Emulsion: Methods of preparation Notes PDF Books Pharmaceutics
Emulsions may be prepared by several methods, depending upon the nature of the components and the equipment. On a small scale, as in the laboratory or pharmacy, emulsions may be prepared using a dry Wedgwood or porcelain mortar and pestle or a mechanical blender or mixer. On a large scale, large mixing tanks may be used to form the emulsion through the action of a high-speed impeller.
In the small-scale extemporaneous preparation of emulsions, three methods may be used.
They are the Continental or dry gum method, the English or wet gum method, and the bottle or Forbes bottle method. In the first method, the emulsifying agent (usual acacia) is mixed with the oil before the addition of water, that is, dry gum.
In the second method, the emulsifying agent is added to the water (in which it is soluble) to form mucilage, and then the oil is slowly incorporated to form the emulsion, that is, wet gum.
The bottle method is reserved for volatile oils or less viscous oils and is a variation of the dry gum method.
Continental or Dry Gum Method
The continental method is also referred to as the 4:2:1 method because for every 4 parts by volume of oil, 2 parts of water and 1 part of gum are added in preparing the initial or primary emulsion. In this method, the acacia or other o/w emulsifier is triturated with the oil in a perfectly dry Wedgwood or porcelain mortar until thoroughly mixed.
A mortar with a rough rather than smooth inner surface must be used to ensure proper grinding action
and reduction of the globule size. After the oil and gum have been mixed, the two parts of water are added all at once, and the mixture is triturated immediately, rapidly, and continue until the primary emulsion is creamy white and produces a crackling sound to the movement of the pestle. Provided the dispersion of the acacia in the oil is adequate, the dry gum method can almost be guaranteed to produce an acceptable emulsion.
Sometimes, however, the amount of acacia must be adjusted upward to ensure that an emulsion can be produced. For example, volatile oils, liquid petrolatum (mineral oil), and linseed oil usually require a 3:2:1 or 2:2:1 ratio for adequate preparation
English or Wet Gum Method
By this method, the same proportions of oil, water, and gum are used as in the continental or dry gum method, but the order of mixing is different, and the proportion of ingredients may be varied during the preparation of the primary emulsion as is deemed necessary by the operator. Generally, a mucilage of the gum is prepared by triturating in a mortar granular acacia with twice its weight of water. The oil is then added slowly in portions, and the mixture is triturated to emulsify the oil.
Bottle or Forbes Bottle Method
The bottle method is useful for the extemporaneous preparation of emulsions from volatile oils or oleaginous substances of low viscosities. Powdered acacia is placed in a dry bottle, two parts of oil are added, and the mixture is thoroughly shaken in the capped container. A volume of water approximately equal to that of the oil is then added in portions and the mixture thoroughly shaken after each addition. When all of the water has been added, the primary emulsion thus formed may be diluted to the proper volume with water. This method is not suited for viscous oils because they cannot be thoroughly agitated in the bottle when mixed with the emulsifying agent.
Biphasic Liquids: Suspension: Definition, advantages, and disadvantages, Classifications, Preparation of suspensions, Flocculated and Deflocculated suspension Emulsions: Definition, Advantages & Disadvantages, Classification, Emulsifying agent, Test for the identification of the type of Emulsion, Methods of preparation, Stability of emulsion
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