ISO 13317-5:2025

Overview - ISO 13317-5:2025 (Photosedimentation techniques)

ISO 13317-5:2025 specifies principles and methods for using gravitational photosedimentation to determine particle size distributions in suspensions and emulsions. Photosedimentation techniques monitor gravity‑induced phase separation by recording photometric signals (transmitted, reflected or scattered light) as a function of vertical position and/or time. Where Stokes’ law applies, recorded sedimentation velocities can be converted to Stokes diameters and particle size distributions. Typical working ranges for aqueous systems are about 200 nm to 100 µm (size) and sedimentation velocities from 0.6 µm/s to 10 mm/s; practical concentration ranges are generally well below 1 vol%.

Key technical topics and requirements

• Measurement principle and instrumentation: how photometric detection records sedimentation and the required opto‑electronic components.
• Primary and derived measurands: sedimentation velocity as primary data, and derivation of size metrics (Stokes diameter).
• Data analysis and distribution functions: conversion from photometric signals to intrinsic and volume‑weighted distributions, including start‑position determination and model assumptions.
• Assumptions and applicability: explicit limits (validity of Stokes’ law, uniform particle density/shape, no chemical/physical changes during measurement).
• Sample handling and measurement procedure: sampling, dispersion, primary/secondary sample preparation, instrument setup, measurement and reporting.
• Quality and system qualification: use of reference materials, performance qualification and guidance on measurement uncertainty.
• Scope exclusions: the standard does NOT cover centrifugal, electric or magnetic migration, zone sedimentation at high concentrations, balance‑ or X‑ray based sedimentation, nor properties other than sedimentation velocity and particle size (e.g., particle concentration, shape, density, zeta‑potential, apparent viscosity).

Practical applications and users

Photosedimentation is suited to industries and laboratories needing high‑resolution granulometric characterization of dispersed systems:

• Quality control and R&D in pharmaceuticals, paints & coatings, food, cosmetics, chemicals and materials research.
• Academic researchers studying sedimentation, stability, agglomeration, clarification and cream/settle layer formation.
• Instrument manufacturers and test laboratories implementing or verifying photosedimentation methods and establishing performance qualification and uncertainty budgets.

Related standards and annexes

• ISO 13317 series (other parts on gravitational sedimentation techniques).
• Normative reference: ISO 9276‑1 (representation of particle size results).
• Informative annexes in ISO 13317‑5 cover number‑weighted calculations, multi‑wavelength approaches, uncertainty guidance and advanced analyses beyond size/velocity.

ISO 13317-5:2025 is essential for consistent, reproducible photosedimentation measurement practice and for integrating photometric sedimentation into laboratory quality systems and reporting.