How reliably can a material be classified as a nanomaterial? Available particle-sizing techniques at work

TLDR

Regulatory frameworks mandate classifying materials as nano or non‑nano based on particle size. The study investigates whether current particle‑size measurement techniques can reliably classify materials that may fall under these regulatory definitions. A range of counting, fractionating, and spectroscopic methods were applied under harmonised conditions to both well‑defined quality‑control materials and complex industrial samples. Each technique was assessed for its ability to determine the number‑weighted median size, and the authors provide recommendations on the most suitable and efficient methods for different material types.

Abstract

Currently established and projected regulatory frameworks require the classification of materials (whether nano or non-nano) as specified by respective definitions, most of which are based on the size of the constituent particles. This brings up the question if currently available techniques for particle size determination are capable of reliably classifying materials that potentially fall under these definitions. In this study, a wide variety of characterisation techniques, including counting, fractionating, and spectroscopic techniques, has been applied to the same set of materials under harmonised conditions. The selected materials comprised well-defined quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity. As a result, each technique could be evaluated with respect to the determination of the number-weighted median size. Recommendations on the most appropriate and efficient use of techniques for different types of material are given.