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Alkaloid Extraction Document

by Osmium

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To isolate alkaloids from plants, the dried and powdered plant material is extracted with pet ether (or hexane, colemans etc.) first. This removes fats, oils, terpenes, waxes etc. This extract is discarded.

The material is now subjected to an alcohol extraction, eg with methanol or ethanol. The extract is evaporated to leave the crude alkaloids mixture.

This extract is partitioned between an diluted aq. tartaric acid solution and ethyl acetate. Other acids like citric acid can be used, and other solvents may substitute here. The ethyl acetate layer contains neutral and weakly basic alkaloids. Evaporate the solvent to isolate them.

The aq. layer is neutralised with NH3 or Na2CO3 and again extracted with ethyl acetate. The organic layer now contains basic alkaloids, while the aq. layer contains quarternary ammonium ions.

Many alkaloids can be isolated directly from the alkoholic extract by chromatographic methods. This is a separation which works well for tropane alkaloids (atropine, cocaine, scopolamine).

The alcohol extract is fractionated by column chromatography on SiO2, solvent chloroform followed by chloroform with rising methanol content. This separates lipids and terpenes from the crude alkaloid fraction. The alkaloid fraction is again chromatographed (SiO2; CHCl3 : MeOH = 10:1) to isolate the pure alkaloids.