Overview
EN ISO 19749:2023 (identical to ISO 19749:2021) defines standardized methods for measuring particle size and shape distributions using scanning electron microscopy (SEM). The standard guides acquisition, image evaluation and reporting so results are accurate, reproducible and traceable. It applies primarily to nanoparticles (1–100 nm) but is also suitable for larger-than-nanoscale particles; the practical lower size limit depends on required measurement uncertainty and demonstrated SEM performance.
Key topics and technical requirements
- SEM qualification: Procedures to demonstrate that an SEM is suitable for nanoparticle measurements and achieves the required performance and uncertainty.
- Sample preparation: Best practices for preparing powders, liquid dispersions and substrate deposition (e.g., wafers, TEM grids) to ensure representative, well-dispersed particles for imaging.
- Image acquisition: Guidance on selecting imaging conditions (magnification, pixel resolution, contrast, detector choice) to capture reliable 2D morphological information.
- Particle analysis: Methods for individual and automated particle detection, segmentation, and descriptor extraction for size and shape.
- Data analysis and uncertainty: Screening raw data for artefacts, handling touching/overlapping particles, fitting distributions, and assessing measurement uncertainty for size and shape descriptors.
- Reporting results: Required information and example reporting formats to ensure transparency and comparability of SEM-based particle distribution data.
- Informative annexes: Case studies, practical examples (including an ImageJ workflow), and studies of acquisition/thresholding effects that help implementers adapt procedures to real samples.
Practical applications and users
This standard is intended for organizations and professionals involved in nanomaterials characterization, including:
- Analytical and materials characterization laboratories performing SEM-based sizing
- Nanomaterials manufacturers and quality control teams ensuring product consistency
- Research groups developing nanomaterials for pharmaceuticals, cosmetics, electronics, coatings and catalysis
- Regulatory bodies and conformity assessment bodies evaluating particle metrics for safety and compliance
- SEM instrument vendors and software developers who implement automated image analysis workflows
Typical uses include quality control of nanopowders and dispersions, R&D characterization of morphology, regulatory submissions requiring documented measurement methods, and inter-laboratory studies.
Related standards
EN ISO 19749:2023 is part of the ISO/TC 229 “Nanotechnologies” family and is published as an EN ISO standard. Users should consider other ISO/CEN nanotechnology standards addressing terminology, metrology principles and complementary measurement techniques when developing a complete characterization strategy.
Keywords: nanotechnologies, SEM, scanning electron microscopy, particle size distribution, particle shape distribution, nanoparticles, measurement uncertainty, sample preparation, image analysis.