Extraction

Definition:

It can be defined as the process of obtaining the constituents by separating it from the crude drug by the use of solvent.

Powdered material is extracted with suitable solvent or mixtures of solvents for extracting the various phytoconstituents present in the crude drug.

Solvent chosen for extraction is expected to possess the following properties:

1- Should dissolve the Phytoconstituents.2- Non-inflammable.3- Inert.4- Non-toxic.5- Easily removable.6- Should be distilled or double distilled.

Solvent chosen depending upon the characteristic of the secondary metabolites, polarity, PH and thermo stability of the constituents are also to be considered during extraction.

Solvent Formula Boiling Point PolarityAcetic Acid C2H4O2 118 0.648Acetone C3H6O 56.2 0.355Acetonitrile C2H3N 81.6 0.46Benzene C6H6 80.1 0.1111-butanol C4H10O 117.6 0.6022-butanone C4H8O 79.6 0.327T-butyl alcohol C4H10O 82.2 0.389Carbon tetrachloride CCl4 76.7 0.052Chloroform CHCl3 61.2 0.259Cyclohexane C6H12 80.7 0.006Diethylene glycol C4H10O3 245 0.713Diglyme C6H10O3 162 0.244Dimethoxy-Ethane (Glyme)

C4H10O2 85 0.231

Dimethyl-Formamide (DMF)

C3H7NO 153 0.404

Dimethyl-Sulfoxide (DMSO)

C2H6OS 189 0.444

Dioxane C4H8O2 101.1 0.164Ethanol C2H6O 78.5 0.654Ether C4H10O 34.6 0.117Ethyl acetate C4H8O2 77 0.228Ethylene glycol C2H6O2 197 0.79Glycerin C3H8O3 290 0.812

Heptane C7H16 98 0.012Hexane C6H14 69 0.009Methanol CH4O 64.6 0.762Methyl t-butyl Ether (MTBE)

C5H12O 55.2 0.148

Methylene Chloride CH2Cl2 39.8 0.309Pentane C5H12 36.1 0.0091-propanol C3H8O 97 0.6172-propanol C3H8O 82.4 0.546Tetrahydrofuran C4H8O 66 0.207Toluene C7H8 110.6 0.099Water H2O 100 1Water, heavy D2O 101.3 0.991

Basics of Extraction:

- Extraction is the process of leaching out active constitution from the crude plant material.

- The choice of extraction procedure depends on the nature of the plant material and the component to be isolated.

- During the extraction of the herbal drugs two processes run parallel with each other in the extraction of drugs.

- Rinsing of extractive substance out of disintegrated plant cells- The dissolution of extractive substance out of intact plant cell by

diffusion which requires:-- Prior steeping and swelling of drug plant material in order to increase

the permeability of cells and swelling of cells.- Penetration of the solvent into the plant cells and swelling of cells.- Dissolution of extractive material.- Diffusion of the dissolved substance out of the plant cells.- Some general points should be considered in terms of the extraction

procedure, such as the overall characteristics of the secondary metabolites to be extracted e.g. some glycosides are thermo labile or pH sensitive.

Classification:

- Extraction with organic solvents: Percolation Maceration Extraction using Soxhlet Apparatus

- Extraction with water: Infusion Decoction Steam distillation

- Other special methods: Supercritical fluid extraction Enflurage Expression Phytonics Microwave treatment Extraction by electric energy Per evaporation Sublimation Counter current extraction Ultrasound extraction

1- Maceration:Maceration is the process of extraction of a drug with the solvent with several days shaking or stirring at room temperature. Compared to other methods, the intensity of movement is so slow that we can use the term “Stationary conditions”.IP 1966: “Place the solid material with the whole mensruum in a closed vessel and allow standing for 7 days, shaking occasionally, and strain, press the marc and mix the liquids obtained. Clarify by subsidence or filtration”.7 days are considered to an adequate period of time to bring about an equilibrium between solutes and solvent.Closed vessel is preferred to avoid undue loss of solvent due to evaporation.E.g. Senna liquid extract, Squill tincture, Compound benzoin tincture, Catechu tincture, Opium tincture.Modified macerationFor unorganized drugs such as gums and resins, Pressing is avoided as these drugs form compact mass and volume is making up finally to avoid variation in final concentration.Multiple macerationsTo obtain concentrated extract, the total mensruum is divided into two (double maceration) or three parts (triple maceration) and each part is separately used for maceration.Vacuum macerationWhen pressure is reduced to desired extent the menstuum is allowed to inter, this increases the permeability of cell walls and thus short time required for maceration.Kinetic macerationIt is carried out at room temperature, like simple maceration, but differs in that the material is kept constant.Re-maceration

In this case some of the solvent is added to the drug, and after filtration the residue is extracted with the remainder of the solvent and the drug residue squeezed out to express as much solvent as possible.Circulation macerationThe solvent is continuously circulated by pumps. It is used for large scale extraction.Advantages: Small sample is required Very simple process Can be done on small scale in the pharmacist laboratory only In the preparation of homeopathic mother tinctures in small scale

as they are prepared the same way in the industry Versatile, drugs showing strong swelling properties and high

mucous content can be effectively extracted

Disadvantages:

Not exhaustive extraction, so less yield More expensive Time consuming in comparison to other methods

Factors affecting maceration:

There are certain parameters which affect the efficiency of extraction maceration

Influence of the particle size of the drug:Some experiments show that the degree of comminution for the extraction must be kept as fine as possible. This is acceptable for small samples where the sediment can be quickly and effectively separated by centrifugation, but for large batches it must be remembered that; fine, swollen sediment frequently cause difficulties in filtration. That’s why on large scale the particle size should be kept moderate for effective extraction.

The type and intensity of movement:It is an important factor effecting maceration. It has been proved that increasing the speed of stirrer from 20 – 30 rev/min to 50 – 250 rev/min in a bucket mixer has significant influence on the extraction results.

Temperature:Another important parameter is the temperature at which the maceration is carried out in accordance with the laws of reaction kinetics “a rise in temperature results in a more rapid establishment of conc. Equilibrium and in certain cases it improves yield.

Additives:Other additives play major role which are also significant. The following can be considered as important additives:Solvent additives for altering the polarity when water is being used e.g. alcohol, acid or base added to form salts or to retrain dissociation.Surfactants added to improve wetting and to increase the permeability of the cell membrane

2- Digestion:Digestion is maceration at higher temperature, normally at 40 – 50 C. higher temperature enhances solvent action.

3- Percolation:Short successive maceration/extraction by method of displacementPercolate: I pass throughIn the percolation the drug plant material is exhaustively extracted by fresh solvent.The process of percolation implies a slow passage of the menstruum under the influence of gravity through a column of drug powder and during this movement it goes on extracting the drug particles layer wise, it bring displaced by other layers above.IP 1966: “Moisten the solid materials with sufficient quantity of the menstruum, allow to stand for four hours in a well closed vessel, packed in a percolator, and add sufficient menstruum to saturate the material. When the liquid commences to drop from the percolator, close the outlet, add sufficient menstruum to leave a layer above the drug, and allow macerating for 24 hours. Allow percolation to proceed slowly until the percolate measures about 3 quarters of the volume required for the finished tincture. Press the marc, mix the expressed liquid with the percolate, add sufficient menstruum to produce the required volume. Clarify by subsidence or filtration.Intermittent percolation24 hours maceration and subsequent 12 hours maceration are altered with percolation to effect greater extraction.Re-percolationDrug powder is divided into 4 or 5 lots; first lot is being treated as same simple percolation and the percolate of this is used as a menstruum for next lot, and that from second lot is menstruum for next.Hot percolationPercolation at elevated temperature as higher temperature increases extraction efficiency.Reserved percolation

Reserving the first part of percolate and subsequent percolate is collected separately. This allows that most of active constituents present in first percolate are not subjected to any heat treatment.Circulating percolationMenstruum continuously circulates in sequentially attached percolator receivers.Diffusion percolationMenstruum is made to flow from the bottom upwards to the top under hydrostatic pressure.DiacolationSame as diffusion just instead of hydrostatic pressure positive pressure of compressed air is utilized.Hot continuous counter-current extractionProcess where in same quantity of menstruum is made to circulate through a column of drug by evaporation and subsequent condensation. In this method, the material to be extracted is placed in a “thimble”

made of cellulose or cloth in a central compartment. The solvent is placed in a round buttom flask RBF and a reflux condenser is attached above the central sample compartment.

Solvent container RBF, sample compartment and reflux condenser is a separate item of glassware, which is assembled together with the appropriate content to make the complete apparatus.

The solvent in the lower container is heated to boiling and the vapor passes through the side arm up into the reflux condenser. Here the vapor liquefies and drip into the thimble containing material to be extracted. The condensed liquid gradually increases level liquid in extractor and in siphon tube. Siphon tube is set up as liquid reaches the point of return, and contents of the extraction chamber are transferred to flask.

The cycle of solvent evaporation and siphoning back can be continued as many times as possible without changing solvent, so as to get efficient extraction.

Advantages:

Small amount of solvent is used as solvent re-circulated Effective extraction Takes less time in comparison to other methods Exhaustive extraction almost complete Varying sizes of soxhlet apparatus are available to suit the scale of

the operation

Disadvantages:

Thermo labile active constituents cannot be extracted as there is continuous heating of the solvent plus the extracted material

The total amount of certain substances extracted will exceed their solubility level in that particular solvent, thus they may precipitate out in the lower container and require much more solvent for later dissolution

For large scale extraction it is not suitable for use with solvents with relatively high boiling points, such as CH3OH and water, since the whole apparatus below the condenser needs to be at this temperature for effective movement of the solvent vapor

4- Infusion:These are very simple methods of extraction, in which powdered drug is extracted with hot or cold waterIn this method the powdered drug is soaked in hot water at room temperature for the specified period with or without stirring and filteredIf necessary the marc can be extracted again with fresh water

5- Decoction:In this method the drug powder is boiled with water for 15 min and then filteredThese two methods are suitable for drugs containing water soluble constituentsApplication:These are mainly used for making “Herbal Tea”

6- Steam distillation:This method is most suitable for extraction of essential oils (volatile oils)The plant material is heated to boiling with water in a distillation unit. The vapors of the volatile oil component are allowed to condense along with the vapor of the steam. The oil separates from water upon coolingThis method is not suitable for volatile compounds which deteriorate because of prolonged boiling at high temperatureIn hydro-distillation, steam is generated and passed through the plant material suspended in water, steam vaporizes the volatile components, condensed and separatedIn direct steam distillation, the material to be extracted is spread on a mesh as thin layers and the generated ateam is passed through the material

7- Expression:This method is adopted for the extraction of fixed oils from the seeds and other parts of plantMechanical pressure is applied to the crushed material of the plant part either in cold or at specified temperature to express the oil. Hydraulic pressure can be used for extraction

8- Enflurage:This method is used for extraction of delicate oils from the petalsSolvent used for the extraction of the oils is fat, which dissolves the oils from the material upon prolonged contact. Fat is applied onto the glass plate as a thin layer and petals are exhausted, fresh petals are spread. This continued till the fatty layer is saturated with volatile oil. Dissolved oil is separated from the fatty layer can be preserved for a longer time before being separated

9- Phytonics method of extraction:This method is used for the extraction of volatile oilsSome substances are gaseous at room temperature and atmospheric pressure. By changing the pressure, they become liquids of low viscosity and have good penetration power. 1,1,1,2 tetrafluroethane is a gas and can be liquefied. This can be used for extraction of fluid and is called “Phytosols”. Solvents which can solubilise phyto-constituents from the drugAdvantages:Phytosols are better than steam distillation, solvent extraction and SCFE & the temperature of extraction is not too highCost of production is lowQuality of essential oil is better & also the yield is very high

10-Ultrasound extraction:Sound waves above 2000 Hz are used to accelerate the extraction. The waves are generated in a magnetic stricture transmitter or piezoelectric transmitterThe sound waves increases cell wall permeability and causes mechanical stressing of the cells. Because of this, extraction happens faster

11-Extraction by electrical energy:Electric energy accelerates the extraction and improves the yield. Electromagnetic field is created in the drug powder for extractionApplication:This method is used for the extraction of scoplolamine from stramonium and valerianic acid from valerian

12-Counter current extraction: This is a liquid – liquid extraction process and is based on the

principle of partition chromatography It is developed by Craig in 1944 The apparatus consist of a series of tubes connected and contain a

lower, stationary phase and an upper moving immiscible liquid. The mobile phase can be transferred from one tube to another after shaking and allowing to separate

The extract is placed in the first tube and the apparatus is agitated and the layers are allowed to separate. The components of a

mixture will be distributed between the two layers according to their partition coefficients. The upper moving phase is moved along to the second tube containing the lower phase. More moving phase is brought into contact with the lower phase of tube 1. The process is repeated and fraction is done

The distribution of each substance over given number by the tubes can be increased by the use of series of buffer solution of graded pH

This method is best suited for separation than extraction

Application:

Extraction of alkaloids, amino acids, phenols, antibiotics, anthraquinones, cardiac glycosides, prostaglandins, vitamins, steroids etc

13-Prevaporation:In this method, substances dissolved in a liquid phase are removed by binding onto a membraneHydrophilic membranes may be used to remove polar materials, including water from organic solvents and, conversely hydrophobic membranes can be used to remove organic compounds from aqueous phaseApplication:This method has been used to remove aroma compounds from fruit juicesThis method is currently being developed, and its success will depend on the generation of new membranes which show selective binding for particular chemical groups, perhaps even for specific enantiomers

14-Sublimation:In this process some substances, on heating or cooling, change from solid to gas or vice versa without passing through the liquid state. This property can be used to obtain the substance from dried plant material or dry crude extractPlant material is warmed and the vapor allowed coming into contact with a cold surface. The sublimation substance vaporizes from the plant material and condensed as a solid on the cold surface, from which it can be scrapped offApplication:Caffeine of high purity can be obtained by this method from dry tea leaves

15-Supercritical fluid extraction: The critical point of a pure substance is defined as the highest

temperature and pressure at which the substance can exist in vapor-liquid equilibrium

Above this temperature and pressure fluid is formed and this point is said to be supercritical point

Supercritical fluid can dissolve wide variety of organic compounds and their solvent power can be varied near their critical points by small pressure and temperature changes

Supercritical fluid possess superior mass transfer properties by virtue of their low viscosity and high solute diffusivity along with the ability to penetrate micro-porous materials

Supercritical dioxide (SCO2) with its particular attractive properties such as:Non-toxic, non-flammable, non-corrosive, inert, low critical temperature (304 C), moderate low critical pressure (73 atm), easy availability, cost effectiveness, environment acceptability is the preferred solvent for many supercritical fluid extraction

Supercritical or liquid CO2 extraction processes are highly technical processes. Equipment operating under high pressure transforms carbon dioxide (normally a gas at atmospheric pressure) into a fluid with enhanced solvent characteristicsAdvantages:

CO2 is non-hazardous and leaves no undesirable solvent residue CO2 extraction is an environmentally friendly process Extraction conditions can be controlled for optimal results Low extraction temperatures preserve product integrity and quality CO2 extracted-products exhibit storage stability Advantages of supercritical extraction:

1- No environmental pollution2- No solvent residue in the product3- Permits the low temperature process and thermo labile, delicate,

expensive fragrances can be extracted4- Non corrosive in nature

Disadvantages of supercritical extraction:Use of high temperature and pressure may cause problems in some cases

Application:1- Pyrethrins from pyrethrum flower heads (increase upto 60%)2- Decaffeination of green coffee3- Isolation of bitter principle from hops4- Isolation of vindoline from Catharanthus roseus5- Extraction of taxol from Taxus brevifolia & Taxus cuspidate6- Extraction of pigments from Annatto seeds7- Volatile oil from Rose petals, Rosemary, Coriander, Illicium,

Juniper, Piment etc

Purification steps:

Physical:

1- Chromatography2- Dropler counter current chromatography (DCCC)3- Distillation4- Evaporation5- Crystallization6- Sublimation7- Precipitation

Chemical:

1- Hydrolysis (acid, alkali or enzyme)2- Salt formation3- Acetylation