Once the chromatographic column was prepared, it was important to allow the leve

Question

Once the chromatographic column was prepared, it was important to allow the level of the liquid in the column to drop to the level of the stationary phase before applying the solution of the compounds to be separated. Why? Since Ethanol/water was used as the eluting solvent, what would have been the result if only water was used as the eluting solvent during the separation? During a mixture separation with column chromatography, why must the level of the solvent be kept above the top of the stationary phase once the procedure is started? Normally, a TLC experiment is performed before starting a column separation. Why? Compare TLC and Column Chromatography techniques. Indicate the similar principle they are based on and the differences with respect to time, quantity of material, and utility. What are the two methods of packing a chromatographic column?

Explanation / Answer

1) we need to bring solvent to the level of stationary phase becouse if we don't then the mixture which we are separating will not make a thin bed. Also it will come down with solvent and separation will not be good.

2) ethanol is polar solvent and easily bring down the components. If only water is used organic compounds will not move down with it hence will not get separetion

3)if at any point solvent level goan below the stationary phase . It will dry the stationary phase. There will air gap and it will distrup the bed hence uneven bed will not give proper separtion

4) TLC and coloumn have same principle both work adsorption principle . Coloumn is upside down TLC so if we do TLC before coloumn we can get an idea about polarity , number of components and Rf diffrence

5)Both TLC and coloumn work adsorption principle, that is compound which is strongly absorbed will move slowly and vice versa.

But TLC is qulitative and used only to identify the number of compounds where as a column is quntitative and used to separate miligram to gram mixtures.

Hence TLC required little time where as coloumn sepation need more time.

6) we can pack the column in two ways dry and wet packing

Dry packing is the one in which stationary phase is added and then mobile phase is added afterwards.

In wet packing a slurry of stationary and mobile phase is made and added to the coloumn

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