Study of the dispersion behaviour of l-leucine containing microparticles synthesized with an aerosol flow reactor method

l-leucine containing particles having salbutamol sulphate or sodium chloride as a main component have been produced by an aerosol flow reactor method. In the method, aqueous solute droplets were transferred into a heated laminar flow reactor where droplet drying took place. The geometric number mean diameter (GNMD) of the produced particles varied between 0.50 and 1.01 μm. Amino acid l-leucine, due to its surface-active nature in water, formed the outer layer of the initial droplet and in the product composite salbutamol and NaCl powders. The morphology of the amorphous salbutamol particles changed from spherical to wrinkled and that of the crystalline NaCl particles from faceted to rounded but fractured due to incorporated l-leucine. These powders mixed with coarse lactose powder were tested in a novel deagglomeration apparatus where they experienced continuous turbulent flows with jet flow rates from 15 to 90 l/min intended to disperse powder agglomerates. In general, the incorporation of l-leucine improved dispersion efficiency as well as decreased dependence on dispersing flow rate of all the powders. The influence of l-leucine was observed particularly at low flow rates: The particle number concentration of the dispersed NaCl particles increased ∼ 19 times and that of the salbutamol particles ∼ 12 times with 20 wt.% of l-leucine at a flow rate of 15 l/min. Added l-leucine affected the dispersion of salbutamol particles more than that of NaCl particles due to different particle surface. Moreover, the salbutamol-l-leucine agglomerates were reduced to the primary particles at high flow rates. This was not observed for the NaCl-l-leucine agglomerates. Fine particle fractions (FPF, D ≤ 5 μm) of NaCl-l-leucine and salbutamol-l-leucine composite particles at a flow rate of 60 l/min increased, respectively, from 0.14 to 0.29 and 0.19 to 0.39 with increasing l-leucine content. Commercial micronized salbutamol powder gave an FPF of 0.15.