Fig. 2.

CID product ion mass spectrum of the doubly charged ion of the phosphorylated peptide p[FVIAFILHLVK+2H]²⁺ at m/z 690.5, indicating a heterogeneous population of [FVIAFILpHLVK+2H]²⁺ and [FVIAFILHLVpK+2H]²⁺, whose specific y-ions are labeled in italics (gray). (Δ) Loss of 80 Da (HPO₃); (*) Observation of both phosphorylated and non-phosphorylated product ions.