An IMS−IMS Analogue of MS−MS

The development of a new ion mobility/mass spectrometry instrument that incorporates a multifield drift tube/ion funnel design is described. In this instrument, individual components from a mixture of ions can be resolved and selected on the basis of mobility differences prior to collisional activation inside the drift tube. The fragment ions that are produced can be dispersed again in a second ion mobility spectrometry (IMS) region prior to additional collisional activation and MS analysis. The result is an IMS-IMS analogue of MS-MS. Here, we describe the preliminary instrumental design and experimental approach. We illustrate the approach by examining the highly characterized bradykinin and ubiquitin systems. Mobility-resolved fragment ions of bradykinin show that b-type ions are readily discernible fragments, because they exist as two easily resolvable structural types. Current limitations and future directions are briefly discussed.