Principles Of Raman Spectroscopy And Application To Pharmaceutical Development

Raman spectroscopy is a powerful technique used for applications including polymorph identification, analysis of API form, and evaluation of component distribution within a formulation.¹ This article discusses the basic principles of Raman spectroscopy and how it is used to analyze a chemical compound’s structure, and further provides an example of how this technique is used to analyze amorphous material created through a hot melt extrusion process. 

Raman spectroscopy is a light scattering technique based on the principle of inelastic scattering of monochromatic light (Figure 1). Under normal circumstances, light is scattered at the same wavelength as that of the incident light (Rayleigh scattering). However, a small percentage of the time, light can scatter at a higher energy state (anti-Stokes shift) or a lower energy state (Stokes shift) due to interactions between the light and the material. During Raman spectroscopy, the scattered light (usually the Stokes shift) is collected and analyzed while the Rayleigh scattered light is filtered out. When analyzing a material by Raman spectroscopy, each material will produce a unique spectral pattern which is then used to identify compounds by comparing the results to a known reference.¹