Ultrahigh Performance Liquid Chromatography Interfaced with Mass Spectrometry and Orthogonal Ion Mobility Separation for the Microstructure Characterization of Amphiphilic Block Copolymers

Abstract

The performance of amphiphilic materials, such as polystyrene-co-poly(ethylene oxide) (PS-co-PEO) copolymers, is highly dependent on the balance between hydrophilic and hydrophobic comonomers and the topology of these units in the macromolecular construct. Elucidation of the latter structural features as well as the number and nature of any end groups present is critical for assessing the amphiphile’s quality and utility. This study introduces a multidimensional method for the analysis of the composition, microstructure, and architecture of amphiphilic copolymer mixtures, encompassing ultrahigh performance liquid chromatography (UPLC) interfaced with ion mobility mass spectrometry (IM-MS). The combination of two orthogonal separation methods (LC and IM) with mass analysis (MS), viz. UPLC-IM-MS, was utilized to characterize a polystyrene-block-poly(ethylene oxide), PS-b-PEO, mixture containing structural isomers and isobars. Reverse-phase LC afforded separation of the copolymer and a byproduct according to their hydrophobic block sizes, IM dispersion provided information on the macromolecular architectures of the separated components (linear or cyclic), and MS analysis using electrospray ionization (ESI) unveiled the hydrophilic block sizes and the overall copolymer composition. LC-IM-MS effects separation by polarity in the LC step and by shape in the IM step prior to mass-sensitive detection. Such 3-dimensional approach is particularly suitable for the molecular characterization of complex amphiphilic copolymer blends and for the differentiation of similar samples from different sources or different batches.