Design of micron-sized salt particles by ethanol vapour drying

Abstract

Antisolvent vapour drying precipitation is a new spray drying technique in which each droplet behaves like an individual ‘precipitation vessel’. As the aqueous droplet absorbs the convective ethanol vapour, the initially dissolved solutes precipitates out as ultrafine particles within the droplet. This work sought to examine the feasibility of applying the antisolvent vapour drying method to produce salt particles. Using the modified single droplet drying rig, spherical magnesium sulphate and iron sulphate particles <10μm were produced from relative large droplets of 1–2mm in diameter. The fine particles produced exhibited rough gravel-like surface morphology. Mixtures of iron sulphate and vitamin C at different proportions were tested and gravel-like iron sulphate particles within a bulk vitamin C matrix were produced. Rough gravel-like surface morphology was also observed for sodium chloride particles. Lactose was then incorporated into the formulation to assess if spherical ultrafine particles of a lactose-salt matrix can be produced. The precipitated particles, however, resembled the smooth ultrafine amorphous particles of lactose without distinct indication on the location of the salt material.