1. Introduction
Active ingredients in nanoparticulate form can have advantageous properties; for example, nanoparticulate drugs can show higher bioavailability [1] and catalysts higher activity [2]. Nanoparticulates are not readily attainable through conventional crystallization routes and a subsequent comminution stage is often necessary, which may disadvantageously alter the physicochemical properties of the product. In principle, supercritical processes are more attractive because they can deliver a narrow particle size distribution [3] and [4], consist of only one process step, do not require liquid solvents and can be undertaken at moderate temperatures. A further advantage is that they offer control over solid state properties, producing either amorphous or crystalline material and sometimes polymorphs which are not obtainable by other means [5] and [6].