Stable Isotopes as internal standard
An internal standard is used when performing bioanalysis with mass spectrometry detection. The best internal standard for bioanalysis is an isotopically labeled version of the molecule you want to quantity. Internal standards should contain enough mass increase to show a signal outside the natural mass distribution of the analyte.
Generally, because of the abundance of hydrogen in organic molecules, the use of deuterium is proffered compared to 13C and 15N, which are generally more expensive solution for stable isotope labeled internal standards.
A deuterated internal standard will have the same extraction recovery, ionization response in ESI mass spectrometry and the same chromatographic retention time, and therefore deuterated standards are ideal for bioanalysis.
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