Characterization of Solid-State Complexities in Pharmaceutical Materials via Stimulated Raman Scattering Microscopy

In this study, we employed stimulated Raman scattering (SRS) microscopy, augmented with sum frequency generation, to characterize complex solid-state mixtures, containing many solid-state forms of the same compound, for the first time. Five crystalline forms and one amorphous form of lactose were characterized and resolved, including two more recently defined anhydrous solid-state forms. Additionally, the complex solid-state character of several commercially available pharmaceutical tableting and inhalation grades of lactose was profiled. The advanced multimodal label-free microscopy method enabled visualization of the distribution of the solid-state forms with submicron spatial resolution, including the detection of trace levels. In addition, quantitative solid-state compositions of the lactose products were estimated. Overall SRS microscopy allows sensitive and specific spatially resolved solid-state characterization of complex mixtures, beyond what is possible with established (nonspatially resolved) characterization methods.