A Review on Solid-State UV Spectroscopy: A Paradigm Shift in Direct Analysis of Active Pharmaceutical Ingredients (APIs)

Ultraviolet-visible (UV-Vis) spectroscopy is a cornerstone of pharmaceutical analysis; however, conventional solution-based methods face limitations owing to solvent dependency, including drug degradation risks, environmental concerns, and operational costs. Solid-state UV spectroscopy, which is rooted in the principle of diffuse reflectance, has evolved as a transformative solvent-free alternative. Originally adapted from material science and mineralogy, diffuse reflectance UV spectroscopy (DRUVS) was refined in the late 20th century for pharmaceutical applications, with pioneering work by researchers such as Kubelka and Munk establishing a theoretical framework for analyzing powdered solids. Modern advancements in instrumentation, such as integrating sphere detectors and high-resolution optics, have enhanced the precision of direct analysis of undissolved samples. By leveraging scattered light measurements, DRUVS avoids solvent use while enabling the spectral acquisition of crystalline or amorphous pharmaceuticals, overcoming the challenges posed by poor solubility and polymorphic diversity