434 PHG
Recent Approaches in
Medicinal Plant Analysis
‫الطرق المتقدمة في تحليل النباتات الطبية‬
Isolation and Purification of Active
Constituents from Plants
1
Purification of
secondary metabolites
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Purification of secondary metabolites
(Organic Compounds)
 Compounds obtained from natural sources or from
reaction mixtures almost always contain impurities.
 The impurities may include some combination of
insoluble, soluble, and colored impurities.
 To obtain a pure compound these impurities must be
removed.
 Each is removed in a separate step.
3
Techniques Used for Purification of
Organic Compounds
• These techniques include:
1. Filtration
2.
3.
4.
5.
6.
Centrifugation
Recrystallization‫التبلور (أو البَ ْل َو َرة‬
Differential Solvent extraction
Fractional distillation
Chromatographic techniques
The selection of a proper technique
 depends on the particular differences in physical
properties of the substances present in the mixture
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1. Filtration
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2. Centrifugation
3. Recrystallization
Separate materials of different
densities
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4. Differential Solvent extraction
•
Used to extract pure organic compounds
from their aqueous solution by shaking
with suitable organic solvent in which they
are highly soluble.
•
Non-aqueous solvents (e.g. CHCl3 and
diethyl ether) can be used to extract
organic products
•
Eg. Atropin alkaloidal base from its
aqueous solution using CHCl3 or CH2Cl2.
Successive
extraction
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5. Fractional Distillation
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Fractional Distillation
6. Chromatography
•Based on selective adsorption or partition between
stationary and mobile phase.
• Column Chromatographybased on adsorption, and used for bulk quantities.
• Thin layer Chromatographybased on adsorption, and used for quantitative and
qualitative analysis.
•Paper Chromatography• based on partition and used for quantitative and
qualitative analysis.
Gas Chromatography• used to separate and analyse volatile organic liquids.
High performance liquids Chromatography
(HPLC)- used for qualitative and quantitative analysis of
organic compounds.
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Terminology
• Mobile phase:
phase which sample is dissolved in may be gas, liquid, or
supercritical fluid.
• Stationary phase: phase which mobile phase is forced through.
• Mobile and stationary phases are chosen so the analyte will
distribute itself between the two phases.
Adsorbent: finely divided homogenous solid having uniform particle
size and large surface area which is capable of attracting
molecules to its surface.
Chromatogram: a record at the end of chromatographic
separation.
Development:
description of the process of chr. (running of the mobile phase
through the stationary phase).
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Terminology
• Retention volume:
volume of mobile phase required to elute a particular
solute
• Tailing:
disadvantage of chromatography and solute is eluted in
several fraction
• Visualization: making the colourless bands visible
• partition coefficient:
Conc. of the component in the St. Phase
K=
Conc. of the component in the Mob. Phase
• The greater the value of K, the greater the affinity of the
compound for a particular stationary phase.
N = L / H N: number of theoretical plates
 Efficiency of a column goes up as N increases and H decreases
 Typical 250 – 10,000 plates
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Illustrative problem
A mixture of benzene and aniline
can be separated by
(a) alcohol
(b) NaOH
(c) HCl
(d) Hot water
Solution
Amines are basic in nature. Therefore, aniline reacts
with HCl to form a salt which dissolves in water.
Hence, aniline can be separated from benzene by
using HCl.
Hence, answer is (c).
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Illustrative problem
The most suitable method for the
separation of mixture of ortho and
para nitrophenol in the ratio of 1:1
is
(a) distillation
(b) crystallization
(c) vaporization
(d) colour spectrum
The boiling point of o-nitrophenol is 210oC and
that of p-nitrophenol is 245oC.
Solution
Therefore, vapours of o-nitrophenol will be formed
first (lower boiling point) and collected seperately and
vapours of p-nitrophenol will be formed latter.
Hence, answer is (a).
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