Overview
ISO 13320:2020 - Particle size analysis - Laser diffraction methods - is the international guidance document for measuring particle size distributions (PSDs) using laser diffraction. It covers instrument qualification, measurement procedures, data conversion and reporting for many two‑phase systems (powders, sprays, aerosols, suspensions, emulsions and gas bubbles in liquids). The standard applies typically to particle sizes from approximately 0.1 µm to 3 mm, with extensions possible using special instrumentation and conditions.
Key technical topics and requirements
ISO 13320:2020 provides practical, technical guidance rather than prescriptive material‑specific limits. Major topics include:
- Principle and theory of laser diffraction and optical arrangements, including detector and scattering considerations.
- Instrument qualification: protocols for evaluating accuracy, repeatability and intermediate precision.
- Operational requirements: instrument location, sample inspection, preparation, dispersion (liquids and gases) and concentration control.
- Measurement procedures: blank measurements, data collection of scattering patterns, selection of optical models, and conversion of scattering data into PSDs.
- Measurement modes: off-line, in-line, online and at-line applications and their specific considerations.
- Reporting: standardized reporting of results, sample and dispersion details, and analyst identification.
- Annexed guidance: theoretical background (Annex A), dispersion liquids and methods (Annexes B–C), instrument preparation and error diagnosis (Annexes D–E), refractive index recommendations (Annex F), robustness/ruggedness (Annex G), and use of certified reference materials (Annex H).
Important technical note: the optical model assumes spherical particles, so for non‑spherical particles the reported PSD reflects the equivalent spherical volume distribution and can differ from results obtained by sedimentation or sieving.
Practical applications
Laser diffraction per ISO 13320:2020 is widely used for:
- Quality control and batch release in pharmaceuticals, chemicals, pigments and coatings
- R&D and formulation development in food, cosmetics and personal care products
- Environmental and aerosol monitoring (airborne particles)
- Process monitoring and optimization in powder processing, sprays and suspensions
- Materials science characterization where rapid, automated PSDs are required
The standard supports reliable comparison of results by defining instrument qualification, method repeatability and reporting expectations.
Who should use this standard
- Laboratory analysts and quality control teams performing PSD measurements
- Instrument manufacturers and service engineers developing or validating laser diffraction systems
- R&D scientists developing particulate formulations or processes
- Regulatory and compliance personnel seeking standardized measurement evidence
Related standards and keywords
Related ISO documents: ISO 9276‑1 and ISO 9276‑2 (representation and calculation of PSD results).
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