Defining, specifying, registering and labelling, as well as characterizing particulate (nano)materials for risk assessment, require measurement of the physicochemical properties of their constituent particles. Because of its resolution covering 1-100 nm, its possibility to identify constituent particles in aggregates and agglomerates and to measure key parameters such as their minimal external dimension on a number-basis, electron microscopic measurement of (nano)particles is necessary in a regulatory context.

Approaches, selected examples and new developments of transmission electron microscopic characterization are proposed from the perspective of the Belgian national reference laboratory responsible for control of particulate (nano)materials applied in the food and feed chain, and in consumer products. The importance of optimizing sample (dispersion) and specimen (EM-grids) preparation will be demonstrated, application of conventional TEM for characterizing pristine materials will be shown, and the possibilities of STEM-EDX analyses for control purposes requiring identification and measurement of specific particles in complex food matrices and mixtures will be presented. Further, approaches to validate these EM-based methods and to determine the measurement uncertainties are given. Initiatives to make EM analyses more time- and cost-efficient by automation of STEM EDX imaging and image analysis with constituent particle detection supported machine learning are proposed.