The Use of Wetting Agent in Suspension

Title

The Use of Wetting Agent in Suspension

Objective

The objective of this experiment is to investigate the the effect of different amount of tragacanth on the sedimentation rates of suspensions.

Date of Experiment

15^th September 2015

Introduction

            The term "suspension" refers to a two-phase system consisting of a finely divided solid dispersed (suspended) in a liquid (the dispersing medium). Suspensions are heterogeneous mixture containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than one micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain excipients or suspending agents. Unlike colloids, suspensions will eventually settle. An example of a suspension would be sand in water. The suspended particles are visible under a microscope and will settle over time if left undisturbed. This distinguishes a suspension from a colloid, in which the suspended particles are smaller and do not settle.^[2] Colloids and suspensions are different from solutions, in which the dissolved substance (solute) does not exist as a solid, and solvent and solute are homogeneously mixed.

Suspensions are intended for oral administration as sweetened, flavored formulations or for topical application where they are referred to as "lotions." Suspensions are also used as non-sweetened, non-flavored formulations for many parenteral routes of administration.

Suspensions possess more advantages than other dosage forms. Some drugs are insoluble in all acceptable media and must, therefore, be administered as a tablet, capsule, or as a suspension. Moreover, drugs in suspension are chemically more stable than in solution. However, 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. Therefore, the best strategy is not to try to eliminate separation, but rather to decrease the rate of settling and to permit easy re-suspension of any settled particulate matter. One of the strategies is to use wetting agent like tragacanth to reduce surface tension.

Experimental Method

Apparatus

1.      Graduated pipette

2.      Pipette Bulb

3.      Weighing boat

4.      Mortar and pestle

5.      Graduated cylinder 50ml

6.      Graduated cylinder 200ml

7.      Parafilm

8.      Weighing balance

9.      Beaker 100ml

10.  Viscometer

Chemicals

1.      Chalk

2.      Tragacanth

3.      Concentrated peppermint water

4.      Double strength chloroform water

5.      Syrup BP

6.      Distilled water

Experimental Procedures

1.       Suspensions of Pediatric Chalk Mixture (150 mL) were prepared according to the following formula:

Ingredients	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 each formulation was labeled. Texture, clarity and color of each suspension were observed and compared.

 

3.     The sedimentation rate of each suspension was determined. The suspension was shook vigorously making sure all of the particles are uniformly suspended, and time was noted. The boundary between the sediment and the supernatant was observed and the time it takes for the boundary to pass each 10 mL graduation until the volume of sediment has reached 30 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 suspensions A to C, the sedimentation volume of the suspensions was recorded at t=0, 2, 5, 10, 15, and 30 min.

6.         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 the sediment at a particular time

Ho: initial height of the total suspension

7.       The ease of re-dispersibility of each formulation was observed after the last measurement. 

          To do this:

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

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

                            iii.            Observations were recorded.

8.       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.

9.        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 which system is most acceptable was determined.

Results

Table 1 : Sedimentation volume of suspensions at pre-determined time

Suspension	Sedimentation volume at pre-determined time (min)					Distict boundary
	0	2	5	10	15
A	100	40	18	12	11	Yes
B	100	100	100	98	98	No
C	100	100	100	100	99	No

Table 2 : Time taken for the boundary between sediment and supernatant  to pass each 10ml graduation

	Time taken for the boundary to pass each 10ml graduation (s)
	Suspension A	Suspension B	Suspension C
10ml	40	More than 15mins	More than 15mins
20ml	45	More than 15mins	More than 15mins
30ml	62	More than 15mins	More than 15mins
40ml	80	More than 15mins	More than 15mins
50ml	105	More than 15mins	More than 15mins
60ml	112	More than 15mins	More than 15mins
70ml	135	More than 15mins	More than 15mins
80ml	168	More than 15mins	More than 15mins

Table 3 : Number of inversions needed to redisperse the drug

Suspension	Number of Inversion needed
A	4
B	2
C	1

Table 4 : Viscosity of suspension

Formula of standard deviation

SUSPENSION A

Reading	1	2	3	4
Viscosity (cP)	0.5	0.4	0.6	0.5
Mean + SD	0.5 ± 0.07

SUSPENSION B

Reading	1	2	3	4
Viscosity (cP)	0.5	0.8	1.5	1.5
Mean + SD	1.075 ± 0.438

SUSPENSION C

Reading	1	2	3	4
Viscosity (cP)	1.5	1.5	1.5	1.5
Mean + SD	1.5 ± 0

Table 5 : Texture, Clarity and Colour of Suspension

Suspension	Texture	Clarity	Colour
A	-          Less viscous -          Easily sediment -          Easily redisperse	-          Less cloudy	-          White but less milky
B	-          Viscous -          Hardly sediment -          Moderately easy to redisperse	-          Cloudy	-          Milky white
C	-          Very concentrated -          Hardly sediment -          Hardly redisperse	-          Very cloudy	-          Milky white

Discussion

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

Suspension B is less viscous compared to suspension C but observably more viscous compared to suspension A. This is due to the presence of Tragacanth powder in Suspension B is literally less compared to in suspension C while the absence of Tragacanth powder in solution A. Tragacanth powder acts as a viscous factor due the amount poured into the suspension and also the physical form of tragacanth which is powder form.

Suspension B is difficult to sediment compared to solution A but easier to sediment compared to suspension C. This is due to the presence of Tragacanth powder that slows the sedimentation of chalk in the suspension. Solution A is very easy to sediment because of large surface tension of the solution. Tragacanth powder acts as wetting agent in suspension B and C thus it will slow sedimentation.

The colour of the solution A and Suspension B and C are white due to the presence of Chalk powder. However, the solution A is less milky due to the presence of the tragacanth powder.

Sedimentation volume ratio: Hu/Ho Hu: Height of the sediment at a particular time Ho: initial height of total suspension

2. Plot Hu/Ho vs Time for each of the suspensions (Table 1). Discuss the findings.

Sedimentation volume ratio: Hu/Ho

Solution A: 11/100= 0.11

At time 15 min: Solution A: 11/100= 0.11 Suspension B: 98/100= 0.98 Suspension C: 99/100= 99

At time 10 min: Solution A: 12/100= 0.12 Suspension B: 98/100= 0.98 Suspension C: 100/100= 1

At time 2 min: Solution A: 40/100= 0.4 Suspension B: 100/100= 1 Suspension C: 100/100= 1

At time 5 min: Solution A: 18/100= 0.18 Suspension B: 100/100= 1 Suspension C: 100/100= 1

At time 0: Solution A: 100/100= 1 Suspension B: 100/100= 1 Suspension C: 100/100= 1

Suspension B: 98/100= 0.9

GRAPH OF HU/HO AGAINST TIME

 

Based on the graph plotted above, for the solution A, it is distinctively dropped until 0.11 for 15 minutes. This shows that Solution A sediments easily as the viscosity of the solution A is very low. This may due the chalk which has low solubility in the solution.

While for suspension B and C, they have very indistinctively results for 15 minutes experiments. This may due to the presence of wetting agent(or suspending agent) which is Tragacanth powder that wets the Chalk particles so that it can dissolve in the solution forming suspension. Suspension is very hard to be sediment but  it is possible for a long period of time.

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

Tragacath (g)	Vicocity (cP)
	1	2	3	4	Mean ± SD
0.0	0.5	0.4	0.6	0.5	0.5 ± 0.07
0.1	0.5	0.8	1.5	1.5	1.075 ± 0.438
0.3	1.5	1.5	1.5	1.5	1.5 ± 0

Rotational viscometers use the idea that the torque required to turn an object in a fluid is a function of the viscosity of that fluid. They measure the torque required to rotate a disk or bob in a fluid at a known speed. It is operates as the motor of viscometer rotate with the speed 300rpm. Stirrer is rotated by disc which in turn moved by spring more than 180°.LED emit infra red radiation and diffuse through the disc and then detected by a photo diod. The infra red radiation detected and read by the photo diod is depend on the change of degree of disc rotation.

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.

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

Suspension A is easy to redispers because it do not have any tragacath, follow by suspension B and suspension C.

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

    Explain.

The higher the amount of tragacanth powder, the lower the height of sediment formed. The more amount of tragacanth powder added, suspension will be smooth, cloudy and stable. A stable suspension is the suspension which take longer time for sedimentation to occur. With higher content of tragacanth powder in suspension, there is less flocculation.  For suspension with lesser amount of tragacanth powder, it will be less smooth, less stable and clearer. Sedimentation occurs more easily but it will be easier to redisperse if compared to higher content of tragacanth powder because only one inversion is needed to redisperse them. Therefore suspension C is the most stable suspension.

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

The materials used in this suspension preparation are chalk, tragacanth, concentrated peppermint oil, syrup BP, double strength chloroform water and distilled water.

- Chalk is the active ingredient in this suspension. Chalk function as the adsorbent and used to treat diarrhea as it can adsorbs excessive fluids in watery faeces.

- Tragacanth powder acts as the suspending agent and wetting agent that used to decrease interfacial tension between solid particle and liquid from continuous phase. It increases the viscosity of a solution and the stability of the preparation because the suspended particles will take longer time to settle down.

- Concentrated peppermint oil is a flavouring agent, as it gives a nice scent.

- Syrup BP functions as sweetening agent and help increasing the viscosity of the suspension.

- Double strength Chloroform water is used as a preservative and dissolving solvent.

- Distilled water is used as a vehicle and diluent.

Conclusion

We can conclude that higher content of tragacanth produces more smooth and viscous texture while preventing from formation of cake or sedimentation. On the other hand, suspension with lower content of tragacanth is less smooth, less viscous and easily spread. Thus, content with high content of tragacanth can produce stable suspension.

References

1. http://formulation.vinensia.com/2011/12/list-and-characteristic-of-suspending.html

2. http://priory.com/pharmacy/Suspension_Gum_SuspendingAgent.htm

3. John F. Marriott, Pharmaceutical Compounding And Dispensing, 2006, Pharmaceutical Press Sdn Bhd