Evaluation of the effects of different ingredients on the characteristics of emulsion
Objectives:
1. To determine the effect of HLB surfactant on the emulsion stability.
2. To study the effect on physical and stability of the emulsion when the different amount of emulsifying agent have been used.
Introduction:
An emulsion is a liquid composed of two immiscible liquids mainly are oil and water, in which one liquid is dispersed in small globules throughout the other liquid. An emulsion usually consists of two distinct liquids called phases. One phase consists of tiny globules, known as dispersed phase. The other phase is the liquid surrounding the globules which is known as continuous phase. An emulsion usually consists of oil and water. When the oil is the internal phase and the water is the external phase, the emulsion is said to be an oil-in-water (o/w) emulsion. When the water is the internal phase and the oil is the external phase, it is water-in-oil (w/o) emulsion.
Emulsions are thermodynamically unstable systems. They tend to give phase separation after force is removed. However, by using appropriate emulsifying agent the interfacial tension can be decreased, and the stability of these systems can be significantly increased for the emulsion to stand mixing. Emulsifying agent can be divided into 3 types:
- hydrophilic colloid
- finely divided solid particles
- surface active agent or surfactant.
Surfactants can be classified using the HLB system established by Griffin. This system provides a scale of surfactant hydrophilicity (HLB value range from 1 to 20 which from most hydrophobicity to hydrophilicity). Generally, 2 emulsifying agents are usually used to form a stable emulsion preparation. The HLB value can be determine using the equation below:
In this experiment, different composition of Span 20 and Tween 80 are used and the HLB value of the different combination of these two emulsifying agents is determined using formula above. The different volume of emulsifying agents used is to determine the effect of each kind of emulsifying agents. Different HLB value give sifferent emulsifying effect.
Methods:
Part 1
1. First, 8 test tubes are labeled and 1cm from the bottom is marked at the tests tube.
2. 4ml of oil (referred to Table I) is mixed with 4ml of distilled water in the test tube.
3. Then, Span 20 and Tween 80 is added to the mixture according to the amount given in the Table II. The mixture is mixed using the Vortex mixing machine for about 45 seconds. The time taken for separation to occur until it reaches the 1cm marked is recorded. The HLB value for each sample is determined.
4. After that, a few drops of Sudan III solution is dripped into 1g of emulsion formed in the weighing boats and is spread. The colour dispersion is described and compared with other emulsion formulation. The emulsion is then observed under the light microscope. The structure and globule size are determined and drawn to compare with other emulsion.
Part 2
7. 2g of the sample before and after been homogenized is taken out and placed in the weighing boats. Sudan III solution is dropped into the emulsion. The texture, consistency, appearance of the oil and the color dispersion is determined and compared which is it is observed under the light microscope.
8. 15g of the emulsion that have been homogenized is taken and the viscosity is determined using the viscometer that has been calibrated using the “Spindle” LV-4 type. The sample is placed at 45oC water bath for about 15 minutes and at 4oC for another 15 minutes. The viscosity is then determined and recorded.
Determining viscosity
Results and observations:
Part 1
HLB of Span 20= 8.6
HLB of Tween 80= 15.0
Table 1a: The Time
Taken for Palm Oil Emulsion Separation to Occur until It Reaches 1cm
Table 1b: The Time
Taken for Arachis Oil Emulsion Separation to Occur until It Reaches 1cm
Table 1c: The Time
Taken for Olive Oil Emulsion Separation to Occur until It Reaches 1cm
Table 1d: The Time
Taken for Mineral Oil Emulsion Separation to Occur until It Reaches 1cm
Colour Spreading
Figure 1
According to figure 1,the spreading of
orange-red colour of Sudan III getting less evenly from weighing boat 1 to
weighing boat 8. At weighing boat 1, Sudan III mixed homogenously with the
emulsion and the colour appeared to be even. At weighing boat 8, Sudan III did
not mix very well with the emulsion. The emulsion colour was not even and
looked a bit reddish.
Shape and size of
globule formed
Figure 2
The HLB value of emulsion increased from tube
1 to tube 7. According to figure 2, with presence of surfactant, such as Span
20 and Tween 80, the globules appeared to be a regular shape of sphere. HLB
value of emulsion in tube 8 is 0, since there is no surfactant used. The shape
globule of emulsion in tube 8 in appeared to be irregular.
The higher the value of
HLB, the larger the size of globules formed. When HLB value is 0, the globule
size is big and unstable. Phase separation occurred very fast.
Table 2a: Viscosity of Emulsion I (20ml mineral oil)
Table 2b: Viscosity of
Emulsion II (25ml mineral oil)
Table 2c: Viscosity of
Emulsion III (30ml mineral oil)
Table 2d: Viscosity of
Emulsion IV (35ml mineral oil)
Table 2e: Different in Viscosity of Different Amount of Mineral Oil
Table 3: Separation
Phase Ratio of Various Oils
Discussion:
- What the HLB values that produce a
stable emulsion? Discuss.
Emulsifiers with HLB values ranging
from 3 to 6 will produce water-in-oil emulsions which are stable. On the other
hand, in order to produce oil-in-water emulsions which are stable, emulsifiers
with HLB values ranging from 8 to 18 should be used. For the HLB value between 7-9,
emulsifying agents normally act as wetting agent, while between 13-15, they act
as detergents, and value of 15-16, they are become solubilizing agent.
The
HLB value for each tube increase from tube 1 to tube 7. The surfactants used in
this experiment is Span 20 is basically the fatty acid esters of anhydro
sorbitols which are good oil soluble emulsifying agents and also Tween 80,
which a nonionic surfactant and emulsifier derived from polyethoxylated
sorbitan and oleic acid, and is often used in foods. A high HLB value of the
surfactant indicates strongly hydrophilic character while a low value is an
indication of a strong hydrophobic nature. Span 20 has HLB value of 8.6 while
tween 80 has HLB value of 15.
We can determine the stability of an
emulsion more easily from the separation phase time. Emulsion which has the
longest separation phase time is the most stable emulsion. A stable emulsion
contains emulsifying agents added that able to mix and stabilize the two phases
well for a very long time. From our experiment, a very short time (0.5 minutes)
is required to separate the two phases in test tube 8 because there is no
emulsifying agents added. In test tube 7 where there is only Tween 80, emulsion
that is formed is not stable as it contains shorter separation phase time (18minutes).
This shows that a combination of surfactants can give much better emulsifying
effect than they are used alone.
The time taken for
test tube 4 is 28 minutes, followed by test tube 5(29min) and 6 (15min).
However, for test tube 1, the time taken for the phase to separate is more than
50 minutes, for tube 2 (50min) and tube 3 (24min). This shows that the emulsion
in test tube 1 and 2 are much more stable due to the presence of more drops of
emulsifying agent. The longer time for test tube 1 can also be explained by the
hydrophobicity of span 20. Span 20 has a more hydrophobic character and a
higher concentration of span 20 in test tube 1 makes it to have a longer
separation time compared to the other test tube which has a lower amount of
span 20.
In
comparison with group 4 that use the same oil as our group, the time taken for
test tube 1, 2 and 3 are the same, in which the time taken for interphase to
reach 1 cm is more than 50 minutes. For test tube 4, the time taken is 84minutes
compared to what our group obtained is 28minutes. In short, the time taken for
interphase to reach 1 cm for group 8 is a little bit faster than group 4.
Some drops of Sudan
III solution is dropped into 1g of the emulsion. The color in tube 1 spreads with “difficulty”
(meaning spread slowly) than tube 2, 3, 4, 5, 6, 7 and 8. According to figure 1,the spreading of
orange-red colour of Sudan III getting less evenly from weighing boat 1 to
weighing boat 8. At weighing boat 1, Sudan III mixed homogenously with the
emulsion and the colour appeared to be even. At weighing boat 8, Sudan III did
not mix very well with the emulsion. The emulsion colour was not even and
looked a bit reddish.
Based
on the microscope at 4x10 lens, in test tube 1, 2 and 3, the droplet size in
the test tube is a binomial distribution. Most of the particles/droplets have
the same size and the distance between particle also near to each other. For
test tube 4, 5 and 6, the particles mostly have the same size and a little
apart from each other. But for test tube 7, the droplets is far from each other
and also bigger in size. While in test tube 8, the size is irregular and the
distance more far apart from each other.
2. Compare the physical nature or
mineral oil emulsion formed and give comments. What is Test Sudan III?
Compare the colour spread in the emulsion that formed and give comments.
The physical characteristics of mineral oil emulsion that will be discussed are the globule shape and size, texture, greasiness, consistency and dispersion before and after homogenization.
Before
homogenization, the globules are not in uniform size and are coarse. There has
a combination of small, intermediate and large size globules. However, the size
of globules becomes uniform after homogenization and all globules are in
smaller size. About the greasiness, the emulsion is greasy and less viscous
before homogenization due to the reason of unemulsified oil. However, the
emulsion becomes smoother and more viscous after homogenization. This is
because the sample tube is spun in the high rate and breaks the globules into
smaller sizes. Besides that, the emulsion is less consistent before
homogenization. However, the consistency of the emulsion increased and the
degree of greasiness decreased after homogenization because during
homogenization, forces are applied to the emulsion and thus it causes a better
emulsifying effect to take place. After adding Sudan test III solution, the
colour of the emulsions becomes milky. It shows good colour dispersion in the
emulsions.
Sudan test is a group of azo compound used as biological
stains for fat. It is used to show the shape and physical characteristic of
oily emulsion. It can differentiate which emulsion is oil-in-water emulsion or
water-in-oil emulsion by determining the amount of globules in red colour and
the colourless globules. Sudan solution is a red colour solution. It is
dissolved in oily phase of the emulsion. So, it will cause the oily globules
stain in red colour. The colour dispersion of the emulsions before
homogenization is not consistent. However after the homogenization,the colour
of dispersion is more consistent. Thus, the emulsion formed is considered as
o/w emulsion.
3. Plot and discuss
a. Graphs of emulsion viscosity
before and after heat exposure against various amounts of mineral oil
added.
b. Graph of viscosity difference against various amounts of mineral oil added.
From the
1st graph it shows that after each cycle of temperature change, the sample
shows an increase of viscosity. It is coincidence with the theory since the
theory stated the more mineral oil inserted, the more viscous it will be which
it means it’s more thicker and less ability to flow. From the 2nd graph, it
shows increase in the viscosity difference with increasing amount of mineral oil,
but it decrease when the amount of mineral oil is 35mL. This experiment was done to test the stability
of the emulsions and the name of this test is accelerated stability test which
is done by exaggerating the temperature fluctuations by heating it at usually
40°C followed by refrigeration or freezing. According to “Aulton’s
Pharmaceutics – The Design and Manufacture of Medicine” this process have been
used successfully since it can shows the instability evidently. As we know increasing
the temperature will cause an increase rate of creaming, making a decrease in
the rate of viscosity of the continuous phase. Increase in temperature will
also increase the kinetic motion. This effect on the disperse phase will enable
the energy barrier to be easily surmounted and thus the number of collisions
between globules will result in a coalescence or coagulation in certain
emulsifying agent. As for freezing, it will do the opposite which it will
reduce the rate of creaming and increase the viscosity by producing ice
crystals in the aqueous phase. When this process done in a cycle, this
continuation of melting and freezing of small ice crystals will disrupt the
adsorbed layer of emulgent at the oil/water interface and any weakness in the
structure will quickly become exposed.
Therefore
from this theory of testing, it shows that the higher percentage of increase in
the viscosity shows it is more unstable. From the data it shows the 30ml amount
mineral oil have the most increase percentage viscosity of 134.38% shows how
instable it’s structure has become. This is followed in descending order by
25ml, 20ml and 35ml. Considering personal error in compounding, it can be
ignored that the face 35ml mineral oil have lower increase in percentage than
30ml. From this experiment, we can conclude that the larger the amount of
mineral oil used, the higher the increase in percentage of viscosity which
means more unstable it is.
4. Plot and explain a graph of
separation phase after homogenize versus amount of turpentine oil.
Phase separation ratio is used to indicate
stability of an emulsion. A high ratio of phase separation will be resulted in
unstable emulsion which it will have two separated, unhomogenised phase. This
will cause uniformity of drug in the emulsion to be altered and inaccurate
dosage being administered.
Based on the graph plotted, separated phase
ratio of 20mL mineral oil emulsion and
25mL mineral oil emulsion are the same, then deccrease from 25mL mineral oil
emulsion to 35mL mineral oil emulsion.
Emulsion with 20mL mineral oil and
emulsion with 25mL mineral oil has highest separated phase ratio while
35mL mineral oil emulsion has lowest separation phase ratio.
According to theory, as the amount of oil increase,
the separated phase ratio will increase. This is because the added amount of
oily phase in emulsion has exceeded the oil amount at which stable emulsion is
formed. Separation will occur in faster rate.
Centrifuge
is used to separate an emulsion into its aqueous phase and oily phase. After
the centrifugation, the oily phase is above the aqueous phase. Ratio of
separation phase indicates the stability of an emulsion. The higher the ratio
of separation phase, the lower the stability of the emulsion. Therefore, a
stable emulsion will have a low ratio of separation phase. Compared to a
non-homogenous emulsion, a homogenous emulsion will not separate easily.
However the results obtained from graph do not follow
this theory. This may be due to several errors that occur during experiment.
For example, inaccuracy in measuring amount of oil before forming the emulsion,
insufficient homogenisation that has been carried out on emulsion or the height
of separated phase is not measured accurately. Besides, these
errors may be due to the method of preparation of emulsion, that is, the wet
gum method. May be some of the groups failed to produce good emulsions. This
will definitely affect the stability of emulsion which will then affect the
result of the experiment.
5. What are the
functions of each ing
Conclusion:
The HLB value of the surfactant used will affect the
stability of the emulsion formed. Stability of an emulsion depends both on the
volume of the oil phase and aqueous phase, together with the amount and
capacity of the emulsifying agent to function in the system. Homogenization
causes the reduction in size of the globules in the emulsion and the emulsion
formed is more homogenous and smooth.
References:
Aulton, M.E. Pharmaceutics: The science of dosage form
design. 2002, Edinburgh: Churchill Livingstone.