Various Methods of Preparation of Dispersed system (1).docx

Various Methods of Preparation of Dispersed system (1).docx

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  Various Methods ofPreparation of Dispersed system Dispersed System: A kinetically stable mixture of one phase in another largely immiscible phase. Usually at least one length scale is in the colloidal range. Emulsions: An emulsion is a dispersion in which the dispersed phase is composed of small globules of a liquid distributed throughout a vehicle in which it is immiscible. General Types of Pharmaceutical Emulsions: 1. Lotions 2. Liniments 3. Creams 4. Ointments 5. Vitamin drops Methods of Preparation of Emulsions: These are the methods used for the Preparation of Emulsions: 1. Continental or Dry Gum Method 2. English or wet Gum Method 3. Bottle or Forbes Bottle Method Continental or Dry Gum Method
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  i. The continentalmethod is also referred to as the 4:2:1 method because for every 4 parts by volume of oil, 2 parts of water and 1 part of gum are added in preparing the initial or primary emulsion. ii. For instance, if 40 mL of oil is to be emulsified, 20 mL of water and 10 g of gum would be employed iii. In the primary emulsion, with any additional water or other formulation ingredients added afterward. iv. In this method, the acacia or other o/w emulsifier is triturated with the oil in a perfectly dry Wedgwood or porcelain mortar until thoroughly mixed. A mortar with a rough rather than smooth inner surface must be used to ensure proper grinding action and reduction of the globule size. v. A glass mortar is too smooth to produce the proper reduction of the internal phase. vi. Solid substances such as preservatives, stabilizers, colorants, and any flavoring material are usually dissolved in a suitable volume of water (assuming water is the external phase) and added as a solution to the primary emulsion vii. Rather than using a mortar and pestle, the pharmacist can generally prepare an excellent emulsion using the dry gum method and an electric mixer or blender. English or Wet Gum Method: i. By this method, the same proportions of oil, water, and gum are used as in the continental or dry gum method ii. but the order of mixing is different, and the proportion of ingredients may be varied during the preparation of the primary emulsion as is deemed necessary by the operator.
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  iii. Generally, amucilage of the gum is prepared by triturating in a mortar granular acacia with twice its weight of water. The oil is then added slowly in portions, and the mixture is triturated to emulsify the oil. iv. Should the mixture become too thick, additional water may be blended into the mixture before another portion of oil is added for several minutes v. After all of the oil has been added, the mixture is thoroughly mixed vi. Then, as with the continental or dry gum method, the other formulative materials are added, and the emulsion is transferred to a graduate and brought to volume with water. Bottle or Forbes Bottle Method: i. The bottle method is useful for the extemporaneous preparation of emulsions from volatile oils or oleaginous substances of low viscosities. ii. Powdered acacia is placed in a dry bottle, two parts of oil are added, and the mixture is thoroughly shaken in the capped container. iii. When all of the water has been added, the primary emulsion thus formed may be diluted to the proper volume with water or an aqueous solution of other formulative agents. iv. This method is not suited for viscous oils because they cannot be thoroughly agitated in the bottle when mixed with the emulsifying agent. Suspensions: Suspensions, micro heterogeneous dispersion systems consisting of
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  solid medicinal substancesin the suspended state, which are in the liquid dispersion medium (water, non-aqueous solvents). Classes Of Suspensions: These are: 1. Lotions 2. Gels 3. Magmas and Milk 4. Mixtures Methods Of Preparation Of Suspensions: The methods which are used for Preparation of Suspensions are: 1. Dispersion Methods 2. Precipitation Methods Dispersion Methods: i. In this method large particles of the substances are broken, into particles of colloidal dimensions in presence of dispersion medium. ii. When the dispersion method is utilized for suspension preparation, the vehicle must be formulated so that the solid phase is easily wetted and dispersed. iii. The use of surfactants is desirable to ensure uniform wetting of hydrophobic Solids. iv. The use of suspending agents, Such as the synthetic polymeric polyelectrolytes, natural gums, or clay, may be indicated, depending un the specific application.
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  v. The actualmethod of dispersing the solid is one of the more important considerations because Particle size reduction may or may not result from the dispersion Process. vi. If Particle size reduction occurs, the particles obtained may have different solubilities if a metastable state is involved, and this may lead to transient Supersaturation of the System. Precipitation Method: i. Precipitations methods involved organic solvent precipitation, Precipitation effected by changing the pH of the medium and double decomposition. ii. Water insoluble drugs Can be precipitated by dissolving them in water miscible organic solvents and then adding adding the organic phase to distilled water under standard conditions. iii. several important Considerations are involved when this method is used, Perhaps the most important factor next to Particle size control is that the correct polymeric form. iv. Formulation of Suspensions by double decomposition only involves the simple chemistry v. Some Physical factors also Come into play. vi. Insulin Suspensions also may be Prepared by PH change method ,Insulin has an isoelectric point of approximately pH 5.when it is mixed with basic protein such as Protamine, it is readily precipitated when the pH is between the isoelectric points of two components, i.e. ,pH 6.9 to 7.3. Colloids: By definition, dispersions in which the size of the dispersed Particles is within the range of 1nm to 0.5µm are termed as Colloid Methods of Preparations:
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  Lyophilic sols maybe prepared by simply warming the solid with liquid dispersion medium. E.g. Starch with water. On the other hand, lyophobic sols have to be prepared by special methods. These methods fall into two categories; 1. Condensation or Aggregation Methods. 2. Dispersion Methods. Condensation or Aggregation Methods: i. These methods consists of chemical reactions or change of solvent whereby the atoms or molecules of the dispersed phase appearing first, aggregate to form colloidal particles. ii. The important chemical methods for preparing lyophobic sols are as follows; a. Double Decomposition: i. An Arsenic Sulphide (AS2S3) sol is prepared by passing a slow stream of hydrogen sulphide gas through cold solution of arsenious oxide (AS2O3). This is continued till a yellow colour of sol attains maximum intensity. AS2O3 + 3 H2S → AS2S3(Yellow Sol) + 3H2O b. Oxidation: i. A Colloidal sol of sulphur can be obtained by passing hydrogen Sulphide into solution of sulphur dioxide in water or through a solution of an oxidizing agent (Bromine water, nitric acid). c. Reduction:
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  i. A colloidalsolution of a metal like silver, gold and platinum can be prepared by reducing their salt solutions with suitable reducing agents, such as stannous chloride, formaldehyde, hydrazine, tannic acid etc. 2AuCl3 + 3SnCl2 → 2Au(Gold sol.)+ 3 SnCl4 d. Hydrolysis: i. The method is used to prepare hydroxides and oxides of weakly electropositive metals like Fe, Al or Sn. ii. A red sol of ferric hydroxide, is obtained by adding few drops of 30% ferric chloride solution to a large volume of almost boiling water and stirred with a glass rod. Dispersion Methods: In this method large particles of the substances are broken, into particles of colloidal dimensions in presence of dispersion medium. 1. Mechanical Dispersion 2. Bredig’s Arc Method 3. Peptisation a. Mechanical Dispersion: i. In this method, the coarse particles along with dispersion medium is brought into colloidal state by grinding it in colloidal mill, ball mill or ultrasonic disintegrator. The solid particles along the dispersion medium are fed into the colloidal mill. ii. The solid particles are torn off to colloidal size and are then dispersed in liquid to give the sol
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  b. Bredig’s ArcMethod: i. This process involves dispersion as well as aggregation. Colloidal solutions of metals such as gold, silver, platinum etc. can be prepared by this method.
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  c. Peptisation: i. Peptisationmay be defined as the process of converting a precipitate into colloidal form by shaking it with dispersion medium in the presence of small amount of electrolyte ii. During peptisation, the precipitate adsorbs one of the ion of the electrolyte on its surface. The adsorbed ion is generally common with those of the precipitate