Simultaneous synthesis and coating of salbutamol sulphate nanoparticles with l-leucine in the gas phase

Salbutamol sulphate nanoparticles have been simultaneously prepared and coated with l-leucine in the gas phase. Three different ways of coating can be separated based on the operation temperatures used in an aerosol flow reactor. Below the temperature of l-leucine sublimation, formation of the l-leucine layer on the core particle surface takes place via diffusion of l-leucine molecules on the droplet surfaces during droplet drying. At intermediate temperatures, the extent of sublimation of l-leucine depends notably on the concentration, and thus partial evaporation was expected. The l-leucine coating was solely formed via vapor deposition at high reactor temperatures when complete sublimation of l-leucine was obtained. The geometric mean diameter of the core salbutamol particles was approximately 65 nm. In general, particle size increased with the addition of l-leucine. The size distribution remained the same or broadened when the coating layer of the particles was formed via surface diffusion whereas notable narrowing of the distribution was observed when the coating was formed via vapor deposition. Upon desublimation and heterogeneous nucleation on the surfaces of smooth, spherical core particles, l-leucine formed a discontinuous coating with leafy crystals a few nanometers in size.