High-Resolution Mass Spectrometry
Mass spectrometry capable of measuring mass to four or more decimal places, allowing molecular formulae to be determined.
Unit
Da
In depth
Because isotopic masses are not exact integers, compounds with the same nominal mass have different exact masses. Measuring to within a few parts per million therefore identifies the molecular formula uniquely without any need for elemental analysis.
Examples in the real world
Distinguishing CO (27.9949) from N₂ (28.0062) and C₂H₄ (28.0313), all of nominal mass 28.