OBJECTIVE : To investigate the effect of different amount
of tragacanth on the sedimentation rate of the suspensions
INTRODUCTION:
Suspension is a
heterogeneous mixture in which the solute particles do not dissolve but get
suspended throughout the bulk of the medium. It consists of at least two
phases; the continuous or external phase is generally a liquid or a semi-solid
and the dispersed or internal phase is solid that generally insoluble in the
continuous phase. The internal phase (solid) is dispersed throughout the
external phase (fluid) through mechanical agitation, with the use of certain excipients or
suspending agents. Unlike colloids, suspensions will eventually settle.
Suspension can
be found in several uses. It can be used for oral administration in the form of
sweetened, flavoured formulations and also topical application as what we
referred as lotion. Suspensions can also be intended for parenteral
administration as non- sweetened, non- flavoured formulations.
Suspension has
its own pros and cons. One of the advantage of suspension is suspension is
the only choice if the drug is not soluble in water and non-aqueous solvent is
not acceptable, for example corticosteroids suspension. Besides, suspension is
most suitable for drugs having unpleasant taste and odour. Moreover, Drug in
suspension exhibits a higher rate of bioavailability compared to the same drug
of equivalent dose formulated in tablets or capsules. This is due to larger
surface area and high dissolution of suspension, for example antacid
suspension.
Meanwhile, the
disadvantage of the suspension is it is physically unstable, in other words
they tend to settle after a period of time without agitation. This may lead to
lack of uniformity of the drug and affect the therapeutic effect. However this
can be overcome by shaking the suspension before each dose is delivered so that
the solute is fully redispersed. To improve this condition, we should try to
reduce the rate of settling and permit easy redispersion. These can be achieved
by using wetting agent such as tragacanth to minimize the surface tension.
APPARATUS
1 mL graduated
pipette
Pipette bulb
Weighing boat
Mortar and
pestle
50 mL graduated
cylinder
200 mL
graduated cylinder
100 mL beaker
Parafilm ®
Weighing
balance
Viscometer
MATERIALS
Chalk
Tragacanth
Concentrated
peppermint water (or any flavouring agent )
Double strength
chloroform water
Distilled water
Syrup BP
PROCEDURE
1. A suspension of
Pediatric Chalk Mixture (150 mL) was prepared according to the following
formula:
Ingredient
|
Suspension
|
|||
A
|
B
|
C
|
D
|
|
Chalk (g)
|
3
|
3
|
3
|
-
|
Tragacanth
(g)
|
0.0
|
0.1
|
0.3
|
0.5
|
Concentrated
peppermint water (mL)
|
0.6
|
0.6
|
0.6
|
0.6
|
Syrup BP (mL)
|
15
|
15
|
15
|
15
|
Double
strength chloroform water (mL)
|
75
|
75
|
75
|
75
|
Distilled
water q.s. (mL)
|
150
|
150
|
150
|
150
|
2.
5mL of the
suspension was poured into a weighing boat and each formulation was labelled.
The texture, clarity and colour of each suspension was observed and compared.
3. The
sedimentation rate of each suspension was determined. The suspension was shaken
vigorously to make sure all of the particles were uniformly suspended, and the
time was noted. The boundary between the sediment and supernatant was observed
and the time taken for the boundary to pass each 10 mL graduation until the
volume of the sediment had reached 80 mL was recorded.
4. The graduated
cylinder was set down on the lab bench, and the lab timer was started at this
point.
5. For suspension
A to C, the sedimentation volume of the suspensions at t = 0, 2, 5, 10, 15 and
30 minutes were recorded.
6. The
sedimentation volume ratio was calculated using the following formula:
7. The ease of re-
dispersibility of each formulation were examined by :
i)
The Parafilm ® was snugged on the mouth of the graduated
cylinder and the seal was re-enforce with gloved hand.
ii)
The number of inversions it took to completely re-disperse
the drug was recorded.
iii)
The observations were recorded.
8. 95 mL of the
suspension was poured into a 100 mL beaker and the viscosity of the suspension
was determined using viscometer at 12000 rpm for 2 minutes. Data was recorded.
 |
| During Lab Session |
 |
| After 4 Days |
RESULT :
AFTER 4DAYS
Suspension
|
Amount of
Chalk (g)
|
Amount of
Tragacanth (g)
|
Texture
|
Clarity
|
Colour
|
A
|
3
|
0.0
|
Less Viscous
|
Cloudy
|
White
|
B
|
3
|
0.1
|
Moderately Viscous
|
Cloudy
|
Milky White
|
C
|
3
|
0.3
|
More Viscous
|
Cloudy
|
Milky White
|
D
|
0
|
0.5
|
Less Viscous
|
Opaque
|
Yellowish
|
Height of boundary (mL)
|
Time Taken (min)
|
|||
A
|
B
|
C
|
D
|
|
150
|
0
|
0
|
0
|
-
|
140
|
0.47
|
1.12
|
1.90
|
-
|
130
|
0.70
|
2.25
|
2.32
|
-
|
120
|
0.95
|
2.55
|
2.95
|
-
|
110
|
1.33
|
2.72
|
3.22
|
-
|
100
|
1.71
|
3.02
|
3.47
|
-
|
90
|
2.00
|
3.38
|
3.82
|
-
|
80
|
2.42
|
3.70
|
4.13
|
-
|
Table 1
Suspension
|
Sedimentation volume at pre-determined time
(min)
|
Distinct boundary (yes/no)
|
|||||
0
|
2
|
5
|
10
|
15
|
30
|
||
A
|
150
|
90
|
34
|
26
|
22
|
18
|
yes
|
B
|
150
|
135
|
24
|
22
|
20
|
19
|
yes
|
C
|
150
|
138
|
66
|
22
|
22
|
22
|
no
|
D
|
150
|
-
|
-
|
-
|
-
|
-
|
no
|
Sedimentation Volume ratio of Suspension A:
18/150 = 0.120
Sedimentation volume ratio of Suspension B:
19/150 = 0.127
Sedimentation volume ratio of Suspension C:
22/150 = 0.147
Suspension
|
Number of Inversions
|
A
|
2
|
B
|
1
|
C
|
1
|
D
|
-
|
Table 2
Suspension
|
A
|
B
|
C
|
D
|
|
Viscosity
|
First
|
4.8
|
5.4
|
8.4
|
10.2
|
Second
|
4.8
|
5.1
|
7.8
|
9.9
|
|
Third
|
4.8
|
6.6
|
7.8
|
10.2
|
|
Mean
|
4.8
|
5.7
|
8.0
|
10.1
|
|
SD
|
0
|
0.648
|
0.283
|
0.141
|
|
Suspension
|
A
|
B
|
C
|
D
|
|
Viscosity
|
First
|
4.8
|
5.4
|
8.4
|
10.2
|
Second
|
4.8
|
5.1
|
7.8
|
9.9
|
|
Third
|
4.8
|
6.6
|
7.8
|
10.2
|
|
Mean
|
4.8
|
5.7
|
8.0
|
10.1
|
|
SD
|
0
|
0.648
|
0.283
|
0.141
|
|
DISCUSSION:
1.
Compare and
discuss physical appearances of all the suspensions produced.
Suspension
|
Amount of Chalk (g)
|
Amount of Tragacanth (g)
|
Texture
|
Clarity
|
Colour
|
A
|
3
|
0.0
|
Less Viscous
|
Cloudy
|
White
|
B
|
3
|
0.1
|
Moderately
Viscous
|
Cloudy
|
Milky White
|
C
|
3
|
0.3
|
More Viscous
|
Cloudy
|
Milky White
|
D
|
0
|
0.5
|
Most Viscous
|
Opaque
|
Yellowish
|
In
this experiment, four suspensions are prepared with varying amount of tragacanth.
Suspension A is less viscous due to the absence of tragacanth as wetting agent.
Tragacanth gives viscosity to the suspension whereby it is of great importance
for stability and pourability of suspensions. The presence of wetting agent
facilitates the distribution and dispersion of the lyophobic powders. Absence
of the tragacanth as the suspending agent caused the suspensions to sediment
very fast and the particles separated into two distinct boundaries. Suspension
A looks white and cloudy due to the distribution of the insoluble chalk
powders.
Suspension
B is moderately viscous due to the presence of small amount of tragacanth. It
is cloudy due to the insoluble chalk powder which does not dissolve in the
solution. The viscosity contributed by the tragacanth gives the colour of milky
white.
Suspension
C has greater viscosity compared to B because of the increased amount of
tragacanth. The texture is very smooth and cloudy because tragacanth helped to
suspend and distribute the insoluble particle evenly. The colour of milky white
is due to the viscosity and the chalk powder.
Suspension
D is the most viscous because it contains the highest amount of tragacanth. It
has the thickest texture causes it to be opaque. Tragacanth dissolves and gives
the yellowish colour. Thus, we can say that the viscosity of suspension is
depends on the amount of tragacanth.
2.
Plot Hu/Ho vs.
time for each of the suspensions (Table 1). Discuss the findings.
Suspension
A:
Time (min)
|
Hu
|
Ho
|
Hu/Ho
|
0
|
150
|
150
|
1.000
|
2
|
90
|
150
|
0.600
|
5
|
34
|
150
|
0.227
|
10
|
26
|
150
|
0.173
|
15
|
22
|
150
|
0.147
|
30
|
18
|
150
|
0.120
|
Suspension
B:
Time (min)
|
Hu
|
Ho
|
Hu/Ho
|
0
|
150
|
150
|
1.000
|
2
|
135
|
150
|
0.900
|
5
|
24
|
150
|
0.160
|
10
|
22
|
150
|
0.147
|
15
|
20
|
150
|
0.133
|
30
|
19
|
150
|
0.127
|
Suspension
C:
Time (min)
|
Hu
|
Ho
|
Hu/Ho
|
0
|
150
|
150
|
1.000
|
2
|
138
|
150
|
0.920
|
5
|
66
|
150
|
0.440
|
10
|
22
|
150
|
0.147
|
15
|
22
|
150
|
0.147
|
30
|
22
|
150
|
0.147
|
The graph of sedimentation volume
ratio against time is plotted. In general, the sedimentation volume ratio
decreases as the time increases. The lyophobic chalk powder dispersed evenly in
the solution in the beginning. Over a period of time, the insoluble chalk
powder sediments to the bottom of the cylinder. The use of tragacanth as
wetting agent facilitates the distribution of chalk powder.
The rate of sedimentation of suspension A is highest because there is
no suspending agent to facilitate the dispersion of powder. Absence of
suspending agent causes the suspension to become easily separated because it
has less viscosity. Thus, the denser dispersed phase sediment in a short
time. The sedimentation volume decreases due to gravitational force. Further
decrease of the sedimentation volume occurs as the powder settles forming a
distinct compact layer. There is a distinct boundary observed due to the
absence of suspending agent. This suspension forms a flocculated system. Over
time, the floc is pulled downwards and formed sediment.
Suspension B has a slower
sedimentation rate at the beginning. However, the sedimentation rate
accelerated after 2 minutes. This may due to error occurred during the
compounding procedure. The tragacanth might not be mixed evenly causing the
drastic increase of sedimentation rate.
3.
After storing the
suspensions for a period of 4 days, determine the ease of redispersion of each.
A
is the easiest to redisperse followed by B, C and D. Suspension A is the
easiest to be redispersed because it has low viscosity. Weak force applied by
shaking can easily redisperse the suspension.
Suspension
D is the hardest to redisperse. This is because suspension D has the highest
amount of tragacanth making it the most viscous. Viscosity hinders the
dispersion of the insoluble particles. The
suspension with higher amount of suspending agent takes longer time to be
redispersed. High viscosity is not totally beneficial in suspension
formulation as when it sediments, it is not easily re-disperse even shaking
with strong force. This causes unequal and inaccurate dosing.
4.
Briefly explain
the principle of analysis using viscometer. Plot the viscosity vs tragacanth
content (Table 2). Discuss the findings.
There
are many types of viscometer for example Gravimetric Capillary viscometer, Stabinger viscometer and Stabinger
viscometer. In this experiment rotational viscometer is used. Rotational
viscometers use a motor drive which provide dynamic or shear viscosity results.
A rotational viscometer consists of a sample-filled cup and a measuring bob or
spindle that is immersed into the sample. The motor turns a measuring bob or
spindle in a container filled with sample fluid. While the driving speed is
preset, the torque required for turning the measuring bob against the fluid’s
viscous forces is measured.
The viscosity of
the suspension increases as the tragacanth content increase. Tragacanth is used
as wetting agent in which it decreases the surface tension, allow it to spread drops onto a surface and
makes the suspension more viscous. It also allows removing of air from the
surface and to easy penetration of the vehicle into the pores. Viscosity of
suspension is important as it will affect the velocity of sedimentation. From
the graph, highest tragacanth content of 0.3g has the highest viscosity of 8.0
cP in which proved that the viscosity of the
suspension is directly proportional to the amount of the tragacanth powder in
the suspension.
5.
Based on all the
observations, which product would be considered to be most acceptable? Explain.
Product/suspension
C is the most acceptable because it has the highest amount of tragacanth of 0.3
g which makes it more stable, more viscous and has a smooth and cloudy
appearance. Cloudy appearance shows that the white chalk is homogenously and
uniformly dispersed in the liquid media. Suspension C settles more slowly and
take longer time for sedimentation to occur as the tragacanth keep the finely
insoluble materials which is chalk suspended in the liquid by preventing
agglomeration and by imparting viscosity. The high viscosity of suspension C
also decreases the sedimentation rate. The other suspension with a less amount
of tragacanth, have a higher sedimentation rate. The number of inversion of
suspension C is only one which indicates it is easily to redisperse back.
6.Briefly explain
the function of each excipients used in the suspension formulation. Explain the
influence of tragacanth on the physical characteristics and stability of a
suspension.
The
concentrated peppermint water and syrup is used as flavoring agents to mask or
impart taste of medications. The double strength chloroform water is used for
preservatives to avoid microbial growth. Tragacanths is used as wetting agent
and influence the physical characteristics of suspension by making it more
viscous. Tragacanths act as wetting agents where it forms film around particle
and reduce the surface tension. Therefore, the insoluble chalk suspended in the
liquid media. The more content of tragacanth, the more uniform the chalk is
dispersed in the liquid which make it more viscous. High viscosity prevent
sedimentation and thus aggregation or caking in which contribute to the high
stability of suspension. Tragacanth also retards crystal growth which makes the
formulation stable for a longer period of time.
CONCLUSION
Followed
by the result , we can conclude that the trend is less surfactant , easier to
redisperse . Viscosity of suspension is important in order to determine
sedimentation rate . The suspension easily got separate when we decrease amount
of tragacanth (suspending agent) .
REFERENCE
1. Michael E.Aulton, Aulton’s Pharmaceutics The
Design And Manufacture of Medicines, third edition, 2007, Churchill Livingstone
Elsevier
