USE OF LASER-LIGHT DIFFRACTION IN DETERMINING THE SIZE DISTRIBUTIONS OF DIFFERENT SHAPED PARTICLES

Laser light diffraction (LLD) is rapid and highly repeatable method in determining the particle size distributions of pharmaceutical powders . The materials used in this study were narrow sieve fractions of sphe rical Pellets, cubic sodium chloride and acicular anhydrous theophylli ne. The size distribution determinations were made by Malvern 2600c dr oplet and particle sizer as dry dispersions. An interactive image anal ysis (IA) system (Kontron Vidas+) was used as an absolute control meth od The results showed that in all determinations the LLD method broade ned the size distributions compared to the IA method Furthermore, the LLD method overestimated the particle size of spherical Particles even by 40%. The error increased clearly with increasing particle size. Th e differences between the two methods increased with increasing differ ence in Particle dimensions. Because of so significant errors in the u se of LLD method, the analysis should be restricted only to preliminar y studies. The final particle size determinations should always be che cked by some more absolute methods if proper validation curves are not available.