Functionality-type and chemical-composition separation for poly(lactide-co-glycolide) using gradient elution with basic and acidic additives in normal-phase liquid chromatography

Abstract

The end groups of poly(lactide-co-glycolide) (PLGA) play a crucial role in determining the properties of polymers used in drug delivery systems. Research has shown that the encapsulation efficiency in PLGA microspheres can vary significantly between ester-terminated and acid-terminated PLGA. To study the functionality-type distribution (FTD) in PLGA polymers, researchers have used methods such as matrix-assisted laser desorption/ionization – high-resolution mass spectrometry and electrospray ionization – mass spectrometry. However, these methods are typically limited to PLGA polymers with a molecular weight of up to 4kDa. 13Carbon-nuclear-magnetic-resonance has also been used to differentiate and quantify PLGA end groups, but this method is time-consuming, taking over 12 hours per sample. To address these limitations, we have developed a normal-phase liquid chromatography method that can separate FTD and partial chemical composition distribution (CCD) in PLGA polymers. Our method can separate PLGA polymers with a molecular weight of up to 185 kDa and simultaneously separate the difference in lactic acid (LA)/glycolic acid (GA) ratios. To achieve this, we used a cross-linked diol column with a ternary gradient from hexane to 0.1% v/v triethylamine in THF to 0.1% v/v formic acid in THF. This allowed for the elution of ester-terminated PLGA, followed by acid-terminated PLGA. We also separated ester-terminated PLGA in the difference of the LA/GA ratio. Our method is expected to help understand the correlation between PLGA’s FTD, CCD, and physical properties, which will facilitate product development.