Saturday, 6 May 2017

There are many procedures for obtaining extracts like

Infusion
Maceration
Percolation
Digestion
Decoction
Continuous hot extraction
Solvent-solvent precipitation
Liquid-liquid extraction
Distillation
Specific procedures but i am trying to cover the major ones.

Infusion

In this method, the plant material (herbal tea) is placed in a pot and wetted with cold water. Immediately afterwards, boiling water is poured over it, then left to stand covered with a lid, for about fifteen minutes after which the tea is poured off.

Maceration

The method is use frequently for water soluble active constituents. It consists of macerating the plant material in cold water (15-20°) for several hours.

Percolation

In this method the ground plant material is subjected to a slow flow of fresh solvent.

Digestion

This method is suitable for hard barks or woods which are difficult for water to penetrate. Digestion is also considered as maceration but at a relatively elevated temperature. As a general rule the temperature of the extracting medium should be in the range from 35-40° but not exceeding 50°.

Decoction

If the plant material is boiled for ten minutes or if the boiling water is poured over it and allowed to stand for thirty minutes, the result is called decoction.

Continuous hot extraction method

This procedure is considered as the most common method used for the extraction of organic constituents from dried plant tissue, it can be used both on laboratory and industrial scales. In the lab, the powdered material is continuously extracted in a Soxhlet apparatus with a range of solvents of increasing polarity. | Readings Pharmaceuticals |

Solvent-solvent precipitation

The extract dissolved in a suitable solvent , is mixed with a less polar but miscible solvent causing the selective precipitation of the less soluble plant constituent , e.g. the precipitation of triterpenoid saponins from the methanol extract of Phytolacca dodecandra by the addition of acetone and the precipation of gum from aqueous extract of Olibanum by addition of alcohol.

By the addition of extract to a solvent in which constituent is insoluble or very sparingly soluble e.g. precipitation of resins from the alcoholic extracts by the addition of distilled or acidulated water.

Liquid-liquid extraction

 Liquid-liquid extraction is also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubilites in two different immiscible liquids, usually water and an organic solvent. It is an extraction of substance from one liquid phase into other liquid phase. Liquid-liquid extraction is basically a technique in phytochemical laboratories, where it is performed using a separately funnel.

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