Plant analysis & Constituents PHR103 Nishat Jahan
Extraction Extraction is the first step in the analysis of plant constituents. It is a process of removing or taking out or separating the chemical constituents from the plant tissues with or without the use of solvents. Various methods of extraction are available for this process. The particular method to be used depends on: the nature of the constituents type of the plant material and the purpose of the extraction Extraction of plant constituents may be done with or without the use of a solvent.
Methods of extraction without the use of solvents include the following: Expression: Plant constituents like fixed oils and fats are extracted by this method. In this method the fresh or dry material is subjected to hydraulic pressure with or without the application of heat. When no heat is used the method is called cold expression and any extraction done by expression with the simultaneous application of heat is called hot expression. This method is applied to thermostable fatty constituents. The constituents are extracted or squeezed out from the plant material due to crushing and expressing effects of the heavy pressure applied. On the completion of this extraction procedure the plant material is left as cakes. Most vegetable oils are extracted by this method.
Sublimation Sublimation: This method is applicable to the extraction of sublimable constituents from plant materials such as the extraction of caffeine from tea leaves. In this process, the powdered plant material is heated in a wide mouthed container covered with a glass sheet. The sublimable constituent is first vaporized and then condensed on the lower surface of the cover.
Sublimation
Distillation Distillation is also a method of hot extraction specifically used for the extraction of volatile oils and other volatile plant constituents. The plant material is placed in a distillation flask (with sufficient water in case of dried materials), which is connected to a receiver through a condenser. The material is heated directly or steam, generated in a connecting flask, is passed through it. The volatile oil codistils with the steam. condenses in the condenser and is collected in the receiver along with water. The immiscible oil is then separated from the water and dried by anhydrous sodium sulphate.
Distillatillation
Methods of extraction with the use of solvents are of two types: 1. Extraction with aqueous solvents: This is further classified into two types: A. Infusions are prepared by simply soaking a drug in water for a specified time. This might be hot or cold, depending on whether decomposition of ingredients could occur at higher temperatures. B. Decoctions are prepared in a similar way to infusions but with the ingredients and water boiled for a specified period of time or until a certain volume is achieved.
Infusion
Decoction
2. Extraction with organic solvents This includes the following methods: A. Maceration In this process, the whole or coarsely powdered crude drug is placed in a stoppered container with the solvent and allowed to stand at room temperature for a period of at least 3 days with frequent agitation until the soluble matter has dissolved. The mixture then is strained, the marc (the damp solid material) is pressed, and the combined liquids are clarified by filtration or decantation after standing.
Maceration
B. Percolation Percolation differs slightly from maceration. The powdered drug is dampened with the menstruum (solvent), left for four hours then packed into a percolator. Sufficient menstruum is added to cover the drug and left for twenty-four hours. The liquid is then allowed to very slowly drain from the bottom of the percolator (about twenty drops per minute). More menstruum is added and the process continued until the volume in the collecting flask reaches about three-quarters of the required volume. The marc is pressed, this expressed liquid added to the percolate. Sufficient menstruum then added to make the required volume. The liquid is then clarified using filtration or decanting.
Percolation
Soxhlet Extraction This is a continuous process of extraction with a hot organic solvent. The powdered plant material is taken in a thimble which is placed in the Soxhlet extractor. The extractor, which has a siphoning system, is fitted on top of a round bottom flask. A condenser is fitted at the top of the extractor.
Soxhlet Extraction contd. Enough quantity of the extracting solvent is poured into the flask placed on a heating mantle. On heating, the solvent evaporates, rises to the condenser, where it condenses and drains back to the extractor holding the thimble with the plant material. When the extractor becomes full with the hot solvent. the solvent siphons down to the flask along with the extracted constituents. The recycling of the evaporated solvent is allowed to continue until the extraction is complete.