Question

Explain column chromatography.

Answer 1

Column chromatography is a technique used to separate different components of a mixture. It is a very useful technique used for the purification of elements available in minute quantities. It is also used to remove the impurities that are not very different in chemical properties from the element to be purified. Chromatography is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. In chromatography, there are two phases: mobile phase and stationary phase. The stationary phase is immobile and immiscible. Al₂O₃ column is usually used as the stationary phase in column chromatography. The mobile phase may be a gas, liquid, or supercritical fluid in which the sample extract is dissolved. Then, the mobile phase is forced to move through the stationary phase. The component that is more strongly adsorbed on the column takes a longer time to travel through it than the component that is weakly adsorbed. The adsorbed components are then removed (eluted) using a suitable solvent (eluant).

Answer 2

The basis of this method is the idea that different mixture constituents are adsorbed on an adsorbent in different ways. The process works particularly well for purifying elements that are only found in trace amounts and whose impurities exhibit chemical behaviour that is not significantly different from that of the element that needs to be purified.

In the column chromatographic method, a glass column is filled with an adsorbent, like alumina. The combination that has to be filtered or separated is put on top of the column. To varying degrees, the mixture's constituent parts are adsorbed in the column. An appropriate solvent, or eluent, is now created to flow through the column. The component that is poorly adsorbed elutes first, then the component that is more highly adsorbed, and so on. As a result, each component goes through the column separately before being gathered in different containers.