Tuesday, 14 May 2013


Title : Effects of different ingredients on the characteristics of  suspension formulation

Objective        : 
To know the effects of using different amount of Tragacanth to the formulation of suspension.

       Since some drugs will not dissolve in solvents suitable for medicinal use, they are made into suspensions. Suspensions consist of a finely divided solid dispersed in a water-based liquid. Suspension formulation is a type of dispersed system where the solid molecules do not dissolve homogenously in the liquid phase. It is a heterogeneous mixture containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents.
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.

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

  1. One formulation of Pediatric Chalk Mixture (150 ml) was prepared by the following formulation.

Table 1

  1. 5 ml of suspension was poured into the weighing boat and was labeled. Texture, clarity and color of the suspension was described and compared.
  2. 50 ml of suspension was poured into 50 ml measurable cylinder. Height of the solid phase precipitated in the cylinder was measured at the duration of 0, 5, 10, 15, 20, 25, 30, 40, 50 and 60 minutes.
  3. The rest of the suspension (95 ml) was poured into 100 ml beaker and the viscosity of the suspension was measured by a viscometer.
  4. 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 the suspension formed and give the analysis.

Physical appearance
Paediatric Chalk Mixture
Tragacanth (g)

-ease to precipitate
Slow/not precipitate
Not precipitate
2) Clarity
3) Color

       The color of the suspension I to IV is white. Tragacanth powder is the suspending agent. Suspension without Tragacanth powder will separate into two layers with clear boundary. One is the clear liquid phase and another one is the solid phase. The Chalk mixture I contains no Tragacanth powder and the amount of Tragacanth powder is increasing to Chalk mixture IV. By using Tragacanth powder, suspension is formed where the Chalk is suspended in the liquid and the suspension becomes not clear and more viscous. By using larger amount of Tragacanth powder, the suspension formed becomes more viscous. The time for particles to precipitate is longer and the ability of redispersibility becomes less. This is because as more Tragacanth powder is used, more Chalk will be suspended and the rate of precipitation will become slower.

2.  Plot the graph of height of sedimentation versus time. Give explanation.


For the Pediatric Chalk Mixture type IV, 0.5g Tragacanth powder is used as a suspending agent, there is no sediment formed at the beginning. This is because Tragacanth which used as suspending agent has stabilized the formulation from forming sedimentation and help in the formation of viscous suspension. It forms film around particle and decrease interparticle attraction.
               However, after the Periodic Chalk Mixture has been left to stand for a period of time, the sediment start to form and the height of sediment increase as the time increase. This is because particles in a suspension will settle out if the suspension is allowed to stand undisturbed. Particles in a suspension are larger than those in the solution, and therefore will settle out if left to stand. These particles can be redispersed when it is shaken and the sediment formed does not show decreased in  height. This is due to the present of suspending agent. The addition of the tragacanth, at some critical concentration, negates the surface charge on the suspended particles and allows the formation of floccules or clusters as particles are held loosely together by weak van der Waals forces. Since the particles are linked together only loosely, they will not cake and may be easily redispersed by shaking the suspension.

3.  Plot the graph of height of solid phase against time for different amount of tragacanth in the suspension. Give your comment.


 For the Pediatric Chalk Mixture type II, III, IV using the Tragacanth powder, sedimentation generally does not occur at the beginning due to the presence of Tragacanth powder as a suspending agent. However, the sedimentation starts and the height of sediment increases with time. This is due to the inter–particular attractive forces are stronger than the repulsive forces of the Tragacanth powder on the chalk particles. Therefore, the sedimentation formed increases with time until a maximum sedimentation level.
     The Pediatric Chalk Mixture type II, III, IV contains 0.1g, 0.3g, and 0.5g of Tragacanth powder respectively. Based on theory, the more the amount of Tragacanth powder present, the lower the sediment formed and the time needed for sedimentation to occur is longer. This is due to the sediment formed in the suspension containing higher amount of Tragacanth powder is more stable and less flocculation occur.   They need more time for sedimentation to occur compared to suspension containing less amount of Tragacanth powder. Therefore, the amount of Tragacanth powder in the formulation will influence the height of sediment formed and the time for sedimentation of suspension to occur.
But based on the result we observed, there is increase in volume of sedimentation when increase amount of tragacanth. This is maybe due to some errors occur during experiment. We having a problem during observed and measured the height of sediment. This is because it is quite difficult for us to observe the sedimentation height. So, maybe there is error during observation and reading the height of sediment.

4.      Explain briefly the mechanism of viscometer analysis. Plot a graph of
     viscosity of the suspension versus the amount of Tragacanth (g). Give explanation.

Amount of tragacanth (g)
Viscosity (cP)(average +SD)
1.83 + 0.55278

The motor of the viscometer spin with speed of 300rpm which is fixed by the control centre. There are discs which are connected with the spiral spring at angle more than 180° used to spin the stirrer. The change of the spin angle is directly proportional to the viscosity of the fluid and the rate of spin. The infrared radiation from LED passes through the discs before detected by the photo diod. The change of the angle of spinning disc will affect the infrared radiation and will be detected by the photo diod.
       The viscosity of the suspension is 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. As the amount of Tragacanth powder increases, the suspension formed will be more viscous.
A suspending agent will slow down the sedimentation rate of suspension by increasing the viscosity of the fluid medium. This agent follows the Stokes law which states that the settling velocities of small particles in a fluid medium are resisted by the viscosity of the liquid. Moreover, suspending agents will form film around the insoluble solid particles and decrease the surface tension. Based on the results of the experiment, when we increase the amount of tragacanth used, the viscosity of the suspension will increase. As our group used the highest amount of tragacanth, our suspension has the highest reading of the viscometer.
          Tragacanth solution is viscous in nature. It is a better thickening agent than acacia.It also  provides thixotrophy ability to the solution. Thixotrophy is one of the properties of a well-formulated suspension is that it can be easily resuspended by the use of average shear force. When agitation is applied the viscosity is reduced and provide good flow characteristic from the mouth of the container.

4.  Plot a graph of sediment height ratio after centrifugation versus the amount of Tragacanth (g). Give explanation.

Height ratio (mm)
80 : 7
80 : 12
80 : 15
80 : 20

Suspension I
X = 7 / 80
    = 0.0875

Suspension  II
X = 12 / 80
    = 0.15
Suspension  III
X = 15 / 80
= 0.1875

Suspension  IV
X = 20 / 80
= 0.25

When tabulate the data:

Height ratio (mm)


         By theory, the more the amount of Tragacanth powder present in the formulation, the lower is the sediment formed. Therefore the height ratio should be lower for those containing higher amount of Tragacanth powder. The Tragacanth powder acts as a suspending agent that suspends the solid phase (chalk) in the liquid phase to form a stable suspension. With the addition of the large amount of Tragacanth powder in the formulation, it gives a more stable suspension and less flocculation will formed compared to those containing less amount of Tragacanth powder.
       However, the experimental results show that the amount of sediment increases with the amount of Tragacanth powder present in the formulation except for the mixture IV. This may be due to the experimental errors that occur during preparing the suspension. The amount of chalk to be suspended maybe not accurately measured. This will affect the height of sediment. Also, the amount of the suspending agent, Tragacanth powder may affect the results if not accurately measured.

5.  What is the function of each ingredient used in the suspension preparation? How does the different amount of Tragacanth powder affect the physical characteristics and stability of the suspension formulation?

Chalk is an indiffussible solid that is suspended in the Pediatric Chalk Mixture. The Tragacanth powder acts as a suspending agent to suspend and stabilise the chalk in the suspension. The concentrated peppermint water is the carminative agent and flavouring agent. Syrup BP increases the viscosity of the suspension and acts as a sweetening agent. Double strength chloroform water acts as the flavouring agent, preservative and solvent. Distilled water is the solvent.
      The Tragacanth powder acts as a suspending agent that suspends the solid phase (chalk) in the liquid phase to form a stable and uniform suspension where no two different layers of ingredients present. By using the Tragacanth powder, the suspension will be looked cloudy, viscous and smooth. If higher amount of Tragacanth powder is used, less sedimentation will occur and it will take longer time to occur. The suspension containing large amount of Tragacanth powder is more stable and less flocculation will occur or occur after longer duration of time compared to those having smaller amount of Tragacanth powder.

 The amount of different Tragacanth powder will affect the rate of sedimentation and the height of sediment formed in the suspension.

1.      Pharmaceutics: the science of dosage form design, Aulton, M.E.2002\


Suspension from Group 1A to 4A

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