Distribution of the micronized drug, salmeterol xinafoate (green) in a binary dry powder inhaler blend (Serevent™).

Cathodoluminescence (CL) analysis complements other spectroscopic and imaging tools that researchers use to understand, develop, and manufacture solid-dosage medicinal products. The luminescence signatures of an organic molecule stem from the molecule's chemical structure (HOMO-LUMO gap), rather than sample composition. Up to 80% of active pharmaceutical ingredients (APIs) strongly exhibit CL in the scanning electron microscope when compared to only 20% of excipients.

Due to the different crystal structures, researchers also use CL to distinguish solid forms of some drug compounds. For example, the four polymorphs of carbamazepine, and crystalline, and amorphous forms of indomethacin. These observations enable identification of changes to the solid form of an API after it is formulated into a tablet, pellet, or blend.

CL spectra of some APIs and commonly used excipients.

Experimental brief

A new role for cathodoluminescence spectroscopy and imaging as an analytical tool to support the development of pharmaceutical products