Comprehensive Characterization of Oligolactide Architecture by Multidimensional Chromatography and Liquid Chromatography–Mass Spectrometry

Oligolactides (OLA) are increasingly finding applications in drug delivery systems, implant coating, and tissue engineering. The most common synthetic route to OLA, ring-opening polymerization, produces polymer chains with complex architecture, including cyclic structures, chains with acid end groups, and initiator-bound oligomeric species. This inherent molecular heterogeneity presents significant challenges in analytical characterization. To address this complexity, it is essential to develop a robust separation method for comprehensive analysis. In this study, we developed a novel and robust high-performance liquid chromatography (HPLC) method using ethanol-modified chloroform as an eluent on a normal-phase column, which effectively separates the OLA chains. Additionally, the impact of different initiators on the molecular heterogeneity of OLA chains was investigated. To elucidate the separation mechanism, the HPLC method is hyphenated with size exclusion chromatography in a two-dimensional liquid chromatography setup. The results indicate that OLA chains are separated based on increasing degree of polymerization or increasing lactide incorporation. Furthermore, online coupling of HPLC with mass spectrometry provided deeper insight into the heterogeneity of the bulk. This study highlights the importance of correlative characterization techniques as a preferred approach for determining microstructural heterogeneity in low molar mass OLA samples.