Extraction

Vikrant SalujaFaculty of Pharmaceutical SciencesPCTE Group of Institutes, LudhianaPunjab, India

Extraction involves the separation of medicinally active portions of plant or animal tissues from the inactive components through the use of selective solvents

The extracted preparation are known as Galenicals

A medicinal preparation composed mainly of herbal or vegetable matter prepared by extraction of crude vegetable drugs (active principles) with suitable solvent(s).

Menstrum: Solvent used for extraction (ex. water,

alcohol, ether)

Marc: The inert fibrous and other insoluble materials remaining after extraction

Extracts are preparations of liquid (liquid extracts and tinctures), semi-solid (soft extracts) or solid (dry extracts) consistency, obtained from herbal drugs or animal matter

LIQUID EXTRACTS :• Liquid extracts are liquid preparations of which, in general, 1 part by mass or volume is equivalent to 1 part by mass of the dried herbal drug or animal matter. • Liquid extracts are prepared by using ethanol of a suitable concentration or water to extract the herbal drug or animal matter, or by dissolving a soft or dry extract of the herbal drug or animal matter in either ethanol of a suitable concentration or water.

TINCTURES: • Tinctures are liquid preparations that are usually obtained using either 1 part of herbal drug or animal matter and 10 parts of extraction solvent, or 1 part of herbal drug or animal matter and 5 parts of extraction solvent.

• Tinctures are prepared by maceration or percolation  using only ethanol of a suitable concentration for extraction of the herbal drug or animal matter, or by dissolving a soft or dry extract of the herbal drug or animal matter in ethanol of a suitable concentration.

SOFT EXTRACTS

• Soft extracts are semi-solid preparations obtained by evaporation or partial evaporation of the solvent used for extraction.

DRY EXTRACTS

• Dry extracts are solid preparations obtained by evaporation of the solvent used for their production. • Dry extracts usually have a  water content of not greater than 5  per  cent .

General method of Extraction:

1- Comminution (reducing substances to small size).

2- Penetration of the crude drug by the menstrum.

3- Dissolution of the active principles by the menstrum.

4- Diffusion of the dissolved active principles through the cell wall to the surrounding menstrum.

5- Separation of the dissolved active principles from the marc by filtration or expression.

Choice of menstrum The ideal solvent for a certain pharmacologically active

constituent should:

1. Be highly selective for the compound to be extracted.

2. Have a high capacity for extraction.

3. Not react with the extracted compound or with other compounds in the plant material.

4. Have a low price.

5. Be harmless to man and to the environment.

6. Be completely volatile.

The generally used solvents includes: Water Aliphatic alcohols with up to three carbon atoms Ether Chloroform Glycerine

Water AlcoholAdvantages: Cheap Non toxic Non inflammable

Advantages: Selective No additional preservative is required (>20%) Non toxic

Disadvantages: Non selective Promote hydrolysis Promote enzymatic degration Good media for microbial growth

Disadvantages: Costly

Solvent of choice for: Proteins Colouring matter Gums Alkalodal salts Glycosides Sugars Enzymes Anthraquinone derivatives Organic derivatives

Solvent of choice for: Alkaloids Alkalodal salts Glycosides Volatile oilsTannins Resins

Infusion

Infusions are dilute solutions containing the readily

soluble constituents of crude drugs.

It involves pouring water over the drugs and then allowing it to keep in contact with water for the stated period(15 min) with occasional stirring and finally filtering off the liquid.

Fresh infusion is prepared by macerating the drug for a short period of time with cold or hot (boiling) water.

Concentrated infusions are prepared by a modified percolation or maceration process.

Infusion pot

• Consist of covered jar ( made of earthenware, stainless-steel, ceramic, glass, porcelain…) to which is fitted at certain height a perforated tray upon which the crude drug may be allowed to rest in water being poured over it.

• The drug may be enclosed loosely in a small muslin bag and suspended in the jar at a height where it will be just covered by the liquid.

• The perforated tray or muslin bag confers two advantages:

A- Complete extraction because when the menstrum surrounding the drug becomes saturated, it will sinks to the bottom due to its increased density and another amount of fresh menstrum displace it leading to circulatory diffusion

B- At the end of infusion time, the drug can be lifted out, leaving clear liquid which can be strained quickly.

Fresh (Dilute) Infusion• A fresh infusion is an aqueous solution of active constituents of a

vegetable drug prepared by the process of infusion.• Water is used as menstrum • Fresh infusion should be used within 12 hrs after its preparation

because it gets spoiled due to bacterial and fungal growth.• eg. Fresh infusion of Quassia

Concentrated (stock) infusion• Prepared by double or triple maceration • 8 times stronger than fresh infusion• Alcohol in the concentration of 20-25% is used as menstrum.• Avoid rapid decomposition to which the fresh (dilute) infusions are

subjected.• The dilution of 1 volume of concentrated infusion with 7 volumes

of water resembles corresponding fresh infusion in potency.• eg. Concentrated infusion of Quassia

Decoction

• In this process, the crude drug is boiled in a specified volume of water for a defined time (10 mins ); it is then cooled and strained or filtered

• This procedure is suitable for extracting water-soluble, heat-stable constituents and drugs of hard and woody nature.

• This process is typically used in preparation of Ayurvedic extracts called “quath” or “kawath”.

• The starting ratio of crude drug to water is fixed, e.g. 1:4 or 1:16; the volume is then brought down to one-fourth its original volume by boiling during the extraction procedure

• Then, the concentrated extract is filtered and used as such or processed further

Comparison between infusion and decoction

Infusion Decoction

1- Plant Soft structure (ex. Senna leaves)

Hard woody structure (ex. Cinchona bark)

2- Menstrum Boiling or cold water Boiling water

3- Procedure Infusing the drug with cold or hot water

Boiling the drug with water

4- Time Calculated as soon as water is added to drug

Calculated as soon as the water begins to boil

5- Adjustment of final volume

No adjustment Adjustment is necessary

6- Apparatus Infusion earthenware pot Any covered apparatus

7- Storage Used fresh within 12 hours Used fresh and when stored in refrigerator used within few days

Digestion

In this process the plant cells are subjected to the effect of menstrum at 40 to 60°C (higher temperature than that used for maceration and lower temperature than that used in infusion and decoction) for longer period than that for infusion and decoction.

Apparatus: Thermos bottles (for maintenance of a definite temperature over the prescribed period of time)

Advantage: Increasing the solvent power of extraction by keeping the liquid hot throughout the period of extraction without causing damage to the drug constituents

Maceration:

Term derived from latin word “macerare” meaning to soak.

Process in which the properly comminuted drug is permitted to soak in the menstruum and the soluble constituents are dissolved

Officially, maceration is used for

a) Tinctures made from organized drugs.b) Tinctures made from unorganized drugs.c) Concentrated preparation, involving double

and triple maceration.

Organized drugs Unorganized drugs

Drug +Entire volume of menstrum

Drug + 4/5 of menstrum

Shake occasionally for 7 days. Shake occasionally on days 2-7

Strain Liquid and press the marc

Decant liquid. Marc is not pressed

Mix the liquids and clarify by filtration. Final volume is not adjusted

Filter the liquid and final volume is adjusted by remaining menstrum

Eg. Vinegar of squillOxymel of squillTincture of orangeTincture of lemonTincture of squill

Compound tincture of benzoinTincture of MyrrhTincture of Tolu

Multiple Maceration

Same as simple maceration process but the menstrum is divided into parts (two for double and three for triple).

Double maceration Drug is macerated twice Menstrum is divided in to two equal parts

Volume of menstrum required for first maceration

Total vol. of menstrum- vol. to be retained by the drug + vol. to be retained by the drug 2Volume of menstrum required for second maceration

Total vol. of menstrum- vol. of menstrum used for first maceration

Drug is macerated for 48hrs (with the quantity of menstrum required for 1st maceration)

Strain the liquid and press the marc

Macerate again for 24 hrs (with remaining menstrum required for 2nd maceration)

Strain the liquid and press the marc

Mixed the liquid obtained from the two maceration

Allow it to stand for 14 days and then filter

Percolation

Simple percolation – for tincturesEg. Tincture of BelladonaStrong tincture of Ginger

Reserve process - for concentrated preparation.

Continous hot percolation or Soxhelation.

Percolation (Exhaustive Extraction)Process A preliminary uniform moistening of the raw material with the menstruum for a period of 4 h in a separate closed vessel; this process is called imbibition.

After imbibition, the drug is packed evenly into the percolator.

Sufficient menstruum is now poured over the drug slowly and evenly to saturate it, keeping the tap at the bottom open to allow the occluded gases between particles to pass out.

When the menstruum begins to drip through the tap, the tap is closed; sufficient menstruum is added to maintain a small layer above the drug and allowed to stand for 24 h.

The 24-h maceration period allows the solvent to diffuse through the drug, solubilize the constituents and leach out the soluble material.

After the maceration, the outlet is opened and the solvent is percolated at a controlled rate with continuous addition of fresh solvent.

About 75% of the volume of the finished product is collected. The marc is pressed and the expressed liquid is added to the percolate, giving about 80%-90% of the final volume

,. Modifications of the General Process of Percolation

In general process of percolation, particularly in the manufacture of concentrated preparations like liquid extracts, the following problems may arise:

a) If the active substances are thermo-labile, evaporation of large volume of dilute percolate, may result in partial loss of the active constituents.

b) In the case of alcohol- water mixture, evaporation results in preferential vaporization of alcohol leaving behind an almost aqueous concentrate which may not be able to retain the extracted matter in solution and hence get precipitated.

In such cases the modification in general process of percolation is required as given below:

Reserved Percolation

Reserved Percolation

In this case , a part of the percolate , generally ¾ th the volume of finished preparation is reserved . Then the percolation is continued till the drug is completely exhausted.

At the last, the evaporation is done under reduced pressure in equipment like a Climbing evaporator to the consistency of a soft extract (semi solid) such that all the water is removed.

This is then dissolved in the reserved portion which is strongly alcoholic and easily dissolves the evaporated portion with any risk of precipitation.

Continuous hot percolation process or Soxhlet extraction

Apparatus

The apparatus consists of

A flask

A soxhlet extractor

A reflux condenser

A side tube

A syphon tube

Process

The raw material is usually placed in a thimble made of filter paper and inserted into the wide central tube of the extractor.

Solvent is placed in the flask and brought to its boiling point.

Its vapour passes up the larger right hand tube into the upper part of the drug and then to the condenser where it condenses and drops back on to the drug.

During its percolation, it extracts the soluble constituents.

When the level of the extracts reaches the top level of syphon tube, the whole of the percolates syphon over into the flask.

The process is continued until the drug is completely extracted and the extract in the flask is then processed.

This extraction is series of short maceration.