40 Questions
What is the most challenging operation in phytochemical research?
Isolation and purification of plant constituents
Which method is used to separate the components of volatile mixtures?
Fractional distillation
What is the main limitation of exploiting chemical properties of functional groups for separation?
It might not fractionate components of the same class
Which modern equipment employs low pressures with a strict control of temperature?
Sublimation equipment
What is the purpose of fractional crystallization?
To separate components of the same class
What is the advantage of sublimation in phytochemistry?
It can be used for the purification of crude extracts
What is the application of fractional distillation in phytochemistry?
Isolation of the components of volatile oils
What is typically used on a laboratory scale to separate minor components of a mixture in a pure state?
Gas chromatography
What is the basis of fractional liberation of a mixture of alkaloid salts in aqueous solution?
Basicity of the salts
What is the purpose of shaking the mixture with an organic solvent after each addition of alkali in fractional liberation?
To separate the liberated bases
What is the principle behind the separation of organic acids by fractional liberation?
Differences in solubility of acids in water-immiscible solvents
What is the advantage of using derivatives in fractional crystallization?
Enhanced differences in solubility of the components
What is the characteristic of a mixture that makes it suitable for separation by fractional crystallization?
Differences in solubility of the components in a particular solvent
What is the significance of fractional crystallization in traditional isolations?
It is still a valuable method for resolving intractable mixtures
What is the fundamental principle of adsorption chromatography?
Selective adsorption of substances on the surface of solids
What is the purpose of using charcoal in solution separation?
To decolorize and clarify solutions
What is the result of filtration after using charcoal for solution separation?
A colourless solution
What is the role of powdered calcium carbonate in Tswett's original experiment?
To act as a substrate for the adsorption of pigments
What is the outcome of the percolation process in Tswett's original experiment?
Pigments are separated into distinct bands
Which pigments are accumulated in distinct, characteristically coloured bands near the top of the column?
Xanthophyll and the chlorophylls
What is the characteristic of the pigments that accumulate lower down in the column?
Less strongly adsorbed on the calcium carbonate
What is the primary purpose of allowing more of the pure solvent to percolate through the column?
To separate the constituents into distinct bands
Why is the use of a different solvent sometimes more efficient?
Because it makes the substances 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 in chromatography?
Elution
What is the solution obtained through the process of elution called?
Eluate
What is the origin of the term 'chromatography'?
From the experiments of Tswett on the separation of coloured compounds
What is the primary goal of chromatography?
To separate and isolate constituents
What is the effect of adding a little alcohol to light petroleum in chromatography?
The bands become wider apart and pass down the column more rapidly
What is the purpose of the column in chromatography?
To separate the constituents into distinct bands
What is the reason for the incomplete separation of constituents during the first adsorption stage?
Overcrowding of bands near the top of the column
What is the purpose of allowing more of the pure solvent to percolate through the column?
To facilitate the separation of constituents
Why is the use of a different solvent sometimes more efficient?
Because it allows for less strong adsorption of substances
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 obtaining a pigment in a solution through chromatography?
Elution
What is the significance of Tswett's experiments on the separation of coloured compounds?
They gave rise to the term 'chromatography'
What is the effect of adding a little alcohol to light petroleum in chromatography?
It makes the bands wider apart and faster-moving
What is the primary goal of chromatography?
To separate mixtures into their individual constituents
What is the role of the column in chromatography?
To separate the substances based on their adsorption properties
What is the outcome of the percolation process in chromatography?
The separation of constituents into distinct bands
Study Notes
Separation and Isolation of Constituents
- Separation and isolation of plant constituents is a challenging task in phytochemical research.
- The chemical properties of functional groups and moieties can be exploited for separation, but new techniques are constantly being developed to fractionate components of the same class.
Sublimation
- Sublimation can be used to isolate or purify materials present in a crude extract.
- Modern equipment employs low pressures with a strict control of temperature.
- Example: isolation of caffeine from tea.
Distillation
- Fractional distillation is traditionally used for separating volatile mixtures.
- It has been widely used in phytochemistry for isolating components of volatile oils.
- However, it is not easy to separate minor components of a mixture in a pure state on a laboratory scale, and gas chromatography is now routinely used.
Fractional Liberation
- Some groups of compounds can be fractionally liberated from a mixture.
- Example: a mixture of alkaloid salts in aqueous solution, treated with alkali, gives first the weakest base in the free state followed by base liberation in ascending order of basicity.
- Similar scheme can be used for organic acids soluble in water-immiscible solvents.
Fractional Crystallization
- A method that exploits differences in solubility of components in a particular solvent.
- Frequently, derivatives of the components are employed (e.g. picrates of alkaloids, osazones of sugars).
- Valuable for resolving intractable mixtures.
Adsorption Chromatography
- A technique that exploits the phenomenon of selective adsorption.
- Finely divided solids have the power to adsorb other substances on their surfaces.
- All substances are capable of being adsorbed, some more readily than others.
- Example: A light petroleum extract of green leaves is allowed to percolate through a column of powdered calcium carbonate, resulting in separation of pigments.
Elution
- The process of desorption is termed elution.
- The solution obtained is the eluate.
- Example: using light petroleum containing a little alcohol to percolate through the chromatogram, resulting in wider separation of bands and elution of the pigment.
Test your knowledge on the separation and isolation techniques used in pharmacognosy to extract and purify plant constituents. This quiz covers sublimation, distillation, fractional crystallization, and adsorption chromatography. Learn how to overcome the challenges of isolating and purifying plant compounds.
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