PHARMACEUTICAL TECHNOLOGY II
NFNF 2263
SEMESTER 2
SESSION 2012/2013
LAB REPORT 1
TITLE: ASSESSMENT OF THE EFFECTS OF DIFFERENT COMPOSITIONS
OF INGREDIENTS USED ON THE CHARACTERISTICS OF AN EMULSION FORMULATION
NAME:
LIM ANNE YEE (A131494)
LIM GUCCI (A136085)
LIM ZEN HUEI (A136194)
THE THIAN SIANG (A136169)
PUTERI EFFY NASTASHEA BINTI HOSLAM (A136042)
LECTURER: DR. NG
SHIOW FERN
DATE: 11/3/2012
FACULTY OF PHARMACY
UNIVERSITI KEBANGSAAN
MALAYSIA
Title
Assessment of the Effects of Different Compositions of Ingredients Used
on the Characteristics of an Emulsion Formulation.
Objective
To determine:
1.
The
effects of HLB surfactant on the stability of the emulsion
2.
The
effects of different emulsifying agent used in the formulation on the physical
characteristics and stability of the emulsion
Introduction
Emulsion is a 2 phase system that is not stable thermodynamically. It
contains at least 2 immiscible liquids where one of them (internal/dispersed
phase) is dispersed homogenously in another liquid (external/continuous phase).
Emulsion can be categorised into 2 types, oil-in-water emulsion (o/w) and
water-in-oil emulsion (w/o). Emulsion is stabilised by adding emulsifying
agent. Emulsifying agent can be divided into 3 types: (1) hydrophilic colloid,
(2) finely divided solid particles, (3) surface active agent or surfactant.
The HLB method
(hydrophilic-lipophilic balance) is used to determine the quantity and type of
surfactant that is needed to prepare a stable emulsion. Every surfactant is
given a number in the HLB scale, that is, from 1 (lipophilic) to 20
(hydrophilic). 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 and Material
a. 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 Coulter
counter apparatus
Weighing boat Centrifugation
apparatus
1 set of mortar and pestle Viscometer
Light microscope Water
bath (45°C)
Microscope slides Refrigerator
(4°C)
b. Materials
Palm oil Span
20
Arachis oil Tween
80
Olive oil Sudan
III solution (0.5%)
Mineral oil ISOTON III solution
Distilled water
Procedures
1. Each test tube is labelled and marked 1cm straight line from the bottom
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 are added into the mixture of oil and water (refer
Table II). The test tube is closed and its content is mixed with vortex mixer
for 45 seconds. The time needed for the interface to reach 1cm line is
recorded. The HLB value for each sample is determined.
Table II
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
|
·
Palm Oil:-
Tube number
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Span 20 (drop)
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
Tween 80 (drop)
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
HLB Value
|
9.667
|
10.733
|
11.343
|
12.44
|
13.171
|
14.086
|
15
|
0
|
Time taken for
interphase to reach 1cm- Group 1 (minute)
|
*
|
*
|
*
|
58
|
61
|
45
|
25
|
0.5
|
Time taken for interphase
to reach 1cm- Group 5 (minute)
|
*
|
*
|
*
|
16
|
30
|
39
|
16
|
7
|
Average time
(minute)
|
*
|
*
|
*
|
37
|
45.5
|
42
|
20.5
|
3.75
|
Stability
|
Most stable
|
Most stable
|
Most stable
|
Intermediate
|
Intermediate
|
Intermediate
|
Less stable
|
Least stable
|
*Interphase did not reach 1cm after
120 minutes
·
Arachis Oil:-
Tube number
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Span 20 (drop)
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
Tween 80 (drop)
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
HLB Value
|
9.667
|
10.733
|
11.343
|
12.44
|
13.171
|
14.086
|
15
|
0
|
Time taken for
interphase to reach 1cm- Group 2 (minute)
|
12
|
76
|
82
|
27
|
40
|
55
|
19
|
9
|
Time taken for
interphase to reach 1cm- Group 6 (minute)
|
*
|
*
|
*
|
38
|
49
|
61
|
19
|
25
|
Average time
(minute)
|
66
|
98
|
101
|
32.5
|
44.5
|
58
|
19
|
17
|
Stability
|
Intermediate
|
Most stable
|
Most stable
|
Less stable
|
Intermediate
|
Intermediate
|
Least stable
|
Least stable
|
*Interphase did not reach 1cm after
120 minutes
**To find the average for the time
taken, if the interphase did not reach 1cm after 120 minutes, the time taken is
just assumed to be 120 minutes.
·
Olive Oil:-
Tube number
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Span 20 (drop)
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
Tween 80 (drop)
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
HLB Value
|
9.667
|
10.733
|
11.343
|
12.44
|
13.171
|
14.086
|
15
|
0
|
Time taken for
interphase to reach 1cm- Group 3 (minute)
|
*
|
*
|
8
|
14
|
87
|
58
|
19
|
0.5
|
Time taken for
interphase to reach 1cm- Group 7 (minute)
|
*
|
*
|
*
|
*
|
63
|
*
|
45
|
2.5
|
Average time
(minute)
|
*
|
*
|
64
|
67
|
75
|
89
|
32
|
1.5
|
Stability
|
Most stable
|
Most stable
|
Intermediate
|
Intermediate
|
Intermediate
|
Stable
|
Least stable
|
Least stable
|
*Interphase did not reach 1cm after
120 minutes
**To find the average for the time
taken, if the interphase did not reach 1cm after 120 minutes, the time taken is
just assumed to be 120 minutes.
·
Mineral Oil:-
Tube number
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Span 20 (drop)
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
Tween 80 (drop)
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
HLB Value
|
9.667
|
10.733
|
11.343
|
12.44
|
13.171
|
14.086
|
15
|
0
|
Time taken for
interphase to reach 1cm- Group 4 (minute)
|
119
|
114
|
108
|
94
|
80
|
34
|
8
|
0.5
|
Time taken for
interphase to reach 1cm- Group 8 (minute)
|
*
|
50
|
24
|
28
|
29
|
15
|
18
|
0.5
|
Average time
(minute)
|
119.5
|
82
|
66
|
61
|
54.5
|
24.5
|
13
|
0.5
|
Stability
|
Most stable
|
Stable
|
Intermediate
|
Intermediate
|
Intermediate
|
Less stable
|
Least stable
|
Least stable
|
*Interphase did not reach 1cm after
120 minutes
**To find the average for the time
taken, if the interphase did not reach 1cm after 120 minutes, the time taken is
just assumed to be 120 minutes.
1. A few drops of Sudan III solution is added to some (1g) emulsion formed
in a weighing boat and mixed homogenously. The spread of the colour in the
sample is stated and compared. Some of the sample is spread on a microscope slide
and observed under light microscope. The appearance and globule size formed is
drawn, stated and compared.
Magnification (40x10)
|
Physical appearance
|
Colour distribution
|
Test tube 1
 |
Water droplets dispersed in oil. This is water in oil emulsion. This
emulsion is not dispersing very well due to error.
|
Sudan III colour dispersed in the emulsion. The emulsion stained light
orange.
|
Test tube 2
 |
Water droplets dispersed better in oil. This is water in oil emulsion.
HLB value of the emulsion in this test tube is not in the optimum range.
|
Sudan III colour dispersed in the emulsion. The emulsion stained light
orange.
|
Test tube 3
 |
Water droplets dispersed best in oil. This is water in oil emulsion.
Only one drop of water in oil. However, the HLB value of the emulsion in this
test tube is not in the optimum range.
|
Sudan III colour dispersed in the emulsion. The emulsion stained light
orange.
|
Test tube 4
 |
Sudan III colour dispersed in the emulsion. The emulsion stained light
orange.
|
|
Test tube 5
 |
Water droplets are not properly dispersed in oil. HLB value of the
emulsion in this test tube is not in the optimum range.
|
Sudan III colour dispersed in the emulsion. The emulsion stained light
orange.
|
Test tube 6
 |
Water droplets are not properly dispersed in oil. HLB value of the
emulsion in this test tube is not in the optimum range.
|
|
Test tube 7
 |
Water droplets are not properly dispersed in oil. HLB value of the
emulsion in this test tube is not in the optimum range.
|
Sudan III colour dispersed in the emulsion. The emulsion stained light
orange.
|
Test tube 8
 |
The emulsion is totally not formed without surfactant, phase
separation occur very fast.
|
Sudan III does not disperse in the emulsion, globules of Sudan red
form on surface of emulsion.
|
5. A Mineral Oil Emulsion (50g) is prepared from the formulation below by
using wet gum method:
Mineral Oil
|
(refer Table III)
|
Acacia
|
6.25 g
|
Syrup
|
5 ml
|
Vanillin
|
2 g
|
Alcohol
|
3 ml
|
Distilled water qs
|
50 ml
|
Table
III
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 formed is put into a 50ml beaker and homogenization is
done for 2 minutes using a homogenizer.
7. Some (2g) of emulsion formed is taken (before and after homogenization)
and put into a weighing boat and labelled. A few drops of Sudan III solution
are added and mixed. The texture, consistency, the degree of oily appearance
and the spreading of colour in the sample is stated and compared under the
light microscope.
Group 1 and 5
Description
|
|
Before homogenization
|
Texture: coarse, less milky
Consistency: not consistent, less viscous
Degree of greasiness: more greasy, more globules
Shape: spherical globules
Size: bigger and not uniform size
Colour dispersion: unevenly dispersed, less red spot
|
After homogenization
|
Texture: smooth, milky
Consistency: consistent, more viscous
Degree of greasiness: less greasy, less globules
Shape: spherical globules
Size: smaller and uniform size
Colour dispersion: evenly dispersed, more red spot
|
Group 2 and 6
Description
|
|
Before homogenization
|
Texture: not evenly (oil phase can be observed clearly), mliky
Consistency: not consistent
Degree of greasiness: greasy, many globules
Shape: spherical globules
Size: uneven and big
Colour dispersion: unevenly dispersed
Viscosity: less viscous
|
After homogenization
|
Texture: even (oil phase is not clear or almost
disappear), yellowish
Consistency: consistent
Degree of greasiness: less greasy
Shape: spherical globules, less globules
Size: small (nearly cannot observed)
Colour dispersion: evenly dispersed, more red spot
Viscosity: more viscous
|
Group 3and 7
Description
|
|
Before homogenization
|
Texture: coarse and not homogenous, cloudy,yellowish
Consistency: not consistent, less viscous
Degree of greasiness: more greasy, more globules
Shape: spherical globules
Size: large globules far from each other and of
different sizes
Colour dispersion: unevenly dispersed, less red spot
|
After homogenization
|
Texture: smooth and homogenous, milky
Consistency: consistent, more viscous
Degree of greasiness: less greasy
Shape: spherical globules
Size: smaller and uniform size
Colour dispersion: evenly dispersed, more red spot
|
Group 4 and 8:
Description
|
|
Before homogenization
 |
Texture: smooth, cloudy
Consistency: not consistent, less viscous
Degree of greasiness: very greasy, more globules
Shape: spherical globules
Size: not uniform in size, large and small globules
(predominantly large globules)
Colour dispersion: unevenly dispersed, less red spot
|
After homogenization
 |
Texture: smooth, milky
Consistency: consistent, more viscous
Degree of greasiness: less greasy, less globules
Shape: spherical globules
Size: small globules only and uniform in size
Colour dispersion: evenly dispersed, more red spot
|
8. The viscosity of the emulsion formed after homogenization (15g in 50ml
beaker) is determined using the viscometer that is calibrated with “Spindle”
type LV-4. The sample is then exposed to 45°C (water bath) for 30 minutes and
then to 4°C (refrigerator) for another 30 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.
For 35ml of Mineral Oil
Readings
|
Viscosity (cP)
|
Average + SD
|
|||||
1
|
2
|
3
|
4
|
5
|
6
|
||
Before Temperature cycle
|
740
|
820
|
920
|
650
|
650
|
600
|
730 + 121.66
|
After temperature cycle
|
900
|
920
|
960
|
300
|
300
|
300
|
613.33 +
343.78
|
Difference (%)
|
15.98%
|
||||||
9. 5g of homogenised emulsion is put
into a centrifugation tube and centrifuged (4500 rpm, 10 minutes, 25°C). The
height of the separation formed is measured and the ratio of the height
separation is determined.
Mineral Oil(ml)
|
Ratio of
separation phase
|
Average
|
Ratio of
separation phase
|
||||
20
|
Group 1
|
0.6122
|
Group 5
|
0.7291
|
0.6707
|
0.0585±0.6707
|
|
25
|
Group 2
|
0.7826
|
Group6
|
0.5128
|
0.6477
|
0.1349±0.6477
|
|
30
|
Group 3
|
0.7000
|
Group7
|
0.7400
|
0.7200
|
0.0200±0.7200
|
|
35
|
Group 4
|
0.5800
|
Group8
|
0.6667
|
0.6234
|
0.0434±0.6234
|
|
Discussion:
1. What are the values of HLB that will yield
a stable emulsion? Discuss.
HLB (Hydrophile-Lipophile Balance)
method is a way that utilizes the ratio of hydrophobic
to the lipophilic portion of a molecule. An emulsifier that is lipophilic in character is assigned a low HLB value (below
(9.0) and one that is hydrophilic in character
is assigned a high HLB value (above 11.0). Those in between 9-11 are intermediate. The HLB method applies to
non-ionic (uncharged) surfactants. Since emulsion
is a mixture of water and oil, it need an emulsifying agent for the emulsion to
stay in one phase and not separated
during after the process of manufacturing until it reach and use by the consumers. Stable emulsions may be obtained
with emulsifier with lower HLB
values because most probably the higher emulsifier concentration resulting in viscous emulsion and thereby, the rate of
creaming is retarded. Based on the experiment, the
time taken for the emulsion to separate into two phases and for the interphase
to reach the marked height is longer when
the HLB value is at the lowest compared to the higher HLB values. When the HLB values is zero, meaning that no
emulsifying agents are added, the
time taken to separate into two phases is less than one minute which shows that
water and oil can stay in the same
phase without any use of emulsifying agent. Although not all the results from the experiment
shows this type of stability, but majority of the result seems to provide proof for this statement. The
inconsistency may be caused by error in handling
and mixing of the substances used in the experiment by the person in charge. Type of oil also may play an important role in
determining the stability of the emulsion. As
we can see from the result, the emulsion containing palm oil seems to be more
stable compared when other types of
oils are used. Therefore, the conclusion is that the more stable an emulsion is, the longer time
it takes to separate out into two phase.
2. Compare the physical appearance of the mineral oil emulsions produced and give your comments. What is Sudan III test? Compare the colour dispersion in the emulsions produced and give your comments.
2. Compare the physical appearance of the mineral oil emulsions produced and give your comments. What is Sudan III test? Compare the colour dispersion in the emulsions produced and give your comments.
In this experiment, four types of mineral
oil (turpentin oil) emulsions are prepared using different contents of mineral oil. Emulsion I contains 20ml of
mineral oil, Emulsion II contains 25
ml of mineral oil, Emulsion III contains 30ml of mineral oil while Emulsion IV contains 35ml of mineral oil.
Before homogenization,
no emulsion is formed. In general, Emulsion Ι, ΙΙ, ΙΙΙ and ΙV have a coarse and
non homogenous texture before homogenization. However, the emulsions produced
after homogenization is smooth and homogenous. Before homogenization, the
Emulsion Ι, ΙΙ, ΙΙΙ and ΙV are not consistent. There is a tendency for phase
inversion to occur. However, the emulsions produced after homogenization is
more consistent and stable. Besides that, Emulsion Ι, ΙΙ, ΙΙΙ and ΙV are more
greasy before homogenization compared to after homogenization.
From the observation under the light
microscope, we found out that the red globules of Emulsion Ι, ΙΙ, ΙΙΙ and ΙV
have a large and non uniform size before homogenization. After homogenization,
the red globules have a smaller and more uniform size. The shape of the
globules is the same before and after homogenization, that is spherical.
Furthermore, the red globules are unevenly distributed with its colourless
background before homogenization but become evenly distributed after
homogenization.
Under the light
microscope, Emulsion I only have a small amount of red globules and the amount
of red globules increases from Emulsion Ι to ΙV. This shows that the presence
of red globules increases as the composition of mineral oil in the emulsion
increases.
Sudan ΙΙΙ solution is used in this
experiment to indicate the position of oily globules in the emulsion. Sudan ΙΙΙ solution has a red colour and it will
dissolve in the oil phase to give
a red colour to the oily globules. The aqueous globules will not be stained red
and appear as colourless globules.
Hence, it can be used to determine the type of emulsions formed either oil in water (o/w) emulsion or
water in oil (w/o) emulsion. Oil in water (o/w)
emulsion has red globules on a colourless background while water in oil (w/o) emulsion has colourless globules on a red
background.
The colour dispersion of
Emulsion Ι, ΙΙ, ΙΙΙ and ΙV is uneven before homogenization. Therefore, the
emulsion formed before homogenization is water in oil emulsion. After
homogenization, the colour dispersion is even and the red globules are
dispersed uniformly on a colourless background. The size of the globules is
small. Hence, oil in water emulsion is formed after homogenization. Here, phase
inversion occurred before and after homogenization.
Edinburgh : Churchill Livingstone.
3.
Plot and discuss:
Type of Oil
|
Amount of Oil (ml)
|
Viscosity average (cP)
(x ± SD)
|
Difference in viscosity (%)
|
|
Before
|
After
|
|||
Palm Oil
|
20
|
100 ± 14.14
|
120.02 ± 23.42
|
20.02%
|
Arachis Oil
|
25
|
409.9 ± 15.49
|
775.37 ± 72.98
|
89.16%
|
Olive Oil
|
30
|
136.65 ± 91.99
|
254.95 ± 229.53
|
86.57%
|
Mineral Oil
|
35
|
730 ± 121.66
|
613.33 ± 343.78
|
15.98%
|
a. Graph of sample viscosity before and
after the temperature cycle vs. the content of mineral oil.
This
experiment carried out in wrong method. We use different types of oil with
different types of amount. Theoretically, this experiment has to carry out
using the same type of oil with different amount of oil. From the graph, the
viscosity of the emulsion at room temperature and after subjected to
temperature cycle is different according to each type of oil and each amount.
For palm oil, arachis oil and olive oil, the viscosity after subjected to
temperature cycle increased due to took longer time to let the emulsion become
room temperature again. Whereas the viscosity of mineral oil decreased after
subjected to temperature cycle due to it turns to room temperature faster.
Theoretically,
using the same type of oil, the viscosity of emulsion sample will increase when
put in the water bath at 450c for 30 minutes in the temperature
cycle. An increased temperature will cause a fall in apparent viscosity of the
continuous phase and increased kinetic motion of the disperse droplets and the
emulsifying agent at o/w interface. Subsequently, it is put into freezer at 40c
for 30 minutes. At low temperature (40c), kinetic energy of the
system is reduced and this will increase the viscosity of the continuous phase.
This will decrease the rate of migration of the globules in the disperse phase.
Thus, the viscosity of the emulsion will increase after the temperature cycle.
b.
Graph
of difference of viscosity (%) vsamount of oil (ml).
Due
to the error in this experiment, from the graph, we can see that the difference
of viscosity increase and then decrease by increasing the amount of oil.
Different type of oil have different type of viscosity, hence we cannot get the
correct graph.The arachis oil and olive oil showing more viscous than palm oil
and mineral oil from the graph.
Theoretically,
using the same type of oil, the higher amount of oil globules in the continuous
phase will increases the viscosity of the emulsion. The graph will show
directly proportional graph, which the difference of viscosity is directly
proportional to the amount of oil.
4.
Plot graph of separated phase ratio formed
from the centrifugation process versus the different amount of Oil. Explain.
The above table and graph
indicate the stability of the emulsion. The preparation of good emulsion need
the well stability, not easily coalesce and undergo phase separation to form two layer. However, there
is no ideal emulsion. A high ratio of phase separation shows that is unstable
emulsion. Unstable emulsion will give the detrimental effect such as increase
tendency of inappropriate dose deliver to the patient. As a result, the desired
outcome of the therapeutics cannot be observed.
In this experiment, 25 ml of Arachis oil
mix with 6.25g of acacia and other excipients show the highest ratio of phase
separation followed by 30 ml of olive oil, 20ml of palm oil and 35ml of
themineral oil. Theoretically, the separation phase ratio should be increasing
with the increasing of the mineral oil contain in the formulation.
The inaccuracy of the data obtained may
be due to some error in the process which the experiment is carried out. The
main reason is due to the different types of oil used in this experiment.
Different types of oil needs different amount of acacia to obtain a good
emulsion. Besides, this may be due to the homogenous process was not done
properly. Inaccurate measurement of the highly viscous surfactant that is to be
added into the formulation is also one of the reasons. In addition, the height
of the separated phase might not be measure accurately too.
5.
What
are the functions of each ingredient used? How these different ingredients
affect the physical characteristics and stability of an emulsion formulation?
Acacia is an emulsifying agent
which used to increase the viscosity among the interphase of the oily and aqueous phase. Since acacia is
a natural product and can enhance the growth of the microorganism. Benzoic acid
0.1%, which is the antibacterial agent is added to reduce the growth of
microorganism. The difference between the emulsifying agent and the surfactant
is the surfactant can tend to reduce the surface tension but emulsifying agent
cannot do so.
Mineral oil form the dispersed phase in the
oil in water emulsion (o/w emulsion).The water is the vehicles and also act as
the continuous phase in the emulsion.The ratio of the water and the oil must be
specified in preparing the emulsion because it will affect the stability of the
emulsion.The stability of emulsion formed will decrease if the volume of dispersed
phase exceeds 50% of the emulsion. Phase inversion tends to occur for emulsions
containing more than about 70% dispersed phase.
Alcohol is a natural preservative
that is generally derived from natural means, such as through fermented sugar,
cereals and yeast.Itcan prevent microbiological contamination of the emulsion.
The emulsion will have stable physicochemical properties for longer duration.
Since it produces toxicity in larger amount, we should not exceed the amount of
alcohol stated in Pharmacopeia.
Besides,vanillin serves as vanilla
taste flavouring agent. It gives the taste to the emulsion. Syrup is a
sweetening agent and tends to increase the viscosity of the emulsion too. This
is mainly to increase patient’s compliance.However, it is not suitable for the
diabetic patient.
CONCLUSION:
Combination of surfactants will give the
accurate HLB value required to form a stable emulsion. Different types of oil
have different viscosity. The higher the amount of oil, the higher the
viscosity and the more the separation phase.
REFERENCE:
1. Collett, D.M. & Aulton , M.E. Edinburgh :
Churchill Livingstone.
2. Aulton , M.E.
3.
British Pharmaceutical
Codex 1973.
