Space Charge Induced Dissociation Due to Extended Ion Accumulation Preceding Cyclic Ion Mobility Separation

Cyclic ion mobility spectrometry (cIMS) provides the potential for high resolution separations of small molecule isomers using multiple passes in a closed-loop geometry. Achieving this potential, however, is limited by the analyte stability in the instrument. Fragile ions are susceptible to dissociation when employing long analysis times required by multipass separations. Correctly identifying the causes of analyte ion loss is critical to facilitating high resolution ion mobility separations. Our previous work with dexamethasone and betamethasone demonstrated that the separation of these two epimers was partially limited by fragmentation over long multipass separations. Further investigations into the cause suggest that most analyte loss occurs because of accumulating many ions in the trap prior to cIMS injection rather than long exposure times to the cIMS region of the instrument. This observation aligns with previous observations of ion activation due to space charge effects in high density trapped ion populations. This work demonstrates the unique aspects of space charge induced fragmentation in cIMS directly resulting from variable pre-cIMS ion accumulation times due to multipath separations while reinforcing the importance of regulating ion accumulation prior to IMS.