Extraction of Alkaloids

• The normal procedures followed are to treat the moistened drug with alkali so as to set free the base as it exists in salt form and then to separate free base with organic solvent. This is known as Stas Otto process.

• First, the plant is defatted with petroleum ether, especially in case of seed and leaf forms of drugs.

  • • Precaution: Before applying this treatment, the alkaloid should be tested for its solubility in petroleum ether.

• The drug should be pretreated with acid to convert alkaloids' into their salts.

  • • • This happens in case of extraction of ergotamine from ergot.

• In the second stage, the drug may be extracted with polar solvents. like water, ethanol, methanol, aqueous alcohol mixtures or with acidified aqueous solutions.

• By this treatment, the alkaloidal salts are transferred to polar solvent. It also helps in removing pigments, sugars and other organic secondary constituents.

• In the following stage, the alcohol solution is evaporated to a thick syrup and is subjected to partition between aqueous acid solution and an organic solvent.

• After continuous extraction with organic solvent for some time, the aqueous phase is made alkaline with either sodium carbonate or ammonia.

• The basic aqueous solution is then extracted with convenient organic solvent followed by drying of alkaloid containing solution, normally with sodium sulphate; filtered and evaporated to yield alkaloid residue.

Process A-

• The powdered material is moistened with water and mixed with lime which combines with acids, tannins and other phenolic substances and sets free the alkaloids (if they exist in the plant as salts).

• 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.

• Alkaloid salts are now in the aqueous liquid, while many impurities remain behind in the organic liquid.

Process B-

• 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.

• 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.

References:

1. Trease D. & Evans W.C.: Text Book of Pharmacognosy: W.B. Saunders.

2. Tyler V. E. Brady L. R. & Robbers J. E.: Pharmacognosy; Lea Feibger, USA.

3. Wallis T. E.; Text Book of Pharmacognosy; CBS Publishers, Delhi.

4. Kokate C. K., Purohit A. P. & Gokhale S. B.: Pharmacognosy; Nirali Publications, Pune.

5. Harbone J. B.: Phytochemical Methods: A guide to modern techniques Analysis: Chapman & Hall, London.

6. Bruneton J.: Pharmacognosy, Phytochemistry, Medicinal Plants: Intercept Limited.