2.2.3 Sequential Extraction by Polarity Gradient

Sequential (or successive) extraction applies solvents of progressively increasing polarity to the same plant material in turn, on the rationale that each...

Sequential (or successive) extraction applies solvents of progressively increasing polarity to the same plant material in turn, on the rationale that each solvent will selectively recover the constituent class most closely matched to its own polarity, thereby achieving a form of preliminary fractionation simultaneously with extraction itself. The petroleum ether fraction (boiling range 40–60°C) typically contains fixed oils, fats, waxes, chlorophylls, and non-polar terpenoids; the chloroform fraction recovers free-base alkaloids, terpenoids, flavonoid aglycones, and coumarins; the ethyl acetate fraction recovers moderately polar flavonoids, phenolic acids, and certain glycosides; the methanol or ethanol fraction recovers glycosides, tannins, saponins, polar alkaloids, and polyphenols; and the final aqueous fraction contains sugars, amino acids, gums, mucilages, and mineral salts. This polarity-graded approach is widely used in preliminary phytochemical screening precisely because the fraction in which a given biological activity concentrates provides an immediate indication of the likely chemical class responsible.