Inductively-coupled mass spectrometry (ICP-MS) shows the signal strength of the mass/charge ration of atoms. An atom generally is ionized in ICP to lose one electron so that it bears one positive charge.
In the ICP-MS analysis of table salt, the analyst saw one predominant peak at the mass/charge ration of 23, which corresponds to the atomic weight of sodium. However, the analyst saw two big peaks around the atomic weight of chlorine (35.5) with mass/charge ratio f 35 and 37, respectively.
The intensity ratio of these two peaks was about 3:1.