Desiccation ,sublimDesiccation ,sublimation & tirturationation & tirturation

By: Dr. Tahseen By: Dr. Tahseen IsmailIsmail

DesiccationDesiccation

Desiccation is the process of Desiccation is the process of removing adhered moisture from removing adhered moisture from liquid or solid substancesliquid or solid substances. The term . The term "desiccated" should be used for those "desiccated" should be used for those substances from which water has substances from which water has been completely removed.been completely removed.

DesiccationDesiccation

DesiccationDesiccation On laboratory scale desiccation can be carried On laboratory scale desiccation can be carried

out in a desiccator, which consists of a tightly out in a desiccator, which consists of a tightly closed glass vessel containing a drying agent at closed glass vessel containing a drying agent at its bottom, which absorbs moisture from the its bottom, which absorbs moisture from the substance being desiccated. The commonly used substance being desiccated. The commonly used drying agents include concentrated sulphuric drying agents include concentrated sulphuric acid, phosphorous pentoxide, exsiccated calcium acid, phosphorous pentoxide, exsiccated calcium chloride and silica gel. The drug to be dried is chloride and silica gel. The drug to be dried is taken in a dish, which is placed inside the taken in a dish, which is placed inside the desiccator above the surface of drying agent. For desiccator above the surface of drying agent. For continuous operation the desiccator may continuous operation the desiccator may sometimes be connected to a vacuum pump.sometimes be connected to a vacuum pump.

DesiccationDesiccation The substances which are very The substances which are very

sensitive to moisture are formulated sensitive to moisture are formulated as tablets or capsules which are as tablets or capsules which are further protected by enclosing them further protected by enclosing them in sealed vials, on the bottom of which in sealed vials, on the bottom of which a small cloth bag containing silica gel a small cloth bag containing silica gel is placed which acts as a desiccant. is placed which acts as a desiccant.

DesiccationDesiccation ApplicationsApplications Desiccation helps in preserving the vegetable Desiccation helps in preserving the vegetable

and animal drugs which get destroyed in the and animal drugs which get destroyed in the presence of moisture.presence of moisture.

2. Comminution of drugs is difficult if they are 2. Comminution of drugs is difficult if they are wet but if they are dry, can be easily powdered.wet but if they are dry, can be easily powdered.

3. Desiccation reduces the bulk and weight of 3. Desiccation reduces the bulk and weight of the substances due to loss of adhering the substances due to loss of adhering moisture in them therefore they become easy moisture in them therefore they become easy to handle.to handle.

4. Stability of certain drugs is also increased.4. Stability of certain drugs is also increased.

SUBLIMATIONSUBLIMATION

Sublimation is the process in which Sublimation is the process in which transforming the solid to vapors without transforming the solid to vapors without intermediate passage through the liquid intermediate passage through the liquid state.state.

Triple point.Triple point. Triple point is the point having a Triple point is the point having a

definite temperature and pressure at definite temperature and pressure at which the solid, liquid and vapor phases which the solid, liquid and vapor phases of a chemical substance co-existof a chemical substance co-exist

Triple point is a point in a graph Triple point is a point in a graph between temperature and pressure at between temperature and pressure at which three phases like solid, liquid and which three phases like solid, liquid and vapours may co exist.vapours may co exist.

Method of sublimationMethod of sublimation The pressure below the triple point is called as The pressure below the triple point is called as

Sublimation pressure.Sublimation pressure. In the diagram the line (AO) is known as In the diagram the line (AO) is known as

sublimation pressure. At this (O) point solid sublimation pressure. At this (O) point solid and liquid are at equilibrium. If the sublimation and liquid are at equilibrium. If the sublimation pressure is below this triple point the solid will pressure is below this triple point the solid will directly converted into vapor phase and the directly converted into vapor phase and the vapor phase is directly change into solid. vapor phase is directly change into solid.

Two factors in the diagram indicate that:Two factors in the diagram indicate that: When the vapor pressure of the substance is When the vapor pressure of the substance is

less then that of sublimation pressure, it will less then that of sublimation pressure, it will directly change into solid or vapor phase directly change into solid or vapor phase without changing into liquid phase. without changing into liquid phase.

Method of sublimationMethod of sublimation When the vapor pressure of the When the vapor pressure of the

substance is high then that of the substance is high then that of the sublimation pressure, then it will first sublimation pressure, then it will first convert into liquid phase and then into convert into liquid phase and then into solid state on further cooling.solid state on further cooling.

The common sublimed substances are as The common sublimed substances are as follows:follows:

Iodine Iodine NaphthalineNaphthaline CamphorCamphor Para-dichloride benzenePara-dichloride benzene Thus the vapor pressure of Iodine, Thus the vapor pressure of Iodine,

camphor, Naphthaline and camphor, Naphthaline and pp-dichloride -dichloride benzene are less triple point.benzene are less triple point.

Method of sublimationMethod of sublimation In laboratory it consists of a china dish, a In laboratory it consists of a china dish, a

perforated filter paper, funnel, and a cotton perforated filter paper, funnel, and a cotton plug.plug.

The material to be sublimed is placed in the The material to be sublimed is placed in the china dish; the china dish is covered with a china dish; the china dish is covered with a perforated filter paper. A glass funnel is placed perforated filter paper. A glass funnel is placed in the inverted position over the filter paper; the in the inverted position over the filter paper; the open end of the funnel is plugged with cotton to open end of the funnel is plugged with cotton to prevent the escape of sublimed product.prevent the escape of sublimed product.

The china dish is heated and vapors pass The china dish is heated and vapors pass through the perforations of the filter paper, and through the perforations of the filter paper, and are collected on the inner surface of the glass are collected on the inner surface of the glass funnel which is kept cool from out side by funnel which is kept cool from out side by wrapping a wet filter paper or cotton wool. The wrapping a wet filter paper or cotton wool. The vapors on cooling are condensed into solid vapors on cooling are condensed into solid which is collected.which is collected.

APPLICATIONSAPPLICATIONS

This process is used in the This process is used in the purification of many pharmaceutical purification of many pharmaceutical substances such as iodine, camphor, substances such as iodine, camphor, naphthalene, benzoic acid, mercuric naphthalene, benzoic acid, mercuric chloride, ammonium chloride.chloride, ammonium chloride.

This process is also employed to This process is also employed to purify volatile solids contaminated purify volatile solids contaminated with non volatile impurities. with non volatile impurities.

TriturationTrituration

By triturating the grinding of a solid substances By triturating the grinding of a solid substances is done to fine powder by continuous strike in or is done to fine powder by continuous strike in or rubbing the particles in a mortar with a pestle. rubbing the particles in a mortar with a pestle. The term trituration is also emloyed to designed The term trituration is also emloyed to designed the process by which two or more powders are the process by which two or more powders are intimately mixed with each other. For this intimately mixed with each other. For this purpose a pestle and mortar made of, porcelain purpose a pestle and mortar made of, porcelain or glass is used. For hard materials steel mortar or glass is used. For hard materials steel mortar and pestle may be used. and pestle may be used.

Trituration may be carried out with a tile and Trituration may be carried out with a tile and spatula or using a mortar and pestle. spatula or using a mortar and pestle.

Trituration using tile and Trituration using tile and spatulaspatula

Small quantities of finely powdered solids may be Small quantities of finely powdered solids may be mixed on a tile by means of a spatula.mixed on a tile by means of a spatula.

Tiles are usually made of glass and should be large Tiles are usually made of glass and should be large enough for the quantity of powder to be mixed or enough for the quantity of powder to be mixed or ointment to be prepared. Usually for small scale work ointment to be prepared. Usually for small scale work 300mm square is a useful size for a tile.300mm square is a useful size for a tile.

Spatula is made of stainless steel except for the few Spatula is made of stainless steel except for the few medicaments those react with stainless steel (iodine), medicaments those react with stainless steel (iodine), should be flexible and long blade (25mm by200mm) to should be flexible and long blade (25mm by200mm) to provide a large rubbing surface. provide a large rubbing surface.

Powders for Trituration are placed on the tile and Powders for Trituration are placed on the tile and gently mixed until the mixture is smooth and gently mixed until the mixture is smooth and homogeneous, but in the case of ointment if base is homogeneous, but in the case of ointment if base is very soft it may be helpful to warm the tile but very soft it may be helpful to warm the tile but overheating should be avoided because the base will overheating should be avoided because the base will become too fluid and may run off the edge of the tile. become too fluid and may run off the edge of the tile. The dispersion is then diluted with increasing amount The dispersion is then diluted with increasing amount of base, doubling the quantity each on the tile of each of base, doubling the quantity each on the tile of each dilution. Finally any liquid ingredient is incorporated.dilution. Finally any liquid ingredient is incorporated.

Trituration using mortar & Trituration using mortar & pestlepestle

A mortar should be used when the quantities are A mortar should be used when the quantities are too large . A mortar with a fairly flat base and a too large . A mortar with a fairly flat base and a pestle with a flat head will give best results.pestle with a flat head will give best results.

It is impossible to ensure intimate dispersion of one It is impossible to ensure intimate dispersion of one powder in another by mixing the two substances all powder in another by mixing the two substances all at once.at once.

The purpose is to add a substance that is present in The purpose is to add a substance that is present in greater amount to the whole of the substance greater amount to the whole of the substance present in lesser amount. Substance present in present in lesser amount. Substance present in greater amount is introduced into the mixture in greater amount is introduced into the mixture in very small quantities at first, but gradually very small quantities at first, but gradually increasing the quantities, until the whole of the increasing the quantities, until the whole of the substance has been added.. substance has been added..