Abstract: The isomeric disaccharides are difficult to distinguish due to their similar structures. The non-covalent interaction between disaccharides and alkali metal ions will change their spatial configurations. In this work, drift time ion-mobility spectrometry-mass spectrometry (DTIMS) was used to measure the drift times for alkali metal ion adducts of four disaccharides including lactose, maltose, cellobiose, and sucrose. The results show that Cs⁺ has a better distinguishing effect on cellobiose and lactose, and its bimodal resolution R_p-p is 0.39; while K⁺ has a better effect on sucrose and maltose, and R_p-p is 0.74. Besides, the experiment used a single-field correction method to measure the collision cross-section (CCS) values of those disaccharide alkali metal ion adducts. Contemporary, quantum mechanics density functional theory (DFT) was performed to predict the possible structure of those disaccharide alkali metal ion adducts, followed by the calculation of its theoretical CCS value using three models including the projection approximation (PA), the exact hard-sphere scattering (EHSS) and the trajectory method (TM). The relative deviations obtained by the three models are -23.05%, 11.79%, and 0.44%, respectively, indicating that the TM model agrees best with the experimental values. According to this method, the binding site of alkali metal ion and disaccharide structures can be summarized, and the structure of unknown disaccharide metal ion adduct can be further predicted.

Key words: Drift time ion mobility mass spectrometry, Collision cross-section, Trajectory method, Disaccharide