Nanoparticle size distribution quantification: results of a small-angle X-ray scattering inter-laboratory comparison

Area of Science:

• Materials Science
• Nanotechnology
• Analytical Chemistry

Background:

• Accurate nanoparticle sizing is crucial for material properties and applications.
• Small-angle X-ray scattering (SAXS) is a powerful technique for characterizing nanoscale materials.
• Standardization of SAXS methods for nanoparticle characterization is needed.

Purpose of the Study:

• To conduct the first worldwide inter-laboratory comparison of SAXS for nanoparticle sizing.
• To assess the consistency and reliability of SAXS measurements across different laboratories and instruments.
• To determine key nanoparticle parameters: mean radius, size distribution width, and concentration.

Main Methods:

• Dispersed silver nanoparticles with a poly(acrylic acid) shell were used as the test sample.
• Three distinct data evaluation methods were applied: generalized indirect Fourier transformation, SASfit model fitting, and McSAS Monte Carlo fitting.
• Data were collected from multiple laboratories using synchrotron and commercial/in-house SAXS instruments.

Main Results:

• Consistent mean number- and volume-weighted core radii (Rn = 2.76(6) nm, Rv = 3.20(4) nm) were obtained.
• Consistent lognormal radius distribution widths (σn = 0.65(1) nm, σv = 0.71(1) nm) were determined.
• Particle concentration was consistently measured as 3.0(4) g L⁻¹ or 4.2(7) × 10⁻⁶ mol L⁻¹.

Conclusions:

• SAXS is a reliable and consistent method for determining nanoparticle size distributions in the sub-20 nm range.
• Inter-laboratory comparison yielded highly consistent data, independent of the specific SAXS instrument used.
• The choice of data evaluation procedure had a minor effect on the results, highlighting the robustness of SAXS for nanoparticle characterization.