Stereochemistry plays an important role in biochemistry, particularly in therapeutic applications. Indeed, enantiomers have different biological activities, which can have important consequences. Many analytical techniques have been developed in order to allow the identification and the separation of stereoisomers. Here, we focused our work on the study of small diastereomers using the coupling of traveling wave ion mobility and mass spectrometry (TWIMS-MS) as a new alternative for stereochemistry study. In order to optimize the separation, the formation of adducts between diastereomers (M) and different alkali cations (X) was carried out. Thus, monomers [M + X](+) and multimers [2M + X](+) and [3M + X](+) ions have been studied from both experimental and theoretical viewpoints. Moreover, it has been shown that the study of the multimer [2Y + M + Li](+) ion, in which Y is an auxiliary diastereomeric ligand, allows the diastereomers separation. The combination of cationization, multimers ions formation, and IM-MS is a novel and powerful approach for the diastereomers identification. Thus, by this technique, diastereomers can be identified although they present very close conformations in gaseous phase. This work presents the first TWIMS-MS separation of diastereomers, which present very close collision cross section thanks to the formation of multimers and the use of an auxiliary diastereomeric ligand.