PREPARATION OF EMULSIONS

PREPARATION OF EMULSIONS

Several factors are considered.:

            We need to Specify

·         Type of emulsion, that is whether it will be o/w or o/w.

·         The use of the product i.e. whether it will be for external use, internal use or injectable.

Consider

·         The ingredients taking into accounting the chemical structure, physical properties (m.p., solubility and stability)

·         Dose of the preparation (which has an impact on the overall volume)

·         Incompatibilities of the ingredients

·         Choice of emulgents

Equipment needed in the preparation of emulsions:

1. Mortal and pestle:

This is used with emulsifying agents that form multi molecular film such as acacia, tragacanth and agar. Emulsions for internal use are made with acacia unless otherwise stated.

Using a mortal and pestle, the thick or primary emulsion is made first in the rations of oil:water:Gum as follows:

Oil   :   Water  :      Gum

Fixed oil            4            2               1 (e.g. Almond, Arachis, Castor and

cod-liver oil

Mineral oil         3            2               1 (e.g. Liquid paraffin)

Volatile oil        2            2               1 (e.g. Turpentine, peppermint and cinnamon

oil

The primary emulsion can be prepared by one of the following methods:

1. DRY-GUM METHOD (BRUTE FORCE OR CONTINENTAL METHOD)

Measure the oil accurately in a DRY measure. Pour it to the bottom of a large DRY FLAT BOTTOMED mortar. Measure the aqueous phase (vehicle) and acacia powder.

Place the gum on the oil, mix to disperse it gently, then add water ALL AT ONCE.  Triturate continuously but lightly in one direction until the mixture thickens, then triturate vigorously to produce a thick cream.  A good primary emulsion usually produces a cracking sound.  The finer the globule the whiter the product.  If any of these steps is overlooked, the primary emulsion might not form properly due to phase inversion.

2. WET GUM METHOD (PERSUASION)

This is an old, slow and less good technique. Weigh the gum and measure the water triturate to form mucilage.  This should not be stored for it becomes acid and lose viscosity.  The oil is added slowly with constant rapid and light trituration.  Then (after adding all the oil) triturate vigorously.

Dilution. For both dry gum and wet gum,  Gradually dilute the primary emulsion so prepared with a small volume of vehicle fully incorporating the portions before adding the next, then make up to volume.

Bottle method: The method is the same as mortar and pestle except a bottle is used instead. Trituration is equated to shaking.

NASCENT METHOD

These are soap type emulsions meant for external use – alkali soap, NH4+Soap, and lime cream type.

Alkali soap – made by preferred soap e.g. soft soap in Turpentine liniment BP.

Powder ingredients, mix with soap in mortar, and add oil to form suspension.  Add suspension to water ( 1/3 of oil + soap) in a bottle, add other ingredients almost to volume, pass thru muslin strainer (to avoid frothing on shaking) these transfer to connect container.

Ammonia soap type: 

Here soap is made in situ by interaction by a fatty acid and ammonia in the prep.  Then emulsion is made by agitation e.g. white liniment BPC (NH3+Ollic acid)

Lime cream type –

Emulgent is Calcium Soap, formed in situ – some oils have enough Free Fatty Acids e.g Olive but some e.g. Arachis oil need addition of a little Free Fatty Acids usually oleic acid.

FUSION METHOD

This method is used mainly for syntheticc emulgents (which have become popular). . Oil soluble ingredients aredissolved in oil while water soluble ingredients are dissolved in water). Each heated to 70 – 75 C, then after the ingredients have dissslved, the two are mixed, stirred until cold. Only Simple equipment i.e :  2 beakers, thermometer and source of heat.

ALTERNATE  METHOD(English method)

This is employed in industries.  Water and oil are added alternately to the emulgent.  It is particularly suitable for preps of food emulsions e.g. mayonnaise.

USES OF EMULSIONS

Water insoluble liquids are conveniently formulated as emulsions. Actually emulsions offer some advantages over other dosage forms:

ORRALY:

·         Emulsions disguise the taste of oiliness of medicinal oils. For example cod-liver oil, liquid paraffin. In O/w emulsions one cad add water soluble flavors and colours.

·         0/w emulsions are easily rinsed from the mouth

·         Some oil-soluble compounds are easily and rapidly absorbed in emulsion form than oily solutions, for example vitamins. This is because emulsions are finely divided and hence have an increased rate of absorption.

·         The emulsification principle can be used for formulating sustained release preparations.

PARENTERAL ADMIISTRATION:

• Emulsions can be used to administer nutritive oils.
• Administration of contrast media for radiological examinations whereby radiopaque emulsions are used.
• Parenterals can be formulated to exhibit sustained release characteristics.

EXTERNAL USE

• Liquid emulsions are used as Applications, Lotions, and Liniments.
• Semi-solids are creams which could be oily or aqueous. Creams are more acceptable than ointments
• Emulsions can be used formulating aerosols to produce foam (propellant is the  dispersed phase and vaporizes to produce foam upon release).