EXPERIMENT 2 : ASSESSMENT OF THE EFFECTS OF DIFFERENT COMPOSITIONS OF INGREDIENTS USED ON THE CHARACTERISTICS OF A SUSPENSION FORMULATION

LECTURER'S NAME: PROF DR HALIZA KATAS

TITLE:

Assessment of the Effects of Different Compositions of Ingredients Used on the Characteristics of a Suspension Formulation

AIM:

To study the effects of using different amounts of tragacanth on a suspension formulation

INTRODUCTION:

Suspensions possess certain advantages over other dosage forms. Some drugs are insoluble in all acceptable media and must, therefore, be administered as a tablet, capsule, or as a suspension. Because of their liquid character, suspensions represent an ideal dosage form for patients who have difficulty swallowing tablets or capsules. This factor is of particular importance in administration of drugs to children. Suspensions of insoluble drugs may also be used externally, often as protective agents. Suspensions also possess some disadvantages relative to other dosage forms. The primary disadvantage is their physical instability; i.e., that they tend to settle over time leading to a lack of uniformity of dose. This can, however, be minimized by careful formulation and by shaking the suspension before each dose is delivered. An additional disadvantage is that the texture of suspensions may be unpleasant to patients and should be carefully considered during formulation. A suspension formulation is a type of disperse system where the insoluble solid particles are dispersed homogenously in the liquid phase. A good suspension must be in a homogenous form after shaking, easily poured from the container, has a uniform solid particle size and possess better feel and taste. Sediment that is formed upon storage has to be easily redispersed after shaking, forming homogenous suspension. Suspension can be classified into a coarse suspension where the diameter of the particles is more than 1 µm or a colloidal suspension where the particle size is less than 1 µm. In pharmaceutical practice, suspension is used to improve the stability of the active ingredient, taste, and bioavailability.

 APPARATUS:

Weighing balance	Viscometer
Weighing boat	1 centrifugation tube 15ml
Mortar and pestle	pipette (1ml) and bulb-pipette
Plastic bottle 150ml	Measuring cylinder 200ml
Centrifugation equipment	Measuring cylinder 50ml
100ml beaker

MATERIALS:

Chalk	Double-strength Chloroform Water
Tragacanth	Concentrated Peppermint Water
Syrup BP	Distilled water

                                                     

PROCEDURE:

1.      A suspension of Paediatric Chalk Mixture (150ml) is prepared using the formulation below:   

   

Chalk                                                                                  3g Tragacanth                                                                    Refer to table 1 Concentrated Peppermint Water                                           0.6mL Syrup BP                                                                           15mL Double Strength Chloroform Water                                      75mL Distilled Water, q.s.                                                            150mL

Table 1

Paediatric 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.      Some of the suspension formed (5ml) is poured into the weighing boat and labelled. State and compare the texture, clearness and colour of the suspension formed.

3.      50ml of suspension formed is poured into the 50ml measuring cylinder and the height of the solid phase sediment in the cylinder is measured at intervals of 0, 5, 10, 15, 20, 25, 30, 40, 50 and 60 minutes.

4.      The remaining suspension (95ml) is poured into a 100ml beaker and viscosity of the suspension formed is determined using a viscometer.

5.      10ml of suspension is poured into a centrifugation tube and the height of the solid phase formed after centrifugation (1000rpm, 5 minutes, and 25°C) is determined.

RESULTS:

1.      Height of suspension formed in the cylinder in 0,5,10,15,20,25,30,35,40,45,50,55 and 60 min

Time/min	0	5	10	15	20	25	30	35	40	45	50	55	60
Height/mm	11.9	11.9	11.8	11.7	11.7	11.4	11.2	11.1	10.8	10.7	10.6	10.6	10.4

2.      Viscosity of suspension formed

0.0g Tragacanth

Reading	1	2	3	4	5	6
Viscosity (Cp)	1.9	1.8	2.0	3.0	3.4	4.2
Average + SD	2.72±0.9766

0.1g Tragacanth

Reading	1	2	3	4	5	6
Viscosity (Cp)	1.5	1.3	1.6	1.2	1.6	1.2
Average + SD	1.4±0.1835

0.3g Tragacanth

Reading	1	2	3	4	5	6
Viscosity (Cp)	3.4	3.7	3.8	3.9	4.0	3.8
Average + SD	3.767±0.2066

0.5g Tragacanth

Reading	1	2	3	4	5	6
Viscosity (Cp)	2.3	3.4	2.7	3.2	2.8	3.5
Average + SD	2.98±0.4622

3.      Height of suspension after undergo centrifudge (1000rpm,5 minute, 25 ˚C )

0.0g Tragacanth

	Height (mm)
Before centrifuge	24
After centrifuge	6
Height ratio before and after centrifuged	4:1

0.1g Tragacanth

	Height (mm)
Before centrifuge	0
After centrifuge	10
Height ratio before and after centrifuged	0:10

0.3g Tragacanth

	Height (mm)
Before centrifuge	7.9
After centrifuge	1.4
Height ratio before and after centrifuged	7.9 : 1.4

DISCUSSION

1.      Compare the physical characteristics of the suspensions and give your comment.

Physical characteristic	Paediatric Chalk Mixture
	I	II	III	IV
Texture -smoothness -viscosity -redispersibility
	+	++	+++	++++
	+	++	+++	++++
	++++	+++	++	+
Clarity	Cloudy	Cloudy	Cloudy	Cloudy
Colour	White	Milky white	Milky white	Milky white
Layer	2 layers	1 layer	1 layer	1        layer

Mixture I does not contain any Tragacanth in their formulation. Thus, the suspension has a rough or less smooth and less viscous texture. However, it is easy to redisperse when shaken. It forms 2 layers where one is clear and another one is white. Mixture II, III and IV contain 0.01g, 0.03g and 0.05g of Tragacanth respectively. The increasing weight of Tragacanth makes the texture become smoother and more viscous. The three suspensions share the same characteristics like cloudy, milky white and one layer.

2.      Plot a graph of UV absorption against time. Explain.

Time/min	0	5	10	15	20	25	30	35	40	45	50	55	60
Height/mm	11.9	11.9	11.8	11.7	11.7	11.4	11.2	11.1	10.8	10.7	10.6	10.6	10.4

The graph above shows the relationship between the heights of sedimentation with time. The suspension was white in colour, we need to use some light to observe the sedimentation clearly to avoid from making error. As observed on the graph, it is shows that the longer time taken the lower the heights of sedimentation. The result shows error as the correct observation should have increased heights of sedimentation instead of decreasing heights of sedimentation. This may be due to reading error or the mistake in the procedure during the experiments.

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

Time (minute)		Height of the sediment (millimetre)
		0	5	10	15	20	25	30	35	40	45	50	55	60
Amount of tragacanth (g)	0	95	20	16.5	14.5	13.5	13	13	13	13	13	13	13	13
	0.1	11.95	11.85	11.7	11.6	11.6	11.6	11.3	11.2	11.05	11	10.9	10.85	10.65
	0.3	0	4.5	8	8	11	11.5	19	32	32	32	34.5	34.5	34.5
	0.5	0	1.25	4.5	8.5	10	13	16.5	18	19.5	21	21	21	21

The graph above shows the relationship of the height of sedimentation with time for four different suspensions that contain different amounts of tragacanth. From the graph, it shows that the more the tragacanth content, the more the sediment formed. The experiment show incorrect results which may be due to experimental error.

By concept, the height of sediment decreases as the weight of tragacanth increases. The more the tragacanth content, the less the sediment formed. Suspension which contains more tragacanth is more stable as the tragacanth is the suspending agent. It is added to reduce sedimentation by structuring the continuous phase to produce a deflocculated system. For formulation with optimum amount of tragacanth, the system is stable and no slow flocculation occurs. A good suspension is a suspension that the sedimentation process does not happen quickly when the suspension is shaken. This is to allow that all the material in the suspension can disperse for a longer time to increase the efficiency of suspension administration.

The curve of 0.0g and 0.1g tragacanth illustrates decreasing formation of sediments. This observation is incorrect as along the time, the amount of sedimentation should be increased. This may be due to reading or experimental errors during the experiment. However, in the curve 0.0g tragacanth, initial formation of sedimentation is high. This can be explained due to the absence of tragacanth (suspending agent) and in which the system becomes not stable and the particles tend to flocculate and sediment easily.

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

Viscometer is a device that used to measure and determines the viscosity of a sample fluid. A rotational viscometer is used in this experiment. When immersed in a sample fluid, the rotational viscometer senses torque (twisting force) required to rotate a spindle at constant speed to calculate the viscosity of the fluid. The measured torque is proportional to the dynamic viscosity. Different viscosity of sample fluid requires different type of the spindle to have an accurate measurement on the viscosity. A more viscous suspension should use a thinner spindle and vice versa. Typical rotational viscometer consists of one cylinder rotating inside another stationary cylinder. The sample fluid will occupy the gap in between the two cylinders which will in turn resist rotation. The torque required to maintain constant rotational rate while overcoming viscous resistance and it is correlated with viscosity. Thus it can be said that the dynamic viscosity is proportional to the measured torque. The continuous changes in magnetic field cause the rotor magnet to spin. Thus, viscosity measurement is a direct correlation between fluid friction and applied torque. This measured data is then converted to a viscosity value and output to the users. The standard rotational viscometer is common used for measuring the viscosity of non-Newtonian fluids either in chemical or food industries. 

Amount of Tragacanth (g)	0.0	0.1	0.3	0.5
Viscosity (cP) (average±SD)	2.99±0.2650	1.93±0.5250	4.18±0.4000	2.95±0.0300

Tragacanth is a suspending agent that is used to suspend the chalk powder in this experiment. The viscosity of the suspension increasing with the increasing amount of Tragacanth added. Thus, a more stable suspension can be formed. From the graph plotted based on the result obtained from the experiment, it showed that the viscosity of the suspension increases gradually with the increase amount of Tragacanth added.  Formulation III with 0.3g Tragacanth is the most viscous suspension in this experiment with an average viscosity of 4.18cP. The least viscous suspension is Formulation II which has 0.1g Tragacanth record an average viscosity of 1.93cP.

5.      Plot a graph of height of ratio of sediment as a result of centrifugation vs. weight of Tragacanth. Give explanation.

From the graph, the height ratio is increased as the volume of tragacanth increased. However, this result is not correct due to experiment error which might due to incorrect handling of the experiment procedure .The actual result should be decreased of height ratio when the volume of tragacanth increased. This is because tragacanth acts as a suspending agent and can ensure stability of suspension.

Thus, more adding of tracaganth powder, slower the sedimentation rate and separation of the suspension will be lesser. An ideal suspension is where it has low viscosity after shear is applied and high viscosity when there is no shear. A suspension has to be pour readily and evenly.

6.      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?

The suspension has chalk, tragacanth, peppermint oil, syrup, double strength chloroform water and distilled water.

Chalk is the active ingredient of the suspension, tragacanth as suspending agent, peppermint oil as flavouring, syrup as vehicle of drug; double strength chloroform water gives preservative properties and distilled water as the vehicle.

Tragacanth is the suspending agent or thickening agent which can ensure stability of suspension. In fact, suspension consists of solid as dispersed phase and liquid as dispersed medium. Without any suspending agent, solid will collide each other, form granules which then sediment to form caking. This process is known as sedimentation which is affected by diameter of particle, difference of density between dispersed phase and continuous phase, gravity and viscosity of medium.

When we add tragacanth, it will adsorb on solid surface, reduces surface tension and free energy. Initially, suspension is thermodynamically unstable, solid particles tend to form granules due to high surface tension. When tragacanth is added, reduced surface tension will prevent these solid particles to collide each other. So, no larger granules are formed. As diameter of solid particles is small, so the rate of sedimentation is decreased (according to Stoke’s equation).

An ideal suspension has high viscosity when there is no shear but low viscosity when we apply shear on it. Generally, suspension has to be therapeutically active, physical and chemical stable and has good appealing. Specifically, a good suspension can be poured readily and evenly, uniform particle size range in the suspension and suitable viscosity. Therefore, tragacanth or any other suspending agent must added to the formulation to ensure stability of suspension.

CONCLUSION:

Tragacanth plays an important role in suspension formulation. An increase amount of tragacanth show that the formulation needs a longer time to suspend and the suspended material will retain much longer in the formulations. Suspension with 0.1g tracaganth is only slightly viscous, indicating that it can be redispersed readily upon shaking. Different amount of Tragacanth powder will affect the rate of sedimentation, the height of sediment formed and viscosity of suspension.

REFERENCES:

1. Ghosal & Srivastava, 2009. Fundamentals of Bio analytical Techniques And Instrumentation. PHI Learning Pvt. Ltd.

2. John F. Marriott, Pharmaceutical Compounding and Dispensing, 2006, Pharmaceutical Press Sdn Bhd