Measurement of pharmaceutical particles using a time-of-flight particle sizer

The Aerosizer is an instrument for time-of-flight measurement, which is widely used in particle size determinations. The results of various studies indicate that there are still some problems related to the optimization of the analysis conditions. In this study, the behaviour of a set of different kinds of pharmaceutical particles during Aerosizer measurements was studied. An Aerosizer LD equipment with an Aero-Disperser was validated with particle size standards. Volume particle size distributions of particles with different size and shape characteristics were determined (PVP, Celphere, lactose, a drug substance, PHB microparticles). The aim was to investigate the effects of the shear force and deagglomeration levels during the dispersion of the particles on the particle size distributions that were obtained. The results of this study indicate that the ability of the instrument to disperse particles is highly dependent on the properties of the materials. According to the validation measurements, the instrument gives accurate results for spherical, uncohesive particles. The capability of the dispersing unit to separate particles aerodynamically was well observed with PVP. Time-of-flight measurements were uncomplicated for relatively large particles, such as Celphere, which have little interaction with each other and with the instrument housing. For lactose, increasing shear force rates resulted in size distributions with larger particle sizes. In the case of the PHB microparticles the results indicated that the aggregates became smaller and particles were partly separated to primary particles with all shear force levels.