Mass spectroscopy
how it works
The mass spectrometer "sorts" isotopes according to their mass. It can also be used to analyse organic molecules.
Background
1.14 - 1.17 Atomic structure
If a nucleus was the size of a raisin, the rest of the atom would be the size of a sports stadium
https://www.mychem.co.uk/index.php/igcse-chemistry/principles-of-chemistry/atomic-structure
When an organic molecule is analysed in a mass spectrometer the vaporisation and bombardment by high energy electrons process also fragments the molecule.
This produces a fragmentation pattern which provides a "fingerprint" for the molecule but also other information which can help identify the molecule.