UCLA

Rationale

Recent experiments utilizing photodissociation in linear ion traps have enabled significant development of Radical-Directed Dissociation (RDD) for the examination of peptides and proteins. The increased mass accuracy and resolution available in Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) should enable further progress in this area. Preliminary experiments with photoactivated radicals are reported herein.

Methods

A 266 nm Nd:YAG laser is coupled to a FTICR or linear ion trap mass spectrometer. Radical peptides and proteins are generated by ultraviolet photodissociation (PD) and further activated by collisions or infrared photons.

Results

A 266 nm UV laser and an IR laser can be simultaneously coupled to a 15 Tesla FTICR mass spectrometer. The ultra-low-pressure environment in FTICR-MS makes collisional cooling less competitive, and thus more secondary fragments are generated by UVPD than in linear ion traps. Activation by sustained off-resonance irradiation collision-induced dissociation (SORI-CID) or infrared multiphoton dissociation (IRMPD) also yields additional secondary fragmentation relative to CID in an ion trap. Accurate identification of RDD fragments is possible in FTICR-MS.

Conclusions

Relative to linear ion trap instruments, PD experiments in FTICR-MS are more difficult to execute due to poor ion cloud overlap and the low pressure environment. However, the results can be more easily interpreted due to the increased resolution and mass accuracy.