Pharmaceutical Extraction- Types of Extraction, Extraction Methods, and Important Extraction Applications
A suitable concentration of the active ingredients contained in the plants and that their action can be achieved more effectively.
For this, it is necessary to perform several procedures through which we can extract the active ingredients with adequate solvents, selected according to the solubility and stability of the beneficial substances.
“Extraction is the method of removing active constituents from a solid or liquid by means of liquid solvent. The separation of medicinally active portions of plant or animal tissues from the inactive or inert components by using selective solvents.”
Types of Extraction
Extraction is a process used to separate an organic chemical compound into one or more pure compounds, and it’s done using a chemical solvent known as the menstruum.
Certain pharmaceutical preparations are prepared by extraction, that is, by the withdrawal of desired constituents from crude drugs through the use of selective solvents in which the desired constituents are soluble.
Extractions play a role in the qualitative and quantitative composition of the extracts.
Liquid-Liquid Extraction (Solvent extraction)
- In this extraction the components of the liquid mixture are separated by contacting them with a suitable insoluble solvent which preferentially dissolves one or more components.
- Separation of the components from liquid mixture depends upon the unequal distribution of the components between two immiscible liquids.
- In this extraction the feed solution is phase 1 and the solvent used for extraction is phase 2.
- Both the feed and solvent forms a homogenous mixture which is separated by contacting them with one another to separate out one of the two liquids preferentially.
- This type of extraction is most widely used to separate actives and aromatic compounds from plants.
Solid Phase Extraction
- Solid phase extraction is used for isolation, enrichment and purification of components from aqueous solutions depending upon their physical and chemical properties.
- It involves contacting of aqueous samples with a solid phase or sorbent, where the component under consideration is adsorbed on the surface of the solid phase prior to elution.
- The extract amount is negligible compared to quantity of analyte in the sample.
- This type of extraction is widely used in analytical laboratories.
Solid-Liquid Extraction (Leaching)
- Solid-liquid extraction means the removal of constituents from a mixture of solids by bringing the solid material into contact with a liquid solvent that dissolves these particular constituents.
- Leaching may either be used for production of concentrated solution of a active principle, or in order to free an insoluble constituents from a soluble material with which it is contaminated.
Also Read: 25 Important Pharmaceutical Extraction MCQs
Methods of Extraction
- Maceration is a process that involves soaking of plant materials, usually in powder or coarse form, in a stoppered container with a defined solvent.
- The setup is left to stand at room temperature (+25 “C) for a minimum of 72 hours with shaking.
- The process is conditioned to soften and breakup the plant’s cell wall in order to liberate the soluble bioactive metabolites.
- After 3 days, the whole mixture is pressed and sieved by filtration using Whatman no. 1 filter paper.
- In this method, heat is transferred by convection and conduction and the choice of the solvent is crucial to determine the type of phytochemical extracted from the samples.
- This is the most frequently used method to extract phytochemicals for the preparation of tinctures and fluid extracts.
- A percolator made of a narrow cone-shaped vessel open at both ends is generally used.
- The solid ingredients are moistened with a specified amount of the defined menstruum and allowed to stand for approximately 4 hours in a closed container.
- The wet mass is then packed and the top of the percolator is closed and some extra menstruum is added to form a shallow layer above the mass.
- The mixture is allowed to macerate in the closed percolator for 24 hours
- The outlet of the percolator is then opened and the liquid contained therein is allowed to drip out slowly.
- The percolate is mixed until it measures about three-quarters of the required volume.
- The macerated product is then pressed and the expressed liquid is added to the percolate.
- Properly prepared menstruum is added to produce the required volume, and any excess liquid is eliminated by filtration or by standing followed by decanting.
- In decoction, the harvest crude product is boiled in a specified volume of water for a defined period, cooled and then strained or filtered.
- This procedure is applicable for the extraction of water-soluble, heat stable metabolites.
- The starting ratio of crude product to water is fixed, such as 1:4 or 1:16.
- The extract is then concentrated to one-fourth of its original volume by boiling.
- The concentrated extract is filtered and processed further Decoction is generally suitable for extracting heat-stable compounds in hard plant parts such as the roots and barks.
- Decoction gives more oil-soluble phytochemicals compared to maceration and infusion.
- Digestion is a maceration method that includes application of gentle heat during extraction.
- It is used when a moderately raised temperature is needed to increase the efficiency of the menstruum
- In this process drug is extracted by heating at a particular pressure to increase the penetration power of the menstruum, so that there is complete extraction of the drug.
- The apparatus used is known as ‘Digestor’ which is a vessel made up of metal.
- The whole of the drug is placed in the covered digestor it and bolted with the help of nuts.
- The drug is treated with menstruum for a definite period under specified condition of temperature and pressure.
- Fresh infusions are prepared by macerating the crude drug for a short period with cold or boiling water. These are dilute solutions of the readily soluble constituents of crude drugs.
- Infusion uses the same principle as maceration; crude drug is soaked in cold or boiled water for shorter duration.
Soxhlet Extraction (Hot Continuous Extraction)
- In this method, finely ground crude drug sample is placed in a porous bag or thimble made from a strong filter paper or cellulose, which is placed in thimble chamber of the Soxhlet apparatus.
- Extraction solvent is heated in the round bottom flask, vaporizes into the sample thimble, and condenses in the condenser and drip back.
- When the liquid content reaches siphon arm, it is emptied into the bottom flask again and the process is continued.
Microwave Assisted Extraction (MAE)
- MAE utilizes microwave energy to facilitate partition of analytes from the sample matrix into the solvent.
- Microwave radiation interacts with dipoles of polar and polarizable materials (solvent and sample) that causes heating near the surface of the materials and heat is transferred by conduction.
- Dipole rotation of the molecules induced by microwave electromagnetic disrupts hydrogen bonding; enhancing the migration of dissolved ions and promotes solvent penetration into the matrix.
- In non-polar solvents, poor heating occurs as the energy is transferred by dielectric absorption only.
- MAE can be considered as selective methods that favour polar molecules and solvents with high dielectric constant.
- This method involves the use of ultrasound waves ranging from 20 kHz to 2000 kHz.
- The mechanic effect of acoustic cavitation from the ultrasound waves increases the surface contact between solvents and samples and permeability of cell walls.
- Physical and chemical properties of the materials subjected to ultrasound are altered and disrupt the plant cell wall; facilitating release of compounds and enhancing mass transport of the solvents into the plant cells.
- The procedure is simple and relatively cheap that can be used in both small and larger scale of phytochemical extraction.
Accelerated Solvent Extraction (ASE)
- ASE is an efficient form of liquid solvent extraction due its minimal solvent requirement.
- Sample is packed with inert material such as sand in the stainless steel extraction cell to prevent sample from aggregating and block the system tubing.
- Packed ASE cell includes layers of sand-sample mixture in between cellulose filter paper and sand layers.
- ASE is an automated extraction technology capable of controlling temperature and pressure for each individual samples and completes in less than an hour.
Supercritical Fluid Extraction (SFE)
- Supercritical fluid (SCF; dense-gas) is a substance that shares the physical properties of both gas and liquid at its critical point.
- SCF behaves more like a gas but have the solvating characteristic of a liquid.
- A major drawback of this method is the initial cost of the equipment which is very high.
Applications of Extraction
- It is used in the separation of antibiotics and protein recovery.
- It used to recover high-boiling components such as phosphoric acid, boric acid, and sodium hydroxide from aqueous solutions.
- It is used to obtain therapeutically active constituents from plant parts and to eliminate the inert material
- It is used to isolate enzymes (renin) and hormones (insulin) from animal sources.
- Gelatin is produced by conversion of skin and bone collagen by treatment with lime or diluted acid and is further extracted with warm water.
- It is used in extraction of fixed oils from seeds.
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