Lab Report: Suspension
Experiment 2: Effects of different ingredients on the characteristics of suspension formulation
Date of Experiment: 18th March 2013
Lecturer’s Name: Dr. Haliza Katas
Aim:
To determine the effects of different amount of Tragacanth used to the formulation of suspension.
Introduction:
Suspension formulation is a type of dispersed system where the solid molecules do not dissolve homogenously in the liquid phase. A good suspension must stay in homogenous state after being shaken, be easy to pour out from the container and having a uniform solid particle size and also attractive taste and texture. Precipitation formed from the storage must be easily dispersed again after shaking and the dispersion formed must be homogenous.
Normally, suspension composed of active ingredient (solid phase) dispersed in the liquid carrier, wetting agent, flavoring agent and coloring agent. Wetting agent (eg: Tragacanth) is used to reduce the surface tension between solid particle and liquid. Suspension is classified as coarse suspension where the particle diameter is more than 1 µm, or colloidal suspension where the particle size is less than 1 µm. In pharmaceutics, suspension is used to improve the stability, the taste and the bioavailability of the active ingredient.
Materials and Apparatus:
Apparatus: Ingredients:
Weighing instrument Chalk
Weighing boat Tragacanth
Mortar and pestle Concentrated Peppermint Water
150 ml plastic bottle Syrup BP
50 ml measurable cylinder Double-strength chloroform water
200 ml measurable cylinder Distilled water
1 set of 1 ml pipette and pipette bulb
1 centrifugator tube 15 ml
100 ml beaker
Coulter counter instrument
Centrifugator
Viscometer
Procedures:
1 formulation of Pediatric Chalk Mixture (150 ml) was prepared by the following formulation.
| Chalk | 3 g |
| Tragacanth | (referred to the Table 1) |
| Concentrated Cinnamon Water | 0.6 ml |
| Syrup BP | 15 ml |
| Double Strength Chloroform Water | 75 ml |
| Distilled Water, q.s. | 150 ml |
Table 1
| Pediatric Chalk Mixture | Group | Tragacanth (g) |
| I | 1,5 | 0.0 |
| II | 2,6 | 0.1 |
| III | 3,7 | 0.3 |
| IV | 4,8 | 0.5 |
5 ml of suspension was poured into the weighing boat and labeled. Texture, clarity and color of the suspension formed was described and compared.
50 ml of suspension was poured into 50 ml measurable cylinder. Height of the solid phase precipitated in the cylinder was measured at the interval of 0, 5, 10, 15, 20, 25, 30, 40, 50 and 60 minutes.
The rest of the suspension (95 ml) was poured into 100 ml beaker and the viscosity of the suspension was measured by a viscometer.
10 ml of suspension was poured into centrifugator tube and the height of the solid phase was measured after centrifugation (1000rpm, 5 minutes, and 25°C).
Results and Discussion:
1. Compare the physical appearance of formed suspension and gives comments.
| Suspension | Texture | Clearity | Colour |
| I | Very dilute | Clear when still, cloudy when shaken | Cloudy |
| II | Dilute | Cloudy when still, becomes more cloudy when shaken | Light milky white |
| III | Concentrated | Opaque | Milky White |
| IV | Very Concentrated | Very opaque | Milky white |
In this experiment, the physical appearances of suspension in those formulations are compared by varying the amount of tragacanth. Tragacanth is a suspending agent where it helps prevent caking at the bottom besides to facilitate redistribution of a suspension on shaking. One of the properties of a well-formulated suspension is that it can be easily resuspended by the use of moderate agitation.
Based on the observation done, the absent and present of tragacanth affect the texture, clearity, and colour of suspension formulated. Texture for Formulation I is very dilute due to lack of tragacanth as the suspending agent. As the amount of tragacanth increase, the texture of suspension produce becomes more viscous and concentrated. This is good for the appearances of a suspension. In terms of clearity, the present of tragacanth increase the cloudiness of suspension formulated even when they are not shaken. In the absent of tragacanth in Formulation I, the colour of the suspension is clear white and it turns to milky white when tragacanth is added. Besides that, tragacanth is partly soluble in water, thus forming viscous solution with water. Due to this factor, higher amount of tragacanth will form more viscous and concentrated solution which is like Suspension IV.
2. Plot a graph of height of sediment vs. time. Give explanation.
| Time (min) |
0 |
5 |
10 |
15 |
20 |
25 |
30 |
35 |
40 |
45 |
50 |
55 |
60 |
| Height (mm) |
0 |
3 |
3 |
4 |
5 |
5 |
5 |
5 |
5 |
5 |
5 |
5 |
5 |
The graph above has shown the height of sedimentation of a suspension, Pediatric Chalk Mixture types II which formulated with 0.1g Tragacanth powder over one hours. According to the graph, the height of the sediment formed at the 5th minutes is low which is 3mm only and it is remained until 10 minutes. After 10minutes, the height of sedimentation had increased to 4 mm at 15 minutes and it was continued to increase to 5mm at 20 minutes. Then, the height of the sedimentation reached the maximum sedimentation level with the height of 5 mm for the following 40 minutes till the end of experiment.
According to this graph, the suspension does not contain any sediment at the beginning of the experiment. However, as the time passes, sedimentation will start to form. The height of sedimentation increases as the time increases. This is because the forces of interaction between the inter–particular attractive forces are stronger than the inter-particular repulsive forces of the Tragacanth powder on suspension. Hence, the height of sedimentation will increases with time until a maximum sedimentation level is achieved. Tragacanth that included in the formulation acts as the suspending agent that allows the insoluble solute particles to suspend in the dispersed medium. The amount of tragacanth that added into the suspension can determine the duration for the dispersed phase to remain suspend in the dispersed medium. 0.1g of tragacanth that added is able to allow the insoluble solute to disperse for 5 minutes and it started to settle down.
3. Plot a graph of height of sedimentation against time for the formulations of suspension with different contents of Tragacanth. Discuss.
| Time (min) | Average height of sedimentation (mm) (mean+SD) | |||||||||||||
| 0 | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 | 60 | ||
| Amount of Tragacanth (g) | 0.0 | 0 | 18 | 15 | 12 | 11 | 10 | 10 | 9 | 9 | 9 | 9 | 9 | 9 |
| 0.1 | 0 | 3 | 3 | 4 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | |
| 0.3 | 0 | 2 | 4 | 6 | 7 | 8 | 8 | 9 | 9 | 10 | 10 | 10 | 10 | |
| 0.5 | 0 | 1 | 3 | 7 | 11 | 15 | 18 | 20 | 20 | 21 | 21 | 21 | 21 | |
For suspension 1 which is the one that without tragacanth, there is a sharp increase in the height of sedimentation from 0 to 18 mm from 0 to 5 minutes. After 5th minutes, the height of sedimentation had been decreased gradually until it reached the height where equilibrium is reached. The sharp increase in the height of sedimentation is due to the absence of tragacanth in the formulation. Particles tend to regroup and flocculate. Therefore, the dispersed phase settles to the bottom quickly. At the beginning of sedimentation, there is a lot of space that present in between the particles. As time passing, the height of sediment decreases gradually due to the particles filled in the spaces between the porous structures to make the sediment become more compact. The sediment forms a cake at the bottom of the measuring cylinder. In compacted cake, stronger forces are involved. At the end of the sedimentation process, the spaces between the particles already filled with the particles and no more space available. Thus the sediment do not reduce I height at the end of experiment.
For suspension 2 (with 0.1g of tragacanth), there is an increase from 0 to 20 minutes which is then remained unchanged at height 5mm. The sedimentation of suspension 2 is increased in height as time passed. However in suspension 1, the sedimentation increased initially and started to decrease gradually. This is because of the presence of tragacanth which is acts as the suspending agent that allows the active ingredients suspended in the dispersed medium by increasing the viscosity of suspensions. As time passing, the height of the sediment remain unchanged like in the suspension 1. This is also due to the filling of spaces between the porous structures which in turn makes the sediment to become more compact and forms cake at the bottom of the measuring cylinder as some crystals knit together at point of contact at the bottom of the container and all the space already filled with the particles.
For suspension 3 that with 0.3g of tragacanth, the height of the sediment increases slowly and remains constant from 45 to 60 minutes. From 0 to 5 minutes, the height of sedimentation only increased with 2 mm and the increament is less than the increament in suspension 2. This is due to the presence of greater amount of tragacanth in the suspension which makes suspension 3 become more stable than suspension 2. The greater the amount of suspending agent used, the longer the time taken for the sediment to form since the suspension is more stable. The height of sediment remains unchanged from 45 to 60 minutes also due to the same reason that already mentioned above.
For suspension 4 (with 0.5g tragacanth), the sediment that formed from 0 to 5 minutes only has 1mm and it is the smallest increased in the height among four different suspension since it has the highest amount of the tragacanth. However, the height of the sediment increases dramatically from 10 to 35 minutes. The height of the sediment is then remains constant from 45 to 60 minutes. With a high amount of tragacanth, the particles remain suspend in the suspension which counteract the gravity force, thus there is no caking of suspension. It is readily to be redispersed and it can be considered as a stable suspension.
4. Explain briefly the mechanism of viscometer analysis. Plot a graph of viscosity of the suspension versus the amount of Tragacanth (g). Give explanation.
|
Tragacanth(g) |
Viscometer reading |
|||||
|
1 |
2 |
3 |
4 |
5 |
6 |
|
|
I |
0.0 |
0.0 |
2.0 |
2.0 |
2.0 |
3.5 |
|
II |
2.0 |
2.0 |
2.0 |
3.0 |
2.0 |
3.0 |
|
III |
2.5 |
1.5 |
2.0 |
2.5 |
3.0 |
3.5 |
|
IV |
0.0 |
10.0 |
5.5 |
3.0 |
3.0 |
3.0 |
| Tragacanth content (g) |
0.0 |
0.1 |
0.3 |
0.5 |
| Viscosity (cP) (x ± SD) |
1.58 ± 1.24 |
2.33 ± 0.49 |
2.5 ± 0.65 |
4.08 ± 3.09 |
The graph of viscosity of the suspension versus the amount of tragacanth (g)
By theory, the viscosity of the suspension should be directly proportional to the amount of the tragacanth powder in the suspension. The tragacanth powder acts as a suspending agent which suspends the chalk in the liquid phase and form a suspension. 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’law.
From this experiment, chalk is suspended by tragacanth (suspending agent) in the liquid phase and form suspension. From the graph obtained, the viscosity of suspension is increased when the weight of tragacanth added is increased. Increasing the weight of tragacanth, the gel-like structure formed will be stronger and thus the suspension formed will be more viscous.
5. Plot a graph of the height ratio vs the amount of Tragacanth used in the suspension. Give comments.
| Amount of Tragacanth (g) |
0.0 |
0.1 |
0.3 |
0.5 |
| Height Ratio (mm) |
7:1 |
11:1 |
17:1 |
20:1 |
Based on the graph, it is shown that the height ratio upon centrifuging is increasing with the increased of the amount of Tragacanth. Tragacanth is used as a suspending agent to slow down the sedimentation rate of the powder in the suspension by increasing the viscosity of the vehicle. It forms a less sticky suspension and is a better thickening agent than acacia. Therefore, the more the amount of the Tragacanth used, the height ratio should be decreased as the suspension becomes more viscous and harder to sediment. This is because of the ability of the Tragacanth to hold the heavy and insoluble solids of the suspension, thus increase the difficulty of the separation. However, during the experiment, due to some error, the result is not as expected.
6. What is the function of each ingredients used in this suspension formulation? How does different amount of Tragacanth used can influence the physical characteristics and the stability of certain suspension?
| Chalk | Active ingredient which acts as absorbent which is to treat diarrhea. |
| Tragacanth | Suspending agent to form a less sticky suspension |
| Concentrated Peppermint Water* | Flavouring agent |
| Syrup BP* | Sweetening agent |
| Double Strength Chloroform Water* | Preservative |
| Distilled Water | Diluents in suspension |
* To make the preparation more palatable
As the amount of Tragacanth used increased, the suspension will become more viscous and stable against coagulation. Tragacanth may increase the viscosity of the aqueous vehicle and thus slow the rate of sedimentation of the particles but they will also form adsorbed layers around the particle so that the approach of their surfaces and aggregation to the coagulated state is hindered. Therefore, there will be less flocculation and once the sedimentation occurs; the suspension becomes more difficult to redisperse.
Conclusion:
The amount of different Tragacanth powder will affect the rate of sedimentation and the height of sediment formed in the suspension. As amount of tragacanth powder increase, sedimentation rate will be occurring more slowly and thus sediment height will be lower.
References:
1. Pharmaceutics: the science of dosage form design, Aulton, M.E.2002
2. British Pharmaceutical Codex 1973
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