(1) Sublimation : It is the purification technique based on principle that on heating, some solid substances change from solid to vapour state without passing through liquid state. (2) Distillation : It is used to separate volatile liquids from non-volatile impurities and the liquids having sufficient difference in their boiling point. (3) Chromatography : It is based on separation by using stationary and mobile phase. (4) Crystallization : It is based on difference in the solubilities of the compound and impurities in a suitable solvent.