progeny ion true MS:1000344 MS This child of the former purgatory term ion chemical type was made obsolete. Progeny Fragment Ion OBSOLETE A charged product of a series of consecutive reactions that includes product ions, 1st generation product ions, 2nd generation product ions, etc. Given the sequential fragmentation scheme: M1+ -> M2+ -> M3+ -> M4+ -> M5+. M4+ is the precursor ion of M5+, a 1st generation product ion of M3+, a 2nd generation product ion of M2+ and a 3rd generation product ion of M1+.