Characterization of branched and linear polyethyleneimine by trapped ion mobility-time of flight-mass spectrometry

Polyethyleneimine (PEI) is a common polyelectrolyte that is used in many areas, such as drug delivery, gene therapy, and water treatment. This is because it has a highly branched structure, functional amine groups in its repeating unit, and a high cationic charge density. To understand the behavior and function of PEI, it is important to accurately describe its structure. The ion mobility-mass spectrometry method is expected to yield structural insights into PEI's molecular architecture, encompassing variations in branching patterns, chain conformations, and the potential presence of isomeric forms.

The difference in zeta potential values between B-PEI and L-PEI can be attributed to the distinct types of functional amine groups present in their structures. The trapped ion mobility-time of flight-mass spectrometry (TIMS-ToF-MS) technique was used in this study to elucidate the molecular architecture of linear and branched PEI with varying polymeric distributions of ion series and end groups, concentrating on its dimensions, morphology, conformational variations, variable cationic adducts (Na⁺, K⁺, Li⁺, and Ag⁺), and charge states (+1 and + 2). The singly charged ions, like those in the main series and fragment series of PEI, are more compact than doubly charged ions because of the change in charge repulsion. TIMS, in conjunction with mass spectrometry, facilitated high-resolution separation of PEI conformers according to their collision cross-section (CCS) values and charge states.

The findings indicated that PEI displays a wide range of both compact and extended molecular conformations at various m/z ratios, with specific populations associated with varying branching levels, cationic adducts, and charge distribution. The influence of various metal ions on PEI conformation was examined, indicating substantial alterations in CCS values under diverse conditions of analysis. Hyphenated TIMS and MS technologies make a strong analytical platform for studying polymer structures in depth.