Question

Explain how column chromatography can be used to separate a mixture on a larger scale than TLC?

Answer 1

Column chromatography is best technique for purification of compound, purification of compound can be achieve based on difference in polarity of individual impurities , most polar component  gets eluted last while non polar compounds eluted first from column .So individual impurity eluted from column based on polarity and affinity towards column stationary phase .

First we have to develop TLC plate for selection of mobile phase and it's strength. Once TLC plate with well separated spot gets achieved, then same solvent is implemented on column.Column hight decided based on Rf value of individuals components .  

Let's see column process deeply , column chromatography involves use of stationary phase and mobile phase. Stationary phase would be silica ,alumina etc .Mobile phase is any organic solvent such as Ethyl acetate ,hexane ,dichlromethane,methanol etc . Sometimes mixture of solvent with proper combo percentage also deployed for separation of components .example - ( 60:40% Ethyl -acetate :Hexane ) , (6:94% methanol :dichlromethane )

Let's see  actual process of purification by column chromatography , first take mixture of components into round bottom flask and dissolved into suitable solvent such as Dichlromethane , ethyl acetate etc. Poured silica into dissolved compound. Finally mixture dry over vacuum pump, to get uniform, dry slurry. Once slurry gets ready ,pack column with silica and suitable Mobile phase .

Once compound loaded into column for purification, run column with suitable mobile phase , as results individual component eluted from column based on polarity , strength of mobile phase. Eluted fraction collected independently and dry over vacuum pump to get pure product .

In this way ,we can separate every impurity one by one through column .