Schematic describing the basic steps involved in the CIU assay to determine kinase inhibitor binding modes. Protein ligand complexes are ionized by nESI in a range of charge states (A), a single charge state is selected for activation in a quadrupole mass filter (B). Following selection, collisional activation with argon (varying the amount of accelerating voltage) is used to initiate three different processes: charge stripping, inhibitor dissociation, and gas-phase protein unfolding (C). IM drift time is monitored and recorded over a broad range of collision voltages to create a complete CIU fingerprint, which creates a contour plot of the intensity of ion populations as a function of these two parameters (D).