purification of alkaloids techniques

what are the 5 purification techniques of alkaloids?

• Fractional precipitation

• Fractional crystallisation (oxalates, tartrates, picrates)

• Steam distillation (volatile alkaloids)

• Sublimation (e.g., caffeine)

• Chromatography (TLC/column)

describe fractional precipitation?

Some ions are removed by precipitation, while others are not

describe fractional crystallisation?

Formation of salts of organic acids, such as oxalates, tartrates or picrates.

describe steam distillation?

Where the alkaloid is fairly volatile or has a low boiling point, it may be recovered from the plant material by steam distillation. The alkaloid separates as an immiscible oil in water.

describe sublimination?

Solid phase → vapour phase - Separates relatively volatile solids. Caffeine may be isolated from tea this wayCaffeine melts at 238°C and sublimes at 178°C at approx. 20 mm Hg (reduced pressure).

describe chromatography- TLC or column?

Separates alkaloids according to their polarity

why are these techniques used to overcome difficulty in separation and purification of alkaloids?

Alkaloids can often occur as mixtures of chemically related substances in the same plant.