The Use Of Wetting Agent In Suspension

Date of Experiment : 15^th September 2015

Introduction 

            Suspension is a formulation where insoluble solid is suspended in a liquid when the disperse phase is solid and the continuous phase is liquid by the aid of suspending agent. There are certain types of suspension which are oral, topical, parenteral and ophthalmic suspensions. One of the function of suspension is to mask the bad taste of some drug. A good suspension should be physically and chemically stable, resistant to microbial contamination, homogenously dispersed when shaken , easily poured and consist of uniform dispersed size particles.

            Besides, suspension should be able to redisperse when the solid particles settled. Wetting agents which is also known as surfactants which should be added because the drugs are not readily suspended in the liquid medium which is the aqueous phase. The examples of suspension are tragacanth.Surfactant is use to reduce the interfacial surface tension between the drug particles and the suspension vehicles. Other excipients also added to a suspension include preservatives which is to prevent microbial growth while colouring agent and syrup are to improve the tasteof the suspension. The advantages of suspension are that it improves the stability of the active ingredient, palatability and bioavailability of the formulation. Drugs in suspension are chemically more stable than in a solution.

Objective  

To study the effect of different amount of tragacanth on the sedimentation rates of                                suspensions.

Apparatus 

1 mL graduated pipette                      Pipette bulb

Weighing boat                                     Set of mortar and pestle

50 mL graduated cyclinder                 200 mL graduated cyclinder

100 mL beaker                                    Parafilm

Weighing balance                                Viscometer

Materials 

Chalk                                                   Tragacanth

Concentrated peppermint water          Double strength chloroform water

Distilled water                                     Syrup BP

Methodology 

1.      A suspension of Pediatric Chalk Mixture (150 mL) was prepared according to the following formula:

Ingredient	Suspension
	A	B	C
Chalk (g)	3	3	3
Tragacanth (g)	0.0	0.1	0.3
Concentrated peppermint water (mL)	0.6	0.6	0.6
Syrup BP (mL)	15	15	15
Double Strength Chloroform water (mL)	75	75	75
Distilled water q.s. (mL)	150	150	150

2.      5 mL of the suspension was poured into a weighing boat and labelled each formulation. Observe and compare texture, clarity and colour of each suspension.

3.      The sedimentation rate of each suspension was determined. The suspension was shook vigorously until all the particles were uniformly suspended. The time was noted. The boundary between the sediment and the supernatant was observed the time it takes for the boundary to pass each 10 mL graduation until the volume of sediment has reached 80 mL was recorded.

4.      The gradated 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 suspension was recorded at t=0, 2, 5, 10, 15 and 30 min.

6.      The obtained data was recorded in the table shown in result.

7.      The sedimentation volume ratio was calculated using the following formula:

Sedimentation volume ratio = Hu/Ho

Hu : Ultimate height of the sediment, i.e., the height of sediment at a particular time

Ho: Initial height of the total suspension

8.      The ease of re-dispersibility of each formulation was examined after the last measurement. To do this:

                                i.            The Parafilm was snugged on the mouth of the graduated cylinder and the seal was re-enforced with our gloved hand.

                              ii.            The number of inversions it takes to completely re-disperse the drug were counted.

                            iii.            The observations were recorded.

9.      95 mL of suspension was poured into a 100 ml beaker and the viscosity of the suspension was determined using viscometer at 12 000 rpm for 2 min.

10.  The data was recorded in the table shown in result.

11.  Each suspension was poured into a plastic bottle.  After storing all the suspensions for a period of 4 days, the ease of redispersion in each system was determined and the system which is most acceptable was determined.

Result 

Suspension	Sedimentation volume at pre-determined time (min)						Distinct boundary ( yes/no)
	0	2	5	10	15	30
A	0	36	20	16	13	12	Yes
B	0	3	5	6	6	7	No
C	0	0	0.5	0.5	1	1	No

         Table 1 : The sedimentation volume at pre-determined time (min) of suspensions

Suspension	Volume of sedimentation (ml)
	A						B						C
	0	2	5	10	15	30	0	2	5	10	15	30	0	2	5	10	15	30
Initial volume of total suspension (Vo)	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100
Ultimate volume of sediment (Vu)	0	36	20	16	13	12	0	3	5	6	6	7	0	0	0.5	0.5	1	1
Sedimentation volume ratio (Vu/Vo)	0	0.36	0.20	0.16	0.13	0.12	0	0.03	0.05	0.06	0.06	0.07	0	0	0.005	0.005	0.01	0.01

Table 2 : Sedimentation volume ratio of suspensions

Suspension	A			B			C
Trials	1	2	3	1	2	3	1	2	3
Viscosity (cP)	0.5	0.6	0.5	0.5	1.0	1.5	1.5	1.5	2.0
Mean	0.53			1.00			1.67
SD	0.047			0.486			0.236

Table 3 : The mean of suspension viscosity

Physical	Paediatric chalk mixture
Characteristics	A	B	C
Texture	Coarse texture, less viscous	Smooth texture, viscous	Very smooth texture, more viscous
Clarity	Less cloudy	Moderate cloudy	Cloudy
Colour	White	White	White

Table 4 : Comparison between suspensions physical characteristics

Time (min)		Volume of sediment ( mL )
		10	20	30	40	50	60	70	80
Suspension	A	0.2	1.17	1.75	-	-	-	-	-
	B	>15	-	-	-	-	-	-	-
	C	>15	-	-	-	-	-	-	-

Table 5 : Volume of sediment of each suspensions (mL)

Suspension	A	B	C
Number of inversion	2	6	11

Table 6 : Number of inversion for redisperse

Discussion 

1. Compare and discuss physical appearance of all suspensions produced.

The physical appearance of the suspensions is compared based on the texture, clarity, and color of each suspensions. Texture is determined based on the appearance, feel or consisting of a surface while clarity is based on the quality of being clear. The color of the suspension is determined through an observation of the changes in the color of suspensions.

            For suspension A with 0.0 g of tragacanth powder, the texture is coarse and less viscous. The absence of the tragacanth as the suspending agent caused the suspensions to sediment very fast and the particles separated into two distinct boundaries and become less viscous . This makes the clarity of the suspensions to be clearer and less cloudy due to separation of water from the insoluble ingredients. The color is white at the bottom and colorless at the top of the suspensions.

              For suspension B with 0.1 g tragacanth powder, we can see that the texture is quite smooth with very little sediment at first and the suspension is more viscous than suspension A. This may be by the presence of the suspending agent which helps to prevent settlement of the suspended solids under gravity. The clarity of this suspensions is opaque compared with the clear suspensions A because the suspensions do not seem to separate into two separate layers and they mix together .The color is white.

              Lastly, for suspension C with much higher amounts of tragacanth powder, 0.3 g, the texture is very smooth and very viscous compared to suspension B.This is because an increase in the tragacanth powder helps to mix the excipients very well and prevent sedimentation to occur at a fast rate. While the clarity is much more cloudy because the excipients bind together and no sedimentation occurs.The color is white,same with suspension B.

2. Plot the V_u / V_o vs time for each suspensions (Table 1) . Discuss the findings .

From the graph shown above we can see that the sedimentation rate for suspension A decreases with time while sedimentation rate for suspensions B and C increases with time.

For the suspension A , the sedimentation rate decreases over time because due to absence of the suspending agent which is in this experiment is tragacanth powder caused the suspensions  to sediment at a very fast rate after we shake it. So with time , the particles will continue to sediment in a compact way thus will decreases the volume of sediment.

For the suspension B and C , due to presence of tragacanth powder as the suspending agent , the suspensions tend to sediment in a lower rate and much lower with the increase of the tragacanth powder in the formulation . Therefore , the sediment process is very slower and with time , the volume of the sediment will be increase .

Therefore , suspension with no tragacanth powder will decrease the sedimentation rate while suspensions with tragacanth powder will increase their sedimentation rate.

3. Briefly explain the principle of analysis using viscometer . Plot the viscosity vs tragacanth content (Table 2).Discuss the findings.

All fluids have an internal friction between molecules, and this measures how well it flows. Due to the internal friction, energy is required to move the liquid and viscosity is the measure of the resistance to flow. A viscometer measures the torque required to rotate a spindle in a fluid. The spindle is driven by a synchronous motor through a calibrated spring and the deflection of the spring is displayed by the viscometer. By changing speeds and spindles, a variety of viscosity ranges can be measured. For a given viscosity, the viscous drag, or resistance to flow (indicated by the degree to which the spring winds up), is proportional to the spindle's speed of rotation and is related to the spindle's size and shape. The drag increases with an increase of spindle's size and/or rotational speed. For a given spindle geometry and speed, an increase in viscosity will be indicated by an increase in the deflection of the spring. The minimum range is obtained by using the largest spindle at the highest level; the maximum range by using the smallest spindle at the slowest speed.

Based on the graph, viscosity of suspension is directly proportional to the amount of Tragacanth used in the formulation. Tragacanth is a suspending agent and also imparts viscosity to the solution. The viscosity of suspension should increase when the amount of tragacanth increase. This is due to the function of tragacanth as the thickening agent that reduce the surface tension between particles of solid and liquid. Thus, it will reduce the movement of suspended particles. Therefore,the higher the amount of tragacanth powder , the higher the viscosity of the suspensions.

4. After storing the suspension for a period of 4 days, determine the ease of redispersion of each.

After storing the suspension for a period of 4 days, product A can redispersed very easily because the active ingredient can spread evenly in the solution by only 2 number of inversion. Product B can redispersed moderately easy. The number of inversion is 6. This means that it needs 6 times number of inversion for the active ingredient to redisperse in the vehicle. Last, product C can hardly redispersed in the vehicle. This is because the number of inversion for product C to redisperse is the highest, which is 11. This indicates the time taken for the active ingredient in product C to redispersed is the longest.

5. Based on all the observation, which product would be considered to be most acceptable? Explain.

Based on the observation, product B will be the most acceptable. This is because the amount of tragacanth,0.1g added able to let the chalk dispersed evenly for enough period of time to be poured and dispensed to the patients. Furthermore, it is not too viscous, the number of inversion is 6.  This indicates when the suspension is being shaken, it will not take too long for the active ingredient to redisperse. This will enable the patients to get the exact amount of active ingredients inside the suspension as needed. Hence, it is most acceptable product.

6. Briefly explain the function of each excipients used in the suspension formulation. Explain the influence of tragacanth on the physical characteristic and stability of a suspension.

In this experiment, chalk acts as an active ingredient to determine the sedimentation rate of suspension after the addition of tragacanth. Tragacanth acts as a wetting agent, also known as surfactant. It is added to the suspension in order for the solid to disperse evenly for longer time in the suspension. This can improve the stability of the active ingredient. Concentrated peppermint water is a flavouring agent and masks the unpleasant taste of the drug. It is added to the suspension to increase the palatability of the suspension.  Syrup bp acts as a sweetening agent. Double Strength Chloroform water acts as a preservative for the suspension. Distilled water will act as a vehicle in a suspension.

Conclusion 

In conclusion, the rate of sedimentation and the height of sediment formed in the suspension was influenced by the different amount of  tragacanth powder used to form the suspension. The higher the amount of tragacanth powder used, the lower the height of sediment formed. This is because, the tragacanth powder is a good suspending agent and their action prevents the solution from forming sediment. Furthermore, we found that the viscosity of suspension also increases as the amount of tragacanth powder increases. Viscosity of suspension is important in reducing sedimentation rate. The higher the viscosity of the suspension, the lower the sedimentation rate.

References 

1. http://intranet.tdmu.edu.ua/data/kafedra/internal/pharma_3/classes_stud/%D0%90%D0%9F%D0%A2%D0%95%D0%A7%D0%9D%D0%90%20%D0%A2%D0%95%D0%A5%D0%9D%D0%9E%D0%9B%D0%9E%D0%93%D0%86%D0%AF%20%D0%9B%D0%86%D0%9A%D0%90%D0%A0%D0%A1%D0%AC%D0%9A%D0%98%D0%A5%20%D0%97%D0%90%D0%A1%D0%9E%D0%91%D0%86%D0%92/%D1%84%D0%B0%D1%80%D0%BC%D0%B0%D1%86%D0%B5%D0%B2%D1%82%D0%B8%D1%87%D0%BD%D0%B8%D0%B9%20%D1%84%D0%B0%D0%BA%D1%83%D0%BB%D1%8C%D1%82%D0%B5%D1%82/3%20%D0%BA%D1%83%D1%80%D1%81/%D0%A4%D0%B0%D1%80%D0%BC%D0%B0%D1%86%D1%96%D1%8F/english/Suspensions.htm
2. http://www.viscopedia.com/methods/measuring-principles/
3. http://pharmlabs.unc.edu/labs/suspensions/stable.htm