Overview
ISO 13099-2:2025 - "Colloidal systems - Methods for zeta‑potential determination - Part 2: Optical methods" specifies optical techniques to measure the electrophoretic mobility of particles suspended in a liquid. The document covers two measurement methods: video microscopy and electrophoretic light‑scattering (ELS). Results from these optical measurements (electrophoretic mobility) can be converted to zeta‑potential using theoretical models provided in ISO 13099‑1.
This second edition (2025) updates the 2012 version with new terms and definitions, revised instrument configuration illustrations, removal of cross‑beam optics, an updated description of phase analysis light scattering (PALS), and added information on cell constant.
Key Topics and Requirements
- Measurement principles: electrophoresis and electroosmosis in a cell under an applied electric field; superposition of electrophoretic velocity and electroosmotic flow.
- Methods covered:
- Video microscopy: direct visual tracking of particle motion.
- Electrophoretic light‑scattering (ELS): optical Doppler methods (including PALS and modulated Brownian motion power spectrum methods).
- ELS technical elements:
- Cell design and cell constant determination.
- Optical arrangements (reference beam setups).
- Signal processing techniques: spectrum analysis, autocorrelation functions, phase analysis light scattering (PALS), and modulated Brownian motion approaches.
- Calculation: determination of electrophoretic mobility and translation to zeta‑potential (theoretical conversion methods are detailed in ISO 13099‑1).
- Operational procedures:
- Instrument siting, dispersion liquids, sample cell requirements, sample inspection/preparation, dilution and concentration guidance.
- Verification practices: use of reference materials, assessment of repeatability, intermediate precision, and trueness.
- Error sources: contamination, improper preparation, inappropriate medium, temperature instability, optical surface defects, excessive applied potential, air bubbles, electroosmosis effects, and calculation pitfalls.
- Informative annex on electroosmosis within capillary cells.
Applications and Who Uses This Standard
ISO 13099‑2:2025 is applicable to laboratories, instrument manufacturers, researchers, and quality professionals who need reliable optical measurement of particle electrokinetics. Typical use cases:
- Assessing colloidal stability and predicting suspension/emulsion behavior.
- Surface charge and adsorption studies for nanoparticles, colloids, and macromolecules.
- Method validation, instrument design, and standardized reporting in R&D, pharmaceuticals, cosmetics, materials science, and environmental monitoring.
Related Standards
- ISO 13099‑1 - theoretical models and overview for zeta‑potential determination (required companion document).
- ISO 13099 series and related particle characterization standards from ISO/TC 24.
Keywords: ISO 13099-2:2025, zeta‑potential, electrophoretic mobility, electrophoretic light‑scattering, ELS, PALS, video microscopy, colloidal systems, electroosmosis, cell constant.