Research Library
Understanding molecular weight and compound identification
How molecular weight is used to help confirm the identity of a compound, and how it relates to mass spectrometry results.
Molecular weight
Molecular weight is the sum of the atomic masses of all atoms in a molecule. For a given compound with a defined structure it is a fixed, calculable value, usually expressed in daltons (Da) or g/mol.
Using it for identification
Mass spectrometry measures the mass of ions produced from a sample. When the observed mass agrees with the expected molecular weight, within the instrument's tolerance, it supports the identity of the compound. It is normally read together with chromatographic purity data.