Correlations between cascade impactor analysis and laser diffraction techniques for the determination of the particle size of aerosolised powder formulations

The purpose of the study was to examine the suitability of the Spraytec® laser diffraction technique for measuring the size distribution of aerosol particles generated from dry powder inhalators. A range of formulations with different dispersion properties were produced by spray-drying. The percentage of particles below 5.0 μm of these formulations was measured by laser diffraction (Mastersizer® 2000 and Spraytec®) and inertial impaction (MsLI and NGI) using various inhaler devices and at different flow rates between 30 and 100 l/min. Linear relationships and correlations (R2 > 0.9) existed between the results obtained from, on one hand, the Mastersizer® 2000 and the Spraytec®, and, on the other hand, the MsLI and the Spraytec® regardless of flow rates and inhaler devices. The Spraytec® could be a reliable technique for the development, evaluation and quality control of dry powder aerosol formulations.