Simple and cost-effective powder disperser for aerosol particle size measurement P. Tang a , D.F. Fletcher b , H.-K. Chan a, ⁎ , J.A. Raper c a Faculty of Pharmacy, University of Sydney, NSW 2006, Australia b School of Chemical and Biomolecular Engineering, University of Sydney, NSW 2006, Australia c Department of Chemical and Biological Engineering, University of Missouri-Rolla, MO 65409-1230, USA Received 20 December 2007; accepted 7 January 2008 Available online 16 January 2008 Abstract Commercial dry powder dispersers needed in conjunction with particle size measurement equipment are usually quite expensive (of the order of thousands of dollars). We have found that a simple vacuum generator can be used as a cost-effective disperser (US$50). Comparison with other commercial dispersers, small scale powder disperser (SSPD) model 3433 (TSI, Shoreview, USA) and Scirocco dry powder disperser (Malvern, Worcs, UK), showed that our disperser worked as efficiently as these expensive dispersers. Crystalline mannitol (less than 1% moisture content) and amorphous BSA (8.5–9.2% moisture content) smooth spherical particles were used to test the dispersion capability of the unit. Smooth spherical particles were chosen because they are more cohesive than corrugated particles due to increased contact points. Therefore, sufficient dispersions of other less cohesive particles should be able to be achieved using the optimum conditions reported here. The effects of air pressure, sample weight, and nozzle size of the disperser were investigated. Comparison of the particle size distributions between wet and dry measurements were used to determine the dispersion efficiency. Quantitative comparisons were made using the values of D(v ,0.5) and span. The best dispersion was found using a 1.00 mm nozzle and the maximum percentage differences in D(v ,0.5) and span are 23% and 19%, respectively, with more than 200 mg mannitol powder dispersed with pressures of 50, 70, 90 psi. Using BSA powders, the maximum percentage differences of D(v ,0.5) and span are 37% and 25%, respectively. As was the case for the commercial devices, the dispersion of BSA particles could not be improved even when the pressure of the compressed air was increased. © 2008 Elsevier B.V. All rights reserved. Keywords: Powder disperser; Size measurement; Aerosol 1. Introduction Dry powder dispersers have been widely used and are re- quired to de-agglomerate powder in order for commercial in- struments to measure particle size distributions based on laser diffraction [1] and time-of-flight techniques [2]. It is recognized that complete dispersion of dry particulate solids, especially in the size range below 20 μm, is difficult to achieve due to the strong cohesive forces, namely van der Waals, magnetic, elec- trostatic, and forces due to solid or liquid bridges. In general, the strength of these forces increases with decreasing particle size. It has been reported that the van der Waals force, the main interparticle attraction force, is approximately 100 times stronger than gravity for 10 μm particles [3]. For 1 μm par- ticles, this force increases to 1000 g (g being the gravity force) and for 0.1 μm, it increases to between 10 4 and 10 5 g. De-agglomeration in the dry powder feeder associated with the Malvern Mastersizer 2000 (Malvern, Worcs, UK) laser diffraction instruments is achieved by accelerating the particles close to sonic speed along a tapered transport tube. This mechanism provides the shear forces and collisions between the particles and the feeder's walls in order to break up the aggregates. Pressure titration (from 0.1 to 4.0 bar) is recommended to find the optimum pressure that can break up aggregates without fracturing the individual particles. The optimum pressure is found when the Available online at www.sciencedirect.com Powder Technology 187 (2008) 27 – 36 www.elsevier.com/locate/powtec ⁎ Corresponding author. E-mail address: kimc@pharm.usyd.edu.au (H.-K. Chan). 0032-5910/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2008.01.003