Collision cross sections (CCS) for a set of drug-like molecules were measured using RF-confining drift tube ion mobility experiments in both helium and nitrogen gases. These results enabled accurate calibrated CCS using traveling-wave ion mobility experiments and improved accuracy CCS calculations for ions in nitrogen gas. These experiments demonstrate that ion mobility is sensitive to very subtle differences in molecular structure, including differentiation of the diastereomers betamethasone (left) and dexamethasone (right).
Structural Characterization of Drug-like Compounds by Ion Mobility Mass Spectrometry: Comparison of Theoretical and Experimentally Derived Nitrogen Collision Cross-sections Iain Campuzano, Matthew F. Bush, Carol V. Robinson, Claire Beaumont, Keith Richardson, Hyungjun Kim, Hugh I. Kim. Anal. Chem. 2012, 84, 1026-1033.