Manufacturing procedures of Suspensions and Multiple choice questions on Suspensions for GPAT, NIPER, Pharmacist and Drug Inspector exam
Equipment for Suspensions:
1-Mortar and pestle: It consists of a glass or porcelain mortar and a pestle.
Advantages:
- Small quantity suspenisons can be prepared in the laboratory.
- Low cost.
- Simplest operation among all other instruments.
Disadvantages:
- Generally, the final particle size is considerable larger then in other equipment.
- It is necessary for the ingredients to have a certain viscosity prior to trituration in order to achieve a satisfactory shear.
Figure 1 – Mortar Pestle
2. Agitators / Mechanical stirrers: A suspension may be prepared by means of various impellers (propellers: produce axial movements; turbines produce radial and tangential movements) mounted on shafts. For low viscosity suspensions propeller type can be used but for higher viscosity turbine type is used. The degree of agitation is controlled by the rotational speed of impeller, by the patterns of the liquid flow and the resultant efficiency of mixing are controlled by the type of impeller, its position in the container, the presence of baffles, and the general shape of the container.
Advantages:
- Can be used for small-scale production and laboratory purpose.
Disadvantages:
- Continuous shaking tends to break up not only the phase to be dispersed but also the dispersion medium, in this way, impairs the ease of suspension. Remedy: Slow the speed of agitator. Avoid continuous running.
Figure 2 – Agitators / Mechanical stirrers
3. Colloid mill: The principle of operation of the colloid mill is the passage of the mixed phases of a suspension between a stator and a high speed rotor revolving at speeds of 2000 to 18,000 rpm. The clearance between the rotor and the stator is adjustable, usually from 0.001 inch upward. The suspension mixture, while passing between the rotor and the stator, is subjected to a tremendous shearing action which effects a fine dispersion of uniform size. The shearing forces applied in the colloid mill usually raises the temperature within the suspension. Hence, a coolant is used to absorb the excess heat.
Figure 3 – Colloid mill
Advantages:
- Very high shearing force can be generated.
- Very fine particles can be prepared.
- Particularly useful in preparing suspensions containing poorly wetted solids.
- Useful for the preparation of relatively viscous emulsions.
Disadvantages:
- It has no wide applications in solids.
- Wear of the rotating plates.
- No fine grinding.
- Consume energy.
4. Homogenizers: Impeller type of equipment frequently produce a satisfactory emulsion; however, for further reduction in particle size, homogenizers may be employed. Homogenizers may be used in one of two ways:
- The ingredients in the suspension are mixed and then passed through the homogenizer to produce the final product.
- A coarse suspension is prepared in some other way and then passed through a homogenizer for the purpose of decreasing the particle size and obtaining a greater degree of uniformity and stability.
The coarse suspension (basic product) enters the valve seat at high pressure (1000 to 5000 psi), flows through the region between the valve and the seat at high velocity with a rapid pressure drop, causing cavitation; subsequently the mixture hits the impact ring causing further disruption and then is discharged as a homogenized product. It is postulated that circulation and turbulence are responsible mainly for the homogenization that takes place. Sometimes a single homogenization may produce an emulsion which, although its particle size is small, has a tendency to clump of form clusters. Emulsions of this type exhibit increased creaming tendencies. This is corrected by passing the emulsion through the first stage of homogenization at a high pressure (e.g. 3000 to 5000 psi) and then through the second stage at a greatly reduced pressure (e.g. 1000 psi). This breaks down any clusters formed in the first step (it is a two stage homogenizer).
5. Ultrasonic devices: The preparation of emulsions by the use of ultrasonic vibrations also is possible. An oscillator of high frequency (100 to 500 kHz) is connected to two electrodes between which placed a piezoelectric quartz plate. The quartz plate and electrodes are immersed in an oil bath and, when the oscillator is operating, high-frequency waves flow through the fluid. Emulsification is accomplished by simply immersing a tube containing the emulsion ingredients into this oil bath.
Advantages:
- Can be used for low viscosity and extremely low particle size.
Disadvantages:
- Only in laboratory scale it is possible. Large scale production is not possible.
Equipment for suspension Size Reduction Equipments:
Triple roller mill: Disperse small tightly bound agglomerates and hard discrete particles. Particles are subjected to high shear, mechanical crushing.
Ball Mill: It is used for size reduction fine solid discrete particles or for deagglomeration of very tightly bound agglomerates. The machine consists of cylindrical drum into which a charge of heavy spherical balls usually metal or ceramic is loaded along with the components of the dispersion.
Multiple choice questions:
1.Equipment used for manufacturing of suspensions is/are
a)Mortar and pestle
b)Colloid mill
c)Homogenizers
d)All of these
2.Mortar and pestle is made up of
a)glass
b)porcelain
c)plastic
d)a and b
3.Which of the following is not an advantage of mortar and pestle?
a)Small quantity suspenisons can be prepared in the laboratory
b)Low cost
c)Simplest operation among all other instruments
d)It is necessary for the ingredients to have a certain viscosity prior to trituration in order to achieve a satisfactory shear
4.Disadvantages of mortar and pestle are
a)The final particle size is considerable larger then in other equipment
b)It is necessary for the ingredients to have a certain viscosity prior to trituration in order to achieve a satisfactory shear
c)Small quantity suspenisons can be prepared in the laboratory
d)a and b
5.Propellers produce
a)axial movements
b)radial movements
c)tangential movements
d)all of these
6.Turbines produce
a)axial movements
b)radial movements
c)tangential movements
d)b and c
7.For low viscosity suspensions we use
a)propeller
b)turbine
c)both of these
d)none of these
8.For high viscosity suspensions we use
a)propeller
b)turbine
c)both of these
d)none of these
9.Advantage of Agitators / Mechanical stirrers is
a)Can be used for small-scale production and laboratory purpose
b)Very high shearing force can be generated
c)Can be used for low viscosity and extremely low particle size
d)All of these
10.The principle of operation of the colloid mill is the passage of the mixed phases of a suspension between a stator and a high speed rotor revolving at speeds of
a)1000 to 18,000 rpm
b)2000 to 18,000 rpm
c)2000 to 10,000 rpm
d)2000 to 5,000 rpm
11.Which of the following is not an advantage of colloid mill?
a)It has no wide applications in solids
b)Very high shearing force can be generated
c)Very fine particles can be prepared
d)Useful for the preparation of relatively viscous emulsions
12.Disadvantages of colloid mill are
a)Wear of the rotating plates
b)No fine grinding
c)Consume energy
d)All of these
13.Advantage of Ultrasonic devices is
a)Very high shearing force can be generated
b)Useful for the preparation of relatively viscous emulsions
c)Can be used for low viscosity and extremely low particle size
d)All of these
14.Disadvantage of Ultrasonic devices is
a)Only in laboratory scale it is possible. Large scale production is not possible
b)It has no wide applications in solids
c)Continuous shaking tends to break up not only the phase to be dispersed but also the dispersion medium, in this way, impairs the ease of suspension
d)All of these
15.Equipments used for size reduction of suspensions are
a)Triple roller mill
b)Ball Mill
c)Both of these
d)Size reduction not required
Solutions:
- d)All of these
- d)a and b
- d)It is necessary for the ingredients to have a certain viscosity prior to trituration in order to achieve a satisfactory shear
- d)a and b
- a)axial movements
- d)b and c
- a)propeller
- b)turbine
- a)Can be used for small-scale production and laboratory purpose
- b)2000 to 18,000 rpm
- a)It has no wide applications in solids
- d)All of these
- c)Can be used for low viscosity and extremely low particle size
- a)Only in laboratory scale it is possible. Large scale production is not possible
- c)Both of these
References:
- Pharmaceutical engineering(principles & practices) by C.V.S. Subrahmanyam, page no. 155,161,229.
- Remington Essential of Pharmaceutics, 1st edition 2013, page no. 459.
- Ansel’s Pharmaceutical Dosage Forms and drug Delivery system, 10th edition, page no. 456-459.
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