Mass Spectrometer

Abstract

An isotope ratio mass spectrometer has an ion source, a static field mass filter, a reaction cell to induce a mass shift reaction, and a sector field mass analyser for spatially separating ions from the reaction cell according to their m/z. A detector platform detects a plurality of different ion species separated by the sector field mass analyser. The static field mass filter has a first Wien filter that deflects ions away from a longitudinal symmetry axis of the spectrometer in accordance with the ions' m/z, and a second Wien filter that deflects ions back towards the longitudinal symmetry axis in accordance with the ions' m/z. An inverting lens is positioned along the longitudinal axis between the Wien filters to invert the direction of deflection of the ions from the first Wien filter. The static field mass filter provides high transmission and improved spectrometer sensitivity. The first and second Wien filters permit simple tuning.

What is claimed is: 
     
         1 . A mass spectrometer comprising:
 a static field mass filter;   an ion source arranged upstream of the static field mass filter; and   a mass analyser arranged downstream of the static field mass filter, configured to mass analyze either (a) ions ejected from an exit aperture of the static field mass filter or (b) product ions derived from the ions ejected from the exit aperture of the static field mass filter, wherein the static field mass filter comprises:   an entrance aperture configured to receive an ion beam from the ion source, wherein the static field mass filter defines a longitudinal symmetry axis between the entrance and exit apertures;   a first Wien filter configured to deflect ions away from the longitudinal symmetry axis in accordance with their m/z;   a second Wien filter configured to deflect the ions back towards the longitudinal symmetry axis in accordance with their m/z; and   an inverting lens positioned along the longitudinal symmetry axis between the first and second Wien filters, to invert the direction of deflection of the ions from the first Wien filter.   
     
     
         2 . The mass spectrometer of  claim 1 , further comprising a reaction cell located downstream of the exit aperture of the static field mass filter, wherein the reaction cell is configured to cause the ions received from the static field mass filter to undergo a change in their properties. 
     
     
         3 . The mass spectrometer of  claim 2 , wherein the mass analyser is positioned downstream of the reaction cell, and wherein the reaction cell is configured to eject the reacted ions to the mass analyser. 
     
     
         4 . The mass spectrometer of  claim 1 , wherein the ion source is configured to generate a beam of ions from a sample, and wherein the mass analyser is a sector field mass analyser configured to spatially separate the analysed ions in accordance with their m/z. 
     
     
         5 . The mass spectrometer of  claim 4 , wherein the mass spectrometer further comprises an ion multicollector having either:
 (i) a plurality of ion detectors each arranged downstream of the sector field mass analyser; or   (ii) a single ion detector arranged downstream of the sector field mass analyser, for detecting a plurality of different ion species each separated by the sector field mass analyser.   
     
     
         6 . The mass spectrometer of  claim 1 , in which the ion source is an inductively coupled plasma (ICP) ion source. 
     
     
         7 . The mass spectrometer of  claim 1 , in which the reaction cell is a collision cell. 
     
     
         8 . A method of mass spectrometry, comprising the steps of:
 (a) generating a beam of ions from a sample;   (b) selecting ions from the beam in accordance with their mass to charge ratio, using a static field mass filter by:
 injecting ions from the ion source into the static field mass filter, through an entrance aperture thereof; 
 deflecting ions away from a longitudinal symmetry axis of the static field mass filter using a first Wien filter, so as to separate ions in a direction orthogonal to the longitudinal symmetry axis, in accordance with their m/z; and 
 deflecting ions downstream of the first Wien filter back towards the longitudinal symmetry axis, using an inversion lens; and focusing ions towards an exit aperture of the static field mass filter using a second Wien filter; 
   (c) spatially separating the ions received from the static field mass filter in a sector field analyser, based upon their mass to charge ratio;   (d) detecting a plurality of different ion species from the separated ions in a multicollector; and   (e) inducing a mass shift reaction in ions received from the static field mass filter using a reaction cell before spatially separating the ions.   
     
     
         9 . The method of  claim 8 , wherein the step (a) further comprises generating ions using an inductively coupled plasma (ICP) ion source. 
     
     
         10 . The method of  claim 8 , further comprising determining at least one isotopic ratio of atoms or molecules contained in the sample on the basis of the plurality of different ion species detected by the multicollector.