Emulsification is the process with which a pharmacist is able to prepare a

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					Shenyang Pharmaceutical University           LAB 2: EMULSIONS                    PHARMACEUTICS I



                 LABORATORY 2: Preparation of Emulsions

1. LABORATORY OBJECTIVES
   a) To learn the manufacturing methods of emulsions.
   b) To learn how to determine the emulsion type and how to evaluate the stability of
       emulsion.

2. INTRODUCTION
      An emulsion is a dispersion in which the dispersed phase is composed of small
globules of a liquid distributed throughout a liquid vehicle in which it is immiscible
(Figure 2-1). In emulsion terminology, the dispersed phase is the internal phase and the
dispersion medium is the external or continuous phase. Emulsions with an oleaginous
internal phase and an aqueous external phase are oil-in-water (o/w) emulsions. Conversely,
emulsions having an aqueous internal phase and an oleaginous external phase are termed
water-in-oil (w/o) emulsions. Because the external phase of an emulsion is continuous, an
oil-in-water emulsion may be diluted or extended with water or an aqueous solution. A
water-in-oil emulsion can be diluted with an oil or an oil-miscible liquid.




                                     Figure 2-1 Mineral oil in water emulsion.

      Generally, in order to prepare a stable emulsion, a third ingredient, an emulsifying
agent, is necessary. Emulsification is the process with which a pharmacist is able to
prepare a relatively stable and homogeneous mixture of two immiscible liquids. The use of
this dosage can allow the administration of oil with a dissolved lipophilic drug in the form
of small globules rather than in a bulk liquid form. Many theories have been developed in
an attempt to explain how emulsifying agents can facilitate emulsification and maintain the
stability of the resultant emulsion. Some of these theories apply specifically to certain
types of emulsifying agents under specific conditions relating to the pH of the aqueous
phase and the nature and ratio of the internal and external phases. However, these theories
may be viewed as a general way to describe the mechanism by which an emulsion is
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Shenyang Pharmaceutical University           LAB 2: EMULSIONS                PHARMACEUTICS I
formed and stabilized. Among the most prevalent theories, there are the surface-tension
theory, the oriented-wedge theory, and the plastic or interfacial film theory.
      According to the surface-tension theory of emulsification, the emulsifiers or
stabilizers lower the interfacial tension between the two immiscible liquids, reducing the
repellent force between the two liquids and diminishing the attraction between the
molecules of the same liquid. The oriented-wedge theory assumes the formation of
monomolecular layers of the emulsifying agent which are curved around the droplet of the
internal phase of an emulsion. This theory is based on the presumption that certain
emulsifying agents orient themselves around a liquid droplet in a manner reflective of their
solubility in that particular liquid. The plastic-or interfacial-film theory describes that the
emulsifying agent is located at the interface between the oil and water, forming a thin film
by being adsorbed onto the surface of the internal phase droplets The film prevents the
contact and subsequent coalescence of the dispersed phase; a tougher and more pliable film
will result in greater physical stability of the emulsion.
      Emulsions may be prepared by using different methods, depending upon the nature of
the emulsion components and the equipment available for use. On a small scale, as in the
laboratory or pharmacy, emulsions may be prepared using a dry Wedgewood or porcelain
mortar and pestle, a mechanical blender or mixer such as a Waring blender or a milk-shake
mixer, a hand homogenizer, a bench-type homogenizer, or sometimes a simple mixing
tanks may be used to form an emulsion through the action of a high speed impeller.
      In 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, the in situ
soap method, and the mechanical method. Figure 2-2~2-5 describe the preparation process
of emulsions by using different methods. The Dry Gun Method is also referred to as the
“4:2:1” method because for every 4 parts (volumes) of oil, 2 parts of water and 1 part of
gum are added in preparing the initial or primary emulsion. Generally, about 1 minute of
tituration is required to produce a creamy white primary emulsion, during which the oil
phase is converted into oil droplets producing a cracking sound.



                                         Water              Water
   Emulsifier
                                                 Primary
                             Triturate           emulsion           Dilute   Mix      Emulsion
        Oil


     Figure 2-2 The flow chart of preparation of an emulsion with the Dry Gum Method.




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Shenyang Pharmaceutical University            LAB 2: EMULSIONS                              PHARMACEUTICS I



                                                            Water
      Emulsifier
       Water
                                              Primary
                              Triturate       emulsion                 Dilute              Mix      Emulsion
           Oil

      Figure 2-3 The flow chart of preparation of an emulsion with the Wet Gum Method.

                                Oil

                                                Mix            Stir             Emulsion
                               Lye


     Figure 2-4 The flow chart of preparation of an emulsion with the In Situ Soap Method.

                                Oil, water,                           Stir by
                                emulsifier            Mix             machine          Emulsion



     Figure 2-5 The flow chart of preparation of an emulsion with the Mechanical Method.

3. PROCEDURES
3.1 Preparation of emulsions by manual processes
3.1.1 Using acacia as the emulsifying agent
 a) Formulation
                   Soybean oil (ρ=0.91)     13 mL
                   Acacia (fine powder)      3.1 g
                   Distilled water             q.s.
                   To make                   50 mL

 b) The acacia powder is triturated with soybean oil in a perfectly dry porcelain mortar.
     After the oil and acacia have been thoroughly mixed, based on an oil:water:acacia
     ratio of 4:2:1, 6.5 mL of water is added and the mixture is triturated immediately in
     one direction until a creamy white primary emulsion is formed with a cracking sound
     generated by the movement of pestle. 40 mL of distilled water is then added to the
     primary emulsion and the emulsion is transferred to a graduate and made to the final
     volume of 50 mL with distilled water.
 c) Examine the particle-size distribution of the emulsion under an optical microscope,
     record the particle size data, and determine the maximum and the average particle
     size.
 d) Note
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Shenyang Pharmaceutical University   LAB 2: EMULSIONS                     PHARMACEUTICS I
        1) When producing the primary emulsion, the mortar must be dry and with a rough
     rather than a smooth inner surface, trituration should be done in one direction and must
     be quick and uninterrupted until the primary emulsion is formed.
        2) During the preparation of the primary emulsion, the adequate amount of water
     should be add all at once otherwise a w/o primary emulsion will form, which cannot be
     converted into an o/w emulsion by subsequent dilution with water. If excessive amount
     of water is added, the viscosity of the aqueous phase will be too diluted, which will
     generally result in break down of the emulsion or cause other physical instability
     issues.

3.1.2 Using Tween-80 as the emulsifying agent
  a) Formulation
                     Soybean oil (ρ=0.91)       6 mL
                     Tween-80                   3 mL
                     Distilled water               q.s.
                     To make                    50 mL
  b) Tween-80 is first triturated with soybean oil in a perfectly dry mortar until thoroughly
     mixed. 4 mL of water is added all at once and the mixture is triturated without any
     interruption, giving rise to a creamy white primary emulsion. The emulsion is then
     transferred to a graduate and further diluted with distilled water to the final volume
     (50 mL).
   c) Examine the morphology and measure the particle size of the emulsion under an
      optical microscope, record the data, and calculate the maximum and the average
      particle size.

3.2 Preparation of emulsion with the mechanical dispersion method
3.2.1 Using soy lecithin as the emulsifying agent
    a) Formulation
                    Soybean oil (ρ=0.91)               11 mL
                    Fabaceous Lecithin solution         25 mL
                    Distilled water                        q.s.
                    To make                            50 mL
    b) Preparation of the soy lecithin solution: 1.1g of soy lecithin is thoroughly triturated
       with 1.8mL of glycerin in a mortar. The resultant mixture is further triturated with a
       small quantity of water and is subsequently diluted to 25 mL with distilled water.
    c) Soybean oil, soy lecithin mixture and distilled water are combined in the mixing cup
       of a mechanical homogenizer. After homogenizing at 8000~12000 rpm for 1 min,
       hold the product for 1 min, and homogenize the product for an additional 1 min at
       the same speed.
                                                                                           11
Shenyang Pharmaceutical University     LAB 2: EMULSIONS                  PHARMACEUTICS I
     d) Examine the morphology and particle-size distribution of the emulsion under an
       optical microscope, record the data, and calculate the average particle size.

3.2.2 Using Tween-80 as the emulsifying agent
    a) Formulation
                     Soybean oil (ρ=0.91)            11 mL
                     Tween-80                        5 mL
                     Distilled water                  q.s.
                     To make                         50 mL
  b) Soybean oil, Tween 80 solution (prepared with a small amount of water) and distilled
     water are combined in the mixing cup of a mechanical homogenizer. After
     homogenizing at 8000~12000 rpm for 1 min, hold the product for 1 min, and
     homogenize for an additional 1 min at the same speed.
   c) Examine the morphology and particle-size distribution of the emulsion under an
      optical microscope, record the data and determine the average particle size.

4. RESULTS AND DISCUSSION
4.1 Draw the shape of the oil droplets in the emulsion as observed under the microscope.
4.2 The particle-size results of the emulsions prepared with different emulsifiers and
    different methods are summarized in Table 1. Discuss the experimental results based
    on the theory of emulsion formation.

Table 1 Particle size results of the emulsions prepared with the manual and the mechanical
                                           method
Preparation method                     Manual method              Tissue homogenizer
Emulsifier                           Acacia   Tween 80    Soy Lecithin    Tween 80
Diameter of maximum particle (μm)

Diameter of most particle (μm)



5. QUESTIONS
   a) Which are the factors affecting the physical stability of an emulsion?
   b) How to select emulsifiers for the preparation of an emulsion?
   c) What are the process characteristics of the dry gum method and the wet gum method?

                                                                    (Tongying JIANG)



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