Size-Exclusion Chromatography–Electrospray-Ionization Mass Spectrometry To Characterize End Group and Chemical Distribution of Poly(lactide- <i>co</i> -glycolide) Copolymers

The characterization of the microstructure of <i>in vivo</i> degradable polyesters is gaining increased interest thanks to their high-performance applications, such as drug delivery systems. The design of such material requires a high level of understanding of the critical material attributes of the polyesters, such as molecular-weight distribution (MWD), chemical-composition distribution (CCD), and end-groups (functionality-type distribution, FTD). Size-exclusion chromatography (SEC) hyphenated with mass spectrometry (MS) is an effective method for analyzing the microstructure of polymers. While the MWD can be determined by size-exclusion chromatography hyphenated with ultraviolet spectrometry and refractive index, the CCD and FTD can be determined by SEC-MS. However, previous applications of SEC-MS have not assessed if polymer fragmentation can occur during the analysis process. In order to correctly interpret CCD and FTD, it is important to establish whether SEC-MS methods can be applied to biodegradable polymers and to recognize if fragmentation processes occur. In this study, we investigate whether SEC-MS methods can be applied to PLGA biodegradable polyesters. The research demonstrates that the choice of alkali metal salt used during ionization can influence the stability of PLGA during SEC-MS analysis. CsI was found to minimize fragmentations during ESI-MS, simplifying the MS spectra and allowing isomeric PLGA structures to be distinguished. The resulting method facilitates FTD and CCD determination. Additionally, when combined with selective degradation, the described method can provide insights into the "blockiness" of the polymer and support the development of sequence-controlled PLGA synthesis.