LAB # 5
PREPARATION AND STABILITY OF COLLOIDS
 Dispersed systems consist of particulate matter known as the dispersed phase,
distributed throughout a continuous phase, or dispersion medium.
 Dispersed systems are classified on the basis of mean particle diameter of the
dispersed material:
1. Molecular dispersions (less than 1 nm (mμ)). E.g., O2 molecules, ions.
2. Colloidal dispersions (0.5 μm to 1 nm (mμ)). E.g., colloidal silver sol, natural and
synthetic polymers.
3. Coarse dispersions (> 0.5 μm). E.g., emulsions and suspensions.
 Types of colloidal systems:
1. Lyophilic colloids: (solvent-loving)
 Colloidal particles interact to an appreciable extent with the dispersion medium.
 Attraction between the dispersed phase and the dispersion medium leads to
salvation (formation of a solvent sheath around the dispersed phase).
 It consists of organic molecules e.g., gelatin, acacia, albumin.
 Their stability depends on the presence of solvent sheath . if removed, the sol will
precipitate (unstable).
2. Lyophobic colloids: (solvent-hating)
 There is little attraction between the dispersed phase and the dispersion medium.
 There is no solvent sheath around the particles.
 They composed of inorganic particles e.g., silver, gold, sulfur, and silver iodide.
 Their stability depends on the presence of the surface charges (the like charges
produce repulsion which prevent coagulation of particles). The neutralization of these
charges (by an electrolyte) will cause instability of the sol (ppt or discoloration).
3. Association colloids:
 These colloids consist of amphiphiles or surface active agents.
Preparation of lyophobic colloids
1. silver tannate sol (-ve charge):
 To 500 ml of distilled water, add 20 ml 0.1 N AgNO3 (pipette) and then add 10 ml of
1% tannic acid solution. Heat this solution to 80 oC .
 Add 10 ml of 1% Na2CO3 solution (pipette) dropwise with continuous stirring until a
tea-colored (dark brown, opaque) sol is obtained.
Preparation of lyophilic colloids
1. gelatin sol:
 Soak 5 gm of gelatin powder in 50 ml water for 5 minutes.
 Add 175 ml of water and heat the mixture on a hot plate with stirring until complete
dissolving of gelatin. Cool, and adjust the volume to 250 ml with water.
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PHT 312 Practical notes
Stability of colloids
1. Silver tannate sol (using 0.1 M NaCl):
No.
1
2
3
4
5
6
Silver tannate sol
5 ml
5 ml
5 ml
5 ml
5 ml
5 ml
Distilled water
5 ml
4 ml
3 ml
2 ml
1 ml
--
--
1 ml
2 ml
3 ml
4 ml
5 ml
0.1 M NaCl
 Record the test tube in which precipitation or discoloration may occur, why?
Precipitation may occur due to the neutralization of charge on silver sol.
N.B., if an electrolyte with a higher valency than NaCl is used (e.g., CaCl2 or AlCl3), less
volume will be required to induce the discoloration.
2. Gelatin sol (using ethanol):
No.
1
2
3
4
Gelatin sol
5 ml
5 ml
5 ml
5 ml
Ethanol
5 ml
10 ml
15 ml
20 ml
 Record the test tube in which precipitation may occur, why?
Precipitation may occur due to the removal of the solvent (water) sheath around gelatin sol.
This sol can be redispersed again by the addition of water.
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PHT 312 Practical notes
LAB # 6
PHARMACEUTICAL SUSPENSIONS
 A pharmaceutical suspension may be defined as a coarse dispersion of finely divided
insoluble material randomly distributed in a liquid medium or available in dry form to be
distributed in the liquid when desired.
 An ideal suspension should be:
1. Easily resuspended by moderate shaking,
2. Should remain suspended long enough to withdraw an accurate dosage, and
3. Should have the desired flow properties (i.e., viscosity must not be so high), so it is
pourable,
4. The suspended particles should be small and uniform in size so that the product is free
from a gritty texture.
Flocculated suspension:
Is the one in which the repulsive surface charges of the suspended particles have been
chemically neutralized and the attractive "Van der Waals" becomes dominant. Under these
conditions, the particles may approach each other more closely and form loose aggregates,
termed ' flocs'.
Deflocculated suspension:
Are characterized as dispersions in which the particles exist as single entities with high
repulsive surface charges. In contrast to flocculated systems, a deflocculated system
exhibits well dispersed particles which settle singly but more slowly. The particles have a
tendency to form a sediment or cake that is difficult to redisperse.
The relative properties of flocculated and deflocculated suspensions:
Flocculated
1.
2.
3.
4.
5.
6.
7.
Deflocculated
Particles forms loose aggregates and form a network like
structure
Rate of sedimentation is high, because force of gravity is
dominant.
Sediment is rapidly formed
Sediment is loosely packed and doesn’t form a hard cake
Sediment is easy to redisperse, because when floccules
sediment, they trap solvent which make them easy to
break apart and resuspend again.
Suspension is not pleasing in appearance (due to the
presence of an obvious supernatant layer above a coarse
sediment layer.)
The floccules stick to the sides of the bottle.
1.
2.
3.
4.
5.
6.
7.
Particles exist as separate entities
Rate of sedimentation is slow
Sediment is slowly formed
Sediment is very closely packed and a hard cake is formed
Sediment is difficult to redisperse, because particles settle
into a tighter aggregate without trapping the solvent.
Suspension is pleasing in appearance
They don’t stick to the sides of the bottle
Notes:
 The most frequently used flocculating agents are electrolytes, which reduce the zeta
potential surrounding the solid particles. This leads to decrease in repulsion potential and
makes the particle come together to from loosely arranged structure (floccules). The
flocculating power increases with the valency of the ions.
 Suspending agents can be added to flocculated suspension to retard sedimentation.
Examples include: methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl
cellulose, acacia, gelatin and tragacanth. These agents entrap the particles and reduce
their sedimentation. Also, they increase the viscosity of the formulation and, hence,
decrease the sedimentation velocity. However, high viscosity of suspensions is
undesirable because it causes difficulty in pouring and may affect drug absorption and
suppress the dissolution rate.
 Sedimentation volume (F) of a suspension is expressed by the ratio of the equilibrium
volume of the sediment, Vu, to the total volume, Vo of the suspension. i.e., F = Vu/Vo .
The value of F normally lies between 0 to 1 for any pharmaceutical suspension. When F
= 1, no sedimentation and no clear supernatant will be observed.
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PHT 312 Practical notes
Evaluation of different materials as suspending agents
1. Prepare different formulations of calamine suspension using different suspending agents,
according to the following table:
No.
Ingredients
1.
(control)
1.
(control)
1.
(control)
1.
(control)
Calamine
Water up to
2.
2.
2.
2.
Calamine
Acacia powder
Water up to
3.
3.
3.
3.
Calamine
Tragacanth powder
Water up to
4.
4.
4.
4.
Calamine
Methyl cellulose 5%
Water up to
5.
5.
5.
5.
Calamine
Bentonite powder
Water up to
Sediment height (cm)at each time interval
1.25 g
25 ml
5min
15min
30min
45min
60min
24hr
5min
15min
30min
45min
60min
24hr
5min
15min
30min
45min
60min
24hr
5min
15min
30min
45min
60min
24hr
5min
15min
30min
45min
60min
24hr
F
1.25 g
2%
25 ml
F
1.25 g
2%
25 ml
F
1.25 g
2%
25 ml
F
1.25 g
2%
25 ml
F
2. For each formula: mix the ingredients in a mortar using pestle. Triturate very well, then transfer the
mixture into a graduated cylinder, rinse the mortar with additional part of water and add that to the
graduate. Complete each mixture to 25 ml. Cover with parafilm and mix.
3. Record the height of the sediment after 5 min, 15 min, 30 min, 45 min, 60 min, 24 hr, and 1 week.
4. Calculate the sedimentation volume ratio (F) for each system at each time interval using the
equation:  Sediment volume ratio (F) =
se dim ent..height ..(cm) Vu

total..height
Vo
(N.B., Sedimentation volume is the ratio of the ultimate volume, or height, of the sediment, Vu, to the
original volume of the suspension, Vo, before settling).
5. Based on the value of F, determine the superior suspending agent to be used with calamine
suspension.
The most appropriate suspending agent will show a value of F that is closer to
unity and remains constant, or with minimum changes, during the time of
observation.
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PHT 312 Practical notes
LAB # 7
DISPENSING OF PHARMACEUTICAL SUSPENSIONS
A. Magnesium Trisilicate Mixture (BP, 1980)
Ingredients
Master formula
Scaled formula
Magnesium trisilicate
50 g
2.5 g
Light magnesium carbonate
50 g
2.5 g
Sodium bicarbonate
50 g
2.5 g
Concentrated peppermint emulsion
25 ml
1.25 ml
Double strength chloroform water
500 ml
25 ml
Water
to produce
1000 ml
50 ml
Fiat: mixture
Send: 50 ml
Sig. 15 ml to be taken when necessary.
Calculations:
 F = 50/1000 = 0.05
 Multiply the Rx by Factor.
 Vehicle (water) =50 – (25+1.25) = 23.75 ml.
Procedure:
All powders are diffusible and can be easily wetted, so no need to use a suspending agent, like
acacia, to this formula.
1. In a mortar, mix thoroughly the fine powders of magnesium trisilicate, light magnesium carbonate.
2. Dissolve sodium bicarbonate in two thirds of the amount of vehicle.
3. Pour solution in step #2 gradually with trituration in order to prepare at first a smooth paste and
then a fine suspension devoid of any lumps.
4. Dilute the formed paste with successive small amounts of peppermint emulsion and chloroform
water, until it becomes pourable.
5. Transfer the diluted paste to a cylinder. Wash the mortar with the rest amount of water left, and mix
the washings with the mixture prepared.
6. Transfer the mixture to a suitable bottle and fix the label.
Role of each ingredient:
1. Magnesium trisilicate, Light magnesium carbonate and Sodium bicarbonate are diffusible materials
that act as antacids.
2. Concentrated peppermint emulsion is a flavoring agent.
3. Double strength chloroform water is a flavoring agent, sweetening agent and a preservative.
General use: as antacid preparation.
Label: white
Shake Before Use
Magnesium Trisilicate Mixture
One tablespoonful to be taken when necessary.
Name:
Date:
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PHT 312 Practical notes
B. Calamine lotion BP 1988:
Ingredients
Master formula
Scaled formula
Calamine
150 g
7.5 g
Zinc oxide
50 g
2.5 g
Bentonite
30 g
1.5 g
Sodium citrate
5g
0.25 g
Liquefied phenol
5 ml
0.25 ml
Glycerol
50 ml
2.5 ml
Purified water to
1000 ml
50 ml
Fiat: lotion
Send: 50 ml.
Sig. MDU
Calculations:
 F = 50/1000 = 0.05
 Multiply the Rx by F.
 Water
= 50 – (2.5+0.25) = 47.25 ml
Procedure:
1. Triturate calamine, zinc oxide and bentonite with a solution of sodium citrate in about 35
ml of purified water.
2. Add the liquefied phenol, and glycerol.
3. Add sufficient water to complete to the final volume.
Label : red
Shake Before Use
Calamine Lotion
To be used as directed.
Name:
Date:
General use: antipruritic , mild astringent, soothing and emollient preparation in treatment
of sunburns.
Role of each ingredient:
 Calamine: soothing, and antipruritic agent.
 Zinc oxide: astringent.
 Bentonite: suspending agent.
 Liquefied phenol: preservative.
 Glycerol: emollient.
 Sodium citrate: flocculating agent.
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PHT 312 Practical notes
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PHT 312 Practical notes