Stephan mixer

The focus in this chapter is on small scale preparation with a mortar and a pestle, a rotor stator mixer or an ointment miU. For preparation on a larger scale pharmacies in several countries use the mixing-dispersing apparatus Stephan mixer. This mixer exists in various models and is suitable for the preparation of almost aU cutaneous preparations (see Sect. 28.6.1). 

Sorbic acid has to be dissolved in boiling water due to slow dissolution in cold water. But because sorbic acid is volatile with water vapour, loss of sorbic acid has to be prevented by immediately closing the vessel after the additimi of the boiling water. When the preparation is processed in a Stephan mixer in vacuum the sorbic acid may evaporate fast as well. An alternative is to use potassium sorbate instead of sorbic acid and to adjust the pH of the preparation subsequently. 

Generally gels may also be prepared with the use of a Stephan mixer (see Sect. 28.6.1). Lumps will be dispersed immediately in this way. Processing with a Stephan mixer under vacuum has another advantage. It results in an air bubble free (and thereby transparent) gel. 

This section discusses subsequently the Stephan mixer, the rotor-stator mixer, the planetary mixer, the mortar with pestle, the beaker mixer/blender, the three roll mill, the coffee grinder, the Topitec mixer and Unguator mixers. 

The Stephan mixer is a combined mixing and dispersing apparatus. The brand name Stephan is used because of its specific construction and qualities. The apparatus can be used for the preparation of ointments, creams, emulsions, suspensions, gels, pastes, solutions, powder mixtures and granulates. The apparatus was originally developed for food processing. 

The Stephan mixer is available in different sizes, varying from 5 to 40 L for small scale preparations. The choice for the size will, not taking into consideration the available space in the pharmacy, depend on the volume of the batches. The vacuum version with a mantle is only a standard option... 

The Stephan mixer requires a 380 V (3 phase) socket. The vacuum is realised with a small built-in vacuum pump. For the mantle a connection with a cooling water supply (usually tap water) and a drain is required. 

For dispersion of agglomerates amid another substance usually a (non-rough) pestle and mortar, an three roll mill (ointment miU, see Sect. 28.6.6) or a rotor-stator mixer (see Sect. 28.6.2) are used as a tool. Sometimes a beaker mixer/ blender (Sect. 28.6.5) or the Stephan mixer (Sect. 28.6.1) is used). Trituration of an active substance with eye ointment base is done in a stone mortar with a stone pestle because a lot of force is needed. Sometimes it is possible to disperse agglomerates on an ointment tile with a spatula, but a drawback is that no great force can be exerted. For the dispersion of a sohd substance amid other solids, a plastic or metal mortar can be used. 

For liquid suspensimis rotor-stator, Stephan mixer, other mixers (e.g. Unguator ). 

In the practice of pharmacy preparations, it is usual to try to distribute the dispersed phase more finely with a rotor-stator mixer or a simple mechanical (paddle) mixer (pourable emulsions), or, for semisolid emulsions, with a mortar and pestle or a mixing device. Magnetic stirrers are unsuitable. Impaction of air should be avoided because the liberation of air bubbles can accelerate the creaming process (in case of pourable emulsions) and promote possible oxidation of the lipid base or of an active substance. A Stephan mixer with vacuum (see Sect. 28.6.1) is a suitable device for the preparation of emulsions without inclusion of air. 

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