Isotopic Peak
A peak appearing at a higher mass than the main ion because the molecule contains a heavier isotope.
Formula / equation
M+1, M+2
Unit
Da
In depth
Their relative heights reveal the elements present: chlorine gives an M+2 peak one third the height of M, bromine gives one of equal height, and the M+1 peak from carbon-13 grows by about 1.1% for each carbon atom.
Examples in the real world
A 3:1 pair of peaks two mass units apart immediately identifying a chlorine-containing compound.