Nature And Concentration Of Emulsifying Agent

Published Date: 02 Nov 2017

Emulsion is a liquid dosage form of medication that involve two immiscible liquid phase to be dispersed as fine globule through one another system.

This formulation will help patients to get good medication that have even distribution of drug to achieve therapeutic effect. Before the formulation we need to plan what type of emulsion that we can make for example water in oil emulsion, oil in water emulsion, multiple emulsions and micro emulsion. The choice of emulsion will be give the recommended effect.

After we choose the type of emulsion then we will know the type of continuous phase that we will make either oil phase or aqueous phase. This continuous phase will determine the characteristic of the emulsion that the patient will feel for example feel on skin, appearance and others.

We also must consider the size of particle for the dispersed phase. The size of particle affects the distribution of the drug inside the continuous phase. Although the viscosity affect most in maintain the stability of the emulsion (because of movement restricted) but the particle size will give evenly distribution of drug (particle size small).

We also need to consider the type of surfactant that we need to use in our emulsion. The surfactant will make the oil and water blinding together as they will reduce the surface tension by laying a layer on the globule.

QUESTION 2: CHOICE OF EMULSION TYPE

Choice of emulsion type need to be considering many aspects that will influence the acceptance of the emulsion by the customer. Usually customer prefer the emulsion that will give comfortable effect to them rather than the emulsion that only give certain therapeutic effect to the problem that they got. That why some medicament customer or patient refuses to took them because of the taste, feel or the colour is interesting.

For example:

Oral administration that contain fat or oil.

This type of administration will use oil in water emulsion. In this form of emulsion the unpleasant taste can be mask by adding suitable flavor to the water systems.

Emulsion not only can be prepare only for the oral administration but also prepare for external purpose. Some examples of use of emulsion for external preparation are cream, lotion or liniment. This external emulsion can be preparing either in oil in water or water in oil depend on the effect that we want or the most preferable by the customer.

Oil in water emulsion

Mostly preferable by the customer because of the texture of these emulsion will give comfortable effect during the consuming period. The texture will not greasy although there are oil globules inside the continuous phase. These type emulsion also easily to wash as the continuous phase are water. So, this will give the pleasant usage by the customer

Water in oil emulsion

This type of emulsion usually used when we want to prevent the event of evaporation of the something from our skin. For example we had the hydrated skin that will make our skin loss more water. This is because of the characteristic of w/o emulsion is hardly washable by water. But the problems come out as the texture of these emulsion are greasy. But nowadays many customers are able to use this type of emulsion for example inside the moisturizing cream.

QUESTION 3: CHOICE OF OIL PHASE

Example of the oil phase medicament for oral administration:

Liquid paraffin

Castor oil

Cod liver oil

Arachis oil

Example of the oil phase medicament for externally application:

Turpentine oil

Benzyl benzoate

Mostly use of oil phase is liquid paraffin. There 3 types of liquid paraffin that is hard paraffin, soft paraffin and light liquid paraffin. This type of liquid paraffin can be use alone or by combination. This can be done to unsure that the product can be spread easily and can spread easily on the skin to form the coherent film. The film formation can be modified by adding some of emulgent for example waxes. So, this will prevent the irritant of the aqueous based by prevent the contact.

QUESTION 4: THE AQUEOUS PHASE

The aqueous phase is the phase that usually used in oral preparation. These because of the taste are more palatable. Although the water system as the continuous phase will contribute to the growth of microorganism so we need to add more ingredients that will suppress the growth of microorganism.

The microorganism tends to growing inside this medium because the microorganism only needs the water as the source.

Examples of emulgent that can be choose to use inside the water system:

Polymeric carbohydrate

Protein

Surfactant

Finely divided solid

QUESTION 5: VOLUME CONCENTRATION OF DISPERSED PHASE

The volume concentration of dispersed phase can be done using the Einstein equation to the behavior of emulsion. This equation will show the viscosity of the product as whole would be higher than viscosity of the continuous phase.

Equation of the Einstein equation:

E = E0 (1 + 2.5 V)

E: viscosity of suspension of solid spheres

E0: viscosity of the dispersion medium

V: volume in parts of a cubic centimeter occupied by the dispersed solid

We must make sure that the dispersed phase must not increase above 60%.

QUESTION 6: PARTICLE SIZE OF DISPERSED PHASE

If we want to increase the apparent viscosity of an emulsion is by reduction of the particle size or the globule diameter. This can be achieving by doing the homogenizing process. There are 2 mechanisms that will occur inside the system that are:

Smaller size of globule size can increase the chances to get the flocculation.

If the hydrophilic colloid is used as the stabilizer inside the emulsion system then it will form the film that will surround the dispersed molecule. As the size of the globule smaller so this will make the increase in the total surface area and this will cause many hydrophilic colloid be need to make the film surround the dispersed molecule. So, this will make the increment in the volume concentration of the dispersed phase.

QUESTION 7: VISCOSITY OF THE CONTINOUS PHASE

Viscosity of emulsion is related with the viscosity of the continuous phase. The viscosity of the continuous phase also related to the formation of the sedimentation on top or bottom of the preparation. For example, syrup and glycerol is the sweetening agent that will increase the viscosity of the system but there will be big differences in density of the two phases. So this will accelerate the time taken for the creaming.

So, we will use the emulsifying agent to stabilize the system by forming the film surround the globule. This also will cause the increase the viscosity of the continuous phase.

QUESTION 8: VISCOSITY OF THE DISPERSED PHASE

The dispersed phase should not more viscous than the continuous phase. This is because if the dispersed phase more viscous than the continuous phase the particle become heavy and the coalescence tend to happen. So this will lead to the formation of the creaming and caking.

QUESTION 9: CHOICE OF THE EMULSIFYING AGENT

Emulsifying agent that will be use in certain preparation depend on the route administration of the medication either oral, subcutaneous injection, intravenous injection or intramuscular injection and also depend on its toxicity.

Choose the appropriate emulsifying agent to certain medication must make sure following aspect:

We must to make sure that the emulsifying agent that used less or not irritant to the patient. Irritant effect will make the patient doesn’t want to take because the effect will make patient feel uncomfortable.

Mostly non-ionic emulsifiers are less irritant and less toxic compare to anionic and cationic.

Example of emulsifier that has irritant effect is ionic emulsifying agent. This agent should not give orally due to the irritant effect in GI tract.

Choosing the emulsifying agent also need to check with the HLB value. This to make sure that the emulsifying agent can soluble in that medication.

For example:

Oil in water system

Use emulsifying agent that can soluble in water system. Usually substances that contain HLB more than 10 can dissolve in water system. If HLB 20 is 100% hydrophilicity.

Water in oil system

Use emulsifying agent that can soluble in oil system. Usually substances that contain HLB less than 10 can dissolve in oil system.

QUESTION 10: NATURE AND CONCENTRATION OF EMULSIFYING AGENT

Addition of the emulsifying agent to oil in water emulsion will decrease the surface tension at the surface by forming the monolayer film and parallel to that event it also will increase the viscosity of the emulsion. The emulsifying agent will form the mono layer film by condense its structure and influence the degree of flocculation.

QUESTION 11: IDEAL EMULSIFYING AGENT

Emulsifying agent criteria must be full fill to make sure that preparations are in good condition:

The agent that is taken must not have toxic effect especially when the emulsion is taken orally.

The agent that is used must not have allergy reaction especially when applied to the skin.

The agent that is used must be able to form coherent film around the dispersed globule. This to make sure the stability of the emulsion that will be produce as all the globule are surround by the film.

The agent that is taken must be able to reduce the surface tension between the two immiscible liquid. The surface tension reduce will make dispersed phase to miscible in continuous phase. Reduce in surface tension does not mean increase in viscosity.

The agent also must be capable to give increase in viscosity. This is because the higher the viscosity will increase the stability if the preparation. This higher viscosity will make the movement of the globule inside the system are slow. So, the formation of creaming, caking are much slower than usual.

The agent that is used must be chemically stable. This due to the interaction between the emulsifying agent and drug.

The agent that are used must have good odour and taste and cheap. These criteria can make sure that the acceptance of the emulsion if there are good taste and odour. Furthermore, the price is cheap so many industry can make more profit and can sell at reasonable price. So, many people can have the benefit.

QUESTION 12: FORMULATION BY HLB METHOD

Hydrophilic-lipophilic balance (HLB) is the value of the portion of hydrophilic and lipophilic that can be use to make two immiscible liquid to become miscible for example in oil and water system. This emulsifying agent will reduce the surface tension between systems by forming layer at the surface.

HLB value calculation:

HLB =

Hydrophilic portion of surfactant is a condensed ethylene oxide chain

HLB =

Hydrophilic portion of surfactant contain ethylene oxide chain and polyhydric alcohol in molecule

HLB =

Have analytical data

HLB = ( ) 20

HLB = 7 + hydrophilic group number – lipophilic group number

The HLB scales are range from 0 until 20. The higher the value of the HLB they become more hydrophilicity. 0 indicate 100% lipophilicty while 20 indicate 100% hydrophilicity. So, if the continuous phases are water the HLB values that must use are higher while if the continuous phase are oil the HLB value that must used are lower.

QUESTION 13: OTHER FORMULATION ADDITIVES

Additive that is added to the formulation will make the formulation become more stable and have good appearance for example taste and colour.

Buffers

The addition of the buffer to the emulsion make the emulsion to have greater chemical stability can control the tonicity and great physiological compatibility. Although adding this will make the chemical stability increase and addition of the electrolyte to the emulsion also will affect the physical stability.

Density modifiers

Density of the emulsion can be determining using stroke law that will determine the density of both continuous phase and dispersed phase. In the emulsion system the density of the both phase must be differ to avoid sedimentation and creaming. The modification can be made by addition of the glucose, dextrose, glycerol and propylene.

Humectants

Addition of material that will decrease the evaporation of the water either from the pack product when the closure is open and evaporation from the external application. For the external preparation the high concentration of humectants must be use to remove the moisture form skin.

Antioxidant

Addition of the antioxidant is to prevent the medication from react with oxygen when they are in contact. This because the oxidation of the product may cause the chemically instability. Example of antioxidant that have been use are butylated hydroxyanisole (BHA),butylated hyroxytoluene, propyl, octyl,and dedocyl ester.

Flavor, colour, and perfume

This type of additives are add to the emulsion to make sure that the acceptance from consumer will increase when the bitter taste the colourful colour of the froduct will attract the consumer attract and confidence with that kind of medication.

Sweetening agent

High concentration of the sweting agent for example sucrose, sorbitol, or glycerol will exhibit the Newtonian propreties and may give effect to the rheologically.

QUESTION 14: EVALUATION OF EMULSION AND STABILITY TESTING OF EMULSION

The emulsion can be evaluated by stability testing. There are the scopes of the emulsion that can be used to be test that are:

Degree of creaming can be done by doing the test of the macroscopic examination

The macroscopic examination is carried out by calculate the ratio of the creaming inside the product and will be compare with other product.

Determine the globule size and the changes in the distribution of globule size with time by particle size analyzer.

In this test the size of globule will be measure. As the size of the globule increase these show that the coalescence occurs.

Determination of specific interfacial area, which is the surface area / mass or surface area/ volume of globule of an aging emulsion by viscosity changes.

The viscosity change can be detected when there are formations of the creaming or caking.

Measurement of life time of a number of drop at oil-water interface

Storage at adverse effect by exposing to extreme variation of temperature

The emulsion will be place at many type of temperature for example elevated temperature. How will it affect the system of the emulsion.

Check creaming by centrifuge at 200- 300rpm

This method is to check whether when there is too much movement that mean when the bottle of medicament will undergoes harsh condition what will be the rate of sedimentation and creaming.