Higher-energy collisional dissociation (HCD, formerly higher-energy C-trap dissociation) is a fragmentation technique. Frequently, this type of dissociation is used in conjunction with the orbitrap mass analyzer. In this arrangement, the ions pass through the C-trap and into the HCD cell, an added octopole collision cell, where dissociation takes place. The ions are then returned to the C-trap before injection into the orbitrap for mass analysis. It does not suffer from the low mass cutoff of resonant-excitation collision-induced dissociation (CID), and therefore is useful for isobaric tag–based quantification as reporter ions can be observed.