Quadrupole mass spectrometer

Abstract

A quadrupole mass spectrometer includes means for measuring total ion current having an electron repeller cage disposed about an electron source filament. The electron repeller cage repels electrons emitted by the electron source filament, urging them away from both the repeller and the filament, while also attracting positive ions. When the positive ions contact the electron repeller cage, a current is induced that is measured at the electron repeller cage. The measured current represents total ion current transmitted through the spectrometer. Thus, the need to include a total pressure measurement plate to measure total ion current is eliminated, and since the ion-exposed surface area of the electron repeller cage is greater than the ion-exposed surface area of the total pressure measurement plate, the invention provides improved total pressure measurement sensitivity.

What is claimed is: 
     
       1. A quadrupole mass spectrometer for measuring the relative amounts of the respective constituents of a gas present in said spectrometer, said spectrometer being of the type comprising a quadrupole mass filter, the quadrupole mass spectrometer comprising: means for defining a space for containing a representative sample of said gas;   biased electron repeller means for repelling electrons and attracting positive ions contained within said space;   electron source means, disposed generally within said space, for emitting a plurality of electrons, the plurality of electrons being accelerated into said space so as to produce a plurality of positive ions, a fraction of the plurality of positive ions being attracted to the electron repeller means; and   current measurement means, coupled to the electron repeller means, for measuring a current that results from the fraction of the plurality of positive ions that are attracted to the electron repeller means, and for providing a signal representative of the total ion current entering the quadrupole mass filter.   
     
     
       2. A quadrupole mass spectrometer according to claim 1, further including ion source means, disposed in said space, for providing a second fraction of the plurality of positive ions of said constituents of said gas and for generating the ion current entering said quadrupole mass filter. 
     
     
       3. A quadrupole mass spectrometer according to claim 2, wherein said ion source means comprises an ion source cage. 
     
     
       4. A quadrupole mass spectrometer according to claim 1, wherein said electron source means includes a filament. 
     
     
       5. A quadrupole mass spectrometer according to claim . .1.!. .Iadd.9.Iaddend., wherein electron source means for producing electrons comprises a filament disposed in said space. 
     
     
       6. A quadrupole mass spectrometer according to claim . .1.!. .Iadd.9.Iaddend., wherein said ion source means comprises a ion source cage. 
     
     
       7. A quadrupole mass spectrometer according to claim . .1.!. .Iadd.9.Iaddend., wherein said means for generating an ion current from the ions produced inside said ion source means so that said ion current represents the relative amounts of said constituents comprises a quadrupole mass filter. 
     
     
       8. A quadrupole mass spectrometer according to claim . .1.!. .Iadd.9.Iaddend., wherein said means for propelling said electrons produced by said electron source means through said space into said ion source means so that positive ions of each said constituent are produced in said space includes means for biasing said electron repeller means relative to said electron source means and said ion source means. 
     
     
       9. A quadrupole mass spectrometer for measuring the relative amounts of mass of one or more constituents, respectively of different molecular weights, of a gas, said spectrometer comprising: (a) means for defining a space for containing a representative sample of said gas;   (b) electron source means for producing electrons;   (c) ion source means, disposed in said space, for producing ions of each of said constituents of said gas when particles of each constituent present in said ion source means are struck by electrons;   (d) means for propelling said electrons produced by said electron source means through said space into said ion source means so that positive ions of each said constituent are produced in said space, both inside and outside said ion source means, said means for propelling said electrons including electron repeller means for repelling said electrons toward said ion source means and for collecting ions received from said space; and   (e) means for generating an ion current from the ions produced inside said ion source means so that said ion current represents the relative amounts of said constituents; and   (f) means for generating a signal as a function of the ions collected by said electron repeller means and representative of the total ion current produced inside said ion source means.   
     
     
       10. In a quadrupole mass spectrometer comprising an electron source filament, the electron source filament carrying a current of sufficient magnitude such that electrons having a negative charge are emitted by the electron source filament, the electrons being accelerated towards an ion source cage by an electric field in the region between an electron repeller cage and the ion source cage, positive ions being produced both inside and outside the ion source cage when the accelerated electrons strike neutral gas particles along the path of the electrons, the positive ions within the ion source cage being accelerated towards a quadrupole mass filter by a focus plate, the quadrupole mass filter including a quadrilaterally symmetric parallel array of four charge-balanced rods, the improvement comprising: current measurement means, coupled to the electron repeller cage for providing a signal representative of the total ion current entering the quadrupole mass filter. .Iadd.   
     
     
       11.  A mass spectrometer for measuring the relative amount of the respective constituents of a gas present in said spectrometer and including a gas analyzer, the mass spectrometer comprising: means for defining a space such that a representative sample of a gas present in said spectrometer is present inside and outside of said space:   electron source means, disposed outside said space, for emitting a plurality of electrons, the plurality of electrons being accelerated towards said space so as to produce a plurality of positive ions;   means for generating a first ion current and a second ion current from said plurality of positive ions, said first ion current tending to travel in a first direction towards said gas analyzer, and said second ion current tending to travel in a second direction different from said first direction; and   current measurement means for measuring said second ion current..Iaddend..Iadd.12. A mass spectrometer according to claim 11, wherein said first direction is substantially perpendicular to said second direction..Iaddend..Iadd.13. A mass spectrometer according to claim 11, wherein said second ion current is representative of said first ion current..Iaddend..Iadd.14. A mass spectrometer according to claim 11, wherein said second ion current is representative of a pressure of said gas..Iaddend..Iadd.15. A mass spectrometer according to claim 11, wherein said gas analyzer comprises a quadrupole mass filter..Iaddend..Iadd.16. A mass spectrometer according to claim 11, wherein said means for defining a   
     
     
        space comprises an ion source cage..Iaddend..Iadd.17.  A mass spectrometer according to claim 11, wherein said means for defining a space comprises a closed ion source..Iaddend..Iadd.18. A mass spectrometer for measuring the relative amounts of mass of one or more constituents of a gas, said spectrometer comprising: (a) means for defining a space such that a representative sample of a gas in the spectrometer is present inside and outside of said space;   (b) electron source means, disposed outside said space, for producing electrons;   (c) means for propelling said electrons produced by said electron source means into said space so that positive ions of each said constituent are produced both inside and outside said space;   (d) means for generating an ion current from the ions produced inside said space so that said ion current represents the relative amounts of said constituents inside said space;   (e) ion collector means for collecting ions generated outside said space; and   (f) means for generating a signal as a function of the ions collected by said ion collector means and representative of said ion current..Iaddend..Iadd.19. A mass spectrometer according to claim 18, wherein said means for defining a space comprises an ion source cage..Iaddend..Iadd.20. A mass spectrometer according to claim 18, wherein said means for defining a space comprises a closed ion source..Iaddend..Iadd.21. A mass spectrometer according to claim 18, wherein said signal is representative of a pressure of said gas..Iaddend..Iadd.22. A mass spectrometer according to claim 18, further comprising gas analyzer means for analyzing the ions generated inside said space..Iaddend..Iadd.23. A mass spectrometer according to claim 22, wherein said gas analyzer means comprises a quadrupole mass   
     
     
        filter..Iaddend..Iadd.24.  In a mass spectrometer comprising an electron source filament, the electron source filament carrying a current of sufficient magnitude such that electrons having a negative charge are emitted by the electron source filament, the electrons being accelerated towards a space by an electric field in the region between the electron source and the space, positive ions being produced both inside and outside the space when the accelerated electrons strike neutral gas particles along the path of the electrons, the improvement comprising: ion collector means for attracting a fraction of said ions produced outside the space and for generating therefrom a signal representative of the number of ions produced inside the space..Iaddend..Iadd.25. In a mass spectrometer according to claim 24, wherein said signal is representative   
     
     
        of a pressure of a gas in said space..Iaddend..Iadd.26.  A quadrupole mass spectrometer for measuring the relative amounts of the respective constituents of a gas present in said spectrometer, said spectrometer being of the type comprising a quadrupole mass filter, the quadrupole mass spectrometer comprising: means for defining a space for containing a representative sample of said gas;   biased electron repeller means for repelling electrons;   collecting means within said space for attracting and collecting positive ions contained within said space;   electron source means disposed generally within said space for emitting a plurality of electrons, the plurality of electrons being accelerated into said space so as to produce a plurality of positive ions a fraction of the plurality of positive ions being attracted to the collecting means; and   current measurement means, coupled to the collecting means, for measuring a current that results from the fraction of the plurality of positive ions that are collected by the collecting means, and for providing a signal representative of the total ion current exiting said space and entering the quadrupole mass filter..Iaddend..Iadd.27. A quadrupole mass spectrometer according to claim 26, further including ion source means, disposed in said space, for providing a second fraction of the plurality of positive ions of said constituents of said gas and for generating the ion current entering said quadrupole mass filter..Iaddend..Iadd.28. A quadrupole mass spectrometer according to claim 27, wherein said ion source means comprises and ion source cage..Iaddend..Iadd.29. A quadrupole mass spectrometer according to claim 26, wherein said electron source means includes a filament..Iaddend..Iadd.30. A quadrupole mass spectrometer for measuring the relative amounts of mass of one or more constituents, respectively, of a gas, said spectrometer comprising:   means for defining a space for containing a representative sample of said gas;   electron source means for producing electrons;   ion source means, disposed in said space, for producing ions of each of said constituents of said gas when particles of each constituent present in said ion source means are struck by electrons;   means for propelling said electrons produced by said electron source means through said space into said ion source means so that positive ions of each said constituent are produced in said space, both inside and outside said ion source means, said means for propelling said electrons including electron repeller means for repelling said electrons toward said ion source means;   collecting means for collecting ions received from said space and produced outside said ion source means;   means for generating an ion current from the ions produced inside said ion source means so that said ion current represents the relative amounts of said constituents; and   means for generating a signal as a function of the ions collected by said collecting means and representative of the total ion current produced inside said ion source means..Iaddend..Iadd.31. A quadrupole mass spectrometer according to claim 30, wherein the electron source means for producing electrons comprises a filament disposed in said space..Iaddend..Iadd.32. A quadrupole mass spectrometer according to claim 30, wherein said ion source means comprises an ion source   
     
     
        cage..Iaddend..Iadd.33.  A quadrupole mass spectrometer according to claim 30, wherein said means for generating an ion current from the ions produced inside said ion source means so that said ion current represents the relative amounts of said constituents comprises a quadrupole mass filter..Iaddend..Iadd.34. A quadrupole mass spectrometer according to claim 30, wherein said means for propelling said electrons produced by said electron source means through said space into said ion source means so that positive ions of each said constituent are produced in said space includes means for biasing said electron repeller means relative to said electron source means and said ion source means..Iaddend.