Vikrant Saluja Faculty of Pharmaceutical Sciences PCTE Group of Institutes, Ludhiana Punjab, 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), semisolid (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 are semi-solid preparations obtained by evaporation or partial evaporation of the solvent used for extraction.
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 .
Maceration for Organized drug Maceration for Unorganized drug Multiple Maceration
Simple Percolation Percolation for Concentrated preparation Continous Percolation
General method of Extraction:
1- Comminution (reducing substances to small size). 2- Penetration of the crude drug by the menstrum. 3Dissolution menstrum. of the active principles by the
4- Diffusion of through the menstrum. 5-
dissolved wall to
active principles the surrounding
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
Advantages: Cheap Non toxic Non inflammable Disadvantages: Non selective Promote hydrolysis Promote enzymatic degration Good media for microbial growth
Advantages: Selective No additional preservative is required (>20%) Non toxic Disadvantages: Costly
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.
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.
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
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 ´quathµ or ´kawathµ. 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
1- Plant 2- Menstrum 3- Procedure 4- Time 5- Adjustment of final volume 6- Apparatus 7- Storage Soft structure (ex. Senna leaves) Boiling or cold water Infusing the drug with cold or hot water
Hard woody structure (ex. Cinchona bark) Boiling water Boiling the drug with water
Calculated as soon as water is Calculated as soon as the added to drug water begins to boil No adjustment Infusion earthenware pot Used fresh within 12 hours Adjustment is necessary Any covered apparatus Used fresh and when stored in refrigerator used within few days
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 ³macerare´ 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.
Drug +Entire volume of menstrum Shake occasionally for 7 days. Strain Liquid and press the marc Mix the liquids and clarify by filtration. Final volume is not adjusted Eg. Vinegar of squill Oxymel of squill Tincture of orange Tincture of lemon Tincture of squill
Drug + 4/5 of menstrum Shake occasionally on days 2-7 Decant liquid. Marc is not pressed Filter the liquid and final volume is adjusted by remaining menstrum Compound tincture of benzoin Tincture of Myrrh Tincture of Tolu
Same as simple maceration process but the menstrum is divided into parts (two for double and three for triple).
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 2
Volume 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
Simple percolation ± for tinctures Eg. Tincture of Belladona
Strong tincture of Ginger
Reserve process - for concentrated preparation. Continous hot percolation or Soxhelation.
Percolation (Exhaustive Extraction)
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
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
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.