Presentation description

Steroid identification is an important challenge from healthcare to athletics, as steroids are essential indicators in the detection of diseases and athletic doping. However, the characterization of steroids is difficult due to their structural similarity. (i.e., isomeric heterogeneity). Ion mobility spectrometry-mass spectrometry (IMS-MS) is an analytical technique that allows for the separation of ions in the gas phase by differences in size, charge, and shape. Recently it has been discovered that there are additional factors that affect ion mobility, including the center of mass (CoM) and moments of inertia (MoI) of molecules (i.e., changes in their mass distribution). Herein, we isotopically labeled steroids to induce changes in their centers of mass and moments of inertia. By measuring the induced shifts using relative arrival times (tRel.), we investigated the possibility of isomer specific arrival time shifts. Each steroid was derivatized with a deuterated and non-deuterated version of Girard's Reagent P (GP) as well as methylated with a deuterated and non-deuterated iodomethane. The resulting isomers which only differ in the deuterium positioning (isotopologues), were analyzed with IMS-MS where the relative arrival times of each isotopologue were compared to determine if the difference in tRel. was unique to each isomer. We observed broad differences in tRel. for diastereomers and structural isomers, as well as differences in tRel. for conformers of the same molecule. Interestingly, an inverse shift in derivatized estrone was observed, meaning a heavier isotopologue had an arrival time earlier than the lighter isotopologue. This shift cannot be explained by traditional IMS theory and must be due to the effects of mass distribution. The comparison of isotopologue shifts allows for a multidimensional approach to the identification of steroid isomers and a better understanding of steroid specific isotopic shifts.