Particle-sizing methods: a stationary-phase-based comparison.

Stationary-phase approximation is used to examine and compare the reliability and interpretability of two main methods of particle sizing. The first method, differential light scattering, regards spherical objects having different refractive indices. Theoretical expressions are obtained, enabling the derivation of optical and geometrical properties of the object from its scattering pattern. The second method, automated microscope imaging, is considered with theoretical implications for the finite aperture of the objective lens. It is shown that, besides the well known Rayleigh resolution limit, finite aperture must affect size measurement due to optical properties of the particles. Simulation and experimental results for both differential light scattering and microscope imaging of polystyrene beads are in good agreement with theory.