Saturday, February 26, 2011
Lyophilization
It is also referred to as “freeze-drying”, “sublimation-drying” or “cryodesiccation”.
Definition:
It is the process of isolation of a substance (solid) from solution by freezing it and evaporating the ice under vacuum (by sublimation).
Process of lyophilization:
In the process of lyophilization, water or any other solvent is removed from a frozen solution by sublimation caused by reduction of the temperature and pressure to values at a lower level than the triple point.
Under the application of these conditions, heat applied is used as latent heat and the ice converts directly to the vapor state (by the process of sublimation).
Practically, the following features must be taken into account.
Temperature and pressure are necessary to be at a lower level than the triple point and it is usually -10 ºC to -30 ºC and 10 N/m2 to 30 N/m2 respectively. To achieve this pressure, the vapors must be removed or else the vapor pressure will affect this pressure.
Stages of the freeze-drying process:
Following stages are found in lyophilization:
1. Freezing
2. Vacuum
3. Primary drying
4. Secondary drying
5. Packaging
Freezing:
The material is usually frozen before the application of vacuum. A number of methods are used in freezing of the material.
In shell freezing, the bottle is partially filled with the material to be frozen. It is placed in a refrigerator almost horizontally and rotated slowly. In this way the material freezes along side the walls of the bottle and resulting in large area for heat transfer and sublimation.
In vertical spin freezing, small crystals of ice are produced. In this method, the bottles are first placed in a moderate coldness and rotated quickly in vertical position in a constant flow of very cold air. This result in the liquid becoming super cooled and freezing occurs rapidly.
Vacuum:
Vacuum pumps are used to create the vacuum and reducing the pressure sufficiently.
On small scale, two-stage rotary pumps are used while on large scale ejector pumps are used.
Primary drying:
During the primary drying, two important processes are followed i.e. (1) vapors are removed by applying (2) the latent heat of sublimation. The apparatus similar to the vacuum oven can be used.
Heat transfer is crucial in this process as the extra heat may cause the material to melt and less heat may cause the process to be prolonged or no sublimation. So, heat transfer must be controlled.
Vapor removal is important to reduce a change in pressure. On the small scale, vapor is removed by using desiccant such as phosphorus pentoxide or by using a small condenser. And on the large scale condensation is helpful to remove vapors and by using pumps such ejector pumps.
The rate of drying in lyophilization is very low showing that the rate of drying of ice is about 1 mm depth per hour.
Secondary drying:
The primary drying may leave about 0-5 % of moisture in the solid, which can be removed by secondary drying process.
In this method, temperature may raise above 0 ºC to break any type of physico-chemical interactions between the frozen material and the water molecules resulting in the removal of the moisture.
High temperature can be used, as the risk of hydrolysis is negligible in the secondary drying because the secondary drying is an ordinary vacuum drying phase.
Packaging:
After the completion of freeze-drying process, vacuum is usually removed by the application of an inert gas such as nitrogen before the material is tightly closed. Great care is needed in the packaging of freeze dried products. Containers must be tightly closed to protect from moisture.
Freeze-drying equipment:
There are three types of freeze-dryers:
1. Rotary evaporators
2. Manifold freeze-dryers
3. Tray freeze-dryers
Uses:
Aqueous solutions and/or dispersions of oxygen-sensitive or heat-sensitive drugs, biologicals such as blood products (such as peptides, proteins), antibiotics (other than penicillin), vaccines (such as BCG, yellow fever, smallpox) and enzyme preparations (such as hyaluronidase) and microbiological cultures are usually freeze-dried.
After freeze-drying and packing the material in a vial, the material can be stored, shipped and reconstituted later to the primary form for the use as injection.
It increases the shelf life of some of the pharmaceuticals for many years.
Advantages of lyophilization:
1. Decomposition and hydrolysis of the product is reduced as a result of prevention of the enzyme action due to very low temperature.
2. Oxidation is reduced as a result of high vacuum and less air.
3. The product is light and porous as the original solution was frozen and there is no incorporation of extra materials.
4. As the product is porous so this results in more solubility.
Disadvantages of lyophilization:
1. The high porous nature (results in more solubility) and highly dried state results in a highly hygroscopic product. So special conditions are required up to packaging.
2. The process is very slow and requires expensive instruments and plants.
Definition:
It is the process of isolation of a substance (solid) from solution by freezing it and evaporating the ice under vacuum (by sublimation).
Process of lyophilization:
In the process of lyophilization, water or any other solvent is removed from a frozen solution by sublimation caused by reduction of the temperature and pressure to values at a lower level than the triple point.
Under the application of these conditions, heat applied is used as latent heat and the ice converts directly to the vapor state (by the process of sublimation).
Practically, the following features must be taken into account.
Temperature and pressure are necessary to be at a lower level than the triple point and it is usually -10 ºC to -30 ºC and 10 N/m2 to 30 N/m2 respectively. To achieve this pressure, the vapors must be removed or else the vapor pressure will affect this pressure.
Stages of the freeze-drying process:
Following stages are found in lyophilization:
1. Freezing
2. Vacuum
3. Primary drying
4. Secondary drying
5. Packaging
Freezing:
The material is usually frozen before the application of vacuum. A number of methods are used in freezing of the material.
In shell freezing, the bottle is partially filled with the material to be frozen. It is placed in a refrigerator almost horizontally and rotated slowly. In this way the material freezes along side the walls of the bottle and resulting in large area for heat transfer and sublimation.
In vertical spin freezing, small crystals of ice are produced. In this method, the bottles are first placed in a moderate coldness and rotated quickly in vertical position in a constant flow of very cold air. This result in the liquid becoming super cooled and freezing occurs rapidly.
Vacuum:
Vacuum pumps are used to create the vacuum and reducing the pressure sufficiently.
On small scale, two-stage rotary pumps are used while on large scale ejector pumps are used.
Primary drying:
During the primary drying, two important processes are followed i.e. (1) vapors are removed by applying (2) the latent heat of sublimation. The apparatus similar to the vacuum oven can be used.
Heat transfer is crucial in this process as the extra heat may cause the material to melt and less heat may cause the process to be prolonged or no sublimation. So, heat transfer must be controlled.
Vapor removal is important to reduce a change in pressure. On the small scale, vapor is removed by using desiccant such as phosphorus pentoxide or by using a small condenser. And on the large scale condensation is helpful to remove vapors and by using pumps such ejector pumps.
The rate of drying in lyophilization is very low showing that the rate of drying of ice is about 1 mm depth per hour.
Secondary drying:
The primary drying may leave about 0-5 % of moisture in the solid, which can be removed by secondary drying process.
In this method, temperature may raise above 0 ºC to break any type of physico-chemical interactions between the frozen material and the water molecules resulting in the removal of the moisture.
High temperature can be used, as the risk of hydrolysis is negligible in the secondary drying because the secondary drying is an ordinary vacuum drying phase.
Packaging:
After the completion of freeze-drying process, vacuum is usually removed by the application of an inert gas such as nitrogen before the material is tightly closed. Great care is needed in the packaging of freeze dried products. Containers must be tightly closed to protect from moisture.
Freeze-drying equipment:
There are three types of freeze-dryers:
1. Rotary evaporators
2. Manifold freeze-dryers
3. Tray freeze-dryers
Uses:
Aqueous solutions and/or dispersions of oxygen-sensitive or heat-sensitive drugs, biologicals such as blood products (such as peptides, proteins), antibiotics (other than penicillin), vaccines (such as BCG, yellow fever, smallpox) and enzyme preparations (such as hyaluronidase) and microbiological cultures are usually freeze-dried.
After freeze-drying and packing the material in a vial, the material can be stored, shipped and reconstituted later to the primary form for the use as injection.
It increases the shelf life of some of the pharmaceuticals for many years.
Advantages of lyophilization:
1. Decomposition and hydrolysis of the product is reduced as a result of prevention of the enzyme action due to very low temperature.
2. Oxidation is reduced as a result of high vacuum and less air.
3. The product is light and porous as the original solution was frozen and there is no incorporation of extra materials.
4. As the product is porous so this results in more solubility.
Disadvantages of lyophilization:
1. The high porous nature (results in more solubility) and highly dried state results in a highly hygroscopic product. So special conditions are required up to packaging.
2. The process is very slow and requires expensive instruments and plants.
Statistical Quality Control in Pharmaceutics
Definition:
Statistical quality control (SQC)is defined as:
“The monitoring of quality by application of statistical method in all stages of production.”
Explanation:
Statistical methods of investigation are based on the theory of probability.
• Type of measurement
• Sampling techniques
• Design of Experiments
• Type of Sample distribution
The procedure consists of:
• Proper sampling of product
• Determining quality variations of the sample
• Making inferences to the entire batch under investigation from the observed data
• Once the characteristic data pattern of a process has been determined, the pattern can be utilized to predict the limits within which future data can be expected to fall as a matter of chance, and to determine when significant variations in the process have taken place.
Data Analysis:
Data can be analyzed by using appropriate method of analysis:
t-test:
t-test for comparison of two populations. T-value is calculated and from t-value the P-value is noted from the table:
If
P>0.05; test is non-significant
And if
P<0.05; test is significant.
ANOVA:
It means analysis of variance and is used for comparison of more than 2 parameters.
Objectives:
The objective is to determine whether the major source of observed variations is by chance or assignable.
Types of variations:
Chance variations:
These variations are inevitable because any program of production and inspection has its own unique chance causes of variations which can not be controlled or eliminated and often cannot be identified.
Assignable variations:
These variations can usually be detected and corrected by statistical techniques. Assignable variations are usually caused by machine or a specific batch of production or a container.
Thus the use of SQC permits the:
• Evaluation of magnitude of chance variation of product quality.
• Detection of assignable variations of product quality by means of QC charts.
Statistical quality control (SQC)is defined as:
“The monitoring of quality by application of statistical method in all stages of production.”
Explanation:
Statistical methods of investigation are based on the theory of probability.
It relates to the characteristic of product from both qualitative and quantitative point of views to meet the established standards.
Uses:
It has been used to serve:
• As a basis for improved evaluation of materials through more representative sampling technique
• As a means of achieving sharper control in certain manufacturing processes
• To provide logical approach to variations
Selection:
Selection of appropriate method depends on:• Type of measurement
• Sampling techniques
• Design of Experiments
• Type of Sample distribution
Procedure:
The procedure consists of:
• Proper sampling of product
• Determining quality variations of the sample
• Making inferences to the entire batch under investigation from the observed data
• Once the characteristic data pattern of a process has been determined, the pattern can be utilized to predict the limits within which future data can be expected to fall as a matter of chance, and to determine when significant variations in the process have taken place.
Data Analysis:
Data can be analyzed by using appropriate method of analysis:
t-test:
t-test for comparison of two populations. T-value is calculated and from t-value the P-value is noted from the table:
If
P>0.05; test is non-significant
And if
P<0.05; test is significant.
ANOVA:
It means analysis of variance and is used for comparison of more than 2 parameters.
The objective is to determine whether the major source of observed variations is by chance or assignable.
Types of variations:
Chance variations:
These variations are inevitable because any program of production and inspection has its own unique chance causes of variations which can not be controlled or eliminated and often cannot be identified.
Assignable variations:
These variations can usually be detected and corrected by statistical techniques. Assignable variations are usually caused by machine or a specific batch of production or a container.
Thus the use of SQC permits the:
• Evaluation of magnitude of chance variation of product quality.
• Detection of assignable variations of product quality by means of QC charts.
Sublimation
Definition:
It is conversion of a substance in solid state to a gaseous state, which is not accompanied by the formation of liquid phase.
It is similar in some aspects to the distillation process.
Process of sublimation:
At normal pressures, most of the chemical substances either compounds or elements have three different states of matter at various temperatures. In these circumstances, change from solid state to gaseous state requires a median state that is liquid.
On the other hand, some of the chemical substances such as compounds and elements at certain pressures go directly from solid state to the gaseous state. This occurs when the atmospheric pressure applied on the material is very less to inhibit the molecules from going out of the solid state i.e. a substance go through the process of sublimation only if the vapor pressure is less than that of the triple point for that substance.
Triple point:
The triple point is the point possessing a fixed pressure and temperature at which the solid, liquid and gaseous phases of a material are able to co-exist independently.
If the vapor pressure over the solid substance is more than that of the triple point, the solid will convert to vapor after passage through the liquid phase. The following phase diagram will help to understand the triple point.
Line OA:
In this diagram, line OA shows the melting points of the solid substance at different pressures. In this line, left side shows the existence of solid form while the right side shows the existence of liquid form. This line shows the points of co-existence of the solid and the liquid.
Line OB:
The line OB shows the vapor-pressure curve of the liquid at different temperatures. Above this line liquid phase exists and below this line vapor phase of the substance exists. This line shows the points of co-existence of the liquid and the vapors.
Line OC:
The line OC shows the sublimation curve of the solid. This line shows the points of co-existence of the solid and the vapors at different states of temperatures and pressure.
Point O:
In this diagram, the point O represents the triple point.
Enthalpy:
Enthalpy of sublimation is equal to the sum of enthalpy of fusion and enthalpy of vaporization.
Sublimation process represents an endothermic phase transition as shown by the phase diagram.
Examples:
Nearly all of the solids have some tendency of conversion from solid to gaseous state at a particular temperature and pressure.
Elements:
Cadmium, Zinc, Arsenic, Carbon
Compounds:
CO2 (Dry ice), NH4Cl
Uses:
Its most important use is in freeze-drying.
It is conversion of a substance in solid state to a gaseous state, which is not accompanied by the formation of liquid phase.
It is similar in some aspects to the distillation process.
Process of sublimation:
At normal pressures, most of the chemical substances either compounds or elements have three different states of matter at various temperatures. In these circumstances, change from solid state to gaseous state requires a median state that is liquid.
On the other hand, some of the chemical substances such as compounds and elements at certain pressures go directly from solid state to the gaseous state. This occurs when the atmospheric pressure applied on the material is very less to inhibit the molecules from going out of the solid state i.e. a substance go through the process of sublimation only if the vapor pressure is less than that of the triple point for that substance.
Triple point:
The triple point is the point possessing a fixed pressure and temperature at which the solid, liquid and gaseous phases of a material are able to co-exist independently.
If the vapor pressure over the solid substance is more than that of the triple point, the solid will convert to vapor after passage through the liquid phase. The following phase diagram will help to understand the triple point.
In this diagram, line OA shows the melting points of the solid substance at different pressures. In this line, left side shows the existence of solid form while the right side shows the existence of liquid form. This line shows the points of co-existence of the solid and the liquid.
Line OB:
The line OB shows the vapor-pressure curve of the liquid at different temperatures. Above this line liquid phase exists and below this line vapor phase of the substance exists. This line shows the points of co-existence of the liquid and the vapors.
Line OC:
The line OC shows the sublimation curve of the solid. This line shows the points of co-existence of the solid and the vapors at different states of temperatures and pressure.
Point O:
In this diagram, the point O represents the triple point.
Enthalpy:
Enthalpy of sublimation is equal to the sum of enthalpy of fusion and enthalpy of vaporization.
Examples:
Nearly all of the solids have some tendency of conversion from solid to gaseous state at a particular temperature and pressure.
Elements:
Cadmium, Zinc, Arsenic, Carbon
Compounds:
CO2 (Dry ice), NH4Cl
Uses:
Its most important use is in freeze-drying.
Friday, February 25, 2011
Elutriation
The word “Elutriation” is derived from the Latin word “elutriare” meaning “to wash out”.
Definition:
It is the separation, purification or removal of something from a mixture by decanting, straining or washing.
Process of elutriation:
In the process of elutriation, the movement of the fluid, generally water or air, is in the opposite direction to that of the sedimentation process.
Types of elutriation:
According to direction:
Vertical elutriation:
In the gravitational process, the larger particles present in water (or any other liquid) will move vertically downwards with the affect of gravity while the small particles in the fluid travels straight up with the fluid. This is a type of vertical elutriation.
Horizontal elutriation:
If a water current of suspended particles is flowed through a settling chamber. The particles that move out of the water current are collected in the bottom of the chamber. This is a type of horizontal elutriation.
Centrifugal elutriation:
In this case the water current is caused to spin with some force resulting in the large centrifugal force on the suspended particles. The heavier particles will settle to the walls of the elutriator or to the bottom.
The DorrClone is an example of a centrifugal-type of classifier.
According to the type of fluid:
• Air elutriation
• Water elutriation
If the velocity of the fluid is smaller than the velocity of setting down of the particles then the particles will settle downwards. On the other hand, if the velocity of the fluid is larger than the velocity of setting down of the particles then the particles will be carried up along with the fluid.
Air elutriation will give precise separation of the particles and in less time than water elutriation.
Factors affecting elutriation:
Elutriation is affected by the
• velocity of the fluid
• the particle size : As the small sized particles will flow (upward) along the fluid while the large sized particles will move downwards (against the velocity of the fluid).
• position of the particle in the (tube containing) fluid
• density of the particle
In a tube, there exist different velocities i.e. the velocity is largest in the centre and is smallest along the walls of the tube. So the small sized particles move upward, when in the centre and in the meantime they are also pushed towards the wall of the tube. Where the velocity is smaller and here the small sized particles start to move downwards.
Process of removal of particles:
If the upward flow of the water (or any other liquid) is slightly increased, the small sized particles (which move down slowly) will move along the movement of the water (i.e. upward) and will be removed from the water. In this process, the medium sized particles will remain immobile and the heavier particles will continue to move downward.
The upward flow of water will then again be increased and the next smallest size particles will be removed. And in this way, particles of different sizes will be separated and obtained.
Definition:
It is the separation, purification or removal of something from a mixture by decanting, straining or washing.
Process of elutriation:
In the process of elutriation, the movement of the fluid, generally water or air, is in the opposite direction to that of the sedimentation process.
Types of elutriation:
According to direction:
Vertical elutriation:
In the gravitational process, the larger particles present in water (or any other liquid) will move vertically downwards with the affect of gravity while the small particles in the fluid travels straight up with the fluid. This is a type of vertical elutriation.
Horizontal elutriation:
If a water current of suspended particles is flowed through a settling chamber. The particles that move out of the water current are collected in the bottom of the chamber. This is a type of horizontal elutriation.
Centrifugal elutriation:
In this case the water current is caused to spin with some force resulting in the large centrifugal force on the suspended particles. The heavier particles will settle to the walls of the elutriator or to the bottom.
The DorrClone is an example of a centrifugal-type of classifier.
According to the type of fluid:
• Air elutriation
• Water elutriation
If the velocity of the fluid is smaller than the velocity of setting down of the particles then the particles will settle downwards. On the other hand, if the velocity of the fluid is larger than the velocity of setting down of the particles then the particles will be carried up along with the fluid.
Air elutriation will give precise separation of the particles and in less time than water elutriation.
Factors affecting elutriation:
Elutriation is affected by the
• velocity of the fluid
• the particle size : As the small sized particles will flow (upward) along the fluid while the large sized particles will move downwards (against the velocity of the fluid).
• position of the particle in the (tube containing) fluid
• density of the particle
In a tube, there exist different velocities i.e. the velocity is largest in the centre and is smallest along the walls of the tube. So the small sized particles move upward, when in the centre and in the meantime they are also pushed towards the wall of the tube. Where the velocity is smaller and here the small sized particles start to move downwards.
Process of removal of particles:
If the upward flow of the water (or any other liquid) is slightly increased, the small sized particles (which move down slowly) will move along the movement of the water (i.e. upward) and will be removed from the water. In this process, the medium sized particles will remain immobile and the heavier particles will continue to move downward.
The upward flow of water will then again be increased and the next smallest size particles will be removed. And in this way, particles of different sizes will be separated and obtained.
Centrifugation
It refers to the process of sedimentation by using centrifuge machine.
Basic idea behind centrifugation:
Centrifugation is based on the widely known idea of sedimentation by the use of centrifugal force, which represents a force that apparently moves a spinning or rotating object away from the axis of rotation in a curved path.
Centrifugal effect:
The processes using centrifugal force (F) can be described by the equations involving the gravitational constant (G). In this case, it is easy to determine the centrifugal force in the terms of the ratio of the centrifugal force to the gravitational force. In addition, this ratio represents the centrifugal effect (C).
Centrifugal effect (C) shows that how many times the centrifugal force is larger than gravitational force.
C = 2.013 dn^2
Where
d = diameter of rotation
n = speed of rotation
Here in this equation, “n” has the value in “s-1” and “d” has the value in “m”.
This equation shows that centrifugal effect is directly proportional to the diameter and to the square of the speed of the rotation i.e. greater will be the diameter of the tube or container more will be centrifugation and similarly for the speed of rotation.
Factors affecting centrifugation:
Centrifugation is basically affected by centrifugal effect. Moreover, nature of the liquid medium in which the particles are placed also affects the centrifugation.
Apparatus for centrifugation (Centrifuges):
Container is the most important part of centrifugation apparatus i.e. centrifuges. This container is used for the placement of a mixture or solution of solid and liquid or of a solution of two liquids.
This container is then rotated at greater speed resulting in the separation of the ingredients of the mixture takes place by the use of centrifugal force.
Mechanism for the separation in the apparatus of centrifugation:
A mixture of liquid or solid in a liquid of low density can be separated as the material of larger density is thrown in the outward direction to the bottom of the tube or container with a larger force. This results in the separation of pure, low-density liquid as a transparent or purified supernatant liquid which forms upper layer.
Types of centrifuges:
There are two basic types of centrifuges:
1. Sedimentation
2. Filtration
Sedimentation centrifuges:
The basic principle, in the sedimentation type of centrifuges, is difference in the densities of the ingredients of the mixture. In these types of centrifuges, the particles are settled to the wall by the action of the centrifugal force.
These types of centrifuges are used for the separation of ingredients of the mixture of solid in liquid as well as liquid in liquid.
Two types of centrifuges are based on the principle of sedimentation:
1. Bottle centrifuge
2. Disc type centrifuge
Bottle centrifuge:
It is mostly used centrifuge machine in the laboratories. It consists of a vertical rotating rod that causes the “bottle-type” containers or test tubes, which are fixed symmetrically, to be rotated in a horizontal plane resulting in the separation of the materials of varying densities. The vertical rod is rotated usually by means of electric motor. Sometimes, gas turbines can also be used for the rotation.
Disk type centrifuge:
It consists of vertical pile of thin conical disks, which are arranged in the manner of one on the top of another. The sedimentation of the particles takes place in the space between neighbouring cones. In this way, settling distance is greatly reduced, thereby increasing the rate at which the particles in the material are separated. The cones are adjusted in such a manner that heavier material moves down the surface easily upon reaching the inner surface of the cone.
It is same in the basic operation to the sedimentation types of centrifuges but instead of solid containers or tubes, it contains a porous wall or perforated containers or baskets, which causes the liquid phase to pass through it but keeps the solid phase on it.
Centrifuge based on the principle of filtration is “Basket centrifuge”.
Basket centrifuge:
Basket centrifuge consists of a porous wall and rotor which is cylindrical and tubular in structure. The porous wall is some times replaced by one or more of the fine mesh screens. The fluid go through the screen where as the particles larger in size are left on the screen.
Centrifugation is used for the separation of ingredients of a mixture of solid in liquid or liquid in liquid as the degree of separation achieved by centrifugation is of greater amplitude than the action due to gravity.
It is important specifically when the separation by normal filtration methods is difficult such as in the separation of fluids of highly viscous nature.
In the pharmaceutical research, it is considered as an important tool in determining the stability of emulsions.
Bottle centrifuge can be used for:
1. Finding the sediments present in crude vegetable and mineral oils
2. Determination of the butterfat content in the milk
3. Various clinical trials and tests
Disk type centrifuge can be used for refining of vegetable oils by removing soap stock
Basket centrifuge can be used for:
1. Drying and washing of several different kinds of crystals and fibrous materials
2. The preparation of cane sugar.
Basic idea behind centrifugation:
Centrifugation is based on the widely known idea of sedimentation by the use of centrifugal force, which represents a force that apparently moves a spinning or rotating object away from the axis of rotation in a curved path.
Centrifugal effect:
The processes using centrifugal force (F) can be described by the equations involving the gravitational constant (G). In this case, it is easy to determine the centrifugal force in the terms of the ratio of the centrifugal force to the gravitational force. In addition, this ratio represents the centrifugal effect (C).
Centrifugal effect (C) shows that how many times the centrifugal force is larger than gravitational force.
C = 2.013 dn^2
Where
d = diameter of rotation
n = speed of rotation
Here in this equation, “n” has the value in “s-1” and “d” has the value in “m”.
This equation shows that centrifugal effect is directly proportional to the diameter and to the square of the speed of the rotation i.e. greater will be the diameter of the tube or container more will be centrifugation and similarly for the speed of rotation.
Factors affecting centrifugation:
Centrifugation is basically affected by centrifugal effect. Moreover, nature of the liquid medium in which the particles are placed also affects the centrifugation.
Apparatus for centrifugation (Centrifuges):
Container is the most important part of centrifugation apparatus i.e. centrifuges. This container is used for the placement of a mixture or solution of solid and liquid or of a solution of two liquids.
This container is then rotated at greater speed resulting in the separation of the ingredients of the mixture takes place by the use of centrifugal force.
Mechanism for the separation in the apparatus of centrifugation:
A mixture of liquid or solid in a liquid of low density can be separated as the material of larger density is thrown in the outward direction to the bottom of the tube or container with a larger force. This results in the separation of pure, low-density liquid as a transparent or purified supernatant liquid which forms upper layer.
Types of centrifuges:
There are two basic types of centrifuges:
1. Sedimentation
2. Filtration
Sedimentation centrifuges:
The basic principle, in the sedimentation type of centrifuges, is difference in the densities of the ingredients of the mixture. In these types of centrifuges, the particles are settled to the wall by the action of the centrifugal force.
These types of centrifuges are used for the separation of ingredients of the mixture of solid in liquid as well as liquid in liquid.
Two types of centrifuges are based on the principle of sedimentation:
1. Bottle centrifuge
2. Disc type centrifuge
Bottle centrifuge:
It is mostly used centrifuge machine in the laboratories. It consists of a vertical rotating rod that causes the “bottle-type” containers or test tubes, which are fixed symmetrically, to be rotated in a horizontal plane resulting in the separation of the materials of varying densities. The vertical rod is rotated usually by means of electric motor. Sometimes, gas turbines can also be used for the rotation.
Disk type centrifuge:
It consists of vertical pile of thin conical disks, which are arranged in the manner of one on the top of another. The sedimentation of the particles takes place in the space between neighbouring cones. In this way, settling distance is greatly reduced, thereby increasing the rate at which the particles in the material are separated. The cones are adjusted in such a manner that heavier material moves down the surface easily upon reaching the inner surface of the cone.
Filtration centrifuges:
These types of centrifuges are used for the separation of the mixture of solid in liquid only performing the operation similar to the filtration process. These are also sometimes referred to as clarifiers.It is same in the basic operation to the sedimentation types of centrifuges but instead of solid containers or tubes, it contains a porous wall or perforated containers or baskets, which causes the liquid phase to pass through it but keeps the solid phase on it.
Centrifuge based on the principle of filtration is “Basket centrifuge”.
Basket centrifuge:
Basket centrifuge consists of a porous wall and rotor which is cylindrical and tubular in structure. The porous wall is some times replaced by one or more of the fine mesh screens. The fluid go through the screen where as the particles larger in size are left on the screen.
Application of centrifugation:
Centrifugation is used for the separation of ingredients of a mixture of solid in liquid or liquid in liquid as the degree of separation achieved by centrifugation is of greater amplitude than the action due to gravity.
It is important specifically when the separation by normal filtration methods is difficult such as in the separation of fluids of highly viscous nature.
In the pharmaceutical research, it is considered as an important tool in determining the stability of emulsions.
Bottle centrifuge can be used for:
1. Finding the sediments present in crude vegetable and mineral oils
2. Determination of the butterfat content in the milk
3. Various clinical trials and tests
Disk type centrifuge can be used for refining of vegetable oils by removing soap stock
Basket centrifuge can be used for:
1. Drying and washing of several different kinds of crystals and fibrous materials
2. The preparation of cane sugar.
Bougies
Introduction:
Its name came from the town namely “bougie” in Algeria, which was famous for trading in wax. Its original meaning is “A candle made by wax”. These are the types of suppositories intended for insertion into the urethra, nostrils or ears.
It is also a medical instrument in the shape of cylinder, made up of a flexible tube.
Forms of bougie:
Bulbous bougie:
It is a form of bougie with a bulb shaped tip.
Eder-pustow bougie:
It is a form of metal bougie which resembles olive in shape. It may be used in esophageal stricture.
Elastic bougie:
A bougie made of rubber or latex.
Elbowed bougie:
A bougie with a bent near its tip.
Use:
It is used for opening of constricted areas in tubular organs such as urethra or esophagus and rectum, so, that medicines for local application or another instruments can easily be inserted in that part.
Its name came from the town namely “bougie” in Algeria, which was famous for trading in wax. Its original meaning is “A candle made by wax”. These are the types of suppositories intended for insertion into the urethra, nostrils or ears.
It is also a medical instrument in the shape of cylinder, made up of a flexible tube.
Forms of bougie:
Bulbous bougie:
It is a form of bougie with a bulb shaped tip.
Eder-pustow bougie:
It is a form of metal bougie which resembles olive in shape. It may be used in esophageal stricture.
Elastic bougie:
A bougie made of rubber or latex.
Elbowed bougie:
A bougie with a bent near its tip.
Use:
It is used for opening of constricted areas in tubular organs such as urethra or esophagus and rectum, so, that medicines for local application or another instruments can easily be inserted in that part.
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