This article discusses important misconceptions that from-time-to-time have appeared concerning the analysis of particle size data. It primarily focuses on multi-stage cascade impaction, which is the primary technique for OIP APSD measurement. However, attention is also paid to the analysis of size distribution data from time-of-flight analyzers and laser diffractometer instruments that are also encountered in the evaluation of inhaler performance, particularly the latter for the assessment of nasal products.
A key objective of this article is to guide the newcomer to the field, as well as those with familiarity of the topic. Four misconceptions are discussed: Misconception 1: Impactor-sized mass (ISM) always includes data from all impactor stages; Misconception 2: Geometric standard deviation (GSD) is always suitable as the measure of spread of a size distribution; Misconception 3: The underlying size distribution can be described by a single size-based metric; and Misconception 4. Count/number-weighted size distribution data are a surrogate for volume/mass-based data.