ISO 19749:2021

Overview - ISO 19749:2021 (Nanotechnologies, SEM-based particle measurements)

ISO 19749:2021 specifies standardized methods for measuring particle size and shape distributions using scanning electron microscopy (SEM) images. The standard covers acquisition, image-based particle analysis, statistical evaluation and reporting of results for nanoparticles (roughly 1–100 nm) and also larger particles measured by SEM. It emphasizes that SEM suitability (calibration and performance) must be demonstrated prior to quantitative measurements and that SEM images provide 2D representations of 3D particles (the document does not prescribe 3D reconstruction).

Keywords: ISO 19749:2021, nanotechnologies, scanning electron microscopy, SEM, nanoparticle size, particle shape distributions, measurement uncertainty

Key topics and technical requirements

• Scope & applicability: Procedures for SEM image acquisition and evaluation to determine size and shape distributions; applicable to nanoparticles and larger-than-nanoscale particles.
• SEM qualification: Requirements and annexed guidance to prove suitable SEM performance and image quality before measurements.
• Sample preparation: Detailed guidance on preparing powders, nanoparticle dispersions, deposition on substrates (silicon wafers, TEM grids), and ensuring representative dispersions.
• Image acquisition: Setting magnification, pixel resolution and other SEM parameters to produce images fit for quantitative analysis.
• Particle analysis: Manual and automated workflows for identifying particles, separating touching particles, and extracting size/shape descriptors.
• Statistical data analysis: Recommendations on number of particles (often several hundreds to thousands, depending on required uncertainty), uncertainty assessment, fitting models and bivariate analyses.
• Reporting: Standardized reporting templates and examples (including annexed example for ImageJ) to ensure transparent, reproducible results.
• Informative annexes: Case studies, SEM qualification procedures, example workflows and effects of acquisition/thresholding on results.

Practical applications and intended users

ISO 19749:2021 is designed for professionals needing reliable, traceable SEM-based nanoparticle characterization:

• Analytical and metrology laboratories performing nanoparticle sizing and morphology analysis
• Nanomaterials manufacturers and R&D groups validating product specifications
• Quality control and regulatory teams requiring standardized reporting and uncertainty evaluation
• Instrument vendors and service providers implementing automated SEM-based image analysis
• Academic researchers studying particle morphology and distributions

Practical value: using ISO 19749 helps ensure consistent sample prep, validated SEM performance, statistically sound measurements and clear reporting - improving comparability between labs and supporting compliance with testing and accreditation (e.g., ISO/IEC 17025).

Related standards (normative references)

• ISO 13322-1 (image analysis methods)
• ISO 9276 series (representation of particle size/shape results)
• ISO/IEC Guide 99 (VIM), ISO/IEC 17025 (laboratory competence)
• ISO/TS 80004 series (nanotechnology vocabulary)

Using ISO 19749:2021 aligns SEM-based nanoparticle measurement practices with international best practice for reproducible, traceable particle size and shape distributions.