General method of Extraction of Alkaloids I HINDI

Описание: General method of Extraction of Alkaloids I HINDI (Pharmacognosy)

Introduction to Alkaloids :    • Introduction to Alkaloids (Part-I)  
Classification of Alkaloids:    • Classification of Alkaloids  

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EXTRACTION OF ALKALOID
The general methods of extraction of alkaloids from the plant sources followed five steps namely
(i) Sample preparation
(ii) Liberation of free alkaloidal base
(iii) Extraction of alkaloidal base with organic solvent
(iv) Purification of crude alkaloidal extract
(v) Fractionation of crude alkaloids

Extraction methods vary with the scale and purpose of the operation, and with the raw material. For many research purposes chromatography gives both speedy and accurate results. However, if an appreciable quantity of alkaloid is required, one of the following general methods will usually serve.

Process A
1. Powdered material is moistened with water and mixed with lime which combines with acids, tannins and other phenolic substance sand sets free the alkaloids (if they exist in the plant as salts).
2. Extraction is then carried out with organic solvents such as ether or petroleum spirit. The concentrated organic liquid is then shaken with aqueous acid and allowed to separate.
3. Alkaloid salts are now in the aqueous liquid, while many impurities remain behind in the organic liquid.

Process B
1. The powdered material is extracted with water or aqueous alcohol containing dilute acid. Pigments and other unwanted materials are removed by shaking with chloroform or other organic solvents.
2. The free alkaloids are then precipitated by the addition of excess sodium bicarbonate or ammonia and separated by filtration or by extraction with organic solvents.
3. Large-scale extractions based on the above principles are sometimes done in the field and the crude mixtures of alkaloids afterwards sent toa factory for separation and purification.
4. The separation and final purification of a mixture of alkaloids may sometimes be done by fractional precipitation or by fractional crystallization of salts such as oxalates, tartrates or picrates. Chromatographic methods are particularly suitable if the mixture is a complex one and if small quantities of alkaloids will suffice.
5. Volatile liquid alkaloids such as nicotine and coniine are most conveniently isolated by distillation. An aqueous extract is made alkaline with caustic soda or sodium carbonate and the alkaloid distilled off in steam. Nicotine is an important insecticide, and large quantities of it are prepared from those parts of the tobacco plant which cannot be used for tobacco manufacture.

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