Extraction and fractionation using increasing order of polarity
Answers
Answer: Actually the solvent selection is on the basis of polarity and the nature of phytochemical constituents present in the drug.
If you have an entirely new material of which you don't know anything about the constituents, then you should proceed with solvents in the order of increasing polarity. If you know the phytoconstituents, then on the basis of their solubility in the particular solvent, you can select the solvent.
It is a general practice to defat the plant material with petroleum ether or hexane prior to using any other solvent to ease further process of isolation of constituents. Then choose the solvents in which your constituent is reported to be soluble and you can get it in the particular solvent after extraction.
Explanation: Anextractcanbepreparedbyfollowingvariousextractiontechniquesdependingupontherequirementandtypeofcompoundsneeded.Followingarethegeneralmethodstoperformanextraction;Maceration;Extractionwithshakingatroomtemperature.Percolation;Mostcommonlyusedcontinuousprocesswheresaturatedsolventisreplacedbyfreshsolventuntilexhaustiveextractionachieved.Countercurrentextraction;Movingextractivematerialisextractedbyaliquidphaseflowingagainstit.Hotcontinuousextraction(Soxheletion);PerformedinSoxhletapparatuswithrefluxingsolvent.Itcanbeagoodchoicewhenexhaustiveextractionisrequired.Majordrawbackisuseofhighertemperature.InfusionandDecoction;Extractionwithcold/boilingwater.SteamDistillation;Distillationofvolatileoilswithsteam.Extensivelyusedforessentialoilsandaromachemicalsextractions.ElectrodischargeandUltrasonicextractionmethodsareofverylimitedscope.
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