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Pharmacognosy: Separation and Isolation of Plant Constituents

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24 Questions

What is considered the most difficult operation in phytochemical research?

Isolation and purification of plant constituents

What is the primary purpose of exploiting chemical properties of functional groups in phytochemical research?

To separate compounds from other materials

What is employed in modern sublimation equipment?

Low pressures with a strict control of temperature

What is the traditional use of fractional distillation in phytochemistry?

Separation of the components of volatile mixtures

What is the limitation of exploiting chemical properties of functional groups in phytochemical research?

It might not fractionate components of the same class

What is the application of sublimation in phytochemical research?

Isolation of caffeine from tea

What is a common challenge when using the traditional method of separating and isolating constituents on a laboratory scale?

Separating minor components of a mixture in a pure state

What is the purpose of shaking the mixture with an organic solvent after each addition of alkali in fractional liberation?

To obtain a fractionated series of bases

What is the principle behind fractional crystallization?

Differences in solubility of the components in a particular solvent

What is the purpose of forming derivatives of the components in fractional crystallization?

To facilitate the separation of the components

What is the outcome of treating a mixture of alkaloid salts with alkali in fractional liberation?

The weakest base is liberated first

What is the role of mineral acids in the fractional liberation of organic acids?

To fractionally liberate the acids

What is the fundamental principle of adsorption chromatography?

Selective adsorption of substances on the surface of finely divided solids

What is the purpose of using charcoal in solutions?

To decolorize and clarify solutions

What is the role of the calcium carbonate column in Tswett's experiment?

To separate and isolate the pigments based on their adsorption properties

Which pigments are more strongly adsorbed in Tswett's experiment?

Xanthophyll and the chlorophylls

What is the result of the pigments undergoing separation as percolation proceeds?

Distinct, characteristically coloured bands of pigments

Why do the carotenes accumulate lower down in the column?

Because they are less strongly adsorbed than the chlorophylls

What is the primary purpose of allowing more of the pure solvent to percolate through the column?

To separate the constituents into distinct bands

What is the effect of using a different solvent in the chromatography process?

The substances are less strongly adsorbed

What happens to the lower bands as percolation continues?

They reach the bottom of the column and disappear

What is the term used to describe the process of desorption?


What is the solution obtained after the process of elution?


Who is credited with the development of the term 'chromatography'?


Study Notes

Separation and Isolation of Constituents

  • Separation and isolation of minor components of a mixture are challenging on a laboratory scale, and gas chromatography is often used instead.
  • Fractional liberation involves treating a mixture with a base or acid to liberate constituents in a specific order, and then separating them using an organic solvent.
  • This method is useful for separating alkaloid salts and organic acids soluble in water-immiscible solvents.

Fractional Crystallization

  • Fractional crystallization is a traditional method that exploits differences in solubility of mixture components in a particular solvent.
  • Derivatives of the components, such as picrates of alkaloids or osazones of sugars, are often used to facilitate separation.

Adsorption Chromatography

  • Adsorption chromatography is a technique that separates and isolates plant constituents based on selective adsorption.
  • Finely divided solids have the power to adsorb other substances on their surfaces, and this phenomenon is the fundamental principle of adsorption chromatography.
  • The method involves allowing a solution to percolate through a column of a substance, such as powdered calcium carbonate, and separating the components based on their adsorption strengths.

Sublimation and Distillation

  • Sublimation is a method that can be used to isolate and purify plant constituents, often employed on the whole drug or for the purification of materials present in a crude extract.
  • Distillation, particularly fractional distillation, has been widely used for the separation of volatile mixtures, including the components of volatile oils.

Development of Chromatography

  • The process of adsorption chromatography can be developed by allowing more of the pure solvent to percolate through the column, causing the adsorbed materials to slowly pass downwards and separate into distinct bands.
  • Using a different solvent, one from which the substances are less strongly adsorbed, can also improve the efficiency of the process.
  • The process of desorption, termed elution, can be used to obtain the separated pigments in a solution.

Test your knowledge on the separation and isolation techniques of plant constituents in phytochemical research, including sublimation, distillation, and chromatography. Learn how to purify and isolate plant compounds with these essential methods.

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