Microscopy

Microscopy is a very useful qualitative tool for screening, identifying, and selecting active pharmaceutical ingredient (API) forms. This chapter discusses some types of microscopy and their applications in the characterization of pharmaceutical materials. Light microscopy is a very versatile tool and has numerous uses in analyzing pharmaceutical materials. The major advantages of light microscopy are that one only needs a small sample size and it is nondestructive except when immersion oil or a hot stage are used. The majority of drug substances encountered are crystalline, and crystalline materials produce birefringence in a polarized light microscope. Under a polarized microscope, materials with birefringence are observed as colorful view contributed by refracted light. A thermal microscope is a combination of a light microscope and a hot stage apparatus. Thermal microscopy is widely used to investigate various thermal transitions including melting, desolvation, dehydration, sublimation, crystallization, and polymorph conversion.