ISO 22412:2025 Particle size analysis – Dynamic light scattering (DLS)

ISO 22412:2025 (Edition 3) modernizes the ISO standard for DLS, expanding the 2017 framework to include multi-angle and imaging DLS methods, enhanced treatment of concentrated suspensions, cross-correlation and new backscatter/ polarisation modes, and incorporation of “good practice” material previously in ISO TR 22814. It still focuses on measuring average hydrodynamic diameter (e.g., Z-average) and, with care, particle size distribution for sub-micron-sized particles, emulsions, fine bubbles dispersed in liquids.

Feature	ISO 22412:2017 (Previous)	ISO 22412:2025 (Current)
Measurement Geometry	Primarily single-angle DLS with limited optical configuration details	Expanded coverage including multi-angle DLS (MADLS) and backscatter-based approaches
Concentrated Samples	Covers both dilute and concentrated suspensions, with less detailed guidance for concentrated systems	Enhanced guidance for concentrated systems, including mitigation of multiple scattering and updated good-practice considerations
Advanced Modes	Not explicitly addressed	Includes imaging-based DLS, ultrafast imaging approaches, and polarisation-resolved backscatter cross-correlation techniques
Quality Control	Addressed separately in ISO/TR 22814	Integrated directly into the core standard (performance checks and quality control)

Applies to both dilute and concentrated suspensions, with more detailed requirements for sample prep and measurement in concentrated systems.

New measurement modes included: Multi-angle DLS (MADLS), imaging DLS, ultrafast imaging, and polarisation-separated backscatter photon cross-correlation spectroscopy.

Terms like Z-average, PI (polydispersity index) remain, but new annexes discuss online measurement and performance qualification/quality control in the new contexts.

The standard cancels and replaces ISO 22412:2017.

Key Implications (for CMC / Biologics / Regulatory)

When writing or specifying DLS assays in regulatory or quality documents, refer to 2025 standard.

If using imaging or MADLS modes, ensure compliance with new clauses.

For concentrated suspensions, follow the new sample-preparation, validation, and QC requirements.

Ensure reporting aligns with updated definitions and measurement algorithms (especially for distribution calculations).