Correlative Spectroscopic and Structural Imaging for Resin-Embedded Extended-Release Morphine Sulfate Pellets

Abstract

Correlative spectroscopic and structural imaging provides a powerful approach for characterizing the microstructure of complex pharmaceutical formulations. Laser direct infrared (LDIR) spectroscopy is an emerging, rapid spectroscopic imaging technique that complements traditional approaches by enabling non-destructive chemical and morphological analysis over large sample surfaces within minutes. In this study, the capabilities of LDIR imaging were evaluated alongside Raman mapping, SEM–EDS, laser microscopy, and micro-CT as part of a correlative workflow to characterize the microstructure and chemical composition of pharmaceutical pellets. Resin embedding enabled consistent handling and structural preservation of extended-release pharmaceutical pellets across all imaging modalities. Two commercially available morphine sulfate ER pellets (ER-1 and ER-2) with different excipient compositions were used as model systems. Laser microscopy revealed distinct differences in surface topography, while micro-CT performed before milling confirmed inherent structural features. ER-1 displayed a smooth, intact core, whereas ER-2 exhibited internal cracks and cavities. Hyperspectral LDIR imaging successfully identified major components in both formulations (hit-quality index, HQI ≥ 0.83) with strong concordance to Raman mapping (HQI ≥ 0.85). The spatial distribution of the active pharmaceutical ingredient (API) revealed a layered structure in ER-1 and a homogeneous core in ER-2. This correlative workflow, combining resin embedding with multiple imaging modalities, underscores the value of LDIR and complementary techniques for comprehensive physicochemical characterization of complex drug products. These findings highlight the utility of correlative imaging for regulatory assessment and quality control of complex extended-release formulations.

Graphical Abstract