It is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. The mixture to be separated is put in a liquid or gaseous medium which is moved through the adsorbent. Different components are adsorbed at different levels on the column. Later, the adsorbed components are removed (eluted) by using suitable solvents (eluents). There are several chromatographic techniques such as paper chromatography, column chromatography, gas chromatography, etc. chromatography is used for the purification of elements which are available in minute quantities and the impurities are not very different in chemical properties from the element to be purified.