What is isotope ratio mass spectrometry?





      Although often presumed to be constant and stable, natural 
isotope abundance 
ratios show significant and characteristic variations when measured very 
precisely.  Isotope ratio measurements are useful in a wide range of 
applications, for example, metabolic studies using isotopically enriched 
elements as tracers; climate studies using measurements of temperature-dependent 
oxygen and carbon isotope ratios in foraminifers; rock age dating using 
radiogenic isotopes of elements such as lead, neodymium or strontium; and source determinations using carbon isotope ratios (is a substance 
naturally occurring or is it a pertroleum-based synthetic?).



  
      In isotope ratio mass spectrometry, element isotope ratios 
are determined very accurately and precisely.  Typically, single focusing 
magnetic sector mass spectrometers with fixed multiple detectors (one per 
isotope) are used.  Complex compounds are reduced to simple molecules prior 
to measurement, for example, organic compounds are combusted to CO2, 
H2O and N2.




       
                     
                  
                    
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