Mass Spectrometry

 

 

 1. General information concerning mass spectrometry can be found here, e.g.

 
  2.  Our specialty is noble gas mass spectrometry - see below. The instruments we use are magnetic sector-field mass
    spectrometers. The electrically charged ions are formed through electron impact ionization.		  
     

 

Noble Gas Mass Spectrometry

 

There are three essential steps that take place during analyses in a noble gas mass spectrometer.

- creation of ions: Electrons emitted by a hot filament collide with gas atoms so that electrons are lost from the
   electron shell and the atom becomes an electrically charged ion.

 

 - mass separation: The ions are accelerated by an electric filed (4000 or 6000 Volts in our case) and are deflected
   according to their mass in the magnetic field of a sector magnet

 

 

 - ion detection: After separation according to mass the ion current is measured by a detector.  A Faraday detector
  is used for larger currents; smaller currents are detected by counting single ions. The switchover is at approximately
  1 million ions per second p.

 

 

  

 

 

 In classical sector field mass spectrometry a magnetic field setting is chosen so that only ions of a given mass reach
   the detector. Multiple ion detection is also possible and requires a specific local arrangement of the detectors. Our
   new instrument Noblesse is one of worldwide two instruments that allow simultaneous ion detection by as much as
   eight ion counters.

 

 

  

 
  The gases to be analyzed are set free from the solid sample to be analyzed by either classical heating up to 2000 °C
   using a resistance-heated furnace, by combustion (in case of carbonaceous samples) or by laser heating. Chemically
   active non-noble gases are removed using chemical getters. Using activated charcoal at specific temperatures the
   noble gases are separated into He/Ne, Ar, Kr, and Xe, which are separately admitted to the mass spectrometer.		  
     
  Since the gas amounts to be analyzed are extremely small, noble gas mass spectrometry is usually performed in the so
   called "static mode". During gas extraction and analysis the valves to the pumps remain closed. This puts high
   demands on the quality of the vacuum system. 		 
     

 

 Mass Spectrometry of Selenium

 
  - We analyze selenium using thermal ionization mass spectrometry (TIMS).  
  - The sample to be analyzed is dissolved using acids, the element selenium is separated and deposited onto a heating
   filament together with an emitter.		  
  - When the filament is heated, selenium evaporates. A small fraction evaporates in form of ions and can be analyzed
   using the sector field mass sepctrometer. While TIMS is mostly performed using positive ions, we analyze selenium
   in form of  negative ions (N-TIMS).