This method attempts to identify ion complexes, that is pairs of ions which appear together at the same retention time, and form an ion complex which contains both smaller ions as components. The complexes are identified by 2 conditions: 1) the retention time of the component ions and the complex ion should be same and 2) the sum of the masses of the component ions must be equal to the mass of the complex, except the mass change caused by ionization, such as (de)protonization.
The following figure shows an example of a spectrum with an ion complex in positive ESI mode (both ions are protonized):