Certification of NIST SRM 1961: 30 μm Diameter Polystyrene Spheres

This report describes the certification of SRM 1961, an NIST Standard Reference Material for particle diameter. It consists of an aqueous suspension of monosize 30 μm diameter polystyrene spheres. The primary technique used optical microscopy; it gave a mean diameter value [Formula: see text] and a standard deviation of the size distribution σ = 0.21 μm. Over 2000 spheres were measured. The supporting technique used electron microscopy, which yielded [Formula: see text]. Ninety spheres were measured.