Light-scattering photometer calibration

A Sofica commercial light-scattering photometer has been critically calibrated using three procedures: Comparing the angular scattered intensity with the turbidity of a solution of suitable Rayleigh scatterers. Comparing the experimental and theoretical scattered intensities of a solution of suitably chosen Mie scatterers. Comparing the scattering from benzene with data in the literature. Two silica sols, Ludox HS and Syton 2X, when used in method (i), gave identical calibration constants. These values agree with those obtained using method (ii) if polystyrene latex particles, which act as the Mie scatterers, are carefully chosen for their size, polydispersity and truly spherical shape. The procedure for this method appears to be entirely novel. Method (iii) showed that the n 2 refraction correction which is often used seems to be in error, at least for the cylindrical cells and optical arrangement employed in this photometer. A correction in n more nearly fits the data. This was confirmed by measuring the molecular weight of a narrow fraction of polystyrene ( M w = 59 000) in three solvents of different refractive index.