Characterization of inhalation aerosols: a critical evaluation of cascade impactor analysis and laser diffraction technique

Particle Size Analysis of Aerosols from Medicinal Inhalers

“…Light interaction methods can be further sub-divided into low angle (laser diffraction (LD)) and phase Doppler systems. LD systems measure orientation-averaged size that corresponds closely with volume equivalent diameter, at least for micronized, near spherical powder particles [48]. They are convenient to use, as they typically require few user defined parameters and enable size distribution measurements to be made in 1 min, compared with 1 h by cascade impactor.…”

“…However, the matter does not appear to be so straightforward with dry powder inhaler-produced aerosols. In this context, de Boer et al [48] commented that the L-M procedure is better (more rigorous) than the Fraunhofer technique. However, where d LD λ, they observed that the Fraunhofer approach may provide size distributions with micronized powders having diverse chemical composition as well as size, shape and surface appearance that correlate more closely with cascade impactor-based data, than data obtained applying L-M theory.…”

“…However, the applicability of LD for the size distribution measurement of dry powder aerosols that may comprise non-spherical particles may be questionable without data from an independent technique to validate the LD data. In this context, de Boer et al noted that micronized powders for use in DPIs in most cases comprise particles that approach sphericity, under which circumstances, LDbased size is a measure of the geometric diameters of the particles at random orientation, and d LD Ϸd v [48]. They also commented that comparisons with d ae obtained by cascade impactor or equivalent methods are in many cases possible, since the proportionality constant (ρ p /ρ 0 χ) 1/2 in equation 1, ignoring the Cunningham slip correction factors, is between 0.96 and 1.22 for a range of particle shapes ranging from spherical (χ҃1.0) to cylindrical with aspect ratio (length/diameter) of 4 (χ҃1.3) and densities from 1.2 to 1.5 g cm Ҁ3 ).…”

Effects of Temperature and Humidity on Laser Diffraction Measurements to Jet Nebulizer and Comparison with NGI

“…With a constant flow rate, the airborne particles travel through several stages with progressively decreasing cut sizes. The deposition behavior of particles is relevant to the combined effect of inertial impaction, gravitational sedimentation, and diffusion by way of Brownian motion (15)(16)(17)(18)(19)(20)(21), giving more realistic simulation of impaction in the lungs. It is obvious that aerodynamic size distribution is an important parameter affecting aerosol performance.…”

“…There are many studies confirmed that the most profitable features of laser diffraction are time saving, reproducibility, automatic data recording, and automatic processing. Furthermore, the applicability of laser diffraction technique is evaluated as an alternative for cascade impactor analysis for the in vitro characterization of various types of medical aerosol generators (15,(26)(27)(28)(29)(30)(31). Some commonly used laser diffractometers are the Spraytec laser diffractometer (Malvern Instruments, UK) and the Sympatec HELOS laser diffraction analyzer (Sympatec GmbH, Clausthal-Zellerfeld, Germany) (14).…”