Overview
ISO 17867:2020 - "Particle size analysis - Small angle X‑ray scattering (SAXS)" defines a standardized method for using small‑angle X‑ray scattering (SAXS) to estimate mean particle sizes in the 1 nm to 100 nm range. The standard is intended for dilute dispersions where particle–particle interactions and interparticle scattering are negligible. It covers instrument setup, sample preparation, measurement, data corrections, calculation of mean diameters and the extraction of particle size distributions using multiple evaluation methods.
Key topics and requirements
- Scope and applicability
- SAXS applied to ensemble measurements of particles or pores with electron‑density contrast.
- Limited to dilute systems (interaction effects negligible); largest measurable size typically ~100 nm.
- Data evaluation methods (analyst must select and report the chosen method):
- Guinier approximation - provides an estimate of the mean particle diameter (radius of gyration, Rg).
- Model‑based data fitting - fits physical form factors for basic geometries (sphere, cylinder, disk, core–shell).
- Monte‑Carlo‑based fitting - stochastic extraction of distributions.
- Indirect Fourier transform (IFT) - reconstructs real‑space pair distance distribution.
- Expectation‑maximization (EM) - iterative deconvolution approach for size distributions.
- Instrument and procedure
- Guidance on apparatus, preliminary setup, sample thickness and transmission, measurement protocol, and data correction steps.
- Limitations and interpretation
- Shape information is generally limited to basic geometries; low‑density shells may be undetectable.
- Results are ensemble‑ and time‑averaged; careful reporting of method selection and assumptions is required.
- Quality and reporting
- Sections on repeatability, system qualification, documentation and required content of test reports.
Applications and users
- Practical applications:
- Nanomaterials characterization (particle size, size distribution, surface area).
- Quality control in pharmaceuticals, cosmetics, paints, and colloids.
- Research at laboratory and synchrotron facilities for materials science, polymer science, and porous media (pore size).
- Typical users:
- Analytical labs, R&D scientists, metrology institutes, instrument manufacturers, and regulatory bodies seeking consistent interlaboratory results.
- Benefits:
- Rapid, ensemble‑scale sizing of nanoparticles; complementary to TEM, DLS and SAXS alternatives (e.g., SANS).
Related standards
- Normative references cited in ISO 17867:2020:
- ISO 26824 - Particle characterization of particulate systems - Vocabulary.
- ISO/TS 80004‑2 - Nanotechnologies - Vocabulary - Part 2: Nano‑objects.
- Note: Small‑angle neutron scattering (SANS) is not described in the standard but is theoretically similar and often complementary.
Keywords: ISO 17867:2020, SAXS, small angle X‑ray scattering, particle size analysis, nanoparticle sizing, Guinier, model fitting, Monte‑Carlo, indirect Fourier transform, expectation maximization.
