Determination of particle size distribution and number concentration by particle tracking analysis (PTA)

The ISO series 13318 covers methods for characterising disperse materials in liquids by centrifugation with respect to the particle size distribution and the related distributions of sedimentation velocity and sedimentation coefficient. These methods exploit the centrifugation-induced particle migration by monitoring the spatial distribution of particles in centrifugal fields and allocating the rate of migration to a particle quantity. In principle, the standard does not constrain the direction of particle motion, which depends on the density difference (also: density contrast) between the dispersed and continuous (liquid) phase; yet practical consideration may impose a restriction for specific instrumentation. Centrifugal liquid sedimentation (CLS) methods can be applied to all particles that can be or are dispersed in Newtonian liquids. Particles and liquid should not undergo any interactions, which cause significant changes of the dispersed phase – e.g. due swelling, shrinking, dissolution etc. – in the course of the measurement. Moreover, the particle concentration is restricted to low volume fractions, considering the particles’ motion as that of fully isolated particles. Last but not least, this standard neither covers particle migration by gravity, electric or magnetic forces nor does it deal with deriving particle properties others than size, sedimentation velocity and sedimentation coefficient. This part of ISO series 13318 addresses the principles of particle size analysis by CLS, the corresponding measurement techniques as well as general rules for sample preparation, conducting measurements, data analysis, method validation, determination of the uncertainty budget as well as representation of results. Superposition of sedimentation and diffusion of nanoparticles will especially be discussed. It also reviews the possibility to determine fractional particle concentrations by centrifugal liquid sedimentation techniques.