Tandem infrared multiphoton dissociation and collisionally activated dissociation techniques in a quadrupole ion trap.

Tandem infrared multiphoton dissociation and collisionally activated dissociation methods are implemented in a quadrupole ion trap mass spectrometer and used to characterize an array of antibiotic ions generated by electrospray ionization. The tandem methods prove useful for probing fragmentation genealogies, evaluating the structures of lower mass fragment ions produced from higher mass molecular ions, and differentiating isobaric ions. The infrared multiphoton dissociation method is more efficient for producing an array of fragment ions over a large mass range, whereas collisionally activated dissociation is preferable for the analysis of lower m/z ions.