ISO 23484:2023

Overview

ISO 23484:2023 - Determination of particle concentration by small-angle X‑ray scattering (SAXS) - specifies how to measure particle number and mass concentration in suspensions using SAXS. The standard is limited to sufficiently monodisperse, spherical nanoparticles (size-distribution width typically < ~50% of mean diameter) and to dilute systems where particle–particle interactions are negligible. It describes the principle of SAXS concentration determination, instrument and calibration options, measurement and data-correction procedures, and reporting requirements.

Key technical topics and requirements

• Scope and assumptions
  • Applies to monodisperse spherical particles in liquid suspensions; requires knowledge or assumption of particle shape and electron density contrast.
  • Limited to dilute systems; long-range interactions (e.g., Coulomb) require lower concentrations or special care.
• Principle
  • Concentration is derived from the absolute differential scattering cross section by comparing measured and calculated scattering using the particle form factor P(q,r).
  • Absolute intensity (ratio of scattered to incident beam) must be established for number-concentration determination.
• Calibration approaches
  • Use of primary/secondary standards (e.g., water, Lupolen, glassy carbon) with known scattering cross sections.
  • High-dynamic-range area detectors that can measure direct and scattered beams.
  • Detectors with known quantum efficiency combined with a calibrated photodiode to determine incident flux.
  • If absolute calibration is not possible, mass concentration can be estimated from extrapolated forward scattering using a monodisperse reference material.
• Instrument and measurement controls
  • q-axis and intensity-axis calibration, sample thickness optimization, and data-correction procedures are specified.
  • Each sample should be measured at its original concentration and at a 1:1 dilution to detect concentration artefacts.
• Limits and sensitivity
  • Size sensitivity typically covers ~1 nm to 100 nm (lab SAXS), extendable with USAXS; detection limits depend strongly on particle radius (scattered intensity ∝ radius^6) and electron-density contrast (∝ Δρ^2).
• Quality and reporting
  • Sections on repeatability, documentation, test report contents, and inter-laboratory comparison (informative annex).

Applications and users

• Practical for materials scientists, nanoparticle manufacturers, pharmaceutical analysts, environmental labs, and synchrotron users who need accurate ensemble-averaged nanoparticle concentrations in liquid suspensions.
• Useful in quality control, formulation development, regulatory submissions, and research where knowledge of particle concentration (number or mass) is critical.

Related standards

• ISO 17867 - Particle size analysis - Small angle X‑ray scattering (SAXS) (referenced for size and distribution determination)
• Other ISO terminology and particle-characterization references cited within the document.

Keywords: ISO 23484:2023, small-angle X‑ray scattering, SAXS, particle concentration, nanoparticles, suspensions, monodisperse, differential scattering cross section, calibration, detection limits.