لخّصلي

During fractionation, the selected solvent is added according to the order of increasing polarity, starting from n-hexane, the least polar to water with the highest polarity.[3,9] If a researcher wishes to select five solvents during fractionation, the usual practice is to choose two solvents with low polarity (n-hexane, chloroform), two with medium polarity (dichloromethane, n-butanol), and one with the highest polarity (water). Properties of Solvent of Extractions (i) Water. It is the most polar solvent and is used in the extraction of a wide range of polar compounds.[9,12] Advantages. It dissolves a wide range of substances; it is cheap, nontoxic, nonflammable, and highly polar.[9,12] Disadvantages. It promotes bacterial and mold growth; it may cause hydrolysis, and a large amount of heat is required to concentrate the extract.[9,12] (ii) Alcohol. It is also polar in nature, miscible with water, and could extract polar secondary metabolites.[9,12] Advantages. It is self-preservative at a concentration above 20%. It is nontoxic at low concentration, and as small amount of heat is required for concentrating the extract.[9,12] Disadvantages. It does not dissolve fats, gums, and wax; it is flammable and volatile.[9,12] (iii)Chloroform. It is a nonpolar solvent and is useful in the extraction of compounds such as terpenoids, flavonoids, fats, and oils.[3,12,13] Advantages. It is colorless, has a sweet smell, and is soluble in alcohols. It is also well absorbed and metabolized in the body.[3,12,13] Disadvantages. It has sedative and carcinogenic property.[3,12,13] (iv) Ether. It is a nonpolar solvent and is useful in the extraction of compounds such as alkaloids, terpenoids, coumarins, and fatty acids.[3,12,13] Advantages. It is miscible with water, has low boiling point, and is tasteless in nature. It is also a very stable compound and does not react with acids, bases, and metals.[3,12,13] Disadvantages. It is highly volatile and flammable in nature.[3,12,13] (v) Ionic liquid (green solvent). This is a unique solvent of extraction and is highly polar and extremely heat stable. It can remain in a liquid state even at 3,000o C and usable where high temperature is applicable. It has extreme miscibility with water and other solvent and is very suitable in the extraction of polar compounds.[14] Advantages. It has excellent solvent that attracts and transmit microwave, and hence it is suitable for microwave-assisted extraction. It is nonflammable and is useful for liquid–liquid extraction and highly polar.[14] Disadvantage. It is not ideal for preparation of tinctures.[14] Factors to be considered in selecting solvents of extraction Various factors enumerated below should be taken into consideration when choosing a solvent of extraction