermions are introduced into an inner space thereof,   the opening in the heat blocking member being formed on an axis connecting the filament and a center of the electron injection port, and the heat blocking member being provided in a space between the filament and the ionization chamber.