• Publication Date: 04/01/2021
  • Author(s):
    Mitchell, Jolyon P. Roberts, Daryl L. Svensson, Mårten
  • Organization(s):
    Applied Particle Principles, LLC Emmace Consulting AB Jolyon Mitchell Inhaler Consulting Services, Inc.
  • Article Type: Technical Articles
  • Subjects: Instruments, Particle Characterization, Product Development/Formulation, Testing, Validation, and Regulatory Compliance
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.

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