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Isolation of Compounds from Plant Extracts

  • Botany

In this isolation of compounds from plant extracts post we have briefly explained about isolation of compounds from plant extracts, funnel method, chromatographic techniques, fractional distillation, fractional crystallization, fractional liberation, and sublimation

Fractionation is a process of separation of compounds of plant extracts into various fractions. It further segregates the fractions into portions comprising a number of compounds. The process continues until pure compound is isolated.  When several solvents are required for the fractionation, they should be added according to the order of increasing polarity. Physical methods used in separation of compounds from mixtures include separation funnel method, chromatographic techniques, fractional distillation, fractional crystallization, fractional liberation, and sublimation.

Isolation of Compounds from Plant Extracts

Separation funnel

When four different solvents (n-hexane, chloroform, acetone, and n-butanol) are selected, fractionation begins by moistening or complete dissolution of crude extract with 250mL of water. This isolation of compounds from plant extracts method followed by transfer into a separating funnel, shaken, and allowed to settle. Furthermore, to 250mL of n-hexane, the least polar solvent was added and shaken. The content can settle, and the bottom of the separating funnel opened to remove the aqueous layer. The remaining content in the separating funnel was poured into a clean container to get n-hexane fraction.

Fractional distillation

This isolation of compounds from plant extracts method process of separating or purifying compounds from a mixture. It is usually used in separation of hydrocarbons such as crude oil, citral, and eucalyptol. Purification is achieved based on the differences in their boiling points. Fractional distillation apparatus is constructed in such a manner that when heat is applied each compound will evaporate and separates at its boiling point. Consequently, each compound fractionated will condense and collected as a separate entity through several siphons attached to fractional distillation apparatus.

Fractional Crystallization

Fractional crystallization isolation of compounds from plant extracts method of refining substances based on differences in solubility. It fractionates via differences in crystallization (forming of crystals). If a mixture of two or more substances in solution are allowed to crystallize, for example by allowing the temperature of the solution to decrease, the precipitate will contain more of the least soluble substance. The proportion of components in the precipitate will depend on their solubility products. If the solubility products are very similar, a cascade process will be needed to effectuate a complete separation. This technique is often used in chemical engineering to obtain very pure substances, or to recover saleable products from waste solutions.

Fractional liberation

Some groups of compounds lend themselves to fractional liberation from a mixture , ex : a mixture of alkaloid salts in aqueous solution when treated with aliquots of alkali , will give first the weakest base in the free state followed by base liberation in ascending order of basicity. This isolation of compounds from plant extracts method is suitable for separating compounds that can easily form precipitate from the mixture. The precipitate is usually formed by changing the compounds into their salt form. Fractional liberation is commonly applicable in purification cinnamon alkaloids.

Sublimation

This isolation of compounds from plant extracts method involves changing from solid to gaseous state without passing through liquid state. Substances such as camphor and volatile oils when heated get separated and converted directly into gas. Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. For those of us interested in the water cycle, sublimation is most often used to describe the process of snow and ice changing into water vapor in the air without first melting into water.

Chromatography

These are special techniques used in separation of compounds from mixtures based on their size, shape, and charge. The concept of chromatography involves the use of mobile phase, which is the solvent of extraction and the stationary phase such as silca gel and sephadex mixed with a calcium sulfate as a binder. Silica gel is used for parting amino acids, sugars, fatty acids, lipids, and alkaloids. Sephadex is applicable in isolation of proteins and amino acids. Aluminum is useful in separation of vitamins, carotenes, phenols, steroids, and alkaloids. Cellulose powder is used in separation of amino acids, food dyes, and alkaloids. Celite is applicable in separation of organic cations and steroids.

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