Profiling Multiple Steroid Subclasses Enabled by Rounded Turn SLIM Ion Mobility

Ion mobility-mass spectrometry has shown tremendous potential for improving the analysis of various subclasses of steroids. Its speed and ability to separate isobaric and isomeric species makes it ideal for biomedical, clinical, food, environmental, and antidoping analyses. But while other high-resolution ion mobility (HRIM) techniques have begun to see increased use in steroidomics, Structures for Lossless Ion Manipulations (SLIM) is a relative newcomer to the field. HRIM methods are generally challenged with low molecular weight (MW < 400) analysis, but a recently developed SLIM platform has incorporated rounded turns, helium buffer gas, and increased SLIM RF frequency to enable improved low mass transmission. In the present work, we investigate this low mass-tailored SLIM system for the analysis of anabolic androgens, bile acids, endocrine hormones, and ketosteroids. Linear regression-corrected ^SLIMCCS_He (CCS = collision cross section) values show excellent agreement with values obtained via direct measurement with a drift tube instrument but also underlie the importance of using class- and adduct-specific correction factors. Next, separation performance was evaluated for a range of challenging isomers and demonstrated good resolution for species with ΔCCS of <1%. Finally, the new rounded turn system was compared quantitatively with the traditional 90° (square turn) system in both nitrogen and helium buffer gases and revealed significantly improved signal across the board for rounded turn analyses with helium. Overall, this low mass-tailored system has remarkable promise for development of rapid, targeted steroid analysis in a range of applications.