Ion mobility spectrometry-mass spectrometry (IMS-MS) is a widely used analytical technique, where ions separate in the gas phase based on their size, shape, and charge. Despite new technological advancements, existing theory does not account for all experimental observations. Specifically, mass distribution-based shifts, which stem from both center of mass and moment of inertia contributions are not well understood. Thus, this calls for new experiments that can better understand isotopic shifts related to mass distribution. Tetraalkylammonium salt isotopologues were chosen for this experiment due to their symmetrical structure and fixed charge. Therefore, the only variable affecting separations was a difference in moment of inertia. Gaussian 16 was used to confirm that the isomers had identical center of mass values and varying moments of inertia. The isotopologues were synthesized from deuterium labeled bromopropane and separated in a cyclic IMS-MS platform. Their moment of inertia differences leads to different arrival times and thus structural differences (i.e., collision cross section values). From this, we were able to establish a relationship between moment of inertia and CCS that was found to be linear. Overall, this represents the first demonstration of isolating moment of inertia contributions in experimentally-measured isotopic shifts and will help improve our overall understanding of ion structure.