Mass spectrometer beam monitor

Abstract

The ion beam from a field desorption source in a double focusing magnetic mass spectrometer is monitored by disabling the electric sector of the mass analyzer such that the ion beam is not deflected. An opening is provided in the wall of the electric sector such that the undeflected ion beam may pass therethrough to a detector. This permits the characteristics of the field desorption source to be ascertained more quickly and easily so that a mass analysis may be performed. The monitor may be operated automatically to vary a characteristic of the field desorption source until ions are detected. Thereafter, the electric sector is energized and an analysis performed.

I claim: .[.1. In an ion beam analyzer having an ion source for generating ions of a sample to be analyzed, means for extracting said sample ions from said source, means for focusing the extracted sample ions into a beam, separation means positioned along the ion beam for selectively deflecting species of ions and detecting means for detecting the selected species ions, the improvement comprising: 
     
        magnetic sector until said electric sector has stabilized..]. 4. The analyzer set forth in claim .[.1.]. .Iadd.12 .Iaddend.wherein said separation means includes an electric sector followed by a magnetic sector, and said .[.enabling means.]. .Iadd.control .Iaddend.delays the scanning of said magnetic sector until said electric sector has 
     
     
        stabilized. 5. The analyzer set forth in claim .[.1.]. .Iadd.12 .Iaddend.which includes means responsive to said sensing means for varying .[.a charactertistic.]. .Iadd.an ion emission controlling feature 
     
     
        .Iaddend.of said sample ion source until ions are sensed. 6. The analyzer set forth in claim 5 which includes delay means responsive to said sensing means for further varying said .[.characteristic.]. .Iadd.feature 
     
     
        .Iaddend.after a predetermined period of time. 7. The analyzer set forth in claim 5 wherein said ion source is a field desorption emitter and said 
     
     
        .[.characteristic.]. .Iadd.feature .Iaddend.is emitter temperature. 8. The analyzer set forth in claim .[.1.]. .Iadd.12 .Iaddend.wherein said separation means includes an electric sector followed by a magnetic sector, said electric sector defining a hole in the path of said undeflected ion beam, and said sensing means is located contiguous said 
     
     
        hole outisde said electric sector. .[.9.  A method of ascertaining the field desorption characteristics that produce ions from a sample in a field desorption ion source of an ion beam analyzer having ion separation means comprising the steps of: energizing said ion source,   disabling at least a portion of the separation means to prevent deflection of sample ions from said ion source,   varying the field desorption characteristics of said source, and   detecting said undeflected sample ions to ascertain those field desorption   
     
     
        characteristics of said source that produce ions..]. 10. A method according to claim .[.9.]. .Iadd.13 .Iaddend.wherein the additional step of recording the field desorption .[.characteristics.]. .Iadd.feature 
     
     
        .Iaddend.at which said sample ions are detected. 11. A method according to claim .[.9.]. .Iadd.13 .Iaddend.wherein the field desorption .[.characteristic.]. .Iadd.feature .Iaddend.varied is sample temperature or field strength to which the sample is subjected. .Iadd. 12. An ion beam analyzer having an ion source for generating ions of a sample to be analyzed, comprising, in combination, means for extracting said sample ions from said source,   means for focusing the extracted sample ions into a beam,   separation means capable of being energized or de-energized to selectively deflect or not to deflect species of extracted ions in said beam,   detecting means positioned for detecting the selected deflected species of ions,   means to energize or de-energize said separation means,   sensing means located along the ion beam for sensing said extracted sample ions prior to deflection, and   control means coupled between said sensing means and said means to energize or de-energize and responsive to said sensed sample ions reaching a predetermined intensity level for energizing said separation means.   
     
     
        .Iaddend..Iadd. 13.  A method of ascertaining the features of a field desorption ion source that produce ions from a sample using an ion beam analyzer having ion separation means comprising the steps of: energizing said ion source,   disabling at least a portion of the separation means to prevent deflection of sample ions from said ion source,   varying at least one of said features of said source to produce sample ions,   detecting the occurrence of said undeflected sample ions,   actuating said separation means for a selected period of time upon detecting said occurrence,   thereafter continuing to vary at least one of said features to produce sample ions, and   repeating said detecting and actuating steps. .Iaddend.