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In this article we will discuss about the tests for the detection of alkaloids in plants with the help of experiment.
The alkaloids are a group of basic, secondary plant substance, which usually possess a N-containing hetero-cycle. Their basic character is due to this feature. The alkaloids are mostly colourless, crystalline and non-volatile solids. They are insoluble in water, but soluble in organic solvents viz., ethanol, ether, benzene, chloroform etc.
Requirements for Detection of Alkaloids:
(a) Extraction of Alkaloids from Plant Materials:
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The plant material is dried and finally powdered. The extraction is made with ethanol by solvent distillation process. Then the extract is purified by various methods. However, for qualitative detection, crude extract can be used for chemical tests.
(b) Reagents:
1. Mayer’s reagent:
[HgCl2 — 1.36 gm. in 60 ml dist. water
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KI — 5 gm. in 10 ml dist. water
H2O2 — 30 ml]
2. Dragendorff’s reagent:
[Bi (NO3)3 5H2O — 8 gms in 20 ml liquid NH3]
KI — 27.2 gm. in 50 ml dist. water]
3. Wagner’s reagent:
[Iodine — 1.27 gm.
KI —2 gm.
Dist. water— 100 ml]
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4. Marme’s reagent:
[KI — 20 gm. in 20 ml dist. water
CdCl2 — 10 gm. in 50 ml dist. water]
5. Dilute H2SO4:
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[Dist. water — 30 ml]
Chemical Tests for the Detection of Alkaloids:
Following Tests are performed with the Extract:
Experiment:
1. Mayer’s test:
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To about 3 ml. of extract, a few drops of Mayer’s reagent are added.
2. Dragendorff’s test:
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To about 3 ml of extract, a few drops of Dragendorff’s reagent are added.
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3. Wagner’s test:
To about 3 ml of sample solution, a few drops of Wagner’s reagent are added.
4. Marme’s test:
To about 3 ml of extract, a few drops of Marme’s reagent are added. Then dil. H2SO4 is added to the mixture.
Observations:
Precipitate is formed.
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Brownish fluorescent precipitate is formed.
Brownish precipitate is formed.
White or yellow precipitate is formed. Precipitate may be dissolved on excess addition of Marme’s reagent or ethanol.
Inference:
Presence of alkaloid.
Presence of alkaloid.
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Presence of alkaloid.
Presence of alkaloid.
