An Introduction to Cascade Impaction

Cascade impaction is a fundamental analytical technique for orally inhaled and nasal drug products (OINDPs), enabling precise measurement of aerodynamic particle size distribution (APSD) for the active pharmaceutical ingredient (API). Unlike general particle sizing methods, cascade impactors provide critical metrics such as mass median aerodynamic diameter (MMAD), fine particle fraction (FPF), geometric standard deviation (GSD), and stage-by-stage deposition profiles, which are essential for understanding drug delivery to the lungs and ensuring regulatory compliance. Applied from R&D through quality control, these metrics define the critical quality attributes (CQAs) that determine OINDP performance. Drawing on over 30 years of experience in manufacturing cascade impactors and training analysts, Copley Scientific has distilled this expertise into a practical guide, helping users navigate the principles, applications, and common challenges of cascade impaction.