Combining selected ion monitoring (SIM) with isotope dilution in electron-ionization mass spectrometry allows:

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The use of internal standards allows for the quantification of mass spectrometry results.The internal standard selected should be as chemically and physically similar to the compound being measured as possible.Deuterated compounds where only a hydrogen atom has been replaced with a deuterium are extremely useful as internal standards and can be used in mass-spectrometry applications.The technique of quantification using chemicals that differ from the compound being measured only by its isotopic composition is known as isotope dilution.The use of SIM allows the mass spectrometer to monitor the compound of interest and its deuterated internal standard simultaneously, resulting in quantitative results.

Combining Selected Ion Monitoring (SIM) with Isotope Dilution in Electron-Ionization