OBJECTIVES
- To determine the effects of Tragacanth in different amount on the texture,clarity and colour of suspension.
- To study the effects of Tragacanth on the rate of sedimentation and viscosity of the suspension.
Suspension is a dispersed system in which insoluble
solid particles are dispersed in a homogeneous liquid phase. An acceptable
suspension possesses certain desirable qualities among which are the following
: the suspended material should not settle too rapidly, the particles which do
settle to the bottom of the container must not form a hard mass but should be
readily dispersed into a uniform mixture when the container is shaken and the
suspension must not be too viscous to pour freely from the orifice of the
bottle.
Physical stability of a suspension may be defined as
the condition in which the particles do not aggregate and in which they remain
uniformly distributed throughout the dispersion. There are two classes of
suspension; first is coarse suspension in which the particle size are more than
1µm and colloidal suspension in which the size of particles are less than 1µm.
In pharmaceutical practice, suspension is used to improve the stability of
active ingredient, taste and bioavailability.
APPARATUS
- Weighing boat
- Mortar and pestle
- 150ml plastic bottle
- 50ml measuring cylinder
- 200ml measuring cylinder
- 1ml pipet and bulb pipet
- 100 ml beaker
- Coulter counter machine
- Viscometer
- 15 ml centifugal tube
- Centrifugator
MATERIALS
- Chalk
- Tragacanth
- Concentrated peppermint water
- Syrup BP
- Double-strength chloroform water
- Distilled water
PROCEDURES
1. Formulation of suspension of Pediatric Chalk Mixture (150ml) was prepared according to the table below
Chalk
|
3g
|
Tragacanth
|
Refer
schedule 1
|
Concentrated Peppermint Water
|
0.6ml
|
Syrup BP
|
15ml
|
Double – strength Chloroform Water
|
75ml
|
Distilled water q.s
|
150ml
|
SCHEDULE 1
Pediatric Chalk Mixture
|
Group
|
Tragacanth (g)
|
I
|
1.5.9
|
0.0
|
II
|
2,6,10
|
0.1
|
III
|
3,7,11
|
0.3
|
IV
|
4,8,12
|
0.5
|
2. 5ml of suspension was poured into weighing boat and labelled. The textures, clarity and colours of suspension was compared and explained.
3. Then, 50ml of suspension was poured into 50ml measuring cylinder and the height of the solid suspended in the suspension was measured in time 0,5,10,15,20,25,30,35,40,45,50,55 and 60 minutes.
4. The remainder of suspension(95ml) was poured into 100ml beaker and its viscosity was determined using viscometer.
5. Lastly, 10ml of suspension was poured into centifugal tube and the height of suspended solid formed was measured after centifugation ( 1000rpm,5minute,25’C).
RESULTS AND DISCUSSIONS
1. Compare the physical characteristics of the suspensions formed and give explanation.
Pediatric Chalk
Mixture
|
I
(Group1,5)
|
II
(Group 2,6)
|
III
(Group 3,7)
|
IV
(Group 4,8)
|
Tragacanth (g)
|
0.0
|
0.1
|
0.3
|
0.5
|
Texture
|
More dilute
|
Dilute
|
Concentrated
|
More concentrated
|
Clarity
|
Clear
|
Not clear
|
Opaque
|
More opaque
|
Colour
|
Colourless
|
Milky, chalky
|
White
|
White
|
Among all
dosage forms, suspensions have the least physical stability due to
sedimentation and cake formation. A well-formulated suspension needs to be easily resuspended
by normal agitation and remain in that condition long enough for accurate
dosing. In order to do so, it needs suspending agent such as tragacanth which forms film around particle and decrease the
interparticle attraction. Tragacanth also gives viscosity to the
solution whereby it is of great importance for stability and
pourability of suspensions. For instance, when the viscosity of the
dispersion medium increases, the drug particles settling velocity decreases
thus they remain dispersed for longer time resulting in higher stability and
increase in dosing accuracy. However, the viscosity of suspension should be
maintained within optimum range to yield stable and easily pourable suspensions
because if the viscosity of the suspension is too high, the pourability
decreases and might cause inconvenience to the patients.
From the experiment carried out,
different group uses different amounts of tragacanth. It is observed that the
texture of suspension appeared more dilute in the suspension without tragacanth
and becomes more concentrated in increasing amounts of tragacanth added. When
it looks diluted, it indicates that most of the chalk has undergone
sedimentation and what was observed is just the dispersion medium. On the other
hand, it looks more concentrated due to the homogenous mixture of the chalk and
dispersion medium causing less visible chalk sedimentation. The same reason
also applies for the clarity observed whereby it is clear without tragacanth
and looked more opaque at the highest amount of tragacanth added. The chalk
mixture without tragacanth appeared colourless and it became whiter in the
presence of tragacanth which could also be explained by the reasons stated
above, that is, due to the separation between chalk and the dispersion medium.
2. Plot a graph of the height of sediments against time.
Give explanation.
Time (min)
|
0
|
5
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
50
|
55
|
60
|
Height
(mm)
|
0
|
2
|
4
|
5
|
6
|
6
|
7
|
7
|
7
|
8
|
8
|
8
|
8
|
From
the graph above for the suspension formulation of pediatric chalk mixture in
0.1g of tragacanth, it can be seen that there is a continuous gradual increase
from beginning until the 20th minute. From the 20th
minute to the 25th minute, it became constant and increases in the
30th minute which became constant again and increased to 8mm at the
45th minute and remained constant onwards. There is no sharp
increase but a gradual-increased graph is seen above. This is due to the
presence of tragacanth, that is, a suspending agent which causes the contents
to settle gradually. Tragacanth forms film around particle and decreases the
interparticle attraction resulting in lower sedimentation rate. As time increase, the shape of
the graph starts to appear constant which indicates that mostly all the
particles have been sedimented.
3. Plot a
graph of height of sediment vs. time for the formulation of suspension that
contain varied amount of Tragacanth. Give explanation.
Time (min)
|
Height of
sediment (mm)
|
|||||||||||||
0
|
5
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
50
|
55
|
60
|
||
Amount of Tragacanth powder (g)
|
0.0
|
0
|
10
|
7
|
6
|
6
|
6
|
6
|
6
|
6
|
6
|
6
|
6
|
6
|
0.1
|
0
|
2
|
5
|
5
|
6
|
6
|
7
|
7
|
7
|
8
|
8
|
8
|
8
|
|
0.3
|
0
|
2
|
4
|
6
|
7
|
8
|
8
|
9
|
9
|
10
|
10
|
10
|
10
|
|
0.5
|
0
|
5
|
8
|
5
|
12
|
12
|
12
|
12
|
12
|
12
|
12
|
12
|
12
|
|
The line graph above shows that height of sediment
decreases with increasing the weight of tragacanth. The higher the tragacanth
content, the lower the sediment formed. This is because suspensions contain
more tragacanth is more stable as the tragacanth is the suspending agent.
Tragacanth is a hydrophilic colloid coats the solid
hydrophobic particles with a multimolecular layer. This will impart hydrophilic
character to the solid and promote wetting effect. It also acts as suspending
agents, added to reduce sedimentation by structuring the continuous phase to
produce a deflocculated system.
In formulation 1, the tragacanth is totally absent,
hence, results in sedimentation of solid particles immediately and a
flocculated system is produced. While in formulation 4 with 0.5g of tragacanth,
the system initially has lower height of sedimentation but once sedimention
occured, it is has the highest rate of sedimentation then others.
4.
Briefly
explain on mechanism analysis of viscometer. Plot a graph of viscosity against
the amont of tragacanth. Explain.
Amount of
tragacanth (g)
|
Viscosity (cP)
|
Average
|
|||||
1
|
2
|
3
|
4
|
5
|
6
|
||
0.0
|
7.40
|
9.40
|
7.70
|
9.50
|
8.20
|
10.20
|
8.733
|
0.1
|
7.00
|
6.50
|
6.00
|
6.00
|
6.00
|
8.00
|
6.853
|
0.3
|
3.00
|
4.70
|
5.90
|
4.00
|
5.90
|
5.90
|
4.900
|
0.5
|
13.20
|
6.20
|
16.80
|
19.40
|
18.20
|
4.00
|
12.967
|
Amount
of tragacanth(g)
|
0.0
|
0.1
|
0.3
|
0.5
|
Viscosity
(cP)(x)
|
8.733±1.124
|
6.853±0.801
|
4.900±1.221
|
12.967±6.476
|
Viscometer used in this experiment is rotational
viscometer that works by determines the required force for rotating a disk or
bob in a fluid at known speed. It uses a precision servo motor to drive the
shaft. The Spindle or rotor is attached directly to the shaft. High speed
microprocessors measure the speed from a digital encoder and calculate the
current required to drive the rotor at the test speed. The current required is
proportional to the viscosity of the sample under test.
Tragacanth acts as a suspending
agent. Most suspending agents perform two functions. Besides acting as a
suspending agent they also imparts viscosity to the solution. Suspending agents
form film around particle and decrease interparticle attraction. Suspending
agents also act as thickening agents. They increase in viscosity of the
solution, which is necessary to prevent sedimentation of the suspended
particles as per Stoke’s’s law.
where V = sedimentation rate (cm/sec)
d =
diameter of the suspended particles (cm)
ρ1= density of the suspended particles (g/cm3)
ρ2 = density
of the medium (g/cm3)
g = acceleration of gravity (980.7 cm/sec2)
ƞo = viscosity of the external phase in
poises (g/cm sec).
Suspending
or thickening agents are added to suspensions to thicken the suspending medium,
thereby reducing the movement (sedimentation) of suspended particles and
physically stabilizing the product. This is particularly important in
flocculated systems in which rapid particle settling is the primary factor
leading to physical instability and lack of dosage uniformity in the product.
As from Stoke's Law, applying flocculation as a means of preventing caking, can
be done by increasing the particle diameter, and thus increase the rate of
sedimentation. A good suspension should have well developed thixotropy. At rest
the solution is sufficient viscous to prevent sedimentation and thus
aggregation or caking of the particles. When agitation is applied the viscosity
is reduced and provide good flow characteristic from the mouth of bottle. Thus,
increasing amount of suspending agent used increased the viscosity of
suspension.
5. Plot a graph of height of sedimentation formed after centrifuge against the composition of tragacanth(g). Give your explainations.
5. Plot a graph of height of sedimentation formed after centrifuge against the composition of tragacanth(g). Give your explainations.
Height (mm)
|
||||||||
Suspension I
|
Suspension II
|
Suspension III
|
Suspension IV
|
|||||
Group 1
|
Group 5
|
Group 2
|
Group 6
|
Group 3
|
Group 7
|
Group 4
|
Group 8
|
|
Before centrifuge
|
80
|
80
|
75
|
80
|
80
|
82
|
80
|
74
|
After centrifuge
|
27
|
10
|
10
|
6.7
|
7.4
|
21
|
27
|
18
|
Height Ratio
|
0.088
|
0.125
|
0.133
|
0.838
|
0.325
|
0.256
|
0.350
|
0.243
|
Amount of Tragacanth (g)
|
0.0
|
0.1
|
0.3
|
0.5
|
Height ratio (cP)
 |
0.107 ± 0.006
|
0.258 ± 1.168
|
0.291 ± 0.09
|
0.300 ± 0.138
|
Centrifugation uses the
centrifugal force to make the denser components to sediment. Tragacanth
functions as suspending agent in a suspension formulation. It will suspend the
solid phase (chalk) in the liquid phase to form a stable suspension. Therefore,
more amount tragacanth, the slower the sediment formation. When centrifuged,
the chalk will sediment to the bottom. Hence, the height ratio obtained should
be lower in suspension containing greater amount of tragacanth.
However, the result obtained
is directly opposite of the theory where it should give lower height ratio when
tragacanth increases. The graph obtained is higher height ratio when tragacanth
increases. This might be due to experimental error. The students might have
applied too much pressure when mixing the tragacanth in the mixture. High
pressure may cause the tragacanth to degrade and loses its function. Besides
that, error may occur when the students forgot to stir the suspension in order
to redisperse the sediments before pouring into the centrifuge tube. Tragacanth
is natural product obtained from plant. This might cause variation in its
ability to function as the suspending agent. Also, the tragacanth powder may
have been contaminated with microbe or spoilt during storage.
6. What is the function of each material that has been used in preparation of this suspension? How does the different amount of tragacanth used influence the physical characteristics and stability of suspension formulation?
Material
|
Function
|
Chalk
|
As active ingredient
|
Tragacanth
|
act as suspending agent and thickening agent. They increase in
viscosity of the solution, which is necessary to prevent sedimentation of the
suspended particles.
|
Concentrated Peppermint Water
|
As flovouring and perfuming agents which are capable of masking the
unpleasant taste
|
Syrup BP
|
As sweetening agent and cosolvent by preventing crystallization and
maintaining solubility of all ingredients.
|
Double-strength Chloroform Water
|
Preservative and sweetening agent
|
Distilled Water
|
Act as vehicle
|
Different
amount of tragacanth used in the formulation of suspension may affect the
physical characteristics and stability of suspension by being an effective
stabilizer of colloidal suspension at very low concentrations. The stabilization is a result of the steric
repulsion force, and the stability can be controlled by changing pH. As the pH
is lowered, the steric layer thickness expand, these prove that the gum
tragacanth changes the conformation on the surface. This change is a result of
the formation of loops and tails at lower pH. The flocculated particles can be
spontaneously deflocculated by lowering pH. The peptization is a result o f the
conformational change of the gum tragacanth
molecules on the surface, and the flocculation-deflocculation process is
reversible.
As we
know, tragancath act as suspending agent and thickening agent. They will
increases the viscosity of suspension which is very important in preventing
sedimentation of suspended particles to give a greater stability to suspension.
Viscosity of suspensions is of great importance for stability and pourability
of suspensions. As we know suspensions have least physical stability amongst
all dosage forms due to sedimentation and cake formation. So as the viscosity
of the dispersion medium increases, the terminal settling velocity decreases
thus the dispersed phase settle at a slower rate and they remain dispersed for
longer time yielding higher stability to the suspension. On the other hand as
the viscosity of the suspension increases, its pourability decreases and
inconvenience to the patients for dosing increases.Thus, the viscosity of
suspension should be maintained within optimum range to yield stable and easily
pourable suspensions.
CONCLUSION
The rate of sedimentation and the height of sediment
formed in the suspension depends on the amount of different Tragacanth powder
used to form the suspension. The higher the amount of Tragacanth powder, the
lower the height of sediment formed. This is due to the action of Tragacanth
powder that prevent the solution from forming sediment.
REFERENCES
1.
Pharmaceutical
Practice, Winfield Richards, 2nd Edition
2. Michael
E.Aulton, Aulton’s Pharmaceutics The Design And Manufacture of Medicines, third
edition, 2007, Churchill Livingstone Elsevier
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