Title
Characterisation
of Emulsion Formulations
Objective
To
determine:
1. The effects of HLB surfactant on the
stability of the emulsion.
2. The effects of different oil phases used
in the formulation on the physical characteristics and stability of the
emulsion.
Introduction
Emulsion is can be defined as a disperse system which contains at least
two immiscible liquids where one of them (internal/dispersed phase) is
dispersed homogenously in another liquid (external/continuous phase). Water and
oil are usually used in pharmaceutical formulation as the dispersed phase and
continuous phase. In general, emulsion can be categorised into 2 types,
oil-in-water emulsion (o/w) and water-in-oil emulsion (w/o). Emulsion is not
stable thermodynamically due to the high surface tension between the two phase.
Emulsifying agent is used to stabilised the stabilized the emulsion. The HLB
method (hydrophilic-lipophilic balance) is used to determine the quantity and
type of surfactant that is needed to prepare a stable emulsion. HLB scale which
is from 1 (lipophilic) to 20 (hydrophilic) is given to each surfactant. HLB
value need to be calculated as usually a combination of 2 emulsifying agent is
used to form a more stable emulsion.
HLB value for a combination of emulsifying agents can be
determined by using the following formula:
|
HLB value =
|
(quantity surfactant 1)(HLB surfactant 1) +(
quantity surfactant 2)(HLB surfactant 2)
|
|
Quantity surfactant 1 + quantity surfactant
2
|
Apparatus
8 Test
tubes
1 set of 5ml pipette and bulb
A 50ml
measuring
cylinder
1 50ml beaker
2 sets of
pasture pipettes and
droppers A
15ml centrifugation tube
Vortex mixer Centrifugation
apparatus
Weighing
boat Viscometer
1 set of mortar
and
pestle Water
bath (45°C)
Light
microscope Refrigerator
(4°C)
Microscope
slides
Materials
Palm oil Span
20
Arachis
oil Tween
80
Olive
oil
Sudan III solution (0.5%)
Mineral
oil
Distilled
water
Procedures
1. Each test tube is labelled
and marked 1cm from the base of the test tube.
2.
4ml of oil (according to table 1) and 4ml of distilled water are mixed
into
the test tube.
Table 1
|
Group
|
Oil
|
|
1, 5
|
Palm oil
|
|
2, 6
|
Arachis oil
|
|
3, 7
|
Olive oil
|
|
4, 8
|
Mineral oil
|
3. Span 20 and Tween 80 is added into the mixture of oil
and water (refer Table 2). The test tube is closed and its content is mixed
with vortex mixer for 45 seconds. The time taken needed for the interface to
reach 1cm is measured. The HLB value for each sample is determined using
the formula. Step 1-3 is repeated in order to obtain an average HLB
value of a duplicate.
Table 2
|
Tube no.
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
|
Span 20 (drops)
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
|
Tween 80 (drops)
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
4. A few drops of Sudan III solution is dropped to (1g)
emulsion formed in a weighing boat and mixed homogenously. The spread of the
colour in the sample is compared. Some of the sample is spread on a microscope
slide and observed under light microscope. The appearance and globule size
formed is observed and draw.
5. A
Mineral Oil Emulsion (50g) is prepared from the formulation below by using wet
gum method according to Table 3a & 3b:
Table 3a
|
Mineral Oil
|
(refer Table
3b)
|
|
Acacia
|
6.25 g
|
|
Syrup
|
5 ml
|
|
Vanillin
|
2 g
|
|
Alcohol
|
3 ml
|
|
Distilled water qs
|
50 ml
|
Table 3b
|
Emulsion
|
Group
|
Mineral Oil
(ml)
|
|
I
|
1,5
|
20
|
|
II
|
2,6
|
25
|
|
III
|
3,7
|
30
|
|
IV
|
4,8
|
35
|
6. 40g
of emulsion is placed into a 50ml beaker and homogenized for 2 minutes using a
vortex mixer.
7. 2g of emulsion (before and after
homogenization) is taken and placed into a weighing boat and labelled. A few
drops of Sudan III solution is added and mixed. The texture, consistency,
degree of oily appearance and the spreading of colour in the sample under the
light microscope is observed.
8. The viscosity of the emulsion formed after homogenization (15g in 50ml
beaker) using a viscometer that is calibrated with “Spindle” type LV-4. The sample
tis exposed to 45°C (water bath) for 15 minutes and then to 4°C (refrigerator)
for another 15 minutes. After the exposure to the temperature cycle is
finished and the emulsion had reached room temperature (10-15 minutes), the
viscosity of the emulsion is determined. Step 8 is repeated again to
obtain an average value.
RESULTS:
ARACHIS OIL
|
Tube No.
|
Span 20
(Drops)
|
Tween 80
(Drops)
|
HLB Value
|
Time For
Phase Separation (min)
|
||
|
T1
|
T2
|
Average
|
||||
|
1
|
15
|
3
|
9.66
|
47.22
|
43.18
|
45.20
|
|
2
|
12
|
6
|
10.73
|
41.58
|
36.96
|
39.27
|
|
3
|
12
|
9
|
11.34
|
40.61
|
34.49
|
37.55
|
|
4
|
6
|
9
|
12.44
|
28.47
|
29.11
|
28.79
|
|
5
|
6
|
15
|
13.17
|
19.38
|
19.00
|
19.19
|
|
6
|
3
|
18
|
14.08
|
10.69
|
8.25
|
9.47
|
|
7
|
0
|
15
|
15.00
|
7.34
|
5.16
|
6.25
|
|
8
|
0
|
0
|
0.00
|
5.12
|
4.94
|
5.03
|
Emulsion I (Mineral Oil 20 mL )
|
Before
homogenization
|
After homogenization
|
|
|
Texture
|
Course and
not homogenous
|
Smooth and
even looking, homogenous
|
|
Consistency
|
Less
consistent
|
More
consistent
|
|
Degree of
oily appearance
|
More oily
and globules
|
Less oily
and globules
|
|
Spreading of
colour
|
Spread
evenly
|
Spread
evenly
|
Table
2.1
Emulsion II (Mineral Oil 25 mL )
|
Before
homogenization
|
After
homogenization
|
|
|
Texture
|
Coarse
|
Smooth
|
|
Consistency
|
Less
consistent, more dilute
|
More
consistent, more viscous
|
|
Degree of
oily appearance
|
More oily,
spherical globule
|
Less oily, spherical
globule
|
|
Spreading of
colour
|
Spread
evenly
|
Spread
evenly
|
Table
2.2
Emulsion III (Mineral Oil 30 mL )
|
Before
homogenization
|
After
homogenization
|
|
|
Texture
|
Course and
not homogenous, cloudy
|
Milky,
smooth, homogenous
|
|
Consistency
|
Not consistent,
less viscous
|
Consistent,
more viscous
|
|
Degree of
oily appearance
|
Greasier,
more globules
|
Less greasy,
less globules
|
|
Spreading of
colour
|
Unevenly
distributed color, less red spot
|
Evenly
distributed, more red spot
|
Table
2.3
Emulsion IV (Mineral Oil 35 mL )
|
Before
homogenization
|
After
homogenization
|
|
|
Texture
|
Not
homogenous, course and less milky
|
Homogenous,
smooth and more milky
|
|
Consistency
|
Not
consistent, less viscous
|
Consistent
and more viscous
|
|
Degree of
oily appearance
|
More greasy
and more globules
|
Less greasy
and less globules
|
|
Spreading of
colour
|
Unevenly
distributed
|
Evenly
distributed
|
Table
2.4
Viscosity of Emulsion II (Mineral Oil 25
mL )
|
Readings
|
Viscosity (cP)
|
Average
|
|||||
|
1
|
2
|
3
|
4
|
5
|
6
|
||
|
Before
Temperature cycle
|
1728
|
1578
|
1440
|
1128
|
1026
|
972
|
1312
|
|
After
temperature cycle
|
1524
|
1290
|
1200
|
1326
|
1314
|
1200
|
1309
|
|
Difference (%)
|
(1312 – 1309) / 1312 X 100% = 0.23 %
|
||||||
Table
2.5
Average viscosity of all the emulsion.
|
Readings
|
Average
Viscosity (cP)
|
|||
|
Emulsion I
|
Emulsion II
|
Emulsion III
|
Emulsion IV
|
|
|
Before
Temperature cycle
|
1826
|
1312
|
1312
|
768
|
|
After temperature cycle
|
4689
|
1309
|
1450
|
452
|
|
Difference (%)
|
61.06
|
0.23
|
10.52
|
69.91
|
Table
2.6
|
Mineral Oil(ml)
|
Ratio of
separation phase
|
Average
|
Ratio of separation phase
|
||
|
20
|
2.7
|
2.9
|
2.80
|
2.8/4.6 = 1.61
|
|
|
25
|
2.6
|
4.0
|
3.30
|
3.3/5.0 = 0.66
|
|
|
30
|
3.0
|
2.0
|
2.50
|
2.5/4.0 = 0.63
|
|
|
35
|
3.7
|
3.2
|
3.45
|
3.45/5.0 = 0.69
|
|
Table
2.7
Discussion
The HLB method is used to determine
the quantity and type of surfactant that is needed to prepare a stable
emulsion. The experiment that we have done has clearly shown the effects of HLB
surfactant on the stability of the emulsion. Emulsifier with low HLB value
(below 9.0) is lipophilic in character whereas the one that is hydrophilic in
nature possesses a high HLB value (above 11.0). Those with a HLB value in
between 9-11 are intermediate.
Emulsion is a mixture of water and oil, hence emulsifier, preferably those with low HLB value, is required for the emulsion to stay in one phase. This is proven by result of the experiment, which shows that with an increase in HLB value of surfactant, the average time for phase separation has registered a decreasing trend. Other than that, when the HLB value is zero, that is when no surfactant was added, the average time for phase separation is shortest.
Therefore, based on the result of the experiment, the addition of HLB surfactant improves the stability of the emulsion, and by lowering the HLB value of surfactants, a more stable emulsion will be obtained.
For
the second part, we proceed to prepare mineral oil emulsion using different
amount of mineral oils by wet gum method. Since mineral oil is more
viscous than water, thus, the higher the amount of oil, the more viscous the
emulsion will be. Several excipients are used to ensure the consistency of
emulsion. Acacia acts as surfactant to ensure the dispersed phase and
continuous phase do not break easily. Alcohol is used as antimicrobial agent to
prevent growth of microorganism and prolong the storage duration. Syrup helps
to increase viscosity and retard the diffusion of molecules to merge against
each other.
The purpose of
homogenization is to homogenize two immiscible liquid into a smooth emulsion by
making the droplets into extremely small particles dispersed evenly in the
continuous phase. In this experiment, homogenization plays it role by further
breaking the droplets into extremely small droplets. The unstable emulsion will only become stable after the
homogenization because vibration force applied to the big globules can break
them into smaller globules which is more stable.
Sudan III solution is
added to the emulsion to act as a dye which color the oil phase to give a
better view under the microscope. From the result obtained, in general, the texture of all the four emulsions will
become smooth and more consistent, less oily and the more viscous after
homogenization. Emulsion II show smoother appearance after
homogenizing compared to before. Size of droplet after homogenizing is smaller
than before. Emulsion II becomes less oily and more viscous after
homogenization. Spreading of color are evenly distributed for both before and
after which means the oil phase is well dispersed, making the emulsion II an
ideal emulsion.
The temperature cycle is used to test the physical
stability of the emulsion by passing through the emulsion in water bath of 45 Degree
Celsius for 30 minutes and then keeping it in the freezer for the next 15
minutes. Temperature cycle were repeated 6 times to obtain the average viscosity
of emulsion for before and after. Both average viscosities are used
to calculate the differences. Theoretically, the most stable emulsion
has the lowest difference. According to the result obtained, we can see
emulsion II (emulsion with 25ml mineral oil) has the smallest percentage
difference (%) of viscosity between before cycle and after cycle which is
0.23%. Emulsion III has the second lowest difference (%) which is 10.52%.
Emulsion I and emulsion IV have 61.06% and 69.91% difference respectively. From
the results, we can conclude that Emulsion II has the highest stability and
less change in chemical and physical properties compared to other emulsions.
Rate of sedimentation is
used to check the stability of emulsion. The emulsion is put into centrifuge
tube for 10 minutes, at 25 Degree Celsius. Through centrifugation,
the ratio of separation can be calculated. If the ratio of separation is high,
the emulsion has lower stability. Based on table 2.7, emulsion II and emulsion
III has the lowest ratio of separation which is 0.66 and 0.63. Thus, both
emulsions have higher stability than the other emulsions.
Several
precaution steps are needed to consider during the experiment. Firstly, the
emulsion should be mixed homogenously by using mortar and pestle. Second, the
emulsion should be stirred well before testing its viscosity. The rotor at the
viscometer should be rinsed before being dipped into another emulsion to
prevent any error in viscosity reading. Besides, eyes must be perpendicular to
measuring cylinder’s reading to prevent any parallax error.
Conclusion
From
the experiments conducted, it is found that the HLB surfactant
improves the stability of the emulsion. The lower the HLB value of surfactants,
the more stable the emulsion will be. Emulsion with 25 mL of mineral oil, in
this case is Arachis oil has the smoothest appearance compared to three other.
It has the lowest difference in the average viscosities and lowest rate of
sedimentation, proving its high stability.
References
1.
Pharmaceutical
Practise, A.J. Winfield, J.A. Ress,I.Smith, 4th Edition
2. Collett,
D.M. & Aulton, M.B. 1990. Pharmaceutical practice. Ed. Ke-32, Edinburgh:
Churchill
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