Method for measuring particle size distribution of a population of particles

A method for measuring a particle size distribution of a population of particles using a light scattering particle sizing instrument having a plurality of selectable imaginary component values of the refractive index, and the method comprising the steps of:

• (i) providing a population of the particles;
• (ii) determining a real component of the refractive index of the particles;
• (iii) determining an imaginary component of the refractive index of the particles, wherein the method of determining the imaginary component of the refractive index of the particles comprises the steps of:
• (a) providing a subpopulation of the particles from the population of the particles;
• (b) selecting the largest particle from the subpopulation;
• (c) determining the particle size of the particle by a method which is not by a light scattering particle sizing instrument;
• (d) determining the particle size distribution of the population of the particles using a laser light diffraction instrument for each of the selectable imaginary component values of the refractive index;
• (e) selecting a particle size representing the 100 percentile of the particle size distribution of the population;
• (f) comparing the particle size selected in step (e) and particle size determined in step (c);
• and
• (g) selecting the imaginary component value of the refractive index that provides the particle size in step (e) that is closest to the particle size of the particle determined using the method in step (c);
• and
• (iv) determining the particle size distribution of the particles by the light scattering particle sizing instrument wherein the particle size distribution is determined using the real component of the refractive index measured in step (ii) and the imaginary component of the refractive index determined in step (iii).