Scanning Electron Microscopy and Energy-Dispersive X-Ray Spectrometry

Abstract

The scanning electron microscope (SEM) is used extensively in pharmaceutical development for both drug substance (DS) and drug product (DP). The vast bulk of the work is examination of size and shape of the individual particles making up the drug substance powder. Some of this work is quantitative in the sense that the size and shape of the particles are measured using image analysis (see Chaps. 7 and 9), but most of the work is more qualitative in nature. It is somewhat amazing that the SEM produces images that are readily interpreted by our visual system when you consider we are looking at the interaction of electrons with matter and that, in fact, there is no true optical system to the SEM. Even without numbers, one can get a sense of how the DS powder will behave based just on the appearance of the particles. If well-crystallized with sharp crystal edges, we may suppose the material will flow well. If it is highly agglomerated, with what appear to be particles fused together, we might suppose the powder will not flow as well. Even if those initial suppositions are somewhat naïve and general, just having an image of the particles can help workers understand the system they are dealing with. By the way, it is a rare technical presentation on drug substance that does not include at least one SEM image.