Figure 1.

IT‐MSⁿ mass spectra of the [180 ⋅ H ⋅ NH₃]⁺ ions. A) MS² spectrum of [180 ⋅ H ⋅ NH₃]⁺ at m/z=198; B) MS³ of the dehydrated ion [162 ⋅ H ⋅ NH₃]⁺ at m/z=180 selected from the ion at m/z=198; C) MS⁴ of the ion [144 ⋅ H ⋅ NH₃]⁺ at m/z=162 from the sequential isolation 198→180→162. In red the parent ions. Note that, due to the isobaric H₂O and NH₄ moieties, the molecular mass of the mono‐ and doubly‐ dehydrated ions, [162 ⋅ H ⋅ NH₃]⁺ and [144 ⋅ H ⋅ NH₃]⁺, happens to be 180 and 162 Da, respectively.